Thick-bedded Sandstone Research Articles

River-fed basin-fill and hyperpycnites in an island-arc setting: The Silurian–Devonian Kekexiongkuduke Formation from Western Junggar, China

Sediments from land are primarily transported into basins through hyperpycnal flow, which plays a significant role in the process of basin filling. Various models of hyperpycnites have been proposed. This study examines a Silurian–Devonian basin-fill sequence in NW China to validate existing models and presents a visually compelling case demonstrating the process of basin filling through flood-dominated river discharge.The Utubulak Member of the Kekexiongkuduke Formation can be subdivided into three parts, representing basin floor, slope and shelf environments, collectively representing a regressive basin fill sequence. The lower part consists of flood-related turbidites contain or encompass material of terrestrial and marine origin, their sustained and pulsed velocity structures are similar to river discharge. These turbidites may result from basinal hyperpycnal flow or retrogressive failures of the shelf-edge (hyperpycnal) delta. The middle (slope deposits) contains bi-graded hyperpycnite bed interpreted commonly attributed to deposition by river floods exhibiting the classical waxing-waning configuration. Additionally, fine-grained deposits resulting from river-generated, dilute hyperpycnal or hypopycnal plumes are observed interbedded with the basin turbidites or slope background deposits. In the upper part, the presence of thick-bedded sandstones indicates that sustained hyperpycnal flow can transport sands to the shelf-edge/shelf, facilitating deep-water sand delivery. The vertical distribution of the various flood-related facies in basin floor, slope and shelf strata emphasize the complexity of hyperpycnites in different settings, and particularly highlighting challenges associated with their recognition in basin deposits.The investigated succession accumulated in an island-arc setting which provided a favorable condition for a river-fed turbidite system to develop. The narrow shelf facilitated transport of sediments by hyperpycnal flows directly into the basin, while erosion of high mountains promoted a high sediment supply for hyperpycnal flow. And a river-fed turbidite system commonly developed during the late stages of basin filling.

Provenance Analysis and Diagenesis Using Integrated SEM-Cathodoluminescence and Optical Microscopy for the Sandstones of the Pirispiki Formation, Kurdistan Region, Northern Iraq

The paragenetic history and provenance of framework grains in marginal marine and deltaic sandstones of the Pirispiki Formation in two sections, (Ora and Kaista), northern Iraq were examined. This was achieved using an integrated approach employing scanning electron microscopy-cathodoluminescence (SEM-CL), and optical microscopy. The Pirispiki Formation is lithologically characterized by alternating layers of thin- and thick-bedded sandstones. These were intercalated with thin laminae of grey-black shale. Petrographic analysis revealed that the dominant detrital grains in the mature quartz arenite sandstone were monocrystalline quartz grains with undulose extinction. The diagenetic analysis of the sandstones documented several processes that occur in three distinct stages. The SEM-CL technique enabled the identification of two distinct quartz overgrowth phases. Quartz cementations are of two types, the earliest phase and the most significant by volume is the Q1 cement characterized by dark non-luminescence which led to the destruction of most of the primary pores and the healing of mechanically induced cracks. Q2 cement is formed after major compaction and is characterized by bright luminescence with sector zoning, revealing an intricate SEM-CL zonation. CL revealed five special textures within detrital quartz grains including healed fractures and zoning. The provenance of the detrital quartz grains indicated the dominance of plutonic and metamorphic sources, with trace amounts originating from volcanic sources. These were mostly derived from the Bitlis Massif Zone in Turkey.

Flow dynamics as Froude‐supercritical turbidity currents encounter metre‐scale slope minibasin topography

