Outcrop Samples Research Articles

Organic geochemical characteristics and depositional environment of Lower-Middle Miocene Küçükkuyu Formation, Edremit Gulf, NW Turkey

The Lower-Middle Miocene Kucukkuyu Formation crops out extensively in the Edremit Gulf area (NW Turkey). In this study, shale samples from this unit were investigated to evaluate source rock characteristics, depositional conditions, and hydrocarbon potential. Outcrop samples of the Kucukkuyu Formation were taken from different locations and analyzed by Rock-Eval pyrolysis, vitrinite reflectance (Ro), stable carbon isotope (δ13C), total sulfur (TS), gas chromatography (GC), and gas chromatography-mass spectrometry (GC-MS). The total organic carbon (TOC) values range from 0.23 to 6.1 wt.% with an average of 1.76 wt.% for the northern samples and 0.24 to 2.82 wt.% with an average of 1.66 wt.% for the southern samples around the Edremit Gulf. Hydrogen index (HI) values were up to 606 and 712 mg HC/g TOC in the north and south of the gulf, respectively. Organic matter type in the formation consists predominantly of Type II and III kerogen with a minor component of Type I kerogen. Tmax values ranging from 414 to 496 $^{\circ}$C in the north and 423 to 446 $^{\circ}$C in the south of the gulf indicate that most samples are at the beginning of the oil generation window and are thermally immature or early-mid-mature. Vitrinite reflectance (Ro) and biomarker maturity parameters support this result. Based on geological observations, biomarker distributions, and TOC/TS ratios, the Kucukkuyu Formation was deposited in a freshwater to slightly brackish water environment under anoxic-suboxic conditions with organic matter input from aquatic organisms and from terrestrial higher plants. According to Rock-Eval pyrolysis data, the Kucukkuyu Formation mostly has medium to good hydrocarbon-generation potential. However, as these potential source rocks are in general immature and/or early-mature, the hydrocarbon potential of the study area is very limited.

Using Radiogenic Noble Gases to Trace the Conditions of Crustal Fluid Migration

The radiogenic noble gas isotope composition (e.g., 4He*, 21Ne*, 40Ar*, where * denotes the radiogenic component) of crustal mineral grains was investigated to evaluate their utility as a geochemical tracer for characterizing subsurface processes and conditions of crustal fluid migration, specifically within black shales. Because the production of radiogenic noble gases can be predicted by measuring the relative abundance of parent isotopes (e.g., U, Th, K), the distribution of radiogenic noble gases that are retained in crustal minerals can provide important insight into the behavior of fluids in the crust. We hypothesized that the 4He/21Ne* may be particularly useful for these purposes because the production of each isotope is fixed at a nearly constant rate of 4He/21Ne*=22x106 in the crust. Nonetheless, following radiogenic/nucleogenic production, the rate of diffusional release of each radiogenic isotope (e.g., 4He*, 21Ne*) from mineral grains in the rock matrix can vary as a function of temperature, mineral phase, and potentially the rate and extent of fluid migration. As a result, measuring the 4He/21Ne* in fluids or rocks provides information on effective rock porosity, temperature, rate, and volume of fluid flow. Here, we examine the 4He and 21Ne* concentrations, and their isotopic ratio, in quartz grains from the Marcellus Shale (Appalachian Basin, USA). Samples include outcrop samples, sub-crop samples collected at differing deformation regimes (e.g., along faults), and from samples collected from the lateral legs of producing wells. Each sample type experienced differing rates and maximum thermal maturities associated with their geological burial histories. Our results reflect fractionation of 4He and 21Ne* according to the thermal maturity of each sample set as well as with respect to the proximity of deformational features.

MIGRATED PETROLEUM IN OUTCROPPING MESOZOIC SEDIMENTARY ROCKS IN SPITSBERGEN: ORGANIC GEOCHEMICAL CHARACTERIZATION AND IMPLICATIONS FOR REGIONAL EXPLORATION

