Abstract
During recent studies of the Basal Choteč Event (BCE) at its type locality (Na Škrábku Quarry at Choteč Village, Prague Basin of the Barrandian area, Czech Republic) and selected sections of time-equivalent strata in the Appalachian Basin (USA), palynomorphs and dacryoconarids have proven responsive to changing environmental conditions. To date, there have been no detailed reports of dacryoconarids from the Appalachian Basin (AB) and none of palynomorphs from Bohemia or elsewhere. Palynomorphs of the Barrandian area comprise a more or less monospecific assemblage of prasinophycean algae interpreted here to represent an ecological epibole. Mazuelloids and scolecodonts are also present, whereas acritarchs, spores and chitinozoans are accessory components. Prasinophytes also predominate in coeval strata of the Appalachian Basin's northern region, whereas a chitinozoan species and morphotypes possibly assignable to fungi abound in the central region. Scolecodonts and acritarchs are regionally variable throughout the interval. The former are rare in the central region of the basin but are ubiquitous and sometimes abundant in the northern region. Dacryoconarids of the Appalachian Basin are also regionally variable. The dacryoconarid fauna of the northern region, however, descended from a previous Emsian fauna that diversified during the BCE and subsequently functioned as the foundation of the upper Eifelian faunas, while dacryoconarids of the central region represent an incursion epibole of Old World forms that entered the basin at the onset of the event interval and became extinct at its close. Among the dacryoconarids there are key taxa that serve as excellent biostratigraphic markers to identify the BCE in the Appalachian Basin. In both the Prague and Appalachian basins, the BCE occurs near the maximum transgression of the Devonian Ic sequence. Additional faunal changes are found in the Appalachian Basin leading up to the main body of the event.
House (1985) first recognized the lower Eifelian (Middle Devonian) Basal Choteč Event (BCE) in West Gondwana (North African region: Vaughan & Pankhurst 2008) and the central and southern European peri-Gondwana of the so-called Old World Realm. In its type region of the Prague Basin (Czech Republic), the event interval is recorded in the lower section of the Choteč Limestone near the base of the Polygnathus costatus Zone (Berkyová 2009). The BCE involves the turnover of several faunal groups (Chlupáč & Kukal 1986) and a lithofacies shift to relatively deeper-water environments in temporal concert with a eustatic sea-level rise and the onset of oceanic dysoxic–anoxic conditions (Walliser 1996; House 2002). Chemostratigraphic studies have documented a moderate δ13C excursion and a magnetic susceptibility spike within the BCE interval, both of which are thought to be indicative of a climate regime shift (Buggisch & Mann 2004; Koptíková 2011). Despite its evident significance in the study of Devonian bioevents and palaeobiogeography, the faunal and lithological attributes of the BCE have received scant attention in the Appalachian Basin (AB) of the Eastern Americas Realm beyond the correlation of the event interval with the Nedrow Member of the Onondaga Formation (Ver Straeten 2007; Brett et al. 2009).
This paper presents hitherto unknown findings of palynomorphs and dacryoconarids (including six new species and two species in open nomenclature from the Appalachian Basin) in the BCE of the Prague and Appalachian basins, as well as detailed stratigraphic sections of the BCE interval in the latter, to facilitate comparisons of the style of the event in two separate palaeobiogeographical realms.
Research history of the Basal Choteč Event (BCE)
The term Choteč Event was introduced by House (1985), but he stressed in his 2002 overview (House 2002, p. 13) of mid-Palaeozoic events that Chlupáč & Kukal (1986, 1988) had ‘given more precision’ to the appellation. Even earlier, Walliser (1985) used the term jugleri Event for the event interval, named after the widespread goniatite Pinacites jugleri. However, as this goniatite species enters only at the top of the event interval (Becker & House 1994), he later supported the use of the term ‘Basal Choteč Event’ (Walliser 1996). The event level occurs shortly above the Emsian–Eifelian boundary (Polygnathus patulus/partitus conodont zones) and has been recognized in other areas. For example, in the Eifel Hills it is also known as the OCA (orbignyanus–cultrijugatus–alatiformis) Extinction Event (Struve 1982), characterized by the disappearance of the brachiopods Uncinulus orbignyanus, Paraspirifer cultrijugatus and Alatiformia alatiformis (e.g. Weddige 1988; Struve et al. 1997, 2008). As already pointed out by Walliser (1985, 1996), the Choteč Event is often connected with a lithological change from light grey limestones to dark, often dacryoconarid-rich limestones; Walliser (1985) mentioned the intercalation of dark shales. This facies change was also recorded by Chlupáč (1985) for the Barrandian area, Requadt & Weddige (1978) for the Rheinisches Schiefergebirge and Henn (1985) for northern Spain. Klug et al. (2000) reported it from Moroccan sections, indicating that the ‘Choteč Event level’ occurred within the partitus conodont zone. Recognition of the lithological change in the latter region had already been mentioned for the Tafilalt area in Alberti (1980), Becker & House (1994) and Kaufmann (1998). In recent years, sections in the type area of the Choteč Event have gained increasing attention (e.g. Berkyová 2009; Elrick et al. 2009; Berkyová & Munnecke 2010; Brocke et al. 2011; Koptíková 2011; Vodrážková et al. 2013).
Localities, material and methods
In the Prague Basin of the Barrandian area, our study is based on eight samples from the Na Škrábku Quarry near Choteč (Figs 1, 2, 3, 4). The section at the quarry (49° 59′ 20″ N, 14° 16′ 45″ E) was first mentioned by Chlupáč (1959, p. 457); this outcrop represents the stratotype of the Choteč Formation.
Map showing the location of the Prague Basin in the Bohemian Massif, Czech Republic, and a simplified geological sketch map of the Prague Basin. The local map pinpoints the Na Škrábku Quarry near the village of Choteč, the type locality of the BCE.
Stratigraphy and facies development of the Lower–Middle Devonian of the Prague Basin; modified after Budil et al. (2009).
Stratigraphic section in the Na Škrábku Quarry, showing the uppermost levels of the Třebotov Limestone and the lower portion of the Choteč Limestone. Numbered palynological samples (‘P samples’) are indicated by arrows.
Photographs of study intervals in the Na Škrábku Quarry. (a) Detail of the middle of the quarry wall; position of palynological samples indicated by arrows. (b) Lower surface of bed number 10; blow-up of the goniatite in the lower left. (c) General view of the eastern quarry wall with the boundary between the Třebotov and Choteč limestones.
This section and others in its vicinity have been studied in great detail in the context of the definition of the Emsian–Eifelian boundary and the establishment of the Choteč Event (e.g. Chlupáč 1982, 1985; Chlupáč & Kukal 1986, 1988). Several palaeontological, as well as non-biotic, aspects have been studied at this important section (e.g. Chlupáč 1959; Buggisch & Mann 2004; Koptíková 2011; Vodrážková et al. 2013).
In the Appalachian Basin, eastern USA, over 350 outcrops of the lower Eifelian Onondaga Formation, time-equivalent units and adjacent strata have been examined (Figs 5 & 6). Their stratigraphic trends are discussed in Ver Straeten (2007). Subsequent research by a team including four of the authors of this paper is focused on better refining Emsian and Eifelian biostratigraphy across the Appalachian Basin, utilizing various fossil organisms. Fifteen of these sites, in the northern and central parts of the basin, focus on lower Eifelian strata, including the BCE. These sites occur in the states of New York, Pennsylvania, Maryland, Virginia and West Virginia (Figs 5, 6, 7; Appendix A).
Map of key outcrops and study localities, Appalachian Basin, eastern USA. Key outcrops of the lower Eifelian strata along approximately 1750 km of outcrop belt (modified after Ver Straeten 2007). Stars indicate localities from this study; other identified localities are noted in the text or in photographs. Uppercase letters denote US states and a Canadian province; lower case letters denote localities: a, Auburn; b, Buffalo; c, Cherry Valley; g, Gainesville; h, Hayfield; j, Jamesville–Nedrow; k, Keyser; m, Mapleton; MD, Maryland; o, Oak Corners; OH, Ohio; ONT, Ontario (Canada); n, Newton Hamilton; NJ, New Jersey; NY, New York; PA, Pennsylvania; s, Spring Gap; se, Selinsgrove Junction; st, Stafford; VA, Virginia; WV, West Virginia.
Correlations of key outcrops, Onondaga Formation and correlative strata, Appalachian Basin. Study outcrops along approximately 870 km of outcrop belt, western to eastern New York to northern Virginia. Datum=top of Nedrow Member and time-equivalent strata (= top of Nedrow black beds). Lines denote chronostratigraphic correlations. Grey shaded interval denotes Nedrow black beds interval. Bold lines denote member-level divisions; thin lines denote event bed correlations; lines with arrowheads denote airfall tephra beds (K-bentonites). p, correlatable pyrite zone above twin K-bentonites; Sen, Senenca Mbr; tw, widely correlatable pair of thin K-bentonites. Capital letters A–F denote layers of the Tioga A–G K-bentonites cluster. The Jamesville section is 10 km from the Nedrow study locality. Buffalo, NY section after Oliver (1967).
Photographs of the Onondaga Formation of New York and correlative strata in the study area. (a) Schoharie- and Onondaga-equivalent Needmore Formation (calcareous shale member and Selinsgrove Member, respectively), at Spring Gap, MD (locality ‘s’ in Fig. 5). Chronostratigraphic correlatives of members of New York's units are denoted. Approximately 13 m of a 19 m section along the highway shown in the photograph. (b) Onondaga-equivalent Selinsgrove Member, Needmore Formation at Hayfield, VA (locality ‘h’ in Fig. 5). Chronostratigraphic correlatives of members of New York's Onondaga Formation are denoted. Note the position of the Nedrow black beds along the outcrop. Tioga B K-bentonite is covered at the top of slope, just beyond right-hand edge of the photograph. The Selinsgrove Member is approximately 18 m thick here. (c) Onondaga Formation in the type area, Jamesville, NY (locality ‘j’ in Fig. 5). Key widely correlative marker units denoted, along with member-level divisions. Note the position of the Nedrow black beds at the top of the Nedrow Member, and ‘twin K-bentonites’ low in the Moorehouse Member. The Onondaga Formation is 22.8 m thick here. (d) Lower and upper black beds of the upper Nedrow Member, along Interstate 81 at Nedrow, NY. The lower and upper Nedrow black beds are denoted by lbb and ubb, respectively. Locality is 9.5 km WSW of the Jamesville locality. (e) Nedrow black beds in shallower-marine limestone-dominated facies, at the abandoned Schooley Quarry, Auburn, NY (locality ‘a’ in Fig. 5). (f) Mid-Nedrow- to lower Moorehouse-equivalent strata of Selinsgrove Member, Needmore Formation, along railroad cuts at Newton Hamilton, PA (locality ‘n’ in Fig. 5). Note the black beds and the position of the twin K-bentonites. The black and white bar is 1.5 m. (g) Black beds and adjacent strata, Selinsgrove Member, near Mapleton, PA (locality ‘m’ in Fig. 5). Again, note the twin K-bentonites. The black beds are separated by 36 cm. (h) Lower part of the Selinsgrove Member, at the type section in central Pennsylvania (locality ‘se’ in Fig. 5). Note the position of the black beds and twin K-bentonites. The scale bar at the centre is next to 1.5 m staff. E, Edgecliff Member and correlatives; bb, Nedrow black beds; lbb, lower black bed; M, Moorehouse Member and correlatives; N, Nedrow Member and correlatives; S, Seneca Member and correlatives; tw, closely spaced ‘twin’ K-bentonites in lower Moorehouse and correlative strata; Ti-B, Tioga B K-bentonite; ubb, upper black bed.
Palynological samples of the Prague and Appalachian basins were prepared by utilizing a standard treatment with HCl–HF (e.g. Traverse 2007) without any oxidation. The resulting organic residue was sieved with 10 µm nylon sieves. In some cases, samples that were rich in organic matter were also sieved in an ultrasonic bath to remove the finer organic detritus. In addition, the ‘light organic fraction’, which self-separates by floating away from the rest of the kerogen during the chemical preparation, was extracted for microscopic analysis. This method was tested on a few samples from the Appalachian and the Barrandian Na Škrábku section (e.g. sample 5, enriched in prasinophytes). For all samples, the studied portion of the organic residue was mounted on slides with glycerol gelatine and routinely analysed under a transmitted light microscope (Nikon Eclipse 90i). Dark-coloured to nearly opaque palynomorphs were studied with the same microscope, which was equipped with an infrared (IR) video system (for specifications, see Brocke & Wilde 2001). In order to distinguish fungi from acritarchs, epifluorescence was applied.
The rock samples that were studied for dacryoconarids were collected from the Edgecliff and Nedrow members of the Onondaga Formation, and their equivalents at the localities are shown in Figure 6. They were treated by standard methods (splitting, washing, disaggregation and sieving); the better preserved shells were mounted on scanning electron microscope (SEM) stubs, sputter coated with gold, and then measured, described and documented with a SEM at magnifications of ×35−×3500.
Setting of the Basal Choteč Event in the Barrandian area
In the Barrandian area, the Lower–Middle Devonian boundary interval is characterized by a fully marine succession of carbonates and calcareous shales generally with common fossils (e.g. Chlupáč et al. 1979). The Lower–Middle Devonian boundary is drawn according to the first appearance of the conodont Polygnathus partitus, which falls within the Nowakia holynensis dacryoconarid zone. These levels are situated above the last appearance datum (LAD) of Gyroceratites gracilis and are characterized by a rich ammonoid fauna of the Anarcestes lateseptatus group. The boundary interval comprises upper levels of the Daleje–Třebotov Formation to lower levels of the Choteč Formation (Fig. 2), and is exposed at many natural outcrops and in old quarries. About 10 well-exposed boundary sequences were studied in detail (e.g. Svoboda & Prantl 1947, 1948; Chlupáč 1959; Klapper et al. 1978; Chlupáč et al. 1979, 1980; Koptíková 2011; Vodrážková et al. 2013).
The Daleje–Třebotov Formation includes three members: (1) the Suchomasty Limestone; (2) the Daleje Shale; and (3) the Třebotov Limestone. Interpreted to be a shallow-water deposit, the Suchomasty Limestone is developed on the SW flank of the Prague Basin. It is interpreted as a shallow-water, high-energy equivalent of the Daleje Shale and Třebotov Limestone. The Daleje Shale is characterized by greenish siliciclastic mudrocks with calcareous concretions deposited in a deeper, low-energy environment (Chlupáč et al. 1998). These clastic sediments are overlain by light to dark grey, fine-grained, nodular, bedded micritic–biomicritic carbonates of the Třebotov Limestone (originally defined by Svoboda & Prantl 1947; redefined by Chlupáč 1959). The fauna of the Trebetov and its preservation suggest a low-energy deeper environment. The upper part of the Třebotov Limestone is characterized by calcisiltite deposited from distal storm or turbidite currents alternating with slowly deposited and condensed hemipelagic material (Koptíková 2011).
Eustatic shallowing in the Prague Basin resulted in deposition of the upper levels of the Daleje–Třebotov Formation and is connected with increasing current activity associated with the immigration of new faunal elements (Chlupáč 1985).
The Choteč Formation incorporates two members: the Acanthopyge Limestone and the Choteč Limestone (Fig. 2). The Acanthopyge Limestone was deposited on the SW flank of the Prague Basin and is interpreted as a shallower-water, high-energy equivalent of the Choteč Limestone. The Acanthopyge Limestone is a light grey, platy, biodetrital limestone; it overlies the Suchomasty Limestone. The Choteč Limestone (defined by Svoboda & Prantl 1948; redefined by Chlupáč 1957, 1959) includes two major lithologies: grey, platy crinoidal biodetritic limestone alternating with light grey calcisiltic limestones and shaly intercalations. In more proximal depositional environments, turbidite deposits are present in the lower part of the Choteč Limestone (e.g. the Na Škrábku Quarry).
