COVER Water exchange through the sea-land interface is a major component of the hydrologic cycle. This exchange, called submarine groundwater discharge (SGD), comprises fresh inland groundwater and recycled seawater. SGD is an important pathway as surface runoff for material transport to the marine environment. Owing to the importance of SGD for the marine geochemical cycling of elements, coastal aquifer systems can be regarded as subterranean estuaries. The photo cover shows the interaction between groundwater and ocean associated with SGD within a typical subterranean estuary. The schematic diagram shows that SGD is driven by terrestrial hydraulic gradients, density difference between seawater and inland fresh groundwater, and any number of oceanic processes such as wave pumping, tidal pumping, and thermal gradients. SGD is widespread and, in some areas, of greater marine ecological significance than surface runoff. In particular, terrestrially recharged water (or fresh inland groundwater), which is a component of SGD, may seriously affect the coastal ecological environment. Thus, it is important to carefully consider groundwater issues such as groundwater contamination, circulation, evolution, overexploitation, and seawater intrusion (see the special topic: Groundwater). Volume 58 Number 25 September 2013

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Abstracted/indexed in: Academic Search Alumni Edition EMBio Academic Search Complete Environmental Engineering Abstracts Academic Search Elite Environmental Sciences and Pollution Management Academic Search Premier Google Scholar ASFA 1: Biological Sciences and Living Resources Inspec ASFA 2: Ocean Technology, Policy and Non-Living Resources Mathematical Reviews Biological Abstracts MathSciNet Biological Sciences Meteorological and Geoastrophysical Abstracts BIOSIS Previews Pollution Abstracts CAB Abstracts Science Citation Index Chemical Abstracts SCOPUS Chemical and Earth Sciences Water Resources Abstracts Current Contents/Physical Zentralblatt MATH Current Mathematical Publications Zoological Record Digital Mathematics Registry CONTENTS Volume 58 Number 25 September 2013 CONTENTS

SPECIAL TOPIC: Groundwater

EDITORIAL 3043 A small but important step to enhance groundwater research in China LIN XueYu

REVIEWS 3044 Review of the uncertainty analysis of groundwater numerical simulation WU JiChun & ZENG XianKui

3053 Quantifying tidal contribution to submarine groundwater discharges: A review LI HaiLong & JIAO JiuJimmy

ARTICLES 3060 Delayed drainage of aquitard in response to sudden change in groundwater level in adjacent confined aquifer: Analytical and experimental studies ZHOU ZhiFang, GUO QiaoNa & DOU Zhi

3070 Spatial and temporal evolutions of groundwater arsenic approximately along the flow path in the Hetao basin, Inner Mongolia GUO HuaMing, ZHANG Yang, JIA YongFeng, ZHAO Kai & KIM Kangjoo

3080 Coseismic response of groundwater level in the Three Gorges well network and its relationship to aquifer parameters SHI ZheMing, WANG GuangCai, LIU ChengLong, MEI JianChang, WANG JinWei & FANG HuiNa

3088 Groundwater circulation relative to water quality and vegetation in an arid transitional zone linking oasis, desert and river HUANG TianMing, PANG ZhongHe, CHEN YaNing & KONG YanLong

3098 Suitability assessment of deep groundwater for drinking, irrigation and industrial purposes in Jiaozuo City, Henan Province, north China SHI JianSheng, MA Rong, LIU JiChao & ZHANG YiLong

ARTICLES Geochemistry 3111 Precise measurement of stable (δ88/86Sr) and radiogenic (87Sr/86Sr) strontium isotope ratios in geological standard reference materials using MC-ICP-MS MA JinLong, WEI GangJian, LIU Ying, REN ZhongYuan, XU YiGang & YANG YongHong

Geology 3119 Synchronous drying and cooling in central Asia during late Oligocene DONG XinXin, DING ZhongLi, YANG ShiLing, LUO Pan, WANG Xu & JI JunLiang

3125 Palaeoecological and palaeoenvironmental significance of some important spores and micro-algae in Quaternary deposits TANG LingYu, MAO LiMi, LÜ XinMiao, MA QingFeng, ZHOU ZhongZe, YANG ChunLei, KONG ZhaoChen & BATTEN David J

Geography 3140 The hydrological linkage of mountains and plains in the arid region of northwest China QIN Jia, DING YongJian & YANG GuoJing

3148 Mass change study on Arctic glacier Pedersenbreen, during 1936-1990-2009 AI SongTao, WANG ZeMin, TAN Zhi, E DongChen & YAN Ming

Atmospheric Science 3155 Extremely cold and persistent stratospheric Arctic vortex in the winter of 2010–2011 HU YongYun & XIA Yan

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FORUM Geography 3161 Societal response to challenges of global change and human sustainable development XU GuanHua, GE QuanSheng, GONG Peng, FANG XiuQi, CHENG BangBo, HE Bin, LUO Yong & XU Bing

