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DSDP Site 262 on the axis of the Timor Trough has a thick sequence of Pliocene to Holocene calcareous sediments, which are relatively rich in organic matter (up to 1.5% total organic carbon) of mixed marine-continental origin. The organic geochemistry of the sediments, as reflected in the acid-insoluble total organic carbon, C15+ extract, and kerogen fractions, varies markedly. However, the overall picture is consistent with a progressive increase up the drill hole in the proportion of terrigenous vascular plant material. Both the bottom-hole temperature of 15°C and aspects of the composition of the organic matter indicate that there has been no thermal maturation. Hydrocarbon concentrations are low (<60 ppm). In-situ bacterial activity within the upper sediment column has given rise to high interstitial alkalinities, decreased sulfate concentrations, pyrite (commonly framboidal), and abundant methane. This bacterial activity also may have affected the geochemistry of the residual organic matter. The biogenic methane probably is present as solid methane hydrate. The ultimate hydrocarbon-generating potential of the Timor Trough sediments depends on whether kerogen composition or extract yield is taken as the best indicator. However, there is undoubtedly sufficient sapropel and herbaceous matter to produce both oil and gas if the sediments are subjected to deeper burial and higher temperatures.
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