International Journal of Coal Geology 152 (2015) 159–176

Contents lists available at ScienceDirect

International Journal of Coal Geology

j ourna l homepage: www.e lsev ie r .com/ locate / i j coa lgeo

Palynofacies and geochemical analysis of the Triassic YanchangFormation, Ordos Basin: Implications for hydrocarbon generationpotential and the paleoenvironment of continental source rocks

Mingzhen Zhang, Liming Ji ⁎, Yuandong Wu, Cong HeKey Laboratory of PetroleumResources, Gansu Province/Key Laboratory of PetroleumResources Research, Institute of Geology andGeophysics, Chinese Academy of Sciences, Lanzhou 730000, China

⁎ Corresponding author.E-mail addresses: zhangmzh08@lzb.ac.cn (M. Zhang),

http://dx.doi.org/10.1016/j.coal.2015.11.0050166-5162/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 15 May 2015Received in revised form 7 November 2015Accepted 10 November 2015Available online 11 November 2015

Keywords:PalynofaciesOrganic geochemistrypaleoenvironmentSource rock potentialYanchang FormationOrdos Basin

The petroliferous basins that have formed in China since the Mesozoic are characterized by non-marine organicmatter input, a characteristic that is significantly different from that of marine organic sources. The TriassicYanchang Formation in the Ordos Basin is a suite of typical intra-continental lacustrine sediments that comprisethe most important source rocks for the Triassic oil reservoirs. The Yanchang Formation is divided into ten sub-sections from top to bottom (Chan 1 to Chan 10). Three borehole successions in the southern Ordos Basin (locat-ed in the Huachi, Zhidan and Yichuan areas) cross the Chan 4+ 5 to Chan 10 subsections and have been studiedusing thepalynofaciesmethod combinedwith organic geochemistry data. Palynofacies analysis indicates that thesediments are rich in amorphous organic matter (AOM) and phytoclasts. The AOM content in all of the samplespositively correlated with the hydrogen index (HI). In contrast, the transparent ligno-cellulosic fragments(TLF)+ opaque particles (OP) content are negatively correlatedwith theHI values. Additionally, the gelified par-ticles (GP) content has no linear correlationwith the geochemistry data. Basedon thequantitative composition ofthe particulate organic matter, three palynofacies types are identified, reflecting depositional settings in a distaldysoxic–anoxic deep basin, a shelf-to-basin transition zone and a proximal suboxic shelf. The palynofacies, totalorganic carbon (TOC), and Rock-Eval data together indicate that type I and II kerogen are abundant in the D48and W22 wells in the Zhidan and Yichuan areas, respectively. These kerogen types are uncommon in the L94well in the Huachi area, which suggests low hydrocarbon generation potential. In detail, the Chan 7 and Chan9 subsections of the three wells contain abundant type I and II kerogen, indicating that these layers are likelythe two primary source rocks in the southern Ordos Basin.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

The term palynofacies was defined by Powell et al. (1990) as a dis-tinctive assemblage of specific HCl- and HF-insoluble organic matter(“palynoclasts”) whose composition reflects a specific sedimentary en-vironment. This differs from the organic facies, defined as a body of sed-iment containing a distinctive assemblage of organic constituents,which can either be recognized by microscopy, or is associated with acharacteristic bulk organic geochemical composition (Tyson, 1995).Thus, the use of the palynofacies method on the organic matter compo-sition represents only a specific aspect of organic facies research. The ad-vantage of palynofacies research is that it can quantify the various typesof particulate organic matter within a source rock using transmittedlight microscopy, which was described by Tyson (1995) and is widelyapplied, including in recent work (e.g. Roncaglia and Kuijpers, 2006;Ghasemi-Nejad et al., 2009; Graz et al., 2010; Garcia et al., 2011). ThisHCl- and HF-insoluble organic matter (spores, pollen grains, algae,

jilimin@lzb.ac.cn (L. Ji).

acritarchs, chitinozoa, foraminiferal linings, and fragments of differentplant tissues) depends on primary productivity, depositional processesand biochemical degradation (Tyson, 1995; Ercegovac and Kostić,2006). Thus, it can be used with sedimentological evidence to identifythe depositional environment, such as proximal–distal changes, thetime of maximal marine or terrestrial influx to a depositional area, theoxidation–reduction environment or variations in the water depth(Tyson, 1993; Tyson and Follows, 2000; Zobaa et al., 2011; Muelleret al., 2014). Consequently, the petroleum potential of a sedimentarysuccession can also be successfully identified from the palynofaciestype (e.g. Schiøler et al., 2010; El Atfy et al., 2014). In fact, palynofaciesstudies have been widely used to interpret paleoenvironments and toevaluate source rocks in marine sediments (Carvalho et al., 2013; ElAtfy et al., 2014 and others) but have been rarely used to examine per-formed on continental source rocks.

The Ordos Basin is a large intracontinental sedimentary basin inChinawith an area of approximately 37× 104 km2. The crude oil reservein the Mesozoic reservoirs was estimated to be approximately 10 × 108

metric tons. The basin is considered to be a typical model of a non-marine oil generating sedimentary basin because the crude oils were

160 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

mainly derived from the non-marine source rocks of the YanchangFormation (Duan, 2012; Wang et al., 1995). The molecular and isotopicorganic geochemical data suggest that the oils were generated from asource with mixed terrigenous and algal–bacterial organic matter(Wang et al., 1995; Duan, 2012). The important discovery ofleiosphaerid acritarchs (Leiosphaeridia) and oleaginous Botryococcus inthe Yanchang Formation by Ji et al. (2008, 2010) first demonstratedthe type and character of the algae sources. Although palynofacies arean important parameter for paleoenvironment reconstruction and theevaluation of hydrocarbon generation, few studies have focused onthe palynofacies of the source rocks in the Yanchang Formation.

In recent years, several major oilfields, such as the Xifeng, Huaqingand Jiyuan oilfields, have been discovered, which confirms significanthydrocarbon generation in the Yanchang Formation. The sedimentarysequence exhibits a cyclic pattern formed by alternating lake levels,which led to varying qualities of the different source rock layers in theYanchang Formation. The different water depths, sources and deposi-tional rates in the lake resulted from varying tectonic conditions duringthe same depositional interval, leading the deposition of differentsource rocks in the various regions of the Ordos Basin (Li et al., 2012).Most studies have focused on reservoir researchwith respect to produc-tion units in the oilfields and the difficulties in obtaining drill coremate-rials. There are few studies that involve comparisons of the source rocksin the Yanchang Formation.

In this study, palynofacies, Rock-Eval and total organic carbon (TOC)analyses are performed on source rock samples from the Yanchang For-mation from three wells in different areas of the southern Ordos Basin.The objective of this research is to 1) interpret the composition andcharacteristics of the terrestrially derived organic matter, 2) interpret

Fig. 1. A) The location of the research area and the tectonic units of the Ordos Ba

the depositional environment of the sediments using the palynofacies,and 3) distinguish the hydrocarbon generation potential for various oilsubsections in the three areas and determine the primary hydrocarbonsource rocks.

2. Geological setting

The Ordos Basin, which contains abundant petroleum resources, is asuperimposed multicycle cratonic basin located on the stable NorthernChina Platform. This basin experienced two main developments, Paleo-zoicmarine deposition andMesozoic continental deposition. Depositionin the basin was controlled by paleotopography, which can be dividedinto the Yishan slope, where the studied wells are located; the Yimenguplift zone; the Weibei uplift zone; the Jinxi flexural fold zone; theXiyuan obduction zone; and the Tianhuan depression (Fig. 1A). Thestrata of the Yishan slope have a gentle western tilt with an angle of ap-proximately 1°. This area is presently amajor area of petroleumproduc-tion in the Ordos Basin. The Ordos Basin was filled by Paleozoic toCenozoic sediments. The source rocks were mainly formed in the latePaleozoic and early to mid-Mesozoic (Fig. 1B). The Late Paleozoic stra-tigraphy includes the Carboniferous Jingyuan and Yanghugou Forma-tions and the Permian Taiyuan, Shanxi, Xiashihezi, Shangshihezi andQianfengshan Formations. The Carboniferous deposits are composedof limestone, sandstone and dark mudstone with several coal beds.The Permian succession is mainly composed of sandstone, mudstoneand limestone. Although the Late Paleozoic source rocks have a highTOC (2.0–3.0%), their high maturity means that they are primarily gassource rock. The main oil-bearing sequences in the Ordos Basin arethe Upper Triassic Yanchang Formation and the Lower Jurassic Yanan

sin; B) the generalized stratigraphic column of late Paleozoic and Mesozoic.

161M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

Formation. The Yanchang is the most important due to its cumulative25–35-m of dark graymudstone, with a TOC of 2.0–15.0%. A thick, strat-ified, fine-grained sandstone is the main reservoir in the target zone ofthe Mesozoic oil province. Thus, the Yanchang Formation providesboth the primary source rocks and important oil and gas reservoirs inthe Ordos Basin. Based on lithology, the formation can be upwardly di-vided into five members (Y1 to Y5) and mainly consists of lacustrine,deltaic and fluvial deposits. Ten oil subsections (Chan 1 to Chan 10)are distinguished based on index beds (tuffs, dark mudstones, carbona-ceous mudstones and coal seams), conductance data, and oil bearingcharacteristics from the top to bottom. Due to the controls of the region-al geological structure, the thickness, organicmatter content and type ofeach gas- or oil-bearing subsection differ between various oilfields. Thisvariation is themain reason for the difficulty associatedwith finding thetarget oil horizon in hydrocarbon exploration.

The southern Ordos Basin is the main hydrocarbon-bearing area(Fig. 1), and currently features many large oilfields, such as the Jiyuan,Yanan and Xifeng oilfields, among others. The burial depth of the sourcerocks is usually between 1000- and 2000-m, with a maximum burialphase in the late Mesozoic (Early Cretaceous) that led to the mainstage of hydrocarbon expulsion (Ren et al., 2007). The source rocks of

Fig. 2. Lithostratigraphic correlation of the Triassic Yanchang

the Yanchang Formation have generally entered the oil threshold at amature stage (near Ro = 1.0%) (Ren et al., 2007). The total thicknessof the Yanchang Formation is approximately 500–1500 m, and individ-ual shale layers reaches 30 m in thickness.

3. Materials and methods

3.1. Materials

There were 134 samples that were studied from the L94, D48 andW22 wells, which crossed the Chan 4 + 5 to Chan 10 subsections ofthe Yanchang Formation (Fig. 2). All of the samples were examinedfor microscopic palynofacies, TOC and Rock-Eval pyrolysis analyseswere performed on all of the samples.

The threewells are located in the east, middle andwest of the south-ern Ordos Basin, spanning a distance of 200 km. The L94well was drilledin theHuachi area, which belongs to the Jiyuan oilfield and is situated inthe southwestern Yishan slope. A total of 58 samples were collectedfrom the Chan 4 + 5 to Chan 9 subsections of the drillcore (Fig. 2).The D48well is located in the Zhidan area in the central southern Yishanslope. A total of 53 samples were collected from the Chan 6 to Chan 9

Formation in the studied wells in the Ordos Basin, China.

162 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

163M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

subsections of the well (Fig. 2). The W22 well is located in the Yichuanarea in the southeastern Yishan slope. A total of 22 samples were col-lected from the Chan 7, Chan 9 and Chan 10 subsections of the well(Fig. 2).

3.2. Method

3.2.1. PalynofaciesThese samples were processed for palynofacies analysis that follow-

ed the general procedures by Tyson (1995). Samples of approximately10–30 g of sediments were treated with 10% HCl and 70% HF to removethe carbonates and silica. Then, the samples were cleaned to neutral byfiltered water treatment. Palyno-residues were sieved using 10 μmmesh nylon sieves. Finally, the kerogen residues were mounted onslides using glycerin jelly. In this study, the procedures of oxidativeand heavy liquid separation were not applied. More than 200 organicmatter particulates were determined in each sample to obtain statisti-cally significant organic matter content and diversity. The minimumsizes of the amorphous organic matter (AOM) and phytoclast particleswere 4 μm. The phytoclast size parameter was obtained by countingthe macroaxis size of at least 100 pieces of phytoclast debris in eachsample. All of the samples were studied using a Zeiss AXO 40 micro-scopewith a transmitted lightmode at Key Laboratory of PetroleumRe-sources Research, Institute of Geology and Geophysics, China.

3.2.2. Organic geochemistryAll of the palynofacies sampleswere processed for organic geochem-

istry at the Key Laboratory of PetroleumResources Research in Lanzhou,China. The TOC and Rock-Eval pyrolysis measurements were preparedby crushing the samples to approximately 0.15 mm. Approximately1–2 g of each sample was prepared for TOC analysis using a LECO CS-344 apparatus. For all of the samples, the Rock-Eval pyrolysis analysiswas conducted using a Rock-Eval 16 instrument. Several important pa-rameters were provided by the Rock-Eval pyrolysis, including S1, S2, S3and Tmax (°C). S1 represents the amount of free hydrocarbon (mg HC/grock) volatilized out of the rock at 300 °C, S2 represents the amount ofhydrocarbon (mg HC/g rock) under temperature-programmed pyroly-sis (300–600 °C), and S3 represents the amount of released CO2 at tem-peratures of 300 to 390 °C. Tmax (°C) represents the temperature at thetime of the S2 peak during the pyrolysis process. The hydrogen index(HI = (S2 / TOC) × 100, mg HC/g TOC) and oxygen index (OI = (S3 /TOC) × 100, mg CO2/g TOC) are both deduced parameters. The hydro-gen index indicates the potential to generate petroleum, and the oxygenindex is related to the amount of oxygen in the kerogen (Peters andCassa, 1994).

4. Results

4.1. Characteristics of the dispersed organic matter

In the present study, the particulate organicmatter is all of continen-tal origin, which is obviously different from marine deposits. The algaeand phytoplankton-derived organic matter are relatively scarce. Addi-tionally, some commonmarine algae are missing, which is a prominentmark of non-marine sediment. The palynofacies components in thisstudy are broadly classified as AOM, phytoclasts and palynomorphs,for quantitative analysis. The detailed classified methods and criterionscan be referred to previous research (e.g. Tyson, 1993; Ercegovac andKostić, 2006; Ţabără et al., 2015).

The AOM components are common and represent an important or-ganic matter type in the Yanchang Formation in this study. Based on

Plate I. (Scale bar: 40 μm) Representative photomicrographs of the palynological organicmattehighly fluorescent bisaccate pollen (Protopinus sp.); 2. trilete spore (Asseretospora gyrata); 2a. hLeiosphaerida; 4. isolated coenobium of Botryococcus; 4a. highly fluorescent coenobium of Botryligno-cellulosic fragments (TLF) with structured tracheid; 7. opaque particles.

the shape, color and fluorescence, the AOM can be classified into granu-lar or gelified forms. The granular form ismainly yellow to brown undernatural light and exhibits irregular aggregated shapes formed by fibrousand ultramicro scopic organic particles (b3 μm) (Wang et al., 1993; Xiaoet al., 1997) (Plate II, 2 and 3). Weak or no fluorescence under a bluelight could be due to bacterial degradation (Ţabără et al., 2015). The ag-gregated forms sometimes contain framboidal pyrite and small-sizedphytoclasts (Plate II, 3). These organic matter types are likely derivedfrom phytoplankton, freshwater algae and bacteria that accumulatedin environments of O2-depleted water (Pacton et al., 2011; Ţabărăet al., 2015). The second common type is the gelified AOM, which is or-ange to brown and sometimes contains internal structures (Plate II, 1).Its fluorescence is relatively weak (Plate II, 1a) but is stronger thanthat of the first type. The gelified AOMappeared to form clumpymasseswith angular sharp shapes. The fuzzy fibrousmargins differ significantlyfrom the central parts, which still retain the original texture of a lightyellow smooth surface. This AOM type is usually associated withmicro-bial reworking of terrestrial fragments (Pacton et al., 2011; Ţabără et al.,2015).

Phytoclasts are plant-derived fragments, including cuticles, cortextissues, woody tissues and charcoal (Ercegovac and Kostić, 2006). Thisgroup is the dominant composition for most of the source rock samples.Cuticles are generally translucent yellow to light yellowunder transmit-ted natural light and show typical fluorescence (Plate I, 5 and 5a). Thewell-preserved parts of this component still retain the surface cellularstructure (Plate I, 5a). Cortex tissues are rare and are usually difficultto identify because they do not have obvious characteristics and arevery similar to woody tissues following thermal degradation anddiagenesis. Charcoal has distinct morphological and optical featuresand is easily distinguished. To effectively distinguish the compositionsof the phytoclast group, we decided to categorize them according totheir morphological characteristics under the transmission microscope.In this study, the cortex tissues, woody tissues and charcoal componentsare separated into three categories: 1) transparent ligno-cellulosic frag-ments (TLF), 2) opaque particles (OP) and 3) gelified particles (GP).

The TLF are characterized by typical cellular structures of wood (sec-ondary xylem) and the gray, light-brown, or black color of the lignin.The lack of fluorescence, high translucency, and low lignification are im-portant characteristics of the TLF. This category of grains is common inthe palynodebris of the studied samples. The opaque particles (OP)have no visible structure and often appear to be mostly homogeneous,highly corroded opaque fragmentswith elongated shapes and sharp an-gular outlines. These components are included in the inertinitic maceralgroup (mostly fusinite and inertinite).

The GP group has recently been proposed in several research studies(Sebag et al., 2006; Graz et al., 2010; Ţabără et al., 2015). These studiesfocused more attention on the environmental and climate in formationof the deposits, whereas few studies have focused on the organic originof these common phytoclasts. In this study, a portion of the GP hasweak-to-moderate fluorescence intensity under blue transmitted light(Plate II, 4 and 4a). To explore the plant sources of these constituents,we specifically study the leaf organs of coniferous plants, which repre-sented the dominant vegetation in the Mesozoic. In addition, thepalynoflora of the Yanchang Formation are also dominated by thebisaccate pollen produced by the conifers (Ji and Meng, 2006). Thus,we gathered many Lower Cretaceous conifer leaf fossils from theJiuquan Basin. Their detailed shape features and plant nomenclaturewere studied by Du et al. (2013). The fossil debris was processed bythe same experimental methods as in the palynofacies research. Basedon the comparability of the surface gloss and color between the GPand the leaf cuticles, the shape and color of the leaf fossils are very

r from the studiedwells in the Ordos Basin. 1. Isolated bisaccate pollen (Protopinus sp.); 1a.ighly fluorescent Trilete spore (A. gyrata); 3. isolated Leiosphaerida; 3a. highly fluorescentococcus; 5. dispersed leaf cuticle phytoclast; 5a. a highly fluorescent cuticle; 6. transparent

164 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

165M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

similar to those of theGP under themicroscope using transmittedwhitelight (Plate II, 5). These leaf fossils also have strong fluorescence underblue light (Plate II, 5a). The fluorescent intensity of the leaf fossils is ob-viously higher than that of the GP, which probably results from thehigher biodegradation and stronger weathering of small GP debristhan the large leaf fossils that have been well preserved. However, theestimated leaf-derived sources also ensure that there is sufficient bio-mass material. For this reason, the GP are very common in palynofaciesassociations. Thus, these similar characteristics probably indicate thatthe GP are mainly derived from the leaf organs of plants. The cuticleson the surface are the main cause of the fluorescence excitation forthese leaf fossils and the GP.

Palynomorphs are observed in minor amounts and are dominatedmainly by bisaccate pollen, Monocolpate gingko pollen and triletespores (Plate I, 1, 1a and 2, 2a). Algae are very rare and includeonly Botryococcus and Leiosphaeridia, which have strong fluorescence(Plate I, 3, 3a and 4, 4a).

4.2. Palynofacies assemblages

Based on the quantitative data on the particulate organic matterobtained from the analyzed samples, three palynofacies types havebeen defined.

AOM dominates the palynofacies-I group (PF-I: AOM), whichfeatures a sub-dominance of phytoclast organic matter (Plate III, 2).The phytoclasts are mainly composed of TLF and OP. Cuticles,palynomorphs, and algae are very rare. The average size of thephytoclasts is approximately 15 μm larger than that of the otherpalynofacies types. The color of the organic matter appears to be brown-ish yellow and dark brown. This palynofacies type can also be dividedinto two types. The first type is characterized by a higher AOM content(N60%), which mainly occurs in the Chan 7 and Chan 9 subsectionsof the D48 and W22 wells. The second type has relatively low AOM(40–60%) compared with that of the first type. In comparison, the TLFandOP contents are relatively high. This type is scattered among the var-ious layers of the studied succession.

