Sandstone Beds Research Articles

Fossils remains of even-toed ungulates from the Middle Siwaliks, Punjab, Pakistan

ABSTRACT The Dhok Pathan Formation of Middle Siwaliks is remarkably rich for the fossils of ungulates. The fauna consists of Cervidae, Giraffidae, Tragulidae and Suidae but the fossils of family bovidae are more abundant. The 23 collected and described specimens here belong to seven species which are Selenoportax vexillarius, Pachyportax latidens, Miotragocerus cf. gluten, Gazella lydekkeri, Dorcatherium majus, Propotamochoerus hysudricus and Tetraconodon cf. magnus. The described material consists of both upper and lower dentition. The fossil-bearing locality is located near Padhri village 55 km away from the tehsil Dina, district Jhelum. It is mainly composed of claystone, sand-stone and siltstone beds. The studied locality dated to Late Miocene. This Formation was deposited in subtropical condition. Bovids were predominant in Padhri, which indicate the highly moist conditions with small but numerous open standing water bodies.

Transition from Late Jurassic rifting to middle Cretaceous dynamic foreland, southwestern U.S. and northwestern Mexico

AbstractSubsidence history and sandstone provenance of the Bisbee basin of southwestern New Mexico, southern Arizona, and northern Sonora, Mexico, demonstrate basin evolution from an array of Late Jurassic–Early Cretaceous rift basins to a partitioned middle Cretaceous retroarc foreland basin. The foreland basin contained persistent depocenters that were inherited from the rift basin array and determined patterns of Albian–early Cenomanian sediment routing. Upper Jurassic and Valanginian–Aptian strata were deposited in three narrow extensional basins, termed the Altar-Cucurpe, Huachuca, and Bootheel basins. Initially rapid Late Jurassic subsidence in the basins slowed in the Early Cretaceous, then increased again from mid-Albian through middle Cenomanian time, marking an episode of foreland subsidence. Sandstone composition and detrital zircon provenance indicate different sediment sources in the three basins and demonstrate their continued persistence as depocenters during Albian foreland basin development. Late Jurassic basins received sediment from a nearby magmatic arc that migrated westward with time. Following a 10–15 m.y. depositional hiatus, an Early Cretaceous continental margin arc supplied sediment to the Altar-Cucurpe basin in Sonora as early as ca. 136 Ma, but local sedimentary and basement sources dominated the Huachuca basin of southern Arizona until catchment extension tapped the arc source at ca. 123 Ma. The Bootheel basin of southwestern New Mexico received sediment only from local basement and recycled sedimentary sources with no contemporary arc source evident. During renewed Albian–Cenomanian subsidence, the arc continued to supply volcanic-lithic sand to the Altar-Cucurpe basin, which by then was the foredeep of the foreland basin. Sandstone of the Bootheel basin is more quartzose than the Altar-Cucurpe basin, but uncommon sandstone beds contain neovolcanic lithic fragments and young zircon grains that were transported to the basin as airborne ash. Latest Albian–early Cenomanian U-Pb tuff ages, detrital zircon maximum depositional ages ranging from ca. 102 Ma to 98 Ma, and ammonite fossils all demonstrate equivalence of middle Cretaceous proximal foreland strata of the U.S.-Mexico border region with distal back-bulge strata of the Cordilleran foreland basin. Marine strata buried a former rift shoulder in southwestern New Mexico during late Albian to earliest Cenomanian time (ca. 105–100 Ma), prior to widespread transgression in central New Mexico (ca. 98 Ma). Lateral stratigraphic continuity across the former rift shoulder likely resulted from regional dynamic subsidence following late Albian collision of the Guerrero composite volcanic terrane with Mexico and emplacement of the Farallon slab beneath the U.S.–Mexico border region. Inferred dynamic subsidence in the foreland of southern Arizona and southwestern New Mexico was likely augmented in Sonora by flexural subsidence adjacent to an incipient thrust load driven by collision of the Guerrero superterrane.

