Abstract: Estuarine Facies Architecture and Sequence Stratigraphy of the Mid-Eocene Domengine Formation, Northwest Margin of the San Joaquin Basin, California

Morgan D. Sullivan, Raymond Sullivan

The mid-Eocene Domengine Formation is separated from the underlying strata by a regional unconformity which, when traced westward, progressively truncates older units. The Domengine can be subdivided into 2 members based on the correlation of a regional flooding surface that was used to separate the formation into a lower aggradational member and an upper retrogradational member. The lower Domengine member is about 600 feet in thickness and is composed of a thin basal fluvial unit (0 to 50 feet) which grades upward into a thicker succession (>550 feet) of stacked, upward-fining estuarine sandstones filling east-west trending incised valleys. The estuarine deposits of the lower member consist of massive to sigmoidal cross-stratified, sub-tidal sandstones which grade upw rd into intensely bioturbated inter-tidal silts tones that are in many cases capped by thin supra-tidal coals and mudstones. These valleys were cut by fluvial incision during a relative fall in sea level, and subsequently back-filled with estuarine sandstones associated with the relative rise in sea level during the late lowstand systems tract. The retrogradational upper Domengine member is about 150 feet in thickness and consists of a lower unit dominated by offshore mudstones that is overlain by a more sand-prone interval comprised of hummocky cross-stratified lower shoreface sandstones deposited along a north-south trending wave dominated shoreline. The retrogradational stacking pattern of the upper Domengine member is indicative of deposition during the transgressive systems tract wh n accommodation is typically highest. The aggradational mudstones and sandstones of the overlying Nortonville Formation are interpreted as the highstand deposits associated with the Domengine lowstand and transgressive strata, which together form one third-order depositional sequence.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California