Organisms affected by the event
Diverse fossil groups have been intensively studied in Lower and Middle Devonian sequences, including the boundary interval (for a summary, see Chlupáč et al. 1979).
Radiolarians
Braun & Budil (1999) reported a rich radiolarian fauna from two outcrops in the uppermost levels of the Choteč Limestone (railway cut in Praha 5-Hlubočepy and the Kněží Hora Hill near Karlštejn, Fig. 1).
Foraminifers
Preliminary reports announced the occurrence of Devonian foraminifers more than 100 years ago (Schubert & Liebus 1902; Liebus & Wahner 1904; Pokorný 1958). More recently, Silurian and Devonian foraminifers were described by Holcová (2002). Detailed studies of several sections covering the Basal Choteč Event (BCE) document a distinct decrease in foraminiferal abundance (Holcová 2003, 2004a, b, c; Holcová & Slavík 2013).
Conodonts
Significant studies include papers by Klapper (1977), Klapper et al. (1978), Chlupáč et al. (1977), Weddige & Ziegler (1987), Galle & Hladil (1991), Zusková (1991), Hladil & Kalvoda (1993) and Klapper & Vodrážková (2013). Berkyová (2009) summarized earlier data and provided new results in a comprehensive study. The conodont zonation elaborated in the above-mentioned papers is summarized in Figure 2. The conodont zonation of Berkyová (2009) differs slightly from more recent studies on brachiopods (Mergl & Vodrážková 2012) and on environmental changes (Vodrážková et al. 2013); in these later studies, the base of the Tortodus kockelianus australis Zone is drawn at different levels.
Gastropods
Horný (1955, p. 65) announced the occurrence of 10 species of palaeozygopleurid gastropods in the Choteč Limestone; other early Devonian taxa were studied by Frýda & Bandel (1997) and Frýda et al. (2013). Frýda et al. (2008, p. 94) found out that the highly diverse palaeozygopleurid gastropods originate within the partitus Biozone (e.g. just below the BCE). Palaeozygopleurids are, however, completely absent above the event.
Bivalves
The absence of a modern systematic revision precludes an evaluation of this group.
Cephalopods
Chlupáč & Turek (1983) and Manda & Turek (2011) revealed considerable changes in associations of both goniatite and nautiloid cephalopods connected with the BCE. The important changeover in the goniatite fauna falls very close to the base of the Pinacites jugleri Zone.
Brachiopods
Brachiopods of the shallow-water facies were studied by Havlíček & Kukal (1990), who separated the Karbous–Orbiproetus and Orbiproetus–Scabriscutellum communities in the Suchomasty Limestone, and the Karbous–Acanthopyge Community in the Acanthopyge Limestone. Mergl (2001, 2008) studied linguloid, discinoid and acrotretoid brachiopods. In the first of these papers, an increase in diversity above the BCE was noted. However, more recently, Mergl & Vodrážková (2012, p. 330) came to a quite different conclusion:
lingulate brachiopods do not display any significant change around the Emsian/Eifelian boundary or the Basal Choteč Event (Middle Devonian, Eifelian, Polygnathus costatus Zone) and confirm the general uniformity of lingulate faunas in the Lower and early Middle Devonian.
Dacryoconarids
A dacryoconarid zonation for the Barrandian area was established by Bouček (1964) and new data were later provided by Lukeš (1989). This generally accepted zonation is summarized in Figure 2.
Ostracods
Přibyl & Šnajdr (1950) studied a diverse Lower–Middle Devonian ostracod fauna and reported a distinct extinction associated with the BCE at the Prastav Quarry. Šlechta (1996) revised a large number of the earlier described ostracod taxa established near the Lower–Middle Devonian boundary and also found a distinct extinction event at the Praha Barrandov locality.
Trilobites
Extensive monographs on phacopids (Chlupáč 1977), scutelluids and proetids (Šnajdr 1960, 1980), and numerous short reports on highly diverse trilobites, were summarized by Chlupáč (1983), who distinguished four major trilobite assemblages in the boundary interval:
Phacops–Struveaspis Assemblage in the Třebotov Limestone (Chlupáč 1983, p. 56);
Koneprusites–Cyphaspides Assemblage in the Choteč Limestone (Chlupáč 1983, p. 59) – medium diversity;
Acanthopyge–Phaetonellus Assemblage in the Acanthopyge Limestone (Chlupáč 1983, p. 57) – high diversity;
Orbitoproetus–Scabriscutellum Assemblage in the Suchomasty Limestone (Chlupáč 1983, p. 56) – high diversity (50 species).
Echinoderms
The rich crinoid fauna was studied by Bouška (1948, 1956), and more recently supplemented by Prokop (1970, 1976, 1987, 2012, 2013), Prokop & Petr (1997, 2004) and Hotchkiss et al. (1999, 2007).
Plant remains
Obrhel (1958, 1968) reported the occurrence of several long-ranging species from the Třebotov and Choteč limestones; Chlupáč et al. (1979, p. 141) mentioned, for the first time, a common occurrence of leiospheres (=prasinophytes in Vodrážková et al. 2013) in lower levels of the Choteč Limestone.
Organic-walled microfossils (OWM)
Devonian OWM (e.g. acritarchs, prasinophytes, spores, chitinozoans, scolecodonts and fungi) from the Barrandian are known from several papers, such as Obrhel (1964), Lele (1968, 1972), Čorná (1969), McGregor (1979a, 1980, 1981a, 1983), Vavrdová (1989), Fatka (1999), Fatka & Brocke (2008) and Vavrdová & Dašková (2011). However, until recently, only a few of them dealt in particular with the BCE (Brocke et al. 2011, 2013; Vodrážková et al. 2013). Therein, the extraordinarily high number (mass occurrences) of green algae, namely prasinophytes, is emphasized. The majority of these prasinophytes belong to the genera Tasmanites and Leiosphaeridia. They are present in a dark grey limestone bed just above the base of the Choteč Limestone, which is regarded as representing the BCE level at its type locality (the Na Škrábku Quarry near Choteč village).
Abiotic effects
In an extensive study on carbon isotope stratigraphy of the Lower–Middle Devonian of southern and central Europe, Buggisch & Mann (2004, p. 528, fig. 4) described a positive excursion of δ13Ccarb from sections in the Prague Syncline.
Elrick et al. (2009) compared changes of the δ18O from conodont apatite at two sections in the Prague Basin (the Na Škrábku Quarry and Prague-Barrandov), with one section in the western United States (the northern Antelope Range of central Nevada). They interpreted the oxygen isotopic signal to be global rather than related to local changes in seawater temperature (possibly cooling).
In a comprehensive study, Koptíková (2011) provided results of magnetic susceptibility measurements and gamma-ray logging in combination with geochemical methods. She also identified the presence of Bouma sequences in the Choteč Formation.
Setting of the Basal Choteč Event in the Appalachian Basin, eastern USA
Across the Appalachian Basin (AB), the Basal Choteč Event (BCE) falls within a carbonate–mixed carbonate and shale–bedded chert succession (Figs 5, 6, 7). The precise position of the Emsian–Eifelian stage boundary remains elusive. However, it and the BCE fall within the third-order transgression (transgressive systems tract of sequence stratigraphy) of Devonian Sequence/transgressive–regressive (T–R) Cycle Ic (of Johnson et al. 1985; refined regionally by Brett & Ver Straeten 1994; Ver Straeten 2007; Brett et al. 2011, their sequence Eif-1).
In the northern and western parts of the Appalachian Basin (e.g. New York, western New Jersey, eastern Pennsylvania, in the northern part of the Appalachian Basin (NAB); and Ohio in the western part of the Appalachian Basin (WAB)), the Ic succession occurs within relatively shallow-ramp limestones, sometimes cherty, with minor shales in slightly deeper settings (Fig. 7c–e). In these areas, strata are assigned to the Onondaga Formation, except in central Ohio (i.e. the Columbus Formation of the WAB). Across the central part of the basin (e.g. central Pennsylvania, western Maryland, NW Virginia and NE West Virginia=CAB), the Ic succession occurs largely in deeper, more basinward facies. In the CAB, these strata are characterized by mixed argillaceous limestones and calcareous grey to dark grey shales, with minor black shales (Fig. 7a, b, f–h). These strata are assigned to the Selinsgrove Member of the Needmore Formation (Ver Straeten 2007). In the southern part of the Appalachian Basin, strata of the Selinsgrove Member (sometimes termed the calcareous shale and limestone member) transition laterally into bedded chert-dominated lithofacies, in the upper part of the Huntersville Chert Formation (Ver Straeten 2007).
Correlations of the Onondaga Limestone and its time-correlative strata between key outcrops across the northern and central Appalachian Basin are demonstrated in this study (Fig. 6). In New York's Onondaga Limestone, four member-level subdivisions are recognized: the Edgecliff, Nedrow, Moorehouse and Seneca members (Oliver 1954). These same time-correlative subdivisions are widely recognizable across the basin, although difficult to delineate in the chert-rich facies in the SW part of the basin (Ver Straeten 2007). The Moorehouse and Seneca members are separated by the Tioga B K-bentonite of Way et al. (1986), which has a radiometric age of 390±0.5 Ma (Roden et al. 1990).
The sequence stratigraphy of the Onondaga Formation and equivalents, refined after the Johnson et al. (1985) T–R cycle model (Brett & Ver Straeten 1994; Ver Straeten 2007; Brett et al. 2011), is characterized by a conformable–disconformable third-order sequence boundary at the base of the succession (=base of Edgecliff Member), overlain by a transgressive systems tract (TST) extending to the top of the Nedrow Member. The position of the maximum flooding surface (i.e. the maximum landwards position of the shoreline) in moderate to deeper settings is marked by a pair of black shale beds (the lower (LBB) and upper Nedrow black beds (UBB) of Brett & Ver Straeten 1994; Ver Straeten 2007) separated by a thin limestone bed; in shallower facies, the black beds are represented by a pair of distinctly finer-grained limestone beds (±green shales). Initial aggradational sedimentation (highstand systems tract (HST)) in the lower Moorehouse Member is succeeded by shallowing patterns (falling-stage systems tract (FSST)) into the middle Moorehouse.
Following another third-order lowstand of sea level at the base of Sequence Id (generally appearing conformable), a second TST begins in the upper Moorehouse Member, which continues through the overlying Seneca Member and into the lower part of black shale-dominated strata of the overlying Marcellus strata (the Union Springs Formation of the Marcellus subgroup in New York; i.e. the lower part of the Marcellus Formation of other states except in Ohio, where the time-equivalent strata occur in the limestones of the Delaware Formation).
In the Eastern Americas Realm, the lowermost known occurrence of Polygnathus partitus, which marks the base of the Eifelian Stage (Ziegler & Klapper 1985), is near the base of the Nedrow Member (Klapper & Oliver 1995). The absence of this conodont from the subjacent Edgecliff Member is attributed to environmental exclusion (Klapper 1981). Currently available biostratigraphic data indicate that the base of the Eifelian Stage is at or near the base of the Edgecliff Member (Kirchgasser 2000).
The Choteč interval in the Appalachian Basin may occur through the interval from the mid-Edgecliff to the top Nedrow members and equivalents. However, the key interval of the BCE appears to be focused around the basinwide lower and upper Nedrow black beds (LBB and UBB, respectively) and their shallower-water correlatives. The base of the LBB approximates the base of the costatus Zone, near the maximum flooding surface of the Ic Sequence and the bathymetrically deepest facies of the Onondaga Formation (Ver Straeten 2007).
Data on palynomorphs (e.g. acritarchs, chitinozoans and spores) and dacryoconarids presented in this paper represent the first results of a team project trying to refine Emsian and Eifelian biostratigraphy in the Appalachian Basin. For both groups, no sufficient data are available yet to establish formal zonations in the Appalachian Basin. This lies beyond the scope of this paper. The details of the palynomorph and dacryoconarid records during the BCE interval are described below. Other fossil organisms (e.g. conodonts, goniatites and brachiopods) are considered when possible.
Organic-walled microfossils (OWM)
To date, no palynological data exist from this particular time interval in the Appalachian Basin. The majority of papers on Devonian acritarchs in North America address the Givetian of Ohio (e.g. Wicander & Wood 1979, 1981; Wicander 1983, 1984; Wicander & Wright 1983), Iowa (Wicander & Wood 1997, including chitinozoans) and Kentucky (Wood & Clendening 1985, including chitinozoans), followed by the late Devonian of Ohio (Wicander 1973a, b, c, 1974, 1975; Winslow 1962), Oklahoma (Wilson & Urban 1963, 1971; Wilson & Skvarla 1967), Indiana (Wicander & Loeblich 1977), Iowa (Wicander & Playford 1985, including spores) and, recently, from Illinois (Wicander & Playford 2013), and a brief report from New York (Higgs & Hughes 2012). Early Devonian (Gedinnian) records are from Oklahoma (several papers by Loeblich & Wicander: e.g. Loeblich 1970; Loeblich & Wicander 1974, 1976; Wicander 1986) and from New York State (Wicander & Schopf 1974). A comprehensive catalogue of the stratigraphic distribution of North American acritarchs was given by Wicander (1983). Further reports are from the middle–late Devonian of Canada, Alberta (Staplin 1961; Turner 1986, 1991) and Ontario from the Emsian–Eifelian interval (Legault 1973a, b; Playford 1977). Reports by Deunff from the 1950s were stratigraphically not constrained (Playford 1977).
Chitinozoans have been reported from the mid-Devonian of Michigan (Dunn & Miller 1964), Ohio (Wood 1974; Wright 1976), Indiana (Wright 1980), Illinois (Collinson & Scott 1958), Iowa (Wicander & Wood 1997) and Missouri (Urban & Kline 1970). Chitinozoans from Ontario, Canada were noted by Legault (1973a, b). The distribution and ranges of chitinozoans, including Devonian taxa from North America, are given by Jenkins & Legault (1979).
Devonian spores have frequently been reported from different areas in North America: the Lower Devonian of Cherry Valley, New York (Hughes & Higgs 2011), the Middle Devonian of Illinois (Peppers & Damberger 1969) and Georgia (Ravn & Benson 1988, including the Frasnian), and the Upper Devonian of Ohio (Winslow 1962), Illinois (Wicander & Playford 2013), western New York and Pennsylvania (Richardson & Ahmed 1988) and, recently, of Kentucky (Clayton et al. 2012; Higgs & Hughes, 2012; Rooney et al. 2013). In addition, the Devonian of Canada: Ontario (e.g. McGregor & Owens 1966; McGregor 1973, 1977), eastern Canada (McGregor & Camfield 1976), Canadian Arctic (McGregor 1974, 1981a, b; McGregor & Camfield 1982) and southern Saskatchewan (Playford & McGregor 1993, including acritarchs). A biostratigraphic compilation for spores of North America was published by McGregor (1979b). Richardson & McGregor (1986) introduced a concept of spore zonation for the Silurian and Devonian of the Old Red Continent (ORC).
Owing to the peculiarities within the Appalchian Basin, as mentioned above, a northern and a central part are discriminated.
