Upper Jurassic–Lower Cretaceous stratigraphy in south-eastern Tibet: a comparison with the western Himalayas

Abstract

Lithostratigraphic studies of the Upper Jurassic–Lower Cretaceous sedimentary successions exposed in the Tingri–Gyangze area, south-eastern Tibet resulted in the establishment of a revised stratigraphic framework. A major crustal fault separates the southern Tibetan sedimentary successions into a Southern Zone and a Northern Zone. The Upper Jurassic–Lower Cretaceous strata of the Southern Zone are subdivided into the Menkadun Formation (Oxfordian, Kimmeridgian, up to lower Upper Tithonian), the Gucuo Formation (Upper Tithonian to Lower Albian) and the overlying Dongshan Formation (Upper Albian). The Gucuo Formation is further subdivided into a quartz arenite unit, which is overlain by a shale unit, in turn overlain by a volcaniclastic sandstone unit. The youngest cluster of detrital zircon absolute age data (127.7 ± 1.8 Ma) from the lower part of the volcaniclastic unit of the Gucuo Formation place the volcanic event before the Late Barremian. In the Northern Zone, the Upper Jurassic–Lower Cretaceous strata have been subdivided into four formations: the Zhera Formation (Upper Jurassic), the Weimei Formation (Tithonian), the Rilang Formation (?Berriasian) and the Gyabula Formation (? post-Valanginian). The appearance of silica cemented quartz arenites in both the quartz arenite unit of the Gucuo Formation and the Weimei Formation in the uppermost Jurassic is considered to provide strong evidence for an eustatic sea level drop affecting the northern margin of Greater India. In contrast the appearance of volcaniclastic sandstones in the Gucuo and Rilang formations are interpreted to represent a rift related volcanic event. The Menkadun–Zhera formations, the quartz arenite unit of the Gucuo Formation–Weimei Formation, the volcaniclastic sandstone unit–Rilang Formation in south-eastern Tibet are lithologically similar and broadly correlative with the Spiti Shale, Takh and Pingdon La formations in Zanskar (India), and Spiti Shale, Dangardzong, Kagbeni and Dzong formations in the Thakkhola area (Nepal). The onset of quartzose and subsequently volcaniclastic deposition becomes progressively younger westward, from the Gucuo region toward Zanskar.