Geological Controls on High Production of Tight Sandstone Gas in Linxing Block, Eastern Ordos Basin, China

AbstractTight sandstone gas in the Linxing Block, eastern Ordos Basin, has been successfully exploited. The high performance is mainly a result of the special geological conditions. The key geological controls for high production have been discussed on the basis of seismic data, field observation, sample features, mercury porosimetry, mechanical properties, and basin modeling. Firstly, the coal measures have good gas generation potential, not only because of the existence of coalbeds and organic‐rich shales, but also because coal laminae and microbial mats in the shales significantly increase their total organic carbon (TOC) contents. Secondly, except for the uplifted zone of the Zijinshan complex and the eastern fault zone, rare large faults develop in the Carboniferous–Permian sequence, ensuing the sealing capacity of cap rock. Small fractures generally concentrated in the sandstones rather than the mudstones. Thirdly, gas accumulation in the Linxing Block was controlled by the tectonic, burial and thermal histories. Gas accumulation in the Linxing Block started in the Late Triassic, followed by three short pauses of thermal maturation caused by relatively small uplifts; the maximum hydrocarbon generation period is the Early Cetaceous as a combined result of regional and magmatic thermal metamorphisms. Field profiles show abundant fractures in sandstone beds but rare fractures in mudstone beds. Mechanical properties, determined by lithostratigraphy, confine the fractures in the sandstones, increasing the permeability of sandstone reservoirs and retaining the sealing capacity of the mudstone cap rocks. The modern ground stress conditions favor the opening of predominant natural fractures in the NNW–SSE and N–S directions. These conclusions are useful for exploring the potential tight sandstone gas field.

An Early Cretaceous (Berriasian) fossil-bearing locality from the Rocky Mountains of Alberta, yielding the oldest dinosaur skeletal remains from western Canada

Western North America preserves iconic dinosaur faunas from the Upper Jurassic and Upper Cretaceous, but this record is interrupted by an approximately 20 Myr gap with essentially no terrestrial vertebrate fossil localities. This poorly sampled interval is nonetheless important because it is thought to include a possible mass extinction, the origin of orogenic controls on dinosaur spatial distribution, and the origin of important Upper Cretaceous dinosaur taxa. Therefore, dinosaur-bearing rocks from this interval are of particular interest to vertebrate palaeontologists. In this study, we report on one such locality from Highwood Pass, Alberta. This locality has yielded a multitaxic assemblage, with the most diagnostic material identified so far including ankylosaurian osteoderms and a turtle plastron element. The fossil horizon lies within the upper part of the Pocaterra Creek Member of the Cadomin Formation (Blairmore Group). The fossils are assigned as Berriasian (earliest Cretaceous) in age, based on previous palynomorph analyses of the Pocaterra Creek Member and underlying and overlying strata. The fossils lie within numerous cross-bedded sandstone beds separated by pebble lenses. These sediments are indicative of a relatively high-energy depositional environment, and the distribution of these fossils over multiple beds indicates that they accumulated over multiple events, possibly flash floods. The fossils exhibit a range of surface weathering, having intact to heavily weathered cortices. The presence of definitive dinosaur material from near the Jurassic–Cretaceous boundary of Alberta establishes the oldest record of dinosaur body fossils in western Canada and provides a unique opportunity to study the Early Cretaceous dinosaur faunas of western North America.

Characteristics and context of high-energy, tidally modulated, barred shoreface deposits: Kimmeridgian–Tithonian sandstones, Weald Basin, southern U.K. and northern France

ABSTRACTThe influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces.Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana Ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos Ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10°) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shoreface sandstones was modulated by tidal changes in water depth. The upper, upward-fining part of each sandstone tongue typically comprises an erosionally based bioclastic lag overlain by subtidal lower-shoreface deposits, and constitutes an upward-deepening succession developed during transgression.Regressive–transgressive sandstone tongues fringe the northeastern margin of the basin, which was exposed to an energetic wave climate driven by westerly and southwesterly winds with a fetch of 200–600 km. The high tidal range interpreted from the shoreface sandstone tongues is attributed to resonant amplification in a broad (150–200 km), shallow (18–33 m) embayment as the tidal wave propagated from the Tethys Ocean into the adjacent intracratonic Laurasian Seaway, of which the Weald Basin was a part.

