Facies Analysis Research Articles

Microfacies and mineralogical analyses of the late cretaceous carbonate rocks from The Central Benue Trough, Nigeria

The Cretaceous limestone facies from Yandev section in the central Benue Trough, Nigeria constitutes parts of the potential reservoirs and sources rocks for petroleum prospects in the basin. The central Benue Trough is the least studied basin among its contemporaries due to lack of subsurface data. Detailed mineralogical, facies analysis and diagenesis of these carbonate rocks in the basin have not received significant study. The aim of this study was to employed multifaceted methodology such as sedimentological, facies analysis petrographic and geochemical approaches which was lacking in previous research in the trough. The sedimentological analysis was done to evaluate fabrics grain sizes, and lithology types. For petrographic analysis, thin sections were prepared and examined under a petrographic microscope and categorized according to Dunham's classification. Geochemical analysis involved X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX) techniques to unveil mineralogical, oxide, and elemental compositions. The sedimentological results revealed light to dark grey medium to fine-grained limestone facies with intercalation of dark grey shales and siltstones. The XRD mineralogy data, revealed calcite (60.00 - 64.10%), quartz (14.30 - 51.00%), albite (12.30 - 19.00%), and chlorite (6.30 - 8.10%). Microfacies results revealed distinct sandy bioclastic wackstone and sparitic intraclastic packstone, as well as micritic intraclastic wackestone and sparitic bioclastic packstone. SEM images highlighted the intricate composition, including elongated structures, whites and dark spots suggesting varying conditions of deposition. Elemental analysis through EDX emphasized significant proportions of carbon, oxygen, sodium, potassium, calcium, silicon, aluminum, iron, and magnesium. Based on sedimentological, biofacies, lithofacies and geochemical evidence we infer that the carbonate sediments were mainly deposited in a shallow marine depositional environment (inner to outer neritic).

Facies analysis for the Neoarchean Itchen and Sherpa formations of the Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Facies analysis for the Neoarchean Itchen and Sherpa formations of the Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Integrating facies, mineralogy, and paleomagnetism to constrain the age and provenance of Paleozoic siliciclastic sedimentary rocks along the northern Gondwana margin: insights from the Araba and Naqus formations in western Gulf of Suez, Egypt

The depositional ages and provenance of the Paleozoic Araba and Naqus Formations along the northern Gondwanan margin in Egypt have remained uncertain due to a lack of index fossils. Resolving this issue is crucial for understanding regional geology during deposition and subsequent tectonic development. We integrate detailed facies analysis, anisotropy of magnetic susceptibility (AMS), paleomagnetism, and mineralogical data to elucidate the genesis and depositional ages of the Araba and Naqus Formations. Petrographic analyses identified seven distinct facies types, providing insights into sedimentary textures, maturity, and sources, with contributions from igneous and metamorphic sources indicated by heavy minerals. X-ray diffraction (XRD) analysis identified accessory minerals such as quartz, goethite, kaolinite, hematite, and anatase. Paleomagnetism isolated two magnetic components (CA and CN) providing the first robust paleo pole positions at Lat. = 70.8° N, Long. = 308.2° E and Lat. = 37.8° N, Long. = 233.1° E, indicating Cambrian and Carboniferous ages for the Araba and Naqus formations, respectively. Thermal demagnetization constrained these dates using established polarity timescales. Mineralogical data indicated that the Araba Formation originated from an igneous source, while the Naqus Formation had a mixed metamorphic-igneous provenance. The integrated AMS and paleomagnetic data reveal evidence of post-depositional deformation. Specifically, the clustering of maximum AMS axes in the NW–SE direction for both formations, suggests the initial presence of a primary depositional fabric. However, prevalent tectonic activity during the Cenozoic appears to have overprinted and modified this fabric through deformation related to rifting of the Gulf of Suez region. Through this novel multi-proxy approach, we have resolved long-standing uncertainties regarding the formations' depositional ages. Our study thereby provides the first chronostratigraphic framework for these strategically important sedimentary units, significantly advancing understanding of regional Paleozoic geology.Graphical abstract

