Evaluation of Organic Matter,Hydrocarbon Source,and Depositional Environment of Onshore Warkalli Sedimentary Sequence from Kerala-Konkan Basin,South India

Multidisciplinary analysis of the carbonaceous sediments of Warkalli Formation (Mio-Pliocene) from the Warkalli cliff section has been done to assess the source of organic matter, palaeodepositional settings and the hydrocarbon potential. The n-alkane distribution from n-C₁₂ to n-C₃₃ along with bimodal distribution indicates significant organic matter contribution from microbial activity and higher plants. The contribution from angiosperm source vegetation is indicated by the oleanane type of triterpenoids. The hopanes distribution indicates the immature stage of the organic matter, which is in agreement with the T_max (av. 401 °C) and huminite reflectance (av. 0.28% R_r) values. The total organic carbon (TOC) contents vary between 0.8 and 6.72 wt. % in the studied sediments. Hydrogen index and oxygen index values range from 16 to106 mg HC/g TOC, and 113 to 344 mg CO₂/g TOC, respectively. The maceral content is low, being dominated by the detrohuminite submaceral and the mineral matter accounts for 68 to 77% of the total composition. The phytoclast group (63–87%) is dominant with subordinate amorphous organic matter (4–35%). The study shows that the sediments were deposited in a marginal suboxic basin with intermittent variations. All the parameters unequivocally suggest that the studied sequence holds the potential to generate gaseous hydrocarbons.     

Geochemical and palynological analyses of the Serikagni Formation, Sinjar, Iraq

Serikagni Formation (lower–middle Miocene) was studied at four outcrop sections within Sinjar Anticline, Para (the western plunge), Jaddala, Sinjar, (Southern limb), and Noaniaa (Northern limb) of Sinjar Mountain, which is part of foothill zone in northwest Iraq. This formation is composed of Globigerina limestone, marly limestone intercalated with marl, deposited in quiet, deep marine environment. Palynological analyses and the percentages of palynological matter were determined. Palynofacies analysis was recorded for paleoenvironmental interpretation. Mineralogical investigations and petrographical analyses were done. Geochemical analyses for the determination of the major constituents (CaO, MgO, and I.R.),the secondary constituents (SiO₂, Al₂O₃, Fe₂O₃, Na₂O, K₂O, and trace elements (Sr, Mn, Cu, Zn, Co, Cr, Pb) in the rock samples were accomplished. The calcite is the predominant mineral which is mostly of micrite types as well as spary calcite. The insoluble residue (I.R.) has negative correlation with the carbonate percentages in the rock formation as observed by the XRD analyses. Clay minerals show low occurrence represented by palygorskite, montmorillonite, and sepiolite. Geochemical differences can be noticed between the limy and marly facies constituting the same formation. Differences are also observed between the geochemistry and mineralogy of the four studied localities such as the relatively more pure limestone in Jaddala and Para sections than Sinjar and Noaniaa sections which indicate the higher percentages of marly limestone. This is believed to be due to the geographic location of these sections within the main depositional environment, as well as the consequences of sea level fluctuation. Two palynofacies (PF-1) and (PF-2) were identified. Palynomorphs are more numerous with high percentages (>80%) of amorphous organic matter (AOM) is present in the PF-1. The lithological association of this palynofacies is limestone and marly limestone. This palynofacies 1, indicate the deep marine depositional environment. The second palynofacies (PF-2) reflect low quantities (less than 40%) of AOM, with increase of phytoclasts (translucent-type) to more than 30% and the miospores (small spores and pollen grains) to more than 20%. The lithological association of this palynofacies is marl and marly limestone. This palynofacies 2, indicate the nearshore and shallow marine depositional environment.     

Chemico-petrographic studies of some lignite core samples from Kalol oilfield,Cambay Basin,Gujarat, Western India

The Kalol oilfield in the Cambay graben, Gujarat. western India, is known to contain thick seams of lignite in the Kalol Formation (Middle Eocene), overlying the oil-bearing Cambay Black Shale (Lower Eocene), at depths between 1110 m and 1500 m. The Kalol Formation occurs in the northern portion of the Cambay Basin as a wedge-shaped sequence of regressive and transgressive marine environments, the lignite being confined to the former phase.Chemically, the Kalol lignite is characteristically low in moisture (4.45–4.64%), quite low in ash (1.67-10.82%) and high in volatiles (43.56–55.25%). C is 72.39–77.18%, H is 4.47–5.93%, N is 1.16–1.58%, O is 15.73–18.62%, and S is 0.32–0.86%. According to Seyler's classification, the Kalol lignite can be classified as belonging to rank (a) lower than lignitous, (b) perlignitous, (c) ortholignitous, (d) metalignitous, and (e) bituminous. According to North American (ASTM) classification, utilising data on volatiles and R_{m oil}, the lignite belongs to lignite, sub-bituminous C and low volatile bituminous rank.Petrographically, the Kalol lignite is composed of huminite (50–81%), liptinite (1–16%), and inertinite (6–32%). Inertinite comprises mainly sclerotinite as plectenchyma, fusinite being absent. Exsudatinite is quite common. On the basis of microlithotype, the lignite comprises textile (1–13%), detrite (19–69%), liptitextite (1–10%), liptidetrite (4–16%), inertidetrite (1–25%), detrinertite (3–21%), and inertite (5–26%), with shale (5–12%). R_{m oil} varies from 0.30 to 0.40. The bituminous coal sample is high in shaly matter (53%) and composed of vitrinite (16%) and sclerotinite (29%), the former showing R_m 1.80.These studies indicate that the chemical and petrographic constitution of the lignite is favourable for underground gasification.     

