Depositional Environment Research Articles

Seismic and petrophysical characterization of the Sequoia Pliocene channel reservoirs: insights into hydrocarbon potential in the West Delta Deep Marine, Egypt

The Sequoia Pliocene channel reservoirs within the West Delta Deep Marine (WDDM) concession, located offshore Nile Delta, pose significant challenges due to their complex stratigraphy and variable reservoir properties. This study employs an integrated approach, combining seismic data interpretation with comprehensive petrophysical analysis, to characterize these reservoirs and assess their hydrocarbon potential. Seismic data interpretation revealed a complex depositional environment, characterized by an upward-fining sequence of sandstones and mudstones. High seismic amplitudes were associated with gas sands, while lower amplitudes indicated background shale. The seismic stratigraphy indicates that the Sequoia channel system evolved from an initial high-energy erosional phase to a more subdued depositional environment, leading to significant heterogeneity in reservoir quality. Petrophysical analysis demonstrated that effective porosity values within the reservoir range from 18% to 30%, with water saturation levels between 38% and 68%, reflecting the variability in reservoir properties across different zones. The calculated Gas Initially in Place (GIIP) for the Sequoia channel ranges from 724.1 BCF to 4158.71 BCF, highlighting the substantial hydrocarbon potential within this complex system. This study underscores the importance of integrating seismic and petrophysical data to develop a comprehensive understanding of the Sequoia channel reservoirs. The results provide a robust framework for optimizing field development strategies, which is crucial for maximizing hydrocarbon recovery. The findings also offer valuable insights into the geological complexities of the WDDM concession, serving as a reference for future exploration and production efforts in similar deep-water environments.

Improving interpretability: The role of dimension reduction in multiattribute seismic facies identification

Machine learning (ML) is increasingly recognized for its potential to enhance seismic interpretation by improving the analysis of geologically complex and obscured subsurface features. Integrating ML into seismic processing and interpretation enhances multiattribute analysis, increases resolution, and leads to more precise data interpretations. We emphasize best practices in ML workflows by evaluating these techniques in the Taranaki Basin, located offshore northwest New Zealand. Building on foundational research in deepwater channel systems that have used either/or synthetic and real data, our project advances these methodologies to assess newer dimension reduction (DR) techniques. We aim to refine our workflow for the identification of seismic channel facies and their associated depositional architectures. This effort involves integrating advanced algorithms in conjunction with k-means such as independent component analysis, principal component analysis (PCA), kernel PCA (K-PCA), and uniform manifold approximation and projection (UMAP) — to improve classification methods and address the limitations encountered in previous studies. We detail an advanced methodological approach that combines DR techniques with seismic attribute selection to achieve clearer visualizations of channel signatures and more accurate delineation of architectural elements. This enhanced clarity is crucial for deepening understanding of channel complexes and depositional environments, improving the mapping of reservoir extent and connectivity. Our research highlights ML utility in defining geologic features and its potential to improve seismic interpretation. The project is structured around two main objectives, the first discussed here and the second, a comprehensive statistical analysis, in a subsequent paper. Our primary objective is to verify that DR techniques improve the interpretability of geologic features within this data set. Project findings indicate an improvement in geologic interpretability; in terms of internal structure, K-PCA with three components outperforms other assessed DR techniques for this data set. When evaluating time-slice geologic interpretability, UMAP delineates more features.

Organic geochemistry of Middle Jurassic coal seam in the Sandaoling Coalfield, Northwest China: Insights into the depositional environment

