Sedimentology, Organic Geochemistry, and Petroleum Potential of Jurassic Coal Measures: Tarim, Junggar, and Turpan Basins, Northwest China1

Home , Sedimentology

Marc S. Hendrix,2 Simon C. Brassell,3 Alan R. Carroll,4 and Stephan A. Graham5

ABSTRACT belts indicates that they are entirely nonmarine meandering fluvial deposits with local develop- Lower and Middle Jurassic coal-bearing strata ment of braided fluvial and lacustrine deltaic facies. occur widely throughout central Asia and are well Chinese subsurface data suggest that regional developed in northwestern China, where their Jurassic lacustrine facies are present down deposi- thicknesses in the southern Junggar, northern tional dip, consistent with predictions from global Tarim, and Turpan basins exceed 2500, 2300, and circulation modeling of Early and Middle Jurassic 1500 m, respectively. Examination of these strata monsoonal precipitation. along 13 transects across basin margin outcrop Laboratory analyses of coals and organic-rich shales show a dominance of terrestrial, higher plant components. Visual kerogen analysis indi- ©Copyright 1995. The American Association of Petroleum Geologists. All cates that vitrinite, inertinite, and exinite are the rights reserved. dominant macerals, and elemental analysis charac- 1Manuscript received June 15, 1994; revised manuscript received February 2, 1995; final acceptance February 28, 1995. terizes most kerogens as type III. Rock-Eval analy- 2Department of Geological and Environmental Sciences, Mitchell ses yield moderate hydrogen index values (50–300) Building, Room 138, Stanford University, Stanford, California 94305-2115. and very low oxygen index values (<20). Jurassic Current address: Department of Geology, University of Montana, Missoula, Montana 59812. source rock extracts are characterized by odd-over- 3Biogeochemistry Laboratories, Departments of Chemistry and Geology, even normal alkane distributions, high pristane/ Geology Building, 1005 East 10th Street, University of Indiana, Bloomington, phytane and high hopane/sterane ratios, domi- Indiana 47405-5101. 4Exxon Production Research Company, P.O. Box 2189, Houston, Texas nance of C29 sterane homologs, local abundance of 77252-2189. diterpenoid compounds, and low abundance of tri- 5Department of Geological and Environmental Sciences, Mitchell Building, Room 138, Stanford University, Stanford, California 94305-2115. cyclic terpanes. Field work for this study was conducted in cooperation with the Chinese Geochemical correlation with four petroleums Academy of Geological Sciences and the Xinjiang Bureau of Geology and from the Junggar, Tarim, and Turpan basins strongly Mineral Resources during the summers of 1987, 1988, and 1989. Special thanks are due to Xiao Xuchang, Liang Yunhai, and Wang Zuoxun. We are suggests that the Jurassic coaly deposits and their also grateful for the field assistance of Benjamin Schulein, Ed Sobel, Cleavy lacustrine equivalents downdip are petroleum McKnight, and Chu Jinchi. Stanford research was supported by the Stanford- China Geosciences Industrial Affiliates, a group that has included Agip, source rocks. Sterane and hopane distributions of Amoco, Anadarko Petroleum, Anschutz, ARCO, BHP, BP, Canadian-Hunter, petroleums and extracts of their putative Jurassic Chevron, Conoco, Elf-Aquitaine, Enterprise, Exxon, Fletcher-Challenge, source rock are similar and can be easily distin- Japan National, Mobil, Occidental, Pecten, Phillips, Statoil, Sun, Texaco, Transworld Energy International, Union Texas, and Unocal. Additional guished from published distributions of these com- funding was provided by the David and Lucile Packard Fellowship for pounds in other source rock layers. Additional cor- Science and Engineering (granted to S. C. Brassell to support biomarker relation parameters include high pristane/phytane; research at Stanford). G. Barker and G. Wood (Amoco) and U. Biffi (Agip) identified palynoflora in conjunction with this study. Rock-Eval pyrolysis, low abundance or lack of tricyclic terpanes, but vitrinite reflectance, TOC, and elemental analysis data were provided in part similar distributions where present; and lack of by R. A. Hutton and L. J. Lipke (Amoco), G. J. Demaison (formerly with Chevron), R. J. Moiola, J. M. Armentrout, and C. P. Lacerda (Mobil), R. W. gammacerane (with one exception) and carotanes, Blake, C. R. Robison, and N. P. Carroll (Texaco). L. Lipke and R. Hutton compounds that characterize Permian and (Amoco) provided extractions and HPLC separations of selected samples. Ordovician source rocks and their respective Exxon Production Research Company provided pyrolysis-GC, HPLC separations, and whole-oil and saturate GC and GC-MS analyses of selected petroleums. Pyrolysis–gas chromatography of samples, and permission to publish these results. C. L. Thompson-Rizer selected Jurassic samples suggests that they possess (Conoco) supplied visual kerogen data. J. Clayton (U.S. Geological Survey, Denver) provided the Junggar petroleum sample 94-HU-1. F. J. Fago potential for liquid hydrocarbon generation. (Stanford) assisted in selected GC-MS analyses. We thank M. Golan-Bac, Expulsion of C15+ hydrocarbons from Jurassic G. B. Hieshima, J. A. Kennedy, and L. A. F. Trindade for helpful discussion of source rocks appears likely, despite the traditional these data, and we are especially grateful for constructive reviews of the manuscript by D. D. Miller, J. M. Moldowan, K. E. Peters, D. Waples, and one view that bituminous coals are incapable of anonymous reviewer. expelling long-chain hydrocarbons.

AAPG Bulletin, V. 79, No. 7 (July 1995), P. 929Ð959. 929 930 Jurassic Coal Measures, Northwest China

82¡00' 84¡00' 86¡00' 88¡00' 90¡00' Figure 1—Location of

DETAILED study area, transects MAP AREA N 1 across Jurassic strata, 1.5 1 and collection sites of Beijing J U N G G A R selected oil samples for B A S I N this study. Jurassic Xinjiang Uygur 2 Autonomous isopachs in Junggar and C H I N A Shang- 3 1 44¡00' Region N hai 4 Tarim basins from Lee (1985a, b). M = Manas, 250 KM M N X = Xishanyao, HL J S H A Hong Kong 0 100 km X A B G D B = Badaowan, 94-HU-1 B O 93-QK oils L E G E N D : T Taican oil sample D #1 HL = Heavenly Lake,

Transect through Jurassic strata J = Jimsar, D = Dabanchang, (see caption for locality abbr.) T I A N S H A N TURPAN BASIN T = Taoshuyuan, Kr = Korla, M Y = Yengisar, K = Kuqa, K 92-Bc-101 U R U 42¡00' Bc = Baicheng, Q = oil sample K Y K 3 Jurassic isopach (km) T Bc,Q Kr A Qiugetale, Aw = Awate,

Aw H Kz = Kuzigongsu.

42¡00' Fault 2 f t 1 p l i 1 0 U e i 2 0 a b T ift 1 Upl T A R I M B A S I N lpin 2 Kz Ka 2 0

1 1 0 0 0 0

76¡00' 78¡00' 80¡00' 82¡00' 84¡00' 86¡00' 88¡00' 90¡00'

INTRODUCTION petroleum have been discovered in the Junggar and Tarim basins, and moderate-size accumulations Organic-rich Jurassic strata are widespread have been discovered in the Turpan basin (Nishidai throughout central Asia and have been reported and Berry, 1991; Oil & Gas Journal, 1993; Zhou et from northwestern China, western and southern al., 1993). Mongolia, and adjacent parts of the former Soviet Source rock considerations have rapidly assumed Union (Vakhrameyev and Doludenko, 1977; considerable importance, given China’s recent Ulmishek, 1984; Hendrix et al., 1992, 1994b; decision to open many of its onshore basins, Hendrix and Graham, 1993). Throughout the including the Tarim basin, to international bidding Xinjiang Uygur Autonomous Region of northwest- for exploration. No unequivocal geochemical cor- ern China (Figure 1), Lower through Middle relation between Jurassic strata and petroleum Jurassic coal provides the principal energy source recovered from Xinjiang’s oil fields has been pub- for everything from electrical power plants to local lished. The source potential of these strata remains household ovens. Lee (1985a) estimated that the uncertain, although various Chinese studies have south Junggar basin alone contains in excess of reported similarities between sterane and hopane 270 × 109 t of high-quality bituminous coal. distributions of Lower and Middle Jurassic source Comparisons of estimated total and recoverable rocks and certain crude oils in the East Junggar and tonnages for other coal-bearing basins indicate that Turpan basins (Wang and Chen, 1990; Huang et al., the tonnages of high-quality coal in the Junggar 1991; Zhou et al., 1993). Complicating the picture, basin are comparable to those of other prolific however, are other strata, such as the Permian basins of the world (Table 1). lacustrine oil shales, which provide a source for These coals and their associated organic-rich petroleum in the Junggar basin (Carroll et al., mudstones likely act as a source rock for petroleum 1992). Similarly, the Tarim basin has several poten- and gas accumulations of the southern Junggar, tial petroleum source rocks, including Cambrian– northern Tarim, and Turpan basins within Xinjiang Ordovician, Carboniferous, and possibly Creta- (Lee, 1985a, b; Graham et al., 1990; Huang et al., ceous marine rocks, as well as Permian and Jurassic 1991; Zhou et al., 1993). Petroleum in the Junggar, nonmarine rocks (Fan et al., 1990; Graham et al., Turpan, and Tarim basins has been known for cen- 1990). turies. Natural seeps were exploited from each of The lack of published analyses of potential these basins along the ancient Silk Road. More source rocks for each of Xinjiang’s basins has been recently, large commercial accumulations of a barrier to comprehensive correlation studies with Hendrix et al. 931

petroleum from all three basins. In particular, few details have been reported on the sedimentologic and organic geochemical attributes of Jurassic coaly strata. Although several organic geochemical studies of Mesozoic strata and/or allegedly Mesozoic oils exist in the Chinese literature (Lu, 1981; Li and Jiang, 1987; Fan et al., 1990; Wang and Chen, 1990; Huang et al., 1991; Zhou et al., 1993), they are either limited in scope or difficult to evaluate criti- cally because they provide little data. Geochemical Services, 1977 analyses of organic-rich Jurassic strata reported in the Western literature (e.g., Graham et al., 1990) are too sparse to adequately assess Jurassic source potential. This study provides a detailed organic geochemical database for organic-rich Lower and Middle Jurassic strata throughout central Xinjiang, thereby permitting a more comprehensive interpretation of the area’s petroleum potential. Because our sampling was limited to outcrops on deformed basin margins whose palinspastic origins lay far from producing areas, our goals are not to match specific beds to specific oils, but rather to look for kindred affinities that point to likely source sequences. Bulk and molecular organic geochemical data were acquired from a sample suite collected along 13 transects of Mesozoic strata in the southern Junggar, northern Tarim, and western Turpan basins (Figure 1). Field and laboratory evidence is presented that demonstrates that organic-rich Lower and Middle Jurassic strata are dominated by terrestrial-derived type III kerogens. Molecular geochemical techniques strongly suggest a correlation between these kerogens and four petroleum samples collected from the northern Tarim, southern Junggar, and Turpan basins.

GEOLOGIC SETTING Sedimentary, Tectonic, and Paleoclimatic

Total Estimated Recoverable Number of Thickest Seam Recoverable Framework Thick organic-rich strata of Early through Middle Jurassic age occur throughout the southern Junggar, northern Tarim, and Turpan basins of northwest China (Figures 1, 2). Jurassic sedimentary accumulations in all three basins exhibit fore- land-style isopach configurations (Lee, 1985a, b;

Cretaceous–Eocene 205 22Huang >15 et al., 38 1991; Allen 11 et Glass, 1975; Schmidt, 1979 al., 1993), suggesting that each basin was an asymmetric, flexurally sub- siding trough adjacent to active fold and thrust belts that bounded the Tian Shan (Hendrix et al., 1992). Mesozoic facies and thickness trends, as well as paleocurrent, provenance, and subsidence analysis, indicate that the Tarim and Junggar basins

*NA = data not available. were physiographically partitioned by the Tian Lena (Russia) Cretaceous 2647 3.4 NA NA <1 Fettweis, 1979 Gippsland (Australia) TertiarySydney (Australia)Tungusska (Russia) Tertiary Cretaceous 107 1744 <102 40 <16 3.9 >7 NA NA >60 NA NA 37 <1 16 Gloe, 1984 Fettweis, 1979 Fettweis, 1979 Southern JunggarNorthern TarimAppalachian Early–Middle JurassicCratonic (U.S.)Rocky Mountain (U.S.) Early–Middle Jurassic 270 Pennsylvanian Pennsylvanian-Permian NA 45 18 0.5 NA 5 ~42 0.07 23 NA 25 NA >20 NA 7 NA NA Lee, 1985a Lee, 1985b 5 14 Schmidt, 1979 Schmidt, 1979 Alberta (Canada)Cretaceous–Tertiary Early 127 3 NA NA 2 Canada Ministry Supply & Basin Age of Coal (Gt) (Gt) Seams Mined (m) (%) References Table 1. Estimated Total Tonnages for Several Coal-Bearing Basins and Comparison with Tonnage from the Junggar Basin * Shan throughout the Mesozoic, as the Tian Shan 932 Jurassic Coal Measures, Northwest China

Fig. 3B

Haojiagou Toutunhe Xishanyao Sangonghe Badaowan Qigu

Fm.

