ABSTRACT: Stratigraphy and Provenance of Upper Cretaceous Rocks in South-Central New Mexico

C. M. Molenaar, G. H. Mack, B. A. Black, W. A. Cobban

Three reference sections of Upper Cretaceous strata in south-central New Mexico were selected for study as part of the Western Interior Cretaceous Project of the Global Sedimentary Geology Program. From northwest to southwest, these sections are near Carthage, Truth or Consequences (T or C), and Santa Rita. The basal unit of these sections, the dominantly nonmarine 25-85 m thick middle to upper? Cenomanian Dakota Sandstone or equivalents, unconformably overlies Triassic and older rocks. Strata that overlie the Dakota at Carthage and T or C consist of, in ascending order, 130 m of the upper Cenomanian to middle Turonian part of the marine Mancos Shale, 57-84 m of middle to upper Turonian Tres Hermanos Formation, 80 m of upper Turonian D-Cross Tongue of Mancos Shale, 18-58 of upper Turonian to lower Coniacian? regressive Gallup Sandstone, and 570 m of lower Coniacian to lower Campanian? nonmarine Crevasse Canyon Formation. The strata below the Crevasse Canyon record two transgressive-regressive cycles. At T or C the Crevasse Canyon contains numerous paleosols indicative of diastems; it is unconformably overlain here by the upper Maastrichtian to Paleocene nonmarine McRae Formation. Biostratigraphic data indicate a hiatus or condensed section at the base of the D-Cross Tongue at Carthage. Cretaceous rocks at Santa Rita include 85 m of Beartooth quartzite, 100 m of Mancos Shale, 41 m of regressive Atarque Sandstone, and 37 m of nonmarine Moreno Hill Formation. The Beartooth is probably coeval to or slightly older than the Dakota, and the Atarque and Moreno ill correlate with the lower part of the Tres Hermanos. The Moreno Hill is unconformably overlain by Tertiary volcanic rocks.

Quartzarenites of the Beartooth and Dakota were derived from a sedimentary provenance. In contrast, feldspathic litharenites of the Mancos through Crevasse Canyon were derived from volcanic and sedimentary provenances, with minor contributions from low-grade metamorphic and granitic/gneissic rocks. Fine grain size and east and northeast paleocurrents suggest that the source terrane was far to the west-southwest, although the Beartooth and Dakota may have been, in part, locally derived.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990