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 Langshan Formation, reaching a thickness up to ~1 km, accumulated in an epicontinental seaway over a modern area of 132 × 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 Daxiong/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 Langshan carbonates accumulated, modulated by long-term slow tectonic subsidence and high carbonate productivity.