Thursday, July 07, 2016

Megamonsoons Were Present in Tibet Multiple Times From the Late Permian Through the Middle Triassic

Mesozoic litho- and magneto-stratigraphic evidence from the central Tibetan Plateau for megamonsoon evolution and potential evaporites


Fang et al


The megamonsoon was a striking event that profoundly impacted the climatic environment and related mineral sources (salts, coals and oil-gases) in the Mesozoic. How this event impacted Asia is unknown. Here, we firstly reported a Mesozoic stratigraphic sequence in the northern Qiangtang Basin, in the central Tibetan Plateau, based on lithofacies and chronologies of paleontology and magnetostratigraphy. How the planetary and megamonsoon circulations controlled the Asian climate with time has been recorded. Using the basic principles of physical geography, present analogs and a newly developed model, the evolution of the stratigraphic sequence was interpreted to demonstrate that the Qiangtang Basin has been subjected to a megamonsoon climate with heavy precipitation during its northward movement since the Latest Permian but has been subjected to a dry environment due to moving into the northern hemisphere subtropic high zone in the Middle Triassic and monsoonal retreat in the early Late Jurassic (early Oxfordian) approximately 161 Ma. The coupling of the hot-dry climate and the close of the Meso-Tethys, along with sea retreat in the Late Jurassic, ensured a large potential time window for evaporite (potash) formation in the Qiangtang Basin, while the tropic megamonsoon rain forest in the Late Permian to the Early Triassic and in the Late Triassic to Middle Jurassic favored the formation of coal and hydrocarbon source rocks.

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