Influence Of Depositional Environment Research Articles

Depositional environmental controls on mechanical stratigraphy of Barakar Shales in Rajmahal Basin, India

Understanding mechanical behaviour of shale is essential for efficient shale gas extraction, which can vary in different depositional settings. The impact of sedimentary environment on shale characteristics, such as mineralogical composition, total organic carbon content (TOC), and petrophysical properties, has been extensively researched. However, its influence on shale mechanical properties, especially in defining mechanical stratigraphy for targeting specific fracturing intervals, remains less explored. In this study, the influence of depositional environment on the mechanical properties of shale samples from the Rajmahal Basin is evaluated. Tensile strength of the samples was measured by the Brazilian splitting tensile strength and the brittleness index was calculated as a measure of mechanical properties. In addition, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray fluorescence spectroscopy (XRF), Rock-Eval 6, and X-ray diffraction (XRD) analysis were carried out to assess geochemical characteristics of the samples from different perspectives. The results revealed that such geochemical variations that are generally controlled by the depositional environment, would impact the mechanical properties of the samples. Based on major and trace elements proxies, the depositional environment was determined to be passive continental margin, with hot and humid paleoclimatic conditions and freshwater anoxic settings. Tensile strength and brittleness index of the shale samples was observed to vary between 0.93 and 4.12 MPa and 0.71 to 3.40, respectively, while samples with the TOC exceeding 15 wt% had a strong negative correlation with tensile strength, as reasonably expected, due to weakening impact of the sedimentary organic matter on the shale matrix. Tensile strength and brittleness index correlated positively with clay mineral content, particularly their type, but negatively with the quartz content. Furthermore, samples abundant in biogenic silica exhibited reduced brittleness compared to those with lithogenic silica. Nevertheless, the variation in mechanical properties with burial depth was not substantial, and the examination of stress-strain curves indicated an overall brittle nature of the layer where the samples were retrieved from. Overall, achieving more robust conclusions regarding mechanical stratigraphy within the studied section of the Rajmahal Basin, would necessitate additional vertical sampling.

Construction and validation of the upscaling model of organic-rich shale by considering water-sensitivity effects

Due to the complexity of its microscopic composition, the mechanical changes produced by the hydration process of organic-rich shale are more complicated than those of pure clay minerals. Although predecessors have researched the upscaling model of shale, the construction and evaluation of the water-saturated model remain a long-standing challenge. In this work, the combination of the differential effective medium (DEM) model and the self-consistent (SC) model (DEM-SC) was used to obtain a universal stiffness tensor of the clay matrix based on reverse modeling of ultrasonic pulse velocity (UPV) test results. Subsequently, a new water-sensitivity -based upscaling model was constructed that simultaneously considers: (1) the interlayer swelling, confining, and substitution effects of clay matrix under water-saturated conditions; and (2) the influence of depositional environment on the pore morphology of organic matter and the influence of maturity on its elastic properties. The upscaling model showed that the interlayer swelling effect is the most critical water-sensitivity effect, and the confining and the substitution effect can only compensate for part of the modulus reduction caused by interlayer swelling. In addition, the model behaved better when dealing with problems with a large volume ratio of inclusions (such as marine shale) and achieved good prediction results by controlling the relative errors compared with the microindentation experiments at less than 15%. Finally, the model was further applied to the well scale with better prediction results by considering the water-sensitivity effect, proving that the model has a wide range of application potential in formation evaluation and construction operations in shale gas production.

Influence of depositional environment on coal quality in Jangwa-Shankodi and Lafia-Obi areas, Central Benue Trough, north-central Nigeria

Influence of depositional environment on coal quality in Jangwa-Shankodi and Lafia-Obi areas, Central Benue Trough, north-central Nigeria

The influence of depositional environment on the abundance of microplastic pollution on beaches in the Bristol Channel, UK

Microplastic is a ubiquitous environmental contaminant, but large gaps still exist in our knowledge of its distribution. We conducted a detailed assessment of the extent and variability of microplastic pollution in the Bristol Channel, UK. Sand samples were collected between the 5th and 30th August 2017, with microplastic recovered from 15 of the 16 beaches sampled along a coastal extent of ~230 km. In total, 1446 particles of suspected microplastic were extracted using a cascade of sieves and visual identification. The most common microplastics recovered were fragments (74%) and industrial plastic pellets (13%). We used Fourier-Transform Infrared (FTIR) spectroscopy to analyse 25% of recovered particles, 96.5% of which were confirmed as plastic, with polyethylene (61%) and polypropylene (26%) the most common polymers. Our analysis of local beach environments indicates microplastic burdens were higher on lower energy beaches with finer sediments, highlighting the importance of depositional environment in determining microplastic abundance.