Bio-, Lithostratigraphic and Geochemical Markers of Global Events in the Upper Devonian of the South of Western Siberia and their Value for Inter-regional Correlations

Abstract —Upper Devonian carbonate reef complexes have been studied on the territory of the Kolyvan-Tom’ Folded Area in sections in the right bank of Tom’ River. Facies analysis of the exposed part of the reef complex indicates the predominance of fore-reef and continental margin depositional environments of a tectonically active margin. The identified conodont associations are represented by cosmopolitan representatives of the genera Ancyrodella, Ancyrolepis, Icriodus, Mehlina, Palmatolepis, Polygnathus and “Polylophodonta” suggesting a correlation with the punctata–jamieae, rhenana–linguiformis, triangularis and Lower crepida conodont zones. The largest conodont diversity occurs at the triangularis/crepida boundary. Biofacies analysis of ostracod distribution has led to identification of characteristic associations and their restriction to certain parts of the palaeobasin. Substage boundaries yielded ostracods with both smooth and ornamented shells. In the lower part of the substages, smooth forms predominate, whereas the middle and upper parts of the substages are characterised by forms with tuberculate and reticulated surface. Hollinella valentinae Beds were traced in the Upper Frasnian Solomino Formation, and Acratia granuliformis Beds were traced in the Lower Famennian Kosoy Utyos and lower Mitikha members. Isotope geochemistry of the Upper Devonian sections of the south of Western Siberia reveals Frasnian global events – the Middlesex/punctata and the Upper Kellwasser, their stratigraphic position confirmed by palaeontological data, as well as by the globally expressed negative carbon isotope anomaly. These boundaries are marked by changes in depositional regime reflecting sea-level eustatic fluctuations, which are complemented with faunal changes.

Lahar events in the last 2000 years from Vesuvius eruptions – Part 1: Distribution and impact on densely inhabited territory estimated from field data analysis

Abstract. Lahars represent some of the most dangerous phenomena in volcanic areas for their destructive power, causing dramatic changes in the landscape with no premonitory signs and impacting the population and infrastructure. In this regard, the Campanian Plain turns out to be very prone to the development of these phenomena, since the slopes of the Somma–Vesuvius and Campi Flegrei volcanoes, along with the Apennine reliefs, are mantled by pyroclastic deposits that can be easily remobilized, especially after intense and/or prolonged rainfall. This study focuses on the analysis of pyroclastic fall and flow deposits and of the syn- and post-eruptive lahar deposits related to two sub-Plinian eruptions of Vesuvius in 472 CE (Pollena) and 1631. To begin with, historical and field data from the existing literature and from hundreds of outcrops were collected and organized into a database, which was integrated with several new pieces of data. In particular, stratigraphic, sedimentological (facies analysis and laboratory), and archeological analyses were carried out, in addition to rock magnetic investigations and impact parameter calculations. The new data are also referenced to the finding of ash beds in more distal areas, which were included in new isopach maps for the two sub-Plinian eruptions. The results show that for both eruptions the distribution of the primary deposits is wider than previously known. A consequence of these results is that a wider areal impact should be expected in terms of civil protection, as the sub-Plinian scenario is the reference one for a future large eruption of Vesuvius. Such a distribution of the pyroclastic deposits directly affects the one of the lahar deposits, also because a significant remobilization took place during and after the studied eruptions, which involved distal phreatomagmatic ash. From these integrated analyses, it was possible to constrain the timing of the deposition and the kind of deposits remobilized (pyroclastic fall vs. flow), and it was possible to calculate the velocities and dynamic pressures of the lahars and ultimately infer the lahar transport and emplacement mechanisms. The multidisciplinary approach adopted in this work shows how it is crucial to assess the impact of lahars in densely populated areas even at distances of several to tens of kilometers from active volcanoes. This especially applies to large parts of the densely populated areas around Somma–Vesuvius up to the nearby Apennine valleys.

