SCHOLL, DAVID W.
Department of Geophysics, Stanford University, and U.S. Geological Survey, Menlo Park, CA

Abstract: A "Monterey" Scenario to Appraise the Energy Resource Potential of the Deep Water Basin of the Bering Sea

The deep-water (~3500 m) floor of the Bering Sea Basin is underlain by a thick (3-12 km), undeformed, sequence of mostly Eocene and younger terrigenous and pelagic beds. Heat flow is high, ~55 mW/square meter, the corresponding thermal gradient is 50-60<deg>C/km. Middle Miocene to early Pliocene strata beneath the central basin floor are lithified siliceous mudstone units topped by poorly consolidated diatomaceous mud. The overlying late Pliocene and Quaternary section is a weakly consolidated turbidite sequence (- 1 km) interlayered with diatomaceous beds. Acoustic velocity and amplitude anomalies record columns of thermogenic gas ascending through the siliceous mudstone sequence. Within the overlying diatomaceous turbidite section, these columns are capped by dense accumulations of methane hydrate.

The depositional processes and diagenetic evolution of the Neogene Bering Sea Basin can be liken to those of a "Monterey" basin that evolved in an offshore, non-tectonic setting. Such a scenario states that organic-rich mud and diatomaceous beds of middle and late Neogene age accumulated over the floor of the Aleutian Basin prior to their burial by a glacial-age section of terrigenous turbidite deposits. Rapid thickening of these water-rich beds warmed and accelerated the conversion of underlying muddy diatomaceous units to porcelaneous mudstone and chert and began basin-wide production of thermogenic methane and, presumably, oil. Silica diagenesis (opal-A to opal-CT to quartz) contributed additionally to heating the subsurface section. Diagenetic contraction and vertical fracturing of the siliceous mudstone and chert channeled methane upward toward the much colder sea floor, beneath which, and within porous turbidite and diatomaceous beds, methane accumulated in dense masses of hydrate. Presumably, oil migration followed a similar vertical escape path. The "Monterey" scenario implies that during the past 2-3 my large volumes of petroleum gas and oil have been generated in the Bering Sea Basin.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California