Influence of depositional environment on coalbed methane accumulation in the Carboniferous-Permian coal of the Qinshui Basin, northern China

Based on analyses of the lithofacies palaeogeography of the Taiyuan and the Shanxi Formations in the Qinshui Basin, the spatial variations of the coal seam thickness, coal maceral composition, coal quality, and gas content, together with the lithofacies of the surrounding rocks in each palaeogeographic unit were investigated. The results show that the thick coals of the Taiyuan Formation are mainly distributed in delta and barrier island depositional units in the Yangquan area in the northern part of the basin and the Zhangzi area in the southeastern part of the basin. The thick coals of the Shanxi Formation are located within transitional areas between delta plain and delta front depositional units in the central southern part of the basin. The Taiyuan Formation generally includes mudstone in its lower part, thick, continuous coal seams and limestones in its middle part, and thin, discontinuous coal seams and limestone and sand-mud interbeds in its top part. The Shanxi Formation consists of thick, continuous sandstones in its lower part, thick coal seams in its middle part, and thin coal seams, sandstone, and thick mudstone in its upper part. From the perspective of coal-bearing sedimentology and coalbed methane (CBM) geology, the lithology and thickness of the surrounding rocks of coal seams play more significant roles in controlling gas content variation than other factors such as coal thickness, coal macerals, and coal quality. Furthermore, it is found that the key factors influencing the gas content variation are the thicknesses of mudstone and limestone overlying a coal seam. At similar burial depths, the gas content of the Taiyuan coal seams decreases gradually in the lower delta plain, barrier-lagoon, delta front, barrier-tidal flat, and carbonate platform depositional units. The CBM enrichment areas tend to be located in zones of poorly developed limestone and well-developed mudstone. In addition, the gas content of the Shanxi Formation is higher in the coals of the delta front facies compared to those in the lower delta plain. The CBM enrichment areas tend to be associated with the thicker mudstones. Therefore, based on the lithologic distribution and thickness of the rocks overlying the coal seam in each palaeogeographic unit of the Taiyuan and Shanxi Formations, the areas with higher gas content are located in the north-central basin for the Taiyuan coals and in the southern basin for the Shanxi coals. Both of these areas should be favorable for CBM exploration in the Qinshui Basin.

Influence of depositional environment and diagenesis on petrophysical properties of clastic sediments (Buntsandstein of the Thuringian Syncline, Central Germany)

Influence of depositional environment and diagenesis on petrophysical properties of clastic sediments (Buntsandstein of the Thuringian Syncline, Central Germany)

Influence of depositional environment in fossil teeth: a micro-XRF and XAFS study

The formation of metal-rich phases during the fossilization of vertebrate fossil teeth, recovered from various deposition environments in northern Greece, is studied by means of synchrotron radiation X-ray fluorescence (SR-XRF) as well as Fe and Mn K edge X-ray absorption fine structure (XAFS) spectroscopy. XRF line-scans from the samples' cross-sections revealed different contamination paths for Mn and Fe. The two-dimensional XRF maps illustrate the spatial distribution of P, Ca, Mn and Fe as well as the precipitation of Fe-rich phases in cementum, dentin and dentinal tubules. Goethite, lepidocrocite and ferrihydrite were detected in the samples' cross-section by means of Fe K edge EXAFS spectroscopy. Moreover the Fe and Mn K edge EXAFS revealed the presence of vivianite and birnessite (MnO2) on the external surface of two samples.

