Submillennial resolution carbon isotope stratigraphy across the oceanic anoxic event 2 horizon in the tappu section, hokkaido, Japan

摘要

Highest resolution carbon isotope stratigraphy was established for terrestrial organic carbon through the uppermost Cenomanian in Hokkaido, Japan. The interval of the main phase of Cretaceous oceanic anoxic event 2 (OAE2) has a carbon isotope curve that almost mirrors the profile of the reference section in Eastbourne, United Kingdom, but does not show any signature of oxygen depletion in the bottom environment. A negative excursion of 2.6%, which cannot be recognized in any carbonate sections, is observed within the "second build-up phase". This horizon in the Eastbourne and Pueblo sections is known from recent studies to be evidence of an intensive volcanic eruption associated with the Caribbean-Colombian large igneous province. The negative carbon isotope excursion observed here is plausibly explained by a change in the ~(13)C/~(12)C ratio of the terrestrial plant community as a reaction to a warmer and more humid climate induced directly by volcanically elevated atmospheric pCO_2 and ultimately by the large igneous province emplacement. Accepting this scenario, the negative excursion allows us to estimate the maximum duration of the volcanic pulse (12.6kyr). As the duration of the recovery from the negative excursion is expected to be subject to equilibration of the ΣCO_2 concentration in the whole ocean-atmospheric CO_2 reservoir, the mean time scale of thermohaline circulation during OAE2 is estimated as 5.3-6.3kyr.