TY  - JOUR
A1  - Govin, Gwladys
A1  - Najman, Yani
A1  - Dupont-Nivet, Guillaume
A1  - Millar, Ian
A1  - van der Beek, Peter
A1  - Huyghe, Pascale
A1  - Mark, Chris
A1  - Vogeli, Natalie
T1  - The tectonics and paleo-drainage of the easternmost Himalaya (Arunachal Pradesh, India) recorded in the Siwalik rocks of the foreland basin
JF  - American Journal of Science
N2  - The Siwalik sedimentary rocks of the Himalayan foreland basin preserve a record of Himalayan orogenesis, paleo-drainage evolution, and erosion. This study focuses on the still poorly studied easternmost Himalaya Siwalik record located directly downstream of the Namche Barwa syntaxis. We use luminescence, palaeomagnetism, magnetostratigraphy, and apatite fission-track dating to constrain the depositional ages of three Siwalik sequences: the Sibo outcrop (Upper Siwalik sediments at ca. 200-800 ka), the Remi section (Middle and Upper Siwalik rocks at >0.8-<8.8 +/- 2.4 Ma), and the Siang section (Middle Siwalik rocks at <9.3 +/- 1.5 to <13.5 +/- 1.5 Ma). Cretaceous-Paleogene detrital zircon and apatite U-Pb ages, characteristic of the Transhimalayan Gangdese Batholiths that crop out northwest of the syntaxis, are present throughout the Sibo, Remi, and Siang successions, confirming the existence of a Yarlung-Brahmaputra connection since at least the Late Miocene. A ca. 500 Ma zircon population increases up section, most strikingly sometime between 3.6 to 6.6 Ma, at the expense of Transhimalayan grains. We consider the ca. 500 Ma population to be derived from the Tethyan or Greater Himalaya, and we interpret the up-section increase to reflect progressive exhumation of the Namche Barwa syntaxis. Early Cretaceous zircon and apatite U-Pb ages are rare in the Sibo, Remi, and Siang successions, but abundant in modern Siang River sediments. Zircons of this age range are characteristic of the Transhimalayan Bomi-Chayu batholiths, which crop out east of the syntaxis and are eroded by the Parlung River, a modern tributary of the Siang River. We interpret the difference in relative abundance of Early Cretaceous zircons between the modern and ancient sediments to reflect capture of the Parlung by the Siang after 800 ka.
KW  - Himalaya
KW  - Siwaliks
KW  - Namche Barwa syntaxis
KW  - Brahmaputra River
KW  - Parlung River
KW  - detrital geochronology and thermochronology
Y1  - 2018
U6  - https://doi.org/10.2475/07.2018.02
SN  - 0002-9599
SN  - 1945-452X
VL  - 318
IS  - 7
SP  - 764
EP  - 798
PB  - Kline Geology Laboratory, Yale University
CY  - New Haven
ER  - 
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  -