|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.