Abstract: Triassic Stratigraphy and Correlation, East-Central New Mexico and West Texas

Spencer G. Lucas, Orin J. Anderson, Adrian P. Hunt

Nonmarine Upper Triassic strata exposed in east-central New Mexico (principally San Miguel, Guadalupe and Quay counties) and west Texas (from Oldham to Mitchell counties) are readily correlated using lithostratigraphy and biostratigraphy. In east-central New Mexico, Chinle group strata rest disconformably on Middle Triassic red beds of the Moenkopi Formation (Anton Chico member), which are mostly grayish-red litharenites and mudstones of fluvial origin. These Moenkopi strata can be correlated lithostratigraphically across northern New Mexico to the Holbrook Member of the Moenkopi Formation in northeastern Arizona, a correlation supported biostratigraphically. However, no Moenkopi strata or correlative rocks are present in West Texas.

The lowermost portion of the Chinle group in east-central New Mexico is the Santa Rosa formation consisting of three members (ascending order): Tecolotito (mostly quartzarenite), Los Esteros (mostly variegated bentonitic mudstone) and Tres Lagunas (mostly quartzarenite). The overlying Garita Creek formation is red-bed mudstones, sandstones, and intraformational conglomerates. Fossil plants and vertebrates indicate a late Carnian age for the Santa Rosa and Garita Creek formations. Lithostratigraphy and biostratigraphy indicate that their west Texas correlatives are the Camp Springs, Iatan, and Tecovas members of the Dockum Formation: Camp Springs = Tecolotito, Iatan = Los Estaros, and Tecovas = Los Esteros, Tres Lagunas, and at least part of Garita Creek. Facies differences reflected i lithology and thickness differences allow ready distinction of the New Mexico and Texas units, thus justifying their separate lithostratigraphic names.

The younger part of the Chinle group in east-central New Mexico begins with the sandstones and intrabasinal conglomerates of the Trujillo Formation, which disconformably overlies older Chinle group strata. It is readily traced into west Texas as the Trujillo member of the Dockum Formation. Fossil plants and vertebrates indicate an early Norian age for the Trujillo in east-central New Mexico and west Texas. Suggestions that it is correlative to the late Carnian Santa Rosa formation or Camp Springs member are refuted by lithostratigraphic correlations. The lower-middle Norian Bull Canyon formation of east-central New Mexico conformably overlies the Trujillo, and this thick red-bed sequence of mudstones and sandstones can be traced into west Texas as the Bull Canyon member of the Dockum Cooper Canyon member is an unnecessary synonym). The youngest Chinle group strata in east-central New Mexico are the cyclically bedded siltstones and sandstones of the Rhaestian Redonda Formation. They have no correlative in west Texas.

AAPG Search and Discovery Article #90980©1994 AAPG Southwest Section Meeting, Ruidoso, New Mexico, April 24-26, 1994