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Cenozoic |
Petrobrás-Cenpes, Cidade Universitária, Quadra 7, Ilha do Fundão, 21949-900 Rio de Janeiro, Brazil
In the aftermath of the Cretaceous-Tertiary (K/T) boundary event it appears that unusual phytoplankton blooms were boosted by the abundant nutrient levels left over from a short-lived ‘Strangelove Ocean’ period, which possibly gave rise to the negative-to-positive
The highly plastic morphology of the planktonic foraminifera at the base of the Palaeocene appeared, most likely, as an adaptive response of functional morphology to the pelagic habitat of the species and its mode of life. The diversification episodes of Danian planktonic foraminifera appear to correspond to times of reduced oceanic mixing, stratified water masses, recovery of the surface water productivity and a progressive expansion of the trophic-resource continuum, with periods of maximum diversity corresponding to widespread oceanic surface-water oligotrophic conditions. These suggest a parallel adaptive trend of feeding strategies caused by the changing availability of nutrients in the water column, with probable increasing reliance in symbiosis under low nutrient conditions later in the Danian.
Guembelitria cretacea, one of the few Cretaceous survivors, has been recorded in northeastern Brazil up to the lower part of the P2 Zone. A triserially coiled planktonic morphotype, this species started to diversify immediately after the K/T transition. After only a few thousand years, in the earliest Danian, the first Tertiary taxa (the Guembelitria- Woodringina lineage) appeared; these are microperforate nonspinose forms that were probably restricted to shallow epipelagic waters. There is a trend towards uncoiling of the triserial pattern by progressively changing the positioning of the aperture, without any detectable ecophenotypic preference at first.
The first specimens of the Eoglobigerina-Pseudosubbotina, Eoglobigerina-Subbotina and Praemurica lineages, cancellate spinose and non-spinose forms, also evolved in the Danian in a nearly coeval and parallel evolutionary trend from a probably ancestral Hedbergella stock.
A revised phylogeny is suggested for the early Palaeocene planktonic foraminifera based on recorded stratigraphic ranges and morphological affinities (chamber arrangement and surface texture ornamentation).
13C surface-to-bottom gradient in the Danian.
