A Sedimentologic Description of a Microtidal, Flood-Tidal Delta, San Luis Pass, Texas

Abstract

ABSTRACT San Luis Pass is a microtidal tidal inlet located at the southwest end of Galveston Island, Texas. Continuous cores taken with a portable vibracoring rig, and surface grab samples provide data for constructing vertical sequences and three-dimensional sedimentologic descriptions of the flood-tidal delta complex. These descriptions are based on the type and vertical and lateral distribution of lithofacies, sedimentary structures, textures, and trace fossils. A vertical sequence through the flood-tidal-delta complex consists, from base to top, of: highly bioturbated bay muds and associated oyster reefs; highly bioturbated clayey sand/sandy clay of the tidal delta margin; burrowed sand and shelly sand of the tidal delta; and rooted or burrowed mud of the marsh or mud flat. Washover shell hash deposits may occur at random intervals throughout this sequence. A vertical sequence in the vicinity of San Luis Pass consists of a basal tidal inlet deposit of graded layers of sand and shell overlain by burrowed to shelly sand of the barrier spit. This description of a microtidal, flood-tidal delta differs significantly from descriptions presented for mesotidal, flood-tidal-delta systems in the 1) general lack of large-scale, high-angle sedimentary s ructures; 2) presence of intense bioturbation; 3) presence of washover deposits; and 4) general coarsening-upward nature of the vertical sequence.