The study of coal seams provides valuable insights into the environmental changes that have occurred throughout Earth's geological history. Coal formation was notably widespread during the Jurassic period in mid-latitude East Asia. To reconstruct the paleoenvironmental conditions prevailing during the formation of peat in the Turpan-Hami Basin, China, we conducted a comprehensive study of 44 Middle Jurassic coal samples. Our investigative approach encompassed coal petrographic analysis, and gas chromatography-mass spectrometry to compare our findings with existing literature. Biomarkers from steranes and diterpenes suggest OM in coals of No. 4 seam predominantly originated from terrestrial higher plants, with conifers being one of the important sources of OM. Vitrinite reflectance, hopane, and sterane maturity biomarkers indicate that most of the samples exhibit low thermal maturity. Previous studies suggested that the No.4 coal seam formed in a saline water environment based on trace element indicators. However, this study, based on biomarker analysis (low gammacerane index, high Pr/Ph ratio, and low sulfur content), suggests that peat accumulation occurred in freshwater environments. The anomaly of element indicators in previous studies may be attributed to the introduction of trace elements from overlying strata into the coal seams via surface (groundwater) water or hydrothermal fluids. Since the vegetation and depositional environments indicated by biomarkers are more consistent with the Jurassic geological setting, biomarkers offer a more reliable indication of depositional environment compared to trace element indicators.

Petrography and geochemistry of the Early Cambrian phosphorites from district Abbottabad, Pakistan: insights into depositional environment and origin

Petrography and geochemistry of the Early Cambrian phosphorites from district Abbottabad, Pakistan: insights into depositional environment and origin

First Report of Associated Gold Mineralisation in the Bansiyal Area, Sikar/Jhunjhnun District, Rajasthan, India: An IOCG Earth System of Mineralisation

The Khetri Copper Belt is known for copper mineralisation in Rajasthan. The North Khetri is specifically rich in copper mineralisation while the south Khetri belt is marked with the small isolated deposits of copper with sharing nearly similar depositional and lithotectonic environment. One such location is Bansiyal in Sikar District, Rajasthan, where copper mineralisation is known from as early as 1994 and hosted within Ajabgarh metasediments of Delhi Supergroup of rocks. We report the occurrence of gold for the first time from the area to the tune of 74ppb, which is 7 times higher than the threshold required for (which is 10ppb, as a convention) exploration. The Gold occurrence here is associated with copper and iron. The values of Copper up to 1.3% and Fe2O3 up to 52% indicates enrichment of these elements. Other trace elements like Cr, V and Sc have also slight enrichment indicating towards the possibility of this mineralisation being an IOCG earth system of mineralisation.

Comprehensive Assessment of Coalbed Methane Content Through Integrated Geophysical and Geological Analysis: Case Study from YJP Block

The study block is located on the eastern edge of the Ordos Basin and is one of the typical medium coalbed methane blocks in China that have previously been subjected to exploration and development work. The rich CBM resource base and good exploration and development situation in this block mean there is an urgent need to accelerate development efforts, but compared with the current situation for tight sandstone gas where development is in full swing in the area, the production capacity construction of CBM wells in the area shows a phenomenon of lagging to a certain degree. In this study, taking the 4 + 5 coal seam of the YJP block in the Ordos Basin as the research object, we carried out technical research on an integrated program concerning CBM geology and engineering and put forward a comprehensive seismic geology analysis method for the prediction of the CBM content. The study quantitatively assessed the tectonic conditions, depositional environment, and coal seam thickness as potential controlling factors using gray relationship analysis, trend surface analysis, and seismic geological data integration. The results show that tectonic conditions, especially the burial depth, residual deformation, and fault development, are the main controlling factors affecting the coalbed methane content, showing a strong correlation (gray relational value greater than 0.75). The effects of the depositional environment (sand–shale ratio) and coal bed thickness were negligible. A weighted fusion model incorporating seismic attributes and geological parameters was developed to predict the gas content distribution, achieving relative prediction errors of below 15% in validation wells, significantly outperforming traditional interpolation methods. The integrated approach demonstrated enhanced spatial resolution and accuracy in delineating the lateral CBM distribution, particularly in structurally complex zones. However, limitations persist due to the seismic data resolution and logging data reliability. This method provides a robust framework for CBM exploration in heterogeneous coal reservoirs, emphasizing the critical role of tectonic characterization in gas content prediction.