AbstractSeafloor topography can affect turbidity current dynamics on deep‐water slopes, significantly influencing the dispersal of sediment. Despite the common occurrence of topographic complexity, there are few detailed investigations of topographic interactions and their effect on downslope flow evolution in intraslope environments. In this study, the sedimentology and architecture of an Upper Cretaceous intraslope fan succession deposited within an extensional, fault‐bound minibasin are described from a rare, well‐exposed, near‐continuous, oblique depositional‐dip outcrop of the Tres Pasos Formation, Chile. The 2 to 8 m thick studied interval transitions downslope from high‐energy heterolithic strata, including metre‐scale steep‐faced scours, to non‐amalgamated thick‐bedded sandstones. Abrupt increases in sandstone percentage, sandstone bed thickness and grain size occur on the hangingwall blocks of south‐east and north‐east‐dipping normal faults that bound the minibasin. Sandstone beds are dominated by backset or wavy low‐angle stratification proximally, contain compositional banding near faults, and are characterised by increased proportions of planar laminated and structureless turbidite divisions downslope along the transect. Experimental observations of turbidity current interactions with topography are synthesised into a qualitative framework, which is used to interpret flow processes and characteristics from deposit trends. The results reconstruct the response of Froude‐supercritical, stratified turbidity currents with denser basal layers when encountering metre‐scale fault scarps. The analysis shows that metre‐scale topographic features can substantially alter the flow properties of stratified turbidity currents, and their downslope flow evolution to include the development of transitional, depositional and flow‐stripped sediment gravity currents. However, in comparison to base‐of‐slope settings, overall flow conditions are interpreted to be more uniform over slope breaks and zones of flow expansion in a partially confined intraslope environment. These findings have considerable implications for understanding flow response to similar scale morphological features on the seafloor and the potential for flow transformations in intraslope settings.

A Carbon Nanocomposite Material Used in the Physical Modelling of the Overburden Subsidence Process.

Carbon nanomaterial is widely used in structural health monitoring due to the advantage of sensitivity and good mechanical properties. This study presents a novel approach employing carbon nanocomposite materials (CNMs) to characterize deformation and damage evolution in physical modelling. As the primary measurement method, the CNM is used to investigate the deformation characteristics of a 200-400 m thick sandstone bed at a 1 km deep longwall mine. The sandstone unit is identified as an ultra-thick key stratum (UTKS), with its thicknesses varying across different mining panels of the UTKS. The results of CNM monitoring show that the UTKS remains stable even after a consecutive excavation of 900 m in width. This stability impedes the upward propagation of overlying strata failure, leading to minimal surface subsidence. The study demonstrates the huge potential of CNM in the mining area, which can be useful for investigating material damage in physical modelling studies. The findings suggest that the cumulative extraction width in individual mining areas of the mine should be controlled to avoid a sudden collapse of the UTKS, and that special attention should be paid to where the UTKS's thickness changes substantially. The substantial variation in UTKS thickness significantly impacts the pattern of overburden subsidence.

Surface-subsurface connectivity in the morphological evolution of sandstone-capped tabular hills – How much analogy to karst?

This paper presents geomorphic evidence for the significant role of surface-subsurface connectivity in the geomorphological evolution of tabular hills (mesas) capped by moderately thick sandstone beds. The study area is located in Central Europe, in the Sudetes mountain range (Poland, Czechia), in an area built of a clastic succession of Late Cretaceous age. Research involved analysis of high-resolution LiDAR DTM and its various derivatives, providing insights into characteristics of drainage routes and patterns of ruiniform relief, as well as fieldwork. The latter included landform recognition and mapping, surveying representative cleft and cave systems. Specific surface landforms indicative of drainage diversion underground and subterranean pathways of sand removal include boulder-filled troughs and hollows, open clefts and plazas, pseudo-sinkholes and tilted blocks. Further evidence is provided by abundant, joint-aligned roofed slots and boulder caves, whose origin is attributed to selective sandstone weathering, sand evacuation by groundwater, and gradual subsidence. Sandy cones and sheets below exits of slots and fractures are the complementary sedimentary evidence. The percentage of caprock area drained via subterranean outflow varies from 16 % to 89 %. Reasons for the high efficacy of subterranean water and sediment transport include both structural factors (regular jointing pattern, high porosity) and, very likely, pre-conditioning role of dissolution of cement in the quartz arenites (arenization), which facilitates detachment of individual grains even by low flows under low hydraulic gradient. Thus, the sandstone-capped mesas show numerous analogies to the karst proper, especially silicate karst. They are manifested in both similar landform inventories, main preparatory processes, and considerable surface-subsurface connectivity.

Movable fluid evaluation of tight sandstone reservoirs in lacustrine delta front setting: Occurrence characteristics, multiple control factors, and prediction model

