Abstract:
Lower Cretaceous foraminiferal assemblages recovered from ODP Site 962 (leg 159) provide time constraints for the onset of marine sedimentation in the Deep Ivorian Basin and offer insights into the early palaeoenvironments of the Cote d'Ivoire-Ghana Transform Margin. Ninety-seven samples from a 270m mixed carbonate siliclastic unit at the base of Hole 962 are analysed. They contain upper Albian planktonic foraminifera, including Hedbergella delrioensis, Schackoina and Heterohelix spp., as well as abundant, small benthic foraminifera (less than 0.125mm), including various species of Berthelina, Gavelinella, Osangularia and Bolivina and diverse Nodosariids. Marked fluctuations in test size, abundance and diversity reflect a pulsed sedimentation pattern with an overall high accumulation rate, probably related to tectonic activity and to the close proximity of a rapidly subsiding margin. The intermittent occurrences of Patellinids, Miliolids and diatoms suggest that the sediment was periodically redeposited from a proximal, shallower source. The predominantly small size of benthic calcareous tests may be attributed to the granulometric sorting of allochthonous tests at a distal depositional setting above the CCD, and for autochthonous assemblages, to the prevalence of unfavourable dysoxic conditions on the seafloor, due to high accumulation rates. Both benthic and planktonic assemblages display some degree of endemism, which suggests that circulation was restricted in the basin during the late Albian and that connections with the Tethys were limited.