Spheroidal carbonaceous particles and other black carbon from Crawford Lake, Ontario, Canada

Spheroidal carbonaceous particles (SCPs) are formed from the incomplete, high-temperature combustion of fossil fuels. They are transported to a variety of depositional environments downwind of their sources and thus have the potential to be used to measure human activity on a regional scale. Composed mainly of elemental carbon, these fly ash particles are chemically inert and survive acid treatment, including HF. However, unlike microcharcoal, SCPs are typically overlooked during palynological analysis. Both types of black carbon are common in palynological preparations of varved sediments from Crawford Lake, Ontario where they can be correlated with the historic record of land use over the past two centuries. Increases in microcharcoal concentration correlate with historic records of land clearing in the early-mid 19th century and logging and lumber milling between 1885 and 1957 CE. The rapid increase in SCP concentration during the mid-20th century is attributed to the global increase in fossil fuel combustion and industrial activity (the Great Acceleration) and the decline during the early 1980s records increasingly stringent air quality standards as well as decreased demand for steel (and coking coal) in nearby Hamilton. Palynologists are urged to pay attention to these useful proxies of fossil fuel combustion in their slides.

Depositional Setting, Origin and Evolution of Organic Matter in Eocene Kopili Formation, Shillong Plateau, India

ABSTRACT The Late Eocene Kopili Formation in the Shillong Plateau, India, features a sequence of alternating strata, including shale, siltstone, and sandstone, with thick sandstone beds at the top. This study investigates the carbonaceous shales within these layers by analyzing palynofacies assemblages, maceral composition, pyrolytic hydrocarbons, and biomarkers. The palynofacies are predominantly rich in phytoclasts, exhibiting significant compositional variation across three distinct palynofacies units, which reflect fluctuations in depositional settings within a nearshore fluvio-deltaic environment. The organic matters are mostly represented by telovitrinite and inertinite macerals, with a complete absence of liptinite, indicating minimal humification and redox processes during early diagenesis. The kerogen types identified are predominantly Type III and IV, sourced mainly from terrestrial plants. Biomarker analysis reveals a significant contribution from severely biodegraded terrestrial angiosperms. The depositional environment is characterized as clay-rich, oxic to dysoxic-anoxic, and highly proximal, with variable water depths. Rock-Eval pyrolysis indicates an average Total Organic Carbon (TOC) of 0.64%, suggesting moderate to low hydrocarbon generation potential for the Kopili Formation. Various maturity indicators, such as vitrinite reflectance, TAI, Tmax and, biomarker maturity indices, suggest that a significant portion of the organic material is in an immature to early mature stage. In contrast to similar sequences found in the Assam and Bengal shelves, the Kopili Formation shows a reduced hydrocarbon potential, likely resulting from its deposition in a shallower, more oxygen-rich environment.

Taphonomy and diagenesis of submerged bone: An experimental approach.

Bone taphonomy and diagenesis contribute to anthropological analysis in forensic investigations by attempting to reconstruct the relationship between human cadaveric remains and their postmortem depositional environment. The rare aquatic taphonomic experiments have been delivering conflicting results on the influence of time and the environment on the decay of bone and teeth, especially considering that the main diagenetic processes can lead to fragmentation, progressive dissolution or fossilization. The aim of this experimental, quantitative, randomized and controlled 2-year study was to analyse the taphonomy and diagenesis of submerged terrestrial mammalian bones to achieve a more accurate estimation of both the post-mortem interval (PMI) and the post-mortem submersion interval (PMSI) in the short term. Three parameters of bone diagenesis, the Oxford Histological Index (OHI), the total porosity and the collagen content of cortical bone were analysed by MicroCT Scan, bright-field Light Microscopy (Picrosirius Red stain), Scanning Electron Microscopy (SEM) and Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on 75 sheep femurs and tibias placed in four distinct types of environment (natural saltwater, natural freshwater, an artificial seawater solution and exposed to the air) vs. non-exposed controls. LA-ICP-MS was soon discontinued because no measurable changes of the elemental profiles could be detected. Multivariate statistical analysis was applied to the collected data. The macroscopical preservation was consistently excellent (OHI=5). The total porosity and the degradation of collagen were greater underwater than in subaerial exposure, whereas demineralization zones and bioerosion tunnelling appeared after 12 months in the air-exposed samples only. Underwater, the continuous movement, the correlated abrasion by sand and sediment and the constant alkaline pH (≥ 8) can explain the progressive removal of the mineral component and the subsequent exposure of collagen to bioeroders and chemical hydrolysis. On land, the same process occurs at a slower rate on account of the seasonality of the water flow, however, the action of the more abundant and diversified species of bioeroding microorganisms appears more efficient. Despite some limitations, this study indicates that three parameters of bone diagenesis can predict the depositional environment of terrestrial mammalian bone characterized by a PMI and/or PMSI of at least 12 months.

