Geosystems and Geoenvironment最新文献

A new biostratigraphic biozonation for the Paleocene to Late Oligocene succession of the onshore Niger Delta has been developed based on the identification of significant stratigraphic dinoflagellate cyst events. This study is aimed at applying rarely used dinoflagellate cysts events in dating, correlating and inferring the paleoenvironment of penetrated sedimentary successions in the studied area. Palynological processing and analysis were carried out on two hundred and twenty ditch cutting samples recovered from two exploration wells (BN-1 and FJ-1) located in the Greater Ughelli and Northern Depobelts of the onshore Niger Delta respectively. Abundant and diverse dinoflagellate cysts recovered included marker Peridinales species Apectodinium sp., Palaeocystodinium australinum, and Gonyaulacales such as Areosphaeridium arcuatum, Cordosphaeridium gracile, Tuberculodinium vancampoae, Polysphaeridium zoharyi and Hystrichokolpoma rigaudiae. Three dinoflagellate cysts Palynological Zones - DPZ 100 (Early to Late Paleocene), DPZ 200 (Early to Late Eocene) and DPZ 300 (Late Eocene to Late Oligocene) are proposed herein. The biozones were subdivided into ten subzones based on the Top occurrence, Quantitative Tops and Quantitative base as well as ACME events of dinoflagellate cysts marker taxa which are used to date the rock sequence to be Paleocene to Late Oligocene. Abundant and diverse shallow outer neritic to inner neritic dinoflagellate cysts are identified from thick grey soft shales at the lower section of the studied wells. The upper section show significant reduction in dinocysts assemblage dominated by inner (coastal) neritic taxa. This dinocysts occurrence and distribution suggests inner (coastal) neritic paleoenvironment at the upper sections which deepened into shallow outer neritic conditions at the lower intervals of the studied wells. The thick brown to grey shales at the lower section and the medium to fine grained, moderately well sorted sandstone interbeds at the middle section of the studied wells are interpreted to be potential source and reservoir rocks respectively. These datasets are useful for correlating possible hydrocarbon source rocks and potential reservoir carrier beds in the Gulf of Guinea.

The Ground magnetic study in the Wajrakarur Kimberlite Field and adjoining area has unveiled prominent geological variations, including felsic doming beneath the PGC-II formation to the west of the Cuddapah Basin and mafic doming beneath the Closepet Granite zone. These doming features within the upper mantle are identified as sources of mantle upwelling, which influence the emplacement of corresponding intrusive rocks. The presence of mafic chambers enhances the magnetic response, leading to localized high signatures in magnetic data and contributes to a better understanding of the subsurface composition and distribution of rock types. The present magnetic data throw lights to study the complexity of the sub-surface structure and geological activities, have shaped the study area and serve as valuable markers for understanding the geological evolution of the area. The intersections of magnetic lineament oriented in NW-SE, NE-SW, E-W yield crucial insights into geological structures and the emplacement of Kimberlite intrusions. Through comprehensive magnetic data analysis, the study offers a unique cross-sectional view of the subsurface, reaching depth up to 60 km. This perspective unveils magnetic sources and structures, revealing shallow features, interfaces of the Archaean basement, crustal roots, and upper mantle configuration. Profound magnetic gradients observed in the study area serve as indicators of fault lines influenced by tectonic activity, kimberlite intrusion, and other fault-related mineralization if any. These features contribute to a deeper understanding of the structural configurations and geological history of the area. The present study provides information about the lateral and vertical layouts of major structures as well as the deep-seated channels. It also introduces the mafic and felsic categories of rocks, explaining the complex relationships between underlying structures, geological characteristics, and magnetic anomalies.

Minerals from > 200 mantle xenoliths from Komsomolskaya kimberlite pipe were studied by electron microprobe and LA-ICP-MS. They are metasomatised garnet and spinel peridotites containing phlogopite, amphibole and ilmenite with garnets (up to 12.5 wt% Cr₂O₃) and clinopyroxenes (up to 5 wt% Na₂O) or rarer Fe-pyroxenites and A, B, C eclogites.

Thermobarometry indicates that the lithospheric mantle beneath the Komsomolskaya pipe is layered. Heated porphyroclastic, deformed peridotites at the lithosphere base (7–6 GPa) are enriched in Fe. The cold group at 6.0–5.5 GPa (34 mW/m²) are depleted peridotites with sub-Ca garnets. Cpx-fertilized varieties belong to the middle part of the mantle section. Amphiboles range from Cr-hornblendes to edenites (2–6 GPa), showing K-Ti enrichment. Picroilmenites yield two pressure intervals from 6.5 to 5.0 GPa and from 5.0 to 4.0 GPa, forming two differentiation branches. Eclogites mainly occur in the lower part of the section with a peak at pressures of 4–6 GPa.

