Sand Sheets Research Articles

A new chronology for tsunami deposits prior to the 1700 CE Cascadia earthquake from Vancouver Island, Canada

Coastal deposits at Tofino, Ucluelet, and Port Alberni in Vancouver Island along the Cascadia subduction zone were re-examined to improve the earthquake history of the southwest coast of Canada. We found sand sheets interbedded within peat and mud, suggesting deposition by strong flows in a low-energy environment. Based on limiting maximum and minimum ages derived from plant macrofossils, the age of one of the sand sheets below the tsunami deposits of the great Cascadia earthquake in 1700 CE was estimated to be 1330–1430 CE. Onshore paleoseismic evidence has been documented in Vancouver Island, northern Washington, and northern Oregon during this period. However, the newly constrained age is between those of coseismic subsidence Y and W events in southern Washington, which have been recognized as the 1700 CE and the penultimate Cascadia earthquakes, respectively. Moreover, the new age partly overlaps with the age of offshore paleoseismic evidence for T2, interpreted to have originated from the penultimate Cascadia earthquake, based on offshore turbidite records. The new chronology prior to the 1700 CE Cascadia tsunami deposit from Vancouver Island contributes to a better understand of the timing of the penultimate Cascadia earthquake.

Detrital zircon age signatures of the basal Cambrian sandstone unit in North China: implications for drainage divides during global Sauk transgression and separation from Gondwanaland

ABSTRACT The basal Cambrian sandstone unit in the North China craton (NCC) is an example of globally widespread siliciclastic succession that resides on the Great Unconformity and deposited on a hypothesized low-lying peneplain during the Cambrian global eustatic sea-level rise. Detrital zircon age signatures from this distinct sequence enable recognition of the ancient drainage system of the NCC in deep time and track its potential linkage with the Gondwana landmass. LA-ICP-MS U–Pb dating of the fossil-calibrated basal Cambrian (Series 2) detrital zircon samples from seven measured sections reveal marked spatial changes in their age signatures that can be divided into three distinct types. The first is generally characterized by the bimodal age populations with broad peaks at ~1.85 Ga and ~2.5 Ga that correlate with the Archean to Paleoproterozoic basement inboard of the NCC. The second is featured by multimodal distribution with diagnostic Neoproterozoic peaks that correspond to subregional magmatic record. The third also shows multiple-zircon age populations, but yields significant crystallization ages close to the early Cambrian age. Comparing our new data with existing age spectra for the Cambrian strata across the NCC and the northern Gondwana demonstrates that separate drainage systems did exist in the peneplained basement during global Cambrian transgression and the basal Cambrian unit in the NCC was not a part of the far-travelled sand sheet across the northern margin of Gondwana. The most suitable source for Cambrian-aged grains constrained by paleogeographic restoration is the arc terrane developed along the northern margin of the NCC as a result of subduction of the Paleo-Asian oceanic plate. Our new continental-scale detrital zircon provenance signatures in the basal Cambrian unit suggest that the NCC should be considered a discrete continental block separated by the Proto-Tethys Ocean in the Cambrian, rather than an integral part of the northern Gondwana.

Seismic diagenetic facies prediction of tight sandstone in the offshore sparse well area: An example from the Xihu Depression of the East China Sea Basin

