| Title: | Understanding Abrupt Climatic Disturbance in the Aptian-Albian |
| Author: | Isabel P Montanez |
| Date Submitted: | 06/11/2002 |
| Address: | One Shields Drive, University of California, Davis
Davis
CA
USA
95616
|
| Phone: | 530-754-7823 |
| Email: | montanez@geology.ucdavis.edu |
| Co-Authors: | Osleger, David A., UC-Davis; Bralower, Tim J., University of North Carolina; Montanez, Isabel, UC-Davis; Lehmann, Christoph, BP-Amoco |
| Affiliation: | Dept. of Geology, University of California, Davis |
| | |
| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725668 |
| Author Homepage: | http://www-geology.ucdavis.edu/~mrl |
| Keywords: | oceanic anoxic events, Sierra Madre Oriental, Mexico, sequence stratigraphy, eustasy, carbon isotope excursion, greenhouse gas forcing, environmental perturbation |
| Abstract: | A negative C isotope excursion of similar magnitude (-2
to -3 ) to that associated
with the Paleocene-Eocene Thermal Maximum has
recently been identified at the base of the Aptian
Oceanic Anoxic Event (OAE) 1a (Jenkyns, 1995;
Menegatti et al., 1998; Bralower et al., 1999), and
documents a more complex relationship between
Corg burial and observed changes in the
oceanic carbon reservoir than previously suggested.
Moreover, this isotope anomaly is likely correlated to a
negative excursion of even greater magnitude (~-5) that is delineated by the
 values of
terrestrial flora (Gröcke et al., 1999; Jahren et al., 2001).
This apparent link may record concomitant changes in
marine and terrestrial carbon cycling, perhaps brought
on by greenhouse gas forcing. In an effort to better
constrain the boundary conditions of the environmental
perturbation associated with the Aptian-Albian OAEs,
and to provide insight into potential forcing
mechanisms, we have recently initiated a collaborative
study of mid-Cretaceous deposits of the Sierra Madre
Oriental of Mexico that integrates a series of
stratigraphic, paleontologic, geochemical and isotopic
proxies of carbon cycling, nutrient/productivity, and
sea-level at a 105 to 103
year time scale.
To date we have documented the temporal and spatial
evolution of the Barremian-Albian Cupido and Coahuila
carbonate platforms of northeastern Mexico, and of the
contemporaneous hemipelagic deposits that were laid
down along the continental margin. Our
chronostratigraphic framework places OAE1a in the
"Cupidito" (shallow subtidal facies of the upper Cupido
Fm.), and contemporaneous deep-shelf to hemipelagic
facies of the Lower Tamaulipas Fm., and OAE1b in the
upper Aptian to lower Albian ramp margin facies of the
Aurora Fm. and coeval hemipelagic facies of the shaly
La Peña Fm.. The sequence stratigraphic framework
and relative sea-level curve for the Barremian-Albian
platform carbonates of northeastern Mexico were
defined using facies relationships, cycle stacking
patterns, and the regional correlation of
sequence-bounding unconformities integrated with
biostratigraphic and chemostratigraphic (Sr and C
isotopes) control (Lehmann et al., 1999; 2000).
Correlation of our relative sea-level curve for the region
with composite 'global' sequences and 'eustatic' curves
indicates that three sequence boundaries record
eustatic events. OAE1a occurred during the early
phases of a long-term rise in sea level, whereas
OAE1b is coincident with the peak of maximum flooding
and demise of the Cupido platform. Our regional
understanding of depositional relationships, sequence
stratigraphy and sea-level history of the
mid-Cretaceous in the Sierra Madre Oriental thus
provides an ideal framework in which to evaluate the
mode and temporal relationship between proxies of
biological and chemical oceanographic change and
records of sea level oscillation in OAE intervals. |
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