Mid-Cretaceous thick carbonate accumulation in Northern Lhasa (Tibet): eustatic vs. tectonic control?

Widespread accumulation of thick carbonates is not typical of orogenic settings. During the mid-Cretaceous, near the Bangong suture in the northern Lhasa terrane, the shallow-marine carbonates of the Lang-shan Formation, reaching a thickness up to -1 km, accumulated in an epicontinental seaway over a modern area of 132 X 103 km2, about half of the Arabian/Persian Gulf. The origin of basin-wide carbonate deposits located close to a newly formed orogenic belt is not well understood, partly because of the scarcity of paleogeographic studies on the evolution of the northern Lhasa. Based on a detailed sedimentological and stratigraphic investigation, three stages in the mid-Cretaceous paleogeographic evolution of northern Lhasa were defined: (1) remnant clastic sea with deposition of Duoni/Duba formations (Early to early Late Aptian, ca. 125-116 Ma); (2) expanding carbonate seaway of Langshan Formation (latest Aptian-earliest Cenomanian, ca. 116-99 Ma); and (3) closure of the carbonate seaway represented by the Dax-iong/Jingzhushan formations (Early Cenomanian to Turonian, ca. 99-92 Ma). Combined with data on tectonic subsidence and eustatic curves, we emphasized the largely eustatic control on the paleogeographic evolution of the northern Lhasa during the latest Aptian-earliest Cenomanian when the Lang-shan carbonates accumulated, modulated by long-term slow tectonic subsidence and high carbonate productivity.