Sedimentary Depositional Environments Research Articles

Variations and Quartz Grain Microtextures in Sediments from the Central Part of the Gulf of Guinea: Implications for Sedimentary Processes and Depositional Environment

Variations and Quartz Grain Microtextures in Sediments from the Central Part of the Gulf of Guinea: Implications for Sedimentary Processes and Depositional Environment

Using Element/Ca Response to Cleaning in Foraminifera From Endmember Depositional Environments to Infer Contaminants and Inform Pretreatment

AbstractPast ocean conditions are often reconstructed using the elemental composition of foraminiferal calcite. However, foraminiferal remains are often impacted by post‐depositional contaminants; thus, they require cleaning prior to element/Ca (El/Ca) analysis. To explore the impact of sample pretreatment on foraminiferal El/Ca ratios (Li, Na, Mg, Al, Mn, Fe, Zn, Sr, I, Ba, and U) we performed six cleaning procedures on four foraminifera populations from distinct depositional environments: Two from South Pacific carbonate ooze (ELT25‐11) and two from the hemi‐pelagic sediments of the California Margin (ODP1017E, SPR0901‐04BC). Despite differences in regional oceanography, sample type (i.e., surface‐ or deep‐dwelling planktic, benthic), and cleaning procedure, the main driver of El/Ca variability in the data set is the sedimentary depositional environment, suggesting site‐specific differences in element concentrations and contaminants. This finding challenges the notion that sample cleaning procedures should be informed by the El/Ca of paleoclimate interest, as elements may be found in different contaminants and/or elemental abundances in unique environments. Our data also show that traditional cleaning methods which use a combination of rinsing, sonication, oxidation/reduction, and complexation reactions effectively remove contaminants found on foraminifera in either depositional environment. However, even after contaminant removal, some elements (i.e., U and Fe) remain higher in California Margin foraminifera relative to South Pacific foraminifera. This suggests that the range of acceptable El/Ca values in the literature must be expanded when working with foraminifera from unusual depositional environments (i.e., hemipelagic, siliciclastic sites with high sedimentation regimes) versus values associated with more typical sites (i.e., a pelagic carbonate ooze).

Exceptional preservation of three-dimensional dunes on an ancient deep-marine seafloor: implications for sedimentary processes and depositional environments

Depositional and erosional bedforms can be used to reconstruct sedimentary processes and aid palaeoenvironmental interpretations. Using exhumed deep-marine strata in the Eocene Aínsa Basin, Spain, we document a 3-dimensional package of dunes, a rarely identified bedform in deep-marine environments. Our analysis shows that the dunes have curvilinear crests in planform, with smaller superimposed oblique dunes and ripples across the stoss sides. Beds containing these dunes have two main internal divisions: a lower inversely-graded (fine-to-coarse sandstone) and predominantly structureless division, and an upper coarse-grained sandstone division with well-developed cross-stratification, which is scoured and mantled with mudclasts and coarse-grains on the stoss-side. The rugose remnant relief of the bedforms controls the location of subsequent bedforms. Following recently reported direct measurements of natural turbidity currents, we interpret the basal division as recording deposition from the dense basal head of a high-velocity turbidity current, followed by the development of dunes beneath the more sustained but relatively high-velocity and unsteady flow body that reworked the initial sandy deposit into downstream migrating dunes and scours. These dune-forming beds have been identified in different deep-water environments in the Aínsa Basin stratigraphy, including channel overbank and channel mouth settings and scour-fills. These locations suggest that the dunes were intimately tied to high-velocity flows that bypassed through channel axes before expanded and depositing in less confined channel overbank or channel mouth settings. Preservation of these dunes in the Aínsa Basin was likely enhanced by tectonically-forced lateral migration of channels, which prevented cannibalisation of bypass-zones, in combination with high aggradation rates due to confinement, or periodic supply of flows from a particularly clay-poor source area. Where identified these dune-like bedforms are considered diagnostic of substantial sediment bypass downslope to deep-water basins.

