Late Miocene environmental change in Nepal and the northern Indian subcontinent: Stable isotopic evidence from paleosols

Abstract

Research Article| December 01, 1995 Late Miocene environmental change in Nepal and the northern Indian subcontinent: Stable isotopic evidence from paleosols Jay Quade; Jay Quade 1Desert Laboratory, Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar John M.L. Cater; John M.L. Cater 2PGG Limited, 47 Dunbar Drive, Woodley, Reading RG5 5HA, United Kingdom Search for other works by this author on: GSW Google Scholar Tank P. Ojha; Tank P. Ojha 3Petroleum Exploration Promotion Project, Department of Mines and Geology, Lainchaur Kathmandu, Nepal Search for other works by this author on: GSW Google Scholar Jon Adam; Jon Adam 1Desert Laboratory, Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar T. Mark Harrison T. Mark Harrison 4Department of Earth and Space Sciences, University of California at Los Angeles, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information Jay Quade 1Desert Laboratory, Department of Geosciences, University of Arizona, Tucson, Arizona 85721 John M.L. Cater 2PGG Limited, 47 Dunbar Drive, Woodley, Reading RG5 5HA, United Kingdom Tank P. Ojha 3Petroleum Exploration Promotion Project, Department of Mines and Geology, Lainchaur Kathmandu, Nepal Jon Adam 1Desert Laboratory, Department of Geosciences, University of Arizona, Tucson, Arizona 85721 T. Mark Harrison 4Department of Earth and Space Sciences, University of California at Los Angeles, Los Angeles, California 90024 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (12): 1381–1397. https://doi.org/10.1130/0016-7606(1995)107<1381:LMECIN>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Jay Quade, John M.L. Cater, Tank P. Ojha, Jon Adam, T. Mark Harrison; Late Miocene environmental change in Nepal and the northern Indian subcontinent: Stable isotopic evidence from paleosols. GSA Bulletin 1995;; 107 (12): 1381–1397. doi: https://doi.org/10.1130/0016-7606(1995)107<1381:LMECIN>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Neogene sediments belonging to the Siwalik Group crop out in the Himalayan foothills along the length of southern Nepal. Carbon and oxygen isotopic analyses of Siwalik paleosols from four long Siwalik sections record major ecological changes over the past ∼11 m.y. The carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca. 7.0 Ma, marking the displacement of largely C3 vegetation, probably semi-deciduous forest, by C4 grasslands. By the beginning of the Pliocene, all the flood plains of major rivers in this region were dominated by monsoonal grasslands. The floral shift away from woody plants is also reflected by the decline and final disappearance of fossil leaves and the decrease in coal logs in the latest Miocene. A similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of Pakistan, and in terrigenous organic matter from the Bengal Fan, showing that the floral shift was probably continentwide. The latest Miocene also witnessed an average change of ∼4‰ in the oxygen isotopic composition of soil carbonate, as observed previously in Pakistan. The reasons for this are unclear; if not diagenetic, a major environmental change is indicated, perhaps related to that driving the carbon isotopic shift. Recently described pollen and leaf fossils from the Surai Khola section show that evergreen forest was gradually displaced by semi-deciduous and dry deciduous forest between 11 and 6 Ma. The gradual nature of this floral shift, which culminated in the rapid expansion of C4 grasses starting ∼7.0 m.y. ago, is difficult to explain by a decrease in atmospheric pCO2 alone (Cerling et al., 1993) but fits well with a gradual onset of monsoonal conditions in the late Miocene in the northern Indian subcontinent. Himalayan uplift, driving both monsoonal intensification and consumption of CO2 through weathering, may be the common cause behind major late Miocene environmental change globally. However, the decline of effective moisture associated with monsoon development has probably slowed, not increased, the rate of consumption of CO2 by chemical weathering of Himalayan sediments. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.