Journal
GLOBAL AND PLANETARY CHANGE
Volume 170, Issue -, Pages 163-171Publisher
ELSEVIER
DOI: 10.1016/j.gloplacha.2018.08.012
Keywords
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Funding
- Japan Society for the Promotion of Science (JSPS) [26800266, 18K13647]
- Center for Advanced Marine Core Research (CMCR), Kochi University, Japan [13A015/13B015]
- Grants-in-Aid for Scientific Research [26800266, 18K13647] Funding Source: KAKEN
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One of the most profound environmental changes in the Mesozoic occurred during the Pliensbachian-Toarcian (Pl/To) time interval, including massive black shale deposition across Pl/To boundary and early Toarcian Oceanic Anoxic Event (T-OAE). These events are associated with negative carbon isotope excursions (CIEs), but their temporal link with C-12-rich carbon injection, possibly related with Karoo-Ferrar volcanisms and carbon cycle feedbacks, such as terrestrial methanogenesis and methane hydrate dissociation, is still debated. Here we present a new chemostratigraphy of the carbon isotopic ratio of organic matter (delta C-13(org)) from Pl/To deep-sea successions, in conjunction with bio-astrochronology. The deep-sea successions are located at the Katsuyama and Sakahogi outcrops in the Inuyama area, Japan, and contain two black bedded chert intervals named T-BBCs 1 and 2, which have astrochronologic ages of 183.25-183.01 +/- 0.2 Ma and 183.55-182.80 +/- 0.2 Ma. Negative CIEs of similar to 2 parts per thousand and similar to 5 parts per thousand are recognized across the base of T-BBCs 1 and 2, respectively, which are correlated with Pl/To boundary and classical T-OAE in shallow marine sections based on biostratigraphy. Astrochronologic ages of the onset of T-BBCs 1 and 2 are within the errors of the oldest high-precision U-Pb ages of Karoo and Ferrar LIPs, respectively. These temporal relations suggest a link between the C-12-rich carbon injection associated with Karoo and Ferrar volcanism, and CIEs associated with widespread black shale deposition across the Pl/To and T-OAE, respectively. Obliquity cycles in classic T-OAE CIE could have linked with terrestrial methanogenesis and methane hydrate dissociation in high-latitudes areas, whereas 405-kyr pacing of termination of T-CIE and T-BBCs deposition would be related with decreased chemical weathering and nutrient supply under weaker monsoon intensity, and possibly suppressed methane cycle across the termination of Pl/To and T-OAE periods.
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