LABORATORY SIMULATION OF HYDROTHERMAL PETROLEUM FORMATION FROM SEDIMENT IN ESCANABA TROUGH, OFFSHORE FROM NORTHERN CALIFORNIA

Petroleum associated with sulfide rich sediment is present in Escanaba Trough at the southern end of the Gorda Ridge spreading axis offshore from northern California within the Exclusive Economic Zone (EEZ) of the U.S. This location and occurrence are important for evaluation of the mineral and energy resource potential of the seafloor under U.S. j urisdiction. In Escanaba Trough, petroleum is believed to be formed by hydrothermal processes acting on mainly terrigenous organic material in Quaternary, river-derived sediment. To attempt to simulate these pr ocesses in the laboratory, portions of a Pleistocene gray-green mud, o btained from similar to 1.5 m below the seafloor at a water depth of s imilar to 3250 m in Escanaba Trough, were heated in the presence of wa ter in four hydrous-pyrolysis experiments conducted at temperatures ra nging from 250 to 350 degrees C and at a pressure of 350 bar for 1.0-4 .5 days. Distributions of n-alkanes, isoprenoid hydrocarbons, triterpa nes, and steranes in the heated samples were compared with those in a sample of hydrothermal petroleum from the same area. Mud samples heate d for less than 4.5 days at less than 350 degrees C show changes in so me, but not all, molecular marker ratios of organic compounds that are consistent with those expected during hydrothermal petroleum formatio n. Our results suggest that the organic matter in this type of sedimen t serves as one possible source for some of the compounds found in the hydrothermal petroleum.