Triassic-Jurassic biodiversity, ecosystems, and climate in the Junggar Basin, Xinjiang, Northwest China

Abstract

The Junggar Basin, one of the largest continental basins in Central Asia, represents a landlocked sedimentary environment that has been cut off from marine influence since the late Palaeozoic (Hendrix et al. 1992). The basin contains a largely fossiliferous sedimentary succession from the Permian to the Late Cretaceous (Dong 1992). Throughout the Mesozoic, the Junggar Basin maintained a mid-latitude position, making it particularly interesting for palaeoecologic and palaeoclimatic studies (e.g., Eberth et al. 2001). The focus of this issue is on the Late Triassic and Jurassic fluvio-lacustrine strata in the southern Junggar Basin that have yielded a wealth of continental biota in the last decade (e.g., Maisch et al. 2003), but other areas of the basin are also considered. The nine articles of the Special Issue report on the palaeontological and sedimentological research that has been conducted by the “Sino-German Joint Group of Palaeontology and Geosciences” funded between 2005 and 2009 by the Sino-German Center for Research Promotion (Beijing). The topics addressed are basin development, sedimentology, reconstruction of the Jurassic forest, palaeoclimate, and the palaeobiogeographic and palaeoecologic implications of aquatic and terrestrial organisms such as hybodontid sharks, turtles, crocodiles, squamates, mammals, and plants. In its multidisciplinary approach, the Special Issue provides the first comprehensive overview of the evolution of the Late Triassic to the Late Jurassic ecosystems in the Junggar Basin with an emphasis on its southern part. Bian et al. provide an overview on the geological evolution of the Junggar Basin from the Early Permian onward when the sea regressed to the southeast and the basin became landlocked. The Lower to Middle Triassic is characterised by alluvial fan and delta systems that are overlain by lacustrine deposits of the Upper Triassic. In the Lower and Middle Jurassic, coal-bearing braid delta systems developed while the Upper Jurassic was widely eroded except for a depocentre along the southern part of the Junggar Basin between the cities Manas and Urumqi. The Cretaceous is characterised by continuous and homogeneous lacustrine conditions with the depocentre located in the basin centre. During the Paleogene, braid delta systems developed, whereas with the early Neogene, sedimentation was restricted to the southern part of the basin, when the north Tianshan experienced a rapid uplift and northward over-trust. Ashraf et al. present a review and new data on the Triassic and Jurassic palaeoclimate development in the Junggar Basin. New lithological data mainly derive from the southern part of the basin and cover a period from the Late Triassic (Norian) to the latest Jurassic (Tithonian). Based on new palynological data, the authors convincingly demonstrate that the base of the Middle Jurassic does not coincide with the lithostratigraphical formation boundaries. T. Martin (*) Steinmann-Institut fur Geologie, Mineralogie und Palaontologie, Universitat Bonn, Nussallee 8, 53115 Bonn, Germany e-mail: tmartin@uni-bonn.de