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ABSTRACT: Holocene Geologic Framework of Lake Pontchartrain Basin and Lakes of Southeastern Louisiana


The Pontchartrain Basin is about 200 km along strike and 75 km along dip with the modern lakes (Lakes Maurepas, Pontchartrain, and Borgne) covering the southern portion of the basin. The basin is bounded by incised Pleistocene terraces to north, the Mississippi River delta plain to the south/southwest and the Pine Island barrier shoreline to the south/southeast. Existing geological information has been integrated with new high resolution seismic profiles (>700 line km), vibracores (76), and geochemical data (>1000 samples) to develop a geologic history and sediment distribution of the basin.

The Pontchartrain Basin has a complex depositional history controlled by sea-level change. During the late Wisconsin low-stand, the region was entrenched by rivers. Sea level rose during deglaciation, depositing transgressive nearshore sediments across the area. A stillstand at (approx.) 4,000 BP initiated formation of a barrier shoreline. Sediments eroding from the Pleistocene terraces combined with sandy material moving westward along-shore built the large recurved spit and barrier (Pine Island barrier trend) that bounds the southeast portion of the basin. Backbarrier deposits and shell reefs partially filled the open estuary. The next depositional event (at ~3,000 BP) was the eastward progradation of the St. Bernard delta complex from the Mississippi River valley. Deltaic sediments enclosed the Pontchartrain Basin to the south and eventually included the Pine Island barrier. At that time, the basin began to accumulate prodelta, delta front, and crevasse deposits. Holocene sedimentation has been differential in Lake Pontchartrain to the north (~0.3 m) compared to the south (~5.0 m).

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana