Identifier

etd-07052012-181939

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

Saltwater encroachment northward into freshwater sands of the Baton Rouge aquifer system, southeast Louisiana, poses a serious environmental threat to the metropolitan water source. The aquifer consists of a 0.6 mile-thick succession of interbedded, unconsolidated south-dipping siliciclastic sandy units and confining mudstones dating from the Upper Miocene through the Pleistocene. The study area is crosscut by the Baton Rouge fault, a west-east trending listric fault that serves as a leaky barrier to saltwater intrusion from the south. A better understanding of the connectivity, morphology and depositional setting of this aquifer system and hydraulic properties of the Baton Rouge fault is necessary for developing strategies to halt or control saltwater intrusion. This study provides an in-depth geologic evaluation of the depositional environments of these sediments. Seventy five well logs for boreholes located in East Baton Rouge, West Baton Rouge and Livingston parishes provided data for interpreting environments of deposition, correlating sand-rich and mudstone-rich zones, and identifying periods of low and high sediment aggradation. The correlation of units immediately south of the fault provided the basis for a separate study of the permeability architecture of the fault zone. It was concluded that sandy units of the Baton Rouge aquifer system were fluvially deposited and have complex geometries representing channel fill, floodplain, levee and crevasse splay facies. Aquifer sands are interpreted as zones of amalgamated sand bodies deposited during times of low aggradation associated with sea-level falling-stage and lowstand system tracts. The amalgamation created a high degree of connectivity which causes these zones to behave hydraulically like single units. Mudstone-rich sequences are interpreted as having been deposited during times of high aggradation associated with sea-level highstand. Roughly 10 cycles that correlate to USGS-designated aquifer sands were identified in lithology-depth curves. The number of sandy units is less than the 24 sea-level reversals documented in the northern Gulf of Mexico for the Upper Miocene through the Pleistocene. Fluvial systems are sensitive to changes in relative sea-level up to 400 miles inland but numerous and major unconformities in the study area have removed portions of the geologic record.

Date

2012

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hanor, Jeffrey

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