Large amplitude variations in global carbon cycling and terrestrial weathering from the late Paleocene through the early Eocene: carbon isotope and terrigenous accumulation records at Mead Stream, New Zealand
Abstract
Global temperatures rose ~6°C from the late Paleocene ca. 58 Ma to the Early Eocene Climatic Optimum (EECO) ca. 52 - 50 Ma. Superimposed on this were at least two geologically brief (<200 kyr) intervals of extreme warming, the Paleocene-Eocene thermal maximum (PETM) and Eocene thermal maximum 2 (ETM-2). Both the long-term rise and short-term “hyperthermals” have been linked to massive injections of 13C-depleted carbon into the ocean-atmosphere system and greater continental weathering. However, relationships remain uncertain, principally because detailed and coupled proxy records do not extend across the entire interval of interest. Mead Stream, New Zealand, exposes a ~650-m-thick sequence of limestone originally deposited on an upper continental slope from the late Cretaceous to the middle Eocene. Previous work has provided fairly accurate ages for this expanded section, and has shown that the PETM and ETM-2 (as well as the suspected H-2, I-1 and I-2 hyperthermals) are marked by pronounced negative carbon isotope excursions (CIEs) and clay-rich horizons (marls), the latter caused by excess terrigenous dilution. 283 new samples were collected, mostly between ETM-2 and the EECO; these were analyzed for carbonate content, lithology, and bulk carbonate carbon isotopes. Five marl-rich beds occur in upper Paleocene and lowermost Eocene strata. These mark the known and suspected hyperthermals: PETM, ETM-2, H-2, I-1 and I-2. Above is a greatly expanded (100 m-thick) unit represented by a series of marl beds which correlates to the EECO. Carbonate contents are generally 60-90% throughout the studied interval, with lows being marls. Similar to findings elsewhere, there is an overall long-term drop in δ13C from the late Paleocene to early Eocene. This is punctuated by multiple short-term CIEs of variable magnitude (PETM: 2.5‰; ETM-2: 1.0‰; H-2: 0.2‰; I-1: 0.6%). The EECO is a series of negative CIEs with magnitudes ranging between 0.2 - 0.6‰. Of these, the K/X/ETM-3 event (another suspected hyperthermal) is the most pronounced (0.6‰). The late Paleocene-early Eocene δ13C record at Mead Stream is remarkably similar to other records generated at deep-sea sites, except that lows in δ13C span intervals of relatively high sedimentation (terrigenous dilution) rather than intervals of relatively low sedimentation (carbonate dissolution). We suggest that over ~6 million years, there was a series of short-term climate perturbations, each characterized by massive carbon input and greater continental weathering. The suspected link involves global warming and enhanced seasonality in precipitation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP23B1752S
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1050 GEOCHEMISTRY / Marine geochemistry;
- 4948 PALEOCEANOGRAPHY / Paleocene/Eocene thermal maximum;
- 4999 PALEOCEANOGRAPHY / General or miscellaneous