The structure and rate of late Miocene expansion of C4 plants: Evidence from lateral variation in stable isotopes in paleosols of the Siwalik Group, northern Pakistan

Abstract

Research Article| November 01, 2007 The structure and rate of late Miocene expansion of C4 plants: Evidence from lateral variation in stable isotopes in paleosols of the Siwalik Group, northern Pakistan Anna K. Behrensmeyer; Anna K. Behrensmeyer 1Department of Paleobiology, MRC 121, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, Washington, DC 20013–7012, USA Search for other works by this author on: GSW Google Scholar Jay Quade; Jay Quade 2Dept. of Geosciences and the Desert Laboratory, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Thure E. Cerling; Thure E. Cerling 3Dept. of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA Search for other works by this author on: GSW Google Scholar John Kappelman; John Kappelman 4The University of Texas at Austin, Department of Anthropology, University Station C3200, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Imran A. Khan; Imran A. Khan 5Deputy Director General, Geological Survey of Pakistan, Jauhar Town, Phase–II, Lahore, Pakistan Search for other works by this author on: GSW Google Scholar Peter Copeland; Peter Copeland 6Department of Geosciences, University of Houston, Houston, Texas 77204, USA Search for other works by this author on: GSW Google Scholar Lois Roe; Lois Roe 7907 Eton Way, Neptune, New Jersey 07753, USA Search for other works by this author on: GSW Google Scholar Jason Hicks; Jason Hicks 8Denver Museum of Nature and Science, 2001 Colorado Blvd., Denver, Colorado 80205, USA Search for other works by this author on: GSW Google Scholar Phoebe Stubblefield; Phoebe Stubblefield 9Forensic Science Department, Babcock Hall, Room 208, University of North Dakota, Grand Forks, North Dakota 58202, USA Search for other works by this author on: GSW Google Scholar Brian J. Willis; Brian J. Willis 10Shallow Marine Stratigraphy, Chevron Energy Technology Company, 1500 Louisiana St., Houston, Texas 77002, USA Search for other works by this author on: GSW Google Scholar Claudio Latorre Claudio Latorre 11CASEB-Departamento de Ecología, Pontifica Universidad Católica de Chile, Santiago 114-D and Institute of Ecology & Biodiversity, Las Palmera 3425, Santiago, Chile Search for other works by this author on: GSW Google Scholar Author and Article Information Anna K. Behrensmeyer 1Department of Paleobiology, MRC 121, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, Washington, DC 20013–7012, USA Jay Quade 2Dept. of Geosciences and the Desert Laboratory, University of Arizona, Tucson, Arizona 85721, USA Thure E. Cerling 3Dept. of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA John Kappelman 4The University of Texas at Austin, Department of Anthropology, University Station C3200, Austin, Texas 78712, USA Imran A. Khan 5Deputy Director General, Geological Survey of Pakistan, Jauhar Town, Phase–II, Lahore, Pakistan Peter Copeland 6Department of Geosciences, University of Houston, Houston, Texas 77204, USA Lois Roe 7907 Eton Way, Neptune, New Jersey 07753, USA Jason Hicks 8Denver Museum of Nature and Science, 2001 Colorado Blvd., Denver, Colorado 80205, USA Phoebe Stubblefield 9Forensic Science Department, Babcock Hall, Room 208, University of North Dakota, Grand Forks, North Dakota 58202, USA Brian J. Willis 10Shallow Marine Stratigraphy, Chevron Energy Technology Company, 1500 Louisiana St., Houston, Texas 77002, USA Claudio Latorre 11CASEB-Departamento de Ecología, Pontifica Universidad Católica de Chile, Santiago 114-D and Institute of Ecology & Biodiversity, Las Palmera 3425, Santiago, Chile Publisher: Geological Society of America Received: 27 Jun 2006 Revision Received: 09 Jan 2007 Accepted: 31 Jan 2007 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 The Geological Society of America, Inc. GSA Bulletin (2007) 119 (11-12): 1486–1505. https://doi.org/10.1130/B26064.1 Article history Received: 27 Jun 2006 Revision Received: 09 Jan 2007 Accepted: 31 Jan 2007 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Anna K. Behrensmeyer, Jay Quade, Thure E. Cerling, John Kappelman, Imran A. Khan, Peter Copeland, Lois Roe, Jason Hicks, Phoebe Stubblefield, Brian J. Willis, Claudio Latorre; The structure and rate of late Miocene expansion of C4 plants: Evidence from lateral variation in stable isotopes in paleosols of the Siwalik Group, northern Pakistan. GSA Bulletin 2007;; 119 (11-12): 1486–1505. doi: https://doi.org/10.1130/B26064.1 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 This study uses stable isotope variation within individual Mio-Pliocene paleosols to investigate subkilometer-scale phytogeography of late Miocene vegetation change in southeast Asia between ca. 8.1 and 5 Ma, a time interval that coincides with dramatic global vegetation change. We examine trends through time in the distribution of low-latitude grasses (C4 plants) and forest (C3 plants) on Indo-Gangetic floodplains using carbon (δ13C) and oxygen isotopic (δ18O) values in buried soil carbonates in Siwalik Series sediments exposed in the Rohtas Anticline, north-central Pakistan. Revised, high-resolution magnetostratigraphy and a new 40Ar/39Ar date provide improved age control for the 2020 m Rohtas section. Carbon isotope results capture lateral variability of C3 versus C4 plants at five stratigraphic levels, R11 (8.0 Ma), R15 (6.74–6.78 Ma), R23 (5.78 Ma), R29 (4.8–4.9 Ma), and upper boundary tuff (UBT; 2.4 Ma), using detailed sampling of paleosols traceable laterally over hundreds of meters. Paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fluvial sediments: channel fill, crevassesplay, and floodplain environments. δ13C results show that near the beginning (8.0 Ma) and after (4.0 Ma) the period of major ecological change, vegetation was homogeneously C3 or C4, respectively, regardless of paleo-landscape position. In the intervening period, there is a wide range of values overall, with C4 grasses first invading the drier portions of the system (floodplain surfaces) and C3 plants persisting in moister settings, such as topographically lower channel swales. Although abrupt on a geologic timescale, changes in abundance of C4 plants are modest (∼2% per 100,000 yr) compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the Quaternary. Earlier research documented a sharply defined C3 to C4 transition in Pakistan between 8.1 and 5.0 Ma, based on vertical sampling, but this higher-resolution study reveals a more gradual transition between 8.0 and 4.5 Ma in which C3 and C4 plants occupied different subenvironments of the Siwalik alluvial plain.δ18O values as well as δ13C values of soil carbonate increase up section at Rohtas, similar to isotope trends in other paleosol records from the region. Spatially, however, there is no correlation between δ13C and δ18O values at most stratigraphic levels. This implies that the changes in soil hydrology brought about by the shift from forest to grassland (i.e., an increase in average soil evaporation) did not produce the shift through time in δ18O values. We interpret the trend toward heavier soil carbonate δ18O values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 Ma. 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