[Abstracts] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]

Alexandre Grassi, Seirin Shimabukuro:
Calcareous nannofossil biostratigraphy and palaeoecology across the Cretaceous/Tertiary boundary on the Brazilian eastern coast
(Poster)

Quantitative analyses of calcareous nannofossils of three Cretaceous/Tertiary (K/T) boundary sections from the Pernambuco-Paraíba and Campos Basins (Brazilian eastern coast) revealed an abrupt change in assemblages. The integration of these sections made possible the recognition of two biozones in the uppermost Maastrichtian and five in the lowermost Danian. In the Campos Basin, the Ceratolithoides kamptneri extinction was identified below the K/T boundary. This event brought about the proposition of a new biozone (Tetrapodorhabdus decorus Biozone) in the uppermost Maastrichtian. Above the boundary, the main bioevents are (Figure 1): Thoracosphaera bloom, Neobiscutum romeinii bloom, first occurrence (FO) of Cruciplacolithus primus, FO of Futyania petalosa, first consistent abundance of Futyania, and FO of Cruciplacolithus intermedius.

It was possible to identify three different palaeoecological phases in the nannoplankton recovery in the Danian. In Phase 1, just above the boundary, the energy and the trophic resources were high, and there was an environmental eutrophication caused by the abrupt decrease of the primary productivity. As a result, this open niche was occupied by the surviving organisms, generally opportunists (Phase 2). Phase 1 probably did not last more than a few thousand years. Phase 2 is well represented in the studied cores of the Campos Basin by the Thoracosphaera and Neobiscutum blooms in a low-diversity environment (oligotaxic biocoenosis). During the blooms, there was a quick depletion of the nutrients, generating an increase in the diversity (polytaxic biocoenosis) due to the necessity of interdependence among organisms (Phase 3). In the third phase, more complex Tertiary species appeared (Cruciplacolithus primus, C. intermedius) but Futyania petalosa blooms suggest unstable palaeoceanographic conditions at least upto the base of NP2 (~500ky). This very last phase is represented in the upper deposits of the Poty Quarry (Pernambuco-Paraiba Basin), which are dominated by Tertiary nannofossils.

Figure 1: Calcareous nannofossil species ranges and biostratigraphical framework across the Cretaceous/Tertiary boundary on the Brazilian eastern coast

[INA8] 

[Registration and Accomodation Form]
[First Circular and Pre-Registration]
[Second Circular]

 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

 [INA Europe]  

Copyright © 2000, most recent revision July 24, 2000