Stable Isotope Investigations Research Articles

Oil migration from internal and external source rocks in an unconventional hybrid petroleum system, Montney Formation, western Canada

Unconventional hybrid petroleum systems are partially to entirely self-sourced. Their hydrocarbons are generated within internal (intraformational) organic-rich mudstone source rocks and subsequently migrate into adjacent organic-lean reservoir beds composed of sandstone, siltstone or carbonate. Hybrid systems with volumetrically dominant reservoir-quality rocks can additionally receive hydrocarbon charge by longer-range migration from external source rocks. However, few previous studies of hybrid systems have focused on the migration and mixing of hydrocarbons from both internal and external sources. To address this shortfall, this study presents an integrated organic geochemistry and stable carbon isotope investigation of drill-core and produced hydrocarbon liquid samples from two wells in a major unconventional hybrid petroleum system in the Montney Formation of western Canada. The results reveal distinct geochemical trends with increasing depth through the upper part of the Montney Formation including decreased C30+ biomarker compounds, increased depletion of saturate compared to aromatic δ13C values, and increased proportions of saturates and mobile oil. These trends indicate that oil from external source rocks of the overlying Doig Formation migrated into the upper part of the Montney Formation. Downward migration of externally sourced Doig oil resulted in a broad transition zone where Doig-sourced oil mixed with locally migrated lighter oil generated within internal Montney source rocks of slightly higher thermal maturity. This study sheds new light on the migration and mixing of disparate oil charges in the Montney Formation, and likely has widespread applicability to other similar unconventional hybrid petroleum systems that had hydrocarbon contributions from both internal and external source rocks.

Identifying the Groundwater Sources of Huangtupo Landslide in the Three Gorges Reservoir Area of China

Groundwater plays a crucial role in triggering and reactivating deep-seated landslides. However, classical hydrogeological investigations have limitations in their applicability to deep-seated landslides due to anisotropic and heterogeneous media. The Huangtupo landslide in the Three Gorges Reservoir area has garnered significant attention due to its high hazard potential. Of particular interest is the NO.1 Riverside Sliding Mass (HTP-1), which has shown notable deformation and has become the primary focus of landslide research. The study aims to investigate the sources of water in the HTP-1 landslide through hydrochemical analysis. This was achieved by monitoring the major ion content in the groundwater within the landslide for one year. Furthermore, stable isotope investigations were conducted on the groundwater in and around the landslide area, and an analysis of the mineral composition of the landslide soil was also performed. The results indicate that the groundwater in the landslide area (LGW) is a mixture of karst groundwater (KGW) from the adjacent upslope and local precipitation (LP). The karst groundwater is a major contributor to the recharge of the landslide groundwater system, causing a high component of groundwater that can easily exceed the critical level that causes landside failure during heavy rainfall events. Furthermore, prior to the relocation of residents from the Huangtupo landslide, the landslide groundwater was also impacted by human sewage, which not only affected the chemical composition of groundwater, but also had potential implications for slope stability. These findings provide a more scientific basis for the design and implementation of interception and drainage measures for the Huangtupo landslide and other large-scale landslides with similar geological conditions in the Three Gorges Reservoir area.

Turning up the heat: Assessing the impact of charring regime on the morphology and stable isotopic values of cereal grains

The stable isotopic values of charred crops are now frequently analysed in archaeology. While previous research has highlighted how grain morphology and stable carbon and nitrogen isotope values change with grain charring temperature, such research has been limited to temperature ranges under 260 °C and using predominately Mediterranean cereals and pulses. For the first time, this study provides experimental data on the impact of charring on two northern European cereals, rye and oat, both morphologically and isotopically. New experimental charring of rye, oat, bread wheat and hulled barley extends the charring window to 300 °C, providing an insight into the morphological changes to the grains as well as the difference between charred and uncharred isotopic values. This range of cereals and conditions opens up potential for stable isotopic investigation of medieval agricultural growing conditions and practices in Britain. The results indicate that isotopically, a 0.16‰ and a 0.32‰ offset should be applied to δ13C and δ15N values, respectively, of grains charred between 230 and 300 °C. Morphological and internal structural changes, as well as external distortion, are key attributes which vary with charring temperature and duration. Guidelines are provided to enable assessment of whether archaeological grains of bread wheat, hulled barley, rye and oat fall within the acceptable charring window for isotopic analysis.

