NOAA/WDS Paleoclimatology - Zhada Basin, SW Tibetan Plateau Miocene-Pleistocene Grain Size and Stable Isotope Data

Mechanisms controlling the long- and short-term variability of the Indian Summer Monsoon (ISM) and high-elevation environmental change have largely been examined using low-elevation or marine records with less emphasis on high-elevation non-marine records. We address this using a high-resolution, long-term record from upper Miocene-lower Pleistocene (~9.0-2.2 Ma) fluvio-lacustrine strata in the Zhada Basin, southwestern Tibetan Plateau. Long-term changes include the onset of lacustrine deposition, a decrease in mean grain size, and an increase in d18Ocarb and d13Ccarb values at ~6.0 Ma in response to basin closure following regional extension. This was followed by a return to palustrine/fluvial deposition, an increase in mean grain size, and a decrease in d18Ocarb and d13Ccarb values at ~3.5 Ma in response to tectonically driven long-term ISM weakening. Spectral analysis reveals that high-frequency variations in the d18Ocarb record are dominated by 100 and ~20 kyr cycles from ~6.0-2.2 Ma. Wavelet and spectral analysis of the most densely sampled interval (4.23-3.55 Ma), tuned to the record of daily insolation (21 June at 35N) confirms and highlights 100 and 20 kyr cycles. The tuned Pliocene d18Ocarb record is coherent with the record of Northern Hemisphere insolation at precession periods but not at obliquity or eccentricity periods. Additionally, the tuned d18Ocarb record is anticorrelated to the insolation record, indicating that stronger Northern Hemisphere insolation correlates with a stronger ISM. These results suggest that variations in daily insolation drove late Miocene-early Pleistocene high-frequency ISM variability and environmental changes in the high-elevation southwestern Tibetan Plateau.