Differences In Depositional Environment Research Articles

Assessing the geochemical correlation between petroleum source rocks in the Brazilian Equatorial margin basins and global oceanic anoxic events

This research aims to investigate the correlation between the Cretaceous Oceanic Anoxic Events (OAEs) and the source rocks of the Brazilian Equatorial Margin (BEM) basins. These source rocks, particularly from the Cenomanian-Turonian interval, are known to contain high levels of Total Organic Carbon (TOC) and exhibit significant hydrocarbon potential. The principal focus is on how global anoxic events, such as OAE-1b, OAE-1d, and OAE-2, influenced the depositional environments and organic matter types across the BEM basins, which include Foz do Amazonas, Pará-Maranhão, Barreirinhas, Ceará, and Potiguar. Key results indicate a strong correlation between periods of anoxia and the accumulation of organic-rich sediments in these basins. The Foz do Amazonas Basin features predominantly terrestrial-derived kerogen (Type III), while the Ceará and Potiguar basins show marine-derived kerogen (Type I and II), aligning with global productivity patterns during anoxic events. These variations in kerogen type reflect differences in depositional environments influenced by sea-level changes and nutrient influx. The research concludes that the OAEs significantly impacted organic matter preservation and hydrocarbon generation in the BEM basins. The study's findings contribute to the broader understanding of how Cretaceous OAEs shaped the geochemical and sedimentary processes in equatorial Atlantic margins, highlighting the potential for further oil and gas exploration in these regions.

The prevalence of invertebrate bioerosion on Mesozoic marine reptile bone from the Jurassic and Cretaceous of the United Kingdom: new data and implications for taphonomy and environment

AbstractInvertebrate bioerosion on fossil bone can contribute to reconstructions of benthic taxonomic assemblages and inform us about oxygenation levels, water depth and exposure time on the seafloor prior to burial. However, these traces are not commonly described in the fossil record. To date, there have been only 13 published studies describing a total of 15 instances of invertebrate bioerosion on marine reptile fossil bones from the Mesozoic globally. We surveyed the collections of several UK museums with substantial occurrences of Mesozoic marine reptiles for evidence of invertebrate bioerosion. Here, we document 153 specimens exhibiting 171 newly recorded instances of invertebrate bioerosion on Jurassic and Cretaceous marine reptile bones. Several major bioeroding taxonomic groups are identified. Within the geological strata of the United Kingdom, there is a higher prevalence of bioerosion in the Cretaceous relative to the Jurassic, despite greater sampling of specimens from the Jurassic. Although biotic turnover and food web restructuring might have played a role, potentially pertaining to heightened productivity during the later stages of the Mesozoic Marine Revolution, we consider it more likely that this temporal change corresponds to differences in depositional environment and taphonomic history between the sampled rock units. In particular, the Cretaceous deposits are characterized by heightened oxygenation levels relative to their Jurassic counterparts, as well as reworking, which would have allowed two phases of bioerosion. A spatiotemporally broader dataset on invertebrate bioerosion on vertebrate bone will be important in further testing this and other hypotheses.

210Pb geochronology and metal concentrations in sediment cores recovered in the Alvarado Lagoon system, Veracruz, Mexico

Three sediment cores recovered from the Alvarado Lagoon System (ALS) in the Gulf of Mexico were used to reconstruct the history of metals and metalloids and their environmental importance. The sedimentary profiles were dated with 210Pb and verified with 137Cs. Maximum ages of 77 and 86 years were estimated. Sediment provenance was described by sedimentological and geochemical proxies. The chemical alteration index (CIA) and weathering index (CIW) revealed moderate to high intensity of weathering in the source area that is controlled tropical climatic conditions, runoff, and precipitation in the basin that feeds sediments to this coastal lagoon. The Al2O3/TiO2 ratios indicated that the sediments were derived from intermediate igneous rocks. The enrichment factor values revealed the lithogenic and anthropic contribution of metals and metalloids. Cd is classified under the category extremely severe enrichment; agricultural activities, fertilizers, herbicides, and pesticides containing Cd are expected to supply this metal to the ecosystem. Factor Analysis and Principal Components provided two main factors, terrigenous and biological origins; ANOVA indicated that there are significant differences between the cores for the parameters analyzed and revealed that there are differences in depositional environments between the recovery zones of the cores. The ALS presented natural variations associated with the climatic conditions, terrigenous input, and its relationship with the hydrological variations of the main rivers. The contribution of this work was to identify the magnitude of the natural component versus the human contribution, mainly of risk metals such as Cd, to support better management of the hydrological basin that affects the ALS.

