ANTONIO CREEK SECTION MILANKOVITCH CYCLE DETECTION AND OAE 2 CORRELATION TO OTHER LOCATIONS IN THE WESTERN INTERIOR SEAWAY DESPITE HIATUSES

Stratigraphic sections spanning oceanic anoxic event 2 (OAE 2) in the Western Interior Seaway (WIS) are rarely complete. Significant undetected hiatuses undermine classical methods for analyzing facies cyclicity from outcrop and core. However, advances in statistical methods (wavelet analysis), and visualization of those results (Morlet and Haar scalograms, for example) permit simultaneous quantitative evaluations of both cyclicity and hiatuses. Here, comparisons are made among cyclicity, stratigraphic completeness, and portions of the OAE 2 signature isotope curve for Antonio Creek outcrop site (near Langtry, in Terrell County, Texas), Cenomanian–Turonian GSSP outcrop (Pueblo, Colorado), and the USGS Portland #1 core (Fremont County, Colorado). Analyses used for cycle detection include magnetic susceptibility, handheld spectral gamma-ray, and laboratory gamma-ray spectroscopy of ⁴⁰K. Each of these data sets were collected at fixed intervals ranging from 0.05 m to ~0.30 m. Data curves, logs, and scalogram results from the Antonio Creek section show obliquity-scale (~40 kyr at ~93.9 Ma) cyclicity in ⁴⁰K and magnetic susceptibility readings, at a frequency of 1.5 cycles/meter; possible higher-frequency cyclicity detected in thorium readings; and hiatuses in ⁴⁰K, thorium, and uranium data curves at 1.8, 4.0, and 6.5 m heights in the section. The δ¹³C isotope curve was used to roughly correlate the Antonio Creek section to the Cenomanian–Turonian GSSP and USGS Portland #1 core. Orbitally-forced deposition preserved in the Antonio Creek section reveals duration of segments of δ¹³C isotope curve locally, aiding in correlation to southwest Texas outcrops and cores.