The presence of migrated petroleum in outcropping rocks on Spitsbergen (Svalbard archipelago) has been known for several decades but the petroleum has not been evaluated by modern geochemical methods. This paper presents detailed organic geochemical observations on bitumen in outcrop samples from central and eastern Spitsbergen. The samples comprise sandstones from the Lower Cretaceous Carolinefjellet Formation, the Upper Triassic – Middle Jurassic Wilhelmøya Subgroup and the Upper Triassic De Geerdalen Formation; a limestone from the De Geerdalen Formation; and carbonates from the Middle Jurassic – Lower Cretaceous Agardhfjellet Formation. In addition a palaeo‐seepage oil was sampled from a vug in the Middle Triassic Botneheia Formation. This data is integrated with the results of analyses of C1–C4 hydrocarbon fluid inclusions trapped in quartz and calcite cements in these samples.Organic geochemical data suggest that the petroleum present in the samples analysed can be divided into two compositional groups (Group I and Group II). Group I petroleums have distinctive biomarker characteristics including Pr/Ph ratios of about 1.3–1.5, high tricyclic terpanes relative to pentacyclic terpanes, and relatively high methyl‐dibenzothiophenes compared to methyl‐phenanthrenes. By contrast Group II petroleums have low tricyclic terpanes relative to pentacyclic terpanes and low methyl‐dibenzothiophenes compared to methyl‐phenanthrenes, and most Pr/Ph ratios range from 1.90 to 2.57. The petroleum in both groups was derived from marine shale source rocks deposited in proximal to open marine settings.Group I petroleums, present in the sandstones of the Wilhelmøya Subgroup and the De Geerdalen Formation and as a palaeo‐seepage oil in the vug in the Botneheia Formation, are likely to have been sourced from the Middle Triassic Botneheia Formation. Group II petroleums, found in the sandstone of the Carolinefjellet Formation, the limestone from the De Geerdalen Formation and in carbonates of the Agardhfjellet Formation, are inferred to have been generated from the Jurassic‐Cretaceous Agardhfjellet Formation.The analysis of biomarker and aromatic hydrocarbons in the petroleums indicate three relative maturation levels, equivalent to expulsion at vitrinite reflectances of about 0.7–0.8%Rc, 0.8–0.9%Rc and 1.0–1.6%Rc. On average, Triassic host rocks contain petroleum of higher maturity compared to the Jurassic and Cretaceous host rocks.The fluid inclusion data suggest that gaseous hydrocarbons from the sandstones of the Wilhelmøya Subgroup are thermogenic, and are of similar maturity to the petroleum in extracts from these sandstones, suggesting that the gas was generated together with oil in the oil window. By contrast the inclusion gases from carbonate rocks analysed have a mixed (thermogenic / biogenic) origin.The outcropping rocks in which these oils occur are analogous to offshore reservoirs on the Norwegian Continental Shelf. The study may therefore improve our understanding of the subsurface offshore petroleum systems in the Barents Sea and possibly also in other circum‐Arctic basins.

A revised chemo-chrono-stratigraphic 4-D model for the extrusive rocks of the Paraná Igneous Province

The statistical analysis of a lithogeochemical database from whole Paraná Igneous Province (PIP), containing 5974 outcrop and drillhole samples, stresses natural gaps separating SiO2, Zr, TiO2 and P2O5 in high and low values. Their combination delimits 16 chemical types, which have been adopted to classify a sub-set of extrusive rocks with <2% LOI, comprising 3296 samples. The SiO2×Zr diagram, where only extrusive rock samples were plotted, shows two major trends connecting low silica (LSi) with high silica (HSi) types. The set formed by Type 4 (LSi-LZr-HTi-HP)+Type 3 (LSi-LZr-HTi-LP)+Type 2 (LSi-LZr-LTi-HP) outcrop samples constitutes a continuous strip that contours the North-Central portion of the Paraná Igneous Province - PIP, subdividing the Type 1 (LSi-LZr-LTi-LP) into Type 1 (Southern) and Type 1 (Central-Northern). The rocks of Type 9 (HSi-LZr-LTi-LP) are mainly exposed in the Central-Southern region and the Zr contents divide them into Type 9 (Central-Southern)<303ppm Zr and Type 9 (South-East)≥303ppm Zr. Both Type 13 (HSi-HZr-LTi-LP) and Type 14 (HSi-HZr-LTi-HP) are exposed on the eastern rim of the PIP. Types are characterized and correlated by typical major and minor elemental associations as well as specific geographical locations throughout the province, composing a robust 3-D model. The combination of maps, cross-sections and 40Ar/39Ar and U/Pb ages found in the literature resulted in a 4-D model (spatial and temporal) for the province. Thus, it is proposed to subdivide the PIP into Southern Sub-province and Central-Northern Sub-province, each one with its own evolution, based on the chemo- and chrono-stratigraphy of its volcanic sequence.