The giant tin polymetallic mineralization in southwest China:Integrated geochemical and isotopic constraints and implications for Cretaceous tectonomagmatic event

The Gejiu-Bozushan-Laojunshan W-Sn polymetallic metallogenic belt(GBLB) in southeast Yunnan Province is an important part of the southwestern Yangtze Block in South China.Tin polymetallic mineralization in this belt includes the Niusipo,Malage,Songshujiao,Laochang and Kafang ore fields in the Gejiu area which are spatially and temporally associated with the Kafang-Laochang and Songshujiao granite plutons.These granites are characterized by variable A/CNK values(mostly 1.1,except for two samples with 1.09),high contents of SiO_2(74.38-76.84 wt.%) and Al_2 O_3(12.46-14.05 wt.%) and variable CaO/Na_2 O ratios(0.2-0.65) as well as high zircon δ~(18)O values(7.74‰-9.86‰),indicative of S-type affinities.These rocks are depleted in Rb,Th,U,Ti,LREE[(La/Yb)N=1.4-20.51],Ba,Nb,Sr,and Ti and display strong negative Eu and Ba anomalies.The rocks possess high Rb/Sr and Rb/Ba ratios,relatively low initial ~(87)Sr/~(86)Sr ratios(0.6917-0.7101),and less radiogenic εNd(t)values(-8.0 to-9.1).The zircon grains from these rocks show negative ε_(Hf)(t) values in the range of-3.7 to-9.9 with mean T_(DM2)(Nd) and T_(DM2)(Hf) values of 1.57 Ga and 1.55 Ga.They show initial ~(207)Pb/~(204)Pb ranging from15.69 to 15.71 and ~(206)Pb/~(204)Pb from 18.36 to 18.70.Monazite from Songshujiao granites exhibits higher U and lower Th/U ratios,lower δ~(18)O values and higher ε_(Hf)(t) values than those of the zircon grains in the KafangLaochang granites.The geochemical and isotopic features indicate that the Laochang-Kafang granites originated by partial melting of Mesoproterozoic crustal components including biotite-rich metapelite and metagraywacke,whereas the Songshujiao granites were derived from Mesoproterozoic muscovite-rich metapelite crustal source.Most zircon grains from the Songshujiao,Laochang and Kafang granites have high-U concentrations and their SIMS U-Pb ages show age scatter from 81.6 Ma to 88.6 Ma,80.7 Ma to 86.1 Ma and 82.3 Ma to 87.0 Ma,suggesting formation earlier than the monazite and cassiterite.Monazite SIMS U-Pb ages and Th-Pb ages of three same granite samples are consistent and show yielded 206 Pb/~(238)U ages of 83.7 ± 0.6 Ma,83.7±0.6 Ma,and 83.4±0.6 Ma,and ~(208)Pb/~(232)Th ages of 83.2 ± 0.5 Ma,83.8 ± 0.4 Ma,and 83.5±0.9 Ma,which are within the range of the SIMS zircon U-Pb ages from these rocks.The data constrain the crystallization of the granites at ca.83 Ma.In situ U-Pb dating of two cassiterite samples from the cassiterite-sulfide ore in the Songshujiao ore field and Kafang ore field,and two from the cassiterite-oxide+cassiterite bearing dolomite in the Laochang ore field yielded weighted mean 206 Pb/~(238)U ages of 83.5±0.4 Ma(MSWD=0.6),83.5 ± 0.4 Ma(MSWD=0.5),83.6 ±0.4 Ma(MSWD=0.6) and 83.2 ±0.7 Ma(MSWD=0.6),respectively.Combined with geological characteristics,the new geochronological data indicate that the formation of the granites and Sn polymetallic deposits are coeval.We correlate the magmatic and metallogenic event with lithospheric thinning and asthenosphere upwelling in continental extension setting in relation to the eastward subduction of the Neo-Tethys beneath the Sanjiang tectonic domain during Late Cretaceous.     