Manas Locality

Wu, 1990 1990 Wu, (plant remains) (plant E a r l y J u r a s s i c i s s a r u J y l r a E

(nonmarine bivalves) (nonmarine

Late Triassic Late

E a r l y J u r a s s i c M i d d l e J u r a s s i c i s s a r u J e l d d i M c i s s a r u J y l r a E

Gu, 1982 Gu,

Huang, 1993 1993 Huang, Jurassic Early (sporopollen)

(sporo-pollen)

late Early Jur. Early late early Mid. Jur. late Middle Jurassic Middle late Jur. Mid. early early Early Jurassic Early early

Liu, 1993 Liu,

L a t e T r i a s s i c i s s a i r T e t a L Zhang, 1983 Zhang, (palynoflora)

e. Middle Jurassic Middle e. (palynoflora) SOUTHERN JUNGGAR BASIN 1990 Liu, Z.

(palynoflora)

E a r l y J u r a s s i c M i d d l e J u r a s s i c i s s a r u J e l d d i M c i s s a r u J y l r a E Yang and Sun, 1986 1986 Sun, and Yang 216 19 bpd bpd conglomerate sandstone

producing horizon

oil show

fang tai

Taliqik Badaowan Xishanyao

Taican #1 well Taican Sangonghe

Sanjiang-

(Huang et al. 1991) (Huang et al. Qike-

Fm.

(plant remains) (plant

Early to Middle Jurassic Middle to Early Late Tr Early Jurassic Early Tr Late

Wu and Zhou, 1986 1986 Zhou, and Wu yy yy yy yy yy yy yy L E G N D

TURPAN BASIN (plant remains) (plant Wu, 1990 1990 Wu, Early Jurassic Early

claystone coal siltstone

Sun, 1989 1989 Sun, (sporo-pollen) Late Lias Middle Jur. Middle Lias Late Early Lias Early

Fig. 3A

aeaeQigu Kalemake Kezilenuer Yengisar Ahe Haojiagou

Fm.

E. Jurassic E.

E a r l y J u r a s s i c i s s a r u J y l r a E (plant remains) (plant

Kuqa Locality Kuqa 1990 Wu, Late Triassic Late

(conchostracans)

? ? ? Middle Jurassic Middle

Triassic Early S. Liu, 1990 1990 Liu, S.

(sporo-pollen) Zhang and Li, 1990 1990 Li, and Zhang Jurassic Middle Jurassic Early L a t e T r i a s s i c i s s a i r T e t a L

( palynoflora)

NORTHERN TARIM BASIN Kuzigongsu Section Kuzigongsu Callovian Aalenian U.Biffi (1993, pers. comm.) pers. (1993, U.Biffi 1 0 (km) Scale 0.5 Vertical Hendrix et al. 933 was repeatedly deformed in response to various lack of interbedded, datable volcanic units and lit- tectonic accretion events at the southern Asian tle reported magnetostratigraphic work (although, continental margin (Hendrix, 1992; Hendrix et al., see McFadden et al., 1988a, b). The strata are highly 1992). Paleocurrent, organic facies, and isopach fossiliferous, however, and many floral and faunal configurations indicate that the Turpan basin studies have been conducted to constrain the age evolved as a discrete physiographic entity by the of these rocks. As a result, there is general agree- Early Jurassic (Huang et al., 1991; Hendrix et al., ment that the organic-rich sequences are as old as 1992). Flexurally driven Early and Middle Jurassic Triassic and as young as Middle Jurassic. However, subsidence rates for basin depocenters in central more detailed assignments differ from study to Xinjiang were in excess of 55 m/m.y. (>30 m/m.y. study due to the highly endemic nature (e.g., Li, for the Turpan basin), leading to the accumulation 1993) and moderate to poor preservation of of 2600 m of sediment in the south Junggar, 2500 Mesozoic nonmarine flora and fauna in the Xinjiang m in the north Tarim, and 1500 m in the west basins (Figure 2). In addition, the Chinese practice Turpan depocenters (Figure 2) (Hendrix et al., of extensive taxonomic subdivision hampers corre- 1992). lation of Chinese flora and fauna with areas outside Lower and Middle Jurassic organic-rich strata China (Zhang and Li, 1989). deposited in basins of central Xinjiang are entirely Biostratigraphic age assignments have been pub- nonmarine, based on their floral and faunal assem- lished based on vertebrate (Wu, 1987), molluskan blages (Figure 2) (Zhang, 1981; Lai and Wang, (Gu, 1982), conchostracan (S. Liu, 1990), and high- 1988). During this period, abundant, probably er plant remains (Wu, 1990) (Figure 2), but palyno- monsoonal, rainfall led to the development of logic studies appear to be the most successful. extensive meander-belt fluvial systems transverse Published age estimates of Mesozoic organic-rich to the ancestral Tian Shan range, as suggested by strata based on palynology fall into two broad cate- facies assemblages in basin margin outcrops and by gories. The first group of studies maintains that the paleocurrent measurements (Hendrix et al., 1992). deposits are largely or entirely Triassic in age (e.g., Regionally extensive, occasionally anoxic, lakes or Zhang, 1983; Zhang and Li, 1990; Figure 2). The bogs probably occupied interior foredeep regions second and larger group of studies contends that of these basins (Lai and Wang, 1988; Huang et al., the coal-bearing deposits are of Early through 1991). In some outcrops we examined, Jurassic Middle Jurassic age (He and Wu, 1986; Wu and strata appear to be lacustrine deltaic, as along the Zhou, 1986; Yang and Sun, 1986; Sun, 1989; Z. Liu, Manas transect (southern Junggar basin; Figure 1), 1990, 1993; U. Biffi, 1993, personal communica- where coal-bearing strata are laterally continuous. tion) (Figure 2). Coal-bearing strata in central Xinjiang are divid- Exact placement of the Triassic–Jurassic bounded into several formations by Chinese stratigra- ary remains controversial. Various studies have phers (Figure 2). According to Zhang (1981), most noted the presence of Triassic survivor species in coal is mined from the Badaowan and Xishanyao Jurassic coal-bearing strata (e.g., Yang and Sun, formations in the southern Junggar and Turpan 1986; Liu and Sun, 1992). Wu (1990) further added basins and from the Ahe and Kezilenuer formations to the uncertainty by reporting Early Jurassic floras in the northern Tarim basin (Figure 2). Our obser- from the Taliqik Formation, which is usually vations of the stratigraphy of central Xinjiang basins assigned a Late Triassic age. More biostratigraphic suggest that, although most coal is mined from studies are needed to clarify the age of central these formations, abundant organic-rich strata are Xinjiang organic-rich Mesozoic deposits, particular- present throughout Lower and Middle Jurassic ly in terms of correlation with well-constrained flo- deposits in each basin (Figure 2). ral assemblages outside China (e.g., Sarjeant et al., 1993). In this paper, we provisionally refer to the coaly deposits as Lower through Middle Jurassic, Chronostratigraphic Control because the literature and the palynology of our samples (U. Biffi, 1993, personal communication) Precise dating of Mesozoic nonmarine coal-bear- favor such a conclusion. Given uncertainties, it is ing strata in central Xinjiang is difficult due to a possible that parts of these deposits may be Triassic.

Figure 2—Complete Jurassic sections for the Kuqa and Manas localities (northern Tarim and southern Junggar basin depocenter sections), and Jurassic section for Taican-1 well, reported by Huang et al. (1991) on the basis of core. Age interpretations and formation names, derived from Chinese literature, are plotted adjacent to each section. Note that significant controversy exists, particularly with regard to the exact placement of the Triassic–Juras- sic boundary. Also shown are the locations of sections in Figure 3. 934 Jurassic Coal Measures, Northwest China

Figure 3—Detailed measured sections of the meandering fluvial lithofacies from Kuqa and Manas. Exact place- A. B. ment of these sections in the complete Jurassic sections Yengisar Fm. Toutunhe Fm. measured for each locality is shown in Figure 2. Kuqa section Manas section (northern Tarim) (southern Junggar) In the following discussion, we do not attempt to 35m differentiate or correlate samples from specific for- crevasse mations, because of the lack of sufficient age con- splay dep. trol and the difficulty in correlating specific formations or organic-rich intervals between localities. y

FIELD METHODS AND SAMPLING STRATEGY

yy At the 13 locations where Jurassic strata were Iron oxide examined, recent exposures were suitable to permit 30concretions 35m detailed inspection of facies. Most natural outcrops

y of the organic-rich facies were too weathered for reliable analysis. Where possible, stratigraphic sections were measured to document the style of sedi- rhyzoids mentation (Figure 3) (Hendrix et al., 1992). 25 yy Unweathered samples were collected from subsur- y Channel face coal mines at each locality. With the exception 20Complex 25 30 of samples 87-D-5A, 89-K-112, and 89-Bc-6A, collect- rhyzoids

yy ed from natural outcrops, all geochemical work was y performed on unweathered subsurface samples. 20 Our access to subsurface workings was restricted, so exact stratigraphic placement of individual sam-

yy ples within the mined interval is unknown. y Channel Jurassic sediments are thickest in the southern Complex Junggar and northern Tarim depocenters near the Manas and Kuqa localities, respectively (Figures 1, yy y

2). These two localities also contain the largest 10 15 number of operating coal mines. Samples were also rhyzoids

log jam collected from localities away from the basin

yy depocenters (Figure 1). Currently, more than one y coal seam is being mined at most locations. 10 15

Individual seams in the northern Tarim and south- 5 crevasse ern Junggar Mesozoic foredeeps are reported in splay dep. excess of 25 m thick, and as many as 42 separate yy

coal seams are being mined in the subsurface at the 5 Badaowan locality (Figure 1) (Hendrix, 1992). crevasse

To better assess the petroleum potential of yy

0m splay dep. Jurassic rocks, we investigated the organic geochemistry of four petroleum samples likely to have L E G E N D been generated from these rocks in Xinjiang basins,

based on geologic relations. These samples include coal yy0m a produced oil from the southern Junggar basin claystone (94-HU-1), a seep oil collected from the northern intraclasts Tarim basin (92-Bc-101), and one seep oil and one siltstone produced oil from the north central Turpan basin ripples (93-QK-6 and 93-QK-101, respectively; Figure 1). sandstone

