--> ABSTRACT: Post-Permian Epirogenic Uplift and Fracturing Within the Midland Basin of West Texas, by Keith E. Winfree; #91020 (1995).

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Post-Permian Epirogenic Uplift and Fracturing Within the Midland Basin of West Texas

Keith E. Winfree

Many major Permian oil and gas fields in West Texas produce from unfaulted anticlines and domes. Data from two of these fields, Spraberry Trend Area and Wasson, indicates that these structures are the result of post-Guadalupian epirogenic uplift.

The Spraberry Trend Area field produces from Leonardian basinal sandstones and siltstones. In Upton County, the Spraberry was folded into a series of plunging anticlines and monoclines with structural relief up to 400 feet. The folds occur along the margins of a large structural block of lower Paleozoic rocks. The Spraberry thickness does not vary in this area so differential compaction was not significant Furthermore, the Spraberry had a very low depositional dip. Restoration of the Spraberry surface to a uniform low dip suggests that the underlying basement involved fault blocks were reactivated after Guadalupian time thereby producing forced folds in the Permian section.

The Wasson San Andres field produces from Guadalupian carbonate ramp sediments. The structural crest of Wasson is a dome with over 300 feet of closure. There was no depositional high in the vicinity of the dome during late Leonardian-early Guadalupian time. There is thinning associated with differential compact ion but it occurs over the dome. This thinning decreases the amount of structural relief so the dome would be even higher if differential compaction had not occurred. Therefore the current structure appears to be the result of basement-involved uplift of a lower Permian carbonate buildup.

There is no data to precisely date the timing of these uplifts. However, both the Spraberry and San Andres in these fields have fractures with east-northeast orientations. The folding and fracturing may be the result of east-northeast compression during the early Tertiary Laramide Orogeny.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995