Palynomorph stratigraphy,palynofacies and organic geochemistry assessments for hydrocarbon generation of Ratawi Formation,Iraq

Seventy-two core and cutting samples of the Ratawi Formation from selected wells of central and southern Iraq in Mesopotamian Foredeep Basin are analysed for their sedimentary organic matters. Dinoflagellates, spores and pollen are extracted by palynological techniques from these rocks. Accordingly, Hauterivian and late Valanginian ages are suggested for their span of depositional time. These palynomorphs with other organic matter constituents, such as foraminifer’s linings, bacteria and fungi, are used to delineate three palynofacies types that explain organic matter accumulation sites and their ability to generate hydrocarbons. Palaeoenvironments of these sites were mainly suboxic to anoxic with deposition of inshore and neritic marine environments especially for palynofacies type 2. Total organic matters of up to 1.75 total organic carbon (TOC) wt.% and early mature stage of up to 3.7 TAI based on the brown colour of the spore species Cyathidites australis and Gleichenidites senonicus with mottled interconnected amorphous organic matter are used for hydrocarbon generation assessment from this formation. On the other hand, these rock samples are processed with Rock-Eval pyrolysis. Outcomes and data calculations of these analyses are plotted on diagrams of kerogen types and hydrocarbon potential. Theses organic matter have reached the mature stage of up to T _max?=?438 °C, hydrogen index of up to 600 mg hydrocarbons for each gram of TOC wt.% and mainly low TOC (0.50–1.55). Accordingly, this formation could generate fair quantities of hydrocarbons in Baghdad oil field and Basrah oil fields. Organic matters of this formation in the fields of Euphrates subzone extends from Hilla to Nasiriyah cities have not reached mature stage and hence not generated hydrocarbons from the Ratawi Formation. Software 1D PetroMod basin modelling of the Ratawi Formation has confirmed this approach of hydrocarbon generation with 100 % transformations of the intended organic matters to generate hydrocarbons to oil are performed in especially oil fields of East Baghdad, West Qurna and Majnoon while oil fields Ratawi and Subba had performed 80–95 % transformation to oil and hence end oil generation had charged partly the Tertiary traps that formed during the Alpine Orogeny. Oil fields of Nasiriyah and Kifle had performed least transformation ratio of about 10–20 % transformation to oil, and hence, most of the present oil in this field is migrated from eastern side of the Mesopotamian Foredeep Basin that hold higher maturation level.     

Petrogenesis and tectonic implications of Indosinian granitoids from Western Qinling Orogen,China:Products of magma-mixing and fractionation

The Western Qinling Orogen(WQO) is characterized by voluminous distribution of Indosinian granitoids,the formation of which provides an important window to unravel the geochemical and geodynamic evolution and associated metallogeny.Here we investigate a group of intrusions termed "Five Golden Flowers" based on petrological,geochemical,zircon U-Pb geochronological and Lu-Hf isotopic studies on the granitoids and their mafic microgranular enclaves(MMEs).Our results show that these intrusions are genetically divided into two types,namely,magma-mixing and highly fractionated.The Jiaochangba,Lujing,Zhongchuan,and Luchuba granitoids are biotite monzogranites(220±0.8 Ma to 217±2.6 Ma) with abundant coeval MMEs(220±.1 Ma to 217±2.7 Ma).The rocks contain moderate to high SiO_2,high MgO,Rb,Sr,Ba,and Th contents,but low TiO_2,P_2 O_5,and Sc values,A/CNK of 1.1,and a range of ε_(Hf)(t) values of-11.7 to +2.23 with corresponding T_(DM2)values of 1967-1228 Ma.The MMEs possess K-feldspar megacrysts,abundant acicular apatites,and show lopsided textures.They have lower SiO_2,Al_2 O_3,and Th contents,but higher MgO,TiO_2,and Sc,with ε_(Hf)(t) values of-18.0 to +3.18 and T_(DM1) of 849-720 Ma.The data indicate that the MMEs were derived from a magma sourced from the enriched lithospheric mantle.We suggest that these host granitoids were produced by partial melting of latePaleoproterozoic to early-Mesoproterozoic lower crust with the involvement of Neoproterozoic SCLM-derived mafic magmas.The Baijiazhuang pluton is dominantly composed of leucogranite(muscovite granite and twomica monzogranite,216±1.5 Ma) without MMEs.The rocks are peraluminous with high A/CNK(1.06-1.27).Compared with the other four granitoids,the Baijiazhuang leucogranite shows higher SiO_2 content,markedly lower concentrations of TiO_2,MgO,Al_2 O_3,CaO,and Fe_2 O_3~T,and lower LREE/HREE and(La/Yb)N values.These leucogranites are also rich in Rb,Th,and U,and display marked depletions in Ba,Sr,Ti,and Eu,indicating that they experienced significant fractionation.Zircon ε_(Hf)(t) values(-10.2 to-3.27) and T_(DM2)(1868-1424 Ma),as well as the Nb/Ta and K_2 O/Na_2 O values are similar to the other four granitoids,indicating that they are likely to have been derived from a similar source;with sediments playing only a minor role in the magma generation.The low contents of Yb and Y suggest that their partial melting was controlled by garnets and micrographic texture of K-feldspar reflects high-temperature melting through undercooling.Based on the above features,we infer that the Baijiazhuang leucogranite likely represents the product of high degree fractionation of the I-type biotite monzogranite magma which generated the other four granitoids at relatively high temperatures,within magma chambers at mid-crust depths.We propose that the granitoid suite was formed in the transitional setting from synto post-collision during the collisional orogeny between the SCB and NCB,following break-off of the subducted South China Block lithosphere during 220-216 Ma.     

