Lake-type controls on AUTHORS Alan R. Carroll ϳ Department of petroleum source rock potential Geological and Geophysical Sciences, University of Wisconsin, 1215 W. Dayton St., in nonmarine basins Madison, Wisconsin, 53706; [email protected] Alan R. Carroll and Kevin M. Bohacs Alan R. Carroll has been an assistant professor at the University of Wisconsin, Madison, since 1996, specializing in sedimentary basins in western China and the western United States. ABSTRACT He received geology degrees from Carleton College (B.A. degree, 1980), the University of Based on numerous empirical observations of lacustrine basin strata, Michigan, Ann Arbor (M.Sc. degree, 1983), we propose a three-fold classification of lacustrine facies associa- and Stanford University (Ph.D., 1991). He tions that accounts for the most important features of lacustrine worked as an exploration geologist for Sohio petroleum source rocks and provides a predictive framework for (1983–1986) and a research geologist for exploration in nonmarine basins where lacustrine facies are incom- Exxon Production Research Company (1991– pletely delineated. 1995). He is an associate editor of the AAPG (1) The fluvial-lacustrine facies association is characterized by Bulletin. freshwater lacustrine mudstones interbedded with fluvial-deltaic Kevin M. Bohacs ϳ ExxonMobil Upstream deposits, commonly including coal. Shoreline progradation domi- Research Co., 2189 Buffalo Speedway, nates basin fill, resulting in the stacking of indistinctly expressed Houston, Texas, 77252; cycles up to 10 m thick. In map view, the deposits may be regionally [email protected] widespread but laterally discontinuous and contain strong facies Kevin M. Bohacs is a sedimentologist and contrasts. Transported terrestrial organic matter contributes to stratigrapher with the Petroleum Geochemistry mixed type I–III kerogens that generate waxy oil (type I kerogen is section of ExxonMobil Upstream Research hydrogen rich and oil prone; type III kerogen is hydrogen poor and Company (URC) in Houston, Texas. He mainly gas prone). The Luman Tongue of the Green River For- received his B.Sc. (honors) degree in geology mation (Wyoming) and the Honyanchi Formation (Junggar basin, from the University of Connecticut in 1976 China) provide examples of this facies association, which is also and his Sc.D. degree in experimental present in the Songliao basin of northeastern China, the Central sedimentology from M.I.T. in 1981. At URC, he Sumatra basin, and the Cretaceous Doba/Doseo basins in west- leads the application of sequence stratigraphy central Africa. and sedimentology to organic-rich rocks from (2) The fluctuating profundal facies association represents a deep sea to swamps and lakes in basins combination of progradational and aggradational basin fill and in- around the world. As a research associate, his cludes some of the world’s richest source rocks. Deposits are re- primary focus is to keep the geo- in geochemistry, integrating field work, gionally extensive in map view, having relatively homogenous subsurface investigation, and laboratory source facies containing oil-prone, type I kerogen. Examples include analyses. He has written numerous articles on the Laney Member of the Green River Formation (Wyoming), the the stratigraphy and sedimentology of Lucaogou Formation (Junggar basin, China), the Bucomazi For- mudrocks, hydrocarbon source rocks, and mation (offshore west Africa), and the Lagoa Feia Formation (Cam- lake systems. He was co-recipient of the AAPG pos basin, Brazil). Jules Braunstein Memorial Award for best (3) The evaporative facies association represents dominantly poster session paper in 1995 for work on coal aggradational fill related to desiccation cycles in saline to hyper- sequence stratigraphy and the AAPG saline lakes and may include evaporite and eolianite deposits. Sub- International Paper Award in 1998 and was littoral organic-rich mudstone facies are relatively thin but may be an AAPG Distinguished Lecturer for 1999– 2000.

Copyright ᭧2001. The American Association of Petroleum Geologists. All rights reserved. Manuscript received December 15, 1998; revised manuscript received June 28, 2000; final acceptance August 31, 2000.

AAPG Bulletin, v. 85, no. 6 (June 2001), pp. 1033–1053 1033 quite rich and widespread. The highest organic enrichment co- ACKNOWLEDGEMENTS incides with the deepest lake stages. Low input of land plant organic matter results in minimal lateral contrasts in organic content. In This article benefited from discussions with some cases a distinctive type I-S (sulfur-rich) kerogen may generate many individuals, including S. C. Brassell, Y. Y. oil at thermal maturities as low as 0.45% vitrinite reflectance equiv- Chen, R. Cunningham, D. J. Curry, G. Genik, alent. Examples include the Wilkins Peak Member of the Green K. S. Glaser, G. J. Grabowski Jr., G. B. Hiesh- ima, G. H. Isaksen, B. J. Katz, M. R. Mello, K. River Formation (Wyoming), the Jingjingzigou Formation (Junggar Miskell-Gerhardt, J. E. Neal, P. Olsen, D. J. basin, China), the Jianghan and Qaidam basins (China), and the Reynolds, C. Scholz, and K. O. Stanley. G. J. Blanca Lila Formation (Argentina). Grabowski and H. B. Lo collected some of the data used in this article. M. Wartes provided useful comments on an early draft of the INTRODUCTION manuscript. Field studies in the Junggar basin in 1987, 1988, and 1992 were funded by the The deposits of nonmarine sedimentary basins account for a grow- Stanford-China Industrial Affiliates, a group of ing segment of current petroleum exploration and exploitation op- companies that included AGIP, Amoco, An- portunities, especially in areas of rapid market growth such as schutz, BHP Petroleum, Chevron, Conoco, Elf- China, southeast Asia, and western Africa. The specific techniques Aquitaine, Enterprise Oil, Exxon, Mobil, Occi- needed for locating, assessing, and developing hydrocarbon reserves dental, Pecten, Phillips, Sun, Texaco, Transworld Energy International, and Unocal. within lacustrine basins remain relatively undeveloped compared Conoco provided additional support for this to those for marine systems, and they constitute a significant source article. The Donors of The Petroleum Research of financial risk (cf. Sladen, 1994). This uncertainty stems not from Fund, administered by the American Chemical a lack of data on lacustrine systems, but instead from their great Society, also provided support for this re- sedimentologic complexity, as evident from numerous studies of search. We thank Exxon Production Research modern and ancient lakes. Furthermore, most lacustrine source rock Co. for permission to publish this article. J. A. models have focused on inferred climatic controls (e.g., Eugster and Curiale, B. J. Katz, B. Wiggins, and an anony- Kelts, 1983; Talbot, 1988), although paleoclimate modeling has mous reviewer all provided very helpful had only limited success in predicting the actual occurrence of reviews. organic-rich lacustrine facies (e.g., Barron, 1990). Fortunately, some of the complexity evident in modern lakes resolves itself in ancient lacustrine deposits, resulting in the ex- pression of three commonly recurring motifs in the lithology and stratigraphy of lacustrine deposits. For example, Bradley (1925) was able to generalize a trend within the heterogeneous Eocene Green River Formation (Utah, Colorado, and Wyoming) from “relatively shallow fresh-water lakes,” to “depositional basins that alternately flooded and evaporated either partially or completely,” and finally to a period when “the lakes became playa-like” and evaporites pre- cipitated. A similar division, based on geography rather than on geologic time, was proposed over 60 years later by Olsen (1990) for the widespread lacustrine deposits of the Triassic–Jurassic New- ark Supergroup (eastern United States). Olsen idealized lacustrine facies associations as either Richmond-type, Newark-type, or Fundy-type and proposed that these associations reflect differences in climatically controlled basin hydrology. Mello et al. (1988) de- veloped similar concepts involving organic facies, subdividing Bra- zilian source rocks into freshwater and brackish-saline lacustrine facies based on relative concentrations of biological marker com- pounds that are sensitive to lake salinity and organic matter input. Others have characterized biomarker distributions indicative of hypersaline lacustrine source rocks (e.g., Jiang and Fowler, 1986). Carroll and Bohacs (1995, 1999) proposed a classification of ancient

1034 Lacustrine Petroleum Source Rocks lake basins into three end-member types that corre- LACUSTRINE SEDIMENTARY FACIES spond to commonly recurring lacustrine facies associ- ASSOCIATIONS ations. The terms “overfilled,” “balanced-fill,” and “un- derfilled” lake basins refer to the balance between Lacustrine deposits may be characterized according to tectonically controlled potential accommodation and (1) their sedimentary facies, fauna, and flora, (2) their climatically controlled water plus sediment supply. A internal stratigraphic relations (such as parasequence unique advantage of this model is that it permits broad stacking), and (3) the character of associated deposits. characteristics of hydrocarbon source rock richness and In particular, evidence for open vs. closed basin hy- gas vs. oil generation to be predicted from limited geo- drology and the presence and nature of depositional logic observations of nonsource sedimentary facies cyclicity provide the fundamental bases for categoriz- (typically encountered on structure and along basin ing ancient lake systems according to types. Note that margins). This information can also be incorporated these types represent end-member ideals and as such into basin thermal history models to estimate the tim- need not be 100% representative of any one occur- ing of generation. rence. Furthermore, the interpretation of depositional Several previous studies have presented overviews cycles necessarily implies simultaneous observation of of lacustrine petroleum source rocks (e.g., Powell, several different subfacies, resulting in time averaging 1986; Katz, 1988, 1990; Kelts, 1988; Mello et al., of diachronous but evolutionary depositional environ- 1988; Mello and Maxwell, 1990; Williams et al., ments. The concept of lake type as applied to ancient 1995). This article is the first to classify petroleum deposits therefore may not be directly applicable to source rocks in accordance with the lake-type classifi- modern lakes, for which only a synoptic or snapshot cation of Carroll and Bohacs (1995, 1999), and one of view is available. very few to systematically integrate detailed observa- The Green River Formation in Wyoming consists tions of lacustrine sedimentary facies with geochemical of approximately 2500 m of Eocene lacustrine and data on organic facies. We emphasize detailed, non- associated alluvial strata deposited in several foreland biased sampling of carefully described stratigraphic in- basins adjacent to Laramide-style uplifts (Sullivan, tervals as the basis for interpreting the geologic controls 1985; Roehler, 1992) (Figure 1). Late Permian basin on organic enrichment. In contrast to previous work, subsidence resulted in the preservation of more than the model we present suggests specific, practical tech- 5000 m of nonmarine facies in the southern Junggar niques for predicting source rock richness, distribution, basin, including more than 1000 m of organic-rich la- oil vs. gas potential, and generation timing based on custrine mudstone (Liao et al., 1987; Carroll et al., sparse geochemical or geologic data. Conversely, our 1990, 1992, 1995; Wartes et al., 1998) (Figure 2). model permits broad aspects of the tectonic and cli- Three lacustrine facies associations may be identified matic history of nonmarine basins to be predicted in within both deposits, as detailed subsequently: the part from the character of petroleum and of source fluvial-lacustrine facies association, the fluctuating rock extracts. Such data may be very useful in assessing profundal facies association, and the evaporative facies other exploration play elements, such as reservoir dis- association. tribution and quality, migration pathways, fault tim- ing, and basin thermal history. Fluvial-Lacustrine Facies Association Two important intervals of lacustrine strata are used for illustrative purposes in this article: the The Luman Tongue consists of freshwater to mildly carbonate-rich Eocene Green River Formation of the alkaline facies deposited in the Washakie basin as the Washakie basin (Wyoming) and the predominantly si- earliest lacustrine phase of the Green River Forma- licic Upper Permian lacustrine formations of the Jung- tion (Roehler, 1992; Horsfield et al., 1994) (Figure gar basin (northwest China). Despite gross differences 1). As such, it resembles the Black Shale facies of the in geologic age, lithology, and paleogeography, the Green River Formation in the Uinta basin, a source same three idealized facies associations are recognized of petroleum in Altamont-Bluebell and other fields in both cases and in many other lake basins. The pe- (Fouch, 1975; Ruble and Philp, 1998). The Luman troleum generative characteristics of mudrocks within Tongue contains generally poorly expressed, shallow- each of these facies associations differ significantly ing-upward packages (parasequences) that were de- from each other and must be considered for successful posited by processes of shoreline progradation (Figure exploration of nonmarine basins. 3). Where evident, the base of these parasequences

