High‐resolution lithostratigraphy and organic carbon isotope stratigraphy of the Lower Triassic pelagic sequence in central Japan

Abstract

After the severest mass extinction event in the Phanerozoic, biotic recovery from the extinction at the Permian–Triassic boundary required approximately 5 my, which covers the entire Early Triassic. It is important to obtain information on the superocean Panthalassa, which occupied most of the world ocean, to explore paleoenvironmental changes during the Early Triassic at the global scale. In order to establish the continuous lithostratigraphy of pelagic sediments in Panthalassa during the Early Triassic, high‐resolution reconstruction of the Lower Triassic pelagic sequence in Japan was conducted for the first time based on detailed field mapping and lithostratigraphic correlation in the Inuyama area, central Japan. The reconstructed Early Triassic sequence is approximately 9.5 m thick, consists of five rock types, and is divided into eight lithological units. For the reconstructed continuous sequence, measurement of carbon isotopic composition of sedimentary organic matter (δ13Corg) was carried out. Stratigraphic variation of the δ13Corg value shows large‐amplitude fluctuations between −34.4 and −21.0‰ throughout the sequence. In order to establish a higher resolution age model for the reconstructed Lower Triassic pelagic sequence, we correlated δ13Corg records in the Inuyama area with high‐resolution isotopic profiles of carbonate carbon (δ13Ccarb) from shallow‐marine carbonate sequences in southern China based on the similarity in general variation patterns with age constraints by radiolarian and conodont biostratigraphy. The result provides a high‐resolution time scale for the pelagic sequence of Panthalassa during the Smithian and Spathian. The age model suggests a drastic increase in sedimentation rate during the late Smithian, which should have been caused by the increase in terrigenous input to this site.

A diagenetic control on the Early Triassic Smithian–Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)

“…). Three of these studies provide the δ 13 C org signals of siliciclastic sediments and siliceous rocks from the Spitsbergen (Boreal Ocean, Galfetti et al ., ), Arctic Canada (north‐eastern Panthalassa, Grasby et al ., ) and Japan (western Panthalassa Sakuma et al ., ). Due to low carbonate contents in these sedimentary rocks, the reported organic isotopic signals are compared to the δ 13 C carb isotope excursions recorded in distant sediments from the Tethyan (Hermann et al ., ; Payne et al ., ) and Panthalassan (Horacek et al ., ) sections using available biostratigraphic correlations.…”

Petrography of Late Cambrian to Middle Ordovician radiolarian chert in Kazakhstan with special reference to the emergence of benthic animals in the pelagic realm

“…Conodont and radiolarian biostratigraphy typically provide exceptional age control. Numerous recent papers published on the Permian to Jurassic radiolarian chert record in Japan document the following the change in oxygenation level of seawater during the Permian/Triassic and Triassic/Jurassic mass extinction events and the Toarcian anoxic event, which was a critical time for the biosphere (Kakuwa, 2008;Takahashi et al, 2009Takahashi et al, , 2014Takahashi et al, , 2015Wignall et al, 2010;Gr€ ocke et al, 2011;Sato et al, 2011;Sakuma et al, 2012;Sano et al, 2012;Ikeda & Hori, 2014;Ikeda et al, 2015;Fujisaki et al, 2016), an impact event in the Upper Triassic (Onoue et al, 2012;Sato et al, 2013Sato et al, , 2016, the astronomical cycles during the Triassic (Ikeda & Tada, 2013) and the climate change in continental areas during the Triassic (Nakada et al, 2014). These studies indicate that radiolarian chert is an excellent recorder of global events.…”

Astronomical cycles recorded in the sedimentary rhythms of deep-sea bedded chert and its significance on biogeochemical cycle

“…The cycle can be subdivided into two subcycles involving organic matter (left-hand side) and silicate weathering and carbonate deposition (right-hand side). 2 Hori et al, 1993;De Wever et al, 2015Winguth and Winguth, 2012De Wever et al, 2014Zhang et al, 2015;Ikeda et al, 2016Winckler et al, 2008Woodard et al, 2011Ikeda et al, 2010 1 mm 1994 SiO 2 /Al 2 O 3 K 2 O/Al 2 O 3 Ti 2 O/Al 2 O 3 10 Sugitani and Mimura, 1996;, 10 Grocke et al, 2010Sakuma et al, 2012;Sato et al, 2015;Ikeda et al, 2018, Abe-Ouchi et al, 2013, Winguth and Winguth, 2012Ando et al, 2001Uno et al, 2012Uno et al, , 2015; , --Newark Kent et al, 2017Guandao Li et al, 2016Takemura, 2007Hori et al, 2011 Re-Os 2 1000 , Fischer and Arthur, 1977…”

“…(A) Lithostratigraphy of the studied sections, and (B) the composite litho-biostratigraphy for the Lower Triassic to Lower Jurassic deep-sea sequence in the Inuyama area, Japan, compared with (C) the Geological Time Scale 2012(Ogg, 2012; Ogg and Hinnov, 2012) and published U-Pb ages (modified afterIkeda and Tada, 2014). Lithologic types are fromSugiyama (1997),Ikeda et al (2010), andSakuma et al (2012). Radiolarian and conodont biostratigraphy are fromSugiyama (1997), Ando et al (2001), Carter and Hori (2005), Gröcke et al (2011), Takahashi et al (2009), Sakuma et al (2012), and Yamashita et al (2018).…”