Paleohydraulic Interpretation of Upper Yates Formation Sheet Sandstones, Guadalupe Mountains, New Mexico

Magell P. Candelaria

Study of the upper two siliciclastic intervals of the Yates Formation, southern Guadalupe Mountains, New Mexico, has provided strong evidence for deposition on a shallow marine shelf. Sedimentary structure distribution along 36 km parallel with, and 5 km normal to, the shelf edge defines three distinct facies: (1) small-scale cross-laminated, (2) ripple cross-laminated, and (3) wavy laminated. This facies progression is interpreted to be the product of rapid shelfward diminution of hydraulic energy.

The absence of primary sedimentary structures of medium scale or greater is believed attributable to the very fine sand size. Bed form stability field analyses indicate that aqueous megaripples do not form in sediment with average grain size less than 0.1 mm diameter, irrespective of flow velocity. Thus, aqueous megaripple cross-sets could not have formed in upper Yates sandstones if they were deposited in a shallow marine environment. Because no eolian stratification types have been identified and all primary sedimentary structures appear to be subaqueous in origin, both sandstone units are interpreted as sheet sands deposited in a shallow marine shelf environment. The hydraulic regime in this area of the shelf was probably low energy and rapidly decreased toward the inner shelf. How ver, net basinward transport and uniform distribution of very fine grained siliciclastics across the shelf was by a variety of enigmatic shallow marine processes. Only the finest siliciclastic fraction was transported in suspension across the shelf edge to the Delaware basin.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.