New palynostratigraphical data of Jurassic series in Tian Shan Range (Xinjiang, China)
Résumé
The reconstruction of the Jurassic paleotopography and paleoenvironments surrounding the Chinese Tian Shan Range is an important data for the understanding of the Mesozoic tectonic evolution of the range. In fact, the landscape prevailing at this period is poorly known. Several studies (sedimentology and low temperature thermochronology) have been carried out during the last two decades both within the range and the associated basins (e.g. Jolivet et al., 2010). However, the topographic evolution of the range is under discussion, mostly because of the difficulty to obtain depositional age constraints and detailed climate signal from the associated sediments in the basins. Within that evolution, the Jurassic represents a key period between the nearly eroded major Late Paleozoic range and a suspected Late Jurassic – Early Cretaceous tectonic reactivation phase coeval with more arid climate conditions. Several sections, on the foothills of the Chinese Tian Shan offer well-exposed Jurassic to Tertiary sediment series. While the Jurassic palynoflora is locally well preserved, no detailed palynological data have been reported from field outcrops in this area yet. The new assemblages found are very rich, well-preserved and diversified. They present similarities with those described by Jiang & Wang (2002) for the Yan’an Fm. in Dongsheng, Dxin, Jiang et al. (2009) in Wuqia and Kimyai (1975) for the Shahrund region (Iran). They correspond to the palynological zones proposed in the compilation work of Sha & et al. (2010).