The Delaware Mountain group is 3,000 feet of a deep-water, terrigenous facies, almost encircled by contemporaneous reef limestone. Abundant detrital feldspar in basin rocks and in corresponding fine sand grains on the shelves at the north and northeast suggests back-reef sources of this basin sand.

Some basin sand grains are small enough to have been carried by wind, but no feature indicates its necessity. Scarcity of clay may have resulted from source and history of weathering or from sorting during transport. Ripple marks, channeling, aligned fusulines, and flow casts in basin rocks indicate bottom currents directed basinward. Even distribution of sand with slight thickening basinward reflects control of deposition in deep water by gravity and submarine topography. Back-reef sandstones that are coarser than basin rocks indicate that the reefs were partial barriers to sand transport.

Upper Guadalupian basin rocks are cyclic, typically with successive units of thin clastic limestone, laminated sandy siltstone, and massive fine-grained sandstone, totaling more than 100 feet. These cycles are interpreted as deposits controlled by rates of relative subsidence. Some calcareous debris spilled into the basin when subsidence permitted active reef growth and deposition of carbonate material and evaporite in shallow water. Quartz sand was masked by non-terrigenous deposits. As subsidence slowed, sand was sorted in shallow water, and fine grains reached the basin to form laminated beds. When relative subsidence ceased, sand was transported to the basin and deposited rapidly by turbidity currents as massive beds. This repeated depositional pattern caused concentration of sandstone in the deep-water facies.

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