The palynofacies-II group (PF-II: gelified phytoclasts and AOM) isdominated by yellow AOM and GP (Plate III, 2). The obvious feature ofthis facies is the highGP content. TheGP usually have a large size and fea-ture a yellow color under natural light andmoderate yellowfluorescenceunder blue light. The color of all of the organic matter for this type is yel-low,which is usually lighter than that of the other palynofacies types. Cu-ticles and palynomorphs/algae are also common constituents and aremarkedly obviously more prevalent than in the other types. The meanphytoclast size is approximately 25 μm, which is obviously larger thanthat in PF-I. This palynofacies type is common in the L94 well samplesand occurs occasionally in the Chan 4 + 5 subsections of the D48 well.

The palynofacies-III group (PF-III: phytoclasts) is characterized by ahigh phytoclast content with good preservation (Plate III, 2). TLF andOP are the main types of phytoclasts. Cuticles are rare in the organicmatter. Themean size of the phytoclasts has a large range, from approx-imately 15 to 25 μm. Palynomorphs are relatively common and usuallyhavewell-formed shapes under good preservation conditions. The colorof this type has a large range, from brownish yellow to dark brown. Thistype dominates the large samples of the L94 well sequence, is moder-ately common in the Chan 4 to Chan 6 subsections of the D48 well,and are very rare in the Chan 7 and Chan 9 subsections of the D48 andW22 wells.

Plate II. (Scale bar: 40 μm) 1. Under natural light, yellowish brown gelified AOM; 1a. idem prevbrown granular AOMwith a diffuse edge; 3. brown granular AOM that contains framboidal pyrimage (blue-light fluorescence), GP exhibits weak fluorescence; 5. under natural light, yellowishrescence), leaf fossil debris exhibits strong fluorescence.

4.3. TOC and Rock-Eval pyrolysis data

The TOC represents insoluble kerogen and soluble bitumen, whichare the common parameters used to express organic matter quantity.In general, the TOC values of the Chan 4 + 5 to Chan 10 subsections ofthe L94 well vary from 0.47 to 3.29 wt.% (excluding the outlier fromChan 9 at 1975.5 m) with a mean of 1.07 wt.% (Table 1). The Chan 6 toChan 9 subsections in the D48 well have relatively higher TOC valuesthat range from 0.29 to 8.21 wt.%, with an average of 2.58 wt.%(Table 1). In theW22well samples, the Chan 7, Chan9 and Chan 10 sub-sections feature much higher values between 0.21 and 15.6 wt.%, withan average of 2.6 wt.% (Table 1).

The Rock-Eval pyrolysis values for S1, S2 and S3 and the derived pa-rameters HI and OI are important criteria for determining petroleumgeneration potential. The detailed results are shown in Table 1. The S1,S2, HI and OI values are presented and discussed in detail with respectto the hydrocarbon generation potential and the associated palynofaciescomponents in the sections below.

5. Discussion

5.1. Kerogen characteristics

5.1.1. Thermal maturityThe term maturation refers to the extent of the temperature- and

time-dependent reactions involved in hydrocarbon generation (Petersand Cassa, 1994). These reactions significantly affect the color, shapeand formof the organicmatter. In this study, the degree of thermalmat-uration is mainly evaluated using the Rock-Eval Tmax data and the sporecolor index (SCI).

The correlation between HI and Tmax is a useful tool for determiningthe organicmattermaturation (Fig. 3). The Tmax readings of the samplesfrom the three wells range between 429 and 476 °C and mostly clustertogether at 460 °C. The HI values vary from 50 to 300 mg HC/g rock.These results indicate mature to over-mature stages (after Peters,1986) for the majority of the Yanchang source rock. The Tmax valuesalso show a slight increasing trend with depth in the three wells(Table 1, Fig. 4). The burial depth is likely a major factor in the thermalevolution of the organicmatter of the Yanchang Formation. The SCI is anopticalmethod for evaluating thematuration degree of the organicmat-ter (e.g. Marshall, 1991). In the studied samples, the colors of mainlysmooth-walled palynomorphs were correlated with previouslyestablished SCI standards (e.g. Pearson, 1984; Pross et al., 2007;Suárez-Ruiz et al., 2012). Most or nearly all of the examinedpalynomorphs have a yellowish brown color, which corresponds to anearly mature to mature stage. Comparatively, the L94 samples havelower Tmax values and lighter palynomorph colors than the samplesfrom the D48 andW22wells, indicating lower extents of thermal evolu-tion. The HI versus Tmax plots show that most of the samples in the esti-mated field have a Ro value of 1.0% (Fig. 3). In the D48 well, the Tmax

values have a relatively narrow range, from 445 to 470 °C (excludingthe outliers from the Chan 6 and Chan 8 subsections, 1233.8 m and1424.5 m, respectively), which is mostly higher than the range calculat-ed for the L94 well samples. The HI versus Tmax plots indicate a mainlymature stage for the source rock samples (Fig. 3). The W22 samplesshow a mature to highly mature stage, which is estimated by a highTmax and SCI standard values. The Tmax values of all the samples rangefrom 448 to 473 °C, which are higher than those of the L94 and D48well samples. Most of the samples were close to the 1.35% Ro field in

ious image (blue-light fluorescence), weak fluorescence exhibited by the gelified AOM; 2.ite (black arrow); 4. brown gelified phytoclast (GP) under natural light; 4a. idem previousbrown leaf fossil debris from Fig. 3 in this plate; 5a. idem previous image (blue-light fluo-

166 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

167M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

the HI versus Tmax plot. In summary, all the thermal maturity data indi-cate that the studied Yanchang Formation source rock samples have en-tered the mature to highly mature stage of hydrocarbon generation.

5.1.2. The hydrocarbon potential of the particulate organic matterThe composition and characteristics of the particulate organic mat-

ter are those of a hydrocarbon-generating material that could formthe basis of a source rock. The TOC and Rock-Eval parameters arewell-accepted traditional evaluation methods for determining the hy-drocarbon generation potential of a source rock. Thus, the hydrocarbongeneration potential and original material sources can be derived by thecorrelation between the above two factors. In this study, four main or-ganic matter groups (AOM, GP, TLF and OP) are chosen for correlationwith the TOC and Rock-Eval parameters.

The AOM is the main component, but it has a large range among thedifferent samples from the three wells. Fig. 5A–C shows that the AOMcontent is linearly associated with the HI, indicating that the AOM hasa high potential for hydrocarbon generation. The high AOM content re-flects the high quality of the source rock, which is an essential factor forthe hydrocarbon generation of kerogen. This trait can be estimatedusing the material sources and the preservation condition of the AOM.The granular AOMmost likely originates fromphytoplankton and fresh-water algae. Another important component is the gelified AOM, whichmost likely originated from the liptinite content of high plants(Ercegovac and Kostić, 2006; Pacton et al., 2011; Ţabără et al., 2015).The AOM is initially an organo–mineral association that is interpretedto be an early flocculation at or near the sediment–water interface(Tyson, 1995; Ercegovac and Kostić, 2006). AOM is widely accepted toform in anoxic environments (e.g. Tyson, 1995; Ercegovac and Kostić,2006). Anoxic environments are also favorable for the deposition ofhigh-quality source rocks.

The phytoclasts originated from the various tissues of terrestrialplants, and they have different hydrocarbon generation abilities. In gen-eral, the fluorescent cuticles have high hydrocarbon generation poten-tial, and they are classified as oil-prone kerogen types. However, thiscomponent usually comprises a minor portion of the total particulateorganic matter; thus, it cannot be the main source of the hydrocarbons.The GP, TLF and OP of phytoclasts are the main components of the totalparticulate organic matter. The xylogen-derived TLF and OP are bothlow hydrogen-containing components; therefore, they have low hydro-carbon generation potential. Thus, the two components are combinedinto a single group to study. The TLF +OP and HI show a good negativecorrelation (Fig. 5D–F), whereas the GP and HI show a relatively poorcorrelation comparedwith the TLF+OP compositions (Fig. 4G–I). A rel-atively good correlation of the first analysis result can be easily under-stood. Similar to the usual vitrinite component, TLF are classifiedaccording to the gas-prone kerogen types, which have low hydrocarbongeneration capabilities. The OP theoretically has no hydrogen content.These components are often present in proximal delta zones with oxicenvironments, which are not good for the preservation of sourcerocks. Although few studies have addressed the hydrocarbon genera-tion potential of GP compositions, the relatively higher fluorescence ofthese constituents indicate the existence of a certain amount of lipidswith hydrocarbon generation potential. However, this composition iscommon in various palynofacies assemblages and deposited in variousenvironments, from shallow to deep water. Thus, a poor correlation be-tween GP and HI is observed.

Plate III. (Scale bar: 40 μm) 1. PF-I: Abundant AOM (granular and gelified) with yellow color ingest a dysoxic–anoxic environment. This sample has high TOC andHI values, i.e., 2.21wt.% and 1type I (oil prone) (Chan 6 subsection of the Yanchang Formation, 1302.1 m of the D48 well). 2(GP). The depositional environment was mainly dysoxic. The sample has a high TOC conten(Chan 7 subsection of the Yanchang Formation, 1837.6 m of the L94 well). 3. PF-III: Abundant Twater oxic environment. The kerogen is likely type III (gas prone). This sample has low values fo1857.2 m of the L94 well).

The palynomorph/algae have a high capability for hydrocarbon gen-eration (e.g. Dutta et al., 2013) but contributed only a minor proportionto the total particulate organic matter. Thus, these components can notbe the major contribution for the total hydrocarbon content of thesource rock.

5.2. Paleoenvironmental reconstruction

The palynofacies represent the primary composition of the organicmatter in the sedimentary rock after the long process of sedimentationand organic diagenesis. The paleoenvironments control the organic mat-ter composition. The quantitative assemblages of particulate organicmatter exhibit an excellent capacity to record environmental evolutionunder different climatic and sedimentary settings (de Araujo Carvalhoet al., 2006; Sebag et al., 2006). Thus, the palynofacies analysis was ap-plied as one of the traditional parameters for paleoenvironmental inter-pretation (Buchardt and Nielsen, 1991). According to the principle thatthe relative abundances of different organic matter groups primarily re-flect oxygenation conditions, it is similarly suitable for considering thelake level changes and estimated distances from the lakeshore (Sebaget al., 2006).