New insights into marine-based paleo-ice sheet dynamics and glaciomarine depositional environment in an interfan area between ice stream-derived trough mouth fans, off west Svalbard

New insights into marine-based paleo-ice sheet dynamics and glaciomarine depositional environment in an interfan area between ice stream-derived trough mouth fans, off west Svalbard

Lithofacies and depositional environments in the Saltpond Basin of Ghana: A well log analysis

Lithofacies and depositional environments in the Saltpond Basin of Ghana: A well log analysis

Depositional Environment of Mallawa Formation Using Palynomorphs in the Southern Arm of Sulawesi, Indonesia

This study investigates the ancient age and depositional environment of the Mallawa Formation through palynomorph fossil and geochemical proxy analyses. The Mallawa Formation, dating from the Middle to Late Eocene, represents a significant geological unit in the region. Our research was conducted along two tracks, Massenrengpulu and Tellumpanuae, where we identified 26 pollen taxa and six spore taxa, along with marine palynomorphs. The analysis of palynomorph abundance and lithological characteristics places the Mallawa Formation within the Proxapertites operculatus zone, confirming its Middle to Late Eocene age. Geochemical proxy analysis indicates that the paleoclimate during deposition was dominated by semi-humid conditions with intervals of semi-arid conditions. Furthermore, paleoredox analysis suggests fluctuations from oxic to dysoxic conditions, reflecting variability within the Deltaic depositional environment. We interpret the depositional environment of the Mallawa Formation as a Delta influenced by precipitation, lithological factors, and the interplay between fluvial and marine processes. This research enhances understanding of the depositional evolution of the Mallawa Formation during the Eocene period and provides a foundation for future studies on palynomorphs, sedimentary rock deposition, and ancient environmental changes.

Textural Analysis of Soil Deposits from Archaeological Sites: Paturda and Bhon, District Buldhana, Maharashtra

Soil texture is a key factor influencing the formation and characteristics of soil deposits. Defined by the relative proportions of sand, silt, and clay, soil texture provides critical insights into the depositional environment. In archaeological contexts, the textural analysis of ancient soil layers significantly aids in understanding the processes that contributed to site formation. This study focuses on the soil texture of deposits from two significant archaeological sites in Sangrampur Taluka, Buldhana District, Maharashtra—namely, the Early Historic site of Bhon and the Early Medieval site of Paturda. A total of 54 soil samples were collected and analyzed using the international pipette method to determine their textural composition. Both sites are strategically located along the banks of the Purna River, suggesting a strong geomorphological influence on soil deposition. The findings reveal that the archaeological deposits predominantly exhibit a silty loam texture, indicating the contribution of riverine alluvium in their formation. In contrast, the virgin and modern surface soils from the region are characterized by a silt texture, highlighting variations in depositional processes over time.

