Magnetostratigraphic Correlation and Dating of West Texas and New Mexico Late Permian Strata

M. Steiner
Dept. Geology and Geophysics, University of Wyoming, Laramie, WY ([email protected])

Ochoan formations in west Texas-New Mexico have been investigated magnetostratigraphically for the purpose of obtaining absolute age information. The locally-named Dewey Lake Formation has been studied in two areas of northwest Texas and in southeastern New Mexico. The upper part of the subjacent Alibates and parts of the Rustler Formations also have been studied. The Dewey Lake Formation is magnetized dominantly in Late Permian normal polarity. Fifty-four meters of the underlying “Alibates Beds” are dominantly reversely magnetized. Farther down section, the Magenta Dolomite Member of the Rustler Formation near Carlsbad, NM, is reversely magnetized. The subjacent Castile Formation was tested and found, surprisingly, to carry a stable magnetization that appears to be Permian reversed polarity. Magnetostratigraphic correlation within the Dewey Lake of the Texas Panhandle shows that relative thicknesses of volcanic ash beds are not a reliable correlation tool; ash beds of similar thickness located 120 km apart lie in different magnetic polarity intervals. Magnetostratigraphy shows that the 0.6 m ash layer at Dickens, TX, corresponds to a 0.02 m ash layer, the higher of two ash beds, at Caprock Canyons State Park. Magnetostratigraphy also demonstrates that fully one-half of the Dewey Lake Formation present in northwest Texas (Caprock Canyons) has been removed by pre- Late Triassic erosion in the more southerly localities. The Dewey Lake strata give Late Permian, rather than Triassic, paleopoles, removing any question of the Dewey Lake being Triassic in age. Reference to the best Tethyan Late and Middle Permian magnetostratigraphic data (Changsingian, Wujiapingian, and Capitanian Stages) suggests that the “Alibates Beds” and the Rustler strata are latest Capitanian in age and that the Dewey Lake/Quartermaster strata were deposited in the Wujiapingian and early Changsingian Stages of the Late Permian. Late Changsingian strata are inferred to be missing inWest Texas. The magnetostratigraphic correlations suggest that the early Ochoan of West Texas-New Mexico is really latest Guadalupian in so far as Tethyan fauna are concerned.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas