Geobios 43 (2010) 403–431 Original article Smithian (Early Triassic) ammonoids from Tulong, South Tibet§ Ammonoïdes du Smithien (Trias inférieur) de Tulong, Tibet du Sud Thomas Brühwiler a,*, Hugo Bucher a,b, Nicolas Goudemand a a Paläontologisches Institut und Museum der Universität Zürich, Karl Schmid-Strasse 4, 8006 Zürich, Switzerland b Department of Earth Sciences, ETH, Universitätsstrasse 16, 8092 Zürich, Switzerland Received 6 August 2009; accepted 8 December 2009 Available online 26 May 2010 Abstract Intensive sampling of the Tulong Formation in South Tibet has facilitated the construction of a highly-resolved middle and late Smithian ammonoid succession. The new biostratigraphical sequence comprises the middle Smithian Brayardites compressus beds, Nammalites pilatoides beds, and the Nyalamites angustecostatus beds followed by the late Smithian Wasatchites distractus beds and Glyptophiceras sinuatum beds. This faunal succession correlates very well with that of other Tethyan sequences such as the Salt Range (Pakistan), Spiti (India), Oman and South China. The Smithian faunal sequence from Tulong contains several taxa with broad geographic distribution (e.g., Owenites, Paranannites spathi, Shigetaceras, Wasatchites), thus enabling correlation with faunal successions from areas outside the Tethys (e.g., USA, British Columbia, Arctic Canada, South Primorye, Siberia). Early Smithian ammonoid faunas are almost absent in Tulong because of a preservation bias (absence of carbonate rocks). Five new ammonoid genera (Brayardites, Nammalites, Nyalamites, Shigetaceras, Tulongites) and six new species (Brayardites crassus, Brayardites compressus, Prionites involutus,?Subflemingites compressus, Tulongites xiaoqiaoi, Urdyceras tulongensis) are described. # 2010 Elsevier Masson SAS. All rights reserved. Keywords: Ammonoidea; Early Triassic; South Tibet; Smithian; Biostratigraphy Résumé Un échantillonnage intensif de la Formation Tulong du sud-Tibet permet l’établissement d’une séquence très détaillée des faunes d’ammonites du Smithien moyen et supérieur. Cette nouvelle séquence comprend les faunes d’assemblage du Smithien moyen à Brayardites compressus,à Nammalites pilatoides,etàNyalamites angustecostatus, suivies par les faunes du Smithien supérieur à Wasatchites distractus et à Glyptophiceras sinuatum. Cette succession faunique se corrèle très bien avec celles d’autres localités téthysiennes telles que les Salt Ranges (Pakistan), le Spiti (Inde), l’Oman et le Sud de la Chine. Les faunes smithiennes de Tulong contiennent également plusieurs taxons ayant une large distribution géographique (p. ex., Owenites, Paranannites spathi, Shigetaceras, Wasatchites) permettant ainsi des corrélations avec d’autres successions en dehors de la Téthys (p. ex. USA, Colombie britannique, Arctique canadien, sud du Primorye, Sibérie). Les faunes du Smithien inférieur sont par contre quasiment absentes de Tulong en raison d’un biais de préservation (absence de roches carbonatées). Cinq genres (Brayardites, Nammalites, Nyalamites, Shigetaceras, Tulongites) et six espèces (Brayardites crassus, Brayardites compressus, Prionites involutus,?Subflemingites compressus, Tulongites xiaoqiaoi, Urdyceras tulongensis) sont nouvellement décrits. # 2010 Elsevier Masson SAS. Tous droits réservés. Mots clés : Ammonoidea ; Trias inférieur ; Sud-Tibet ; Smithien ; Biostratigraphie 1. Introduction Sepkoski, 1982), ammonoids recovered very fast in compar- ison with other marine clades (Brayard et al., 2006, 2009c). In the aftermath of the end-Permian mass extinction that Following low values in the Griesbachian, diversity increased wiped out more than 90% of all marine species (e.g., Raup and slowly during the Dienerian and first peaked in the Smithian. This first major evolutionary radiation was followed by a § Corresponding editor: Gilles Escarguel. * Correspondant author. severe extinction event in the end Smithian, after which a E-mail addresses: [email protected], [email protected] second major and explosive radiation took place during the (T. Brühwiler). Spathian. 