Palynological evidence sheds new light on the age of the Liuqu Conglomerates in Tibet and its geological significance

Abstract

The Liuqu Conglomerates consist of a suit of terrestrial molasse deposits formed in a foreland basin of the Himalaya-Tibet orogenic belt before the collision of India and Eurasia. These deposits record considerable geological information regarding the late tectonic evolution of the Neotethyan ocean. The palynological study of interlayers of mudstone and mud-sandstones indicates an Oligocene age. The palynological assemblage consists mainly of deciduous broad-leaved angiosperms, with some coniferous gymnosperms and evergreen broad-leaved angiosperms. The deposits reflect a broad-leaved deciduous forest or mixed with conifer-broad-leaved forest ecotypes, showing a warm-temperate or temperate zone climatic environment. This work provides significant new information about the tectonic evolution, paleogeography, and paleoenvironment of southern Tibet during the Cenozoic. Southern Tibet, Yalung Zangpo suture zone, Liuqu Conglomerates, palynological assemblage, Oligocene Citation: Wei L J, Liu X H, Yan F H, et al. Palynological evidence sheds new light on the age of the Liuqu Conglomerates in Tibet and its geological significance. Sci China Earth Sci, 2011, 54: 901 -911,

The Liuqu Conglomerate, southern Tibet: Early Miocene basin development related to deformation within the Great Counter Thrust system

“…These intervals bear striking visual similarity to paleosols in the Siwalik Group of India and Pakistan (Tandon and Narayan, 1981;Quade and Cerling, 1995;Brozović and Burbank, 2000;Ojha et al, 2000), which were deposited in a warm, subhumid environment. This is supported by the presence of root casts and by paleobotanic (Tao, 1988;Fang et al, 2006) and palynologic (Wei et al, 2011) evidence. The abundant slickensided surfaces are interpreted as pedogenic slickensides, formed by physical alignment of clays during swelling and shrinking of soil by wetting and drying (Gray and Nickelsen, 1989).…”

“…Palynological assemblages reported by Wei et al (2011) led those authors to suggest that the Liuqu Conglomerate is Oligocene in age. They described a diverse assemblage consisting mostly of temperate deciduous angiosperms with conifers and a few evergreen, broad-leafed angiosperms.…”

“…Other workers have found evidence of both Indian-and Asian-derived sediment, requiring the Liuqu Conglomerate to have been deposited after India-Asia collision . Analysis of plant fossils has produced age estimates of Cretaceous-Eocene (Tao, 1988;Fang et al, 2006), and an Oligocene age was assigned based on palynologic analysis (Wei et al, 2011). The absence of tuffaceous rocks in the Liuqu Conglomerate has contributed to the difficulty in applying radiometric dating; however, recent work points to an early Miocene age based on detrital zircon U-Pb and (U-Th)/He (G. analyses.…”

A tectonic model reconciling evidence for the collisions between India, Eurasia and intra-oceanic arcs of the central-eastern Tethys

“…Another recent palynological study (Wei et al, 2011), suggests that the Liuqu conglomerates were actually deposited during Oligocene time, above sea-level and within warm-temperate climates.…”

Provenance of the Upper Cretaceous to Lower Tertiary Sedimentary Relicts in the Renbu Mélange Zone, within the Indus-Yarlung Suture Zone

“…This suture zone is bounded by the Great Counter Thrust and the Zhongba-Gyantse thrust (Yin 2006) and is defined by ophiolitic rocks of late Jurassic to early Cretaceous age (Aitchison 2000;Malpas et al 2003;Miller et al 2003;DuboisCôté et al 2005;Wang et al 2006;Aitchison et al 2007). These ophiolitic rocks are associated with late Jurassic-early Cretaceous island-arc volcanic rocks (McDermid et al 2002;Aitchison et al 2007) and the controversial Liuqu Conglomerate Fang et al 2006;Wei et al 2011). The ophiolitic rocks are locally in thrust contact with a 10-to 50-km-wide mud-matrix turbidite mélange exposed in the hanging-wall Zhongba-Gyantse or Lhunze thrusts (Ding et al 2005;Yin 2006;Li et al 2010Li et al , 2011Dunkl.…”