Vol. 58 No. 25 September 5, 2013 (Published three times every month)

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Geology September 2013 Vol.58 No.25: 31193124 doi: 10.1007/s11434-013-5821-3

Synchronous drying and cooling in central Asia during late Oligocene

DONG XinXin1,2*, DING ZhongLi1, YANG ShiLing1, LUO Pan3, WANG Xu1 & JI JunLiang4

1 Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 2 University of Chinese Academy of Sciences, Beijing 100049, China; 3 Petroleum Geology Research and Laboratory Center, Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China; 4 Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, Wuhan 430074, China

Received December 31, 2012; accepted March 4, 2013; published online April 12, 2013

Aridification of central Asia during late Oligocene and Early Miocene has been documented by numerous eolian records from the North Pacific and central Asia. However, direct evidence of aridity from the interior of the arid zone is still rather scarce. To better reconstruct the climate history in central Asia during the late Oligocene, we have analyzed ostracod assemblages and gypsum content in the sediments from the lacustrine Jingou River section in the northern Tianshan Mountains. Our results show that the cold water species Candona cf. Neglecta and Pseudocandona albicans replaced the warm water species Ilyocypris bradyi and Ilyocypris sp. to become the dominant species at 23.8 Ma, indicating significant cooling in central Asia at that time. At the same time, a substantial increase in gypsum content indicates the intensification of central Asian drying. The synchronous cooling and drying approximately coincided with the Oi2b.1 and/or Mi1 events, implying a causal linkage between late Oligocene global cooling and central Asian aridity. central Asian aridification, cooling, ostracod, gypsum, Oligocene, Jingou River section

Citation: Dong X X, Ding Z L, Yang S L, et al. Synchronous drying and cooling in central Asia during late Oligocene. Chin Sci Bull, 2013, 58: 31193124, doi: 10.1007/s11434-013-5821-3

Central Asia is the largest inland arid region in the mid- Asian arid region, direct evidence from the arid region is latitudes on Earth. Eolian records in deep-sea sediments [1,2] particularly important. Such evidence is relatively scarce at and dust deposits from the periphery of arid regions [3,4] this point. have shown that central Asian aridity began to intensify Recently, a palynological record from the Jingou River from the late Oligocene to the early Miocene. Eolian depos- section in the Junggar Basin of the northern Tianshan its within central Asian arid regions [5] have implied that an Mountains [10] revealed that aridity began to intensify dur- arid pattern similar to that of today may have formed before ing the late Oligocene. This record provided direct evidence the late Oligocene. However, these interpretations based on of inland aridification, but multiple proxies need to be ana- eolian deposits can be regarded as only indirect evidence lyzed to better understand the history of climate change in because the processes of dust transport and sedimentation central Asia. The Jingou River section is composed of a have been affected by locally varying factors such as geo- sequence of nearly consecutive, green-colored lacustrine morphological conditions, the configuration of loess-desert sediments spanning the late Oligocene. Non-marine ostra- distribution, and wind trajectories [6–9]. Therefore, to un- cod assemblages have been considered good indicators of derstand the late Oligocene climate history of the central paleoenvironmental conditions, especially in lacustrine sediments, because they are sensitive to water temperature *Corresponding author (email: [email protected]) and chemistry [11,12]. In this paper, we have studied fossil,

© The Author(s) 2013. This article is published with open access at Springerlink.com csb.scichina.com www.springer.com/scp 3120 Dong X X, et al. Chin Sci Bull September (2013) Vol.58 No.25 non-marine ostracods and gypsum content in the section. sediment lithology is primarily gray-green mudstone in the We have then combined the ostracod assemblage and gyp- total 200 m of strata, the lower part (0−67 m) contains a sum content with the pollen record [10] to reconstruct the small amount of thin layers of plaster, the middle to the up- climate history during the late Oligocene and try to explore per part (67−181 m) contains gray-black shale, thin layers the causal linkage between central Asian aridity and global of gray-white marl and, rarely, yellowish-brown siltstone cooling. bands, and the top part (181–200 m) in the Anjihaihe for- mation is characterized by the alternation of gypsum and mudstone layers and no traversing-layer phenomena was 1 Geological setting observed. Magnetostratigraphic analysis has shown that the Anjihaihe Formation covered the interval from 28.0 to 23.3 The Jingou River section is located in the heart of the cen- Ma [10] (Figure 1). tral Asian arid region (Figure 1) and close to the sedimenta- tion center of Mesozoic to Neogene deposition on the north pediment of the Tianshan Mountains [13]. Thick Cenozoic 2 Materials and methods sediments were deformed into east-west fold-thrust belts that are made up of linear anticlines. The Jingou River All of the ostracod samples were collected from green la- formed a perpendicular incision through the center of the custrine mudstone in the Anjihaihe Formation. Ostracod Huoerguosi Anticline. The Jingou River section is exposed sampling was designed to produce a temporal resolution of on the southern limb of the anticline and consists of the An- 25 ka or less per sample. The timescale of our samples was jihaihe, Shawan, Taxihe, Dushanzi and Xiyu formations established by linear interpolation between magnetostrati- from the core to the south [14]. graphic age control points. A total of 200 samples in the The Anjihaihe Formation in the Jingou River section was Anjihaihe Formation were analyzed. selected for this study. The strata in this formation are The extraction of fossil ostracod valves followed the above the boundary of the thrust fault, underlying the peroxide method described by Zhai et al. [15]. We identi- Shawan Formation with a conformable contact [14]. While fied ostracods in the samples according to the taxonomy of

