Chronocorrelation of Eagle Ford-Equivalent Stratigraphy in West Texas Through Integration of Biostratigraphic, Chemostratigraphic and Astrochronologic Data With High Resolution U/Pb Zircon Geochronology of Ash Beds From the Ernst Member (Boquillas Formation: Big Bend National Park) and Eagle Ford Group (Lozier Canyon)

Abstract

The Cenomanian-Turonian Ernst Member of the Boquillas Formation in west Texas was deposited near the southern aperture of the Cretaceous Western Interior Seaway (KWIS) and reflects the time-transgressive onset of sediment accumulation following subaerial exposure of the Buda Limestone. The Ernst Member within Big Bend National Park (BBNP) in Brewster County, Texas provides unique opportunities for high-resolution chronocorrelation of Eagle Ford-equivalent strata between the Ojinaga Formation and Eagle Ford Group in Hudspeth and Terrell counties in Texas. The Ernst Member also is stratigraphically equivalent to the Eagle Ford Group in south and central Texas, where it becomes a prolific, unconventional reservoir. We present six new U/Pb Isotope Dilution – Thermal Ionization Mass Spectrometry (ID-TIMS) bentonite ages from the Ernst Member and eight additional ages from Lozier Canyon to integrate with biostratigraphic markers (e.g., ammonites, nannofossils), spectral gamma ray (U, Th and K components), d13C stable isotopes and astrochronologic data to improve regional correlation and calibration of biostratigraphic and isotopic events during deposition of Eagle Ford-equivalent stratigraphy across west Texas. Astrochronologic age models using Markov Chain Monte Carlo (MCMC) simulation improve temporal constraints for regionally correlative stratigraphic surfaces and provide a temporal quantification for duration of hiatuses in section. Sedimentation rates between isochrons were delineated using MCMC simulation, with statistical H?-significance (Null-hypothesis) and harmonic component values determined via Average Spectral Misfit (ASM). A new paleogeographic map of the southern mouth of the KWIS during the Cenomanian-Turonian stages is presented to illustrate the regional position and relationship of basins, carbonate platforms/ramps and structural highs with one another by incorporation of data from Texas, Mexico and New Mexico.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017