More than 1,000 km 620 mi) of high resolution ore-Boomer and 3.5 kh_z subbottom seismic profiles correlated to seventeen 10-12 m (33-56 ft) vibracores provide the data base for analyzing the sedimentologic and stratigraphic framework of transgressive sand shoals on the Louisiana inner continental shelf. Trinity and Ship Shoals are comprised of reworked sands of the abandoned Holocene Teche and Maringouin deltas and provide a possible modern analog for some Cretaceous shelf sandstones of the Western Interior.

Ship Shoal transgressive sands lie disconformably over Maringouin deltaic muds. The sand body pinches out seaward on the erosional inner shelf and is terminated landward by a depositional surface. Maximum sand body thickness is 7 m (23 ft) in the western shoal region. Internally, the sand body is characterized by landward dipping subhorizontal reflectors. The underlying Maringouin deltaic sequence contains a series of low-angle seaward-dipping clinoforms and numerous small channels in the western shoal area. Core analysis reveals a 3-7 m (10-23 ft) thick upward-coarsening sequence of very fine to fine-grained (100-125µ) well-sorted, clean, quartzose sand. Grain size, percent sand and shell, and percent cross bedding increase upwards. The shoal sequence is capped by a 1-2 m (3-6 f ) thick deposit of horizontally laminated fine-grained (125-175µ) sand and shell. The lower two-thirds of the shoal sequence is massive in appearance with minor amounts of burrowing. The shoal sequence abruptly overlies a dark, organic rich, silty clay (prodelta?) with numerous wavy and lenticular interbeds of silt; burrowing is rare.

The Trinity Shoal sand body is 5-7 m (16-56 ft) thick and lies disconformably over Teche deltaics. Internally, the sand body is composed of a set of westward-dipping clinoform reflectors. Three levels of channeling related to sea level stands in the early Wisconsin, late Wisconsin, and Holocene (Maringouin delta) underlie and occur seaward of Trinity Shoal. Continued Atchafalaya delta sedimentation will soon encase Trinity Shoal in mud.

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