Vase-shaped microfossils and possible trochamminid foraminifera from the Ediacaran Dhaiqa Formation of Saudi Arabia

We report the first discovery of vase-shaped microfossils (VSMs) and possible multichambered foraminifera from the Ediacaran rocks of Saudi Arabia. The Ediacaran successions of Saudi Arabia are well exposed in the northwestern and central part of the Arabian plate but are relatively understudied due to the lack of economic potential. The exposures can be found in different small sedimentary basins distributed along the flanks of Najd Fault system of the western Arabian Plate. The Dhaiqa sub-basin located near the historic city of Al-Ula contains some of the best exposures of Ediacaran Mattar and Dhaiqa Formations with collective exposure almost 400 m thick. These formations (especially the Dhaiqa Formation) were investigated to describe sedimentary facies, depositional environment, and possible microfossils. This study focuses on the identification of vase-shaped microfossils and possible trochamminid foraminifera of Ediacaran age that are herein recognized for the first time in Saudi Arabia. Outcrop samples were thin-sectioned and analyzed to reveal nine sedimentary facies belonging to four facies associations. The observed microfossils were found in a total of four samples from the cherty/siliceous carbonate and sandy microbialite facies. The microfossils are observed to be associated with diagenetic chert, which is abundant in these facies. The two facies contain a sparse microfossil assemblage with vase-shaped microfossils, which are single-chambered microfossils of uncertain taxonomic affinity, and possible multichambered agglutinated foraminifera that resemble trochamminids.

The Mousty Formation (Brabant Massif, Belgium): state of the art

The Mousty Formation has unique and particularly interesting lithological, mineralogical, sedimentological, metamorphic and tectonic characteristics which have been the subject of much research in connection with the new geological map of Wallonia, but also within the framework of a large amount of academic research, sometimes unpublished. An effort to synthesise and upgrade it in an updated framework seemed necessary. After a history of its definition, mapping and outcrop areas, the following topics are successively addressed in detail and illustrated with diagrams and photos: its lithostratigraphy with the probable discovery of its base near the Court-St-Etienne anticline, its well-constrained biostratigraphy and chronostratigraphy, a new estimate of its minimum thickness, its sedimentology—a subject little addressed until now—, and the resulting depositional sedimentary environment. Its geochemistry, never addressed, is comparable to black shale international standards, except for abnormally high manganese and very low calcium contents; high radon levels in buildings are related to the black slate presence in outcrops. Its mineralogy is rich in manganese-bearing metamorphic minerals, its metamorphism in which we go beyond the strict framework of the formation to deal with the entire southern outcropping rim of the Brabant Massif. Finally, the relationship between the Mousty Formation and the tectonic is discussed, with additional field data, in the context of the innovative and unifying concept of a low-angle extensional detachment called the Asquempont Detachment System. All these observations, some old and some very recent, discussed in the updated framework of the geology of the Caledonian basement of Brabant and in the global stratigraphy and palaeogeography of the lower Palaeozoic, allow us to renew in depth the vision we had of the Mousty Formation and of its place in the Brabant Massif.

Microtextures on quartz grain surfaces in the Bay of Bengal shoreline sediments, Bangladesh: Implications for sediment transport process and depositional environment

SEM and SEM-EDS studies of quartz grains in the shoreline sediments of the Bay of Bengal, Bangladesh were carried out to evaluate the mode of origin, paleoclimate, and depositional environment. A total of 38 microtexture types were identified, which were grouped into mechanical (23 features), mechanical/chemical (6 features), and chemical (9 features) origins. The morphology of quartz grains in the shorelines was dominantly sub-angular to sub-rounded in shape, which represents robust energy conditions, short residence time, low weathering, and nearby sediment provenance. The microtextures of mechanical origin such as straight and curved scratches, pits, broken edges, and crescent-shaped features were relatively abundant in the eastern site samples (Section-I) indicating high-energy, fluvial, and beach environments. The abundance of V-shaped marks and smooth surfaces of quartz grains indicate high-velocity storm conditions and/or high-energy impact events. The well-rounded outline, low relief with dish-shaped depressions, mechanically upturned plates, and arcuate steps were also observed on quartz grain surfaces. These features suggest that they were developed during an aeolian process in the beach berm environment. Etching, solution/irregular pits, and differential relief on quartz grains were somewhat elevated in the western site samples (Section-III), reflecting that these microtextures were associated with a subaqueous collision and humid climates in the fluvial and nearshore environments. Quartz grains in all sections represented microtextures of high energetic subaqueous environment as well as wind events. However, the absence of corrosion channels and high density of voids in the quartz grains revealed low degree of weathering.