The purpose of this study is to forecast the spatial distribution of diagenetic facies (DF) of tight sandstone in the offshore sparse wells area. Analytical test data, rock physics experiment data and prestack seismic data were used to study the spatial distribution of seismic diagenetic facies (SEISDF) of tight sandstone of the second (H4b) submember of the fourth (H4) member of the Huagang (E3h) Formation in the N gas-field, Xihu Depression, East China Sea Basin. Based on diagenesis and diagenetic minerals, core-based DF of the H4b sandstone were divided into chlorite-coated facies (CHF), calcite-cemented facies (CAF), dissolution facies (DIF), tightly compacted facies (TIF), and quartz-cemented facies (QUF). Various seismic elastic parameters were obtained by prestack elastic parameter inversion method, and sensitive seismic elastic parameters were selected according to the seismic identification principle of DF. In order to predict the spatial distribution of DF, four DF and sensitive seismic elastic parameters were integrated to establish a SEISDF prediction model based on supervised learning, and obtain a diagenetic facies comprehensive index (DFCI) that can distinguish four DF. Then, the 90° phase conversion technique of seismic lithology was used to realize the consistency of the DFCI between isochronous stratigraphic interfaces with core-based DF. The stratal slicing technique of seismic geomorphology was used to make stratal slices of the DFCI between isochronous stratigraphic interfaces. Representative stratal slices were singled out, and the spatial distribution of the SEISDF was interpreted. This study shows that the H4b1 sublayer primarily develops the TIF, while the H4b2 and H4b3 sublayers chiefly develop the QUF, CHF, and DIF. Compared with the H4b2 and H4b3 sublayers, the areas of the QUF and DIF in the H4b4, H4b5, and H4b6 sublayers slightly increase. The QUF are mainly distributed in the subaqueous distributary channel and a small number of sheet sand and channel bar depositional facies in the form of continuous sheets. The CHF are primarily developed in lenticular shape in the channel bar and a small amount of sheet sand and subaqueous distributary channel depositional facies. The most favorable DIF are chiefly developed in the subaqueous distributary channel, channel bar, and sheet sand depositional facies near the fault, which are distributed in strips. This study proposes a very valuable method for the SEISDF prediction of tight sandstone, which can provide a reference for the study of DF of similar strata in other sedimentary basins.

Factors controlling reservoir quality of a retreating delta-front in shallow-water lacustrine in the Songliao Basin, Northeast China

Shallow-water lacustrine delta sand bodies with large areas of high-quality reservoirs are widespread in the first member of Yaojia Formation (k2y1) of the Upper Cretaceous in Qijia–Gulong area, central depression of the Songliao Basin. The analysis of elements affecting reservoir quality has always been a focus and difficulty of oil and gas exploration and development. Seismic profile interpretations, well log analysis, lithological associations, core observations, and heavy mineral assemblage determinations are used to interpret sequence stratigraphic framework and sedimentary evolution of K2y1. The latter is interpreted as a transgressive systems tract comprising three fourth-order sequences (SQ1–SQ3). Based on core observations and wireline logs, K2y1 primarily contained a shallow lake, distal bars, sand sheets, interdistributary bay, and subaqueous distributary channel deposits. The sand ratio and scale of the channels in the formations from SQ1 to SQ3 decreased which was reflecting the continuously retrograding sedimentary evolution of deltas to the lakeshore, as observed based on mutual calibration of single well sedimentary facies and root mean square amplitude attributes. Based on petrographic analysis of thin sections, particle sizes, scanning electron microscope (SEM) as well as X-ray diffraction, the effects of diagenesis and sedimentary facies on reservoir quality are investigated. In the process of delta-front retrogradation, the changes in reservoir quality in different sequences are primarily a result of the following factors: (1) the fine sandstone has better reservoir quality and more primary pores than the siltstone, which has higher argillaceous content. Additionally, in the fine sandstone, more primary pores can be preserved in the compaction process with higher reservoir quality. (2) Less authigenic illites have little influence on reservoir quality. When the authigenic illite content is >6%, the flocculent characteristics of authigenic illite crystals easily separate the intergranular pores into tinier micropores, thereby reducing the reservoir physical properties. (3) More than 3% of Pompon-like authigenic chlorites may occupy the pore throats of sandstone reservoirs. (4) The feldspars and rock fragments in the sandstone reservoir adjacent to the source rock easily form numerous secondary dissolution pores and improve the reservoir quality. The present study reveals that large-areas of subaqueous distributary channel sand bodies with stable lateral distribution, high reservoir quality, and significant petrophysical characteristics are the best-qualities of reservoir within the early stage of retreating delta-front system.