The method for paleoenvironmental interpretation of theYanchang Formation is not the same as for traditional marine de-posits due to its continental depositional setting. The AOM-Phytoclasts-Palynomorphs ternary plot after Tyson (1993, 1995)has been widely applied to infer the depositional conditions andthe transportation pathways of the organic matter in a shallow seadepositional environment. In this study, we modify the classificationof organic matter for the ternary plot by Tyson (1993, 1995) to theAOM–TLF + OP–GP + Cuticles + Palynomorphs (AOM–TO–GCP)ternary plot. The TLF and OP are derived from the stem xylogen ofterrestrial plants, which have a large volume and are deposited inthe proximal shallow or high-energy aquatic environment. GP andcuticles likely originate from leaf organs, which can be easilytransported by the wind and water currents. This transport propertyis theoretically similar to that of the palynomorphs. Thus, in thisstudy, the GP and cuticles are classified into the palynomorph fieldin the ternary plot. In addition, the phytoclast size parameter is auseful indicator of the proximity to land or debris flows in deepwater settings (Tyson, 1995; Tyson and Follows, 2000), and this indi-cator is also employed in this study.

5.2.1. Palynofacies-I (PF-I: AOM): distal dysoxic–anoxic deep basinThe high percentage of AOM and low to intermediate percentage of

degraded phytoclasts characterize palynofacies-I (Fig. 6). AOM is gener-ally deposited in environments with high preservation rates and lowenergy (Tyson, 1993). Dysoxic conditions are associated with the pres-ervation of AOM,which correlateswith but is not necessarily dependentupon high primary productivity (Tyson, 1993). In general, deep andlow-energy aquatic environments result in anoxic deposits. Algal andaerobic microbe blooms increase the organic matter input, which is animportant source of granular AOM. Furthermore, algal blooms can resultin an anaerobic depositional environment (Liu and Wang, 2013). Theremarkable laminated structures in most of the source rock samplesare commonly associated with anoxic bottom conditions (Liu andWang, 2013). The samples of this type plot close to the AOM field inthe AOM–TO–GCP ternary diagram, which indicates a tendency toward

associationwith palynomorphs and phytoclasts. The color and abundance of the AOM sug-82mgHC/g rock, respectively, and the contained organicmatterwas identified as kerogen. PF-II: AOM with a yellow-to-sunny-yellow color in association with gelified phytoclastst and hydrocarbon index, with values of 1.93 wt.% and 137 mg HC/g rock, respectivelyLF, opaque phytoclasts and GP in the particulate organic matter, which suggests a shallowr TOC (0.87wt.%) andHI (62mgHC/g rock) (Chan 7 subsection of the Yanchang Formation,

Table 1The palynofacies, TOC and Rock-Eval pyrolysis data of the studied samples.

Well name Sample Depth(m)

Subsections Lithology AOM(%)

Phytoclasts (%) Palynomorphs(%)

Phytoclastsize (um)

TOC Rock-Eval pyrolysis

GP TLF OP Cuticle Tmax S1 S2 S3 HI OI

L94 L3 1630.4 Chan 4 + 5 Gray silty mudstone 8.5 35.9 15.9 15.4 23.4 1.0 23.6 0.49 454 0.09 0.37 0.11 75 22L94 L4 1635.5 Gray silty mudstone 41.0 15.2 7.6 24.3 12.0 0.0 18.4 0.54 456 0.1 0.36 0.18 66 33L94 L5 1649.3 Dark gray silty mudstone 5.0 24.1 18.2 32.6 18.5 1.5 24.8 0.48 453 0.09 0.32 0.17 66 35L94 L6 1651.2 Gray silty mudstone 1.0 60.7 9.1 16.1 13.0 0.0 24.8 0.61 455 0.11 0.37 0.1 60 16L94 L7 1707.6 Chan 6 Dark gray silty mudstone 29.8 17.9 8.6 34.5 9.2 0.0 18.4 0.47 455 0.14 0.36 0.16 76 34L94 L8 1708.8 Dark gray mudstone 75.2 2.0 5.6 15.7 1.5 0.0 13.6 0.67 455 0.26 0.62 0.15 92 22L94 L9 1720.5 Dark gray silty mudstone 15.0 38.6 13.9 27.1 5.4 0.0 20 0.63 459 0.19 0.41 0.13 65 21L94 L10 1727.5 Dark gray mudstone 81.8 1.5 1.5 13.9 1.2 0.0 12.4 0.82 450 0.43 1.15 0.16 140 20D48 D3 1233.8 Dark gray mudstone 27.3 14.5 21.3 24.2 1.0 11.7 13.6 0.64 507 0.02 0.13 0.06 20 9D48 D4 1235.4 Black carbon mudstone 35.7 29.8 9.3 8.4 11.1 5.7 20.4 1.9 447 0.53 6 0.1 315 5D48 D5 1249.8 Dark gray mudstone 19.8 1.9 32.7 37.5 0.3 7.8 20.8 0.39 468 0.08 0.1 0.12 25 30L94 L11 1758 Gray mudstone 46.4 19.1 15.2 17.5 0.7 1.0 21.6 0.65 458 0.15 0.51 0.17 78 26L94 L12 1762.6 Dark gray silty mudstone 4.5 30.0 17.0 19.6 27.0 2.0 22.4 2.78 451 0.78 5.28 0.24 189 9L94 L13 1771.3 Dark gray mudstone 4.1 25.8 25.8 19.2 24.3 0.9 22.4 0.64 457 0.13 0.38 0.08 59 13L94 L14 1775.1 Dark gray silty mudstone 51.2 14.2 11.3 19.6 2.3 1.4 18.4 2.13 446 0.41 4.06 0.11 190 5D48 D7 1277.8 Dark gray mudstone 9.4 13.7 34.1 24.6 1.8 16.4 16.4 0.96 457 0.2 0.89 / 92 /D48 D8 1278.7 Dark gray mudstone 34.4 3.9 21.1 24.3 2.1 14.1 20.4 0.59 457 0.14 0.37 0.08 62 13D48 D9 1302.1 Black mudstone 50.1 16.9 15.7 3.4 0.7 13.1 14.4 2.21 445 0.61 4.03 0.24 182 10D48 D10 1317.8 Black silty mudstone 42.5 24.6 20.2 2.3 0.2 10.2 16.8 1.58 451 1.3 3.24 0.1 205 6D48 D11 1319 Dark gray silty mudstone 3.6 20.1 29.6 32.1 1.4 13.2 18.4 0.36 461 0.14 0.02 / 55 /L94 L15 1777.9 Chan 7 Dark gray mudstone 40.7 19.1 11.1 28.1 1.0 0.0 17.6 0.6 459 0.11 0.37 0.18 61 30L94 L16 1780.2 Dark gray mudstone 6.1 30.6 20.1 22.6 17.9 2.7 25.2 0.59 456 0.11 0.31 0.14 52 23L94 L17 1783.8 Dark gray mudstone 45.2 31.4 2.9 6.8 12.8 1.0 21.6 1.71 448 0.33 2.79 0.12 163 7L94 L18 1787.3 Dark gray mudstone 2.9 31.7 15.8 36.8 10.4 2.4 27.2 1.03 452 0.2 0.88 0.16 85 15L94 L19 1793.3 Dark gray mudstone 2.0 30.4 21.8 36.9 8.9 0.0 19.6 0.5 461 0.07 0.18 0.14 36 28L94 L20 1794.3 Dark gray mudstone 26.0 8.9 16.4 37.3 10.0 1.4 16.4 0.45 462 0.1 0.2 0.12 44 26L94 L21 1797 Gray mudstone 30.6 11.4 14.9 36.7 6.4 0.0 20.4 0.59 463 0.13 0.3 0.19 50 32L94 L22 1800 Gray silty mudstone 6.1 35.9 9.8 25.1 21.4 1.6 20.8 0.49 459 0.1 0.24 0.19 48 38L94 L23 1802 Dark gray mudstone 14.2 10.5 21.0 44.6 9.7 0.0 18.8 0.61 454 0.13 0.36 0.18 59 29L94 L24 1802.9 Dark gray silty mudstone 63.3 11.8 4.9 17.8 1.3 0.9 18.4 3.29 447 0.75 7.42 0.34 225 10L94 L25 1804 Dark gray mudstone 2.4 29.1 18.1 31.8 15.4 3.2 23.2 1.18 454 0.18 0.91 0.33 77 27L94 L26 1805 Gray silty mudstone 1.0 32.9 26.7 26.2 11.8 1.4 22.8 0.63 456 0.12 0.35 0.32 55 50L94 L27 1811.8 Dark gray silty mudstone 1.0 38.3 9.2 24.4 25.1 2.0 24.4 0.85 453 0.21 0.82 0.23 96 27L94 L28 1813.5 Dark gray silty mudstone 16.6 38.9 9.3 24.4 10.8 0.0 24.8 0.89 456 0.22 0.67 0.16 75 17L94 L29 1820.7 Dark gray mudstone 65.2 4.5 8.1 12.6 8.7 0.8 20 1.92 439 0.28 2.02 0.14 105 7L94 L30 1823.5 Dark gray mudstone 2.0 35.1 18.3 23.5 21.1 0.0 26.8 1.05 451 0.22 0.89 0.29 84 27L94 L31 1825.9 Gray silty mudstone 13.0 28.1 10.1 38.1 10.7 0.0 22.8 0.48 458 0.1 0.26 0.28 54 58L94 L32 1827.4 Gray silty mudstone 3.0 40.7 16.3 18.1 20.4 1.5 26 0.63 454 0.13 0.39 0.21 61 33L94 L33 1829.7 Gray silty mudstone 1.0 40.7 27.2 13.4 16.7 1.0 27.2 1.18 450 0.22 1.64 0.25 138 21L94 L34 1831.9 Dark gray silty mudstone 75.0 6.4 3.7 12.4 2.5 0.0 20.4 0.55 455 0.12 0.35 0.24 63 43L94 L35 1837.6 Gray silty mudstone 17.4 35.2 11.7 21.5 13.5 0.8 22.8 1.93 448 0.41 2.65 0.35 137 18L94 L36 1839.5 Gray silty mudstone 6.0 25.7 36.3 20.0 9.1 2.9 24.8 1.13 453 0.23 1.04 0.06 92 5L94 L37 1841.6 Gray silty mudstone 49.0 10.9 17.3 13.4 8.3 1.1 20 1.46 458 0.22 1.31 0.32 89 21L94 L38 1844.1 Gray silty mudstone 65.0 8.1 8.8 14.4 3.1 0.6 19.6 1.77 451 0.49 2.2 0.11 124 6L94 L39 1845.8 Dark gray silty mudstone 24.7 13.2 32.4 21.6 7.0 1.1 22.4 1.17 455 0.41 0.99 0.04 84 3L94 L40 1846.5 Dark gray muddy siltstone 73.1 2.6 7.6 4.4 10.7 1.5 25.2 2.76 447 0.97 2.89 0.22 140 7D48 D12 1373.3 Black carbon mudstone 72.3 1.4 4.3 16.4 1.5 4.2 15.6 5.18 451 3.15 11.6 0.28 224 5D48 D13 1374.5 Black shale 78.4 0.5 1.6 14.0 0.3 5.1 16 3.01 459 2.25 6.2 0.19 205 6D48 D14 1375.2 Dark gray mudstone 84.0 0.0 1.5 12.4 0.0 2.1 17.2 3.83 449 2.46 7.8 0.47 203 12D48 D15 1376.5 Black carbon mudstone 87.0 0.3 1.2 10.4 0.0 1.2 15.6 4.86 453 2.76 9.6 0.3 197 6D48 D16 1377.3 Black carbon mudstone 76.4 3.1 8.7 7.7 0.9 3.2 16.8 3.42 458 0.99 6.28 0.22 183 6D48 D17 1378.1 Dark gray silty mudstone 38.6 0.6 13.7 45.0 1.0 1.0 12.4 0.48 451 3.38 0.71 0.29 147 60D48 D18 1379.1 Dark gray mudstone 17.2 30.7 20.2 19.4 0.3 12.2 12.8 0.31 470 0.1 0.16 0.15 51 48L94 L41 1853.5 Gray silty mudstone 6.5 28.7 43.4 13.3 6.2 1.9 26 1.17 456 0.22 0.93 0.18 79 15

