Poor Sorting Research Articles

Sedimentological analysis and reservoir quality of the early Cenomanian transgressive sandstones, northern Western desert, Egypt

Depicting depositional models of transgressive sandstone reservoirs is challenging due to their internal complexity and limited case studies. This study presents an example for transgressive sandstone reservoirs from the Bahariya Formation at Hayat-Yasser oil field, Shushan Basin (northern Western Desert, Egypt). The upper part of the Bahariya Formation accumulated in an estuarine setting as a consequence of a successive sea level rise. Detailed reservoir characterization, employing sequence stratigraphic and sedimentological approaches, revealed that the studied reservoir consists of a mixed siliciclastic-carbonate transgressive estuarine-shelf succession. Four conventional core samples of this succession at Khalda ridge (Shushan Basin), permit the analysis of their sedimentology and internal architecture (mesoscopic heterogeneities) along correlation lines parallel or slightly oblique to depositional dip. The succession consists of six backstepping parasequence sets that record the overall shift from tidal-dominated to wave-dominated estuaries/bays. The transgressive component of the parasequences sets includes bay mudstones, flood-tidal deltas, and shoreface/barrier deposits; while the regressive component includes estuarine point bars, bay head deltas, and tidal deltas. The reservoir properties show significant variation according to the facies assemblages. The tidally-dominated estuarine channels show low net-to-gross, as it is characterized by lenticular sandstone bodies with several lateral and vertical baffles and barriers. On the other hand, the shoreface/barrier and tidal delta sandstones show high net-to-gross and consist of amalgamated sandstone bodies with little mud barriers or baffles. Petrographically, the upper Bahariya reservoir includes intergranular and secondary porosities. The microscopic heterogeneities are mainly due to the fine grain nature, poor sorting, presence of matrix, and continuous mud barriers or baffles. Destruction of porosity, affecting the reservoir quality, occurred by silica overgrowths, ferroan calcite, grain coating chlorite, and kaolinite cementation, as well as compaction. Feldspar dissolution is the main diagenetic process responsible for the formation of secondary porosity, enhancing the reservoir quality.

Diagenetic variations with respect to sediment composition and paleo-fluids evolution in conglomerate reservoirs: A case study of the Triassic Baikouquan Formation in Mahu Sag, Junggar Basin, Northwestern China

Understanding reservoir heterogeneity and associated diagenesis, have a paramount importance for efficient petroleum exploration and development strategies. Diagenetic variations and factors that control these processes have, therefore, been investigated in this study using petrographic and geochemical methods, including cathodoluminescence, scanning electron microscopy, x-ray fluorescence, electron probe microanalyses and stable isotope analysis. Mechanical compaction and chemical diagenesis trends have obviously varied as a function of rock types and geological locations. The conglomerate reservoirs with high content of tuffaceous matrix and characterized by poor sorting showed stronger compaction. The tuffaceous matrix displays a large degree of dissolution during the progressive burial diagenesis due to its thermodynamic instability. The tuffaceous matrix in Na-rich conglomerate reservoir rocks mainly transformed into analcite, while it transformed into illite in K-rich conglomerate reservoir rocks. In most conglomerate reservoirs far away from deep-rooted faults, calcite cements are indicated to have been sourced from the decarboxylation of organic matter in the interbedded mudstones. Carbonate cements in conglomerate reservoirs near the deep-rooted faults possibly formed from hydrothermal fluids or thermochemical oxidation of pre-existing methane accumulations. This study can serve us an excellent example for the control of sediment composition and paleo-fluid evolution on diagenetic variations in fan-delta conglomerate reservoirs.

Using sediment grain size characteristics to assess effectiveness of mechanical sand barriers in reducing erosion

