One of the prominent structural features of the Gulf basin of North America is the down-to-basin Vicksburg fault zone. Located in the Rio Grande embayment of south Texas, this tectonic feature has controlled the accumulation of more than 3 billion bbl of oil and 20 trillion cu ft of gas, and it has done so in an effective and efficient manner.
During a period of maximum faulting which coincided with the deposition of petroliferous Oligocene Vicksburg and lower Frio beds, a greatly thickened and downbent, downthrown block was formed. The downbending occurred in a direction opposite to the regional dip, contributing to the formation of anticlinal closures which were present to trap the earliest migration of oil. The paper describes the nature of this trapping mechanism.