Carroll and Bohacs 1035 SIERRA SIERRA SIERRA 107˚ MADRE MADRE MADRE CO CO CO WY WY WY 108˚ 0 BASIN BASIN BASIN 300 SAND WASH SAND WASH SAND WASH Figure 3B BASIN BASIN BASIN BASIN BASIN BASIN 100 Figure 3A WASHAKIE WASHAKIE WASHAKIE 300 GREAT DIVIDE GREAT DIVIDE GREAT DIVIDE

800 200

700 400 100

CO CO

600 CO 0

UT UT UT 109˚ 500 ROCK ROCK ROCK UPLIFT UPLIFT UPLIFT SPRINGS SPRINGS SPRINGS

100

S S S

400

IN IN IN

200

A A A 0 Figure 3C

300

T T T

300

N N N 300

1100

U U U 200

1000

O O O 400 900 200 1200

800

M M M 500

BASIN BASIN

A A A 700

110˚

T T T 100 600 (1992). 100

GREEN RIVER GREEN RIVER

IN IN IN

U U U 100

0

200

T T T

S S S

U U U

R R R

H H H

T T T

G G G

IN IN IN

M M M

O O O Y Y Y Roehler W W W

WY WY WY

Laney Member

Luman Tongue ID ID ID UT UT UT Wilkins Peak Member 111˚ from 41˚ 41˚ 41˚ 42˚ 42˚ 42˚ Ј modified 100 50 Km

Miles Wyoming, Chemistry:

n Coal i lake Water lake 0 0

Evap. Fresh Fresh Alkal. Alkal.

interval = 100 interval feet) (8200

East Isopach contour Isopach 2500 m 2500 Formation River N reen G Washakie Basin the of

Lwr. LaClede maps

Bed (Figure 3B)

(Figure 3A)

Luman Tongue Saline lacustrine Mudflat/saline lacustrine Evaporite/saline lacustrine isopach 250 km and (156 miles) Rock Springs Uplift facies, USA

Laney Member

COAL sedimentary (Figure 3C)

Map Area Wilkins Peak Member

Location, Flood plain Freshwater lacustrine Sandstone

Lower

Green River Basin Middle 1. Eocene West Figure

1036 Lacustrine Petroleum Source Rocks is typically a sharp surface overlain by organic-rich Fluctuating Profundal Facies Association calcareous mudstone and shale or organic-poor bio- turbated mudstone and siltstone (Horsfield et al., The lower LaClede Bed of the Laney Member of the 1994; Bohacs, 1998). These facies grade upward into Green River Formation consists of alkaline lake depos- littoral coquinas, small sandy deltas, and occasional its that are widely distributed over the greater Green thin coals. Flood-plain and fluvial facies also are com- River basin (Roehler, 1992; Horsfield et al., 1994) (Fig- mon. Cyclicity caused by lake-level fluctuation is ures 1, 3). It resembles similar facies in the Parachute subtle or absent, consistent with relatively open lake- Creek Member of the Green River Formation in Utah basin hydrology. The laterally equivalent and super- and Colorado, which, although immature with respect jacent Niland Tongue of the Wasatch Formation con- to petroleum generation, constitutes the well-known tains predominantly lake-plain to alluvial deposits Green River oil shale deposits. In contrast to the Lu- (including coals) and is closely related to the Luman man Tongue, the lower LaClede Bed contains well- Tongue (Figure 1). defined parasequences that record major lake desicca- The Hongyanchi Formation in the southern Jung- tion and flooding (Horsfield et al., 1994). The gar basin consists of interbedded profundal mudstone, parasequences typically begin with algal and oolitic fa- siltstone, limestone, and fluvial sandstone and con- cies, followed by deposition of finely laminated glomerate (Carroll et al., 1992, 1995) (Figures 2, 4). It organic-rich calcareous shale. Subsequent evaporative too lacks any strongly expressed depositional cyclicity, contraction of the lake resulted in a gradual vertical although indistinct deepening and shoaling deposi- increase in dolomicrite, magadii-type chert, and ef- tional trends on the scale of 10 m or more are evident. florescent crusts of saline minerals, typically culminat- Mudstone units are commonly slightly calcareous and ing in mud-crack horizons. During uncommonly hu- laminated in places but are commonly homogenous. mid phases, limited progradation of fluvial clastic facies Amalgamated fluvial sandstone and conglomerate beds occurred at the lake margins, resulting in mixed may reach thicknesses up to tens of meters, recording aggradational/progradational stratal geometries. channeled flow within well-developed stream systems. The Lucaogou Formation (Junggar basin, China) Desiccation cracks and other evidence of prolonged consists primarily of profundal laminated mudstone subaerial exposure are absent. Limestone beds 20 to and occasional siltstone interbeds and includes the 50 cm thick occur in places and generally comprise most organic-rich facies in the southern Junggar basin argillaceous micrite without visible fauna; they may be (Carroll et al., 1992; Carroll, 1998) (Figures 2, 4). The algal in origin. Coals are not present in the Hongyanchi Lucaogou Formation is predominantly siliciclastic, Formation, but overlying fluvial units do contain frag- with the exception of occasional nodular dolomite. ments of petrified wood that have coaly residues (Car- Distinct 1–4 m scale cycles occur near its base and are roll et al., 1992). punctuated by mud-cracked desiccation surfaces. The aforementioned features are common to many These cycles grade upward into the most organic-rich other hydrologically open lake basins, such as the Rich- interval of the Lucaogou Formation, where there are mond and several other basins filled by elements of the no obvious signs of subaerial exposure. Cyclicity con- Newark Supergroup. Olsen (1990) characterized tinues to be expressed, however, as variations in the Richmond-type basins as containing significant coals thickness and preservation of lamina. Flooding surfaces and bioturbated shallow-water and fluvial facies and have not been identified within this interval; therefore, thick intervals of laminated siltstone. Evidence for lamina thicknesses appear to record varying input of subaerial exposure is absent, consistent with high clay and silt in an area distant from any shoreline (Car- precipitation/evaporation ratios. Other examples of roll, 1998). These variations in detrital grainsize may this fluvial-lacustrine facies association include the Pa- in turn be linked to fluctuating lake level. Occasional leocene of the Fort Union Formation in Wyoming (Liro centimeter-scale graded beds record fine-grained tur- and Pardus, 1990), some Cretaceous units in the Son- bidite deposition, and minor soft-sediment slumping is gliao basin of northeastern China (Yang et al., 1985; common. Xue and Galloway, 1993; D. Li et al., 1995), some Fluctuating profundal facies were also described by Paleocene intervals in the Central Sumatra basin (Kel- Van Houten (1962) in the Newark and related basins. ley et al., 1995), and the Cretaceous strata of the Olsen (1990) attributed these cycles to lake level Doba/Doseo basins in west-central Africa (Genik, changes driven by Milankovitch-scale climate changes 1993). in basins where long-term water inflows were closely

Carroll and Bohacs 1037 1400 Hongyanchi Fm. measured section (Figure 4A)

1300 84 86 88 90

10 00 ? 1200 LAKE MARGINAL FACIES 46 JUNGGAR 500 46 BASIN Karamay 1500 1100 CHINA ?

HONGYANCHI FORMATION ? 1000 ? 1000 FLUVIAL FACIES 5 KELAMEILI 5 500 SHAN 45 JUNGGAR 900 0 ? 100 BASIN 500 10 1000

800 1500 ?

44 44 700 2000 ? T BOGDA ? NORTH U SHAN TIAN 600 SHAN DEEP LAKE FACIES N 50 KM 86 88

500 Upper Permian Sandst. and Congl. (approximate) Permian Lake Deposits (approximate)

400 Pre-Permian Outcrops LUCAOGOU FORMATION T U Urumqi measured section

300 TIANCHI SECTION T Tianchi measured section 800 Oil Fields Upper Permian Lucaogou Fm. Thickness (m) meas. section 1000 200 700 (Figure 4B) Thrust belts 5 Mesozoic-Cenozoic Thickness (km)

LAKE MARGINAL FACIES 100 600

1 5 20 TOC (%) DEEP LAKE FACIES 0 m DEEP 500 U URUMQI SECTION 400 LUCAOGOU FORMATION

LAMINATED ORGANIC-RICH 300 MUDSTONE

MUDSTONE

SILTSTONE 200 TO SANDST.