Dental calculus and isotopes reveal information about ancient diet of Boccone del Povero community (1st-2nd century CE, Latium, central Italy)

Evidence about the dietary habits of the 42 individuals recovered in the necropolis of Boccone del Povero (1st-2nd century CE; Rome, Italy) was obtained by a multidisciplinary approach. Dental calculus analysis (through optical microscopy and gas chromatography-mass spectrometry) and stable isotope investigation from bone proteins were carried out on the human skeletal series, with a particular focus on the young female unearthed from the richest burial (no. CLXXXI) of the archaeological site. Overall, carbon and nitrogen stable isotope data indicated an omnivorous diet mainly based on C3-terrestrial proteins, although for some individuals C4 plant consumption cannot be excluded. In fact, evidence from calculus suggests the use of Andropogoneae (e.g., sorghum), Triticeae, together with Rosaceae seeds (e.g., almonds), milk and dairy products. The application of morphological, biochemical, and biomolecular techniques provided a reconstruction of the subsistence pattern of this ancient population living in a suburb of the Imperial Rome.

Extreme dietary specialisation in adult male southern elephant seals: determining variation between individual trophic diets

Although dietary studies have provided important insights into the causes and ramifications of diet variation for the southern elephant seal (SES) (Mirounga leonina), adult males are comparatively underrepresented within that literature. Individual males can vary morphologically as well as behaviourally, leading to differences in their life history trajectories and outcomes. Therefore, to improve our understanding of the male diet, we sought to determine the degree of dietary variation between as well as within individuals from the West Antarctic Peninsula. Secondly, we investigated whether individual morphological traits, seasonality, and year influenced their dietary variation. Whiskers were sampled from 31 adult male seals and used to measure the bulk stable isotope nitrogen (δ15N). We sequentially segmented each whisker to create a time series of datapoints for each individual, allowing us to compare δ15N variation within each seal as well as assess variation between the seals. We then investigated the relationships between male dietary variation and body length, girth, season, and year. We found that adult male SESs maintained an extremely specialised diet. Variation between individuals was strongly correlated with their body size, with larger seals feeding higher up the trophic web. Interestingly, seasonality and year both influenced variation within the seals’ diets, but only year was seen to influence the variability between seals. We discuss the possible causes and ramifications of dietary specialisation for the SES and highlight the need for combined tracking and stable isotope investigations to improve our understanding of the ontogeny of the seals’ dietary specialisation.

Climatic significance of modern minute land snail shells δ13C and δ18O on the Chinese Loess Plateau

Land snails are abundant and well preserved in loess-paleosol sequences on the Chinese Loess Plateau (CLP) and are often regarded as valuable climatic indicators in paleoclimate reconstruction. To date, many stable isotope investigations have been carried out on land snail shells (e.g., δ13Cshell and δ18Oshell) from diverse geographical and climatic regions. However, few studies have been conducted on modern minute land snails (2–10 mm) on the CLP, and their climatic significance has not been adequately understood. Here, we present new δ13Cshell and δ18Oshell data from four minute modern land snails (Pupilla aeoli, Gastrocopta armigerella, Opeas striatissimum, Vallonia tenera), and analyses of their correlations with climatic factors (growing season temperature, precipitation and relative humidity) were conducted to examine their climatic significance across the CLP. The results show that δ13Cshell can record local vegetation information and has the potential to be a reliable precipitation proxy. Interestingly, δ18Oshell exhibits spatially scattered values in the studied region, and these data yielded poor correlations with various climatic parameters, such as precipitation amount, temperature and relative humidity. Given the similar spatial characteristics of observed precipitation δ18O (δ18Op), these phenomena may support the dominant control of δ18Op on δ18Oshell.

Differential food utilization of benthic amphipods of a tropical estuary: a stable isotopic (δ13C and δ15N) investigation.