Nutrient Level Change Based on Calcareous Nannofossil Assemblages During Late Miocene in Banyumas Subbasin

DOI:10.17014/ijog.3.3.183-194Hydrographic situation on surface waters is more challenging to be understood, related to global and regional climate change in tropical regions. In addition, records from these tropical areas are limited compared to other areas of subtropical and polar regions. The aim of this study is to reconstruct Cenozoic paleoceanography, in particular nutrient level, using outcrop samples from Kali Pasir, Banyumas, Indonesia. This study is focused on the relationships of the relative abundance of Discoaster, coccolith size of Reticulofenestra, and lithofacies characteristics. Nutrient level is reconstructed using quantitative analysis of calcareous nannofossil by counting calcareous nannofossils on 400 fields of View (FOV) for each sample. The abundance of Discoaster and the large Reticulofenestra represent a deep thermocline and nutricline, which is a typical of oligotrophic condition. This condition also associated with the muddy facies in the early stages of Late Miocene (NN8-NN10a). Conversely, decreasing Discoaster abundance and the abundance of small Reticulofenestra indicate a shallow thermocline and nutricline, resulting strong eutrophication of surface waters in the later stage of Late Miocene (NN10b-NN11). A high nutrient content in this stage is related to classical turbidite deposits. A change in a sea surface resulted in strong eutrophication, which is in this section similar to the eastern Indian Ocean micropaleontology records during the Late Miocene (NN10). This finding shows that strong eutrophication in Kali Pasir section is probably driven by nutrient-rich terrestrial material related to the onset of Indian monsoon during the Late Miocene.

Evaluation of the shale gas potential of the lower Silurian Longmaxi Formation in northwest Hunan Province, China

Commercial gas production has been achieved in China's marine shale of the Silurian Longmaxi formation in the eastern Sichuan area, and experience for developing shale gas in complex structural areas has been gathered. A set of Longmaxi Formation shales deposited in the northwestern Hunan area has close relationship with the eastern Sichuan Longmaxi shale on both depositional environment and tectonic evolution. Therefore, it is important to undertake an integrated evaluation of the Longmaxi formation shale in the northwestern Hunan area. This work combined field investigations and the laboratory measurements using outcrop samples to study the petrology, geochemistry, reservoir and adsorption characteristics of the Longmaxi shale in the northwestern Hunan area. The geological settings and reservoir properties were compared with those of the eastern Sichuan Longmaxi shale using publically available data. The results show that the hydrocarbon generation ability, organic matter maturity, sealing capacity and reservoir stimulation effectiveness of the Longmaxi Formation shale in the northwestern Hunan area are comparable to those in the eastern Sichuan area. The Longmaxi shale in the northwestern Hunan area therefore shows early signs of development potential, and the drilling of exploration wells is thus warranted to further evaluate its gas content and other in-situ reservoir properties for possible shale gas development in the near future.

Organic geochemistry of the Lower Toarcian Posidonia Shale in NW Europe

A suite of core and outcrop samples of the Lower Toarcian Posidonia Shale and time-equivalent deposits was collected from multiple locations, including southern Germany (Swabian Alb and Franconian Alb), northern Germany, the east coast of Great Britain, the Netherlands, and Luxembourg, in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data. All samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from Great Britain (about 0.7% vitrinite reflectance). Molecular geochemical maturity parameters were used to quantify maturation in detail.During shale deposition in the West Cleveland Basin, Great Britain, H2S was immediately consumed in the water column by terrigenous input, supplying abundant reactive iron to form pyrite. These samples are characterized by low dibenzothiophene/phenanthrene ratios (<0.2) and gammacerane indices (<0.1) and are accompanied by high sulfur contents and abundant tiny pyrites (>95% of<7μm in diameter), generated within the water column due to the immediate reaction of Fe2+ and H2S. In contrast, sulfidic (euxinic) bottom waters, possibly with enhanced salinity and stratified water column, prevailed due to a more restricted iron supply in Luxembourg, northern Germany and the Franconian Alb of southern Germany. A more oxygenated (dysoxic) bottom water column associated with anoxic sediments, i.e., anoxic/dysoxic boundary close to the sediment/water interface, prevailed in the Swabian Alb of southern Germany. Despite observed changes within each vertical profile at each site, large scale regional trends in depositional conditions can be clearly identified for the Early Toarcian.