LIMESTONE LAKE MARGINAL FACIES 100 COVERED Jingjingzigou Fm. INTERVAL measured section

TOC < 0.5% (Figure 4C)

JINGJINGZIGOU FM. 1 5 20 0 m TOC (%)

1038 Lacustrine Petroleum Source Rocks balanced by outflows. Van Houten cycles possess ex- cause of interactions between sheetfloods and rising treme lateral continuity, except where they intersect lake levels (Smoot, 1983). basin-marginal alluvial fans. The ratio of organic-rich The Jingjingzigou Formation (Junggar basin, to organic-poor units in the Newark basin, however, is China) (Figures 2, 4) consists of dolomitic gray and relatively low compared to the lower LaClede Bed or gray-green mudstone, medium gray to dark gray mud- Lucaogou Formation. The preservation of fine laminae stone, wave-rippled dolomitic siltstone, and fine- implies the lack of burrowing in fauna or resuspension grained sandstone (Carroll et al., 1992; Carroll, 1998). of bottom sediments by currents. Laminated intervals, Although evaporite minerals are absent from basin- therefore, are interpreted to have been deposited in marginal outcrop exposures, possible evaporite water depths below storm wave base, and anoxic con- pseudomorphs occur. Displacive dolomite nodules ditions prevail below the sediment-water interface ranging in size from 1 to 10 cm are common, particu- (Olsen, 1990). Similar profundal facies also occur in larly within the upper parts of siltstone beds. Shoaling- the Bucomazi Formation offshore west Africa (Bur- upward lacustrine cycles 10 to 2 m thick occur wood et al., 1995) and in the Lagoa Feia Formation throughout the measured section. Tabular siltstone offshore Brazil (Campos basin) (Trinidade et al., and sandstone beds ranging from 20 to 50 cm in thick- 1995). ness appear at the base of many of the cycles. Minor scour at the base of siltstone and sandstone beds is Evaporative Facies Association common, as is soft-sediment loading into underlying mudstone. The sandstone beds are interpreted to rep- The Wilkins Peak Member of the Green River For- resent relatively unconfined, episodic flows across a mation (Figures 1, 3) encompasses a wide variety of lake plain during onset of flooding and lacustrine trans- facies, ranging from alluvial fan and sheetflood sand- gression. Mudstone facies typically possess relatively stone to laminated oil shale (e.g., Bradley and Eugs- thick, discontinuous, wavy laminae (Ͼ1 mm) and com- ter, 1969; Smoot, 1983). This member is best monly grade upward into poorly laminated or homog- known, however, for its bedded trona and halite, enous intervals. Thin intervals (Ͻ10 cm) of submilli- which are interpreted to have been deposited in meter scale laminae occur rarely. Abundant mud evaporative playas (Eugster and Surdam, 1973; Eugs- cracks, commonly sand or silt-filled, occur near cycle ter and Hardie, 1975). Basin-center deposits record tops and attest to frequent subaerial exposure and dominantly aggradational stacking of organic-rich desiccation. mudstone facies during lake flooding and carbonate Although the composition of Wilkins Peak evap- and evaporite facies during lake desiccation. The orites is unusual, evaporative lake facies occur in many basin-center organic-rich mudstone facies grade ver- other lacustrine basins. For example, desiccation cycles tically and laterally into littoral and supralittoral de- in parts of the Fundy and similar basins of the Newark posits of dolomitic and siliciclastic mudstone and Supergroup include shallow lake and playa facies and grainstone facies that have desiccation cracks and are associated with gypsum nodules, salt-collapse evaporitic minerals or their replacements (Bohacs, structures, and eolian dunes (Hubert and Mertz, 1984; 1998). The lake-margin lithofacies intertongue with Smoot and Olsen, 1988). Other examples include the carbonate and siliciclastic sandstone and mudstone Blanca Lila Formation (Pleistocene of Argentina) facies probably deposited in alluvial-fan and fluvial (Vandervoort, 1997) and deposits within several Ter- systems. The basin-center evaporite beds lap margin- tiary basins in China (e.g., Fu et al., 1986). ward onto subaerially exposed lake and lake-margin strata. Laterally equivalent eolian reworked grain- stone and mudstone facies are uncommon. Figure 3C LACUSTRINE ORGANIC FACIES illustrates the distribution of lithologies in a repre- sentative vertical section. Stratigraphic relationships Each of the sedimentary facies associations described among littoral and lake-plain facies are complex be- previously correspond to distinctive organic facies as

Figure 2. Location of Junggar basin Permian lacustrine facies (modified from Carroll et al., 1992, and Carroll, 1998). Master sections from Tianchi and Urumqi are aligned according to an approximate lithostratigraphic correlation between these localities. Permian isopach contours represent the Jingjingzigou, Lucaogou, and Hongyanchi Formations but do not include the entire Upper Permian interval.

Carroll and Bohacs 1039 A. Luman Tongue B. Lower LaClede Bed, Laney Member C. Wilkins Peak Member

xxxxx

xxxxx

xxxxx

(36)

xxxxx

0 30 0 1000 Ss Sh Ms

MSs SMs %TOC HI

ϳ15 m 50 ft

xxxxx 10 m xxxxx

xxxxx

xxxxx xxxxx xxxxx

xxxxx

0 0 Ss Sh

Ms 0 30 0 1000 MSs SMs %TOC HI LEGEND

Scour Intraclast Mudstone Trough cross-beds conglomerate Laminated Mudstone Current ripples Evaporite (42) Sandstone Wave ripples Stylolites Limestone (48) Combined-flow ripples Concretions Evaporite Climbing ripples Oolite

Planar lamination Stromatolite Ss Sandstone Flaser or lenticular bedding Plant fossils MSs Muddy sandstone

Convolute bedding Ostracods SMs Sandy mudstone

Fining-upward bed Molluscs Ms Mudstone Mudcracks Fish Sh Shale Ss Sh 0 30 0 1000 Flooding surface Ms Coal xxxxx Tuff MSs SMs %TOC HI Figure 3. Green River Formation measured sections from (A) outcrop of Luman Tongue at Hiawatha locality (21-T12N-R100W), (B) outcrop of lower LaClede Bed of the Laney Member at Trail Dugway locality (18-T14N-R99W), and (C) core of Wilkins Peak Member Rock-Eval hydrogen ס total organic carbon (%); HI ס from the UPR 41–43 well (23-T17N-R109W; see Figure 1 for locations). TOC index (mg/g). Carroll, 1000 mud rom f intraclasts mud cracks HI (mg/g) (desiccation) 0 5 (modified 4 ace 3 dolomitic limestone concretions 2 ianchi % TOC T 1 t a 0 Legend Flooding surf

FS = siltstone mudstone nonlaminated Formation . Jingjingzigou Formation C 9 7 5 2 4 8 6 3 1 0 M 11 12 10 shallow

FS FS FS FS FS FS FS FS FS FS FS FS Water Depth deep laminated Jingjingzigou submillimeter mudstone (>1mm) (C) laminated mudstone and 1000 ianchi, HI (mg/g) T t a 0 0 2 Formation 0 1 % TOC 0 Lucaogou (B) . Lucaogou Formation B 9 7 5 2 8 4 6 3 1 0 M 11 12 10 13 rumqi, coarse U t a Lamination fine Formation 1000 HI (mg/g) Hongyanchi 0 (A) 5 4 from 3 2 % TOC 1 locations). 0 sections or f 2 Measured Figure 0 M 10 20 30 4. A. Hongyanchi Formation shallow see Water Depth deep 1998; Figure

Carroll and Bohacs 1041 determined from such features as total organic carbon tongues and in the Hongyanchi Formation. The ma- (% TOC), Rock-Eval hydrogen indices (HIs), visualker- jority of TOC values in Luman Tongue and Niland ogen descriptions, pyrolysis products, and biomarker Tongue mudstone facies lie between 2 and 8% (Figures geochemistry. Biomarkers, or biological marker com- 3A, 5A), but some coaly samples exceed 50% TOC pounds, are complex molecular fossils derived from (Figure 6). Rock-Eval hydrogen indices (HIs) for indi- once-living organisms (Peters and Moldowan, 1993). vidual samples from a continuous section of the Luman They have the capacity to provide detailed qualitative and Niland tongues are highly variable (Table 1). Their information on organic matter input, water column ox- average HI is 310, in sharp contrast to type I kerogen ygenation, and thermal maturity. A unique advantage HI values that range between 600 and 900 and can of biomarkers over other geochemical measurements is exceed 1000 (e.g., Graham et al., 1990). Closer ex- that the same compounds are found in both rock ex- amination suggests the presence of two distinct organic tracts and expelled oils, making it possible to interpret matter populations within these units; one population source rock depositional environments in cases where averages 4.87% TOC and HI Ͼ 500, and the other the rocks themselves are inaccessible. Biomarkers are averages 9.34% TOC and HI Ͻ 500 (Figure 6). Visual also commonly used to assess the relative salinity of kerogen descriptions indicate that organic macerals source rock depositional environments, based on the likewise contain two populations; they are dominated partial record they provide of the types of organisms by alginite but also contain varying proportions of vi- that were present. This information can be correlated trinite (Horsfield et al., 1994). Luman Tongue and Ni- with physical characteristics that suggest a particular sa- land Tongue source rocks, therefore, record mixed linity range, such as abundant mud cracks or the pres- aquatic and terrestrial organic matter input. Population ence of evaporites. It should be noted, however, that in 1 samples are tightly clustered around a linear regres- this context, terms such as “fresh”, “brackish”, “saline”, sion line representing HI 805 (Figure 6), attesting to or “hypersaline” do not normally imply specific solute the constancy of organic matter type within these sam- concentrations, but instead represent interpreted rela- ples. Variation in their TOC content likely resulted in tive salinity levels. The following discussion summa- part from higher dilution of organic matter by silt and rizes the application of several biomarker parameters to clay. Population 2 samples are much more widely scat- the interpretation of lacustrine depositional environ- tered around a line representing HI 324, suggesting a ments and organic matter sources; see Peters and Mol- more heterogenous mixture of aquatic and terrestrial dowan (1993) for more detailed documentation. organic matter. Biomarker concentrations in extracts Table 1 summarizes bulk organic matter and bio- from the Luman Tongue and Niland Tongue are indic- marker parameters for Green River Formation and ative of relatively oxic freshwater environments that Junggar basin samples, as well as data reported for other have mixed input of aquatic and terrestrial organic lacustrine units. These occurrences are subdivided into matter (Table 1). Analysis of kerogen structure via algal-terrestrial, algal, and algal-hypersaline organic fa- pyrolysis–gas chromatography techniques indicates cies. Note that for each facies, considerable variation that at higher thermal maturities, Luman Tongue may occur in a given biomarker parameter, both within mudstone would generate waxy oil (Horsfield et al., one unit and among different units. This variation re- 1994). sults from differing lake ecologies, differing levels of The TOC values in the Hongyanchi Formation thermal maturity, heterogeneous depositional environ- are lower on average than the Luman and Niland ments, and possibly different analytical methods used tongues (Figures 4A, 5B), although values up to 7.7% by different workers. Because only limited stratigraphic have been reported (Carroll et al., 1992). The TOC data are available in most of the studies cited, some re- and HI values are also lower in part because of sig- ported occurrences probably also include samples from nificantly greater thermal maturity of the Hongyanchi more than one organic facies. Despite these uncertain- Formation (Figure 5A, B). Overall organic matter ties, however, each organic facies exhibits a distinct pat- composition appears similar to the Luman and Ni- tern when all the parameters are considered together. land tongues, although too few samples have been collected for a full assessment. HI ranges from 58 to Algal-Terrestrial Organic Facies 444. The highest organic enrichments correspond to more profundal intervals, whereas the lowest enrich- The fluvial-lacustrine facies association corresponds to ments correspond to massive limestone and mud- algal-terrestrial organic facies in the Luman and Niland stone (Figure 4A). Vitrinite and inertinite combine

