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Weathering Processes (weathering + process)
Selected AbstractsWeathering processes and Quaternary origin of an alpine blockfield in Arctic SwedenBOREAS, Issue 2 2009BRADLEY W. GOODFELLOW The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigated through an examination of fine matrix and clasts from two pits excavated across ridge-top sorted circles; one on a summit, the other in a saddle. At the summit, fine matrix chemical weathering is limited to the production of poorly crystallized Al- and Fe-oxyhydroxides, whereas some additional vermiculitization and gibbsite crystallization occurs in the saddle. In both locations, volumes of clay-sized matrix are low, mass balance calculations indicate only minor elemental losses and no chemically etched grains are visible under a scanning electron microscope (SEM). In addition, soil horizons are absent and chemical weathering intensity is uniformly low across both excavated sorted circles. Minor clast chemical weathering consists of Fe oxidation, which dominates in the matrix-rich circle centres, and some rind development, which increases in frequency in the clast-rich rings. The dominance of physical weathering processes and the presence of only minor chemical weathering, in both fine matrix and clasts, indicate that the blockfield is not a Neogene weathering remnant. Rather, the blockfield has a Quaternary origin, developing during interglacials, interstadials and the Holocene, primarily through subsurface weathering processes. [source] Pore properties as indicators of breakdown mechanisms in experimentally weathered limestonesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2001Dawn T. Nicholson Abstract The results are reported of four experimental weathering tests , freeze , thaw, wetting and drying, slake durability and salt weathering , on five different types of limestone. Effective porosity, mercury intrusion porosimetry and scanning electron microscopy were used to evaluate changes in pore properties, while weight loss and fracture density were used to assess deterioration severity. A primary aim was to observe modifications in porosity due to weathering and to draw inferences about the internal rock deterioration mechanisms taking place. It is concluded that the five limestones not only show a wide range of resistance to weathering in general but considerable difference in resistance to particular weathering processes. Consequently, when assessing durability it is essential to consider rock properties in the context of the weathering process to which the rock is subject. The type of deterioration indicator used is also important in interpretation of durability. A variety of pore modification mechanisms operate, including changes in pore connectivity, pore infilling, and the introduction of additional void space. There are indications that changes to the internal pore structure of rocks due to weathering may be a precursor to more substantial macrodeterioration. Copyright © 2001 John Wiley & Sons, Ltd. [source] Patterns of damage in igneous and sedimentary rocks under conditions simulating sea-salt weatheringEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2003C. Cardell Abstract A saline-spray artificial ageing test was used to simulate the effects produced in granites and sedimentary rocks (calcarenites, micrites and breccia) under conditions in coastal environments. Three main points were addressed in this study: the durability of the different kinds of rock to salt decay, the resulting weathering forms and the rock properties involved in the weathering processes. For this, mineralogical and textural characterization of each of the different rocks was carried out before and after the test. The soluble salt content at different depths from the exposed surfaces was also determined. Two different weathering mechanisms were observed in the granite and calcareous rocks. Physical processes were involved in the weathering of granite samples, whereas dissolution of calcite was also involved in the deterioration of the calcareous rocks. We also showed that microstructural characteristics (e.g. pore size distribution), play a key role in salt damage, because of their influence on saline solution transport and on the pressures developed within rocks during crystallization. Copyright © 2003 John Wiley & Sons, Ltd. [source] Pore properties as indicators of breakdown mechanisms in experimentally weathered limestonesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2001Dawn T. Nicholson Abstract The results are reported of four experimental weathering tests , freeze , thaw, wetting and drying, slake durability and salt weathering , on five different types of limestone. Effective porosity, mercury intrusion porosimetry and scanning electron microscopy were used to evaluate changes in pore properties, while weight loss and fracture density were used to assess deterioration severity. A primary aim was to observe modifications in porosity due to weathering and to draw inferences about the internal rock deterioration mechanisms taking place. It is concluded that the five limestones not only show a wide range of resistance to weathering in general but considerable difference in resistance to particular weathering processes. Consequently, when assessing durability it is essential to consider rock properties in the context of the weathering process to which the rock is subject. The type of deterioration indicator used is also important in interpretation of durability. A variety of pore modification mechanisms operate, including changes in pore connectivity, pore infilling, and the introduction of additional void space. There are indications that changes to the internal pore structure of rocks due to weathering may be a precursor to more substantial macrodeterioration. Copyright © 2001 John Wiley & Sons, Ltd. [source] Post-excavation deterioration of the Copney