Quartz Sand Grains Research Articles

Imprint of late Pleistocene continental processes visible in ice-rafted grains from the central Arctic Ocean

Ice-rafted quartz sand grains of sediment samples representing marine isotope stages (MIS) 3 and 4 from the Lomonosov Ridge, Arctic Ocean, are here analysed with a scanning electron microscope (SEM) to characterise processes in the sediment source area. The microtextural characteristics of the grains were observed and their microtexture frequencies calculated. Specific sets of microtextures were identified and classified (Group I–III) using principal component analysis (PCA) and cluster analysis. The statistically analysed microtextural data were used to identify signals of continental processes that operated during the late Pleistocene (MIS 4 to MIS 3) in the Eurasian Arctic. The microtextures of Group I generally formed as a result of prolonged fluvial/alluvial or aeolian transport. The glacial microtextures of Groups II and III indicate subglacial conditions and transport. Based on the data, two principal components seem to characterise late Pleistocene continental environmental conditions – glacial and non-glacial. There is a signal of non-glacial continental processes in the ice-rafted grains at around 62, 64 and 67 ka ago. A signal of subglacial processes was observed in the grains at around 26, 34, 42 and 45 ka and, concurrent with non-glacial, at around 62 and 64 ka ago. We suggest that these signals in MIS 4 sediments are related to deglaciation with an increased supply of glacial sediment to the Arctic Ocean, whereas during MIS 3 they were probably related more to iceberg calving from the oscillating Barents-Kara ice sheet.

Bulbobaculites gorlicensis n. sp. – a new agglutinated foraminifera from Eocene of flysch Carpathians

A new foraminiferal species, Bulbobaculites gorlicensis n. sp., is described from the Bartonian (Middle Eocene) succession of the Hieroglyphic beds deposited in the Silesian Basin, Outer Carpathians (South Poland). It occurs in association with deep-marine bathyal and abyssal assemblages dominated by agglutinated forms. The test of Bulbobaculites gorlicensis is relatively large, free, and elongated, consisting of 3-4 spherical chambers quickly increasing in size and composed of coarse quartz sand grains. The initial part of the test is in low trochospiral coil, terminally uniserial with terminal aperture on the last, largest chamber.

Influence of activation of quartz grain surface on efficiency of the process of processing the quartz sand grains with fluoride technology

The influence of grinding the initial quartz sand on the degree of activation of the sand-grain surface during processing using a fluorinating reagent has been studied. Using the method of the synchronous thermal analysis, the technological parameters of producing ammonium hexafluorosilicate using mixtures of different fractions of sand at temperatures in the range of 25–400°C were examined. The investigation of intermediate phases, formed during the thermogravimetric experiment was carried out with the X-ray analysis. It was established that formation of ammonium hexafluorosilicate with crushed quartz sand occurs at temperatures of 30–40°C lower than the source conditions.

Stratigraphy and optical dating of Pleistocene coastal deposits in the Port Campbell australite strewn field, SW Victoria

Alluvial-channel and overlying eolian deposits exposed in coastal cliffs in the Port Campbell australite (Australian tektite) strewn field, SW Victoria, were studied stratigraphically and dated by optically stimulated luminescence (OSL) for quartz sand grains to illuminate the occurrence of australites in this area. The channel deposits, termed the Dog Trap Bay Sand, yielded OSL ages from 420 ± 40 to 230 ± 15 ka for four sites, and the two eolian units OSL ages of 203 ± 16 and 93 ± 11 ka. The ages support field evidence that, contrary to the conclusions of a previous study by others, the channel deposits are stratigraphically distinct from and much younger than the Pliocene Hanson Plain Sand, which forms a regionally extensive system of marine strandlines to the north and NE of Port Campbell. The OSL ages show some preference for times of negative temperature anomalies marking the last four glacial periods of the Middle and Late Pleistocene as indicated by ice-core data from Antarctica. Eolian and at least some alluvial deposition evidently occurred when sea-level was low and rivers extended across the exposed continental shelf. Others have suggested that the Dog Trap Bay Sand contains rare australite fragments in situ. However, these occurrences may have resulted from reworking of sandy material, with the australites possibly derived from overlying younger units known to contain numerous specimens. The OSL ages imply that a discrepancy of ca 350 ka or more exists between the apparent stratigraphic occurrence, as distinct from the terrestrial age, of australites in the Port Campbell strewn field and the australite 40Ar/39Ar age of 770 ± 20 ka. Stratigraphic evidence in this area for the terrestrial age of australites is inconclusive.

