Organic geochemistry of ODP Sites 128-798 and 128-799

The organic matter consists of a variable mixture of marine and terrigenous contributions, the ratio of which is not correlated to the total organic carbon content. Marine organic particles clearly dominate in the deeper section of Hole 799B.

The extractable bitumen is strongly dominated by long-chain alkenones from microalgae in the shallower sediments, whereas bishomohopanoic acid (C32) of eubacterial origin is the single most abundant compound in deeper samples. Normal alkanes and straight-chain carboxylic acids, both of which show a bimodal distribution with odd and even carbon-number predominance, respectively, are two other groups of compounds which are important constituents of the extracts.