昌黎海岸风成沙丘砂组构特征及其与海滩砂的比较

对昌黎海岸沙丘砂进行薄片统计,重砂矿物分析,电镜扫描,粒度分析及与海滩砂的对比研究发现,沙丘砂在物质组成、颗粒形态、石英砂表面结构特征和粒度特征方面均继承了海滩砂特征,不过,海滩砂中也有沙丘砂的某些特征,反映了两者沉积的混合。这是由于向岸风和离岸风共同作用的结果。     

Provenance of coastal dune sands along Red Sea,Egypt

Texture, mineralogy, and major and trace element geochemistry of 26 coastal dune sand samples were studied to determine the provenance and tectonic environment of two dune fields close to the beaches of Safaga (SF) and Quseir (QS) at the Egyptian Red Sea coast. Onshore winds generate fine, moderate, moderately-well to well-sorted, coarse-skewed to near-symmetrical dune sands with mesokurtic distributions. Winds pick up and transport grains from nearby beach sands and alluvial deposits into a wide Red Sea coastal plain at the border of the beach. The mineralogical (Qt–Ft–Lt) and geochemical composition of the sands, indicate that SF and QS coastal dune sands are mature and influenced by quartz-rich sands. The average CIA values in SF and QS coastal dune sands are low relative to the range of the PAAS, suggesting an arid climate and a low intensity of chemical weathering. The SF and QS coastal dune sand samples are plotted in the recycled orogen and partly in craton interior fields suggesting recycled older sedimentary and partly metamorphic-plutonic sources. The high content of quartz with shell debris and carbonates in coastal dune sands support the recycled sedimentary beach and alluvial sand sources. The dominance of heavy minerals like amphiboles (hornblende) and biotite in the coastal dune sands also supports the effect of metamorphic-plutonic source rocks. The new tectonic discriminant-function diagrams suggest that the coastal dune sands were deposited in a passive margin of a synrift basin. The results provide a good evidence for the extension in the Red Sea rift system during Oligocene-post Pliocene, which is consistent with the general geology of Egypt.     

Distribution of trace and major elements in the −180 + 75 μm and −75 μm fractions of the sandveld regolith in northwest Ngamiland,Botswana

An orientation survey was undertaken in northwest Ngamiland to evaluate, among other criteria, an optimum size fraction for trace element analysis in the Kalahari sandveld regolith samples for a regional geochemical mapping project in the area. The most prominent geomorphological features of the region are the longitudinal rolling sand dunes and floodplain sediments adjacent to the unique, mid-continent Okavango Delta. Most of the dune sands were deposited in the Late Quaternary, and they show evidence of both pluvial and and environments. Presently the a lab dunes support varied shrub/grass vegetation with intermittent tree cover. Extensive forest fires have affected the region for generations, and the occurrences of remnants of large trees indicate that the region may have also supported large forests at some stage.The sandveld regolith comprises 70% quartz sand (−1000 + 63 μm) and 10–20% silt/clay (< 63 μm) material. There are no size variations between material from dune crests, dune depressions and down the soil profile to a depth of a metre. The process of regolith formation is relatively young and dynamic, being widely churned by a variety of boring animals, termites, ants and other insects. Hence no distinct zonation of soil horizons in the top 100 cm of the soil catena were observed. Remarkably, the significant proportion of the silt/clay fraction in the regolith indicates progressive weathering and possible deposition of precipitates.Trace element contents are invariably enhanced in the fine fractions, a characteristic widely observed elsewhere in residual soils. On the Xaxa-Cheracheraha traverse Zn values range from 2 to 98 ppm (mean 9 ppm); Pb varies from 1 to 101 ppm (mean 27 ppm) and Cu from 0 to 18 ppm (mean 5 ppm) in the −75 μm fraction. Contents in the −180 + 75 μm are, however, significantly lower than in the fine fractions. The variations in element concentrations along each of the orientation survey traverses at Qangwa-Nokaneng, Nxaunxau-Qurube and Nxaunxau-Ghane, in the coarse and fine fractions, generally remain sympathetic, showing that the enhanced values in the fines are a result of secondary dispersion, rather than mere compositional differences in the sandveld regolith.     