Wind and sand control features are important tools for limiting desertification. Sand barriers are one of the oldest engineering measures used to reduce wind-sand hazards. Their efficacy and exact mechanism by which they work has remained a topic of scientific debate however. Sediment grain-size distributions can help constrain their utility and function. This research analyzed sediment grain size distributions in samples collected from areas around six different types of sand barriers installed along the southeastern margin of the Tengger Desert. Results were compared with sediment from a bare dune area (no barriers) used as a control. The barrier area samples contained high proportions of coarse sand and relatively low proportions of silty sand and very fine sand. Fine and medium sand were present but clay was not. The lower proportions of fine sand and higher proportions of coarse sand relative to bare dunes documented an effective reduction in aeolian transport by the barriers. Samples from the barrier areas also showed poorer sorting relative to bare dune areas. This appeared as lower kurtosis values and wider frequency distribution curves relative to those measured from bare dunes samples. The wider cumulative frequency curves for samples from the barrier areas likely reflects the higher proportion of coarse-grained material. The Straw/1.5 and PLA/1 barrier types hosted greater sediment accumulation than that observed for the other barrier types (Straw/1, PLA/1.5, Mixed/1 and Mixed/1.5). Sediment grain size distributions showed that the base and middle slope areas of the dune experienced deposition, while the top of the dunes experienced erosion. The Straw/1 barrier (straw installed as a 1 × 1 m grid) performed best in terms of installation costs and protective effects for the study area. This study demonstrates how sediment grain size distributions can be used as quantitative proxies for sand barrier performance in reducing desertification.

Elutriation pipes in ignimbrites: An analysis of concepts based on the Huichapan Ignimbrite, Mexico

The upper portion of the Huichapan Ignimbrite (UHI), central Mexico, is a non-welded massive ignimbrite characterized by large and well-developed fines-poor elutriation pipes. We conclude that the most important pipe-forming process in the Huichapan Ignimbrite was deposition-triggered aggregative-type segregation, and this process is enhanced by positive pore-pressure feedback during the rapid settling of the pyroclastic material. In experiments, pumice concentration zones and elutriation pipes have been formed in separated portions of the deposits. Contrary to the experimental results, in the UHI both pumice concentration zones and elutriation pipes have been observed alongside one another within the deposit. We interpret this association to have formed during time periods of unusually high deposition rate within a long-lived, sustained pyroclastic density current system. Elutriation pipes were formed because of low shearing and vertical channeling of gases, and the pumice concentration zones formed because of pumice segregation during hindered settling. Nevertheless, the deposition rate was so high that the segregated pumice was “frozen” before it could bypass, within the deposit, right next to the elutriation pipes. We present a classification scheme of five types of elutriation pipes based on our field observations in the UHI and a review of field and experimental work from other authors: 1) tubular pipes; 2) irregular tubular pipes; 3) anastomosing pipes; 4) pinch-out pipes; 5) deflected pipes. Irregular tubular pipes are the most common in the volcanic geological record and they form because of deposition-triggered aggregative-type segregation and/or post-depositional upward fluid flow. Likely, anastomosing elutriation pipes are a unique product of deposition-triggered aggregative-type segregation. A comparison between the lower and upper portion of the Huichapan Ignimbrite leads to the conclusion that deposition-triggered pipe formation is enhanced by poor sorting, low shearing, and presence of large clasts (>−5Φ, 32 mm). Pipe-free ignimbrites in the volcanic geological record likely come from relatively better-sorted dispersions with few coarse clasts, but more importantly, strong shearing during deposition may be the main processes that diminish pipe formation.

Seasonal changes in sediment erodibility associated with biostabilization in a subarctic intertidal environment, St. Lawrence Estuary, Canada

The sediment dynamics and the long-term evolution of intertidal environments depend on the erosion threshold, which is often increased by microbial biofilms. Intertidal biostabilization has been well studied in temperate and subtropical environments, but little is known for subarctic conditions with strong seasonal changes in vegetation cover and sea ice presence in winter because of the difficulty in studying the sediments under ice cover. The present project investigated the role of biofilms and their seasonal as well as spatial variations for sediment biostabilization in a subarctic intertidal area near Rimouski (Quebec, Canada). Grain size distribution reflected a seaward increasing trend in sand content and mean grain size. The poor sorting of sediments results from the contribution of sediment transport by ice rafting in addition to the hydrodynamic transport processes in this subarctic intertidal area. A Cohesive Strength Meter (CSM) was used to measure the erosion threshold (τcrit) across the entire intertidal area. Chlorophyll a (Chl a) and extra polymeric substances (EPS) were measured in the top 3 mm. The high marsh had a far higher τcrit than the low marsh, but there was much less variation between low marsh, mudflat and sandflat. τcrit was significantly correlated with Chl a, elevation, and organic matter content. EPS was not a good indicator for τcrit, except for the low marsh/high marsh difference. The results showed a seasonal cycle in intertidal bed erodibility. Lower intertidal areas had highest τcrit in autumn during the storm season, followed by lowest τcrit in winter under sea-ice cover, and no major difference between summer and spring. This study highlights the characteristics of cold climate intertidal areas, where low temperatures in autumn and land-fast ice cover during winter severely affect biofilms and intertidal vegetation, and ultimately their capacity to shield sediments from erosion.