Geochemistry of Iron Ore in Kadong-Kadong, South Sulawesi, Indonesia

Iron (Fe) is an element present in every rock; its availability in large quantities and economic value involves geological processes related to mineralization zoning. Economical iron ore is generally in the form of magnetite (Fe3O4), hematite (Fe2O3), limonite (Fe2O3.H2O), and siderite (FeCO3). Iron ore deposits can be formed primary or secondary. The formation of primary iron ore can occur through magmatic, contact metasomatic, and hydrothermal processes; secondary iron ore deposits are formed by sedimentary, residual, and oxidation processes. This research aims to determine the content of major elements, trace elements, rare earth elements, rock types, magma series, and geotectonic environment in iron ore deposits in the Kadong-kadong Area, Luwu Regency, South Sulawesi Province, based on geochemical data. The research method was carried out in the field. Laboratory analysis uses ICP MS/OES analysis. The results show the highest major oxide composition is the SiO2 compound, which is 54.81%. The second highest major oxide composition is the Al2O3 compound, which is 17.81%. The highest major element composition is Fe, which is >50%. The second highest major element composition is Al at 92,700 ppm. The highest tracer element composition is Ti element, which is 3280 ppm. The second tracer element composition is Mn 1170 ppm. Some elements, such as Ba, U, and Pb, show very significant enrichment. The data show that the study area is rich in rare earth elements, especially in heavy rare earth elements such as Dy, Ho, and Er. The results also show that the chemical composition of the research area shows that the rock types are andesite and basaltic andesite based on the TAS diagram. The SiO2-K2O and Co-Th diagrams show that the rock properties belong to the tholeiite series rock types. The Ta/Yb-Th/Yb diagram shows that the tectonic environment is in a volcanic arc with a tholeiitic magma series.

Sedimentology and depositional environment of Injana Formation's sandstone member, Kurdistan Region, Iraq

Fourteen thin sections from the sandstone bed of Injana Formation in Chamchamal area were studied by scanning electron microscopy (SEM) and polarized microscope. The petrographic component, and fauna content were determined. Sandstone is calclithite-sedarinite (litharenite) according to Dott’s (1964) and Folk’s (1980) classifications. The major petrographic constituents are: quartz, K-feldspar, calcite, chert, plagioclase, and fossil (algae). The Injana Formation in Chamchamal area was interpreted as littoral and later in a fluviolacustrine environment deposit.

Localization and further extraction of residual recoverable oil reserves in low-permeability sandstone reservoirs with chaotic oblique layering in a late-stage field: a case study of the Achimov sequence

Achimov sequence is characterized by high heterogeneity and low reservoir properties. Development of Achimov sequence occurs using horizontal wells with multistage hydraulic fracturing. Despite the adoption of advanced technologies, the oil recovery factor in these deposits ranges from 5% to 14%. As part of the article, we studied the localization’s process of residual recoverable oil reserves in low-permeability, macro-heterogeneous sandstones with chaotic layered structures in a late-stage field. We studied belonging of sandstones to the filtration-capacitance matrix of the reservoir and the current state of field development. In addition, we analyzed production well operation. As a result, we found areas with undeveloped reserves for infill drilling on the base of depositional environments and facies. We considered all these factors to adapt a hydrodynamic simulation model of a highly heterogeneous reservoir. We utilized this model to select the design system that is optimal in terms of technical and economic indicators.

Petrophysical Evaluation of the Zubair Formation’s Main Pay Zone Using Conventional and NMR Log Data: Insights from the North Rumaila Field, Southern Iraq

This study investigates the calculation of petrophysical properties using both conventional logging tools and Nuclear Magnetic Resonance logs for the main pay zone of the Zubair Formation, Recognized as one of the most significant hydrocarbon-producing formations in the North Rumaila Field, located in southern Iraq, the main pay zone is categorized into three permeable units (AB, DJ, and LN) and two impermeable isolated zones (C and K) based on log responses. The petrophysical analysis of these zones indicates that the shale volume increases toward the northern part of the field due to the depositional environment. Effective porosity values across these zones range from fair to good; however, some wells in the AB layer exhibit excellent porosity, notably wells X-7, X-62, X-83, and X-110. Additionally, hydrocarbon saturation levels remain consistently high in the AB and DJ layers, whereas certain wells in the LN layer display lower saturation values, particularly wells X-85, X-78, X-63, X-110, X-84, X-19, and X-115. Furthermore, permeability values were calculated using the KSDR equation based on Nuclear Magnetic Resonance logs that span from good to very good, except well X-115, demonstrating excellent permeability in the AB layer.

