Conodont-based age calibration of the Middle Triassic Anisian radiolarian biozones in pelagic deep-sea bedded chert

Abstract

The age of pelagic Panthalassic deep-sea bedded chert has been assigned based on radiolarian biostratigraphy. However, Triassic radiolarian biostratigraphy is in many cases not precisely correlated to the conodont zones and the standard geological timescale. In this study, we investigated the conodont biostratigraphy of two radiolarian-controlled bedded chert sections of Anisian age: the Ajiro Island section in Oita Prefecture and the Kurusu section in Aichi Prefecture. We recognised six conodont biozones in the studied sections: the upper Olenekian Novispathodus brevissimus-Icriospathodus collinsoni and Triassospathodus homeri Zones, the lower Anisian Chiosella timorensis Zone, the middle Anisian Paragondolella bulgarica Zone, the upper Anisian Paragondolella excelsa Zone and the uppermost Anisian to lowermost Ladinian Paragondolella trammeri Zone. These conodont zones were successfully correlated to the standard Triassic radiolarian zonation proposed by Sugiyama (1997, Bull. Mizunami

Spathian to Aegean (upper Lower Triassic to lower Middle Triassic) carbon isotope stratigraphy constrained by the conodont biostratigraphy of carbonates on top of a mid‐oceanic seamount formed in the Panthalassic Ocean

“…Triassospathodus symmetricus and T. homeri are characteristic Spathian species, and show wider distributions and longer ranges than other Spathian taxa, such as Aduncodina unicosta and Neostrachanognathus tahoensis (Y. L. Chen et al, 2015;Koike, 2004;Lehrmann et al, 2015;Muto et al, 2019;this study). Triassospathodus homeri is distinguished from T. symmetricus by a posterior elongated blade-like P 1 element, which has a well-differentiated posterior process and a narrow basal cavity (Orchard, 1995).…”

“…pingdingshanensis during the early Spathian and commonly occurs with early Spathian conodonts, such as Icriospathodus crassatus, I. collinsoni, and Nv. abruptus worldwide (Y. L. Chen et al, 2015, Y. Chen et al, 2016, 2019Lehrmann et al, 2015;Maekawa et al, 2018;Muto et al, 2019;Orchard, 1995;Solien, 1979;Zhao et al, 2007). Neospathodus crassatus was originally described by Orchard (1995), and was recently assigned to the genus Icriospathodus (Maekawa et al, 2018).…”

“…Triassospathodus homeri is distinguished from T. symmetricus by a posterior elongated blade-like P 1 element, which has a well-differentiated posterior process and a narrow basal cavity (Orchard, 1995). The range of T. homeri generally starts after that of T. symmetricus (Y. L. Chen et al, 2015, Y. Chen et al, 2016, 2019Payne et al, 2004), and those species have also been used as Spathian index fossils in pelagic deep-sea sequences in Japan (Agematsu et al, 2008;Motoki & Sashida, 2004;Muto et al, 2018Muto et al, , 2019Sashida et al, 1992;Takahashi et al, 2009).…”

“…Chiosella timorensis is a well-known Anisian species and typically indicates the Olenekian-Anisian boundary (OAB) in conodont biostratigraphy (Gr adinaru et al, 2007;Ji et al, 2011;Krystyn et al, 2004;Lehrmann et al, 2015;Muto et al, 2018Muto et al, , 2019Nicora, 1977;Orchard, 2010;Orchard, Lehrmann, Wei, Wang, Taylor, 2007;Sweet, 1970) The genus Magnigondolella, with a 15-element apparatus including a segminiplanate P 1 element, was established by Golding and Orchard (2018). The species belonging to this genus are identified on the basis of the characteristic P 1 element and generally occur in Anisian strata in British Columbia, Canada, and Nevada, USA (Golding et al, 2014;Golding & Orchard, 2016.…”

Untitled

“…The generic assignement of the species gondolelloides has also been interpreted either as Spathognathodus (Bender, 1970), Neospathodus (Sweet, 1970a(Sweet, , 1973Orchard, 1995), Gondolella (Kozur, 1973b;Gaetani et al, 1992), Kashmirella (Budurov et al, 1988b(Budurov et al, , 1989Budurov & Sudar, 1995;Kiliç et al, 2016) or Chiosella (Kozur, 1989b;Orchard & Bucher, 1992). More recently, the assignement of the species gondolelloides was limited to Chiosella (e.g., Klets, 2008;Orchard, 2010;Plasencia et al, 2013;Muto et al, 2019). Furthermore, Nicora (1977), Kozur (1989b) and Gaetani et al (1992) treated Neogondolella aegaea Bender, 1970 as a junior synonym of Chiosella timorensis, thus implying the equivalence between the Timorensis Zone of Sweet (1970a), placed in the top of the Spathian, with "Die aegaea -Zone" of Bender (1970b), placed in the Anisian.…”