Sedimentary Facies, Paleogeography, and Depositional Models of the Middle–Late Permian in the Sichuan Basin, Southwest China

This study focuses on the analysis of the sedimentary facies of the Middle–Late Permian, including the Qixia, Maokou, Wujiaoping/Longtan, and Changxing/Dalong Formations, in the Sichuan Basin, southwest China. Integrating drilling data and field outcrop data, various sedimentary facies indicators were employed to define eight sedimentary facies types in the Sichuan Basin during the Middle–Late Permian, namely, mixed tidal flat, tidal flat, restricted platform, open platform, platform margin, slope, basin, and volcanic facies. Detailed facies analysis was conducted on selected well logs, and sedimentary facies distribution maps were compiled for different time intervals, establishing depositional models. During the Qixia to Maokou stages, an extensive open platform was developed in the Sichuan Basin, accompanied by shallow intra-platform shoals. Towards the west along the Dayi–Ya’an line, platform margins were developed, followed by slope facies and basin facies in a northwest direction. During the Changxing stage, the Kaijiang–Liangping fault block subsided, forming the “Kaijiang-Liangping” paleochannel, which controls reef–shoal deposition in the region. This study provides comprehensive insights into the sedimentary facies characteristics and depositional environments of the Middle–Late Permian in the Sichuan Basin, contributing to the understanding of the regional sedimentary history and geological evolution.

Characterizing facies and porosity-permeability heterogeneity in a geothermal carbonate reservoir with the use of NMR-wireline logging data

If they are to be economically and technically sustainable, geothermal projects require the production of hot fluid at high flow rates over a 30-year thermal lifetime. The combined use of multiple logging tools in making petrophysical assessments of reservoir quality helps to optimize drilling in areas of high geothermal potential. The present paper focuses on four geothermal wells intercepting Middle Jurassic (Dogger) carbonate rocks of the Paris Basin where for the first time Nuclear Magnetic Resonance (NMR) log data have been successfully used to investigate reservoir porosity-permeability heterogeneities. A total of ten facies have been identified from recovered cuttings and cores and grouped into four facies associations along a schematic carbonate ramp profile. From the wells studied, four reservoir units exhibiting porosities exceeding 15% and permeabilities of up to 1 Darcy (D) were traced in the Calcaires de Comblanchien, the Oolithe Blanche and the Calcaires marneux à Pholadomyes formations. The well's sub-horizontal trajectory and well-logs correlations between two wells, made it possible a priori to identify porous and permeable layers extending over at least 500 m and up to 2000 m within the Bathonian reservoir, providing useful pointers for further 3D reservoir geomodeling. Permeabilities derived from well testing proved to be overestimated when compared with NMR-derived permeabilities, illustrating the upscaling problem that is invariably a challenge in carbonate systems. NMR can be combined with production logging tool (PLT), that provides data on the distribution and thickness of productive layers, to give indications for example about continuous permeability record along the geothermal wells or about the proportion of micro and macroporosities in rocks. Based on the geological classification derived from examination of cores and cuttings, four rock-types (including mean T2 pore-size distributions) have been identified and attributed to a given sedimentary facies and depositional environment by extending a clustering method to NMR log distributions from wells.