168M.Zhang

etal./InternationalJournalofCoalGeology

152(2015)

159–176

L94 L42 1855.5 Gray silty mudstone 15.0 25.4 36.4 9.0 11.9 2.3 24.8 1.42 455 0.23 1.18 0.17 83 11L94 L43 1857.2 Gray silty mudstone 1.0 28.5 34.9 12.4 23.2 0.0 27.2 0.87 458 0.19 0.54 0.2 62 22L94 L44 1860.1 Dark gray silty mudstone 70.4 3.5 12.9 8.8 4.2 0.0 20.8 0.82 467 0.24 0.4 0.8 48 97D48 D19 1380.2 Dark gray mudstone 28.6 4.9 9.1 40.1 1.0 16.3 14 2.04 460 0.76 3.52 0.1 172 4D48 D20 1380.8 Black mudstone 54.2 5.2 20.9 14.6 0.3 4.6 13.2 1.88 456 0.97 2.71 0.08 144 4D48 D21 1381.6 Dark gray mudstone 7.4 51.7 27.4 6.3 1.1 6.2 13.6 0.29 465 0.08 0.09 / 31 /W22 W1 299.3 Dark gray shale 76.1 1.0 3.0 16.0 3.4 0.5 14 2.58 460 0.88 4.44 0.19 172 7W22 W2 300.2 Dark gray shale 76.7 0.5 3.6 16.4 2.4 0.5 12.8 3.3 457 1.52 5.92 0.22 179 6W22 W3 303 Dark gray shale 74.3 0.0 2.6 18.0 5.1 0.0 11.2 3.32 457 1.79 5.76 0.47 173 14W22 W4 304 Dark gray shale 81.3 0.0 1.9 15.5 1.3 0.0 10.4 3.54 457 1.68 6.12 0.39 172 11W22 W5 322.3 Dark gray mudstone 69.2 4.0 7.9 6.3 10.0 2.7 19.2 1.71 462 0.42 2.2 0.27 128 15L94 L46 1901.6 Chan 8 Dark gray silty mudstone 5.6 20.9 19.0 36.8 16.0 1.8 24.4 0.71 469 0.12 0.29 0.3 40 42L94 L47 1915 Dark gray silty mudstone 9.0 16.7 13.8 50.3 10.2 0.0 23.2 0.79 469 0.11 0.3 0.14 37 17L94 L48 1916 Black silty mudstone 4.9 25.1 11.6 52.7 4.8 0.9 22.8 0.69 473 0.11 0.22 0.1 31 14D48 D22 1424.5 Dark gray silty mudstone 73.3 0.2 6.0 17.2 0.0 3.2 14.4 0.83 437 0.94 1.38 0.05 166 6D48 D23 1425.4 Dark gray silty mudstone 40.2 8.0 15.0 22.2 0.5 14.1 12.4 2.73 460 0.94 4.09 0.02 149 1D48 D24 1426.3 Dark gray mudstone 64.9 3.2 13.0 9.0 1.1 8.8 15.2 2.55 461 1.03 4.07 0.03 159 1D48 D25 1427.2 Dark gray mudstone 62.1 3.2 8.2 17.1 0.0 9.4 16.8 1.47 453 0.58 2.35 0.03 159 2D48 D26 1428.1 Gray silty mudstone 7.6 9.1 29.8 38.1 0.3 15.1 18.4 0.31 450 0.45 0.26 0.02 83 6D48 D27 1429.2 Gray silty mudstone 57.6 9.8 12.6 11.2 0.2 8.6 19.2 1.13 456 0.51 1.25 / 110 /D48 D28 1430.3 Dark gray silty mudstone 71.1 3.6 8.6 10.4 0.7 5.6 16.8 2.78 458 0.88 4.6 0.21 165 7D48 D29 1431.2 Dark gray silty mudstone 55.1 5.4 11.2 12.0 1.0 15.4 14 0.59 457 0.31 0.59 0.08 100 13D48 D30 1431.9 Dark gray mudstone 39.0 12.7 16.3 15.4 0.3 16.3 19.6 1.07 458 0.42 1.21 0.18 113 16D48 D31 1432.8 Dark gray silty mudstone 45.1 15.5 21.7 11.6 0.0 6.1 19.6 0.72 460 0.31 0.58 0.11 80 15L94 L49 1938.9 Dark gray mudstone 79.8 11.6 1.3 6.1 1.2 0.0 20 1 469 0.17 0.45 0.2 45 20L94 L50 1940.2 Dark gray silty mudstone 71.7 16.4 1.0 8.6 2.3 0.0 21.2 2.95 455 0.6 3.67 0.21 124 7D48 D32 1477.2 Gray silty mudstone 13.2 12.0 43.2 14.3 0.0 17.3 20.4 0.34 469 0.12 0.15 / 44 /D48 D33 1478.3 Dark gray silty mudstone 54.4 7.0 24.6 10.6 0.3 3.1 12.4 0.76 465 0.28 0.55 0.04 72 5D48 D34 1479.6 Dark gray mudstone 54.4 4.9 11.6 21.0 0.0 8.1 12.8 3.89 460 1.55 5.69 0.19 146 4D48 D35 1480.4 Dark gray mudstone 54.8 2.3 13.5 26.1 0.0 3.2 12.6 0.49 456 0.21 0.39 0.25 79 51D48 D36 1481.3 Black carbon mudstone 57.8 11.7 16.2 7.9 0.3 6.2 19.2 1.79 462 0.5 2.3 0.06 128 3D48 D37 1481.8 Black carbon mudstone 35.4 22.0 28.2 12.3 0.0 2.1 20 0.49 468 0.14 0.2 0.11 40 22D48 D38 1482.3 Dark gray silty mudstone 41.6 15.3 19.7 16.8 0.4 6.2 16.4 0.4 469 0.12 0.16 0.03 40 7D48 D39 1483.6 Black carbon mudstone 80.2 10.8 6.1 1.6 0.0 1.2 18.4 5.18 461 1.52 9.16 0.21 176 4D48 D40 1484.6 Dark gray mudstone 16.2 11.4 31.8 23.5 0.9 16.2 22.4 0.65 466 0.18 0.38 0.16 58 24D48 D41 1485.6 Dark gray silty mudstone 50.8 5.7 20.5 11.0 0.0 12.1 17.2 0.97 469 0.28 0.53 0.11 54 11L94 L51 1963.4 Chan 9 Dark gray silty mudstone 2.0 23.3 25.8 34.7 14.2 0.0 22.8 0.74 470 0.11 0.33 0.08 44 10L94 L52 1964.7 Dark gray silty mudstone 3.8 24.5 23.2 31.8 14.9 1.7 22.8 0.69 476 0.1 0.23 0.03 33 4L94 L53 1966.2 Dark gray mudstone 1.0 16.3 41.2 33.7 7.8 0.0 22.4 0.52 476 0.09 0.15 0.13 28 25L94 L54 1974.4 Dark gray mudstone 3.6 26.1 22.2 36.2 10.8 1.1 23.2 0.98 466 0.16 0.57 0.06 58 6L94 L55 1975.5 Dark gray mudstone 57.4 28.7 8.9 2.8 2.1 0.0 19.2 12.7 456 2.78 25.1 0.97 197 7L94 L56 1976.3 Dark gray silty mudstone 53.0 21.7 10.9 9.3 5.1 0.0 18.4 3.02 455 0.51 4.42 0.42 146 13L94 L57 1977.1 Dark gray shale 3.0 9.2 27.5 47.5 10.9 2.0 21.2 0.99 464 0.14 0.68 0.21 68 21L94 L58 1977.8 Dark gray carbon mudstone 3.2 40.0 27.4 7.3 22.1 0.0 20.8 0.49 429 0.3 0.2 0.33 40 67L94 L59 1978.6 Gray silty mudstone 17.5 27.4 13.4 23.3 17.4 1.0 22.4 0.77 471 0.11 0.32 0.08 41 10W22 W6 441.2 Gray mudstone 21.1 12.7 28.4 23.1 14.7 0.0 16.8 0.21 470 0.04 0.04 0.03 19 14W22 W7 443.1 Dark gray mudstone 54.6 8.2 17.8 12.0 7.0 0.3 20.4 0.85 463 0.18 0.51 0.05 60 5W22 W8 444 Gray silty mudstone 12.4 10.2 37.0 31.6 8.8 0.0 24.4 0.36 469 0.11 0.19 0.02 52 5L94 L60 2058 Dark gray shale 60.2 18.0 7.2 12.5 2.1 0.0 20.4 1.05 465 0.16 0.7 0.1 66 9W22 W10 452 Dark gray mudstone 5.5 7.1 39.3 34.3 13.5 0.3 23.2 0.27 472 0.05 0.05 0.21 18 77W22 W12 454.2 Dark gray mudstone 17.9 2.1 27.3 46.3 6.4 0.0 16.4 0.36 473 0.06 0.1 0.01 27 2W22 W13 455.2 Dark gray mudstone 28.5 3.4 23.6 33.8 9.7 0.9 21.6 0.48 473 0.09 0.21 / 43 /W22 W14 460.5 Dark gray shale 67.2 0.0 1.9 29.6 1.3 0.0 12.4 3.41 455 1.36 6.45 0.21 189 6W22 W15 461.2 Dark gray mudstone 59.0 0.0 4.1 30.8 6.1 0.0 16.8 3.27 454 1.4 7.2 0.23 220 7W22 W16 462 Dark gray shale 78.4 0.0 2.0 17.3 2.3 0.0 14 3.77 462 0.88 5.26 0.27 139 7W22 W17 462.9 Dark gray silty mudstone 76.7 1.1 7.2 9.8 4.6 0.6 15.2 3.39 460 1.11 5.5 0.21 162 6W22 W18 463.5 Dark gray silty mudstone 8.2 11.3 56.2 11.3 12.5 0.4 21.2 0.57 470 0.2 0.44 0.09 77 15W22 W19 464.6 Dark gray silty mudstone 53.4 11.7 11.6 11.6 10.1 1.6 21.6 1.36 463 0.29 1.89 0.05 138 3W22 W20 466.8 Gray silty mudstone 52.9 16.3 10.0 7.4 13.2 0.3 18 1.12 454 0.76 1.76 0.1 157 8

