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Figure 5: Three vibracores showing examples of sediments from the primary depositional environments that have constructed the Big Branch Shoreline and Bayou Lacombe areas.

A Sand Source: Offshore Point Platten - Gray fluvial Pleistocene Prairie Formation sediments overlain by transgressive sands. Pre-existing Pleistocene sediments eroded and served as a source of shoreline sand, allowing the formation of protective beaches.

B Mechanism: Nearshore Goose Point - Holocene marsh deposit overlain by transgressive beach sand. Once a back beach protected marsh, it was overwashed by a retreating beach during a storm event. This retreat mechanism allows the maintenance of a beach in a subsiding environment, which in turn protects the interior marshes.

C Result: Inland within the Bayou Lacombe incised valley - Coarse basal valley sub-stratum grades up into a thick black marsh deposit. The inland marshes flourished relatively uninterrupted behind the line of beaches to the south.

Three vibracores showing examples of sediments from the primary depositional environments that have constructed the Big Branch Shoreline and Bayou Lacombe areas.

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Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Environmental Atlas of Lake Pontchartrain

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