Trace elements of melts that formed harzburgitic garnets-pyroxenes refer to oceanic MORB like melt interaction with peridotites. The sub-calcic S-type garnets are similar to subduction-related melts (S-type REE) with troughs in HFSE. Adakite-like hybrid metasomatism formed Na, Al-rich pyroxenes with peaks in Sr and HFSE. K-bearing pyroxenes and amphiboles refer to shoshonitic metasomatism. Trace elements for Cpx of re-fertilized mantle peridotites reveal high LREE, Nb-Ta troughs and peaks in Zr, Th, Sr, U. They are reacted to carbonatite –alkaline melts. Protokimberlite (essentially carbonatitic) interaction produced HFSE-enrichment. Type B eclogites show more subduction-related features with HFSE troughs while type A eclogites are closer to hybrid and peridotitic signatures. We suggest six types of major metasomatic agents. The ⁴⁰Ar/³⁹Ar ages of phlogopites vary in the 440–690 Ma range, with some at 1.6 Ga, suggesting multistage metasomatism.

The seismic susceptibility and mitigation management is paramount concern in tectonically active area like Northeastern India. This area has been devastated innumerably during the 1950 Assam great earthquake. The present study area falls in the foreland basin (Brahmaputra Valley) of Eastern Himalaya. This region is seismically vulnerable due to the tectonic complexity caused by the convergence of the Eurasian, Indian, and Burmese plates. In such, an area optimal disaster management and preparedness is necessary to define the non-linear character of seismic susceptibility, where population and unscientific urbanization have increased manifold. Therefore, for the present study, various multi-criteria decision making (MCDM) methods such as analytical hierarchy process (AHP), fuzzy-AHP (FAHP), and maximum entropy technique (MaxEnt) have been used for determining the seismic susceptibility, by assigning weightage to nine controlling factors such as: predominant frequency (f0), geology (G), vulnerability index (K), peak amplification (A0), liquefaction potential (LP), groundwater condition (WT), shear wave velocity (Vs30), peak ground acceleration (PGA), and land use/land cover (LU). The MaxEnt model exhibits the highest accuracy (87.5%) when the performance of the models was compared using the receiver operating characteristic curve (ROC) and area under the curve (AUC) value. Further, overlay analysis of best seismic susceptibility model using MaxEnt and PGV-based Japan Meteorological Agency (JMA) intensity shows that 40% the study area is in the very high and high seismic risk zone. In tectonically active areas, this kind of integration work is essential to improves the mitigation strategy and aids urban planners in designing earthquake-resistant buildings.

Climate change is considered a long-term change in precipitation, temperature and other meteorological variables. The pattern of meteorological variables is changing due to anthropogenic activities globally. Climate change has posed threat to natural and human systems. Thus, assessing and forecasting climate variability have become imperative for making resources sustainable and society resilient. This study examined trend and forecasted climate change using parametric and non-parametric methods in the Godavari Middle Sub-basin, India. Mann-Kendall and Sen's slope methods were utilized to analyze trend and magnitude of meteorological variables such as rainfall, maximum and minimum temperature, mean wind speed, mean evaporation and relative humidity. Forecasting of meteorological variables was carried out using the autoregressive integrated moving average (ARIMA) and seasonal autoregressive integrated moving average (SARIMA) models. Increasing trend in maximum and minimum temperature was observed at various level of significance. Decreasing trend was observed in mean evaporation at 0.05 level of significance. Decreasing trend in wind speed was also recorded in the sub-basin. February, March, April, June, October and December have shown increasing trend in relative humidity. Total monthly rainfall has shown decreasing trend in the south-eastern part of the sub-basin. Forecast of meteorological variables have also shown decrease in rainfall, increase in maximum and minimum temperature during 2017–2027 creating the sub-basin more prone to dry climate condition. Thus, a policy intervention-oriented climate action plan for lessening the impact of climate change is required in the sub-basin.

Land use and land cover (LULC) changes are important indicators of environmental and socio-economic changes made by the natural and anthropogenic sources. The present study is based on the Cellular Automata (CA) Markov model for predicting the LULC changes in the Tawi Basin. To decipher the spatio-temporal distributions of LULC, the Landsat images of 2010 and 2020 were used to analyse the LULC classification. Further, CA Markov model simulations of various scenarios of eight decades (2030 to 2100) were generated based on LULC of 2010 and 2020 data to know the LULC perspective changes in the Tawi Basin, which has witnessed the enormous developmental activities such as growth in settlement, population, and agriculture sector over the years. The model predicts that a population explosion leading to rapid urbanization and rural expansions.

Settlement is expected to increase from 5.29% of the total area in 2020 to 13.975% in the year 2100. The CA–Markov model results paint a picture of significant changes in land use and settlement patterns in the Tawi Basin. The study serves as a crucial tool for guiding future planning efforts, urging environmentalists, planners, and decision-makers to prioritize sustainable practices and make informed decisions for the well-being of the region.

