Depositional Systems and Holocene Evolution of Baffin Bay, Texas

Using over 65 km of high-resolution seismic profiles and 10 cores from Baffin Bay, Texas we present a depositional and evolutionary model for an estuary formed in a semi-arid climate. Baffin Bay is the flooded incised valley of San Fernando, Los Olmos, and Petronila Creeks. It is currently situated in a semi-arid climate and isolated from the open Gulf of Mexico by Padre Island. As a result, the salinities within Baffin Bay vary widely but average around 50-60 ppt. Baffin Bay initially flooded before 8 ka, most likely around 9.5 ka. During the early part of its Holocene history, it was less restricted and/or more humid than today as evidenced by oysters (Crassostrea virginica) and a well-developed fluvial system, neither of which are found in the bay system today. Around 8.0 ka, the estuary experienced a rapid landward expansion as evidenced by sharp contacts in marine cores and seismic profiles. This event most likely resulted from a small-amplitude global sea-level rise event associated with the drainage of Lake Agassiz-Ojibway. By ~5 ka, the estuary became more restricted and/or drier, similar to the conditions prevalent today. As a result of its isolation and semi-arid setting, the bay has developed some depositional elements different from the other estuaries of Gulf of Mexico over the last 5 ka. These include several “fetch-limited” barrier islands and spits composed almost exclusively of shell hash, serpulid worm-tube reefs, and prograding mud flats covered in algal mats.