克里雅河沿线沙丘沉积物石英砂表面特征分析

对沙漠内部典型河流沿线沙丘石英颗粒表面微形态特征的系统研究尚少。沿塔里木盆地南缘克里雅河下游丹丹乌里克、喀拉墩、圆沙古城、北方墓地及其北部塔里木河一带的沙丘顶部采到5件表沙样品。扫描电镜观察172颗经能谱挑选的石英颗粒表面微形态,筛析法测定5件样品的粒度。结果表明:1）丹丹乌里克样品以极细沙为主,其余均以细沙为主,各样品几乎不含黏土;2）样品磨圆度特征以次棱和次圆状为主,圆状很少,未见棱状特征,次棱状与次圆状特征之间消长关系显著,沙漠南北边缘样品的次棱状特征出现频率较腹地高;3）颗粒中V形坑频率呈现出沙漠边缘较高腹地低的特征,而沙漠边缘的化学作用结构特征低于腹地。石英砂表面特征结构以机械作用为主,同时伴生化学环境作用特征,可认为克里雅河下游沙物质包括了河流、冰川与戈壁成因及风输送而来的颗粒;颗粒表面特征总体新鲜,沙丘应较年轻。纵穿塔克拉玛干沙漠沉积物样品的表面微形态观察与粒度测定,为该地区沉积环境分析与沙丘砂溯源研究增添了新数据。     

Soil erosion on a sub-tropical coastal dune complex,Transkei, Southern Africa

A fossil dune complex on the east coast of southern Africa is presently undergoing extensive accelerated erosion, with concomitant dune reactivation and degradation, unconfined erosion (sheetwash and wind deflation) and extensive development of V-shaped, ravine-type gully forms on hillslopes composed of thick sequences of Quaternary (Berea Formation?) dune sands. The sands comprise a thick, reddened, ferralitic sand carapace overlying white, poorly cemented quartzitic sands. Soil erosion has resulted from degradation of the red dune sand cover. Despite the cohesionless nature of the host materials, gully forms developed on dune sands are typologically similar to those developed in regolith or soft bedrock. This demonstrates that gully forms are influenced by the degree of homogeneity, rather than the absolute strength, of the host material subject to erosion. Factors which have contributed to erosion are discussed.     

Luminescence chronology of the inland sand dunes from SE India

Records of past climate changes have been preserved variously on the earth's surface. Sand dunes are one such prominent imprint, and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases. We report inland sand dunes from Andhra Pradesh (SE India) spread over an area of ~ 500 km², ~ 75 km inland from the east coast. The dune sands are examined to understand their provenance, transportation, timing of sand aggradation and their relationship to past climates. The dune distribution, grain morphology and the grain-size studies on sands suggest an aeolian origin. Physiography of the study area, heavy mineral assemblage, and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first-order streams emanating from hills in the region and from weathering of the Nellore schist belt. It appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area. OSL dating of 47 dune samples ranged from the present to ~ 50 ka, thereby suggesting a long duration of sand-dune aggradation and/or reworking history.     

Rare earth elements of the Altar Desert dune and coastal sands, Northwestern Mexico

Twenty-one surficial sand samples from the Altar Desert coastal and desert dune systems were analysed for rare earth elements (REE) content. This was done to observe the provenance signatures for four strategic dune localities near the Colorado River Delta, the El Pinacate dune fields, and the beaches of the north of the Gulf of California in the state of Sonora, Mexico. Our goals are to show which mechanisms (i.e., aeolian, marine) exert more influence on the composition of the Altar Desert dune sands. This study also shows the usefulness of REE spatial distribution to determine the relative mobility of the sand. Some sand samples from the dune systems in San Luis Río Colorado (SLRC), Golfo de Santa Clara (GSC), and Puerto Peñasco (PP) displayed dissimilar REE concentrations with respect to the rest of the sand samples from the same sites. These differences can be related to short aeolian transport distance in the sands with high REE concentrations and long aeolian transport distance in the sands with low REE concentrations. Besides, high REE concentration in the sands might be due to their closeness to the Colorado River Delta sediments and to recycled sands derived from granitic rocks. In contrast, all the sand samples from the El Pinacate (EP) site have similar REE concentration values, suggesting that the El Pinacate dune sands are influenced by more selective aeolian processes and less diverse heavy mineral content. The Altar Desert dune sands are derived from granitic sources eroded by the Colorado River. Our results also indicate that the Altar Desert dune sands are low in heavy mineral content (with the exception of Fe and Ti bearing minerals) and enriched in carbonates with phosphates (especially at the PP site) yielding poor correlations between REE and major element concentrations. The REE geographical distribution values in the Altar Desert dune sands indicate that light and heavy REE concentration values are related to aeolian transport, maturity of the sands, their low weathering rates, proximity of the source rocks, and the biogenic debris input from beach sands into the dune.     

