T53 Bridging Two Continents: Mid-Latitude Climate during Cretaceous Greenhouse States: Comparison between East Asia and North America

Sunday, 1 November 2015
1:30 PM - 5:30 PM
Room 347/348

A 15-MYR LATE CRETACEOUS CARBONATE CARBON ISOTOPE CHEMOSTRATIGRAPHY FROM THE WESTERN INTERIOR BASIN FOR GLOBAL CORRELATION

Paper number: T53-1
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

Global climatic and geochemical events (e.g. Oceanic Anoxic Events) preserved in Late Cretaceous marine sequences have proven challenging to investigate in coeval terrestrial environments such as the Songliao Basin. This is due to limited age control stemming from a lack of biostratigraphy and isolated horizons with datable ashes. Carbon isotope (δ13C) chemostratigraphic correlations from locations with strong time control, such as the N. American Western Interior Basin (WIB), may provide an alternative method for developing chronostratigraphic frameworks since marine and terrestrial carbon reservoirs are linked via the atmosphere. A relatively continuous 15-Myr (Mid-Cenomanian to Early Campanian) carbonate carbon isotope chemostratigraphy (δ13Ccarb) from the Denver Basin’s Aristocrat Angus 12-8 Core (AA-core) is presented spanning the Greenhorn and Niobrara Cyclothems. Results are compared with prior bulk organic carbon isotope (δ13Corg) measurements to more accurately understand variation in δ13C of dissolved inorganic carbon (δ13CDIC) in the WIB, as well as underlying sedimentological processes controlling the δ13C records.

Roughly 325 powdered samples from the AA-core, previously analyzed for δ13Corg, %TOC, and %carbonate, were analyzed for δ13Ccarb and δ18Ocarb. Excursions of δ13Ccarb and δ13Corg occurring at the same horizons add confidence to an interpretation of changing δ13CDIC within the seaway, while discrepancies in excursions are attributed to either variation in fractionation between DIC and photosynthate, diagenetic alteration of carbonates, or changing organic matter type. Absolute δ13Ccarb values and covariation of δ13Ccarb and δ18Ocarb data tested among windowed depth intervals are used to probe for evidence and extent of diagenesis in the AA-core. When combined with δ13Corg records, δ13Ccarb chemostratigraphies from the WIB have the potential to distinguish changes in marine δ13CDIC from localized alteration of carbonate or changes in type of organic matter. This analysis better constrains the Late Cretaceous δ13C reference curve for the WIB permitting correlation to chemostratigraphies in disparate basins where chronostratigraphic frameworks are limited by lack of bentonites or biostratigraphy.