U-Pb-Hf isotopes and shape parameters of zircon from the Mozaan Group (South Africa) with implications for depositional ages, provenance and Witwatersrand – Pongola Supergroup correlations

The Mozaan Group represents the youngest unit of the c. 2.9 Ga Pongola Supergroup located along the south-eastern margin of the Kaapvaal Craton. It comprises a ca. 4800 m thick succession of clastic sedimentary rocks intercalated by minor chemical and volcano-sedimentary rocks deposited in shallow marine to fluvial environments, and is stratigraphically correlated with the auriferous Witwatersrand Supergroup. This correlation, however, is speculative, in particular as systematic information about depositional ages and sediment provenances are absent. To address these problems, we present new combined sets of U-Pb ages, Hf isotopes, and shape parameters (width, length, aspect ratios and roundness) of >700 detrital zircon grains from seven samples of the Mozaan type profile in the Hartland area. These data reveal a switch in provenance between the lower and upper Mozaan Group. Zircons in sandstones of the lower Mozaan Group (Sinqeni to Ntombe formations) were supplied from surrounding proto-Kaapvaal Craton, and those in upper Mozaan Group rocks (Delfkom to Ntanyana formations) predominately from a juvenile hinterland, comprising sources as far as the Pietersburg and/or Kimberley blocks, which became amalgamated to the proto-Kaapvaal Craton at 2.97–2.87 Ga. Significant overlap of zircon age spectra, Hf isotope data, and maximum depositional ages (2908 ± 8 Ma to 2866 ± 7 Ma) suggest similar sources for upper Mozaan Group and Central Rand Group sediments of the Witwatersrand Basin. In contrast, sedimentary rocks of the West Rand Group have no counterparts in the Pongola Basin, except for the Orange Grove Formation, which shows good agreement with the Sinqeni Formation. The provenance switch indicated by the age-Hf isotope data is not identified by zircon shape parameters. These rather reflect differences in depositional environment (littoral, fluvial, volcanogenic), related to the duration and energy of sediment transport and reworking, as indicated by specific patterns in grain size vs. roundness diagrams.

Organic-rich shale caprock properties of potential CO2 storage sites in the northern North Sea, offshore Norway

Assessment of the geomechanical properties of organic-rich shale caprocks is critical for a successful CO2 storage into a saline aquifer. In this study, we investigated the geochemical properties of the organic-rich shale caprocks of the Draupne and Heather formations, overlying the potential sandstone reservoirs of Sognefjord, Fensfjord, and Krossfjord formations in the northern North Sea, offshore Norway. The caprock's depositional variations within the sub-basins are established by analyzing the gamma-ray shape and stacking patterns. The effect due to differences in depositional environments, on the caprock compaction behavior is investigated by integrating petrographical analysis of core and cutting samples from 3 wells and by rock physical analysis of wireline log data from 27 exploration wells. Three rock physics templates are used where the wireline log data are interpreted using the published background trends. The effect of kerogen type, maturation level, and deposition environment on caprock properties within the study area are also evaluated. Moreover, the caprock property, such as brittleness, is estimated by using four mineralogy and elastic property-based, empirical relations, which is a quantitative measure of caprock property with respect to changes in stress-state. Finally, the seismic inversion method is assessed for the possibility of extracting caprock properties from surface seismic data. Regardless of compaction processes, the results indicate that the Heather Formation is mechanically stronger than the Draupne Formation. However, both formations appear to be ductile in nature. The depositional environments control the mineralogical composition and fabric of the Draupne and Heather formations, which influence the caprock properties significantly. Results also show that the effect of TOC on caprock properties is insignificant in the study area. The brittleness of the organic-rich shale caprocks in the study area follows a different trend compared to the published trends. We also observed an excellent correlation between the log-derived elastic properties and geomechanical parameters. Still, it is difficult to assess the caprock elastic properties from seismic due to the overlap of data clusters. The evaluation of caprock geomechanical behaviors is challenging as these properties are site-specific and also influenced by other factors such as exhumation, in-situ stress conditions, the existence of natural fractures, and their orientations.

