Erosion Of Rocks Research Articles

Advances in Sustainable Conservation Practices in Rupestrian Settlements Inscribed in the UNESCO's World Heritage List

Rupestrian settlements were among the first man-made works in the history of humanity. The most relevant masterpieces of such human history have been included in the UNESCO World Heritage List. These sites and remains are not always in equilibrium with the environment. They are continuously impacted and weathered by several internal and external factors, both natural and human-induced, with rapid and/or slow onset. These include major sudden natural hazards, such as earthquakes or extreme meteorological events, but also slow, cumulative processes such the erosion of rocks, compounded by the effect of climate change, without disregarding the role of humans, especially in conflict situations. Many rupestrian sites have been carved into soft rock, generally with UCS<25MPa (ISRM, 1981), in vertical cliffs, and show major conservation issues in the domain of rock slope stability and rock weathering. The present paper reports the experience of rock fall mitigation in rupestrian sites, mainly from the UNESCO World Heritage List (Bamiyan in Afghanistan; Lalibela in Ethiopia; Petra in Jordan and Vardzia in Georgia). The general approach, implemented in the reported activities, include field conservation works enhancing traditional knowledge and sustainable practices, primarily based on local conservation techniques.

RADIONUCLIDES DISTRIBUTION NEAR FORMER URANIUM MINING

The paper shows, that radionuclides from the stony rocks of uranium mines can be leached by atmospheric precipitations. In acid conditions, a degree of leaching is greater. Goal. The aim of this investigation was to study the distribution of radionuclides in uranium minings and their impact on the environmental contamination. Materials and methods. The study was carried out in two stages. In the first stage, a blade of rock was mixed with distilled water in proportions of 0,3 kg of gravel and 1 liter of water. After thirty days of soaking, water was sent to the gamma-spectrometric analysis to Canberra’s spectrometer (USA) with a high-purity germanium detector. In the second stage, we carried out the similar experiment with water, wich was acidified to pH = 3. Contamination levels of areas near the in-situ leaching mine were determined. Intervention levels were used to estimate risk and possible water consumption by the population. Estimations were carried out taking into account the combined presence of several radionuclides in the water. Results. The results of these studies have shown that the distribution of radionuclides from the source of the contamination is about 360 meters during the 30 y period. The stream, along which samples of soil were collected and studied, was formed by the miner waters that flow along small ruts towards a village, thereby increasing the likelihood of water use by the public. Conclusions. The uranium mines are the source of radioactive contamination. Radionuclides are distributed due to the erosion of rocks and leached out of the stony rock by precipitations. The extent of leaching is significantly increased in an acidic environment, which takes place near the in-situ leaching mines.

Streamlined hard beds formed by palaeo-ice streams: A review

Fast-flowing ice streams occur within modern ice sheets and also operated in Pleistocene ice sheets. The reconstruction of palaeo-ice streams normally relies on the mapping of mega-scale glacial lineations (MSGLs) and drumlins composed of soft sediment, mainly till. Analysis of new satellite imagery and digital terrain models, demonstrates the presence of large fields of kilometre-scale glacial lineations comprising rock drumlins, megagrooves and megaridges. In this paper we describe and analyse a number of such ‘hard-bed’ landform systems from the former Laurentide and British–Irish ice sheets, occurring in a variety of palaeo-ice stream settings. These are attributed to erosion of crystalline and sedimentary rock below fast flowing ice streams. Bedrock properties such as hardness, fracture spacing and bedding and their orientation with respect to ice flow have a profound effect on the occurrence and character of elongate rock bedforms. Elongate streamlined forms on hard crystalline rock, as on the Canadian Shield, only form under special circumstances; in contrast, sedimentary strata are highly susceptible to form streamlined hard beds, specifically if bedrock strike is parallel to ice flow. Large-scale elongate rock bedforms are erosional in origin, formed by preferentially focused abrasion or by lateral plucking, depending on bedrock type. Many palaeo-ice stream footprints previously mapped in the Laurentide Ice Sheet on the basis of soft-bed bedforms are shown to be significantly larger, extending up-ice across sedimentary strata and onto Precambrian crystalline rocks. Hard-bed streamlined forms further show that ice streaming does not necessitate a deformable bed, but can equally occur on smooth hard beds.

