Carbon Isotope Analysis Research Articles

In-situ experiment reveals CO2 enriched fluid migration in faulted caprock

The sealing characteristics of the geological formation located above a CO2 storage reservoir, the so-called caprock, are essential to ensure efficient geological carbon storage. If CO2 were to leak through the caprock, temporal changes in fluid geochemistry can reveal fundamental information on migration mechanisms and induced fluid–rock interactions. Here, we present the results from a unique in-situ injection experiment, where CO2-enriched fluid was continuously injected in a faulted caprock analogue. Our results show that the CO2 migration follows complex pathways within the fault structure. The joint analysis of noble gases, ion concentrations and carbon isotopes allow us to quantify mixing between injected CO2-enriched fluid and resident formation water and to describe the temporal evolution of water–rock interaction processes. The results presented here are a crucial complement to the geophysical monitoring at the fracture scale highlighting a unique migration of CO2 in fault zones.

Tropical and temperate differences in the trophic structure and aquatic prey use of riparian predators.

The influence of aquatic resource-inputs on terrestrial communities is poorly understood, particularly in the tropics. We used stable isotope analysis of carbon and nitrogen to trace aquatic prey use and quantify the impact on trophic structure in 240 riparian arthropod communities in tropical and temperate forests. Riparian predators consumed more aquatic prey and were more trophically diverse in the tropics than temperate regions, indicating tropical riparian communities are both more reliant on and impacted by aquatic resources than temperate communities. This suggests they are more vulnerable to disruption of aquatic-terrestrial linkages. Although aquatic resource use declined strongly with distance from water, we observed no correlated change in trophic structure, suggesting trophic flexibility to changing resource availability within riparian predator communities in both tropical and temperate regions. Our findings highlight the importance of aquatic resources for riparian communities, especially in the tropics, but suggest distance from water is less important than resource diversity in maintaining terrestrial trophic structure.

Circular waste management: Superworms as a sustainable solution for biodegradable plastic degradation and resource recovery

Bioplastics offer a promising solution to plastic pollution, however, their production frequently relies on edible biomass, and their degradation rates remain inadequate. This study investigates the potential of superworms (Zophobas atratus larvae) for polybutylene succinate (PBS) waste management, aiming to achieve both resource recovery and biodegradation. Superworms exclusively fed on PBS for a month exhibited the same survival rate as those on a standard bran diet. PBS digestion yielded a 5.13% weight gain and a 23.23% increase in protein composition in superworms. Additionally, carbon isotope analyses substantiated the conversion of PBS into superworm components. Gut microbes capable of PBS biodegradation became progressively prominent, further augmenting the degradation rate of PBS under composting conditions (ISO 14855-1). Gut-free superworms fed with PBS exhibited antioxidant activities comparable to those of blueberries, renowned for their high antioxidant activity. Based on these findings, this study introduces a sustainable circular solution encompassing recycling PBS waste to generate insect biomass, employing insect gut and frass for PBS degradation and fertilizer, and harnessing insect residue as a food source. In essence, the significance of this research extends to socio-economic and environmental spheres, impacting waste management, resource efficiency, circular economy promotion, environmental preservation, industrial advancement, and global sustainability objectives. The study's outcomes possess the potential to reshape society’s approach to plastic waste, facilitating a shift toward more sustainable paradigms.

Distinctive microfossil supports early Paleoproterozoic rise in complex cellular organisation.

The great oxidation event (GOE), ~2.4 billion years ago, caused fundamental changes to the chemistry of Earth's surface environments. However, the effect of these changes on the biosphere is unknown, due to a worldwide lack of well-preserved fossils from this time. Here, we investigate exceptionally preserved, large spherical aggregate (SA) microfossils permineralised in chert from the c. 2.4 Ga Turee Creek Group in Western Australia. Field and petrographic observations, Raman spectroscopic mapping, and in situ carbon isotopic analyses uncover insights into the morphology, habitat, reproduction and metabolism of this unusual form, whose distinctive, SA morphology has no known counterpart in the fossil record. Comparative analysis with microfossils from before the GOE reveals the large SA microfossils represent a step-up in cellular organisation. Morphological comparison to extant micro-organisms indicates the SAs have more in common with coenobial algae than coccoidal bacteria, emphasising the complexity of this microfossil form. The remarkable preservation here provides a unique window into the biosphere, revealing an increase in the complexity of life coinciding with the GOE.

