Browsing by Subject "Reef"

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Impact of Increased Terrigenous Sediment in Near-Shore Reef Systems
(2020-12) Logie, Tyler
Changes in the flux of terrestrial sediment into the ocean can cause marine ecosystems to suffer severe environmental stress. The physical effects of increased terrestrial erosion towards the shallow ocean can decrease light quality, increases the energy that reef builders must expend, and in extreme cases can cause burial of near-shore reefs. The influx of new terrestrial sediment can also have a notable effect on the chemistry of the ocean by increasing the flux of nutrients. This can alter the trophic state of the area, favor the expansion of algae over metazoan reef builders such as corals, and potentially cause a decrease in free oxygen available in the water column. The effects of increased terrestrial sediment flux can be seen most clearly during time intervals during which a spike in atmospheric CO2 concentration causes the global silicate weathering rate to increase. These events are commonly associated with global marine extinctions, as is the case at the Permian/Triassic boundary and during the Toarcian Ocean Anoxic Event. Isotope and trace element geochemistry can be used to reconstruct changes in the global silicate weathering rate, marine nutrient content, and fraction of terrestrial sediment in a marine setting. By combining these geochemical data with modern studies of reefs under sediment stress, the mechanisms driving reef collapses in the geologic record are better understood. This information can be applied to research attempting to predict the impact of increased sediment flux associated with climate change.
Kinta S. - A New Artificial Reef in Texas - View from the Galley
(2014-09-18) University of Texas Marine Science Institute; Barroso Ruiz, Alfredo; Erisman, Brad
Middle-Hauterivian to Lower-Campanian sequence stratigraphy and stable isotope geochemistry of the Comanche platform, south Texas
(2011-05) Phelps, Ryan Matthew, 1982-; Kerans, C. (Charles), 1954-; Loucks, Robert G.; Janson, Xavier; Scott, Robert W.; Fisher, William L.; Quinn, Terrence M.
Carbonate platforms contain a wealth of information regarding the changing biota, sea level, ocean-chemistry, and climate of the Cretaceous Period. The Comanche platform of the northern Gulf of Mexico represents a vast, long-lived carbonate system that extended from west Texas through the Florida panhandle. In central and south Texas, excellent outcrops and an extensive suite of subsurface data provide an opportunity to document the evolution of this system, from the shoreline to the shelf-margin and slope. This study examines the changing facies, platform morphologies, and shelf-margin architectures of the mixed carbonate-siliciclastic, middle-Hauterivian to lower-Campanian interval. Stratigraphic results are integrated with stable-isotope geochemistry to document the detrimental effects of oceanic anoxic events on the carbonate platform. Seven second-order, transgressive-regressive supersequences of 3-14 Myr duration are defined in south Texas using sequence stratigraphic analysis of shelf-interior facies successions. Second-order supersequences are subdivided into several third-order depositional sequences of 1-3 Myr duration. In these sequences, facies proportions and stratal geometries of the shelf-interior are found to be the result of changing platform morphology and temporal evolution from distally-steepened ramp to rimmed-shelf depositional profiles. Shelf-margin trajectories, stratigraphic architectures, and facies proportions are a function of long-term accommodation trends expressed in second-order supersequences. These characteristics are modified by lateral variability in the underlying structural/tectonic setting and localized syndepositional faulting. The stratigraphic equivalents of oceanic anoxic events 1a, 1b, 1d, 2, and 3 are documented in the Cretaceous section of south Texas. These oceanic anoxic events coincided with maximum flooding zones of supersequences and are linked to carbonate platform drowning events on four separate occasions. The occurrence of oceanic anoxic events is found to be a fundamental driver of carbonate platform morphology, faunal composition, and facies evolution in transgressive-regressive supersequences of the northern Gulf of Mexico.
