Late Cretaceous Biostratigraphy and Sea-Level Change in the Southwest Tarim Basin

Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Late Cretaceous biostratigraphy and sea-level change in the southwest Tarim Basin

Dangpeng Xi a,⁎,WenxinCaoa,YiChenga,TianJiangb, Jianzhong Jia c,YuanhuiLia, Xiaoqiao Wan a a State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Xueyuanlu 29, Haidian District, Beijing 100083, China b College of Zijin Mining, Fuzhou University, Fuzhou, Fujian 350108, China c Research Institute, China National Offshore Oil Corporation, Taiyanggong Nanjie NO 6, Chaoyang District, Beijing 100083, China article info abstract

Article history: The Upper Cretaceous sediments of the southwest Tarim Basin include the remnants of a large epicontinental sea. Received 1 March 2015 In this study, based on the analyses of sedimentation, foraminifera, ostracods, bivalves, and other fossils from the Received in revised form 10 September 2015 Simuhana Section, as well as published biostratigraphy data, we present a ﬁeld-based biostratigraphy and review Accepted 21 September 2015 of sea-level change for the Upper Cretaceous strata in the southwest Tarim Basin. The Upper Cretaceous marine Available online 21 October 2015 strata include the Kukebai and Dongba formations. Relatively abundant foraminifera, ostracods, and bivalves were discovered and identiﬁed. Based on the biostratigraphy and correlation, the proposed age of the Lower Keywords: Cretaceous and Middle Kukebai Formation is Cenomanian to earliest Turonian; the Upper Kukebai is of Turonian to early Tarim Basin Coniacian age. The Lower Dongba Formation is late Coniacian to early Campanian, the Middle Dongba Formation Biostratigraphy is late Campanian to early Maastrichtian, and the Upper Dongba Formation is late Maastrichtian in age, possibly Sea level extending into the Danian. The relative sea level began to rise during sedimentation of the Lower Kukebai Forma- Paleoenvironment tion (Cenomanian), and reached a maximum by the time of the middle to upper part of the Upper Kukebai For- mation (Turonian to early Coniacian). After a subsequent sea level fall, another transgression began during sedimentation of the Middle Dongba Formation. Above the Upper Dongba Formation, the sea level fell dramatically. The sea level of the southwest Tarim Basin shows a close relationship with the global sea level curve, and with the sea level of south Tibet. © 2015 Elsevier B.V. All rights reserved.

1. Introduction us to understand the level of the epicontinental sea, and the paleoenvironment of the northwest Tethys. During the Cretaceous Period, the existence of enhanced greenhouse This paper presents a ﬁeld-based biostratigraphy and sea-level of conditions and high sea level are generally accepted (Huber et al., 2000; Upper Cretaceous strata in the SW Tarim Basin. The aim of the study Skelton, 2003; Hu et al., 2012). The global Cretaceous sea level and the was to provide a stratigraphic framework, by which to assess and dis- level of the western and eastern Tethys Sea have been widely studied cuss the relative evolution of the Late Cretaceous sea level, in the (Haq et al., 1987; Haq, 2014; Wan, 1992; Zhang, 2000; Wang et al., study area. 2005; Miller et al., 2005; Cloetingh and Haq, 2015). The Late Cretaceous to Paleogene sediments of the southwest (SW) Tarim Basin in western 2. Geological setting China include the remnants of a large epicontinental sea (Tang et al., 1992; Bosboom et al., 2011). During that period of global rise in sea 2.1. Tectonics and stratigraphy level and tectonic forcing, the Neo-Tethys covered the SW Tarim Basin (Late Cretaceous to Paleogene). The Paleogene sediments of the SW The Tarim Basin is a large Mesozoic–Cenozoic composite inland Tarim Basin have been recently studied in detail (Bosboom et al., basin, superimposed upon a Paleozoic platform (Zhou, 2001). It is situ- 2011; Sun and Jiang, 2013; Wang et al., 2014). Though the biostratigra- ated south of the Tianshan Mountains (Tianshan Mts.) and north of the phy and sedimentation of Cretaceous marine strata have been the sub- West Kunlun Moutain (Kunlun Mts.) and Altun Mountain (Fig. 1A). The ject of much work (Hao et al., 1982, 2001; Mao and Norris, 1988; Tang areal extent of the basin is 560,000 km2, and the basin is part of a rela- et al., 1989, 1992; Zhong, 1992; Lan and Wei, 1995; Yang et al., 1995; tively undeformed crustal block within the India–Asia collision system Jiang et al., 1995; Guo, 1990, 1995), the Late Cretaceous biostratigraphy (Yin and Harrison, 2000). The Tarim is a poly history superimposed and sea level are still not perfectly understood. The SW Tarim can help basin that has seven evolutionary stages: (1) Sinian–Cambrian– Ordovician aulacogen stage, (2) Silurian–Devonian intracratonic ⁎ Corresponding author. depression stage, (3) Carboniferous marginal sea stage, (4) Permian E-mail address: [email protected] (D. Xi). rift-basin stage, (5) Triassic–Jurassic foreland basin stage,

Fig. 1. Topography of the Western Tarim Basin (A, modiﬁed from Sun and Jiang, 2013) and geological map of the study area (B, modiﬁed from He et al., 2004).

