Late Quaternary evolution and stratigraphic framework influence on coastal systems along the north-central Gulf of Mexico, USA

Abstract

Coastal systems in the Gulf of Mexico are threatened to reduced sediment supply, storm impacts and relative sea level rise (RSLR). The geologic record can provide insights of geomorphic threshold crossings (formation, progradation, transgression, destruction) to these forcing mechanisms to predict future barrier evolution to climate change. The stratigraphic framework and antecedent topography directly influence coastal evolution over geologic timescales. This study synthesizes ~2100km of geophysical data, 700+ sediment cores, and 63 radiocarbon dates to regionally map two sequence boundaries, multiple ravinement surfaces and fourteen depositional facies. One marine isotope stage (MIS) 6 valley's fill provided up to 300 x10 6 m 3 of sand to modern systems through transgressive ravinement during the Holocene. Repeated storm breaches or tidal inlets correspond to paleotopographic low's in the MIS 2 surface. A Holocene geomorphic evolutionary model was created for Petit Bois and Dauphin Island from available data, highlighting RSLR rates and sediment supply. As the MIS 2 surface was flooded, tidal/wave scour supplied sand to migrating marine shoals. These rapidly transgressing shoals converted drowned paleovalleys to estuaries starting about 9ka. Islands formed in their modern positions about 6ka, when sediment supply was high and RSLR rates were 2mm/yr. Between 4ka-1750 CE. Islands prograded due to RSLR rates of 1-0.4mm/yr and sufficient sand supply from alongshore and inner shelf sources. Currently, the islands experience RSLR rates of 3.61 mm/yr and reduced sediment supply resulting in barrier degradation. This study provides geologic evidence of coastal geomorphic thresholds related to RSLR, sediment supply and antecedent topography. iii ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Davin Wallace for his guidance and great support through this project. I would also like to thank my committee members Dr. Michael Miner and Dr. Jessica Pilarczyk, and lab mates, Clayton Dike, Nina Gal, and Shara Gremillion for their helpful and insightful feedback and guidance. This project was funded by the Bureau of Ocean and Energy Management, as part of a Gulf of Mexico sand resource mapping effort. Thank you to colleagues at the University of Alabama, the Geological Survey of Alabama and USGS for allowing core sampling. The USGS and UTIG shared archive geophysical data. Mollusk bivalve identification was greatly aided by Dr. Jennifer Walker. Dr. John Anderson (Rice) and Dr. Ervin Otvos (USM) also provided valuable insight. iv DEDICATION This thesis is dedicated to friends, family and loved ones especially Bob, Ellen, Joey and Alli. Their love, appreciation and support allowed me to pursue my scientific passion. v

Tracking Barrier Island Response to Early Holocene Sea-level Rise: High Resolution Study of Estuarine Sediments in the Trinity River Paleovalley

“…The presence of a fluvial terrace underlying this switch in tidal flow direction is thus interpreted as the underlying fluvial topography providing a direct "pinning point" for the barrier (e.g., Raff et al, 2018;Shawler et al, 2020). However, the underlying fluvial geology does not act as a sediment source for the paleo-barrier island system, which may be expected from previous studies (e.g., Riggs et al, 1995;Anderson et al, 2016;Hollis et al, 2019;Shawler et al, 2020). This is demonstrated by the top of fluvial sediments (H6) very rarely being truncated and reworked by overlying tidal (H4, H4a, H4b) or wave erosional surfaces (H2) (Figs.…”

“…Deep, topographic lows cut by the paleodrainage system form the incised valley and are important in defining the estuaries which transgress them, including controlling the location of the tidal inlet (Morton and Donaldson, 1973). Additionally, topographic highs in the form of fluvial interfluves and terraces provide both increased elevation in which barrier islands are pinned upon (e.g., Raff et al, 2018;Shawler et al, 2020), as well as sediment supply to the barrier via wave and tidal forces (e.g., Riggs et al, 1995;Anderson et al, 2016;Hollis et al, 2019). This study supports this growing body of literature, and finds that the estuarine system is intimately controlled by its antecedent geology.…”

Application of Random Effects to Explore the Gulf of Mexico Coastal Forest Dynamics in Relation to Meteorological Factors

“…To study this region is valuable for understanding global climate change and its ecological consequences [11]. Coastal environments along the Gulf of Mexico are altered by the consequences of climate change [40]. As such, changes in temperature and precipitation within the Gulf of Mexico coastal region were expected to be able to explain forest dynamics in this study.…”

Response and recovery of Horn and Petit Bois Islands, Mississippi, USA to tropical cyclone impacts: 2004–2016

“…The initiation of the MS-AL barrier chain took place between 6 ka and 4 ka years BP (Hollis, 2018;Otvos, 2005) when the western side of incipient Dauphin Island, anchored by the Pleistocene Gulfport Formation (Otvos, 1985), intersected with landward migrating marine shoals at a ~2 mm/yr SLR rate. As SLR decelerated below 2 mm/yr, the in-situ shoals received enough sediment from alongshore and offshore sources to vertically accrete and stabilize (Hollis, 2018), forming modern day Dauphin Island. Horn Island formed ~4.5 ka years BP at a ~1 mm/yr SLR rate (Gal, 2018).…”