Distance sampling survey effort to improve density estimates of northern bobwhite

AbstractDistance sampling from aerial platforms can provide researchers with precise and efficient density estimates for wildlife populations, particularly over large areas. The intensity of the distance sampling survey depends on the survey effort. Effort can be referred to as coverage, where transect spacing is determined by the observer's sightability distance of the object or animal. Managers and researchers in Texas often use helicopters to survey and collect data for northern bobwhite (Colinus virginianus) density estimates. For bobwhites, 100% coverage represents transect spacing of 200 m, assuming observers can cover out to 100 m on either side of the transects. Often surveys are conducted at 50% coverage or 400 m spacing to reduce cost. Still, the implications of lowering survey effort on the precision of density estimates are unknown, particularly in coverage prescriptions. We flew 2,641 km of line transects each December from 2014 to 2017 and detected 2,333 bobwhite coveys across 7,648 ha of rangeland on the San Antonio Viejo Ranch in Jim Hogg County, TX, USA. We conducted line‐transect distance sampling from a helicopter platform at 50 and 100% coverage and simulated results at coverage <50% using empirical data. Based on the results of simulated surveys at <100% coverage, surveying for bobwhites using helicopters with less than 50% coverage results in variable density estimates (wide 95% confidence intervals) and low precision (coefficient of variation >20%). Empirical surveys conducted at 50 and 100% coverage show little variation in density estimates between the 2 levels of coverage. However, when broken into substrata (areas less than ~1,000 ha), conducting surveys at 50% coverage resulted in <60 detections, which led to low precision in density estimates (coefficient of variation >20%). Our results are based on surveys conducted at the juncture of the Coastal Sand Sheet and Tamaulipan Thorn Scrub ecoregions in south Texas and need to be evaluated in other arid and semi‐arid rangeland systems.

Review and direct evidence of transgressive aeolian sand sheet and dunefield initiation

AbstractThe multiple hypotheses which exist to explain the initiation of transgressive aeolian sand sheets and dunefields, are reviewed and discussed. Direct evidence supporting many of these hypotheses is largely lacking. In South Australia, the Younghusband Peninsula coastal barrier extends ~180 km and predominantly comprises transgressive and parabolic dunefields. The 42 Mile Crossing area on the barrier is undergoing significant erosion at variable rates of 0.5 to 5.0 m/yr, and a new transgressive aeolian sand sheet has rapidly developed in ~1 year and is extending landwards at an average rate of 13 m/yr. This research provides unequivocal evidence that large‐scale shoreline and dunefield erosion does lead to the development of a new transgressive aeolian sand sheet (and eventual dunefield) phase thereby demonstrating an initiation mechanism that is likely linked to future sea level rise and climate change. We also show that the initiation process, and, in particular, the subsequent rate of sand sheet transgression occurs at an incredibly rapid rate (+100 m in 8 years).Plain Language SummaryCoastal sand dunes border many of the world's coastlines and are highly adapted to local climate and conditions. How coastal dunes transition from predominantly vegetated and stable systems to wind‐blown sand sheets and dunefields transgressing prior terrain is a research area of pressing relevance due to forecasts of sea level rise and climate change. The factors or triggers that are considered to initiate transgressive aeolian sand sheets and dunefields are reviewed. The formation and evolution of a new transgressive aeolian sand sheet phase triggered by large‐scale shoreline erosion in South Australia is presented. According to the results from historical and satellite images, local shoreline erosion began in the late 1970s and has continued at highly variable rates. We show that once the foredune was removed, the high scarp created by wave erosion of the relict, vegetated transgressive dunefield destabilized and was then eroded by wind processes leading to the rapid development of a transgressive aeolian sand sheet. The initiation and evolution of the sand sheet provides an excellent example of how dunefields might respond to future sea level rise and climate change.

A Study on the Inhomogeneous Sedimentation—Diagenesis– Reservoir Formation Mode of Deep Tight Marine Clastic Rock Reservoirs in the Silurian Xiaoheba Formation, Southeast Sichuan

