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ABSTRACT: Estuarine Facies Architecture of a Late Quaternary Incised Valley Fill: Lake Calcasieu, Western Louisiana

NICHOL, SCOTT L., and RON BOYD, Centre for Marine Geology, Dalhousie University, Halifax, Nova Scotia, Canada, and SHEA PENLAND, Louisiana Geological Survey, Baton Rouge, LA

The spatial organization, geometry and sedimentary character of Holocene clastic estuarine deposits within the Lake Calcasieu incised valley are documented here using Vibracore, borehole records and high resolution shallow seismic data. Periods of sea level lowstand during the Late Quaternary allowed the Calcasieu River to excavate a 30 m deep valley in Pleistocene alluvial terraces of the Prairie Formation. At present sea level the valley is 92 km in length. The upper 56 km of the valley is confined by the terraces to an average width of approximately 2.5 km. Here, the river channel displays a strong meandering pattern, indicating a complex history of channel migration. Surface exposures of the Prairie Formation terminate approximately 22 km from the coast.

Seaward of this limit the estuary becomes wider, reaching a maximum width of 22.5 km behind the chenier plain that separates Lake Calcasieu from the Gulf of Mexico.

Sedimentation in the Calcasieu valley has continued since the mid-Holocene under a storm-dominated, low fairweather wave energy, microtidal process regime, coupled with regional subsidence of the coastal plain producing a sea level rise of 0.54 cm per year and an apparent decline in the supply of river-born terrestrial sediment to the estuary.

Preliminary results indicate that the stratigraphic arrangement of facies units within the Lake Calcasieu incised valley conforms to sequence stratigraphic models for transgressive to highstand systems tracts. A type 1 sequence boundary is represented in Calcasieu by an unconformity between Prairie Terrace deposits and lowstand alluvial deposits. The base of the transgressive systems tract correlates with the marine-flooding surface, marked by the contact between lowstand alluvial and progradational bay-head delta deposits. The highstand systems tract is represented by aggradational and progradational parasequences. In Calcasieu, the former include the central basin and marsh facies and the latter comprise bayhead delta and chenier facies.


AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)