In search of Silurian/Devonian boundary conodont markers in carbonate environments of the Prague Synform (Czech Republic)

Conodonts from two of the most representative sections in the Prague Synform were studied in search of alternative biostratigraphic markers of the Silurian/Devonian boundary. The Na Požárech and Praha-Radotín sections, with contrasting lithologies, were chosen to study changes in conodont faunas in relation to different carbonate facies – i.e., shallower- and deeper-water carbonates around the Silurian/Devonian boundary in the type area. Apart from icriodontids, the differences in bathymetry were also expected to affect the diversity of taxa of the family Spathognathodontidae, which is generally the most abundant and the most tolerant clade found in different carbonate environments at this stratigraphic level. Although the Scyphocrinites Horizon is developed at both study localities, the microfacies analysis confirmed significant differences in depositional environments at around the Silurian/Devonian boundary. Abundant conodont material from the two sections (more than one thousand elements) showed a high diversity and disparity in both the Spathognathodontidae and Icriodontidae. Altogether, 18 taxa were identified, but many forms still require a formal description. A new spathognathodontid taxon, Zieglerodina petrea sp. nov., described herein, is easily distinguishable because of its distinct morphology in denticulation of the blade, and its first occurrence is just above the base of the Devonian in both sections. It also has been identified in conodont collections from Morocco and the Carnic Alps, as such its biostratigraphic significance can be extended to peri-Gondwana. Although the stratigraphic occurrence and global significance of this promising conodont taxon still has to be tested in other areas, current data suggest it might have a great potential for identifying the base of the Devonian in sections where critical graptolite and icriodontid taxa are missing.

Prospect analysis of the deep marine shale gas exploration and development in the Sichuan Basin, China

The shale gas exploration and development in Sichuan Basin had achieved a major breakthrough remarkably. However, the business development focused on the marine shale gas in shallow layers (vertical depth < 3500 m) of the Wufeng Formation-Longmaxi Formation alone. Therefore, the deep shale gas (vertical depth > 3500 m) business development in Wufeng Formation-Longmaxi Formation is the key to the rapid growth of shale gas production in the Sichuan Basin. In the literature, authors analyzed the geological characteristics of the deep shale gas of the Wufeng Formation - Longmaxi Formation in southern Sichuan Basin through particular dissection and analysis of deep wells in comparison to the shallow layers. The thickness of organic-rich shale in the deep region of southern Sichuan Basin measures to be more than 120 m, which is larger than that of the shallow layers in Fuling area. The vertical TOC change remains constant whereas the thickness of high-quality shale is approximately forty meters in both regions. Nevertheless, the RO is higher in the deep region of southern Sichuan Basin. The calcareous content of the organic shale increases while the silicon content decreases from the Fuling area down as it gets deeper into the region in southern Sichuan Basin. It is quite evident in research that the shales in the Wufeng Formation – Longmaxi Formation of the deep to shallow layers of southern Sichuan that there are not many differences in depositional environment, lithology, TOC, etc. However, there are four major differences: (1) The porosity of shale in the deep region of southern Sichuan Basin is higher than that in Fulin gas field due to the corrosion pore. (2) The gas-bearing properties are better in the deep regions of southern Sichuan Basin because they have better preservation condition compared to that of the shallow region of Fuling. (3) However, gas-bearing properties are worse in the local region of stronger structure deformation and the basin boundary fault zone. (4) The shale gas resources in the deep regions of southern Sichuan Basin are great and have wide prospects for exploration and development. In order for a breakthrough to be generated in deep shale gas commercial development in the soonest possible time, authors propose the following: utilize strengthening evaluation of small layer contrasting so as to explain fine structure and predict fracture; strengthen the research on drilling and fracturing technology for deep shale gas; strengthen research on wells column; and support technology for efficient production of shale gas.

Depositional environment effects on observed liquefaction performance in silt swamps during the Canterbury earthquake sequence

Stratified silty soils deposited in back-swamp settings are shown through regional CPT-based analyses to have mitigating effects on the manifestation of liquefaction in Christchurch. Liquefaction triggering within these deposits is inadequately captured by simplified liquefaction assessment methodologies. Differing near-surface geology and depositional environments indicated in historical documents explain in part the limitations of current liquefaction evaluation procedures in southwest Christchurch. The historical swamp areas are shown through a regional CPT study to contain stratified silt/sand deposits or thick silt layers. Consideration of depositional environment distinguishes between liquefaction performances that are not able to be differentiated through the CPT-based liquefaction triggering assessment alone. CPT resolution is shown to be insufficient to capture the thin layering at these stratified sites, and the simplified liquefaction assessment methods do not take into account the effects of the stratification on pore water pressure movement within a soil profile. Instead, continuous sampling and careful logging of high-quality samples provide important insights on stratification at these silty soil swamp sites and in discerning differences in stratigraphy resulting from differences in depositional environment.

