32 Hydrogeology

Added due to amount of discipline abstracts submitted.

Tuesday, 10 March 2026
1:30 PM - 5:30 PM
RCC, 106

Deep-Seated Structural Controls on Groundwater Movement within the Coastal Plain at St. Catherines Island, Georgia

Paper number: 32-15
Program: Technical Sessions
Time: 5:15 PM – 5:30 PM

Authors

Abstract

A long-term hydrogeologic study on a barrier island in Georgia has revealed structural controls on groundwater movement in the surficial aquifer and underlying carbonate units of the Floridan Aquifer System. Hydraulic head and chemistry data suggest that groundwater moves upwards through the carbonate system along near-vertical faults and solution collapse features. These data also show that large spring tides cause periodic saltwater intrusion within the shallow aquifer at specific locations on the island. Electrical resistivity and ground-penetrating radar profiles indicate the presence of shallow fractures, faults and sag (collapse) structures near the sites of saltwater intrusion.

Based on hydrogeologic and geophysical data, we hypothesize that the structural controls at the field site originated from reactivated basement faults associated with Mesozoic rifting and opening of the Atlantic. This recurrent fault movement has propagated upwards through the overlying sedimentary section, creating permeable pathways for the vertical and lateral movement of groundwater within the coastal plain. We are currently testing this hypothesis by gathering additional data at two new field sites on the island. Here, there is both geophysical and topographic evidence of solution collapse and relic drainage from past artesian spring flow. Since the new sites fall along the strike of faulting mapped earlier at our original field location, we proposed the existence of a deep-seated, vertical fault that trends northeastward across the island. Moreover, we suspect that this fault is an extension of a large basement fault that has been mapped at Brunswick, Georgia, and known to be associated with vertical saltwater intrusion. Because reactivated basement faults generally have little surface expression on the coastal plain, we believe they are more common and play a more important role in the vertical movement of groundwater than previously thought.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411825

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