Late Cretaceous plateau deserts in the South China Block, and Quaternary analogues; sedimentology, dune reconstruction and wind-water interactions

摘要

Plateau deserts are among those continental systems with the most significant examples of clastic deposits associated with the complex combination of the action of ice, wind and water. The Late Cretaceous rocks of China contain the record of desert systems migration and partial destruction in a palaeoplateau desert. The evolution of the South China Block during Late Cretaceous was characterized by widespread destructive plate margin activity, this favoured orogenic uplift and high-altitude mountain ranges of which a direct consequence was a widespread rain shadow effect, triggering desertification and erg expansion similar to that of Quaternary counterparts in the Tibetan Plateau. This work presents a detailed analysis of the sedimentology, stratigraphic architecture, palaeogeography and palaeocurrent reconstruction of aeolian and associated alluvial depositional systems. The reconstruction of aeolian bedforms based on field-data analysis indicates that, during Late Cretaceous, draas and crescentic dunes accumulated and migrated in extensive intermontane desert systems. Heavy rains led to partial destruction of aeolian dunes and the reworking of aeolian sands in interdraa corridors. The fault-controlled subsidence and an increasing input of windblown sediments favoured the long-lasting accumulation of the erg system. Possible monsoonal rains recharged the groundwater system causing the rise of the regional phreatic level that favoured the ulterior long-lasting preservation of the aeolian system in the Xinjiang Basin. The dimensions and processes inferred from this Cretaceous desert system are similar to those observed today in the linking zone of the Taklamakan-Gobi Deserts, where meltwater flows from alpine glaciers in surrounding mountain ranges recharge the alluvial and fluvial network of the erg margin. The occurrence of striated cobbles in the alluvial facies suggests glacial activity in the catchment areas of the Cretaceous plateau.