(continued on next page)

169M.Zhang

etal./InternationalJournalofCoalGeology

152(2015)

159–176

Table 1 (continued)

Well name Sample Depth(m)

Subsections Lithology AOM(%)

Phytoclasts (%) Palynomorphs(%)

Phytoclasize (um

TOC Rock-Eval pyrolysis

GP TLF OP Cuticle Tmax S1 S2 S3 HI OI

W22 W21 467.7 Gray silty mudstone 69.7 4.7 5.0 16.4 4.1 0.0 19.2 1.63 457 0.74 2.73 0.17 167 10W22 W22 468.5 Gray muddy siltstone 54.3 6.5 20.6 10.0 6.5 2.2 20.4 1.79 459 0.53 2.42 0.04 135 2D48 D42 1507.4 Black carbon mudstone 75.9 1.0 5.0 16.0 0.0 2.1 10 4.57 456 3.08 7.54 0.22 164 4D48 D43 1508.6 Dark gray silty mudstone 65.5 1.1 8.6 21.6 0.0 3.2 12.8 4.24 455 3.44 8.06 0.32 190 7D48 D44 1509.3 Black carbon mudstone 67.1 2.6 7.3 21.8 0.0 1.3 13.2 4.71 457 3.4 9.24 0.27 196 5D48 D45 1510.2 Black carbon mudstone 76.7 1.0 5.0 16.0 0.0 1.3 12.4 4.24 456 3.42 9.9 0.34 233 8D48 D46 1510.8 Dark gray shale 81.8 1.9 2.8 9.9 0.0 3.6 18 5.07 457 3.91 10.3 0.34 203 6D48 D47 1511.1 Dark gray shale 79.6 1.0 3.2 11.2 0.0 5.1 13.6 7.77 462 4.09 14 0.29 180 3D48 D48 1512.2 Black carbon mudstone 92.6 0.5 0.8 2.9 0.0 3.2 12.4 6.71 457 4.5 12 0.3 179 4D48 D49 1513.1 Dark gray silty mudstone 81.2 2.7 2.5 11.1 0.0 2.4 12.8 3.84 453 3.62 7.26 0.23 189 5D48 D54 1527.5 Dark gray shale 82.0 1.1 3.2 12.2 0.0 1.6 13.2 5.13 462 2.57 8.18 0.41 159 7D48 D55 1528.5 Dark gray shale 78.9 1.0 3.0 15.3 0.0 1.8 11.6 4.65 459 2.28 7.38 0.34 158 7D48 D56 1529.4 Dark gray shale 83.7 0.3 1.6 11.2 0.0 3.2 12.4 6.61 458 3.78 12 0.33 182 4D48 D57 1530.5 Dark gray shale 82.8 0.3 1.6 11.2 0.0 4.1 12.8 5.06 461 2.24 9.2 0.3 181 5D48 D58 1531.6 Dark gray shale 84.3 0.3 1.6 11.2 0.0 2.6 11.2 8.21 461 3.45 13.1 0.31 159 3D48 D59 1532.5 Dark gray shale 23.1 13.8 16.1 42.0 0.0 5.1 12.8 0.72 462 0.47 0.61 0.18 84 25D48 D60 1533.4 Gray silty mudstone 25.3 24.6 11.0 32.2 0.0 6.9 13.2 2.02 464 1.19 3.3 0.15 163 7L94 L61 2079.4 Chan 10 Black carbon mudstone 67.5 14.8 3.3 10.2 3.9 0.3 20.8 1.4 461 0.21 1.44 0.08 102 5W22 W23 477.9 Dark gray silty mudstone 76.5 0.0 3.6 18.6 1.2 0.0 12.8 1.88 464 0.49 2.33 0.11 123 5W22 W24 478.3 Dark gray silty mudstone 73.1 0.6 3.4 19.2 3.1 0.6 12.4 1.8 461 0.55 2.21 0.1 122 5W22 W25 480.3 Gray silty mudstone 30.8 8.0 30.8 14.3 14.1 2.0 24.4 7.87 459 1.92 16.2 0.57 205 7

AOM = amorphous organic matter.TOC = total organic carbon, wt.%.GP = gelified particle.OP = opaque particle.TLF = transparent ligno-cellulosic fragments.S1: Volatile hydrocarbon (HC) content, mg HC/g rock.S2: Remaining HC generative potential, mg HC/g rock.S3: Carbon dioxide yield, mg CO2/g rock.Tmax: Temperature at maximum of S2 peak, °C.HI: Hydrogen Index = S2 × 100 / TOC, mg HC/g TOC.OI: Oxygen Index = S3 × 100 / TOC, mg CO2/g TOC.

170M.Zhang

etal./InternationalJournalofCoalGeology

152(2015)

159–176

st)

Fig. 3. Plot of HI versus Tmax for the analyzed source rock samples from the L94, D48 andW22 wells, delineating present-day thermal maturation and kerogen types.

171M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

anoxic depositional environments. The phytoclast sizes are usuallysmall and indicate a distal deposition (Tyson and Follows, 2000). Thus,this palynofacies assemblage is considered to indicate a distal

Fig. 4. Relationship between depth and T

dysoxic–anoxic deep basin environment. This facies mainly occurs inthe Chan 7 and Chan 9 subsections of the studied sequences, especiallyin the D48 and W22 wells (Fig. 6).

max for the L94, D48 andW22 wells.

172 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

5.2.2. Palynofacies-II (PF-II: GP and AOM): shelf-to-basin transitionAOM compositions with high GP content and common

palynomorphs characterize palynofacies-II (Fig. 6). Generally, GP, cuti-cles and palynomorphs are easier to transport than the TLF, which aremost likely sorted in the transportation process. In addition, moderatepercentages of AOM indicate a relatively dysoxic depositional environ-ment. Most samples plot in or near the GCP field in the AOM–TO–GCPternary diagram (Fig. 6). This field is interpreted to represent theheterolithic oxic shelf (proximal shelf) (Tyson, 1995). The phytoclastsizes are larger than those in PF-I, which reflects the fact that the proxi-mal–distal trend requires a certain level of water dynamics. Thispalynofacies also has another characteristic, its high TOC values, whichare an indication of low sedimentation rates and/or high organic input.This facies is mostly interspersed with the PF-III horizons in the L94well sequences. In the anoxic depositional interval in Chan 7 and Chan9 in the D48 and W22 well sequences, this palynofacies type is rare.Thus, the transportation distance, proximity, and oxidation reflected bythis palynofacies, all between the PF-I and PF-III values, are indicativeof a suboxic to dysoxic shelf-to-basin environment.

Fig. 5. Relationships between of TOC, HI and

5.2.3. Palynofacies-III (PF-III: phytoclasts): proximal suboxic shelfPalynofacies-III is characterized by the high percentage of TLF and OP

and the low to intermediate percentage GP (Fig. 6). The percentage andsize of the phytoclasts group is generally inferred to be associated withthe distance from the terrestrial organic matter flux (Tyson, 1995;Tyson and Follows, 2000). TLF mainly originated from terrestrial plantxylogen, which has a relatively large volume and tends to be depositedclose to the source. Thus, the high value of TLF may indicate a shortertransport distance. Additionally, the low AOM content indicates a rela-tively oxic sedimentary environment. The TOC values are usually lessthan 1%, which reflects a low organic matter preservation ratio or highsediment accumulation rates. Most of the samples plot in the TO fieldof the AOM–TO–GCP ternary diagram (Fig. 6), which can be interpretedas a highly proximal shelf or basin environment. The phytoclast sizes arelarger and are mainly in the range of 15–25 μm,which also indicates rel-atively proximal deposits. The sampled horizons are dominated bycoarser-grained rocks, such as sandy or siltymudstones, which generallyoccur in shallow lake or delta depositional environments. Therefore,palynofacies-III most likely accumulated in a shallow near shore

organic components (AOM, GP and TLF).

