Journal of Paleontology, 93(1), 2019, p. 48–71 Copyright © 2018, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2018.46 A new Griesbachian–Dienerian (Induan, Early Triassic) ammonoid fauna from Gujiao, South China Xu Dai,1 Haijun Song,1 Arnaud Brayard,2 and David Ware3 1State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China 〈[email protected]〉, 〈[email protected]〉 2Biogéosciences, UMR 6282, CNRS, Université Bourgogne Franche-Comté, 6 Boulevard Gabriel, 21000 Dijon, France 〈[email protected]〉 3Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany 〈[email protected]〉 Abstract.—Bed-by-bed sampling of the lower portion of the Daye Formation at Gujiao, Guizhou Province, South China, yielded new Griesbachian–Dienerian (Induan, Early Triassic) ammonoid faunas showing a new regional Induan ammonoid succession. This biostratigraphic scheme includes in chronological order the late Griesbachian Ophiceras medium and Jieshaniceras guizhouense beds, and the middle Dienerian Ambites radiatus bed. The latter is recognized for the first time as a separate biozone in South China. Eight genera and 13 species are identified, includ- ing one new species, Mullericeras gujiaoense n. sp. The new data show that a relatively high level of ammonoid taxonomic richness occurred rather rapidly after the Permian/Triassic mass extinction in the late Griesbachian, echo- ing similar observations in other basins, such as in the Northern Indian Margin. UUID: http://zoobank.org/a24a3387-f3dd-4da4-a134-84372352a63d Introduction Early Triassic (Brayard et al., 2006, 2009a; Brühwiler et al., 2010a; Ware et al., 2015). Ammonoids are, therefore, one of the The Permian/Triassic (PT) boundary witnessed the largest biotic most useful index fossils for biostratigraphy in this interval (Jenks crisis among all Phanerozoic mass extinctions, resulting in the et al., 2015). For example, on the Northern Indian Margin, a total disappearance of 80% to 90% of marine species (Raup, 1979; of 12 and 14 regional ammonoid unitary associations have been Song et al., 2013; Stanley, 2016). This major event coincided recognized for the Dienerian and Smithian, respectively (Brüh- with high temperatures (Joachimski et al., 2012; Sun et al., wiler et al., 2010a, 2011; Ware et al., 2015); this represents an 2012; Romano et al., 2013), potential anoxia (Wignall and unprecedented high-resolved biostratigraphic scale compared Twitchett, 1996; Song et al., 2012), and acidification (Clarkson with coeval records from other regions, such as the western USA et al., 2015) in the oceans, as well as pronounced perturbations basin, which has six Smithian ammonoid unitary associations in the carbon cycle (Payne et al., 2004; Galfetti et al., 2007) and (Jattiot et al., 2017; Jenks and Brayard, 2018). intensified continental weathering (Algeo and Twitchett, 2010; South China is renowned for its PT marine and terrestrial Song et al., 2015a). A delayed recovery has often been proposed records, and the Global Stratotype Section and Point (GSSP) of to have followed the PT mass extinction (Hallam, 1991; Tong the PT boundary is located at Meishan, Zhejiang Province (Yin et al., 2007; Chen and Benton, 2012). However, studies of some et al., 2001). In the past 50 years, approximately 100 geological groups, such as conodonts, ammonoids and foraminifers, show sections spanning the PT boundary and the Early Triassic and that the recovery was well under way by at least the Smithian representing various shallow to deep-marine environments (e.g., (Orchard, 2007; Brayard et al., 2009a; Song et al., 2011), less Brayard and Bucher, 2008; Galfetti et al., 2008; Song et al., than 1 million years after the PT mass extinction (Galfetti et al., 2011; Bai et al., 2017; Wang et al., 2017) have been documented 2007; Baresel et al., 2017). Some assemblages documenting in South China. From these rather exhaustive environmental relatively high taxonomic richness during the late Griesba- records, many clades and geochemical proxies were studied to chian–early Dienerian also challenge previous claims of a decipher the regional biotic recovery signal. The diversity of globally delayed recovery (Twitchett et al., 2004; Ware et al., both benthic and nektonic organisms was analyzed mainly from 2015; Foster et al., 2017; Wang et al., 2017). foraminifers (Song et al., 2011, 2015b), brachiopods (Chen To decipher the causes of the PT crisis and associated et al., 2015; Wang et al., 2017), bivalves (Yin, 1985; Huang recovery patterns and processes, a high-resolution biostrati- et al., 2014), gastropods (Pan et al., 2003; Kaim et al., 2010), graphic frame is a prerequisite. With coupled high origination and conodonts (Zhang et al., 2007; Zhao et al., 2007; Jiang et al., extinction rates, the ammonoid turnover was extremely fast in the 2014; Brosse et al., 2015, 2016; Liang et al., 2016; Bai et al., 48 Downloaded from https://www.cambridge.org/core. University of Athens, on 04 Oct 2021 at 01:02:52, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/jpa.2018.46 Dai et al.