Late Cretaceous redbeds from the Gan-Hang Belt in Southeast China: petrography and geochemistry implications for provenance, source weathering, and tectonic setting

ABSTRACTThe distinct basin and range tectonics in Southeast China were generated by crustal extension associated with subduction of the Palaeo-Pacific plate during the late Mesozoic. Compared with adjacent granitoids of the ranges, the redbeds of the basins have not been well characterized. In this article, provenance, source weathering, and tectonic setting of the redbeds are investigated by petrographic and geochemical studies of sandstones from the Late Cretaceous Guifeng Group in the Yongchong Basin, Southeast China. Detrital grains are subangular to subrounded, poorly sorted, and rich in lithic fragments. Variable Chemical Index of Alternation values (59.55–79.82, avg. 66.79) and high Index of Compositional Variability (ICV) values (0.67–3.08, avg. 1.40) indicate an overall low degree of chemical weathering and rapid physical erosion of source rocks. Such features are consistent with an active extension tectonic setting. Other chemical indices (e.g. Al2O3/TiO2, Th/U, Cr/Th, Th/Sc, Zr/Sc) also suggest significant first-cycle sediment input to the basin and a dominant felsic source nature. Thus, the Guifeng Group possibly underwent moderate to low degrees of weathering upwards. Sandstone framework models and geochemical characteristics suggest the provenance was likely a combination of passive margin (PM) and active continental margin (ACM) with minor continental island arc (CIA) tectonic settings. Sediment derivation from Neoproterozoic metamorphic rocks and Cambrian to Triassic granitoids indicates PM provenance, whereas sediments derived from Jurassic to Cretaceous granitoids suggest ACM and CIA nature. Therefore, the Late Cretaceous redbeds were deposited in a dustpan-like half-graben basin under the back-arc extension regime when Southeast China was possibly influenced by northwestward subduction of the Palaeo-Pacific plate beneath East Asia.

Major and Trace Element Geochemistry of Coals and Intra-Seam Claystones from the Songzao Coalfield, SW China

Silicic, mafic and alkali intra-seam tonsteins have been known from SW China for a number of years. This paper reports on the geochemical compositions of coals and tonsteins from three seam sections of the Songzao Coalfield, SW China, and evaluates the geological factors responsible for the chemical characteristics of the coal seams, with emphasis on the influence from different types of volcanic ashes. The roof and floor samples of the Songzao coal seams mostly have high TiO2 contents, consistent with a high TiO2 content in the detrital sediment input from the source region, namely mafic basalts from the Kangdian Upland on the western margin of the coal basin. The coals from the Songzao Coalfield generally have high ash yields and are highly enriched in trace elements including Nb, Ta, Zr, Hf, rare earth elements (REE), Y, Hg and Se; some variation occurs among different seam sections due to input of geochemically different volcanic ash materials. The geochemistry of the Songzao coals has also been affected by the adjacent tonstein/K-bentonite bands. The relatively immobile elements that are enriched in the altered volcanic ashes also tend to be enriched in the adjacent coal plies, possibly due to leaching by groundwaters. The coals near the alkali tonstein bands in the Tonghua and Yuyang sections of the Songzao Coalfield are mostly high in Nb, Ta, Zr, Hf, Th, U, REE and Y. Coal samples overlying the mafic K-bentonite in the Tonghua section are high in V, Cr, Zn and Cu. The Datong coal, which has neither visible tonstein layers nor obvious volcanogenic minerals, has high TiO2, V, Cr, Ni, Cu and Zn concentrations in the intervals between the coal plies affected by mafic and alkaline volcanic ashes. This is consistent with the suggestion that a common source material was supplied to the coal basin, derived from the erosion of mafic basaltic rocks of the Kangdian Upland. Although the Songzao coal is generally a high-sulfur coal, most of the chalcophile trace elements show either poor or negative correlations with total iron sulfide contents. The absence of traditional pyrite-metal associations may reflect wide variations in the concentrations of these elements in individual pyrite/marcasite components, or simply poor retention of these elements in the pyrite/marcasite of the relevant coals.