1042 Lacustrine Petroleum Source Rocks 200 40 15 A. Luman and Niland tongues B. Hongyanchi Formation 35 n = 27 n = 171 12 mean %TOC = 2.72 mean %TOC = 7.09 30 std. dev. = 1.85 std. dev. = 8.63 Ro = 0.86-1.09% Ro = 0.35-0.45% 25 9

100 20 y = 3.87x - 4.79

(mg/g) y = 3.10x - 9.23 2 r 2 = 0.57 requency S 2 6 r = 0.78 15 F >24% 10 3

5

0 0 0

200 15 15 C. Laney Member D. Lucaogou Formation

n = 91 n = 69 12 mean %TOC = 7.84 mean %TOC = 4.41 std. dev. = 3.71 std. dev. = 4.64 R = 0.40% 10 o Ro = 0.77-0.88% y = 8.30x - 7.58 9 y = 8.61x - 9.91 r 2 = 0.95 100 r 2 = 0.98 (mg/g) requency 2 6 F S 5

3

0 0 0

200 60 8 E. Wilkins Peak Member F. Jingjingzigou Formation 7 n = 201 50 n = 8 mean %TOC = 4.09 mean %TOC = 1.44 std. dev. = 3.86 std. dev. = 0.40 6 R = 0.88-0.91% Ro = 0.20-0.45% 40 o 5

y = 7.90x - 2.87 y = 5.60x - 2.55 100 30 4 2 2

(mg/g) r = 0.97 r = 0.82 2 requency S 3 F 20

2

10 1

0 0 0 0 5 10 15 20 25 0 5 10 15 20 25 % TOC % TOC

Figure 5. Percent TOC (determined by LECO) vs. Rock-Eval S2 (points), and % TOC histograms (gray shading) for samples from six lacustrine petroleum source rock units. The slope of the linear regression lines multiplied by 100 gives the average Rock-Eval HI for vitrinite ס each population, corrected for adsorption of pyrolysates on the rock matrix (cf. Langford and Blanc-Valleron, 1990). Ro reflectance in oil for each population. Note that vitrinite reflectances for the Junggar basin samples (B, D, and F) have been affected by outcrop oxidation and thus may be slightly higher than equivalent unweathered rocks (Carroll, 1998). to average 48% of visible kerogen; the remainder is water, suboxic depositional environments that have mostly weakly fluorescent amorphous material. Bio- mixed terrestrial and aquatic organic matter input marker distributions include features typical of fresh- (Table 1).

Carroll and Bohacs 1043 /Steranes 5–15 5–15 .0–4.0 3.8–7.7 2.6–7.7 2.5–5.2 4.2–17.5 1.5–7.7 0.4–0.8 1 28.1–47.5 Hopane 4–11 4–6 7–35 Index (high) 19–36 20–40 20–70 13–150 Gamma. negligible) ( (negligible) reported) reported) reported) reported) 79–85 12–27 48–71 30–100 Index** Tricyclic 100–200 (negligible) (not (not (not (not 27 27 C C 28 27 28 28 28 28 C C C C C C Ͼ Ͼ 4-methyl 4-methyl 4-methyl 4-methyl Ϸ Ͼ Ͼ Ն ס Ն Ͼ 28 27 C C 27 29 27 27 29 28 27 28 C C C C C C C C Steranes Ͼ Ͼ Ͼ Ͼ Ͼ Ͼ Ͼ Ͼ Ͼ Ͼ Ͼ Ն abundant abundant abundant abundant 29 27 29 29 29 27 29 29 29 29 C C C C C C C C C C reported) -carotane detected detected detected? detected detected b resent not p (not not trace present present not not not Oils* and 1.3 1.1 /Phytane** reported) Ͼ Ͼ 2.7–4.0 1.5–4.1 0.1–0.5 1.0–1.6 2.2–3.2 0.8–1.2 1.5–4.8 Rocks (not Pristane Source 779 900 700 HI n.a. Association) Ͻ Յ Ͼ 52–1003 58–365 93–458 55–985 481–766 110–946 Lacustrine Association) Facies f o 9 TOC 6.5% Յ n.a. 0–23 2–24 0–8 .7–9.2 % Յ 1.5–17.1 0 1.0–59.2 0.6–2.2 Facies o R n.a. 0.40 % Characteristics Profundal 0.4–0.8 0.4–0.7 0.4–0.8 (Fluvial-Lacustrine 0.77–0.88 0.56–0.81 0.35–0.45 0.86–1.09 0.65–0.72 | | † † Facies † † ‡ ‡ (Fluctuating Geochemical (rocks) China), China), (rocks) Tongue § Member (Angola) § ‡ ‡ shale § (rocks) Organic (W. (W. Facies zone Fm. oils) oils) oils) oils) Fm. basin basin Selected Laney Luman shales . basin basin † † and and and 1 Kissenda basins basins Formation Organic Sumatra (rocks (rocks (rocks organic-rich Lucaogou (Thailand; Hongyanchi (rocks) (rocks) Brazil C. Brazil Gabon Bucomazi Junggar Phisanulok Junggar Algal Wyoming, Basin Algal-Terrestrial Wyoming, Table

1044 Lacustrine Petroleum Source Rocks (H), ␣ 17 30 /C 0.2–2.0 0.3–2.4 1.7–7.1 0.7–2.2 gammacerane ס 8–82 15–34 31–56 35–216 Index Gamma. 6–21 7–28 79–245 260–580 (H)-hopane); b 21 27 (H), C ␣ 27 27 28 C C C 17 Ͼ 30 Ͼ Ͼ Ͼ Ͼ /C 29 28 28 28 C C C C Ͼ Ͼ Ͼ Ն terpane 27 29 29 29 C C C C tricyclic applicable. 23 not to to 100(C ס ס n.a. dominant dominant Index abundant present abundant abundant Tricyclic (H)-steranes; ␣ 17 Index; (H), ␣ 0.9–2.3 0.1–0.5 0.8–1.1 0.1–1.1 14 R Hydrogen 20 ם S 20 Rock-Eval 29 n.a. ס /C 32–1001 HI 712–838 129–477 Association) carbon; 6.6 (H)-hopane Facies n.a. b Յ 21 4.1–19.0 0.8–2.0 (1996). organic al. (H), ␣ et total 17 ס 30 n.a. C Peters (Evaporative TOC 0.20–0.45 0.88–0.91 0.45–0.55? ס maturity. % † (1987), Facies † oil; in Fan /Steranes thermal # by and | (rocks) | China) 1995). China) China) Peak # | Organic | (1991). (oils) # Hopane (E. Philp Fm. reflectance (W. (W. ffected a (1992, (1994). oils) 1997). Philp ( (1995). l. trend Wilkins (rocks) al. a (1988). l. al. basin t (1986), and a et basin basin e and vitrinite al. t et (1998). e al. (H)-hopane; strongly et ס study. b (1994). et o 21 R this Fu | Jingjingzigou (rocks Karamay Member Kelley Carroll Kuo | # Clayton Burwood § Kulwadee Horsfield Mello † ‡ | | Junggar Jianghan Junggar | | # # † † ‡ ‡ § § *% Hypersaline-Algal Wyoming, **Ratio

Carroll and Bohacs 1045 200 however, also occur in the highest TOC bluebeds, sug- Luman + Niland Tongues gesting that these units were deposited during times of Population 1 enhanced terrestrial runoff. Ectogenic meromixis as a n = 86 mean %TOC = 4.87 result of increased inflow of fresh surface water has std. dev. = 1.54 been proposed as a mechanism for promoting salinity y = 8.05x - 8.08 Population 2 n = 85 r 2 = 0.94 stratification (Boyer, 1982), which in turn may have mean %TOC = 9.34 100 std. dev. = 11.76 helped preserve organic matter. Biomarker distribu- (mg/g)

2 y = 3.24x - 1.01

S tions are consistent with predominantly aquatic or- 2 r = 0.86 ganic matter input in saline lakes with anoxic bottom waters (Table 1). Maximum Lucaogou Formation organic enrich- HI > 500 HI < 500 ment occurs in laminated mudstone, interpreted as an- oxic profundal facies (Graham et al., 1990; Carroll et 0 0 10 20 30 40 50 60 al., 1992). Organic richness is highly variable within

% TOC the Lucaogou Formation, ranging from less than 0.5% to greater than 20% TOC and is highest in submilli- Figure 6. Percent TOC vs. S2 plot for Luman Tongue and Ni- meter laminated intervals (Carroll, 1998) (Figures 4B, land Tongue samples. The samples have been divided into two 5D). The lower average TOC values in the Lucaogou populations according to HI, and separate linear regression lines Formation compared with the lower LaClede Bed may have been calculated for each population. in fact reflect more statistically representative sampling of the Lucaogou Formation. Average Rock-Eval HI val- ues over this interval are essentially identical with the Algal-terrestrial organic facies elsewhere typically lower LaClede Bed (Figure 5C, D), and both are con- have moderately high TOC contents (ϳ1–10%) and sistent with relatively homogenous type I kerogen. mixed type I–type III kerogens (Table 1) and com- Fluorescent amorphous material dominates Lucaogou monly occur in association with fluvial deposits and Formation kerogens, averaging 58% of visible organic coal. High molecular weight n-alkanes (waxes) are ma- matter, and attests to probable algal input (Carroll, jor constituents of both rock extracts and oils because 1998). Very light d13C values in extracts of the richest of input of protective tissues from higher land plants samples (Carroll, 1998) are inconsistent with the hy- (Tissot and Welte, 1984) and membrane lipids from pothesis that organic richness is controlled by high pri- certain classes of freshwater algae (Goth et al., 1988; mary productivity, but correlations between produc- Tegelaar et al., 1989). Selective enrichment in these tivity and organic richness have been reported in other compounds may also result from selective bacterial basins (e.g., Curiale and Gibling, 1994). The absence degradation of other components in oxic to suboxic of subaerial exposure surfaces, presence of fish fossils, depositional environments (Powell, 1986). High and modest elevation of b-carotane and gammacerane pristane/phytane ratios (Table 1) result both from in Lucagogou Formation extracts (Table 1) together higher land plant input and oxic depositional condi- are consistent with deposition within a salinity- tions. High hopane/sterane ratios record bacterial deg- stratified lake. radation of relatively abundant terrestrial organic Algal organic facies in other basins represent some matter. of the world’s richest lacustrine source rocks and con- tain mostly type I kerogen that has HI values that typ- Algal Organic Facies ically reach maxima in the 600–900 range and may exceed 1000 (Espitalie´ et al., 1977). Lower HI values The fluctuating profundal facies association typically reflect temporal variations in primary productivity includes extremely organic-rich laminated mudstone (e.g., Curiale and Stout, 1993), degree of water- facies containing abundant algal-derived organic mat- column anoxia (Demaison and Moore, 1980), and ex- ter. The TOC values in the lower LaClede Bed of the perimental artifacts arising from Rock-Eval pyrolysis Laney Member of the Green River Formation are as (Katz, 1983; Langford and Blanc-Valleron, 1990). Ex- great as 20%, and the average HI is 830 (Figures 3B, tracts and oils are commonly rich in n-alkanes derived 5C). Alginite is the principal organic maceral (Hors- from membrane lipids of aquatic organisms. The dis- field et al., 1994). Subsidiary vitrinite and intertinite, tribution of n-alkanes may differ from freshwater fa-

