C-isotope stratigraphy and paleoenvironmental changes across OAE2 (mid-Cretaceous) from shallow-water platform carbonates of southern Mexico |
| |
| Authors: | Maya Elrick Roberto Molina-Garza Robert Duncan Laura Snow |
| |
| Institution: | 1. Sorbonne Université, CNRS-INSU, ISTeP UMR 7193, 4 Place Jussieu, 75005 Paris, France;2. Université Bourgogne Franche-Comté, Biogéosciences UMR CNRS 6282, 6 Bd Gabriel, 21000 Dijon, France;1. Department of Geology and Geophysics, Yale University, New Haven, CT, USA;2. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA;3. Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, USA;4. Department of Earth Sciences, University of California, Riverside, CA, USA;5. Department of Geology, University of Illinois at Urbana-Champaign, Urbana, IL, USA;2. Department of Earth & Environmental Sciences, University of Mary Washington, 432 Jepson Science Center, 1301 College Avenue, Fredericksburg, VA 2240, USA |
| |
| Abstract: | The stratigraphic and geochemical record of the mid-Cretaceous (Cenomanian–Turonian) Oceanic Anoxic Event 2 (OAE2) has been studied in numerous Tethyan and proto-Atlantic hemi-pelagic/pelagic successions, but little data comes from nearshore carbonate successions from the proto-Pacific region. Here we present the results of a combined stratigraphic and δ13C study of C–T platform carbonates from southern Mexico, which were deposited within the proto-Pacific. Two scales of sedimentary cyclicity are recognized. High-frequency peritidal and subtidal cycles (0.4–8 m) display little evidence of cycle-capping subaerial exposure and are not correlative between sections; these relationships suggest that the amplitudes of high-frequency sea-level changes were minimal during the peak mid-Cretaceous greenhouse. Longer-term transgressive-regressive sequences (18–40+ m) are correlated between sections, and using δ13C trends, can be correlated with sequences developed in northern Europe and India.The Mexican successions were sampled at a high resolution (~ 10 ky) for stable isotopes (inorganic, organic carbon and oxygen), total organic carbon, insoluble residues, and trace metals. The δ13Ccarb curve matches global trends (including 6 distinct isotopic stages) permitting identification of OAE2 despite the lack of characteristic anoxic facies. Using the δ13Ccarb trends, we tie the previously identified ammonite, planktonic foram, and nannofossil biostratigraphy from England and the Western Interior seaway of Colorado into the Mexican sections. The initiation of OAE2, defined by an abrupt positive 3–4‰ δ13C shift, coincides with a long-term sea-level rise, though the sedimentary expression of the deepening is no greater than that observed for any of the other sea-level events across the studied interval. OAE2 termination (transition from gradually decreasing to background δ13C values) is not associated with a particular sea-level trend. Stratigraphic changes in insoluble residues (proxy for continental sediment discharge) across OAE2 are not correlative between sections and do not show consistent systematic relationships with δ13C or sea-level variations, therefore do not support the hypothesis that OAE2 was associated with increased continental-derived nutrient influx. Two peaks in trace metal concentrations coincide with the abrupt increase in δ13C ratios (onset of OAE2) and during the transition from elevated-to-decreasing δ13C values (near the C–T stage boundary). These trends are similar to those recorded in coeval deposits of the Western Interior seaway, and are consistent with the hypothesis that OAE2 development was related to the release of reduced metals during the short-lived (< 1 My) Caribbean oceanic plateau basalt eruption. In this scenario, oxidation of the metals depleted the existing low dissolved-O2 concentrations and thermally-buoyant plumes of seawater enriched in biolimiting elements mixed with surface waters, stimulated primary productivity, and further reduced O2 concentrations leading to widespread anoxia and a large positive δ13C shift. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