Geological dimension of the cultural heritage: A case example of the Ajanta Caves (Maharashtra, India)

International development for the both geoconservation and geotourism requires attention to all kinds of (potential) geological heritage. The Ajanta Caves (western Maharashtra, India) is a famous cultural object consisting of 30 caves carved in the Deccan Traps and inscribed to the UNESCO list of the World Heritage Sites. Its examination permits to indicate four geological features, which are the artificial caves themselves (these mark geological activity of the man in the historical past), the end-Cretaceous floot basalts (these demonstrate the emplacement of Large Igneous Province and the relevant palaeoenvironmental catastrophe), the gorge of the Waghora River (this is peculiar landform resulted from the river erosion of hard rocks), and the rockfall hazard (this is an interesting engineering geological phenomenon linked to the caves construction/maintenance). Geological heritage value of these features is argued. Unfortunately, there is not any geotourism activity at the Ajanta Caves presently. The content analysis of the principal on-line resources (web pages) devoted to this cultural site reveals the absence of sufficient geological information that would facilitate geotourism. Generally, judgements about the Ajanta Caves and the other similar sites in the geological dimension permit to consider the wide spectrum of the geological heritage. They also highlight some extra opportunities for geotourism, which can benefit by its development at cultural sites with thousands of visitors.

40Ar/39Ar ages and geochemical characterization of Cretaceous bentonites in the Nanushuk, Seabee, Tuluvak, and Schrader Bluff formations, North Slope, Alaska

Diagenetically altered volcanic ash deposits (bentonites) found in Cretaceous terrestrial and marine foreland basin sediments have the potential to be used for chronostratigraphy and subsurface correlation across Alaska's North Slope. Detailed age and geochemical studies of these volcanogenic deposits may also shed light on the tectonic evolution of the Arctic. Though these bentonites have been previously studied, there are few published results for regional bentonite ages and geochemistry due to challenges of dating weathered volcanic ash. We analyzed mineral separates from cored bentonites recovered from wells in the National Petroleum Reserve Alaska. The analyses confirm that an intense period of volcanic ash deposition on Alaska's North Slope began by the late Albian and persisted throughout the Cenomanian, an interval of rapid progradation and aggradation in the Colville basin. These results also add to a sparse record of radioisotopic ages from the Nanushuk Formation. A bentonite preserved in delta plain sediments in the upper Nanushuk Formation dates to 102.6 ± 1.5 Ma (late Albian), while a bentonite near the base of the overlying Seabee Formation was deposited at 98.2 ± 0.8 Ma, in the early Cenomanian. The two ages bracket a major flooding surface at the base of the Seabee Formation near Umiat, Alaska, placing it near the Albian-Cenomanian boundary (100.5 Ma). Several hundred feet up-section, the non-marine Tuluvak Formation contains bentonites with 40Ar/39Ar ages of 96.7 ± 0.7 to 94.2 ± 0.9 Ma (Cenomanian), several million years older than previously published K–Ar ages and biostratigraphic constraints suggest.Major and trace element geochemistry of a sub-sample of six bentonites from petroleum exploration wells at Umiat show a range in composition from andesite to rhyolite, with a continental arc source. The bentonites become more felsic from the late Albian (∼102 Ma) to late Cenomanian (∼94 Ma). A likely source for the bentonites is the Okhotsk-Chukotka Volcanic Belt (OCVB) of eastern Siberia, a continental arc which became active in the Albian and experienced episodes of effusivity throughout the Late Cretaceous. Chronostratigraphically anomalous 40Ar/39Ar ages coincide with peaks of magmatic activity in the OCVB, suggesting that these anomalously old ages may be due to magmatic contribution of xenocrysts or recycling of detrital minerals from older volcanic events. An alternative explanation for the chronostratigraphically anomalous ages is mixing of bentonites with detrital sediment derived from unroofing and erosion of metamorphic rocks in the Brooks Range, Herald Arch, and Chukotka throughout the mid to Late Cretaceous.

Impact of natural and man-made factors on migration of heavy metals in the Ardon River basin (North Ossetia)

Purpose The main goal of the study was to evaluate biogeochemical effects of particular factors changing the structure of landscapes due to enhanced mass migration and erosion of the outcropping rocks by studying transformation of chemical composition of the draining waters and flood plain soils; chemical composition of the solid and liquid phases of the Ardon River waters; and by assessing ecological consequences and risk of contamination of the area by heavy metals.