1046 Lacustrine Petroleum Source Rocks cies, however, in having lower odd-carbon-number components. 8 ם preference and less abundant n-C 30 Lake Plain/Alluvial 7 Pristane/phytane ratios are typically close to or less n = 14 mean %TOC = 1.11 than 1.0, reflecting lower terrestrial input, anoxic dep- 6 std. dev. = 0.43 ositional conditions, and possibly elevated salinity. 100 5 Other biomarker characteristics reflect the contribu- 4 tions of specific classes of aquatic organisms, as evi- requency

y = 8.67x - 3.90 F 2 3 denced by the presence of moderate amounts of (mg/g) r = 0.90 2 S b-carotane, elevated tricyclic terpanes, and gammacer- 2 ane. Gammacerane is a commonly cited indicator of 1 salinity (e.g., Mello et al., 1988), although more recent work with compound-specific isotopic analysis sug- 0 0 gests that gammacerane may in fact record input from 10 Supralittoral bacterial communities living at or below the chemoc- n = 25 8 line in stratified lakes (Schoell et al., 1994; Sinninghe mean %TOC = 3.23 Damste´ et al., 1995). std. dev. = 2.94 100 6 Hypersaline Algal Organic Facies y = 7.58x - 2.67 requency 2 4 F

(mg/g) r = 0.96 2 Oil shales in the Wilkins Peak Member of the Green S River Formation are thinner and slightly less areally ex- 2 tensive than those in the lower LaClede Bed but con- tain equally high maximum organic enrichments (up 0 0 to 18% TOC) (Bohacs, 1998) (Figure 5E). The TOC 40 contents in the Wilkins Peak Member vary widely but Littoral 35 n = 86 are generally lowest in littoral and lake-plain mudstone mean %TOC = 1.84 30 facies and highest in sublittoral mudstones and shales std. dev. = 1.11 100 25 (Figure 7). These relationships demonstrate that the y = 8.00x - 3.27 20 highest organic enrichments occur when the lakes were r 2 = 0.92 requency (mg/g)

15 F deepest. Note that average HI values in the Wilkins 2 S Peak Member (determined from S2/TOC plots) are 10 essentially identical for each environment, indicating 5 very little lateral contrast in organic matter type. Amorphous organic matter, derived from algal or bac- 0 0 terial sources, dominates visible organic matter, con- n = 76 10 Sublittoral firming very low input from land plants. Some of the mean %TOC = 7.33 std. dev. = 4.22 most organically enriched strata occur just above the 8 major flooding surface at the base of each sequence

(Figure 3C). Biomarker distributions are consistent 100 6 with deposition under hypersaline, anoxic conditions y = 7.83x - 1.82 r 2 = 0.96 (mg/g) requency 2

(Table 1), although certain biomarker ratios (e.g., F

S 4 pristane/phytane ratios) may also reflect low thermal maturity. 2 Organic enrichment in the Jingjingzigou Forma- tion mudstone is relatively low (TOC less than 2%) 0 0 (Figures 4C, 5F). Total organic carbon is highest in me- 0 5 10 15 20 dium and dark gray laminated mudstones and drops to %TOC less than 1.0% in nonlaminated facies. Rock-Eval HI Figure 7. Percent TOC histograms for core samples from the values reach a maximum of 477, suggesting oxidation Wilkins Peak Member, subdivided according to interpreted dep- of organic matter prior to burial. The Jingjingzigou ositional environment. Formation contains high proportions of amorphous

Carroll and Bohacs 1047 kerogen, presumably of algal or bacterial origin (Car- mation. For example, modern east African lakes pre- roll, 1998). Minor vitrinite, inertinite, and alginite serve organic matter ranging from type I to type III make up the remainder of the visible kerogen. Bio- (Katz, 1988, 1990; Talbot, 1988). Recent studies have marker distributions are commonly dominated by b- demonstrated that these distinctions are critical not carotane, which has been associated with shallow, hy- only for estimating the relative quality and quantity of persaline lakes in which certain highly specialized oil and gas that may be generated, but also for deter- organisms occur (Murphy et al., 1967; Hall and Doug- mining the timing of hydrocarbon generation (e.g., An- las, 1983; Brassell et al., 1988; Duncan and Hamilton, ders et al., 1992; Tegelaar and Noble, 1994; Peters et 1988; ten Haven et al., 1988). al., 1996). The following discussion considers genera- Hypersaline organic facies commonly feature tive characteristics of mixed type I–III kerogen typical lower overall TOC values than do brackish-saline fa- of the algal-terrestrial organic facies (fluvial-lacustrine cies, although relatively thin intervals of high TOC oc- facies association), type I kerogen typical of algal or- cur during periods of maximum lake expansion. ganic facies (fluctuating profundal facies association), Mixtures of type I and type III kerogens appear to re- and type I-S kerogen that has been reported in associ- sult from varying degrees of preservation of aquatic or- ation with some hypersaline-algal organic facies (evap- ganic matter and from the admixture of minor terres- orative facies association). trial material. Maximum HI values equal or exceed those seen in algal organic facies (Table 1), but average Oil and Gas Generation from Mixed Type I–III Kerogens values tend to be lower. Biomarker distributions reflect low-diversity assemblages of highly specialized organ- Tegelaar and Noble (1994) demonstrated through py- isms living under harsh environmental conditions. rolysis experiments that vitrinite-dominated (terres- Pristane/phytane ratios substantially below 1.0 may re- trial) kerogen generally generates hydrocarbons over a sult either from anoxic depositional conditions in a broader range of temperatures than do most algal- stratified, hypersaline lake, or from contributions from dominated kerogens and that generation continues halophilic bacteria (Goosens et al., 1984). b-carotane well above the range of temperatures associated with is commonly an abundant to dominant constituent, as generation from algal-dominated kerogen. This result are elevated concentrations of tricyclic terpanes and suggests that given the same burial and thermal history, gammacerane (Table 1). Hopane/sterane ratios are mixtures of aquatic and terrestrial organic matter typically low. In addition to the examples cited previ- should generate petroleum over a broader range of ously, hypersaline lacustrine organic facies are known thermal maturities than purely algal source facies. Data from several Tertiary basins in China (Shi et al., 1982; from the Uinta basin in Utah are consistent with this Fu et al., 1986; Sheng et al., 1987; Brassell et al., 1988; hypothesis. Oils in the Altamont-Bluebell fields were R. Li et al., 1988, 1992; Z. Chen et al., 1994; J. Chen sourced primarily from freshwater lake facies of the et al., 1996; Peters et al., 1996) and in Spain (e.g., lower Green River and underlying formations that re- Salvany and Ortı´, 1994; Sanz et al., 1994). semble the Luman Tongue (Fouch, 1975; Ruble and Philp, 1998). Based on Rock-Eval transformation ra- tios, light hydrocarbon yields, and atomic H/C ratios, DISCUSSION: PETROLEUM GENERATION hydrocarbon generation from these facies occurred in FROM LACUSTRINE SOURCE ROCKS the deep Uinta basin over a broad range of thermal maturities, ranging from approximately 0.70 to 1.35 %

Bradley (1925) noted that for certain members of the Ro (Anders et al., 1992). Green River Formation, “large volumes of microscopic Uinta basin oils are solid at surface temperatures plants and perhaps also animals accumulated.” Studies because of their very high wax content. High wax con- of oil-shale facies of the Mahogany ledge of the Para- tent and pour point are also associated with freshwater chute Creek Member led to the recognition of type I lacustrine source rocks in the Central Sumatra basin lacustrine kerogen, characterized by high atomic H/C (Kelley et al., 1995), in the Songliao basin of north ratios and HI (van Krevelen, 1961; Espitalie´ et al., China (Yang et al., 1985), in central African rift basins 1977). Subsequent experience has shown, however, (Genik, 1993), and in some Brazilian rift basins (Mello that kerogens in many modern and ancient lake sys- et al., 1988; Mello and Maxwell, 1990). Minor tems differ from type I, and that type I is not even amounts of natural gas are also common in oil fields representative of all members of the Green River For- sourced by mixed type I–III mixed kerogens (e.g.,

1048 Lacustrine Petroleum Source Rocks Clem, 1985; Rice et al., 1992; Genik, 1993; Kelley et Such oils have been reported from onshore exten- al., 1995), but the sources of these gases have not been sions of the Bohai Bay basin (Shengli oil field) (Shi clearly established. et al., 1982; Z. Chen et al., 1994), the Dongpu basin (R. Li et al., 1988, 1992), the Jianghan basin (Fu et Oil Generation from Type I Kerogen al., 1986; Sheng et al., 1987; Brassell et al., 1988; Peters et al., 1996), and the Qaidam basin (Huang Waples (1980) and Sweeney et al. (1987) showed that et al., 1991) and are commonly associated with saline type I kerogens generate oil over a very narrow range or hypersaline source rocks. Based on source rock–oil of thermal maturities, reflecting little variation in correlations and biomarker maturity measurements, chemical bond type within these homogenous kero- significant generation appears to have occurred from gens. Tegelaar and Noble (1994) found that the onset these rocks at vitrinite reflectance values as low as of oil generation from Green River type I kerogen 0.45%. Several molecular maturity measurements, in-