By means of thin section authentication, physical characteristics analysis, scanning electron microscopy (SEM), X-ray diffraction, and vitrinite reflectance analysis, this paper, based on regional geological research achievements, studies the sedimentary facies and diagenesis of the southern and northern Silurian Xiaoheba Formation areas of Southeast Sichuan and their relationships with the physical characteristics of the reservoirs. The results indicate that, in the northern study area, the microfacies are mainly deposited in the underwater distributary main channel of the distal shallow-water delta front; while in the south, the microfacies include an estuary bar, sheet sand, distal bar, and interdistributary bay, which are far away from the main channel. The physical characteristics of sandstone are positively correlated with its particle sizes and thickness. The sand body of the underwater distributary main channel microfacies features high porosity, large crack opening, and good connectivity, followed by the sandstone of the estuary bar microfacies regarding those characteristics. By contrast, the physical characteristics of the sandstone reservoirs corresponding to the microfacies including the distal bar, sheet sand, and interdistributary bay are poor. The Xiaoheba Formation reservoir is located in the late diagenetic stage, with the reservoir space dominated by dissolved pores and micro-cracks; the diagenesis and pore evolution in the south are significantly different from those in the north. The Xiaoheba Formation reservoir in the northern area is far away from the carbonate rock platform of the same period in the south but is close to the center of hydrocarbon generation. Besides, the reservoir was sufficiently reformed by organic acid dissolution in the early-medium diagenetic stage, with only a little carbonate cementation formed in the early stage, while the cementation in the late diagenetic stage was weak. Therefore, the reservoir pores were relatively well preserved. However, the Xiaoheba Formation reservoir in the southern area has a large amount of calcite cement that was formed in the early diagenetic stage and the pores were blocked due to the influence of the carbonate platform. Since the dissolution was weak at the same time, the reservoir in the southern area is tight. Based on the understanding above, this paper established the inhomogeneous sedimentation–diagenesis–reservoir formation mode of the northern and southern areas of the study area.

Foredune responses to the impact of aggregate extraction in an arid aeolian sedimentary system

AbstractCoastal dunes have long suffered the effects of human interventions that have altered the landscape and operation of these ecosystems. Aggregate extractions have been shown to modify the biogeomorphological processes in aeolian sedimentary systems. The impacts associated to aggregate extraction include the reduction of available sediment and changes to the topography and vegetation patterns, thereby altering the sedimentary dynamics and limiting the recovery capacity of the dunefield. The aim of this article is to analyse the environmental effects produced by historical aggregate extraction in the foredune area of an arid aeolian sedimentary system (El Médano, Tenerife, Spain) through a study of the airflow dynamics and spatial distribution of vegetation, sediment and topographic changes. The methodology was designed with two temporal scales: (i) a long‐term approach which compares historical sources and current ones; (ii) a short‐term approach through experimental data collection to characterize the present functioning. For the latter, a field study was carried out in June 2021, collecting wind speed and direction data at a height of 0.50 m, sediment data (sand sheet thickness, grain size and sorting), and vegetation data (cover and species richness) at 40 sample points. The main results show that when the anthropic stress ceased the foredune did not follow a natural environmental pattern, and that the way it functions at the present time is determined by the changes induced by the aggregate extraction. Changes include alterations to the topography, the creation of a lagoon, and the generation of an aeolian deflation area and flow acceleration zones with the associated sand transport. This research contributes to an understanding of the environmental consequences of aggregate extractions on the foredunes of arid aeolian sedimentary systems and can enable the relevant authorities to make better‐informed decisions that help the management of these ecosystems.

PERKERASAN JALAN MENUJU ECO CAMP MANGUNKARSA PANTAI GRIGAK KELURAHAN GIRIKERTO,KAPANEWON PANGGANG,KABUPATEN GUNUNGKIDUL

Mangunkarsa Ecocamp is located on Grigak Beach, the village of Karang, Gunungkidul egency. It was built as the conservation area. However, there is almost no connection between Ecocamp and Karang village ; then it is required to build the roadway connecting those two locations. To meet the requirement, this public service programs attempted to provide the connecting roadway of those two locations. The roadway was designed with the length of 2,00 km and 3,00 meters width, and the surface course was designed as sand sheet pavement. The budget for material was supported by the government, and it was also provided by the local society for project execution . There were three steps to complete the program. The first step was location field-survey to make sure the site conditions, followed by soil sampling for subgrade design. The second was to perform laboratory experiment to verify physical and mechanical properties of soil, and it was followed with design the pavement , and the last was to execute the project. The laboratory experiment was done according to the standard, the pavement design was done according to the guidance issued by the Ministry of PUPR, and the project execution was done according to the basic standard. The results showed that the soil was met the requirement as subgrade, the thickness of the pavement was obtained 6 cm thick. The project execution was finished within 10 days

The lithostratigraphic Tidwell Member of the Morrison or Summerville Formations (Upper Jurassic)—who, what, where, when?

