Ka. Kvenvolden et al., LABORATORY SIMULATION OF HYDROTHERMAL PETROLEUM FORMATION FROM SEDIMENT IN ESCANABA TROUGH, OFFSHORE FROM NORTHERN CALIFORNIA, Organic geochemistry, 22(6), 1994, pp. 935-945
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.