(6) Cretaceous–Paleogene Neo-Tethys bay stage, and (7) Neogene– Group, Lower and middle Kukebai Formation, and Section 2 includes Pleistocene foreland and inland basin stage (Li et al., 2004). the Upper Kukebai Formation and Dongba Formation. This work was The SW Tarim Basin is located between the West Kunlun Mts. (Pamir carried out in the Upper Cretaceous Kukebai Formation and Dongba For- Mountains) and the Tianshan Mts. (Fig. 1). It sits on the southwest part mation (Wuyitage, Yigeziya and Keziluoyi formations). of the basin with an area of 121 300 km2 (Jia, 1997). The SW Tarim Basin presents a continuous stratigraphic sequence deposited since the Juras- 3. Material and methods sic to the present (Tang et al., 1989; Hao et al., 2001; Jia et al., 2004). The paleogeography of the SW Tarim can be divided into the Tianshan Mts. About 100 microfossil and bivalve fossil samples were collected from and Kunlun Mts. (Tang et al., 1992). The Mesozoic SW Tarim Basin is 193.2 m thickness of the Simuhana section. Samples of 100 g dry weight composed of a non-marine sequence below (Jurassic Shalitashen, were dispersed in water for several weeks prior to sieving through a 200 Kangsu, Yangye, Taerga, Kuzigongsu formations, Lower Cretaceous microns sieve. Ostracods and foraminifera were picked from the sam- Kezilesu Group) and marine sequence above (Upper Cretaceous ples under a low-power binocular microscope. Microfossil and bivalve Kukebai, Dongba (Wuyitake, Yigeziya, Tuyiluoke) formations), while studies were carried out at the micropaleontological laboratory of the the Cenozoic SW Tarim Basin consists of a marine sequence below China University of Geosciences (Beijing). (Aertashi, Qimugen, Kalatar, Wulagen, and Bashibulake formations) and a continental sequence above (Keziluoyi, Anjuan, Pakabulake and 4. Lithostratigraphy Artushi formations) (Fig. 2; Hao et al., 1982; Zhou, 2001; Yin et al., 2002). 4.1. Kukebai Formation The Upper Jurassic Kuzigongsu Formation is characterized by lami- nated gray–white sandstone and mudstone with coal beds and abun- The lower Kukebai Formation (51.9 m) is divided into eight beds dant non-marine plant fossils (Zhou, 2001). It is overlain by the Lower (Fig. 4A). The first bed (1.1 m) is composed of gray coarse to medium Cretaceous Kezilesu Group, which contains reddish and white sand- sandstone with parallel bedding and cross bedding (Fig. 4C). The second stone. The Upper Cretaceous assemblages include the Kukebai and bed (7.8 m) is composed of brown red silty mudstone, with intercalated Dongba formations in the Tianshan Mts. area, and the Kukebai, gray green mudstone and gypsum layers (0.5–1 cm for each layer). The Wuyitake, Yigeziya, and Tuyiluoke formations in the Kunlun Mts. area horizontal bedding appears at the top of this bed. The third bed (1.8 m) (Fig. 2). The Kukebai Formation is subdivided into three members. The is mainly composed of gray green mudstone, with horizontal bedding lower one is dominated by purple–red mudstone with intercalated and intercalated thin gypsum layers upwards. The fourth bed (15.1 m) thin gypsum layers, while the middle and upper parts are made up of is composed of brown red mudstone and silty mudstone, with interca- gray–green mudstone with abundant marine fossils (Tang et al., 1989; lated gray–green mudstone and a great many thin gypsum layers. The Hao et al., 2001). The Dongba Formation, conformably overlying the fifth bed (8.6 m) is composed of gray–green mudstone and, silty mud- Kukebai Formation, is subdivided into three members. The lower and stone, with intercalated purple red mudstone and gypsum layers. upper ones consist of red mudstone with intercalated thin gypsum Brown yellow siltstone and silty mudstone appeared at the top of this rock, and the middle part is made up of carbonate and gray–green mud- bed (Figs. 4D, 5A). The sixth bed (7 m) is composed of bioclastic limestone with abundant marine fossils (Tang et al., 1989). stone (Fig. 4D). Abundant bivalves, gastropods, and other biological de- bris were found in this unit (Figs. 4C, 5B). The seventh bed (3 m) is 2.2. The study section composed of intercalated calcareous shale, with relatively abundant ostracod fossils (Fig. 5C). The eighth bed (7.5 m) is composed of bioclastic The study area is located in the Tianshan Mts. area of the SW Tarim limestone and calcirudite. Besides relatively abundant bivalves and gas- Basin. Cretaceous sediments are well exposed along the Kezilesu River tropods, some gravel stone (0.2–1 cm) appeared at the top of the (Fig. 1B). The Simuhana Section is situated in Simuhana Village of limestone. Wuqia County, and crops out along the Kezilesu River (Fig. 3). The mea- The Middle Kukebai Formation (29.9 m) can be divided into three sured section contains Cretaceous to Cenozoic strata. The Simuhana sec- beds (Fig. 4B). The first unit (9.3 m) is made up of dark gray–green mud- tion includes two separated sections: Simuhana Section 1 located along stone with intercalated silty mudstone (Fig. 5C). Two thin shelly layers the south bank of the Kezilsu River (39°43′36.92″ N; 73°59′38.03″ E), have been found in this bed. The second bed (0.2 m) is made up of shelly and Simuhana Section 2 along the north bank of the Kezilesu River layer, which is mainly composed of bivalve. The third bed (18 m) is (39°43′44.92″ N; 73°59′39.29″ E). Section 1 includes the Kezilesu made up of dark gray–green mudstone, with more thin shelly layers. 518 D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527