Oligocene–Miocene development and evolution of the south Dome Rock Mountains basin, lower Colorado River corridor, Arizona, USA

Sedimentary basins in the Colorado River extensional corridor record large-magnitude Basin and Range extension and younger dextral shear deformation in the evolving Pacific−North America plate boundary. The south Dome Rock Mountains basin is located in west-central Arizona (USA), where the history of basin evolution, style of deformation, and timing of the transition between extension and dextral shear are not well constrained. We integrate new geologic mapping of the south Dome Rock Mountains basin with zircon U-Pb geochronology of six marker beds to characterize the timing of basin evolution and the slip history of the south Dome Rock Mountains normal fault. Structural analysis defines structures consistent with regional extension and younger dextral shear deformation. We use sedimentological and petrological analysis to interpret the depositional environments of three basin sequences. A lower basin sequence consists of fluvial strata deposited in an internally drained intermontane basin from ca. 35 Ma to 24.4 Ma. A sequence of volcanic rocks was emplaced in the basin between 24.4 Ma and 23.3 Ma, before the onset of local extensional faulting. An upper basin sequence of coarse conglomerate and sedimentary breccia was deposited on the hanging wall of a half graben structure after 23.3 Ma and through ca. 12.8 Ma, synchronous with 3−7 km of dip slip on the west-dipping, listric south Dome Rock Mountains fault. The basin was subsequently deformed by dextral shear after 12.8 Ma and before 4.8 Ma. These results document how distributed deformation related to the evolving Pacific−North America plate boundary occurred >100 km from the primary plate boundary.

Applications of Laser Ablation Inductively Coupled Plasma Mass Spectrometry in Microbialites

Microbialites are critical for documenting early life on Earth and potential early life in other regions of the solar system. However, the criteria for identifying microbialites remain controversial. Trace element geochemistry provides two types of information that aid in the recognition of putative microbialites. First, as most microbialites are composed of authigenic precipitates, trace elements can be used to investigate the fluids involved in their formation, thereby helping to identify paleoenvironmental conditions. For example, rare earth elements (REEs) preserved in microbialites are highly useful in distinguishing deposi-tional environments. Second, microorganisms utilize and accumulate significant quantities of elements, including many metals. The preservation of such ele-mental enrichments may offer valuable biomarkers. Although research in this field is relatively nascent, high-precision in situ measurements (now with spa-tial mapping) of metals in microbialites-using techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) have confirmed persistent enrichments of biologically significant metals in microbialites. Con-sequently, trace element studies are increasingly proving valuable for investi-gating microbialites. Provided that diagenetic effects and the extent to which specific precipitates represent microenvironments are considered, trace ele-ment signatures may yield critical insights into depositional environments and metabolic processes within biofilms.

Detrital zircon geochronology and sedimentary provenance of the fossiliferous Ediacara Member, South Australia

The Ediacara Member of the Rawnsley Quartzite hosts the Ediacara biota in South Australia. These fossils are internationally recognised as representing the earliest complex life on Earth, with the South Australian section representing the global boundary stratotype section and point of the Ediacaran Period. Constraining the age, provenance and depositional environment of the sediments that host the fossils is therefore of great value. The Rawnsley Quartzite is also the terminal package of Neoproterozoic sediments in the Flinders Ranges region, and therefore a comprehensive understanding of sediment provenance and paleoenvironments will aid basin and paleoenvironment reconstruction. This study focuses on detrital zircon from a broad geographic spread of sites across the region of Ediacara Member deposition. LA-ICP-MS zircon U–Pb analysis yielded a total of 924 concordant zircon grains. The primary peak in age probability distributions is centred between ca 1260 and 1060 Ma with smaller peaks in the ranges of ca 640–620 Ma and ca 1800–1480 Ma. The youngest concordant zircon is 574 ± 8 Ma, and the youngest statistically coherent group is 623 ± 5 Ma (n = 4). We concur with previous studies that the primary sediment sources are the uplifted regions of the Petermann and Paterson orogens, which correlate to the basement provinces of the Musgrave and Rudall provinces, respectively. Younger detritus may have been sourced from the Mount Arrowsmith Volcanics (ca 585 Ma) in the Koonenberry Belt, western New South Wales.