Travertine deposits (i.e. hydrothermal spring carbonates) are common on the Tibetan Plateau but remain severely under-researched. A multidisciplinary approach, including sedimentological, petrographic and geochronological investigations, was carried out at two travertine sites Chusang and Tirthapuri in central-southern and southwestern Tibet respectively in order to gain insights into the depositional environments and processes responsible for travertine precipitation and the paleoclimatic and geoarcheological implications of these travertine deposits from Tibet. Both Chusang and Tirthapuri sites are characterized by vast ancient travertine deposits in the form of travertine mounds and/or cones as well as laterally extensive travertine sheets and platforms. Furthermore, the travertine deposits are often intercalated or mixed with terrigenous sediments, for example colluvial sediments (mainly debris-flow facies) sourced from the adjacent periglacial hillslopes at Chusang and fluvial sediments on river floodplains at Tirthapuri, developing travertine-colluvium succession and travertine platforms capping individual fluvial terraces, respectively. Detailed petrographic analyses reveal that the travertine deposits from both sites are composed of various lithofacies, including a laminated/layered travertine lithofacies dominated by crystalline dendritic or aragonitic crystals and a granular lithofacies (e.g. lime-mudstone or intraclastic travertine lithofacies). These distinct lithofacies and associated fabrics in travertines reflect specific depositional environments (e.g. spring mounds/cones, slopes and distal flats or pools) and sedimentary processes (mainly abiotic precipitation but often biologically-influenced). The lamination or layering is subjected to cyclic (likely seasonal) changes in climate and spring flow as well as organism growth during summer, thereby enabling high-resolution climatic signals to be stored in travertine. Early diagenetic alteration in the form of extensive recrystallization and formation of various pore cements is common in the investigated travertine deposits, resulting in great challenges to the proper interpretation of fabrics and routine 230Th/U dating. The 230Th/U dating with an optimized protocol, combined with OSL and/or 14C dating suggests that extensive travertine deposition was concomitant with colluvial sedimentation (in the case of Chusang) or fluvial incision (in the case of Tirthapuri) and these processes are principally linked to phases of intensified Indian summer monsoon, such as the last Interglacial and the Early Holocene. Combined chronometric dating demonstrates that the human hand and footprints that are encased in the Chusang travertine have a minimum age of ca. 7.4 ka (230Th/U dating) with a maximum age of 8.212.7 ka (14C assays and OSL dating), establishing the Chusang site as the oldest securely dated Paleolithic site in the interior of the Tibetan Plateau. Archeological data and travel cost modelling also suggest that the Chusang site was part of an annual, permanent, pre-agricultural occupation of the central Tibetan Plateau in the Early Holocene under a favorable climatic condition due to enhanced Indian summer monsoon. At Tirthapuri archeological surface artifacts have been found on the investigated fluvial terraces and dating of these terraces and associated travertine platforms provides a first-order chronological framework of landscape dynamics into which the archeological record can be linked.
It is concluded that the widespread travertine deposits from the Tibetan Plateau warrant further sedimentological and archeological investigations, because (i) several of these travertine deposits are potentially valuable archives for past monsoonal climate change and monsoon-driven landscape evolution and (ii) in a cold-arid landscape, hot spring sites probably attracted people throughout prehistory and archaeological finds are thus likely associated with these springs and the respective mineral precipitates.