Paleoenvironments, stratigraphic evolution and reservoir characteristics of the Upper Cretaceous Yingjisha Group, southwest Tarim Basin

Accepted Manuscript Paleoenvironments, Stratigraphic Evolution and Reservoir Characteristics of the Upper Cretaceous Yingjisha Group, Southwest Tarim Basin Feng Guo, Dan Yang, Kenneth A. Eriksson, Ling Guo PII:

S0264-8172(15)30002-7

DOI:

10.1016/j.marpetgeo.2015.05.023

Reference:

JMPG 2251

To appear in:

Marine and Petroleum Geology

Received Date: 9 April 2015 Revised Date:

22 May 2015

Accepted Date: 24 May 2015

Please cite this article as: Guo, F., Yang, D., Eriksson, K.A., Guo, L., Paleoenvironments, Stratigraphic Evolution and Reservoir Characteristics of the Upper Cretaceous Yingjisha Group, Southwest Tarim Basin, Marine and Petroleum Geology (2015), doi: 10.1016/j.marpetgeo.2015.05.023. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Paleoenvironments, Stratigraphic Evolution and Reservoir Characteristics of the Upper Cretaceous Yingjisha Group, Southwest Tarim Basin

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Feng Guoa, Dan Yanga, Kenneth A. Erikssonb, Ling Guoc School of Earth Sciences and Engineering, Xi’an Shiyou University, Xi’an 710065, China

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Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States

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Department of Geology, Northwest University, Xi’an 710069, China

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a

Corresponding authors:

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E-mail addresses: [email protected] (K.A. Eriksson), [email protected] (Feng Guo)

Abstract

The Upper Cretaceous Yingjisha Group in the southwestern Tarim Basin is an important host of hydrocarbons with the highest-quality reservoirs are a product of depositional environment,

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diagenesis and tectonics. The Yingjisha Group is composed, in ascending order, of the Kukebai, Wuyitak, Yigziya and Tuyiluok formations. Strata are thickest in the Kashgar Sag in the northwest and the Yecheng Sag (up to 635 m) in the southeast and thin over the central Qimugen

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Uplift (less than 70 m). Six facies associations (1 - 6) are interpreted, respectively, as braided fluvial, lagoon, nearshore-shelf, playa-lake, restricted carbonate platform and open carbonate

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platform to platform margin. Stratigraphic evolution of the Yingjisha Group, recorded in vertical changes in inferred depositional environments, is related to changes in water depth and climate. At least two transgressive (Kukebai and Yigziya formations) - regressive (Wuyitak and Tuyiluok formations) cycles are recognized that can be correlated with the global eustatic curve of Haq et al. (1988). Detailed paleoenvironmental analysis forms the basis for understanding and predicting the occurrence of reservoir rocks in this mixed siliciclastic-carbonate succession. 1

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High-energy, braided-fluvial sandstones and carbonate platform and platform-margin grainstones (locally dolomitized) comprise the best reservoirs. The most important diagenetic processes in sandstones that resulted in porosity and permeability changes are: 1) mechanical compaction, 2)

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cementation, and 3) replacement and dissolution of unstable clastic grains and cements, whereas in carbonate rocks the dominant diagenetic processes are cementation and dissolution.

Fracturing played an important role in enhancing the quality of sandstone and especially

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carbonate reservoirs notably in terms of their permeability by connecting previously isolated pores. Stratigraphic evolution of the Yingjisha Group resulted in stacking of seal rocks above

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reservoirs during the late transgressive and regressive phases of sedimentation.

Key words: Depositional Environments, Stratigraphic Evolution, Reservoir Characteristics,

1.Introduction

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Upper Cretaceous, Tarim Basin

Tarim Basin is China's largest inland basin and extends west to east for 1500km, ranges from

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100 to 600 km wide and covers an area of 530,000 km2 (Fig. 1A). The Tarim Basin evolved from a Paleozoic cratonic basin to a Meso-Cenozoic foreland basin (Gu, 1996; He and Li, 1996; Kang,

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1996; Sobel, 1999; Jin and Lu, 2000; Jin et al., 2005; Zhao and Li, 2003). Cretaceous strata are well developed along the southwestern margin of the Tarim Basin (Fig. 1B, C; Sobel, 1999; Ding et al., 2002; Sun, 2004; Zhang et al., 2008; Liu et al., 2012). The Upper Cretaceous Yingjisha Group that consists of a lower interval of siliciclastic strata and an upper interval of carbonate strata is the focus of this study.

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For many decades, southwestern Tarim Basin was a low-priority exploration area because of its remote location from the existing pipeline infrastructure (Kang, 1996; Jin and Lu, 2000). However, following the discovery of deeply buried oil in the Kekeya area (Fig. 1C) in 1970's and

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Cretaceous petroleum reservoirs in the Kedong-1 well in 2010 (Fig. 1C), the southwestern part of the Tarim Basin has become an attractive exploration target. Recent studies of the Cretaceous strata at various locations along the Kunlun and Tianshan Mountains have used modern facies

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analysis (Wang and Fu, 1996; Hu et al., 1997; Mou et al., 2002a, b; Jia et al., 2004; Zhang et al., 2005; Fang et al., 2009) and sequence-stratigraphic interpretations (Ding et al., 2002; Sun, 2004;

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Zhang et al., 2008; Liu et al., 2012) to establish that the Upper Cretaceous consists of variable mixture of braided alluvial, tidal flat, and carbonate platform facies (Hao and Zeng, 1984; Bosboom et al., 2011; Robertson et al., 2012). However, these studies have been mainly reconnaissance in scope and details about temporal and spatial trends in depositional facies in the

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southwest Tarim depression during the Cretaceous remain poorly constrained. Upper Cretaceous strata in the southwest Tarim Basin are exposed in continuous outcrops affording an opportunity for detailed facies analysis. The purpose of this study is to develop a

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stratigraphic framework and to characterize facies variability for the Yingjisha Group. The results of this evaluation have broader implications for interpretations of depositional

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environments and for predicting reservoir characteristics in Upper Cretaceous strata in Tarim Basin. This study demonstrates that detailed paleoenvironmental analysis, coupled with an understanding of diagenesis and tectonic setting, is critical to understanding and predicting the occurrence and geometry of reservoir rocks in mixed siliciclastic-carbonate successions, in general, and in the Upper Cretaceous Yingjisha Group in particular.

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2. Geologic Setting 2.1 Tectonics

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With a basement of Precambrian crystalline metamorphic rocks, Tarim Basin underwent several phases of tectonism from the Late Precambrian to the Neogene (He and Li, 1998; Jia, 1999; Jin et al., 2005; He et al., 2005; Burtman, 2012; He et al., 2013). Tarim Basin is delineated by major bounding structures: the Tianshan orogen to the north, the Altyntagh Mountains to the southeast

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and the Kunlun mountains to the southwest (Fig. 1B). The southwestern margin of the Tarim

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Basin evolved from a narrow transtensional basin in the Late Triassic and Early Jurassic to a broader foreland basin in the Late Jurassic and Early Cretaceous. Basin formation resulted from successive collisions of the Chantang and mega-Lhasa blocks to the south of the Tarim Basin with the Eurasian plate associated with the northward migration of the Indian plate (Willett and Beaumont, 1994; Matte et al., 1996; Sobel, 1999; Xiao et al., 2000; Robinson et al., 2003;

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Scharer et al., 2004; Wittlinger et al., 2004; He et al., 2013). A post-orogenic, quiescent phase existed in the western Tarim basin during the Late Cretaceous. The southwestern margin of the Tarim Basin is referred to as the Piedmont Zone of Kunlun Mountains (PZKM) and includes the

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Kashgar Sag, Qimugen Uplift and Yecheng Sag (Fig. 1C; He and Li, 1996; Jia, 1997).

2.2 Regional Stratigraphy Cretaceous strata in the southwestern Tarim Basin are well exposed in badlands across

the southwestern Xinjiang Uygur Autonomous Region of China (Fig. 1A, Table 1) and especially in the Kunlun and Tianshan mountains along the western margin of the Tarim Basin. In 1950s, the Thirteenth Aerial Geological Survey Team belonging to the former Soviet Union constructed a 1:200,000 scale geological map of the Kashgar area of Tarim Basin and in the 4

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1980’s a preliminary lithostratigraphy for the Cretaceous was established (Hao and Zeng, 1980; Tang et al., 1989). In 1975, the Geological Survey Department of the Xinjiang Petroleum Administration Bureau compiled a regional stratigraphic chart formally establishing a

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lithostratigraphic nomenclature and a chronostratigraphic correlation of Cretaceous strata across the study area.Cretaceous strata in the study area are subdivided into two groups. The lower unit is the Lower Cretaceous Kezilesu Group that consists of conglomerate, sandstone and local

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siltstone-mudstone (Sobel, 1999) and is conformably overlain by the Upper Cretaceous

Yingjisha Group. The Yingisha Group is unconformably overlain by is the Paleocene Artashi

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Formation that consists predominantly of gypsum. A few key wells intersect both the Kezilesu and Yingjisha Groups (Fig. 1) providing ties between the outcrops and the subsurface.

3. Materials and Methods

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This study, located in the southwestern Tarim Basin, incorporates 14 sections (9 measured in detail and 5 surveyed) in the south Tianshan Mountains, Kashigar Sag, Qimugen Uplift and Yecheng Sag and 10 wells drilled by the Tarim Oil-field Company (Fig. 1C).

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Photomosaics were prepared of each of the nine outcrops and photographs and samples for thin section analysis were keyed to the mosaics. Five sections located between the detailed measured

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sections were described to constrain lateral stratigraphic and facies changes. Correlations were established between outcrop sections and wells based on lithostratigraphy and well logs. To assist in stratigraphic correlation between outcrops and wells, hand-held gamma-ray surveys, at a spacing of 25 cm, were measured at six of the outcrop sections. The nine detailed sections were described at a centimeter scale and a total of 3,600 samples were collected from nine outcrops and 30 samples from three cores. A total of 883 thin sections were analyzed for composition, 5

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texture and fossil content based on point counting. Thin sections were prepared from core plugs taken from the detailed measured sections along vertical and horizontal traverses to measure petrophysical properties. In addition, grain size analyses were determined for 186 samples by

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crushing and sieving. Classification of siliciclastic facies follows the nomenclature of Folk (1974) and of carbonate facies the nomenclature of Dunham (1962).