Figure 1 General information about the Jingou River section. (a) Location of the section; (b) photo of the Anjihaihe Formation; (c) lithology of the An- jihaihe Formation; (d) magnetostratigraphic age model of the Anjihaihe Formation [10]. Dong X X, et al. Chin Sci Bull September (2013) Vol.58 No.25 3121

Jiang et al. [16], Meisch [17] and Hou et al. [18]. Can- Zone 1 (28.0–26.4 Ma, 0–67 m). Ilyocypris bradyi, doniella albicans was identified as Pseudocandona albicans, Ilyocypris cornea and Ilyocypris sp. were the dominant spe- following Meisch [17]. Stratigraphically constrained cluster cies, while Cypris magnifica appeared piecemeal in this analysis (CONISS [19]) was used to divide the ostracod zone. Additionally, Hemicyprideis intercedens and Hemi- abundance diagram of the Anjihaihe formation into ostracod cyprideis rhenana were found at 59 m (−26.63 Ma). Fossil assemblage zones based on the number of each species of ostracod concentration was 31 valves per 100 grams on av- fossil ostracod. In addition, gypsum content was determined erage. Gypsum content fluctuated between 8.2% and 19.4%, using the rapid detection method [20] in the Anjihaihe for- with a mean value of 16.8% ± 2.6%. mation sample sequence. Zone 2 (26.4–23.8 Ma, 67–181 m). Ilyocypris bradyi, Ilyocypris cornea and Ilyocypris sp. were still the prevailing species in this zone. Six other species, i.e. Cypris magnifica, 3 Results Eucypris ignis, Eucypris notabilis, Eucypris profundis, Kas- sinina beliaevskyi and Heterocypris subsinuatus, appeared Of the 200 samples from the Anjihaihe Formation, only 98 occasionally. Fossil ostracod concentration was 78 valves samples contained fossil ostracods. A total of 6015 valves per 100 grams on average. Gypsum content varied between were picked from the 98 samples, and 16 species of ostra- 9.0% and 19.4%, with a mean value of 13.4% ± 2.1%. cods belonging to 11 genera were identified. These species Zone 3 (23.8–23.3 Ma, 181–200 m). Candona cf. ne- were Ilyocypris bradyi, Ilyocypris cornea, Ilyocypris sp., glecta, Candoniella marcida, Pseudocandona albicans, Hemicyprideis intercedens, Hemicyprideis rhenana, Cypris Cypria schichoensis, Cyprinotus tutunchous, Eucypris ignis magnifica, Eucypris ignis, Eucypris notabilis, Eucypris and Kassinina beliaevskyi prospered in this zone, while profundis, Kassinina beliaevskyi, Heterocypris subsinuatus, Ilyocypris bradyi, Ilyocypris cornea and Ilyocypris sp. be- Candona cf. neglecta, Candoniella marcida, Pseudocan- came extinct. Fossil ostracod concentration was 45 valves dona albicans, Cypria schichoensis and Cyprinotus tutun- per 100 grams on average. Gypsum content ranged from chous. 19.0% to 96.6%, with a mean value of 62.5% ± 13.1%. The ostracod abundance diagram of the Anjihaihe For- mation was subdivided into three ostracod assemblage zones based on the stratigraphically constrained cluster 4 Discussions analysis (CONISS [19]). The record of gypsum content in the sequence corresponds well with these ostracod assem- The occurrence of ostracod species is related to the salinity blage zones (Figure 2). and/or temperature of the host water [17]; hence, the