13C enrichment in the Palaeoproterozoic carbonate rocks of the Aravalli Supergroup, northwest India: Influence of depositional environment

The dolomitic carbonates from the Jhamarkotra Formation of the Palaeoproterozoic Aravalli Supergroup are characterized by widely variable carbon isotope ratios ( δ 13C) ranging from near zero to as high as + 12‰ V-PDB. The estimated maximum age (ca. 2150 Ma) of the Aravalli carbonates help bracketing these with the coeval carbonate bodies of the world that show high positive carbon isotope values. The intriguing existence of normal marine δ 13C values in some pockets suggest influence of local scale depositional conditions prevailing in different sub-basins. Amongst these two sub-basins which showed high δ 13C values, a hypersaline evaporative condition is considered responsible for the necessary enrichment in one, while methanogenesis (possibly in conjunction with sulphate reduction processes) might have caused such enrichment in the other. From the empirical association of the sub-basins with profuse stromatolitic phosphorite we infer that the depositional setting that favoured cyanobacterial growth (leading to formation of stromatolites) prevented growth of methanogenetic archaea in such anoxic environments. Our study therefore highlights the fact that the early Palaeoproterozoic 13C excursion in the Aravalli Supergroup is not essentially a time-specific event but is greatly dependent on the variation in the depositional palaeoenvironment prevailing in different sub-basins.

TAPHONOMY OF DIPTERA IN LACUSTRINE ENVIRONMENTS: A CASE STUDY FROM FLORISSANT FOSSIL BEDS, COLORADO

The purpose of this paper is to study the taphonomy of fossil flies (Diptera) preserved in the lacustrine deposits of the Florissant Fossil Beds (late Eocene), Colorado, United States. Three hundred and twenty-six fossil Diptera were examined, collected from a nearshore (n = 215) and an offshore (n = 111) site. The degree to which a specimen's preservation quality correlated with the ability to identify the specimen to various taxonomic levels and whether specimen size, orientation, or disarticulation had an effect on a preservation quality were evaluated. Also examined was the influence of depositional environment on these variables. Preservation quality was found to be important for identification to species level, but specimens of low preservation quality were still identifiable to the family and genus levels. Specimen size, orientation, and disarticulation were not correlated with the identifiability of a specimen. There was no significant difference in the orientation, disarticulation, or preservation quality of specimens found in the nearshore and offshore sites. There was a significant difference in the size of specimens preserved at each site, with larger specimens being found offshore. More specimens were found in the offshore site, but species richness did not differ between the two sites. Composition of taxa did differ depending on the site. These results demonstrate the importance of collecting all specimens, as even poor quality and disarticulated specimens are identifiable and useful in studies of insect ecology and evolution. In addition, depositional environments should be documented, as size sorting can bias the taxonomic composition of assemblages.

A comparison of temperate and boreal peats from Ontario, Canada: possible modern analogues for Permian coals

Peat profiles were sampled from a raised bog and an interior fen located in the boreal James Bay Lowlands, Northern Ontario, and a cold-temperate swamp and a cold-temperate bog in the Great Lakes–St. Lawrence Lowlands, southern Ontario. An examination of the micromorphology and maceral compositions of the peats indicates that considerable differences exist between environments. The boreal bog and fen both consist predominantly of relatively unaltered textinite (commonly Sphagnum-derived), with higher liptinite contents in the fen profile attributable to the more diverse vegetation. Both the cold-temperate swamp and bog show high levels of humification at the surface, possibly partially attributable to recent climatic warming trends causing a decline in water table elevation. In all profiles, funginite was persistent, ranging from 2 to 10% of the total maceral content, indicating that aerobic conditions generally prevailed at the surface at the time of deposition. The influence of depositional environment and vegetation type on the resulting peat was born out in plots of Tissue Preservation Index vs. Gelification Index. The petrographic study also demonstrated that none of the profiles contained high inertodetrinite/semifusinite contents comparable to those within cold-climate cratonic Permian Gondwana coals. Since the oxidation processes leading to the formation of inertinite are considered to take place at the peat stage, if the peats studied were to contain a similar maceral assemblage upon coalification, inertinite precursors may be present in the peat. The lack of petrographic similarity between the Holocene peats and the Permian coals may be related to a number of factors. The decrease in water table elevation possibly responsible for the inertinization of the Permian coals may have occurred following the cessation of peat formation, not concurrently with accumulation, and is potentially attributable to long-term factors such as climatic warming. The change in the peat-forming vegetation (from Permian Glossopteris- and Gangamopteris-dominated communities to Holocene Sphagnum and coniferous vegetation) alters the characteristics of the initial botanical starting materials, and some aspects of the ecology, particularly trophic and pH conditions, which control the post-depositional alteration of the plant materials and the resulting maceral assemblages.