Holocene evolution of the Banni Plain at the north‐east margin of the Arabian Sea: Constraints from a ca 50 m long sediment core

AbstractHolocene evolutionary history of the Banni Plain in the Great Rann of the Kachchh Basin is reconstructed from a subsurface sediment core of ca 50 m. Detailed data on textural and lithofacies variations, grain‐size analysis, environmental magnetism and accelerator mass spectrometry 14C dates on seven samples were generated on the sediment core retrieved from the Banni Plain near Berada. A high‐resolution record extending back to 10 ka has been reconstructed from the top ca 40 m of the core section comprising shallow marine sediments. The core is divisible into five depositional units. The basal part is a fluvial depositional unit followed upward by estuarine, sub‐tidal, intertidal and supra‐tidal environments. The sediment accumulation rate is highest in the sub‐tidal to intertidal facies (1.9 cm year−1) and decreases towards the supra‐tidal facies to 0.09 cm year−1. Environmental magnetic analysis, χlf coupled with the S‐ratio, indicates high magnetic mineral concentrations during the Early Holocene, suggesting a wet period accompanied by high monsoon precipitation. This is followed by the onset of semi‐arid conditions in the Great Rann of the Kachchh Basin as indicated by the low values of the χlf and S‐ratios. A westward and northward shift in the shoreline towards the deeper part of the basin is suggested during the Late Holocene, which is coupled with aridity and reduced monsoonal conditions. The change in depositional pattern from the retrogradational deposit of fluvial (Unit 1) to estuarine sediment (Unit 2), progressing to sub‐tidal (Unit 3), is attributed to sea‐level transgression followed by regressive intertidal (Unit 4) to supra‐tidal deposition (Unit 5), culminating in complete withdrawal of the sea, aided by tectonic uplift, during the Late Holocene. The results reveal that the sediment accumulation rates and depositional environments changed over time in response to changes in sea level from minima to maxima and then eventually to the present level.

Spatial variations in the consolidation of sediments in the Neogene Miyazaki forearc basin, Southwest Japan

The Neogene Miyazaki Group comprises forearc basin sediments exposed onland in South Kyushu in Southwest Japan, and is characterized by significant spatial variations in consolidation despite the minor differences in depositional ages. The Miyazaki Group is divided into three lithofacies (the Aoshima, Miyazaki, and Tsuma facies) from south to north. To evaluate the factors controlling lithification in the basin, the physical properties of the sedimentary rocks and the calcareous nannofossil biostratigraphy were investigated. The upper parts of the Aoshima and Miyazaki facies and the lower part of the Tsuma Facies were deposited at the same time (5–6 Ma), and have minor differences in maximum paleo-temperatures (97–116, 85–99, and 80–94 °C, respectively), but major differences in porosity (15.9%, 25.5%–26.9%, and 26.1%–31.6%) and consolidation yield stress (38.2, 13.8–16.2, and 13.6–15.5 MPa). These findings indicate that the porosity reduction associated with consolidation is a more important control on the lithification than the depositional age and maximum temperature. There is a large difference in maximum burial depth between the Aoshima (>3500 m) and Miyazaki facies (<1600 m). It represents variations in sedimentary depositional environments in the Miyazaki Group: the Aoshima Facies were deposited in the deep-marine depocenter and deeply buried, whereas the Miyazaki and Tsuma facies were in the shallower marine facies and shallowly buried. After the deposition, only the southern part of the Miyazaki forearc basin was largely uplifted, making distribution of the highly consolidated sedimentary rocks there. The large amount of uplift in the Aoshima Facies was apparently due to the subduction of the Kyushu–Palau Ridge beneath the forearc basin.

Grain size distribution of modern beach sediments in Sri Lanka

Grain size distributions are widely used to describe sedimentary geochemistry, depositional environment, and sediment transportation. The objective of this study is to analyze grain size distributions of modern sandy beach sediments in Sri Lanka. Sediment samples (n = 90) were collected from beach berm, representing the entire coastline of Sri Lanka. Grain sizes were determined by the dry-sieving method. Statistical parameters such as mean size, sorting, skewness, and kurtosis were calculated using GRADISTATV9.1 software for all the sieved sediment samples. Grain size variations (108.2 – 609.8 µm) show that Sri Lanka mainly consists of medium sand, whereas the northeast part of the country mixes with fine sand due to the influence of Bengal fan sediments. The variations of skewness (-0.229 – 0.446) and sorting (1.305 – 2.436) indicate symmetrical distributed moderately sorted samples. These variations specify a moderate energy depositional environment/wave action around the coastline of Sri Lanka. In addition, grain size analysis confirmed relatively high and low energy deposition environments on the west and east coasts, respectively. Accordingly, the west coast is more vulnerable to coastal erosion compared to the east coast of Sri Lanka. Therefore, this study provides the baseline grain size distribution data that can be used in decision-making for coastal zone management by mitigating beach erosion.