Metamorphism and geochronology of garnet amphibolite from the Beishan Orogen,southern Central Asian Orogenic Belt:Constraints from P-T path and zircon U-Pb dating

Numerous lenses of garnet amphibolite occur in the garnet-bearing biotite-plagioclase gneiss belt in the Baishan area of the Beishan Orogen,which connects the Tianshan Orogen to the west and the Mongolia-Xing'anling Orogen to the east.The study of metamorphism in Beishan area is of great significance to explain the tectonic evolution of Beishan orogen.According to the microstructures,mineral relationships,and geothermobarometry,we identified four stages of mineral assemblages from the garnet amphibolite sample:(1) a pre-peak stage,which is recorded by the cores of garnet together with core-inclusions of plagioclase(Pl_1);(2) a peak stage,which is recorded by the mantles of garnet together with mantle-inclusions of plagioclase(Pl_2)+amphibole(Amp_1)+Ilmenite(Ilm_1)+biotite(Bt_1),developed at temperature-pressure(P-T) conditions of 818.9-836.5℃ and7.3-9.2 kbar;(3) a retrograde stage,which is recorded by garnet rims + plagioclase(Pl_3)+amphibole(Amp_2)+orthopyroxene(Opx_1)+biotite(Bt_2)+Ilmenite(Ilm_2),developed at P-T conditions of 796.1-836.9℃ and5.6-7.5 kbar;(4) a symplectitic stage,which is recorded by plagioclase(Pl_4)+orthopyroxene(Opx_2)+amphibole(Amp_3)+biotite(Bt_3) symplectites,developed at P-T conditions of 732 ±59.6℃ and 6.1 ±0.6 kbar.Moreover,the U-Pb dating of the Beishan garnet amphibolite indicates an age of 301.9 ±4.7 Ma for the protolith and 281.4±8.5 Ma for the peak metamorphic age.Therefore,the mineral assemblage,P-T conditions,and zircon U-Pb ages of the Beishan garnet amphibolite define a near-isothermal decompression of a clockwise P-T-t(Pressure-Temperature-time) path,indicating the presence of over thickened continental crust in the Huaniushan arc until the Early Permian,then the southern Beishan area underwent a process of thinning of the continental crust.     

Detrital zircon constraints on late Paleozoic tectonism of the Bogda region(NW China) in the southern Central Asian Orogenic Belt

The Chinese North Tianshan(CNTS) in the southern part of the Central Asian Orogenic Belt(CAOB) has undergone multistage accretion-collision processes during Paleozoic time,which remain controversial.This study addresses this issue by tracing the provenance of Late Paleozoic sedimentary successions from the Bogda Mountain in the eastern CNTS through U-Pb dating and Lu-Hf isotopic analyses of detrital zircons.New detrital zircon U-Pb ages(N=519) from seven samples range from 261±4 Ma to 2827±32 Ma.The most prominent age peak is at 313 Ma and subordinate ages vary from 441 Ma to 601 Ma,with some Precambrian detrital zircon ages(～7%) lasting from 694 Ma to 1024 Ma.The youngest age components in each sample yielded weighted mean ages ranging from 272±9 Ma to 288±5 Ma,representing the maximum depositional ages.These and literature data indicate that some previously-assumed "Carboniferous"strata in the Bogda area were deposited in the Early Permian,including the Qijiaojing,Julideneng,Shaleisaierke,Yangbulake,Shamaershayi,Liushugou,Qijiagou,and Aoertu formations.The low maturity of the sandstones,zircon morphology and provenance analyses indicate a proximal sedimentation probably sourced from the East Junggar Arc and the Harlik-Dananhu Arc in the CNTS.The minor Precambrian detrital zircons are interpreted as recycled materials from the older strata in the Harlik-Dananhu Arc.Zircon E_(Hf)(t) values have increased since ～408 Ma,probably reflecting a tectonic transition from regional compression to extension.This event might correspond to the opening of the Bogda intraarc/back arc rift basin,possibly resulting from a slab rollback during the northward subduction of the North Tianshan Ocean.A decrease of zircon ε_(Hf)(t) values at ～300 Ma was likely caused by the cessation of oceanic subduction and subsequent collision,which implies that the North Tianshan Ocean closed at the end of the Late Carboniferous.     