rhyzoids tangential x-beds

SEDIMENTARY FACIES planar laminations fossil wood In all three basins, Lower Jurassic strata overlie allegedly uppermost Triassic alluvial and braided Hendrix et al. 935 fluvial conglomerate, sandstone, and siltstone of display climbing ripples toward the top and are the Haojiagou Formation (south Junggar and north interpreted as crevasse splay deposits (Figure 3). Tarim basins) and the Taliqik Formation (Turpan One such approximately 70-cm-thick sandstone at basin; Figure 2). This transition appears to be grada- the Manas site has casts of therapod(?) dinosaur tional in all three basins and is interpreted as gener- footprints on its base (Hendrix, 1992). ally conformable. Organic-rich Jurassic strata in These meandering fluvial organic-rich strata each basin consist of interbedded sandstone, silt- grade upward into monotonous fine-grained red stone, and shale (Figures 2; 3; 4A, B). Conglomerate beds of the Qigu Formation (northern Tarim and is minor and, where present, typically occurs as a southern Junggar basins) or Qiketai Formation lag at the base of sandstones. Plant debris is highly (Turpan basin; Figure 2). variable in form and state of preservation throughout organic-rich strata of all three basins. Plant debris ranges from log jams (Figure 3B) to wholly Braided Fluvial Facies articulated plant fossils (Figure 4C), and includes in-situ rhyzoids at the top of many thin sandstones Lower Jurassic strata of the Badaowan Formation and siltstones (Figure 3) (Hendrix, 1992). in the western Turpan basin are considerably coars- Three major sedimentary environments are rep- er than equivalent rocks from the Junggar and resented by Lower and Middle Jurassic strata along Tarim basins and lack organic-rich layers. In uplifted margins of Xinjiang basins. In each basin, Turpan, they comprise well-organized, braided flu- most Jurassic deposits are characterized by mean- vial pebbly sandstone and siltstone, typified by ver- dering fluvial facies. Local braided fluvial deposits tically stacked sandy bar deposits and lenticular characterize parts of the Turpan and northern geometries on a scale of tens of meters (Hendrix et Tarim basins. Within parts of the Junggar basin, al., 1992). Within the Lower Jurassic Yengisar lacustrine deltaic facies are present. Formation along the Kuqa and Yengisar transects (Tarim basin), over 300 m of sand-rich braided fluvial deposits were observed (Figure 2) (Hendrix et Meandering Fluvial Facies al., 1992). Most Lower and Middle Jurassic strata in central Xinjiang basins consist of interbedded sandstone, Lacustrine Deltaic Facies siltstone, shale, and coal interpreted as meandering fluvial sequences. Sandstone beds associated with In the southern Junggar basin depocenter this facies are lenticular on a lateral scale of tens to (Manas), the main coal-bearing portions of the sec- hundreds of meters, and many contain minor con- tion contain sandstone, siltstone, and shale hori- glomeratic lags at their base with associated tool zons, which are commonly tabular for hundreds of marks or rare gutter casts (Figure 4D). Lateral accre- meters and probably represent a lacustrine delta tion surfaces are common, and shallow-water trac- (Figure 4B). Low-angle lateral accretion surfaces are tion-transport structures, such as trough cross-bed- observed in many of the thicker sandstones, sug- ding, planar lamination, and ripples, are also gesting either a very large meandering fluvial sys- common. Detailed outcrop sections were measured tem or perhaps distributary mouth bar prograda- in this facies at both the Manas and Kuqa localities tion (Figure 4F). The richest Jurassic coal layers (Figure 3). Each detailed section contains at least associated with this facies contain abundant “clink- one approximately 10-m-thick major sandstone con- er” rock formed by in-situ burning of subbitumi- sisting of an overall upward-fining sequence (Figure nous and bituminous coal as a result of sponta- 4E) with a scoured and tool-marked base (Figure neous combustion of outgassed methane (Coates, 4D), several amalgamation surfaces, an abundance 1988). Lack of any marine flora or fauna in these of shallow-water traction-transport structures (such strata is consistent with a lacustrine deltaic inter- as trough cross-beds and planar lamination), and a pretation. For additional sedimentologic informa- rippled top. These thick sandstones are interpreted tion on each of these facies, refer to Hendrix as major meandering fluvial channel complexes. (1992) and Hendrix et al. (1992). The finer grained parts of each section contain siltstone layers, commonly with rhyzoids, coaly shale, abundant plant impressions on bedding planes BULK GEOCHEMICAL ANALYSES (Figure 4C), and a series of thin interbedded (≤1 m thick) fine-grained sandstones. These thinner sand- Visual Kerogen Analysis stones are not characterized by substantial upward fining, but are typically uniformly fine grained. They Relative proportions of organic macerals are are commonly planar laminated near the base, but quantified for eight Jurassic coal samples, each from 936 Jurassic Coal Measures, Northwest China

A B

C D

Figure 4—Photographs of outcrops and sedimentary structures typical of organic-rich Jurassic strata from Xinjiang basins. (A) Organic-rich, meandering fluvial facies (Kezilenuer Formation), Kuqa, northern Tarim basin. Trees in foreground are about 5 m high. Note lenticular sandstone geometries and thin, outcropping coal bed. (B) Laterally continuous Middle Jurassic coal-bearing lacustrine facies, Manas, southern Junggar basin. One-story building for scale (circled). Note the tabular geometry of sandstone beds (light-colored), and the thick coal seam (>10 m) at the stratigraphic level of the building. (C) Plant impressions (Baiera sp.?) typical of bedding surfaces in fine-grained Lower and Middle Jurassic strata from Xinjiang basins. (D) Gutter casts on sole of conglomerate bed in meandering fluvial lithofacies, Badaowan Formation, Heavenly Lake. (E) Middle Jurassic fining-upward channel sandstone complex overlying overbank mudstone, Kezilenuer Formation, Kuqa. (F) Large lateral accretion surfaces (>20 m relief) in the meandering fluvial lithofacies of the Sangonghe Formation, Manas, southern Junggar basin. Hendrix et al. 937

Table 2. Visual Kerogen Analysis of Selected Jurassic Samples, Southern Junggar and Northern Tarim Basins*

Ro Vt Ex In Am Mn Py Sample Basin or Location Formation (%) (%) (%) (%) (%) (%) (%) Southern Junggar Basin 88-M-115A Manas Xishanyao 0.71 87 11 2 0 0 0 88-B-2 Badaowan Badaowan 0.64 35 4 60 0 1 0 88-HL-102 Heavenly Lake Badaowan 0.5 25 15 28 0 32 0 88-J-3 Jimsar Badaowan 0.45 43 38 7 0 12 0 88-X-1 Xishanyao Xishanyao 0.52 26 26 63 0 2 0

Northern Tarim Basin 87-K-54 Kuqa Kezilenuer 0.75 84 6 10 0 0 0 87-Y-11 Yengisar Yengisar 0.54 22 0 0 0 77 1 88-Aw-38A Awate Kezilenuer 1.77 75 0 0 25 0 0

*Formation = stratigraphic formation; Ro = vitrinite reflectance; Vt = vitrinite macerals; Ex = exinite macerals; In = inertinite macerals; Am = amorphous macerals; Mn = mineral matrix; Py = pyrite. a different locality in the Junggar or Tarim basin regional post-Jurassic sediment thickness trends. (Table 2). Vitrinite is commonly the dominant com- However, a substantial number of analyses from ponent, as expected for terrestrially derived coal Tarim localities away from the depocenter yield (Figure 5). Four of the five analyzed samples from reflectances markedly higher than depocenter val- the Junggar basin contain significant abundances ues. The Awate, Qiugetale, and Baicheng samples (up to 38%) of exinite. Exinite (also termed “lipti- (Figure 1) account for the high reflectance values nite”) comprises a class of lipid-rich macerals that (Figure 6). All three sites occur basinward of major include waxes, resins, spores, cuticles, and algal thrust faults in the northwestern Tarim basin, sug- bodies (Tissot and Welte, 1984) that may provide a gesting that high Ro values are the result of burial source of oil (Püttman et al., 1986) (Figure 5). The due to stacking of thrust sheets. apparently lower percentages of exinite in Tarim Reflectance values for the Turpan basin are samples is likely an artifact of the small sample size slightly immature to mature with respect to oil and (n =3). The percentage of inertinite (fusinitic or gas generation (Figure 6) (see also Graham et al., charcoal-like material) present in each sample varies 1990). Since post-Jurassic stratal thicknesses for the from a few percent to over 60%, suggesting that sub- western Turpan basin are similar to those of the stantial proportions of Jurassic organic matter may southern Junggar and northern Tarim basin flanks be reworked or charcoal. Much of the vitrinite is (Hendrix et al., 1992), these Ro data suggest that moderately fluorescent, suggesting that it con- post-Jurassic thermal history of these three areas tains bitumen or exudatinite (nonreflective, fluo- was comparable. Hendrix (1992) and Hendrix et al. rescent bitumen, filling apophyses, pores, etc.), (1992) performed geohistory analysis (backstrip- which is indistinguishable from the vitrinite itself ping) of the Manas and Kuqa measured sections, as (C. Thompson-Rizer, 1992, personal communica- well as a composite section for the Turpan basin. tion). Most of the samples yield vitrinite reflectance Because the Manas and Kuqa sections were both values (R average = 0.76%) above that associated compiled from outcrops spanning more than 10 o ∼ with the threshold of oil generation (Ro = 0.6%), km perpendicular to structural and depositional suggesting that the observed fluorescence results strike, and involved correlation across several from liberated or thermally generated bitumen. broad folds at Kuqa, the degree to which these sections represent generative areas within each basin is uncertain. Nevertheless, the results suggest that Vitrinite Reflectance Jurassic strata in basinal areas proximal to each section are currently within the oil window. Vitrinite reflectance data indicate that most samples are slightly immature to mature with respect to oil and gas generation (Table 3; Figure 6), with Elemental Analyses and Rock-Eval Pyrolysis one important exception discussed in the following sections. Samples collected within the south- Interpretation of kerogens in coaly Jurassic sam- ern Junggar and northern Tarim depocenter sec- ples relies more heavily on elemental analysis (Table tions average slightly higher Ro values than those 4; Figure 7) than Rock-Eval pyrolysis results (Table from areas outside the foredeeps, consistent with 3; Figure 8). Most of the variation in composition of 938 Jurassic Coal Measures, Northwest China

Figure 5—Thin-section photomicrographs of coal sample 88-J-3 (Jimsar transect, southern Junggar basin). (A) Reflected light; (B) ultraviolet light. Scale bar = 50 mm. Note the relative degrees of fluorescence between inertinite (I), vitrinite (V), and exinite (E) macerals. the samples on an atomic hydrogen-to-carbon (H/C) of hydrogen-poor type III kerogens indicated by ele- vs. oxygen-to-carbon (O/C) van Krevelen diagram mental analysis is not supported by the Rock-Eval (Figure 7) appears to be caused by the wide range data (Figure 8; Table 3). Rather, most samples from of thermal maturity, consistent with the wide range both the Tarim and Junggar basins plot along the type of vitrinite reflectance values (Figure 6; Table 3). I or type II thermal evolution pathways on an HI vs. The least mature samples from the Junggar basin OI diagram. A subordinate number of samples from flank positions and the Turpan basin provide the the Tarim and Junggar basins, as well as most samples best indication of kerogen type and suggest a domi- from the Turpan basin, appear to follow the thermal nance of hydrogen-poor type III kerogens, consis- evolution pathway for type III kerogens. Reasons for tent with visual kerogen analyses indicating domi- this apparent discrepancy in kerogen characteriza- nance of vitrinitic and inertinitic macerals (Figure 5; tion between the two techniques are not entirely Table 2). However, two samples lie in the region clear, although this phenomenon has been noted by between type II and type III kerogens (Figure 7). other workers during analysis of coal (Teichmüller Visual kerogen analysis of one of these samples (88- and Durand, 1983; Kagya et al., 1991; Mpanju et al., J-3) indicates that it contains 38% exinite (liptinite), 1991; D. J. Curry, 1995, personal communication). which is responsible for the high H/C ratio. Peters (1986) discussed the tendency of Rock-Eval Hydrogen index (HI) vs. oxygen index (OI) dia- pyrolysis to overestimate the liquid hydrocarbon grams constructed from Rock-Eval pyrolysis data potential of coaly samples. Thus, it is likely that the (Espitalié et al., 1977) suggest that the predominance high HI/low OI signature of most Jurassic samples is Hendrix et al. 939 an artifact of Rock-Eval analysis, rather than an indica- the possibility to establish independent evidence tion of hydrogen-rich type I or type II kerogens. for expulsion of some hydrocarbons from these rock sequences.

