Synchronous change in the carbon isotopes, large benthic foraminifera and sea-level recorded in shallow-water carbonate platforms across the Paleocene-Eocene thermal maximum
Abstract
The Paleocene-Eocene Thermal Maximum (PETM) is characterized by a massive perturbation of the global carbon cycle reflected in a large, negative carbon isotope excursion (CIE) associated with global warming. Although multiple PETM sites representing open marine and terrestrial environments have been studied, there are still few records from ecologically diverse shallow-water carbonate ecosystems. Detailed sedimentology and carbon isotopic analysis of two carbonate ramps in Tethys Ocean indicate that the onset of sea level rise coincided with PETM CIE and continued through the duration, then dropping during the PETM recovery, a pattern which is consistent with observations from numerous marine marginal records. At the onset of the CIE, however, we observe no obvious biotic change, primarily in the large benthic foraminifera. Rather the major biotic change occurs later in the PETM recovery. We speculate that the local sea level is the key factor influencing the biota, rather than the temperature. The carbon isotopic composition (δ13C) of platform bulk carbonates are significantly 13C-depleted (-4.5‰ Shenkezha section, Tibetan Himalaya; -6.5‰ Campo section, southern Pyrenees) compared to records from shallow-marine continental shelf and deep-sea bulk carbonates. We tentatively speculate that the unusually negative δ13C values may relate to global sea level fluctuations and local processes. As the carbonate ramps were flooded during the rising sea level, the ramp margin stepped back and were more influenced by deeper water produced carbonate resulting in more negative δ13C values. As the ramp margins prograded toward open ocean, for example, the PETM recovery, the δ13C values became isotopically more positive approaching the values of the sediment produced in the shallow-water carbonate environments. Diagenesis might be influencing the magnitude of the δ13C anomaly, though based on O isotopes we believe the effects are minor.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP31E1689L
- Keywords:
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- 9604 Cenozoic;
- INFORMATION RELATED TO GEOLOGIC TIME;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY;
- 4928 Global climate models;
- PALEOCEANOGRAPHY;
- 4954 Sea surface temperature;
- PALEOCEANOGRAPHY