The tight sandstone, deposited in a lacustrine delta front setting, constitutes substantial new petroleum reserves. Tight sandstone reservoirs' fluid mobility directly affects oil production and recovery efficiency. Consequently, it is crucial to quantitatively and synthetically characterize fluid mobility. This study presented a detailed investigation of the movable fluid of the Yanchang tight sandstone in the Ordos Basin. Multiple experiments were conducted to investigate movable fluid, including casting and cathodoluminescence thin section, nuclear magnetic resonance, X-ray diffraction, and high-pressure mercury intrusion. According to pore-throat structure investigation with petrographical observations, delta front sandstone was divided into four types of lithofacies, pore-throat structure, and three pore-throat spaces (nano-scale, submicron, and micron), which correspond to various occurrence characteristics of the movable fluid. The result shows that the fluid mobility of the micron pore-throat space is higher than the sub-micron scale, and the nano-scale is the lowest. The fluid mobility is driven by petrophysical property, pore-throat structure, diagenetic mineral, lithofacies, and sandstone strata pattern. With the deterioration of the pore-throat structure and petrophysical property, fluid mobility gradually decreases. Movable fluid content significantly correlates with quartz and feldspar content, showing that residual intergranular and feldspar dissolved pores can significantly improve fluid mobility. On the contrary, it is negatively correlated with clay and carbonate cement content. The carbonate cementation and clay mineral filling increase the proportion of nano-scale pore-throat, leading to the deterioration of the reservoir quality and pore-throat structure. Detailed researches on the spatial distribution of fluid mobility show it related to sandstone bed thickness, mudstone proximity, and mudstone/formation ratio. Typically, medium-grained sandstones forming thick beds in mudstone-poor sequences are commonly low in carbonate and clay mineral cement and highest in movable fluid content. In contrast, fine-grained sandstones occurring as thin beds or located near the mudstone-sandstone interface in mudstone-rich sequences generally exhibit high carbonate and clay cement. Hence, its movable fluid content is lowest. The frequent material exchange between sandstone and adjacent mudstone prompts the enhancement of the cementation of clay and carbonate minerals, which is a devastating factor for fluid mobility. The proposed model for predicting fluid mobility can be used for similar delta front sandstones of other lacustrine basins. These findings provide new insights into predicting the best reservoir sandstones with high fluid mobility and effectively exploiting tight sandstone reservoirs.

Sedimentological Controls on the Reservoir Characteristics of the Mid-Triassic Tredian Formation in the Salt and Trans-Indus Surghar Ranges, Pakistan: Integration of Outcrop, Petrographic, and SEM Analyses

The current study uses an integrated lithofacies, optical microscopy, and scanning electron microscopy (SEM) analysis to investigate the sedimentary processes, depositional architecture, and reservoir rock potential of the Tredian Formation’s (Mid-Triassic) mixed siliciclastic and carbonate succession in the Salt and Trans-Indus Ranges. The formation has been divided litho-stratigraphically into two components: the lower Landa Member, which consists of fine-grained sandstone and shale, and the upper Khatkiara Member, which consists of coarse-grained sandstone. Based on sedimentary structures and lithology, four distinct types of lithofacies are identified. Two lithofacies representing sandstones interbedded with shale (LF1) and thick-bedded sandstone (LF2) lithofacies suggestive of fluvio-deltaic settings are among them. Another two lithofacies of thin-bedded sandstone (LF3) and dolomite (LF4) suggest a tidal flat depositional environment, correspondingly. The petrographic examination of the Tredian sandstones indicates a lithology ranging from sub-feldspathic arenite to feldspathic arenite with moderate packing. The presence of primary calcite cement, silica cement, and iron oxide/hydroxide cements were shown by the diagenetic investigation, which was supported by SEM studies. In addition, secondary cements include ferroan-dolomite, chlorite, and illite, which is linked with chemical alteration of unstable grains. The paragenetic sequence depicts the diagenetic evolution of the Tredian sandstone from early to late diagenetic phases. The reservoir quality of the LF1 and LF4 lithofacies has been destroyed by early-stage calcite cementation, but the lithofacies LF2 and LF3 have a strong reservoir potential owing to the scarcity of calcite cement, dissolution of unstable feldspar grains, and grain fracture.

NON-MARINE BIVALVES FROM THE MOSPYNE FORMATION (UPPER BASHKIRIAN) OF THE DONETS BASIN: TAXONOMY, PALEOECOLOGY, AND STRATIGRAPHIC SIGNIFICANCE

