Sedimentology, Palaeoecology and Palaeoenvironmental Evolution of the 1985 Lhasa to Golmud Geotraverse

• Published in: Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences Vol. 327; no. 1594; p. 107
• Main Authors: M. R. Leeder, A. B. Smith, Yin Jixiang
• Format: Journal Article
• Language: English
• Published: The Royal Society 12.12.1988
• ISSN: 1364-503X; 1471-2962
• DOI: 10.1098/rsta.1988.0123

Vertical and horizontal measurements of almost 30 km of sections were made along the Geotraverse route at 113 localities ranging in age from Ordovician to Tertiary. Over 280 palaeocurrent measurements were taken and 200 thin sections were studied. Ordovician strata occur only in the Kunlun Terrane, where thick metamorphosed sequences of clastics and carbonates occur. These are tentatively interpreted as platform margin and slope deposits. During Carboniferous times in the Kunlun Terrane transgressive late-Dinantian marine limestones with tropical to subtropical Eurasian reefoidal faunas overlie fluviatile redbeds derived from an unroofed orogenic belt. The Lhasa Terrane contains shelf basin clastics with low-diversity faunas succeeded by thick late Carboniferous/early Permian glacio-marine mixtites deposited by iceberg meltout. Permian carbonate ramp and shelf facies with reefoidal developments occur over both the Lhasa and Qiangtang Terranes, with coal-bearing clastics and fluviatile redbeds also occurring in the latter. Permian sequences in the Kunlun Terrane comprise resedimented tuffaceous shelf basin clastics overlain by shelf carbonates. Triassic rocks are widely distributed. Those of the Lhasa Terrane are predominantly carbonate ramp and platform margin/slope facies showing evidence for shelf breakup due to extensional tectonics. Qiangtang sequences occur below and above a thick andesite lava development. Those below are mature fluviatile gravels derived from the north. The strata above the arc-related volcanics are typical shoaling-upwards carbonate ramp facies. Thick sequences in the southern Kunlun Terrane are tentatively ascribed to passive continental rise deposits of countourite drift aspects. Those in the northern areas are highly immature coarse clastics derived as alluvial fans from an Anisian--Carnian granitoid intrusive belt to the north. Jurassic sequences are unknown in the Kunlun Terrane. In the Qiangtang Terrane very thick (c. 5 km) sequences of clastic redbeds are interpreted as fluviatile and coastal plain molasse derived from the newly formed Kunlun orogen to the north. These intertongue southwards with marine shelf carbonates and clastics. The northern Lhasa Terrane contains thick clastic mudrocks and turbiditic sandstones of shelf basin aspects. Pelagic cherts and clastics overly oceanic pillow lavas, with ophiolitic ultrabasics capped by ferrosiallitic duricrusts and overlain by late Jurassic marine limestones. Cretaceous rocks are only known in the Lhasa Terrane. North of Lhasa they comprise northerly-derived fluviatile redbeds of molassic aspects which record the formation and uplift of the Jinsha/Banggong orogen. 300 km NW of Lhasa probable Neocomian fluviatile clastics are overlain by Lower Cretaceous marine carbonate buildup and lagoonal facies. Tertiary successions are almost entirely continental and record fluvio-lacustrine deposition in a number of basins which are thought to have originated as thrust-related features during major crustal shortening of the Tibetan Plateau in the Palaeogene and Neogene.