Doctor of Philosophy (Ph.D.)
Degree Granting Department
David J. Hollander, Ph.D.
Brad Rosenheim, Ph.D.
Steven Murawski, Ph.D.
Gregg R. Brooks, Ph.D.
Gert-Jan Reichart, Ph.D.
Event Stratigraphy, Geochronology, Gulf of Mexico, High-Resolution, Sedimentology, Short-lived Radioisotopes
This Dissertation combines the investigation of the sedimentological impacts of the Deepwater Horizon (DwH) blowout event in the deep-sea benthos, with the refinement and advancement of methods and approaches for high-resolution investigations of events preserved in sedimentary records. An approach that combined, rapid collection of cores, a continued annual time series collection of cores, and high-resolution sampling and analyses, in particular short-lived Radioisotopes (SLRad), enabled the temporal resolution required to detect the sedimentary response to the short-duration DwH event, and evaluate post-event sedimentation patterns at a comparable time scale (months).
The collection of 179 sediment cores from 80 sites between the fall of 2010 and 2016 included four sites that were utilized as an annual time-series collection to define the sedimentary response to the DwH blowout event and how the sedimentary system evolved/recovered post-event. High-resolution (2mm) sub-sampling was utilized to maximize the temporal resolution of analyses and age control using SLRad. The rapid collection of cores to define the immediate benthic impact(s), as well as the use of time-sensitive indicators of the event that may degrade over time, as well as indicators for very short time scale (months) sedimentation, such as 234Thxs. 234Thxs inventories and mass accumulation rates (MAR’s) were one of the most diagnostic characteristics of the sedimentary response. The DwH blowout event led to a Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) event that caused a depositional pulse to the seafloor. This was defined by increased sedimentation rates and the shutdown of bioturbation as indicated by 234Thxs inventories and MAR’s. The annual collection of sediment cores as a time-series allowed for continued high-resolution analyses and use of 234Thxs to determine post-event sedimentation rates and baselines on monthly time scales for direct comparison to the depositional pulse. Within ~one year sedimentation rates decreased and within three years site specific return of bioturbation occurred and sedimentation rates on monthly scale (234Thxs) stabilized. Also, within ~three years the sedimentary signature of the depositional pulse became undetectable with respect to sediment texture and composition possibly due to dilution of this indicator by mixing/bioturbation and/or compaction of the event layer.
Without the use of high-resolution sampling and geochronological tools such as 234Thxs the depositional pulse would not have been detected in the sedimentary system. The continued use of these high-resolution methods allowed for further defining the magnitude of the sedimentary response to the DwH event as well as provide baseline sedimentation patterns at a monthly time scale. The annual time series defines the post-event evolution of the sedimentary system as well as the assessment of the post-depositional alterations that influence the integration and preservation of such sedimentation events in the sedimentary record. This includes the potential for re-mobilization of event sediments, potential re-exposure of ecosystems to contaminated sediments and redistribution of event sediments. Alternatively, burial and alteration of the sedimentary signature over time influences the preservation potential of sedimentation events such as DwH, with decreasing ability to detect events due to bioturbation, degradation of signature and compaction.
The refinement of methodology and approaches, in particular short-lived radioisotope (SLRad) geochronology, allowed for the high-resolution determination of the sedimentary impacts of the DwH blowout event. In turn, the opportunity to investigate the DwH event in real time provided the opportunity to advance high-resolution methodologies in an applied fashion. Continued refinement of high-resolution approaches and methods, in particular geochronologies, will allow for the detection of short-duration and subtle sedimentary events in real time as well as in the sedimentary record. Through the application of such approaches and methods to real events, these methods can be further refined and assessed for their utility and limitations.
Scholar Commons Citation
Larson, Rebekka A., "High-Resolution Investigation of Event Driven Sedimentation: Response and Evolution of the Deepwater Horizon Blowout in the Sedimentary System" (2019). USF Tampa Graduate Theses and Dissertations.