—A new Induan ammonoid fauna from South China 49 2017), and ammonoids (Chao, 1959; Xu, 1988; Mu et al., 2007; At Gujiao, the Dalong Formation is ~ 10 m in thickness and Brayard and Bucher, 2008; Brühwiler et al., 2008). Paleoen- is dominated by cherty limestones, siliceous mudstones alter- vironmental and paleoclimatic signals were also intensively nating with black or gray shales, and volcanic ash beds, repre- studied from numerous South Chinese sections (Payne et al., senting a deeper basinal environment. At the bottom of the 2004; Galfetti et al., 2007, 2008; Song et al., 2012, 2017). Dalong Formation, a limestone bed ~30 cm thick contains Regarding these studies, the biostratigraphic framework used is abundant and well-preserved ammonoids with, for example, crucial for correlation among different biotic and environmental Pseudotirolites and Pseudogastrioceras, indicating a late signals and between distant areas. Nevertheless, only a limited Changhsingian age (Zhao et al., 1978). number of ammonoid biostratigraphic schemes have been pro- The lower part of the Triassic Daye Formation is ~ 50 m posed for the Early Triassic of South China (e.g., Tong et al., thick and consists of marlstones interbedded with shales. It 2004; Galfetti et al., 2007; Brayard and Bucher, 2008; Brüh- directly overlies the Dalong Formation without apparent wiler et al., 2008). unconformity, although earliest Griesbachian ammonoids are Early Triassic ammonoid faunas in South China have been missing. Abundant ammonoid and bivalve specimens as well as sporadically studied over the past 80 years. Tien (1933) initially some gastropods were collected in the lowermost 6 m. Trace described some ammonoid specimens from Hubei and Guizhou fossils also occasionally occur. Ammonoids from the shales are provinces. Then Hsü (1937) reported a few ammonoid taxa deformed and cannot be identified. Although generally difficult based on deformed specimens from Jiangsu, Zhejiang, and to extract from the argillaceous limestones, a few specimens Hubei provinces. In 1959, Chao illustrated a diverse, well- could be extracted from some beds. Recrystallized ammonoid preserved ammonoid fauna from Guangxi, but with only rare specimens were abundantly sampled from bed GJ-40. Judging Griesbachian and Dienerian specimens. Following the work of from observed facies, the lower Daye Formation corresponds to Chao (1959), a few Early Triassic ammonoid faunas were a basin or basin-margin environment. described (Xu, 1988; Tong and Wu, 2004; Mu et al., 2007). Due to their relatively poor preservation and spatiotemporally Materials restricted occurrences, the taxonomy, biostratigraphy, and diversity patterns of ammonoids from South China remained A total of 749 ammonoid specimens were collected. Although largely imperfectly known until recently. New ammonoid often not well preserved, they represent eight genera and 13 material from Guangxi and Guizhou provinces provided a species (Fig. 3), including Ophiceras medium Griesbach, 1880, biostratigraphic framework for small parts of the Griesbachian Ophiceras sp. indet., Vishnuites pralambha Diener, 1897, – and Dienerian (Brühwiler et al., 2008) and for the Smithian Ophiceratidae gen. indet., Ambites radiatus (Brühwiler et al., Spathian interval (Galfetti et al., 2007; Brayard and Bucher, 2008), Gyronitidae gen. indet. sp. indet., ?Gyronitidae gen. indet. 2008). However, due to mistakes in the taxonomy and to scat- sp. indet., Proptychites sp. indet., Pseudoproptychites cf. P. hie- tered occurrences of ammonoids in different sections with very malis (Diener, 1895), Jieshaniceras guizhouense (Zakharov and – little superposition information, the preliminary Griesbachian Mu in Mu et al., 2007), Mullericeras gujiaoense n. sp., Ussur- Dienerian (Induan) zonation remained poorly resolved with idiscus cf. U. varaha, and ?Mullericeratidae gen. indet. many uncertainties for large-scale correlation among distant basins. So overall, our knowledge of the Griesbachian–Diener- — ian ammonoid taxonomy and biostratigraphy based on South Repository and institutional abbreviation. YFMCUG: Yifu Chinese data remains very incomplete. Museum of China University of Geosciences, Wuhan. Here, we document a new Griesbachian-Dienerian ammo- noid succession based on