Precambrian reidite discovered in shocked zircon from the Stac Fada impactite, Scotland

Terrestrial impact events have had a profound influence on Earth’s geological, geochemical, and biological evolution. However, the record of Precambrian impacts is poorly constrained due to the dynamic nature of plate tectonics, erosion, and deposition of younger rocks that may destroy or cover the evidence. Here we report the first Precambrian occurrence of the rare mineral reidite (ZrSiO4) within grains of shocked zircon in the ca. 1.18 Ga Stac Fada Member (Stoer Group), northwestern Scotland. The reidite, preserved as <2-µm-wide lamellae, is unambiguous evidence of shock pressures in excess of ∼30 GPa and confirms the impact origin for the Stac Fada deposit. The reidite lamellae are locally deformed, and sites of deformation record its decomposition to baddeleyite (ZrO2) and amorphous silica, the first natural example of this transformation. The findings demonstrate that reidite and baddeleyite may form and be transported in high-energy ejecta without physical or chemical breakdown and are stable during sedimentary diagenesis and low-grade metamorphism. Thus, reidite may be preserved over time scales exceeding 1 b.y., establishing the use of reidite within detrital shocked zircon from Precambrian strata as a viable and valuable means of recognizing and characterizing ancient terrestrial impact events.

Variability of rock erodibility in bedrock‐floored stream channels based on abrasion mill experiments

AbstractWe quantify variations in rock erodibility, Kr, within channel cross sections using laboratory abrasion mill experiments on bedrock surfaces extracted from streams with sandstone bedrock in Utah and basaltic bedrock in the Hawaiian Islands. Samples were taken from the thalweg and channel margins, the latter at a height that is inundated annually. For each sample, a sequence of abrasion mill experiments was completed to quantify variations in erosion rate with erosion depth. Erosion rate data from these experiments shows two things. First, the erosion rate from channel margin samples is greater than for thalweg samples, with the greatest difference observed for the rock surface that was exposed in the stream channel. Second, erosion rate decreases with depth beneath the original rock surface, by an order of magnitude in most cases. The erosion rate becomes steady at depths of 1–3 mm for channel margin samples and 0.1–0.4 mm for thalweg samples. Because only rock properties and microtopography vary throughout the sequence of mill experiments, these results suggest that Kr of the bedrock surface exposed in stream channels is higher at the margins than near the channel center and that Kr decreases over depths of ~1 mm. The simplest explanation for these patterns is that Kr is enhanced, at the bedrock surface and along the channel margins, due to the effects of weathering on rock strength and surface roughness. We hypothesize that a balance exists between weathering‐enhanced erodibility and episodic incision to allow channel margins to lower at rates similar to the thalweg.

Late Cenozoic sedimentation of Nihewan Basin, central North China and its tectonic significance

Late Cenozoic sediments of the Nihewan Basin in the northeastern part of the Shanxi Graben, North China Craton, include buried late Neogene rocks, and exposures of the Pliocene Yuxian formation, the Pleistocene Nihewan Formation and Xiaodukou Formation with the age at least from 3.6 to 0.11Ma. The sedimentary succession records the tectonic processes of the graben. In the eastern Nihewan Basin, on the basis of sedimentary facies and provenance analysis, we have identified three main evolution stages during the late Cenozoic. The first stage was rapid expansion of the basin in the Neogene, which is thought to have commenced at least from 3.6Ma and lasted until 2.6Ma. This stage is characterized by lacustrine-facies dark-colored mud and silt in depocenter of the basin, with a potential source area from the northeast of the basin. The following stage was a period of contraction at ∼2.6–1.8Ma, characterized by deltaic deposits in depocenter of the basin and braided fluvial deposits in northeast margin of the basin, and the deposition of cross-bedded sands that were derived from erosion of Archean, Proterozoic, Paleozoic, and Jurassic rocks from the north–northwest and south of the basin. The last stage was one era of gradually extinction of the basin from ∼1.8 to 0.11Ma, followed by dried up of the basin and replaced by loess. Sediments were deposited in deltaic in depocenter of the basin and alluvial fan in northeast margin of the basin; these coarse-grained sands and pebbles were derived mainly from north and north–northeast of the basin, and generally from Archean, Proterozoic, and Paleozoic rocks. These three stages and the conversion ages, ∼2.6, ∼1.80, and ∼0.11Ma, are largely consistent with three episodes of Tibetan Plateau rapid uplift. Therefore, we infer that the evolution of the Nihewan Basin was predominantly influenced by the far-field effect of the progressive uplift and northeastward expansion of the Tibetan Plateau.