The paleoenvironmental and thermal histories of the Permian Irati Formation shale in the Paraná Basin, Brazil: An integrated approach based on mineralogical and organic imprints

Mineralogical assemblages and organofacies are important sources of information to recover the paleoenvironmental and thermal histories of shale deposits. In this study, a detailed qualitative and quantitative characterization of the Permian Irati Formation (Assistência Member) shale is based on mineralogical (XRD and SEM-EDS) and organic components (TOC, Rock-Eval pyrolysis, organofacies, TAI, fluorescence and vitrinite reflectance measurements) and provides integrated data about sediment provenance, depositional environment, diagenesis, and thermal history, while supporting interpretations on the Paraná Basin (PB), Brazil, paleogeography and its correlation to the southwest Gondwana. The results revealed a prevailing type I/II kerogen, with type III kerogen being also present but mainly confined along the paleoshoreline of the PB. The dominance of fluorescent amorphous organic matter (AOM) combined with framboidal pyrite suggests microbial activity in an anoxic-dysoxic neritic-marine paleoenvironment. Additionally, common to abundant well-preserved phytoclasts, as well as the occurrence of Botryococcus braunii, indicates freshwater influx in a brackish marine depositional setting. Immature to early-oil window thermal maturities prevail across the PB, according to the organic maturation indicators. The combined analysis between the organic matter evolution with clay mineralogy, such as the occurrence of interstratified clays (e.g., I/S) and its positive correlation with depth suggest that burial diagenesis reached the transition to early catagenesis on the north, southeast, and south of the basin, attributing a shale oil potential for the Irati Formation on a regional scale. Local scale imprints of the Early Cretaceous Paraná-Etendeka Large Igneous Province (LIP), and its thermal effect in the Irati Formation shale components, are recorded as clay authigenesis (e.g., smectite webby texture and clay coating development), crystallization of minerals by low to high-grade of thermal alteration (e.g., corrensite, talc, lizardite and diopside), and by local scale gas-window maturities. Such thermal alteration, identified in the proximity to intruded sills and dykes, led to a heterogeneous organic maturation pattern with implications on shale gas and shale oil potential of the Irati Formation shale, demonstrating that these subjects in the Paraná Basin should be assessed locally.

Microtextures on Quartz Grain Surfaces in the Beach Sediments of Southern Hodeidah, Red Sea Coast, Yemen

Surface features of quartz grains on the Al-Haymah and Moushij beaches of the coastal area in the southern Red Sea of Yemen were analyzed by a scanning electron microscope (SEM) to deduce the provenance and depositional environment of sediments. The microtextures on quartz grains were classified into mechanical, chemical, and mechanical/chemical origins. The quartz grains from the two beach areas were rounded to subrounded in shape. Rounded quartz grains with a combination of bulbous and broken edges indicated a recycled provenance. Mechanical features such as V-shaped marks and straight and curved scratches revealed the combination of fluvial and high-energy subaqueous beach environments, whereas aeolian grains are mainly marked by crescentic percussion marks, elongated depressions, and upturned plates. Chemical features such as solution pits, silica globules, trapped diatoms, and adhering particles in quartz grains indicated a diagenetic environment and silica re-precipitation in a coastal environment. In general, the microtextures identified on quartz grains reveal that sediments are influenced by wind, fluvial, and subaqueous marine environments and are derived from nearby and distal sources.

