Angola Continental Margin—Sites 364 and 365

Abstract

A sequence from the Pleistocene down into the upper Aptian was penetrated containing a major erosional disconformity corresponding to most of the Oligocene and the upper Eocene. The drilling terminated with a worn-out bit in dolomitic limestones with very high interstitial salinities just above the Aptian evaporite and salt formations. The Paleogene and Upper Cretaceous series is for the most part pelagic in nature, and contains tropical to sub-tropical faunas deposited in generally tranquil deep-water environments. The Lower Cretaceous faunas include ammonites and Inoceramus and characteristically indicate non-tropical environments and na initial immigration of marine life into the Angola Basin from the south following the termination of the Aptian salinity crisis. There is no evidence of shallow littoral or intertidal sedimentation, even for the deposits directly overlying the evaporites.. Sapropels and sapropelic limestones occur in the upper Coniacian to Cenomanian interval and in the lower Albian and upper Aptian. Albian marly chalks and limestones contain pressure-solution stylolites, steeply dipping bedding contacts overturned folds, and interformational breccias probably linked to salt diapirism. Sedimentation rates range from approximately 40 m/m.y. for the Lower Cretaceous to 18 m/m.y. for the Upper Cretaceous with a significant reduction during the Cenomanian and Turanian. Gaps of 8 million years last across the Cretaceous/ Tertiary boundary and of 16 million years between the upper Oligocene and the middle Eocene. The Neogene sequence is markedly terrigenous and siliceous. It corresponds to a major phase of deltaic out-building and fore-slope progradation recognizable in seismic reflection profiles and reflects climatic changes after the late Eocene. Compressional wave velocities reach 5 km/sec in basal dolomitic limestone.