Journal of the Geological Society of India最新文献

This study provides a comparative evaluation of spatio-temporal distribution of soil erosion in Western (Mago Basin) and Eastern (Dibang Basin) basins of Arunachal Pradesh, India as these two basins are vulnerably exposed to soil erosion due to its topographical characteristics of mountainous steep slope and experiences heavy rainfall. The study was carried out for a ten-years period (2003 to 2014) using RUSLE model which encompasses five important factors contributing to soil erosion. Rainfall erosivity (R factor) map was calculated using Climate Prediction Center gridded precipitation. Soil map and soil samples were used to analyze soil erodibility (K factor) map. Slope length and slope steepness (LS factor) maps were computed from SRTM DEM (30 m resolution). MODIS NDVI images were used to obtain cover management (C factor) map. Landuse Landcover map was used to obtained support practice (P factor) map. Higher value in rainfall erosivity and cover management factor was observed in Mago basin which contributed to higher average annual soil loss of 17.423 t ha⁻¹ y⁻¹ in Mago basin and 5.461 t ha⁻¹ y⁻¹ in Dibang basin, whereas the other three factor values were almost the same. The spatial maps showed 56.65% of Mago basin area and 76.27% of Dibang basin area was under the class of slight erosion, with the remaining areas of moderate to severe erosion risk for both the basins. Temporal average soil erosion in Mago basin varied within moderate to very high erosion classes whereas Dibang basin erosion classes varied from slight to moderate. The temporal trend line showed that the overall soil erosion was increasing at an alarming rate for Mago basin whereas a slight increase in Dibang basin was observed.

The Upper Bhander Sandstone Member exposed along the Agra-Fatehpur Sikri tract near Rasulpur (Rajasthan) was investigated for a rare sedimentary structure, Liesegang rings. The studied unit also yielded other sedimentary structures such as cross-bedding, parallel lamination, ripple marks and trough cross-bedding; Liesegang rings were the most common and abundant. Two types of Liesegang rings were identified, one with a central core with outwardly radiating and alternating iron-rich (dark) and iron-poor (light) rings that were usually aligned parallel to the bedding plane (here designated as the Nucleation-type), and the other, that followed a fracture, and are composed of wavy rings (Wavy-type). The studied sandstone unit is quartzarenite type, wherein the monocrystalline plutonic quartz makes up 91% of the total framework grains. The grains are bound by two types of cementing material: silica (occurring as syntaxial overgrowth around detrital quartz grains) and iron oxide; higher amount of iron oxide and secondary porosity was noted. The formation of Liesegang rings involves iron-rich meteoric waters being infiltrated through fractures, pores and more importantly, by the formation of secondary porosity within the sandstone (diagenetic processess). Addition to this microscopic character, other factors that are responsible for the formation of Liesegang rings include surface water, suitable topographic exposure, condensed grid of joint polygons, and composition and thickness of the sandstone beds under study. Detailed microscopic analysis of rings (iron-rich and iron-poor) may provide a better understanding of the pathways of fluid movement enabling the formation of Liesegang rings.

The present research study aims to analyze flood frequency to relate flood magnitudes with corresponding return periods. These estimates are crucial for the development of flood-preventive hydrological infrastructures and flood plain zoning, etc. Basin-wide high intensity of rainfall and high discharge from the upper riparian region during monsoon months creates flooding in the middle and lower reaches of the Ghagra River basin. Therefore, the flood estimates for three gauging sites situated on the mainstream of the Ghagra River viz., Elginbridge, Ayodhya, and Turtipar, have been comprehended using the Gumbel distribution (Extreme Value Type I) method and the Log-Pearson Type III distribution method. Flood estimates are calculated for 1.01, 1.05, 1.11, 1.25, 2, 5, 10, 20, 50, 100, 200, and 500 years return periods considering flood time series of 50 years to reduce estimation uncertainty. The findings of flood frequency analysis (FFA) revealed that the probability of occurrence of the flood is more than 80% at all three sites because Ghagra River can carry around 7800 to 9000 m³/s of water discharge without posing a high risk of levee break. The upper and lower limits of discharge carrying capacity depend on the river’s desiltation process. Hence, the flood occurs almost every year in the basin; its only variation is its severity. The rainfall-runoff relationship is estimated by integrating a simple linear model and for rainfall trend analysis Mann-Kendall is applied. Linear regression analysis-based rainfall-runoff relationship outcomes revealed a significant relationship with a positive correlation coefficient i.e., 0.2722 for Elginbridge, 0.39624 for Ayodhya, and 0.4844 for Turtipar gauging site in the monsoon season but other factors like a high amount of water discharge from dams in upper riparian regions, etc. are also responsible for flooding in the middle and lower reaches. The Mann-Kendall trend analysis shows a decrease in annual average rainfall and rainfall in the monsoon season. Discharge variability indicates the direct relationship between flood fury and changes in climatic patterns in recent decades. This paper identifies that future research is needed to better inform the policy planners who strive to design sustainable infrastructure.

Understanding the temporal and spatial evolution of the North China Craton (NCC) basement, formed by amalgamation, is a crucial issue in global geosciences. The Huozhou complex is situated at the core of the Trans-North China Orogen (TNCO) in the NCC and comprises a considerable number of Palaeoproterozoic granitic gneisses, providing valuable insights into the tectonic evolution of the TNCO. In this study, comprehensive field geological surveys, petrology, chronology, geochemistry, and Hf isotope analysis were conducted to investigate the genesis and tectonic context of the Xingtangsi and Zhengnangou granitic gneisses and elucidate the TNCO’s tectonic evolution. The Xingtangsi granite gneiss yielded a magmatic zircon age of 2495±34 Ma, implying its Palaeoproterozoic or Archean origin, as previously suggested. Its protolith was I-type peraluminous granite, primarily generated through the partial melting of pre-existing continental crust materials with a small quantity of mantle-derived magma. The Zhengnangou granitic gneiss’s protolith was A-type granite, and its magmatic zircon age was 2,190±11 Ma, indicating its Palaeoproterozoic origin rather than Archean. T_DM1(Ma) for the Zhengnangou granitic gneiss ranged from 2,424 to 2,498 Ma, T_DM2(Ma) varied from 2563 to 2684 Ma, and the ε_Hf(t) value ranged from 1.3 to 3.3. These results suggest that it was primarily derived from newly formed crustal materials without any mantle-derived addition. Integrating our data with the literature, the ∼2.5 Ga magmatic activity in the Huozhou area may have formed in the tectonic setting of the continental arc, and ∼2.2 Ga A-type granite may have formed in a post-collisional extensional environment.