Comprehensive Facies Analysis and Depositional Environments of the Kikim Formation, Garba Mountain, South Palembang Subbasin, Indonesia

This study provides an exhaustive facies analysis of the Kikim Formation within the Garba Mountain area of the South Palembang Subbasin, emphasizing the stratigraphic significance and depositional environments during the Paleogene period. Utilizing field data collected from the Bumi Agung and Batu Belang measurement lines, this research categorizes various lithofacies using Miall’s (1978) classification scheme, identifying eight distinct lithofacies and four facies associations indicative of a predominantly fluvial depositional setting. The results depict a detailed sedimentological framework, showing that the Kikim Formation was characterized by a braided river system with significant gravel and sandstone deposits. This analysis not only sheds light on the geological history and processes shaping the South Sumatra Basin but also enhances the understanding of its potential hydrocarbon reservoirs. By detailing the lithological diversity and facies distribution, this paper contributes to the broader geological knowledge required for effective exploration and management of the region's natural resources.

Tectonic and high-latitude climate controls on Quaternary sedimentary processes on the northern coast of Bohai Bay

Separating the relative roles of tectonics and climate change in geological evolution is complicated. The northern coast of Bohai Bay (NCBB), with a thick accumulation of Quaternary lacustrine sediments, is a subsiding area and is well suited to studying tectonic versus climatic controls on sedimentary processes. We used magnetostratigraphy and sedimentological analyses of borehole core JL01 from the NCBB to provide new insights into the effects of tectonic processes and climate changes in this region. The results show the following: (1) A shallow lacustrine delta, a deep-water lacustrine sedimentary system and a subaqueous fan-delta sedimentary system developed during 2.1–1.4 Ma, 1.4–0.78 Ma, and from 0.78 Ma to the present, respectively, corresponding to the rift-initiation, rift-climax, and late-rift tectonic stages of the evolution of an extensional basin, respectively. These stages constitute a low-order tectono-sedimentary cycle. (2) Tectonic and orbital-scale climate changes can be distinguished, particularly the 2.5 Ma climatic transition and a significant shift from 41- to 100-kyr cyclicity across the Mid-Pleistocene climatic transition. These changes indicate that the sedimentary processes of the NCBB were influenced by high-latitude climate forcing since the Late Pliocene. Our results demonstrate that detailed sedimentary facies analyses can provide valuable information about the effects of tectonics and climate changes on basin sedimentary evolution. This approach can be applied to other regional basins worldwide.

Quantitative facies analysis of a fluvio-aeolian system: Lower Triassic Buntsandstein Group, eastern France