Fig. 2. Mesozonic and Cenozoic stratigraphic frame in the southwest Tarim Basin (Modiﬁed from Hao et al., 1982, 2001; Tang et al., 1992; Zhou, 2001).

The fourth bed (2.4 m) is composed of bioclastic limestone intercalated composed of gray–green calcareous siltstone and argillaceous siltstone with gray–green mudstone, and contains abundant bivalve (Fig. 4E). (Fig. 5 F). Only a few agglutinated foraminifera were discovered in this The Upper Kukebai Formation (47.5 m) can also be divided into five bed. The fifth bed (3 m) is composed of gray–green layered calcareous beds. The first bed (25.7 m) is composed of dark gray–green mudstone mudstone, with intercalated thin siltstone. At the top of this bed, gray with horizontal layers (Fig. 4E). Several thin shelly layers and thin gyp- mudstone interbedded with red mudstone appeared (Fig. 4 F). No sum beds appeared upwards. Compared with the lower and middle fossils were discovered in this bed. Kukebai Formations, more fossils (e.g., bivalves, gastropods, foraminifera, ostracods, fish teeth, and calcareous nannofossil) have been found 4.2. Dongba Formation in this bed. The second bed (0.2 m) is composed of gray–white shelly beds, which mainly includes bivalves. The third bed (15.4 m) is com- The Lower Dongba Formation (Wuyitage Formation) (27.5 m) can posed of dark gray–green mudstone with abundant shelly beds. Abun- be divided into three beds. The first bed (3 m) is composed of purple– dant bivalve, gastropod, foraminifera, ostracods, and calcareous red siltstone and argillaceous siltstone, with intercalated gray–green ar- nannofossils were discovered in this bed. The fourth bed (3.2 m) is gillaceous siltstone and thin gypsum rock (Fig. 4B, F). Ripple marks D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527 519

relatively poorly preserved bivalves Leptosolen sp. and Pholadomya sp. Compared with Tianshan Mts. area, the Kunlun Mts. area yielded very abundant bivalves, especially rudists (Lan and Wei, 1995; Scott et al., 2010).

5.1.2. Foraminifera In this study, relatively abundant foraminifera were discovered in samples from the Middle and Upper Kukebai Formation. The Middle Kukebai Formation samples only yielded agglutinated foraminifera Migros asiatica, M. spiritensis, M. oryzanus, M. hectori, M. lobatulus, and M. sp. The Upper Kukebai Formation samples only yielded agglutinated foraminifera Migros asiatica, M.spiritensis, M. oryzanus, M. hectori, M. lobatulus, M. guttiformis, M. sp., Yuanaia xinjianggensis, Y. sp., and the calcareous benthic foraminifera Discorbis vensus, D.sp.,Nonion sp., and Cibicides sp. Although Hao et al. (2001) found the planktonic foraminifera Archaeoglobigerina cretacea and Hedbergella planispira at the Simuhana area, no planktonic foraminifera were identiﬁed in this study. No foraminifera were identiﬁed from the Dongba Formation at the Simuhana Section in this study. Based on the study of Simuhana and other sections in the SW Tarim Basin, Hao et al. (1982, 2001) suggested that the Lower Dongba Formation (Wuyitage Formation) is characterized by the benthic foraminifera Massilina quadrilateral, Quinqueloculina simplex, and Quinqueloculina sp. These authors found Massilina