Evolution characteristics and exploration targets of Permian clastic rock reservoirs in Bohai Bay Basin, East China

Based on core observation, thin section examination, fluid inclusions analysis, carbon and oxygen isotopic composition analysis, and other approaches, the structural and burial evolution histories were investigated, and the diagenetic evolution process and genetic/development models were systematically discussed of the Upper Paleozoic Permian clastic rock reservoirs in the Bohai Bay Basin, East China. The Bohai Bay Basin underwent three stages of burial and two stages of uplifting in the Upper Paleozoic. Consequently, three stages of acid dissolution generated by the thermal evolution of kerogen, and two stages of meteoric freshwater leaching occurred. Dissolution in deeply buried, nearly closed diagenetic system was associated with the precipitation of authigenic clay and quartz, leading to a limited increase in storage space. Different structural uplifting–subsidence processes of tectonic zones resulted in varying diagenetic–reservoir-forming processes of the Permian clastic reservoirs. Three genetic models of reservoirs are recognized. The Model I reservoirs with pores formed in shallow strata and buried in shallow to medium strata underwent two stages of exposure to long-term open environment and two stages of meteoric freshwater leaching to enhance pores near the surface, and were shallowly buried in the late stage, exhibiting the dominance of secondary pores and the best physical properties. The Model II reservoirs with pores formed in shallow strata and preserved due to modification after deep burial experienced an early exposure-open to late burial-closed environment, where pore types were modified due to dissolution, exhibiting the dominance of numerous secondary solution pores in feldspar and the physical properties inferior to Model I. The Model III reservoirs with pores formed after being regulated after multiple periods of burial and dissolution experienced a dissolution of acidic fluids of organic origin under a near-closed to closed environment, exhibiting the dominance of intercrystalline micropores in kaolinite and the poorest physical properties. The target reservoirs lied in the waterflood area in the geological period of meteoric freshwater leaching, and are now the Model II deep reservoirs in the slope zone–depression zone. They are determined as favorable options for subsequent exploration.

Amorphous carbonaceous material in Paleoproterozoic pillow lavas (Onega Basin, NW Russia): Origin, source and migration

The amorphous carbonaceous material (CM) in mafic igneous rocks is important for deciphering the relationships between igneous and hydrocarbon systems in Earth interior. Deciphering of CM in Precambrian rocks it is a challenge because of reworking by later superimposed events but could give insights into evolution of these systems in time. We report the results of combined field and petrological studies, Raman spectroscopy and carbon isotope analysis of well-preserved ca. 2.0 Ga pillow lavas in the Onega Basin, Karelian craton, Eastern Fennoscandian Shield. In these rocks CM is present in both pillow and inter-pillow areas as poorly ordered carbon. In the MORB-like basalts of the Zaonega Formation, CM occurs in post-magmatic veinlets formed via migration of hydrothermal fluids. In the OIB-type basalts of the Suissary Formation, CM is found in amygdales, inclusions in feldspar, and in devitrified volcanic glass indicating a CM deposition via a rapid cooling of C-rich magma. Despite morphological diversity carbon isotopic composition indicates a biogenic origin of CM in both the MORB- and OIB-like basalts. The most likely source was the Paleoproterozoic oilfield in the Zaonega Formation, commonly referred to as the Shunga event.

Isotopic and proteomic evidence for communal stability at Pre-Pottery Neolithic Jericho in the Southern Levant