The Tidwell Member, a lithostratigraphic unit on the Colorado Plateau, has variously been referred to the Upper Jurassic Morrison Formation or the Upper Jurassic Summerville Formation. Its authorship has been ascribed to U.S. Geological Survey geologists Robert B. O'Sullivan or Fred Peterson. Because Peterson and O'Sullivan have different type sections, a resolution to authorship is needed. Both authors meet the minimum requirements for a new stratigraphic unit as given by the 1983 North American Stratigraphic Code under which Peterson and O'Sullivan operated. However, both authors also operated under the more restrictive Stratigraphic Nomenclature in Reports of the U.S. Geological Survey, which makes it clear that O'Sullivan used Tidwell Member informally, whereas Peterson made a formal proposal. Thus, Peterson is the rightful author and the type section is at Shadscale Mesa, Emery County, Utah. To resolve the issue of which formation the Tidwell Member belongs, its strata were examined across the northern Colorado Plateau in context with both the underlying marine Summerville Formation and the overlying terrestrial Salt Wash Member of the Morrison Formation. Meters-thick gypsum beds, one criterion for including the Tidwell Member in the Summerville, was found to be mostly restricted to the west side of the Colorado Plateau. Numerous low-angled anticlines at the top of the Summerville Formation are truncated beneath this gypsum, thus the gypsum beds cannot be part of the Summerville Formation. The unconformity marks the J-5 unconformity. Detailed analysis of the gypsum beds shows a complex origin indicative of smaller playa lakes rather than broad coastal sabkhas. The gypsum beds show an interfingering relationship with the overlying and lateral interbedded thin sandstone-siltstone-mudstone-limestone facies assemblage of the Tidwell Member. This relationship is interpreted as localized gypsum playa lakes that formed at the terminus of prograding fluvial fans from the Elko highlands to the west, with possible lesser contribution from the growing fluvial fan exiting from the Grand Canyon bight near the present-day Arizona-Nevada border. An isopachous map of the Tidwell Member supports this interpretation, and also indicates additional, less significant source areas to the southeast and east of the northern Colorado Plateau. A widespread tabular sandstone at the base of the Tidwell Member lateral to the gypsum facies known as Bed A, is interpreted to have originated mostly as a sand sheet analogous to the Selima Sand Sheet of the eastern Sahara or the sand sheet of the Gran Dieserto in Sonora, Mexico. The source of the sand is from the fluvial fans to the west. Similarities between the lithofacies of the contemporaneous Tidwell and Ralston Creek Members of the Morrison Formation indicates deposition under similar environmental conditions. This supports the inclusion of the Ralston Creek Member in the Morrison Formation as previously suggested, rather than as a separate formation.

Channel, dune and sand sheet architectures of a strait-adjacent delta, Rifian Corridor, Morocco

Abstract Sea straits are elongated zones where geographical constriction can amplify marine currents. Sediment deposits that formed in sea straits are relatively well studied and robust models of tidal strait depositional systems have been developed. However, models of strait-adjacent systems remain uncommon. In this study, we present such a model which is based on detailed outcrop descriptions of Miocene deposits that formed adjacent to the Rifian Corridor, an ancient sea strait that existed in what is now northern Morocco. The kilometre-scale outcrops at the Ben Allou locality (30 km north of Fez, Morocco) contain a succession of claystones, siltstones and sandstones that formed under a sea strait-adjacent process regime characterized by marine current constriction, tidal amplification and reduced wave activity. Detailed descriptions of the sandstone's sedimentary architectures reflect a development from mud drape-bearing sand sheets in the proximal regions of the system to stacked cross-strata and channel forms nearer to the basin depocentre. In the deep, distal reaches of this system, sediment grain sizes are generally fine (silt and clay) and are sparsely interbedded with sandy turbidites. These results confirm existing models which show that proximal strait-adjacent deposits tend to be tide dominated, and wave and fluvial influence can be overprinted by tidal processes. Some insights into the formation of tidal dunes are discussed. For example, it is shown that compound tidal dunes may not be preserved differently than simple tidal dunes, which is relevant for predicting sedimentary architectures and fluid flow properties of ancient tide-dominated successions.