Trace Fossils and Sedimentary Depositional Environment: A Case Study from Early Permian Barakar Formation, Raniganj Basin, India

Behavioral responses of organisms with respect to changing environment have a wide area of research possibility. For a palaeontologist it is a challenge to interpret the organism-sediment interaction from the study of the trace fossils preserved in the ancient rock record. The ethological significance which is derived out of different intentional or accidental activities of the organisms may be preserved within the rock and is largely controlled by the substrate stability, grain size of the sediments, energy and rate of sedimentation of the driving process, types of nutrients and its supply, salinity, temperature and oxic/sub-oxic/an-oxic conditions etc. So, the viability of this study in sensu stricto depends on the preservation potential of the organism as a whole or in parts or its activities (indirect evidences) on or within the substrate upon which they have survived thousands and millions of years ago. The indirect evidences of the organism’s activities may be its locomotory/respiration/feeding/resting/dwelling/predating traces etc. which have different nomenclature based on their morphological classification. The study area encompassing the major river section of the Barakar, Khudia, Ajoy holds partly enriched and partly impoverished trace fossils within the sedimentary rocks hosting huge reserves of coal. There are several concepts regarding the depositional setting of the studied basin like formerly interpreted fluvio-lacustrine depositional model to recently reinterpreted fluvio-tide-wave dominated depositional model. Several invertebrate traces have been recorded from the study area namely Planolites, Thalassinoides, Ophiomorpha, Palaeophycus, Cylindrichnus, Diplocraterion which indicates diverse environmental settings ranging from supratidal/intertidal/subtidal to continental shelves whereas other solo/uniform traces observed like Chondrites, Skolithos, Rhizocorallium etc. are indicator of shallow subtidal to marine quite water setting. Here the additional challenges include the lack of ample exposures, weathered exposed rock sections, inaccessible mine cut sections, absence of body fossils and controversial identification of trace fossils in differential erosive surfaces. This chapter in short has tried to mitigate these problems by the integrated sedimentary and ichnological facies association studies in delineating the depositional environment of the studied basin.

Sedimentary characteristics and depositional environment of quaternary lacustrine tufa Bent Jedidi spring systems, NE Tunisia

Sedimentary characteristics and depositional environment of quaternary lacustrine tufa Bent Jedidi spring systems, NE Tunisia

Sediment depositional pattern in the northern Japan Sea over the last 1200 ka and its linkages to orbital forcing

The semi‐enclosed marginal Japan Sea is sensitive to global changes and responds to orbital‐scale variability. Sediment core samples from Integrated Ocean Drilling Program Site U1423 were processed for detrital grain size and semi‐quantitative mineral analysis to assess the sediment characterization and depositional environment in the Japan Sea over the last 1200 ka. The mean grain data suggest the dominance of the silt size fraction over sand and clay in the whole period, while sand content increases dramatically between 600 and 150 ka. The end‐member energy modelling of grain size data suggests that sediment deposition took place under two energy conditions over the last 1200 ka. The low‐energy conditions observed during the middle Pleistocene transition (MPT) is mainly related to the wind deposition with the sediment characteristics being moderately to poorly sorted and coarse to nearly symmetrical skewed during global cooling and enhanced East Asian Winter Monsoon (EAWM) winds in the northern Japan Sea. Post MPT, periodic fluctuations between higher and lower energy conditions are observed, and the depositional environment is controlled by the EAWM wind, and precipitation intensity, glacio‐eustatic sea‐level changes and sea‐ice volumes. During the period, detrital sediments are poorly sorted and nearly symmetrically skewed, marked by the dominance of quartz, plagioclase and k‐feldspar. The spectral analysis grain size‐related data shows the presence of 228, 41 and 23 kyr orbital paced cycles, which are also observed in the Chinese Loess Plateau's normalized quartz mean grain size. This study is the first report of 228 kyr cycles from the Pleistocene Japan Sea sediments indicate that sediment deposition in the Japan Sea is associated with ~200 kyr eccentricity cycle as in the Chinese Loess Plateau.

