LATE HOLOCENE RELATIVE SEA LEVEL VARIATIONS RECORDED IN CALCASIEU LAKE, LOUISIANA

Sea level rise projections estimate that coastal areas will experience decimeter scale inundation within the next few centuries. The meter scale resolution of current accepted sea level records does not address the potential effects of these finer scale oscillations. Exactly how coastal environments would respond to increased rates of sea-level rise is difficult to predict, but late Holocene depositional systems preserve small scale relative sea level variations and thus provide a valuable analog for future environmental change.

Low resolution sea level curves document rapid rise during the early Holocene, a slower rise during the middle Holocene, and no rise over the past 3000 years (late Holocene). During transgression (~9000 to 3000 BP), major flooding events associated with rapid environmental changes are manifested in high resolution seismic records and core data as significant litho- and biofacies changes. Small coastal plain alluvial systems along the Louisiana coast record flooding events during the late Holocene. In the absence of large amplitude eustatic sea level fluctuations, these surfaces are attributable to decimeter scale eustatic oscillations, sediment supply variations, or variable subsidence. This study aims to address the forcing mechanisms and shed light on how coastal environments can dramatically adjust to seemingly minor perturbations.

Eighty six kilometers of high-resolution seismic data and 7 continuous cores (<20 m length) were collected in Calcasieu Lake to examine the response of the bay to different forcing mechanisms. Seismic and lithofacies changes are remarkably similar to Galveston Bay for the early Holocene. Middle to late Holocene depositional facies in the middle and upper areas of Calcasieu Lake are different from Galveston Bay. Seismic stratigraphy linked to core facies illustrates bay head delta facies in Calcasieu Lake at a time when middle bay muds dominate Galveston Bay. Additionally, seismic and core data record significant flooding surfaces and facies changes within the middle to lake Holocene deltaic facies. Ongoing efforts include developing a more detailed radiocarbon stratigraphy for Calcasieu Lake. Better chronostratigraphy will shed light on the forcing mechanisms that altered the bay environment.