In order to investigate reservoir characteristics, 710 samples were collected in the field

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for petrography, porosity and permeability studies. Estimates of porosity and primary and

authigenic mineralogy of the sandstone and carbonate rocks were based on point counting (300

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points per thin section) of 883 thin sections and 237 vacuum impregnated thin sections. In addition, Scanning Electron Microscopy (SEM) was carried out on 47 samples using a SEM Model Tescan Vega II to determine diagenetic mineral phases including porosity. XRD analyses were carried on 51 samples using a D8-Discover X-ray Diffractometer to determine the

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compositions of diagenetic clay minerals. To determine the reservoir physical parameters, cylindrical samples 3 cm long and 2.5 cm in diameter were drilled from 20 representative sandstone and 19 carbonate hand specimens. Petrophysical measurements were performed under

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ambient conditions at constant temperature (~26℃).

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4. Lithostratigraphy

The Yingjisha Groupconsists, in ascending order, of the Kukebai (K2k2), Wuyitak (K2w2),

Yigziya (K2y2) and Tuyiluok (K2t2) formations (Table 1; Fang et al., 2009; Liu et al., 2012; Guo et al., 2014). Identification of formation boundaries in the Yingjisha Group is based on analysis of outcrops complemented by well logs and hand-held gamma-ray surveys (Figs. 2, 3, 4 and 5).

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The Kukebai Formation is subdivided into three units, a lower red unit, and middle and upper gray-green units that can be clearly recognized in outcrops (Fig. 5). The lower unit is up to 180 m thick and consists predominantly of brown-red sandstone (Figs. 2 and 3). Locally, this

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unit pinches out as in the Fu-1 well (Fig. 3). The middle unit is up to 163 m thick and is

composed mainly of gray-green mudstone and fine-grained sandstone interbedded with tabular carbonate or gypsum beds. The uppermost unit is less than 45 m thick in most parts of the study

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area but, and thickens into the Kashgar and Yecheng Sags and pinches out to the southeast (Figs. 2 and 3). Lithologies in the upper unit of the Kukebai Formation are similar to those in the

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middle unit except that gypsum is absent. Adjacent to the Tianshan Mountains, the Kukebai Formation consists predominantly of gypsiferous mudstone and subordinate limestone (Fig. 4). The Wuyitak Formation consists of brown-red mudstone interbedded with siltstone, gypsum or carbonates, ranges in thickness from 6.5 to 90 m and thickens into Yecheng Sag.

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The Yigziya Formation consists of lower and upper units. The lower unit ranges in thickness from 2.5 to 58 m but is less than 25 m thick in most parts of the study area. Gray-red grainstone, wackestone, dolostone and lime mudstone are the main lithologies in the lower unit.

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The upper unit is up to 132 m thick and consists predominantly of red-grey grainstone, packstone

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and wackestone. Distinctive red-grey weathering characterizes of these two units allow for easy identification and mapping (Fig. 5). Carbonate units vary in thickness from 5 to 132 m whereas interstratified calcareous mudstone intervals are easy to estimate from their weathering features and range from 0 to 18m in thickness. In general, the Yigziya Formation thins from west to east (Figs. 2 and 3). Adjacent to the Tianshan Mountain, the Yigziya Formation lacks limestones and consists exclusively of gypsiferous mudstone and subordinate dolomite (Fig. 4). The Tuyiluok Formation ranges in thickness from 3 to 28 m and consists of similar facies to the Wuyitak 7

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Formation including brown-red mudstone and gypsum-mudstone interbedded with siltstone and local lenticular or nodular gypsum deposits. These brown-red facies of the Tuyiluok Formation

massive gypsum of the overlying Artashi Formation (Fig. 5).

5. Facies and Facies Associations

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are sandwiched between red-grey carbonates of the underlying Yigziya Formation and white,

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Fourteen lithofacies are recognized and characterized according to lithology, biological features, primary and secondary sedimentary structures, geometry and thickness, and each facies

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is interpreted in terms of depositional processes (Tables 2 and 3). Individual facies are arranged into facies associations (Table 4) each of which records a distinctive depositional environment. Facies assocations contain characteristic fossil assemblages (Table 5).

5.1.1 Description

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5.1 Facies Association 1

Facies association 1 (FA-1) is widely developed in lower Kukebai Formation where it

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forms a continuous belt of conglomerate-sandstone adjacent to the Kunlun Mountains and Tianshan Mountains (Figs. 2 and 3). This facies association consists mainly of facies Cg, St, Fif,

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and Sp with subordinate Sh (Table 2, Fig. 6A-D) and occurs as continuous, tabular bodies that can be traced along strike for hundreds of meters. Framework grains range from angular to subrounded and sandstones are moderately to well sorted (Fig. 7; Table 2). The majority of finegrained sandstone samples are lithic arkoses and feldspathic litharenites (Fig. 8A), whereas, most of the coarse- to medium-sandstone samples are feldspathic litharenites (Fig. 8B). Despite its

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lateral continuity, this facies association possesses a complex multilateral-multistory internal architecture manifested as vertical stacking of scour-based conglomeratic sandstone bodies. The typical motif of this facies association consists of upward-fining cycles between 0.5

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and 2.4 m in thickness in which both grain size and scale of sedimentary structures decreases upwards (Fig. 9A, B). Basal conglomeratic sandstones (Cg) overlie scoured surfaces and range 0.1 to 0.5 m thick. Gravel lag deposits are rare. Scattered quartzite, chert, metamorphic and

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igneous clasts are present in the gravely sandstones. Overlying sandstones are mainly fine- to very fine-grained and are cross and parallel bedded (St, Sh and Sp). Locally, vestiges of

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mudstone drapes with parallel laminations are preserved high up in the section. Paleocurrent rose diagrams derived from cross beds reveal easterly to northerly modes adjacent to the Kunlun Mountains (Fig. 1).

Agglutinated foraminifera are the only fauna recognized in the lower Kukebai Formation

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and only occur locally high up in the section in mudstones and argillaceous siltstones at Wulukeqiat and Birtkuoyi in the northwestern portions of the study area (Fig. 1; Table 5).

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Generic and specific diversities of the assemblage are very low (Zhong, 1984; Hao et al., 1988).

5.1.2 Interpretation: Braided Fluvial

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The scour-based, upward-fining cycles typical of this facies association are compatible

with a braided-fluvial depositional setting as interpreted elsewhere by Miall (1977), Cant and Walker (1978), Miall and Tyler (1991), Bridge (1993), Bridge and Tye (2000) amongst others. The multistory-multilateral architecture resembles stacked channel elements described by Miall (1996) and Miall and Jones (2003) and represents the deposits of lateral switching and scour and fill of braided channels. Within-channel elements overlying basal scour surfaces include 9

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conglomeratic-sandstone that developed during flood peak discharge, and upward-fining cycles containing St, Sp and Sh related to waning stages of discharge (cf. Williams and Rust, 1969; Bridge and Gabel, 1992; Bridge, 1993; Bridge and Tye, 2000). The predominance of St and Sp

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implies the presence of transverse and linguoid, in-channel bars whereas Sh indicates local and short-lived, upper flow regime conditions on channel bars (Allen, 1983; Best et al., 2003).

Channel bar wave lengths in modern rivers may reach several hundred meters, but the longer

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examples probably represent composite, coalesced forms (Miall, 1977). Subordinate

mudstone drapes are interpreted as the deposits of overbank-abandoned floodplain environments.

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Conversely, the presence of mudstone drapes and agglutinated foraminera may support an upward transition to estuarine conditions (e.g. Nio and Yang, 1991; Murray and Alve, 2011). Angular to subrounded framework grains coupled with relatively high feldspar and lithic contents of most samples (Figs. 7 and 8) reflects short-distance transport and relatively rapid

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deposition in the braided alluvial systems.

5.2 Facies Association 2

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5.2.1 Description

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Facies association 2 (FA-2) is widely developed in the middle Kukebai Formation and consists predominantly of gray-green gypsiferous mudstone with interbeds of gypsum and packstone and wackestone up to 25 cm thick, and subordinate wave and current rippled sandstones and siltstones (Fg, Sh, Sr and Fc; Fig. 6E, 9C). The white gypsum typically occurs as concretions or thin beds. Within the Kashgar Sag (Fig. 1), the diversity and abundance of fossil biota are significantly greater in FA-2 compared with FA-1. Fauna include foraminifera, ostracods, 10

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ammonites, bivalves, echinoids and gastropods, and flora consist mainly of algae, coccoliths, dinoflagellates and acritarchs (Table 5; Mao and Norris, 1984; Hao et al., 1988; Pan, 1990). In the Yecheng Sag and on Qimugen Uplift (Fig. 1), foraminifera consist almost exclusively of

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agglutinated forms with low generic and specific diversities (Hao et al., 1988).

5.2.2 Interpretation: Lagoon

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The grey-green color of the sedimentary rocks and the common occurrence of wave ripples in FA-2 favor a reduced depositional setting influenced by waves such as a lagoon (cf. Levy,

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1974; Paik and Kim, 2006). Fossil assemblages (ammonites and echinoids) indicate that salinities closely approached marine conditions in Kashgar Sag whereas in Yecheng Sag and on Qimugen Uplift conditions were too saline for the development of marine organisms as indicated

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by the presence of gypsum (Hao et al., 1988).

