T69 Where Does the Wind Blow? Aeolian Systems in Time and Space II

Sunday, 4 November 2018
1:30 PM - 5:30 PM
Room 138-139

SOIL CARBONATE RECORD OF LATE MIOCENE AND PLIOCENE ENVIRONMENTAL CHANGE FROM THE JIAXIAN RED CLAY SECTION, NORTHERN LOESS PLATEAU, CHINA

Paper number: T69-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

The Chinese Loess Plateau (CLP) hosts some of the most continuous and high resolution terrestrial records of Neogene climate change. At the Jiaxian Red Clay section we collected paleosol carbonate nodules nearly continuously at 25 cm resolution through 60 m of section deposited during the late Miocene and Pliocene in order to investigate changes in vegetation, ecosystem productivity and atmospheric CO2. We measured the stable carbon isotope compositions of both calcite and organic matter occluded within the nodules. The δ13C values of the calcite and the occluded organic matter generally increase from 7.5 to 2.5 Ma (δ13C calcite from -8 to -2 ‰ and δ13C organic matter from -25 to -22 ‰). The difference between δ13C values of calcite and occluded organic matter (∆13C) also increases across this interval from 17 to 20 ‰. The δ13C values of occluded organic matter are consistent with nearly pure C3 vegetation at this location during the late Miocene and Pliocene, and the observed shift to less negative values upsection may indicate an increase in aridity throughout this time interval. The increase in ∆13C values is also consistent with a drying-induced decrease in soil respiration or an increase in atmospheric CO2 concentrations. In order to constrain changes in soil respiration rates, we also measured boron concentrations in the nodular calcite. B concentrations of the nodular calcite [B] measured thus far vary smoothly with maxima at 7 and 3.5 Ma and a minimum at 6 Ma. The increase in [B] from 6 to 3.5 Ma is consistent with a drying-induced decrease of soil respiration rates. We conclude that substantial coverage by C4 vegetation in northern CLP did not occur until the Pleistocene, despite the increase in aridity observed during the late Neogene.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-323343

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.