20R) desmethyl ם should occur between 0.8 and 0.9% Ro, and peak gen- cluding the ratios of 20S/(20S -22R) homohopanes, pro ם eration is at 0.95–1.05% Ro. The overall oil window steranes and 22S/(22S (defined by 10–90% kerogen transformation ratios) vide confirmation of the low thermal maturity of thus spans only about 0.3% Ro on average, or less than these oils. Jianghan basin oils, for example, com- 30ЊC based on a 1ЊC/m.y. heating rate. They found monly have 20S sterane ratios as low as 0.17–0.24, that the peak generation other type I kerogens also gen- in contrast to the observation by (Mackenzie et al., erate over a very narrow range of thermal maturities, 1980) that petroleum generation from marine type II although the absolute thermal maturity at which gen- kerogen begins at values of about 0.40. Likewise, eration begins could vary widely. They calculated that Jianghan oils have C32 22S hopane ratios as low as the onset of oil generation could range between 0.54 0.44 (Fu et al., 1986), in contrast to values of ap- and 0.96% Ro and concluded that bulk chemical proximately 0.50–0.55 that typically mark the onset composition alone was not sufficient to predict gener- of petroleum generation from marine kerogens. If ation timing. Using pyrolysis–gas chromatography these low maturities are representative of a significant techniques to better discern kerogen chemical struc- fraction of the total petroleum generation, then ex- tures, they found that two other factors influence gen- ploration models for basins containing such oils must eration timing: (1) the types and mixtures of biomacro- allow for earlier generation of oil relative to trap for- molecules preserved, and (2) organic sulfur content. mation and other play elements. Whether absolute generation timing can be accurately Two explanations have been offered for these low- determined from bulk chemical measurements such as maturity oils. The first is that they do not represent Rock-Eval HIs is, therefore, currently unclear. thermal degradation of kerogens at all, but instead re- Type I kerogens generate paraffinic oils produced sult from degradation and migration of original soluble from the Karamay and associated fields in the Junggar organic matter that was never incorporated into kero- basin (Clayton et al., 1997). Karamay oils are low in gen. For example, certain coals and carbonaceous sulfur, and except where biodegraded, contain abun- shales rich in higher land plant remains (particularly dant n-alkanes that have molecular weights less than from conifers) may contain abundant resins (soluble

C30. A similar n-alkane distribution was reported for organic matter), which may be expelled as liquids oils sourced from type I kerogen in the Campos basin (Snowdon and Powell, 1982; Stout, 1995). Huang et of Brazil (Mello et al., 1988; Mello and Maxwell, al. (1991) invoked such an explanation for Qaidam ba- 1990). The distribution of n-alkanes in oils generated sin light oils and condensates that have 20S sterane ma- from type I kerogens may vary widely, however, and turity ratios of 0.18–0.23. X. Li et al. (1998) proposed are subject to modifications related to thermal matur- that two distinct pulses of petroleum generation oc- ity and biodegradation. curred in the East China Sea basin, the first occurring

at less than 0.55% Ro and the second between 0.55 and Early Generation from Type I-S Kerogen? 1.30% Ro. Resinite derived oils reported from Canada are naphthenic (high percentage of hydrocarbons hav- Several Tertiary lacustrine basins in China contain ing ring structures) rather than paraffinic, but different oils that appear to have been generated at lower ther- resin types and varying proportions of resinite relative mal maturities than are normally associated with the to other macerals may partly account for more paraf- breakdown of typical marine or lacustrine kerogens. finic oils in China.

Carroll and Bohacs 1049 Another important consideration is the potential put of organosulfur compounds. Sheng et al. (1987) volumetric significance of oil generated from resins, identified long-chain normal alkyl-thiophenes and which typically comprise relatively low percentages of alkyl-thiolanes, long-chain isoprenoid-thiophenes and the total organic matter (Tissot and Welte, 1984). Sa- isoprenoid-thiolanes, and benzothiophenes in sulfur- line or hypersaline lacustrine facies would be expected rich oils. The distribution of these compounds mirrors to contain relatively little resinous land plant organic that of the corresponding alkanes, leading Sheng et al. matter. For example, oils in the Shengli field are (1987) to conclude that the sulfur compounds origi- thought to represent transformation of less than 10% nated through diagenetic reactions between elemental of the total organic matter present in the source rocks sulfur and sulfides with phytol, fatty acids, and alco- (Cheng Keming, Research Institute of Petroleum Ex- hols. The apparent rarity of type I-S kerogen may ploration and Development, Beijing, 1997, personal stem from the fact that most lake waters have low communication). Further volumetric data on the Shen- sulfate concentrations relative to marine systems and gli oil field and other accumulations of low maturity that in siliciclastic lacustrine systems there is com- oils are needed to determine whether expulsion of bio- monly excess iron available to form pyrite or other genic bitumen is adequate to account for the known sulfides. These limitations, however, may be over- oil reserves. come if sulfide scavengers such as Fe and Mn are A second and possibly complementary explanation scarce, especially if sulfate supply to the basin is un- is that low-maturity oils result from thermal degrada- usually high. For example, Sinninghe Damste´ et al. tion of a distinctive type I-S (sulfur-rich) kerogen. type (1993) documented type I-S kerogen in two Tertiary I-S kerogen is defined as having an HI above 600 and Spanish oil shales, which they interpreted as having a S/C atomic ratio greater than 0.04 (Sinninghe formed as a result of weathering of Triassic evaporites. Damste´ et al., 1993; Peters et al., 1996). Jianghan basin Sulfate from the evaporites was microbially reduced oils are generally high in sulfur (3.59–12.91%) (Sheng in a freshwater lake and incorporated into previously et al., 1987), and aromatic organosulfur compounds deposited remains of Botryococcus braunii algae. A are abundant (Philp and Fan, 1987; Sheng et al., 1987). more common setting for type I-S kerogen is probably Peters et al. (1996) presented experimental kinetic in evaporative lakes where siliciclastic sediment input data showing that the type I-S kerogen in Jianghan is low and evaporative concentration of sulfate occurs. hypersaline lacustrine source rocks reacts quickly to In the Chinese basins, the oil source rocks are closely thermal stress, in a manner similar to marine type II-S associated with gypsum and other evaporites and have kerogen in the Monterey Formation. Type II-S kero- biomarker characteristics indicative of anoxic saline to gens have been demonstrated to generate oil at lower anoxic hypersaline environmental conditions (Shi et thermal exposures than other kerogens (Orr, 1986). al., 1982; Fu et al., 1986; Philp and Fan, 1987; Sheng Hydrous pyrolysis experiments using Monterey kero- et al., 1987; Brassell et al., 1988; Huang et al., 1991; gens provide evidence that this generation actually oc- Z. Chen et al., 1994). curs via a two-step process (Baskin and Peters, 1992). In the first step, cleavage of relatively weak S–C bonds generates heavy bitumen that is retained on the kero- CONCLUSIONS gen matrix. Thermal degradation of this bitumen at slightly higher temperatures results in the expulsion of 1. Three end-member lacustrine facies associations oil. Thus, this model appears to combine elements of have been observed to recur in widely disparate the “oil from resins” model discussed previously with geographic settings and over a wide range of geo- thermal degradation of an uncommonly reactive logic time: fluvial lacustrine, fluctuating-profundal, sulfur-rich kerogen. Low maturity Monterey Forma- and evaporative. Significant differences exist among tion oils, however, have low API gravities and are dom- each of the these associations in terms of oil vs. gas inated by asphaltenes and resins, whereas Jianghan oils generation and the timing of petroleum generation are dominantly paraffinic (Philp and Fan, 1987). More relative to basin thermal history. These associations work is clearly needed to resolve the actual generation can be used to make first-order predictions of pe- mechanisms responsible for low-maturity oils in troleum generation type (oil vs. gas) and timing China. from limited geologic data on nonsource facies. Type I-S kerogens appear to result from dia- Conversely, geochemical analysis of source rocks or genetic sulfurization rather than from biological in- oils may aid in predicting lacustrine paleoenviron-

