HCNSO Student Theses and Dissertations

Defense Date

4-30-2019

Document Type

Thesis

Degree Name

M.S. Marine Environmental Sciences

First Advisor

Sam Purkis, Ph.D

Second Advisor

Bernhard Riegl, Ph.D

Third Advisor

Robert Madden, Ph.D

Abstract

Sediment on Cay Sal Bank (CSB) is characterized by its coarse-grain size, poor sorting, predominance of skeletal fragments, and relatively depleted d18O isotope values. CSB is an incipiently drowned platform in close proximity to the Great Bahama Bank (GBB), a carbonate platform which is not incipiently drowned and characterized by fine-grained, non-skeletal sediment. The GBB has locally well-developed oolitic grainstone facies and coral reef margins, which are both lacking on CSB. Platform-top water depths on the GBB are typically 10 m or less, but CSB depth ranges between 7 and 30 m. CSB is devoid of mud, whereas mud-supported depositional texture on GBB comprises 28% of the dataset. Dominant non-skeletal grains are grapestones and pelletoids, and the latter display evidence of micritization. Non-skeletal types on GBB are primarily grapestones and ooids. Surficial sediments from both platforms are primarily composed of aragonite, but high-magnesium calcite is slightly more prevalent on CSB. Similar to other incipiently drowned platforms in the Caribbean, CSB has been subject to rapid Holocene flooding. Common features between these three platforms are a thin sedimentary cover, a dominance of Halimeda plates, and micritized cryptocrystalline grains. Increased nutrient levels have been shown to be related to platform drowning as well as the reduction of coral and algal growth on Serranilla Bank, but rapid Holocene flooding has been more likely for CSB, and appears to be in the second of a three-stage drowning process, ultimately culminating in carbonate platform “turn off”, preventing further carbonate and reef development at the level of GBB.

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