Northern part of the Appalachian Basin (NAB)
Throughout much of New York State, the lowermost bed of the Nedrow Member is an argillaceous lime mudstone–wackestone that abruptly overlies a glauconitic and pyritic, crinoidal, poorly washed biosparite or packstone facies of the uppermost Edgecliff Member. The ichnogenus Chondrites is frequent in the argillaceous beds of the Nedrow Member. Bromley & Ekdale (1984), Bromley (1990) and Seilacher (2007) interpreted the Chondrites trace-maker to have been a chemosymbiotic organism adapted to dysaerobic environments. Schubert (1996) supports this assumption in his paper on the biofacies of the Wissenbach Schiefer of the Rhenohercynian Zone in Germany. This interpretation is also supported by Savrda & Bottjer (1986), who cited examples from the Cretaceous and the Miocene. The assignment of Chondrites to the group of ‘facies-breaking ichnogenera’ (by Seilacher 2007, pl. 71) leaves space for habitat interpretation and does not exclude low-oxygen conditions. The argillaceous Nedrow beds also contain a diverse, although physically diminutive, benthic macrofauna of brachiopods, bryozoans, rugose corals and trilobites: again, suggestive of a dysaerobic environment. Microfossils include ostracods, scolecodonts, Tentaculites scalariformis, Homoctenus sp., palynomorphs and the dacryoconarids described herein.
Central part of the Appalachian Basin (CAB)
At multiple localities in Virginia, Maryland and south-central Pennsylvania, the basal bed of Nedrow-equivalent strata in the Selinsgrove Member (Needmore Formation) and the Nedrow Member of New York is a fissile black shale, which abruptly overlies a medium-grey, crinoidal, poorly washed biosparite of the uppermost Edgecliff bed. Dacryoconarids within the Nedrow Member-equivalent are taxonomically distinct from those of the subjacent equivalents of the Edgecliff Member and the Schoharie Formation.
Dacryoconarids of the basal Nedrow bed and the two UBB occur in exceptionally high numbers as ecological epiboles on shale laminae surfaces. The dacryoconarid shells are frequently aligned parallel to one another to the extent that laminae surfaces may be mistaken for tectonic slickensides. Most dacryoconarids are preserved only as faint impressions of crushed and dissolved shells. Preservation is usually so poor that it is only with diligent effort that one can discern that the ‘slickensides’ are actually aligned, crushed and leached impressions of dacryoconarid shells. In instances where the shells are preserved, it is clear that the dacryoconarid-rich layers were deposited as thin coquinite layers separated by thin shale partings. Neither the coquinite layers nor the shale partings were disturbed by bioturbation and are devoid of a benthic fauna.
The Basal Choteč Event and its equivalents in other areas
As a detailed discussion of the BCE in areas other than the Prague and Appalachian basins is far beyond the scope of the present paper, only some of the more important regions are briefly mentioned here. In the German Rhenohercynian and Saxothuringian zones, the facies of contemporaneous rocks is different or difficult to recognize because they cannot be exactly correlated time-wise with the Choteč strata. However, a change from more oxygenated ‘lighter’-coloured to ‘darker’ mostly shaly rocks of the lower Eifelian ‘Wissenbach-Schiefer’ facies has been recognized (e.g. Requadt & Weddige 1978; Schubert 1996). Recently, the event has been referred to in the context of carbonate facies in the Meinerzhagener Korallenkalk (Ernst et al. 2012). As noted before, within the Rhenohercynian (Eifel Hills) the BCE is associated with the extinction of the upper Emsian–lower Eifelian OCA brachiopod fauna (e.g. Struve 1982; Weddige 1988; Struve et al. 1997, 2008). Similar to the Wissenbach-Schiefer facies, reports from the Iberian Peninsula are known through Henn (1985), Montesinos (1987) and García-López & Sanz-López (2002), and from the Ossa Morena Zone by Machado et al. (2010). In the Moroccan Anti-Atlas, similar observations have been published (e.g. Alberti 1980; Becker & House 1994; Kaufmann 1998; Klug et al. 2000, 2013; Becker & Aboussalam 2013). Elrick et al. (2009) and Pedder (2010) have reported examples from Nevada, USA. In his recent study of rugose coral taxa and palaeobiogeography, the latter author has reported a breakdown in rugosan provincialism and the termination of the Emsian–Eifelian Great Basin coral province of Nevada within the BCE interval (Pedder 2010). The only report from South America was published by Troth et al. (2011), dealing with strata in Bolivia. Therein, the Choteč Event slightly post-dates the sudden incursion of goniatites in a cold-water succession.
Discussion and results
The Barrandian area
Effects on invertebrate fauna in the the Barrandian area caused by the BCE can be summarized as follows:
Chlupáč (1983) documented a gradual change in trilobites: 90% of species and, more importantly, 50% of upper Emsian trilobite genera did not cross the level of the BCE;
the appearance of cosmopolitan proetids, scutelluids and phacopids (Chlupáč 1983);
the disappearance of palaeozygopleurid gastropods (Frýda et al. 2008);
changes between goniatites (innovations in Pinacitidae, a decline of Mimagoniatitidae and Mimoceratidae: Chlupáč & Turek 1983), although Becker & House (1994) emphasized that Gyroceratites (and, subsequently, the Mimoceratidae) did not range into the Eifelian;
in the course of the BCE, rutoceratoid generic diversity dropped dramatically; the recovery of nautiloids was slow (Manda & Turek 2011);
dacryoconarids exhibit a modest faunal turnover (Bouček 1964), whereas Lukeš (1989) reported a stronger turnover in the Prague–Barrandov section.
Organic-walled microfossils
In total, eight palynological samples have been analysed from the type section Na Škrábku Quarry near the village of Choteč. The studied section comprises a calcareous sequence ranging from the upper Třebotov Formation to the lower Choteč Formation. There is a distinct lithological change from a light, bioclastic composition of the Třebotov Limestone to a darker bioclastic limestone alternating with a dark laminated lime–mudstone sequence of the Choteč Limestone (Figs 3 & 4). Palynological sample P 1 from the upper Třebotov Limestone does not yield any determinable figured OWM. Sample P 2 from its topmost level bears a few thin-walled prasinophytes assignable to the genus Leiosphaeridia. The succeeding sample P 3 from the basal Choteč Limestone is more enriched in organic matter with small Tasmanites (Fig. 8f), a few Dictyotidium; spores, such as Acinosporites sp., Dibolisporites sp., cf. Camarozonotriletes sextantii and small-sized trilete forms occasionally occur (Fig. 8g). Sample P 4 is situated just below the limestone bed, which is considered to represent the level of the BCE. Sample P 4 contains a higher concentration of organic matter (often dark brown–black), but only a few palynomorphs can be identified. The main components are marine palynomorphs, such as chitinozoans, scolecodonts and fragments of thin-walled prasinophytes; terrestrial spores are very rare. With the onset of the distinctive dark-grey bioclastic limestone bed (i.e. sample P 5), which is about 20 cm above the base of the Choteč Limestone (Fig. 9), the palynological assemblage changes significantly. This bed is chracterized by mass occurrences of phycomata of prasinophycean algae: large (150–600 µm) Tasmanites spp. (Fig. 8k) and Leiosphaeridia spp. are the dominant groups, forms of Dictyotidium spp. are frequent. Comparatively less frequent, but important for characterizing this assemblage, are mazuelloids that are represented by different morphotypes. Rare to very abundant are scolecodonts, small-sized acritarchs of the Veryhachium trispinosum group, and spores, such as Lophotriletes devonicus (Fig. 8d). In addition to the standard preparation method, the ‘light organic fraction’ of sample P 5 was studied palynologically. The microscopic analysis reveals mostly larger-sized (150–500 µm), thin-walled prasinophytes of Leiosphaeridia type (Fig. 8j), and agglomerations of filamentous and spherical/coccoid cyanobacteria-like organic microfossils (Fig. 8h), along with fungi-like microorganisms. The palynological assemblage of the succeeding sample P 6 differs by the appearance of moderately frequent and diverse acritarchs, such as Cymatiosphaera cf. canadensis (Fig. 8b), C. cf. cornifera (Fig. 8e), Micrhystridium sp., Veryhachium trispinosum (Fig. 8a), Navifusa bacilla and Polyedryxium sp.. Prasinophytes – mainly Tasmanites sp. (Fig. 8j) and Dictyotidium sp. (Fig. 8m) – are present, but they are smaller and not abundant; small-sized apiculate spores are rare. It is likely that this composition points to an initial recovery of the ‘normal marine’ phytoplankton community. However, the presence of Cymatiosphaera spp. may also indicate freshwater influx (see the discussion in the ‘Interpretation’ section). Sample P 7 shows a similar, marine-dominated composition, but the overall frequency of palynomorphs follows the decreasing trend already observed in P 6. The main species are N. bacilla (Fig. 8i), Dictyotidium cf. variatum (Fig. 8c) and V. trispinosum. Spores are represented by apiculate specimens (e.g. Dibolisporites sp.). Samples P 6 and P 7 are derived from the darker lime–mudstone interval; above this, the sequence changes to a medium-grey, more thick-bedded limestone succession, but this part was not sampled for the current study. Sample P 8 is from an interval of platy, greenish-grey limestones with plant fossils. However, the palynological sample yields only sparse organic matter, no palynomorphs could be identified.
Palynomorphs of the Na Škrábku Quarry, Prague Basin. The photographs were taken in transmitted light and with applied infrared video technique (IR). Indicated are localities, stratigraphic position, sample/slide numbers, England Finder (E.F.) coordinates and identification numbers (PMP) of the palynological collection at Senckenberg. (a) Veryhachium trispinosum group; P 5-2, E.F. N56-2, PMP 235. (b) Cymatiosphaera cf. C. canadensis Deunff, 1961; P 6-1; E.F. D 54-1, PMP 236. (c) Dictyotidium cf. D. variatum Playford, 1977; P 5-2, E.F. S 42-4, PMP 235. (d) Lophotriletes devonicus (Naumova ex Chibrikova) McGregor & Camfield, 1982; P 5-2, E.F. K 52-4, PMP 235. (e) Cymatiosphaera cf. C.. cornifera Deunff, 1955; P6-2, E.F. K 37-2, PMP 236. (f) Tasmanites sp.; P 3-2, E.F. T 36-2, PMP 233. (g) cf. Camarozonotriletes sextantii McGregor & Camfield, 1976; P 3-1, E.F. J 37-3, PMP 233. (h) Agglomeration of filamentous and spherical cyanobacteria-like organic microfossils (light fraction of floating kerogen); P 5-C, E.F. G 53-1, PMP 235. (i) Navifusa bacilla (Deunff, 1955) Playford, 1977; P 7-2, E.F. Y 36-4, PMP 237. (j) Arrangement of thin-walled prasinophytes, cf. Leiosphaeridia sp. (light fraction of floating kerogen); P 5-C, E.F. W 35, PMP 235. (k) Tasmanites sp. (light fraction of floating kerogen); P 5-A, E.F. Q 39, PMP 235. (l) Scolecodont; P 5-1, E.F. C 49, PMP 235. (m) Dictyotidium sp.; P 5-2, E.F. C 41-1, PMP 235.
Thin-section of the bed representing the palynological sample P 5. It displays the BCE in the Na Škrábku Quarry: the bed is mostly developed as a peloidal grainstone (in parts mudstone to wackestone, partly bioclastic). Repeated cross-bedding with erosional contacts indicate current activity and associated sediment transport. Prasinophytes (dark spots) occur dispersedly in the entire bed, but are enriched in the middle, in slightly coarser laminae, and also aligned in cross-stratified laminae. The photograph was taken under transmitted light microscope; collection of the Senckenberg palynological section, number PMP 235 DS.
The studied part of the Na Škrábku section shows palynological assemblages, which are characteristic of a relatively deeper, basinward, organic-matter-rich setting. A variable mixture of marine palynomorphs, such as acritarchs, chitinozoans, scolecodonts and prasinophytes, with less frequent spores and phytoclasts represents the ‘normal marine’ composition. However, in the BCE level (palynological sample P 5), a unique proliferation of prasinophytes along with a higher portion of the enigmatic mazuelloids (=muellerisphaerids) took place. Mazuelloids were found in the routine palynological residue, together with a mass occurrence of prasinophytes obtained from the residue of the conodont preparation. (e.g. Brocke et al. 2011). In those residues they are even more frequent and show a higher diversity of morphotypes. It is likely that the preservation potential of such mineralized shells is higher, and shows more diversification and frequency in species.
Northern part of the Appalachian Basin (NAB)
Dacryoconarids
Seven dacryoconarid taxa, including six previously undescribed species, are present in the Nedrow Member of the NAB (Figs 10, 11, 12). The currently known first occurrence of Striatostyliolina mima n. sp. is at the base of the Edgecliff Member, and its currently known uppermost occurrence is in the mid-Givetian Ledyard Member of the Ludlowville Formation. A form of Striatostyliolina similar to S. mima is present in the upper Emsian Carlisle Center Member of the Schoharie Formation, but it is not currently certain that the two are conspecific. Viriatellina manifesta n. sp. may also first occur in the upper beds of the Schoharie Formation, but its currently certain first occurrence is at the base of the Clarence facies of the Edgecliff Limestone. This species may also occur in the upper Eifelian, post-Onondaga Bakoven Shale and possibly higher in the Hamilton Group in conjunction with several additional forms of the genus that appear to be descendants of V. manifesta n. sp.. The first occurrence of Costulatostyliolina vestita n. sp. is also at the base of the Edgecliff Member and its uppermost occurrence is just below the two Nedrow black beds that mark the top of the Nedrow Member. Styliolina robusta n. sp. and Viriatellina exila n. sp. first occur at the base of the Nedrow and last occur immediately below the two Nedrow black beds. If this limited, short-ranged presence of the two taxa holds true in the future (i.e. between the base of the Nedrow and the two Nedrow black beds near the top of the unit), they make up ideal index fossils for the Nedrow Member below the two dark marker beds. Striatostyliolina vitta n. sp., which also first occurs at the base of the Nedrow, is absent from the upper Onondaga, but recurs in the Chestnut Street Beds at the base of the Oatka Creek Formation, which is in the mid-Eifelian kockelianus Zone and part of the Stony Hollow Event (Ver Straeten & Brett 2006; Ver Straeten 2007; Brett et al. 2011; DeSantis & Brett 2011).
Range chart of dacryoconarid taxa through the BCE interval in the northern (NAB) and central part of the Appalachian Basin (CAB). Note the very good time-restricted ranges of some taxa, making them extremely good index fossils; also note the differences in dacryoconarid taxa between the NAB and the CAB. For further explanations, see the text.
Dacryoconarids of the Appalachian Basin. I. All figures are SEM images. New York State Museum (NYSM) numbers, sample localities, position in the section and E/E suite sample numbers are given where applicable. (a) Styliolina robusta n. sp.; holotype, NYSM 17229, NY Route 11, Nedrow, NY, basal Nedrow Member. (b) Styliolina cf. S. decurtata Bouček, 1964; NYSM 17236, Hayfield, VA, mid-Edgecliff-equivalent; E/E.07-1B-14. (c) & (d) Striatostyliolina mima n. sp.; holotype, NYSM 17230, US Route 20, Cherry Valley, NY, basal Nedrow Member. (e) Striatostyliolina vitta n. sp.; holotype, NYSM 17231, US Route 20, Cherry Valley, NY, 25 cm above the base of the Nedrow Member. (f) Costulatostyliolina cf. C. paucicostata (Bouček, 1964); NYSM 17237, Hayfield, VA, Nedrow-equivalent, LBB; E/E. 07-1B-17. (g) Costulatostyliolina vestita n. sp.; holotype, NYSM 17232, United States Route 20, Cherry Valley, NY, 25 cm above the base of the Nedrow Member.
