New Mexico Geological Society Annual Spring Meeting — Abstracts

The Engle coal field of south-central New Mexico contains approximately 3,000 feet of interbedded Upper Cretaceous pebble conglomerates, sandstones, siltstones, mudrocks, and coals. These terrigenous clastics represent a marine to fluvial facies transition deposited during the widespread late Turonian - early Coniacian regression of the western interior seaway.

The Rio Salado Tongue of t he Mancos Shale is overlain by the tripartite Tres Hermanos Formation. The Atarque Sandstone Member represents deposition of a distributary mouth bar in a very shallow epeiric sea. Depositi on of the Atarque provided a near sealevel platform upon which thin channel and crevasse splay sandstones, and carbonaceous mudrocks were deposited. Transgression of the seaway across these marginal marine and fluvial deposits 15 recorded by the Fite Ranch Sandstone Member, which consists of a thin transgressive lag deposit, and a thicker, regressive coastal barrier sandstone. The D-Cross Tongue of the Mancos Shale represents open marine conditions and contains three unnamed tongues of the Gallup Sandstone deposited during several minor progradational episodes.

The overlying Mesaverde Group consists of nearshore marine and continental deposits. Well developed shoreface and beach deposits of the Gallup Sandstone overlie the D-Cross Tongue of the Mancos Shale. The Crevasse Canyon Formation consists of a lower coal-bearing member, a middle barren member, and the Ash Canyon Member. Marginal marine and continental deposits of the Crevasse Canyon represent lagoonal, washover fan, coal swamp, and fluvial environments. Fluvial subenvironments are represented by channel thalweg, point bar, natural levee, crevasse splay, swamp, and overbank deposits.