Accumulation of windblown sand in impact craters on Mars

Abstract Loose sand, blown away from source regions by winds, is transported across Mars's surface into sand sheets and dunes and accumulates within topographic sinks. In the absence of plate tectonics, impact craters constitute a dominant sink for windblown sediments on Mars today. We analyzed the volume of all mapped eolian sands in martian craters >1 km in diameter to reveal spatiotemporal patterns of sediment accumulation on the planet's surface. We combined our results with global climate simulations, maps of depth to the ice table and dust cover, as well as lithologic and age information of the underlying geologic units, to better understand the controls on intracrater sand accumulation rates. We find that crater age, latitude, and lithology influence the accumulation rate of windblown sand and, notably, that it is enhanced in mechanically weaker substrates, high-latitude craters (suggesting that modern cryogenic processes may enhance sand production), and in Late Noachian and Early Hesperian craters (possibly hinting at increased erosion rates at that time).

Braided deltas and diagenetic control on tight sandstone reservoirs: A case study on the Permian Lower Shihezi Formation in the southern Ordos Basin (central China)

The Lower Shihezi Formation, situated in the south of the Chinese Ordos Basin, is a tight sandstone reservoir that is generally influenced by its sedimentary facies and diagenesis, corresponding to distinct petrophysical reservoir properties for each lithofacies type. The existing lithofacies types within the Lower Shihezi Formation were determined through observations in field profiles and drill cores that were combined with the analysis of logging data. Diagenetic processes and their effects were analyzed by using different methods, such as conventional thin section, cast thin section, and scanning electron microscope (SEM) analyses. The results of this contribution indicate that the Lower Shihezi Formation in the southern Ordos Basin is dominated by braided delta facies and locally developed lacustrine facies. During diagenesis of this studied formation, compaction and cementation led to a reduction in porosity with compaction probably forming the main factor. Existing cementation is mainly manifested in the form of clay mineral cements, siliceous and carbonate cements, and induced a somewhat lower pore reduction effect on the reservoir compared to compaction. Minor dissolution led to the break-down of rock fragments, feldspars, and other soluble minerals, and thereby may have caused a subsequent formation of secondary pores, thus effectively improving the reservoir property. Consequently, due to the compositional differences and corresponding unique diagenetic effects, the distributary channels and underwater distributary channels display the highest reservoir properties. These are followed by the mouth bars and sand sheets. The lowest reservoir properties are shown by the natural levee microfacies.

Krol Sandstone-black shale association of the Lesser Himalayan Neoproterozoic succession, Himachal Pradesh, India: An unexplored record of the hothouse aftermath

Citation of the inferred glacial diamictite-cap carbonate association, as the unequivocal evidence of the Snowball Earth hypothesis, fails to explain the absence of the sedimentary record of the intermediate period between the onset of thawing and the restoration of the optimum temperature for carbonate deposition. The Krol Sandstone-black shale association of the Lesser Himalayan Neoproterozoic succession, represents the initial phase of that hothouse aftermath. The black shale is the product of oceanic anoxia developed during the initial thawing phase of late Cryogenian glaciation. As the melting process continued, remobilization of some pre-existing aeolian sand sheet deposit, lying on the melting ice sheet in the upper shelf region, led to the accumulation of deeper shelf fans, the Krol Sandstone, over this black shale. The petrographic composition, detrital zircon age, and the palaeoflow directions, in conjunction with the available reconstructed paleogeography, suggest that the constituent sand particles of Krol Sandstone were possibly derived from a Late Neoproterozoic aeolian sand sheet of South Australia formed during the coldest phase of the late Cryogenian Elatina glaciation. These findings not only document the sedimentary record of the initial phase of the hothouse aftermath, but also open up a new line of evidence for paleogeographic reconstruction.