Surface microtextures of ice-rafted quartz grains revealing glacial ice in the Cenozoic Arctic

Ice-rafted grains of the central Arctic Ocean sediments provide a reliable proxy for Arctic palaeoenvironments and climatic conditions that prevailed at the time of their deposition. To understand ice involvement and implications for environmental advancement, it has proven necessary to ascertain whether these detrital grains were rafted on glacial ice or sea-ice. Surface microtexture identification allows grain differentiation based on the processes and conditions in its environmental provenance. Here, quartz sand grain surface microtextures are used to detect glacially crushed and reworked grains from the Lomonosov Ridge sediments obtained by the Integrated Ocean Drilling Program Expedition 302 (Arctic Coring Expedition). The data show that the most frequent distributions of glacial grains were deposited at the middle–late Miocene and during the Pliocene and early Pleistocene. Especially, the middle Miocene climatic cooling and the presence of glacial ice are well indicated at ~13.5Ma sediment grains. Earliest finding of the high frequency occurrence of glacigenic microtextures represents the age of ~56Ma. This first sedimentological evidence for the late Palaeocene glacial ice supports the existing hypothesis of ephemeral polar glaciations during times of marked global warmth. However, due to lack of uninterrupted sediment recovery and non-continuous nature of sampling, the glacially influenced samples recovered here should be treated as an estimate of the minimum frequency of glacier appearance in the Arctic.

Subterranean transport and deposition of quartz by ants in sandy sites relevant to age overestimation in optical luminescence dating

An artificial layered sandy site was created using a combination of native sand and colored sand (3 parts native uncolored quartz, 1 part colored quartz) in Apalachicola National Forest near Tallahassee, Florida. Twelve layers of sand, each 1 by 1 m in horizontal extent by 10 cm in thickness were emplaced to a depth of 2 m followed by implantation at the surface of a Florida harvester ant (Pogonomymrex badius) colony (the lower two layers were 50 cm thick). The colony excavated a nest, and after 7 months, the sand layers were excavated to the base to test the hypothesis that sand grains were moved upward within the ant nest without reaching the surface. The ants penetrated 11 of the 12 colored layers reaching a depth of 130 cm. Thirty nine sticky-acetate peels of ant chamber floors were collected and colored sand grains were counted under a microscope. More than 16,000 grains were identified in layers that did not originally host them. Of these, more than 80% were unambiguously moved upward. This means that possibly as many as 54,000 upwardly mobile grains were present (ratio of 3:1 uncolored to colored). In relation to optical luminescence (OSL) dating, this means that grains that would not have been optically zeroed by transport to the surface (defined here as subterranean-transported) were present in abundance, and that if the site was ancient, there would have been found many grains that were older than the layers they presently reside in, even if only one colony of harvester ants had disturbed the layers. This is in addition to the fact that backfilling of chambers and tunnels may contribute even more significantly to the presence of a subterranean-transported component of an OSL sample. We conclude that ants can significantly affect the age distributions in sandy archaeological sites. Multiple examples of such disturbances have been documented in the literature. Most relevant to our results are recent studies of the OSL chronology of Pre-Clovis-age and Palaeoindian age archaeological sites in sandy environments in North America that may have been compromised by ant bioturbation of quartz sand grains. Here we have examined in detail the potential effects of one episode of ant nest-building on the age overestimation of affected sediments. From this we found that as few as 12 episodes of bioturbation involving backfilling of chambers in the same volume of sand could lead to the presence of 1 contaminant grain per 50 grains of sample.