Magnetostratigraphy, age and depositional environment of the Lobo Formation, southwest New Mexico: implications for the Laramide orogeny in the southern Rocky Mountains

AbstractThe Lobo Formation of southwestern New Mexico consists of spatially variable continental successions attributed to the Laramide orogeny (80–40 Myr), although its age and provenance are virtually undocumented. This study combines sedimentological, magnetostratigraphical and geochronological data to infer the timing and origin of the Lobo Formation. Measured sections of Lobo strata at two locations, Capitol Dome in the Florida Mountains and in the Victorio Mountains, indicate significant differences in depositional environments and sediment provenance. At Capitol Dome, where Lobo strata were deposited above a syncline developed in Palaeozoic strata, deposition took place in fluvial, palustrine and marginal lacustrine settings, with alluvial‐fan deposits only at the top of the formation. Combined magnetostratigraphy and a young U–Pb detrital zircon age suggest deposition of the section at Capitol Dome from ~60 to 52 Ma. The Lobo Formation in the Victorio Mountains was deposited in alluvial‐fan and fluvial settings; the age of deposition is poorly bracketed between 66 ± 2 Ma, the weighted‐mean age of two young zircons, and middle Eocene (~40 Ma), the approximate age of overlying volcanic rocks. U–Pb zircon ages from sandstones at the Victorio and Capitol Dome localities indicate that different source rocks provided sediment to the Lobo Formation. Local Proterozoic basement (~1.47–1.45 Ga) dominated the source of the Lobo Formation in the Victorio Mountains, consistent with abundant granitic clasts that are present in the proximal facies there; a diverse range of grain ages suggest that recycled Lower Cretaceous strata provided the dominant source for Lobo Formation sediment at the Capitol Dome locality. The U–Pb data suggest that the depositional systems at the two sites were not connected. Contrasts in depositional setting and detrital zircon provenance indicate that the Palaeogene Lobo Formation in southwest New Mexico was deposited in an assemblage of local depositional settings, possibly in separate structural basins, as a consequence of Laramide tectonics in the region.

Multi-proxy palaeoecological responses to water-level fluctuations in three shallow Turkish lakes

Natural or human-induced water-level fluctuations influence the structure and function of shallow lakes, especially in semi-arid to arid climate regions. In order to reliably interpret the effect of water-level changes from sedimentary remains in the absence of historical data, it is crucial to understand the variation in sedimentary proxies in relation to water level measurements. Here, we took advantage of existing water surface elevation data on three large shallow lakes in Turkey to elucidate the impact of lake-level changes on benthic-pelagic primary production over the last 50–100years. Sub-fossil cladocerans, diatoms, plant remains and pigments were investigated as biological variables; X-ray fluorescence (XRF) and loss on ignition (LOI) analyses were conducted as geochemical-physical variables on a set of 210Pb and 137Cs dated cores. Dating of the cores were robust, with the exception of uncertainties in Lake Marmara littoral core due to low unsupported 210Pb activities and high counting errors. Results indicated that Lake Marmara was dominated by benthic species throughout the sediment record, while Lakes Beyşehir and Uluabat shifted from a littoral-dominated system to one with increased pelagic species abundance. In all cores there was a stronger response to longer-term (decadal) and pronounced water-level changes than to short-term (annual-biennial) and subtle changes. It was also noted that degree of alteration in proxies differed between lakes, through time and among pelagic-littoral areas, likely emphasising differences in depositional environments and/or resolution of sampling and effects of other stressors such as eutrophication. Our results highlight lake-specific changes associated with water-level fluctuations, difficulties of conducting studies at required resolution in lakes with rather mixed sediment records and complexity of palaeolimnological studies covering recent periods where multiple drivers are in force. They further emphasise the need to include instrumental records when interpreting effects of recent water-level changes from sediment core data in large shallow lakes.

Palynological records of the Permian Ecca Group (South Africa): Utilizing climatic icehouse–greenhouse signals for cross basin correlations

The Permian formations of the South African Karoo Basin play a crucial role in understanding Gondwana's climate history during this time of major global changes. In this paper we present two data sets, one from the coal-bearing Vryheid Formation (Witbank Basin) and one from the Whitehill and Upper Prince Albert formations of the DP 1/78 core (NE Karoo).Our main goal was to study the vegetation changes during this period of global warming and test if the climatic signals could be used to correlate the basinal Ecca group facies with the fluvio-deltaic coal-bearing strata of the Witbank Basin. The palynological record of the No. 2 Coal Seam of the Vryheid Formation indicates a cold climate, fern wetland community, characteristic of lowland alluvial plains, and an upland conifer community in the lower part of the coal seam. Up section, these communities are replaced by a cool-temperate cycad-like lowland vegetation and gymnospermous upland flora. The data set of the DP 1/78 core is interpreted to represent a cool to warm temperate climate represented by a high amount of Gangamopteris and Glossopteris elements.Both data sets are very different in their composition, which can be explained by the differences in depositional environment; however, our findings reveal a different age of the studied assemblages and thus also suggest that both data sets represent different stages in the transition from icehouse to greenhouse during Permian times. As the stratigraphic correlation between the Main Karroo Basin and the peripheral basins is still under discussion, this paper provides new data to underpin the stratigraphic placement of the Whitehill Formation relative to the coal-bearing Vryheid Formation.