Death in the shallows: The record of Permo-Triassic mass extinction in paralic settings, southwest China

The Permo-Triassic marine mass extinction has been blamed on a range of culprits including anoxia, acidification, high temperature and increased sedimentation and nutrient influx, the last two being a direct consequence of terrestrial biomass die-off and climatic changes. In marine settings, the role of these kill mechanisms is likely to be depth-dependent with siltation and high temperatures potentially the most consequential in shallowest waters. These ideas have been investigated in a study of the Permo-Triassic boundary beds in western Guizhou and eastern Yunnan (WGEY) which record the transition from littoral coal swamps to an inner shelf/platform fringed by a coastal mudbelt. Anoxic conditions were not developed in such shallow waters but weak dysoxia is seen in the extinction interval, recorded by the presence of pyrite framboids and glauconite, and may have been a factor in the crisis even in coastal waters. High temperatures may also be an extinction factor as evidenced by the brief bloom of microgastropods in the immediate aftermath. The Late Permian peat-forming swamps were subject to considerable in situ erosion that reworked authigenic minerals (chamosite and kaolinite). This material, together with considerable amounts of charcoal, was concentrated in distinctive green sandstone beds. However, the notion that the marine extinction was caused by increased sediment supply, a death-by-siltation mechanism following the collapse of terrestrial biomass, is not supported by the field evidence because a surge in clastic influx onto the shelf is not observed during the extinction interval when a range of carbonates, including microbialites, developed. The sediment was likely trapped in alluvial plains during base-level rise and/or a short period of more arid conditions occurred, reducing the clastic supply in the coastal–shallow marine environments. Ocean acidification is another potent kill mechanism but the occurrence of the extinction within a transgressive, carbonate-dominated interval in the shallow-water locations of WGEY does not support this cause.

Monitoring the strata behavior in the Destressed Zone of a shallow Indian longwall panel with hard sandstone cover using Mine-Microseismicity and Borehole Televiewer data

Massive coal extraction from the longwall panel results in the formation large void space (goaf), which is followed by elevation in the stress level of the overlying strata. The increasing stress leads to rock displacements in form of deformation, fracturing and caving of the roof behind the powered supports for regaining the equilibrium state. These rock displacements divided the longwall roof into three zones known as Caved Zone (CZ), Fractured Zone (FZ) and Continuous Deformation Zone (CD). Previous studies have shown that the overlying strata in the Destressed Zone behaves violently in presence of hard rock (such as compact sandstone, shale etc.), which is a major problem faced in the Indian underground mines. Therefore, the present study intends to monitor the roof behavior of a shallow longwall mine (working depth: 68-74m; mining height: 2–3m) of Central India, which is overlain by a thick sandstone bed (average thickness: 37-48m) using six months (Oct’01-Mar’02) mine-induced Microseismicity containing event coordinates (in 3D plane) and event parameters (such as Magnitude, Energy and Apparent Stress) along with Borehole Televiewer (BHTV) data. The paper discusses the results of some important studies, which are very essential for enhancing the safety in the mining area, such as: [a] The height of Destressed Zone was calculated through multiple approaches (empirical relations, mining height and bulking factor) and, found to be around eighteen times the mining height (hc+hf~18h), [b] Microseismicity study of the longwall roof showed that events corresponding to Fractured Zone had the lowest b-value (b=0.3301) and highest occurrence frequency (a=2.3178), [c] Borehole Televiewer (BHTV) data showed the presence of massive fractures and water seepage level in Fractured Zone at depth of about 40-50m, [d] The integrated approach of b-value, Energy-Magnitude (E-m) and Gutenberg-Richter Frequency-Magnitude relation showed that events corresponding Fractured Zone had the highest magnitude (+1.2) and energy (106.6J), and [e] The behavior of microseismic event properties (such as Event Counts, Energy, Apparent Stress and Magnitude) was also studied with respect to mine geology, and abnormal changes were seen when the roof strata was encountered with hard rock (mainly coarse-grained sandstone with RQD>60%) and fault (FF`). The study successfully helped towards obtaining several useful results related to dynamic roof displacement and failures, which very much enhanced the safety in the longwall mines.