As one of the key, long-term occupied sites in the Southern Levant, Jericho was one of the most important early Neolithic centres to witness social and economic changes associated with the domestication of plants and animals. This study applies strontium (87Sr/86Sr), oxygen (δ18O) and carbon (δ13C) isotope analyses to the enamel of 52 human teeth from Pre-Pottery Neolithic (PPN) layers of Jericho to directly study human diet and mobility and investigate the degree of consolidation and the flexibility of social organization of Jericho society in the PPN period. The results indicate only two non-local individuals out of the 44 sampled inhabitants identified by strontium isotope analysis and are consistent with the presence of a largely sedentary community at PPN Jericho with no evidence for large-scale migration. We also construct strontium spatial baselines (87Sr/86Sr map) with local 87Sr/86Sr signatures for the sites across the Southern Levant based on systematic compilation and analysis of available data. In addition, we apply proteomic analysis of sex-specific amelogenin peptides in tooth enamel for sex estimation of the sampled individuals (n = 44), the results of which showed a sex-biased ratio (more male than female detected in this sample pool) in Jericho society during the PPN period, which may be due to the limited sample size or selective ritual practices like particular burial zones used for specific groups. We also pretreated a batch of human bone samples recovered from PPNB Jericho for stable carbon and nitrogen isotope analyses for dietary investigations. However, the extracted collagen showed poor preservation and no valid δ13C or δ15N data were obtained.

Evidence for a Temporary Positive Priming Effect in Aquatic Systems With Certain Substrates and Isotopic Discrimination of DOM Sources

AbstractThe “priming effect” (PE) is well documented in soils, but contradictory results have been reported in aquatic ecosystems. To investigate whether the presence of easily degradable labile dissolved organic matter (LDOM) changes the biodegradation rate of nonlabile DOM (NLDOM), incubations were performed with various sources of LDOM and NLDOM in microcosms amended with nutrients and a microbial inoculum. Stable carbon isotope analysis of DOM was used for the first time to estimate the PE. A significant positive PE (15%–34% of initial NLDOM) was measured, but only with mixed (glucose + amino acids) or complex (disaccharide) LDOM. Regardless of the LDOM, no PE was measured with more recalcitrant NLDOM (half‐life of 128 days here), when the LDOM/NLDOM ratio was low (0.3 versus 1), and when the NLDOM and microbial inoculum were from the same water (no mixing). The presence of sediments likely enhances microbial diversity and NLDOM degradation rate, but it did not increase the PE. Microbial use of LDOM produced new microbial NLDOM that should be discriminated (here by isotopes) from initial NLDOM for accurate PE measurements. The PE was temporary and lasted about 2 weeks after one LDOM addition. In areas with frequent additions of LDOM, a long‐lasting PE is expected and may significantly increase CO2 production. Exposing refractory DOM to new conditions and microbial community, such as during natural water mixing, seems to exert a strong control on its dynamics. Here, the addition of a new microbial inoculum had a stronger effect than adding LDOM or the PE.

A subaerial origin for the mid-Ediacaran Johnnie valleys, California and Nevada: Implications for a diachronous onset of the Shuram excursion

Mid-Ediacaran incised valleys in the Johnnie Formation of eastern California are of interest for their broad time concordance with comparable features elsewhere (e.g., the Wonoka canyons of South Australia), and the largest negative carbon isotope anomaly in Earth history (the Shuram excursion). The Johnnie valleys have been previously interpreted as originating through mass wasting in a submarine setting at a continental margin, and perhaps as a result of syndepositional tectonism. New data suggest an alternative scenario: that the valleys were cut by a combination of fluvial incision and subaerial mass wasting concomitant with sea-level lowering in excess of 200 m, and were subsequently drowned and filled by marine sediments representing paleowater depths as great as tens of meters. Critical evidence from a series of outcrops in the southern Nopah Range includes (1) a new estimate of the erosional relief of the valleys of at least 208 m; (2) the presence in the basal fill of polymictic conglomerate/breccia with a quartz sand matrix that is locally associated with stratified quartz sandstone, suggesting both local and far-traveled fill components; and (3) beds and blocks of giant ooid packstone-grainstone indicative of shallow marine sedimentation during the early stages of valley filling. The conglomerate/breccia is channelized and associated locally with cross-stratification. Our interpretation is based upon a total of forty-five measured sections, physical stratigraphic mapping supported by sub-meter scale resolution 3-D drone imagery, as well as carbon isotope analyses. Comparable valleys, arguably of the same age, and likewise attributed to subaerial incision in earlier studies, are present at or near the top of the Caddy Canyon Quartzite of northern Utah and southeastern Idaho (a straightline distance of ∼ 850 km). Our working hypothesis is that both sets of valleys correspond in time with Gaskiers glaciation (∼580 Ma). Given that negative δ13C values have been obtained from both below and (new data) within the basal valley fill, and correlated by most workers with the Shuram excursion, we infer that the Shuram encompasses rather than postdates the Gaskiers event in eastern California, and that the onset of the excursion may be diachronous at a global scale.