Influence of Depositional Environment on Diagenesis in St. Peter Sandstone, Michigan Basin: ABSTRACT

The Middle Ordovician St. Peter Sandstone in the Michigan basin was deposited in marine peritidal to storm-dominated, outer shelf depositional environments that evolved in a regionally significant transgressive pattern. The formation is bounded by carbonate and shaly clastic strata of the Prairie du Chien Group below and is transitional to condensed sequence clastics and carbonates of the Glenwood Formation above. Sedimentologic and petrographic analysis of conventional core from 25 wells suggests that reservoir quality in the formation is strongly dependent on a complex diagenetic history, especially the nature and subsequent dissolution of intergranular carbonate in the sandstone. Petrographic evidence indicates that porosity in the formation formed by dissolution of precursor dolomite of various origins and, locally, the formation of pore-filling authigenic clay (chlorite-illite). Authigenic clay is the incongruent dissolution product of dolomite, detrital K-feldspar, and, possibly, muscovite and results in diminished reservoir quality where abundant in the St. Peter Sandstone. Authigenic clay is volumetrically more significant in the upper portions of the formation and is associated with higher concentrations of detrital K-feldspar. Depositional facies controlled the distribution and types of intergranular carbonate (now dolomite) and detrital K-feldspar in the St. Peter Sandstone and hence reservoir quality; both components were more more » significant in storm-shelf sandstone facies. « less

Influence of Depositional Environments on Origin of Secondary Carbonates and Diagenesis of Organic Matter, Tertiary Basinal Units, La Honda Basin, Santa Cruz Mountains, California: ABSTRACT

A comparative study of authigenic carbonates formed in five organic-rich, deep-water units of the La Honda basin indicates that sedimentation rate and degree of bottom-water oxygenation ultimately controlled the timing, chemical environment, mineralogy, and rate of authigenic carbonate formation. Additionally, sedimentation rate and oxygenation of bottom water governed the sequence of diagenetic chemical environments, the degree of preservation of organic matter, and the source bed potential of the basinal units. The conditions necessary for the preservation of organic matter and the development of potentially good source rocks were variable. However, the occurrence of anaerobic bottom waters was the critical element in the development of excellent source rocks (i.e., Twobar Shale Member, Lambert Shale) regardless of the rate of sedimentation or the rate of primary productivity. In contrast, in basinal units characterized by oxygenated bottom waters, high rates of sedimentation, and high rates of primary productivity (Monterey Formation and Santa Cruz Mudstone Member), rapid burial of organic matter promoted highly anaerobic diagenetic environments which decreased the rate of organic matter decomposition, thereby producing units with good potential source rocks.

The influence of depositional environments on coal petrographic composition of the Lower Kittaning seam, western Pennsylvania