The largest species of <italic>Asianopodus</italic> footprints from Junggar Basin, Xinjiang, China

A discovery has been made where thirteen footprints, two invertebrate traces and symmetrical ripple marks were found in a greyish green calcareous fine sandstone bed. The discovery was found in the Lower Cretaceous Shengjinkou Formation of Urho area, northwestern Junggar Basin, Xinjiang and it formed three trackways and four isolated tracks. Classic methods were used to study the dinosaur footprints in the Urho area, which included measuring the stratigraphic sections and the footprint parameters in the field. Similar standards of measurements were used for the measurement of footprint length and width, digit length and width, the divarication between digits, the length and width of anterior triangle, pace and stride lengths. In addition, photos of each footprint were taken and the orientation and distance between the neighboured tracks were measured. Distributions and outlines of the footprints were drawn in the computer by using CorelDRAW. On the other hand, silicone rubber demould was used for the well preserved specimens for a detailed research and from the detailed study of the footprints and trackways, two different types of theropod footprints were identified. The large three-toed footprints were a new species, named Asianopodus niui ichnosp. nov., which are large sized tridactyl (47.0–56.0 cm long and 31.0–42.0 cm wide, width/length between 0.66–0.75), the divarication between digits II and IV is 49.00°–55.34°, subsymmetrical, digit III is slightly longer than digit II, but more longer than digit IV, the length/width of anterior triangle between 0.34–0.37, V-shape tracks with a distinct bulbous heel impression, without manus and tail impressions, the phalangeal formula is 3-3-2, the pace length is between 164–180 cm, the stride length is 328–336 cm. It is significant to note that this is the largest Asianopodus footprints that have been discovered. The medium-sized tracks belong to Asianopodus pulvinicalx , which are middle sized tridactyl (21.0–27.0 cm long and 18.0–20.0 cm wide, width/length between 0.72–0.86), the divarication between digits II and IV is 46.63°–51.40°, subsymmetrical, digit III is more longer than digit II and digit IV, the length/width of anterior triangle between 0.44–0.54, V-shape tracks with a distinct bulbous heel impression and without manus and tail impressions, the phalangeal formula is 3-3-3, the pace length is between 76.5–83.2 cm, the stride length is 160 cm. According to the footprint length, pace and stride length, relative stride length of the tracks, we calculated that the body length of A. niui ichnosp. nov. is 5.89 m and the speed is 8.14 km/h, while the body length of A. pulvinicalx is 2.52 m and speed is 6.48 km/h. Based on the symmetric ripple marks and invertebrate traces on the surface of the footprints layer, we infered that both the trackmakers of the Urho dinosaur footprints walked in the shore and shallow lacustrine environment.

THE MODERN MORPHODYNAMICS IN THE QUARRIES OF LVIV AND ITS SUBURBS

The seven big quarries have been explored in and around Lviv. All quarries are sandy and most of them are inactive now. There are 3 quarries located directly in the city: two – within the Znesinnia Regional Landscape Park (western and eastern) and Kryvchytskyi. The four quarries are located in the southeastern outskirt of Lviv within the Davydivskyi Chain near the villages of Davydiv (3 quarries) and Vynnychky. The processes of water erosion (sheet, rill and gully erosion), suffosion, falls, scree formation processes, slides, physical and chemical weathering are widespread in the explored quarries. The specific azonal processes such as aeolian processes (deflation and accumulation of sandy material) and formation of takyrs are also common. The most common are water erosion processes (sheet, rill and gully erosion). They are present in almost all quarries (except of Western Znesinskyi and Kryvchytskyi Quarries). These processes occur in the lower parts of quarry benches and on the slopes of dumps. They are represented by small and medium-sized erosive pre-rills and rills (width 5–30 cm, depth up to 45 cm), small gullies (depth up to 2.2 m), debris cones, deluvial cones. The sheet, rill and gully erosions mainly occur together. The suffosion processes develop in the sandy-loam deposits with low density (the Davydivskyi Quarry № 2, the Vynnychkivskyi Quarry). The result of these processes is the formation of suffosion sinkholes (35–60 cm in diameter) and suffosion “wells”. The processes of rockfalls are locally widespread on steep denudation benches of quarries, where beds of limestone or sandstone are cropped out (the Davydivskyi Quarry № 1, № 3). The scree formation processes are also common in gravitational processes and mainly occur in sandy deposits and are represented by scree cones. Slides occur rarely having small main bodies and are located on the quarry walls and dump slopes. A special type of processes in the studied quarries is the formation of takyrs, which occurs in closed watered areas of the pit floors. After the takyrs dry up, the so-called "desert papyrus" is created. Key words: modern morphodynamics, quarry, water erosion processes, falls, scree formation processes, Lviv.