Pyrolysis–Gas Chromatography BIOLOGICAL MARKER COMPOUNDS Pyrolysis–gas chromatography was conducted on 41 samples to determine the tendency of Biological markers (biomarkers) are geologically Jurassic rocks to generate liquid hydrocarbons. The occurring organic compounds that possess evi- high temperatures of pyrolysis–gas chromatogra- dence, either direct or inferred, of their biological phy produce compounds rarely observed in origin (e.g., Peters and Moldowan, 1993, and refer- petroleum (e.g., abundant n-alkenes) and compli- ences therein). They have been described as cate correlation of source rocks with oils (Gormly molecular fossils, although changes in chemical and Mukhopadhyay, 1983). Nevertheless, pyroly- structure during diagenesis and evolutionary sis–gas chromatography can provide evidence of changes in the chemistry of living organisms make kerogen structure and, by inference, the liquid it difficult or impossible to establish the direct bio- hydrocarbon generation potential of a source rock logical precursor molecule for many biological (Dembicki et al., 1983). Gas-prone kerogens and marker compounds. Nevertheless, biological mark- source rocks tend to liberate abundant low-molecu- ers characterize the organic matter contributed to a lar-weight aromatic compounds, whereas oil-prone sediment and, by extension, aid description of its kerogens and source rocks liberate a larger propor- depositional environment. Distributions of tion of nonaromatic compounds, such as n-alkanes biomarkers provide the best means for direct corre- and n-alkenes (Dembicki et al., 1983; Solli and lation between petroleums and their suspected Leplat, 1986; Tegelaar et al., 1989). source rocks. In addition, maturity-induced Pyrolysis–gas chromatography results suggest changes in many biomarkers can provide informa- that many Jurassic coal samples are capable of gen- tion on the thermal history of organic-rich rocks. erating liquid hydrocarbons. Compound distribu- We investigated biomarker distributions in the tions for most samples lie between two end-mem- aliphatic hydrocarbon fraction of 35 organic-rich ber compositions (Figure 9). In samples dominated Lower through Middle Jurassic samples from the by inertinitic or vitrinitic macerals, chromatograms southern Junggar, northern Tarim, and Turpan are characterized by an abundance of aromatic basins, and four petroleum samples collected from compounds and a lack of alkene/alkane doublets Xinjiang sedimentary basins (Figure 1, Appendix (e.g., Figure 9H; see Hendrix, 1992, for additional 1). Biomarkers are the primary tools used to inter- pyrograms). Although small quantities of high- pret the types of organic matter from which each ∼ molecular-weight (> n-C25) alkanes are present in oil sample was generated and from which we infer the pyrolyzate, the most dominant compounds are their maturity. Most importantly, we compare low-molecular-weight aromatic compounds typical biomarker distributions in the four oils with those of woody tissues (e.g., phenols). Jurassic samples in the Jurassic rocks to explore possible genetic containing abundant exinitic macerals (resins, cuti- relationships. cles, spores) tend to be dominated by alkene/alkane doublets and show low quantities of low- molecular-weight aromatic compounds (e.g., Acyclic Alkanes Figures 9C, 9E) (Hendrix, 1992). This second end member is more representative of oil-prone kero- Normal alkanes are the most abundant com- gens (Dembicki et al., 1983; Solli and Leplat, 1986). pounds for all samples in this study, although vari- Katz et al. (1991) also noted prominent alkane/ ous distributions of n-alkanes and different abun- alkene doublets in a Jurassic sample from dances of n-alkanes relative to other components Xishanyao (southern Junggar basin). Many Jurassic characterize individual samples (Table 5; Figures samples (e.g., Figures 9A, B, D, F, G) yield 10, 11). In nearly all rock samples, the dominant pyrolyzates with characteristics of both end mem- n-alkane is either n-C21, n-C23, or n-C25, and a slight bers: prominent alkene/alkane doublets with sub- to pronounced odd-over-even preference (OEP) is stantial low-molecular-weight aromatic com- present (Figure 10). (Carbon preference index is pounds, suggesting mixed organic matter types. calculated for n-C19 to n-C29.) Due to increased The prominence of alkene/alkane doublets sug- maturity, the OEP for Tarim extracts tends to be gests that these strata are capable of liquid hydro- somewhat less than that of Junggar samples (Table carbon generation, given sufficient thermal stress. 5; Figure 10). Whole oil–GC (gas chromatogram) Geochemical correlation of Jurassic organic-rich traces of the four petroleum samples (Figure 11) strata with samples of Xinjiang petroleum offers indicate that three of the oils are also dominated by 940 Jurassic Coal Measures, Northwest China

Table 3. Vitrinite Reflectance, Rock-Eval Pyrolysis, and TOC Data, Jurassic Coal and Shale, Xinjiang Basins*

Lat. Long. Ro Ro Tmax S1 Sample** (° - ′)(°- ′) (%) (n) (°C) (mg HC/g) Southern Junggar Basin 89-M-3D 43-49 86-06 0.71 50 435 2.9 89-M-3H 43-49 86-06 0.55 43 431 3.0 89-M-17A 43-54 85-51 0.75 97 435 2.2 89-M-17F 43-54 85-51 0.73 96 435 6.0 89-M-20 43-55 85-51 0.58 54 433 1.8 89-M-22A 43-55 85-50 0.82 82 435 2.4 89-M-27 43-55 85-52 0.70 50 434 2.2 88-M-115A 43-54 85-51 0.71 95 433 4.4 88-J-3 43-52 89-06 0.45 50 424 2.8 88-HL-102 44-03 88-04 0.50 50 435 1.9 88-HL-105 44-03 88-04 0.60 50 431 1.5 88-HL-106 44-03 88-04 0.54 90 432 2.3 88-B-1 43-54 87-43 0.54 98 437 0.7 88-B-2 43-54 87-43 0.64 50 434 3.2 88-X-1 43-44 87-15 0.52 50 426 0.3 Junggar Average 0.62 433 2.5 Standard Deviation 0.10 3 1.3

Western Turpan Basin 88-T-5 43-11 89-18 0.42 98 429 0.6 87-D-5A 43-22 88-24 0.75 47 419 0.4 Turpan Average 0.59 424 0.5 Standard Deviation 0.23 7 0.1

Northern Tarim Basin 89-K-19A 42-13 83-12 0.66 93 431 4.4 89-K-20B 42-13 83-11 0.72 75 444 6.2 89-K-20D 42-13 83-11 0.64 76 441 2.8 89-K-21F 42-13 83-11 0.75 96 442 1.5 89-K-22D 42-13 83-10 1.27 50 443 3.6 89-K-112 42-10 83-06 0.82 50 448 0.6 89-Kr-1A 41-53 86-08 0.66 50 433 0.2 89-Kr-1C 41-53 86-08 0.62 50 425 1.3 89-Y-205A 42-05 84-33 0.91 50 438 0.9 89-Q-64 42-11 81-40 0.83 50 444 4.2 89-Q-67 42-11 81-40 0.91 69 445 5.7 89-Q-71 42-11 81-40 0.60 95 442 3.3 89-BC-6A 42-00 81-31 1.16 50 468 0.7 89-Bc-9 42-01 81-32 1.20 31 466 0.8 89-Bc-10C 42-01 81-32 1.03 30 459 2.2 88-Aw-38C 41-42 80-45 2.18 50 529 0.2 90-Kz-35 39-43 75-02 0.70 50 450 0.4 90-Kz-36 39-43 75-02 0.77 50 444 1.6 Tarim Average 0.92 450 2.3 Standard Deviation 0.39 23 1.9

*HI and OI values calculated using Leco TOC measurements; nc = not calculated. **M = Manas, X = Xishanyao, B = Badaowan, HL = Heavenly Lake, J = Jimsar, D = Dabanchang, T = Taoshuyuan, Kr = Korla, Y = Yengisar, K = Kuqa, Bc = Baicheng, Q = Qiugetale, Aw = Awate, Kz = Kuzigongsu, PI = production index. n-alkanes. The lower carbon preference index (i.e., (northern Tarim seep) is highly biodegraded, and closer to 1.0) for these petroleums is attributed to consequently n-alkanes were not detected. higher thermal maturity, relative to rock samples Pristane (Pr) and phytane (Ph) are by far the dom- (Table 5; see Maturity section). Sample 92-Bc-101 inant acyclic isoprenoids in all Jurassic rock extracts Hendrix et al. 941

Table 3—Continued.

S2 S3 TOC (Leco) (mg HC/g) (mg CO2/g) PI S2/S3 (%) HI OI

91.4 4.2 0.03 21.9 65.7 124 5 178.0 4.3 0.02 41.2 80.6 221 5 130.6 2.8 0.02 46.8 75.5 170 3 117.5 4.1 0.05 28.9 75.6 155 5 41.6 0.8 0.04 51.4 26.2 151 2 95.7 2.8 0.02 34.3 73.6 129 3 93.2 14.6 0.02 6.4 74.2 126 19 167.7 4.4 0.03 38.0 72.1 210 5 183.8 7.6 0.02 24.2 53.0 232 9 80.0 2.5 0.02 31.7 42.4 184 5 105.4 3.5 0.01 29.7 74.4 141 4 124.2 5.8 0.02 21.5 77.3 163 7 106.3 8.3 0.01 12.8 70.5 150 11 133.8 1.9 0.02 71.1 78.1 173 2 66.5 12.6 0.00 5.3 74.4 93 17 114.4 5.3 0.02 31.0 67.6 161 7 38.9 3.8 0.01 16.9 14.8 37 5

81.5 18.5 0.01 4.4 63.0 112 25 3.2 30.9 nc 0.1 55.0 4 47 42.4 24.7 nc 2.3 59.0 58 36 55.3 8.7 nc 3.0 5.7 76 16

182.5 5.5 0.02 33.2 74.4 225 6 185.4 2.9 0.03 63.1 73.5 227 3 68.1 1.1 0.04 61.3 32.2 189 3 34.6 14.6 0.04 2.4 nc 50 21 74.0 0.8 0.05 88.1 72.5 102 1 2.9 0.3 0.16 8.9 4.7 53 6 88.8 6.6 0.00 13.6 42.8 121 8 151.8 7.0 0.01 21.8 81.7 194 8 59.9 4.0 0.02 15.0 72.3 84 5 169.3 1.3 0.02 135.4 72.4 228 1 119.9 2.3 0.05 52.6 67.5 166 3 82.2 1.3 0.04 65.7 51.4 194 2 14.9 9.4 0.05 1.6 77.7 22 14 70.8 0.1 0.01 589.8 57.7 102 0 36.8 2.0 0.06 18.4 75.3 53 2 9.9 1.6 0.02 6.3 69.9 15 2 60.6 2.4 0.01 25.3 62.7 98 3 90.9 2.7 0.02 34.0 49.9 167 4 83.5 3.7 0.04 68.7 61.1 127 5 57.6 3.7 0.04 134.6 19.9 73 5

and in each of the petroleums. Pr/Ph ratios for due to biodegradation. With this exception, the Jurassic shales and coals range from 1.3 to 8.0, aver- high Pr/Ph ratios for most extract and oil samples aging 4.5 (2σ = 1.7), whereas Pr/Ph ratios of the (generally greater than 2.5) are consistent with a four petroleum samples range from 4.3 to 5.0, aver- higher plant-dominated nonmarine environment aging 4.7 (2σ = 0.4). Neither Pr nor Ph were detect- (Powell and McKirdy, 1973). Given the many poten- ed in sample 92-Bc-101 (northern Tarim oil seep) tial biological sources and diagenetic pathways for 942 Jurassic Coal Measures, Northwest China

# of GC-MS (gas chromatography–mass spectrometry) samples analyses of saturate fractions, but their concentra- 10 tions were typically too low to permit quantifica- tion except from m/z 217 traces acquired in mul- 5 Junggar Depocenter Manas (M) tiple ion detection (MID) mode. Without exception, the sterane distributions for rock and 0 petroleum samples are dominated by C29 10 homologs, forming a cluster near the C29 apex of Junggar non-depocenter a sterane ternary plot (Table 5; Figure 12). Each Badaowan (B); Heavenly Lake (HL) of the petroleum samples is also dominated by 5 α α α Xishanyao (X); Jimsar (J) C29 regular [i.e., 5 (H), 14 H), 17 (H); hereafter αα, and 5α(H), 14β(H), 17β(H); hereafter ββ] 0 steranes, although petroleum samples 94-HU-1 10 (Junggar) and 92-Bc-101 (Tarim) contain marginally higher proportions of C and C ster- Tarim Depocenter 27 28 5 ane homologs. Many rock extracts are sufficiently Kuqa (K) mature to exhibit complete isomerization of C αα 29 0 steranes at the C-20 position [i.e., S/(S+R) percent ratios of 52–55%; Seifert and Moldowan, 10 1986], although some are incompletely isomer- Tarim basin flank ized (average = 34.3%; 2σ = 13.1%; Table 5). 5 ββ αα Kuzigongsu (Kz); Korla (Kr) Percentages of C29 20S+20R relative to C29 20S+20R also indicate a spread of maturities with- 0 in rock extract samples (average = 42.1%; 2σ = 10 13.2%; Table 5), although none of the samples northwestern Tarim appear to have reached peak maturity (maximum Awate (Aw); Baicheng (Bc); Qiugetale (Q) 5 = 65.5%; peak = 67–71%; Seifert and Moldowan, lower plate structural position? 1986). All four petroleum samples exhibit com- αα plete or nearly complete C29 20S/S+R sterane 0 isomerization (average = 49.8%; 2σ = 6.1%; Table 10 ββ αα ββ 5), but somewhat immature C29 /( + ) Turpan Basin ratios (average = 46.1%; 2σ = 5.8%; Table 5), sug- 5 Taoshuyuan (T); Dabanchang (D); gesting that the oils were not derived from peak Flaming Mountain oil window conditions. The greater relative matu- (42¡ 48′N 89¡ 5′E) 0 rity of the petroleum results in higher abun- 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 dances of C29 diasteranes compared to the abun- R (%) dance of these compounds in most source rocks o (Figure 12). Oil Gas