The genesis of the silica sands of Black River, St Elizabeth, Jamaica

The only reported occurrence of quartz-rich sands in Jamaica is on the plains of Black River, St Elizabeth, where they outcrop in isolated pockets. The sands overlie limestones of the White Limestone Supergroup and the Coastal Group, and partly underlie Holocene peat deposits. Monocrystalline quartz, containing fluid and mineral inclusions, is the dominant mineral of the sands, with the heavy minerals. magnetite, haematite, epidote, rutile, anatase, zircon and tourmaline, occurring in minor amounts. Grain surface texture studies of the quartz grains have identified a series of mechanical and chemical features. Microtextures depicting marine, aeolian and pedological environments have been retained on the grains and represent the last three stages in the history of the grains. The petrography of the sands indicates an igneous provenance, with the major source of the detrital minerals being the Cretaceous granitoids that outcrop in the eastern half of the island. These rocks were unroofed during the uplift of Jamaica in the Late Tertiary and were subjected to extensive chemical weathering, which accounted for the breakdown of the majority of their primary silicate minerals. Fluvial transportation and deposition of detritus onto the shelf of the south coast commenced during this period and continued into the Pleistocene, providing terrigenous sand that was modified along the coast to quartz arenite by moderate to high energy marine conditions. Tidal currents, east-west longshore currents and weathering contributed to the maturity of the sand by the time it had been transported along the shelf to the vicinity of Black River. During low sea level stands in the Pleistocene, some of this sediment that became trapped on the shelf was blown inland by south-east winds.     

Nature and origins of granitic regolith in bauxite mine floors in the Darling Range,Western Australia

Chemical and physical weathering of primary minerals during the formation of laterite profiles in the Darling Range has formed distinct secondary mineral and morphological zones in the regolith. Erosion and human activity such as mining have exposed large areas of lateritic regolith, and its classification is important for land management, especially for mine rehabilitation. Preserved rock fabrics within regolith may enable the identification of parent rock type and degree of weathering, thus providing explanations for variations in important physical properties such as the strength and water retention of regolith. Feldspar, quartz, biotite and muscovite in porphyritic and fine-grained monzogranite in lateritic profiles have weathered via a series of gradational changes to form saprolite and pedolith consisting of kaolin, quartz, iron oxides, muscovite and gibbsite. Local reorganisation in the upper regolith or pedoplasmation zone has included illuviation of kaolin, which may be iron oxide-stained and which has disrupted the preserved rock fabric of saprock and saprolite. Quartz grain- or matrix-supported fabrics have developed, with greater pedoplasmation resulting in a quartz-grain-supported fabric. The recognition of these processes enables the use of gibbsite grainsize and distribution in regolith to infer original feldspar grainsize. Muscovite-rich or muscovite-deficient kaolin matrix indicates where plagioclase or alkali feldspar, respectively, was present in the parent rock. In some regolith, cementing by iron oxides has faithfully preserved rock fabric. The recognition of these various regolith types provides a basis for identifying the parent materials of lateritic regolith developed from granitic and doleritic rocks. Rock fabric is sometimes preserved in iron oxide-cemented bauxite mine floor regolith (Zh) due to the pseudomorphic gibbsite grains and iron oxide cement which forms a porous, rigid fabric. Plagioclase-rich granitoid is more likely to have weathered to dense clay-rich regolith (Zp), whereas albite and alkali feldspar have weathered to quartz-rich regolith (Zm) with the random orientation of quartz grains indicating that substantial reorganisation of rock fabric has occurred. It is possible to predict the response of regolith materials exposed in mine floors to management practices including ripping and re-vegetation, thus allowing targeted use of deep-ripping and planting density based on regolith type.     