Disentangling the record of diagenesis, local redox conditions, and global seawater chemistry during the latest Ordovician glaciation

The Late Ordovician stratigraphic record integrates glacio-eustatic processes, water-column redox conditions and carbon cycle dynamics. This complex stratigraphic record, however, is dominated by deposits from epeiric seas that are susceptible to local physical and chemical processes decoupled from the open ocean. This study contributes a unique deep water basinal perspective to the Late Ordovician (Hirnantian) glacial record and the perturbations in seawater chemistry that may have contributed to the Hirnantian mass extinction event. We analyze recently drilled cores and outcrop samples from the upper Vinini Formation in central Nevada and report combined trace- and major element geochemistry, Fe speciation (FePy/FeHR and FeHR/FeT), and stable isotope chemostratigraphy (δ13COrg and δ34SPy). Measurements of paired samples from outcrop and core reveal that reactive Fe is preserved mainly as pyrite in core samples, while outcrop samples have been significantly altered as pyrite has been oxidized and remobilized by modern weathering processes. Fe speciation in the more pristine core samples indicates persistent deep water anoxia, at least locally through the Late Ordovician, in contrast to the prevailing interpretation of increased Hirnantian water column oxygenation in shallower environments. Deep water redox conditions were likely decoupled from shallower environments by a basinal shift in organic matter export driven by decreasing rates of organic matter degradation and decreasing shelf areas. The variable magnitude in the record of the Hirnantian carbon isotope excursion may be explained by this increased storage of isotopically light carbon in the deep ocean which, in combination with increased glacio-eustatic restriction, would strengthen lateral- and vertical gradients in seawater chemistry. We adopt multivariate statistical methods to deconstruct the spatial and temporal re-organization of seawater chemistry during the Hirnantian glaciation and attempt to isolate the latent magnitude and global perturbation in the carbon cycle. We speculate, using a two component mixing model and residual estimates from principal component analysis, that the secular open ocean Hirnantian C isotope excursion possibly amounts to only ∼ +1.5‰. Such an increase could be mechanistically driven by the combination of sea-level fall, persistent deep water anoxia, and cooler glacial temperatures that increased the organic carbon burial efficiency in the deeper basins.

Apatite fission track and (U-Th)/He thermochronology from the Archean Tanzania Craton: Contributions to cooling histories of Tanzanian basement rocks

Borehole and surface samples from the Archean Tanzania Craton were analysed for apatite fission track (AFT) and (U-Th)/He data with the aim of deciphering cooling histories of the basement rocks. Fission track dates from borehole and outcrop samples are Carboniferous–Permian (345 ± 33.3 Ma to 271 ± 31.7 Ma) whereas (U-Th)/He dates are Carboniferous–Triassic (336 ± 45.8 Ma to 213 ± 29 Ma) for outcrop grains and are consistently younger than corresponding AFT dates. Single grain (U-Th)/He dates from the borehole are likely to be flawed by excessive helium implantation due to their very low effective uranium contents, radiation damage and grain sizes. All AFT and (U-Th)/He dates are significantly younger than the stratigraphic ages of their host rocks, implying that the samples have experienced Phanerozoic elevated paleo-temperatures. Considerations of the data indicate removal of up to 9 km overburden since the Palaeozoic.Thermal modelling reveals a protracted rapid cooling event commencing during the early Carboniferous (ca. 350 Ma) at rates of 46 m/Ma ending in the Triassic (ca. 220 Ma). The model also suggests minor cooling during the Cretaceous of the samples to surface temperatures. The suggested later cooling event remains to be tested. The major cooling phase during the Carboniferous is interpreted to be associated with compressional tectonics during the Variscan Orogeny sensu far field induced stresses. Coeval sedimentation in the Karoo basins in the region suggests that most of the cooling of cratonic rocks during the Carboniferous was associated with denudation.

Reconnaissance study of organic geochemistry and petrology of Paleozoic-Cenozoic potential hydrocarbon source rocks from the New Siberian Islands, Arctic Russia

A reconnaissance study of potential hydrocarbon source rocks of Paleozoic to Cenozoic age from the highly remote New Siberian Islands Archipelago (Russian Arctic) was carried out. 101 samples were collected from outcrops representing the principal Paleozoic-Cenozoic units across the entire archipelago. Organic petrological and geochemical analyses (vitrinite reflectance measurements, Rock-Eval pyrolysis, GC-MS) were undertaken in order to screen the maturity, quality and quantity of the organic matter in the outcrop samples. The lithology varies from continental sedimentary rocks with coal particles to shallow marine carbonates and deep marine black shales. Several organic-rich intervals were identified in the Upper Paleozoic to Lower Cenozoic succession. Lower Devonian shales were found to have the highest source rock potential of all Paleozoic units. Middle Carboniferous-Permian and Triassic units appear to have a good potential for natural gas formation. Late Mesozoic (Cretaceous) and Cenozoic low-rank coals, lignites, and coal-bearing sandstones also display a potential for gas generation. Kerogen type III (humic, gas-prone) dominates in most of the samples, and indicates deposition in lacustrine to coastal paleoenvironments. Most of the samples (except some of Cretaceous and Paleogene age) reached oil window maturities, whereas the Devonian to Carboniferous units shared a maturity mainly within the gas window.