Diagenetic Evolution and Petrophysical Characteristics of Paleogene Sandstone Reservoirs in the Southwest Baiyun Sag, Northern South China Sea

In addressing the critical need to understand the geological and diagenetic factors affecting Paleogene sandstone reservoirs in the Baiyun Sag—a region vital for oil and gas exploration—this study delves into the Paleogene Zhuhai and Enping formations. Advanced methodologies, including petrographic thin-section analysis, scanning electron microscopy, wavelet analysis, and carbon and oxygen isotope analysis, were employed to evaluate their petrological characteristics, pore structures, physical properties, and key diagenetic processes. The results indicate that the Zhuhai Formation is primarily composed of feldspathic quartz sandstones with prevalent intergranular dissolution pores, while the Enping Formation consists mainly of feldspathic sandstones with intragranular solution pores. The diagenetic temperatures across both formations ranged from 42.6 to 116.3 °C. The studied reservoirs have experienced porosity alterations due to mechanical compaction (23.07% reduction), carbonate cementation (9.02% reduction), and dissolution (5.09% enhancement). Notably, feldspar dissolution emerged as a significant contributor to high-quality reservoirs, particularly in the upper Enping Formation. These findings offer invaluable insights into the diagenetic evolution of sandstone reservoirs in the Baiyun Sag and hold significant implications for guiding future oil and gas exploration efforts in the region.

Farming and feasting during the Bronze Age–Iron Age transition in Britain (ca. 900–500 bce): multi-isotope evidence for societal change

The Late Bronze Age saw the rise of a new site type in southern Britain, commonly termed a midden. These vast monumental mounds, some comprising tens of thousands of artefacts/ecofacts dominated by animal bone and ceramics, signal a societal refocus towards agricultural intensification and communal feasting on a grand scale. These sites point to agricultural produce being the mainstay of the economy, with bronze having a reduced social and economic importance. This likely created new regimes of managing landscapes and livestock and new networks and agricultural catchments anchored on the sites. Major questions remain surrounding the strategies employed to enhance agricultural productivity, how landscapes and livestock were managed, and how different sites and regions met these challenges at a time of climatic deterioration. This article employs multi-isotope analyses on domestic and wild fauna to address these questions. It presents carbon, nitrogen, and sulfur (δ13C, δ15N, and δ34S, respectively) isotope analyses on 235 animals from 6 midden sites in 2 major regions of midden accumulation: the Vale of Pewsey in Wiltshire and the Thames Valley. The results demonstrate distinct differences in approaches to maximising agricultural productivity, with varied strategies apparent at a site, species, and regional level. Some sites, such as Potterne and Runnymede, clearly drew domestic fauna from a wide catchment where wide-ranging management and foddering regimes were employed. Other sites, such as East Chisenbury, had a more restricted catchment but a tightly controlled, intensive management regime. These data provide new insights into regional responses to the reorganisation of the economy, landscape use, and developing agricultural networks during the Bronze Age–Iron Age transition in Britain, revealing dynamic and evolving societal change.

Effects of lipid extraction on human bone collagen: Comparing stable carbon and nitrogen isotope values with and without lipid extraction

