Abstract
Abstract Carbonate clumped isotope thermometry has been applied to fossil mollusk shells from Tibet to reconstruct the paleoclimate and paleoelevation of the region. However, inferred paleoelevation and climatic conditions from this proxy are inconsistent with paleontological evidence. Here, we report new clumped isotope data from both modern and fossil (5–4 Ma) freshwater mollusk shells with the results of X-ray diffraction (XRD) analyses of fossil shells from the Himalayan-Tibetan Plateau. Although all of the fossil shells analyzed in this study appeared pristine based on visual inspection, XRD data reveal that more than half of these apparently “pristine” fossil shells contain trace amounts of calcite. Clumped isotope temperatures derived from the fossil shells display a large range of variation (>22 °C). Among the fossil shells analyzed, those containing traces of calcite have yielded temperatures that are on average ∼10 °C lower than those with no detectable calcite from the same strata. These observations suggest that clumped isotope alteration can occur in aragonite shells in low-temperature environments and even in shells with no visible signs of alteration that contain only traces of calcite. The temperatures derived from fossil shells with no detectable calcite are on average 4 °C higher than those derived from modern shells, indicating that southwest Tibet was warmer 4–5 Ma than today. After accounting for temperature change due to global cooling, the difference in clumped isotope temperatures between pristine fossil shells and modern shells suggests that the paleoelevation of the southwestern Tibetan Plateau in the Pliocene was similar to its present-day elevation.
Highlights
The uplift of the Himalayan-Tibetan Plateau is thought to have been a major driver of regional and global climate change during the Cenozoic (An et al, 2001; Ruddiman et al, 1997)
Clumped isotope analyses of modern snail shells from several lakes across the HimalayanTibetan plateau show that temperatures determined from the shells using the existing mollusk specific calibrations differ by ∼6 °C
Some of the temperatures calculated using the Eagle calibration exceed the observed and predicted maximum lake water temperature while those calculated using the Henkes calibration all fall within the variation range of lake surface water temperature, suggesting that the Henkes calibration may be more suitable for freshwater snail shells
Summary
The uplift of the Himalayan-Tibetan Plateau is thought to have been a major driver of regional and global climate change during the Cenozoic (An et al, 2001; Ruddiman et al, 1997). Deng et al (2011, 2012) argued that the Zanda Basin had reached high elevations similar to that of today and that local climate had become cold by the mid-Pliocene based primarily on occurrence in the basin of the most primitive wooly rhinoceroses (Coelodonta thibetana) and three-toed horses (Hipparion zandaense) that were adapted to living in cold climates above the tree line.
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