Latest Pannonian and Quaternary evolution at the transition between Eastern Alps and Pannonian Basin: new insights from geophysical, sedimentological and geochronological data

The transition zone between Eastern Alps and Pannonian Basin is a key area for the investigation of the interplay between regional uplift, local tectonic subsidence and depositional environment. Our study area, the western margin of the Little Hungarian Plain, is characterized by gentle hills, plateaus and depressions, of which several are filled by lakes—including one of Austria’s largest and shallowest lakes, Lake Neusiedl. Geological investigation is hampered by the scarcity of outcrops, and thus direct observation of sedimentological or structural features is difficult. Despite a long research history in the area, a consistent landscape evolution model considering all relevant constraints is lacking so far. In this study, we apply multidisciplinary methods to decipher the complex tectonic and fluvial depositional evolution of the region. Local data from shallow-lake drilling and seismic investigation are combined with regional data from industrial seismics and core data to gain new insights into the latest Pannonian (Late Miocene) and Quaternary evolution. Shallow-lake seismic data show the erosionally truncated Pannonian sediments dipping and thickening toward southeast, toward the modern depocenter of the Little Hungarian Plain. Overlying Quaternary fluvial sediments show a very similar thickening trend except for the area on the plateau north of the lake indicating ongoing subsidence in major parts of the basin. Drill cores from locations along the lake seismic lines were analyzed concerning their age, mineralogy and heavy minerals and compared with outcrop samples from the surrounding plains and the plateau to derive indications on sediment provenance. A key observation is the apparent lack of a significant gravel layer on top of the tilted Pannonian sediments beneath Lake Neusiedl. Small-scale faults can be observed in the lake seismic sections along with key sedimentary features. Significant differences of the current elevation of the top Pannonian between the surrounding plains and the plateau indicate post-Pannonian normal faulting, which is a key process in shaping the present-day morphology of the region. Luminescence ages of samples from the Quaternary fluvial gravels on top of the Pannonian sediments are a significantly higher (>300 ka) compared to the gravels in the plain (102 ± 11 and 76 ± 8 ka), suggesting ongoing tectonic subsidence.

A possible shale gas prospect? First results of the organic composition and thermal maturity of the Carboniferous Namoi Formation, northern NSW, Australia

ABSTRACTThe Namoi Formation in the Werrie Syncline, north and west of Tamworth, is part of the well-preserved Devonian–Carboniferous fore arc in the New England Fold Belt. The formation is between 640–914 m thick and consists of dominant olive-green mudstones with lenses of sandstone and oolitic limestone. To assess shale gas prospectivity, we analysed five outcrop samples from the Namoi Formation in the Keepit area. Well-preserved aliphatic and aromatic hydrocarbon fractions do not show evidence of weathering or biodegradation. n-Alkanes in all samples have a unimodal distribution maximising at C26 to C28. Little odd-to-even n-alkane carbon number predominance and relatively low Pr/n-C17 and Ph/n-C18 ratios are consistent with a high thermal maturity. Based on the distribution of alkylnaphthalenes and alkylphenanthrenes, the Namoi Formation is in the gas window. Calibration of the methylphenanthrene index and ratio with vitrinite reflectance suggests a calculated reflectance around 2.1%, which given a normal geothermal gradient is equivalent to a maximum temperature of 205°C for the deepest burial of the formation. There is a dominance of parent polycyclic aromatic hydrocarbons (PAH) over alkylated PAHs, supporting a high thermal maturity. Some samples contain biomarkers suggestive of a marine depositional environment, including the C30 sterane index and the C31/C30 hopane ratio. The Namoi Formation is a prospective shale-gas source, as it has been buried sufficiently to be well within the gas window. Where it is exposed at the surface gas will have been lost, but elsewhere it will be buried beneath other sediments and may still retain gas. Key exploration uncertainties include information on organic richness, lateral variation in thermal maturity, mineralogy, and porosity–permeability relationships.