Sedimentological, mineralogical and geochemical investigation of Essaouira’s coastal dune system: potential origin and provenance

Quaternary coastal sand dunes occur frequently along the Atlantic coast of Morocco and result from the combined effect of river discharge, littoral drift, winds, vegetation, and other meteorological conditions. In this paper, we investigate the textural and compositional parameters of the coastal dune sands of Essaouira across the Ksob riversides, as well as their provenance. Morphologically, they occur as present-day active dunes, Holocene fossil dunes and Pleistocene aeolianite deposits. To investigate the grain provenance, we have opted for laboratory analyses including grain size, mineralogy, microtextures, and micromorphology of quartz grains. Sands from Holocene fossil and active dunes revealed very fine to medium mean grain size and a moderate sorting, while those of the Pleistocene aeolianites showed fine to very fine mean grain size and very poor sorting. Studied dunes showed the dominance of grain shapes varying from sub-rounded to fresh angular. Regarding mineralogy, calcite bioclasts are prevalent in sands of the right bank of the river, while quartz is more abundant in dunes located at the left bank. In the active dunes of the left bank, other carbonates were also detected in bioclasts such as aragonite, dolomite, and magnesian calcite, suggesting a marine provenance. The siliciclastic grains of the studied generations of aeolian dunes are likely originating from Triassic, Jurassic, and Quaternary units crossed by the Ksob River. In fact, the results revealed the presence of minerals such as albite, plagioclase, microcline, and orthoclase which could have been sourced from Triassic basalts and gypsum which is often associated to Jurassic evaporitic rocks. This study allowed to suggest the probable origin of the sands that form these dunes based on the detailed study of their grains, which has not been studied on previous research works of the area. In addition, this research is of particular relevance as it fits into the current research trend related to understanding the evolution of Plio-Quaternary coastal dune systems in the world and could be applicable to other dune systems of the Atlantic coast of Morocco in the future.

SCHOOL SEGREGATION IN PUBLIC AND SEMIPRIVATE PRIMARY SCHOOLS IN ANDALUSIA

ABSTRACT School segregation by socio-economic background is a feature of most education systems and impacts negatively on educational outcomes for poor children. Evidence on this issue is lacking for the Spanish primary education system and in particular the extent to which a) poor and rich students sort into different types of school and b) the extent of segregation within different school types. We measure the level of segregation of students from different socioeconomic backgrounds into public and semiprivate schools and within these two types of school using the Hutchens Index. The analysis is based on data for students attending 5th grade in the largest region in Spain (Andalusia). Our results indicate significant differences in the level of segregation across and within both school types. Students from higher socioeconomic backgrounds are more likely to attend semiprivate schools. This provides evidence of the inequity of providing public funding for semiprivate schools that are then disproportionately attended by wealthier students.

Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano

The phreatomagmatic eruption at Aso volcano on October 8, 2016, released PDC and fallout up to 320 km from the vent, providing an opportunity to study the dispersal and sedimentation of tephra bearing wet and dry aggregates. We investigated fresh air-fall tephra and conducted both dry- and wet-sieving to assess the size distribution of both aggregate-bearing deposits on the ground and particles in the plume prior to aggregation. The tephra was asymmetrically distributed in the ENE direction, with a relatively wide distribution and small maximum grain sizes north of the depositional axis, reflecting different wind directions at each altitude. The secondary accumulation maxima at 4–8 km NE from the vent was characterized by the segregation of lapilli followed by accretionary pellets that were rapidly created by aggregation in the wet plume, thereby enhancing the removal of airborne ash. Coalesced aggregates possibly arose from salt precipitation processes. For dry aggregates fallen in medial-to-distal regions, observed deposition duration and fall velocity calculations concluded that fine ash was deposited not as individual particles but as aggregates. Most grain-size distributions along the dispersal axis based on the two sieving methods used were multimodal, with the coarser mode fining according to distance from the vent and the finer mode stabilizing at around 4ϕ; this is interpreted as resulting from the mixture of grain-size distributions with different origins, i.e., the normal settling of individual clasts and particle aggregation. The wet-sieved total grain-size distribution included 20.4 wt% fine ash compared with only 2.4 wt% fine ash in the dry-sieved distribution, suggesting that aggregated particles accounted for 18 wt% of the deposit. Total grain-size distributions based on wet-sieving showed extremely poor sorting that could be explained by the following causes: the release of coarse-grained ejecta originating from the host rock of the crater, fine particles due to fragmentation from a phreatomagmatic eruption, the supply of water and salt from the crater to the plume, and aggregation enhancement of the fine ash on the ground, reflecting the effect of the crater lake as external water source.