Dacryoconarids of the Appalachian Basin. II. All figures are SEM images. New York State Museum (NYSM) numbers, sample localities, position in the section and E/E suite sample numbers are given where applicable. (a) Metastyliolina cf. M. striatissima Bouček & Prantl, 1961; NYSM 17238, Spring Gap, MD, Nedrow-equivalent, LBB; E/E. 07-5A-7. (b) Metastyliolina? sp. B; NYSM 17239, Hayfield, VA, Nedrow-equivalent, LBB; E/E 07-1B-17. (c) Nowakia (Dmitriella) sulcata antiqua Alberti, 1981; NYSM 17240, Mapleton, PA, Nedrow-equivalent, LBB; E/E 07-6-21. (d) & (e) Nowakia sp. A; NYSM 17235, 17241, Hayfield, VA, mid-Edgecliff-equivalent; E/E 07-1B-14. (f) Viriatellina manifesta n. sp.; NYSM 17233, Cherry Valley, NY, 25 cm above the base of the Nedrow Member. (g) Viriatellina exila n. sp.; NYSM 17234, Cherry Valley, NY, 25 cm above the base of the Nedrow Member.
Only two of the dacryoconarid species named above are known to occur in either of the two black beds at the top of the Nedrow in the northern AB. Although these beds are commonly devoid of dacryoconarids, Striatostyliolina mima n. sp., Costulatostyliolina vestita n. sp. and Metastyliolina? sp. B are occasionally present in small numbers.
Of the seven dacryoconarid taxa known to be present in the Nedrow of the northern region of the NAB during the BCE, two may predate, at least four originate early in, and five apparently became extinct late in the event interval. Most appear to be derived from similar forms that occur in the upper Emsian Schoharie Formation. Whereas four of the new species described herein are either extirpated or become extinct prior to apex of the BCE, Viriatellina manifesta n. sp. and Striatostyliolina mima n. sp. occur upsection in the Hamilton Group. One form, Metastyliolina? sp. B, which is restricted to one or both of the two UBB, first occurs at the base of the Nedrow in the CAB.
Other fauna
It appears that each faunal group responded to the BCE in its own particular fashion. Brachiopods seem to have been unaffected (Dutro 1981). Whereas conodonts, particularly lineages of Polygnathus, show no apparent deviation from the tempo of originations that had begun during late Emsian times (see Klapper 1981), ostracods underwent a profound extinction event (see Berdan 1981). Rugose coral diversity declined and provincialism began to disintegrate immediately before and during the BCE (Oliver 1977), particularly with the migration of Synaptophyllum into North America (Pedder 2010).
Oliver (1956) reported a subtle shift in benthic faunas during Nedrow deposition, but did not document a significant faunal turnover between the Nedrow and the upper members of the Onondaga. He did, however, document a geographical segregation of benthic faunas within the Nedrow interval between central New York and the SE part of the state. House (1981, p. 33) expanded the magnitude of this geographical segregation of faunas, reporting that his goniatite Fauna 2 in the Edgecliff and lowermost Nedrow, ‘rather widely distributed in the Southern Appalachians is a fauna, not recognized in New York’, and his Fauna 3, of the middle–upper Nedrow in New York, shares only one species, Foordites cf. F. buttsi, with the contemporaneous fauna of the Southern Appalachians. Dacryoconarids show this geographical segregation of AB faunas within the BCE interval more profoundly than do other faunal elements.
Organic-walled microfossils (OWM)
Five sections with a focus on the Nedrow Member (Onondaga Formation) have been studied palynologically in the NAB in New York: Stafford Quarry, Oak Corners Quarry, Schooley Quarry near Auburn, Nedrow (Jamesville) and Cherry Valley. In addition, one sample from the upper Edgecliff Member collected in the Oak Corners Quarry near Phelps has been included. Altogether, 13 samples have been analysed, from which six were palynologically productive. A majority of the lower Nedrow samples are characterized by a relatively low concentration of organic matter and moderate–poor preservation of the OWM; in many cases they are highly altered. Pyrite framboids are frequent in the organic residue, partly occurring in the interior of acritarch vesicles. Most of the palynomorphs are of marine origin, whereas terrestrially derived material is limited to a few spores and phytoclasts (tracheids and woody material of unknown derivation). This type of palynofacies is typical of an overall carbonaceous composition of the sedimentary rocks, associated with a usually lower preservation potential for figured organic matter. Material from the middle and upper Nedrow Member is richer in moderately to well-preserved palynomorphs.
In the basal and lower part of the Nedrow Member (Oak Corners Quarry and Cherry Valley), chitinozoans of Angochitina type (Figs 13, 14, 15), cf. Eisenackitina sp. (mostly fragments) and a few specimens of spherical chitinozoans assigned to the genus Hoegisphaera, namely Hoegisphaera cf. H. glabra, are present. Acritarchs are limited in number and diversity, and are poorly preserved. Most of them are of simple morphology bearing short spines (e.g. ?Winwaloeusia distracta or Gorgonisphaeridium spp.). In addition, a few thick-walled prasinophytes of Tasmanites type and scolecodonts are present. The spores are sparse; specimens of ?Retusotriletes sp. and a few poorly preserved, sculptured trilete spores have been observed at only a few levels at Cherry Valley (sample Ned 1-2, 75 cm above the base of the Nedrow Limestone). In the same sample several chains (? conidia) of morphotypes related to the possible fungi-like Reduviasporonites cf. R. stoschianus are present (Fig. 14: for a discussion see the ‘Systematic section’ later in this paper).
Palynomorphs of the Appalachian Basin. I. Photographs taken in transmitted light and with applied infrared video technique (IR). Indicated are localities, stratigraphic position, sample/slide numbers, England Finder (E.F.) coordinates and identification numbers (PMP) of the palynological collection at Senckenberg. (a) cf. Diexallophasis simplex Wicander & Wood, 1981, specimen with near-homomorphic unbranched, microgranulate processes; Stafford Quarry, west of Stafford, NY, shale at the Nedrow–Moorehouse contact (=the Nedrow black bed); A4-2-2, E.F. T 60-4, PMP 384. (b) Diexallophasis remota (Deunff) Playford, 1977; Stafford Quarry, NY, shale at the Nedrow–Moorehouse contact (=the Nedrow black bed); A4-2-2, E.F. T 37-1, PMP 384. (c) Polyedryxium pharaonis Deunff, 1961; Stafford Quarry, NY, shale at the Nedrow–Moorehouse contact (=the Nedrow black bed); A4-2-2, E.F. K 31-1, PMP 384. (d) Multiplicisphaeridium ramusculosum (Deflandre) Lister, 1970; Spring Gap roadcut, Maryland, close to basal Moorehouse-equivalent; E/E.11-1-13-1, E.F. H 59-2, PMP 737. (e) cf. Exochoderma arca Wicander & Wood, 1981; Stafford Quarry, NY, shale at the Nedrow–Moorehouse contact (=the Nedrow black bed); A4-2-2, E.F. J 43-2, PMP 384. (f) Tasmanites sp.; Stafford Quarry, NY, shale at the Nedrow–Moorehouse contact (=the Nedrow black bed); A4-2-2, E.F. W 44-2, PMP 384. (g) Emphanisporites rotatus McGregor emend. McGregor, 1973; Spring Gap roadcut, Maryland, basal–lower Nedrow-equivalent, IR; E/E.11-1-7A-2, E.F. Q 36-1, PMP 728. (h) Emphanisporites annulatus McGregor, 1961; Stafford Quarry, NY, middle Nedrow Member; A4-1-2, E.F. C 33-4, PMP 383. (i) Emphanisporites annulatus McGregor, 1961; Spring Gap roadcut, MD, basal–lower Nedrow-equivalent, IR; E/E.11-1-7A-2, E.F. Q 36-1, PMP 728. (j) Hoegisphaera cf. H. glabra Legault, 1973a, b; Keyser, WV, Middle Needmore Formation, approximate base of the Edgecliff-equivalent; E/E07.4-3; E.F. V 49-2, PMP 334. (k) Two specimens of Hoegisphaera cf. H. glabra Legault, 1973a, b with fragmentary rest of membrane (indicated by arrows); Hayfield, VA, approximate middle Nedrow-equivalent (below LBB), IR; E/E.11-4-12-1, E.F. F 53-1, PMP 715. (l) Hoegisphaera cf. H. glabra Legault, 1973a, b; Hayfield, VA, approximately middle Nedrow-equivalent (below LBB), IR; 11-4-12-1, E.F. M 60-3, PMP 715. (m) Hoegisphaera cf. H. glabra Legault, 1973a, b; Hayfield, VA, lower–middle Nedrow-equivalent, IR; E/E.11-4-13-2, E.F. P 43-4, PMP 716. (n) Ancyrochitina cf. A. lezaisensis Paris, 1981, with ring-like termination of processes (arrows); Spring Gap roadcut, MD, upper Edgecliff-equivalent, IR; E/E.11-1-5-2, E.F. K 64-4, PMP 726. (o) Angochitina sp.; Oaks Corners Quarry, NY, low in the Nedrow Member (base?); A4-9-2, E.F. X 56-2, PMP 386. (p) Part of the first maxillar of paulinitid or kielanoprionid scolecodont; Hayfield, VA, lower–? middle Nedrow-equivalent, IR; E/E.11-4-11-1, E.F. L 55-3, PMP 712. (q) Pair of carriers of ?paulinitid scolecodont; Hayfield, VA, basal Nedrow-equivalent; E/E.11-1-8-1, E.F. N 39-4, PMP 639.
Palynomorphs of the Appalachian Basin. II. Morphotypes assigned to the species cf. Reduviaspronites stoschianus (Figs 1, 2, 3, 6, 7, 8, 9, 10, 11, 12, 13, 16 & 17) and other unidentified palynomorphs mostly assigned to fungi from the upper Edgecliff Member and Nedrow Member, and equivalent strata in the Selinsgrove Member, Needmore Formation, in studied localities, Appalachian Basin, USA. Photographs were taken in transmitted light and with applied infrared video technique (IR). Indicated are locality, stratigraphic position, sample/slide numbers, England Finder (E.F.) coordinates and identification numbers (PMP) of the palynological collection at Senckenberg. (a) Stafford Quarry, east of Stafford, NY, middle Nedrow Member; A4-1-2, E.F. H 36-2, PMP 383. (b) Stafford Quarry, NY, middle Nedrow Member; A4-1-2, E.F. D 48-3, PMP 383. (c) Hayfield, VA, boundary interval between Edgecliff and Nedrow-equivalents; E/E.11-1-7A-2, E.F. S 32-4, PMP 729. (d) Stafford Quarry, NY, middle Nedrow Member; A4-1-1, E.F K 37-4, PMP 383. (e) Same specimen in IR showing channel-like structure in the centre of the object. (f) Spring Gap roadcut, MD, lower Nedrow-equivalent; E/E.11-1-7-1, E.F. S 32-4, PMP 729. (g) Same specimen in IR, showing internal structures such as segmentation? (h) Spring Gap roadcut, MD, lower Nedrow-equivalent; E/E.11-1-7A-2, E.F. Q 36-1, PMP 728. (i) Same specimen in IR, showing internal structures. (j) Spring Gap roadcut, MD, LBB; E/E.11-1-8A-1, E.F. D 61-3, PMP 731. (k) Spring Gap roadcut, MD, upper Edgecliff-equivalent; E/E.11-1-5-4, E.F. D H 56-2, PMP 726. (l) Same specimen in IR, showing vague segmentation possibly indicating cells. (m) Cherry Valley, NY, lower Nedrow Member; Ned. 1-2, E.F. Y 52-4. (n) Stafford Quarry, NY, middle Nedrow Member; A4-1-1, E.F. L 63-4. (o) Spring Gap roadcut, MD, upper Edgecliff-equivalent; E/E.11-1-5-2, E.F. K 64-4, PMP 726. (p) Spring Gap roadcut, MD, upper Edgecliff-equivalent; E/E.11-1-2-2, E.F. S 40-2, PMP 729. (q) Hayfield, VA, basal Nedrow-equivalent; E/E.11-1-8-1, E.F. N 39-4, PMP 639. (r) Photograph with interference contrast; Stafford Quarry, NY, middle Nedrow Member; A4-1-2, E.F C 44-4, PMP 383. (s) IR photography; Stafford Quarry, NY, middle Nedrow Member; A4-1-1, E.F. H 38-2, PMP 383. (t) Hayfield, VA, lower Nedrow-equivalent; E/E.11-4-11-1, E.F. L 55-3, PMP 712.
Details of section at Spring Gap, MD (north side of Maryland Route 51). The upper part of the informal calcareous shale member and the Selinsgrove Member, Needmore Formation. Correlations with New York members are denoted on the far right. Note the Nedrow black beds as two black bands at and above 15 m. Arrow-heads without a line denote altered airfall volcanic tephra layers (K-bentonites). Palynology samples marked as ‘E/E.11 …’; dacryoconarid samples marked as ‘E/E.07 …’. The key to the symbols is given in Figure 6; for levels of samples, see Table 1. Aq-Saug, Aquetuck and Saugerties members of New York's Schoharie Formation; equiv., equivalent; LBB, lower Nedrow black beds; UBB, upper Nedrow black beds; Zoo, heavily bioturbated bed of Zoophycos traces.
In the middle Nedrow of the Stafford Quarry section (sample A4-1), a different picture appears regarding the preservation of the organic matter in general, and in particular of the frequency and diversity of the OWM. The maturity of the organic matter at this locality is somewhat lower compared with that from Cherry Valley or Oak Corners Quarry. It is indicated by a pale to yellow colour of acritarchs, and a light–middle brown colour of prasinophytes, spores and zooclasts. The assemblage of sample A4-1 is characterized by moderately preserved marine and terrestrial elements. Acritarchs are the prevalent components. Among them Navifusa bacilla, Leiofusa estrecha, Multiplicisphaeridium cf. M. ramusculosum, Diexallophasis spp., Ozotobrachion furcillatus, Cymatiosphaera cornifera, Dictyotidium sp., Gorgonisphaeridium sp., Baltisphaeridium cf. B. distentum sensu Playford, 1977, Polyedryxium spp. and cf. Hapsidopalla chela are present to abundant. Thick-walled specimens of Tasmanites are frequent. Spores are represented by a few specimens of Verrucosisporites cf. V. polygonalis, Emphanisporites annulatus (Fig. 13h), and other altered specimens of Emphanisporites and unclassified trilete forms. Reduviasporonites cf. R stoschianus is, beside the acritarchs, the most common taxon; it occurs as conidia-like chains. Also present are thick-walled dark hyphae (e.g. Fig. 14t). Cuticles of animal origin (zooclasts) exist sporadically.
In the upper Nedrow of Stafford Quarry (= at the position of the Nedrow black beds) palynomorphs are less numerous, but the preservation is moderate–good: acritarchs, such as Diexallophasis simplex (Fig. 13a), D. remota (Fig. 13b) and Tasmanites sp. (Fig. 13f), are predominant. Navifusa bacilla, Polyedryxium pharaonis (Fig. 13c), cf. Exochoderma arca (Fig. 13e), scolecodonts and spores occur occasionally, whereas some hyphae could represent Reduviasporonites (e.g. Fig. 14d, e). Some black palynomorphs are clearly filled by pyrite (no transparency when infrared microscopy is applied), others may point to reworking as they are darker compared to the majority of the pale to brownish palynomorphs.