Understanding the factors that control the temporal and spatial evolution of the Lower Triassic Buntsandstein Group, eastern France, is important not just for palaeoenvironmental reconstruction but also because it is an important reservoir for the lithium-rich geothermal brines in the Upper Rhine Graben region. The interval of interest in this study, the Lower Grès Vosgien Formation (LGV), is made up of c. 200 m of clastic deposits of mixed fluvial and aeolian origin. Given the proximity between the outcrops and the areas of mineral and heat exploration, this region offers a unique opportunity for quantitative analysis and correlation between outcrops and reservoirs. The LGV is the thickest Formation in the Buntsandstein Group. However, hitherto, no detailed architectural analysis has been published to reveal the controlling factors of its depositional elements. In this study, high-resolution facies analysis was applied to thirteen outcrops, and a core, to quantify fluvial and aeolian depositional architectures, and to comprehend palaeoenvironmental conditions during their deposition. Two facies associations were identified. The fluvial channel facies association, composed mainly of sandstones deposited in poorly confined, occasionally ephemeral channels, corresponds to 93 % of the total thickness. The analysis of >800 sets of strata characterised by lower-, transitional-, and upper-flow regime sedimentary structures, distributed within different architectural elements, enabled the distinction of temporal and spatial variabilities, and an estimate of fluvial palaeohydraulic characteristics. The wind- and water-laid facies association, which accounts for 7 % of the total thickness, records an architecture controlled by a fluctuating water-table level, and ephemeral floods. Results revealed that aeolian dunes and sand sheets accumulated in distinct temporal moments. The vertical trends, recorded in the core, indicate an upward increase in the frequency of intercalations between the two facies associations, and a decrease in the occurrences of thicker cross-bedded sandstone sets of fluvial origin, which, associated with the overall retrogradational stacking pattern of the LGV, is interpreted as the preserved record of a large distributive fluvial system (DFS). The occurrence of laterally extensive aeolian deposits, overlying fluvial deposits, is often associated by authors with periods of relatively more arid conditions at a regional scale. However, evidence indicates channel belt avulsion as an alternative interpretation for the establishment of the two facies associations. The findings enhance the knowledge about the depositional controlling factors in braided fluvial and aeolian systems, and improve predictive models that account for reservoir heterogeneity in accumulated successions of this type.

Facies analysis and depositional environment of siliciclastic sediments of Mundhan dome, Northwestern Kachchh, Western India

Facies analysis and depositional environment of siliciclastic sediments of Mundhan dome, Northwestern Kachchh, Western India

Microbial dominated Ca‐carbonates in a giant Pliocene cold‐seep system (Crotone Basin – South Italy)

AbstractThe Pliocene cold‐seep carbonate of the Crotone Basin (South Italy) represents a key site for dimension, outcropping exposure and quality. These deposits form a large carbonate (calcite) body (350 m long, 100 m wide and 40 m thick), and are characterized by a conduit facies made of authigenic calcite interpreted as previously active gas/fluid escape pipes and by a pavement facies, depicted as the surrounding early calcite‐cemented bioclastic and siliciclastic sediments. Pavement facies are commonly colonized by chemosymbiotic and non‐chemosymbiotic macrofauna (Lucinid and Solemyid bivalves, gastropods and serpulids). The conduit microfacies is characterized by the inward accretion of dark micritic laminae alternating with whitish sparitic layers. The micritic laminae show a microbial peloidal to dendrolitic fabric, which commonly incorporates planktonic foraminifera and coprolites, whereas the crystalline layers consist of microsparitic and sparitic crusts of prismatic zoned calcite crystals. The pavement facies shows more variability, because it is typified by laminated microbial boundstones, chemosymbiotic–bivalves packstone, foraminiferal packstone/wackestone and hybrid arenites. The stratigraphic constraint coupled with the foraminiferal assemblage (planktonic taxa) suggest a deep‐water setting occasionally affected by siliciclastic sedimentary flows. The pavement facies also shows common brecciation features, suggesting the establishment of post‐depositional overpressure conditions due to the early cementation of the conduits, which triggered localized rock failure. Stable isotope analysis of the different facies reveals overall negative δ13C values (−6.8 to −37.4‰ Vienna PeeDee Belemnite), indicating the presence of a complex mixture of methane with other hydrocarbons consumed microbially via anaerobic oxidation of methane; whereas δ18O is relatively positive (0.0 to 3.4‰ Vienna PeeDee Belemnite) suggesting the possible dehydration of clay minerals and/or destabilization of gas hydrates. This study, besides helping in the definition of the migration pathways and modality of accumulation of hydrocarbon‐rich fluids, can also help in building more and more realistic models for the complex genesis of cold‐seep carbonates.