A linkage between uranium mineralization and high diagenetic temperature caused by coal self-ignition in the southern Yili Basin, northwestern China

Jurassic sediments in the southern Yili Basin of the Xinjiang Province, northwestern China, host several sandstone-hosted uranium deposits. The Jurassic uranium-enriched white sandstones are in the transitional zone between the oxidized and reduced zones. In addition, burnt rocks are common in nearby outcrops and occur occasionally in drill cores. Mineralogical and geochemical compositions of sediments from the oxidized, the uranium-enriched transitional and the reduced zones were measured using optical microscopy, field-emission scanning-electron microscopy in conjunction with energy-dispersive X-ray spectrometry, X-ray powder diffraction and inductively coupled plasma mass spectrometry (ICP-MS). Chromite, limonite and ilmenite are the typical accessory minerals in the brown sandstones of oxidized zone, whereas calcite and saddle dolomite are typical accessory minerals in the sandstones of transitional zone. The suite of vitrinite reflectance (Ro), illitic crystallinity and homogenization temperature for fluid inclusions in calcites indicates a relatively high diagenetic temperature (>100 °C) in the Jurassic sandstones from both the oxidized and transitional zones in the southern Yili Basin. An interesting relationship was discovered between the diagenetic high-temperature conditions and coal self-ignition. The anomalous uranium concentrations in the burnt claystone from a drill hole and in the altered coals 0–10 cm below the burnt rocks in an outcrop section imply a relationship between the coal self-ignition and uranium mineralization in the southern Yili Basin. One option to interpret the uranium mineralization is a supergene (descending from surface) hydrothermal fluid model in which the downwelling fluids were heated as they penetrated through the warm burnt rocks and then underwent a chemical reaction as they progressively cooled when they traversed down through the underlying permeable sandstone beds. Accordingly we establish the linkage between uranium mineralization and high diagenetic temperature caused by coal self-ignition.

Pebble morphometric analysis as signatures of the fluvial depositional environment of the Katberg Formation near Kwerela River around East London, Eastern Cape Province, South Africa

Pebbles were collected along the Katberg Formation sandstone beds next to Kwerela River (R63) near East London. During the study of pebble morphology, calculations were made to derive values that were used for bivariate plots to confirm the depositional environment of the Katberg Formation. Bivariate plots of MPs against OP showed that 79% of pebbles fall in fluvial environment, whereas 21% of pebbles fall in the beach environment. The plot of flatness index versus sphericity index shows that 87% of pebbles have a sphericity of greater than 0.65 falling into fluvial environment and 13% falling into a beach environment. The average morphometric indices indicated the dominance of river pebbles with an average sphericity of 0.73, which is above 0.65 and considered the limit of sphericity belonging to fluvial environment. The occurrence of a small proportion of beach pebbles suggests that the river reached the marginal marine environment during its flow. The river pebbles have the lowest roundness, highest sphericity index, and neutral Oblate-Prolate Index. Based on calculated indices, it is evident that the pebbles of the Katberg formation were shaped in fluvial environment. Majority of the pebbles yielded a bladed compact shape with a dominating sphericity index symptomatic of fluvial sediments. All the bivariate plots illustrate fluvial depositional environment for the sediments of the Katberg Formation.

Sedimentary and tectonic controls on Lower Carboniferous (Visean) mixed carbonate–siliciclastic deposition in NE England and the Southern North Sea: implications for reservoir architecture