Globally, stable isotopic methods are rapidly being employed in food web studies to quantify the relative proportions of diverse primary carbon sources in an animal diet. Tropical estuarine ecosystems, one of the vital marine habitats, harbor complex food webs due to the multiplicity of habitats and resources. The complex system of inputs and exchanges of organic matter sometimes complicate identification of the carbon sources that support the higher trophic levels. To assess the primary food sources of four abundant amphipod species in the anthropogenically influenced upper Vashishti estuary, Carbon and Nitrogen stable isotopes were employed. Seasonal variations were significant for δ13C and δ15N of suspended particulate organic matter (SPOM) and also for δ13C of sediment organic matter (SOM), but not for the isotopic values of individual amphipod species. Significant variations in the δ13C and δ15N values between amphipods suggested species-specific diets. Mixing model output indicated discrepancies in seasonal variations of food preferences between species. Trophic level values of all amphipod species indicated seasonality with lower values during post-monsoon. The low δ15N values of SPOM, SOM, and amphipod species were possibly due to the anthropogenic input of nitrogen in the estuary.

Stable isotopic investigation of the feeding ecology of wild Bornean orangutans

AbstractObjectivesWe applied stable carbon and nitrogen isotope analyses to wild Bornean orangutans (Pongo pygmaeus morio) to investigate the feeding ecology of wild orangutans. Compared with African great ape species, orangutans are adapted to environments with chronic lower nutrition. But the usefulness of stable isotope analysis in the study of wild orangutan feeding ecology has not been fully explored.MethodsThe study site was a primary lowland dipterocarp forest in the Danum Valley, Sabah, Malaysia. A total of 164 plant and 94 fecal samples collected across 18 months were analyzed.ResultsCarbon and nitrogen stable isotope ratios of plant food samples do not systematically vary by plant parts (i.e., bark, fruits, and leaves). Elemental composition and stable isotope ratios of orangutan feces do not systematically vary by orangutans' sex and age classes, although fecal stable isotope ratios showed seasonal fluctuations. No isotopic contribution of breast milk was found in fecal samples collected from individuals at 2.7–6.5 years of age.ConclusionsThis study revealed key characteristics of the stable isotope ecology of wild orangutans living in a primary lowland forest. Although there was little isotopic variation among plant foods and orangutan individuals, seasonal fluctuations in baseline isotope ratios or orangutans' diet were found in Danum valley.

Mineralogy, geochemistry, fluid inclusion, and stable sulfur isotope investigation of the Terziali shear-related orogenic gold deposit (Central Anatolia, Turkey): implications for ore genesis and mineral exploration

Mineralogy, geochemistry, fluid inclusion, and stable sulfur isotope investigation of the Terziali shear-related orogenic gold deposit (Central Anatolia, Turkey): implications for ore genesis and mineral exploration

Greater than the sum of your parts: Nonlethal stable isotope sampling methods in spiders

AbstractAs top consumers and generalist predators, spiders are ideal organisms to study food webs and complex ecological functions using stable isotopes. Most researchers use whole‐body samples to analyze stable isotope ratios in spiders. Spiders can regrow lost legs and produce multiple molts during a life cycle, and nonlethal sampling utilizing legs and molts may provide a useful alternative to whole‐body sampling especially in larger bodied or threatened species. Furthermore, removing spider abdomens and thus leftover prey in the gut contents may provide a more accurate isotopic value. We tested the hypothesis that the δ15N, δ13C, or δ2H isotopic values in spider legs are reliable proxies for spider prosomas, abdomens, or whole bodies. We used laboratory‐reared large‐bodied spiders (Pterinochilus murinus) and field‐collected Lycosidae to compare lethal and nonlethal tissue isotopic values. We found that nonlethal samples of spider legs and molts are acceptable alternatives to lethal whole‐body samples to determine δ13C and δ15N stable isotope signatures. Nonlethal samples are not suitable proxies for whole‐body samples to determine δ2H isotopic values. Using nonlethal leg or molts samples in stable isotope investigations of spiders will allow researchers to promote conservation efforts and study threatened species while ensuring accurate and repeatable results.

Recent Progresses in Stable Isotope Analysis of Cellulose Extracted from Tree Rings.

