28. LOWER CRETACEOUS BENTHIC FORAMINIFER ASSEMBLAGES, EQUATORIAL ATLANTIC: BIOSTRATIGRAPHIC, PALEOENVIRONMENTAL, AND PALEOBIOGEOGRAPHIC SIGNIFICANCE1Ann E.L. Holbourn2 and Michel Moullade3 |
ABSTRACTLower Cretaceous benthic foraminiferal assemblages from basal sedimentary sequences of Holes 959D, 962B, and 962D provide time constraints for the onset of marine sedimentation on the Côte d’Ivoire-Ghana Transform Margin and show that marine conditions were already established by late Aptian–early Albian near Hole 959D and by mid to late Albian near Hole 962D. The foraminiferal data suggest that older Aptian–Albian marine sequences were subsequently reworked into upper Albian–lowermost Cenomanian sediments within tectonically active sub-basins. Marked fluctuations in test size, abundance, and diversity reflect a pulsed sedimentation pattern with an overall high accumulation rate. Three main cycles of deposition are detected from overall changes in preservation, abundance and diversity, which are possibly related to major shifts in sediment provenance and/or supply. The composition of the benthic foraminiferal assemblages at Holes 959D and 962D indicates an outer shelf to upper bathyal setting and reflects a combination of Tethyan, South Atlantic, and local endemic faunal influences, pointing to restricted connections with the open ocean and Tethys during the late Albian and early Cenomanian. There is no evidence for bottom-water anoxia or severe dysoxia during the deposition of Cores 159-962D-16R through 37R. The high dissolution of planktonic tests and absence or scarcity of benthic foraminifers in the upper part of the sequence (Sections 159-962D-7R-1 through 13R-1 and 159-962B-8H-5 through 9H-6) indicate some later deterioration in bottom-water oxygenation. |
|