Oil Window Gas Window Hopanoid Compounds A prominent suite of hopanes was detected in Figure 6—Frequency plots of mean vitrinite reflectance values for Jurassic samples of central Xinjiang basins. every rock extract except 89-K-112 (Figure 13; Refer to Figure 1 for sample locations and Hendrix (1992) Table 5). Hopane distributions in each of the petroleum samples are notably similar to those of for Ro point-count histograms for individual samples. the rock extracts, irrespective of basin. C29 and C30 17α(H), 21β(H) hopanes (hereafter αβ) are typically the most abundant hopane in rock extracts and these compounds (e.g., Goossens et al., 1984; ten petroleum (Figures 10, 13). Maturity levels of most Haven et al., 1992), Pr/Ph ratios are used here only extracts and all four petroleums are sufficiently high as supporting evidence for contributions of terres- α to result in nearly full isomerization of C31 17 (H), trial organic matter and as a correlation tool. 21β(H) hopanes at the C-22 position (average = 51.9%; 2σ = 11.5% for extracts, average = 59.7%; 2σ Steroidal Hydrocarbons = 1.2% for oils; “peak” isomerization approximately 57–62%; Seifert and Moldowan, 1986). Higher In the Jurassic shales and coals and in the four hopane homologs show progressively lower con- petroleum samples, steranes were detected in centrations, commonly up to C33 or C34 hopanes. Hendrix et al. 943

Table 4. Elemental Analysis of Selected Jurassic Samples, Junggar, Turpan, and Tarim Basins

H C N O S Atomic Atomic Sample Locality (%) (%) (%) (%) (%) H/C O/C Southern Junggar Basin 88-M-113A Manas 3.58 52.39 0.06 21.15 0.30 0.82 0.30 88-M-114 Manas 4.34 70.36 0.51 13.87 0.93 0.74 0.15 88-M-115A Manas 4.53 73.65 1.25 7.84 1.35 0.74 0.08 89-M-3H Manas 5.73 82.13 1.09 7.11 0.30 0.84 0.06 89-M17A Manas 4.45 80.84 0.45 6.68 0.09 0.66 0.06 89-M17F Manas 4.07 84.99 0.41 5.68 0.06 0.57 0.05 89-M-20 Manas 2.07 29.28 0.15 4.63 0.18 0.85 0.12 89-M22A Manas 3.76 82.22 0.97 6.35 0.49 0.55 0.06 88-J-3 Jimsar 4.53 48.23 0.17 15.78 0.29 1.13 0.25 88-J-4 Jimsar 3.41 36.31 0.20 21.97 0.14 1.13 0.45 88-HL-102 Heavenly Lake 2.86 47.95 0.06 21.71 0.44 0.72 0.34 88-HL-106 Heavenly Lake 4.99 73.78 0.11 20.38 0.24 0.81 0.21 88-B-1 Badaowan 4.68 66.73 0.93 16.58 2.48 0.84 0.19 88-X-1 Xishanyao 4.31 71.11 0.20 24.30 0.21 0.73 0.26 88-X-3 Xishanyao 3.22 41.42 0.92 35.07 0.59 0.93 0.64 Junggar Average 4.04 62.76 0.50 15.27 0.54 0.80 0.21 Standard Deviation 0.91 18.46 0.42 8.88 0.64 0.17 0.17

Western Turpan Basin 88-T-4 Taoshuyuan 2.54 48.27 0.77 32.09 0.23 0.63 0.50 88-T-5 Taoshuyuan 3.65 47.71 3.97 17.20 1.02 0.92 0.27 Turpan Average 3.10 47.99 2.37 24.65 0.63 0.77 0.38 Standard Deviation 0.78 0.40 2.26 10.53 0.56 0.20 0.16

Northern Tarim Basin 87-K-46 Kuqa 4.78 76.65 0.65 17.69 0.23 0.75 0.17 89-K-19A Kuqa 5.32 81.21 0.43 8.99 0.47 0.79 0.08 89-K-20B Kuqa 5.72 81.96 1.18 5.42 1.65 0.84 0.05 89-K-20D Kuqa 2.24 38.35 0.18 4.16 0.38 0.70 0.08 89-K-21F Kuqa 4.00 74.12 1.30 13.51 0.45 0.65 0.14 88-Aw-38D Awate 3.75 90.75 0.39 4.66 0.32 0.50 0.04 89-Bc-9 Baicheng 4.02 77.70 1.00 4.10 1.09 0.62 0.04 89-Bc-10C Baicheng 5.23 79.35 0.39 7.59 0.26 0.79 0.07 89-Q-67 Qiugetale 2.70 68.46 0.38 5.27 0.10 0.47 0.06 89-Q-71 Qiugetale 2.74 40.87 0.44 3.33 0.25 0.80 0.06 89-Y-201C Yengisar 5.45 77.37 0.78 8.50 0.41 0.85 0.08 89-Y-205A Yengisar 2.98 80.31 0.33 7.96 0.20 0.45 0.07 Tarim Average 4.08 72.26 0.62 7.60 0.48 0.68 0.08 Standard Deviation 1.22 16.12 0.36 4.27 0.44 0.15 0.04

C αβ hopanes are detectable in many samples, but marine upwelling conditions (e.g., Curiale et al., 35 αβ are not anomalously high with respect to C34 1985; Curiale and Odermatt, 1989), were detected hopanes. This stepwise decrease in hopane abun- in samples 89-M-3D and 89-M-3H from the south αβ αβ dance from C31 to C35 homologs is consistent Junggar basin depocenter. Identification was con- with the presence of free oxygen in the diagenetic firmed by analysis of spectra. We believe this to be environment which has oxidized the precursor the first report of the occurrence of this marker in molecule bacteriohopanetetraol (C35) to a C32 acid, nonmarine strata. possibly followed by loss of the carboxyl group to In addition to homohopanes, distributions of C31 if sufficient oxygen is present (Peters and other pentacyclic terpanes are broadly similar Moldowan, 1993). between the rock extracts and petroleum, but also High concentrations of 28,30-bisnorhopane, com- reflect the greater maturity of the petroleum. Ts α monly regarded as an indicator of high-productivity and Tm [C27 18 (H), 22,29,30-trisnorneohopane 944 Jurassic Coal Measures, Northwest China

2.0 samples recovered from within the Tarim basin. LOCALITY Thus, it is likely that the gammacerane in sample Junggar Depocenter 1.8 Tarim "Flank" 92-Bc-101 reflects derivation from more basinal Type I Junggar "Flank" Turpan basin Jurassic source rocks than the extracts from basin Tarim Depocenter margins reported here. 1.6 Lithologic Classification Type II (inset into locality symbol) 1.4 SHALE (≤ 50% TOC) Tricyclic Terpanes COAL (> 50% TOC) unknown TOC (not meas.) C19 through C29 tricyclic terpanes were detected 1.2 in low abundance in many of the rock extracts, although appreciable quantities of these com- Type III 1.0 pounds were present in the more mature rock extracts, particularly those from the northwestern Tarim margin (Bc, Q, and Aw in Figure 1; Hendrix,

ATOMIC H/C RATIO 0.8 1992; Figure 13). Small but significant quantities of these compounds were also detected in petroleum 0.6 samples 94-HU-1 and 92-Bc-101, which exhibit a higher thermal maturity than most of the rock 0.4 extracts. Aquino Neto et al. (1983) noted that the tricyclic/17α(H) hopane ratio increases for related oils of increasing thermal maturity. Comparisons of 0.2 the distribution of tricyclic terpanes between 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 petroleum and rock extracts are similar, and are ATOMIC O/C RATIO consistent with a correlation between the two (Figure 13). Low C25/C26 ratios (<1) in rock Figure 7—Van Krevelen diagram for selected Jurassic extracts and the two oil samples suggest a lacus- samples from Xinjiang basins. Thermal maturity path- trine source rather than a marine source (Figure ways from Tissot and Welte (1984). Refer to Table 3 for 13) (Zumberge, 1987; Peters et al. 1994). TOC values and Table 2 for specific compositional information. Junggar depocenter = Manas locality; Junggar “flank” = Jimsar, Heavenly Lake, Badaowan, Xishanyao sections; Tarim depocenter = Kuqa section; Tarim “flank” Diterpenoid Compounds = Awate, Baicheng, Qiugetale, and Yengisar localities. A series of bi-, tri-, and tetracyclic diterpenoids was detected in many of the rock extract samples. α and C27 17 (H), 22,29,30-trisnorhopane, respec- The compounds included phyllocladane, nor-lab- tively] were detected in most rock extracts and all dane, nor-isopimarane, isopimarane, 4β(H) nor- four petroleums (Table 5). Ts/(Ts+Tm) ratios isopimarane, and 8β(H) labdane, among others (expressed as a percentage) in the rock extracts (Noble et al., 1985, 1986; Hendrix, 1992). In some are generally low (average = 8.6%; 2σ = 12.9%), cases, individual diterpenoid compounds were con- reflecting the comparative immaturity of these centrated enough to produce a detectable RIC samples (Seifert and Moldowan, 1986; Curiale, (reconstituted ion chromatogram) peak (Figure 10; 1992). The higher Ts/(Ts+Tm) ratios in the Hendrix, 1992). Comparison of the abundance and petroleums (average = 37.7%; 2σ = 10.3%) support diversity of diterpenoids indicates higher abun- their higher maturity, although the values are sta- dances of diterpenoid compounds, relative to tistically indistinguishable from those of high- n-alkanes, in Junggar rather than Tarim samples maturity rock extracts from within and nearby the (Table 5). It is unclear whether these differences Kalpin uplift (i.e., Baicheng, Qiugetale, Awate local- are a function of diagenetic preservation or ities; average = 27.4%; 2σ = 16.9%). Gammacerane, whether they represent diversity of diterpenoid commonly viewed as an indicator of abnormal sources from one side of the Tian Shan to the other. salinity (Brassell et al., 1988), is below detection Diterpenoids were not detected in any of the limits in all Jurassic extracts and three of the four petroleum samples. petroleums (Figure 13). Petroleum sample 92-Bc- Diterpenoids are generally interpreted as being 101 contains detectable gammacerane (gammac- derived from conifers (Simoneit, 1977; Barrick erane/C30 hopane = 0.097) and slightly lower and Hedges, 1981; Noble et al., 1985, 1986). The abundance of C31 hopanes than other petroleum prominent suites of diterpenoids in the rock and rock extract samples. Fan et al. (1990) has extracts therefore suggest land-derived organic reported gammacerane in four of ten Jurassic core matter associated with deposition of the coals and Hendrix et al. 945

JUNGGAR AND TURPAN BASINS TARIM BASIN

Junggar samples described Tarim samples described II 500 II 500 e in this study e in this study p p

Type I y y T Other Junggar samples Type I T

100 Other Tarim samples 100 (Hendrix, 1992) * * (Hendrix, 1992) 400 400 Turpan samples described /TOC) /TOC) in this study 2 2 (S

Other Turpan samples 300 (Hendrix, 1992) 300

200 200

100 Typ HYDROGEN INDEX 100 Type HYDROGEN INDEX e III III

0 0 0 100 200 0 100 200 OXYGEN INDEX (S3/TOC)*100 OXYGEN INDEX (S3/TOC)*100 Figure 8—Hydrogen index (HI) vs. oxygen index (OI) plots for all Jurassic samples collected from Xinjiang basins in this study. HI and OI values derived from Rock-Eval pyrolysis and Leco TOC data. Refer to Table 3 and Hendrix (1992) for Rock-Eval and TOC data for each sample plotted here. organic-rich shales. It is unclear whether the THERMAL MATURITY absence of diterpenoids in the petroleum samples is a function of their greater maturity, compared Sterane isomerization values are consistent with to the source rock samples, or their derivation vitrinite reflectance measurements, which suggests from source rocks without diterpenoid com- that most of the rock samples either have not pounds. Although diterpenoids were prevalent in entered the oil window (R <0.6%) or are mature ∼ o many of the rock extracts, not all of the samples (Ro 0.6–0.9%) with respect to petroleum genera- contained detectable diterpenoids (Table 5). tion. The greater thermal maturity of the northwest- Thus, lack of diterpenoid compounds in these ern Tarim basin, based on vitrinite reflectance data, petroleum samples does not exclude a Jurassic is not evident in sterane and hopane isomerization source. ratios because these processes are complete at lower levels of thermal maturity. Similarly, diasterane/sterane percentage ratios of rock extracts (aver- Other Biomarkers age = 30.0%; 2σ = 10.1%) do not exhibit maturity trends from basin flanks to depocenters. In con- Carotenoids, such as β-carotane and γ-carotane, trast, Ts/(Ts+Tm) ratios (Table 5) (Seifert and were not detected in any of the rock extracts or the Moldowan, 1986; Curiale, 1992) vary widely, with four petroleum samples. This consistent absence of the most mature rock samples from northwest carotanes is particularly significant because of their Tarim yielding the highest Ts/(Ts+Tm) ratios (Table use in the correlation of Permian-sourced 5). For a complete discussion of stereochemical petroleum in the Junggar basin (Carroll et al., maturity parameters measured in Jurassic rock 1992). extract samples from Xinjiang see Hendrix (1992). Pentacyclic triterpanes (e.g., oleanane and Given that rock samples analyzed in this study were lupane), significant components of many Tertiary collected from uplifted basin margins and are far coal deposits (Ekweozor et al., 1979; Hoffman et al., from producing areas, there is considerable uncer- 1984), are absent from rock extracts and petroleum tainty regarding the degree to which maturity of examined here. These compounds are derived from these samples are representative of subsurface angiosperms, which did not radiate significantly Jurassic rocks that may be currently expelling oil. until the Early Cretaceous. Their absence is consis- For this reason, we have restricted our discussion of tent with the Jurassic age of these deposits. Jurassic strata to depositional issues and character of 946 Jurassic Coal Measures, Northwest China

