Abstract

The elevation history of the Tibetan Plateau promises insight into the mechanisms and dynamics that develop and sustain high topography over tens of millions of years. We present the first nearly continuous Cenozoic elevation history from two sedimentary basins on the southern Tibetan Plateau within the latest Cretaceous to Eocene Gangdese arc. Oxygen-isotope and Δ47 clumped-isotope compositions of nonmarine carbonates allow us to constrain carbonate formation temperature and reconstruct the paleoprecipitation record of the Eocene to Pliocene Oiyug Basin and Paleocene to Eocene Penbo Basin. We exploit the systematic decrease of surface temperature and meteoric water δ18O values with elevation to derive paleoelevation estimates for these basins. Minimally altered and unaltered pedogenic and lacustrine carbonates from the Oiyug Basin yield Δ47, CDES (relative to the carbon dioxide equilibrium scale [CDES]) values of 0.625‰ to 0.755‰, which correspond to temperatures of 1–30 °C using a Δ47 thermometer for low-temperature carbonates. Similarly, the Penbo Basin yielded Δ47, CDES values of 0.701‰ to 0.726‰, corresponding to temperatures of 6–12 °C. The apparent evidence for survival of primary clumped-isotope values in the face of substantial burial and heating is an important result for the field of carbonate clumped-isotope thermometry.

Our paleoelevation estimates for the Eocene to Pliocene Oiyug Basin (∼6.5–4.1 km) support previous evidence that high elevations were attained in southern Tibet by at least ca. 30 Ma. Stable-isotope results allow for the possibility of significant topographic subsidence during the Miocene as a result of regional extension. In the Penbo Basin, our paleoelevation estimates for the Paleocene to Eocene Nianbo Formation (4.4 +1.3/–1.7 km) and Eocene Pana Formation (4.1 +1.2/–1.6 km) extend the altitude record of the southern Tibetan Plateau to pre–India-Asia collision. These results support the “Lhasaplano” model of an Andean-type continental margin tectonic system.

The rise of the Himalayas and Tibet is often invoked to understand isotopic proxies for global chemical weathering in the Cenozoic and has constrained the debate on the nature of CO2–climate–weathering feedbacks. The nature of the Tibetan paleoelevations from pre- to postcollision, as presented here, indicates that high relief at low latitude prevailed on the Asian margin much earlier than previously thought. Thus, high topography alone at low latitude is not sufficient to account for the Cenozoic weathering proxy record.

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