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Abstract: Cretaceous Stratigraphy and Biostratigraphy, Sierra Blanca Basin, Southeastern New Mexico

S. G. Lucas, O. R. Anderson

The Sierra Blanca basin of Otero and Lincoln counties, New Mexico contains a Lower (upper Albian)-Upper (Santonian) Cretaceous section of marine and nonmarine strata as much as 700 m thick. These strata represent the upper part of a regressive cycle followed by two transgressive-regressive cycles of deposition. The lower 55 m of the Cretaceous section are the same tripartite Dakota Group units recognized to the north in Guadalupe and San Miguel counties: basal Mesa Rica Sandstone (late Albian), medial Pajarito formation (late Albian) and upper Romeroville sandstone (earliest Cenomanian). The Mesa Rica and Pajarito represent a regression and are overlain disconformably by the transgressive Romeroville sandstone. Overlying transgressive marine clastics and minor carbonates of the Mancos Shale are as much as 73 m thick and include the early Turonian Greenhorn Limestone. The overlying Tres Hermanos formation (up to 91 m thick) consists of the (ascending order) Atarque sandstone, and the Carthage and Fite Ranch sandstone members. These strata represent a mid-Turonian regression in response to regional tectonism (Atarque sandstone and Carthage members), followed by a transgression (Fite Ranch sandstone member) that culminated in the deposition of the D-Cross Tongue of the Mancos Shale and Fort Hays Member of the Niobrara Formation (combined maximum thickness = 152 m) during the late Turonian.

The subsequent regression began with the Coniacian Gallup Sandstone (55 m) followed by coal-bearing Crevasse Canyon Formation (up to 244 m thick). The Coniacian-Santonian Crevasse Canyon Formation is the youngest Cretaceous unit in the basin; it is disconformably overlain by middle Eocene conglomerates and red-bed siliciclastics of the Cub Mountain formation.

Dakota Group age determinations in the Sierra Blanca basin are those of well-dated sections to the north, but ammonites and inoceramid bivalves from the Sierra Blanca basin provide precise age control for Cenomanian-Santonian marine and marginal marine strata. Palynology and megafossil plants provide the age control of nonmarine strata of Coniacian-Santonian age in the Sierra Blanca basin.

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