1050 Lacustrine Petroleum Source Rocks ments and the likely distribution and quality of res- matic and tectonic controls (abs.): First International Limno- Geological Congress, abstract volume, p. 18–19. ervoir and seal facies. Carroll, A. R., and K. M. Bohacs, 1999, Stratigraphic classification 2. Lacustrine source rocks display a high degree of of ancient lakes: balancing tectonic and climatic controls: Ge- geochemical heterogeneity relative to marine facies, ology, v. 27, p. 99–102. therefore their complete characterization requires Carroll, A. R., Y. Liang, S. A. Graham, X. Xiao, M. S. Hendrix, J. Chu, and C. L. McKnight, 1990, Junggar basin, northwest analysis of a relatively large number of samples se- China: trapped late Paleozoic ocean: Tectonophysics, v. 181, lected at fixed, regular intervals. Selective sampling p. 1–14. of a few particularly rich beds may lead to erroneous Carroll, A. R., S. C. Brassell, and S. A. Graham, 1992, Upper Per- mian lacustrine oil shales of the southern Junggar basin, north- conclusions concerning overall generative potential. west China: AAPG Bulletin, v. 76, p. 1874–1902. 3. No typical lacustrine source rock or oil exists. The Carroll A. R., S. A. Graham, M. S. Hendrix, D. Ying, and D. Zhou, default-value kerogen properties and kinetics some- 1995, Late Paleozoic tectonic amalgamation of northwestern China: sedimentary record of the northern Tarim, northwestern times used in basin modeling are therefore of lim- Turpan, and southern Junggar basins: Geological Society of ited utility. For optimal precision, detailed kinetic American Bulletin, v. 107, p. 571–594. measurements should be made from immature Chen, J., Y. Bi, J. Zhang, and S. Li, 1996, Oil-source correlation in equivalents of the suspected source facies, if possi- the Fulin basin, Shengli petroleum province, east China: Or- ganic Geochemistry, v. 24, p. 931–940. ble, and should be supported by molecular maturity Chen, Z., G. Zhou, and R. Alexander, 1994, A biomarker study of measurements from source rock extracts and gen- immature crude oils from the Shengli oilfield, People’sRepublic erated oils. of China: Chemical Geology, v. 113, p. 117–132. Clayton, J. L., J. Yang, J. D. King, P. G. Lillis, and A. Warden, 1997, Geochemistry of oils from the Junggar basin, northwest China: AAPG Bulletin, v. 81, p. 1926–1944. REFERENCES CITED Clem, K., 1985, Oil and gas production summary of the Uinta basin, in M. D. Picard, ed., Geology and energy resources, Uinta basin of Utah: Salt Lake City, Utah Geological Association, p. 159– Anders, D. E., J. G. Palacas, and R. C. Johnson, 1992, Thermal ma- 167. turity of rocks and hydrocarbon deposits, Uinta basin, Utah, in Curiale, J. A., and M. R. Gibling, 1994, Productivity control on oil T. D. Fouch, V. F. Nuccio, and T. C. Chidsey, eds., Hydrocar- shale formation—Mae Sot Basin, Thailand: Organic Geochem- bon and mineral resources of the Uinta basin, Utah and Colo- istry, v. 21, p. 67–89. rado: Utah Geological Association Guidebook 20, p. 53–76. Curiale, J. A., and S. A. Stout, 1993, Monitoring tectonically con- Barron, E. J., 1990, Climate and lacustrine source rock prediction, trolled marine to lacustrine transitions using organic facies— in B. J. Katz, ed., Lacustrine basin exploration—case studies and Ridge basin, California, U.S.A: Chemical Geology, v. 109, modern analogs: AAPG Memoir 50, p. 1–18. p. 239–268. Baskin, D. K., and K. E. Peters, 1992, Early generation characteristics Demaison, G., and G. T. Moore, 1980, Anoxic environments and oil of a sulfur-rich Monterey kerogen: AAPG Bulletin, v. 76, p. 1– source bed genesis: AAPG Bulletin, v. 64, p. 1179–1209. 13. Duncan, A. D., and R. F. M. Hamilton, 1988, Paleolimnology and Bohacs, K. M., 1998, Contrasting expressions of depositional se- organic geochemistry of the Middle Devonian in the Orcadian quences in mudrocks from marine to nonmarine environs, in J. basin, in A. J. Fleets, K. Kelts, and M. R. Talbot, eds., Lacustrine Schieber, W. Zimmerle, and P. Sethi, eds., Shales and mud- petroleum source rocks: Geological Society Special Publication stones I.: Stuttgart, Schweizerbart’sche Verlagsbuchhandlung, 40, p. 173–201. p. 33–78. Espitalie´, J., J. L. Laporte, M. Madec, F. Marquis, P. Lepat, J. Paulet, Boyer, B. W., 1982, Green River laminites: does the playa-lake and A. Boutefeu, 1977, Me´thode rapide de caracte´risation des model really invalidate the stratified-lake model?: Geology, v. 10, p. 321–324. roches me`res, de leur potentiel petrolier et leur degre´ Bradley, W. H., 1925, A contribution to the origin of oil shale: AAPG d’e´volution: Review Institut Franc¸ais du Pe´trole, v. 32, p. 23– Bulletin, v. 9, p. 247–262. 42. Bradley, W. H., and H. P. Eugster, 1969, Geochemistry and paleo- Eugster, H. P., and L. A. Hardie, 1975, Sedimentation in an ancient limnology of the trona deposits and associated authigenic min- playa-lake complex: the Wilkins Peak Member of the Green erals of the Green River Formation of Wyoming: U.S. Geolog- River Formation of Wyoming: Geological Society of America ical Survey Professional Paper 496-B, p. A1–A86. Bulletin, v. 86, p. 319–334. Brassell, S. C., G. Shen, J. Fu, and G. Eglinton, 1988, Biological Eugster, H. P., and Kelts, K., 1983, Lacustrine chemical sediments, markers in lacustrine Chinese oil shales, in D. Leythaeuser, and in A. S. Goudie and K. Pye, eds., Chemical sediments and geo- J. Rulko¨tter, eds., Advances in organic geochemistry 1985: Ox- morphology: precipitates and residua in the near-surface envi- ford, Pergamon Press, p. 927–941. ronment: London, Academic Press, p. 321–368. Burwood, R., S. M. De Witte, B. Mycke, and J. Paulet, 1995, Petro- Eugster, H. P., and R. C. Surdam, 1973, Depositional environment leum geochemical characterisation of the Lower Congo coastal of the Green River Formation of Wyoming: a preliminary re- basin Bucomazi Formation, in B. J. Katz, ed., Petroleum source port: Geological Society of America Bulletin, v. 84, p. 1115– rocks: Berlin, Springer-Verlag, p. 235–264. 1120. Carroll, A. R., 1998, Upper Permian organic facies evolution, south- Fouch, T. D., 1975, Lithofacies and related hydrocarbon accumu- ern Junggar basin, NW China: Organic Geochemistry, v. 11. lations in Tertiary strata of the western and central Uinta basin, p. 649–667. Utah, in D. W. Bolyard, ed., Deep drilling frontiers of the cen- Carroll, A. R., and K. M. Bohacs, 1995, A stratigraphic classification tral Rocky mountains: Denver, Rocky Mountain Association of of lake types and hydrocarbon source potential: balancing cli- Geologists, p. 163–174.

Carroll and Bohacs 1051 Fu, J., G. Shen, P. Peng, S. C. Brassell, G. Eglinton, and J. Jiang, Liu, 1998, Hydrocarbon-generating characteristics of source 1986, Peculiarities of salt lake sediments as potential source rocks in a depression of the East China Sea: Journal of the Jian- rocks in China: Organic Geochemistry, v. 10, p. 119–126. ghan Petroleum Institute, v. 20; p. 26–31. Genik, G. J., 1993, Petroleum geology of the Cretaceous–Tertiary Liao, Z., L. Lu, N. Jiang, F. Xia, F. Sung, Y. Zhou, S. Li, and Z. rift basins in Niger, Chad and Central African Republic: AAPG Zhang, 1987, Carboniferous and Permian in the western part Bulletin, v. 77, p. 1405–1434. of the east Tianshan Mountains: Beijing, Eleventh Congress of Goosens, H., J. W. de Leeuw, P. A. Schenck, and S. C. Brassell, 1984, Carboniferous Stratigraphy and Geology, Guide Book Excur- Tocopherols as likely precursors of pristane in ancient sedi- sion 4, 50 p. ments and crude oils: Nature, v. 12, p. 495–506. Liro, L. M., and Y. C. Pardus, 1990, Seismic facies analysis of fluvial- Goth, K., J. W. de Leeuw, W. Pu¨ ttmann, and E. W. Tegelaar, 1988, deltaic lacustrine systems—upper Fort Union Formation (Pa- Origin of Messel oil shale kerogen: Nature, v. 336, p. 759–761. leocene), Wind River basin, Wyoming, in B. J. Katz, ed., La- Graham, S. A., S. Brassell, A. R. Carroll, X. Xiao, G. Demaison, custrine basin exploration—case studies and modern analogs: C. L. McKnight, Y. Liang, J. Chu, and M. S. Hendrix, 1990, AAPG Memoir 50, p. 225–242. Characteristics of selected petroleum source rocks, Xinjiang Mackenzie, A. S., R. L. Patience, J. R. Maxwell, M. Vandenbroucke, Uygur autonomous region, China: AAPG Bulletin, v. 74, and B. Durand, 1980, Molecular parameters of maturation in p. 493–512. the Toarcian shales, Paris basin, France—I. changes in the con- Hall, P. B., and A. G. Douglas, 1983, The distribution of cyclic al- figurations of acyclic isoprenoid alkanes, steranes, and triter- kanes in two lacustrine deposits, in M. Bjorøy, ed., Advances in panes: Geochimica et Cosmochimica Acta, v. 44, p. 1709– organic geochemistry 1981: Chichester, John Wiley and Sons, 1721. p. 576–587. Mello, M. R., and J. R. Maxwell, 1990, Organic geochemical and Horsfield, B., et al., 1994, Organic geochemistry of freshwater and biological marker characterization of source rocks and oils de- alkaline lacustrine environments, Green River Formation, Wy- rived from lacustrine environments in the Brazilian continental oming: Organic Geochemistry, v. 22, p. 415–440. margin, in B. J. Katz, ed., Lacustrine basin exploration—case Huang, D., J. Li, D. Zhang, X. Huang, and Z. Zhou, 1991, Matu- studies and modern analogs: AAPG Memoir 50, p. 77–97. ration sequence of Tertiary crude oils in the Qaidam basin and Mello, M. R., N. Telnaes, P. C. Gaglianone, M. I. Chicarelli, S. C. its significance in petroleum resource assessment: Journal of Brassell, and J. R. Maxwell, 1988, Organic geochemical char- Southeast Asian Earth Sciences, v. 5, p. 359–366. acterisation of depositional palaeoenvironments of source rocks Hubert, J. F., and K. A. Mertz, 1984, Eolian sandstones in Upper and oils in Brazilian marginal basins: Organic Geochemistry, Triassic–Lower Jurassic red beds of the Fundy Basin, Nova Sco- v. 43, p. 31–45. tia: Journal of Sedimentary Petrology, v. 54, p. 798–810. Murphy, M. T. J., A. McCormick, and G. Eglinton, 1967, Perhydro- Jiang, Z., and M. G. Fowler, 1986, Carotenoid-derived alkanes in oils b-carotene in the Green River shale: Science, v. 157, p. 1040– from northwestern China: Organic Geochemistry, v. 10, 1042. p. 831–839. Olsen, P. E., 1990, Tectonic, climatic, and biotic modulation of la- Katz, B. J., 1983, Limitations of ‘Rock-Eval’ pyrolysis for typing or- custrine ecosystems—examples from Newark Supergroup of ganic matter: Organic Geochemistry, v. 4, p. 195–199. eastern North America, in B. J. Katz, ed., Lacustrine basin Katz, B. J., 1988, Clastic and carbonate lacustrine systems: an organic exploration—case studies and modern analogs: AAPG Memoir geochemical comparison (Green River Formation and East Af- 50, p. 209–224. rican lake sediments), in A. J. Fleet, K. Kelts, and M. R. Talbot, Orr, W. L., 1986, Kerogen/asphaltene/sulfur relationships in sulfur- eds., Lacustrine petroleum source rocks: Geological Society rich Monterey crudes: Organic Geochemistry, v. 10, p. 499– Special Publication 40, p. 81–90. 516. Katz, B. J., 1990, Controls on distribution of lacustrine source rocks Peters, K. E., and J. M. Moldowan, 1993, The biomarker guide: in- through time and space, in B. J. Katz, ed., Lacustrine basin terpreting molecular fossils in petroleum and ancient sedi- exploration—case studies and modern analogs: AAPG Memoir ments: Englewood Cliffs, New Jersey, Prentice-Hall, 363 p. 50, p. 61–76. Peters, K. E., A. E. Cunningham, C. C. Walters, J. Jigang, and F. Kelley, P. A., B. Mertani, and H. H. Williams, 1995, Brown Shale Zhaoan, 1996, Petroleum systems in the Jiangling-Dangyang Formation: Paleogene lacustrine source rocks of central Su- area, Jianghan basin, China: Organic Geochemistry, v. 24, matra, in B. J. Katz, ed., Petroleum source rocks: Berlin, p. 1035–1060. Springer-Verlag, p. 283–308. Philp, R. P., and Z. Fan, 1987, Geochemical investigation of oils and Kelts, K., 1988, Environments of deposition of lacustrine petroleum source rocks from Qianjiang Depression of Jianghan basin, a source rocks: an introduction, in A. J. Fleet, K. Kelts, and M. R. terrigenous saline basin, China: Organic Geochemistry, v. 11, Talbot, eds., Lacustrine petroleum source rocks: Geological So- p. 549–562. ciety Special Publication 40, p. 3–26. Powell, T. G., 1986, Petroleum geochemistry and deposition setting Langford, F. F., and M.-M. Blanc-Valleron, 1990, Interpreting Rock- of lacustrine source rocks: Marine and Petroleum Geology, v. 3, Eval pyrolysis data using graphs of pyrolizable hydrocarbons vs. p. 200–219. total organic carbon: AAPG Bulletin, v. 74, p. 799–804. Rice, D. D., T. D. Fouch, and R. C. Johnson, 1992, Influence of Li, D., R. Jiang, and B. J. Katz, 1995, Petroleum generation in the source rock type, thermal maturity, and migration on compo- nonmarine Qingshnkou Formation (Lower Cretaceous), Son- sition and distribution of natural gases, Uinta basin, Utah, in gliao basin, China, in B. J. Katz, ed., Petroleum source rocks: T. D. Fouch, V. F. Nuccio, and T. C. Chidsey, eds., Hydrocar- Berlin, Springer-Verlag, p. 131–148. bon and mineral resources of the Uinta basin, Utah and Colo- Li, R., Z. Wang, D. Lin, and M. Xin, 1988, Organic geochemical rado: Utah Geological Association Guidebook 20, p. 95–109. analysis of environments of Dongpu basin: Chinese Journal of Roehler, H. W., 1992, Correlation, composition, areal distribution, Geochemistry, v. 7, p. 193–206. and thickness of Eocene stratigraphic units, greater Green River Li, R., H. Wu, D. Lin, Z. Wang, R. Chen, X. Tian, and R. Zhang, basin, Wyoming, Utah, and Colorado: U.S. Geological Survey 1992, Biomarker features of the Chinese Meso-Cenozoic saline Professional Paper 1506-E, 49 p. lake deposits: Advances in Geoscience, v. 2, p. 275–292. Ruble, T. E., and R. P. Philp, 1998, Stratigraphy, depositional envi- Li, X., G. Huang, B. Xiong, C. Gan, N. Zhong, T. Wang, and D. ronments, and organic geochemistry of source-rocks in the