In this work, the challenges and progression in stable isotope investigation, from the analytical tools and technical sample preparation procedures to the dendroclimatological experiments, were reviewed in terms of their use to assess tree physiological responses to environmental changes. Since the isotope signature of whole wood is not always a reliable tool in studying the climate changes, cellulose is often preferred as the study material in paleoclimatic studies. Nevertheless, the isotope analysis of cellulose is challenging due to the difficulty to remove the other wood components (extractives, lignin, pectin, and hemicelluloses). Additionally, in the case of hydrogen isotope analysis, about 30% of the hydrogen atoms of cellulose are exchanged with the surrounding water, which complicates the isotope analysis. In recent years, more automated isotope analysis methods were developed based on high temperature pyrolysis of cellulose, followed by the chromatographic separation of H2 from CO and by their individual isotope analysis using isotope ratio mass spectrometry. When used to investigate climate factors, the combined isotope analysis δ13C and δ18O appears to be the most promising isotope tool. In contrast, the role of δ2H values is yet to be elucidated, together with the development of new methods for hydrogen isotope analysis.

Släktskap och neolitiska kulturer

Kinship and Neolithic cultures. As a result of their alkaline soil, due to limestone bedrock, the two Swedish islands of Öland and Gotland, are locations where bone is well preserved. Stable isotope investigations have shown that there were two contemporary populations during Middle Neolithic on the islands. One population was buried in megalithic graves, and shows evidence of a subsistence lifestyle with high proportion of terrestrial food, most probable from agriculture. The other population has had a lifestyle based on marine subsistence, and buried their dead in earth graves at shore sites. Ancient DNA investigations now show that the two populations may also have different origins. The hunter-gathers of the ”Pitted Ware Culture” might descend from a Mesolithic population, while the supposed farmers buried in the megaliths and affiliated with the ”Funnel Beaker Culture”, are more likely to descend from immigrants that arrived in the Ewarly Neolithic and brought agriculture to the islands.

A stable isotope and functional weed ecology investigation into Chalcolithic cultivation practices in Central Anatolia: Çatalhöyük, Çamlıbel Tarlası and Kuruçay

The integration of stable isotope analysis of crop remains with the ecological analysis of archaeological weed flora allows for a detailed reconstruction of crop husbandry and arable growing conditions. This paper presents the first such study for developed Neolithic and Chalcolithic Central Anatolia, exploring crop husbandry at the large (8 ha) early 6th millennium BC site of Çatalhöyük West and the last phases of the preceding Neolithic Çatalhöyük East, located on the western end of the Konya Plain, and the small 4th millennium sites of Çamlıbel Tarlası (0.25 ha), located in the loop of the Kızılırmak river, and Kuruçay Höyük (~1 ha), located on the shore of Lake Burdur. The results reveal the mosaic nature of Çatalhöyük cultivation; the complex ecosystem, naturally 15N enriched, was additionally anthropogenically improved, while inhabitants also chose to cultivate barley in drier conditions to the wheats and pulses. The smaller, Late Chalcolithic site of Çamlıbel Tarlası cultivated each individual crop species in variable conditions instead of selecting a specific species for cultivation in drier or wetter conditions. Each single species was cultivated in conditions with a wide range of water availabilities while receiving low-level manure application. Variation in water availability is possibly a consequence of the variable topography surrounding the site, with the hills potentially used for cultivation, providing a wide range of conditions due to their slope. Functional weed ecology complements the isotopic data, indicating the wider range of cultivation intensities surrounding Çatalhöyük West, compared with more consistent, narrower ranges of growing conditions at Çamlıbel Tarlası and Kuruçay Höyük. Settlement date, site size and environment seem to be key contributing factors shaping the method used to cultivate crops at these Chalcolithic sites. The larger, earlier community of Çatalhöyük West, located in a complex riverine ecosystem around the dryland anabranching channels of the Çarşamba river, cultivated species in different conditions and maintained a range of crop husbandry intensities, potentially reflecting differential access to limited resources. The smaller Late Chalcolithic sites, with communities consisting of one household to several households and located in less complex ecosystems with higher precipitation, maintained more stable crop growing conditions and management intensities. This is plausibly a consequence of equal access and sharing of critical resources for crop cultivation, such as labour, manure and land, coupled with the adequate precipitation rates.