Surface facies analysis of the Gangotri and neighbouring glaciers, central Himalaya

Glaciers are primarily monitored using medium-to-high resolution satellite data, undermining the potential of coarse-resolution data. In pursuance of this, high resolution 10 m super-resolved glacier maps derived from 56 m coarse-resolution AWiFS data are applied here to assess the facies, firn-line altitude, and frontal variations of the Gangotri and neighbouring glaciers, central Himalaya between 2005 and 2017. The wet and warming trends estimated over the study area appear to have caused excess firn (56.53 ± 6.22%) and ice (27.50 ± 3.03%) melting, contributing to the significant progression in fresh and slightly metamorphosed snow (12.09 ± 1.33%), wet-snow (21.79 ± 2.40%), ice-mixed debris (9.24 ± 1.02%) and supraglacial debris (2.49 ± 0.27%) during 2005–2016. Mean firn-line of the study glaciers has ascended from 5327 ± 23 m to 5376 ± 24 m at an average rate of 3.44 ± 0.45 m a−1 during 2005–2016. Mean firn-line altitude ascent is the highest for the sparsely debris-covered (<10% debris) Arwa glacier followed by the extensively debris-covered (≥35% debris) Gangotri, Bhagirathi-Kharak and Satopanth glaciers. Contrastively, the moderately debris-covered (17–29% debris) Raktvarn and Chaturangi glaciers show slight variations in their mean firn-line altitudes. These firn-line variations are governed by the rising average annual temperature, glacier size and predominant glacier facie. All the glaciers show an overall tendency of termini retreat at variable rates during 2005–2017. The highest retreat rate is estimated for the Gangotri glacier (12.01 ± standard deviation: 8.16 m a−1) followed by Chaturangi (7.97 ± 5.79 m a−1), Bhagirathi-Kharak (5.99 ± 9.26 m a−1), Raktvarn (3.28 ± 2.28 m a−1), Satopanth (1.89 ± 2.87 m a−1), and Arwa (0.85 ± 1.90 m a−1) glaciers. These retreat rates vary significantly with the exclusion of static points in the retreat estimation, revealing its subjective nature. The temporal facies maps obtained here have the potential for the hydrological modelling of meltwater production of the study glaciers.

Mapping palaeoshorelines of river-dominated deltas in lacustrine ramp settings: Application of sedimentological analyses to the Triassic Yanchang Formation (Ordos Basin, China)

In the preserved successions of clastic lacustrine systems receiving substantial sediment input from fluvial sources, the boundary between delta-plain and delta-front facies belts marks the position of ancient lacustrine shorelines. Placing and predicting the position of this boundary in nearshore lacustrine deposits of the Triassic Yanchang Formation (Ordos Basin, China) is of considerable applied significance, since sandstone deposits of this succession host numerous geological resources; yet, delta-top and delta-front deposits differ fundamentally in terms of sandstone fraction, sandbody geometries, and petrophysical properties. However, established sedimentological criteria for shoreline identification relevant to marine environments are only partially applicable to this lacustrine setting. For example, in lacustrine systems, (i) water salinity can be considerably lower, (ii) tidal processes are negligible, (iii) wave activity is often limited and of local significance (e.g., distal and lateral delta-front fringes; transgressive periods of delta-lobe reworking), (iv) seasonal fluctuations in water chemistry and biogenic productivity may be common, and (v) the rate, frequency and magnitude of oscillations in base level differ from marine counterparts. Collectively, these factors hinder the differentiation of delta-plain and delta-front deposits in the Yanchang Formation. The establishment of effective criteria with which to make such distinction is important for palaeogeographic restorations, and for resource exploration and exploitation. On the basis of detailed sedimentological descriptions of well cores and outcrop exposures of the Yanchang Formation in the southeastern Ordos Basin, sedimentary facies accumulated as part of different sub-environments and facies belts are studied. Delta-plain deposits can be readily differentiated from those of delta-front origin on the basis of criteria relating to sediment texture, sedimentary structures, palaeontological content, well-log profiles, and vertical facies successions. These criteria are summarized and applied to better characterize the deltaic setting and to reconstruct the evolution of lacustrine shorelines during accumulation of the Yanchang Formation, particularly for the northeastern area of the basin. A key outcome of this study is the development of a broadly applicable model for the recognition of sub-environments in river-dominated lacustrine deltaic successions. A generalized workflow is established to demonstrate how techniques in sedimentary facies analysis can be employed to reconstruct siliciclastic lacustrine delta shorelines, and thereby predict reservoir characteristics.

