San Salvador Island is a small isolated carbonate platform on the southeastern edge of the Bahamian Archipelago. The Line Hole well field is located on an eogenetic karst aquifer on San Salvador Island's northern coast. The island's negative water budget and extensive lake cover have resulted in the upconing of saline water that has fragmented the once continuous freshwater lens. The Line Hole well field consists of several 15-cm diameter wells drilled into the fresh-water lens and arranged in a line perpendicular to the shore. The well field also has two monitoring wells (LH 1, and LH 13), that penetrate approximately 7 m below the water table into higher salinity groundwater. The well field was abandoned in 2016 upon saltwater intrusion to the aquifer. To evaluate the connectivity between the eogenetic karst aquifer monitored by the Line Hole well field and the ocean, we instrumented wells with HOBO U20L-04 loggers to measure pressure and temperature timeseries. We instrumented wells LH4, and LH8, in addition to the monitoring wells LH1 and LH13.
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Flank margin caves can connect to regionally extensive touching vug networks before burial: Implications for cave formation and fluid flow
Flank margin caves are extreme endmembers of vuggy porosity that form as diagenesis drives the progressive coalescence of smaller solutional pore spaces. Due to their morphological isolation during formation, the prevailing hypothesis has been that fluid flow in and out of flank margin caves occurs via the matrix permeability and that adjacent chambers only become hydraulically connected through nonmatrix porosity during burial, collapse, and fracturing. To our knowledge, however, no studies have evaluated how flank margin caves are connected to regional flow systems in modern carbonate platforms. In this study, we evaluate the connectivity of wells, boreholes, blue holes, and flank margin caves in increasingly older bedrock on San Salvador Island, Bahamas, using tidal attenuation analysis. Phreatic karst features are not reported in Holocene bedrock, and permeability magnitudes from wells suggest Holocene deposits connect to the ocean along matrix‐dominated flow paths. Permeability magnitudes in bedrock surrounding wells, boreholes, and karst features deposited during Marine Isotope Substage (MIS) 5e suggest connection to the ocean through matrix and touching vug porosity. Boreholes, blue holes, and flank margin caves in pre‐MIS5 bedrock connect to the ocean via touching vugs. We suggest that increasing bedrock permeability, cave number, and cave size observed within progressively older bedrock on San Salvador is a function of the cumulative number of freshwater lenses emplaced over successive sea‐level stillstands. We suggest that the morphologies of the two largest caves are consistent with dissolution in multiple lenses occupying lower elevations, collapse resulting in breakout domes, and overprinting of collapse chambers during subsequent highstands. As a result, some caves may not reflect connectivity of the bedrock surrounding the main chambers but may reflect connectivity of more diagenetically mature bedrock at lower elevations where their antecedent chambers formed.
more » « less- Award ID(s):
- 1743383
- NSF-PAR ID:
- 10450774
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Earth Surface Processes and Landforms
- Volume:
- 46
- Issue:
- 8
- ISSN:
- 0197-9337
- Page Range / eLocation ID:
- p. 1458-1481
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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