Barrier-island aggradation via inlet migration: Mustang Island, Texas

Abstract

After establishing its present location around 9.5 ka, Mustang Island aggraded, stacking over 20 m of barrier-island sand in the same location. Throughout Mustang Island's history, tidal inlets shifted within nearly the same location from 7.5 ka to the present, leaving 10–15 m thick deposits of clean, well-sorted, quartz sand deposited within only a few centuries. These deposits lack some of the sedimentary features normally associated with tidal inlets, such as tidal couplets and shell hash. The lack of such features is attributed to the uniform nature of the deposits cut by the inlets during the island's relatively long period of aggradation. Mustang Island was able to maintain an aggradation character throughout most of the Holocene due to the sediment eroded from three sources: Pleistocene headlands, the transgressive Colorado River delta of Texas, and the OIS 3 shoreline of the central-Texas shelf. Each of these sources was exposed to waves and accompanying longshore drift during the island's early history when sea level rose quickly, but was flooded or capped by transgressive muds by the time sea-level rise slowed during the middle Holocene.