Figure 9—Pyrolysis–gas chromatograms (using techniques in Colling et al., 1986) for selected Jurassic samples from the (A–D) southern Junggar, (E–G) northern Tarim, and (H) western Turpan basins. The abundance of n-alkene/ n-alkane doublets, relative to low-molecular-weight aromatic compounds, is typical of samples with oil generative potential. Note the diversity of traces for this suite of samples, suggesting that a significant number of samples are oil prone, whereas several others are likely gas prone. The suggestion that some of these samples are oil prone is consistent with the abundance of exinitic macerals observed in Jurassic rock samples (Table 2; Figure 5) and a positive biomarker correlation between rock extracts and four petroleums from the Junggar, Turpan, and Tarim basins.

source sequences, rather than generative issues. For indexed to Ro data, see Hendrix et al. (1994a) and detailed discussions of the thermal history of basin Sobel and Dumitru (in press). Constraints on burial margins based on apatite fission-track data and history and geologic evolution for these basins are Hendrix et al. 947 discussed in Graham et al. (1990), Hendrix et al. Jurassic organic-rich deposits across much of cen- (1992), and Carroll et al. (1993). tral Asia are the result of monsoonal circulation induced by the configuration of the large Pangean landmass. According to Parrish (1993), during the DISCUSSION Late Triassic–Early Jurassic, seasonally alternating high and low pressure cells formed over proto- Early and Middle Jurassic Lake Development Laurasia and proto-Gondwana (Hendrix et al., 1992). These pressure cells forced seasonal air The widespread distribution of exclusively non- masses to flow across the warm, equatorial Tethys marine Lower and Middle Jurassic organic-rich stra- Ocean, accumulating moisture and depositing it ta across the study area and adjacent regions onshore in the form of monsoonal rainfall. The (Vakhrameyev and Doludenko, 1977; Lai and Wang, existence of widespread organic-rich facies is con- 1988; Hendrix et al., 1994b) led Huang et al. (1991) sistent with such a monsoonal climate. Hendrix et and Hendrix et al. (1992) to postulate regionally al. (1992) suggested that the Early and Middle extensive lakes in the southern Junggar, northern Jurassic Tian Shan apparently did not possess suffi- Tarim, and Turpan basins. Indeed, all three basins cient relief to produce a rain shadow. Given the have had a protracted history of lacustrine develop- thick, widespread nature of organic-rich meander- ment. Extensive Late Permian lakes (Carroll et al., ing fluvial sediments and the apparent duration of 1992) and Late Cretaceous lakes (Shen and Mateer, their deposition, any basinward lacustrine system 1992) have been inferred from the Junggar sedi- was probably a long-lived feature existing, albeit mentary record. Regional lacustrine deposition perhaps intermittently, for millions of years. characterized the Turpan basin in the Jurassic and Cessation of the monsoon by the Late Jurassic is in the Pleistocene (Huang et al., 1991; Nishidai and predicted by global atmospheric circulation models Berry, 1991), and large ephemeral lakes continue to (e.g., Kutzbach and Gallimore, 1989), and is consis- occupy significant portions of central Asia (e.g., tent with regional development of Upper Jurassic Lop Nur in the eastern Tarim basin, Manas and red beds (e.g., Qigu Formation, Figure 2) and rela- Ebinur Lakes in the Junggar basin). tive increases in Classopollis pollen, derived from Most of the Lower and Middle Jurassic strata drought-tolerant, probably opportunistic Cheiral- exposed on the flanks of the three basins bear ipidiaceae conifers (Vakhrameyev and Doludenko, meandering fluvial rather than lacustrine affinities. 1977; Vakhrameyev, 1982). Nevertheless, the ubiquity of organic-rich strata, their considerable thickness, and the likelihood that the present basin edges expose only proximal litho- Sources of Organic Matter facies strongly suggest that regional lacustrine facies occupy basin depocenters in the subsurface. Many lines of evidence suggest that higher plants Additional circumstantial evidence supports this were the principal source of organic matter for conclusion. The fossil remains of a large aquatic Lower through Middle Jurassic rock samples. dinosaur in Jurassic outcrops near Baicheng (Bc in Abundant higher plant detritus, ranging from log Figure 1) (Wu, 1987) attests to the existence of a jams to well-preserved leaf impressions and rhy- deep water body. Huang et al. (1991) reported zoids, is common throughout the deposits in all widespread Jurassic lacustrine deposits from the three basins. Vitrinite is a major, if not dominant, subsurface of the Turpan basin. Zhou et al. (1993) maceral for all organic-rich Jurassic samples exam- analyzed a series of produced oils from the Turpan ined (Table 2). Atomic H/C and O/C ratios suggest a basin and cited their low sulfur content (0.03– higher plant source (Table 4). Moderate to strong 0.06%), pristane predominance (average ∼2.3), high odd-over-even carbon preference indices and a dom- paraffinic content relative to conventional oil, and inance of medium- to high-molecular-weight n-al- low asphaltene content as consistent with a lacus- kanes, typical for higher plant-derived organic mat- trine source. Zhou et al. (1993) also reported similar ter (Gagosian et al., 1981; Tegelaar et al., 1989), sterane and hopane distributions between these oils characterize most samples. C29 steranes are the dom- and a series of Jurassic lacustrine mudstones collect- inant homolog, consistent with higher plant-derived ed from core. Regional facies distributions and pale- bitumens and oils (Huang and Meinschein, 1979; Ra- ocurrent measurements along uplifted basin mar- manampisoa et al., 1989). Diterpenoids, recognized gins (Hendrix et al., 1992) suggest that meandering biomarkers from conifers (Simoneit, 1977; Barrick fluvial/deltaic strata trend into regional lacustrine and Hedges, 1981; Noble et al., 1985, 1986), were strata down depositional dip. detected in over 85% of the rock extracts. Clearly Global paleoclimatic modeling predictions Early and Middle Jurassic rainfall patterns permitted (Kutzbach and Gallimore, 1989) and regional paleo- vast coniferous forests to develop on both sides of climate syntheses (Parrish, 1993) suggest that the the Tian Shan and also within the intermontane Table 5. Summary Biomarker Parameters for Jurassic Rock Extracts and Selected Petroleums, Xinjiang Basins

C St 29 αα Dominant C27 St C28 St C29 St (S/S+R ) Sample n-Alkane CPI Pr/ Ph (%) (%) (%) (%) Junggar Basin 89-M-3D 21 1.0 6.6 5.0 17.8 77.2 30.3 89-M-3H ** 23 1.8 4.4 3.0 14.8 82.3 33.2 89-M-17A nc nc nc 1.3 22.0 76.7 44.1 89-M-17F ** 23 1.1 5.4 3.8 23.1 73.1 41.3 89-M-20 ** 20 1.1 5.4 9.7 14.9 75.4 37.3 89-M-22A 23 1.1 3.4 2.1 22.6 75.3 40.7 89-M-27 25 1.3 2.1 2.9 6.2 90.9 39.6 88-M-115A 23 1.1 3.4 2.3 17.1 80.6 50.0 88-J-3 23 2.1 6.9 4.0 14.8 81.2 5.0 88-HL-102 23 1.3 3.4 6.1 20.5 73.4 33.2 88-HL-105 23 1.3 4.5 2.0 15.8 82.2 22.9 88-HL-106 23 1.5 5.5 1.2 18.7 80.1 21.6 88-B-1 21 1.3 2.6 3.7 4.6 91.8 32.6 88-B-2 23 1.3 8.0 1.5 20.3 78.3 41.0 88-X-1 23 1.7 3.8 2.6 17.3 80.2 2.3 Junggar Average 22.8 1.4 4.5 3.4 16.7 79.9 31.7 Standard Deviation 1.2 0.3 1.8 2.2 5.4 5.5 13.6 Turpan Basin 88-T-5 23 2.0 4.6 4.4 12.8 82.9 nd 87-D-5A 22 nc nc 2.1 22.9 74.9 32.4 Turpan Average 22.5 nc nc 3.3 17.8 78.9 nc Standard Deviation 0.7 nc nc 1.6 7.2 5.6 nc Tarim Basin 89-K-19A 23 1.2 6.6 3.0 11.2 85.8 33.9 89-K-20B ** 23 1.1 4.3 22.5 9.1 68.3 38.3 89-K-20D ** 23 1.0 3.4 15.0 14.6 70.5 41.1 89-K-21F 21 1.1 nc 6.3 10.4 83.3 45.1 89-K-22D 18 0.9 1.3 1.4 18.8 79.8 44.8 89-K-112 17 0.9 5.3 nd nd nd nd 89-Kr-1A ** 25 1.7 4.9 1.7 21.1 77.2 9.1 89-Kr-1C 25 1.6 6.9 1.7 15.6 82.6 10.3 89-Y-205A 21 1.1 5.7 3.2 16.8 80.0 12.7 89-Q-64 nc nc nc 3.5 18.1 78.4 44.8 89-Q-67 ** 20 1.0 nc 9.4 17.9 72.6 42.5 89-Q-71 17 0.9 2.4 3.5 0.9 95.6 45.4 89-Bc-6A 17 nc 2.6 16.2 18.0 65.8 41.2 89-Bc-9 ** 20 1.0 nd 14.7 15.6 69.7 35.7 89-Bc-10C 25 1.0 nd 14.8 20.1 65.1 43.8 88-Aw-38C 22 nc nc 38.7 17.4 43.9 44.6 90-K-35 23 1.1 3.8 3.2 19.1 77.7 46.5 90-K-36 25 1.0 4.9 5.1 12.4 82.4 46.3 Tarim Average 21.3 1.1 4.3 9.6 15.1 75.2 36.8 Standard Deviation 2.9 0.2 1.7 9.9 5.0 11.3 13.0 Selected Xinjiang Petroleum Samples 94-HU-1 (Junggar) nc 1.0 4.3 3.8 32.9 63.2 45.6 93-QK-6 (Turpan) nc 0.9 5.0 16.4 14.9 68.7 44.3 93-QK-101 (Turpan) nc 0.9 5.0 12.7 18.9 68.4 51.9 92-Bc-101 (Tarim) nc biodegr. biodegr. 19.1 19.9 60.9 57.6 Petroleum Average nc 0.9 4.7 13.0 21.7 65.3 49.8 Standard Deviation nc 0.0 0.4 6.7 7.8 3.8 6.1

*nc = not calculated; nd = not detected. CPI (carbon preference index) = (n-C19 + n-C21 + n-C23 + n-C25 + n-C27 + n-C29)/(n-C20 + n-C22 + n-C24 + n-C26 + n-C28); quantified using RIC (where possible) or m/z 85. Pr/Ph = pristane/phytane; quantified using RIC. Percent C27 St = 100 × (C27/C27 + C28 + C29 20S + 20R 5α(H),14α(H),17α(H) steranes; quantified using m/z 217. Percent C28 and C29 steranes were calculated in a similar fashion. Percent C29 St S/(S + R) = 100 × C29 5α(H), 14α(H), 17α(H) sterane 20S/(20S + 20R); quantified using m/z = 217. Percent C29 St ββ/αα + ββ = 100 × C29 5α(H), 14β(H), 17β(H) 20S + 20R sterane/(C29 5α(H), 14α(H), 17α(H) 20S + 20R sterane + C29 5α(H), 14β(H), 17β(H) 20S + 20R sterane); quantified using m/z = 217. Percent C29 DSt/(DSt + St) = 100 × (C29 13β(H), 17α(H) 20S + 20R diasterane)/(C29 13β(H),17α(H) 20S + 20R diasterane + C29 5α(H), 14α(H), 17α(H) 20S + 20R sterane); quantified using m/z 217. Percent Ts/(Ts+Tm) = 100 × 18α(H)-22,29,30-trisnorneohopane/(18α(H)-22,29,30-trisnorneohopane + 17α(H)-22,29,30-trisnorhopane); quantified using m/z 191. Percent C31 Hop 22S/(S + R) = 100 × C31 17α(H), 21β(H) hopane 22S/(C31 17α(H), 21β(H) hopane 22S + 22R); quantified using m/z 191. Hop/St = C30 17α(H), 21β(H) hopane/C29 20S + 20R 5α(H), 14α(H), 17α(H) steranes; quantified using m/z 217 and m/z 191. Diterpenoid diversity values = number of compounds. Diterpenoid abundance: t = trace, l = low, mod = moderate, maj = major component; quantified using m/z 123. **Fractionated by liquid chromatography. All ratios are based on integrated peak areas. Table 5—Continued.