Microscopic, biochemical and stable isotopic investigation of seven multi-nutritional food-balls from Indus archaeological site, Rajasthan (India)

During excavation of a Harappan archaeological site 4MSR (29°12′24.48″N, 73°09′20.16″E) from western Rajasthan (India), seven closely spaced similar sized spheroids (food-balls) were recovered. Detailed microscopic, biochemical (organic), elemental and stable isotopic composition of the spheroidal-material was studied. δ13C value of organic fraction (−22.5‰) indicated agricultural origin of organic matter. Significant excesses of Magnesium (Mg) and Calcium (Ca) and Potassium (K) further supported organic (food material) dominance in the spheroids. Gas chromatography mass-spectrometry (GCMS) analysis showed dominance of plant derived organic compounds in the spheroid sample. Microscopic stain analysis using safranin and iodine dyes confirmed bulk of the spheroids was composed of organic material. Majority of starch granule morphotypes found in spheroid-material were made of legumes and cereals dominated by Mung (Vigna radiata). Siliceous phytoliths, Ca and Mg oxalate crystals along with a few Mg sulphate crystals were also observed in spheroids composition. We surmise these spheroids were mainly made up of food grains comprising both cereals and legumes. The concept of offerings for some ritual or multi-nutritive compact food balls for instant nutrition as food-supplement, perhaps prevailing during that period. The presence of bull figurines, hand held copper adze and a Harappan seal in the vicinity of these seven food balls signify that humans revered all these commodities due to their utility and importance to them.

Vallisneria natans detritus supports Daphnia magna somatic growth and reproduction under addition of periphyton

Submerged macrophytes are regarded as being hardly assimilated by zooplankton for their lack of essential nutrients such as polyunsaturated fatty acids (PUFAs) thus serve as poor quality food, contrary to field stable isotopic investigations with observed macrophyte carbon contributions to zooplankton. However, periphyton growing on them produces the PUFAs and is thus a nutrient supplement. We hypothesize that with this supplement, zooplankton can be supported by macrophyte carbon. To test this hypothesis, we fed zooplankton with (1) 13C enriched Vallisneria natans detritus, (2) periphyton and (3) a mix of the two. We compared growth and reproduction of zooplankton under these three food treatments and calculated zooplankton assimilation of macrophyte carbon when fed a mixed diet, using a stable isotope-mixing model. The fatty acid profile of the two carbon resources was also analyzed. Our results demonstrate that Daphnia magna can grow and reproduce well, and use V. natans carbon when a supplement of periphyton is available.

A combined geochemical, Nd, and stable Ca isotopic investigation of provenance, paleo-depositional setting and sub-basin connectivity of the Proterozoic Vindhyan Basin, India

Geochemical and isotopic investigation of Proterozoic clastic and chemical sedimentary rocks provide insights into surface conditions of the early Earth. The mid-Proterozoic Vindhyan Basin of central India, comprising ~5 km thick, mostly undeformed and unmetamorphosed clastic and chemical sediments, is one such archive which is exposed in two sub-basins, the Son Valley Vindhyan sub-basin in the east (SVV) and Chambal Valley Vindhyan sub-basin in the west (CVV). Geochemical and Nd isotopic compositions of siliciclastic sedimentary rocks from the CVV sub-basin are reported in order to understand the provenance of the Vindhyan sediments in this sub-basin and the results are compared with the provenance of the sediments exposed in the SVV sub-basin to evaluate whether the two sub-basins had shared a common provenance. Elemental ratios, such as Th/Co, La/Sc suggest that the clastic sedimentary rocks from the CVV have dominantly upper crustal silicic/felsic provenances and are broadly similar to those of equivalent stratigraphic horizons from the SVV. Initial Nd isotopic composition (εNd(t)) of the siliciclastic rocks from the Lower Vindhyans of the CVV, calculated at their respective times of deposition, suggest sediment derivation from the Banded Gneissic Complex, Berach Granitoids, 1.82 Ga continental arc granitoids of the Aravalli Range and the Hindoli Volcanics. In contrast, the εNd(t) values of the Upper Vindhyan siliciclastics suggest that the Delhi Belt granitoids were the primary source of detritus during the deposition of these sediments. Paleo-depositional environment and connectivity between the SVV and CVV sub-basins are evaluated using geochemical, radiogenic Nd, and stable Ca isotopic compositions of carbonates from both sub-basins. Non-redox sensitive REY anomalies and Y/Ho ratios of carbonates from the two sub-basins suggest deposition in an epeiric sea with limited connection to the open ocean. Neodymium isotopic compositions of the carbonate units suggest that the two sub-basins were connected during the deposition of both Lower and Upper Vindhyan sediments. Carbonates from both sub-basins record a significant shift towards more radiogenic Nd isotopic compositions around 1.6 Ga, possibly as a result of an Andean-type arc magmatism in near vicinity of the Son Valley sub-basin. The δ44/40Ca compositions of the SVV carbonates are typically lower than the CVV carbonates. This difference is likely due to greater freshwater input in the SVV sub-basin which is consistent with the existence of paleo-gradients in the Vindhyan Basin.

