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Holocene Sedimentary Responses to Growth Faulting in a Back-barrier Setting: East Matagorda Peninsula, Texas, USA

Phillip C. Wolfe1, Kevin M. Yeager1, Rusty A. Feagin2, Charlotte A. Brunner3, and Kimberly J. Schindler1
1Department of Earth & Environmental Sciences, University of Kentucky
2Department of Ecosystem Science and Management, Texas A&M University
3Department of Marine Science, University of Southern Mississippi

The structural framework of the northern Gulf of Mexico coastal zone is characterized by numerous growth fault systems. Neotectonic processes in coastal marshes in this region have been shown to be important drivers of relative sea-level rise as well as having significant influence on marsh accretion processes. One active growth fault breached the surface of East Matagorda Peninsula, Texas as early as the 1970’s and displacement there is ongoing, leading to significant wetland losses over the past several decades. To characterize the Holocene behavior of this fault and the consequent sedimentary responses, a suite of fallout radionuclides (beryllium-7, cesium-137, lead-210) and radiocarbon, supplemented by sediment mass physical property data have been used to determine sediment mixing depths, rates of sediment accumulation, and sediment geochronology.

Correlation of time-equivalent stratigraphic boundaries reveals a maximum total Holocene fault offset of ~1 meter. Determination of fault slip rates from these values reveals a linear trend of displacement as a function of distance along the fault trace with maximum slip occurring to the southwest and minimum slip to the northeast. Mean fallout radionuclide-derived sediment accumulation rates for the past ~100 years are relatively uniform across the fault trace. However, rates from the downthrown station nearest to the fault trace display a dramatic increase over the last 30 years. Sediment bulk density and grain size data suggest an interaction between fault-driven geomorphic change and sedimentation where a migrating land-water interface has influenced the type of sediment accumulation here.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013