Dust accumulation in the Carpathian Basin during marine isotope stage 2 and its possible climatic effects

Micromorphology of quartz sand grains is used to reconstruct processes occurring in the glacial environment and to distinguish the latter from other environments. Two processes dominate in the glacial environment, i.e., crushing and abrasion, or a combination thereof. Their effect is a wide range of microstructures on the surface of quartz grains, e.g., chattermarks, conchoidal fractures and multiple grooves.However, the periglacial environment also effectively modifies the surface of quartz grains. The active layer of permafrost is considered to have a significantly higher contribution to the formation of crushed grains and the number of microstructures resulting from mechanical destruction (e.g., breakage blocks or conchoidal fractures), as compared to deposits which are not affected by freeze–thaw cycles. However, only a few microstructures are found in both environments. At the same time, there are several processes in subglacial environments related to freeze–thaw cycles, e.g., regelation, congelation, basal adfreezing, and glaciohydraulic supercooling. Most likely, therefore, the role of the glacial environment in the destruction of quartz grains has been misinterpreted, and consequently the conclusions regarding environmental processes drawn on the basis of the number of crushed grains and edge-to-edge contacts are erroneous.

Investigation of quartz grain surface textures by atomic force microscopy for forensic analysis

This paper presents a study of quartz sand grain surface textures using atomic force microscopy (AFM) to image the surface. Until now scanning electron microscopy (SEM) has provided the primary technique used in the forensic surface texture analysis of quartz sand grains as a means of establishing the provenance of the grains for forensic reconstructions. The ability to independently corroborate the grain type classifications is desirable and provides additional weight to the findings of SEM analysis of the textures of quartz grains identified in forensic soil/sediment samples. AFM offers a quantitative means of analysis that complements SEM examination, and is a non-destructive technique that requires no sample preparation prior to scanning. It therefore has great potential to be used for forensic analysis where sample preservation is highly valuable.By taking quantitative topography scans, it is possible to produce 3D representations of microscopic surface textures and diagnostic features for examination. Furthermore, various empirical measures can be obtained from analysing the topography scans, including arithmetic average roughness, root-mean-square surface roughness, skewness, kurtosis, and multiple Gaussian fits to height distributions. These empirical measures, combined with qualitative examination of the surfaces can help to discriminate between grain types and provide independent analysis that can corroborate the morphological grain typing based on the surface textures assigned using SEM. Furthermore, the findings from this study also demonstrate that quartz sand grain surfaces exhibit a statistically self-similar fractal nature that remains unchanged across scales. This indicates the potential for a further quantitative measure that could be utilised in the discrimination of quartz grains based on their provenance for forensic investigations.

Quartz OSL sensitivity as a proxy for storm activity on the southern Brazilian coast during the Late Holocene

Natural cycles of irradiation during burial and bleaching due to solar exposure during transport increase the Optically Stimulated Luminescence (OSL) sensitivity of quartz sand grains. The relationship between the OSL sensitivity and sediment transport allows to discriminate quartz sand grains with different depositional histories. In this paper, we evaluate the variation of OSL sensitivity in quartz grains deposited during the progradation of the Ilha Comprida barrier on the southern Brazilian, coast. Changes in sand sensitivity recorded by barrier growth since 6 ka ago are controlled by the variation in the proportion of low versus high sensitivity quartz grains. Low sensitivity grains with short sedimentary history are supplied by the Ribeira de Iguape River and reach the barrier through southward alongshore currents during fair weather conditions. Storm conditions shift the alongshore currents to northeast and permit the transport of high sensitivity grains with long sedimentary history from distal southern coastal sectors to the barrier. Therefore, the input of distal sediments for the Ilha Comprida barrier depends on the frequency and intensity of storms. Thus, the OSL sensitivity can be used as proxy for storm activity. The variation of OSL sensitivity through time indicates that the Ilha Comprida barrier changed from a relatively stable to an unstable storm pattern around 2 ka ago. Periods with increased storm activity peaked around AD 500, AD 1500 and AD 1850, approximately on the boundaries of the Medieval Climate Anomaly and the Little Ice Age.