5.3 Facies Association 3

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5.3.1 Description

Facies association 3 (FA-3) is widely developed in upper Kukebai Formation and consists

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of thick mudstone intervals with intercalated fine-grained, rippled sandstone-siltstone beds and thin tabular to lenticular beds (0.1 to 0.5 m) of packstone (Pm) or wackestone (Wm) (Sh, Sr , Fc and Fif; Fig. 6F; 9D). Sandstone-siltstone beds range between 5 and 30 cm thick and consist of parallel-laminated overlain by wave-rippled intervals. Argillaceous beds typically are dark graygreen and carbonates beds are grey in color. Mudstones are either massive or horizontally laminated (Fc) whereas fine-grained sandstones typically are rippled (Sr). Mudstone beds contain

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tabular or lenticular beds of wackestone and packstone especially in the Tongyuluk and Birtkuoyi sections. Fauna in FA-3 occur mainly in the intercalated limestone facies and include diverse,

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open-marine fauna including foraminifera, ostracods, ammonites, bivalves, brachiopoda,

echinoids and gastropods (Fig. 11A, B; Table 5). Flora consisting of coccolithes, dinoflagellates

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and acritarchs are common in the mudstone facies (Hao et al. 1988; Pan, 1990).

5.3.2 Interpretation: Nearshore to Shelf

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Interbedded dark gray-green mudstone and sandstone-siltstone of FA-3 reflect waning energy conditions in a wave-dominated setting. Similar cycles have been documented from shallow-shelf settings and related to waning wave oscillatory flow (De Raaf et al., 1977). Dark gray-green mudstones with horizontal laminations and interbedded fossiliferous carbonates

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indicate relatively slow sedimentation in relatively clear water typical of a low-energy nearshoreshelf setting. The diversity and abundance of fossil assemblages, supports normal-salinity, openmarine conditions (Thorson, 1957; Pan, 1990). Fossils (gastropods, foraminifera, brachiopoda

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and bivalves) in the carbonate facies support a setting with low terrestrial input. However, several beds of packstone or wackestone are composed of skeletal fragments suggesting the

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periodic occurrence of storms that lowered wave base temporarily (cf. Maynard et al., 2006). These storms caused intermixing of packstones and wackestone with lower-energy, muddominated facies.

5.4 Facies Association 4 5.4.1 Description 12

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Facies Association 4 (FA-4) comprises most of the Wuyitak and Tuyiluok formations and consists brown-red mudstone containing variable proportions of nodules and layers of gypsum (Fg) (Figs. 9E, F; Fig. 10A, B). Gypsum layers are up to 10 cm thick and nodules up to 20 cm in

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diameter. Thin beds (5 to 20 cm) of grey-white dolostone are developed locally. Rare beds of sandstone and siltstone display upward-fining cycles between 5 and 35 cm thick of parallellaminated and massive beds of very fine- to fine-grained sandstone-siltstone capped by massive

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or laminated brown-red beds of mudstone or randomly interbedded the coarser- and finer-grained facies (Sh, Sm, Sr and Fif). Symmetrical and asymmetrical ripples (Sr) are developed locally on

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bedding planes. Mudstones contain rare desiccation cracks.

Fossils are rare in this facies association. Foraminifera and other open-marine organisms are lacking in the lower Wuyitak Formation that contains only rare bivalves and ostracods. However, mudstones in the middle part of this formation are rich in foraminifers, ostracods,

al. 1988; Pan, 1990).

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ostreans and algae. Algae are the only fossils present in the Tuylouk Formation (Table 5; Hao, et

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5.4.2 Interpretation – Playa Lake

Brown-red mudstone interbedded with layers or nodules of gypsum in FA-4 implies a

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evaporitic, semi-arid to arid and oxidizing climatic setting. A playa lake setting is inferred based on the sedimentology and the highly restricted fossil assemblages in most of FA-4 (cf. Warren and Kendall, 1985; Warren, 1999; Becker and Bechstädt, 2006). The lateral extent of this facies indicates formation in a shallow evaporitic setting larger than any known today and the term shelf rather than playa-like may be more appropriate (Kendall, 1992). The more diverse fossil assemblage in the middle Wuyitak Formation is indicative of short-lived, less saline conditions 13

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(Tang et al, 1982; Yong, 1984; Hao et al, 1988; Pan, 1990). Cycles of parallel-laminated sandstone–siltstone and mudstone facies of Motif A2 are interpreted as sheet-flood deposits. Symmetrical and asymmetrical ripples and desiccation cracks provide evidence for very shallow

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water and subaerial exposure

5.5 Facies Association 5

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5.5.1 Description

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Facies association 5 (FA-5) is developed mainly in the lower Yigziya Formation and predominates in the Yecheng Sag (Fig. 3). It consists of white-gray to red-grey grainstone (Gb), packstone (Pm), wackestone (Wm) and dolostone (Dm) in tabular, apparently massive beds up to 100 cm thick (Fig. 9G, 11C). Interbedded, thin layers (5 to 30 cm) of carbonate mudstone (Mm) are parallel laminated. Local dolomitisation is more common in FA-5 than in other facies

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associations especially in the Kushanhe, Qimeigan and Keliyang sections (Fig. 1). Facies are associated in cycles averaging 1m thick that consist of mudstone, wackestone or dolomite gradational upwards into packstone of grainstone (Fig. 9G). From west to east, the proportion of

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carbonate facies decreases and mudstone content increases.

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The diversity of fossils in FA-5 is low and consists of a stenohaline assemblage of abundant rudists, ostreans, pectens, gastropods, dinoflagellates, foraminifera and ostracodes (Fig. 11D; Table 5; Hao et al. 1988; Pan, 1990).

5.5.2 Interpretation: Restricted Platform Facies association 5 records deposition on a restricted carbonate platform. The sedimentary cycles typical of FA-5 (Fig. 9G) are commonly referred to as meter-scale cycles because of their 14

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characteristic range of thicknesses (Wilkinson, 1982; Wright, 1984). They indicate an upward increase in energy and are interpreted as upward shoaling (cf. Tucker, 1985; Schlager, 1992; Wright and Burgess, 2005). Basal carbonate mudstone-dominated layers (Mm) with fossils of

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euryhaline organisms are typical of restricted and low-energy environments (Wilson, 1975;

Tucker et al., 1990) and developed following a sea-level rise. Wackestone-packstone dominated intervals in the middle of the cycles represent intermediate energy conditions whereas the

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packstone-grainstone at the top of cycles is considered record high-energy conditions. The facies succession of FA-4 records a shallowing-upward trend following a marine transgression. The

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proportion of carbonate facies decreases and the mudstone content increases from northwest to southeast indicating that energy conditions were lower in the southeastern parts of southwest Tarim Basin. Low diversity but abundant stenohaline organisms are typical of restricted and low-

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energy environments (Wilson, 1975; Hao et al., 1988; Tucker et al., 1990; Pan, 1990).

5.6 Facies Association 6 5.6.1 Description

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Facies association 6 (FA-6) is developed in the western and northern parts of the study

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area from the Birtkuoyi to the Heshilafu sections and is confined mainly to the upper Yigziya Formation (Figs. 1, 2 and 3). This facies association consists of bioclastic, oolitic and intraclastic grainstone (Gb, Gr), packstone (Pm), wackestone (Wt) and dolomite (Dm)(Fig. 11E, F). Grainstones and packstones contain abundant sand-sized, well-sorted, and well-rounded intraclasts and oolites. Oolites occur in beds between 10 and 55 cm thick. Facies are associated in cycles averaging 1 to 2 m thick and consist of wackestone, packstone or dolomite gradational upwards into grainstone (Fig. 9H, I). 15

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The diversity of fossils in FA-6 is significantly greater than in FA-5 and consists of an open-marine assemblage of gastropods, bivalves, rudists, brachiopods, bryozoa, echinoids, ammonoids, foraminfera, dinoflagellates and ostracodes (Figs. 9E, F; 11D, F; Table 5; Hao et al.

5.6.2 Interpretation: Open Platform to Platform Margin

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1988; Pan, 1990). Fossils are most abundant in the middle and upper parts of cycles.

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Grainstone and packstone dominated cycles of facies association 6 (Fig. 9H, I) are

interpreted as intermediate- to high-energy deposits of open carbonate platform and platform

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margin environments. Grainstone (Gb, Gr) and packstone (Pm) developed on an open platform or platform margin where wave energies were high (Wilson, 1975; James and Mountjoy, 1983). In common with facies association 5, the cycles in this facies association are upward shoaling and imply an upward increase in energy following initial transgression.

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The greater diversity and abundance of fossils in FA-6 relative to FA-5 also indicates that FA-6 developed under open-marine conditions within nutrient-rich waters of the photic zone (cf.

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Wilson, 1975; James and Mountjoy, 1983; Hao et al., 1988; Pan, 1990).

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6. RESERVOIR CHARACTERISTICS 6.1 Lithology and Petrography Hydrocarbon reservoirs are developed in two formations of the upper Cretaceous

Yingjisha Group: 1) sandstones of the lower Kukebai Formation and, 2) carbonate rocks of the Yigziya Formation. Reservoir rocks of the lower Kukebai Formation typically are unfossiliferous and crossbedded sandstones with minor intercalations of mudstone and pelitic siltstone (Fig. 6). 16

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Sandstones are predominantly fine- to medium-grained and locally coarse, moderately to well sorted and comprised of angular to subrounded framework grains (Figs. 8, 12). Quartz is the dominant detrital constituent ranging from 23% to 65% with an average of 55%. Some of the

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quartz grains show overgrowth and are highly fractured. Feldspars are the second most abundant detrital grains and include plagioclase, microcline and orthoclase; percentages of feldspar range up to 42% with an average value of about 31%. SEM and thin section studies show fractured,

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altered and replaced feldspars. Most feldspar grains show intense diagenetic alteration and

replacement by kaolinite. The proportion of lithic fragments ranges from 12% to 35% with an

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average of 14%. Lithics fragements, in decreasing order of abundance, include metamorphic, volcanic, and sedimentary grains. Some sandstone facies are texturally immature owing to the abundance of angular grains and poor sorting. These sandstones also are characterized by high proportions of feldspar. Carbonate reservoir rocks are represented by lime grainstones and

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dolomites. Grainstones (Gb, Gr) consist of bioclasts (e.g. foraminifera, brachiopoda, bryozoa, gastropods and bivalves) or sand-sized intraclasts (Fig. 11).