This study analyzes 24 human bone fragments to assess how lipid extraction affects stable carbon and nitrogen isotope ratios. Eighteen samples were archaeological bone and six were modern bone. Each bone was split into two pieces, producing 48 bone samples, and half underwent lipid extraction and half did not. This was done to assess whether the two techniques yielded statistically significant differences in δ13C and δ15N. The results are an important contribution for establishing standard stable isotope preparation protocols, which affect time and cost of laboratory procedures. Further, given that many dietary stable isotope studies compare original results to published material, this study addresses whether those comparisons are suitable if some samples undergo lipid extraction while others do not.We also examine 144 articles that report stable carbon and nitrogen isotope results to evaluate the proportion of studies that conduct lipid extraction versusthose that do not. We explore those outcomes by archaeological geographic region and by stable isotope laboratories. Findings show that 15% of the published studies do lipid extraction, and they tend to be grouped by researchers and laboratories who conduct research in specific global regions. The meta-analysis of the published articles and the findings that some laboratories conduct lipid extraction, while others do not, prompted the experimental portion of this study.Results of the experimental study show no significant differences in δ13C between samples prepared with and without lipid extraction and no significant differences in δ15N between samples prepared with and without lipid extraction. These results suggest that stable carbon and nitrogen isotope analysis of human bone collagen may not require lipid extraction for certain dietary reconstruction studies, specifically for non-coastal contexts (i.e., non-marine based diets). The isotope data was analyzed overall and among subgroups (e.g., archaeological bone, modern bone, mid-valley Peruvian ecological zones, and highland Peruvian ecological zones). In all cases, stable isotope ratios from samples prepared with and without lipid extraction were not significantly different.

A 900-Year Isotopic Proxy Rainfall Record from Northeastern Botswana

A high-resolution climate archive was reconstructed based on carbon isotope analysis and radiocarbon dating of the Chapman baobab in northeastern Botswana. The Chapman baobab, which exhibited an open ring-shaped structure composed of six stems, collapsed in January 2016 during an intense El Niño event. Two samples belonging to the oldest stems were investigated in order to obtain a proxy rainfall record, which provides insight into the precipitation regime over the last millennium, evincing centennial and decadal scale variability. The results indicate that the Medieval Warm Period was marked by relatively stable precipitation, whereas rainfall variability and drought frequency increased during the Little Ice Age. The investigated area has experienced both wetter and drier conditions in the past. The wettest conditions of the last millennium were registered before 1450 while the driest period occurred in 1835. For southern Africa, inter-annual rainfall variability is mainly associated with sea surface temperatures in the Agulhas Current core region, which determine the east–west displacement of tropical temperate troughs. Previous studies suggested that positive sea surface temperature anomalies in the Mozambique Channel led to an eastward movement of the troughs but the Chapman record demonstrates a westward displacement in the past, causing drought in northeastern South Africa and wetter conditions in the central part of southern Africa. The positive rainfall correlation with SST anomalies reversed after 1900, causing a gradual decrease in precipitation and confirming the current aridity trend for Botswana. The results contribute to a better understanding of the past climate of southern Africa for which paleoclimate reconstructions remain scarce.

Assessment of kerogen types and source rock potential of Lower Jurassic successions in the Mandawa Basin, SE Tanzania

Variability in organic matter types and quality of source rock intervals across evolving rift-basins has been the focus of previous studies, which have shown that due to dynamic sedimentary regimes and water depths such source intervals occur sporadically and restricted to specific stratigraphic horizons. Such heterogeneous settings require detailed geochemical analysis to document variations in source quality. This study presents a comprehensive geochemical analysis of source rock intervals in Lower Jurassic successions (Mbuo, Nondwa and Mihambia Formations) in the Mandawa Basin, on-shore Tanzania, in order to constrain organic matter types and quality. Organic matter richness was measured by Total Organic Carbon (TOC) analysis, while quality and thermal maturity of organic matter was assessed by programmed pyrolysis, complemented by organic carbon isotope analysis (δ13Corg) of sediment samples collected from outcrops, cores, and cuttings samples. TOC and programmed pyrolysis datasets from existing literature were synthesized in this study to better understand organic matter quality and thermal maturity evolution on regional scale. These data were examined in relation to paleogeography to gain insight into the factors regulating the distribution of organic matter quality within the Mandawa Basin.Average TOC contents in Lower Jurassic sediments fluctuate from 0.31 to 4.83 wt% with an average of 1.4 wt%, whereas, kerogen yield (S2) and hydrogen index (HI) remain generally low, with values ranging from 0.01 to 8.6 (mg HC/g rock) with an average (0.92 mg HC/g rock) as well as from 2 to 233 (mg HC/g TOC) with an average of 46 (mg HC/g TOC), respectively. Organic matter is composed mainly of type III (gas prone) to IV (inert) kerogens with lesser admixture of type II-III kerogen (oil-gas prone), which have been deeply buried and undergone a wider range of thermal diagenesis, from early to overmature stage. The δ13Corg isotopic composition of organic matter is consistent with kerogen typing, indicating terrestrial organic matter with a heavier signature during sea level low stands. Upon marine incursions δ13Corg shifts to isotopically more depleted marine organic matter. This implies that the investigated source intervals have poor to fair source potential. Only a few intervals of limited thickness in the Upper Mbuo, Nondwa, and Mihambia Formations of the Mita Gamma-1 and East Lika-1 wells, as well as in the Lower Mbuo Formation in the Mbuo-1 well, have been locally enriched. The enrichment is attributed to periodic marine ingressions that have persisted since the Pliensbachian period and suggests the presence of oil generation potential.A comparison of TOC and programmed pyrolysis borehole data from this study to those compiled from literature in a paleogeographical context reveals high spatial variability. The southeastern and northwestern parts of the study area have the highest source potential, indicating high organic matter productivity in the dysoxic to anoxic water column, which promoted the preservation of organic matter. In contrast, the eastern and western parts generally show low source potential, indicating degraded organic matter and significant terrestrial influxes from emergent land that were deposited in shallow, mixed oxygenated water with low to moderate organic matter productivity.

