TY - JOUR A1 - Grujic, Djordje A1 - Govin, Gwladys A1 - Barrier, Laurie A1 - Bookhagen, Bodo A1 - Coutand, Isabelle A1 - Cowan, Beth A1 - Hren, Michael T. A1 - Najman, Yani T1 - Formation of a Rain Shadow BT - O and H Stable Isotope Records in Authigenic Clays From the Siwalik Group in Eastern Bhutan JF - Geochemistry, geophysics, geosystems N2 - We measure the oxygen and hydrogen stable isotope composition of authigenic clays from Himalayan foreland sediments (Siwalik Group), and from present day small stream waters in eastern Bhutan to explore the impact of uplift of the Shillong Plateau on rain shadow formation over the Himalayan foothills. Stable isotope data from authigenic clay minerals (<2 μm) suggest the presence of three paleoclimatic periods during deposition of the Siwalik Group, between ∼7 and ∼1 Ma. The mean δ18O value in paleometeoric waters, which were in equilibrium with clay minerals, is ∼2.5‰ lower than in modern meteoric and stream waters at the elevation of the foreland basin. We discuss the factors that could have changed the isotopic composition of water over time and we conclude that (a) the most likely and significant cause for the increase in meteoric water δ18O values over time is the “amount effect,” specifically, a decrease in mean annual precipitation. (b) The change in mean annual precipitation over the foreland basin and foothills of the Himalaya is the result of orographic effect caused by the Shillong Plateau's uplift. The critical elevation of the Shillong Plateau required to induce significant orographic precipitation was attained after ∼1.2 Ma. (c) By applying scale analysis, we estimate that the mean annual precipitation over the foreland basin of the eastern Bhutan Himalayas has decreased by a factor of 1.7–2.5 over the last 1–3 million years. KW - authigenic clay KW - stable isotope KW - orographic precipitation KW - Siwaliks KW - Himalaya KW - foreland basin Y1 - 2018 U6 - https://doi.org/10.1029/2017GC007254 SN - 1525-2027 VL - 19 IS - 9 SP - 3430 EP - 3447 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Bernhardt, Anne A1 - Stright, Lisa A1 - Lowe, Donald R. T1 - Channelized debris-flow deposits and their impact on turbidity currents: The Puchkirchen axial channel belt in the Austrian Molasse Basin JF - Sedimentology : the journal of the International Association of Sedimentologists N2 - Deposits of submarine debris flows can build up substantial topography on the sea floor. The resulting sea floor morphology can strongly influence the pathways of and deposition from subsequent turbidity currents. Map views of sea floor morphology are available for parts of the modern sea floor and from high-resolution seismic-reflection data. However, these data sets usually lack lithological information. In contrast, outcrops provide cross-sectional and lateral stratigraphic details of deep-water strata with superb lithological control but provide little information on sea floor morphology. Here, a methodology is presented that extracts fundamental lithological information from sediment core and well logs with a novel calibration between core, well-logs and seismic attributes within a large submarine axial channel belt in the Tertiary Molasse foreland basin, Austria. This channel belt was the course of multiple debris-flow and turbidity current events, and the fill consists of interbedded layers deposited by both of these processes. Using the core-well-seismic calibration, three-dimensional lithofacies proportion volumes were created. These volumes enable the interpretation of the three-dimensional distribution of the important lithofacies and thus the investigation of sea floor morphology produced by debris-flow events and its impact on succeeding turbidite deposition. These results show that the distribution of debris-flow deposits follows a relatively regular pattern of levees and lobes. When subsequent high-density turbidity currents encountered this mounded debris-flow topography, they slowed and deposited a portion of their sandy high-density loads just upstream of morphological highs. Understanding the depositional patterns of debris flows is key to understanding and predicting the location and character of associated sandstone accumulations. This detailed model of the filling style and the resulting stratigraphic architecture of a debris-flow dominated deep-marine depositional system can be used as an analogue for similar modern and ancient systems. KW - Basin axial submarine channel KW - debris-flow topography KW - deep-marine sedimentary processes KW - foreland basin KW - lithofacies proportion modeling KW - Molasse Basin KW - multi-attribute KW - multi-scale (MA-MS) proportion calibration KW - sea floor morphology KW - turbidites Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-3091.2012.01334.x SN - 0037-0746 VL - 59 IS - 7 SP - 2042 EP - 2070 PB - Wiley-Blackwell CY - Hoboken ER -