Tectonic Evolution of Val Verde-Delaware Basin, Texas: ABSTRACT

Abstract

The Val Verde-Delaware basin is a marginal foreland basin genetically related to the Ouachita overthrust belt and its associated subduction zone. Proximal structures to the overthrust belt evidence compressional folding and faulting indicative of a horizontal maximum principal stress, but the dominant principal stress of the more distal and productive structures is vertical. A similar tectonic style is evidenced for the Permian basin as a whole. Isopachs indicate that structural growth began early and continued intermittently throughout the Paleozoic. Maximum End_Page 420------------------------------ instability occurred during the Mississippian, Pennsylvanian, and Wolfcampian with concurrent uplift of the producing structures and subsidence of the intervening grabens. The period of instability is coincident with the period of maximum activity along the Ouachita subduction zone. Thermal and isostatic activity related to the subduction zone may have caused the differential vertical uplift and subsidence. The stress system appears to be caused by fluid movements in the crust or subcrust. As lighter material was subduced to mantle depths there was some partial melting and diapiric rise of these lighter materials. The complete process is not fully understood. Rigid basement blocks were tilted and uplifted along basement faults. The overlying sediment behaved plastically, and basement faults die out abruptly upward in the section. Faulting is rarely found in the borehole, but steep to overturned beds are common. Minor faulting in the producing fields appears to have served as a conduit for rising hydrothermal fluids which cause some secondary cementation and loss of porosity and permeability. This has caused some structurally well-located wells to be dry or noncommercial. The tectonic style of the Val Verde-Delaware basin is similar to that of many foreland basins throughout the world. End_of_Article - Last_Page 421------------