The Oak Corners Quarry assemblage in the mid-Edgecliff-equivalent is even poorer in OWM, but, in contrast to the Stafford Quarry, terrestrial plant remains (tracheids) and spores are more common; cuticles of zooclasts and tubular filaments (? hyphae of cf. R. stoschianus: Fig. 14s) are present in low numbers. Acritarchs and prasinophytes are more or less absent.
At the Schooley Quarry, a sample from the UBB (00-03) yields mainly small-sized sculptured acritarchs, such as Gorgonisphaeridium sp., and other unidentified forms with short processes. Phytoclast, spores, degraded prasinophytes and zooclasts are rarely present. This sample and the one from the LBB (00-04) are rich in organic matter, but its high degree of alteration hampers the identification of the palynomorphs.
To summarize, studies of palynological assemblages from the NAB focused largely on the Nedrow Member. In the lower Nedrow, they are mainly characterized by the presence of acritarchs, whereas chitinozoans and spores are less frequent. However, the chitinozoan Hoegisphaera cf. H. glabra is also present in low numbers. Hoegisphaera glabra has previously been reported from higher parts of the Eifelian Columbus and Delaware limestones of Ohio (Wright 1976, 1978). Wright (1980) described a somewhat similar composition from the Middle Devonian of Indiana, but there the typical H. glabra occurs higher in the Hamilton Group (i.e. in the Givetian). Other reports of H. glabra in the Givetian are from Kentucky (Wood & Clendening 1985) and Iowa (Urban 1972; Urban & Newport 1973; Wicander & Wood 1997). Acritarchs in the middle Nedrow Member are diverse and represented by forms with longer processes (e.g. Diexallophasis spp., Exochoderma arca and Polyedryxium pharaonis), both indicative of open, normal marine, shelf conditions. This is also consistent with the relatively rare occurrence of spores and phytoclasts. Tasmanites is abundant in some levels of the middle and upper Nedrow Member; the same is true for Reduviasporonites cf. R. stoschianus. The proliferation of both taxa is in accordance with the concept of an ecological epibole, as defined by Brett & Baird (1997).
Stratigraphically important is the occurrence of Emphanisporites annulatus; its range is from the Emsian to the Givetian worldwide, but it is also typical of the Eifelian in North America (e.g. McGregor & Camfield 1982; Ravn & Benson 1988; Traverse & Schuyler 1994).
Central part of the Appalachian Basin (CAB)
Dacryoconarids
In the CAB, the dacryoconarid fauna of the mid-Edgecliff-equivalent strata of the Selinsgrove Member includes at least four Old World taxa (Figs 10, 11, 12) that have not previously been reported from the Eastern Americas Realm. All occur upsection in the Nedrow-equivalent to the lower of the two Nedrow black beds and two also occur in the UBB, which marks the top of the BCE interval. Only Nowakia (Dmitriella) sulcata cf. N. (D.) s. antiqua has been observed higher in the section as a member of the Stony Hollow Event fauna at the base of the Oatka Creek Formation at Cherry Valley, New York.
Although the Emsian dacryoconarid fauna of the CAB has yet to be described formally, it has been studied in sufficient detail to state with certainty that the BCE dacryoconarid fauna of the CAB was not derived from dacryoconarids that occur in either the subjacent Edgecliff-equivalent strata or below that in the upper Emsian Schoharie-equivalent strata. The Nedrow-equivalent dacryoconarid fauna consists of Old World Realm (OWR) species or their descendants, which immigrated into the CAB at the onset of the BCE and departed one way or another at the close of the event. One of these taxa immigrated to the NAB during the T–R Cycle Ic maximum flooding, which is the acme and termination of the BCE.
Organic-walled microfossils (OWM)
Palynologically, two sections in the CAB – Spring Gap (Maryland) and Hayfield (Virginia) – have been analysed in great detail (Figs 15 & 16; Table 1); further samples have been studied from Gainesboro (Virginia), Keyser (West Virginia) and Mapleton (Pennsylvania).
Details of the section at Hayfield, VA (NE side at the intersection of US Route 50 and Virginia Route 600). The upper part of the informal calcareous shale member and the Selinsgrove Member, Needmore Formation. Correlations with New York units are denoted on the far right. The key to the symbols is given in Figure 6; for levels of samples, see Table 1. Nedrow black beds are seen in the middle of the section. An additional section below this is visible on western side of Route 600. Palynology samples marked as ‘E/E.11 …’; dacryoconarid samples marked as ‘E/E.07 …’. Symbols and abbreviations as in Figures 5 and 15.
The Spring Gap section reaches from Schoharie Formation-equivalents to equivalents of the Edgecliff, Nedrow and lower Moorhouse members, and is represented by 18 palynological samples (Fig. 15). In addition, two samples from the Nedrow black beds had previously been studied. In general, samples are characterized by a comparatively high content of organic matter with generally poor preservation and an apparent higher level of maturity compared to the NAB. Palynomorphs are mainly dark brown to opaque and often determinable only when infrared microscopy (IR) is applied. However, some levels yield material of better preservation with light–medium brown palynomorphs. Samples from the Schoharie Formation-equivalent are very poor in palynomorphs or are even barren. Only some remains of spores (retusotrilete forms), chitinozoans, Navifusa sp. and possible phytoclasts have been detected. The first good record comes from the transition to the Edgecliff-equivalent (sample E/E.II-1-4). This sample yields few phytoclasts, small acritarchs of the Multiplicisphaeridium type and a few specimens of cf. Reduviasporonites stoschianus. The next sample up in the section, E/E.II-1-5, is quite rich in spores (e.g. Apiculiretusispora plicata, Retusotriletes rotundus, Emphanisporites annulatus, E. rotatus and several other undetermined taxa); rarely present are phytoclasts, acritarchs, such as Multiplicisphaeridium sp., specimens of Dictyotriletes sp. and chitinozoans, such as ?Ancyrochitina cf. A. lezaisensis (Fig. 13n). Sample E/E.II-1-6 displays poorly preserved spores and a few cf. R. stoschianus (only assignable by IR method) and no marine palynomorphs so far. Samples E/E.II-1-7a, E/E.II-1-7b and E/E.II-1-7c in the mid-Nedrow-equivalent show the highest number of specimens and a better preservation of palynomorphs (pale to medium brown). Some of them (mainly spores) are darker, perhaps owing to reworking. Prevalent are cf. R. stoschianus (? conidia and hyphae) and N. bacilla; spores, such as E. annulatus (Fig. 13i), E. rotatus (Fig. 13g), Retusotriletes spp. and Apiculiretusispora sp., and chitinozoans (Angochitina spp., ?Ancyrochitina) are common. Acritarchs are represented by species of the genera Diexallophasis and Polyedryxium. Sample E/E.II-1-8 from the LBB is rich in organic matter, but palynomorphs are difficult to identify owing to poor preservation. Samples were additionally treated in an ultrasonic bath in order to clear them from amorphous organic matter (AOM). The most common forms are phytoclasts and cf. R. stoschianus (mainly hyphae up to 500 µm in length). The presence of zooclasts is likely. The UBB (E/E.II-1-9 and additional sample E/E07-5A) shows a similar picture, but spores (cf. Grandispora, but mostly unidentified), chitinozoan remains (cf. Ancyrochitina) and a few acritarchs, such as Veryhachium polyaster, N. bacilla and Micrhystidium spp., occur occasionally. Forms of cf. Reduviasporonites are common. The next prolific samples (E/E.II-1-11–E/E.II-1-13) are already located in the lower Moorehouse-equivalent. The palynospectrum is characterized by a dominance of AOM, phytoclasts, questionable spores and probable hyphae of cf. R. stoschianus. Marine components are represented by acritarchs, such as Veryhachium and Multiplicisphaeridium ramusculosum (Fig. 13d), chitinozoans, such as Hoegisphaera cf. H. glabra, scolecodonts in higher numbers and zooclasts.
The Hayfield roadcut section comprises upper Schoharie Formation-equivalent, Edgecliff-equivalent, Nedrow-equivalent, Moorhouse-equivalent and Seneca-equivalent strata (the last not sampled for palynomorphs). The studied interval is represented by 22 palynological samples (Fig. 16).
Samples from the upper Schoharie Formation-equivalent are poor in palynomorphs, but cf. Reduviasporonites and few spores have been identified. One of them recalls a specimen of Rhabdosporites; others belong to unidentified apiculate and zonate/pseudosaccate forms. The next prolific sample is from the basal Edgecliff-equivalent (E/EII-4-03), which bears chitinozoan fragments of possibly Alpenachitina eisenacki origin, scolecodonts, spores (Acinosporites cf. A. lindlarensis) and, further, unidentified opaque specimens (due to reworking?). Sample E/E.II-4-05 from a shaly interval in the Edgecliff-equivalent yields spores and N. bacilla; other acritarchs are rare; cf. R. stoschianus is sporadically present. Samples from the top of the Edgecliff-equivalent (E/E.II-4-07 and E/E.II-4-07/08) are quite rich in acritarchs (Diexallophasis spp., Veryhachium sp., cf. Hapsidopalla chela, N. bacilla and Multiplicisphaeridium spp.). Spores are represented by aff. Dibolisporites sp.; chitinozoans are preserved as fragments only. Samples E/E.II-4-09 and E/E.II-4-10 from the basal Nedrow-equivalent up to the last sample before the Nedrow black beds interval display frequent occurrences of chitinozoans (e.g. Angochitina sp.) and scolecodonts; some of them are comparatively large (up to 800 µm) in contrast to specimens found in older assemblages. In addition, few spores and questionable Reduviasporonites forms are present. Samples from the Middle Nedrow-equivalent (E/E.11-4-11–E/E.11-4-13) up to the LBB (E/E.II-4-11-15, E/E07-1b-16 and E/E.11-4-17) are distinct from most previous ones by their general high content of organic matter and significant palynological composition. Prevalent are Hoegisphaera cf. H. glabra (Fig. 13k, m) associated with aff. Alpenachitina eisenacki (mostly dark fragments) and large-sized scolecodonts (Fig. 13p, q). Spores are represented by Apiculiretusispora sp. and other unidentified retusotrilete forms. Hyphae of cf. Reduviasporonites occur in lower number whereas acritarchs are very rare; only few small specimens of Micrhystridium have been observed.
Upper Nedrow black bed (UBB) assemblages (E/E.II-4-16/17; E/E07-1b-19) are different from those of the LBB. Acritarchs, such as Triangulina alargada, Veryhachium polyaster and Micrhystridium spp., are more frequent, as is Tasmanites sp.; chitinozoans and scolecodonts are rare. Terrestrial material is represented by small trilete spores (e.g. cf. Aneurospora minuta) and phytoclasts.
Our highest sample E/E.II-4-18 from the basal Moorehouse-equivalent is less productive than those from the black beds. Few acritarchs, chitinozoans and prasinophytes have been found along with spores, whereas those species typical for the black beds (Hoegisphaera cf. H. glabra and cf. R. stoschianus) are absent.
From the Gainsboro section (Virginia), two samples representing the LBB and the UBB have been investigated. Sample E/E07-2-6 from the LBB yields hyphae of cf. Reduviasporonites. Phytoclasts are common, trilete spores are present, but are highly altered or too dark – even using the IR method – to assign them systematically.
The sample from the UBB (E-E07-2-8) displays a much better preservation of the OWM. Acritarchs are the dominant group; common are Hapsidopalla chela and Micrhystridium spp. Thin-walled prasinophytes (Leiosphaeridia sp.), cf. Reduviasporonites stoschianus and scolecodonts, as well as spores, such as Retusotriletes sp., cf. Cymbosporites proteus and Dibolisporites sp., are frequent.
Additional samples are available from the Keyser section (West Virginia), but only a few have been studied in detail. A comprehensive analysis will be the matter of future investigations, including the application of SEM studies. In general, the overall impression of the palynological composition of the entire section is similar to that from Hayfield. However, in Keyser, morphotypes of Hoegisphaera occur earlier, close to the base of the Edgecliff-equivalent, just below the base of Devonian Sequence Ic (sample E/E 07.04.3: Fig. 13j). In consequence, at least the genus Hoegisphaera is not restricted to the middle and upper Nedrow, in particular to the black beds interval. Subsequent taxonomical studies on these forms will be directed to resolve a possible conspecific relationship to H. cf. H. glabra.
The LBB sample from the Mapleton Quarry (Pennsylvania) is very rich in AOM, but only very few figured specimens (possibly algae and spores) can be identified.
CAB samples from the boundary interval between the Edgecliff and Nedrow units up through the entire Nedrow Member-equivalents (including the black beds) show, in parts, a significantly large number of cf. Reduviasporonites stoschianus and Hoegisphaera cf. H. glabra, interpreted here as an ecological epibole in the respective succession. Those samples are often accompanied by large numbers of larger scolecodonts. Chitinozoans, acritarchs and spores vary in frequency and diversity in the entire Nedrow-equivalent, but, in the upper Edgecliff-equivalent, acritarchs can be abundant and diverse. The increase in chitinozoan diversity in some levels indicates a ‘deeper-water’, more basinal depositional setting. Stratigraphically important acritarchs are Triangulina alargada and Hapsidopalla chela, the latter is common in the Eifelian–lower Givetian of the Silica Formation of Ohio (e.g. Wicander & Wood 1981). Among the spores, Emphanisporites annulatus and E. rotatus and specimens tentatively assigned to the genera Grandispora and Rhabdosporites indicate a late Emsian–early Eifelian age.
Interpretation
This paper represents the first comparison of the Basal Choteč Event (BCE) interval between the Barrandian type area and the Appalachian Basin. As the focus clearly was set on the palynomorphs and the dacryoconarids (a comparison of these organisms has never been carried out before), other faunal elements and abiotic features have only been considered when additional information was needed (Fig. 17). Therefore, conclusions on the two groups of organisms are given in some detail; for the dacryoconarids, formal descriptions are added – eight of them represent new taxa for the AB.
Ranges of selected dacryoconarid and palynomorph taxa connected to the BCE, not to scale. In the Appalachian Basin, endemic forms exist besides the given species, see Figure 10. In the NAB, the last occurrence of Nowakia (D.) sulcata antigua is recorded from the Chestnut Street Bed (base of the Oatka Creek Formation), and the supposed (?) last occurrence of Viriatellina manifesta from the Bakoven Member. According to the dacryoconarids, an interval for the BCE ranging from the mid-Edgecliff Member to the top Nedrow Member can be identified. However, a culmination/acme in the black beds of the Nedrow Member is obvious by the restricted occurrence of Metastyliolina? sp. B.; cf. Reduviasporonites stoschianus and the chitinozoan Hoegisphaera sp. cf. H. glabra are present in the entire Nedrow Member, but seem to also prevail in the black beds. However, in the Na Škrábku section of the Barrandian area, this event is apparently restricted to a single bed (=palynological sample P 5, compare Figs 4a & 9) close to the base of the Choteč Limestone.