Record of Gondwana Plant Mega- and Microfossils in Nimugudem Area, Telangana, India:Palynodating and Palaeoenvironmental Interpretation

The present study is a record of Permian (Lower Gondwana) and late Jurassic-early Cretaceous (Upper Gondwana) palynomorphs in megafossilbearing beds in Nimugudem area, Godavari subbasin, Telangana, India. Detailed palynological studies were carried out on outcrop samples from the exposure in a nala of Nimugudem area where leaf impressions of plant megafossils were also observed. Leaf impressions of Ptilophyllum and Pterophyllum recorded in this section indicate Upper Gondwana affinity for these sediments. Presence of different species of palynomorphs of Upper Gondwana affinity in sandstone beds indicates late Jurassic-early Cretaceous (Tithonian- Berriasian) age for these sediments. It is equivalent to Kota/Gangapur Formation of Godavari Graben. Reworked Permian palynomorphs were recorded in these sediments. The coal exposure yielding late Permian palynomorphs belongs to Raniganj Formation.

Ocean upwelling and intense monsoonal activity based on late Miocene diatom assemblages from Neil Island, Andaman and Nicobar Islands, India

The late Miocene (Tortonian) diatoms in 21 outcrop samples from Neil Island, Andaman and Nicobar Islands were investigated with eighty two planktonic and benthic taxa belonging to 35 genera. Principal Component Analysis reveals the existence of two distinct groups; samples dominated by Thalassionema nitzschioides and Thalassiothrix longissima, belong to one group and the other group is dominated by Actinocyclus ellipticus, Azpeitia nodulifera, Coscinodiscus asteromphalus and C. radiatus. Five palaeoecological zones have been proposed with the help of CONISS cluster analysis according to the dominance of diatom taxa. To ascertain high resolution palaeoecological zones SHEBI analysis was carried out, which reveals seven zones. The studied outcrop is also characterised by the late Miocene marker radiolarians of RN8 and RN9 zones. The overall analysis indicates a strong monsoonal system; however there are evidences of relatively weaker intermittent monsoonal activity. The diatom planktonic/benthic ratio shows evidence of minor sea level fluctuations during that period. The dominance of the upwelling diatom taxon Thalassionema nitzschioides confirms the strong monsoonal activity during the late Miocene in the study area.

Weathering characteristics of the Lower Paleozoic black shale in northwestern Guizhou Province, south China

The northwestern Guizhou in the Yangtze Craton of south China has a tremendous potential of shale gas resource. In this paper, we present results from major and trace elements, total organic carbon, mineralogical composition analysis and petrophysical parameters to characterise shale weathering features. Further, the differences of black shale between underground and outcrops have also been presented to examine the changes of black shale after weathering. Our results show that the trace elements of shale have varying degrees of loss in the weathering leaching process, both in Niutitang shale and Longmaxi shale, the loss of B, V, Ni, Cu, Zn and Ba is obvious, but the element migration quantity in the former is greater than in the latter. Decomposition of minerals such as pyrite, feldspar and calcite result in the leaching of Na, Ca, Mg and Fe. The loss rate of total organic carbon (TOC) in black shales ranges from 18% to 70% with an average of 43%; moreover, the loss of organic carbon in samples with high TOC content is larger than in those samples with low TOC content. Results following the testing of porosity and permeability show that porosity increases significantly after weathering but permeability changes little. Furthermore, the increment of porosity is greater in the Niutitang shale (with more sulphide minerals) than in the Longmaxi shale, suggesting that the oxidation of sulphide minerals may have led to the formation of an acidic environment, causing the other minerals in the black shale to weather more quickly, thus resulting in increased porosity. The content of clay minerals in the core samples is slightly lesser than the outcrop samples, but the TOC content in the core samples is greater and has a larger specific surface area. This suggest that the TOC content played a decisive role on the specific surface area of shale. In addition, changes in the black shale caused by the weathering process mainly depend on the mineral composition and the TOC content in shale. In this study, we try to establish relations between outcrop samples and core samples, in order to better understand the underground characteristics of shale reservoir.