C29 St C29 (DSt/ (Ts/ C31 Hop (ββ/αα+ββ) DSt+St) Ts+Tm) (22S/S+R) Diterp. Diterp. (%) (%) (%) (%) Hop/St Diversity Abundance

38.0 44.1 2.5 58.1 4.1 6–10 mod 29.7 22.1 1.7 54.3 3.9 >10 maj nc 22.9 2.0 58.6 5.3 nc nc nc 29.0 1.6 53.1 nc 1–2 t 21.1 19.5 0.9 56.0 8.5 6–10 t 18.4 25.4 1.9 57.7 nc 3–6 mod 20.9 13.6 1.2 58.3 10.0 6–10 t 27.8 20.1 1.8 59.1 9.6 6–10 l 51.4 15.0 0.4 29.0 5.8 3–6 maj nc 29.9 3.0 57.2 nc >10 maj nc 28.2 0.9 53.2 4.8 1–2 maj nc 16.5 0.7 55.8 1.9 1–2 maj nc 22.7 0.3 57.7 19.6 1–2 mod nc 28.0 1.8 58.1 3.2 1–2 mod nc 41.0 2.0 23.0 6.5 nd nd 29.6 25.2 1.5 52.6 6.9 11.7 8.7 0.8 11.0 4.7

nc 42.2 1.3 15.7 4.9 6–10 mod 65.5 27.4 13.6 23.9 nc 3–6 t nc 34.8 7.4 19.8 nc nc nc nc 10.5 8.7 5.8 nc nc nc

nc 27.7 1.0 58.5 nc 1–2? t? 50.5 44.3 11.5 54.9 nc 3–6 t 47.5 38.2 11.5 57.8 36.5 1–2? t? 43.6 41.5 7.8 56.0 13.1 1–2 t 28.3 27.4 2.5 59.5 3.7 1–2? t? nc nd nd nd nc nd nd nc 22.2 nd 54.8 nc 1–2 l nc 23.1 0.6 46.2 10.8 1–2 mod nc 38.0 1.5 49.5 5.1 6–10 l 48.2 40.8 19.1 59.8 nc nc nc 45.4 38.6 15.9 55.4 nc 3–6 t 44.8 29.8 2.8 58.8 17.8 3–6 t 58.3 32.8 45.1 50.4 nc 6–10 mod 52.8 28.7 21.1 51.2 nc 3–6 t 55.5 27.9 44.4 44.6 nc nd nd 53.1 60.5 43.7 60.2 nc 3–6 t 39.1 19.3 2.8 58.0 2.4 6–10 maj 45.3 29.8 2.3 59.2 22.1 >10 l 47.1 33.6 15.4 55.0 13.9 nc nc 7.7 10.1 16.2 4.9 11.4 nc nc

51.2 33.8 39.4 61.5 11.6 nd nd 48.5 37.8 31.1 59.2 3.8 nd nd 46.8 37.1 28.8 58.9 4.4 nd nd 37.8 34.7 51.6 59.4 15.3 nd nd 46.1 35.8 37.7 59.7 8.8 nc nc 5.8 1.9 10.3 1.2 5.6 nc nc

portions of the range such as the Turpan basin. Abundant hopanes in most of the rock extracts Vakhrameyev and Doludenko (1977) studied Jurassic indicate significant contributions of organic matter floras of central Asia, and concluded that a robust from bacteria (Ourisson et al., 1979). Hopane/ster- and varied coniferous flora inhabited the present ane ratios are a measure of the relative contribu- study area during the Early and Middle Jurassic. tions from bacteria and algae (Table 5) (Hoffman et 950 Jurassic Coal Measures, Northwest China

100% 100% 17 23 89-M-20 19 (southern Junggar) 89-Bc-6A Ro = 0.58 19 (northern Tarim) S2 = 41.62 Ro = 1.16 Hopanes S2 = 14.93 Pr

17Pr 27 23 Hop-31 Hop-29

D Hop-30 27

0 1000 2000 3000 4000 0 1000 2000 3000 4000 time (sec.) time (sec.)

23 100% 19 100%

89-K-20B 19 (northern Tarim) 89-Q-67 Ro = 0.72 23 (northern Tarim) 27 S2 = 185.41 Ro = 0.91 17 S2 = 119.87 Pr 29

17 27 D 29 Pr

0 1000 2000 3000 4000 0 1000 2000 3000 4000 time (sec.) time (sec.) Figure 10—Reconstituted ion chromatograms (RIC) for saturate hydrocarbon fractions for selected Jurassic rock extracts, southern Junggar and northern Tarim basins. Labels on peaks refer to carbon number of n-alkanes. Pr = pristane. Hop-29, Hop-30, and Hop-31 = hopanes with 29, 30, and 31 carbon numbers, respectively. Evaporative loss of low molecular weight (

organic-rich Upper Permian lacustrine facies is the dominant petroleum source for the basin (Graham et al., 1990; Carroll et al., 1992). In addition, Jiang and Fowler (1986) suggested Carboniferous marine mudstones as a significant source for the giant Karamay field, although no evidence was presented to document the age of the analyzed source rocks. The northern Tarim basin lacks the organic-rich Upper Permian lacustrine facies of the Junggar basin, but contains Ordovician marine black shales generally regarded as the basin’s most significant source rock (e.g., Graham et al., 1990); these shales have been geochemically correlated with various Tarim oils (Fan et al., 1990; Yang, 1991). Fan et al. (1990) also suggested that Cambrian dolomites and Carboniferous–Permian organic-rich shales and coals from the northern Tarim basin are additional local sources of petroleum, although Graham et al. (1990) found the source rock quality of these strata to be poor. Our geochemical results from four selected crude oils from all three basins suggest a geochemical correlation with Jurassic organic-rich rocks. Pristane/phytane ratios are high in each petroleum and the Jurassic rock extracts, typical of terrestrial oils (e.g., Powell and McKirdy, 1973). Sterane and hopane distributions are similar to those of the rock extracts (Figures 12, 13) and are notably different from distributions reported for Ordovician or Permian source rocks or oils from the Tarim and Junggar basins, respectively. For example, a strong predominance of C29 steranes in all four oils is consistent with sterane distributions in Jurassic rock extracts and different from Cambrian–Ordovician source rocks and oils in Tarim, which have considerably larger relative abundances of C27 and C28 steranes (Yang, 1991) (Figure 12), or Permian lacustrine source rocks from Junggar, which have sube- qual amounts of C28 and C29 steranes (Carroll et al., 1992) (Figure 12). The abundance of tricyclic terpanes relative to pentacyclic terpanes (Figure 13) is considerably lower for the rock extracts and petroleum reported here than for Cambrian– Ordovician or Carboniferous–Permian sources and their corresponding oils reported from the Tarim basin (Fan et al., 1990). The presence of minor gammacerane in oil sample 92-Bc-101 (northern Tarim basin) is an anomaly Figure 11—Whole-oil gas chromatogram traces for four in the correlation with Jurassic source rocks. petroleums from Xinjiang basins. Numbers above peaks Gammacerane is absent from all of the Jurassic rock refer to number of carbons in n-alkanes. Pr = pristane, extracts and all petroleums except this sample Ph = phytane. Paraffins and isoprenoids are biodegrad- (Figure 13). Results from Zhou et al. (1993) suggested in sample 92-Bc-101 (northern Tarim basin). On the ed that basinal lacustrine mudstones, which locally basis of biomarker correlations, each of these contain gammacerane, and basin margin fluvial petroleums is consistent with derivation from Jurassic coaly strata, which lack gammacerane, both provide strata. significant petroleum source rock contributions to the Turpan basin. A similar change in source rock facies may also characterize the northern Tarim 952 Jurassic Coal Measures, Northwest China basin because other geochemical parameters sug- Saxby and Shibaoka, 1986). In addition, composi- gest that the sample was derived from lacustrine tional studies of bitumens and kerogens from coal Jurassic source rocks down depositional dip rather suggest that cracking to gas or condensate is not a than fluvial coaly strata observed along uplifted prerequisite for expulsion of liquid hydrocarbons basin margins. Hopane and sterane biomarker from coals (Huc et al., 1986; Horsfield et al., 1988). parameters are consistent with a correlation The oil-generative character of Jurassic coals and between oil sample 89-Bc-101 and Jurassic rock shales of Xinjiang basins (Figure 9) is almost cer- extracts (Figures 12, 13). The relative distribution of tainly due to the locally high percentages of hydro- C27, C28, and C29 steranes for this oil are notably dif- gen-rich macerals, such as exinite, as noted for ferent from those values reported for northern other oil-generative coals (Curry et al., 1994). The Tarim well Shacan 2 oil, considered to be derived geochemical parameters that support the ability of from Ordovician source rocks in the northern Tarim these strata to generate oil and their biomarker cor- basin (Figure 12). Oil sample 92-Bc-101 contains relation with petroleum from each of the three 0.14% sulfur, consistent with a nonmarine source, basins examined are consistent with this idea. This especially considering the highly biodegraded char- work indicates that Jurassic coaly deposits are a acter of the oil. This value is lower than the sulfur critical component of exploration risk reduction in content of 0.3% reported for the Shacan 2 oil (Yang, northwestern China. 1991). Yang (1991) also reports that Carbon- iferous–Lower Permian source rocks from north Tarim contain β− and γ-carotane, both of which are CONCLUSIONS lacking in oil sample 92-Bc-101. Increasing evidence suggests that coals and asso- (1) Lower and Middle Jurassic coal-bearing strata ciated type III kerogen can yield not only gas or are widespread across much of central Asia and are condensate (e.g., Tissot and Welte, 1984), but also well developed in the southern Junggar, northern significant quantities of oil (Murchison, 1987; Tarim, and western Turpan basins of northwestern Curry et al., 1994). According to Hunt (1991), the China. Thicknesses and estimated volumes of two main relevant criteria are the liptinite content Jurassic coal in these basins make these among the of the coal and the importance of adsorption world’s largest coal deposits. Jurassic coaly strata effects during primary migration, which are related exposed along uplifted basin margins in northwest to seam thickness. In part, the traditional view that China were deposited in meandering fluvial and, coals are largely gas prone may be the result of his- locally, in lacustrine deltaic systems. Regionally torical bias in the study of North American and extensive Jurassic lakes probably developed basin- European Paleozoic coals, prior to the study of ward from present-day outcrop belts. High runoff Mesozoic–Cenozoic coals containing contributions conditions and possible regional lake development from resinous conifers and angiosperms (Thomas, are consistent with global circulation modeling pre- 1982). Coals and related continental strata with dictions of Early and Middle Jurassic monsoons in type III kerogen provide the source for commercial the study area (Kutzbach and Gallimore, 1989; oil accumulations in sedimentary basins of New Hendrix et al., 1992; Parrish, 1993). Zealand (Collier and Johnston, 1991; Johnston et (2) Field and laboratory data indicate a domi- al., 1991; Curry et al., 1994), Australia (Philp and nance of terrestrial organic matter in the Jurassic Gilbert, 1986; Curry et al., 1994), Indonesia deposits. Preserved plant remains, ranging from log (Hoffman et al., 1984; Bjorøy et al., 1988), Tanzania jams to leaf impressions and in-situ rhyzoids, are (Kagya et al., 1991; Mpanju et al., 1991), and China common in Jurassic deposits. Maceral composi- (Fu et al., 1991; Luo et al., 1991). Reports of lipti- tions are dominated by vitrinite and inertinite, but nite-rich coals as oil source rocks (e.g., Püttman et substantial exinitic material also occurs. Elemental al., 1986) are generally accepted, and recent TEM analysis indicates that the kerogens are dominantly (transmission electron microscopy) observations of type III. Mean vitrinite reflectance values range type III kerogens (Liu and Taylor, 1991) have sug- from 0.42 to 2.18%, but indicate that Jurassic strata gested that vitrinite-rich and even inertinite-rich from most sample locations are slightly immature coals may constitute important oil source rocks (cf. to mature with respect to petroleum generation.