Provenance control on chemical indices of weathering (Taiwan river sands)

Geochemical parameters obtained from the analysis of sediments and sedimentary rocks are widely used to infer weathering and paleo-weathering conditions in source areas. Chemical indices of weathering, however, may not reflect weathering only, or even principally. The concentration of chemical elements in terrigenous sediments is constrained by the original mineralogy of source rocks, and is thus provenance-dependent. Moreover, the mineralogy and consequently the geochemistry of sediments may undergo substantial modifications by diverse physical processes during transport and deposition, including recycling and hydraulic sorting by size, density or shape, and/or by chemical dissolution and precipitation during diagenesis.Around the island of Taiwan, temperature and rainfall are consistently high and relatively homogeneous, and no significant correlation is observed between geochemical and climatic parameters. Physical erosion, fostered by landslides induced by frequent earthquakes and typhoons, prevails because of high relief and extreme rates of tectonic uplift. In such a dynamic orogenic setting, all chemical indices of weathering are controlled principally by the geology of source terranes. Sedimentaclastic and metasedimentaclastic sands carried by western Taiwan rivers draining the pro-wedge display the strongest depletion in Na, Ca, Mg and Sr relative to average upper continental crust, and no depletion or even enrichment in K, Rb and Ba. Low WIP indices reflect erosion of phyllosilicate-dominated rocks in the Slate Belt and extensive recycling of clastic rocks exposed in the Western Foothills. Instead, metamorphiclastic sands carried by eastern Taiwan rivers draining the retro-wedge show no depletion or even enrichment in Mg and Ca, and low CIA and PIA, reflecting contributions from the Tailuko Belt and Coastal Range. Volcaniclastic sands have the same CIA values of their andesitic source rocks (47±1 versus 47±7), indicating that weathering is subordinate both along the eastern side of the island and at its northern edge where annual rainfall is double.Full caution is required when chemical weathering indices are used to extract climatic and paleoclimatic information from the sedimentary archive, especially in the case of diagenized sandstones where commonly massive precipitation of authigenic carbonate is very difficult to accurately correct for, especially in the absence of detailed petrographic and mineralogical data.

Himalayan Cambrian brachiopods

AbstractA synoptic analysis of previously published material and new finds reveals that Himalayan Cambrian brachiopods can be referred to 18 genera, of which 17 are considered herein. These contain 20 taxa assigned to species, of which five are new: Eohadrotreta haydeni, Aphelotreta khemangarensis, Hadrotreta timchristiorum, Prototreta? sumnaensis and Amictocracens? brocki. Well‐preserved topotype material from the classic Parahio Valley section is described for three species that have not previously been illustrated photographically. A biostratigraphical scheme based on Cambrian brachiopod occurrence is integrated with that recently proposed for trilobites. Regional correlations based on shared taxa within and across Himalayan lithotectonic belts demonstrate that erosion of Cambrian rocks in the Kurgiakh orogeny in the Parahio Valley removed little of the Parahio Formation and that all of the fossil‐bearing lithotectonic zones share similar late early Cambrian brachiopods, suggesting regional faunal continuity at the time. Palaeobiogeographical analysis of the Cambrian brachiopod faunas from the Himalaya shows that they occupied a marginal position of the Australasian segment of Gondwana.

Evaluation of Weathering and Erosion of Cone-Shaped Pyroclastic Rocks of Kandovan Village

روستای کندوان از مناطق گردش گری استان آذربایجان شرقی است که خانه های روستایی آن صدها سال پیش در داخل سنگ های آذرآواری مخروطی شکل موسوم به کران حفاری شده اند. در مقاله حاضر بر اساس پژوهش های صحرایی و آزمایشگاهی به بررسی نقش ویژگی های زمین شناسی مهندسی سنگ های آذرآواری کندوان در هوازدگی، فرسایش و تخریب آن ها پرداخته شده است. سنگ های آذرآواری کندوان به دلیل داشتن درصد زیادی از کانی های پلاژیوکلاز و قطعات پامیس با مقاومت کم، جوش خوردگی و جورشدگی اندک سنگ و کرویت و گردشدگی زیاد اجزای تشکیل دهندۀ آن ها، مقاومت کمی در برابر عوامل هوازدگی و فرسایش دارند. اگر چه هوازدگی و فرسایش در امتداد درز و شکستگی های موجود در سنگ ها مهم ترین عامل به وجود آمدن شکل های مخروطی در کندوان است، اما ادامۀ این فرآیند موجب تخریب و نابودی سنگ ها می شود. تخلخل زیاد سنگ ها این امکان را فراهم کرده است که آن ها ظرفیت جذب آب زیادی داشته باشند. درصد جذب زیاد آب، حساسیت سنگ ها در برابر انبساط و انقباض ناشی از تر- خشک شدن و ذوب- انجماد متوالی را افزایش داده است و سختی و استحکام درونی اندک آن ها، باعث شده که بافت سنگ ها در اثر عوامل محیطی هوازده شده و متلاشی گردد. هم چنین بافت سست سنگ های آذرآواری مذکور باعث فرسایش نسبتا سریع آن ها در اثر بارندگی و جریان آب های سطحی و باد شده است.