Discovery of the Breagh gas field in the Southern North Sea (SNS) has demonstrated the potential that the Lower Carboniferous (Visean, 346.7–330.9 Ma) Farne Group reservoirs have to contribute to the UK's future energy mix. New biostratigraphic correlations provide a basis to compare Asbian and Brigantian sedimentary cores from the Breagh Field and age-equivalent sediments exposed on the Northumberland Coast, which has proved critical in gaining an understanding of exploration and development opportunities. Thirteen facies associations characterize the mixed carbonate–siliciclastic system, grouped into: marine, delta front, delta shoreface, lower delta plain and upper delta plain gross depositional environments. The facies associations are interpreted as depositing in a mixed carbonate and siliciclastic fluvio-deltaic environment, and are arranged into coarsening- and cleaning-upward cycles (parasequences) bounded by flooding surfaces. Most cycles are characterized by mouth bars, distributary channels, interdistributary bays and common braided rivers, interpreted as river-dominated deltaic deposits. Some cycles include rare shoreface and tidally-influenced deposits, interpreted as river-dominated and wave- or tide-influenced deltaic deposits. The depositional processes that formed each cycle have important implications for the reservoir net/gross ratio (where this ratio indicates the proportion of sandstone beds in a cycle), thickness and lateral extent. The deltaic deposits were controlled by a combination of tectonic and eustatic (allocyclic) events and delta avulsion (autocyclic) processes, and are likely to reflect a changing tectonic regime, from extension within elongate fault-bounded basins (synrift) to passive regional thermal subsidence (post-rift). Deep incision by the Base Permian Unconformity across the Breagh Field has removed the Westphalian, Namurian and upper Visean, to leave the more prospective thicker clastic reservoirs within closure. Thematic collection: This article is part of the Under-explored plays and frontier basins of the UK continental shelf collection available at: https://www.lyellcollection.org/cc/under-explored-plays-and-frontier-basins-of-the-uk-continental-shelf

Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA)

AbstractMouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings.

First Middle Ordovician conodont record related to key graptolites from the western Puna, Argentina: perspectives for an integrated biostratigraphy and correlation of the Central Andean Basin

Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindström) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.

Microfossil assemblages (diatoms, calcareous nannofossils, and silicoflagellates), paleoenvironment, and hydrocarbon source rock potential of the Oligocene Ruslar Formation at Karadere, Bulgaria

The Oligocene Ruslar Formation, an equivalent of the Maykop Suite, is a potential hydrocarbon source rock in the western Black Sea Basin. In contrast to the offshore areas, the depositional environment and hydrocarbon source rock potential of onshore Bulgaria sediments are largely unknown. Hence, a 14-m-thick section of the Ruslar Formation, exposed near Karadere (Black Cape) along the Black Sea coast, provides an excellent opportunity to study the upper part of the Ruslar Formation. Here, laminated diatomrich mudstones with frequent thin sandstone beds and a prominent concretion horizon are exposed. Furthermore, the fossil diatom assemblages provide a key component to understand the paleoenvironment. Overall, Paleogene diatoms are understudied in the Black Sea Basin and therefore only a genus-level study is undertaken here. The studied Ruslar Formation contain remarkably diverse and wellpreserved diatom assemblage with 23 different genera. The most frequent genera are Paralia, Distephanosira, and Stephanopyxis. Common genera include Coscinodiscus, Hemiaulus, Pseudopodosira, Rouxia, and Xanthiopyxis. Rare taxa include Actinoptychus, Asterolampra, Azpeitia, Delphineis, Distephanosira, Diploneis, Eunotogramma, Eurossia, Lyrella, Liradiscus, Plagiogramma, Radialiplicata, Rutilaria, Saeptifera, and Triceratium. The diatom assemblages together with calcareous nannoplankton, silicoflagellates, and the presence of rare foraminifera indicate a fully marine neritic environment without major salinity variations. The calcareous nannoplankton investigated can be assigned to biozone NP23 (Early Oligocene). The exposed fragment of the Ruslar Formation was deposited after the low salinity Solenovian event, which represents the maximum isolation of the Paratethys present in the lower part of the NP23. Bulk geochemical parameters from 35 samples (avg. TOC: 1.80% wt.; avg. HI: 226 mg HC/g TOC) show that the exposed part of the Ruslar Formation contains type II-III kerogen and a fair to good hydrocarbon potential. The Ruslar Formation is immature (avg. Tmax: 424 °C), but may generate about 0.5 tons of hydrocarbons per square meter if mature. Biomarker proxies support the low maturity and are characterized by diatom-related biomarkers (24-norcholestane; C25HBI alkanes and thiophenes). Land-plant-derived biomarkers suggest a significant input of angiosperms. Based on biomarker ratios, the depositional environment was oxygen-depleted but probably not strictly anoxic. Reworking of biomass by chemoautotrophic bacteria is suggested by the presence of 28,30-bisnorhopane.