Figure 12—m/z 217 fragmentograms and sterane distributions for Jurassic rock extracts and petroleums. Ternary α α diagram shows relative percentages of C27, C28, and C29 14 (H), 17 (H) steranes for all rock extracts, compared to petroleums. The similarity in m/z 217 traces and distribution of C27, C28, and C29 sterane components between rock extracts and petroleums suggests that the petroleums are derived from Jurassic strata. Shown also are comparative values for selected other oils and source rocks from Xinjiang basins. Hendrix et al. 953

Jurassic Rock Extracts Petroleums Rock Extract 89-M-17F (southern Junggar basin) Junggar 94-HU-1 (Junggar) 6 Turpan 93-QK-6, 93-QK-101 (Turpan) m/z 217 2 7 Tarim 92-Bc-101 (Tarim) 4 5 1 3 8 C28 (60%) C28

Permian oil shale 60% 7 & Karamay oils Petroleum 94-HU-1 9 (Carroll et al., 1992; 8 Jiang et al., 1988; (southern Junggar basin) 6 Philp et al., 1989) m/z 217 2 4 C29 C27 60%

1 3 5

Sha-2 oil (Yang, 1991) 7 9 8 Petroleum 93-QK-6 C 4 6 C27 29 (Turpan basin seep) 2 (60%) (100%) m/z 217

1 3 5

STERANE IDENTIFICATION KEY 7 8 1. C 5α(Η)14α(Η)17α(Η) 20S 27 Petroleum 93-QK-101 4 6 9 (Turpan basin) 2 2. C 13β(Η)17α(Η) 20S diasterane m/z 217 29 3 1 5

α(Η)14α(Η)17α(Η) 3. C27 5 20R

13β(Η)17α(Η) 4. C29 20R diasterane Petroleum 92-Bc-101 7 8

9 I N T E S Y (northern Tarim basin seep) 2 6 4 m/z 217 1 3 5. C 5α(Η)14α(Η)17α(Η) 20R 28 5

α(Η)14α(Η)17α(Η) 6. C29 5 20S sterane

α(Η)14β(Η)17β(Η) 7 7. C29 5 20R sterane Rock Extract 89-Q-67 89 (northern Tarim basin) 2 6 m/z 217 4 α(Η)14β(Η)17β(Η) 8. C29 5 20S sterane

1 α(Η)14α(Η)17α(Η) 3 5 9. C29 5 20R

T I M E 954 Jurassic Coal Measures, Northwest China

5 Rock Extract 89-M-17F TERPANE IDENTIFICATION KEY 3 2 7 (southern Junggar basin) α m/z 191 1. Ts = 18 (H)-22,29,30-trisnorneohopane 6 2. Tm = 17α(H)-22,29,30-trisnorhopane 9 10 C 17α(H)21ß(H)-norhopane 29 11 3. α 12 C2917§(H)21 (H)-norhopane 1 4 α 4. C3017 (H)21ß(H)-diahopane (Moldowan et al., 1991) 5 α 3 Petroleum 94-HU-1 5. C3017 (H)21ß(H)-hopane α 7 (southern Junggar) 6. C3017§(H)21 (H)-hopane m/z 191 α 7. C3117 (H)21ß(H)-homohopanes 10 (22S+22R isomers) 2 11 8. Gammacerane 4 6 12 1 β α 9 9. C3117 (H)21 (H)-homohopanes α 10. C3217 (H)21ß(H)-homohopanes R α 11. C3317 (H)21ß(H)-homohopanes 12. C 17α(H)21ß(H)-homohopanes 3 5 34 Petroleum 93-QK-6 7 BNH. 28,30-Bisnorhopane (Turpan basin) (samples 89-M-3D and 89-M-3H only) m/z 191 2 10 C19, C20, C21, C23, C24, C25, 6 11 12 C26 (22R), C28 (22R), C29 (22R), R 4 C29 (22S) Tricyclic Terpane 1 9 (labeled separately on trace)

Rock Extract 89-M-3H 3 5 Petroleum 93-QK-101 (southern Junggar basin) 7 3 (Turpan basin) Presence of 28,30-Bisnorhopane m/z 191 (confirmed by mass spectra) 5 2 10 BNH 7 m/z 191 6 2 11 4 12 6 1 9 9 10 11 12 1 5

Petroleum 92-Bc-101 I N T E S Y Rock Extract 89-Q64 2 (northern Tarim basin) m/z 191 (northern Tarim basin) 3 m/z 191 Tricyclic Terpanes 7 C 10 C19 C26 C29 29 (22R)(22S) C20 1 4 8 11 1 2 6 12 C23 9 C21 C28 C24 C25

5 Rock Extract 89-Q-67 Petroleum sample 94-HU-1 3 (northern Tarim basin) (southern Junggar basin) m/z 191 2 m/z 191 Tricyclic Terpanes C29 C291 7 (22R)(22S) C 2 10 19 C26 C C23 6 20 C 11 C C 28 12 21 24 C25 1 4 9

T I M E T I M E Hendrix et al. 955

Samples from the northwestern Tarim basin are (1977), Katz (1983), and Peters (1986) for more detailed discus- mature to overmature. Biomarker distributions sup- sions of the Rock-Eval pyrolysis technique and its limitations.] In addition to Rock-Eval and TOC analyses, bulk organic geochemical port the conclusion that higher land plant organic techniques employed in this study included visual kerogen (Table contributions are dominant, but also indicate sub- 2), elemental analysis (Table 4), and vitrinite reflectance (Table 3). stantial bacterial contributions. (3) Jurassic coaly strata have significant potential as petroleum source rocks. Pyrolysis–gas chro- Hydrocarbon Extraction, Fractionation, and Analysis matography of selected samples in this study (Figure 9) yields prominent alkene-alkane doublets, Detailed organic geochemical analyses were performed on selected samples to address issues of organic matter source, matu- typical of petroleum source rocks (Dembicki et al., ration, hydrocarbon generation potential, and comparison with 1983). Positive correlations with oils from the known petroleum. Selected samples were trimmed (approximate- southern Junggar, northern Tarim, and Turpan ly 10 g), rinsed in CH2Cl2 to remove organic contaminants, and basins have been established for Jurassic coals. pulverized to approximately100 µm. Approximately 2 to 9 g of Biomarker parameters, indicating a positive correla- each sample were solvent-extracted via Soxhlet (3:1; CH2Cl2:CH3OH). Extraction typically proceeded for over 72 hr (3 tion between rock extracts and petroleum, include days) before negligible coloration of solvent was observed. The similar sterane and hopane distributions, low abun- resulting extract/solvent mixture was roto-evaporated and dried in dance to absence of tricyclic terpanes with similar a nitrogen stream at or less than 40°C. distributions where present, lack of gammacerane Because iron sulfide (FeS2) is commonly observed on fresh frac- ture surfaces, especially in the coals, two methods were used to in all but one oil, lack of carotanes, and high pris- remove sulfur. For all but eight samples (Table 5), extracted bitumen tane/phytane ratios typical of terrestrially derived was percolated through Cu powder, reduced by cleaning with HCl, organic matter and petroleum. Anomalies in the oil- and rinsed with deionized H2O, acetone, CH3OH, and CH2Cl2. In source correlation include marginally higher C27 addition, sample extracts with excessive elemental sulfur were dried and C steranes in the Junggar and Tarim oils, pres- and exposed to direct contact with CH2Cl2-rinsed Hg. Desulfurized 28 extracts were fractionated into aliphatic, aromatic, and NSO-com- ence of gammacerane in the Tarim oil, and lack of pound fractions using thin-layer chromatography (glass plates coated diterpenoids in all four oils. Each of these anoma- with 0.25 mm silica gel, eluted for 24 hr with ethyl acetate and acti- lies can be attributed to derivation of petroleum vated at 300°C for 1 hr prior to use) and hexane eluant. from more distal, Jurassic lacustrine facies rather Eight samples (Table 5) were extracted and fractionated as fol- lows. Powdered samples were Soxhlet extracted (100% CH2Cl2). than the proximal coal-bearing facies described Extracts were dissolved in methylene chloride and concentrated here. Recent advances in assessing coal as a to 1 mL volume; 25 mL pentane was added to precipitate petroleum source rock suggest that certain coals asphaltenes (precipitation accelerated by refrigeration for 4 hr at may be significant sources of oil, consistent with 1–2°C). Asphaltenes were removed by centrifuging. Deasphalted the oil source potential interpreted for Jurassic coal extracts were fractionated using a gravity-fed, silica-gel liquid chromatography column (100–200 µm silica gel supports activated at measures from northwestern Chinese basins. 400°C prior to use). Saturates, aromatics, and NSO-compounds were eluted with 100% CH2Cl2, 50:50 CH2Cl2:CH3OH, and 100% CH3OH, respectively. Fractions were removed under a 40°C water APPENDIX 1 bath in a nitrogen stream. Fractionation of all four petroleums analyzed in this study was performed using this method. Gas chromatography–mass spectrometry (GC–MS) of aliphatic Bulk Geochemical Analyses compounds was performed using a Varian Model 3400® gas chro- matograph (on-column and split-splitless injectors used; 30 m × A total of 159 organic-rich samples were collected for this study. 0.25 mm i.d., fused silica capillary column with a 0.25 µm DB-5 A Delsi Instruments® Rock-Eval II was used to pyrolyze 144 samples coating). The GC was directly interfaced with a Finnigan-Mat TSQ- to provide bulk geochemical information prior to more detailed 70® mass spectrometer. Full data acquisition GC-MS and multiple organic geochemical analysis (Table 3) [see Hendrix (1992) for addi- ion detection GC-MS (m/z 156, 217, 231, 253, 400, 191) were per- tional data]. Total organic carbon (TOC) was determined using a formed for 39 total samples (19 samples plus 16 from Junggar and Leco® instrument after crushing the samples and treating with HCl 4 from Turpan, including petroleum). to remove carbonates. 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Figure 13—m/z 191 fragmentograms and hopane distributions for Jurassic rock extracts and petroleums and tricyclic terpane distributions for two samples. The similar distributions of hopanes and tricyclic terpanes in rock extracts and petroleums suggest that the petroleums are derived from Jurassic strata. m/z fragmentogram for extract sample 89-M-3H is included to show the presence of 28,30-bisnorhopane, the first known occurrence of this biomarker in nonmarine strata. 956 Jurassic Coal Measures, Northwest China

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ABOUT THE AUTHORS

Marc S. Hendrix Simon C. Brassell Marc S. Hendrix received his Simon C. Brassell graduated B.A. degree in geology from from the University of Bristol, Wittenberg University (Springfield, United Kingdom, with a B.Sc. Ohio) in 1985 and his M.S. degree degree in chemistry and geology in geology at the University of (1976) and a Ph.D. in organic geo- Wisconsin–Madison in 1987. He chemistry (1980). He was the began his studies of Mesozoic recipient of a Royal Society 1983 basins in western China as a Ph.D. University Research Fellowship at candidate at Stanford University. Bristol, then moved to the U.S. as He received his degree in 1992 and an associate professor at Stanford has since conducted sedimentary University (1987–1991). Since basin analysis and petroleum potential assessment stud- 1991, he has been professor of geological sciences at ies of Mongolian sedimentary basins. In 1994, he joined Indiana University. His research interests lie in biogeo- the faculty at the University of Montana as an assistant chemistry, focused on the use of the molecular and iso- professor. topic characteristics of organic matter to assess and interpret stratigraphic, environmental, and climatic vari- ations in the sedimentary record. Hendrix et al. 959

Alan Carroll S. A. Graham Alan Carroll is a research special- Stephan A. Graham holds three ist in the integrated basin analysis degrees in geology (B.A., 1972, division for Exxon Production Indiana; M.S., 1974, and Ph.D., Research Company. Between 1983 1976, Stanford), and spent 1976– and 1986, he worked as an explo- 1980 with Exxon Production ration and production geologist for Research and Chevron. Since 1980, Sohio. He received geology degrees Graham has been a professor at from Carleton College (B.A., 1980), Stanford University, specializing in the University of Michigan (M.S., basin studies, particularly in the 1983), and Stanford University United States, Mongolia, and (Ph.D., 1991). His research inter- China. He received AAPG’s Sproule ests include sedimentary basin analysis, lacustrine sedi- Award (1985) and was an associate editor of the AAPG mentology and sequence stratigraphy, organic geochem- Bulletin from 1983 to 1989. istry, and the tectonic evolution or northwestern China.