New Mexico Geological Society Annual Spring Meeting — Abstracts

Abstract—The Cerro de Cristo Rey uplift in Doña Ana County, New Mexico, outside of El Paso, Texas, is the westernmost exposure of Cretaceous strata deposited on the Comanche Shelf (Lucas et al., 2010). Recent research on Cretaceous paleontology of the area has yielded an extensive collection of echinoids from Albian-Cenomanian age strata. More than 200 complete or nearly complete tests of 13 species of echinoids were recovered. Regular echinoids are: Cottaldiabenettiae (König), Loriolia whitneyi (Ikins), Phymosoma mexicanum (Böse), Phymosoma texanum (Roemer), Salenia stenzeli (Ikins), Tetragramma variolare (Brongniart). Irregular echinoid ares: Coenholectypus castilloi (Cotteau), Coenholectypus planatus (Roemer), Globator parryi (Hall), Heteraster texanus (Roemer), Holaster simplex (Shumard), Macraster elegans (Shumard), and Palhemiaster calvini (Clark). By stratigraphic unit (ascending order) the echinoids are:Finlay Formation -- Loriolia whitneyi, Phymosoma mexicanum, Coenholectypus planatus, and Heteraster texanus; Del Norte Formation-- Phymosoma texanum, Coenholectypus planatus, and Heteraster texanus; Smeltertown Formation -- Coenholectypus castilloi; Muleros Formation -- Phymosoma mexicanum, Phymosoma texanum, Tetragramma variolare, Coenholectypus castilloi, Globator parryi, Heteraster texanus, Holaster simplex,Macraster elegans; Del Rio Formation -- Cottaldiabenettiae, Salenia stenzeli, and Heteraster texanus; Buda Formation --Cottaldiabenettiae and Palhemiaster calvini. The polymorphic nature of echinoids, especially Irregularia, is due in part to biogenic factors such as ontogeny, sexual dimorphism, and fitness, as well as environmental factors like climate, morphoclines, and microfacies, and these factors complicate taxonomic identifications (Cooke, 1946, 1955; Néraudeau, 1990, 1992, 1993; Smith and Bengtson, 1991). Using functional morphology and lithology we show that the echinoids of Cerro de Cristo Rey occupied a shallow, normal marine setting on a tropical sublittoral calcareous shelf during much of the depositional interval of the upper Comanchean Series. These findings are consistent with other Middle Albian- Early Cenomanian age Tethyan echinoid localities from North and South America, North Africa, and Asia Minor.

The occurrence of Loriolia whitneyi in association with the benthic foraminifera Dictyoconus walnutensis (Carsey, 1926) as well as the absence of the foraminifera Coskinolinoides texanus (Keijzer, 1942) from thin sections throughout the Finlay Formation at Cristo Rey calls into question which portion of the Finlay Formation is exposed at Cerro de Cristo Rey. We used forensic biostratigraphy to trace the assignment of the ammonite zone Oxytropidoceras (o.) powelli (Young, 1966) to the Finlay Formation and find it was arbitrary, and no fossil evidence of that zone has been reported from Cristo Rey. Therefore, we revise the ammonite zonation for the Finlay Formation at Cerro de Cristo Rey to the older Oxytropidoceras salasi (Young, 1966) ammonite zone. This revision reveals an unconformity between the Finlay Formation and the overlying Del Norte Formation at Cristo Rey that matches other unconformities between the Finlay Formation and Del Norte Formation equivalent strata reported from Trans-Pecos Texas and Northern Mexico, considered to represent a sequence boundary at the base of the Washita depositional interval (Brand and DeFord, 1958; Steinhoff, 2003; Lucas et al., 2010).

References:

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