Graduation Year

2021

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Jason D. Gulley, Ph.D.

Committee Member

Patricia D. Spellman, Ph.D.

Committee Member

Mark C. Rains, Ph.D.

Committee Member

Bogdan P. Onac, Ph.D.

Keywords

Carbonate stratigraphy, Karst Geomorphology, Hydrogeology, Eogenetic, Seismic

Abstract

Integrative characterizations of karst systems on low-lying eogenetic carbonate platforms are rare and often limited to areas of direct observation where caves can be entered and explored. Because hydraulic properties of eogenetic limestones have been implicitly assumed to be homogeneous, classical models of carbonate island karst development stressed the importance of geochemical interfaces in controlling cave and vug development. These studies have explained the largest cavern systems as results of either 1) mixing dissolution at platform margins or 2) microbially-mediated dissolution processes at water tables.

New data from core descriptions and wireline logs obtained in 18 boreholes drilled in the Columbus Landing region of San Salvador Island, Bahamas, suggest that sharp contrasts in facies’ permeability control the development and localization of non-matrix porosity, including caves. This analysis recognizes seven stratigraphic units, including: Late Pleistocene, Mid-Pleistocene 1-2, Early Pleistocene 1-3, and the Pliocene Dolomite. Cave and vug distribution maps reveal a distinct spatial control by several of the stratigraphic boundaries. Boreholes intersected the largest caves just above the contact between Miocene-Pliocene dolomites and Pleistocene limestones. Boreholes also intersected smaller horizons of caves and vugs above low permeability exposure surfaces.

We interpret the association of cavernous and vuggy horizons with lithofacies contacts and exposure surfaces to indicate that they formed during lower sea levels when vadose infiltration encountered laterally extensive, low permeability bedrock, which redirected the flow of water. Cave formation by transient perching of vadose infiltration would allow for more reasonable timescales for cave development than phreatic mixing models, which require anomalously high bedrock dissolution rates. These results assist in understanding the complex development and distribution of non-matrix pore systems on low-lying eogenetic platforms and their fundamental relationships to platform geology.

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