(Table 1) Organic- and carbonate-carbon and extract for DSDP Leg 64 Holes

We determined the quantity, type, and maturity of organic matter in Pleistocene sediment from the Gulf of California. We analyzed extractable hydrocarbons by capillary column chromatography and combined gas chromatography/ mass spectrometry (GC/MS). We investigated kerogens by Rock-Eval pyrolysis and microscopy. Organic carbon is mostly between 1 and 2% in samples from the mouth of the Gulf (Holes 474 and 474A) and in the Guaymas Basin (Holes 478, 481, and 481A) and between 2 and 4% at the Guaymas Basin slope (Hole 479). We determined total extracts of about 10 mg/g Corg for all samples. The organic matter seems to be mostly terrigenous in Holes 474, 474A, 478, 481, and 481A, as indicated by the extractable hydrocarbons and the macefal analysis. But we believe that the large amounts of steroid and triterpenoid hydrocarbons in some samples indicate marine and bacterial biomass, which probably is finely disseminated and cannot readily be identified under the microscope. Rederived, inert organic matter is common in these holes. In Hole 479, the terrigenous contribution is less pronounced, and algal liptinites exceed terrigenous liptinites. But in all samples, perylene is the predominant aromatic hydrocarbon. Optical and chemical investigations show that the organic matter in the Gulf of California sediment is immature, despite the high heat flow and local basaltic intrusions. We could not establish a regular maturity trend with increasing depth.