Lateral variations in maceral composition of the Lower Kittanning seam can be explained in terms of differential preservation of plant materials, which is influenced by the pH/Eh of water within the peat swamp and by the rate of subsidence. Within the central part of the basin, high telocollinite contents are observed; this type of vitrinite represents large, well-preserved pieces of woody tissue whose preservation was favored by rapid burial. Towards the margins of the basin, high desmocollinite contents are seen; slower burial, combined with the influx of neutral, oxygenated fresh water permitted decomposition of the precursor materials, producing this highly degraded type of vitrinite. Vertical variations in telocollinite and desmocollinite content can also be related to burial rates and pH/Eh conditions within the swamp. Throughout the basin, high telocollinate contents observed in the lower part of the seam resulted from rapid burial under relatively low pH conditions. Continued high rates of subsidence led to an influx of neutral pH, oxidizing waters associated with the encroaching marine environment. Under these new conditions, more degradation of plant tissues occurred, producing the high desmocollinite contents observed in the upper part of the seam. This effect was most pronounced in the center of the basin. An alternative explanation would be a change in vegetation type in response to the changing conditions; the high desmocollinite content would then reflect a shift to a community dominated by smaller, possibly herbaceous, plants. In addition to a change in vitrinite type towards the top of the seam, a decrease in total vitrinite content, and increases in total liptinite and inertinite contents are observed. The increase in liptinite content is due to either (1) the higher resistance to decomposition of liptinite precursor materials (when compared to vitrinite precursors) in the more neutral conditions, or (2) a change from a dominantly arborescent vegetation to a more herbaceous one. The increase in inertinite results from an increase in transported material (inertodetrinite) and/or an increase in the formation of inertinite macerals, such as degrado-fusinite, possibly in response to the encroaching marine conditions. An additional control on maceral composition is the level of metamorphism of the coal. Total liptinite content decreases towards the southeast; in this area, the coal has attained a sufficiently high rank that the reflectance of liptinite macerals approaches that of vitrinite, thus making their identification difficult.

Influence of Depositional Environment and Diagenesis on Gas Reservoir Properties in St. Peter Sandstone, Michigan Basin: ABSTRACT

The St. Peter Sandstone in the Michigan basin subsurface is rapidly becoming a major exploration target for natural gas. This reservoir was first proven with the successful completion of the Dart-Edwards 7-36 (Falmouth field, Missaukee County, Michigan) in 1981. Fifteen fields now are known, with a maximum of three producing wells in any one field. The production from these wells ranges from 1 to more than 10 MMCFGD on choke, with light-gravity condensate production of up to 450 b/d. Depth to the producing intervals ranges from about 7000 ft to more than 11,000 ft. The St. Peter Sandstone is an amalgamated stack of shoreface and shelf sequences more than 1100 ft in thickness in the basin center and thinning to zero at the basin margins. Sandstone composition varies from quartzarenite in the coarser sizes to subarkose and arkose in the finer sizes. Thin salty/shaly lithologies and dolomite-cemented sandstone intervals separate the porous sandstone packages. Two major lithofacies are recognized in the basin: a coarse-grained, well-sorted quartzarenite with various current laminations and a fine-grained, more poorly sorted subarkose and arkose with abundant bioturbation and distinct vertical and horizontal burrows. Reservoir quality is influenced by original depositional and diagenetic fabrics, but there more » is inversion of permeability and porosity with respect to primary textures in the major lithofacies. The initially highly porous and permeable, well-sorted, coarser facies is now tightly cemented with syntaxial quartz cement, resulting in a low-permeability, poor quality reservoir. The more poorly sorted, finer facies with initially lower permeabilities did not receive significant fluid flux until it passed below the zone of quartz cementation. This facies was cemented with carbonate which has subsequently dissolved to form a major secondary porosity reservoir. « less

Depositional Environments and Diagenetic Features of a Cretaceous Clastic Sequence, Fox Hills Sandstone of Northern Great Plains Province: ABSTRACT

The Fox Hills Sandstone, youngest formation of the Montana Group, is a geographically extensive, thin unit that is composed primarily of silty sandstone and shale. This formation records the final withdrawal of the Upper Cretaceous epicontinental sea from the Western Interior of the US. It extends from central Canada southward through Montana, the Dakotas, Wyoming, and Colorado. This typical shoreline sequence is exposed along the flanks of the Cedar Creek anticline, which trends southeastward from eastern Montana into North and South Dakota. The upper Fox Hills consists of stacked, upward-fining, trough to planar cross-bedded sandstone bodies. These sequences grade laterally and vertically into interbedded clay and silt units containing root casts and are interpreted as deposits of a braided-stream system. A matrix mineral assemblage of chlorite, montmorillonite, calcite, and minor dolomite is characteristic of distributary channels and river mouth-bar facies. The lower Fox Hills consists of either irregularly stacked upward-coarsening, trough cross-bedded sand sequences or massive sand bodies separated by erosional surfaces. Outcrops locally contain the trace fossil Ophiomorpha or limestone concretions containing marine to brackish-water fossils, and have been interpreted as deposits of a rapidly advancing shoreline and strand plain. In the matrix, illite, kaolinite, and montmorillonite with minormore » calcite characterize beach, subtidal, and crevasse-splay environments. Diagenetic features include quartz overgrowths, clay alterations of potassium feldspar and rock fragments, and authigenic clay rims. Petrographic evidence indicates multiple source areas for these sediments and the primary influence of depositional environments on clay formation.« less