Explanations for major catastrophes in the history of life commonly focus on their time-spans. Less biotic crises are worth attention as well, however, which requires their investigation in a longer-lasting context. The present study relates the Taghanic (Givetian) and mid-Carboniferous (Serpukhovian) biotic crises to some long-term changes in their environmental developments. The trends in these developments are interpreted on the basis of changes of the global sea level, the global average temperatures, the total surface area of exposed land, the total number of lithospheric plates, and the concentration of atmospheric oxygen. It is found that the Taghanic and mid-Carboniferous biotic crises can be related directly or indirectly to some long-term environmental changes.

Peripheral volcano sedimentary belts around the nucleus of Singhbhum-Granite-Complex are a part of one of the oldest continental crusts, known as the Singhbhum Craton (SC). Deciphering mutual relationship among these volcano-sedimentary packages offers considerable challenges. Badampahar-Gorumahisani Belt (BG Belt), Tomka Daitari Belt (TD Belt) and Bonai-Kendujhar Belt (BK Belt) draping Singhbhum-Granite-Complex as long linear belts from east, south and west, have some certain difference, primarily in terms of lithology. While the sedimentaries of BG Belt is mainly chemogenic, BK Belt is dominated by terrestrial sediments and TD Belt contains the both. Available data suggests the younger age of BK Belt than the rest couple of belts. Between TD Belt and BG Belt, another volcano sedimentary belt, commonly known as Hadgarh Belt, is present and it is less studied. The present study aims to characterize the Hadgarh Belt based on lithology and structure, which indicates its similarity with TD Belt. Almost identical lithologies are manifested by these two volcano sedimentary sequences barring the fact that the Hadgarh Belt has minor dominance of metasediments over metavolcanics, which is in subequal proportion in Tomka-Daitari and sensustricto BIF bands are absent in Hadgarh Belt. Both the belts have undergone uniform polyphase deformation and metamorphism. In both the belts, volcano sedimentary sequence of IOG is overlain by less deformed younger Mahagiri Quartzites and they are separated by an angular unconformity, marked by an impersistent conglomerate horizon. The intermediate area also sustains the similarities in depositional and deformational history with respect to the TD and Hadgarh belts on either side. Petrological studies also invoke similar mineral assemblage in the two belts, which is also in corroboration with the petrochemistry of the litho-units concerned. All the data thus generated, shows that the area, in totality, was evolved in an island arc setting varying from deep to shallow marine environments and sequence of deformations, intrusion of ultramafics followed by granite are also similar. In a nut shell, Hadgarh Belt can be referred as an extended part of the TD Belt.

This study investigates the evolving dry-wet climate patterns in southern India during 2020–2023, focusing on the impact of climate change. Spanning all 30 districts of Tamil Nadu, our analysis employs the HadGEM3-GC31-LL climate model, projecting a significant increase in humidity levels from 2021 to 2100. Key findings reveal consistently higher post-monsoon aridity indices compared to the monsoon season, exceeding 0.65 and raising concerns about potential flash floods. Regions most affected include Kanniyakumari, Nilgiris, Chennai and others. To address these challenges, the study recommends urgent policy interventions, emphasizing water conservation through initiatives like farm pond construction. Tailored policies are crucial to shield farmers and dairy producers from economic fallout, with an emphasis on integrating indigenous knowledge for effective climate change adaptation. In summary, this research highlights the need for immediate action, advocating for comprehensive strategies such as water conservation and tailored policies to enhance resilience and mitigate the impact of climate change in the studied regions.

The Bhavani Suture Zone, a region in the Southern Granulite Terrane (SGT), is where the Neoarchean Madurai Block and the Southern Madurai Block in western Tamil Nadu have been joined. The Mettupalayam Mafic-Ultramafic Complex, located in the eastern section of the BSZ, is made up of metagabbros, metadiorites, amphibolites and mafic granulites. The mafic-ultramafic outcrops are viewed and mafic-ultramafic rocks collected from Nellimalai, Togamalai, Sakkitiyan Karadu, Karudamalai, Karattur, Odhimalai, Tenkalmalai, Ramakavundanur hills. This study methodology is composed of three perspectives such as remote sensing study, laboratory spectral signature study and geochemical study. Firstly this study applied on Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) and Sentinel-2A used as a tool for mapping mafic-ultramafic rocks and applied the remote sensing techniques like color composites, BR (band ratio), PCA (Principal Component Analysis), MNF (Minimum Noise Fraction), SAM (Spectral Angle Mapper) and SVM (Support Vector Machine). Secondly laboratory spectral signature study is conducted for the 19 samples with ASD FieldSpec Pro® spectroradiometer was used to get the reflectance spectra in the 350–2500 nm spectral region. For different host rocks, the continuum-removed reflectance spectra offer diagnostic absorption features. Critical analysis was done on how the rock samples' elemental composition and related important minerals affected the absorption bands. The major and minor elements geochemical compositions of the BMUC rock samples identified by XRF method. The aim of this research is to characterize the BMUC using remote sensing studies, spectral signature study and geochemical analysis. The Sentinel-2A showing discriminating the lithology well than ASTER data and the spectral signatures absorptions are indicating presence of Fe and Mg contents. The rock samples are falling the series of tholeiitic to calc alkaline characteristics in geochemistry.