Well preserved Palaeogene and Cretaceous biomarkers from the Kilwa area, Tanzania

There is a clear distinction in the biomarker distributions between the Oligocene-age sediments collected at the end of the peninsula near Kilwa Masoko and the older sediments collected from elsewhere, indicating differences in depositional environment. Sediments from the end of the peninsula have higher branched and isoprenoid tetraether index values, indicating a relatively higher terrestrial input. They also contain two tentatively assigned C28 hopenes (28,30-dinorneohop-13(18)-ene and 28,30-dinorhop-17(21)-ene), (aromatic) des-A-triterpenes, des-E-hopenes, aromatic pentacyclic triterpenoids, C33 DGD, archaeol and BHPs, which are absent from or only present in small amounts in the other sediments. These differences likely reflect an evolution of the depositional area from a relative open shelf environment with substantial water depth to a shallower setting during the early Oligocene.