Hydrocarbon source potential of the Jurassic sediments of Salam-3X borehole,Khalda Concession,Northern Western Desert,Egypt

A total of 51 samples, collected from the Jurassic sediments (Ras Qattara, Yakout, Khatatba, Masajid, and Alam El Bueib (member 6) formations) of Salam-3X well, were subjected to organic geochemical analysis. Of the samples, nine have been subjected to palynofacies investigation. Based on the sedimentary organic matter, these sediments show only one palynofacies type, indicating the presence of gas- and oil-prone source rocks and reflecting deposition under marginal dysoxic–anoxic to shelf-to-basin transition conditions. The total organic content of the samples analyzed is characterized by a wide range of content, including fair, good, very good, and excellent. The organic matter quality of these samples is concentrated around types III (gas prone), III–II (gas and oil prone), and II (oil prone), reflecting gas- and oil-prone sediments, with a tendency to generate gas rather than oil; the result matches with the palynological analysis data. The temperature of maximum pyrolytic hydrocarbon generation of analyzed samples are ranging between 440 and 457 °C, reflecting thermally mature organic matter.     

Constructing the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western Bainaimiao arc terrane,southeastern Central Asian Orogenic Belt

Identifying the crust-mantle interactions in association with the evolution of the Precambrian microcontinents provides critical constraints on the accretionary evolution in the Central Asian Orogenic Belt(CAOB).The Bainaimiao arc terrane(BAT) is one of the most important Precambrian microcontinents in southeastern CAOB,however,few studies have paid attention to the types and the evolving processes of the crust-mantle interactions that occurred before its final accretion onto the northern North China Craton.This study presents an integrated study of geochronology,zircon Hf isotope and whole-rock geochemistry on the latest Neoproterozoic diabases and the Early Paleozoic arc intrusions in the western BAT.The latest Neoproterozoic(ca.546 Ma) diabases display low SiO_2(46.52-49.24 wt.%) with high MgO(8.23-14.41 wt.%),Cr(66-542 ppm) and Ni(50-129 ppm),consisting with mantle origin.Their highly negative zircon ε_(Hf)(t)(-12.0 to-24.7) and high Fe/Mn ratios(62.1-81.7)further indicate a significantly enriched mantle source.Considering that the BAT maybe initially separated from the Tarim Craton with a thickened crustal root,we propose that these diabases were generated through partial melting of an enriched lithospheric mantle source that had been hybridized by lower-crustal eclogites during foundering of the BAT lower crust.The Early Paleozoic(ca.475-417 Ma) arc intrusions in western BAT can be divided into Periods Ⅰ and Ⅱ at approximately 450 Ma.The Period Ⅰ(450 Ma) intrusions contain abundant mafic minerals like hornblende and pyroxene,and show positive zircon ε_(Hf)(t)(+1.5 to+10.9).They are predominantly medium-K calc-alkaline with broad correlations of SiO2 versus various major and trace elements,which correlate well with the experimental melts produced by the fractional crystallization of primitive hydrous arc magmas at 7 kbar.We assume they were formed through mid-crustal differentiation of the mantle wedge-derived hydrous basaltic melts.By contrast,the Period Ⅱ(≤450 Ma) intrusions are characterized by variable zircon e_(Hf)(t)(-15.0 to+11.5) with irregular variations in most major and trace elements,which are more akin to the arc magmas generated in an open system.The general occurrence of elder inherited zircons,along with the relatively high Mg#(45) of some samples,call upon a derivation from the reworking of the previously subduction-modified BAT lower crust with the input of mantle-derived mafic components.In combination with the Early Paleozoic tectonic melanges flanking western BAT,we infer that the compositional transition from Period Ⅰ to Ⅱ can be attributed to the tectonic transition from south-dipping subduction of Solonker ocean to north-dipping subduction of South Bainaimiao ocean in southeastern CAOB.The above results shed light not only on the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western BAT,but also on the associated crustal construction processes before the final arc-continent accretion.     