Stratigraphy, depositional history, and pore network of the Lower Cretaceous Sunniland carbonates in the South Florida basin
(2016-05) Liu, Xinggang Christopher; Kerans, C. (Charles), 1954-; Loucks, R. G.; Fisher, William
The South Florida Basin of the eastern Gulf of Mexico represents a vast, undisturbed carbonate system that extended from the Florida Keys through the Tampa-Sarasota Arch. In South Florida, extensive subsurface data and analogous modern environments provide an opportunity to unravel the evolution of this system from shoreline to shelf-margin. This study examines the changing facies and the pore network of the Latest Aptian-Early Albian Sunniland interval. Stratigraphic results are closely comparable with contemporary carbonate platform studies in the northern Gulf of Mexico. The Sunniland Formation was deposited during a major transgressive-regressive sequence. The Sunniland interval is divided into five third-fourth order, transgress-regressive depositional cycles (S-1 to S-5) in south Florida using sequence analysis of shelf-interior facies succession. In these sequences, facies proportion, faunal composition, and stratal geometries of the shelf-interior are found to be the result of the changing accommodation trends and ocean chemistry. As in the Comanche Platform in South Texas, the detrimental effects of oceanic anoxic event 1B may fundamentally drive the evolution of platform morphology in the eastern Gulf of Mexico as: • Rimmed shelf (crisis phase: S1) • Distally steepened ramp (anoxic/dysoxic phase: S2, recovery phase: S3, S4) • High-angle rimmed shelf (recovery to equilibrium phase: S5). Within this hydrocarbon-producing trend, the lowered sea level at the end of S4 enhances the reservoir quality in the high-energy settings including back-reef debris aprons, tidal shoal-complex and carbonate beach by dissolution. The tight sabkha-tidal flat facies in S5 forms the reservoir seal, whereas the medium-fine crystalline dolomites in S3 may not adversely affect and likely facilitate the migration of hydrocarbon self-sourced from the high TOC, argillaceous mudstone in S2.
Turnover of corals and reef ecosystems during the Early Cenozoic hyperthermal events, with a focus on the Paleocene-Eocene thermal maximum (~56 Ma)
(2019-05-09) Weiss, Anna Marissa; Martindale, Rowan C.; Breecker, Daniel; Foster, William; Kerans, Charles; Matz, Mikhail
The early Cenozoic was a time of major environmental and evolutionary change, especially for shallow water carbonate ecosystems. Of particular importance is the major global carbon-cycle perturbation known as the Paleocene-Eocene Thermal Maximum (PETM) that occurred approximately 56 million years ago. The release of greenhouse gasses in the late Paleocene and early Eocene led to increased temperatures, ocean acidification, as well as increased weathering in coastal environments. On carbonate platforms globally, Paleocene coral patch-reefs were replaced by non-metazoan reef-builders by the early Eocene. In spite of apparently inhospitable conditions and a phase-shift in reef-building taxa, there was no major mass extinction of shallow benthic taxa (e.g. corals and large benthic foraminifera) on carbonate platforms. The goals of this research are to understand how climate and environmental change in the early Cenozoic impacted diversity and structure of reefs, and how reef-dwellers were able to survive. This research shows that during the late Paleocene, coral reefs on the Adriatic Carbonate Platform (Slovenia) were replaced by microbial reefs, likely due to increased temperatures and turbidity. The microbial reef communities are statistically similar to those they replace, showing that losing a keystone species (i.e., corals) did not impact overall community structure. The largest change in community composition happens at the Paleocene/Eocene boundary. Petrography, sedimentology, and geochemistry are used to analyze a truncated surface at the Paleocene/Eocene boundary at a site in Slovenia, hypothesized to be caused by localized ocean acidification during the PETM. Additionally, paleontological databases are analyzed to show that corals with particular physiological traits or behaviors were associated with survival or low extinction rates during the PETM. Analysis of databases also confirms that coral reefs with more integration of coralline algae over their 156 million year evolutionary history have higher diversity and stronger framework. This research is important from a paleontological perspective because it reports quantitative data from poorly studied environments during an important interval of Earth history. It is also significant for reef conservation because it provides clear examples of corals and reefs that have been resilient through past crises, either through physiology and life history or community associations.