Formation of a Rain Shadow
- 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 HimalayaWe 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.…
Author details: | Djordje GrujicORCiD, Gwladys GovinORCiD, Laurie BarrierORCiD, Bodo BookhagenORCiDGND, Isabelle CoutandORCiD, Beth Cowan, Michael T. Hren, Yani NajmanORCiD |
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DOI: | https://doi.org/10.1029/2017GC007254 |
ISSN: | 1525-2027 |
Title of parent work (English): | Geochemistry, geophysics, geosystems |
Subtitle (English): | O and H Stable Isotope Records in Authigenic Clays From the Siwalik Group in Eastern Bhutan |
Publisher: | American Geophysical Union |
Place of publishing: | Washington |
Publication type: | Article |
Language: | English |
Date of first publication: | 2018/05/25 |
Publication year: | 2018 |
Release date: | 2021/10/06 |
Tag: | Himalaya; Siwaliks; authigenic clay; foreland basin; orographic precipitation; stable isotope |
Volume: | 19 |
Issue: | 9 |
Number of pages: | 18 |
First page: | 3430 |
Last Page: | 3447 |
Funding institution: | France-Stanford Foundation; Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada [RGPIN 371671, RGPIN 04297]; National Geographic SocietyNational Geographic Society [83118-07]; Fondation Herbette UNIL; Swiss National Science FoundationSwiss National Science Foundation (SNSF); Shell SELF Student Research Project at Dalhousie University |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Umweltwissenschaften und Geographie |
DDC classification: | 5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften |
Peer review: | Referiert |
Publishing method: | Open Access / Green Open-Access |