Evaluating nitrogen isotopes as proxies for depositional environmental conditions in shales: Comparing Caney and Woodford Shales in the Arkoma Basin, Oklahoma

In this study, we assessed the use of stable nitrogen isotopes (δ15N) to evaluate differences in water column conditions during the deposition of the Woodford Shale and Caney Shale in the Arkoma Basin in Oklahoma by comparing bulk δ15N values. The Woodford Shale was mainly deposited under anoxic bottom water column conditions, whereas the Caney Shale shows evidence of deposition under a suboxic/dysoxic deep water regime. Therefore, these two units can be used to test the utility of δ15N as a proxy for the differentiation of these intervals based on depositional environment and post-depositional processes, and provide insights into differences that may impact their assessments as reservoir and source rocks. We measured δ15Nbulk, organic carbon isotopes (δ13Corg), total organic carbon (TOC) and total nitrogen (TN) values from a core from the Arkoma Basin that contains sections of both Caney Shale and Woodford Shale. Bulk δ15N values are higher in the Caney Shale (average δ15Nbulk=9.5±0.8‰) than in the Woodford Shale (average δ15Nbulk=3.1±0.7‰); TOC values in the Woodford Shale are slightly higher than those in the Caney Shale (6±2% and 4±2%, respectively). No significant differences were identified in the δ13Corg and TN values between the two units. Given the depositional history of these units, we suggest that the difference in δ15N between the Caney Shale and the Woodford Shale primarily reflects differences in depositional environment, and that changes in δ15Nbulk values due to diagenesis or catagensis are subordinate.

Influence of migration distance, maturity and facies on the stable isotopic composition of alkanes and on carbazole distributions in oils and source rocks of the Alpine Foreland Basin of Austria

The Austrian part of the Alpine Foreland Basin has been studied previously by organic geochemical methods to establish oil–oil and oil–source rock correlations. The lateral distance of oil fields to the position of mature source rocks (Lower Oligocene Schöneck and Eggerding formations) beneath the Alpine nappes in the south suggests long distance migration up to 50km. Minor compositional trends in W–E direction were obtained reflecting differences in depositional environment (facies) and maturity of potential source rocks. Therefore, the oil and source rock samples are thought to provide valuable insights into carbazole distributions in relation to migration distance, maturity and facies. Compound specific carbon isotope analyses on n-alkanes and isoprenoids reflect the W–E trend, already seen within the total hydrocarbon fractions. The observed trend toward lighter δ13C values of alkanes from oil fields in a W–E direction are consistent with lower δ13C values of organic matter in unit c and similar differences obtained from sediments of the Schöneck Formation at wells Oberhofen 1 (W) and Molln 1 (E). The δ13C patterns of n-alkanes and isoprenoids are in agreement with data obtained from the potential marine source rocks (Schöneck Formation) of the oils. The hydrogen isotopic composition of short chain n-alkanes (C15–19) of most oil samples are lower than the data obtained from the extracts of the marine Permian Kupferschiefer of the Polish Zechstein Basin at similar maturation stages. Only the oils from the western oil fields yield δD values of n-alkanes comparable to those obtained from marine source rocks. The data imply brackish water conditions during deposition of ‘unit c’ of the Schöneck Formation. Differences in the position of δD of isoprenoids in relation to the respective maturation trend line are most probably related to calibration errors. Alkylated carbazoles and benzocarbazoles are only present in sufficient amounts for quantification in oils sampled from the eastern fields. Rock extracts of the Schöneck Formation from drill cores Molln 1 (5200m depth, 0.92% Rr) and from the marginally mature (ca. 0.6% Rr) samples from well Oberhofen 1 (4300m depth) obtained sufficient amounts of carbazoles. The significantly different concentrations of benzocarbazoles in the extracts (around 10μg/g at Oberhofen 1; > 50μg/g at Molln 1) are related to maturity differences, whereas the predominance of 1-methylcarbazole in the Oberhofen samples is inferred to reflect differences in source rock facies. In the oils from the eastern deposits, neither the concentration ratios of methylcarbazoles, nor the benzocarbazole ratio show indications for the influence of facies differences. Maturity of oil expulsion is estimated on the basis of MPI 1 (Rc=0.76–0.88%), confirmed by sterane isomerization parameters. The results argue for a minor influence of maturity differences on the benzocarbazole ratios of the oil samples. The obtained ratios and the reservoir source fractionation parameters, calculated from the data of Molln 1 source rocks and the respective oils, show a systematic decrease with the estimated migration distance. The results argue for the applicability of benzocarbazoles for the assessment of relative differences in migration distances in oil plays characterized by minor differences in source rock facies and maturity during oil expulsion.