Fig. 3. Detailed geographic location of the study region. quadrilatera, M. planoconvexa, and Quinqueloculina simplex in the Middle Dongba Formation (Yigeziya Formation), while from the Upper Dongba Formation they described the Cibicides-Cibicidoides assemblage. (Fig. 4G) and burrow was observed in this bed. The second bed (8.8 m) is composed of gray–green and brown–red mudstone, and argillaceous 5.1.3. Ostracods siltstone with abundant gypsum layers (1–3 cm). The third bed Carbonate of the Lower Kukebai Formation yielded ostracod speci- (15.7 m) is thick gypsum, thin gray–green mudstone, and gypsum mud- mens of Ovocytheridea sp., Pontocyprella sp., and Cytherella sp. In the stone. No fossils were discovered in the Lower Dongba Formation. Middle Kukebai Formation a few ostracods Pontocyprella sp. and The Middle Dongba Formation (Yigeziya Formation, 7.5 m) includes Cytherella sp. were found. The Upper Kukebai Formation yielded gray–green marl, bioclastic limestone and mudstone (Fig. 3H), with relatively abundant ostracods: Ovocytheridea sp., Pontocyprella sp., abundant bivalves, as well as gastropods and ostracods (Fig. 5G). Cytherella sp., Schuleridea irina, Lexoconda sp., Bythocypris sp., and The Upper Dongba Formation (Tuyiluoke Formation) (28.9 m) is di- Paracypris cf. princeps. The Middle Dongba Formation yielded the vided into four beds. The first bed (2.5 m) consists of red siltstone, and ostracods Cythereis sp., Bronsteiniana, Pontocyprella facilis, Veenia the second bed (4.5 m) consists of gray–white calcareous medium sand- mandelstami, Sarlatina yigeziyaensis, and Ovocytheridea sp. Although stone (Fig. 5H). Abundant gypsum beds have been found in these two Hao et al. (2001) discovered a few ostracoda (Cythereis sp. and beds. The third bed (10.8 m) is composed of gypsum, while the fourth Ovocytheridea sp.) in the lower Dongba Formation, no foraminifera bed (11.6 m) mainly consists of silty mudstone, with intercalated gyp- were identified from the Lower or Upper Dongba Formation in this sum beds. No fossils were discovered in the Upper Dongba Formation. study. 5. Biostratigraphy and the age of the Kukebai and fl Dongshan formations 5.1.4. Dino agellates and nannofossils The Middle Kukebai Formation yielded the dinoflagellate 5.1. Distribution of bivalves and microfossils Cyclonephelium brevispinatum zone, and the Upper Kukebai Forma- tion yielded the dinoflagellate Alterbidinium emulatum zone (Mao The samples of bivalve and microfossils were collected from and Norris, 1988). The Middle and Upper Kukebai Formation contain representative marine beds throughout the Kukebai and Dongba calcareous nannofossils of the Quadrum gartneri zone (Hao and Su, formations. Relatively abundant foraminifera, ostracods, bivalves, 1988). nannofossils, dinoflagellates (Table 1), and a few gastropods and fish Within the lower and middle units of the Dongba Formation fl teeth are present in the study section. Foraminifera, ostracods, and bi- (Wuyitage and Yigeziya formations) the dino agellate Canningia reticu- fi valves were identified in this study (Fig. 6). For the nannofossils and di- late zone was identi ed (Mao and Norris, 1988). In the Upper Dongba fl noflagellates, the results of Mao and Norris (1988) and Hao and Su Formation (Tuyikuoke Formation), the dino agellate taxa Alterbidinium (1988) were cited in this study. sp., Kiokansium sp., Eucladiniun gambangense, Paleohystrichophora ubfusorioides, Trithyrodinium sp., and Diconodinium sp. occur (Mao and 5.1.1. Bivalves Norris, 1988). The Kukebai Formation yielded abundant bivalve fossils. The carbonate of the Lower Kukebai Formation yielded the bivalves Flaventia 5.2. The age of the Kukebai and Dongshan formations ovalis,Ostrea oxiana,andLima aff. subrigida.Inaddition,Andara sp. has been identified from the lowermost sandstone of the Lower Kukebai 5.2.1. Relative age of the Kukebai Formation Formation at the Bashibulake Section, SW Tarim Basin (Lan and Wei., The bivalve species Flaventia ovalis of the Lower Kukebai Formation 1995). The Middle Kukebai Formation is characterized by Ostrea was discovered from late Albian to early Cenomanian (Lan and Wei, vatonnoides, Ostrea oxiana,andLima aff. subrigda in the mudstone. The 1995). The ostracod assemblage Ovocytheridea bashenbulake-Cytherella Upper Kukebai Formation is characterized by Lima marrotiana,Pycnodonte Wuqiaaensis-Schuleridea irinae was widely found in the Cenomanian costei,andCyprimeria? paba. The Middle Dongba Formation yielded the sediments of Central Asian Ferghana Basin (Yang et al., 1995; Zhou, 520 D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527

Fig. 4. Photographs of the lithology identiﬁed in the outcrops of the Simuhana section: (A) Lower Kukebai Formation, (B) Middle Kukebai Formation, Upper Kukebai Formation and Dongba Formation, (C) Parallel bedding of the sandstone from the Lower Kukebai Formation, (D) Bioclastic limestone of the Lower Kukebai Formation, (E) Bioclastic limestone of the Middle Kukebai Formation, (F) Red mudstone interbed with intercalated gray–green mudstone, the Lower Dongba Formation, (G) Ripples of the lower Dongba Formation, (H) Marl of the Middle Dongba Formation.