Modern sands of South America: composition,provenance and global significance

Standard petrographic methods were used to study 604 modern sands from South America, of which 351 came from rivers and 253 from beaches. In spite of the wide geomorphic contrasts, these sands belong to only three great families: (1) an immature Andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30% of South America; (2) a cratonic association rich in quartz that covers about 62% of the continent; and (3) a transitional, molasse association, which occurs between these two and covers only about 8% of the continent. The grand arithmetic average Q:F: Rf ratio for the entire continent is 60:11:29 and the area-weighted, carbonate-free average Q_a:F_a:Rf_a is 68:10:22, a superior continental estimate, and the first ever for an entire continent.Rock fragments are the most informative of all the provenance indicators and in South America they range from tropical alterites of the cratonic family through the dominant volcanic and metamorphic grains of the Andean family to biogenic carbonate in beach sands. Carbonate grains are almost totally absent in modern South American rivers because of present day tropical weathering and a long geological evolution that has favored sand production. They are present in many of the beach sands, however, and are most abundant along the tropical Brazilian and Caribbean coasts. Metamorphic grains rival volcanics as earmarks of the Andean family and survive tropical weathering far better than volcanic grains.There is a strong association between continental soil types and the composition of river sand, but the ultimate controls are tectonic history — the ancient landscapes preserved on the Gondwana shields of South America versus the tectonically young landscapes of the Andes — and climate. Climate can either cause leaks to a far distant ocean where weathering is retarded by aridity or it can serve as a barrier to continental sand dispersion, where tropical weathering eliminates unstable grains in transit to the sea.When provenance studies are conducted across an entire, unglaciated continent, events in the far distant past need to be considered when seeking fundamental explanations of its contemporary, surficial sands.     

Index test for the degradation potential of carbonate sands during hydraulic transportation

Carbonate sands undergo degradation when transported hydraulically from a dredging vessel to the reclamation site. Risks involved in the production of fines during hydraulic transport are a deterioration of the mechanical properties of the fill in certain areas of the reclamation area where these fines concentrate. In order to assess sand degradation in the concrete and road construction industry, the Micro-Deval test for fine aggregates was developed in France and Canada. During Micro-Deval testing, aggregates degrade when tumbled in a rotating steel drum with water and steel balls. In the Canadian standard, the steel charge is lower than in the French standard and balls have the diameter of the smallest balls used in the French test. During testing, the quantity of fines produced is measured. This makes the Micro-Deval test an option for assessing the degradation of sand during hydraulic transportation of slurries in the dredging industry. Three sands are tested: two shelly carbonate sands and one quartzic river sand for comparison. The carbonate sands were sampled on reclaimed land and had been subjected to hydraulic transportation in pipeline before artificial deposition. Due to differences in particle shape, the carbonate sands and the quartz sand have a different number of contacts with the steel charge in the drum of the Micro-Deval and are not exposed to the same degradation forces during testing. It was found that the quartzic sand suffers relatively much degradation as compared to the carbonate sands, despite its greater hardness and resistance to crushability. The French test appears to create turbulence that promotes floatation of the curved shells of the carbonate sands instead of shell grinding at the bottom of the drum by contact with the steel balls. Microscopic observations of sand samples before and after testing showed that the French Micro-Deval test is too destructive. The test leads to the fragmentation by impact of the quartz sands and the destruction of certain particle types that had survived hydraulic transportation. With respect to the Canadian test, microscopic examination of sand grains before and after testing shows there is still much fragmentation of quartz grains. A lower rotational speed combined with a limited steel charge made of uniform balls of a smaller diameter, reduces turbulence, shell floatability and last but not the least, impact forces. It produces the desired result: a high Micro-Deval loss for the carbonate sands in comparison to that for the quartz sands and a very limited fragmentation of the quartz grains. Once the slurry reaches its destination, the grain size distribution of the fines fraction will influence the mechanical behaviour of mixed sands. A procedure is proposed to measure the particle size distribution of the fines fraction produced during Micro-Deval testing.Field validation is needed to validate preliminary laboratory results.     