Remains of non-marine bivalves are widespread in the Carboniferous of the Donets Basin (Eastern Ukraine). The studies of this group of fauna are important for stratigraphy, paleoecology and paleobiogeography. The remains of non-marine bivalves were found in sediments of the Mospyne Formation; Carbonicola obtusa (Hind) and Naiadites sp. were found in the roof shale of the g2 coal bed; Curvirimula trapeziforma (Dewar) and C. tesselata (Jones) were identified in the roof shale of the g12 coal bed, and Carbonicola rectilinearis Trueman et Weir and C. limax Wright were found in the siltstone below G12 limestone layer. The upper part of the lower half of the Mospyne Formation is attributed to the Carbonicola rectilinearis Member, which probably corresponds to the upper part of the lenisulcata Zone (Langsettian) of Western Europe. The lower limit of this member is in the floor of a thick sandstone bed 43 m below G12 limestone layer. The upper boundary of Carbonicola rectilinearis Member is situated at the g12 coal layer. The Carbonicola pseudorobusta Zone, previously identified by M.T. Sergeeva as member with fauna, is distinguished between the roof shale of the g12 coal bed and h61 coal bed. This zone corresponds to the communis Zone in Western Europe. Bivalves from the roof shale of the g12 coal layer and roof shale of the g2 coal layer lived in shallow-water eutrophic freshwater or brackish lakes in the coastal accumulation lowland. These basins were characterized by significantly reduced aquatic organism assemblage and hydrogen sulfide contamination of silts and, possibly, the bottom layer of the water column. Representatives of the genera Curvirimula and Naiadites were found in the sediments of these lakes. These genera apparently led a pseudoplanktonic lifestyle, attaching themselves to various bottom objects with byssus. The bivalves from the siltstones below the G12 limestone layer (Carbonicola) lived in a shallow-water, refreshed lagoon.

Geotouristic bicycle path around Nowy Targ (Carpathians, Poland)

The area in the vicinity of Nowy Targ is located within the northern part of the Orawa-Nowy Targ Basin and the southern slopes of the Gorce Mountains in the Polish sector of the Outer Carpathians. Geologically, the region is built of the Upper Cretaceous–Palaeogene turbiditic deposits representing sedimentary successions of the Krynica Subunit of the Magura Nappe and the Neogene–Quaternary fresh-water deposits filling the Orawa-Nowy Targ Basin. The Magura Nappe in the described area is represented by the thick-bedded sandstones of the Magura Formation and thin-and medium-bedded sandstone-shale deposits of the Malcov Formation, which are well-exposed in numerous outcrops, especially in the Łopuszna stream valley. The Magura Nappe deposits were folded and cut by a fault system in the Miocene. The presented area displays varied geomorphological relief and picturesque landscapes. Moreover, rare species of fauna and flora occurring here, as well as the still-alive culture of the Podhale Highlanders and continuously improving tourist infrastructure additionally contribute to the development of geotourism in this area. In addition, this area is an increasingly popular place among cyclists, thanks to the development of a network of bicycle paths, therefore the proposed geotourist bicycle path will extend the offer for this group of tourists.

Crack Propagation Mechanism of Hydraulic Fracturing in Thick-Bedded Sandstone Coal Mine Roof

The thick-bedded sandstone roof of the Bayangaole coal mine is at risk of rock burst accidents. Hydraulic fracturing technology has been used to prevent these accidents by controlling coal seam roof collapse. To research the crack propagation mechanism of hydraulic fracturing in thick-bedded sandstone roof, hydraulic fracturing experiments are conducted on thick roof sandstone with a hole drilled in the center, and RFPA2D-Flow software is adopted to conduct numerical simulations of the formation mechanism and spatial distribution of hydraulic fracture cracks in bedded sandstone. The physical experiments reveal that cracks are generated from the weak parts and stress-concentration area of the hole wall due to hydraulic pressure; main cracks either form along the bedding or spread toward the bedding. Numerical simulations show that the crack propagation mechanism for specimens without preset slotting is consistent with the experimental results. For the preset-slot specimens, micro-cracks generate in the region where tensile stress is applied, which gradually increase and penetrate the preset slotting tip; the specimen continues to crack until failure occurs. When the main crack encounters the bedding, it turns and propagates along the bedding when the bedding angle is small, which results in tensile failure. However, when the angle is large, the crack passes directly through the bedding, forms a new hydraulic crack, and continues to propagate forward, which results in the tensile failure of the cutting bedding.