Реконструкция условий осадконакопления меловых и юрских продуктивных песчаных пластов полуострова Гыданский (на примере Геофизического месторождения)

Based on the analysis of seismic attributes, the shape of the SP curves, lithological and petrophysical data, and well test results, the sedimentation environments of the Bajocian, Berriasian-Hauterivian, Aptian and Cenomanian sandstone beds of the Geophysical field were reconstructed; its facies and zones of sandstone beds distribution and its claying are determined.

Kremeňovo-karbonátové žily s U-Mo-Cu mineralizáciou v permských intermediárnych až bázických vulkanitoch hronika na lokalite Kravany (Kozie chrbty, východné Slovensko)

Historical uranium ore deposit Kravany is located in the eastern part of Kozie Chrbty Mts., approximately 9 km SW of the district town Poprad. Stratiform, infiltration U-Cu-Pb mineralization is bound to the Upper Permian clastic sediments (Kravany Beds, member of Malužiná Formation, Hronicum Unit), which are enriched in fragments of carbonized flora. Vein U-Mo-Cu mineralization was found in the Upper Permian intermediate to basic volcanics intersecting the sediments of the Kravany Beds (also ore lenses). Vein filling originated in the following development stages: I.) Quartz-pyrite (quartz, pyrite, marcasite), II.) Dolomite-pyrite (dolomite, pyrite, marcasite, galena), III.) Copper (tetrahedrite, tennantite, chalcopyrite), IV.) Uranium-molybdenum (uraninite, Pb-Mo-S phase, coffinite, quartz), and V.) Calcite (calcite, chalcopyrite). The formation of mineralization can be explained by the geological position: random emplacement of the diorite porphyrite, resp. basalt-andesite dikes, directly in the preexisting U,Mo-bearing sediments. Vein U-Mo-Cu mineralization could thus most likely have formed according to the following scenario: I.) sedimentation of Kravany Beds in the Permian riftogenic basin: formation of beds of arkoses and arkosic sandstones with abundant fragments of charred flora, II.) formation of infiltration U mineralization: reduction and accumulation of U in sediments rich in organic matter, III.) emplacement of dikes of intermediate to basic volcanics: intersection of sediments with organics and with high U and Mo content, mobilization of formation fluids, assimilation of U and Mo into intermediate-basic magma, IV.) cooling of volcanic bodies → their contraction (formation of contraction cracks) → filling of contraction cracks with quartz, carbonates and ore minerals (crystallization from residual magmatic solutions mixed with formation waters). From this point of view it is syngenetic volcanogenic vein U-Mo-Cu mineralization, originally of the Permian age, with subsequent Alpine (most probably Cretaceous) reworking (this is evidenced by the variable composition of uraninite). It belongs to the Neohercynian late- to postorogenic metallogenetic stage. The possible younger, post-Permian age of mineralization from alpine hydrothermal solutions must also be assumed, but this consideration has several inconsistencies.

A New Species of Pennsylvanian Plant Fossil (Cyclopteris N.Sp.) from the Placid Shale Member, Brad Formation, Near Ranger, Eastland County, Texas

A new species of Cyclopteris sensu was discovered in the upper sandstone beds of the Placid Shale. New species is distinguished by chevronate veins present between major radiating veins characteristic of Cyclopteris. Discovery of this species expands this genus into the Carboniferous delta deposits of Central Texas, and demonstrates the need to revisit these classic sites.