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6.2 Diagenesis and Pore Types

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6.2.1 Sandstones

The most important diagenetic processes in sandstones of the lower Kukebai Formation

that resulted in porosity and permeability changes are: 1) mechanical compaction, 2) cementation, 3) replacement and dissolution of unstable clastic grains and cements, and 4) fracturing. Mechanical compaction is evidenced by pressure-solved, concavo-convex contacts (Fig. 8). Clay minerals and iron oxides form rims around detrital grains (Fig. 13A) whereas mixed layer illitesmectite clays occurs as masses (Fig. 13B, E) that may represent authigenic cement or epimatrix 17

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formed at the expense of feldspar. Authigenic cements observed in thin section and in SEM images include iron oxide, quartz, calcite, dolomite, feldspar and gypsum (Fig. 13). Quartz overgrowths post-date rim cements (Fig. 13A) and pre-date calcite cements (Fig. 13D) but

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temporal relationships of the other cements are unclear except that gypsum is the latest cement (Fig. 13E). Porosity types include primary intergranular (Fig. 13B, C, E), secondary intergranular and intragranular related to dissolution of feldspar and igneous and metamorphic rock fragments

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and of replacement and cement calcite (Fig. 13D). Secondary microporosity associated with kaolinite replacement of feldspar (Fig. 8B). Compaction-related fracture porosity is most

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common in poorly sorted sandstone in the form of local cracking of quartz and feldspar grains (Fig. 8B). Larger fractures are filled with calcite, gypsum or mud-matrix.

6.2.2 Carbonate Rocks

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The main diagenetic processes recognized in carbonate rocks of the Yigziya Formation are cementation and dissolution. Cements observed in thin section and SEM are dominated by calcite and dolomite (Figs. 11D, E, F, 14A, B, C). Dissolution of bioclasts and intraclasts (Fig.

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14D, E), dolostone (Fig. 14F) and calcite cement (Figs. 11D, F, 14D, E) increased porosity. Pore types in carbonate include intergranular (Figs. 11D, 14A, D) intragranular (Fig. 14B),

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intercrystalline (Fig, 14B, F) most of which are secondary in origin. Fractures are common in carbonate rocks and are partially or completely filled with calcite cement (Figs. 11B, 14C).

6.3 Porosity (Φ) and Permeability (ҡ)

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Petrophysical parameters including porosity, permeability and mercury saturation were measured under ambient conditions for 510 sandstone and 200 carbonate samples from six outcrops and two well cores to evaluate the reservoir potential of the strata across the study area.

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Porosity values for sandstones range from 2.3% to 27.3% with a mean value of 13.5% (Fig. 15A). Samples with porosity values greater than 10% account for 79% of the samples. Porosity values are slightly higher for outcrop than well samples. Sandstone permeabilities range from 0.02×10-3

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µm2 to 9860×10-3 µm2 (Fig. 15A). In comparison to sandstone reservoirs, carbonate reservoirs have much lower porosities ranging from as 0.8% to 17.5% with a mean value of 5.1%, whereas

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permeabilities range from 0.02×10-3 µm2 to 98×10-3 µm2 (Fig. 15B).

Sandstone reservoir rocks of lower Kukebai Formation show a good positive correlation between porosity and permeability. However, carbonate reservoir rocks of the Yigziya Formation show a weak positive correlation between porosity and permeability (Fig. 15). The

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weak relationship is attributed to the presence of matrix and differences in pore throat sizes (cf. Mohamed et al., 2014). In sandstone and especially in carbonate reservoirs, samples with low porosity but high permeability are a result of fractures that acted as migration pathways.

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The data demonstrate that sandstones of the lower Kukebai Formation have the highest reservoir potential at Tongyuluk and the lowest reservoir potential at Qimeigan (Fig. 15A).

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Carbonate rocks of the Yigziya Formation have the highest reservoir potential at Saigertashi (Fig. 15B) close to the Kekeya Oilfield that produces from the same strata. Fractured carbonate rocks in the Birtkuoyi area are another potential exploration target. The final mercury saturation values for sandstone (78.6% to 96.7%) and carbonate rocks

(58.5 % to 86.8%) show that connectivity between pores in sandstone (Fig. 16A) is better than in carbonate rocks (Fig. 16B). For the same mercury saturation values displacement pressures for 19

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sandstone are lower than for carbonate rocks (Fig. 16), indicating that pore throats are larger in sandstone than in carbonate rocks (cf. Schowalter, 1979; Katz and Thompson, 1987; Pittman,

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1992).

7. Discussion 7.1 Stratigraphic Evolution

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A model depicting the stratigraphic evolution of the Yingjisha Group is proposed for the

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southwest Tarim basin based on vertical changes in inferred depositional environments that reflect changes in water depth and climate with time (Fig. 17). The model portrays at least two transgressive-regressive cycles that can be correlated with the global eustatic curve of Haq et al. (1988). The local presence of foraminifera in the lower Kukebai Formation is consistent with initial transgression from the northwest through a narrow passage between the Kunlun and

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Tianshan mountains (Fig. 19A; Hao et al., 1988; Pan, 1990) and related to expansion of the Tethys Sea (Vinogradov, 1967-69; Hao et al., 1988; Jia, 1997). However, the low abundance of fossils indicates that conditions were unfavorable for the development of diverse marine

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organisms because of high-energy and/or low-salinity conditions (Hao et al., 1988).

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Transgression in the Cenomanian and early Turonian is recorded in the transition from braided-fluvial deposits of Facies Association 1 to lagoonal and nearshore-shelf facies of Facies Associations 2 and 3 in the Kukebai Formation (Figs. 2, 3, 17A, 18A). This succession is assigned to a lowstand and transgressive systems tract (cf. Posamentier and Vail, 1988). Highenergy braided-fluvial deposits developed along the entire southwestern margin of Tarim Basin except for local playa-lake deposition adjacent to the Tianshan Mountains (Fig. 4). Paleocurrent data from facies association 1 reveal a paleoslope to the east and northeast away from the rising 20

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Kunlun Mountains (Fig. 1). With continued transgression from the northwest during middle to late Cenomanian coupled change to an arid climate (Jia, 1997), lagoonal environments developed in the Kashgar Sag (Fig. 2) and extended across Qimugen Uplift and into the Yecheng Sag where

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more restricted circulation existed (Fig. 18B). Open-marine, nearshore to shelf conditions developed across much of the study area by the late Cennomanian except in the extreme

southeast. The depositional model and inferred paleogeography (Fig. 18A - C) for the Kukebai

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Formation illustrate only continental and marginal marine siliciclastic facies of facies

associations 1, 2 and 3 but it is possible that these passed down paleoslope and more distally into

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carbonate facies of facies associations 5 and 6. However, this cannot be substantiated in the absence of subsurface data east of the study area.

Playa-lake, brown-red mudstone with gypsum and fine-grained sandstone of Facies Association 4 of the Wuyitak Formation indicates a major regression in the late Turonian (Figs.

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17B, 18D; Hao et al., 1988; Zhou and Barthan, 2000; Guo et al., 2002; Fang et al., 2009). This interval of strata is assigned to a highstand systems tract (cf. Becker and Bechstädt, 2006). Many outcrops and wells show that Facies Association 4 developed uniformly throughout the Kashgar

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and Yecheng sags under saline, uniformly arid conditions (Figs. 2, 3) on what may have been an extensive evaporitic shelf with no modern counterpart (cf. Kendall, 1992). Mudstones in the

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middle part of Wuyitak Formation rich in foraminifers, ostracods, ostreans and algae (Table 5) reflect a short-term transgression leading to more marine conditions. The Yigziya Formation records a second major transgression commencing in the

Coniacian (Wang and Fu, 1996; Zhou and Barthan , 2000; Guo et al., 2002; Fang et al., 2009) as exemplified by the development of open and restricted marine carbonates of Facies Associations 5 and 6, with the local development of playa lake deposits of Facies Association 4 adjacent to the 21

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Tianshan Mountains (Figs. 17C, 18E). This succession is assigned to a transgressive systems tract (cf. Handford and Loucks, 1993). Restricted platform facies predominate over and adjacent to the Qimugen Uplift (Qimeigan, Tuo 1, Artashi) and in the southern part of the study area

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(Heshilafu – Keliyang) whereas open platform facies predominate within the sags (Birtkuoyi – Kushanhe, Ganjiat) (Figs. 2, 3, 18E, F). The depositional model for the Yigzia Formation

illustrates only marine carbonate facies of Facies Associations 5 and 6 but it is possible that these

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passed up the paleoslope into more proximal braided alluvial facies that were eroded with uplift of the Kunlun Mountains.

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A second major regression in the late Campanian on a scale larger than that represented by the Wuyitak Formation is recorded by playa-lake facies of the Tuyiluok Formation (Fig. 17D) (Guo et al., 2002; Fang et al., 2009; Liu et al., 2012). Non-fossiliferous gypsum-mudstone of Facies Association 4 record restricted, high-salinity, arid conditions (Fig. 18G). No modern

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counterpart exists for this succession that is interpreted as a highstand systems tract deposit (cf. Kendall, 1992; Becker and Bechstädt, 2006).

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7.2 Controls on Reservoir Quality

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7.2.1 Paleoenvironment

Reservoir characteristics such as thickness and lateral continuity as well as sediment

composition, grain size and sorting are a product of the paleoenvironment. Scatter plots of porosity and permeability values as a function of grain size for lower Kukebai Formation braided- alluvial sandstones show that both porosity and permeability increase with the increasing grain size (Fig. 19A). Lagoonal, shelf and playa lake deposits have poor reservoir quality because of their fine grain size and poor sorting. For carbonate reservoirs, open platform 22

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to platform margin bioclastic and intraclastic grainstones have the best reservoir quality whereas some of the dolostone also possess good reservoir properties (Fig. 19B). Packstones and wackestones have the lowest potential as reservoir rocks. In general, the porosity and

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permeability values for both sandstone and carbonate reservoirs display a positive correlation with depositional energy conditions. Sandstone reservoirs of lower Kukebai Formation range in thickness from 10 to 145 m and extend laterally for tens of kilometers whereas carbonate

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reservoirs of Yigziya Formation are 0.5 to 36 m-thick tabular bodies that have limited lateral

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continuity.