THE CARBONATE FRACTION OF BEACH AND DUNE SANDS

The sand size carbonate fractions of beach and dune sands from the southeastern U.S. Atlantic coast were investigated from the standpoint of mineralogy, roundness and size distribution. The carbonate fractions of beach-dune sands used in this study range in abundance from less than 1% to over 40% and average about 10%. Calcium carbonate is least abundant in Georgia beaches and increases slightly to the north and greatly to the south. The size distribution of the carbonate fraction is similar to that of the non-carbonate fraction since both have been distributed by the same processes. The variable flat shape of calcareous fragments causes the carbonate fraction to be usually coarser and more poorly sorted than the acid insoluble residues of the samples. No regional relationship between roundness and wave energies was found in sand size materials although field observations indicate high energies strikingly round gravel sized calcareous fragments. There is some tendency for angularity to increase with decreasing grain size in the sand sizes as with quartz grains. The mineralogy of beach sand carbonate fractions is characterized by the almost total absence of high My calcite. Aragonite is the dominant mineral.     

图门江下游沙丘粒度分布与石英表面结构研究

图门江下游沙丘粒度频率累积曲线形态全部为双峰,负偏态,粒度变化范围大,平均粒度数值小,标准偏差平均值为0.61;粒度分布特征方法判断沙丘沉积环境以河流成因为主。通过扫描电镜研究其石英颗粒表面结构,机械作用以贝壳状断口、V形坑和次棱角状形态组合为主,化学作用为中等-强烈溶蚀特征;石英颗粒表面结构特征表明沙丘为河口沉积;热释光测年结果表明沙丘受全新世海平面变化的影响,经历海水及风力改造。     

Mineralogical and geochemical implications of weathering rates in coastal dunes and beach sands close to a volcanic rock source in the western Gulf of Mexico,Mexico

Coastal dune (CD) and beach sand samples were mineralogically and chemically studied to assess the weathering rates in a coastal area surrounded by the Trans-Mexican Volcanic Belt (TMVB). The study area is a narrow coastal plain with sub-humid warm weather and vigorous coastal dynamics located in the Western Gulf of Mexico (WGM). Our results show that the grain size parameters remain homogeneous along nine CD and beach sites, probably due to the hydrodynamic mechanisms prevailing in the area, i.e. wind deflation, longshore currents, and waves. The minerals found in the CD and beach sands are enriched in recycled, highly corroded monocrystalline quartz (Qm), with loss of plagioclase (P) and olivine (ol), with ilmenite fractions (op) especially in the northern sites. The geochemical data show that the sands are controlled by the exhumation of the TMVB rocks composed of a high volcanic lithic content with lathwork, microlithic, and negligible vitric textures. These volcanic fractions are in agreement with the presence of lavas of calc alkaline, andesite, Na-alkaline lavas, and rhyolite tuffs derived from the TMVB. Significant Spearman Rank Correlations (SRCs) resulted from high silica, titanium, iron, magnesium, calcium, vanadium, chromium, cobalt, associated with the presence of Qm, ilmenite, clinopyroxene, shell fragments, and volcanic lithics. Monocrystalline quartz enrichments, compared to a quartz dilution effect (<Qm; < Qm) at the northern and southern beach sites, reflect the vigorous coastal dynamics. The presence of ilmenite lag deposits in the northern sites indicate that high energy hydrodynamic conditions prevail at the site. The rare earth element (REE) patterns support the mineralogical and compositional framework of the CD and beach sands as part of the TMVB exhumation. We used various chemical indices such as the Chemical Index of Alteration (CIA), the Chemical Index of Weathering (CIW), the Plagioclase Index of Alteration (PIA), and the Weathering Index of Plagioclase (WIP). The WIP values reflect the depletion of mobile elements such as Ca, Na, K, and enrichment of Qm at the northern beach sites, e.g. the Istirinchiá site. The CIA/WIP ratio of 2.13 indicates intermediate weathering under warm climatic conditions and recycling of CD and beach sands.     

