Evolution of San Simon Channel, Gaines County, Texas, Northern Midland Basin

S. J. Mazzullo, A. M. Reid

The San Simon channel, separating the northern Midland and Delaware basins, presently has production from Devonian to Upper Permian structural and stratigraphic traps. During the Pennsylvanian, the ancestral San Simon channel was a structurally low feature characterized by generally northwest-trending block-faulted synclines. On the east, a prominent north-northwest-trending arch (between the channel and Midland basin proper) was present over which the Atoka through Cisco sections are absent. Where present, Atokan facies in this region consist of a thin section of dark shales and fine-grained offshore marine sandstones. Lower Strawn facies here similarly consist of a thin sequence of shaly limestones and shales. By the time of upper Strawn deposition, however, thicker sec ions of shelf carbonate had prograded from the North platform and Central Basin platform to define the northern and southern margins of the ancestral channel. This framework of shelf facies flanking the channel persisted into the early Leonardian, although the channel was not very deep during most of the Pennsylvanian.

Open connection between the Midland and Delaware basins and formation of a deep San Simon channel occurred by the time of upper Cisco(?) to lower Wolfcampian deposition as a result of rapid subsidence. During the Wolfcampian, the channel was the site of deposition of a thin sequence of shales and foreshelf detrital carbonates. Renewed subsidence during the early Leonardian (Wichita) resulted in a pronounced deepening of the channel and deposition of relatively thick basinal Wichita-equivalent and Dean sections but a thin Lower Clear Fork-equivalent section. Basinal facies of the Wichita and Lower Clear Fork also include shales and detrital carbonates. With the upper Wolfcampian, these carbonates locally are prolific hydrocarbon reservoirs immediately east of the channel, in northern G ines County and adjoining counties. Similar reservoirs are productive in the northern Delaware basin and, accordingly, the San Simon channel should have hydrocarbon potential in foreshelf detrital carbonates.

AAPG Search and Discovery Article #91026©1989 AAPG Southwest Section, March 19-21, 1989, San Angelo, Texas.