Palynological studies from the Na Škrábku Quarry reveal a distinct palynological assemblage of the bed, which represents the level of the BCE. The palynological composition of this characteristic bed (sample P 5) is dominated by prasinophycean phycomata up to 600 µm in diameter. In addition, cyanobacterial agglomerations and fungi-like microfossils are present; other palynomorphs occur in very low numbers. Because this exceptional proliferation is restricted to this bed, we conclude that it represents an ecological epibole, as redefined by Brett & Baird (1997). It is widely accepted that prasinophytes are able to tolerate specific ecological conditions compared to normal marine phytoplankton, and are able to form blooms when, for example, acritarchs retreated or disappeared. When occurring in the geological record, such prasinophytes are frequently called ‘disaster species’, a term introduced by Tappan (1980) and subsequently applied by several authors (e.g. Riegel et al. 1986; Van de Schootbrugge et al. 2007). Causes for phytoplankton blooms are still speculative. Often such mass occurrences are explained by a temporal stratification of the water column, (e.g. by lowered salinity induced by the input of freshwater and/or restricted ocean circulation). Another possible cause is higher nutrient load (e.g. nitrogen, iron, phosphate) derived from land by fluvial or aeolian transport or as a result of marine upwelling. However, green algae, such as the prasinophytes, are able to use reduced nitrogen (i.e. ammonium) much more effectively than other algal groups, especially under conditions of black shale deposition (Prauss 2007; Riegel 2008). In this case the blooming of these opportunistic algae at the BCE might be related to enhanced nutrient supply coming from land (fluvial and/or aeolian), together with the establishment of a pycnocline induced by lower salinity from freshwater input during maxiumum transgression. In the BCE sample P 5, and particularily in the succeeding samples P 6 and P 7, the possibly freshwater tolerant genus Cymatiosphaera is common. Since it was also reported from the Lower Devonian freshwater ecosystem of the Rhynie chert (Dotzler et al. 2007), a freshwater influence seems likely. Mazuelloids, which co-occur in the same sample, are considered to reflect specific environmental conditions (e.g. nutrient-rich waters); their appearance as blooms is also associated with black shales (Kremer 2005).
In the Appalchian Basin, the interval of the BCE does not show such a distinctive bloom of prasinophytes, as is revealed in the Barrandian section. However, a higher abundance of these algae exists in the Nedrow Member of the NAB, although the relevant assemblages are not exclusively formed by prasinophytes. Here, they are accompanied by the appearance of comparatively high proportions of cf. Reduviasporonites stoschianus and Hoegisphaera cf. H. glabra. In the CAB, prasinophytes are present, but not abundant; dominant are cf. R. stoschianus and H. cf. H. glabra.
Proliferations of fungi or microfossils attributed to fungi have been frequently reported from different time periods and areas, and are usually interpreted to reflect ecological crisis – they clearly do co-occur with various bioevents. Well known is the Permian–Triassic Extinction Event, in which a fungal spike is considered to be one indicator of a disrupted ecosystem following the mass extinction (e.g. Visscher et al. 1996, 2011; Bercovici et al. 2015). Such fungi were also found in higher numbers in the Pennsylvanian of Peru (Wood & Elsik 1999) and, more recently, from the Cretaceous–Palaeogene boundary (e.g. Vajda & Bercovici 2014) and the Oligocene–Miocene boundary in Egypt (El Atfy et al. 2013). In the latter, the fungal peak co-occurs with freshwater algae.
Mass occurrences of chitinozoans are little known, but have been reported from the Kellwasser Crisis interval near the Frasnian–Famennian boundary in France (Paris et al. 1996), in which Angochitininae bloom in the respective layers of the La Serre section (Montagne Noire). Hoegisphaera cf. H. glabra does not occur in masses, but is relatively abundant in the Nedrow Member or its equivalents, more or less simultaneously with cf. R. stoschianus, and has not been reported in significant numbers from underlying or overlying strata of our sections. We consider that both taxa characterize the BCE and interpret their proliferation as an ecological epibole.
While in the Na Škrábku Quarry (Prague Basin), the BCE is best seen in a distinct level (sample P 5), in the Appalachian Basin, the interval ranges probably from the uppermost Edgecliff Member and its equivalents up to the top of the Nedrow Member and its equivalents. However, there the UBB obviously represents the termination of the BCE.
From a stratigrapical point of view, spores, such as Emphanisporites annulatus and E. rotatus, and acritarchs, such as Triangulina alargada, Hapsidopalla chela and Ozotobrachion furcillatus, are common from the upper Emsian to the Givetian. Such forms and related taxa may have the potential to refine the lower Eifelian. However, more detailed taxonomy, in particular by SEM studies of the prolific palynological assemblages, is required.
Dacryoconarids are an important tool in dealing with the globally detectable BCE. They are present in the Old World Realm (OWR: e.g. Barrandian area, German Rhenohercynian, and Saxothuringian Belts, Carnic Alps, North Africa) and in the North American New World Realm (NWR: e.g. Nevada, Appalachian Basin). Dacryoconarid occurrences on continents other than Europe and North America are beyond the palaeogeographical scope of this paper. A main point of the dacryoconarid studies presented here is to show – for a number of taxa for the first time – the relationships (or discrepancies) between the ‘classical’ areas of the OWR and regions within the Appalachian Basin.
In the classical regions of Central Europe, numerous dacryoconarid taxa are very good indicators of both the brief time interval of the BCE and the Lower–Middle Devonian (=Emsian–Eifelian) boundary. For the history and discussion of the boundary see, for example, Ziegler & Klapper (1985), Chlupáč & Kukal (1986), Walliser (1996), Ziegler (2000) and detailed references therein. Special aspects with respect to dacryoconarids are dealt with in Bouček (1964), Alberti (1985a, b, 1993), Lukeš (1989) and Chlupáč (1985, 1998). The classical sections of Holyně (in the Barrandian area: see Lukeš 1989; Chlupáč 1985, 1998) and Haiger Hütte (in the German Rhenohercynian: see Alberti 1985b, 1993) yielded many of the taxa mentioned in this paper. For the regional zonation in the Carnic Alps, see Alberti (1985a). Main ‘actors’ among the dacryoconarids are Nowakia (Nowakia) maureri (with the subspecies N. (N.) m. maureri and N. (N.) m. holynensis), N. (N.) holyocera, N. (Dmitriella) sulcata (with the subspecies N. (D.) s. antiqua and N. (D.) s. sulcata) and N. (Maureriana) procera. Taxa, such as N. (N.) m. maureri and N. (N.) m. holynensis, are characteristic of the interval immediately below and right at the Emsian–Eifelian boundary. The same holds true for N. (N.) holyocera and N. (D.) s. antiqua. In the OWR, two taxa are critical markers for the onset of the Eifelian stage: N. (M.) procera and N. (D.) s. sulcata, both of which are present in the Haiger Hütte section above the boundary. This is supported by Lütke (1985) for N. (M.) procera from the costatus Zone of Nevada.
Nowakia (M.) procera is of special interest for comparison with the AB because it seems to be very closely related to a new species (Nowakia sp. A) from the CAB covering (most probably) a similar time interval (see Figs 10 & 17). Currently, research on dacryoconarids of the AB (and correlation with the OWR) is in progress, but some remarkable conclusions can be drawn based on the present data (for details see the ‘Systematic section’ later in this paper). No Eifelian taxa have previously been described formally from the AB. Ranges of the dacryoconarids from the northern and central parts of the Appalachian Basin (AB) are shown in Figure 10. There is no doubt that the AB was occupied by two discrete faunas with disparate origins and histories. The fauna of the NAB evolved from endemic Emsian ancestors and, whereas new species first and last occur within the BCE, those that survived the crisis are the founders of much of the Hamilton Group dacryoconarids. However, the BCE fauna of the CAB is an immigrant fauna of conspecific or closely related Old World taxa, which supplanted the endemic Emsian fauna and, for the most part, became extinct during the acme of the BCE. The occurrence of these taxa is an incursion epibole sensu Brett & Baird (1997). The taxa have immigrated within the short time interval of the BCE to the CAB, possibly migrating SW from the Old World into the Appalachian Basin embayment (Fig. 18). As far as the dacryoconarids are concerned, the event interval extends from the middle Edgecliff Member of the Onondaga Formation to the LBB and UBB of the uppermost Nedrow Member strata, and their equivalents. We regard the LBB–UBB, where most dacryoconarids became extinct, to be the acme or culmination of the BCE.
Palaeogeographical reconstruction modified from Blakey (2007), with the suggested immigration path (red line) of dacryoconarid taxa from the OWR now recognized in the Appalachian Basin. BA, Barrandian area (Prague Basin, Czech Republic); RS, Rheinisches Schiefergebirge (Germany); AB, Appalachian Basin (eastern USA); south tropical current adopted from Wilde et al. (1991).
Only two dacryoconarid taxa occur in both the NAB and the CAB, and both yield peculiarities. Metastyliolina sp. B is present in the NAB in the LBB and probably in the UBB; in the CAB, it is present exclusively in the LBB. Regardless of the questionable specimen in the UBB of the NAB, the taxon is an excellent index fossil for the upper part of the Nedrow Member and its equivalents, and even for the very short time interval of the widespread Nedrow black beds. The second taxon shared by the northern and central areas of the Appalachian Basin is Nowakia (Dmitriella) sulcata antiqua. In the CAB, it covers the interval from equivalents of the middle Edgecliff Member to the UBB of the Nedrow Member. In the NAB, however, it is present only in the Chestnut Street Beds of the Cherry Valley area: that is, in much younger strata of the basal Oatka Creek Formation, probably related to the acme of the Stony Hollow Event (compareVer Straeten & Brett 2006; Ver Straeten 2007; Brett et al. 2011; DeSantis & Brett 2011). There is, at present, no explanation for this late appearance in the NAB; however, the range of the taxon, including a late occurrence in the upper part of the Choteč Limestone in the Barrandian area (Alberti 1993), is similar to the OWR. Nowakia (D.) s. antiqua has not previously been reported from the AB. All other taxa differ between the two subregions of the Appalachian Basin. However, they make very good index fossils and are partly conspecific with forms from the OWR (e.g. Costulatostyliolina cf. paucicostata). In the NAB, Styliolina robusta n. sp. and Viriatellina exilia n. sp. represent perfect index fossils for the lower part of the Nedrow Member. Costulatostyliolina vestita n. sp. and Viriatellina manifesta n. sp., as well as Striatostyliolina vitta n. sp. and Striatostyliolina mima n. sp., have a somewhat wider time range (for details see Figs 10 & 17).
In addition to the results derived from the two groups of fossil organisms, the presence of the two widely distributed black beds (LBB and UBB) of the upper Nedrow Member (e.g. Brett & Ver Straeten 1994; Ver Straeten & Brett 2006; Ver Straeten 2007) is a striking phenomenon. They resemble features known as ‘time-specific facies’ (Walliser 1984a, b, 1986; for further explanations see Brett et al. 2012), at least within the Appalachian basins. Recent recognition of dark shales within the Choteč Limestone of the Barrandian Holyně section (R. Brocke & O. Fatka work in progress) may even allow comparisons across much more widely separated areas.
Concluding remarks
Based on two fossil groups (palynomorphs and dacryoconarids), the Barrandian type area (Prague Basin) has been compared for the first time with the Appalachian Basin with respect to the globally recognizable BCE. In addition, previous results on sea-level fluctuations in the AB by one of us (C.A. Ver Straeten) are given. The critical event interval, through the Edgecliff and Nedrow members, represents a third-order transgressive systems tract (TST). Culmination of the transgressive phase (=maximum transgression: i.e. ‘the surface of maximum flooding’ in sequence stratigraphic terms) lies in the topmost Nedrow Member: that is, at the position of the widely distributed ‘black beds’ of the Nedrow. The transgressive succession represents the lower half of the Ic Sequence (=Ic T–R Cycle of Johnson et al. 1985; =Eif-1 Sequence of Brett & Ver Straeten 1994; Ver Straeten 2007; Brett et al. 2011) which is considered to be a third-order sequence.
The palynological studies show two distinct proliferations of OWM in the investigated areas. Palynological assemblages of the distinctive bed of the BCE level in its type locality are characterized by mass-occurrences of large prasinophytes, while those from strata below and above reveal, to a large extent, palynospectra of ‘normal marine’ composition. Thus, the BCE represents a bioevent recognizable by an ecological epibole of a distinct phytoplankton group. The AB palynological assemblages show abundances of the fungi-like cf. Reduviasporonites stoschianus and of the glabrous chitinozoan Hoegisphaera sp. cf. H. glabra. They co-occur in many levels of the Nedrow Member and its equivalents, but are absent or very rare in the strata below and above. Therefore, we interpret their occurrence in the AB to represent a somewhat similar and contemporaneous ecological epibole to the prasinophyte epibole in the Barrandian area, which corresponds to the BCE. However, whilst in the Barrandian, the event is best recognizable in a distinct bed, in the Appalachian Basin it covers an interval of several metres, terminating with the two black beds in the upper Nedrow Member. This accords with the dacryoconarid record.
Further results of the dacryoconarid studies include the recognition of an immigration event (incursion epibole) of taxa from the OWR into the Central Appalachian Basin, and a separation of dacryoconarid faunas between the northern and central parts of the Appalachian Basin. At least four Old World taxa that have not previously been reported from the Eastern Americas Realm were discovered. Only two taxa are shared by both subregions of the AB. An immigration path from the Prague Basin–Rhenohercynian Zone along the SE margin of Laurussia is suggested (Fig. 18). In addition, faunal connections with North Africa also existed in the critical time interval, as indicated by House (1973) and Oliver (1977) regarding goniatites and rugose corals, respectively. As for the dacryoconarids, at least two of the taxa detected now in the AB (Nowakia (Dmitriella) sulcata antiqua and Costulatostyliolina paucicostata) are also known from the uppermost Emsian of North Africa (Alberti 1993). Concerning biostratigraphy, some of the taxa serve as excellent index forms. Hence, correlation of the BCE interval between the studied areas is now clearly shown by their dacryoconarid successions (Figs 10 & 17).
Furthermore, the widely distributed black beds of the upper Nedrow Member (LBB and UBB) can be regarded as representing, at least regionally, a ‘time-specific facies’ development in the sense of Walliser (1984a, b, 1986).
Systematic section
Palynology
Fungi-like palynomorphs
In the studied upper Nedrow Member-equivalent sequences (e.g. the Nedrow black beds), palynomorphs were discovered that are morphologically close to the supposed fungal structure Reduviasporonites stoschianus, as described from the Pennsylvanian of Peru (Wood & Elsik 1999). Other Carboniferous records of Reduviasporonites (R. chalastus) are known from Scotland (Stephenson et al. 2004). The Appalachian material is, to our knowledge, the oldest record of morphotypes attributable to Reduviasporonites. Studied specimens are tentatively assigned to R. stoschianus by following the classification and morphological nomenclature of Wood & Elsik (1999). However, systematically, they are classified here as Incertae sedis. In doing so, we are aware of the ongoing discussion about the biological origin of the genus Reduviasporonites, mainly in the context of the Permian–Triassic Extinction Event. Whether those microfossils represent fungi (e.g. Visscher et al. 1996, 2011; Steiner et al. 2003), acritarchs or zygnemataceaen algae (Afonin et al. 2001; Foster et al. 2002), or whether they are even of animal origin (e.g. coelenterate polyps: Kalgutkar & Jansonius 2000), is not yet clear. Further detailed analysis, including SEM studies on the given material and comparisons with co-equal specimens from other localities, are required.
The studied material does not show fluorescence, which is typical for an algal origin. Furthermore, the morphology is variable; some forms resemble skeletal hyphae of fungi. Other specimens are uniserial tubular, often branched filaments with or without clear segmentation, which could be interpreted as conidiophores. A third morphotype shows chains of cells or dispersed cells interpreted as coinids, which is typical for Reduviasporonites.
In some aspects, morphotypes are similar to the so-called tubiphytes, which have been assigned to cyanobacteria (e.g. see the discussion in Riding & Guo 1992). Banded tubes, very common in palynological residues from the Silurian to Devonian, are often classified as nematoclasts (e.g. Porcatitubulus: Taylor & Wellman 2009; Filipak & Zaton 2011), but in many cases their origin is still uncertain. However, subspherical to elongated, relatively thin-walled forms occur, which may represent single elements of fungal chains that form conidia, but which also show morphological similarities to the acitarch Navifusa. Thus, a confusion of identification is possible, in particular as both ‘taxa’ occur in the same assemblages.