Figure 2 (a) Ostracod assemblages; (b) Ostracod zones; (c) CONISS; (d) gypsum content; (e) pollen concentrations [10]; (f) ODP 1218 δ18O of benthic foraminifera [21]. 3122 Dong X X, et al. Chin Sci Bull September (2013) Vol.58 No.25 environmental requirements of living and fossil taxa found sia and Chenopodiaceae gradually occupied the region, and in the Anjihaihe Formation can be utilized to draw conclu- pollen flux and concentration observably decreased [10]. sions regarding the environmental conditions prevailing These proxies suggest that terrestrial cooling and drying during the past [11]. Ilyocypris bradyi prefers warm water may have occurred starting at 23.8 Ma. and lives in wide temperature range [22], but shows very In summary, ostracod assemblage, gypsum content and low abundance in cool water body [23], it tolerates salinity pollen records consistently show a significant drying at 23.8 up to 4.5‰ [17], thus we consider that high concentration of Ma in central Asian arid regions. This finding not only pro- I. bradyi may indicate warm, fresh water. Hemicyprideis vides direct evidence of late Oligocene aridification in cen- intercedens and Hemicyprideis rhenana, which are fossil tral Asia, but it also explains speculations of central Asian species, are considered to be brackish or salty types [24]. aridification based on eolian records, such as the appearance Pseudocandona albicans lives in shallow lakes, ponds and of dust deposition in the Junggar Basin [5] and the Loess other bodies of water, has a bias towards cold water tem- Plateau [4] during the late Oligocene and the doubling of perature [11,25] and has a salinity tolerance up to 5.5‰ [26]. North Pacific eolian flux from the Eurasian continent during Extant records of Pseudocandona albicans reported in re- the same period [1,2]. cent years were mainly from areas with low mean annual Although numerous studies have linked central Asian temperatures or areas where cold water was directly injected, aridity with regional tectonism [31–34], an increasing such as Alpine foothill lakes [27], the Qaidam Basin [28] amount of evidence has shown a direct linkage of central and Hulun Lake [29]. Candona neglecta is always found in Asian aridity to global cooling [35,36]. Worldwide glacial cold host water, with a salinity range of 0.5‰–16‰ [17]. events Oi2b.1 and Mi1 occurred between 24 and 23 Ma, The ostracod assemblage recovered from the Anjihaihe near the Oligocene/Miocene boundary. The Oi2b.1 event formation indicates qualitative changes in water temperature was recorded by δ18O of benthic foraminifera in ODP Sites and salinity. Gypsum content in the river section indicates 1090 [37] and 1218 [21], and the Mi1 event was identified hydrogeological processes of the saline water [30]. These in benthic foraminiferal δ18O in DSDP Sites 522, 529, 563 two proxies together with the pollen sequence [10] thus and 608 [38], and in ODP Sites 926, 929 [39], 1090 [37], reveal a detailed climate change history in the area during 1218 and 1219 [40]. With ongoing interpretation of isotopic the late Oligocene. indicators and the development of new proxies, details of From 28 to 26.4 Ma, the dominance of Ilyocypris bradyi the Oi2b.1 and Mi1 events have been gradually revealed. Of and Ilyocypris sp. indicates warm, fresh to brackish host the 1‰ shift in δ18O at ODP Site 929, 0.5‰ was likely due water. The occurrence of salty species Hemicyprideis inter- to ice-volume effects, and the remaining 0.5‰ resulted cedens and Hemicyprideis rhenana reflect brackish to salty from a 2°C cooling of bottom waters [41]. Peak δ18O values water. These four species thus show that the aquatic envi- and a 2-step increase in δ18O before the peak Mi1 δ18O val- ronment was warm and brackish. Low gypsum content in ues at ODP Site 1218 represent a significant rise in conti- this interval indicates low salinity in this water body. The nental ice-volume, and a rapid decrease in Mg/Ca ratios pollen records are mainly composed of Cyatheaceae, Quer- during 23.1−23.0 Ma indicates a 2°C cooling of Pacific cus, Labiatae, Pinus and Ephedra in this band [10]. All Bottom Water [21]. Coral-zooxanthellate in the Mediterra- three proxies together indicate that the climate was warm nean also indicates that SST decreased near the Oligo- and semi-humid during this period. cene/Miocene boundary [42]. Meanwhile, continental areas From 26.4 to 23.8 Ma, high concentrations of warm spe- likewise underwent significant climate change during cies Ilyocypris bradyi and Ilyocypris sp. indicate a tempera- Oi2b.1 and Mi1. The palynological record of the Cape ture maximum in this period. Salty water ostracods disap- Roberts Drillhole CRP-2/2A in the Victoria Land Basin in peared, indicating a decline in salinity of the host water. The Antarctica shows a cooling trend in the summer tempera- minimum gypsum content in this band also reflects a salini- tures from the late Oligocene to the early Miocene [43], and ty minimum in the host water. Cyatheaceae, Potamogeto- the Drillhole CRP-2 recorded the expansion of the Antarctic nacea and Sparganiaceae increased, while Pinus and ice sheet during Mi1 [44]. Temperatures and precipitation Ephedra decreased in the pollen records [10]. We infer that levels reconstructed using flora assemblages in central Eu- the climate became warmer and more humid than that of the rope also decreased during 24–23 Ma [45]. 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