Geologic Model of Quaternary and Tertiary Deltaic Stratigraphy and the Impacts on Saltwater Encroachment in the Greater New Orleans Area

James Ayrer and Carol Wicks
[email protected]

A major environmental and economic problem currently faces the New Orleans area in southeastern Louisiana, stemming from salinization of freshwater aquifers that are important resources for the community. Major pumping of these aquifers has altered the potentiometric flow, allowing saltier bodies of water to flow into the region. The impact of pumping wells on encroachment of saltwater and the time/route for saltwater to travel from the current saltwater-freshwater interface to pumping centers is not well constrained. Water planners need additional information to make decisions about future management of groundwater resources. The most appropriate way to analyze pumping effects on groundwater is to build a computer simulated flow model. However, such a model is reliable only if the permeability pathways and structures through which the water moves are well constrained, which necessitates a clear picture of the subsurface geology. The lithology and structure is controlled by the deltaic environment that characterized southeastern Louisiana during the Pleistocene and Holocene periods. The Mississippi River delta has migrated throughout southern Louisiana over time. The deltaic lobes that migrate back and forth likely do not return to the exact same spatial coordinates upon return to southeastern Louisiana, creating complications in defining stratigraphic features. Therefore, a geologic model was produced using well log correlation to characterize both lateral continuity and thickness of lithologic units. The geologic model highlights proposed locations of geologic units, including deltaic lobes, only when the units are clearly indicated in geophysical logs. This geologically constrained model represents a contrast to approaches previously taken in the New Orleans area.

AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63^rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013