T254 Applications of Bio-, Chemo-, and Lithostratigraphy to Sequence Stratigraphy (Posters)

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

A BIO-CHEMOSTRATIGRAPHIC FRAMEWORK OF OCEANIC ANOXIC EVENT 2 AT LOZIER CANYON, TX: CORRELATIONS TO THE WESTERN INTERIOR SEAWAY AND COMPARISON TO SEQUENCE STRATIGRAPHIC SURFACES

Paper number: T254-5
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The Cenomanian-Turonian (C-T) boundary is marked by a major perturbation of the ocean-climate system known as Oceanic Anoxic Event 2 (OAE2). OAE2 is characterized in marine rock records by global transgression, increased carbon burial and atmospheric CO2 and assemblage turnover in several fossil groups (e.g. ammonites, inoceramids, foraminifera and calcareous nannofossils). Bio-sequence stratigraphic analysis of C-T boundary sections is vital to understanding paleoceanographic changes and distribution of hydrocarbon source rocks associated with OAE2. Many studies have focused on understanding the central Western Interior Seaway (WIS), but few detailed studies have focused on its southern limits. We discuss calcareous nannofossil and carbon isotope stratigraphy from Lozier Canyon, TX, located on the margin of what was a broad carbonate platform separating the WIS and tropical Gulf of Mexico. The resulting bio-chemostratigraphic framework allows for robust correlation to the C-T GSSP in the Bridge Creek Limestone at Pueblo, CO and supports a sequence stratigraphic interpretation.

The C-T boundary at Lozier is based on the recognition of a 2-3 ‰ δC13 excursion and calcareous nannofossil datums including the highest occurrence of Helenia chiastia, Corollithion kennedyi and Rhagodiscus asper and lowest occurrence of Eprolithus eptapetalus and Quadrum gartnerii. The boundary is well above organic rich units often attributed to OAE2 near the top of an interbedded limestone/calcareous mudstone facies in the Rock Pens Member of the Eagle Ford Formation (of Donovan and Staerker 2010). The base of this facies corresponds to the onset of OAE2 and a maximum flooding surface identified in the subsurface of west Texas and from outcrop gamma ray readings, while missing and condensed biostratigraphic horizons support the interpretation of sequence boundaries in the Turonian (Donovan et al. 2011). Facies and nannofossil assemblages are comparable to the Bridge Creek Limestone of the central WIS, which has distinctive limestone/calcareous mudstone couplets and is also relatively low in organic carbon with respect to underlying units, supporting a direct tie between Lozier Canyon and the GSSP and suggesting the environment in the southern seaway remained separate from the Gulf of Mexico.