The onset of the Early Eocene Climatic Optimum at Branch Stream, Clarence River valley, New Zealand

The onset of the Early Eocene Climatic Optimum at Branch Stream, Clarence River valley, New Zealand

BS Slotnick, GR Dickens, CJ Hollis, JS Crampton, C Percy Strong & Andy Phillips (2015)

New Zealand Journal of Geology and Geophysics, DOI: 10.1080/00288306.2015.1063514

Abstract. We present new lithologic, biostratigraphic and carbon isotope records for a calcareous-rich ∼84m thick, early Eocene, upper continental slope section now exposed along Branch Stream, Marlborough. Decimetre-scale limestone-marl couplets comprise the section. Several marl-rich intervals correspond to carbon isotope excursions (CIEs) representing increased 13C -depleted carbon fluxes to the ocean. These records are similar to  those at nearby Mead Stream, except marl-rich intervals at Branch Stream are thicker with a wider δ13C range. Comparison to other sites indicates the section spans ∼53.4–51.6 Ma, the onset of the Early Eocene Climatic Optimum (EECO). The most prominent CIE is correlated with the K/X event (52.9 Ma). Prominent marl-rich intervals resulted from increased fluxes of terrigenous material and associated carbonate dilution. We find multiple warming events marked lowermost EECO, each probably signaling enhanced seasonal precipitation. Branch Stream bulk isotopic records suggest ’differential diagenesis’ impacted the sequence during sediment burial.

Keywords: Carbon isotope stratigraphy; Clarence Valley; Early Eocene Climatic Optimum; Eocene hyperthermals; global carbon cycling

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