Organic geochemical study of Ypresian sediments at Jebel Ousselat,Tunisia

This new study was carried out in order to accurately characterize the geochemical pattern of Ousselat organic-rich facies from the Ypresian basin in central-northern Tunisia. It has been found that the organic matter is located towards the end of diagenesis/beginning of catagenesis. This assumption is supported by the relative low T _max values (429–439°C) and by steranes maturity parameters such as C₂₉ αα 20S/(20S + 20R), and C₂₉ ββ/(ββ + αα). High HI values and the abundance of saturates (1–83%) compared to aromatics (2–27%) are unequivocal evidence of type-II organic matter as indicated by a high abundance of cholestane and the predominance of short-chain n-alkanes centred at n-C₁₈ and at n-C₂₀. Total organic carbon (TOC) content and petroleum potential values suggest that the Ypresian period corresponds to an anoxic event which led to the accumulation and preservation of large quantities of organic matter with high primary production. Due to their geochemical characteristics, the Lower Eocene facies represent a new potential source rocks in central-northern Tunisia.     

Petrographic and depositional characteristics of Tadkeshwar lignite deposits (Cambay Basin), Gujarat

Tadkeshwar lignite deposits are one of the important Lower Tertiary lignite deposits of Cambay Basin, Gujarat. These lignites are rich in huminite macerals followed by liptinite and inertinite with moderate to high proportions of associated mineral matter. Under fluorescence mode these are found to be rich in liptinite macerals, in particular the liptodetrinite and resinite. The type of huminite suggests that the lignite is formed from mixed vegetal source, i.e. woody forest vegetation and herbs, shrubs. The composition of macerals indicates the deposition of lignite in sub-aqueous condition in wet-reducing environment with intermittent exposure and subsidence of the peat surface. The rank of the Main and the Leader seams, determined through reflectance measurement, indicate that the lignite is less mature. The considerable amount of perhydrous huminite may have contributed to the lower reflectance values in some of the samples. Low rank and appreciable amount of mineral matter make the lignite suitable for its utilization in thermal power plants, however when upgraded or mixed with better quality coals it can be used for other industries.     

Organic geochemical characteristics and oil generating potential of the Upper Jurassic Safer shale sediments in the Marib-Shabowah Basin,western Yemen

The organic rich Safer shales exposed in the north-central part of onshore Marib-Shabowah Basin are evaluated and their depositional environments are interpreted. Total organic carbon contents (TOC) of the shales range from 1.02–16.8 wt%, and yield hydrogen index (HI) values ranging from 130 to 820 mg HC/g TOC, consistent with mainly Type II with minor contributions from Type I and mixed Types II–III kerogens. The Safer shale samples have vitrinite reflectance values in the range of 0.5–1.0 R_o%, indicating early mature to peak mature stage for oil generation. T_max values range from 429–438 °C, which are in reasonably good agreement with vitrinite reflectance data. Kerogen microscopy shows that the Safer shales are characterized by high amounts of organic matter, consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin. This is supported by their high content of hydrogen rich Type II and I oil-prone kerogen.The biomarker distributions of the Upper Jurassic Safer extracts are characterized by dominant low to medium molecular weight compounds (n-C₁₄ to n-C₂₀), low Pr/Ph ratio (<1.0), high phytane/n-C₁₈ ratios (0.82–2.68), and predominant regular sterane C₂₇. All biomarker parameters clearly indicate that the organic matter was derived from marine algal inputs and deposited under anoxic (reducing) conditions. Hypersaline conditions also prevailed during deposition of these sediments, as indicated by the presence of gammacerane.     

A snapshot into the terrestrial ecosystem of an exceptionally well-preserved dinosaur (Hadrosauridae) from the Upper Cretaceous of North Dakota,USA

A palynological investigation of sedimentary rocks enclosing an exceptionally well-preserved fossil dinosaur (Hadrosauridae) discovered in the upper part of the Hell Creek Formation in south western North Dakota was conducted in order to document the immediate paleoenvironment of this dinosaur. The specimen, an Edmontosaurus annectens is remarkable in having exceptional three-dimensional preservation of soft tissue around the skeleton, indicating rapid burial. A well-preserved palynological assemblage dominated by fern and bryophyte spores, with lesser gymnosperm and angiosperm pollen was recovered. Sparse fresh-water algae and marine dinoflagellate cysts were also recorded. The palynofacies is dominated by wood fragments, including charcoal, with little amorphous organic matter. The presence of some typical pollen taxa of the Wodehouseia spinata Assemblage Zone including Striatellipollis striatellus, Tricolpites microreticulatus, Leptopecopites pocockii as well as a diverse suite of Aquilapollenites, is fully consistent with a Late Cretaceous (late Maastrichtian) age. The palynoflora indicates a local vegetation composed of a canopy of conifers dominated by Pinaceae and a minor sub-canopy of Taxodium and cycads, as well as an understory of hydrophilous ferns, mosses and herbaceous angiosperms, indicative of a warm and humid climate – an environment where this specific hadrosaur roamed over 66 million years ago.     