7.2.2 Diagenesis

Depositional environment controls the original properties of reservoirs whereas burial diagenesis and diagenetic alterations of framework grains play an important role in the

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destruction, preservation and development of pore types, pore volumes, permeability and pore distribution (Nichols, 2009). Post-depositional compaction resulted in initial porosity loss in sandstones (Fig. 20). Cementation particularly by quartz, calcite and dolomite in sandstones and

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calcite and dolomite in limestones was the predominant porosity reduction mechanism with burial (Fig. 20). Epigenetic or authigenic mixed-layer illite-smectite also resulted in pore

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destruction in sandstone reservoirs. The presence of corroded grains (feldspar, volcanic framework grains in sandstone and bioclasts in carbonate rocks) (Fig. 8A, B), corroded carbonate cements (Fig. 11D, F) and oversized pores (Fig. 14E, F) suggests that aggressive fluids caused partial or complete dissolution of minerals to produce secondary pores (cf. Schmidt and McDonald, 1979; Curtis, 1983; Giles and Marshall, 1986; Giles, 1987).

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8. Conclusions This study has demonstrated the utility of detailed paleoenvironmental analysis in

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understanding and predicting the occurrence of potential reservoir rocks in mixed siliciclasticcarbonate successions in general, and in the Upper Cretaceous, Yingjisha Group in the southwest Tarim Basin in particular. Specifically, high-energy braided-fluvial sandstones and carbonate platform grainstones that are dolomitized locally comprise the best reservoirs in the Yingjisha

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Group. Sandstone reservoirs are up to 145 m thick and extend laterally for tens of kilometers whereas carbonate reservoirs are only 0.5 to 36 m thick and have limited lateral continuity.

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Porosity and permeability values for both sandstone and carbonate reservoirs display a positive correlation with depositional energy conditions. Reservoir quality expressed in terms of porosity and permeability is a function of not only the paleoenvironment but is related also to burial diagenesis, fracturing, and the competency of basement rocks. Diagenesis, in particular grain

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dissolution, was important in developing reservoir-quality strata. The Yingjisha Group records at least two transgressive - regressive cycles that can be correlated with the global eustatic curve of Haq et al. (1988) and that stacked seal rocks above reservoirs during the late transgressive and

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regressive phases of sedimentation (Figs. 2, 3, 17).

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Acknowledgements

The authors thank the Tarim Oilfield Company facility for their assistance with access to

core samples. We also acknowledge NSFC (project 410023 /2011; 41302076/2013) and the Education Department of Shaanxi (project 14JS081/2014) for financial support. Ren Kangxu and Lu Yuhong are thanked for porosity and permeability analysis, SEM manipulation and photomicrograph acquisition. We also thank Yang Zhilin, Zeng Changmin, Liu Hongfei and Yin 24

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Baosen for their assistance in outcrop surveying and sampling in the field. This paper was prepared while the senior author was a visiting scientist in the Department of Geosciences at

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Virginia Tech. The authors benefitted from the valuable comments of two anonymous reviewers.

References

Allen, J.R.L., 1983. Studies in fluviatile sedimentation: Bars, bar-complexes and sandstone

SC

sheets (low-sinuosity braided streams) in the brownstones (L. Devonian), Welsh Borders.

M AN U

Sediment. Geol. 4, 237-293.

Becker, F., Bechstädt, T., 2006. Sequence stratigraphy of a carbonate-evaporite succession (Zechstein 1, Hessian Basin, Germany). Sedimentology 53, 1083–1120. Best, J.L., Ashworth, P.J., Bristow, C., Roden, J., 2003. Three-dimensional sedimentary architecture of a large, mid-channel sand braid bar, Jamuna River, Bangladesh. J.

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Sediment. Res. 73, 516-530.

Bosboom, R.E., Dupont-Nivet, G., Houben, A.J.P., et al., 2011. Late Eocene sea retreat from the Tarim Basin (west China) and concomitant Asian paleoenvironmental change.

EP

Palaeogeog. Palaeoclim. Palaeoecol. 299, 385-398.

AC C

Bridge, J.S., 1993. The interaction between channel geometry, water flow, sediment transport and deposition in braided rivers. In: Best, J.B. and Bristow, C.S. (Eds.), Braided Rivers, The Geological Society of London, Special Publications, vol. 75, pp. 13-71.

Bridge, J.S., Gabel, S.L., 1992. Flow and sediment dynamics in a low sinuosity, braided river: Calamus River, Nebraska Sandhills. Sedimentology 39, 125-142.

25

ACCEPTED MANUSCRIPT

Bridge, J.S., Tye, R.S., 2000. Interpreting the dimensions of ancient fluvial channel bars, channels, and channel belts from wireline-logs and cores. Bull. Am. Assoc. Petrol. Geol. 84, 1205-1228.

RI PT

Burtman, V.S., 2012. Geodymanics of Tibet, Tarim, and the Tien Shan in the Late Cenozoic. Geotectonics 46, 185-211.

Cant, D. J., Walker, R. G., 1978. Fluvial processes and facies sequences in the sandy braided

SC

South Saskatchewan River, Canada. Sedimentology 25, 625-648.

Curtis, C.D., 1983. Geochemistry of porosity enhancement and reduction in clastic sediments. In:

pp. 113-125.

M AN U

Brooks, J. (Ed.), Petroleum Geochemistry and Exploration of Europe. Blackwell, Oxford,

DeRaaf, J.F.M., Boersma, J.R., Van, Gelder, A., 1977. Wave-generated structures and sequences from a shallow marine succession, Lower Carboniferous, County Cork, Ireland.

TE D

Sedimentology 24, 451-483.

Ding, X.Z., Guo, X.P., Peng, Y., Ji, Y.L., 2002. A study of Cretaceous-Tertiary sequence stratigraphy of Tarim Basin, Xinjiang. Acta Geosci. Sinica 23, 243-248 (in Chinese with

EP

English abstract).

Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In:

AC C

Hamm, W.E. (Ed.), Classification of Carbonate Rocks, A Symposium. American Association of Petroleum Geologists, Memoir 1, pp. 108-121.

Fang, A.M., Ma, J.Y., Wang, S.G., 2009. Sedimentary tectonic evolution of the southwestern Tarim Basin and west Kunlun orogen since the Late Paleozoic. Acta Petrol. Sinica. 25,

3396-3406 (in Chinese with English abstract). Folk, R.L, 1974. Petrology of Sedimentary Rocks. Hemphill’s, Austin, Texas, pp.182 26

ACCEPTED MANUSCRIPT

Giles, M.R., 1987, Mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs. Mar. Petrol. Geol. 4, 188-204 Giles, M.R., Marshall, J.D., 1986, Constraints on the development of secondary porosity in the

RI PT

subsurface: reevaluation of processes. Mar. Petrol. Geol. 3, 243-255.

Gu, J.Y., 1996. Characteristics and Evolution of Depositional Sequences in Tarim Basin. Petroleum Industry Press, Beijing, pp. 19-96 (in Chinese).

SC

Guo, X.P., Ding, X.Z., He, X.X., 2002. New progress in the study of marine strata of marine transgressional events in the Meso-Cenozoic in the Tarim Basin. Acta Geologica Sinica

M AN U

76, 299-307(in Chinese with English abstract).

Guo, Q.Y., Li, Y., Zhang L., Zeng, C.M., 2014. Sedimentary facies characteristics of the Cretaceous in southwestern Tarim Basin. J. Palgeog. 16, 169-178 (in Chinese with English abstract).

TE D

Handford, C.R., Loucks, R.G., 1993. Carbonate depositional sequences and systems tracts – responses of carbonate platforms to relative sea-level changes. In: Loucks, R.G. and Sarg, J.F. (Eds.), Carbonate Sequence Stratigraphy, American Association Petroleum

EP

Geologists, Memoir 57, pp. 3–41.

Hao, Y.C., Zeng, X.L., 1980. Early Tertiary foraminifera from the Kashgar Basin of Xinjiang.

AC C

Acta Palaeont. Sinica. 1, 152-167 (in Chinese with English abstract).

Hao, Y.C., Zeng, X.L., 1984. On the evolution of the west Tarim gulf from the Mesozoic to Cenozoic in terms of characteristics of foraminiferal fauna. Acta Micropalaeont. Sinica. 1, 1-16 (in Chinese with English abstract).

27

ACCEPTED MANUSCRIPT

Hao, Y.C., Zeng, X.L., Guo, X.P., 1988.The marine Cretaceous in the western part of the Tarim Basin of Xinjiang and its depositional environments. Acta Geologica Sinica 1, 13-27 (in Chinese with English abstract).

RI PT

Haq, B.U., Hardenbol, J., Vail, P.R., 1988. Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change. Society of Economic Paleontologists and Mineralogists, Special Publication , vol. 42, pp. 71-108.

SC

He, D.F., Li, D.S., 1996. Tectonic Evolution and Hydrocarbon Accumulation in Tarim Basin. Geological Publishing House, Beijing, pp. 167 (in Chinese).

M AN U

He, D.F., Li, H.H., 1998. History and counter measures of petroleum exploration in Tarim southwest depression. Petrol. Expl. 3, 37- 42 (in Chinese with English abstract). He, D.F., Jia, C.Z., Li, D.S., 2005. Formation and evolution of the poly-cyclic superimposed Tarim Basin. Oil & Gas Geology 26, 64-77 (in Chinese with English abstract).

TE D

He, D. F., Li, D. H., He, J. Y., 2013. Comparison of petroleum geology between Kuqa depression and Southwest depression in Tarim Basin and its exploration significance. Acta Petrol. Sinica 34, 201-218 (in Chinese with English abstract).

EP

Hu, W.H., Chen, Y., Xiao, A.C., 1997. Tectonic evolution and petroleum systems in the southwest depression of Tarim Basin. Petrol. Expl. Dev. 24, 14-17 (in Chinese with

AC C

English abstract).

James, N.P., Mountjoy, E.W., 1983, Shelf-slope break in fossil carbonate platforms - an overview. In: Stanley, D.J., and Moore, G.T., (Eds.), The Shelfbreak - Critical Interface

on Continental Margins. Society of Economic Paleontologists and Mineralogists, Special

Publication, vol. 33, 189-206.