Sedimentary Facies, Architectural Elements, and Depositional Environments of the Maastrichtian Pab Formation in the Rakhi Gorge, Eastern Sulaiman Ranges, Pakistan

An integrated study of sediments was conducted to examine the facies architecture and depositional environment of the Cretaceous Pab Formation, Rakhi Gorge, and Suleiman Ranges, Pakistan. This research focused on analyzing architectural elements and facies, which are not commonly studied in sedimentary basins in Pakistan. To identify lithofacies, outcrop analysis and section measurement were performed. The identified lithofacies were then categorized based on their depositional characteristics and facies associations, with a total of nine types identified within a stratigraphic thickness of approximately 480 m. These facies were mainly indicative of high-energy environments, although the specifics varied by location. Sedimentary structures such as planar and trough crossbedding, lamination, nodularity, load-casts, and fossil traces were found within these facies, indicating high-energy environments with a few exceptions in calm environments. The identified facies were grouped into seven architectural elements according to their depositional environments: delta-dominated elements, including laminated shale sheet elements (LS), fine sandstone elements (SF), planar cross-bedded sandstone elements (SCp), trace sandstone elements (ST), and paleosol elements (Pa); and river-dominated elements, including trough cross-bedded sandstone elements (SCt), channel deposit elements (CH), and paleosol elements (Pa). These architectural elements, along with their vertical and lateral relationships, indicate a transitional fluvio-deltaic environment within the Pab Formation. In conclusion, by interpreting facies and architectural elements, it is possible to gain a better understanding of the depositional history of the formation and the distribution of reservoir units.

Depositional Environment of Sediments in Tonle Sap Sedimentary Basin, Western Part of Cambodia: Insights from Field and Geochemical Studies

Depositional Environment of Sediments in Tonle Sap Sedimentary Basin, Western Part of Cambodia: Insights from Field and Geochemical Studies

Applying biomarkers as paleoenvironmental indicators to reveal the organic matter enrichment of shale during deep energy exploration: a review.

Analysis of biomarkers in geological materials such as shales is very crucial because they can provide useful information on the depositional conditions and environments, organic matter input, thermal maturity as well as the geological age of shales in some cases. The paleoenvironment, and its impact on organic matter enrichment of the shales, plays a vital role in the exploration and development of the resource. Paleoenvironmental reconstruction can be conducted using elemental, isotopic, maceral, and biomarker proxies. However, the literature on the biomarkers for paleoenvironment reconstruction to reveal the organic matter enrichment of shales in many petroleum systems throughout the world is still insufficient. Hence, this paper seeks to critically review the application of biomarkers during paleoenvironmental reconstruction in shales. The uses of biomarkers as indicators of modern and ancient marine and brackish/saline lacustrine depositional environments are considered. This review shows that biomarkers could be used to establish the sedimentary depositional environments, redox conditions, and organic matter enrichments of shales that are critical to deep energy exploitation. Nevertheless, despite the fact that biomarkers are significant indicators of depositional conditions, secondary processes such as source facies, thermal maturity, migration, and reservoir alteration can greatly influence their uses as paleoenvironmental condition indicators in source rocks and oils. Hence, for a reliable paleoenvironmental evaluation, there is a need to combine isotopic, elemental and maceral proxies with biomarkers.

Geochemistry of the Transitional beds between Disang and Barail Successions of the Imphal Valley, Indo-Myanmar Ranges

Major and trace element concentrations were studied from the tansitional beds between Disang and Barail Successions of the Imphal valley, Indo-Myanmar Ranges. Various major and trace element ratios and discrinant diagrams were used to descipher paleoclimate, paleo-redox condition and sedimentary depositional environment of the Disang-Barail Transitional beds. SiO2 vs Al2O3+K2O+ Na2O diagram and Rb/Sr ratios indicates that paleoclimate during the deposition of the sediments changed from arid to semi-arid and humid climate. Ni/Co, V/Cr, V/(Ni+V), V/Sc ratios suggest that these sediments were deposited in oxic, suboxic to anoxic conditions. V/(Ni+V) vs V/Cr diagram suggests paleo-redox environment dominated by sub-reduction to oxidization during Disang –Barail Transitional deposition. The sediments were deposited in transitional to marine depositional environment.