Fluid inclusions,C-H-O-S-Pb isotope systematics,geochronology and geochemistry of the Budunhua Cu deposit,northeast China:Implications for ore genesis

The Budunhua Cu deposit is located in the Tuquan ore-concentrated area of the southern Great Xing'an Range,NE China.This deposit includes the southern Jinjiling and northern Kongqueshan ore blocks,separated by the Budunhua granitic pluton.Cu mineralization occurs mainly as stockworks or veins in the outer contact zone between tonalite porphyry and Permian metasandstone.The ore-forming process can be divided into four stages involving stage Ⅰ quartz-pyrite-arsenopyrite;stage Ⅱ quartz-pyrite-chalcopyrite-pyrrhotite;stage Ⅲ quartz--polynetallic sulfides;and stage IV quartz-calcite.Three types of fluid inclusions(FIs) can be distinguished in the Budunhua deposit:liquid-rich two-phase aqueous FIs(L-type),vapour-rich aqueous FIs(V-type),and daughter mineral-bearing multi-phase FIs(S-type).Quartz of stages Ⅰ-Ⅲ contains all types of FIs,whereas only L-type FIs are evident in stage Ⅳ veins.The coexisting V-and S-type FIs of stages Ⅰ-Ⅲ have similar homogenization temperatures but contrasting salinities,which indicates that fluid boiling occurred.The FIs of stages Ⅰ,Ⅱ,Ⅲ,and Ⅳyield homogenization temperatures of 265-396℃,245-350℃,200-300℃,and 90-228℃ with salinities of3.4-44.3 wt.%,2.9-40.2 wt.%,1.4-38.2 wt.%,and 0.9-9.2 wt.% NaCl eqv.,respectively.Ore-forming fluids of the Budunhua deposit are characterized by high temperatures,moderate salinities,and relatively oxidizing conditions typical of an H_2 O-NaCl fluid system.Mineralization in the Budunhua deposit occurred at a depth of0.3-1.5 km,with fluid boiling and mixing likely being responsible for ore precipitation.C-H-O-S-Pb isotope studies indicate a predominantly magmatic origin for the ore-forming fluids and materials.LA-ICP-MS zircon U-Pb analyses indicate that ore-forming tonalite porphyry and post-ore dioritic porphyrite were formed at 151.1±1.1 Ma and 129.9±1.9 Ma,respectively.Geochemical data imply that the primary magma of the tonalite porphyry formed through partial melting of Neoproterozoic lower crust.On the basis of available evidence,we suggest that the Budunhua deposit is a porphyry ore system that is spatially,temporally,and genetically associated with tonalite porphyry and formed in a post-collision extensional setting following closure of the Mongol-Okhotsk Ocean.     

Palynostratigraphy and palaeoenvironmental significance of the Cretaceous palynomorphs in the Qattara Rim-1X well,North Western Desert,Egypt

Palynological and palynofacies analyses were carried out on some Cretaceous samples from the Qattara Rim-1X borehole, north Western Desert, Egypt. The recorded palynoflora enabled the recognition of two informal miospore biozones arranged from oldest to youngest as Elaterosporites klaszii-Afropollis jardinus Assemblage Zone (mid Albian) and Elaterocolpites castelainii–Afropollis kahramanensis Assemblage Zone (late Albian–mid Cenomanian). A poorly fossiliferous but however, datable interval (late Cenomanian–Turonian to ?Campanian–Maastrichtian) representing the uppermost part of the studied section was also recorded. The palynofacies and visual thermal maturation analyses indicate a mature terrestrially derived organic matter (kerogen III) dominates the sediments of the Kharita and Bahariya formations and thus these two formations comprise potential mature gas source rocks. The sediments of the Abu Roash Formation are mostly dominated by mature amorphous organic matter (kerogen II) and the formation is regarded as a potential mature oil source rock in the well. The palynomorphs and palynofacies analyses suggest deposition of the clastics of the Kharita and Bahariya formations (middle Albian and upper Albian–middle Cenomanian) in a marginal marine setting under dysoxic–anoxic conditions. By contrast, the mixed clastic-carbonate sediments of the Abu Roash Formation (upper Cenomanian–Turonian) and the carbonates of the Khoman Formation (?Campanian–Maastrichtian) were mainly deposited in an inner shallow marine setting under prevailing suboxic–anoxic conditions as a result of the late Cenomanian and the Campanian marine transgressions. This environmental change from marginal to open (inner shelf) basins reflects the vertical change in the type of the organic matter and its corresponding hydrocarbon-prone types. A regional warm and semi-arid climate but with a local humid condition developed near/at the site of the well is thought to have prevailed.     