The Origin and 3D Architecture of a Km-Scale Deep-Water Scour-Fill: Example From the Skoorsteenberg Fm, Karoo Basin, South Africa

Scours, and scour fields, are common features on the modern seafloor of deep-marine systems, particularly downstream of submarine channels, and in channel-lobe-transition-zones. High-resolution images of the seafloor have improved the documentation of the large scale, coalescence, and distribution of these scours in deep-marine systems. However, their scale and high aspect ratio mean they can be challenging to identify in outcrop. Here, we document a large-scale, composite erosion surface from the exhumed deep-marine stratigraphy of Unit 5 from the Permian Karoo Basin succession in South Africa, which is interpreted to be present at the end of a submarine channel. This study utilizes 24 sedimentary logs, 2 cored boreholes, and extensive palaeocurrent and thickness data across a 126 km2 study area. Sedimentary facies analysis, thickness variations and correlation panels allowed identification of a lower heterolithic-dominated part (up to 70 m thick) and an upper sandstone-dominated part (10–40 m thick) separated by an extensive erosion surface. The lower part comprises heterolithics with abundant current and sinusoidal ripples, which due to palaeocurrents, thickness trends and adjacent depositional environments is interpreted as the aggradational lobe complex fringes. The base of the upper part comprises 2-3 medium-bedded sandstone beds interpreted as precursor lobes cut by a 3–4 km wide, 1–2 km long, and up to 28 m deep, high aspect ratio (1:100) composite scour surface. The abrupt change from heterolithics to thick-bedded sandstones marks the establishment of a new sediment delivery system, which may have been triggered by an updip channel avulsion. The composite scour and subsequent sandstone fill support a change from erosion- and bypass-dominated flows to depositional flows, which might reflect increasingly sand-rich flows as a new sediment route matured. This study provides a unique outcrop example with 3D stratigraphic control of the record of a new sediment conduit, and development and fill of a large-scale composite scour surface at a channel mouth transition zone, providing a rare insight into how scours imaged on seafloor data can be filled and preserved in the rock record.

Campanian–Paleocene Jaworzynka Formation in its type area (Magura Nappe, Outer Carpathians)

The Campanian–Paleocene Jaworzynka Formation, a part of the Magura Nappe succession in the Polish Outer Carpathians, is described in terms of its detailed litho- and biostratigraphy. The formation stretches along the marginal part of the Siary Unit, from the Jaworzynka stratotype area in the Silesian Beskid Mts up to the Mszana Dolna area in the Beskid Wyspowy Mts. Its equivalent in the Moravskoslezské Beskydy Mts of the Czech Republic is the Soláň Formation. In the stratotype area, the formation displays complex structure. We distinguish four lithological units, i.e., Biotite Sandstone and Shale (I), Shale (II), Mutne Sandstone Member (III) and Thin-bedded Turbidite (IV) and provide the first detailed biostratigraphy of particular units. The first unit forms the most prominent part of the formation. It was deposited in the Middle Campanian–earliest Maastrichtian within the upper part of Caudammina gigantea Zone up to the lower part of the Rzehakina inclusa Zone. The second unit occurs only locally and its age is limited to the Maastrichtian, to the Rzehakina inclusa Zone. The third unit is composed of thick-bedded sandstones that in some parts may form more than the half of the total thickness of the formation. It is Late Maastrichtian–Danian in age and is placed in the upper part of the Rzehakina inclusa Zone and the lower part of the Rzehakina fissistomata Zone. It is usually covered by a thin package of thin-bedded turbiditic sandstone and shales of Danian–Thanetian age with foraminifera of the Rzehakina fissistomata Zone.

Sedimentary facies, stratigraphy, and depositional environments of the Ecca Group, Karoo Supergroup in the Eastern Cape Province of South Africa

Abstract The stratigraphy of the Ecca Group has been subdivided into the Prince Albert, Whitehill, Collingham, Ripon, and Fort Brown Formations in the Eastern Cape Province, South Africa. In this article, we present detailed stratigraphic and facies analyses of borehole data and road-cut exposures of the Ecca Group along regional roads R67 (Ecca Pass), R344 (Grahamstown-Adelaide), R350 (Kirkwood-Somerset East), and national roads N2 (Grahamstown-Peddie) and N10 (Paterson-Cookhouse). Facies analysis of the Ecca Group in the study area was performed to deduce their depositional environments. Based on the lithological and facies characteristics, the stratigraphy of the Prince Albert, Whitehill, Collingham, and Fort Brown Formations is now subdivided into two informal members each, while the Ripon Formation is subdivided into three members. A total of twelve lithofacies were identified in the Ecca Group and were further grouped into seven distinct facies associations (FAs), namely: Laminated to thin-bedded black-greyish shale and mudstones (FA 1); Laminated black-greyish shale and interbedded chert (FA 2); Mudstone rhythmite and thin beds of tuff alternation (FA 3); Thin to thick-bedded sandstone and mudstone intercalation (FA 4); Medium to thick-bedded dark-grey shale (FA 5); Alternated thin to medium-bedded sandstone and mudstone (FA 6); and Varved mudstone rhythmite and sandstone intercalation (FA 7). The FAs revealed gradually change of sea-level from deep marine (FA 1, FA 2, FA 3 and FA 4, FA 5, and FA 6) to prodelta environment (FA 7). This implies that the main Karoo Basin was gradually filling up with Ecca sediments, resulting in the gradual shallowing up of the water depth of the depositional basin.