Diagenesis effects on the conglomerate reservoir quality of the Baikouquan Formation, Junggar Basin, China

Large accumulations of oil and gas have been found in fan delta conglomerate reservoirs in the upper Triassic Baikouquan Formation in the Mahu Sag at the northwestern margin of the Junggar Basin. To effectively explore strongly heterogeneous, high-quality, conglomerate reservoirs, their deposition, diagenesis, and genetic mechanisms must first be thoroughly studied. Analyses of cores, thin sections, fluid inclusions, oxygen isotopes, logging, physical properties data, X-ray diffraction, scanning electron microscopy, and cathodoluminescence confirm that the conglomerates have high feldspar contents as well as volcanic fragments that comprise a variety of micro-lithofacies. The heterogenous reservoir properties include permeability values of less than 1 mD, 1–10 mD, and higher than 10 mD, which correspond to 44.19%, 37.06%, and 18.75% of the reservoir, respectively. The tight reservoirs, mostly developed in the fan delta plain, have experienced extensive compaction and/or calcite cementation and consist of only a few secondary pores. Reservoirs with high porosity and permeability developed in subaqueous channels and experienced relatively weak compaction. These reservoirs contain large numbers of secondary pores that were mainly formed by the dissolution of K-feldspars and volcanic rock fragments. Comprehensive studies of sedimentation and diagenesis in the Baikouquan Formation indicate that these high porosities originated from the chronological coupling of the following three important geological processes: (1) Conglomerate reservoirs with better sorting and roundness and lower mud content are mainly developed in subaqueous distributary channels and have higher porosity and permeability than reservoirs with poorer sorting and roundness. (2) Strong dissolution of K-feldspar and volcanic debris occurred in reservoirs with good original physical properties, forming large numbers of secondary pores. Acidic fluids from source rocks in the Fengcheng Formation led to dissolution. (3) The byproducts of dissolution, which consist mostly of mixed-layer illite/smectite and illite, reduced porosity and permeability. In reservoirs with good original physical properties and fault development, dissolution plays an obvious role in improving physical properties in such relatively open diagenetic systems.

Particle-Size Analysis of Modern Bottom Sediments by the Laser Diffraction and Sieve Methods

A combination of laser diffraction and wet sieving through a nylon screen with a 0.1-mm mesh has been suggested for the particle-size analysis of silty bottom sediments from estuarine and coastal sea areas. The necessity of individual determination of sand fractions even in case of the technical ability of the device to analyze the content of coarse particles to 2 mm in size is shown. This is related to poor sorting of coastal silts and inadequately represented weighed samples used for the standard laser diffraction particle-size analysis. In addition to sand fractions, the pre-sieving affects the determination of the 0.1–0.01 mm silt fractions, while its impact on the analysis of pelite fractions of less than 0.01 mm is minimal. The effectiveness of the proposed modified method is proved by the closer correlation between the content of pelite fractions and the concentration of metals and organic carbon in bottom sediments.