Paleoenvironmental reconstruction of the Late Santonian Songliao Paleo-lake

The Late Cretaceous is often characterized as having a variable greenhouse climate, however, the relatively few continental sites preserving geologic records from this time exist limiting information on terrestrial climate and environments. Worldwide, the Songliao Basin (SLB) of northeastern China is one of the largest Cretaceous-age continental rift basins. Thus, this well-preserved lacustrine deposit provides a unique record of terrestrial paleoenvironmental conditions during the Cretaceous. Here, we report organic geochemical data from Late Cretaceous-age lacustrine deposits (lower Nenjiang Formation) from the eastern side of the SLB. Outcrop samples were collected from the Houjingou section and the following analyses were performed: (1) total organic carbon (TOC) content and isotopic composition, (2) biomarker distribution, including the identification and determination of relative amounts of both aliphatic and aromatic hydrocarbons and steranes, and (3) compound specific stable carbon and hydrogen isotopic compositions of n-alkanes. The biomarker distribution and stable carbon isotopic values (δ13C) of the TOC indicate organic matter (OM) from the uppermost section of the first member of the Nenjiang Formation (Upper K2n1) was mainly sourced from aquatic macrophytes and land plants. In the lower part of the second member of the Nenjiang Formation (Lower K2n2) the biomarker distribution and δ13C of both the TOC and n-alkanes indicate that OM was sourced from a mixture of algae, bacteria, and higher plants. As a result of marine transgression, seawater incursions, indicated by the presence of 24-n-propyl-cholestanes and 24-iso-propyl-cholestanes, occurred episodically in Lower K2n2. The negative hydrogen isotopic composition (δ2H) of short chain n-alkanes in Lower K2n2 indicates an extremely humid environment and it is likely that an influx of freshwater caused large-scale flooding of the Songliao Paleo-lake. High-resolution biomarker and stable isotope records from the Houjingou section demonstrate abrupt environmental changes in the Songliao Paleo-lake following seawater incursions during the Late Cretaceous.

Determination of elemental composition of shale rocks by laser induced breakdown spectroscopy

In this study laser induced breakdown spectroscopy (LIBS) is used for elemental characterization of outcrop samples from the Marcellus Shale. Powdered samples were pressed to form pellets and used for LIBS analysis. Partial least squares regression (PLS-R) and univariate calibration curves were used for quantification of analytes. The matrix effect is substantially reduced using the partial least squares calibration method. Predicted results with LIBS are compared to ICP-OES results for Si, Al, Ti, Mg, and Ca. As for C, its results are compared to those obtained by a carbon analyzer. Relative errors of the LIBS measurements are in the range of 1.7 to 12.6%. The limits of detection (LODs) obtained for Si, Al, Ti, Mg and Ca are 60.9, 33.0, 15.6, 4.2 and 0.03ppm, respectively. An LOD of 0.4wt.% was obtained for carbon. This study shows that the LIBS method can provide a rapid analysis of shale samples and can potentially benefit depleted gas shale carbon storage research.

Impact of diagenetic and depositional fabric on reservoir quality; a synthesis from Late Cretaceous and Early Paleocene sandstones in Eastern Sulaiman Range, Pakistan

The Maastrichtian Pab Sandstone and the Danian Khadro Formation are among the major reservoirs of the region but are considered to be tight and are therefore poorly evaluated. A 551-m-thick section of the Pab Sandstone and 128-m-thick section of the Khadro Formation are measured and logged in detail. The measured units mainly composed of thin- to thick-bedded sandstone with subordinate mudstone and occasional marls that were deposited in the western passive margin of the Indian Plate. Eight and four depositional facies have been identified in the Pab and Khadro Formations, respectively, and are grouped into pro-delta, delta-front, and delta-plain facies associations which were deposited in fluvial-wave-dominated deltaic settings. Thirty-two samples of sandstones from Pab Sandstone and 20 from Khadro Formation are collected for reservoir and petrographic studies. The sandstone of studied formations are classified as quartz aernite, subarkosic, sublitharenite, and wackes. These are fine to coarse grain, subangular to rounded, and poorly to moderately sorted. The intense burial diagenesis resulted in compaction, extensive cementation, and authigenic mineralization which cause low values of porosity/permeability. Cements have filled all the available pore spaces and clay minerals block pore throats, thus resulting in major destruction of porosity and permeability. The late stage dissolution of unstable framework grains and cements has resulted in appreciable increase in secondary porosity. The petrographic studies and plug porosity/permeability results of outcrop samples suggest that laterally continuous and vertically stacked thick sandstone sequences of delta-plain and delta-front facies associations possess good values of porosity.