1052 Lacustrine Petroleum Source Rocks Green River petroleum system, Uinta basin Utah, in J. K. Pit- Sweeney, J. J., A. K. Burnham, and R. L. Braun, 1987, A model of man and A. R. Carroll, eds., Modern and ancient lake systems: hydrocarbon generation from type I kerogen: application to new problems and perspectives: Utah Geological Association Uinta basin, Utah: AAPG Bulletin, v. 71, p. 967–985. Guidebook 26, p. 289–321. Talbot, M. R., 1988, The origins of lacustrine oil source rocks: evi- Salvany, J. M., and F. Ortı´, 1994, Miocene glauberite deposits of dence from the lakes of tropical Africa, in A. J. Fleet, K. Kelts, Alcanadre, Ebro basin, Spain: sedimentary and diagenetic pro- and M. R. Talbot, eds., Lacustrine petroleum source rocks: cesses, in R. W. Renault, W. M. Last, and P. A. Scholle, eds., Geological Society Special Publication 40, p. 29–43. Sedimentology and geochemistry of modern and ancient saline Tegelaar, E. W., and R. A. Noble, 1994, Kinetics of hydrocarbon lakes: SEPM Special Publication 50, p. 203–215. generation as a function of the molecular structure of kerogen Sanz, M. E., J. P. Rodrı´gez-Aranda, J. P. Calvo, and S. Ordo´n˜ ez, as revealed by pyrolysis-gas chromatography: Organic Geo- 1994, Tertiary detrital gypsum in the Madrid basin, Spain: cri- chemistry, v. 22, p. 543–574. teria for interpreting detrital gypsum in continental evaporitic Tegelaar, E. W., R. M. Matthezing, J. B. H. Jansen, B. Horsfield, and basins, in R. W. Renault, W. M. Last, and P. A. Scholle, eds., J. W. de Leeuw, 1989, Possible origin of n-alkanes in high-wax Sedimentology and geochemistry of modern and ancient saline crude oils: Nature, v. 342, p. 529–531. lakes: SEPM Special Publication 50, p. 217–228. ten Haven, H. L., J. W. de Leeuw, J. S. Sinninghe Damste´, P. A. Schoell, M., R. J. Hwang, R. M. K. Carlson, and J. E. Welton, 1994, Schench, S. E. Palmer, and J. E. Zumberge, 1988, Application Carbon isotopic composition of individual biomarkers in gil- of biological markers in the recognition of paleo-hypersaline sonites: Organic Geochemistry, v. 21, p. 673–683. environments, in A. J. Fleets, K. Kelts, and M. R. Talbot, eds., Sheng, G., J. Fu, S. C. Brassell, A. P. Gowar, G. Eglinton, J. S. S. Lacustrine petroleum source rocks: Geological Society Special Damste´, J. W. de Leeuw, and P. A. Schenk, 1987, Sulphur- Publication 40, p. 123–130. containing compounds in sulphur-rich crude oils from hyper- Tissot, B. P., and D. H. Welte, 1984, Petroleum formation and oc- saline lake sediments and their geochemical implications: Geo- currence: Berlin, Springer-Verlag, 699 p. chemistry, v. 6, p. 115–126. Trinidade, L. A. F., J. L. Dias, and M. R. Mello, 1995, Sedimento- Shi, J. Y., A. S. Mackenzie, R. Alexander, G. Eglinton, A. P. Gowar, logical and geochemical characterization of the Lagoa Feia For- G. Wolff, and J. R. Maxwell, 1982, A biological marker inves- mation, rift phase of the Campos basin, in B. J. Katz, ed., Pe- tigation of petroleums and shales from the Shengli oilfield, the troleum source rocks: Berlin, Springer-Verlag, p. 149–165. People’s Republic of China: Chemical Geology, v. 35, p. 1–31. Vandervoort, D. S., 1997, Stratigraphic response to saline lake-level Sinninghe Damste´, J. S., F. X. C. Heras, P. F. V. Bergen, and J. W. fluctuations and the origin of cyclic nonmarine evaporite de- de Leeuw, 1993, Characterization of Tertiary Catalan lacus- posits: the Pleistocene Blanca Lila Formation, northwest Ar- trine oil shales: discovery of extremely organic sulfur-rich type gentina: Geological Society of America Bulletin, v. 109, p. 210– I kerogens: Geochimica et Cosmochimica Acta, v. 57, p. 389– 224. 415. Van Houten, F. B., 1962, Cyclic lacustrine sedimentation and the Sinninghe Damste´, J. S., F. Kenig, M. P. Koopmans, J. Ko¨ster, S. origin of analcime-rich Upper Triassic Lockatong Formation, Schouten, J. M. Hayes, and J. W. de Leeuw, 1995, Evidence west-central New Jersey and adjacent Pennsylvania: American for gammacerane as an indicator of water column stratification: Journal of Science, v. 260, p. 561–576. Geochimica et Cosmochimica Acta, v. 59, p. 1895–1900. van Krevelen, D. W., 1961, Coal: typology-chemistry-physics- Sladen, C. P., 1994, Key elements during the search for hydrocarbons composition: Amsterdam, Elsevier, 514 p. in lake systems, in E. Gierlowski-Kordesch and K. Kelts, eds., Waples, D. W., 1980, Time and temperature in petroleum forma- Global geological record of lake basins: Cambridge, Cambridge tion: application of Lopatin’s method to petroleum exploration: University Press, p. 3–17. AAPG Bulletin, v. 64, p. 916–926. Smoot, J. P., 1983, Depositional subenvironments in an arid closed Wartes, M. A., T. J. Greene, and A. R. Carroll, 1998, Permian la- basin: the Wilkins Peak Member of the Green River Formation custrine paleogeography of the Junggar and Turpan-Hami ba- (Eocene), Wyoming, U.S.A: Sedimentology, v. 30, p. 801–827. sins, northwest China (abs.): AAPG Annual Convention Ex- Smoot, J. P., and P. E. Olsen, 1988, Massive mudstones in basin tended Abstracts, v. 2, p. A682. analysis and paleoclimatic interpretations, in W. Mannspeizer, Williams, H. H., M. Fowler, and R. T. Eubank, 1995, Characteristics ed., Triassic–Jurassic rifting, continental breakup, and the origin of selected Paleogene and Cretaceous lacustrine source basins of the Atlantic ocean and passive margins, part A: Amsterdam, of Southeast Asia, in J. J. Lambiase, ed., Hydrocarbon habitat Elsevier, p. 249–274. in rift basins: Geological Society Special Publication 80, p. 241– Snowdon, L. R., and T. G. Powell, 1982, Immature oil and conden- 282. sate: modification of hydrocarbon generation model for terres- Xue, L., and W. E. Galloway, 1993, Genetic sequence stratigraphic trial organic matter: AAPG Bulletin, v. 66, p. 775–788. framework, depositional style, and hydrocarbon occurrence of Stout, S. A, 1995, Resin-derived hydrocarbons in fresh and fossil the Upper Cretaceous QYN formations in the Songliao lacus- dammar resins and Miocene rocks and oils in the Mahakam trine basin, northeastern China: AAPG Bulletin, v. 77, p. 1792– Delta, Indonesia, in K. B. Anderson and J. C. Crelling, eds., 1808. Amber, resinite and fossil resins: Washington, D.C., American Yang, W., Y. Li, and R. Gao, 1985, Formation and evolution of non- Chemical Society, p. 43–75. marine petroleum in Songliao basin, China: AAPG Bulletin, Sullivan, R., 1985, Origin of lacustrine rocks of the Wilkins Peak v. 69, p. 1112–1122. Member, Wyoming: AAPG Bulletin, v. 69, p. 913–922.

Carroll and Bohacs 1053