Stable Isotopes of Biotic Fossils across Central Himalaya as Indicators of Paleoelevation and Paleoclimate

The initial of Neogene sedimentation is related to normal faults along the north-south trending grabens. The Gyirong Basin is sensitive to reveal elevation change in central Himalaya. Analyzing δ18Omwvalues and correcting catchment elevations for 39 surface water data along the Gyirong River and the Kali Gandaki, a new fitting equation is established. The Δ(δ18Omw) of modern surface waters match very well with previous curve for Rayleigh fractionation with initial T=295 K and relative humidity=80%. Stable isotopic values from modern meteoric water and ostracoda shells are analyzed based on local empirical dataset and the Rayleigh fractionation. In addition to the isotopic data, many pollen data are available to reveal paleoclimatic variation and paleoelevation reconstruction. Both of estimated data documented surface uplift to 6 km since 7.2 Ma and down to 5.3 km during 4.7-3.2 Ma in the central Himalaya, with the underestimate reduction of550-900 m. Three warm-humid transitions were observed during 7.2-4.7 Ma followed by cooling condition since 4 Ma. The overall uplift history of the Himalaya since 7.2 Ma, underwent an elevation loss phenomenon of the mountain area and an equilibrium position of the basin floor during 4.7-3.2 Ma, which might be as a result of E-W extension and intense weathering and erosion of regional drainage.