Environmental Atlas of the Lake Pontchartrain Basin

	Basin Geology: Geology | Quarternary Framework | Geomorphology | Bathymetry | Geologic Resources

Basin Geology - Geology

• Introduction
• Geologic Map of the Lake Pontchartrain Basin
• Geologic Setting of the Big Branch Shoreline

Alluvium Gray to brownish gray clay and silty clay, reddish brown in the Red River Valley. Some sand and gravel locally. Includes all alluvial valley deposits except natural levees of major streams. Natural Levees Gray and brown silt, silty clay, some very fine sand, reddish brown along the Red River. Shown only on past and present courses of major streams. Delta Plain, Fresh Marsh Gray to black clay of very high organic content, some peat. Area of active and abandoned delta lobes of the Mississippi River. Delta Plain, Saline Marsh Gray to black clay of high organic content, some peat. Area of active and abandoned delta lobes of the Mississippi River. Deweyville Terrace Gray mixed with brown-to-red clay and silty clay. Some sand and gravel locally. Topographically higher than Holocene alluvium and lower than Prairie terraces. Found along streams of intermediate size. Prairie Terraces Light gray to light brown clay, sandy clay, silt, sand and some gravel. Surfaces generally show little dissection and are topographically higher than the Deweyville. Three levels are recognized: two along alluvial valleys, the lower coalescing with its broad coastwise expression and the third, still lower, found intermittently gulfward. Prairie Terraces - Loess Tan to reddish brown massive silt with some clay and minor amounts of very fine sand. Intermediate Terraces Light gray to orange-brown clay, sandy clay, and silt. Much sand and gravel locally. Surfaces show more dissection and are topographically higher than Prairie. Intermediate Terraces - Loess Tan to reddish brown massive silt with some clay and minor amounts of very fine sand. See detailed description of Qti. High Terraces Tan to orange clay, silt, and sand with a large amount of basal gravel. Surfaces are highly dissected and less continuous than lower terraces. Composed of terraces formerly designated as Willana, Citronelle and the highest Bentley lignitic clays with interbeds of limonitic sands or lignite. Near the base, calcareous, glauconitic and fossiliferous beds may weather to black soil. High Terraces - Loess Tan to reddish brown massive silt with some clay and minor amounts of very fine sand. See detailed description of Qth.