2001). This puts the age of the Lower Kukebai Formation in the range of of the Cyclonephelium brevispinatum zone are likely Cenomanian to the early Cenomanian. Turonian in age (Mao and Norris, 1988). In addition, based on the pres- The bivalves Ostrea vatonnoides, Ostrea oxiana,andLima aff. subrigida ence of the calcareous nannoplankton species Quadrum gartneri (Hao of the Middle Kukebai Formation range from middle to late Cenomanian and Su, 1988) from the middle and upper part of the Kukebai Formation, (Lan and Wei, 1995). Migros spiritensis was discovered from the it is suggested that the age of the Middle and Upper Kukebai Formation Cenomanian Kaskapau Formation (Hao et al., 2001). The dinoﬂagellates is Turonian to early Coniacian (Lamolda et al., 1994; Burnett, 1998; Erba, D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527 521

Fig. 5. Microfacies of the Kukebai and Dongba Formations: (A) Silty mudstone, Lower Kukebai Formation, (B) Bioclastic limestone, Lower Kukebai Formation, (C) Silty mudstone, Lower Kukebai Formation, (D) Muddy siltstone, Middle Kukebai Formation, (E) Mudstone, Upper Kukebai Formation, (F) Siltstone, Upper Kukebai Formation, (G) Bioclastic limestone, Middle Dongba Formation, (H) Sandstone, Upper Dongba Formation. Microphotographs at LM (light microscope).

2004; Melinte-Dobrinescu et al., 2013a, 2013b). Hence, the relative age planispira from Aptian to early Coniacian, H. holmdelensis from of the Middle Kukebai Formation might be middle Cenomanian to earli- Coniacian to earliest Maastrichtian (Caron, 1985), while Whiteinella est Turonian. inornata is typically uppermost Cenomanian to lowermost Turonian The Upper Kukebai Formation yielded the foraminifer (BouDagher-Fadel, 2012), indicating that the age of Upper Kukebai For- Archaeoglobigerina cretacea, Hedbergella planispira, H. holmdelensis, and mation is possibly extended within Turonian to early Conician interval. Whiteinella inornata (Hao et al., 1982, 2001). Archaeoglobigerina cretacea The ostracod Sarlatina leguminoformis was discovered in the Turonian to ranges from the Coniacian to earliest Maastrichtian, Hedbergella Santonian of the Tadiik and Ferghana Basin (Yang et al., 1995). 522 D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527

Table 1 Bivalves, microfossils, and age of Kukebai and Dongba Formation.

Stratigraphy Foraminifera Ostracods Bivalves Nanofossils Dinoﬂagellates (Mao and Norris, 1988) Stage (Hao and Su, 1988)

Upper Alterbidinium sp., Kiokansium sp., L. Danian?—U. Dongba Eucladiniun gambangense, Maastrichtian Paleohystrichophoraubfusorioides, Trithyrodinium sp., Diconodinium sp. Middle Cythereis sp., Bronsteiniana, Leptosolen sp., L. Maastrichtian—U. Dongba Pontocyprella facilis, Veenia, Sarlatina Pholadomya sp. Campanian yigeziyaensis, Ovocytheridea sp. Lower L. Campanian-U. Dongba Coniacian Upper Migros Ovocytheridea sp., Pontocyprella sp., Lima marrotiana, Quadrum Alterbidinium emulatum Zone L. Kukebai asiatica, Cytherella sp., Schuleridea irinae, Pycnodonte gartneri Coniacian–Tunonian M.spiritensis, Loxoconcha sp., Bythocypris sp., costei,Cyprimeria?faba zone M. oryzanus, Paracypris cf. princeps M. hectori, M. lobatulus, M. guttiformis, Yuanaia xinjianggensis ,Y. sp., Discorbis vescus, D.sp., Nonion sp., Cibicides sp. Middle Migros Pontocyprella sp., Cytherella sp. Ostrea vatonnoides, Cyclonephelium brevispinatum Zone L. Turonian–M. Kukebai asiatica, Ostrea oxiana, Cenomanian M.spiritensis, Lima aff. subrigida M. oryzanus, M. hectori, M. lobatulus, M. sp. Lower Ovocytheridea sp., Pontocyprella sp., Flaventia ovalis, E. Cenomanian Kukebai Cytherella sp. Ostrea oxiana, Lima aff. subrigida