0016-6995/$ – see front matter # 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.geobios.2009.12.004 404 T. Brühwiler et al. / Geobios 43 (2010) 403–431 For more than a century, Smithian ammonoids have been the Early Carboniferous. A second rifting phase during the Early known from various localities in the Tethyan realm, such as the Permian detached the Lhasa block from the Gondwanian margin, Salt Range in Pakistan (Waagen, 1895; Noetling, 1905; Guex, thus giving birth to the Neotethys. In this process the southern 1978), Afghanistan (Kummel and Erben, 1968), Spiti in Neotethyan Indian margin was acting as the upper plate, thereby Northern India (Diener, 1897; Krafft and Diener, 1909; Krystyn inducing basalt flows (Panjal Traps) and volcanism (Stampfli et al., 2007a, b), Kashmir (Diener, 1913), Madagascar et al., 1991; Baud et al., 1996; Garzanti et al., 1996). During the (Collignon, 1933-1934), Guangxi in South China (Chao, expansion of the Neotethys in the Early Triassic, the Indian 1959; Brayard and Bucher, 2008), Vietnam (Khuc, 1984) and margin underwent thermal subsidence and was characterized by Timor (Welter, 1922). However, the number of studies based on large tilted blocks. This may at least partly explain the differences bed-by-bed sampling is very limited (Guex, 1978; Krystyn in lithological successions between closely spaced localities such et al., 2007a, b; Brayard and Bucher, 2008). Therefore, as Tulong and Selong (35 km apart) in South Tibet (Garzanti additional high-resolution ammonoid successions from various et al., 1998; Brühwiler et al., 2009). localities are crucial for establishing a precise and laterally reproducible biochronological subdivision of the Smithian 3. The Tulong succession within the Tethys and within the Early Triassic tropics. Recently, we provided the first complete and detailed For the Tulong area (Fig. 2), previously published reports of description of the Lower Triassic sedimentary and carbon the Lower Triassic sedimentary succession (Liu, 1992; Liu and isotope records from the Tulong area in South Tibet (Brühwiler Einsele, 1994; Garzanti et al., 1998; Shen et al., 2006) are et al., 2009). Extensive sampling enabled us to precisely date incomplete and/or poorly or incorrectly dated. Only recently the section by means of detailed ammonoid and conodont has the complete Lower Triassic sedimentary record from this biostratigraphy. Our investigations have yielded abundant, area been described and dated by means of detailed ammonoid diverse and reasonably well preserved Smithian ammonoid and conodont biostratigraphy (Brühwiler et al., 2009). In that faunas including several new taxa. Here, we focus on the work we subdivided the Lower Triassic succession of Tulong description of these faunas. They add significantly to our into six lithostratigraphic units as follows (Fig. 3; Supplemen- knowledge of Smithian ammonoid taxonomy and biostrati- tary data, Fig. S1). graphy and provide valuable data for biogeographical, The basal Triassic sequence consists of three meters of phylogenetic and chemostratigraphic studies. carbonates (Unit I) that are subdivided into two meters of Griesbachian yellow dolomite (Subunit Ia), and one meter of 2. General palaeogeographical and geological setting Dienerian light grey, thin-bedded limestone (Subunit Ib). These are followed by about 50-100 m of Dienerian-early Smithian During Early Triassic times, the Tulong area was located in a aged, dark green, silty shales (Unit II) devoid of macrofossils. distal position of the northern Gondwanian margin, on the This interval is overlain by nine meters of thin-bedded, light grey southern side of the Tethys Ocean (Ogg and von Rad, 1994; fossil-rich limestone of middle to late Smithian age (Unit III; Fig. 1). As shown by different authors (Marcoux and Baud, 1996; subdivided into four Subunits IIIa-d). These are followed by four Ricou, 1996; Garzanti and Sciunnach, 1997) at least two rifting meters[(Fig._2)TD$IG] of early Spathian shales containing a few limestone beds processes affected the North Indian plate. The first event is linked to[(Fig._1)TD$IG] the break-off of the Quiantang block from Gondwana during Fig. 1. Simplified Early Triassic palaeogeography (modified after Brayard et al., 2006, 2009b; Shigeta et al., 2009a) with the position of South Tibet Fig. 2. Geological sketch map of the study area (modified after Burg, 1983) and other localities mentioned in the text. and location of studied sections. [(Fig._3)TD$IG] T. Brühwiler et al. / Geobios 43 (2010) 403–431 405 Fig. 3. (a) Classical section (Tu) near the village of Tulong, with lithologic units (Brühwiler et al., 2009). (b) Subunits IIIb and IIIc, with stratigraphic positions of ammonoid faunas. (c) Subunits IIIc and IIId, with stratigraphic positions of ammonoid faunas. Abbreviations: W. d. Wasatchites distractus; Glypt. sin. Glyptophiceras sinuatum. Hammer (28 cm in length) for scale. and nodules (Unit IV). The shales are typically green in the lower The studied sections were sampled bed-by-bed in order to part (Subunit IVa) and red in the upper part (Subunit IVb). The obtain a precise, detailed ammonoid record (Supplementary late early and middle Spathian consists of six meters of red, data, Fig. S1). The dark green shales of Unit II are essentially bioclastic nodular limestone (‘‘Ammonitico Rosso’’ type facies; barren and only one incomplete floated specimen (Kashmirites Unit V). The late Spathian-Anisian part of the succession