An investigation of the source of salinity in groundwater using stable isotope tracers and GIS: A case study of the Urmia Lake basin, Iran

Salinization of groundwater resources, especially in arid areas, limits their use. This problem can be aggravated by low annual precipitation, greater evaporation, and an excessive water discharge. The various sources of salinization, particularly in the unconfined aquifers, make it difficult to manage these resources. The sources of salinity can be detected through detailed sets of tracer data and a spatial analysis of their variation over the aquifer. Regarding the intense computational effort needed for this purpose, the geographic information system (GIS) can be used as a powerful tool for spatial analysis. This study aims to reveal the sources of salinity in the Azarshahr and Shabestar-Sufyan aquifers located in the Urmia basin, northwest Iran. The study is based on a comprehensive geochemical and stable water isotope (δ18O, δ2H) investigation of groundwater. We conclude the effectiveness of using isotope tracers to observe the effect of basin geology on water salinity. Evaporation and the dissolution of evaporative rocks in these regions is greatly effective in the isotopic concentrations. As is evident from a Piper diagram, in some parts of the study area, the main groundwater source is precipitation and there is no significant relationship between precipitation and the Urmia Lake.

Deposition characteristics of pliocene coals in the denizli region (SW Turkey) via organic petrography, geochemistry, and stable isotope composition

The objective of this study is to identify and evaluate the organic geochemical properties, paleo vegetation, and paleo depositional environment of coals in Denizli (SW Turkey). Organic geochemical and petrographic investigations, scanning electron microscopy, X-ray diffractometry, and palynological and stable isotope (δ2H, δ13C, δ15N, δ18O and δ34S) investigations have been performed. Coal, clayey coal, and coaly claystone samples from the study area have gas and oil production potential according to their total organic carbon (0.59–48.30 wt%), hydrogen index (56–286 mg HC/g TOC), oxygen index (30–121 mg CO2/g TOC) and S2/S3 (0.47–9.59) values. Dominant maceral assemblages included huminites and low amounts of liptinite group macerals. Tissue preservation index (0.39–5.13), gelification index (4.11–96.83), groundwater index (0.40–8.77) and vegetation index (0.49–42.67) parameters indicate a limno-telmatic environment and increased woody tissue. Mean random huminite/vitrinite reflectance values (ranging from 0.23 to 0.41 %Ro) denote lignite and sub-bituminous C and B ranked coals. Carpinus, Alnus, Zelkova, Platanus-Salix, Carya, and Ostrya were found through palynologic investigations. In addition, freshwater algae Botryococcus was detected in coal samples from Denizli. δ13C, δ15N values and C/N ratios indicated a terrestrial C3 ecosystem. Some sterane and tricyclic terpane ratios and aromatic biomarkers have shown that high plant input, immature organic matter and oxic-suboxic conditions are predominant in the depositional environment.