Quartz grain characteristics of the late Pleistocene hard clay in the Yangtze River delta and implications for sedimentary environment and provenance

AbstractThe sedimentologic fingerprinting in detrital deposit is vital to reconstruct sedimentary environments and discriminate sources. In this study, grain size and microtextural characteristics of quartz from the late Pleistocene hard clay in the Yangtze River delta (YRD) were analyzed by using a laser particle size analyzer and a scanning electron microscope. Subaqueous quartz from the Yangtze River and Yellow River sediments and eolian quartz from the Chinese Loess Plateau loess were also analyzed by scanning electron microscopy to obtain the microtextural characteristics. Quartz grains of the hard clay were characterized by poor sorting, fine skew, bimodal grain-size distributions, and numerous eolian microtextures. The comparison of the quartz grain characteristics of the hard clay with these in eolian loess indicated that the hard clay belonged to an eolian deposition. Moreover, the fine quartz grains of the hard clay were dominated by eolian microtextural characteristics, representing long-distance transportation. The coarse quartz grains of the hard clay exhibited more subaqueous microtextural characteristics, which indicated that the coarse fraction of the hard clay was derived from the proximal source regions in the YRD. The determination of buried eolian deposition with multiple sources in the YRD implies a southward westerly jet stream, strengthened eolian dust transportation, and extensive aridification in the YRD due to the increased Northern Hemisphere ice sheets in Marine Oxygen Isotope Stage 2.

Depositional and diagenetic processes in the pre-salt rift section of a Santos Basin area, SE Brazil

ABSTRACT This study aims to provide a better understanding of the genesis and diagenetic evolution of the rift pre-salt deposits of the Santos Basin, in the context of evolution of the lake system in which the sediments were deposited. The study of the syngenetic and early diagenetic constituents and their paragenetic relations allowed reconstruction of the evolution of lacustrine environmental conditions during the rift stage in the central area of the basin. A petrological study was performed on cores and sidewall samples of a well drilled through the pre-salt rift section in the Lower Cretaceous of the central Santos Basin, eastern Brazilian coast. The studied rocks consist of carbonate and non-carbonate intrabasinal components, with extrabasinal non-carbonate contribution. During Barremian early rift sedimentation, intense syngenetic precipitation of magnesian clay minerals under highly alkaline conditions deposited arenites constituted by stevensite ooids and peloids, as well as hybrid, resedimented deposits of the Piçarras Formation. Freshening of the lacustrine environment provided the conditions required for the proliferation of bivalves and sedimentation of the coquinas of the Itapema Formation. The massive structure of the deposits, poor sorting, chaotic to concave-up orientation of the bioclasts, and mixing of bivalves with stevensite particles indicate redeposition by gravity flows. The main diagenetic processes in rift stevensite and hybrid rocks are the cementation and replacement of grains by calcite, dolomite, and subordinately, silica and smectite. Siliciclastic-volcaniclastic mudrocks present intense replacement by dolomite. In the bivalve rudstones, the main diagenetic processes were dissolution of the shells and cementation of the intraparticle and interparticle pores by calcite and, subordinately, dolomite and silica.

The Roccacaramanico Conglomerate (Maiella Tectonic Unit) in the frame of the Abruzzo early Pliocene Foreland Basin System: stratigraphic and structural implications

In the upper Tertiary succession of the Maiella Tectonic Unit (Abruzzo, Italy), coarse calciclastic layers, hereinafter referred to as Roccacaramanico Conglomerate (RCC), were deposited during a short time span which approximates the Miocene-Pliocene boundary. The biostratigraphic characterization of RCC is well constrained by previous studies of foraminifer and nannofossil assemblages. In fact the pelitic interbeds of the RCC are attributed to the Sphaeroidinellopsis spp. Biozone and to the MNN12 Nannofossil Zone belonging to the earliest Pliocene.Previous works referred this conglomerate to Apennine- fed sediment gravity-flows however, in the absence of detailed compositional data and of a regional-scale sedimentological study of the layers, only generic hypotheses on the source-area and on the nature of the event which triggered the RCC deposition, were formulated.Here we present the results of an original investigation on the RCC cropping out within the Maiella Tectonic Unit, in the area delimited westward by the Morrone-Porrara thrust and, towards south-east, by the Molise allochthonous Units.In this area, a fairly continuous RCC horizon, exposed on both limbs of the Maiella anticline, was mapped and logged in detail. Our lithostratigraphic analysis allowed to make hypotheses on depositional mechanisms of RCC and revealed that it consists of several (six to ten) major depositional events producing locally amalgamated pluri- metric clastic layers.Our facies analysis highlighted that previous studies had generally underestimated the overall thickness of the layers and that in the southernmost examined outcrops (Palena, Taranta Peligna and Lama dei Peligni), the RCC is characterized by higher thickness, coarser grain-size, poorer sorting and more pronounced channeling compared to that cropping out in northernmost areas (Roccacaramanico, San Nicolao and San Valentino). The recognition of facies-types characterized by greater proximality in the southern Maiella area, and the overall geometric reconstruction of the depositional architecture of the RCC horizon, suggests that, contrary to what was previously assumed, the major sediment gravity-flows were fed from the south-eastern edge of the basin. This result is also confirmed by the paleocurrent data, testifying northward flowing currents directed SSE-NNW.The compositional analysis of RCC, highlighted an almost totally calcareous composition of the clasts and a poor and scattered siliciclastic fraction, mainly occurring as fine grained matrix. Clasts showing inner platform, bio-constructed margin, ramp, transitional and basinal facies, of different ages, are mixed throughout the layers. Nevertheless, these data allowed us to make inferences on the provenance of the sediment supply and on the stratigraphic successions that were undergoing erosion in the area surrounding the basin, around the Messinian-Pliocene boundary.A quantitative assessment of the RCC volume was finally achieved, taking into account either the thickness values we measured in the field or other obtained from deep well-logs, and applying these thicknesses to a set of restored geological sections crossing the Maiella anticline. Our calculation provides a minimum area extent of ~ 700 km2 and a conservative volume estimates of ~ 7 km3 which allows to effectively apply to the RCC, the definition of “mega-bed”. This highlights its importance as a regional marker horizon of the easternmost Abruzzi succession, an importance that is even more emphasized by its clear stratigraphic position, straddling the Miocene/ Pliocene chrono-stratigraphic boundary.