Well preserved Palaeogene and Cretaceous biomarkers from the Kilwa area, Tanzania

We have investigated the biomarker composition of sediments ranging in age from 30 to 70 Ma from the Kilwa area of Tanzania. They are dominated by material of terrestrial ( n-alkanols, n-alkanoic acids, n-alkanes and triterpenoids) and [bacterial hopanoids and a dipentadecyl glycerol diether (DGD)] origin with only a minor contribution of marine origin (crenarchaeol and some algal steroids). This indicates a marine setting dominated by higher plant input, which most likely stimulated sedimentary microbial activity, including sulfate reduction. The lipid composition, specifically the presence of bacteriohopanepolyols (BHPs) and the stereochemistry of hopanoids, suggests a low degree of thermal maturity. Many biomarkers have still retained functionality even after 30–70 million years. This is in good agreement with the exceptional preservation of foraminifera and nannofossils and can probably be attributed to the very low sediment permeability and burial depth. There is a clear distinction in the biomarker distributions between the Oligocene-age sediments collected at the end of the peninsula near Kilwa Masoko and the older sediments collected from elsewhere, indicating differences in depositional environment. Sediments from the end of the peninsula have higher branched and isoprenoid tetraether index values, indicating a relatively higher terrestrial input. They also contain two tentatively assigned C 28 hopenes (28,30-dinorneohop-13(18)-ene and 28,30-dinorhop-17(21)-ene), (aromatic) des- A-triterpenes, des- E-hopenes, aromatic pentacyclic triterpenoids, C 33 DGD, archaeol and BHPs, which are absent from or only present in small amounts in the other sediments. These differences likely reflect an evolution of the depositional area from a relative open shelf environment with substantial water depth to a shallower setting during the early Oligocene.

Geochemical paleoredox indicators in Devonian–Mississippian black shales, Central Appalachian Basin (USA)

The degree of anoxia that existed during accumulation of Devonian–Mississippian black shales in central Kentucky has been debated widely. In this study, geochemical data were used to elucidate paleodepositional environments for these units. Using analyses from ten cores collected from the outcrop belt in central Kentucky, sulfur, carbon, and selected trace-element relationships were compared. The Sunbury Shale (Tournasian, Lower Mississippian) and the Cleveland and Huron members of the Ohio New Albany Shale (Fammenian, Upper Devonian) show different relationships between carbon, sulfur, and trace elements. C–S–Fe relationships for the Sunbury suggest anoxic, possibly even euxinic, conditions prevailed during sediment accumulation. Analysis of C–S–Fe data suggests that the Cleveland may have accumulated under anoxic conditions, with intermittent dysoxia, whereas the Huron Member may have accumulated under a relatively wide range of conditions, from anoxic, to dysoxic, to possibly oxic. These three units exhibit different degrees of trace-element enrichment, with the approximate order of enrichment relative to an average shale being Mo>Pb>Zn>V>Ni>Cu>Cr>Co. The Sunbury shows the highest levels of enrichment, followed by the Cleveland, with the Huron showing only slight enrichment for most of these trace elements. Differing degrees of enrichment may reflect differences in depositional environment during accumulation. High Mo concentrations in the Sunbury (generally 200–550 ppm) may infer euxinic conditions prevailed during sediment accumulation. The Cleveland and the Huron both show considerably lower Mo contents (averaging around 100 ppm). Geochemical ratios, including Ni/Co, V/Cr, and V/(V+Ni), also indicate variable paleoredox conditions for these shales. Based on previously established thresholds, V/Cr and Ni/Co ratios infer at least anoxic conditions during accumulation of the Sunbury, anoxic to dysoxic conditions during Cleveland accumulation, and dysoxic to oxic conditions for the Huron. V/(V+Ni) ratios tend to indicate consistently lower oxygen regimes than do other paleoredox indicators, and this discrepancy is greatest for the Huron Member. It is suggested that thresholds established for paleoredox indicators in previous studies should not be applied strictly, but that relative differences in these indicators collectively can infer variations in the degree of anoxia. In addition, relationships between C org and redox elements may help elucidate the role of anoxia in OM accumulation. It may be concluded from this study that the Devonian–Mississippian black shales of central Kentucky accumulated under variable bottom-water conditions. At least anoxic conditions prevailed during accumulation of much of the Sunbury Shale and the upper part of the Cleveland Member, and possibly euxinic conditions for the Sunbury. Bottom-water conditions may have been intermittently anoxic and dysoxic during deposition of the lower Cleveland. During accumulation of the Huron Member, it is likely that conditions ranged from anoxic to dysoxic to marginally oxic, possibly being close to normal marine conditions at times during accumulation of the lowermost Huron sediments.