混积岩一例--滇东震旦系陡山沱组砂质砂屑白云岩的成因

滇东震旦系陡山沱组顶部的砂质砂屑白云岩是一例典型的混积岩,即狭义的混合沉积。岩石中的石英砂分选好,圆度和球度高,它们时稀时密地呈“悬浮”状散布在白云石砂屑沉积物中。其产状及结构构造特征表明,它是当时的海滩砂在海进过程中被搬运到海洋中,并与白云石砂屑混合而形成的。     

Sedimentological characteristics and morphology of the aeolian sand dunes in the eastern part of the UAE,a case study from Ar Rub' Al Khali

The Umm Az Zimul–Al Wijan area is located in the southeastern part of the UAE and covers about 1600 km². It is bounded to the east by the Oman Mountains and to the south and west by the extensive dune area of Ar Rub' Al Khali. Field investigation revealed the common occurrence of parallel to sub-parallel sand ridges with a general east–west orientation. Also present, but less frequent, are barchan, barchanoid and star dunes. Interdune areas are classified into four types that include: dolomite, mixed ancient sabkha and ophiolitic rock fragments, mixed sand sheet and ophiolitic rock fragments, and recent sabkha. The textural characteristics of the sand forming the dunes are unimodal with a modal class in fine sand size, moderately to very well sorted, positively skewed and mesokurtic. Quartz grains are mainly subrounded to subangular. The similarity in roundness properties in different dune types in the eastern province of the UAE seems not to be influenced by dune form. Based on the heavy mineral suites and the angularity of quartz grains, it is believed that the sand sediments are mostly derived from the ultrabasic rocks forming the ophiolitic sequence of the Oman Mountains, acidic rocks of Iran and from the coastal area.     

Textural characteristics and genesis of the aeolian sediments in the Kuwaiti desert

Several types of aeolian deposits have been recognized in Kuwait: (a) smooth sand sheets that resemble desert floor sand, (b) immobile sands that include rugged vegetated sand sheets and wadi fill deposits, and (c) mobile sands that form active sand sheets and sand dunes. Simple size frequency curves illustrate the genetic relationship between the various aeolian sediment types. The four size parameters, namely, mean size, sorting, skewness and kurtosis, were calculated. Scatter plot diagrams of sorting versus mean size and sorting versus kurtosis are effective in differentiating smooth sand sheet deposits from dune sands. Active sand sheet deposits can also be recognized because they are usually located between the two end members–smooth sand sheets and dune sands. Size parameters change with location regardless of their types. Coarsening and positive skewness usually increase downwind. Mineralogical and textural characteristics of the aeolian deposits in Kuwait revealed that they are mostly derived from the lower Mesopotamian muddy flood plain deposits, the sand fraction of the Al-Dibdibba gravelly deposits and the disintegrated material from calcretic and gypcretic duricrusts. Distribution of depositional and deflational areas indicates that the northern desert of Kuwait is characterized by a positive sand budget, whereas the southern desert has a negative sand budget.     

Assessing the engineering properties of concrete made with fine dune sands: an experimental study

Sand dunes cover an area of 16.6% of the total area of Egypt. This paper presents the results of an extensive laboratory testing that was carried out to determine the engineering properties of concrete. The concrete fine aggregate is fine dune sands obtained from three sites in the Kharga Oasis, Western Desert, Egypt. All samples were classified as poorly graded sand according to the Unified Soil Classification system. Fineness modulus values of the studied dune sands range from 0.89 to 0.97. The percentage of sulfates and chlorides are very low and nearly negligible. Sodium and calcium hydroxides were recorded in some samples with scarce concentration. Organic impurities were not recorded. The degree of workability of the studied dune sands ranged from low to medium, which are suitable for normal reinforced work without vibration and heavily reinforced section with vibration. The measured compressive strength of concrete decreases with increasing dune sand content.     