Occurrence and Genesis of Cold‐Seep Authigenic Carbonates from the South‐Eastern Mediterranean Sea

AbstractMethane‐derived authigenic seep carbonates occur globally along continental margins. These carbonates are important archives to identify seep dynamics, the source of the ascending methane‐enriched fluids together with their timing, and are an important carbon sequestration mechanism. Recently, seep carbonates were discovered in the Levant Basin in the south‐eastern Mediterranean Sea. To elucidate past seepage activity and dynamics across the basin, different seep carbonate morphologies (chimneys, crusts and pavements) retrieved from the Levant Basin were mapped based on remotely operating vehicle data and analysed using standard sediment petrographic techniques, X‐ray diffraction and stable carbon and oxygen isotope analyses. Carbonate chimneys consist of micrite (δ13CVPDB of −10‰ to +5‰) with dispersed baryte and dolomite crystals, fan‐shaped aragonite (δ13CVPDB of −52‰ to −30‰) and high‐magnesium calcite cements, with the latter often growing from low‐magnesium calcite spherules. Botryoidal low‐magnesium calcite cements are forming in small cavities. Carbonate crusts consist of micrite with low‐magnesium calcite breccias, high‐magnesium calcite nodules (δ13CVPDB of −35‰ to −20‰) and cements, and partially replaced fan‐shaped aragonite cements. Carbonate pavements consist of low‐magnesium calcite microsparite, micritic dolomite and high‐magnesium calcite. Fan‐shaped aragonite is locally present as pore‐lining cement. Iron oxides are often seen coating the low‐magnesium calcite, high‐magnesium calcite and dolomite cements. Chimneys and crusts, characterised by high amounts of high‐magnesium calcite and aragonite, are interpreted to have formed through advective methane fluxes. Pavements, with high quantities of dolomite, are explained as the product of diffusive methane flux. Sediment petrographic and geochemical analysis of the different carbonate morphologies and cement phases therein witness distinct modes of ascending fluid fluxes and their mixing with marine pore water and/or sea water during precipitation of the individual phases.

Development characteristics and genetic analysis of dense limestone reservoirs in the Taiyuan Formation of the Ordos Basin, China

