Abstract: Sedimentology and Origin of Sabine Bank, a Holocene Shelf Bank on the East Texas Inner Continental Shelf

F. P. Siringan, John B. Anderson, M. D. Hamilton

Sabine Bank is the largest bank on the Texas shelf. Sediment cores, born hole descriptions, grab samples and high-resolution seismic data are used to establish its origin and sedimentology. The base of the bank is a ravinement surface. On its seaward half, the ravinement surface amalgamates with the Holocene-Pleistocene unconformity. Five sediment facies comprise the bank,

namely; well sorted sand and shell bed, shelly muddy sand, interbedded sand and clay, clay with interbeds of sand, and sandy shelly mud. Individual sand beds commonly exhibit fining upward trends and clay-rip-ups; these are indicative of deposition during storms. In general the facies coarsen upward fine landward and to the west (the direction of prevailing flow on the shelf). These trends reflect an onshore and downcoast growth of the bank.

Overall, Sabine Bank is a muddy shelf bank. Formation of the bank was initiated in an inner shelf setting, triggered by an episodic rise in sea-level. The primary source of sediments that comprise the bank is located to the east. During the rapid rise of sea-level coastal lithosomes associated with a 6,000- to 4,000-year BP paleoshoreline within the Sabine Bank region were reworked onshore. This is evidenced by preserved tidal inlet/delta deposits under the ravinement surface at the base of Sabine Bank. To the east of this region, on the Louisiana shelf, sediments of coeval paleoshoreline features were stranded on the shelf and later reworked by strong storm-generated currents. These storm currents flowed parallel to slightly oblique to the shelf contours, from the Louisiana shelf to he east Texas shelf. Sediments entrained by these currents were deposited on and around topographic highs of the Holocene-Pleistocene surface. Enhancement of initial topographic relief resulted in the increased deposition of sand in the area during each successive storm and subsequent development of Sabine Bank.

Preliminary work on the other banks on the Texas shelf indicates that the stratigraphy and facies distribution of Sabine Bank is not unique; this indicates similar origin. Comparison of Sabine Bank with these other banks is an objective of ongoing research.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994