ORGANIC PETROLOGY OF DEEP-SEA SEDIMENTS - A COMPILATION OF RESULTS FROM THE OCEAN DRILLING PROGRAM AND THE DEEP-SEA DRILLING PROJECT

A comprehensive overview of the organic petrology of Triassic to Recent deep sea sediments is presented. The data, which are derived from studies in the framework of the Ocean Drilling Program and the former Deep Sea Drilling Project, are discussed with respect to the plate tectonic setting and the oceanographic environment. The discussion reveals the following trends: (1) Early stages of the evolution of oceans are often characterized by deposition of sediments with high proportions of terrigenous organic matter including wood and coal on the one hand and by the deposition of black-shales, rich in marine macerals, in silled basins with restricted water circulation on the other hand. (2) Turbidity sedimentation which carries terrigenous material into the deep ocean plays an important role along passive continential margins, e.g., in submarine fans. Here, the inertinite/vitrinite ratio increases with increasing distance to the continents. The organic matter in central oceans is consequently also characterized by high proportions of often small-sized inertinite. A very special depositional setting occurs within central oceans on top of drowning volcanoes. There, alginite- and vitrinite-rich sediments are deposited in shallow water. Vitrinite is derived from plants on the adjacent still subaerial volcanic areas. (3) Sediments deposited along active continental margins in trench-slope transition zones are often rich in recycled vitrinite. This is caused by the erosion of sedimentary rocks in the near mountain ranges and the extreme frequency of turbidity currents transporting the reworked organic matter into the deep ocean. (4) Organic sedimentation not only depends on the flux of terrigenous material, but also on bioproductivity. Therefore, upwelling-related high productivity may greatly affect the maceral composition along active and passive continental margins. Organic matter-rich sediments in upwelling areas are usually characterized by very high proportions of amorphous organic matter of marine origin. (5) Similar to rifted continental margins, a variety of sedimentary processes occur in back-arc basins. For example, black shales rich in marine macerals and turbidites and slumps often rich in terrigenous macerals may be deposited. Back-arc basins and areas where midocean ridges are subducted are characterized by thermal hydrocarbon generation at shallow depth.