Tight limestone reservoirs in the Permian Taiyuan Formation of the Ordos Basin have garnered increasing attention in recent years, emerging as a pivotal domain in the quest for natural gas exploration. This research delves into the comprehensive investigation of petrology, reservoir space, reservoir physical properties, and microscopic characteristics through the examination of field outcrops, core observations, thin section identification, scanning electron microscopy, stable carbon and oxygen isotope analysis, and testing. The systematic analysis focused on elucidating the development characteristics of these reservoirs and identifying the controlling factors governing favorable reservoir conditions. Based on our research analysis, the specific rock types with the potential to serve as excellent reservoirs, includes bioclastic silty limestone, bioclastic micrite limestone, and algal-rich limestone. The predominant reservoir spaces within these formations were found to consist of dissolved pores, residual bioclastic cavity pores, intercrystalline pores, and microfractures. These reservoirs exhibit an average porosity of 2.1%, and an average permeability of 0.22 × 10−3 μm2, indicating their classification as low porosity and low permeability reservoirs. The formation of favorable reservoirs in the Taiyuan Formation limestone was determined to be influenced by many factors; notably, the favorable sedimentary microfacies associated with bioclastic shoals and bioherms provided the foundational material basis for the formation of reservoirs, influencing the type of reservoir space and its extensive planar distribution. Penecontemporaneous karstification, guided by high-frequency cycles, was favorable for the formation of dissolution holes, effectively improving reservoir performance and facilitating the development of thick limestone reservoirs. Furthermore, fractures were identified as crucial agents in improving the seepage capacity of these tight limestone reservoirs. Drawing from our research results, this study offers valuable guidance for the future exploration of limestone formations in the Taiyuan Formation in the Ordos Basin. Additionally, these findings hold considerable significance as a reference point for research and exploration endeavors focused on bioclastic limestone reservoirs in the North China Platform.

Controls on preservation of organic matter during the Cenomanian Ocean Anoxic Event II (OAE2) and Turonian global sea-level rise: Agadir Basin, Morocco

The Ocean Anoxic Event II (OAE2) was a significant global event associated with a positive carbon isotope excursion, occurring from the Late Cenomanian to the Early Turonian (C/T). It has been commonly associated with enhanced organic carbon preservation. Carbon isotopic analysis carried out over the C/T interval in the Agadir Basin, Morocco, integrated with previous biostratigraphic data, allows a refined correlation of the OAE2 interval. Detailed sedimentary facies analysis identifies ten lithofacies that record the transition from shallow marine environments in the Late Cenomanian to relatively deeper conditions in the Early Turonian. The variation in lithofacies can be correlated to relative sea level changes that show a correlation to the global eustatic curve.The OAE2 interval comprises dark grey mudstones beds that display low total organic carbon (TOC) values. Trace element and facies analysis suggest dilution from high detrital influx, along with oxic water conditions and low productivity. OM-rich black mudstones are identified in post-OAE2 Early Turonian strata. Trace element analysis suggests this increase in organic matter accumulation was related to increased sea surface productivity and oxygen-depleted bottom water conditions, which facilitated organic matter preservation. Deposition of OM-rich black mudstones is widely reported during the global Early Turonian marine transgression, suggesting the very high sea level was a major control on organic matter generation and preservation.

Reconstruction of the Late Miocene to Pliocene continental succession of Samos Island: Palaeoenvironmental implications for the Eastern Aegean domain

AbstractOn the Island of Samos (East Aegean region, Greece), two sedimentary basins are filled by thick continental series dated to the Late Miocene to Early Pliocene. A multidisciplinary study has been performed including (1) the definition of 21 sedimentary facies, (2) a review of the biological components and (3) carbon, oxygen and strontium stable isotope analyses. The succession is characterised by various depositional settings and hydrochemical compositions. Five main stages of basin evolution have been identified: (1) The Late Serravallian is marked by the development of alluvial fans and fan delta; (2) during the Lower Tortonian, isolated shallow lakes with variable salinity, from fresh to brackish, developed under warm and relatively humid conditions; (3) the Middle to Upper Tortonian is marked by the development of a large and deep lake with saline and alkaline waters, under colder and drier conditions; (4) the Latest Tortonian to Messinian period is represented by an ephemeral alluvial system, developed under a dry climate; (5) during the Zanclean, a palustrine and paludal wetland system, dominated by tufa carbonates, developed under moderately humid conditions. This succession is of particular interest for the reconstruction of the palaeoenvironmental evolution of the transition zone between the Mediterranean domain, and the Paratethys and circum‐Paratethys areas. The geochemical data and the presence of flora (diatoms) and fauna (gastropods) of marine affinity suggest transient ingressions of marine‐related water or groundwater inflows as early as the Lower Tortonian. The Samos succession records the complex interaction between the regional geodynamics and climate. The extensional regime of the Eastern Aegean zone generates subsidence, interrupted in the mid‐Tortonian (9 Ma) by a brief compressive event and a major exposure of the basins. Furthermore, the Late Miocene progressive aridification, followed by a change to a more humid climate (Pliocene) is also a major driver of the sedimentation.