Sulfur isotopes in Archaean crustal reservoirs constrain the transport and deposition mechanisms of nickel-sulfides in komatiites

Assimilation and prolonged suspension of crust-derived sulfide liquid in komatiites are essential to form Ni-rich mineralisation. Evaluating the spatial relationship between komatiite-hosted Ni mineralisation and crustal S sources may thus provide insights into mechanisms of transport, metal enrichment and deposition of assimilated sulfide liquid. This study applied facies analysis and S isotopes to sulfides in Ni-mineralised komatiites and stratigraphically underlying bimodal volcanic-volcaniclastic and sedimentary rocks, which formed during rifting in the Agnew-Wiluna Greenstone Belt, Western Australia. The results revealed a lateral variation from rift-distal sedimentary sulfides, through sulfidic BIF, to rift-proximal VMS-style sulfides, the latter of which was predominantly assimilated by komatiites. Both crustal and komatiite-hosted sulfides were overprinted by granite-related skarn alteration during later basin inversion. Spatial S isotopes correlation revealed that Ni mineralisation in komatiites predominantly formed < 5 km from their crustal S sources, excluding long lateral transport as the main metal enrichment mechanism. Rather, metal enrichment likely happened through multiple cycles of sulfide entrapment and entrainment in lava flow vortices that formed in the wake of topographic steps represented by syn-rift faults. These faults were the main loci for pre-existing crustal weaknesses, hydrothermal fluid circulation, and VMS-style sulfide deposition, which were subsequently utilised by komatiites for enhanced thermo-mechanical erosion and crustal sulfide assimilation. This study shows that proximity to the syn-rift faults was the dominant control on the formation of komatiite-hosted Ni–sulfide mineralisation, regardless of substrate lithology. The S isotope signatures of crustal sulfides may be used as a proxy to identify syn-rift faults in highly deformed terranes.

Tectonostratigraphy of the Upper Jurassic-Lower Cretaceous siliciclastic (Shurijeh Formation) in the eastern Kopeh Dagh fold and thrust belt, Iran

During the Late Jurassic-Early Cretaceous, a significant gas-bearing siliciclastic succession was deposited in the Kopeh Dagh fold-thrust belt in northeastern Iran. Study of the regional evolution of depositional system and geodynamic setting of the red beds continental strata can help in a better understanding of the development of an intracontinental extension in this part of the Eurasia Plate. However, this evolution is driven by faulting events that are not fully understood. Facies analysis in wells and outcrops of the Upper Jurassic-Lower Cretaceous Mozduran and Shurijeh formations in the Saleh Abad area, the easternmost part of the Kopeh Dagh Basin, led to the identification of two fluvial braided river systems in the Shurijeh Formation. Provenance and sedimentological studies indicate that siliciclastic sediments were supplied from the south into the north during the Late Jurassic-Early Cretaceous in the Kopeh Dagh Basin. The higher compositional and textural maturity in the upper part of the Shurijeh Formation relative to the lower part indicate more recycling and more extensive transport of the sediments. Two stages of normal faulting can be identified based on the tectonostratigraphic evolution in this interval: The first phase was initiated with polymictic conglomerates during the Late Jurassic in the lower part of the Shurijeh Formation, while the basin-controlling fault was a buried structure. The second phase started with an influx of quartz conglomerates when the basin-controlling fault reached the surface in the middle part of the Shurijeh Formation. This study integrates new field observations and interpretations to enhance understanding of a complex history of multiphase deformation controlled facies patterns, structural geometries of the Late Jurassic-Early Cretaceous. Renewed Cretaceous extension generated accommodation space for the transgressive Shurijeh Formation.

