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Geological Society, London, Special Publications; 2000; v. 173; p. 163-170;
DOI: 10.1144/GSL.SP.2000.173.01.07
© 2000 Geological Society of London

Tethyan Evolution

Aspects of Jurassic Radiolarite Sedimentation in a Ramp Setting Following the ‘Mid-Late Jurassic Discontinuity’, Barla Dag Area, Western Taurus, Turkey

Anna Farinacci1, Andrea Fiorentino2 & Valerio Ridolfi3

1 Dipartimento di Scienze della Terra, Università La Sapienza, P.le Aldo Moro, 00185 Roma, Italy farinacci{at}axrma.uniromal.it
2 , Via Tacito 41, 00193 Roma, Italy
3 , Via Senofane 216, 00124 Roma, Italy

The Barla Dag area of southwestern Turkey and its surroundings represent one of the most characteristic Tethyan regions in which the unique characteristics of the Jurassic radiolarite deposits permit detailed study of this enigmatic facies. Hitherto, radiolarites of Western Tethys have not been studied in sufficient detail to yield the information required for unequivocal interpretation of this siliceous sedimentary event. Moreover, few of the occurrences of Tethyan radiolarites during the Jurassic have been adequately explained by palaeoenvironmental causes deduced from facies analysis. In the Barla Dag area, the main radiolarite episode began after the ‘main gap’ or mid-Late Jurassic discontinuity, a 25 Ma hiatus extending from the Early Bajocian to the Kimmeridgian. These radiolarites are interbedded with biocalcarenites characterized by shallow-water shells. They formed in a ramp environment subject to strong storm oscillatory movements and were deposited within, or just below, wave base.

Pre-existing platforms were converted into ramp settings by a widespread drowning episode, mainly following postulated regional warping that led to creation of the ‘main gap’. Coincident with this event, the differentiation of rimmed platform lagoonal organisms and typical ramp inhabitants, such as Tubiphytes, took place. Furthermore, nearby platforms, unaffected by the extensional faulting (e.g. the Davras Dag), were sites of carbonate accumulation receiving only a few radiolarians. On the other hand, displaced shallow-water organisms of the same age (typical of the restricted lagoons flanking the rimmed platforms such as pfenderinas, kurnubias and Clypeina jurassica) are absent from the sequences of calcarenites interbedded with radiolarian cherts. Replacement of deep basins by ramps is indicated by the changing depositional bathymetry of some radiolarites. It is tentatively attributed to the extension of shallow seas and narrowing of the oceanic realm between Eurasian and African Plates in Western Tethys.





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[Abstract] [PDF]