Dinoflagellates of the Cyclonephelium brevispinatum zone are likely The age of the Upper Dongba Formation (Tuyiluoke Formation) is Turonian to Coniacian or Turonian to Santonian in age (Mao and still in debate. Hao et al. (1982, 2001), Tang et al. (1992),andZhou Norris, 1988). The bivalve Rhynchostreon suborbiculatum was discov- (2001)) proposed a latest Cretaceous age, while Guo (1990, 1995) ered in the Cenomanian to lower Turonian sediments of Europe assigned this unit to the Paleogene. In samples from the Lower Keziluoyi (Pojarkova, 1984; Dhondt, 1985), and Corbula muschketowi in Turonian Formation of the Aertashi Section, Mao and Norris (1988) discovered di- sediments of the Korobkovitrigonia darwaseana area (Pojarkova, 1984; noflagellates including Palaeohystrichophora granulata, P. infusorioides, Dhondt, 1985). Therefore, the age of the Upper Kukebai Formation Spiniferites sp., and Pterospermella sp., which range from the Santonian might be Turonian to early Coniacian. to the Maastrichtian. Hao et al. (2001) discovered Cibicidoides succedens in the Lower Keziluoyi Formation, and Quinqueloculina, Massilina and Spiroloculina in the Upper Keziluoyi Formation. The species 5.2.2. Relative age of the Dongba Formation Cibicidoides succedens was discovered in Cretaceous sediments, while Foraminifera of the Lower Dongba Formation (Wuyitage Formation) Quinqueloculina, Massilina, and Spiroloculina occurred in the Paleogene are relatively abundant in the Akecheyi area, including a small amount sediments (Hao et al., 2001). Therefore, the Lower Keziluoyi Formation of planktonic foraminifera, such as Hedbergella holmdelensis (Hao et al, is likely late Maastrichtian, but the Upper Keziluoyi Formation perhaps 2001). This species extended from the Coniacian to Maastrichtian ranges into the early Danian. (Caron, 1985). Based on the comprehensive analysis of foraminifera, Hao et al. (2001) suggested an age from the Coniacian up to Campanian. 6. Discussion In addition, based on calcareous nannofossils, Hao and Su (1988) suggested that the age was not younger than mid-Campanian. Therefore, 6.1. Paleoenvironment the age of the Lower Dongba Formation (Wuyitake Formation) might be late Coniacian to early Campanian. Baed on the analysis of sedimentology, paleontology and Foraminifera were mainly discovered in the Middle Dongba Forma- paleocology, the paleoenvironment of the Kuhebai and Dongba Forma- tion (Yigeziya Formation) of the Wuyitage area of the Kunlun Mts area. tion is discussed bellow (Fig. 7). The identified foraminifera mainly belong to the assemblage of Quinqueloculina-Triloculina (Hao et al., 2001)thatsuggestesa 6.1.1. Kukebai Formation Maastrichtian age. The bivalve fauna of the lower and middle part of The first bed of the Lower Kukebai Formation is composed of the Wuyitage units are inferred to be Coniacian to Campanian in age, sandstone, with parallel bedding and cross bedding, and includes the bi- but the rudists of the upper part of the Yigeziya Formation are consid- valve Andara sp., indicating a coastal inshore facies (Lan and Wei, 1995). ered to be Maastrichtian (Lan and Wei, 1995). The age of the ostracod The second to five units of the Lower Kukebai Formation are dominated Sarlatina longielliptica is suggested as Campanian to Maastrichtian by purple to red mudstone and silty mudstone, with intercalated gray– (Yang et al., 1995). Hence, the age of the Wuyitake might be late Cam- green mudstone and a lot of thin gypsum layers. There are a few benthic panian to early Maastrichtian. foraminifers and ostracods. Foraminifera Ammobaculites generally lived D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527 523

in high-energy lagoons or estuarine environments (Kaminski et al., 2005), such as that of Chesapeake Bay (Murry, 2006). Foraminifera be- longing to the genus Migros have been found in shallow water environments of the Kilwa Group (Nicholas et al., 2006). The environment might be lagoonal to supratidal, and sea level began to rise slowly. The sixth to eighth beds of the Lower Kukebai Formation mainly consist of bioclastic limestone, containing relatively abundant bivalves in the carbonate, such as Ostrea and Flaventia, which lived in the intertidal zone (Lan and Wei, 1995). It appears that the sea level was still rising, and this environment was perhaps in the intertidal zone (Fig. 7). Relatively abundant ostracods and calcareous shale were identified in the seventh bed, indicating a relatively deep and low energy water environment. A few gravelstone were discovered in the calcirudite of the upper eighth bed, indicating a more shallow and high energy water environment. During sedimentation of the Middle Kukebai Formation, species abundance and diversity began to increase, and the sediment changed to dark gray mudstone, indicating a relatively deep-water environment. The biota is dominated by the bivalve Ostrea and agglutinated foraminifera Migros, which lived in intertidal and subtidal zone (Hao and Zeng, 1984; Lan and Wei, 1995). The paleoenvironment might be intertidal to subtidal (Fig. 7). The uppermost Middle Kukebai Formation, however, is similar to the sixth bed of the lower Kukebai Formation, which most probably deposited in the intertidal zone. The Upper Kukebai Formation also contained a large number of reefs, mainly composed of bivalves that lived far away from the coast (Lan and Wei, 1995). In addition, ammonites, echinoids, gastropods, dinoflagellates, algae, and other neritic fossils have been discovered, along with calcareous nannofossils (Zhou, 2001). The green algae Pterospermella and Cymatiosphaera indicate a relatively stable neritic environment (He, 1991). In the Simuhana Section, the abundance and diversity of marine fossils is very high in the middle to upper part of this member, including agglutinated foraminifer Migros asiatica, M.spiritensis, M. oryzanus, M. hectori, M. lobatulus, M. guttiformis, M. sp. Yuanaia xinjianggensis, and Y. sp.; the calcareous benthic foraminifera Discorbis vensus, D.sp.,Nonion sp., and Cibicides;aswellasostracods,bivalves, gastropods, and fish teeth. This indicates that during deposition of the lower and middle part of the Upper Kukebai Formation, paleoenvironment gradually changed from an intertidal—subtidal environment to a normal neritic environment one (Fig. 7). However, upwards to the uppermost part of this member, the sea level decreased dramatically.

