| Title: | Cycle stratigraphy and chemostratigraphy of Cenomanian-Turonian (Late Cretaceous) shallow- through deep-marine carbonates and siliciclastics, southern Mexico |
| Author: | Maya B. Elrick |
| Date Submitted: | 04/30/2002 |
| Address: | Earth and Planetary Sciences
University of New Mexico
Albuquerque
NM
USA
87131
|
| Phone: | (505) 277-5077 |
| Email: | dolomite@unm.edu |
| Co-Authors: | Molina, Roberto, S., Universidad Nacional Autonoma de Mexico (UNAM), rmolina@unicit.unam.mx |
| Affiliation: | University of New Mexico |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725556 |
| Keywords: | Cenomanian-Turonian, C-isotopes, cycle stratigraphy, Mexico, Late Cretaceous |
| Abstract: | Albian through Turonian marine deposits are well exposed along a westward-dipping carbonate platform in southern Mexico (Guerrero state). The Albian through early Turonian Morelos Formation (800 m) is composed of weakly cyclic subtidal through intertidal carbonates (peloidal wackstones to skeletal grainstones) and is abruptly overlain by the Turonian Mexcala Formation (2000+ m) which is composed of pelagic limestone-marl rhythmites and/or terrigenous turbiditic mudstones and sandstones. Stratigraphic and geochemical studies of these shallow- to deep-water deposits at four locations across the platform-to-basin transition provide an opportunity to evaluate the relationships between changes in sea-level, stable isotopes, siliciclastic input, total organic carbon (TOC), and changes in marine biota.
The upper few 10's of meters of the shallow subtidal Morelos carbonate platform deposits show evidence of gradual deepening and an associated increase in fine siliciclastic input. The ensuing maximum flooding zone (MFZ) is recorded by the abrupt transition from benthic fossil-rich carbonates to thin-bedded pelagic limestone-marl rhythmites and/or thin-bedded terrigenous turbidites (Morelos-Mexcala contact).
Preliminary C-isotope analysis records a positive shift in
 carb of 3.5-4.0
 which begins within the upper 50 meters of the Morelos subtidal limestones (or >50 meters below the MFZ). Uniform elevated C-isotope values continue for 10-15 meters of section and are followed by a gradual negative shift of 3.5-4.0 ; the negative shift ends approximately 5-10 meters below the MFZ. org trends are variable through this same stratigraphic interval, but generally record a similar magnitude of C-isotopic shift. No obvious trends in TOC values are observed as of yet. Previous foraminiferal biostratigraphy of these deposits suggests that the Cenomanian-Turonian boundary lies at the MFZ (Morelos-Mexcala contact); however, given the observed C-isotope trends, the C-T boundary lies well below the Morelos-Mexcala contact (MFZ) and occurs within shallow subtidal carbonates. |
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