Petrological and geochemical considerations to predict oil potential of Rajpardi and Vastan lignite deposits of Gujarat, western India

This paper entails the results of the investigations undertaken to assess the oil potential of two lignite deposits, Rajpardi and Vastan, from Gujarat, western India. They are ‘Low rank B’ type lignite. Petrographically, they are enriched in huminite and are low in liptinite and inertinite. Their elevated hydrogen content, in relation to carbon, has probably made them perhydrous in nature and oil prone. The reactivity of these coals during liquefaction has also been discussed in the light of petrofactor. Good correlation has been noticed between oil yield and conversion (r² = 0.999) in both the lignite deposits. The VRr (0.24–0.35% in both lignites), H/C atomic ratio (0.11–1.39 in Rajpardi and 1.09–1.88 in Vastan), reactive maceral content (91.6–99.8 vol % mmf in Rajpardi lignite and 75.5–99.7 vol % in Vastan lignite) and VM_daf (64.8–67.9 wt % in Rajpardi lignite and 42.1–80.0 wt % in Vastan lignite) of these lignites have a favourable range required for a coal to generate oil. Huminite is seen to play a vital role in conversion and maintains a good correlation with it. The calculations show that these lignites have a high conversion (> 95%) and oil yield (> 65%).     

Petrographic characterization of Khadsaliya lignites,Bhavnagar district,Gujarat

The petrological studies on Khadsaliya lignites from Bhavnagar district have been carried out for their microconstituent’s characterization. Quantitative estimation of macerals reveal, due to high amount of macerals of huminite group, that this lignite deposits has formed from forest dominated vegetation in a fast subsiding basin, experiencing almost uniform environmental conditions, with slight intermittent fluctuations. The rank based on R_{o max} % values indicates that lignites are less mature and have not reached the sub-bituminous stage of coalification as those of the lignites from Panandhro (Gujarat) and Neyveli (Tamil Nadu) fields. High pyrite content in the Khadsaliya lignite makes it not much suitable for combustion purpose.     

Geochemical characteristics of the lower part of Shayi Member in Lixian Slope,Raoyang Sag,Bohai Bay Basin,Northern China: Implications for organic matters origin,thermal maturity and depositional environment

The lower part of Shayi Member (Es1x Sub-Member) composed mainly of dark mudstones and shales is the dominant source rocks for the Lixian Slope. Based on organic petrology, organic and inorganic geochemistry analyses of several mudstone and shale samples selected from Es1x Sub-Member, this research provides an overview on type, origin and thermal maturity of organic matters, as well as depositional environment of Es1x Sub-Member. Kerogen microscopy observation shows that the macerals are dominated by sapropelinite with a significant mixture of vitrinite and inertinite, indicating that aquatic algal-bacterial organic matter inputs are dominate with a significant contribution of terrigenous organic matter inputs. This statement is supported by n-alkane patterns distribution characteristics, high (n-C₂₁ + n-C₂₂)/(n-C₂₈ + n-C₂₉) values (average = 1.77), the plot of high Ph/n-C₁₈ values (average = 4.15) versus low Pr/n-C₁₇ values (average = 1.13), and high proportion of C₂₇ sterane and C₂₉ sterane (average = 37.7 and 42.0%, respectively). In addition, the rather low Pr/Ph values (average = 0.38), high gammacerane index values (average = 0.30), high V/Ni and V/(V + Ni) values (average = 11.84 and 0.89, respectively), high Sr/Ba and Sr/Cu values (average = 8.54 and 108, respectively), indicative of a saline water condition and a anoxic depositional environment. The low C29 sterane ααα 20S/(20S + 20R), C₂₉ sterane αββ/(αββ + ααα), C₃₁ homohopane 22S/(22S + 22R), C₃₂ homohopane 22S/(22S + 22R), Ts/(Ts + Tm) values and relatively high moretane/hopane values show that the level of thermal maturity of organic matters in Es1x Sub-Member are low.     

The potential of hydrocarbons generation in the Chia Gara Formation at Amadia area, north of Iraq

Sixteen rock samples of outcrop of Chia Gara Formations from the type locality area, south of Amadia, North Iraq showed evidences for hydrocarbon generation potential by palynological studies. These analyses include age assessment of Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) age based on assemblages of mainly dinoflagellate cyst constituents. Qualitative studies are done in this study by textural microscopy used in assessing amorphous organic matter for palynofacies type belong to kerogen type A of Thompson and Dembiki (Int J Coal Geol 6:229–249, 1986) which contain brazinophyte algae, Tasmanites, and foraminifera test linings, as well as the dinoflagellate cysts and spores, deposited in dysoxic–anoxic environment. The palynomorphs are of dark orange and light brown, on the spore species Cyathidites australis, that indicate mature organic matters with thermal alteration index of 2.7–3.0 by Staplin’s scale. These characters and total organic carbon of 0.5–8.5 wt% have rated the succession as a source rock for high efficiency for generation and expulsion of oil with ordinate gas that charged mainly oil fields of Tawqi. Some oil is released from the Chia Gara Formation to charge the Cretaceous–Tertiary total petroleum system.