6.1.2. Dongba Formation During sedimentation of the Lower Dongba Formation, the fossil diversity and abundance declined significantly, while the agglutinated foraminifera are dominant in the microfossil assemblages. Ripples were observed at the bottom of this member. This finding, together with the presence of Haplophragmium that was found in the Cretaceous near-shore environment of western Morocco (Butt, 1982), suggest a coastal environment. Dinoflagellates were mainly discovered in the lower part of the unit, characterized by Hystrichosphaeridium, the presence of which implies a turbulent, supratidal flat to lagoon environment (He, 1991). These suggest that the sea began to retreat from the SW Tarim Basin (Fig. 7). The Middle Dongba Formation is mainly composed of carbonate sediments, with relatively abundant bivalves, ostracods, and gastropods, indicating a carbonate platform. The thickness of this is much greater in the Kunlun Mts. area than in the Tianshan Mts. area, indicating a marginal-carbonate-platform environment in the study area. Thus, it appears that during the sedimentation of the Middle Dongba Formation, sea level began to rise again (Fig. 7). The Upper Dongba Formation is composed of red mudstone and sandstone with intercalated thin gypsum rock, with no fossils in the studied section. In the Kunlun Mts. area, just a few benthic foraminifera, such as Cibicides,werediscovered(Hao et al., 2001) suggesting a lagoon Fig. 6. Distribution of bivalves and microfossils in the study area (L: lower, U: upper). environment. In addition, He (1991) discovered the algal genus 524 D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527

Fig. 7. Upper Cretaceous stratigraphy and sea level change of the Simuhana Section. D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527 525

Fig. 8. Paleogeography of the Tarim Basin and adjacent areas (modiﬁed from Tang et al., 1992). The Upper Cretaceous marine strata are spread between the Kunlun Mts. and South Tianshan Mts. by only 50 km in width. For the entire area between the India and Eurasia Plates, the Pamir Arc was continuously rising close to the South Tianshan Mts.

Pediastrum, indicating an inshore environment. Hence, during deposi- was continuously rising close to the South Tianshan Mts. (Burtman, tion of the Upper Dongba Formation, it appears that sea level began to 2000). By analyzing the lithological and sedimentological features, as fall again (Fig. 7). well as the macro and microfossil assemblages, it was supposed that the Late Cretaceous Tarim Gulf was initially at least 500 km wide at 6.2. 2 Late Cretaceous sea-level change in the western Tarim Basin the Pamir region (Tang et al., 1992).