Fig. 6. Ternary AOM–TO–GCP kerogen plot of the sample data from the three studied wells showing the palynofacies types and depositional sedimentary environment (ternary diagrammodifiedby Tyson, 1993, 1995). AOM=amorphous organicmatter; TO= transparent ligno-cellulosic fragments+opaque particles;GCP=gelifiedparticles+ cuticles+palynomorphs.

173M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

environment. This palynofacies type is mainly observed in the samplesfrom the L94 well and in a few from the D48 andW22 wells.

5.3. Source rock potential

The dispersed original organic matter was preserved in the sedi-ments and experienced favorable temperature and pressure conditions.These conditions formed kerogen as a diagenetic product, and this ker-ogen was converted to bitumen, oil and gas, depending on the type oforganic matter and the diagenetic conditions. The original organic mat-ter information can be estimated using the composition of the sourcerock's particulate organic matter (kerogen) that is resistant to the inor-ganic acids HCl and HF (Tyson, 1995). Thus, palynofacies analysis wassuccessfully used to evaluate the hydrocarbon source rock potential,which can be compared to the results of traditional geochemicalmethods, such as TOC, vitrinite reflectance (Ro%) and Rock-Eval pyroly-sis (Zobaa et al., 2011; El Beialy et al., 2010; El Atfy et al., 2014). In thepresent study, we combined palynofacies analysis and instrumentalgeochemical analysis (TOC and Rock-Eval Pyrolysis) results from theL94, D48 andW22wells to determine the hydrocarbon source rock po-tential of the Yanchang Formation in the southern Ordos Basin.

5.3.1. Comparison among the different areasUnlike gentle marine petroliferous basins, continental basins feature

larger basement relief and are controlled by the regional structure. Eachdepression in the Ordos Basin has a different hydrocarbon generationpotential for each subsection of the Yanchang Formation (Zhang et al.,2008; Li et al., 2012). The average AOM value from the D48 well in the

Zhidan area is 56.7%, which is equivalent to the samples from the W22well in the Yichuan area, which have an average of 55.2%. These valuesare far higher than those of the L94 well, which have an average of26.8%. Therefore, most oil- and gas-prone materials that have the char-acteristics of type I and II kerogen are contained in the D48 and W22samples from the Zhidan area. However, type III kerogen samples areabundant in the Huachi area, as demonstrated by the L94 samples.The plot of HI versus Tmax (Fig. 3) also corresponds to the palynofaciesresults and indicates better kerogen quality in the source rocks fromthe Zhidan and Yichuan areas.

The AOM-rich source rocks usually have corresponding high TOCand pyrolytic hydrocarbon values, as shown in Fig. 5. The average TOCvalues of the source rocks in the D48 and W22 wells are 2.8 wt.% and2.7 wt.%, respectively. The TOC values of the L94 well samples are rela-tively lower, with an average of 1.1wt.%. Organic geochemists have sug-gested that effective source rocks composed of non-marine shalecontain at least 1.0wt.% TOC (Xia andDai, 2000). Such rocks contain suf-ficient organic matter for significant generation and expulsion. TheZhidan and Yichuan areas are superior to the Huachi area. The HI valuesinferred by Rock-Eval pyrolysis are commonly used as a proxy for thehydrogen content of the OM, which is the most important factor con-trolling the generation of hydrocarbons (Hunt, 1996; El Atfy et al.,2014). The value of 100 mg HC/g TOC is a widely acceptedhydrocarbon-generating minimum criterion for non-marine shales inChina (Xia andDai, 2000). The HI values of the D48 andW22wells sam-ples are similar, and they vary from 20 to 315 mg HC/g TOC. Approxi-mately 70% of the samples are over 100 mg HC/g TOC. Although the HIvalues of the L94 well samples vary from 31 to 225 mg HC/g TOC, only

Fig. 7. Plot of S2 versus the TOC of the sample data from three wells, showing the hydrocarbon potential and source rock efficiency.

174 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

25.4% of the samples have over 100mgHC/g TOC. The low TOC contentsand pyrolysis S2 production values in most of the L94 samples indicatepoor to fair hydrocarbon generation potential (Fig. 7). The D48 andW22 well samples have relatively high TOC contents and pyrolysis S2production values, which mostly indicate good to very good hydrocar-bon generation potential (Fig. 7). Therefore, the correlation of the kero-gen characteristics among the three well samples shows that the sourcerock qualities of the Zhidan and Yichuan areas are obviously better thanthose of Huachi area.

5.3.2. Comparison among the various oil subsectionsThe ten oil subsections of the Yanchang Formation also have differ-

ent hydrocarbon generation potential. The TOC, palynofacies andRock-Eval pyrolysis data are used to evaluate the hydrocarbon genera-tion potential of different oil subsections in the studied wells. In theL94 well, the Chan 7 layer has the thickest shale deposits (Fig. 2) withthe highest TOC values, followed by the Chan 8 and Chan 9 layers. Thehighest AOM content and HI value also occurred in the Chan 7 layer,which features abundant oil to gas-prone type I and II kerogen. A goodhydrocarbon generation potential is also indicated by the high TOC con-tent and the pyrolysis S2 yields (Fig. 7). These analysis results indicatethat Chan 7 maybe the primary source rocks in the Huachi area in thesouthern Ordos Basin. This finding is also supported by previous explo-ration data (Zhang et al., 2006). Similarly, we examined the D48 andW22 wells in the Zhidan and Yichuan areas, respectively. The Chan 9and Chan 7 layers have abundant oil-shale layers that are greater than10 m thick (Fig. 2). The TOC value in the Chan 9 layer of the D48 wellranged from2.02wt.% to 6.71wt.%, with an average of 5.2wt.% (exclud-ing an outlier in the D48 well, 1532.5 m). The Chan 7 has relatively lowTOC values, which range from 0.29 to 5.18 wt.%, with an average of

2.53 wt.%. The plot of S2 versus TOC shows that the Chan 9 sampleshave higher hydrocarbon potential than other subsections (Fig. 7). Thehigh-quality source rock of Chan 9 in the Zhidan area is also demon-strated by several geochemical parameters, sedimentary characteristicsand drilling data (e.g. Zhang et al., 2008). Based on the W22 samplesfrom the Yichuan area, Chan 7 and Chan 9 both have high hydrocarbongeneration potential, which is indicated by the TOC, palynofacies andpyrolysis results (Table 1; Figs. 3 and 7). The hydrocarbon generationpotential of Chan 7 is slightly higher than that of Chan 9.

In conclusion, the Chan 7 and Chan 9 oil layers are the primarysource rocks. In the Huachi and Yichuan areas, Chan 7 likely has thehighest hydrocarbon generation potential among the oil layers. In con-trast, Chan 9 exhibits a relatively high hydrocarbon generation potentialin the Zhidan area.

6. Conclusions

A palynofacies and organic geochemical study was conducted using134 samples of the Yanchang Formation from the L94, D48 and W22wells in the southern Ordos Basin, China. This study is the first to com-bine optical palynofacies and organic geochemistry for source rock eval-uation of Triassic continental sediments in the Ordos Basin. This study'sobservations can be summarized as follows:

1) The particulate organic matter is mainly composed of terrestriallyderived AOM, phytoclasts (GP, TLF, OP and cuticles), andpalynomorphs. Three distinct palynofacies assemblages are recog-nized in the Yanchang Formation on the basis of the quantitativecontent of the particulate organic matter. PF-I is dominated by theAOMcomponents. PF-II is characterized by the dominance of gelified

175M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

particles and AOM. PF-III has high contents of TLF and OPconstituents.

2) The PF-I samples are mainly from the D48 and W22 wells in theZhidan and Yichuan areas, respectively, and from the Chan 7 subsec-tion of the L94 in the Huachi area of southern Ordos. Based on theirpalynofacies characteristics, these sampled sequences were deposit-ed in a distal dysoxic–anoxic deep basin setting with a large contri-bution of degraded aquatic organisms. The PF-II samples arecommon in the L94 well and represent a proximal suboxic shelf set-ting with amoderate production of degraded aquatic organisms andan influx of terrestrial plant matter. The PF-III samples are scatteredthroughout the L94 well and in a few sections of the D48 and W22wells. These samples represent a shallow shelf to basin transitionsetting that received a large influx of terrestrial plant matter.

3) The palynofacies, TOC and Rock-Eval data indicate that type I and IIkerogen are abundant in the Yanchang Formation in the southernOrdos Basin. These parameters also indicate a mature to highly ma-ture stage for the examined organic matter and present an increas-ing maturity trend with burial depth. In detail, the Yanchangsource rocks in the D48 and W22 wells have higher hydrocarbongeneration potentials than the L94well in theHuachi area. Addition-ally, these parameters from the D48 well indicate that the Chan 9subsection is the primary source rock stratum in the Zhidan area.In contrast, the Chan 7 source rocks exhibited the highest hydrocar-bon generation potential in the L94 andW22wells in theHuachi andYichuan areas, respectively, of the southern Ordos Basin.

Acknowledgments

This work was financially supported by grants from the NationalNatural Science Foundation of China (No. 41172131), the “Strategic Pri-ority Research Program” of the Chinese Academy of Sciences (No.XDB10010103), and the Key Laboratory Project of Gansu Province(No. KFJJ2015-06 and No. 1309RTSA041). We are grateful to Xu Jinli,the Senior Engineer of the Geology Science Academy of the ShengliOilfield for his assistancewith sample handling and fossil identification.

References

Buchardt, B., Nielsen, M.V., 1991. Comparison of organic geochemical and palynofaciesmethods: example from the Upper Triassic Gassum Formation in Denmark. Bull.Geol. Soc. Den. 38, 267–277.

Carvalho, M.D.A., Ramos, R.R.C., Crud, M.B., Witovisk, L., Kellner, A.W., Silva, H.D.P., Grillo,O.N., Riff, D., Romano, P.S., 2013. Palynofacies as indicators of paleoenvironmentalchanges in a Cretaceous succession from the Larsen Basin, James Ross Island,Antarctica. Sediment. Geol. 295, 53–66.

De Araujo Carvalho, M., Mendonça Filho, J.G., Menezes, T.R., 2006. Paleoenvironmental re-construction based on palynofacies analysis of the Aptian–Albian succession of theSergipe Basin, Northeastern Brazil. Mar. Micropaleontol. 59, 56–81.