Microcrystalline Quartz Generation and the Preservation of Porosity In Sandstones: Evidence from the Upper Cretaceous of the Subhercynian Basin, Germany

Abstract Formation of microcrystalline quartz formation has proven to be effective at preserving porosity in deeply buried sandstone petroleum reservoirs, typically cemented by syntaxial quartz cement. There remains much uncertainty about what controls the growth of microcrystalline quartz and how it prevents syntaxial quartz overgrowths. Here, the Cretaceous Heidelberg Formation, Germany, provides a natural laboratory to study silica polymorphs and develop an understanding of their crystallography, paragenetic relationships, and growth mechanisms, leading to a new understanding of the growth mechanisms of porosity-preserving microcrystalline quartz. Data from scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) data illustrate that porosity-preserving microcrystalline quartz cement is misoriented with respect to the host grain upon which it grows. In contrast, ordinary quartz cement grows in the same orientation (epitaxially) as the host quartz sand grain, and typically fills pore spaces. EBSD and TEM observations reveal nanofilms of amorphous silica (~ 50–100 nm in thickness) between the microcrystalline quartz and the host grain. The microcrystalline quartz is interpreted to be misoriented relative to the host grain, because the amorphous silica nanofilm prevents growth of epitaxial quartz cement. Instead, the microcrystalline quartz is similar to chalcedony with perpendicular to the growth surface and c axes parallel with, but randomly distributed (rotated) on, the host quartz grain surface. Development of pore-filling quartz growing into the pore (in the fast-growing c-axis direction) is thus inhibited due to the amorphous silica nanofilm initially and, subsequently, the misoriented microcrystalline quartz that grew on the amorphous silica.

Bedrock versus superficial deposits in the Swiss Jura Mountains: what is the legitimate soil parent material?

ABSTRACTSoils are generally considered to be the result of in situ weathered products of geological substrata. Nevertheless, the Earth's surface is mainly composed of superficial deposits made of sediments reworked during periods of climate instability (glaciation, aridification, flooding, etc.). But to what extent do these deposits influence present‐day soil development and/or lessen the contribution of the geological substratum? In the Swiss Jura Mountains, characterization and distribution of superficial deposits along a toposequence are used in order to decipher the polygenic sources of soil parent materials and question the importance of lithodependence in soil development. The in situ weathering material and the allochtonous deposits are discriminated through analysis of mineralogical composition, grain size distribution of the soil mineral fraction, and multivariate statistical treatment. As expected, calcite is dominant in the autochonous mineral phase, leading to high pH values in deep soil layers. However, the mineralogical composition of the surficial deposits is made of local mineral components mixed with allochtonous aeolian deposits. This exogenous material is dominated by quartz and phyllosilicates, and is reflected by low pH values in soil surficial horizons. The grain size distribution curves of the insoluble residue from bedrocks are unimodal and dominated by fine loam and clays. In contrast, surficial deposits display polymodal curves, demonstrating the contribution of various aeolian episodes and/or sources. Analysis of the surface texture of quartz sand grains shows glacial marks intersected by aeolian shock marks, indicating the posteriority of wind transportation. Loess material originates from Alpine moraines of the Swiss Plateau and is mixed with deposits originating from more proximal Jura moraines, diluting the Alpine signature. Consequently, the soil development does not follow the expected and conventional decalcification process, but is directly influenced by the origin of the primary sediments (even when present only in small amounts) and their evolution. Copyright © 2012 John Wiley & Sons, Ltd.

Automated Texture Recognition of Quartz Sand Grains for Forensic Applications*

Quartz sand surface texture analysis has been automated for the first time for forensic application. The derived Basic Image Features (BIFs) provide computer-generated texture recognition from preexisting data sets. The technique was applied to two distinct classification problems; first, the ability of the system to discriminate between (quartz) sand grains with upturned plate features (indicative of eolian, global sand sea environments) and grains that do not exhibit these features. A success rate of grain classification of 98.8% was achieved. Second, to test the ability of the computer recognition system to identify specific energy levels of formation of the upturned plate surface texture features. Such recognition ability has to date been beyond manual geological interpretation. The discrimination performance was enhanced to an exact classification success rate of 81%. The enhanced potential for routine forensic investigation of the provenance of common quartz sand is indicated.