High-Resolution Stratigraphic Correlations and Geochemical Analyses, Cretaceous Niobrara Formation, Northwestern Denver-Julesburg Basin: ABSTRACT

The middle Santonian-lower Campanian part of the Smoky Hill Member of the Niobrara Formation represents a fourth-order regressive-transgressive cyclothem. Studies of this interval have improved our understanding of the influence of depositional environments and structural setting on distributions of organic matter in epicontinental marine strata. Geochemical analyses of fresh quarried sections at Lyons and LaPorte, Colorado, show that, in general, Corg (organic carbon) levels are highest between mid-regression and mid-transgression. Rhythmic fluctuations of Ccarb (carbonate carbon) and Corg correspond to limestone-marlstone bedding couplets at a scale of 15-20 cm (6-8 in.). Pronounced lateral variations between Lyons and LaPorte exist in C SUB>org, HI (pyrolytic hydrogen index), sediment accumulation rates, and Tmax (temperature of maximum pyrolytic yield). Comparisons of geochemical averages at Lyons (Corg = 2.5%, Ccarb = 9%, HI = 100, Tmax = 445°C) and LaPorte (Corg = 4%, Ccarb = 9.5%, HI = 450, Tmax = 422°C) indicate an elevated thermal maturity at Lyons and depositional conditions more favorable for preservation of marine organic matter at LaPorte. In both sections, Corg and Ccarb show strong negative correlations, possibly reflecting cyclic climatic controls on the development of bedding couplets. High-resolution stratigraphic correlations of 100,000-year or smaller intervals between Boulder and Owl Canyo , Colorado, based on widespread bentonites and bedding couplets, reveal a paleostructural high near Lyons. Shallow-water conditions and increased turbulence over this high are reflected in sediment accumulation rates only 60% of those at LaPorte. Increased amounts and hydrogen richness of organic matter at LaPorte may reflect a deeper water, more quiescent depositional setting. End_of_Article - Last_Page 863------------

Influence of Depositional Environment on Type and Probability of Encountering Coal-Bed Discontinuities: ABSTRACT

Predictive models that characterize coal bed discontinuities enable mine operators to be better judges of the size, geometry, and influence of these features in unmined portions of the coal bed. An analysis of depositional environments in initial geologic studies of prospective mine properties will indicate the specific types of coal bed discontinuities that can be anticipated. The type of coal bed discontinuity and the frequency of occurrence are functions of the depositional environment. Peat, the precursor of coal, accumulated in swamps that may form on fluvial plains, on delta plains, and in littoral areas. Using generalized depositional models for these environments, the types of coal bed discontinuities that can be expected and an estimate of the likelihood of their occurrence can be determined. Coal beds deposited on fluvial plains generally are thin, erratic, and discontinuous because of the highly oxidizing character of this environment. Discontinuities due to irregular topography and fluvial channel activity are common, as displayed by Upper Pennsylvanian and Permian coal beds of the Dunkard basin. Coal beds formed in deltaic settings are generally thick and laterally extensive, as they commonly infill broad interdistributary areas. These coal beds are typically plagued by discontinuities associated with distributary channels (e.g., avulsion, splays). The Freeport and Kittanning coal beds in west-central Pennsylvania demonstrate features characteristic of delta-plain coals and the discontinuities that beset them. Coal beds deposited landward of barrier bar sequences generally are irregular and are interrupted by tidal channels and washover deposits. The Pocahontas 3 coal bed of southern West Virginia exhibits many of the characteristics of this paralic setting. Although some clastic dikes may be depositionally related, such discontinuities, as well as faulting, may be overprinted by tectonic activity on coal beds from any depositio al environment. End_of_Article - Last_Page 1922------------