Basin margin tectonics and morphology as controls of delta type and architecture: examples from the Mio-Pliocene Yalvaç Basin (SW Turkey)

This study describes the sedimentary facies and depositional architectures of Gilbert-type and shoal-water delta deposits developed on opposed margins of the extensional fluvio-lacustrine Yalvaç Basin during the late Cenozoic. The roles of syndepositional tectonism, basin dynamics, and hinterland morphology on the development of different delta types are assessed. This asymmetric trough initially opened as an intramontane molasse basin to the southwest of the Sultandağları massif. Its northern and southern margins are bounded by normal faults, which controlled both tectono-sedimentary evolution of the basin and the surrounding palaeomorphology. The lacustrine deposits consist of thin-bedded limestones, marls, and medium to thick-bedded sandstones and conglomerates. The coarse-grained Gilbert-type delta, up to 150 m thick, was deposited just in the front of the steep northern basin margin. The clinoformal architecture of this delta comprises steeply inclined foreset beds, which are overlain by horizontal alluvial topset units and underlain by subhorizontal bottomset deposits. The Yarıkkaya normal fault controls the northern margin of the basin and plays an active role in both local uplift and subsidence, giving rise to new sediment sources and increasing the accommodation space. Abundant coarse-grained sediment supply into this relatively deep basin across the steep scarp of the Yarıkkaya Fault led to creation of a delta with Gilbert-type architecture. Contemporaneously, on the shallow southern margin of the Yalvaç Basin, several small shoal-water deltas up to 3.5 m thick, were deposited on a smooth basin floor. The gently mound-shaped depositional architecture of these shoal-water delta deposits comprise erosive-based mouth-bar and distributary channel deposits. These observations show that, in this case, the river deposited its bedload shortly after entering the basin, generating small shoal-water deltas that, through stacking over time and some lateral offset, built a shoal-water delta complex.

The Bawang Member, a unique unit of Belaga Formation in the Miri Zone, Central Sarawak, NW Borneo Malaysia: Revised stratigraphic and sedimentological characteristics

Bawang Member (Unit 4) of Late Eocene age is the fifth and the youngest member of Belaga Formation. In general, the Late Cretaceous to Late Eocene turbidite sequence of Rajang Group in the lower Rajang area (Central Sarawak) is characterized by Belaga Formation. This member is unique and is only exposed in the vicinity of the Tatau area (Arip valley and Tatau High region) with limited exposures. In this research we present new evidence, to support its position on the stratigraphic column, based on field observations (stratigraphic and sedimentological characteristics) and lab analysis (TOC). Numerous recently exposed sections were visited in the study area. Four litho-facies were identified in the Bawang Member based on sedimentological observations; (1) Massive sandstone facies (SF1), (2) Medium to thick-bedded sandstone facies (SF2), (3) Thin bedded heterolithic facies (SF3), and (4) Mudstone or Shale facies (SF4). Reddish maroon and green shales exposed in Tatau High region are only exposed in another member of Belaga Formation i.e. Kapit Member. The Bawang Member sediments differ from the Tatau High region sediments in absence of cleavage and internal sedimentary features (rip-up clasts), the occurrence of bioturbation, and with lesser exposures of mud facies. On the contrary, the Tatau High sediments show higher ratios of mud facies, presence of cleavage in shales and even in few sandstones, and absence of major bioturbation of strata. The presence of internal sedimentary features (rip-up clasts) in Tatau High and in Kapit Member supports the idea that these are the parts of the same rock unit. Furthermore, contrasting TOC values between these two units (Bawang and Tatau High), and the similarity of TOC among Tatau High and Kapit Member are also in support of the same idea. Based on the differences of facies (rock) types, the effect of cleavage, absence of rip-up clasts, the occurrence of bioturbations and different TOC values, we confirm that the Tatau High rocks must be older than most of Bawang Member exposures and are actually the faulted blocks of Kapit Member.

