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Late Miocene Uplift of the Tian Shan and Altai and
Reorganization of Central Asia Climate

Jeremy K. Caves*, Earth System Science, Stanford University, Stanford, California 94305, USA; Bolat U. Bayshashov, Institute of
Zoology, Academy of Sciences, Almaty 050060, Kazakhstan; Aizhan Zhamangara, L.N. Gumilyov Eurasian National University,
Astana 01000, Kazakhstan; Andrea J. Ritch, Daniel E. Ibarra, Earth System Science, Stanford University, Stanford, California
94305, USA; Derek J. Sjostrom, Geology Program, Rocky Mountain College, Billings, Montana 59102, USA; Hari T. Mix,
Environmental Studies and Sciences, Santa Clara University, Santa Clara, California 95053, USA; Matthew J. Winnick, Geological
Sciences, Stanford University, Stanford, California 94305, USA; and C. Page Chamberlain, Earth System Science, Stanford
University, Stanford, California 94305, USA

ABSTRACT China, and increasing the incidence of the precipitation to the east (Fig. 2B) (Baldwin
lee cyclones that deposit dust on the Loess and Vecchi, 2016).
The timing of high surface topography Plateau. We conclude that paleoclimatic
and the corresponding climatic impacts of changes in Central Asia in the Neogene Unfortunately, there is little paleoclimatic
the many high ranges north of the Tibetan are more tightly controlled by the interac- data that unequivocally indicate when the
Plateau, such as the Altai and Tian Shan, tion of the mid-latitude westerlies with the surface topography of these ranges became
remain poorly constrained. Most Neogene bounding ranges of northern Central Asia sufficiently prominent to impact climate
reconstructions of Central Asia climate than by changes in the height or extent of in Asia. Basin analysis and sedimentologi-
come from interior China, where the the Tibetan Plateau. cal data indicate that residual topography
influences of Altai and Tian Shan uplift has continuously separated many of the
are difficult to deconvolve from effects INTRODUCTION inward-draining basins in Central Asia
due to Tibetan Plateau uplift and changes since the Mesozoic (Carroll et al., 2010).
in global climate. We present a new pedo- Research on tectonic-climatic coupling Thermochronological and sedimentologi-
genic carbonate oxygen and carbon iso- in Asia has focused primarily on the cal studies demonstrate that reactivation
tope record from terrestrial Neogene sedi- importance of the Tibetan Plateau in of Paleozoic structures in the Tian Shan
ments of the Zaysan Basin in eastern strengthening monsoonal circulation and and Altai began in the late Paleogene and
Kazakhstan, which lies upwind of the in aridifying Central Asia (Zhisheng et al., accelerated and/or propagated northward
Altai and Tian Shan, in contrast to the 2001; Zhang et al., 2007). However, recent by the late Miocene (Charreau et al., 2009;
numerous paleoclimate records from inte- work places Plateau uplift in the De Grave et al., 2007). However, most
rior China. The δ18O values of pedogenic Paleogene (Rowley and Currie, 2006), paleoclimatic records in Asia come from
carbonate exhibit a robust 4‰ decrease in challenging the mechanisms that couple the arid expanses of interior China, where
the late Neogene—a trend that sharply Plateau orography with increasing Central the competing influences of uplift,
contrasts with nearly all downwind Asian aridity in the Neogene (Molnar et Paratethys retreat, and global climate are
records of δ18O from Central Asia. We al., 2010; Caves et al., 2016). In contrast, difficult to deconvolve (Sun et al., 2013;
attribute this decrease to the establishment many of the high ranges north of the Tang et al., 2011; Molnar et al., 2010).
of the modern seasonal precipitation Plateau—including the Tian Shan and General circulation models (GCMs) con-
regime whereby Kazakhstan receives the Altai—appear to have uplifted more figured with paleo-boundary conditions
majority of its moisture in the spring and recently (Charreau et al., 2009; De Grave also produce equivocal results because
fall, which lowers the δ18O of pedogenic et al., 2007), suggesting that they may play their relatively low resolution hinders
carbonates. The dominance of spring and a role in the Neogene paleoclimatic his- proper treatment of Tian Shan and Altai
fall precipitation in Kazakhstan results tory of Central Asia (Fig. 1). Today, these uplift. Therefore, most work has focused
from the interaction of the mid-latitude jet ranges cast substantial rain shadows, with on Tibetan Plateau uplift or westward
with the high topography of the Altai and substantially more precipitation on their retreat of the Paratethys (Zhisheng et al.,
Tian Shan during its movement northward windward flanks than in the lee deserts of 2001; Zhang et al., 2007).
in spring and southward in fall. The late the Gobi and Taklamakan (Fig. 2A).
Miocene interaction of the jet with these Further, these ranges demarcate a stark To test when the Altai and Tian Shan
actively uplifting northern Central Asia precipitation seasonality boundary, with became sufficiently prominent to impact
ranges reorganized Central Asia climate, dominantly spring and fall precipitation to climate, we collected pedogenic and lacus-
establishing starkly different seasonal pre- the west and primarily summertime trine carbonates for isotopic analysis from
cipitation regimes, further drying interior the Zaysan Basin in Kazakhstan, a long-
lived basin that lies windward of the Altai

GSA Today, v. 27, no. 2, doi: 10.1130/GSATG305A.1.
*Corresponding author: jeremy.caves@gmail.com; now at Earth Surface Dynamics, ETH Zürich, 8092 Zürich, Switzerland.

20 GSA Today | February 2017