Bronze Age Stone Circle Complex: A geomorphological perspectiveGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2010Patricia A. Warke Post-excavation deterioration of stones from under blanket peat at the Copney Bronze Age Stone Circle Complex in County Tyrone, Northern Ireland, proceeded through widespread scaling, flaking, and splitting of stones. Investigation showed that prior to burial the porphyritic stones already possessed a complex legacy of geological weaknesses derived from hydrothermal alteration and tectonic deformation. Analysis indicated that significant alteration occurred during approximately 2000 years of burial under acidic peat cover, with development of a secondary porosity, alteration of primary minerals, and the opening of preexisting lines of weakness within the stones. Burial under peat also resulted in "bleaching" the stones so that they appeared white in color following excavation. These alterations during burial left the stones in a significantly weakened state and particularly susceptible to the effects of subaerial weathering processes. Data underline the potential fragility of excavated stonework and highlight the need to plan for its aftercare before complete excavation is undertaken. © 2010 Wiley Periodicals, Inc. [source] Uranium and thorium isotopes in the rivers of the Amazonian basin: hydrology and weathering processesHYDROLOGICAL PROCESSES, Issue 1 2003Aguinaldo N. Marques Jr. Abstract Two expeditions (October 1989 and May 1992) were carried out to two points of the main Amazon River channel and four tributaries. The Solimões and Madeira rivers, taking their origin in the Andes, are whitewater rivers. The Negro River is a typical acid, blackwater river. The Trombetas River flows through bauxite-rich areas, and is characterized by low concentrations of dissolved humic substances. The 238U, 234U, 232Th and 230Th activities were recorded from dissolved, suspended particulate phases and river bank sediments. The latter were analysed for their 226Ra, 228Ra and 210Pb contents, and also subjected to leaching with 0·2 M hydroxylamine,hydrochloride solution to determine the concentrations of radionuclides bound to amorphous Fe hydroxides and Mn oxides and hydroxides. The dissolved U average concentration in the Amazon system is ten times lower than the mean world river concentration. The uranium concentration observed at Óbidos in the lower Amazon (0·095 µg L,1), where the U content in the river bank sediments and suspended matter is lowest, suggests U release from the solid phase during river transport. About 485 t of U are transported annually to the Amazon delta area in dissolved form, and 1943 t bound to suspended particulate matter. Total U and Th concentrations in the river bank sediments ranged from 1·59 to 7·14 µg g,1 and from 6·74 to 32 µg g,1, respectively. The highest concentrations were observed in the Trombetas River. The proportion extracted by means of the hydroxylamine solution (HL) was relatively high for U in the Trombetas river bank sediment (31%) and for Th in the Solimões sediment (30%). According to the alpha recoil effects, the 234U/238U activity ratios of the Andean river waters and downstream Amazon water (Óbidos) were >1, but were <1 in the Negro River (at Manaus). The activity ratios of dissolved U correlate with pH and also with the U activity ratios in the river bank sediment hydroxylamine extracts. As expected, the 234U/238U activity ratios in river bank sediments were <1 in the Andean rivers and in the downstream Amazon, but they were >1 in the Trombetas and Negro rivers. Such ratios probably result from the binding of dissolved uranium to solid sediment. The 228Th/232Th ratios of river bank sediments were close to unity (except for the Negro River, where it is lower), suggesting no significant Th exchanges between the river water and the sediment. The 226Ra/232Th activity ratios were <1, and the 226Ra/228Ra activity ratios generally were significantly higher than the activity ratios of their respective parents. This perhaps is the result of easier leaching of the 226Ra parent, 230Th, from solid material (owing to the alpha recoil effect) than of the 228Ra parent. Uranium and thorium isotopes were used as tools to evaluate the chemical weathering rate of rocks in the Amazon system, which was estimated to be 2·7 cm 1000 year,1 s,1. Copyright © 2002 John Wiley & Sons, Ltd. [source] The first Raman spectroscopic study of San rock art in the Ukhahlamba Drakensberg Park, South AfricaJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2008Linda C. Prinsloo Abstract San rock art sites are found throughout southern Africa; unfortunately this unique heritage is rapidly being lost through natural weathering processes, which have been the focus of various studies conducted in the uKhahlamba Drakensberg Park since 1992. It has recently been shown that the ability of Raman spectroscopy to identify salts on rock faces on a micro, as well as nano scale, can make a contribution to these projects. In order to test the feasibility of undertaking on-site analyses, a small rock fragment with red and white pigments still attached, which had weathered off the rock face, was analysed with Raman spectroscopy under laboratory conditions, using a Dilor XY Raman instrument and a DeltaNu Inspector Raman portable instrument. A small sample of black pigment (<1 mm2), collected from a badly deteriorated painting and a few relevant samples collected on site, were analysed as well. It was possible to identify most of the inorganic pigments and minerals detected with previous XRD and EDX measurements including whewellite and weddellite coatings, which could be a tool for carbon dating purposes. Two carotenoid pigments were detected for the first time in San rock art pigments. Animal fat was also observed for the first time on both red and white pigments, on the rock face adjacent to the paintings and in highest concentrations on