Thousands of Potholes in the Mekong River and Giant Pedestal Rock from North-eastern Thailand: Introduction to a Future Geological Heritage Site

A site with thousands of potholes, locally named “Samphunbok (SPB),” and a giant pedestal (mushroom) rock possess a very high geological value. The potholes are being formed on the riverbed of the Mekong River; whereas the giant pedestal rock is the largest on the Khorat Plateau, and is located in Ubon Ratchathani province, north-eastern Thailand. Based on detailed geological, geomorphological, and sedimentological perspectives, this paper presents the geological history of both erosional features for the future promotion of the Global Geopark Network. The giant pedestal rock is likely to be a remnant of degradation and weathering after a regional tectonic event. It is sculptured in the fracture zone of thick sandstone beds after uplifting and folding. No evidence of abrasion by wind was found. The formation of potholes is limited inside the Mekong River bankfull elevation. The appearance of potholes in different levels of the sandstone beds infers their formation in relation to the vertical evolution of the Mekong River. All geological data shown in this paper confirm the rareness of potholes and the giant pedestal rock in terms of how they were sculptured and preserved through time. These erosional features at SPB are discussed and introduced in this paper as a global geological heritage site.

Lithostratigraphy of the Siwalik Group along the Muksar Khola section, Siraha-Udayapur District, Eastern Nepal Himalaya

The Siwalik Group extending east to west co-linear to the main Himalayan range is well exposed along the Muksar Khola section, Siraha-Udayapur district, eastern Nepal Himalaya. Siwalik Group in the present study area is divided into the Lower, Middle, and Upper Siwaliks based on grain size and sandstone-mudstone proportion. The Lower Siwaliks is characterized by very fine- to fine-grained, light grey sandstone interbedded with dark grey to olive black mudstone. The Middle Siwaliks, is characterized by the domination of fine- to coarse-grained sandstone, and based on the lithology and bed thickness it is divided into two members. The lower member is dominated by fine- to medium-grained “salt and pepper” sandstone with dark greenish to olive-grey mudstone while, the upper member is dominated by light grey to white medium- to coarse-grained sandstone with grey, dark grey to black mudstone. Increase in the grain size and thickness of sandstone beds, increase in the proportion of mudstone, decrease in induration of sandstone and decrease in the proportion of biotite grain in sandstone makes upper member different from lower member of the Middle Siwaliks. The Upper Siwaliks is characterized by very thick beds of clast supported conglomerate associated with coarse- to very coarse-grained, very thick bedded sandstone and dull yellowish-grey to grey mudstone. The boundary between the Lower Siwaliks and the Middle Siwaliks, lower member and upper member of the Middle Siwaliks, and the Upper Siwaliks are 10.0 Ma, 5.7 Ma, and 3.5 Ma, respectively. The present study records the presence of a large succession of intra-formational conglomerate succession in the Lower Siwaliks.

Mineralogical and geochemical imprints to determine the provenance, depositional history and tectonic settings of Triassic turbidites in the Semanggol and Semantan Basins, Peninsular Malaysia

• Semanggol and Semantan formations are part of Triassic successions in SE Asia. • Triassic turbidites exemplify inner to outer fan in a deep-marine fan system. • Semanggol turbidites were sourced from felsic rocks and represent passive margin. • Semantan rocks have felsic-intermediate origin and show active-continental margin. • Based on redox-sensitive metals, depositional conditions fluctuate from anoxic-oxic. • Type-III kerogen, mature-overmature proposing terrestrial input of organic matter. The present study provides systematic mineralogical, inorganic geochemical and Rock-Eval analyses of turbidite deposits of the Semanggol and Semantan formations to investigate their provenance, depositional environment and tectonic setting as well as type, origin and maturation of organic matter in black shale. These deposits are extensively distributed in Peninsular Malaysia and are observed in the field as conglomerate, pebbly sandstone, thick-bedded sandstone, interbedded sandstone and shale, laminated black shale, and tuffaceous sandstone. These sedimentary sequences are predominantly deep-marine and occasional shallow-marine deposits characterizing a deep-marine fan system. Based on Al 2 O 3 /TiO 2 ratios, more felsic rocks for the Semanggol Formation and felsic-intermediate rocks for the Semantan Formation are proposed as sources for their detrital fractions and this interpretation is also substantiated by the binary plot of Zr vs Ti. V/(V + Ni), V/Ni and Ni/Co analyses indicate anoxic/oxic conditions. Ternary diagram of immobile- trace-elements inferred passive margin for Semanggol turbidites and an active-continental margin for Semantan turbidites. The dissimilarity between geochemically and geologically derived tectonic settings, mainly for the Semanggol turbidites, is because of changing tectonic setting and recycled nature of sediment sources that were deposited in diverse tectonic settings. The black shale clay fractions from both formations dominantly contain illite and kaolininte with abundant traces of quartz. The illite content varies from 43 to 56% and illite crystallinity index (IC) from 0.2° to 0.4° Δ2θ (average: 0.28° Δ2θ), showing studied black shale fall in anchizone. Rock-Eval pyrolysis reveals Type-III kerogens, suggesting a terrestrial source of organic matter in black shale of both formations.