Contourite porosity, grain size and reservoir characteristics

Contourites are now recognised as having a significant potential as hydrocarbon reservoirs in the subsurface, and several fields have been interpreted as comprising bottom-current reworked turbidite sands. However, very little has been published on the porosity characteristics of contourites. This study documents porosity data from IODP Expedition 339 sites in the Gulf of Cadiz. We use grain size analyses, porosity-depth plots and exponential models to yield a better understanding of grain size characteristics and facies, porosity characteristics, and the reservoir potential of contourites in the subsurface. New grain size data for over 350 samples from the Cadiz contourites is presented, building on earlier work. These data confirm the distinctive trends in textural properties linked to depositional processes under the action of bottom currents. The finest muddy contourites (<20 μm) show normal grain size distributions, poor to very poor sorting becoming better with decreasing grain size, and zero or low skewness. These are contourite-hemipelagite hybrids. Muddy to fine sandy contourites (20–200 μm) trend towards better sorting and initially fine-tail and then coarse-tail skew. These represent typical depositional trends for contourites, affected by current capacity and then increased winnowing at higher current speed. Clean sandy contourites (around 200 μm) are the best sorted. Medium and coarser-grained contourites show a trend towards poorer sorting. They result from the action of dominant bedload transport, extensive winnowing, and mixed sediment supply. Porosity-depth relationships from four Cadiz sites show a moderately high initial porosity for both sand and mud facies (50–60%) and a systematic decrease with depth to around 35–40% near 500 m burial depth. According to the exponential models of porosity with depth, contourite porosity should exceed 10% at 2500 m burial depth. We compare the data from the Gulf of Cadiz Contourite Depositional System, with those of the Eirik Drift, Newfoundland Drift, Gardar Drift and Canterbury Slope Drifts. Similar depth trends are observed, and all show anomalies linked to interbedded sandy and muddy facies, composition (carbonate vs siliciclastic), and the presence of hiatuses in the sediment record. These data provide good insight into the likely reservoir characteristics of contourites, for both conventional and unconventional reservoirs. They are comparable with those of existing contourite fields, most of which are mixed turbidite-contourite systems.

Fractionation Trends and Variability of Rare Earth Elements and Selected Critical Metals in Pelagic Sediment from Abyssal Basin of NE Pacific (Clarion-Clipperton Fracture Zone)

