Deluca, Michael James (2016-06). Ash Bed Analysis of the Cretaceous Eagle Ford Shale Using ID-TIMS U/Pb Methods: Implications for Biostratigraphic Refinement and Correlations Within the Western Interior Seaway. Master's Thesis.
Thesis
The Cenomanian-Turonian Eagle Ford Group was deposited within the Southern Cretaceous Western Interior Seaway (KWIS) and records the onset and duration of the Oceanic Anoxic Event 2 (OAE2). Lozier Canyon in Val Verde country, Texas provides a unique opportunity to integrate subsurface data and core with a laterally continuous and exposed outcrop section. This study provides U/Pb ID-TIMS (Isotope dilution thermal mass spectrometry) zircon ages for ash beds within the Eagle Ford Group. These high precision age markers are utilized for detailed regional correlations as well as calibration of globally recognizable isotopic events. Astrochronologic age models provide an estimate for the duration of the hiatus observed near the C/T boundary across much of North America, as well as reasonable estimates of significant isotopic events, biostratigrahic datums, and regionally identifiable stratigraphic surfaces. A minimum age constraint of the Buda/Eagle Ford contact is 97.14 +- 0.36 Ma, and a maximum age constraint for the Eagle Ford/Austin contact is 91.23 +- 0.13 Ma. ASM derived rock accumulation rates range from 0.599-0.794 cm/ka for the Lower Eagle Ford and from 0.866-0.876 cm/ka for the Upper Eagle Ford. Integration of bandpass short eccentricity signals, bulk ?^13C isotope data, and zircon age constraint from directly below the C/T unconformity suggests an overall duration of ~0.71 Ma for OAE2, which is similar with other duration estimates of this event throughout the KWIS. This suggests that Lozier Canyon contains a relatively complete OAE2 record, and potentially records the C-T boundary. Biostratigraphy and ?^13C suggest moderate (10's-100's ky) amount of time missing at the C-T unconformity.
