Palaeogeographic and palaeotopographic evolution of the chinese tian shan during the mesozoic : A sedimentological synthesis

Gloria Heilbronn , Cecile Robin (1) , Marc Jolivet (2) , Laurie Barrier (3) , Sylvie Bourquin (1)

1 GR - Géosciences Rennes
2 Terre, Temps, Traçage
3 IPGP - Institut de Physique du Globe de Paris

The Tian Shan range occupies the southwestern edge of the Central Asian Orogenic Belt. Our aim is to reconstruct the pre-Tertiary history of relief building in the Chinese Tian Shan. We use the sedimentary facies, sediment provenances and paleocurrent directions of the 6 exposed Mesozoic sections in the northern and southern piedmonts as well as in intra-mountain basins. The correlation of these 6 sections allows us to propose some palaeogeographic maps for the middle Jurassic, the upper Jurassic - lower Cretaceous transition, the upper Cretaceous and the late Cretaceous - Paleogene transition. The dismantling of reliefs associated to the late-paleozoic tectonic phase is largely completed by upper Triassic. The Jurassic is characterised by a low tectonic activity and results in a general planation phase of the Tian Shan area. The upper Jurassic - lower Cretaceous transition is characterized by a huge conglomeratic event at the scale of all the northern foothills, associated with some eolian deposits implying a arid climate during this period. We propose that the alluvial fans are resulting from the erosion of relatively small and local reliefs, caused by normal faults activity, in contradiction with the existing hypothesis supporting compressional tectonic and reactivation of the range during the Upper Jurassic (Hendrix et al., 1992). However it fits to the interpretation of low thermochronology data. During the Upper Cretaceous, the widespread occurrence of alluvial fans indicates the ongoing erosion of a local positive topography in the Tian Shan area. A significant late Lower - early Upper Cretaceous unconformity is observable in the S-Junggar, N-Tarim and Turfan Basins. It is confirmed by low temperature thermochronology data that show a « major » late Lower Cretaceous unroofing event near Kuqa on the southern foothills (Dumitru et al., 2001) and some late Lower to early Upper Cretaceous exhumation ages within the range (Jolivet et al., 2010). This marks the onset of a new exhumation phase that goes on during the Upper Cretaceous and seems to stop after a peak of activity in the late Upper Cretaceous. Following the Upper Cretaceous inversion episode, a tectonic quiet period characterises the late Upper Cretaceous - Early Paleogene and enables the formation of a widespread calcrete in both piemont of the range.

Domains: Earth Sciences

Gloria Heilbronn, Cecile Robin, Marc Jolivet, Laurie Barrier, Sylvie Bourquin. Palaeogeographic and palaeotopographic evolution of the chinese tian shan during the mesozoic : A sedimentological synthesis. 24 ème Réunion des sciences de la Terre 2014, Oct 2014, Pau, France. pp.68. ⟨insu-01080485⟩