What Role Has the Presence of the Deweyville Terraces Played in the Formation of Galveston Island and West Galveston Bay?

Abstract

The purpose of this study is to investigate how the presence and distribution of the Pleistocene Deweyville terraces have influence the formation of Galveston Island and West Galveston Bay. The northwestern Gulf of Mexico (GOM) Coastal Plain contains a series of Pleistocene aged incised valleys. The Deweyville Terraces are a sequence of three terraces identified regionally in numerous of these valleys. Galveston Island is a barrier island which separates West Galveston Bay from the GOM. Although the Deweyville Terrraces have been identified within the Trinity River incised valley, within the mainstem of Galveston Bay, they have yet to be fully mapped or investigated in West Galveston Bay. West Galveston Bay naturally divides into an eastern and western half by the Caranacahua Reef, an oyster reef that extends north south across nearly the entire bay, with a crest that is regularly exposed and much of it is in less than 0.5 m of water. East of this reef, Galveston Island is 1.5 to 3.5 km wide. West of the reef, the island is generally 1.5 to 0.5 km wide. One goal of this study is to determine if the Caranacahua reef marks the division between two of the Deweyville Terraces and if the elevation of the respective terraces can be correlated to the relative width of the island. Galveston Island is a progradational barrier island, which means that the shore of the island is seaward of where it originally formed. This would imply that ravinement removed a significant volume of Pleistocene strata earlier in the history of the island formation. Another aspect of this study is to determine if the strata within the terraces within West Galveston Bay would have been capable of sourcing the sand for progradation of Galveston Island. This work is being conducted by collecting a series of CHIRP subbottom profiler lines in West Galveston Bay, coupled with submersible vibra cores up to 10 m long.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017