Integrated facies analysis of the Late Cretaceous Simsima Formation in northwestern Oman mountain, Jabel Al-Rawdah, Hatta area, Oman

Integrated facies analysis of the Late Cretaceous Simsima Formation in northwestern Oman mountain, Jabel Al-Rawdah, Hatta area, Oman

Tracking of uranium and thorium natural distribution in the chemical fractions of the Nile Valley and the Red Sea phosphorites, Egypt

The present study aims to elucidate the possible sources of uranium and thorium content in the Campanian–Maastrichtian phosphorites from the Duwi Formation in the Nile Valley and Red Sea by conducting facies analysis and sequential leaching method. Nile Valley samples were collected from the El-Sibaiya East area, while those of the Red Sea were collected from two locations: Hamadat and Zug El Bahar. The petrographic investigation revealed that the Sibaiya East phosphorites exhibit peloidal bioclastic phospharenite–phospharudite microfacies, while Hamadat and Zug El Bahar phosphorites display peloidal bioclastic phosphalutite and silicified peloidal bioclastic phospharenite microfacies, respectively. Besides, U–Th bearing accessory minerals, such as zircon and monazite occur in Sibaiya East phosphorites. Thorium is present in Zug El Bahar phosphorites as minute accumulations associating apatite and quartz. Moreover, uranium is found with vanadium and iron as fine patches in the Sibaiya East phosphorite, and as small disseminations associated with Ca and Si in the Hamadat phosphorite. The X-ray diffraction shows that the investigated phosphorites are essentially built up of hydroxyl apatite Ca5(PO4)3(OH) and quartz SiO2. To accurately evaluate the bioavailability and mobility of uranium and thorium in the investigated phosphorites, it was necessary to identify the overall concentration and the various chemical forms of these elements by a five-step sequential leaching technique. The results indicate that Th and U are more abundant in the Red Sea phosphorites than in the Nile Valley phosphorites. Furthermore, Th is not bio-available and it is mostly found in the residue as Th-bearing minerals. Uranium, unlike Th is bio-available and fractionates among all fractions, indicating that U accumulation is the result of various diagenetic processes.

Deposition Environment Interpretation of Lemat Formation in the West Tanjung Jabung, Jambi Province

The study of facies analysis and interpretation of the depositional environment of the Lemat Formation located on Bukit Tigapuluh aimed to clarify the problems found in Paleogene sediments in the South Sumatra Basin. The results of research on facies analysis and interpretation of the depositional environment of the Lemat Formation will provide an explanation and description of the history of the formation and stratigraphic evolution of Paleogene-aged sedimentary rocks in the South Sumatra Basin as reflected in their lithological and facies characteristics. A detailed analysis of fluvial facies was carried out in the West Tanjung Jabung area, Jambi Province. A stratigraphic cross-section was prepared with an accumulated thickness of ± 25 m. The stratigraphic section included two rock deposits, namely sandstone-quartz deposits and conglomerate deposits. Analysis of lithofacies and architectural elements of the study area indicated a fluvial depositional environment. The resulting architectural elements consisted of six associations: channel (CH), scour hollows (HO), gravel bedform (GB), sediment gravity flows (SG), sandy bedform (SB), and floodplain fines (FF). The dominance of sedimentary material, which tends to be coarse, and the many facies associations GB, SG, and SB indicated many river bars and were characteristic of braided rivers. The obtained interpretation of the depositional environment was Conglomerate deposits in the Alluvial Fans System with Gravity Flow River environment or gravel bed braided river, and sandstone-gravel deposits in the shallow environment or gravel bed braided river.

