The Ancestral Lhasa River: A Late Cretaceous trans-arc river that drained the proto–Tibetan Plateau

Late Cretaceous trench basin strata were deposited in the subduction zone that consumed Neo-Tethyan oceanic lithosphere along the southern margin of the proto–Tibetan Plateau. We conducted detrital zircon (DZ) U-Pb geochronology on six trench basin samples (n = 1716) collected near Dênggar, Tibet (∼500 km west of Lhasa), to assess the provenance of these rocks and reconstruct Late Cretaceous sediment transport pathways. They contained DZ ages that point to a unique source around Lhasa city, north of the Late Cretaceous Gangdese magmatic arc. The modern Lhasa River catchment contains the requisite sources, and its main trunk transects the Gangdese magmatic arc, joining with the Yarlung River at a barbed junction at the India-Asia suture. We infer that the Lhasa River is an ancient feature that transported sediment to the subduction zone in Late Cretaceous time and persisted during India-Asia collision.

The Jurassic–Cretaceous lithostratigraphy of Kilen, Kronprins Christian Land, eastern North Greenland

Kilen, Kronprins Christian Land, contains the thickest and stratigraphically most complete Jurassic and Cretaceous sediment succession in North Greenland. This study revises and formalises the lithostratigraphic framework of these deposits. The work is based on recent extensive stratigraphic field work supplemented by photogeological mapping and biostratigraphic studies, and builds on the earlier stratigraphic work conducted mainly in the 1980s and 1990s. According to the new stratigraphic scheme, the more than 500 m thick Jurassic succession is divided into four formations. The poorly dated Gletscherport Formation comprises lagoonal heterolithic sandstones. The Mågensfjeld and Birkelund Fjeld Formations consist of shallow marine fine-grained sandstones of Bajocian–Bathonian and Kimmeridgian age, respectively. The Kuglelejet Formation comprises mainly shallow marine sandy mudstone and sandstone of Volgian age and includes the mudstone-dominated Splitbæk Member. The Lower Cretaceous interval is estimated to be more than 1500 m thick and is divided into three formations. The Dromledome Formation comprises deep shelf to offshore transition, black mudstones of late Ryazanian to Hauterivian age. It is erosively overlain by unfossiliferous, fluvial and estuarine sandstones of the Lichenryg Formation. The overlying, late Aptian to middle Cenomanian Galadriel Fjeld Formation comprises six members, of which the Tågekyst and Kangoq Ryg Members occur in the Gåseslette area, whereas the Pil, Valmue, Stenbræk and Hondal Members occur in the Kilen Fjelde area. The Galadriel Fjeld Formation is characterised by interbedded mudstones and sandstones from offshore–shoreface environments. The 650 m thick Upper Cretaceous succession is assigned to the Sølverbæk Formation, which is undivided in the Gåseslette area and divided into the Skalbæk and Scaphitesnæse Members in the Kilen Fjelde area. The Sølverbæk Formation is dominated by marine mudstones and sandstonemudstone heteroliths of late Cenomanian to Santonian age. The new lithostratigraphic framework and significant biostratigraphic advances allow a closer correlation of the Mesozoic units between North Greenland and other Arctic basins.