St. Petersburg Coastal and Marine Science Center
Western Chenier Plain
The chenier plain consists of a thin wedge of Holocene sediments overlying stiff over-compacted Pleistocene sediments that were subaerially exposed during the late Pleistocene sea-level lowstand. Sabine and Calcasieu Lakes are unfilled remnants of incised valleys excavated by the Sabine-Neches and Calcasieu Rivers, respectively, during the same lowstand. Beginning about 3,000 years ago, the chenier plain was constructed by primarily alongshore processes resulting in the progradation of broad mudflats capped by wetland vegetation with intervening narrow, sandy beach ridges (cheniers). Below the chenier-plain surface, muddy sediments above the Pleistocene-Holocene unconformity range in thickness from less than a meter to about 6 meters, with thickness generally increasing toward the Gulf of Mexico. In general, the direction of sediment supply for the chenier plain was parallel to the gulf shoreline because sediment transport by coastal-plain rivers was trapped in Sabine and Calcasieu Lakes. As a result, only a few tidal channels formed within the chenier-plain wetlands.
The 6 western chenier-plain study areas were located in Sabine National Wildlife Refuge, which encompasses about 500 km2 of coastal wetlands between Sabine and Calcasieu Lakes in the western chenier plain. The refuge occupies a broad, shore-parallel, topographically low area that formed between the topographically higher beach ridges along the gulf shoreline to the south and Pleistocene upland areas to the north.