28

ACCEPTED MANUSCRIPT

Jia, C.Z., 1997. Tectonic Characteristics and Petroleum, Tarim Basin, China. China Petroleum Industry Press, Beijing, pp. 182-383 (in Chinese with English abstract). Jia, C.Z., 1999. Structural characteristics and oil/gas accumulative regularity in Tarim basin.

RI PT

Xinjiang Petrol. Geol. 20, 177-183 (in Chinese with English abstract).

Jia, C.Z., Zhang, S.B., Wu, S.Z., 2004. Tarim Basin and its Peripheral Formation. Beijing, Science Press, pp. 1-23 (in Chinese).

SC

Jin, Z.J., Lu, X.X., 2000. Hydrocarbon resources and exploration of foreland basin in southwest Tarim basin. Oil Gas Geol. 21, 110-117 (in Chinese with English abstract).

M AN U

Jin, Z.J., Zhang, Y.W., Chen, S.P., 2005. Tectonic-depositional evolution of Tarim Basin. Sci. China (Ser. D Earth Sciences) 6, 530-539 (in Chinese with English abstract). Kang, Y.Z., 1996. Petroleum Geology Characteristics and Resource Evaluation of Tarim Basin in China. Geological Publishing House, Beijing, pp. 316-324 (in Chinese).

TE D

Katz, A. J., Thompson, A. H., 1987. Prediction of rock electrical conductivity from mercury injection measurements. J. Geophys. Res. 92, 599-607. Kendall, A.C., 1992. Evaporites. In: Walker, R.G. and James, N.P., (Eds.), Facies Models:

EP

Response to Sea Level Change. Geological Association of Canada, pp. 375-409. Liu, C.S., Zhang, L.T., Guo, J.H., 2012. Sequence of Cetaceous in Tarim Basin. J. Central South

AC C

Univ. (Science and Technology) 7, 2683-2690 (in Chinese with English abstract).

Levy, Y., 1974. Sedimentary reflection of depositional environments in the Bardawil lagoon, northern Sinai. J. Sediment. Petrol. 44, 219-227.

Mao S., Norris, G., 1984. Dinoflageooate and acritarches stratigraphy (late Cretaceous and Early Tertiary), Western Tarim Basin, Xinjiang Autonomous Region, Northwest China. Earth Sci. 2, 7-22 (in Chinese). 29

ACCEPTED MANUSCRIPT

Matte, P., Tapponier, P., Arnaud, N., Bourjot, L., et al., 1996. Tectonics of western Tibet, between the Tarim and the Indus. Earth Planet. Sci. Lett. 142, 311-330. Maynard, J.P., Eriksson, K.A., Law, R.D., 2006. The upper Mississippian Bluefield Formation in

RI PT

the Central Appalachian basin: A hierarchical sequence-stratigraphic record of a greenhouse to icehouse transition. Sediment. Geol. 192, 99-122.

62.

SC

Miall, A.D., 1977. A review of the braided-river depositional environment. Earth Sci. Rev. 13, 1-

Miall, A.D., 1985. Architectural-element analysis: a new method of facies analysis applied to

M AN U

fluvial deposits. Earth Sci. Rev. 22, 261-308.

Miall, A.D., 1996. The Geology of Fluvial Deposits. Springer-Verlag, New York, p. 582. Miall, A.D., Jones, B.G., 2003. Fluvial architecture of the Hawkesbury Sandstone (Triassic), near Sydney, Australia. J. Sed. Res. 73, 531-545.

TE D

Miall, A., Tyler, N., 1991. (Eds.) Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery. SEPM, Concepts in Sedimentology and Paleontology no. 3, Tulsa, pp. 309.

EP

Mohamed, A.K., Ibrahim, M.H., Alaa, M., 2014. Petrography, diagenesis and reservoir characteristics of the Pre-Cenomanian sandstone, Sheikh Attia area, East Central Sinai,

AC C

Egypt. J. Afr. Earth Sci. 96, 122-138.

Mou, Z.H, Zhao, K.B., Tang, Y., Yang, J., 2002a. Paleozoic seismic-stratigraphy of the southwest Tarim Basin. Xinjiang Geol. 20, 83-88 (in Chinese with English abstract)

Mou, Z.H., Tang, Y., Cui, B.F., 2002b. Erosion thickness restoration in southwest Tarim Basin. Acta Petrol. Sinica 23, 40-44 (in Chinese with English abstract)

30

ACCEPTED MANUSCRIPT

Murray, J. W., Alve, E., 2011. The distribution of agglutinated foraminifera in NW European seas: Baseline data for the interpretation of fossil assemblages. Palaeontologia Electronica 14, 14.2.14A.

RI PT

Nichols, G., 2009. Sedimentology and Stratigraphy (second edition). Wiley-Blackwell, Oxford, United Kingdom, p. 419.

Nio, S.D., Yang, C.S., 1991. Diagnostic attributes of clastic tidal deposits: a review. In: Smith,

SC

D.G., Reinson, G.E., Zaitlin, B.A. and Rahmani, R.A., (Eds.), Clastic Tidal

Sedimentology, Canadian Society of Petroleum Geologists, Memoir 16, pp. 3-28.

M AN U

Paik, I.S., Kim, H.J., 2006. Playa lake and sheetflood deposits of the Upper Cretaceous Jindong Formation, Korea: Occurrences and palaeoenvironments. Sediment. Geol. 187, 83 - 103. Pan, H.Z., 1990. Late Cretaceous gastropod dominated communities of the Western Tarim Basin, Southern Xinjiang, China. Lethaia 23, 273-289.

TE D

Pittman, E.D., 1992. Relationship of porosity and permeability to various parameters derived from mercury injection-capillary pressure curves for sandstone. Bull. Am. Assoc. Petrol. Geol. 76, 191-198.

EP

Posamentier, H., W., Vail, P., R., 1988. Eustatic controls on clastic deposition. II sequence and systems tract models. In: Wilgus, C., K., Hastings, B., S., Posamentier, H., W., Van

AC C

Wagoner, J., Ross, C., A., Kendall, G., C., St., C. (Eds.), Sea-Level Changes - An

Integrated Approach. Society of Economic Paleontologists and Mineralogists, Special Publication 42, pp. 125–154.

Robertson, A.H.F., Parlak, O., Ustaomer, T., 2012. Overview of the Palaeozoic-Neogene evolution of Neotethys in the Eastern Mediterranean region (southern turkey, Cyprus, Syria). Petrol. Geosci. 18, 381-404. 31

ACCEPTED MANUSCRIPT

Robinson, D.M., Dupont-Nivet, G.., Gehrels, G. E., Zhang, Y.Q., 2003. The Tula uplift, northwestern China: Evidence for regional tectonism of the northern Tibetan Plateau during late Mesozoic–early Cenozoic time. Bull. Geol. Soc. Am. 115, 35-47.

RI PT

Scharer, K.M., Burbank, D.W., Chen, J., et al., 2004. Detachment folding in the southwestern Tian Shan-Tarim foreland, China: shortening estimates and rates. J. Str. Geol. 26, 2119 2137.

SC

Schlager, W., 1992. Sedimentology and sequence stratigraphy of reefs and carbonate platforms.

Geologists, Tulsa, pp. 71.

M AN U

Continuing Education Course Note Series 34, American Association of Petroleum

Schmidt, V., McDonald, D.A., 1979. The role of secondary porosity in the course of sandstone diagenesis. Society of Economic Paleontologists and Mineralogists, Special Publication, vol. 26, pp. 175-207.

Bull. 63, 723-760.

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Schowalter, T. T., 1979, Mechanics of secondary hydrocarbon migration and entrapment. AAPG

Sobel, E. R., 1999. Basin analysis of the Jurassic-Lower Cretaceous southwest Tarim Basin,

EP

northwest China. Bull. Geol. Soc. Am. 111, 709-724. Sun, L.D., 2004. Sedimentary facies and exploration of petroleum of the Early Cretaceous in

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Kuqa depression and southwest depression in Tarim Basin. J. Paleogeog. 2, 252-260 (in Chinese with English abstract).

Tang, T.F., Yang, H.G., Hu, L.Y., et al., 1982. The marine strata of the Late Cretaceous and the Early Tertiary and its depositional environment. Papers of the Symposium of Petroleum and Earth Science, Acad. Sinica, pp. 117-126 (in Chinese with English abstract).

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Tang, T.F., Yu, H.R., Lan, X., et al., 1989. Marine Late Cretaceous and Early Tertiary stratigraphy and petroleum geology in western Tarim Basin. Science Press, Beijing. p. 155.

America, Memoir 67, pp. 461-534.

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Thorson, G. 1957. Bottom communities (sublittoral or shallow shelf). Geological Society of

Tucker, M.E., 1985, Calcitized aragonite ooids and cements from the Late Precambrian Biri

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Formation of southern Norway. Sediment. Geol. 43, 67-84.

Tucker, M.E., Wilson, J.L., Crevello, P.D., et al. (Eds.), 1990. Carbonate Platforms - Facies,

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Sequences and Evolution, Blackwell, Oxford, p. 328.

Vingradov, A.P., 1967-69. Atlas of the lithological-paleogeographical maps of the USSR. Minist. Geol. USSR & Acad. Sci. USSR, 4 pts., 255 maps. Moscow. . Wang, Y., Fu, D.R., 1996. The sedimentary-tectonic evolution of southwest Tarim Basin from

English abstract).

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Cretaceous to Paleocene. Bull. Chinese Acad. Geol. Sci. 17, 32-40 (in Chinese with

Warren, J.K., 1999. Evaporites – Their Evolution and Economics. Blackwell Science, Oxford, pp.

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438.

Warren, J.K., Kendall, C.G.St.C., 1985. Comparison of sequences formed in marine sabkha

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(subaerial) and salina (subaqueous) settings – modern and ancient. Bull. Am. Assoc. Petrol. Geol. 69, 1013–1023.

Wilson, J.L. 1975. Carbonate Facies in Geologic History. Springer, New York, p. 471. Williams, P.F., Rust, B.R., 1969, The sedimentology of a braided river. J. Sediment. Petrol. 39, 649-679.

