Estimation of Pressuremeter Modulus and Limit Pressure in Weathered Granite Based on the SPT-N Value and Chemical Weathering Index: A Case Study in South Korea

A pressuremeter test (PMT) is a representative and highly reliable in situ test for assessing the stress–strain behavior of weathered granite. Its application, however, is restricted by its cost and time requirements. Many researchers have also investigated the correlations between the SPT-N value and the pressuremeter modulus (Em) and limit pressure (PL) of soils, but they have mostly focused on sand, silt, and clay and have employed simple regression analysis. In this study, equations for Em and PL were derived for weathered granite through multiple nonlinear regression analyses using a chemical weathering index that quantitatively represents the degree of weathering. Nonlinear multiple regression analyses were conducted by combining the allometric models that produced the optimal correlations between Em, PL, energy corrected SPT-N (SPT-N60), and normalized VR (Vogt’ ratio) with vertical effective stress. The obtained equations for Em and PL had higher R2 values (0.76 and 0.46, respectively) compared with the simple regression equations reported in previous studies. Because local characteristics are important determinants of the engineering properties of geo-materials, the Em and PL equations proposed in this paper are intended for use in geotechnical surveys of weathered granite in South Korea.

Provenance and weathering index of the Upper Cretaceous São Carlos Formation and its tectonic significance in the eastern Bauru Basin, SE Brazil

Geochemistry of major and trace elements has been used as an important tool for the study of provenance and tectonic and climatic evolution of sedimentary basins. The São Carlos Formation is an Upper Cretaceous unit that lies on the eastern border of the Bauru Basin. Despite the paleontological and paleodepositional studies performed in this unit in the last years, little is known about the correspondence between tectonic and climatic conditions acting during the first stages of sedimentation. The hypothesis of this paper is to evaluate São Carlos and Araçatuba formations and understand the evolution of the eastern border of the basin. Thus, were conducted geochemical studies using X-ray fluorescence on sandstones, siltstones, and shales from the São Carlos Formation. According to the chemical weathering index, which presented values ranging from 57.12 to 71.58%, the oxides of major elements indicate that moderate weathering processes affected the source area, possibly associated with the arid-semiarid climate. Alkaline rocks, granites, gneisses, and metasediments were the main lithotypes of the source area. Ternary diagrams show that the tectonic environment was equivalent to the passive continental margin, coinciding with the Serra do Mar and, secondarily, Alto Paranaíba Uplift regions. Based on major and trace elements, their ratios, and published data on the basin, was elaborated a paleogeographic model of the eastern border of the Bauru Basin, concluding that the source area of the sediments was constituted by intermediate and felsic rocks, sometimes recycled by sedimentary processes.

Geochemical and Petrographical Evolution of the Weathering Mantle Derived from Basalt in Bangam Locality (West-Cameroon): Implication in the Bauxitisation Process

A petrographical and geochemistry study of weathering mantle derived from the basaltic parent rock (plagioclase, olivine, pyroxene, zircon) has been conducted in the locality of Bangam (West-Cameroon). The weathered profile shows a vertical lithology succession of weathered parent rock, isalteritic clayed domain and superficial duricrust (alloterite). The weathering of basalt started by the formation of “pain d’epices” structure rich in gibbsite, metahalloysite, kaolinite. The geochemistry analysis of major elements indicate that SiO2 (46% -1.33%), K2O (0.84% - 0.01%), Na2O (3.6% -0.01%), MnO (0.3% - 0.04%), P2O5 (1.9% - 0.38%) and CaO (5% -0.02%) decrease from the bottom to the surface, however TiO2 (2.3% - 4.08%) remain constant, Fe2O3 (24.2% - 24,6%) and Al2O3 (14.5% - 45.2%) increase. The different weathering index such as, chemical index of alteration (55% - 99%), index of lateritization (41% - 103.5%) and Ruxton Ratio (0.12 - 3.21) just indicate an evolution of parent rock dominated by an alumina and iron phases under a control of hydrolysis phenomenon as bisialitisation, monosiallitisation and allitisation with the formation of minerals smectites group, kaolinite group gibbsite and iron oxides group. The fractionation patterns of rare earth elements (REE) show a positive and negative anomaly in Cerium and other rare earth elements, one more, the correlation between major, trace and REE prove a link of different pedological horizons developed on the basalt in redox condition.

Climate changes recorded by Hani Peat in Northeast China over the past 13.8 cal ka BP

The Hani peatland is one of the few that remain well-preserved in northeast China, which makes it a valuable site for paleoclimate research. Here, two sediment cores, which cover the past 13.8 ka, were collected, and loss on Ignition (LOI550°C) and X-ray Fluorescence Scanning (XRF) were carried out to build organic matter content and Rb/Sr ratio profiles, in order to assess the climate changes and associated East Asian Summer Monsoon (EASM) evolution since the last deglaciation. The results show that organic content and the chemical weathering index increased from the early to mid Holocene, possibly reflecting increased precipitation and an enhanced EASM. During the mid to late Holocene, the organic content and the chemical weathering index values decreased, implying that the EASM weakened. The variations of monsoon intensity during the Holocene derived from the Hani peat are consistent with the EASM reconstructions from the Gonghai, Daihai, Qinghai Lake, Hexiazi Island and the Yulin loess-paleosol section. Thus the Hani and other published EASM records from northern China demonstrate that the evolution of EASM during the Holocene was likely to be dominated by the combination of the influences from changing solar insolation and northern hemisphere ice volumes. In addition, a 0.5–2 ka band filtering analysis of LOI550°C data show that millennial scale climate changes in northeast China were teleconnected with the North Atlantic ice-rafted debris and solar irradiance records, indicating that both North Atlantic climate changes and solar activity probably affected EASM variations.

A preliminary study on the new geotechnical weathering index in the evaluation of altered biotite granite

The existing chemical index of alteration has a difficulty to evaluate the degree of weathering in biotite granites due to an assumption that K2O content decreases along with Na2O, CaO, and MgO. We found that relative K2O content increases during weathering of biotite granite, as it is retained within such rocks due to (1) the chemical and physical stability of K-feldspar and (2) the formation of illite via incorporation of K ions released from biotite. The calculated ranges of most chemical indexes for biotite granite weathering do not show a good correlation with the weathering grade except the CIW, WIP and V indexes. The range of the CIW, WIP and V indexes according to the weathering grade were very small, and thus small errors in whole-rock chemical analyses can produce large discrepancies in calculated values. Further, the WPI index is a relative weathering index that depends on the composition of a fresh standard sample and cannot be applied to determine the absolute degree of weathering in granites if no protolith is available. We suggest a new weathering index (BWI; Biotite weathering index) based on a decrease in the number of K ions in the interlayer site of biotite during weathering of granite. Newly calculated values show a much wider range than the CIW, WIP and V indexes with a good relationship with a weathering grade. Therefore, it is necessary to establish the new index for a detailed classification of weathering degree.