Microbial diversity and authigenic siderite mediation in sediments surrounding the Kedr-1 mud volcano, Lake Baikal.

The gas hydrate-bearing structure-mud volcano Kedr-1 (Lake Baikal, southern basin)-is located near the coal-bearing sediments of the Tankhoy formation of Oligocene-Miocene age and can be an ideal source of gas-saturated fluid. A significant amount of siderite minerals (FeCO3 ) were collected from sediments at depths ranging from 0.5 to 327 cm below the lake floor (cmblf). An important feature of these carbonate minerals is the extremely strong enrichment in the heavy 13 C isotope, reaching values of +33.3‰ VPDB. The δ13 C of the siderite minerals, as well as their morphology and elemental composition, and the δ13 CDIC of the co-existing pore water, differed across layers of the core, which implies at least two generations of siderite formation. Here, we leverage mineralogical and geochemical data with 16S rRNA data from the microbial communities in sediments surrounding layers containing siderite minerals. Statistical data reveal the formation of three clusters of microbial communities based on taxonomical composition, key taxa among bacteria and archaea, and environmental parameters. Diversity and richness estimators decrease with sediment depth, with several similar prevailing clades located at the bottom of the core. Most of the taxa in the deep sediments could be associated with putative metabolisms involving organotrophic fermentation (Bathyarchaeia, Caldatribacteriota, and Chloroflexota). Various groups of methanogens (Methanoregulaceae, Methanosaetaceae, and Methanomassiliicoccales) and methanotrophic (Methanoperedenaceae) archaea are present in the sediment at variable relative abundances throughout the sampled depth. Based on the physicochemical characteristics of the sediment, carbon isotope analysis of carbonate minerals and DIC, and phylogenetic analysis of individual taxa and their metabolic potential, we present several models for subsurface siderite precipitation in Lake Baikal sediments.

Intramolecular carbon isotope geochemistry of butane isomers from laboratory maturation and Monte-Carlo simulations of kerogen types I, II, and III

Position-specific (PS) carbon isotope compositions of light hydrocarbons such as propane and butane isomers (n-butane and i-butane) can provide a wealth of information on the history of natural gases in the subsurface reservoirs and other environments. For PS carbon isotope analysis of butane isomers, we have established a GC-pyrolysis-GC-isotope ratio mass spectrometry method with demonstrated accuracy. With this method, we analyzed PS δ13C values of butane isomers generated from the systematic laboratory pyrolysis experiments of three different kerogen types (I, II, and III) at temperatures of 310–430 °C with corresponding thermal maturity (Easy %Ro) ranging from 0.7 to 3.3. The observed evolution in the abundances of butane isomers can be interpreted and semi-quantitatively modeled based on the abundances of different CC bonds within the kerogens at low maturity and thermal degradation of butane isomers at high maturity. The δ13C values at the central sites of both nC4 and iC4 were heavier than those at the terminal positions, similar to our previous observations of propane. Their isotopic evolution with the maturity were controlled largely by kinetic isotope effects associated with breaking of different CC bonds during the generation and degradation of butane isomers. Kinetic Monte Carlo (kMC) simulations of n-butane generated from thermal cracking of model kerogens (I, II, and III) and an oil with a series of reactions (homolytic cleavage, β-scission, radical isomerization, H-abstraction, and termination by radical recombination) provided generally consistent results with the experimental observations, although the difference in PS δ13C values between the central and terminal positions are somewhat overestimated. On the other hand, the kMC simulation with homolytic cleavage and capping reactions alone produced significant deviations from the experimental results. Re-assessment of very limited data of PS δ13C values of natural butanes with our experimental and simulation results show that biodegradation significantly increased δ13C values at the central positions, not only of propane, but also of both butane isomers. This study lays a foundation and demonstrates the potential of PS isotope geochemistry of butane isomers to further improve our understanding of the sources, and geochemical and microbial processes of light hydrocarbons in the subsurface and other natural environments.