Incertae sedis
Genus Reduviasporonites Wilson, 1962
Type species Reduviasporonites catenulatus Wilson, 1962
cf. Reduviasporonites stoschianus (Balme, 1980) Elsik, 1999
(Fig. 14a–c, f–m, p, q)
Remarks
The Devonian specimens of cf. Reduviasporonites stoschianus from the Appalachian Basin show a close morphological similarity to the Pennsylvanian specimens of Peru (Wood & Elsik 1999), and in parts to those described from the Upper Permian Bellerophon Formation in Italy (Elsik 1999). Specimens of cf. R. stoschianus show a variety in morphology, they occur in chains of cells (‘conidia’), as well as branched or unbranched hyphea-like tubes (‘conidiophores’) in the same samples. The ‘conidiophores’ are often thicker walled and provided with septa, and may show distal furcation or bulbous to truncate morphology. The inner wall is characteristically shrunken. Conidia are usually elongated rather than spherical with septa. These may also morphologically refer to Reduviasporonites chalastus (M. Stephenson pers. comm. 2014). Kalgutkar & Jansonius (2000) discussed the morphological variety and stratigraphic occurrence of the illustrated fossils in Elsik (1999) and Wood & Elsik (1999), and are sceptical if they are plant or fungal remains. However, since all morphotypes mentioned above are found in the same samples, we consider that they may belong to a complex of Reduviasporonites. If this assignment is accepted, the Reduviasporonites morphotypes shown in this paper are the oldest known representatives of this genus.
Chitinozoa
Numerous glabrous chitinozoan specimens found in the Appalachian assemblages recall Hoegisphaera glabra, which was first described from the Late Devonian (Frasnian) of Alberta, Canada (Staplin 1961), and therein designated as being restricted to this time interval (see Paris et al. 1999). The subsequent occurrence of comparable material is mainly from the Middle Devonian (Givetian) of North America; in consequence, these taxa with a younger record and vesicle ornamentation were considered as Hoegisphaera sp. cf. H. glabra (e.g. Legault 1973a, b). However, they were also classified as Hoegisphaera glabra neglecting the stratigraphic limitation (e.g. Wright 1980; Wood & Clendening 1985). Our material from the Appalachian Basin is supposedly older (? early Eifelian) and thus we follow the argument of a somewhat open designation until a more detailed analysis (i.e. SEM studies) may show their conspecific relationship.
Chitinozoa Eisenack, 1931
Order Operculatifera Eisenack, 1931
Family Desmochitinidae Eisenack, 1931, emend. Paris, 1981
Subfamily Demochitininae Paris, 1981
Genus Hoegisphaera Staplin, 1961, emend. Paris, Grahn, Nestor & Lakova, 1999
Type species: Hoegisphaera glabra Staplin, 1961
Hoegisphaera cf. H. glabra, Legault 1973a, b (p. 91, pl. 8, figs 4–6, 8 & 10)
Description
Spherical–subspherical body shape with a circular opening bordered by a low rim, surrounding an operculum that often is dislocated. Surface smooth or slightly ornamented, a few may show degraded membranes (mat-like structure). In our material, two individuals are arranged close to each other in the equatorial plane. Legault (1973a, b) discussed the presence of membraneous sheets completely surrounding specimens. In some cases, the membraneous tissue possibly served as a connection between individuals, representing a specific mode of aggregation. It is not clear from our material whether these membraneous sheets did exist and completely enclosed the specimen or even more than one specimen. However, we cannot exclude that these membranes were lost during the diagenetic processes and/or palynological preparation.
Diameter of body: (chamber) 75–95 µm, operculum 19–42 µm.
Remarks
Specimens of Hoegisphaera cf. H. glabra found in the CAB sections (e.g. Hayfield, Spring Gap) occur in samples of coarser-grained, silty sediments, enriched in in organic matter; mostly AOM, a few spores but very rare acritarchs. They are associated with large scolecodonts, cf. Reduviasporonites stoschianus, and probably land-derived organic matter (OM). In sections of the NAB (e.g. the Stafford Quarry), acritarchs are more common in the contemporaneous level along with cf. Reduviasporonites, whereas Hoegisphaera sp. is less common.
Occurrences (Hoegisphaera glabra and Hoegisphaera sp. cf. H. glabra)
North America: Columbus and Delaware limestones (lower and upper Eifelian, respectively), Ohio (Wright 1976, 1978); Cedar Valley Formation and Wapsipinicon Formation (Givetian), Iowa (Urban 1972; Urban & Newport 1973; Wicander & Wood 1997); North Venon Limestone (Givetian), Indiana (Wright 1980); Boyle Dolomite (Givetian), Kentucky (Wood & Clendening 1985); Rockport Quarry Member, Hamilton Formation (Middle Devonian), Ontario (Legault 1973a, b); Duvernay Shale (Frasnian), Alberta (Staplin 1961).Amazon Basin, Brazil: Hoegisphaera sp. cf. H. glabra (early Givetian, Grahn 2011, p. 35). France: Lezais, Armorican Massif, upper Emsian (Paris 1981).
Dacryoconarids
Class Tentaculita Bouček, 1964
Order Dacryoconarida Fisher, 1962
Family Styliolinidae Grabau & Shimer, 1910
Genus Styliolina Karpinsky, 1884
Discussion
Concepts of Styliolina Karpinsky, 1884 and the family Styliolinidae Grabau & Shimer, 1910 are founded on the attributes of S. nucleata Karpinsky and S. fissurella (Hall), which Karpinsky (1884) regarded to be conspecific (see Fisher 1962). Lindemann & Yochelson (1994) reported that the shell walls of both species consist of a single layer of homogeneous calcite and, based largely on this attribute, proposed that the Styliolinidae be removed from the Order Dacryoconarida Fisher, 1962. Having re-examined numerous topotypes at high SEM magnifications, it is now certain that the shell wall of S. fissurella (Hall) is not homogeneous but is microlaminated in the manner of the shells of the dacryoconarid genera Striatostyliolina, Viriatellina and Costulatostyliolina (Bouček 1964; Lardeux 1969; Lindemann & Yochelson 1994). Accordingly, Styliolina Karpinsky is no longer regarded to be separate from the dacryoconarids.
Styliolina robusta Lindemann & Schindler n. sp.
(Fig. 11a)
Etymology
Latin, robusta, meaning strong, referring to the shell profile and thickness relative to that of Styliolina fissurella (Hall).
Holotype
The holotype NYSM 17229 (Fig. 11a) from the lowermost bed of the Nedrow Limestone in a roadcut on the east side of South Salina Street, NY, Route 11 at Nedrow, NY (N42° 57′ 40″, W76° 08′ 18″).
Material and occurrences
In excess of 50 complete individuals and many partials from the lower beds of Nedrow Member of the Onondaga Formation at the type locality and at Cherry Valley, NY.
Diagnosis
Styliolina, with a 25 µm-thick microlaminated shell up to 1.5 mm long and 0.53 mm wide, with a blunt-based, 0.12–0.14 mm-wide initial chamber separated by a nearly obsolete constriction from the conical proximal region, which has a growth angle of 15–18° that diminishes to 8–10° in the distal region.
Description
The shell is straight, short and wide, with relatively large growth angles in the proximal, medial and distal regions. The apex is blunt, not rounded or pointy, and devoid of an apical node.
Discussion
Styliolina fissurella (Hall), the only species of the genus that has been reported formally from the Devonian of the Appalachian Basin, has a shell that is only 6–10 µm thick and up to 5 mm long, with an apical growth angle of 5–7°, becoming subcylindrical in the distal region. Styliolina robusta n. sp. is distinct from S. fissurella (Hall) in each of these attributes.
Styliolina cf. S. decurtata Bouček, 1964
(Fig. 11b)
Figured specimen
NYSM 17236 (Fig. 11b) from the middle Edgecliff-equivalent at Hayfield, VA.
Material and occurrences
In excess of 20 complete shells and numerous partials from the middle of the Edgecliff-equivalent interval of the Selinsgrove Member of the Needmore Formation at Hayfield, VA, and from the Nedrow-equivalent upper black bed at Mapleton, PA.
Description
Styliolina with a 12–14 µm-thick, microlaminated shell that is up to 2.5 mm long and 0.22 mm wide, with a rounded to slightly pointy 0.8–0.95 mm-wide initial chamber separated by a long constriction from the conical proximal region, which has a growth angle of 9–12° that diminishes to subparallel in the distal region.
Discussion
Styliolina cf. S. decurtata is distinct from S. fissurella and S. robusta n. sp. in the width of its initial chamber, proximal growth angle and shell thickness. It is most similar to S. decurtata Bouček, 1964 from the upper Emsian–lower Eifelian Třebotov Limestone at Holyně, Czech Republic. The two differ only in the shape of the initial chamber, with that of Styliolina cf. decurtata being slightly less pointy than the specimens figured by Bouček (1964, pl. 32, figs 1 & 2).
Family Striatostyliolinidae Bouček, 1964
Genus Striatostyliolina Bouček & Prantl, 1961
Striatostyliolina mima Lindemann & Schindler n. sp.
(Fig. 11c, d)
Etymology
Latin, mima, actress; referring to morphological mimicry of Styliolina fissurella (Hall).
Holotype
NYSM 17230 (Fig. 11c, d) from the basal bed of the Nedrow Limestone in a roadcut on the north side of US Route 20 north of Cherry Valley, NY (N49° 28′ 37″, W74° 44′ 18″).
Material and occurrences
Many hundreds of complete and partial specimens. The species may first occur in the upper Emsian Schoharie and Bois Blanc formations (Oliver 1966), but that is not currently certain. Its first certain occurrence is in the basal bed of the Edgecliff Limestone. It occurs throughout the Onondaga Formation and ranges upwards into the Hamilton Group, at least as high as the mid-Givetian Ledyard Member of the Ludlowville Formation.
Diagnosis
The 20 µm-thick microlaminated shell is up to 1.3 mm long and 0.3 mm wide, with a teardrop-shaped to slightly pointy 130–140 µm-wide initial chamber separated by a long, gradual constriction from the proximal region, which has a growth angle of 10° that diminishes to subcylindrical in the distal region. Approximately 16–20 striae on a semi-circumference extend from apex to aperture.
Description
The shell is straight and narrow, with an initial chamber that varies from teardrop shaped to slightly pointy, sometimes terminating in a nearly obsolete apical node. Striae are very weak and poorly preserved. As is the case with Styliolina, the Striatostyliolina mima n. sp. shell is microlaminated, but may falsely appear to be homogeneous.
Discussion
Striatostyliolina mima n. sp. is the most abundant non-annulated dacryoconarid in Eifelian and Givetian strata of NY, and the main source of erroneous reports of Styliolina fissurella. It differs from species of Striatostyliolina described from the OWR by Bouček (1964) and Lardeux (1969) in that it is far shorter than the others, and that it has 2–4 times the number of striae. However, the striae are weakly incised into the shell surface and, even when preserved, cannot be reliably discerned with a light microscope or at low magnifications with the SEM.
Striatostyliolina vitta Lindemann & Schindler n. sp.
(Fig. 11e)
Etymology
Latin, vitta, a ribbon; with reference to the overall profile of the shell.
Holotype
NYSM 17231 (Fig. 11e) from the second argillaceous bed above the base of the Nedrow Member at Cherry Valley, NY.
Material and occurrences
Approximately 20 complete specimens and numerous partials from the Nedrow Member and a vast number of specimens from the basal bed of the Oatka Creek Formation. Beyond the type locality and bed, the only other currently known occurrence in the Onondaga Formation is in the basal bed of the Nedrow Member at Nedrow, NY. The currently known uppermost occurrence of S. vitta n. sp. is in the Chestnut Street Beds at the base of the Oatka Creek Formation at Cherry Valley, NY.
Diagnosis
The microlaminated 15 µm-thick shell is up to 2.2 mm long and 0.23 mm wide, with a round to slightly pointy 95–112 µm-wide initial chamber separated by a nearly obsolete constriction from the proximal region, which has a growth angle of 6° that diminishes to 2–3° in the distal region. The six or seven striae on a semi-circumference extend from apex to aperture.
Description
The shell is straight and exceptionally narrow. The apex of some individuals bears a nearly obsolete, 40–45 µm-wide node. Striae are 2–3 µm wide, separated by flat, 25–40 µm-wide interspaces.
Discussion
Among currently known dacryoconarid species, Striatostyliolina vitta n. sp. is most similar in size and shape to Styliolina minuta (see Bouček 1964, pl. 33).
Genus Costulatostyliolina Lardeux, 1969
Costulatostyliolina cf. C. paucicostata (Bouček, 1964)
(Fig. 11f)
Figured specimen
NYSM 17237 (Fig. 11f) from the lower of the two upper Nedrow-equivalent black beds of the Selinsgrove Member, Needmore Formation at Hayfield, VA.
Material and occurrence
In excess of 50 compressed shells and surficial impressions. At Hayfield, VA, Costulatostyliolina cf. C. paucicostata (Bouček) ranges from the middle of the Edgecliff-equivalent up to the above-stated bed. It has not been observed at any other locality.
Description
The 15 µm-thick microlaminated shell is up to 3.5 mm long and 0.4 mm wide, with a rounded, 140–160 µm-wide initial chamber separated by a nearly obsolete constriction from the proximal region, which has a growth angle of approximately 9° that diminishes to subcylindrical in the distal region. There are six–seven costae on the initial chamber and in the proximal region, and from eight to ten in the distal region of the shell.
Discussion
Lardeux (1969) designated Costulatostyliolina paucicostata (Bouček) as the type species of the then newly erected genus. Although Bouček (1964) described Striatostyliolina paucicostata as having five–seven ‘ribs’ (=costae) on the semi-circumference, on his plate 38 (figs 1–4) he illustrated individuals with between five and 10 costae (note that the figure references in Bouček's text and figure captions incorrectly switch plates 36 and 38). The species’ type unit is the upper part of the Třebotov Limestone, which places it only a little below the base of the Choteč Formation. The only discernable difference between the figured type material from the Třebotov Limestone and the specimens from the Nedrow Limestone is that the costae of the latter may be somewhat narrower and that the interspaces are somewhat wider in the distal region of the shell than those of the originals. However, this is within the range of intraspecific variability illustrated by Bouček (1964, pl. 38, figs 1–4).
Costulatostyliolina vestita Lindemann & Schindler n. sp.
(Fig. 11g)
Etymology
Latin, vestitus, costume; with reference to the appearance of a Styliolina dressed up with costae.
Holotype
NYSM 17232 (Fig. 11g) from the second argillaceous bed above the base of the Nedrow Member at Cherry Valley, NY.
Material and occurrences
Several dozen partial and complete shells. The currently known first occurrence of this species is at the base of the Edgecliff Member at Cherry Valley, NY. It also occurs in the argillaceous interval of the lower Edgecliff at Clarence, NY, the argillaceous beds of the upper Edgecliff and Nedrow members at Phelps, NY, and the basal to lower argillaceous beds of the Nedrow throughout central and east-central NY.
Diagnosis
The microlaminated 25 µm-thick shell is up to 3 mm long and 0.3 mm wide, with a round to slightly pointy, 135–145 µm-wide initial chamber separated by a long, gradual constriction from the proximal region, which has a growth angle of 9–12° that diminishes to less than 6° in the distal region. The 14–18 costae on a semi-circumference extend from apex to aperture.