The action of wind and water in a mid‐Cretaceous subtropical erg‐margin system close to the Variscan Iberian Massif,Spain

Aeolian processes and ephemeral water influx from the Variscan Iberian Massif to the mid‐Cretaceous outer back‐erg margin system in eastern Iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements. Remains of aeolian dunes encased in ephemeral fluvial deposits (aeolian pods) demonstrate intense erosion of windblown deposits by sudden water fluxes. The alternating activity of wind and water led to a variety of facies associations such as deflation lags, desert pavements, aeolian dunes, pebbles scattered throughout dune strata, aeolian sandsheets, aeolian deposits with bimodal grain‐size distributions, mud playa, ephemeral floodplain, pebble‐sand and cobble‐sand bedload stream, pebble–cobble‐sand sheet flood, sand bedload stream, debris flow and hyperconcentrated flow deposits. Sediment in this desert system underwent transport by wind and water and reworking in a variety of sub‐environments. The nearby Variscan Iberian Massif supplied quartzite pebbles as part of mass flows. Pebbles and cobbles were concentrated in deflation lags, eroded and polished by wind‐driven sands (facets and ventifacts) and incorporated by rolling into the toesets of aeolian dunes. The back‐erg depositional system comprises an outer back‐erg close to the Variscan highlands, and an inner back‐erg close to the central‐erg area. The inner back‐erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits. In the inner back‐erg area ephemeral wadis, desiccated after occasional floods, were mud cracked and overrun episodically by aeolian dunes. Subsequent floods eroded the aeolian dunes and mud‐cracked surfaces, resulting in largely structureless sandstones with boulder‐size mudstone intraclasts. Floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes. The remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands. Upon desiccation, deflation resulted in lags of coarser‐grained sediments. A renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions. Synsedimentary tectonics caused the outer back‐erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands. Ephemeral water flow to the outer back‐erg area supplied pebbles, eroded aeolian dunes, and produced hyperconcentrated flow deposits. Fluidization and liquefaction generated gravel pockets and recumbent folds. Dune damming after sporadic rains (the case of the Namib Desert), monsoonal water discharge (Thar Desert) and meltwater fluxes from glaciated mountains (Taklamakan Desert) are three potential, non‐exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the Cretaceous desert margin system. An increase in relief driven by the Aptian anti‐clockwise rotation of Iberia, led to an altitude sufficient for the development of orographic rains and snowfall which fed (melt)water fluxes to the desert margin system. Quartzite conglomerates and sands, dominantly consisting of quartz and well‐preserved feldspar grains which are also observed in older Cretaceous strata, indicate an arid climate and the mechanical weathering of Precambrian and Palaeozoic metamorphic sediments and felsic igneous rocks. Unroofing of much of the cover of sedimentary rocks in the Variscan Iberian Massif must therefore have taken place in pre‐Cretaceous times.     

Experimental investigation of cephapirin adsorption to quartz filter sands and dune sands

Batch experiments were performed to investigate cephapirin (a widely used veterinary antibiotic) adsorption on various size sands of low total organic carbon content (0.08–0.36 wt%). In the aqueous concentration range investigated (11–112 μmol/L cephapirin), adsorption to nearly pure quartz filter sands (0.50–3.35 mm diameter) is low. Isotherms are S-shaped and most display a region of minimum adsorption, where decreased adsorption occurs with increasing solution concentration, followed by increased adsorption at higher concentrations. Cephapirin adsorption to quartz-rich, feldspar-bearing dune sands (0.06–0.35 mm diameter), and the smallest quartz filter sand investigated (0.43–0.50 mm), can be described by linear sorption isotherms over the range of concentrations investigated. Distribution coefficients (K _d) range from 0.94 to 3.45 L/kg. No systematic relationship exists between grain size and amount of adsorption for any of the sands investigated. Cephapirin adsorption is positively correlated to the feldspar ratio (K-feldspar/(albite + Ca-plagioclase). Feldspar-ratio normalization of distribution coefficients was more effective than organic carbon normalization at reducing variability of K _d values in the dune sands investigated.