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Wilkinson, B.H., 1982. Cyclic cratonic carbonates and Phanerozoic calcite seas. J. Geol. Ed. 30, 189-203. Willett, S.D., Beaumont, C., 1994. Subduction of the Asian lithospheric mantle beneath Tibet

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inferred from models of continental collision. Nature 369, 642-645.

Wittlinger, G.,Vergne, J., Paul, T., et al., 2004. Teleseismic imaging of subducting lithosphere and Moho offsets beneath western Tibet. Earth Planet. Sci. Lett. 221, 117-130.

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Wright, V.P., 1984. Peritidal carbonate facies models: A review. Geol. J. 19, 309-325. Wright, V.P., Burgess, P., 2005. The carbonate factory continuum, facies mosaics and

sedimentology. Facies 51, 17-23.

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microfacies: an appraisal of some of the key concepts underpinning carbonate

Xiao, A.C., Yang, S.F., Chen, H.L., 2000. Tectonic characteristics of thrusts in the west Kunlun mountains. Earth Science Frontiers, Suppl. 2, 128-135 (in Chinese with English abstract).

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Yong, T.S., 1984. Late Cretaceous to Early Tertiary lithofacies palaeogeography in Tarim Basin. Petrol. Geol. and Expt. 1, 1-17 (in Chinese with English abstract). Zhang, B., Lu, X., Cao, C.C., 2008. Natural gamma energy spectrum data for strata correlation in

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system tracts of Wushi depression, Tarim Basin. Natural Gas Geosci. 1, 89-93 (in Chinese with English abstract).

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Zhang, H.L., Shen, Y., Zhang, R.H., Li, Y.W., 2005. Characteristics of sedimentary facies and petroleum geological significance of the Lower Cretaceous in front of Kunlun Mountains in southwestern Tarim Basin. J. Paleogeog. 7, 157-168 (in Chinese with English abstract).

Zhao, J.Z., Li, Q.M., 2003. Oil and Gas Reservoir Formation and Distribution in Tarim Basin. Beijing, Petroleum Industry Press, pp. 12-25 (in Chinese).

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Zhong, S.L., 1984. Calcareous nannofossils from the Cretaceous Kukebai Formation in the Western Tarim Basin, South Xinjiang, China. Acta Micropalaeont. Sinica 2, 201-205.

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Zhou, S.Y., Barthan S., 2000. Paleogeography of the Cretaceous in Xinjiang. Xinjiang Geol. 4, 347-351.

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Figure Captions Figure 1: (A) Location of the Tarim Basin in NW China; (B) Location of the study area in the

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Tarim Basin; (C) Simplified tectonic map of the Piedmont Zone of the Kunlun Mountains. Rose diagram insets show paleocurrent azimuths for cross beds from braided-river facies (FA-1). Two different colors are used for the dashed line (red for Figure 2 and blue for Figure 3).

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Figure 2: Cross section of measured outcrop sections and boreholes subparallel to depositional strike showing formation boundaries, facies and depositional environments, Kashigar Sag

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and Qimugen Uplift. Refer to Figure 1 for location of cross section (red broken line). LST - Lowstand Systems Tract; TST - Transgressive Systems Tract; HST - Highstand Systems Tract.

Figure 3: Cross section of measured outcrop sections and boreholes subparallel to depositional

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strike showing formation boundaries, facies and depositional environments, Yecheng Sag and Qimugen Uplift. Refer to Figure 1 for location of cross section (blue broken line). LST - Lowstand Systems Tract; TST - Transgressive Systems Tract; HST - Highstand

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Systems Tract. Refer to Figure 2 for Legend. Figure 4: Stratigraphic column and facies interpretations for the upper Cretaceous of Ake-1 well.

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The location of the well is shown in Figure 1. Refer to Figure 1 for location of section.

Figure 5: Photomosaic (A) showing outcrops characteristics of the upper Cretaceous Yingjisha Group in the Aoyitag section (refer to Figure 1 for location). K1k-Kezilesu Formation; K2k1 - Lower Kukebai Formation; K2k2 - Upper Kukebai Formation; K2w2 - Wuyitak Formation; K2y2 - Yigziya Formation; K2t2 - Tuyiluok Formation. Insets show: (B) Lower Kukebai Formation: Brown-red, coarse- to fine-grained sandstone; (C) Upper Kukebai 36

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Formation: Mudstone interbedded with white gypsum; (D) Wuyitak Formation: Brownred gypsiferous mudstone; (E) Yigziya Formation: Grainstone and packstone with

Tuyiluok Formation: Brown-red gypsiferous mudstone.

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brachiopoda and bivalve fossils; (F) Yigziya Formation: Red-gray carbonates; (G)

Figure 6: Outcrop photographs of siliciclastic facies in the Kukebai Formation. (A) Facies Cg: Poorly sorted, grain-supported conglomerate; upward fining, scour-fill structures,

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Keliyang; (B) Facies St: Moderately- to well-sorted, coarse to medium-grained sandstone; trough cross bedding, Birtkuoyi; (C) Facies Sp: Moderately- to well-sorted, coarse to

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medium-grained sandstone; tabular cross bedding, Birtkuoyi; (D) Facies Sh: Well-sorted, fine-grained, sandstone; horizontal bedding, Tongyuluk; (E) Facies Sr: Well-sorted, finegrained sandstone with wave ripples, Saigrtashi; (F) Facies Sr: Well-sorted, fine-grained sandstone with current ripples, Ganjiat.

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Figure 7: Compositional ternary diagrams showing mineral compositions of sandstones. (A) Very fine- to fine-grained sandstones: arkoses, lithic arkoses and feldspathic litharenites; (B) Coarse- to medium-grained sandstone: lithic arkoses, feldspathic litharenites and

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litharenites. Sandstone samples are mainly from the Kukebai Formation (95%) and include some very fine-grained samples from Wuyitak and Tuyiluok formations (5%).

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Figure 8: Photomicrographs of sandstones from the Kukebai Formation. (A) Medium- to finegrained lithic arkose, Aoyitag; (B) Medium- to fine-grained lithic arkose, Birtkuoyi; (C) Medium- to fine-grained feldspathic litharenite with partial to complete replacement of feldspar by calcite, Birtkuoyi; (D) Medium-to fine-grained lithic arkose, Artashi. XPL: cross-polarized light; PPL: plane-polarized light; Q: quartz; F: feldspar; L: lithic fragment;

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aq: quartz overgrowth; Ca: calcite; Pink color represents porosity (Figs. 8A and B), red stain represents calcite (Fig. 8C). Figure 9: Vertical successions of facies within facies associations. The location of the section is

and Table 3 are modified from Miall (1985).

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shown in figure 1. Facies codes, sedimentary structures and interpretations as in Table 2

Figure 10: Outcrop photographs of siliciclastic mudstone and carbonates facies. (A) Facies Fg:

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Mudstone with nodular, white gypsum, Wuyitak Formation, Keliyang; (B) Facies Fg: Mudstone with nodular, white gypsum, Wuyitak Formation, Birtkuoyi; (C) Facies Fc and

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Wm: Calcareous mudstone interbedded with tabular wackestone, Kukebai Formation, Saigrtashi; (D) Facies Fc: Photomicrograph of wackestone showing bioclasts floating in muddy matrix, Kukebai Formation, Saigrtashi; (E) Facies Gb: Grainstone consisting of framework-supported bioclasts, Yigziya Formation, Aoyitag; (F) Facies G: Grainstone

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consisting of framework-supported intraclasts, Yigziya Formation, Birtkuoyi. Figure 11: Photomicrographs of carbonate facies. (A) Facies Pm: packestone consisting of bioclasts in a muddy matrix, poorly to moderately sorted, brachiopoda and bivalves,

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Birtkuoyi, Kukebai Formation; (B) Facies Wm: Wackestone consisting of matrixsupported bioclasts, Aoyitag, Kukebai Formation; (C) Facies Dm, Dolostone consisting

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of irregular, semi-euhedral rhombic crystals, Artashi, Yigziya Formation; (D) Facies Gb: Grainstone consisting of framework-supported bioclasts, moderately to well sorted, foraminifera fossils, Heshilafu, Yigziya Formation (E) Facies Gr: Grainstone-packstone consisting of framework-supported ooids in a mudstone matrix with local calcite cements, moderately to well sorted, Heshilafu, Yigziya Formation (F) Facies Gr: Grainstone

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consisting of framework-supported intraclasts, moderately to well sorted, Heshilafu, Yigziya Formation. Figure 12: Grain-size probability curves of braided alluvial sandstones of the lower Kukebai

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Formation from sieved, disaggregated samples. Curves from different locations demonstrate very-fine to medium sand grain size and moderate to good sorting.

Figure 13: Authigenic minerals and pore types in sandstones of the lower Kukebai Formation. (A)

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Quartz overgrowths and dissolution intergranular and intragranular pores, Birtkuoyi; (B) Scanning electron microscope (SEM) image showing mixed-layer illite/smectite and

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quartz cements, and intergranular pores, Aoyitag; (C) Scanning electron microscope (SEM) image of quartz cement and intergranular pores, Birtkuoyi; (D) Quartz and calcite cements and calcite dissolution pores, Keliyang; (E) Scanning electron microscope (SEM) image of dolomite and mixed-layer illite/smectite cements, and intergranular pores,

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Keliyang; (F) Scanning electron microscope (SEM) image of gypsum and calcite cements within intergranular pores, Birtkuoyi. Figure 14: Pore types in carbonate rocks of Yigziya Formation. (A) Scanning electron

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micrograph (SEM) showing intergranular pores of grainstone, Keliyang; (B) SEM showing intercrystalline pores of dolostone, Heshilafu; (C) Photomicrograph showing

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fractures in dolomite, Yuliqun; (D) Photomicrograph showing intergranular and intragranular secondary pores in grainstone, Tongyuluk; (E) Intragranular and intergranular secondary pores in grainstone, Heshilafu; (F) intercrystalline dissolved pores in dolomite, Heshilafu.