Stable-isotope and fluid inclusion constraints on the timing of diagenetic events in the dolomitized Dolomia Principale inner platform (Norian, Southern Alps of Italy)

The petrographic, cathodoluminescence (CL), stable isotope, and microthermometry investigation of inner platform facies of the pervasively dolomitized carbonate platform of the Norian (Upper Triassic) Dolomia Principale (Southern Alps, N Italy) identified two major dolomite phases. An early replacement fabric-retentive dolomite (D1 and D2, respectively replacing the sedimentary facies - from fenestral mudstone/wackestone to bioclastic packstone and mudstone and stromatolites- and early marine cements) is followed by a later, vug- and fracture-filling dolomite cement phase (D3, planar-s texture).The fabric-retentive dolomitized carbonates (<4 μm−30 μm, D1) and marine fibrous cements (30 μm−250 μm, D2) exhibit dull luminescence under CL whereas the burial dolomite cement (200 μm−500 μm, D3) exhibits zoned luminescence. Microthermometric measurements of the primary two-phase fluid inclusions in D3 yielded a mean homogenization temperature of 112.4 ± 8.2 °C. Supposing a surface seawater temperature of at least 20–25 °C and a geothermal gradient of about 40 °C/km during the Early Jurassic rifting that led to the opening of the Alpine Tethys, such temperature might be reached at reasonable burial depth ranging from 2.0 km to about 2.5 km. According to the subsidence curve this depth, compatible with the temperature recorded by the fluid inclusions, was reached during the Early Jurassic, with D3 cement precipitation causing a significant reduction of the porosity.The δ13C values of the investigated dolomites (D1, D2, and D3) show a narrow range of variation (2.0–3.1‰ VPDB), pointing toward a fluid-buffered system. Differently, the δ18O values largely varies, ranging from −12.8 to +1.9‰ VPDB. In this range, D3 values cluster distinctively between −6.0 to −12.8‰ VPDB with respect to D1 and D2, which cluster from about −4 to +1.9‰ VPDB. The estimated oxygen isotope composition of the parent fluid of D1 and D2 (~0 to −5‰ VSMOW) suggests possible contributions from marine to slightly evaporated seawater, which is consistent with the arid climate and some basin restrictions suggested by earlier studies, whereas that of D3 (+1 to +5‰ VSMOW) is consistent with burial fluids.The followed integrated approach highlights the possibility to better characterize the occurrence of multiple diagenetic events in time and space, as well as their feedback effects on the porosity evolution of dolomitized carbonate reservoirs, framing the diagenetic events at regional scale.

Paleoenvironmental significance of biomarker and stable isotope (2H, 13C, 15N, 18O, and 34S) investigations on a Pliocene coal-bearing sequence (Denizli Basin, southwestern Turkey)

Pliocene coal, clayey coal, and coaly claystone sediments from the Yatağan Formation (Denizli Basin, southwestern Turkey) have been investigated with respect to maceral association, mineralogical composition, n-alkane, isoprenoid and saturated-aromatic biomarker characteristics, and stable isotopes (2H, 13C, 15N, 18O, and 34S). The main purpose of the present study was to determine the hydrocarbon potential and paleodepositional conditions of coals in the Denizli Basin. The abundances of huminite, liptinite, and inertinite macerals were 46.14%, 8.06%, and 1.57%, respectively. The huminite/vitrinite reflectances (%Ro) of the coal, clayey coal, and coaly claystone samples ranged between 0.26 and 0.37 %Ro, implying sub-bituminous B and C coal ranks. The total organic C (TOC, wt.%) content and the Tmax values of the investigated samples ranged between 0.74 and 43.80 wt% and 390–440 °C, respectively. In addition, the coaly horizons were characterized by very low H index (HI), O index (OI), production index (PI), and Tmax values. Moreover, a high waxiness degree, C preference index (CPI), odd-to-even predominance (OEP), terrigenous/aquatic ratio (TAR), and high C19 tricyclic terpane/C23 tricyclic terpane (C19/C23 TT) and C24 tetracyclic terpane/C26 tricyclic terpane (C24*/C26 TT) biomarker ratios indicated a terrestrial plant input. These results were supported by stable isotope (2H, 13C, and 15N) investigations. Although the Pliocene coals have source rock potential according to the TOC content and pyrolysis analyses, they have been determined to be at the diagenesis and immature stages as a result of organic petrographic, and saturated-aromatic biomarker investigations.