Loss of Coastal Wetlands in Lake Burullus, Egypt: A GIS and Remote-Sensing Study

Lake Burullus is the second largest lake at the northern edge of the Nile Delta, Egypt, and has been recognized as an internationally significant wetland that provides a habitat for migrating birds, fish, herpetofauna, and mammals. However, the lake is experiencing severe human impacts including drainage and conversion to agricultural lands and fish farms. The primary goal of this study was to use multispectral, moderate-spatial-resolution (30 m2) Landsat satellite imagery to assess marsh loss in Lake Burullus, Egypt, in the last 35 years (1985–2020). Iterative Self-Organizing Data Analyses (ISODATA) unsupervised techniques were applied to the Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager–Thermal Infrared Sensor (OLI–TIRS) satellite images for classification of the Lake Burullus area into four main land-use classes: water, marsh, unvegetated land surfaces (roads, paths, sand sheets and dunes), and agricultural lands and fish farms. The overall classification accuracy was estimated to be 96% and the Kappa index was 0.95. Our results indicated that there is a substantial loss (44.8% loss) in the marsh aerial coverage between 1985 and 2020. The drainage and conversion of wetlands into agricultural lands and/or fish farms is concentrated primarily in the western and southern part of the lake where the surface area of the agricultural lands and/or fish farms doubled (103.2% increase) between 2000 and 2020. We recommend that land-use-policy makers and environmental government agencies raise public awareness among the local communities of Lake Burullus of the economic and environmental consequences of the alarming loss of marshland, which will likely have adverse effects on water quality and cause a reduction in the invaluable wetland-ecosystem services.

A multi-faceted approach to determine the provenance of Eocene converging deltas, Dongying Depression, Bohai Bay Basin (E China)

The middle interval of the 3rd member of the Shahejie Formation (Es3m) of the Dongying Depression accumulated as part of a system of converging deltas derived from multiple source regions. These complex deposits that are targets of oil/gas exploration and development in eastern China have yet to be studied at the level of detail necessary to elucidate their origin and sedimentary evolution. This paper relies upon a multi-faceted investigation of the Es3m depositional system that includes analysis of clastic compositions, heavy mineral assemblages and mineral ratios, and clay mineralogy to illuminate the provenance of Es3m deposits. Compositional data is obtained by analysis of logs and core material. Our results reveal that Es3m deposits were derived from source regions to northeast (Qingtuozi Uplift and Chenjiazhuang Uplift) and southeast (Weibei Uplift and Guangrao Uplift) of the Dongying Depression. Each source region shed sediment to the study area that accumulated in distributary channels, interdistributary swamps, natural levees, mouth bars, underwater distributary channels, sand sheets and underwater distributary interchannel regions. Moreover, lacustrine shore and semi-deep lacustrine deposits that include turbidites are recognized in the studied succession. The separate deltas appear to have converged approximately halfway through the depositional history of the Es3m Formation. Convergence continued in association with delta progradation, forming overlapping sand bodies that are targets of hydrocarbon exploration.

Caracterização e evolução da história natural da zona costeira de Tibau, Grossos e Areia Branca/RN

Geodiversity encompasses several aspects; pedological, hydrological, geological among others, of which we will deal with the geomorphological component, which acts as a record of different evolutionary processes throughout the Earth's natural history. Within this context, the present work aims to define the elements that occurred on the coast of Tibau, Grossos and Areia Branca/RN, serving as basis for undertanding the morphology of the area, serving as a basis for the further study or geodiversity. Recovering natural history, from the formation of the Potiguar Basin, with the separation of the Gondwana Super Continent, to the most recent morphological changes, bringing the constitution and age of constitution of the geological formations, the Tibau Formation, Jandaíra and Barreiras. As for the features, it was identified as barcanoid dunes(active and inactive dunes and sand sheets), marine deposits (Beach rocks), as well as alluvial deposits associated with the Apodi-Mossoró estuary , coastal plains, cliffs and association with coastal plateaus and presence of a reef line (Beach rocks).

Sedimentary and diagenetic characteristics of the Z21 field in the Huizhou depression, Pearl River Mouth basin, South China Sea