Outcrop reservoir analogous and porosity changes in continental deposits from an extensional basin: The case study of the upper Oligocene Sardinia Graben System, Italy

Several recent hydrocarbon discoveries were detected in extensional areas located around fault-bounded tectonic highs. These tectonically-controlled mini-basins are diffusely characterised by terrestrial and shallow-marine successions with complex geometrical relationships. The degree of seismic resolution and the punctual well-log lithostratigraphic data do not allow suitable reconstructions of these plays and, thus, the use of good outcrop analogues is crucial in their reservoir characterisations.In this paper, we present the results of a sedimentological study carried on continental deposits filling a segment of the Oligo-Miocene south-eastern basin margin of the Sardinia Graben System, in the central-western Mediterranean. This well-exposed terrestrial succession results from the erosion of Palaeozoic metamorphic and magmatic basement rocks exposed along the basin margin. Continental, coarse-grained eluvio-colluvial, alluvial and fluvial sediments exhibit changes both in thickness and lateral extensions due to the existence of several endorheic depocentres, which were aligned along major normal faults.Based on the stratigraphic and sedimentological analysis of a number of exposed stratigraphic sections, the main depositional processes are identified for each specific facies association. Due to the grain-size of the dominant deposits, porosity is estimated by using an image analysis software on high-resolution digital photographs from a number of outcrop samples. The results show how porosity changes dramatically across the reconstructed sections due to the complexity of the reciprocal geometrical passages among all these lithofacies.The dominance of colluvial/alluvial fans or river braidplain systems and the different nature of sediment occupying each depositional areas are interpreted as the response to the interplay between the capacity generated by the vertical tectonic displacement of major normal-faults and the interception of the base-level with the topography of these mini-basins. Our observations suggest six possible depositional scenarios that resume as many reservoir types in fault-controlled half-grabens with dominant continental lithofacies.

What Are the Current Findings Concerning Arsenic in Foods?

What Are the Current Findings Concerning Arsenic in Foods?

Results of the U-Pb age of detrital zircons from Upper Proterozoic deposits of the eastern slope of the Anabar uplift

The Upper Proterozoic sequence in the southern part of the East Anabar Basin, as throughout the entire framing of the Anabar uplift, has a two-unit terrigenous-carbonate structure. The results of the U-Pb dating of detrital zircons show that there is a difference in stratigraphy of Riphean strata in the north and south of the Anabar Uplift. In the north, deposits of the entire sequence are regarded as Early Riphean; in the south, the thickness of these deposits is reduced to 70 m. The overlying stratum is regarded as Upper Riphean-Vendian. As the strata in the southern part of the East Anabar Basin strata are of younger (Late Riphean-Vendian) age, they cannot be assigned to the Mukun and Billyakh groups. The Riphean-Vendian deposits accumulated mainly through erosion of crystalline rocks of the Anabar Uplift. In the upper part of the sequence, the Vendian magmatic complexes located probably within the Taimyr Orogen played a significant role as provenance areas.

The detrital zircon U–Pb–Hf fingerprint of the northern Arabian–Nubian Shield as reflected by a Late Ediacaran arkosic wedge (Zenifim Formation; subsurface Israel)