6.2.1. Late Cretaceous sea-level change in the study area 6.2.2. Correlation of sea-level change during the Late Cretaceous The SW Tarim Basin was a typical non-marine environment during It has been accepted that sea level was high during the Cretaceous the Jurassic (Zhou, 2001). Although it is suggested that a small seawater Period (Haq et al., 1987; Haq, 2014). It appears that sea level reached transgression occurred during the Early Cretaceous, as indicated by a a maximum during the Cenomanian–Turonian, then declined gradually, few marine fossils in the Upper Kezilesu Group (Guo, 1991,alargesea- and was relatively lower at the end of the Cretaceous (Fig. 9). Based on water transgression began at the time of the Lower Kukebai Formation the analysis of foraminifera and sedimentation of south Tibet, it is sug- in the Cenomanian (Hao and Zeng, 1984). The sea level began to rise gested that sea level rose from the Albian to the Cenomanian, reached during the sedimentation of the Kukebai Formation, and reached a max- its peak at the Cenomanian–Turonian boundary, and then it began a imum at the time of the Upper Kukebai Formation (around 118–122 m gradual decline, but declined dramatically at the end of Cretaceous in the study section). The sea level fell again during the uppermost (Fig. 6; Wan, 1992; Wang et al., 2005). In the SW Tarim Basin, signiﬁcant Kukebai Formation and Lower Dongba Formation, and then began to seawater transgression began during the early Cenomanian, then the rise during the Middle Dongba Formation during the late Coniacian. sea level rose gradually, and was highest during the Turonian. The sea After sedimentation of the Upper Dongba Formation, the sea level fell level declined gradually, but there was a new rise of sea level during dramatically. During the Late Cretaceous to Paleocene, the SW Tarim the Campanian to the early Maastrichtian. There was also a dramatic de- Basin was a gulf, known as the Tarim Gulf (Hao and Zeng, 1984; Tang cline in sea level at the end of the Cretaceous. The sea level in the SW et al., 1989), an epicontinental sea environment of the northwest Te- Tarim Basin was controlled by global sea level change, and can be corre- thys. The depth and area of sea level reached a maximum in the time lated with the global sea level, and with sea level change in south Tibet. of the Turonian Upper Kukebai Formation during a global sea level rise However, the study area was a gulf during the Late Cretaceous up to (Haq, 2014). The Upper Cretaceous marine strata are spread between early Paleogene interval (Hao and Zeng, 1984). The marine environ- the Kunlun Mts. and South Tianshan Mts. by only 50 km in width. For ment was very shallow, so the sea level was also affected by regional the entire area between the India and Eurasia Plates, the Pamir Arc factors, such as the basin sedimentary ﬁll and the tectonic evolution of 526 D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527

Fig. 9. Comparison of Cenomanian up to Maastrichtian sea levels of the southwest Tarim Basin, south Tibet and the global trend. the Tibet, as well as the surrounding regions, such as the Tianshan Mts. Education Young Elite Teacher Project (YETP0665). We would like to and Kunlun Mts. (Jia, 1997; Zhang, 2000; Yin et al., 2002; Wang et al., thank the following colleagues for their help: Liuqin Chen, Yang Shen 2014). (See Fig. 8.) for useful suggestions for this paper; Xiaopeng Fan, Zuohuan Qin, Wenping Zhang, Qian Zhang, Zhongye Shi and Can Cui for their labora- 7. Conclusions tory assistance. This paper also benefited a lot from two anonymous re- viewers, Prof. Melinte–Dobrinescu and Prof. Michael Wagreich. This The Upper Cretaceous marine strata include the Kukebai and paper is a contribution to UNESCO-IUGS IGCP project 609 "Climate-en- Dongba formations of the Simuhana Section, which have herein been vironmental deteriorations during greenhouse phases: Causes and con- described and sampled. Relatively abundant foraminifers, ostracods, sequences of short-term Cretaceous sea-level changes". and bivalves were discovered and identified. Based on the biostratigraphy and correlation, the age of the Lower Appendix AA.1. Bivalves Kukebai Formation is proposed to be early Cenomanian; the Middle Kukebai Formation is middle Cenomanian to earliest Turonian; and Corbula muschketowi Böhm, 1911 the Upper Kukebai Formation is Turonian to early Coniacian in age. Cyprimeria faba Sowerby, 1827 The lower Dongba Formation appears to be late Coniacian to early Cam- Flaventia ovalis Sowerby, 1827 panian, the Middle Dongba Formation is late Campanian to early Leptosolen Conrad, 1865 Maastrichtian, and the Upper Dongba Formation is late Maastrichtian, Lima aff. subrigida Roemer, 1836 possibly extending into the Danian in age. Lima marrotiana d'Orbigny,1847 The sea level began to rise during sedimentation of what is now the Ostrea oxiana Romanovskiy, 1884 Kukebai Formation, and reached a maximum at the time of the Upper Ostrea vatonnoides Linne, 1758 Kukebai Formation. The sea level fell again during the Lower Dongba For- Pholadomya Sowerby, 1823 mation, and then began to rise during the Lower Dongba Formation. From Pycnodonte(Costeina) costei(Coqand), 1869 there to the Upper Dongba Formation, the sea level fell dramatically. The Rhynchostreon suborbiculatum Lamarck, 1801 sea level of the southwest Tarim Basin shows a good correlation with global sea level fluctuation and with the ones recorded in the south Tibet. A.2. Foraminifera

Acknowledgments Cibicides Cushman, 1927 Cibicidoides succedens Brotzen, 1948 This study was ﬁnancially supported in part by funds from the Discorbis vescus Bykova, 1939 National Basic Research Program of China (973 Program, Migros asiatica Bykova, 1939 NO.2012CB822002), the National Natural Science Foundation of China M.spiritensis Stelck & Wall, 1955 (41302008, 41172037), the State Key Laboratory of Biogeology and M. oryzanus Zeng, 1982 Environmental Geology (GBL215010), the Fundamental Research M.hectori Nauss,1947 Funds for the Central Universities (No. 2652015042), and Beijing Higher M. lobatulus Cushman & Barbat,1932 D. Xi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 441 (2016) 516–527 527

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