Remnants of from Early Mississippi River Delta Complex: Sedimentology, Stratigraphy, and Depositional History
Tiger and Trinity Shoals are shore parallel-to-concave-landward marine sand bodies located on the western Louisiana inner continental shelf, and are thought to represent the final transgressive stage of separate delta lobes of the middle Holocene Teche delta complex. A re-assessment of Tiger and Trinity Shoals as a potential sand resource for coastal restoration projects is being conducted. The initial marine geophysical survey collected approximately 1,150 km of “chirp seismic” lines using an Edgetech sub-bottom profiler, a sonar system that uses a linearly swept FM pulse of a 2-12 kHz frequency range to penetrate shallow sediments with a vertical resolution of approximately 10 cm. Seismic data were brought to LSU, loaded into a Petrel workstation, and preliminary stratigraphic and geological interpretations were established. Based on these interpretations, 46 vibracores with a maximum length of 4.5 m were extracted. Core locations were chosen so as to 1) evaluate grain size distribution across the shoals, and 2) penetrate various facies for further geological interpretations, modeling, and dating. Cores will be logged (P-wave velocity and Gamma density measurements) and imaged using a GEOTEK core logger, then split for texture descriptions: grain size will be analyzed at 10 cm intervals. However, in-field observations recognized clean fine-grained sand across both Tiger and Trinity Shoals. Both were observed to overly, on their landward sides, what appears to be muddy lagoonal facies. In addition to fine-grain sands, abundant shell mass constituted east Tiger Shoal. Further field work will involve collecting a second “boomer” seismic survey, which will allow for deeper penetration through the underlying Maringouin delta complex, and perhaps the Pleistocene Prairie surface. Additional vibracores will also be collected. Cores already extracted will be integrated into the seismic grid for interpretation: where data are insufficient, those sites will be targeted. Besides assessing sand resource potential, this research will evaluate the depositional history and chronostratigraphy of this region, model facies relationships, and add additional constraints to the Holocene sea-level curve for the northern Gulf of Mexico.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009