Applying geologic unit distribution and chemical weathering indices to evaluate potential lithologic sources of Al, As, and Pb to the San Juan River, Four Corners region, USA

Changes in mineralogical, chemical, and mechanical properties of a rock mass during the weathering process allow calibrating the degree of weathering. Based on those properties, various weathering indices can be used as tools for this purpose. This study focuses on using chemical weathering indices that represent the chemical behaviour of a rock mass and their relationship with other properties for better evaluation of weathering grades. Metamorphic rocks that undergo weathering due to both chemical and operational means at Smanalawewa hydropower station in Sri Lanka, where tropical climate exists, were selected for this study. Among the chemical weathering indices calculated, the product index, Ruxton ratio, silica-titania index, alumina-titania index, chemical weathering index by Sueoka, and S/SAF index change consistently with progressive weathering. They correlate well with the weathering potential index, Miura index, bulk density, and point load strength. Among the six indices mentioned, the product index, Ruxton ratio, silica-titania, and alumina-titania indices have been recognised as better measures to classify metamorphic rocks in Sri Lanka for chemical means. Since there is a good correlation with physical and mechanical properties, the chemical weathering index and S/SAF index also appear to be better indices in the same context. Weathering potential, Parker, and modified weathering potential indices, which are widely used, show minor fluctuations during weathering. On the contrary, the chemical index of weathering and chemical index of alteration fluctuate with progressive weathering. These changes exhibit the influence of bulk mineral composition of the rock, where aluminium rich minerals are present. This study clearly shows that chemical weathering indices of a particular rock mass are more reliable when they correlate well with physical and mechanical properties.

Re-assessment of chemical weathering indices: case study on pyroclastic rocks of Hong Kong

The negative effects of elevated concentrations of inorganic aluminium on aquatic organisms are well documented. Acid deposition is often cited as a main driver behind the mobilisation and speciation of aluminium in soils and surface waters. In the study, we tested the hypothesis that sulphur deposition is the main driver for elevated concentrations of inorganic aluminium in 114 base poor, boreal Swedish streams. However, the deposition of anthropogenic sulphate has decreased substantially since it peaked in the 1970s, and at the current deposition levels, we hypothesise that local site parameters play an important role in determining vulnerability to elevated concentrations of inorganic aluminium in boreal stream waters. Presented here are the results of a principal components analysis of stream water chemistry, acid deposition data and local site variables, including forest composition and stem volume. It is shown that the concentrations of both organic and inorganic aluminium are not explained by either historical or current acid deposition, but are instead explained by a combination of local site characteristics. Sites with elevated concentrations of inorganic aluminium were characterised by small catchments (<500 ha) dominated by mature stands of Norway spruce with high stem volume. Using data from the Swedish National Forest Inventory the area of productive forest land in Sweden with a higher vulnerability for elevated inorganic aluminium concentrations in forests streams is approximately 1.5 million hectares or 7% of the total productive forest area; this is higher in the south of Sweden (10%) and lower in the north (2%). A better understanding of the effects of natural processes and forest management in controlling aquatic inorganic aluminium concentrations is therefore important in future discussions about measures against surface water acidification.

