Rights statement: An edited version of this paper was published by AGU. Copyright 2018 American Geophysical Union. Grujic, D., Govin, G., Barrier, L., Bookhagen, B., Coutand, I., Cowan, B., et al. (2018). Formation of a rain shadow: O and H stable isotope records in authigenic clays from the Siwalik Group in eastern Bhutan. Geochemistry, Geophysics, Geosystems, 19, 3430–3447. https://doi.org/10.1029/2017GC007254
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Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Formation of a Rain Shadow
T2 - O and H Stable Isotope Records in Authigenic Clays From the Siwalik Group in Eastern Bhutan
AU - Grujic, D.
AU - Govin, Gwladys
AU - Barrier, L.
AU - Bookhagen, B.
AU - Coutand, I.
AU - Cowan, B.
AU - Hren, M.T.
AU - Najman, Yani
N1 - An edited version of this paper was published by AGU. Copyright 2018 American Geophysical Union. Grujic, D., Govin, G., Barrier, L., Bookhagen, B., Coutand, I., Cowan, B., et al. (2018). Formation of a rain shadow: O and H stable isotope records in authigenic clays from the Siwalik Group in eastern Bhutan. Geochemistry, Geophysics, Geosystems, 19, 3430–3447. https://doi.org/10.1029/2017GC007254
PY - 2018/9
Y1 - 2018/9
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. ©2018. American Geophysical Union. All Rights Reserved.
AB - 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. ©2018. American Geophysical Union. All Rights Reserved.
KW - authigenic clay
KW - foreland basin
KW - Himalaya
KW - orographic precipitation
KW - Siwaliks
KW - stable isotope
KW - Isotopes
KW - Rain
KW - Authigenic clays
KW - Foreland basin
KW - Himalayas
KW - Orographic precipitation
KW - Stable isotopes
KW - Clay minerals
U2 - 10.1029/2017GC007254
DO - 10.1029/2017GC007254
M3 - Journal article
VL - 19
SP - 3430
EP - 3447
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
SN - 1525-2027
IS - 9
ER -