The Oligocene Vicksburg formation of South Texas was deposited as a coarse clastic delta system on the fringe of the uplifted Sierra Madre mountains in Mexico. Earliest Vicksburg sediments were initially deposited in a simple delta lobe, which detached due to gravity from underlying Eocene formations and crept seaward as a block, creating a depositional center. The upper Early Vicksburg contains expanded sets of deltaic sediments which infilled a depression formed by the initial movement. Downlap surfaces indicate that the expansion was oriented northeast-southwest.

Middle Vicksburg uplift in the Sierra Madre mountains to the south caused erosion and a change...

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