Objectives: This study aimed to conduct a detailed chemical analysis of the Samanalawewa dam to provide information on its weathering conditions. Method: The mineralogical composition of the dam was analyzed by powder Xray diffraction (PXRD), atomic absorption spectroscopy (AAS), gravimetric, and X-ray fluorescence (XRF) analysis in order to identify chemical changes that have taken place. Findings: Widespread discoloured (brick red) and crushable areas in the dam and the quarry site indicate weathering of the compositional rocks. Each weathered rock sample showed a similar compositional pattern to each other as well as charnockite (CHA) rather than the other structural rocks of the dam; biotite gneiss (BIO), garnet biotite sillimanite gneiss (GAR), and limestone (LIM) indicating that only CHA has been weathered rapidly. Since LIM is not affected and the contact water (pH; reservoir 6.79 - 7.12 and holes in the quarry site 6.43-6.78) is almost neutral, this rapid weathering has not been governed by general chemical weathering processes like acid rains or stormwater. The relative contents of aluminium and magnesium have decreased during the weathering process while increasing the relative content of iron as well as sodium, which is a mobile element. The potassium content also has not decreased significantly. Moreover, chemical weathering indices like chemical index of alteration (CIA) and chemical index of weathering (CIW) values for completely weathered rocks were less than 50 revealing their unsuitability to assess the degree of weathering of the Samanalawewa dam. Novelty: Charnockite in the Samanalawewa dam has been weathered rapidly and chemical weathering indices; CIA and CIW are not valid to assess its degree of weathering. Keywords: Metamorphic; Charnockite; Rock weathering; Rock composition; Chemical weathering indices

Applicability of chemical weathering indices of eolian sands from the deserts in northern China

Black Mesa is an isolated remnant of Upper Cretaceous rocks lying in northeastern Arizona between more extensive areas of rocks of similar age in northwestern New Mexico and in southern Utah. The Dakota sandstone is the basal Cretaceous formation of Black Mesa. It is overlain by the Mancos shale, which, in the Black Mesa area, represents only a small part of the type Mancos of southwestern Colorado. Overlying the Mancos in the Black Mesa area are three newly defined formations in the Mesaverde group. All these formations are older than any part of the Mesaverde in the type area in southwestern Colorado. The basal formation herein defined as part of the Mesaverde group of Black Mesa is the Toreva formation. In the southern part of the area, the Toreva comprises a lower sandstone member, a middle carbonaceous member, and an upper sandstone member, and it is of late Carlile age. In the northern part of Black Mesa the Toreva formation is somewhat younger than in the southern part; it is equal in age to the upper part of the Carlile shale and the basal part of the Niobrara formation of the Front Range. In that area also the formation is divided into three units, but these are not correlative throughout with those present on the south, and they are not herein recognized as map units or as members of the formation. It is realized however, that such recognition is possible and may be desirable at a later date. Overlying the Toreva formation is the newly defined Wepo formation, of lower Niobrara age, a succession of continental shale, sandstone, and coal some marine sandstone. The Wepo is overlain by the Yale Point sandstone of middle Niobrara age. The Yale Point sandstone is the youngest Cretaceous formation of the Black Mesa area. It is believed to be correlative with a similar unit in the middle of the Straight Cliffs sandstone of the Kaiparowits Plateau in southern Utah and with the Hosta tongue of the Point Lookout sandstone of the southern part of the San Juan Basin in northwestern New Mexico. The Cretaceous rocks of Black Mesa are a result of neither the oldest nor the youngest deposition of Cretaceous time in the western interior of the United States, but represent deposition during the relatively short span of time involved in the greatest southwestward extension of Cretaceous seas in this part of the continent. They illustrate plainly that the initial inundation, although gradual, was persistent and was rather rapid in comparison to the long history of shoreline fluctuation that accompanied the slow and hesitant retreat of the sea from the interior of the United States.

Chemical weathering of sediment (CWS): A web-based application for chemical weathering study of rocks and sediment

Chemical weathering of monsoonal eastern China: implications from major elements of topsoil

The use of cation packing index for characterizing the weathering degree of granitic rocks

Mineral resources of Fort Defiance and Tohatchi quadrangles, Arizona and New Mexico

Highly weathered granites exist in thick subsurface layers in most regions of South Korea and are often used as a bearing stratum of geotechnical structures. However, because of the difficulty of retrieving samples for laboratory tests and the cost and time constraints of in situ testing, researchers mostly estimate the geotechnical properties of highly weathered granite using the standard penetration test (SPT)-N values or directly adopt the literature values. In this study, in situ testing was performed to evaluate the geotechnical properties of highly weathered granite in South Korea, and the chemical weathering indices were calculated using the retrieved samples. Particular attention was given to the development of a geotechnical properties estimation method that could consider the degree of weathering and site-specific characteristics using both in situ test results and chemical weathering indices. Correlation analysis was performed between the geotechnical properties of the highly weathered granite predicted by the proposed method and the measured geotechnical properties. The results show that the pressuremeter modulus values (Em and Eur) that were estimated using the modified weathering potential index (MWPI) showed a strong correlation (R2 > 0.7) with the measured values.