Overview of potential geothermal reservoirs in Denmark

AbstractThe Danish onshore subsurface contains very large geothermal resources that have the potential to make a significant contribution to transforming Danish energy consumption toward a more sustainable energy mix. Presently, only a minor fraction of this green energy is exploited in three small plants. The main factors that have hampered and delayed larger-scale deployment are related to uncertainties in the geological models, which inevitably lead to high economic risks that are difficult for smaller district heating companies to mitigate without support from a compensation scheme. To facilitate and stimulate much wider use of the Danish geothermal resources, the Geological Survey of Denmark and Greenland (GEUS) and other research institutes have conducted several regional research projects focusing on the geological and geochemical obstacles with the principal objective of reducing the exploration risks by selecting the best geological reservoirs.One of the most important geological factors causing uncertainty is the quality of the reservoirs and their ability to produce the expected volume of warm geothermal brine. Thus, great emphasis has been placed on investigating and understanding the relationships between reservoir sandstone, porosity, permeability, petrography, diagenetic processes and alterations related to variable sediment sources, basin entry points, depositional systems and climate, burial and thermal history. Mesozoic sandstones comprise the most important geothermal reservoirs in Denmark. Details concerning the reservoir quality are compiled and compared for the Lower Triassic Bunter Sandstone, Triassic Skagerrak, Upper Triassic – Lower Jurassic Gassum and Middle Jurassic Haldager Sand formations. The Bunter Sandstone Formation contains extensive aeolian and more confined fluvial sandstones with high porosity and permeability. However, highly saline formation water could be unfavourable. The Skagerrak Formation comprises well-sorted braided stream sandstones in the centre of the basin, and is otherwise characterised by muddy sandstones and alluvial fan conglomerates. An immature mineralogical composition has caused intensive diagenetic changes in the deepest buried parts of the basin. The Gassum Formation consists of shoreface, fluvial and estuarine sandstones interbedded with marine and lacustrine mudstones. In the upper part of the formation, the sandstone beds pinch out into mudstones towards the basin centre. Pervasive siderite- and calcite cement occurs locally in shallowly buried sandstones, and with burial depth the maximum abundances of quartz and ankerite cement increase. Sandstones of shallow burial represent excellent reservoirs. The relatively coarse grain size of the Haldager Sand Formation results in high porosity and permeability even at deep burial, so the formation comprises a high-quality geothermal reservoir.Substantial progress has been made, and a well-established regional geological model combined with reservoir quality is now available for areas with cored wells. This has enabled an improved estimation of reservoir quality between wells for exploration of geothermal reservoirs.

Tempestite facies variability and storm‐depositional processes across a wide ramp: Towards a polygenetic model for hummocky cross‐stratification

AbstractThe hydrodynamic mechanisms responsible for the genesis and facies variability of shallow‐marine sandstone storm deposits (tempestites) have been intensely debated, with particular focus on hummocky cross‐stratification. Despite being ubiquitously utilized as diagnostic elements of high‐energy storm events, the full formative process spectrum of tempestites and hummocky cross‐stratification is still to be determined. In this study, detailed sedimentological investigations of more than 950 discrete tempestites within the Lower Cretaceous Rurikfjellet Formation on Spitsbergen, Svalbard, shed new light on the formation and environmental significance of hummocky cross‐stratification, and provide a reference for evaluation of tempestite facies models. Three generic types of tempestites are recognized, representing deposition from: (i) relatively steady and (ii) highly unsteady storm‐wave‐generated oscillatory flows or oscillatory‐dominated combined‐flows; and (iii) various storm‐wave‐modified hyperpycnal flows (including waxing–waning flows) generated directly from plunging rivers. A low‐gradient ramp physiography enhanced both distally progressive deceleration of the hyperpycnal flows and the spatial extent and relative magnitude of wave‐added turbulence. Sandstone beds display a wide range of simple and complex configurations of hummocky cross‐stratification. Features include ripple cross‐lamination and ‘compound’ stratification, soft‐sediment deformation structures, local shifts to quasi‐planar lamination, double draping, metre‐scale channelized bed architectures, gravel‐rich intervals, inverse‐to‐normal grading, and vertical alternation of sedimentary structures. A polygenetic model is presented to account for the various configurations of hummocky cross‐stratification that may commonly be produced during storms by wave oscillations, hyperpycnal flows and downwelling flows. Inherent storm‐wave unsteadiness probably facilitates the generation of a wide range of hummocky cross‐stratification configurations due to: (i) changes in near‐bed oscillatory shear stresses related to passing wave groups or tidal water‐level variations; (ii) multidirectional combined‐flows related to polymodal and time‐varying orientations of wave oscillations; and (iii) syndepositional liquefaction related to cyclic wave stress. Previous proximal–distal tempestite facies models may only be applicable to relatively high‐gradient shelves, and new models are necessary for low‐gradient settings.