Quantifying a tide-dominated, wave-, and river-influenced delta in Miocene facies of the Niger Delta basin

ABSTRACT The modern Niger Delta has long been classified as a mixed tide-, wave-, and river-influenced delta. Still, no detailed studies have quantified the relative proportions of formative processes and facies. This work presents the first quantitative estimate of the relative influence of formative processes in Miocene deposits based on core data from the Greater Ughelli, Central Swamp, and Coastal Swamp depositional belts of the Niger Delta basin. Facies analysis of 288.2 m of core from four wells shows approximately 53% tidal facies, 33% fluvial facies, and 14% wave-formed facies, indicating deposition in a prograding tide-dominated, wave-, and river-influenced delta. Cores from the Greater Ughelli and Central Swamp depobelts exhibit coarsening-upwards, prograding deltaic facies successions overlain by fluvial mudstone. Tidal deposits in the Coastal Swamp depobelt show coarsening-upwards prograding deltaic facies successions with well-developed tidal bundles indicating seasonal deposition. The basal part of these facies successions also reveals repeated floods characterized by slump and load structures and dewatering features. Delta-plain and delta-front–prodeltaic facies associations are identified based on physical sedimentary and biological structures. The delta-plain facies association consists of weakly bioturbated mudstone, fissile mudstone, and coarse-pebbly stratified sandstone facies with sparse trace fossils. The delta-front–prodeltaic facies association contains muddy and sandy heteroliths, stratified, medium and coarse-grained, cross-bedded sandstone, and convoluted mudstone facies. The facies vary but characteristically contain trace-fossil assemblages of the recently proposed Rosselia and Phycosiphon Ichnofacies, indicating delta-front and prodeltaic settings, respectively. Variability in the facies is determined by the relative influence of hydrodynamic processes (tide, wave, and river), variations in physicochemical stress, and the episodic character of deposition. In addition, based on the relative influence of each hydrodynamic processes, the facies differ through the successions, sometimes subtly.

Depositional Structures, Tectonic and Stratigraphic Units and Their Effect on The Reservoir Rock Units of South Lake Albert Basin, Albertine Rift, Uganda.

The study focused on interpretation of three-dimension (3D) seismic and suites of wireline log datasets, to construct and interpret models and facies analysis to assess the depositional structures, tectonic and stratigraphic unit’ settings. Challenges and uncertainties of low to moderate reservoir quality parameters attributed to limited understanding of depositional structures, tectonic and stratigraphic units had been identified in previous studies within the study area. From the study undertaken, the study area is structurally complex with compartments and flower structures. The stratigraphic interpretation, realized that sediments were highly intercalated (clay, silt, fine and coarse sands) majorly attributed to the short changes in climatic (wet and dry) conditions. It was further deduced that compartmentalization and intercalations of sediments had a very high effect on the reservoir rock properties which might affect the recovery of the available fluids.

Lithofacies association and stratigraphy of the Quixaba and Remédios formations, Fernando de Noronha archipelago, Brazil

This work presents facies analysis of pyroclastic and effusive deposits present in areas of the Fernando de Noronha Archipelago (FNA), South Atlantic Ocean. A detailed stratigraphic study was carried out for the Remédios Formation at the Caieira beach and the Quixaba Formation at the Capim-Açu Edge, Americano, and Bode beaches. The lithofacies association for the deposits of the Remédios Formation characterizes non-welded ignimbrites of phonolitic composition generated by concentrated ground-hugging density currents originated from collapses of a buoyant eruption column. Possibly, this phase was followed by a caldera collapse and the exposition of a complex system of dikes at Caieira Beach. For the deposits of the Quixaba Formation, the lithofacies association characterizes scoria and ash flow/grain avalanching deposits, proximal fallout deposits, and Pahoehoe lava flows. The Quixaba volcanism shows evidence of pulses of Strombolian and possibly Violent Strombolian activity alternated with effusive Hawaiian activity. A later stage of magma-water interaction during the Quixaba volcanism led to the formation of a sustained eruption column and fallout deposits with ash aggregates formed through wet aggregation.