Wind Erosion in the Qaidam Basin, Central Asia: Implications for Tectonics, Paleoclimate, and the Source of the Loess Plateau
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2011 GSA Annual Meeting & Exposition Call for Papers, p. 15 VOL. 21, NO. 4/5 A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA APRIL/MAY 2011 Wind erosion in the Qaidam basin, central Asia: Implications for tectonics, paleoclimate, and the source of the Loess Plateau Inside: L Call for Committee Service, p. 50 L Special GSA Foundation Update, p. 54 L Position Statement Draft: Geoheritage, p. 56 VOLUME 21, NUMBER 4/5 APRIL/MAY 2011 SCIENCE ARTICLE GSA TODAY (ISSN 1052-5173 USPS 0456-530) prints news 4 Wind erosion in the Qaidam basin, and information for more than 23,000 GSA member read- ers and subscribing libraries, with 11 monthly issues (April/ central Asia: Implications for tectonics, May is a combined issue). GSA TODAY is published by The paleoclimate, and the source of the Geological Society of America® Inc. (GSA) with offices at 3300 Penrose Place, Boulder, Colorado, USA, and a mail- Loess Plateau ing address of P.O. Box 9140, Boulder, CO 80301-9140, USA. Paul Kapp, Jon D. Pelletier, Alexander GSA provides this and other forums for the presentation Rohrmann, Richard Heermance, of diverse opinions and positions by scientists worldwide, regardless of race, citizenship, gender, sexual orientation, Joellen Russell, and Lin Ding religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Cover: Field of wind-sculpted yardangs in the north- © 2011 The Geological Society of America Inc. All rights western Qaidam basin. Photo by Paul Kapp. See “Wind reserved. Copyright not claimed on content prepared wholly erosion in the Qaidam basin, central Asia: Implications by U.S. government employees within the scope of their for tectonics, paleoclimate, and the source of the Loess employment. 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Housing 49 GeoCorpsTM America Fall/Winter 2011–2012 50 Call for GSA Committee Service 52 Call for Nominations: 2011 GSA Division Awards 54 GSA Foundation Update 56 Position Statement Draft: Geoheritage 59 About People 60 Classified Advertising Wind erosion in the Qaidam basin, central Asia: Implications for tectonics, paleoclimate, and the source of the Loess Plateau Paul Kapp*, Jon D. Pelletier, Alexander Rohrmann**, Dept. of pans) carved in cohesive material by strong, unidirectional Geosciences, University of Arizona, 1040 E 4th St., Tucson, winds and saltating particles carried by the wind, with spacing Arizona, 85721, USA; Richard Heermance, Dept. of Geological and relief on the order of hundreds of meters and tens of me- Sciences, California State University, Northridge, California 91330- ters (locally up to ~50 m), respectively. In most places, wind- 8266; Joellen Russell, Dept. of Geosciences, University of carved substrata consist of relatively friable, Plio-Quaternary Arizona, 1040 E 4th St., Tucson, Arizona, 85721, USA; and Lin lacustrine deposits. Ding, Institute of Tibetan Plateau Research, Chinese Academy of Yardang ridges form parallel to and taper in the direction of Sciences, Beijing 100085, People’s Republic of China prevailing winds. The geometries of yardangs, and dune forms in ergs where present, reveal the prevailing wind pattern dur- ing their development (Fig. 2A). Northwesterly winds entered ABSTRACT the Qaidam basin through topographic lows in the Altyn Tagh Liquid water and ice are the dominant agents of erosion and Range along its northwestern margin (Fig. 2A; Halimov and sediment transport in most actively growing mountain belts. An Fezer, 1989). Moving from west to east in the basin, the wind exception is in the western Qaidam basin along the northeast- directions become more westerly, paralleling the trends of the ern margin of the Tibetan Plateau, where wind and wind- >5000-m-high basin-bounding mountain ranges (Fig. 2A). Locat- blown sand have sculpted enormous yardang fields in actively ed downwind of the Qaidam basin is one of the most volumi- folding sedimentary strata. Here, we present observations sug- nous and best-exposed accumulations of Neogene-Quaternary gesting that since the late Pliocene, wind episodically (during loess on Earth—the Loess Plateau (e.g., Kukla, 1987; Porter, glacial and stadial periods) removed strata from the western 2007) (Fig. 1). The alternating loess/paleosol stratigraphy of the Qaidam basin at high rates (>0.12–1.1 mm/yr) and may have Loess Plateau provides one of the richest terrestrial records of accelerated rates of tectonic folding. Severe wind erosion likely climate change since the Pliocene. Loess accumulation oc- occurred during glacial and stadial periods when central Asia curred primarily during glacial and stadial periods, when cli- was drier and the main axis of the polar jet stream was located matic conditions were drier in central Asia because of a ~10° closer to the equator (over the Qaidam basin), as pre- weakened East Asian summer monsoon (e.g., An, 2000; Porter, dicted by global climate models. Reconstructed wind patterns, 2007). Knowledge of the source regions for the loess, and how the estimated volume of Qaidam basin material removed by they have varied through time, is critical for assessing numeri- wind, and numerical models of dust transport all support the cal models of atmospheric circulation during the Pliocene and hypothesis that the Qaidam basin was a major source of dust Quaternary and the provenance of the nutrient-rich dust trans- to the Loess Plateau. ported by high-level westerly winds into the Pacific Ocean, which may have increased marine productivity and contributed INTRODUCTION to the drawdown of atmospheric carbon dioxide during glacial The 700-km-long, up to 300-km-wide Qaidam basin (Figs. 1 periods (Rea, 1994; Bopp et al., 2003; Mahowald et al., 2006). and 2A) encompasses one of the highest (~2800 m elevation) In addition, Chinese loess input into the ocean has strongly and driest (<50 mm/yr precipitation in its western part) deserts altered seawater chemistry (e.g., Jacobson, 2004). Although it is on Earth, and it is actively shortening NE-SW in response to the widely argued that the bulk of Loess Plateau deposits was ongoing collision between India and Asia (Tapponnier et al., sourced from the Gobi and adjacent sand deserts (e.g., Sun, 2001). A common inference, likely because of its low relief 2002; Sun et al., 2008), observations of spatially extensive fields (<300 m), intermontane and internally drained setting, and of yardangs and the prevailing northwesterly to westerly wind thick accumulations of late Cenozoic sediment, is that the Qai- pattern in the Qaidam basin suggest that its importance as a dam basin is actively filling with sediment. However, roughly Loess Plateau source may presently be underappreciated. one-third of the modern Qaidam basin floor (~3.88 × 104 km2) actually exposes folded sedimentary strata (Fig. 2A) exhumed HISTORY OF QAIDAM WIND EROSION since the Pliocene due to uplift and wind erosion. Severe wind The wind erosion that produced the modern Qaidam yar- erosion is demonstrated in the western Qaidam basin by the dangs must be younger than late Pleistocene because lacustrine presence of extensive fields of mega-yardangs (Figs. 2A–2C strata of this age are widely exposed in the wind-eroded part and 3A) (Goudie, 2007), which are ridges (and parallel troughs/ of the basin (Pan et al., 2004). However, it does not appear that GSA Today, v.