Preliminary Palynological Results: Site 361, Leg 40, Deep Sea Drilling Project

Abstract

Site 361 lies about 180 miles west-southwest of Cape Town. A single hole drilled to 1314 meters (subbottom) intersected a nearly continuous sequence of sediments ranging in age from Aptian to Eocene. Palynological studies were undertaken on 48 samples from the Cretaceous interval (Cores 12 to 48) and palynomorphs were recovered from nearly all the cores treated. The age indications generally support those based on foraminifers and coccoliths. Further information is provided on depositional environments, sediment provenance, and climate. The sapropelic lower lithological interval was probably deposited in a near-shore situation. The climate is interpreted as having been dry and the organic material was derived from a Classopollis-domimted local plant community. A benthic microfauna did exist, but the calcareous shells were mostly destroyed during early burial by acid interstitial fluids associated with the carbonaceous sediment. A diverse assemblage of dinoflagellate cysts with many cosmopolitan species indicates a free circulation of the surface water and a connection with the oceanic seas. The basin was probably silled, with restricted circulation of bottom water. The phytoplankton ratio increases markedly in the Upper Cretaceous as a result of the diminished supply of terrigenous spores and pollen, but species diversities remain constant. Bottom waters were generally well oxygenated. There is a suggestion of shallowing or a closer sediment source at three intervals within the Upper Cretaceous, where the delicate nature of the cuticular material suggests minimal transport of the plant debris. The climate at this time was probably wet and floras were dominated by ferns and angiosperms. Striated bisaccate pollen characteristic of the Permian and Triassic is persistently present in the Upper Cretaceous and points to a provenance in the south- western Cape in South Africa. The sapropelic basal lithological unit has the appearance of a good petroleum source rock and is interpreted to be near the upper limit of thermal maturity necessary for the generation of hydrocarbons.