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Multiple early Eocene hyperthermals: Their sedimentary expression on the New Zealand continental margin and in the deep sea

¹ Department of Earth Sciences, Rice University, Houston, Texas 77005, USA
² Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, New Zealand
³ Earth and Planetary Sciences Department, University of California–Santa Cruz, Santa Cruz, California 95064, USA

The Paleocene–Eocene thermal maximum (PETM) ca. 55.5 Ma was a geologically brief interval characterized by massive influx of isotopically light carbon, extreme changes in global climate, and profound variations in Earth system processes. An outstanding issue is whether it was an isolated event, or the most prominent example of a recurring phenomenon. Recent studies of condensed deep-sea sections support the latter, but this finding remains uncertain. Here we present and discuss lithologic and carbon isotope records across two lower Eocene outcrops on South Island, New Zealand. The PETM manifests as a marl-rich horizon with a significant negative carbon isotope excursion (CIE). Above, in sediment deposited between 54 and 53 Ma, are four horizons with similar though less pronounced expressions. Marl beds of all five horizons represent increased terrigenous sedimentation, presumably linked to an accelerated hydrological cycle. Five corresponding clay-rich horizons and CIEs are found in deep-sea records, although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution. The presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of ¹³ C-depleted carbon during the early Eocene.

Key Words: Paleocene–Eocene thermal maximum • PETM • carbon isotope excursion • CIE

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