The geochemical and mineralogical characteristics of pelagic sediments collected from the Interoceanmetal Joint Organization (IOM) claim area, located in the eastern part of the Clarion-Clipperton Fracture Zone (CCFZ; eastern tropical Pacific), are described in this paper. The concentrations of rare earth elements (REE), as well as other selected critical elements contained in 135 sediment samples of siliceous clayey silts, are presented. The vertical and spatial variabilities of elements, with particular emphasis on REE as well as metals of the highest economic interest such as Cu, Ni, and Co, are detailed. The applied methods include grain size analysis by laser diffraction, geochemistry examination using ICP-MS, XRF, AAS, and CNS spectrometry, and XRD analysis of mineral composition (Rietveld method). Additionally, statistical methods such as factor analysis (FA) and principal components analysis (PCA) were applied to the results. Finally, a series of maps was prepared by geostatistical methods (universal kriging). Grain size analysis showed poor sorting of the examined fine-grained silts. ICP-MS indicated that total REE contents varied from 200 to 577 ppm, with a mean of 285 ppm, which is generally low. The contents of critical metals such as Cu, Ni, and Co were also low to moderate, apart from some individual sampling stations where total contents were 0.15% or more. Metal composition in sediments was dominated by Cu, Ni, and Zn. A mineral composition analysis revealed the dominance of amorphous biogenic opaline silica (27–58%), which were mostly remnants of diatoms, radiolarians, and sponges associated with clay minerals (23% to 48%), mostly Fe-smectite and illite, with mixed-layered illite/smectite. The high abundance of diagenetic barite crystals found in SEM−EDX observations explains the high content of Ba (up to 2.4%). The sediments showed complex lateral and horizontal fractionation trends for REE and critical metals, caused mostly by clay components, early diagenetic processes, admixtures of allogenic detrital minerals, or scavenging by micronodules.

Characteristics and controlling factors of Chang 8 Reserviorof the Jiyuan Area in the Ordos Basin

By analyzing the thin sections and physical property,the petrology feature and pore characteristics of the Chang 8 Formation in the Jiyuan Area,the microscopic reservoir pore structure characteristics,characteristics of porosity and permeability are studied and the reservoir performance′s main influencing factors were analyzed.The results suggest that delta sediments are the main deposits in the Chang 7 Formation,and delta front underwater distributary channel sand is the main reservoir.The lithological characteristics mainly include fine-grained lithic feldspathic sandstone and feldspathic detritus sandstone,with low compositional maturity and middle textural maturity.Granular pore and secondary feldspar-dissolution pore are the main pore types.Pore throat presents fine pore fine throat with poor sorting and high micro-heterogeneity.The Chang 7 reservior has low permeability of which the porosity is below 9.448%and the permeability is less than 0.685×10-3μm 2.The reservoir characteristics are influenced by deposition and diagenesis primarily.Sedimentary facies zone controlled development and distribution of reservoir.Besides,compaction and cementation lead to porosity decreased,but the dissolution improves the reservoir propert.

Integrated Geological, Hydrogeological, and Geophysical Investigations of a Barchan Sand Dune in the Eastern Region of Saudi Arabia

In arid countries such as Saudi Arabia, aeolian sand often covers a large area of the country. Understanding the variations of sand properties in dunes, including grain size, sorting, mineral composition and water content, can be important for groundwater recharge, environmental, and construction applications. Earlier studies examined properties of sand dunes by collecting samples from the surface. This study aims to investigate variations of sand properties within a Barchan sand dune in the coastal area of Saudi Arabia, by collecting samples and measurements from two vertically drilled boreholes up to the ground water level; one drilled in the dune crest and another one in the limb. Representative samples were collected and analyzed for their texture parameters, water content, and mineralogy. Electrical resistivity survey data was also acquired to map water content variation in the dune limb, and for comparison with well bore data. The reported results show no vertical variations in grain size or sorting in the dune crest. In contrast, the upper 0.5 m of the dune limb shows a relatively poorer sorting than found in deeper parts of the dune. Laterally, no variations in minerology were observed between crest and limb sands while grain size tended to be slightly coarser in the dune limb compared to the crest. Regarding the water content, it was found to vary vertically, probably due to previous cycles of rainfall infiltration through the sand body. Such observed variation in water content is consistent with the measured resistivity profile which could clearly identify the water table and areas with higher water content. This study concludes that beyond the upper 0.5 m, the Barchan sand dune body can be treated as a homogeneous medium in terms of mineralogy and sorting while grain size increases slightly toward the limb side.