Description
The shell is straight and narrow. The apex of some individuals bears a weak node that is commonly absent. Costae are weak, submicron in width, separated by flat, 10–20 µm-wide interspaces.
Discussion
The overall morphology of Costulatostyliolina vestita n. sp. closely resembles that of both Styliolina fissurella (Hall) and Striatostyliolina mima n. sp., but is differentiated from them by the presence of costae, which are easily corroded from the shell surface. The overall morphology of C. vistita n. sp. also resembles that of C. strigata (Hall) from the Chestnut Street Beds of the Oatka Creek Formation, which has only six–seven costae on a semi-circumference (Lindemann 2008) as opposed to 14–18.
Metastyliolina cf. M. striatissima Bouček & Prantl, 1961
(Fig. 12a)
Figured specimen
NYSM 17238 (Fig. 12a) from the lower of the two upper Nedrow-equivalent black beds of the Selinsgrove Member, Needmore Formation at Spring Gap, MD.
Material and occurrences
External impressions of several hundred specimens. No shells or steinkerns have been found. Beyond its occurrence at Spring Gap, MD, the taxon ranges from the middle of the Edgecliff-equivalent to the lower of the two UBB at Hayfield, VA, and Gainesboro, VA.
Description
The shell is up to 7 mm long, with a slightly pointy 80–90 µm-wide initial chamber separated by a nearly obsolete constriction from the acicular proximal region, which has a growth angle of less than 7° that diminishes to subcylindrical in the medial and distal regions. There are between eight and 10 costae on a semi-circumference in the proximal region, 18–26 in the medial region, and 32–42 in the distal region. Growth lines with irregular spacings of 75–250 µm occur in the medial and distal regions of most individuals.
Discussion
In the Prague Basin, Metastyliolina striatissima is the predominant dacryoconarid in the Choteč Limestone (Bouček 1964). Metastyliolina cf. M. striatissima has a comparable occurrence in the southern Appalachian Basin (AB), where its morphological attributes accord well with the species’ written description and with the individuals figured by Bouček (1964, pl. 37, figs 8 & 9). The sole exception is that the AB specimens are somewhat wider in the medial and distal regions than those of the Prague Basin. This may be attributed to different degrees of secondary compaction and the consequent widening of the shell profile, which is far more pronounced in the AB. An alternative possibility, prompted by the erection of M. striatissima grueti by Lardeux (1969), is that either geographical or temporal subspecies exist and the AB form might be among them.
Metastyliolina? sp. B
(Fig. 12b)
Figured specimen
NYSM 17239 (Fig. 12b) from the lower of the two upper Nedrow-equivalent black beds of the Selinsgrove Member, Needmore Formation at Hayfield, VA.
Material and occurrences
Approximately 20 impressions of compressed partial specimens and four partial compressed shells. This form occurs in the lower of the two upper Nedrow-equivalent black beds at Gainesboro, VA, and Mapleton, PA, as well as in a thin bed of black shale proximal to the top of the Nedrow Limestone in the Oak Corners Quarry at Phelps, NY.
Description
The shell is up to 5 mm long with a proximal growth angle of 4–6° that diminishes to subcylindrical in the distal region. There are six–eight costae in the proximal region and 14–20 distally.
Discussion
This form is poorly known from crushed partial shells. It is questionably referred to Metastyliolina as opposed to Costulatostyliolina owing to its length, slender profile and relatively numerous costae in the distal region. Although it is poorly documented, it is included here because it occurs near the top of the Nedrow interval in both the central and northern regions of the AB.
Family Nowakiidae Bouček & Prantl, 1960
Subfamily Nowakiinae Bouček & Prantl, 1960
Genus Nowakia Gürich, 1896
Subgenus Nowakia (Dmitriella) Ljaschenko, 1966
Nowakia (Dmitriella) sulcata antiqua Alberti, 1981
(Fig. 12c)
Figured specimen
NYSM 17240 (Fig. 12c) from the lower of the two upper Nedrow-equivalent black beds of the Selinsgrove Member, Needmore Formation at Mapleton, PA.
Material and occurrences
In excess of 50 unaltered shells and an equal number of partially to fully compressed specimens. The lowermost known occurrence of this taxon is at the base of the middle of the Edgecliff-equivalent at Hayfield, VA, and Gainesboro, VA. In the CAB, its zone extends to the top of the Nedrow-equivalent at Spring Gap, MD. In the NAB, this taxon is absent from the Onondaga Formation, but occurs in the Chestnut Street Beds, Hurley Member, Oatka Creek Formation at Cherry Valley, NY.
Description
The 8–10 µm-thick microlaminated shell is up to 6 mm long and 0.7 mm wide, with a 100–110 µm-wide initial chamber separated by a nearly obsolete constriction from the proximal region, which has a growth angle of 8–10°, becoming subcylindrical in the distal region. Transverse sculpture is nearly obsolete in the proximal region, progressively strengthening to narrow, blunt crested rings separated by broad, rounded swales (=sulca) with wavelengths of 200–280 µm in the medial and distal regions. There are between seven and 10 costae on the initial chamber and in the distal region, progressively increasing to 25–30 in the distal region of full-length shells.
Discussion
Nowakia (Dmitriella) sulcata has long served as an index for the Choteč Limestone (Bouček 1964) and the BCE (Chlupáč & Kukal 1986). Bouček (1964, p. 90) reported that it also occurs in the Třebotov Limestone. Although this taxon is common in Europe and North Africa, a subspecies rarely occurs in the AB (Fig. 10) (see also Brill et al. 2014).
Alberti (1981) first described Nowakia (D.) s. antiqua from the upper Emsian as the presumed ancestor of the Eifelian N. (D.) s. sulcata. The primary difference between the two subspecies is an evolutionary reduction in number of costae on a semi-circumference from 25 or more on N. (D.) s. antiqua to about half that number on N. (D.) s. sulcata. Alberti (1982) reported forms that are transitional between the two varieties in strata just above the base of the partitus Zone (i.e. the base of the Eifelian Stage) and subsequently reported on N. (D.) s. antiqua from the Choteč Limestone (Alberti 1993).
Nowakia sp. A
(Fig. 12d, e)
Figured specimen
NYSM 17235 (Fig. 12d, e) from the lower of the two upper Nedrow-equivalent black beds of the Selinsgrove Member, Needmore Formation at Hayfield, VA.
Material and occurrences
In excess of 100 more or less compressed specimens, most of which are external impressions of the shell. The taxon is currently known to range from the middle of the Edgecliff-equivalent at Hayfield, VA, and Gainesboro, VA, as well as the upper Nedrow-equivalent at Spring Gap, MD.
Description
The shell is up to 5.5 mm long and 0.4 mm wide, with a rounded, 130–140 µm-wide initial chamber that passes abruptly into the juvenile region, which has a growth angle of approximately 8–10° that diminishes somewhat in the distal region. Transverse sculpture consists of bluntly rounded, symmetrical ripples separated by wide swales with an average wavelength of 130–160 µm over most of the shell, diminishing in strength and wavelength behind the aperture in full-length specimens. Although there is variability between individuals, the juvenile region is typically devoid of transverse sculpture up to a shell length of 1.2–1.5 mm. There are between eight and 10 costae in the proximal region, approximately 25 in the medial region, and 30–35 in the distal region.
Discussion
The overall morphology of this form is markedly similar to that of the lower Eifelian Nowakia (Maurerina) procera (Maurer). This is particularly so in the long, smooth juvenile region, as well as in the apparent shape and pacing of transverse rings in the medial and distal regions. However, Alberti (1981) described N. (Maurerina) as being unique among Nowakia subgenera in that it is devoid of costae. Lütke (1985, pl. 3, figs 1 & 2) figured two well-preserved N. (M.) procera (Maurer) that are clearly devoid of costae. Thus, the form of Nowakia under consideration herein is precluded from the subgenus and species, and is not referred to any taxon below the generic level.
Genus Viriatellina Bouček, 1964
Viriatellina manifesta Lindemann & Schindler n. sp.
(Fig. 12f)
Etymology
Latin, manifesta, evident; referring to the obvious transverse shell sculpture of uncompressed individuals.
Holotype
NYSM 17233 (Fig. 12f) from the second argillaceous bed above the base of the Nedrow Member at Cherry Valley, NY.
Material and occurrences
Dozens of complete specimens and several hundred partials. The species is currently known from the argillaceous interval of the lower Edgecliff Limestone at Clarence, NY, and argillaceous beds of the upper Edgecliff in west-central NY, extending up to the lower 0.7 m of the Nedrow Limestone at Cherry Valley, NY. Similar forms of Viriatellina occur in the upper Emsian Schoharie Formation of eastern NY and the upper Eifelian Bakoven Shale of central NY, but it is not currently certain whether they are conspecific with V. manifesta or are steps in an evolving lineage.
Diagnosis
The microlaminated 10 µm-thick shell is up to 2.5 mm long and 0.4 mm wide, with a slightly pointy 130–150 µm-wide initial chamber separated by a weak constriction from the proximal region, which has a growth angle of 13–15° that diminishes to 8–10° in the distal region. Transverse sculpture consists of symmetrical ripples and intervening swales that begin late in the proximal region and strengthen distally. There are 16–20 costae on the semi-circumference over the full length of the shell.
Description
Costae are submicron in width, separated by flat 15–40 µm-wide interspaces in the distal region. The narrow costae are easily lost to dissolution, whereupon they appear as secondary striae, particularly in the proximal region and the initial chamber. Transverse sculpture consists of low-amplitude ripples beginning in the medial region with wavelengths of less than 0.14 mm, which progressively strengthen and lengthen to wavelengths in excess of 0.3 mm in the distal region. The ripples are flattened out during compaction of the shell, which can cause them to vanish all together. Compaction also widens the shell, producing a distinctive chevron morphology, which other dacryoconarid taxa of the Onondaga Formation do not attain.
Discussion
Only two species of this genus, Viriatellina gracilistriata (Hall) and V. porteri, have been reported formally from the Appalachian Basin (Lindemann & Yochelson 1992). Although V. manifesta n. sp. bears some similarity to V. gracilistriata (Hall), they differ markedly in that the former has 16–20 costae on a semi-circumference and the latter 36–42 in the distal region. Bouček (1964, p. 99, pl. 19) described and illustrated specimens of what he regarded to be V. gracilistriata (Hall) from Emsian strata of Bohemia, which Lütke (1985, p. 211) subsequently referred to V. fortistriata n. sp., designating one of Bouček's figured specimens as the holotype. Lardeux (1969, p. 124, text fig. 92; pl. 43, fig. 1) described and illustrated specimens of V. cf. gracilistirata (Hall) from Emsian and Eifelian strata of Brittany, which are very distinct from V. gracilistiata (Hall) as described by Lindemann & Yochelson (1992) and differ from V. manifesta n. sp. in having only 12–16 costae on a semi-circumference.
Viriatellina exila Lindemann & Schindler n. sp.
(Fig. 12g)
Etymology
Latin, exilis, slim; referring to slender morphology of the shell relative to Viriatellina gracilistrata (Hall) and V. manifesta n. sp.
Holotype
NYSM 17234 (Fig. 12g) from the lower 0.7 m of the Nedrow Limestone at Cherry Valley, NY.
Material and occurrences
Twenty-five specimens from the lower beds of the Nedrow at Cherry Valley, NY. This is the only locality and interval from which this taxon is currently known for certain, although somewhat similar forms occur in the basal bed of the Nedrow at Nedrow, NY.
Diagnosis
The 25 µm-thick microlaminated shell is up to 1.4 mm long and 0.35 mm wide, with a slightly pointy, 120–130 µm-wide initial chamber separated by a nearly obsolete constriction from the proximal region, which has a growth angle of 14°–16° that diminishes to about 4° in the distal region. Transverse sculpture consists of low-amplitude ripples that begin in the proximal region, and gradually strengthen distally in amplitude and wavelength over the length of the shell. There are between eight and 12 costae on the semi-circumference over the full length of the shell.
Description
The shell is straight and slender with low-amplitude transverse ripples, the crests of which nearly mirror images of the intervening swales. The ripples begin in the proximal region with wavelengths of 120 µm, which progressively increase to 260 µm in the distal region. The low, submicron-wide costae are separated by 25–40 µm-wide interspaces. The initial chamber is slightly pointy but devoid of an apical node.
Discussion
Viriatellina exila n. sp. differs from V. manifesta n. sp. in being more slender in the medial and distal regions, and having fewer costae and a thicker shell wall. It is most similar to the upper Emsian V. hercynica of Bouček (1964, p. 95) but differs in being far shorter, having much weaker costae and lower-amplitude transverse ripples.
Acknowledgments
We would like to thank Stana Vodrážková and Petr Budil (Praha) for assistance during sampling at the Na Škrábku Quarry, and for subsequent discussions. We also thank Carl Brett (Cincinnati, OH) for constructive discussion on the Choteč Event during the SDS meeting in Morocco 2013. Petra Tonarová (Tallinn) is thanked for determining the two pictured scolecodonts. Michael Krings (München) and Michael Stephenson (Keyworth, Nottingham) contributed to the discussion on the systematics of Reduviasporonites stoschianus. Rachel Barrachina (Skidmore College, Saratoga Springs, NY) is thanked for help with the SEM images of the dacryoconarids. Michael Ricker and Haytham El Atfy are acknowledged for their assistance in the production of graphical charts; Jutta Oelkers-Schaefer and Gunnar Riedel (all at Senckenberg Forschungsinstitut und Naturmuseum Frankfurt) are thanked for their assistance in palynological preparation. John Marshall (Southampton) and an anonymous reviewer are thanked for constructive remarks and R. Thomas Becker (Münster) for final formal corrections. This paper is a contribution to the IGCP Project 596 ‘Climate change and biodiversity patterns in the Mid-Palaeozoic’.
Appendix A: Appalachian Basin study localities
Goodrich Road roadcut, Clarence, NY: 42.984960°, −78.637273°
Stafford Quarry, west of Stafford, NY: 42.979964°, −78.088233°
Oaks Corners Quarry, SE of Phelps, NY: 42.932542°, −77.023682°
Abandoned Schooley Quarry, Auburn, NY: 42.954130°, −76.562183°
US Route 11 roadcuts, Nedrow, NY: 42.961129°, −76.138772°
East end of Jamesville Quarry, Jamesville, NY: 42.994283°, −76.024205°
US Route 20 roadcuts, north of Cherry Valley, NY: c. 42.822617°, −74.725097°
Abandoned quarry SW of Mapleton, PA: 40.377664°, −77.953548°
Roadcut at Spring Gap, MD: 39.564570°, −78.713113°
Roadcut Route 8, east of Keyser, WV: 39.448554°, −78.954074°
Abandoned quarry along Route 684, Gainesboro, VA: 39.284756°, −78.262652°
Roadcut, NE side of intersection, US Route 50 west of Winchester, VA: 39.233224°, −78.290060°
- © 2016 The Author(s). Published by The Geological Society of London. All rights reserved
References
Palynology, dacryoconarids and the lower Eifelian (Middle Devonian) Basal Choteč Event: case studies from the Prague and Appalachian basins
- Article
- Abstract
- Research history of the Basal Choteč Event (BCE)
- Localities, material and methods
- Setting of the Basal Choteč Event in the Barrandian area
- Setting of the Basal Choteč Event in the Appalachian Basin, eastern USA
- The Basal Choteč Event and its equivalents in other areas
- Discussion and results
- Interpretation
- Concluding remarks
- Systematic section
- Acknowledgments
- Appendix A: Appalachian Basin study localities
- References
- Figures & Data
- Info & Metrics