An investigation of factors affecting the interaction of CO2 and CH4 on shale in Appalachian Basin

Depleted unconventional gas reservoirs have been proposed reservoirs for long-term storage of anthropogenic CO2. The injection of CO2 in such reservoirs may benefit from, (1) the presence of existing infrastructure and right-of-way to reduce sequestration costs, (2) the presence of an existing network of fractures to increase reservoir contact efficiency, and (3) potential to enhanced gas recovery using CO2. However, there remain significant technical challenges and uncertainties about the behavior of these reservoirs, and how they might respond to CO2 flooding. Toward addressing those uncertainties, the present study considers results of select experiments intended to improve understanding of the fundamental characteristics of shale matrix and shale interactions with methane and carbon dioxide. Outcrop samples from the low permeability sedimentary Marcellus formations in the Appalachian Basin of the eastern United States were characterized using various analytical techniques, including FTIR, XRD, ICP-OES, TOC analyzer, surface analysis, and pycnometry. FTIR confirmed CO2 adsorption by appearance of an absorption band near 2349cm−1, however, CH4 absorption band at 1303cm−1 was comparatively weak. Total organic carbon (TOC) exhibits significant statistical correlation with Cu, K, and Ni, while several other metals (As, Ba, Ca, Cd, Co, Cr, Fe, Mg, Mn, Na, Sr, and Ti) correlated with total inorganic carbon (TIC). Shale adsorption capacities of both CO2 and CH4 showed linear relationships to the organic matter content with CO2 exhibiting consistently higher adsorption capacities than CH4. At organic matter content greater than 2wt%, the ratios of adsorption capacity of CO2 over CH4 were in a range between 1.3 and 1.9, which is similar to the ratios of critical temperatures between CO2 and CH4. This study evaluates the role of various physical and chemical parameters on CO2/shale and CH4/shale interaction, and considers implications for sequestration of CO2 in depleted shale reservoirs.

Organic petrology and geochemistry of Eocene Suzak bituminous marl, north-central Afghanistan: Depositional environment and source rock potential

Organic geochemistry and petrology of Eocene Suzak bituminous marl outcrop samples from Madr village in north-central Afghanistan were characterized via an integrated analytical approach to evaluate depositional environment and source rock potential. Multiple proxies suggest the organic-rich (TOC ∼6 wt.%) bituminous marls are ‘immature’ for oil generation (e.g., vitrinite Ro < 0.4%, Tmax < 425 °C, PI ≤ 0.05, C29 ααα S/S + R ≤ 0.12, C29 ββS/ββS+ααR≤0.10, others), yet oil seeps are present at outcrop and live oil and abundant solid bitumen were observed via optical microscopy. Whole rock sulfur content is ∼2.3 wt.% whereas sulfur content is ∼5.0–5.6 wt.% in whole rock extracts with high polar components, consistent with extraction from S-rich Type IIs organic matter which could generate hydrocarbons at low thermal maturity. Low Fe-sulfide mineral abundance and comparison of Pr/Ph ratios between saturate and whole extracts suggest limited Fe concentration resulted in sulfurization of organic matter during early diagenesis. From these observations, we infer that a Type IIs kerogen in ‘immature’ bituminous marl at Madr could be generating high sulfur viscous oil which is seeping from outcrop. However, oil-seep samples were not collected for correlation studies. Aluminum-normalized trace element concentrations indicate enrichment of redox sensitive trace elements Mo, U and V and suggest anoxic-euxinic conditions during sediment deposition. The bulk of organic matter observed via optical microscopy is strongly fluorescent amorphous bituminite grading to lamalginite, possibly representing microbial mat facies. Short chain n-alkanes peak at C14–C16 (n-C17/n-C29 > 1) indicating organic input from marine algae and/or bacterial biomass, and sterane/hopane ratios are low (0.12–0.14). Monoaromatic steroids are dominated by C28 clearly indicating a marine setting. High gammacerane index values (∼0.9) are consistent with anoxia stratification and may indicate intermittent saline-hypersaline conditions. Stable C isotope ratios also suggest a marine depositional scenario for the Suzak samples, consistent with the presence of marine foraminifera including abundant planktic globigerinida(?) and rare benthic discocyclina(?) and nummulites(?). Biomarker 2α-methylhopane for photosynthetic cyanobacteria implies shallow photic zone deposition of Madr marls and 3β-methylhopane indicates presence of methanotrophic archaea in the microbial consortium. The data presented herein are consistent with deposition of Suzak bituminous marls in shallow stratified waters of a restricted marine basin associated with the southeastern incipient or proto-Paratethys. Geochemical proxies from Suzak rock extracts (S content, high polar content, C isotopes, normal (αααR) C27–29 steranes, and C29/C30 and C26/C25 hopane ratios) are similar to extant data from Paleogene oils produced to the north in the Afghan-Tajik Basin. This observation may indicate laterally equivalent strata are effective source rocks as suggested by previous workers; however, further work is needed to strengthen oil-source correlations.