The Neoproterozoic Arabian–Nubian Shield (ANS), which comprises the northern sector of the East African Orogen (EAO), has been deeply denuded in Ediacaran times and its erosional products were deposited across NE Africa and Arabia; they are also found in a number of peri-Gondwana terranes. A vast Late Neoproterozoic clastic wedge, locally interbedded with volcanics, developed on the northern outskirts of the ANS and spread into areas currently at the foothills of the Taurus and Zagros belts to coalesce into a wide peri-Arabian-Mesopotamian basin. The southern limit of this basin is manifested in the subsurface of Israel and Jordan by a few km thick arkose sequence, the Zenifim Formation, which underlies the Cambro–Ordovician quartz-rich sandstones. The detritus stored in this formation was mostly eroded from the adjacent ANS at the cessation of Neoproterozoic orogeny.Along a ∼150km long transect in the subsurface of Israel, the arkosic facies of the Zenifim Formation changes from a proximal alluvial fan in the south, to a sea marginal facies in the north reflecting the transgression of the proto-Tethys onto the decaying Neoproterozoic orogen. We studied the detrital zircon U–Pb–Hf from core samples of arkose from different parts of the Zenifim Formation in order to constrain the composition of its provenance and to obtain the Late-Neoproterozoic detrital fingerprint of the ANS.The proximal alluvial fan and plain facies is dominated by a remarkable concentration of U–Pb detrital zircon ages between 0.6 and 0.7Ga with a peak around 0.63Ga, alongside a few older grains (0.8Ga and 0.9Ga). Pre-Neoproterozoic detrtital zircons are absent. The youngest detrital zircon population peaks at 0.60Ga. The entire inventory of detrital zircons yielded positive ɛHf values between +11 and +5, generally overlapping ɛHf values of Neoproterozoic rocks of the northern ANS. It is notable that little indication for the exposure of the Cryogenian rocks of the ANS is represented by the detrital zircon signal in the alluvial fan deposits, a feature indicating the prevalence of Ediacaran granitoids in the provenance. Towards the north, the youngest detrital zircons in the sea marginal facies concentrate at 0.58Ga implying this part of Zenifim Formation is among the youngest Late Neoproterozoic sedimentary units in the northern ANS. The detrital zircon signal exhibits a preponderance of Neoproterozoic-aged detrital zircons peaking at 0.6Ga and 0.75–0.8Ga, but Grenvillian-like age peaks at 0.92, 1.0 and 1.1Ga are also identified. Additionally, a small number of 1.8, 2.1 and 2.6Ga-aged zircons, and a few Late Neoproterozoic detrital zircons with negative ɛHf values also occur. Erosion of basement rocks in the northern ANS was generally capable of accounting for most of the detrital zircon spectra in the sea marginal facies, but we point out two other potential sources. Our preliminary investigations indicate that dike swarms that invaded the northern ANS in the mid Ediacaran carry abundant inherited pre-Neoproterozoic zircons and Neoproterozoic-aged zircons with negative ɛHf values. The presence of such zircons in post −0.58Ga sediments, subsequently to the major diking phases, can thus be accounted for, at least partly, by the erosion of dikes and associated volcanics. Likewise, a northern provenance that resided within the Cadomian realm or laterally along the Gondwana margin could also play a role in delivering zircons of this type to the sea marginal facies of Zenifim Formation.

Historical record of trace elements input and risk in the shallow freshwater lake, North China

Approximately 80-year input of trace elements (Cr, Cu, Mn, Ni, Zn, Fe, and P) based on 210Pb analysis in sediment cores was studied to assess the contamination status of these elements in the Baiyangdian Lake in China. The pollution concentration and enrichment factor, geoaccumulation index, and ecological risk index of these metals indicate that the degree of pollution and risk of these metals in the lake is higher in the upper layers (0–5cm) and in recent years (1997–2012), but still at a moderate level. Among these metals, Cr and Ni may cause slight adverse biological effects in the area. Although the study indicated that the lake was not significantly affected by anthropogenic activities, a good logarithmic relationship (R2≥0.85) between the ecological risk index and gross domestic product per capita in Baoding City, China, during 1943–2012 confirmed the effect of increasing human activity on the lake. The correlation and principal component analyses indicated that Cr, Zn, Mn, and Fe mainly originated from natural input with weathering and erosion of rocks and soil parent materials; however, Cu, Ni, total organic carbon, and P mainly originated from anthropogenic activities such as agriculture, industry, and sewage effluents.

A Refined Model for Solid Particle Rock Erosion

A procedure for the estimation of distribution parameters of a Weibull distribution model K 1 = f(K Ic 12/4 /σ C 23/4 ) for solid particle erosion, as recently suggested in Rock Mech Rock Eng, doi: 10.1007/s00603-014-0658-x , 2014, is derived. The procedure is based on examinations of elastic–plastically responding rocks (rhyolite, granite) and plastically responding rocks (limestone, schist). The types of response are quantified through SEM inspections of eroded surfaces. Quantitative numbers for the distribution parameter K 1 are calculated for 30 rock materials, which cover a wide range of mechanical properties. The ranking according to the parameter K 1 is related to qualitative rock classification schemes. A modified proposal for the erosion of schist due to solid particle impingement at normal incidence is introduced.