Authigenic P formation and reactive P burial in sediments of the Nazaré canyon on the Iberian margin (NE Atlantic)

Profiles of different forms of sedimentary phosphorus were measured at four sites at the Iberian margin (NE Atlantic), which were chosen on the basis of differences in depositional environment: a shelf site (113 m), a mid-slope station (1387 m) and two stations at the head (396 m) and base (3097 m) of the Nazaré Canyon. The sediment was sequentially extracted for Fe-bound P, carbonate fluorapatite (CFA)+biogenic P+CaCO 3-bound P and detrital Ca-P, and non-sequentially for total P and inorganic P, where the difference between total and inorganic P was assumed to be organic P. Measurements of organic carbon and nitrogen, citrate–dithionite–bicarbonate- and citrate–ascorbate–bicarbonate-extractable Fe, carbon oxidation rates, Fe reduction rates, phosphate effluxes and sedimentation rates were used to quantify the cycling and burial of phosphorus at each site. CFA formation was observed only in sediments of the Nazaré canyon, where enhanced rates of organic matter decomposition and Fe reduction provided the necessary conditions. The concentrations of reactive P were similar at all sites, but the sediment accumulation rates differed greatly. The high bulk accumulation rate at the base of the canyon results in a reactive P burial rate exceeding those estimated for continental margins including the Iberian margin by an order of magnitude. The estimated P burial efficiency is smallest at the slope station (3–24%), reasonably high (63–86%) at the shelf and head of the canyon stations and extremely high (>97%) at the base of the canyon. We propose that local depositories such as those at the base of canyons may be key sites for reactive P burial.

Diagenesis of the Lower Cretaceous Kanmon Group sandstones, SW Japan

The Kanmon Group (Lower Cretaceous) is a non-marine sequence in the Inner Zone of southwest Japan and is divided into the lower Wakino (lacustrine) and the upper Shimonoseki (fluvial) subgroups. Major diagenetic changes in this group are compaction, iron-oxide cementation, calcite cementation and grain replacement, quartz overgrowth and pore-fill cementation, illite authigenesis, chlorite pore-fill cementation and grain replacement, albitization of feldspar, and grain replacement by pyrite. Two subgroups of the Kanmon Group present no significant differences in general diagenetic features, paragenetic sequence, or the degree of diagenetic changes despite differences in depositional environments (lacustrine vs. fluvial) and stratigraphic positions. However, some differences are recognized in the content and chemistry of authigenic minerals caused by different sandstone framework compositions. The content of authigenic clay minerals is higher in sandstones of the Shimonoseki Subgroup containing abundant volcanic rock fragments. In addition, the composition of chlorite, the most abundant authigenic clay mineral in Kanmon sandstones, is Mg-rich in the volcanoclastic Shimonoseki sandstones, compared to an Fe-rich variety in Wakino sandstones. The original sandstone composition played a significant role in pore-water composition and diagenetic reactions. The Wakino sandstones lost most of its porosity by compaction, whereas Shimonoseki sandstones are only compacted in the vicinity of the basin-bounding fault. The weakly compacted Shimonoseki sandstones, instead, were largely cemented by pore-filling calcite during early diagenesis; cementation prevented compaction during further burial. The Kanmon Group sediments were heated to about 300 °C based on illite crystallinity values.

00/01713 Structure analysis of oil shale and the development of fuel production technology

