Research paper

End-Permian mass extinction pattern in the northern peri-Gondwanan region

The end-Permian mass extinction is the most severe in the geologic record (Raup, 1979, Sepkoski, 1984, Erwin, 1993, Hallam and Wignall, 1997). Previous research has suggested a very abrupt extinction event among marine and terrestrial organisms (Rampino and Adler, 1998, Bowring et al., 1998, Jin et al., 2000, Twitchett et al., 2001, Twitchett et al., 2004, Smith and Ward, 2001, Erwin et al., 2002, Shen and Shi, 2002). Recent popular mechanisms for the mass extinction include: bolide impact (Becker et al., 2001, Becker et al., 2004), volcanism related to the Siberian Trap (Renne et al., 1995, Bowring et al., 1998), and global anoxia associated with sea-level rise (Wignall and Hallam, 1992, Hallam and Wignall, 1997, Isozaki, 1997). Information on the timing, magnitude and nature of the event has come mostly from low and middle palaeolatitude sites in and around the Palaeo-Tethys (Wignall and Hallam, 1992, Bowring et al., 1998, Jin et al., 2000, Kaiho et al., 2001, Krull et al., 2004, Mundil et al., 2001, Mundil et al., 2004), Panthalassa from Japan (Isozaki, 1997) and northern temperate and Arctic sites (Henderson, 1997, Henderson and Baud, 1997, Wang et al., 1994, Wignall et al., 1998, Wignall and Newton, 2003, Twitchett et al., 2001). The Permian-Triassic boundary succession in southern higher palaeolatitude settings has also been a region for major research on the PTB (e.g. Wignall and Hallam, 1993, Jin et al., 1996, Morante, 1996, Shen and Jin, 1999) and has recently become a focus of research to unravel the latest Permian extinction pattern of marine and non-marine faunas (Smith and Ward, 2001, Shen and Cao, 2002, Brookfield et al., 2003, Krystyn et al., 2003, Sarkar et al., 2003, Retallack et al., 2003, Wignall and Newton, 2003, Twitchett et al., 2004). This paper contributes considerable new and newly interpreted data that have significant bearing on PTB interval interpretations for the region.

The peri-Gondwanan region straddles the northern margin of Gondwana and the southern margin of the Palaeo-Tethys/Neo-Tethys. Three key areas have been chosen as the focus of the present study: southern Tibet, Kashmir, and the Salt Range of Pakistan (Fig. 1E). Palaeogeographically, this region was located within the temperate mesothermal zone. Palaeobiogeographically during the Permian, the region has been classified as representing a transitional biogeographical zone between the palaeoequatorial Cathaysian Province and the temperate/polar provinces of the Gondwanan Realm (Shi et al., 1995) or the peri-Gondwana Cool Water Province of Mei and Henderson (2001).

Despite its critical palaeogeographical and palaeobiogeographical settings during the Permian-Triassic transition, our understanding of the peri-Gondwanan region in connection to the end-Permian mass extinction remains equivocal. In part, this uncertainty can be attributed to the longstanding misunderstanding with regard to the age of the Late Permian deposits in this region. Prior to the 1990s, many workers considered that there was a major Late Permian hiatus across the peri-Gondwanan region (e.g. Grant, 1970, Wang et al., 1989, Xia and Zhang, 1992, Wang and Wang, 1995). However, more recent biostratigraphical, sedimentological and geochemical studies, particularly those from southern Tibet (e.g. Jin et al., 1996, Shen et al., 2003a, Wignall and Newton, 2003), demonstrate in fact that the Late Permian succession in southern Tibet is continuous across the Permian-Triassic transitional interval and bears no evidence for hiatus. This conclusion is significant because it means that these higher palaeo-latitude peri-Gondwanan PTB sections may be used to investigate the nature of the marine faunal shift across the PTB in southern higher palaeolatitude settings (Fig. 1E).

In this paper we present: (1) additional data and new interpretations from previous studies of the Selong Xishan section in southern Tibet; (2) end-Permian extinction patterns of two new marine PTB sections in southern Tibet (Fig. 1, Fig. 2); and (3) a comparison with other peri-Gondwanan sections in Kashmir and the Salt Range, Pakistan (Fig. 1E) in view of end-Permian mass extinction patterns. The focus of the paper is on palaeontological, sedimentological, stratigraphical and isotope geochemical characteristics of the PTB sections, although brief discussions on the cause of the recognised patterns are provided where appropriate. It is hoped that our study can serve as a starting point for further synthesis and elucidation of higher latitude end-Permian mass extinction events and processes that will provide a contrast to equatorial signatures.