Fluvial facies and petrography of Late Pleistocene Baneta sediments, Central Narmada Basin, Madhya Pradesh, India

Baneta Formation, comprising of fining upward sequences of pebbly conglomerate, sandstone and siltstone, exhibits development of five distinct lithofacies, viz., massive pebbly conglomerate, large scale tabular cross bedded sandstone, horizontal parallel bedded coarse-grained sandstone, parallel laminated fine-grained yellowish sandstone and siltstone; representing channel lag, point bar and overbank flood plain deposits of mixed load meandering river. In these sediments, development of nodular, buckled bedded calcrete, rhizoliths and tepee is noticed. Granulometric studies of these sediments revealed presence of wide range of grain size classes, polymodal grain size distribution, moderate to very poor sorting, positive skewness and leptokurtic nature, supporting fluvial environment of deposition. Lithic arenitic nature, heavy mineral assemblage with dominance of augite and low ZTR index of these sediments indicate mineralogical immaturity and presence of illite, kaolinite and montmorllionite together with geochemical composition indicate their derivation from mixed provenance of Precambrian granite, metapelites, Vindhyan Supergroup, Gondwana Supergroup, Deccan trap basalt, and laterite. The thin sections studies reveal signatures of meteoric phreatic and vadose zone diagenesis related with semi-arid climate and subaerial exposure. The δ13C and δ18O content of calcretes indicate their pedogenic and/or shallow groundwater origin under semi-arid climatic conditions, and C3–C4 mixed vegetation with dominance of C4 vegetation. OSL and 14C dates of the samples from Baneta Formation suggest deposition of these sediments in Late Pleistocene.

A Lightweight Feature Fusion Single Shot Multibox Detector for Garbage Detection

To solve the problems of a poor manual garbage sorting environment, including heavy tasks and low sorting efficiency, we propose the Lightweight Feature Fusion Single Shot Multibox Detector (L-SSD) algorithm to realize intelligent trash classification and recognition. Since waste has a small volume and the image resolution of garbage is always low, the algorithm that we propose is an enhanced single shot multibox detector (SSD) with a lightweight and novel feature fusion module. This SSD can significantly improve the performance of rubbish detection. In this feature fusion module, features from different layers with different scales are connected in series. A new feature pyramid was generated by using downsampling blocks, which will be fed to appointed multibox detectors to predict the final detection results. Due to the extremely unbalanced ratio of positive samples to negative samples, which leads to a low accuracy of SSD, Focal Loss using balanced cross-entropy is employed, which is provided by easy examples that corresponds to difficult samples with a decline in the loss weight. Thus, the training is biased towards meaningful samples. We have replaced the backbone network of VGG16 with ResNet-101 to achieve more accurate detection. We analyzed the performance of a nonmaximum suppression (NMS) algorithm and discovered that Soft-NMS was more suitable for learning better image representations. The strategy of Soft-NMS is to suppress the undesirable detection box rather than remove it completely. The experimental results show that the L-SSD exceeds a large number of state-of-the-art object detection algorithms in both accuracy and speed.

Quantitative analysis of stylolite networks in different platform carbonate facies

Abstract Stylolites are rough surfaces that form by pressure solution, and present variable geometries and spatial distributions. Despite being ubiquitous in carbonate rocks and potentially influencing fluid flow, it is not yet clear how the type and distribution of stylolite networks relate to lithofacies. This study investigates Lower Cretaceous platform carbonates in the Benicassim area (Maestrat Basin, Spain) to statistically characterise stylolite morphology and stylolite network distributions in a selection of typical shallow-marine carbonate lithofacies, from mudstones to grainstones. Bedding-parallel stylolite networks were sampled in the field to quantify stylolite spacing, wavelength, amplitude, intersection morphology and connectivity. Grain size, sorting and composition were found to be the key lithological variables responsible for the development of rough anastomosing stylolite networks. Poorly-connected stylolites with large vertical spacings were found to be dominant in grain-supported lithofacies, where grains are fine and well sorted. Anastomosing stylolite networks appear well developed in mud-supported lithofacies with poorly-sorted clasts that are both heterogenous in size and composition. Mud-supported facies feature stylolites that are closely spaced, have high amplitudes and intersection densities, and predominantly present suture and sharp-peak type morphologies. Larger grains and poor sorting favour the formation of stylolites with small vertical spacings, low wavelengths and high amplitudes. This statistical analysis approach requires only limited information, such as that from drill core, and can be used to characterise stylolite morphology and distributions in subsurface carbonate reservoirs.