Reflectance FTIR microspectroscopy has been used to investigate the chemical structure of the liptinite macerals, alginite, bituminite, sporinite, cutinite and resinite in bituminous coals of Carboniferous to Tertiary age. In comparison with the spectra of vitrinite in the same coals, the micro-FTIR spectra of liptinite macerals are characterized by stronger aliphatic CHx absorptions at 3000–2800 and 1460–1450 cm−1, less intense aromatic CC ring stretching vibration and aromatic CH out of plane deformation at 1610–1560 and 900–700 cm−1 respectively and various intense acid CO group absorptions at 1740–1700 cm−1. The peaks at 1000–900 cm−1 due to aliphatic CH2 wagging vibrations in olefins and at 730–720 cm−1 due to CH2 rocking vibration in long chain aliphatic substances ([CH2]n, n≥4), are characteristic of liptinite macerals. Collectively the micro-FTIR spectral characteristics indicate that liptinite is composed of greater numbers of long chain aliphatics, fewer aromatics and a broader range of oxygen-containing groups than other macerals. Marked differences exist in micro-FTIR spectra within the liptinite maceral group. Alginite has the strongest aliphatic and least aromatic absorptions followed by bituminite, resinite, cutinite and sporinite. The aliphatic components in alginite are the longest chained and least branched whereas those in sporinite are the shortest chained and most branched. Bituminite, resinite and cutinite are intermediate. Notable differences in micro-FTIR spectra of individual liptinite macerals, such as intensities and peak locations of aromatic CC in alginite, CO groups in bituminite and resinite and substituted aromatic CH and C–O–C groups in cutinite and sporinite, also exist, which are attributed to differences in depositional environments or biotaxonomy.

99/03571 Expulsion of oil from petroleum source rocks: inferences from pyrolysis of samples of unconventional grain size: Inan, S. et al. Org. Geochem., 1998, 29, (1–3), 45–61

Reflectance FTIR microspectroscopy has been used to investigate the chemical structure of the liptinite macerals, alginite, bituminite, sporinite, cutinite and resinite in bituminous coals of Carboniferous to Tertiary age. In comparison with the spectra of vitrinite in the same coals, the micro-FTIR spectra of liptinite macerals are characterized by stronger aliphatic CHx absorptions at 3000–2800 and 1460–1450 cm−1, less intense aromatic CC ring stretching vibration and aromatic CH out of plane deformation at 1610–1560 and 900–700 cm−1 respectively and various intense acid CO group absorptions at 1740–1700 cm−1. The peaks at 1000–900 cm−1 due to aliphatic CH2 wagging vibrations in olefins and at 730–720 cm−1 due to CH2 rocking vibration in long chain aliphatic substances ([CH2]n, n≥4), are characteristic of liptinite macerals. Collectively the micro-FTIR spectral characteristics indicate that liptinite is composed of greater numbers of long chain aliphatics, fewer aromatics and a broader range of oxygen-containing groups than other macerals. Marked differences exist in micro-FTIR spectra within the liptinite maceral group. Alginite has the strongest aliphatic and least aromatic absorptions followed by bituminite, resinite, cutinite and sporinite. The aliphatic components in alginite are the longest chained and least branched whereas those in sporinite are the shortest chained and most branched. Bituminite, resinite and cutinite are intermediate. Notable differences in micro-FTIR spectra of individual liptinite macerals, such as intensities and peak locations of aromatic CC in alginite, CO groups in bituminite and resinite and substituted aromatic CH and C–O–C groups in cutinite and sporinite, also exist, which are attributed to differences in depositional environments or biotaxonomy.

Micro-FTIR spectroscopy of liptinite macerals in coal

Reflectance FTIR microspectroscopy has been used to investigate the chemical structure of the liptinite macerals, alginite, bituminite, sporinite, cutinite and resinite in bituminous coals of Carboniferous to Tertiary age. In comparison with the spectra of vitrinite in the same coals, the micro-FTIR spectra of liptinite macerals are characterized by stronger aliphatic CH x absorptions at 3000–2800 and 1460–1450 cm −1, less intense aromatic CC ring stretching vibration and aromatic CH out of plane deformation at 1610–1560 and 900–700 cm −1 respectively and various intense acid CO group absorptions at 1740–1700 cm −1. The peaks at 1000–900 cm −1 due to aliphatic CH 2 wagging vibrations in olefins and at 730–720 cm −1 due to CH 2 rocking vibration in long chain aliphatic substances ([CH 2] n , n≥4), are characteristic of liptinite macerals. Collectively the micro-FTIR spectral characteristics indicate that liptinite is composed of greater numbers of long chain aliphatics, fewer aromatics and a broader range of oxygen-containing groups than other macerals. Marked differences exist in micro-FTIR spectra within the liptinite maceral group. Alginite has the strongest aliphatic and least aromatic absorptions followed by bituminite, resinite, cutinite and sporinite. The aliphatic components in alginite are the longest chained and least branched whereas those in sporinite are the shortest chained and most branched. Bituminite, resinite and cutinite are intermediate. Notable differences in micro-FTIR spectra of individual liptinite macerals, such as intensities and peak locations of aromatic CC in alginite, CO groups in bituminite and resinite and substituted aromatic CH and C–O–C groups in cutinite and sporinite, also exist, which are attributed to differences in depositional environments or biotaxonomy.