In order to assess the relationship between chemical weathering indices and physical properties of granite, physical and chemical analyses were performed on both natural and artificially weathered granite samples from the Seoul area, where the pH of the rainfall occasionally drops to below 5. The results suggest that slake durability, uniaxial compressive strength, Ruxton ratio, Parker index, modified weathering potential index, chemical alteration index and loss on ignition effectively revealed changes of the degree of chemical weathering. However, the study showed no such good correlation between chemical and physical properties except dry density against loss on ignition and modified weathering potential index against uniaxial compressive strength. It is recommended that both physical and chemical indices should be used for the classification of weathering grade for the granites in the Seoul area.

As a consequence of acid depositions on poorly buffered catchments underlain by hard rocks, aluminum is mobilized and transported from terrestrial systems to the aquatic environment. Loss of fishes has been related to low pH and elevated aluminum concentrations in surface waters which present a low ionic content especially during acid stress such as snowmelt and heavy rainfalls. Among the causes of fish population decline in acid waters, aluminum is considered a toxic cofactor. Different studies have clearly shown that aluminum is accumulated in different organs such as kidneys, liver and gills. Research on fish has demonstrated that aluminum may be toxic, but the toxicity is markedly influenced by the pH, organic compounds and calcium content of the water. Field surveys have shown clearly that macroinvertebrates are also affected by surface-water acidification. However, little is know about the possible effects of aluminum on aquatic invertebrates and, particularly, on aquatic insects exposed to acidic conditions. Hall et al. have shown that the whole-body concentration of aluminum decreases in blackflies and mayflies transplated from neutral water to acid water. Similar results have been reported for Daphnia and chironomid. On the contrary, Ormerod et al. demonstrated the absence of relationship between water pHmore » and insect aluminum concentrations. When aluminum occurs in aquatic insects, it has been shown that it is primarily adsorbed on the external surface and/or accumulates in gut contents. To our knowledge, the subcellular location as well as the toxicity of aluminum to acid-sensitive aquatic insects remains unclear and existing hypotheses are often based on research on fish. In this content the purpose of this study was to investigate the presence of aluminum at a subcellular level in the acid-sensitive species of stonefly, Perla marginata, after exposure to low pH and elevated aluminum concentrations. 18 refs., 1 fig., 1 tab.« less

In South Korea, weathered granite is widely distributed and has been used as a bearing stratum for various structures. Therefore, it is important to determine the shear strength of the weathered granite. However, it is difficult to obtain reliable shear strength parameters with laboratory tests or standard penetration test (SPT) because weathered granite is easily crushed during the sampling process, and the penetrability of SPT is not secured. On the other hand, it is well known that weathering affects the variation of geotechnical properties. Based on this concept, this study reports a correlation between the shear strength parameters and the chemical weathering indices of the weathered granite. In this study, the pressuremeter test (PMT) was adopted to determine the friction angle of the weathered granite. For the identical granite, the chemical weathering indices (Vogt’s Ratio (VR), Chemical Index of Alteration (CIA), and Mobiles Index (Imob)) were measured by X-ray fluorescence (XRF). An estimating model considering both site-specific characteristics and degree of weathering was used, and the CIA showed the best correlation (R2 = 0.66) with friction angle among the weathering indices. Since the ratio of measured friction angle over the predicted one was distributed in the range from 0.8 to 1.2, it is more reasonable to predict friction angles based on CIA comparing to using the SPT-N value. It can contribute to a better estimation of friction angles of weathered granite.

Chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks