ABSTRACT: Sequence Stratigraphy and Depositional Facies of the Silurian-Devonian Interval of the Northern Permian Basin

CANTER, K. LYN, Coyote Geologic Services, Boulder, CO, DAVID WHEELER, Ensign Oil and Gas, Denver, CO, and RICHARD C. GEESAMAN, Coyote Geologic Services, Boulder, CO

The Silurian and Devonian intervals of the northern Central Basin platform area of west Texas and southeastern New Mexico include the Fusselman, Wristen, and Thirtyone formations and the Woodford Shale. The carbonate-rich Fusselman, Wristen, and Thirtyone formations record a transition from ramp to platform deposition. Oolite grainstones of the lower Fusselman Formation were deposited in a ramp setting during an Upper Ordovician/Lower Silurian transgression. The overlying crinoid packstones and grainstones represent shoals that developed along a break in slope separating the evolving platform from a southward-dipping starved basin. By the close of Fusselman deposition, the platform was well developed, with shallow peridtidal mudstones and wackestones, and high-energy grainstones depos ted as near-parallel facies tracts over the platform area. A type 1 unconformity marks the boundary between this formation from the overlying Wristen Formation.

The platform system became fully developed during the deposition of the Wristen Formation. Porous dolomitic peridtidal and platform margin facies grade downdip into nonporous, limy and argillaceous open-shelf facies. Platform facies are typified by numerous shallowing-upward parasequences that terminated at subaerial exposure surfaces. Contained within the lower part of the Wristen Formation are transgressive deposits above disconformities. A type 1 unconformity at the top of this unit is indicated by erosional truncation and significant regional karst development.

The rocks of the Lower Devonian Thirtyone Formation were deposited as a wedge that onlaps the exposed Silurian platform margin. This formation contains a porous, chert-rich, lowstand deposit; a transgressive disconformity; and variably porous, grain-rich highstand deposits representing an overall sea level rise. A major unconformity marks the contact between the karsted upper surface of the Thirtyone Formation and the overlying organic-rich, anoxic Woodford Shale.

AAPG Search and Discovery Article #91018©1992 AAPG Southwest Section Meeting, Midland, Texas, April 21-24, 1992 (2009)