Carbon cycle dynamics linked with Karoo-Ferrar volcanism and astronomical cycles during Pliensbachian-Toarcian (Early Jurassic)

• Published in: Global and planetary change 2018-11, Vol.170, p.163-171
• Main Authors: Ikeda, Masayuki, Hori, Rie S., Ikehara, Minoru, Miyashita, Ren, Chino, Masashi, Yamada, Kazuyoshi
• Format: Article
• Language: English
• ISSN: 0921-8181; 1872-6364
• DOI: 10.1016/j.gloplacha.2018.08.012

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 12C-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 (δ13Corg) 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 ~2‰ and ~5‰ 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 12C-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. [Display omitted] •δ13Corg record of Pliensbachian-Toarcian deep-sea section show two negative excursions (T-CIEs 1 and 2).•T-CIEs 1 and 2 are correlated with Pliensbachian/Toarcian boundary and classic Toarcian OAE black shales, respectively.•Astrochronologic ages of T-CIEs 1 and 2 are correlated with oldest U-Pb ages of Karo and Ferrar LIP volcanisms, respectively.