Facies and provenance analysis of Paleogene‐age alluvial conglomerates from the northern part of the Mesta Basin, SW Bulgaria

The Mesta Basin in southwest Bulgaria is a graben that contains a Paleogene‐age siliciclastic and volcaniclastic succession deposited in alluvial and fluvial settings. A sedimentological analysis has shed light on conglomerate provenance, and the links between deposition and tectonic setting. Petrographical and chemical analysis of conglomerate clasts and matrix from the Dobrinishka, Gradinishka, Osikovo (or Osenovo) and Zlataritsa formations reveal both local, and more distal source provenance ages. The basal conglomerates are subdivided into three types, a lower and upper polymictic and a middle granitic conglomerate type. Petrographical and chemical analysis reveals granite, gneiss and amphibolite clasts that were sourced from the Sidironero–Mesta Unit of the Middle Allochthon of the Rhodope Metamorphic Complex, and the Rila–Rhodope Batholith to the east of the basin. Cathodoluminescence analysis of quartz sand grains reveals an increased input of red‐ and violet‐luminescent volcanic grains. Volcanic quartz in the oldest conglomerates indicates a hitherto unknown early (pre‐Oligocene) phase of volcanic activity in the vicinity of the Mesta Basin. The conglomerates were deposited in association with movement on the Ribnovo low‐angle normal fault during the Late Eocene, creating subsidence and the development of considerable accommodation space. The establishment of a fluvial environment followed subsequent Oligocene‐age volcanic activity. Copyright © 2012 John Wiley & Sons, Ltd.

A Sediment Sink for Possible Tertiary Aeolian Sediment in Galway Bay, Western Ireland

There is substantial evidence to suggest that Ireland during the Tertiary Period was subject to a period of intense chemical weathering. Two exposures illustrating this environment in western Ireland are described, adding to the known examples of this type of weathering elsewhere in Ireland. The surface features of quartz sand grains may be used to distinguish the environments through which they have passed during transport and deposition. Quartz grain surface features photographed by a scanning electron microscope are described from a sediment facies, ~ 10,000 years old, retrieved from cores taken from beneath the floor of Galway Bay. Many of these show the action of glacial activity by characteristic fracture patterns, as might be expected in Holocene sediment in an Irish context. Some of the grains, however, show features that suggest a prior aeolian component to their transport history. These grains are compared with quartz grains previously described and with the product of Tertiary Period weathering recovered from a sand pit at Pollnahallia, Co. Galway. Similarities suggest that some of the sand grains found at depths of ~2-5m beneath the substrate surface of Galway Bay may have originated from chemical weathering and aeolian transport during the late Tertiary Period and then been reworked in glacial and subsequent deltaic environments. Introduction limestone. The stratigraphy at this locality comprises a 5m-thick organic deposit (lignite) containing a Vestiges of Tertiary landscapes and sediments are Pliocene pollen assemblage, possibly up to the Plio still visible in Ireland, despite the subsequent eroPleistocene transition. The lignite is overlain by ~ 8m sional processes of the Pleistocene glacial advances of white silica sand, itself overlain by Pleistocene and retreats. Over 30 years ago, Mitchell (1980) lodgement till. Further details of the geology were proposed that some landforms of central and southpresented in Coxon et al. (2005) and Coxon (2005). ern Ireland were of Tertiary origin. In western Such evidence from western Ireland suggests a Ireland, Coxon (2005) has described buried tors in period during the Tertiary of intense chemical a granite terrain at Gowlaun East in Connemara. weathering of granite and possibly the Dalradian The tors are separated by weathered granite and a schists and metaquartzites of Connemara to pro palaeosol containing pollen that indicates dates of duce quartz-rich sands such as those fortuitously 2.6-5 million years ago (Coxon 2001a). At Pollnapreserved in the gorge at Pollnahallia. Such intense hallia, near Headford, Co. Galway (Fig. IB), Coxon chemical weathering has been recorded elsewhere, and Flegg (1987) described a quartz-rich sand for example, Scotland, during the Tertiary (e.g., Hall deposit situated in gorges and caves in Carboniferous 1991 ; Knox 2002). Irish Journal of Earth Sciences 30 (2012), 41-47 © 2012 Royal Irish Academy doi: 10.3318/1 JES.2012.30.41 41 This content downloaded from 207.46.13.156 on Sat, 10 Sep 2016 05:26:56 UTC All use subject to http://about.jstor.org/terms 42 Irish Journal of Earth Sciences (2012)

