Abstract
Hundreds of late Paleozoic stratigraphic traps in fluvial, deltaic, and marine sandstones are present on the Eastern shelf and slope of the Midland basin in west-central Texas. Widespread fluvial sandstones on the shelf are well known, but there appears to be little recognition of the depositional environments of sandstones in ancient deltas on the shelf and submarine channels and fans on the slope.
The Cook sandstone is a depositional model of late Paleozoic fluvial, deltaic, and slope sandstone facies in the Midland basin. Each of two Cook fluvial and deltaic systems mapped is about 100 mi (160 km) long from outcrop to shelf edge. The “Blackwell” field, in one system, is an excellent example of a Cook point-bar stratigraphic trap.
Basinward from the basal Permian Eastern shelf edge, sand and mud supplied by the two Cook fluvial systems prograded into a shallow sea and became two high-constructive lobate deltas. Delta-plain aggradational facies, delta-front sheet and distributary-channel sandstones, and prodelta facies are present in the deltas. The Group 4000 “Pennsylvanian Cisco” sandstone field produces from Cook deltaic sandstone.
The deltas are the proximal parts of a clastic wedge of sediments on the Eastern slope. The wedge has a maximum thickness of 1,300 ft (396 m) at midslope and thins basinward. The Northeast Bloodworth “Pennsylvanian Canyon” field produces from mid-slope Cook sandstone which probably was deposited in a submarine channel. The Jameson “Pennsylvanian Strawn” sandstone field produces from Cook lowerslope sandstone and appears to be a submarine fan.
