The Liuqu Conglomerate, Southern Tibet: Paleoclimate and Paleoelevation

The post-India-Asia collision paleoelevation history of southern Tibet remains enigmatic. Isotopic results from the Everest region suggest that this area attained modern elevations by ca. 18 Ma; however, records of warm, productive lakes within the India-Asia suture zone to the north suggest low elevation during Oligo-Miocene time. Here, we use paleoprecipitation and paleoweathering estimates from the early Miocene Liuqu Conglomerate, located within the central India-Asia suture zone, to constrain the paleoelevation history of this region. The Liuqu Conglomerate was deposited in alluvial fans and other coarse-grained fluvial deposystems. Sedimentological analysis shows the unit to be composed of mixed fluvial and sediment-gravity flow lithofacies assemblages, locally punctuated by mature, clay-rich paleosols. Analysis of rare pedogenic carbonates within paleosols yielded δ13C (VPDB) values between -12‰ and -8‰ indicating deposition in a well vegetated setting. Major element analyses of profiles across Liuqu paleosols allow calculation of paleoprecipitation and paleoweathering estimates. Major element analyses normalized to paleosol parent material show that Liuqu paleosols experienced an average collapse of ca. 50% and average cation losses of 58% (Na), 27% (Al), 47% (Si), and 42% (Ca). These values are within the same range as modern soils formed in humid, subtropical environments as well as paleosols within the Siwalik Group, formed at low elevation within Indo-Gangetic foreland basin. CALMAG index values suggest that Liuqu paleosols received a minimum of 1500 mm/yr mean annual precipitation. Together, these data suggest that the Liuqu Conglomerate formed in a humid, sub-tropical environment in stark contrast to the modern Tibetan climate. This suggests that at 20 Ma, the India-Asia suture zone was at low to moderate elevation and that some pathway existed that allowed moisture to penetrate deep into southern Tibet.