Du, B.X., Sun, B.N., Ferguson, D.K., Yan, D.F., Dong, C., Jin, P.H., 2013. TwoBrachyphyllum species from the Lower Cretaceous Jiuquan Basin, Gansu Province,NW China and their affinities and palaeoenvironmental implications. Cretac. Res.41, 242–255.

Duan, Y., 2012. Geochemical characteristics of crude oil in fluvial deposits from Malingoilfield of Ordos Basin, China. Org. Geochem. 52, 35–43.

Dutta, S., Hartkopf-Fröder, C., Witte, K., Brocke, R., Mann, U., 2013. Molecular characteri-zation of fossil palynomorphs by transmission micro-FTIR spectroscopy: implicationsfor hydrocarbon source evaluation. Int. J. Coal Geol. 115, 13–23.

El Atfy, H., Brocke, R., Uhl, D., Ghassal, B., Stock, A.T., Littke, R., 2014. Source rock potentialand paleoenvironment of the Miocene Rudeis and Kareem formations, Gulf of Suez,Egypt: an integrated palynofacies and organic geochemical approach. Int. J. CoalGeol. 131, 326–343.

El Beialy, S.Y., El Atfy, H.S., Zavada, M.S., El Khoriby, E.M., Abu-Zied, R.H., 2010. Palynolog-ical, palynofacies, paleoenvironmental and organic geochemical studies on the UpperCretaceous succession of the GPTSW-7 well, North Western Desert, Egypt. Mar. Pet.Geol. 27, 370–385.

Ercegovac, M., Kostić, A., 2006. Organic facies and palynofacies: nomenclature, classifica-tion and applicability for petroleum source rock evaluation. Int. J. Coal Geol. 68,70–78.

Garcia, Y.C., Martinez, J.I., Velez, M.I., Yokoyama, Y., Battarbee, R.W., Suter, F.D., 2011.Palynofacies analysis of the late Holocene San Nicolás terrace of the Cauca paleolakeand paleohydrology of northern South America. Palaeogeogr. Palaeoclimatol.Palaeoecol. 299, 298–308.

Ghasemi-Nejad, E., Head, M.J., Naderi, M., 2009. Palynology and petroleum potential ofthe Kazhdumi Formation (Cretaceous: Albian–Cenomanian) in the South Pars field,northern Persian Gulf. Mar. Pet. Geol. 26, 805–816.

Graz, Y., Di-Giovanni, C., Copard, Y., Laggoun-Défarge, F., Boussafir, M., Lallier-Verges, E.,Baillif, P., Perdereau, L., Simonneau, A., 2010. Quantitative palynofacies analysis as anew tool to study transfers of fossil organic matter in recent terrestrial environments.Int. J. Coal Geol. 84, 49–62.

Hunt, J.M., 1996. Petroleum Geochemistry and Geology. 2nd edition. W.H. Freeman andCompany, New York (743 pp.).

Ji, L.M., Meng, F.W., 2006. Palynology of Yanchang Formation of Middle and Late Triassicin Eastern Gansu Province and its paleoclimatic significance. J. China Univ. Geosci. 17,209–220.

Ji, L.M., Meng, F.W., Schiffbauer, J.D., Xu, J.L., Yan, K., Shu, J.W., 2008. Correlation betweenhighly abundant oil-prone leiosphaerid acritarchs and hydrocarbon source rocksfrom the Triassic Yanchang Formation, eastern Gansu Province, NorthwesternChina. Gondwana Res. 14, 554–560.

Ji, L.M., Yan, K., Meng, F.W., Zhao, M., 2010. The oleaginous Botryococcus fromthe Triassic Yanchang Formation in Ordos basin, Northwestern China: mor-phology and its paleoenvironmental significance. J. Asian Earth Sci. 38,175–185.

Li, X., Liu, X., Zhou, S., Liu, H., Chen, Q., Wang, J., Liao, J., Huang, J., 2012. Hydrocarbon originand reservoir forming model of the Lower Yanchang Formation, Ordos Basin. Pet.Explor. Dev. 39, 184–193.

Liu, C.L., Wang, P., 2013. The role of algal blooms in the formation of lacustrine petroleumsource rocks—evidence from Jiyang depression, Bohai Gulf Rift Basin, eastern China.Palaeogeogr. Palaeoclimatol. Palaeoecol. 388, 15–22.

Marshall, J.E.A., 1991. Quantitative spore colour. J. Geol. Soc. 148, 223–233.Mueller, S., Veld, H., Nagy, J., Kürschner,W.M., 2014. Depositional history of the Upper Tri-

assic Kapp Toscana Group on Svalbard, Norway, inferred from palynofacies analysisand organic geochemistry. Sediment. Geol. 310, 16–29.

Pacton, M., Gorin, G.E., Vasconcelos, C., 2011. Amorphous organic matter — experi-mental data on formation and the role of microbes. Rev. Palaeobot. Palynol.166, 253–267.

Pearson, D.L., 1984. Pollen/spore Color ‘Standard’. Phillips Petroleum Company Explora-tion Projects Section (reproduced in Traverse, A. 2007. Paleopalynology, Figure 19.2. Springer).

Peters, K.E., 1986. Guidelines for evaluating petroleum source rock using programmed py-rolysis. Am. Assoc. Pet. Geol. Bull. 70, 318–329.

Peters, K.E., Cassa, M.R., 1994. Applied source rock geochemistry. In: Magoon, L.B., Dow,W.G. (Eds.), The Petroleum System—From Source to Trap. American Association ofPetroleum Geologists Memoir 60, pp. 93–120.

Powell, A.J., Dodge, J.D., Lewis, J., 1990. Late Neogene to Pleistocene palynological facies ofthe Peruvian continental margin upwelling, Leg 112. In: Suess, E., Von Huene, R.(Eds.), Proceeding of the Ocean Drilling Project, Scientific Results 112. ODP, CollegeStation, Texas, pp. 297–321.

Pross, J., Pletsch, T., Shillington, D.J., Ligouis, B., Schellenberg, F., Kus, J., 2007. Thermal al-teration of terrestrial palynomorphs in mid-Cretaceous organic-rich mudstones in-truded by an igneous sill (Newfoundland Margin, ODP Hole 1276A). Int. J. CoalGeol. 70, 277–291.

Ren, Z.L., Zhang, S., Gao, S.L., Cui, J.P., Xiao, Y.Y., Xiao, H., 2007. Tectonic thermal his-tory and its significance on the formation of oil and gas accumulation and min-eral deposit in Ordos Basin. Sci. China Ser. D Earth Sci. 50 (Suppl. II), 27–38(2007).

Roncaglia, L., Kuijpers, A., 2006. Revision of the palynofacies model of Tyson (1993)based on recent high-latitude sediments from the North Atlantic. Facies 52,19–39.

Schiøler, P., Rogers, K., Sykes, R., Hollis, C.J., Ilg, B., Meadows, D., Roncaglia, L., Uruski, C.,2010. Palynofacies, organic geochemistry and depositional environment of the TartanFormation (Late Paleocene), a potential source rock in the Great South Basin, NewZealand. Mar. Pet. Geol. 27, 351–369.

Sebag, D., Copard, Y., Di-Giovanni, C., Durand, A., Laignel, B., Ogier, S., Lallier-Verges, E.,2006. Palynofacies as useful tool to study origins and transfers of particulate organicmatter in recent terrestrial environments: synopsis and prospect. Earth-Sci. Rev. 79,241–259.

Suárez-Ruiz, I., Flores, D., Filho, J.G.M., Hackley, P.C., 2012. Review and update of the appli-cations of organic petrology: part 1, geological applications. Int. J. Coal Geol. 99,54–112.

Ţabără, D., Pacton, M., Makou, M., Chirilă, G., 2015. Palynofacies and geochemical analysisof oligo-miocene bituminous rocks from the moldavidian domain (easternCarpathians, Romania): implications for petroleum exploration. Rev. Palaeobot.Palynol. 216, 101–122.

Tyson, R.V., 1993. Palynofacies analysis. In: Jenkins, D.J. (Ed.), AppliedMicropalaeontology. Kluwer Academic Publishers, Dordrecht, The Netherlands,pp. 153–191.

Tyson, R.V., 1995. Sedimentary Organic Matter; Organic Facies and Palynofacies. Chapmanand Hall, London (615 pp.).

Tyson, R.V., Follows, B., 2000. Palynofacies prediction of distance from sedimentsource: a case study from the Upper Cretaceous of the Pyrenees. Geology 28,569–571.

Wang, H.D., Allen, J., Philp, R.P., 1995. An organic geochemical investigation of oils andsource rocks from two Mesozoic formations of Shanganning Basin, China. J. SEAsian Earth Sci. 11, 277–288.

Wang, F.Y., FU, J.M., Liu, D.H., Shi, G.S., Lei, J.J., 1993. Submicroliptinite in coal source rock(in Chinese). Chin. Sci. Bull. 38, 1968–1971.

Xia, X.Y., Dai, J.X., 2000. A critical review on the evaluation of hydrocarbon potential ofmarine carbonate rocks in China (in Chinese). Acta Pet. Sin. 21, 36–41.

176 M. Zhang et al. / International Journal of Coal Geology 152 (2015) 159–176

Xiao, X.M., Liu, Z.F., Shen, J.G., 1997. The fluorescence alteration patterns and origintypes of immature and low-mature amorphous kerogen in terrestrial source rocks(in Chinese). Chin. Sci. Bull. 42, 1968–1971.

Zhang, W.Z., Yang, H., Li, S.P., 2008. Hydrocarbon accumulation significance of Chang 9–1high-quality lacustrine source rocks of Yanchang Formation, Ordos Basin (in Chi-nese). Pet. Explor. Dev. 35, 557–562.

Zhang, W.Z., Yang, H., Li, J.F., Ma, J., 2006. Leading effect of high-class source rock of Chang7 in Ordos Basin on enrichment of low permeability oil–gas accumulation–hydrocar-

bon generation and expulsion mechanism (in Chinese). Pet. Explor. Dev. 33,289–293.

Zobaa, M.K., Oboh-Ikuenobe, F.E., Ibrahim, M.I., 2011. The Cenomanian/Turonian oceanicanoxic event in the Razzak Field, north Western Desert, Egypt: source rock potentialand paleoenvironmental association. Mar. Pet. Geol. 28, 1475–1482.