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Abstract

Global sea-level changes strongly impact within-basin depositional patterns and the evolution of palaeoclimate, palaeogeography and palaeoecology. During the long, worldwide ice-free period in the mid-Cretaceous greenhouse time interval, high-frequency global sea-level changes were recorded in sedimentary archives. However, the causes of these global sea-level changes are still debated. In central Tibet, the 1 km-thick Langshan Formation has been dated to the late Aptian to early Cenomanian based on larger benthic foraminifera and accumulated in an epeiric seaway, thus, it provides a good opportunity to reconstruct the sea-level change and their controlling factors. Eleven distinct microfacies corresponding to three sedimentary environments have been identified in the Langshan Formation. Calcispheres marlstone and bioclastic wackestone with calcispheres were deposited in an open marine environment; coral rudstone, rudist rudstone and benthic foraminifera–rudist wackestone characterize were deposited in a rudist bank environment; and orbitolinids floatstone–rudstone, green algae packstone, bioclastic grainstone, orbitolinids wackestone with small benthic foraminifera, spicules wackestone and small benthic foraminifera wackestone–mudstone were deposited in a lagoonal environment. The Langshan Formation accumulated on an epeiric platform. This unit documents a sudden deepening event from a rudist bank to an open marine environment during the late Albian (c. 107 Ma). Integrating these findings with regional data from the literature, we infer that this deepening event was a widespread, roughly synchronous feature across the globe, and was controlled by a global sea-level rise related to the decay of polar ice sheets or the release of water from continental aquifers.

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