Activation of Quartz Grain Surface with Chloride Ions

Alteration of technological and optical states of glass activated with chloride ions, entered to the surface of quartz sand and quartz grain by way of sodium chloride was investigated in the article. Concentration optimum of activating agent was determined.

Experimental verification of the fracture density and shear‐wave splitting relationship using synthetic silica cemented sandstones with a controlled fracture geometry

ABSTRACTWe present laboratory ultrasonic measurements of shear‐wave splitting from two synthetic silica cemented sandstones. The manufacturing process, which enabled silica cementation of quartz sand grains, was found to produce realistic sandstones of average porosity 29.7 ± 0.5% and average permeability 29.4 ± 11.3 mD. One sample was made with a regular distribution of aligned, penny‐shaped voids to simulate meso‐scale fractures in reservoir rocks, while the other was left blank. Ultrasonic shear waves were measured with a propagation direction of 90° to the coincident bedding plane and fracture normal. In the water saturated blank sample, shear‐wave splitting, the percentage velocity difference between the fast and slow shear waves, of <0.5% was measured due to the bedding planes (or layering) introduced during sample preparation. In the fractured sample, shear‐wave splitting (corrected for layering anisotropy) of 2.72 ± 0.58% for water, 2.80 ± 0.58% for air and 3.21 ± 0.58% for glycerin saturation at a net pressure of 40 MPa was measured. Analysis of X‐ray CT scan images was used to determine a fracture density of 0.0298 ± 0.077 in the fractured sample. This supports theoretical predictions that shear‐wave splitting (SWS) can be used as a good estimate for fracture density in porous rocks (i.e., SWS = 100εf, where εf is fracture density) regardless of pore fluid type, for wave propagation at 90° to the fracture normal.

Micro-CT and Wettability Analysis of Oil Recovery from Sand Packs and the Effect of Waterflood Salinity and Kaolinite

An image-based approach was developed by combining microtomography with electron microscopy and contact angle goniometry to determine the pore-scale distribution of crude oil in plugs after waterflooding and shed light on the molecular-scale mechanisms responsible. The approach was applied to a model rock comprising a pack of quartz sand grains without or with a preapplied lining of kaolinite, imaged prior to and after capillary-driven oil recovery by flooding with a model brine of high or low salinity. The presence of kaolinite increased residual oil and reversed its brine dependence, with high-salinity flooding giving greatest recovery from the clean sand and least recovery from kaolinite-coated sand. These two extremes tended to exhibit the most connected residual oil clusters, while low salinity gave smaller blobs, to the detriment or advantage of oil recovery. Low-salinity flooding in secondary or tertiary recovery mode resulted in comparable oil residuals in kaolinite-coated sand. Surface analysis o...

Pre-requisites, processes, and prediction of chlorite grain coatings in petroleum reservoirs: A review of subsurface examples