Figure 15: Relationship between porosity and permeability for: (A) Sandstone of the Kukebai Formation, and (B) Carbonates of the Yigziya Formation. 39

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Figure 16: Mercury injection-capillary pressure data for: (A) Sandstones of the Kukebai Formation, and (B) Carbonates of the Yigziya Formation. The threshold pressure, as defined graphically by Katz and Thompson (1987), corresponds to the inflection point at

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which the curve becomes convex upward. The displacement pressure was defined by Schowalter (1979) as the pressure at a mercury saturation of 10%. Pc = Capillary Pressure; SHg = mercury saturation.

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Figure 17: Depositional profiles showing facies architecture in response to inferred relative sealevel fluctuations during the Upper Cretaceous. The two transgressive-regressive cycles

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that can be correlated with the global eustatic curve of Haq et al. (1988). Figure 18: Lithofacies paleogeographic maps of each stratigraphic interval in Upper Cretaceous Yingjisha Group: A) lower member of the Kukebai Formation; B) Middle member of the Kukebai Formation; C) upper Member of the Kukebai Formation; D) Wuyitak Formation;

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E) Yigziya Formation; F) Tuyiluok Formation.

Figure 19: Plot of porosity and permeability versus sandstone grain size and type of carbonate rock: (A) Porosity increases with increasing grain size of sandstone. (B) Porosity

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increases from wackestone to packstone to dolostone to grainstone. Figure 20: Schematic figure showing porosity changes with depth related to compaction,

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cementation, dissolution, fracturing and compression for sandstone of the lower Kukebai Formation and carbonate rocks of Yigziya Formation in the southwest Tarim Basin. Porosity values of 13.5% and 5.1% are average values for the lower Kukebai Formation and Yigziya Formation, respectively (refer to text).

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Table Captions Table 1: Lithostratigraphic scheme for Cretaceous strata of the Southwest Tarim Basin (adapted

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from Hao and Zeng, 1984; Tang et al., 1989). Table 2: Descriptions of siliciclastic lithofacies in the Upper Cretaceous, Yingjisha Group, Southwest Tarim Basin.

Table 3: Descriptions of carbonates lithofacies in the Upper Cretaceous, Yingjisha Group,

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Southwest Tarim Basin.

Table 4: Facies associations and paleoenvironmental interpretations.

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Table 5: Fossil assemblages from different facies associations and depositional environments in Upper Cretaceous strata of Southwest Tarim Basin (Fossil assemblages from Tang et al.,

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1982; Hao et al., 1988; Pan, 1990).

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GROUP FORMATION

Paleogene

E. Paleocene

Kashiger

Late Maestrichtian

White massive gypsum

Artashi

Gypsiferous mudstone and siltstone with intercalated fine-grained sandstone

Tuyiluok

Early Maetrichtian Campanian

Upper

Gray-red grainstone, packstone and wackestone, rich in open-marine fossils

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Yigziya Santonian

MAIN LITHOLOGY

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SERIES/EPOCH

Gray-red grainstone, wackestone, Lower dolostone and lime mudstone with restricted fossil population

Late Turonian

Yingjisha

Cretaceous

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-Coniacian

Brown red siltstone and mudstone intercalated with white gypsum

Wuyitak

Gray-green sandstone and mudstone

Early Turonian

Upper

interbedded with grainstone and wackestone

Cenomanian

Kukebai

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Early Cenomanian

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Albian-Berriasian

Jurassic

Tithonian

Gray-green gypsiferous-mudstone,

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Late-Middle

Kezilesu

Middle sandstone and siltstone interbedded with

gypsum, grainstone and dolomite

Brown red sandstone, conglomeraticLower sandstone, silty mudstone, gypsiferous mudstone Brown red sandstone, conglomeraticsandstone , conglomerate and siltstone

Kezilesu

Brown sandstone and conglomeratic-sandstone, conglomerate

Kuzigongsu

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Facies code

Lithology

Sedimentary structures

Cg

Poorly sorted, grain-supported conglomerate; granules and pebbles

Massive and upward fining,

Fig.6A

0.2-15 cm in diameter; clasts of quartzite, mudstone, chert, rhyolite,

scour-fill structures

St

Moderately- to well-sorted, coarse– to medium-grained feldspathic

Fig. 6B

litharenites (Fig. 6B, 7); grains of

Trough cross bedding

Sp

Moderately- to well-sorted, coarse– to medium-grained feldspathic

Fig. 6C

litharenites (Fig. 6A, 7); grains of

Planar cross bedding

quartz, chert, feldspar and

volcanic and metamorphic rock fragments Well-sorted, fine-grained lithic arkoses to feldspathic litharenites

Fig. 6D

(Fig. 6B); grains of quartz, chert and feldspar with rare volcanic and

Horizontal bedding

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Sh

Sr

Well-sorted, fine-grained lithic arkoses to feldspathic litharenites

Symmetrical and

Fig. 6E, F

(Fig. 6B); grains of quartz, chert and feldspar

asymmetrical ripples, ripple

with rare igneous

Muddy heterolithic stata, very fine- to fine-grained sand, sand

Wavy and lenticular bedding

Fg

Mudstone with gypsum layers up to 10 cm thick and nodules up to

Horizontal laminations or

Fig. 10A,, B

20 cm in diameter

massive

Fc

Calcareous mudstone interbedded with wackestone

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content 10-20%; grains are mostly quartz, rare rock fragments

Fig. 10 C, D

Channel lags

Migration of subaqueous dunes

Tabular sets 1–10 cm thick; cosets

Migration of straight-crested

10-50 cm thick

subaqueous dunes

Tabular cosets, 10-50cm thick

Aggradation under upper-flow-regime

Tabular cosets, 10-30cm thick

condition

Wave and current reworking, migration of ripples

cross laminations

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Fif

Trough shaped sets, 1-10cm thick;

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volcanic and metamorphic rock fragments

and metamorphic rock fragments

Tabular beds, 5–30 cm thick

Interpretation

cosets 5-30cm thick

quartz, chert, feldspar and

metamorphic rock fragments

Geometry and thickness

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tuff and schist.

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Table 2: Descriptions of siliciclastic lithofacies in the Upper Cretaceous, Yingjisha Group, Southwest Tarim Basin

Tabular cosets, 10-30cm thick

Suspension setting of fines alternating with sand ripple migration

Tabular beds, 10–100 cm thick

Suspension setting of fines, precipitation of gypsum

Horizontal laminations or massive

Tabular beds; 5–150 cm thick

Suspension setting of fines alternating with carbonate sedimentation

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Table 3: Descriptions of carbonates lithofacies in the Upper Cretaceous, Yingjisha Group, Southwest Tarim Basin Sedimentary structures

Lithology

code

Pm

Packstone, bioclasts and intraclasts,

Massive-, rhythmic

Fig. 11A

clast-supported, moderately sorted,

graded bedding

Geometry and thickness Tabular, 5–100 cm thick

Suspension fall-out of mud and bioclasts following storms

Suspension fall-out of mud and bioclasts following storms

mud matrix Wackestone, matrix-supported

Massive bedding

Tabular, 5–100 cm thick

Carbonate mudstone, <10%

Massive

Tabular, 5-20cm thick

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Wm

bioclasts

Dm

Dolostone and mud dolomite,

Fig. 11C

irregular-, semi-euhedral crystalline

Gb

Grainstone, >80% bioclasts, clast-

Bioturbation, small-scale

Fig. 11 D

supported, moderately sorted

cross bedding

Gr

Grainstone, >80% intraclasts

Rhythmic graded-,

Fig. 11E, F

including oolites, clast-supported,

massive bedding

Tabular, 5–40 cm thick

Suspension deposition below wave base

Dolomitization in meteoric-marine mixing zone under arid to semi-arid conditions High-energy wave reworking

Tabular, 10–150 cm thick

High-energy reworking and suspension fall-out following

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Tabular, 5–100 cm thick

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moderately to well sorted

Massive bedding

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Interpretation

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Lithofacies

Sedimentary Environment

St, Sh, Sp, Cg, Fif

Braided Fluvial

Formation L.Kukebai Wuyitak,

FA-2

Fif, Fg, Sr

Lagoon, Playa Lake

Tuyiluok, M. Kukebai

Fif, Sh, Fc, Sr

Nearshore to Shelf

U. Kukebai,

FA-4

Gr, Pm, Wm, Dm, Mm

Restricted Platform

FA-5

Gb, Gr, Pm, Dm

Open Platform, Platform margin

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FA-3

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Yigziya

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Table 5: Fossil assemblages in different facies associations and depositional environments in Upper Cretaceous strata of southwest Tarim Basin (fossil assemblages from Tang et al., 1982; Hao, 1988; Pan, 1990).

L Yigeziya

Wuyitak

Microfossils

Diversity

Depos. Env.

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Macrofossils

FA-2

None

Spores Pollens

No Marine Fauna

Playa Lake

FA-5

Gastropods Bivalves Rudists Brachiopods Echinoids Ammonoids

Foraminfera Dinoflagellates Ostracodes

Moderate

Open Carbonate Platform

FA-4

Gastropods Algae

??

Low

None?

L/U: Bivalves Ostracods

No Marine Fauna

Playa Lake

M: Foraminera Ostracods

Low

Nearshore - Shelf

Foraminifera Ostracodes Coccoliths Dinoflagellates Acritarchs

ModerateHigh

Nearshore - Shelf

Foraminfera

Low

Lagoon

Foraminifera

Very Low

Braided Fluvial

FA2/3 None?

Middle Kukebai

FA-2

Lower Kukebai

FA-1

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FA-3

Gastropods Bivalves Ammonoids Bryozoans Crabs Echinoids Gastropods Bivalves Algae

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Upper Kukebai

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Tuyilouk

Facies Association

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Restricted Carbonate Platform

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HIGHLIGHTS

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Upper Cretaceous Yingjisha Group, Tarim Basin, an important host of hydrocarbons Best reservoirs a product of depositional environment, diagenesis and tectonics Braided-fluvial sandstones and carbonate platform grainstones contain best reservoirs Porosity related to dissolution of unstable clastic and carbonate grains and cements Fracturing enhanced reservoir quality

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• • • • •