the back of the rock fragment. The spectra quality makes successful on-site measurements a good prospect. Copyright © 2008 John Wiley & Sons, Ltd. [source] Digestive system and feeding mode in Cambrian naraoiid arthropodsLETHAIA, Issue 2 2002JEAN VANNIER The function of the digestive system of naraoiid arthropods is interpreted in the light of new observations on Early Cambrian specimens from China and detailed comparisons with Recent crustaceans and other arthropods. In naraoiids, paired tubular diverticulae ending as blind caeca are present along the entire midgut, and are interpreted as sites for the secretion of digestive enzymes. Naraoia bears one pair of long, ramifying, distensible diverticulae, possibly used for both food storage and digestion as suggested by Recent analogues (e.g. branchiuran and isopod crustaceans and limulids). Naraoiids were probably epibenthic scavengers/predators rather than mud-eaters. They were either opportunistic intermittent feeders (Naraoia) or more regular feeders (Misszhouia). The mud-fills of the alimentary canals are likely to be artefacts due to taphonomic and weathering processes or, less likely, to sediment ingestion by animals trapped alive in turbiditic flows. The case study of naraoiid arthropods adds to other fossil evidence supporting the idea that predation played a key role in the Early Cambrian food-webs and that organs adapted for this purpose had already reached a high level of diversity and anatomical sophistication. [source] Nutrient transport within and between habitats through seed dispersal processes by woolly monkeys in north-western AmazoniaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 11 2010Pablo R. Stevenson Abstract The contribution of vertebrate animals to nutrient cycling has proven to be important in various ecosystems. However, the role of large bodied primates in nutrient transport in neotropical forests is not well documented. Here, we assess the role of a population of woolly monkeys (Lagothrix lagothricha lugens) as vectors of nutrient movement through seed dispersal. We estimated total seed biomass transported by the population within and between two habitats (terra firme and flooded forests) at Tinigua Park, Colombia, and quantified potassium (K), phosphorus (P) and nitrogen (N) content in seeds of 20 plant species from both forests. Overall, the population transported an estimated minimum of 11.5 (±1.2 SD),g of potassium, 13.2 (±0.7),g of phosphorus and 34.3 (±0.1),g nitrogen, within 22.4 (±2.0),kg of seeds ha,1,y,1. Approximately 84% of all nutrients were deposited in the terra firme forest mostly through recycling processes, and also through translocation from the flooded forest. This type of translocation represents an important and high-quality route of transport since abiotic mechanisms do not usually move nutrients upwards, and since chemical tests show that seeds from flooded forests have comparatively higher nutrient contents. The overall contribution to nutrient movement by the population of woolly monkeys is significant because of the large amount of biomass transported, and the high phosphorus content of seeds. As a result, the phosphorus input generated by these monkeys is of the same order of magnitude as other abiotic mechanisms of nutrient transport such as atmospheric deposition and some weathering processes. Our results suggest that via seed dispersal processes, woolly monkey populations can contribute to nutrient movement in tropical forests, and may act as important nutrient input vectors in terra firme forests. Am. J. Primatol. 72:992,1003, 2010. © 2010 Wiley-Liss, Inc. [source] Weathering processes and Quaternary origin of an alpine blockfield in Arctic SwedenBOREAS, Issue 2 2009BRADLEY W. GOODFELLOW The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigated through an examination of fine matrix and clasts from two pits excavated across ridge-top sorted circles; one on a summit, the other in a saddle. At the summit, fine matrix chemical weathering is limited to the production of poorly crystallized Al- and Fe-oxyhydroxides, whereas some additional vermiculitization and gibbsite crystallization occurs in the saddle. In both locations, volumes of clay-sized matrix are low, mass balance calculations indicate only minor elemental losses and no chemically etched grains are visible under a scanning electron microscope (SEM). In addition, soil horizons are absent and chemical weathering intensity is uniformly low across both excavated sorted circles. Minor clast chemical weathering consists of Fe oxidation, which dominates in the matrix-rich circle centres, and some rind development, which increases in frequency in the clast-rich rings. The dominance of physical weathering processes and the presence of only minor chemical weathering, in both fine matrix and clasts, indicate that the blockfield is not a Neogene weathering remnant. Rather, the blockfield has a Quaternary origin, developing during interglacials, interstadials and the Holocene, primarily through subsurface weathering processes. [source] Weathering of Monuments at Jethawanaramaya Complex in North-Central, Sri LankaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009Amila Sandaruwan RATNAYAKE Abstract: Sri Lanka has the richest archaeological sites in Asia. Jethawanarama Complex, one of the valuable sites in the country, is suffering from deterioration due to weathering. Monuments were built mainly from stones (granitic gneiss and marble) and clay bricks. The present study aimed to categorize weathering forms and interpret the recently-developing weathering processes. The growing of lichens on surfaces and the development of saline conditions are the major threats on the survival of monuments other than the typical weathering processes of tropical climates Morinite (NaCa2Al2[PO4)]2 [F,OH]5·2H2O) is identified as a weathering product of monuments and is generated from lichens. [source] | ||||||||||