Sources of Ca2+ in the major carbonate cements in Eocene sandstones and conglomerates: Evidence from Sr isotopes, Sr/Ca ratios, and rare-earth elements

Different sources of calcium have important effects on the formation and distribution of carbonate cements. On the basis of identifying all possible sources of calcium, comprehensive quantitative analyses of Sr, C, and O isotopic values and trace elements (including rare-earth elements) were conducted to determine the Ca2+ sources and their changes in the same type of carbonate cements at different vertical positions in the same reservoirs. Ferroan calcite and ankerite were the major types of carbonate cements. Ca2+ in ferroan carbonate cements in the sandstones near the mudstone-sandstone (M-S) interfaces was derived primarily from diagenetic fluids mixed with Ca2+ originating from the transformation of smectite to illite and from original sedimentary water in the adjacent mudstones. However, Ca2+ in the ferroan carbonate cements in the sandstones away from the M-S interfaces originated from the transformation of smectite to illite, the dissolution of carbonate minerals, and original sedimentary water in source rocks. The gradual change of Ca source of the same type of ferroan carbonate cements indicates the diversity of migration direction of diagenetic paleo-fluid in the same period. During the transformation of smectite to illite, concentration gradients were created from mudstones to sandstones. Ca2+, Mg2+, Fe2+, and other cations in the mudstones diffused to the adjacent sandstones and provided sources of ferroan carbonate cements at the edge of the sandstones. Pore water with Ca2+, Mg2+, Fe2+, CO32−, and other cations in the source rocks was collectively charged into sandstones during oil emplacement and promoted the precipitation of ferroan carbonate cements in residual pore water. Due to oil emplacement and material supplied by the adjacent mudstones, the content of ferroan carbonate cements in the sandstones was lower, and the reservoir porosity was higher at a greater distance from the M-S interfaces. However, in thick-bedded sandstones, due to lack of material supply from the adjacent mudstones, Ca2+, Mg2+, Fe2+, and CO32− in the ferroan carbonate cements were mainly derived from source rocks. As a result, no significant changes were observed in the content of ferroan carbonate cements and reservoir porosity in the vertical direction.

Diagenesis and reservoir quality of lacustrine deep-water gravity-flow sandstones in the Eocene Shahejie Formation in the Dongying sag, Jiyang depression, eastern China

The lacustrine deep-water gravity-flow sandstone reservoirs in the middle of the third member of the Shahejie Formation (43.7–38.2 Ma) are the main exploration targets for hydrocarbons in the Dongying sag, Jiyang depression, eastern China. The impact of diagenesis on reservoir quality of these sandstones has been established by a variety of methods. Petrographically, the sandstones consist mainly of lithic arkose (with 43% of quartz, 33% of feldspar, and 24% of lithic fragment) with reservoirs having average porosity and permeability values of 17.1% and 38.1 md, respectively. In addition to their primary intergranular pores, secondary pores are well developed from feldspar dissolution, with pore-throat radii ranging from 0.01 to 40 μm. The dissolution of feldspar and transformation of smectite to illite may be the sources of silica for the first phase of quartz overgrowth, whereas illitization of kaolinite may be responsible for the second phase of quartz overgrowth. In addition, pressure dissolution of quartz is also an important source of silica for quartz overgrowth. Dissolution of feldspar has little impact on reservoir quality, whereas compaction and carbonate cementation are the main factors significantly reducing reservoir quality. Oil charge may have retarded carbonate cementation and generated overpressure that retarded compaction, thus preserving porosity. Precipitation of vermicular kaolinite, resulting from feldspar dissolution, promoted a change in the wettability of the reservoir, from water wet to oil wet, which is beneficial for oil entrapment. The central parts of medium- to thick-bedded sandstones that have experienced oil charge twice appear to have the highest-quality reservoirs based on petrophysical properties. This work provides a new interpretation of the formation mechanism of high-quality lacustrine deep-water gravity-flow sandstones reservoirs that have experienced multiple periods of oil charge.