Deeply buried reservoirs containing chlorite-coated quartz sand grains commonly have higher than expected porosity and permeability, although prediction of such positive anomalies still remains elusive. A total of 54 published examples based on information and data from 62 scientific papers was collated. Quantification of some of the most common parameters including depositional environment, age and latitude of sand deposition, effect on reservoir quality and chemical composition of chlorite is presented.The dataset indicates that chlorite-coats are found in sandstones deposited in a range of depositional environments, but most commonly occur in delta-related environments (44%), with fluvial environments the second most common (19%). Age relationships indicate that there is an overall exploration bias in published examples, with chlorite-coats becoming increasingly common through time. The latitude at the time of deposition of sands with chlorite-coats is wide (60°N–60°S), and indicates that temperate and tropical climates are important for the generation of this clay mineral. Chlorite can have a variable effect on reservoir quality, but is typically positive. Iron-rich chlorites occur overwhelmingly in coastal environments, while mixed iron- and magnesium-rich chlorites are principally found in marine and terrestrial sandstones.Analysis of these factors suggests that hinterland geology, basinal soil development and geochemical weathering, and proximity to river systems are essential to the formation of chlorite precursor phases. These characteristics have been combined to define situations where chlorite-coats were more likely or more unlikely to form. These parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite-coated sandstones.

Quantitative 3-dimensional Image Analysis of Mineral Surface Modifications—Chemical, Mechanical and Biological

Three principally different mechanisms contribute to the wear-down process of mineral aggregates in sedimentary environments: (1) mechanical abrasion by forces of wind and water and by floating or saltating neighbouring grains, (2) chemical attack and dissolution by fluids, and (3) physical bioerosion and chemical biocorrosion. It is however, difficult to attribute the specific surface changes to specific environments and processes. Quartz sand grains from subaerial and subaquatic environments were analysed by atomic force microscopy (AFM) for traces of natural and experimental aeolian, aquatic and biological wear-down processes. Quantitative topographical parameters of surface alterations were extracted from topography data by non-linear methods derived from digital image analysis. These parameters were examined by multivariate statistic, yielding three well-distinguishable groups. Morphological surface alterations dominated by subaerial, subaquatic and by biological impact could be differentiated. The method may also be used for the detection of aeolian, subaquatic, and biological modification of sedimentary grains and rock surfaces in extraterrestrial environments, and for assessment of environmental damage on monuments and buildings.

Dynamics of the Barents-Kara ice sheet as revealed by quartz sand grain microtextures of the late Pleistocene Arctic Ocean sediments

During the entire Quaternary, ice sheets advanced and retreated across the circum-Arctic margins in a series of climate related glacial-interglacial cycles. It is critical to obtain evaluation of the nature of initiated glaciers at the Arctic margins after the pronounced interglacial periods. In this study this will be done by inferring from glacially generated quartz sand grain surface microtextures and related sedimentology extracted from the central Arctic Ocean sediments. These microtextures can be correlated with the generation and fluctuations in the extent of the late Pleistocene Eurasian Ice Sheet i.e. Barents-Kara Ice Sheet. The central Arctic Ocean sediments in the Lomonosov Ridge, having been deposited after the late Pleistocene interglaciations and having had no internal hiatuses, provide an excellent time window for usage of quartz sand grain surface textures for evaluating possible evolving glaciers and continental ice sheets. This is based on the fact that iceberg and sea-ice transported quartz sand grains and their mechanically formed surface textures, created under high cryostatic stress, are diagnostic for glacier thickness and dynamics having been existed in sediment source areas. Sand-sized quartz grains in deep marine sediments favour iceberg or sea-ice transportation with characteristic content of microtextures formed prior this transportation. The sand grain surface microtextures and their frequencies of the selected submarine Lomonosov Ridge sediments during Marine Isotope Stage (MIS) 5 to MIS 3 are analysed using a scanning electron microscope (SEM). Coring during the Arctic Ocean 96 expedition (core 96/12-1pc) provided alternating clay to silty clay sediments which are characterised by prominent silt to sand-size containing intervals. The specific glacial crushing and high cryostatic stress generated features, such as high angularity, conchoidal fractures, steps and sub-parallel linear fractures, were observed from quartz sand grain surfaces. Continental ice generation and extent are evident soon after the Eemian interglaciation and the following MIS 4 stage shows the highest frequencies of glacigenic microtextures. The microtexture generation under high cryostatic pressure underneath ice more than 1 km thick, can be taken as concurrent signal of the temporal expansion of the northernmost continental ice sheets, which could easily have reached the shelf break of the Barents, Kara and western Laptev seas during that time.