The Huizhou Depression in the Pearl River Mouth basin has prospective hydrocarbon potential, with Miocene sandstones as its main oil and gas-bearing reservoir. The sandstones in Miocene formation of the Z21 offshore oil–gas field composed of medium-grained, moderately sorted subarkose and lithic arkose. In this study, a total of six depositional lithofacies, namely Massive fine- to medium-grained sandstone (Sm), ripple cross-laminated fine-grained sandstone (Sr), parallel-laminated siltstone and claystone (Fl), lenticular siltstone (Sl), parallel-bedded fine-grained sandstone (Sp), wavy laminated siltstone (Sw), and two depositional systems, namely nearshore sand bar (SB) and sand sheet (SS) were identified based on core observations and seismic study. Distributions of the porosity (13.9%) and permeability (35.8 mD) reveal that the Miocene sandstones have characteristics of low porosity and low permeability, with high heterogeneity. The sedimentary system, primary texture and diagenesis jointly control the reservoir quality. Sandstones with sand bars as well coarse-grained tend to exhibit a higher quality. Mechanical compaction and calcite (average 6.81%) cementation are the major determinants to reductions in porosity and permeability. The total clay minerals (average 5.27%) generally lead to reduction of porosity, whereas chlorite coatings and illite within a certain content range may enhance the preservation of porosity in eodiagenesis. Dissolution of feldspar and debris contribute significantly to improving the reservoir quality.

Diagenetic evolution of the lower Yaojia Formation of Songliao Basin, China: Impact on reservoir quality

The oil-bearing layer in the first member of the Upper Cretaceous Yaojia Formation (K2y1) in the middle of the Changling Sag of the southern Songliao Basin, northeast China, has low-permeability and is deemed to be an unconventional reservoir. Therefore, better evaluation of reservoir quality and related controlling factors are crucial for the reduction in exploration risk and sustainable development. The current study integrates diagenesis, sequence stratigraphy, and sedimentary facies to decipher their influence on reservoir quality using core and thin section observations, X-ray diffraction, scanning electron microscopy, fluid inclusion, and carbon and oxygen isotope analyses. The K2y1 is composed of shallow delta sediments of transgressive system (TST) and lowstand system (LST) tracts. The depositional microfacies of the sandstones include TST deltaic front underwater distributary channels and sheet sands, and LST deltaic plain distributary channels, distributary channel intersections, and crevasse splays. The sandstones are dominantly fine-grained moderately sorted feldspathic litharenites and lithic arkoses with silt. Early diagenetic events included compaction, development of smectite, and alteration of feldspar and kaolinite whereas mesogenetic alteration included feldspar dissolution, precipitation of quartz and carbonate cements, and clay mineral alteration. The reservoir quality of the K2y1 sandstones is generally poor, exhibiting variations among different deltaic depositional facies within the LST and TST. The (underwater) distributary channel (intersection) sandstones, particularly those of the LST, have relatively higher reservoir quality owing to their larger grain size, better sorting, lower carbonate cement content, mixed-layer I/S and illite, and greater occurrence of chlorite.

Collapse wedges in periglacial eolian sands evidence Late Pleistocene paleoseismic activity of the Vienna Basin Transfer Fault (western Slovakia)

Studies of seismically triggered deformations in the depositional record contribute significantly to our knowledge of earthquake recurrence over geological time. This paper describes soft sediment deformation structures preserved in a periglacial Upper Pleistocene succession of eolian sand in the eastern Vienna Basin, Central Europe. The strata were formed dominantly by wind ripples migrating across a sand sheet, less frequently by deposition of fine-grained sand and silt from suspension during decreased wind speed and by small-scale eolian dunes. Most prominent deformations observed are collapse wedges, which are interpreted as being formed along dilatational fractures. Further detected deformations include chaotically disturbed strata, folded strata, and a pop-up structure caused by sliding. The tensile fractures are oriented systematically in a prevailing N–S direction, perpendicular to the W–E extension suggested for the transtensional Vienna Basin Transfer Fault, which underlies the study area. Repeated seismic shock is identified as the trigger of the deformations. The mechanism of deformation implies some degree of cohesion within the deformed strata, and this may be attributed to seasonal frost and the presence of vadose water within the upper levels of the sediment. These deformations appear periodically, in 25 distinct horizons of strata internally deformed by collapse wedges, and in 40 horizons if deformation both by collapse wedges and/or chaotically disturbed beds is considered. The vertical distribution of deformations allowed the calculation of the recurrence periods of earthquakes with the use of a Bayesian age-depth model; this, in turn, was based on seven OSL ages. The calculation yielded mean recurrence periods of ca. 100 years, though this figure is biased by a relatively high degree of uncertainty in the dating and in the age-depth model. Even with this caveat, the present study reveals the underexplored potential of periglacial eolian deposits to preserve paleoseismological signals.