Geochemical Eccentricity of Ground Water Allied to Weathering of Basalts from the Deccan Volcanic Province,India: Insinuation on CO<Subscript>2</Subscript> Consumption     

N. J. Pawar  J. B. Pawar  Suyash Kumar  Ashwini Supekar 《Aquatic Geochemistry》2008,14(1):41-71

Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline earth elements to total cations and HCO₃>Cl + SO₄ reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO₄, and NO₃ are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO₃ type progressively evolves to Ca + Na–HCO₃ and Na–Ca–HCO₃ class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO₃ and Ca + Mg vs HCO₃ supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation of CaCO₃ supported by improved correlation coefficients between Na + Ca vs HCO₃ and negative correlation of Ca vs HCO₃, respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function of selective dissolution of olivine > pyroxene followed by plagioclase feldspar. The data suggest siallitization (L < R and R _k) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite) products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component range from 6.98 to 36.65 tons/km²/yr, respectively. The values of the CO₂ consumption rates range between 0.18 × 10⁶ mol//km²/yr (groundwater) and 0.9 × 10⁶ mol/km²/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO₂ consumption, an inference, that is, not taken into contemplation in most of the studies.  相似文献   

Primary volcanic structures from a type section of Deccan Trap flows around Narsingpur-Harrai-Amarwara, central India: Implications for cooling history     

Piyali Sengupta  Arijit Ray 《Journal of Earth System Science》2006,115(6):631-642

Field investigations of the Deccan Trap lava sequence along a 70 km traverse in the Narsingpur-Harrai-Amarwara area of central India indicate twenty lava flows comprising a total thickness of around 480 m. Primary volcanic structures like vesicles and cooling joints are conspicuous in this volcanic succession and are used to divide individual flows into three well-defined zones namely the lower colonnade zone, entablature zone, and the upper colonnade zone. The variable nature of these structural zones is used for identification and correlation of lava flows in the field. For twenty lava flows, the thicknesses of upper colonnade zones of eight flows are ∼5 m while those of eight other flows are ∼8 m each. The thicknesses of upper colonnade zones of remaining four flows could not be measured in the field. Using the thicknesses of these upper colonnade zones and standard temperature-flow thickness-cooling time profiles for lava pile, the total cooling time of these sixteen Deccan Trap lava flows has been estimated at 12 to 15 years.  相似文献   

Determination of specific yield using a water balance approach – case study of Torla Odha watershed in the Deccan Trap province, Maharastra State, India     

Dipankar Saha  A. K. Agrawal 《Hydrogeology Journal》2006,14(4):625-635

Specific yield is an essential parameter for any groundwater management plan. Volumetric analysis in the domain of groundwater budgeting for the non-monsoon months has been undertaken for a typical watershed of the Deccan basalt province. The Torla Odha watershed covers an area of over 22 km² on a third-order tributary of the westerly flowing Bhima River. The watershed receives a normal annual rainfall of 643 mm. The entire water demand is supplied by dug wells, which penetrate a shallow aquifer. The specific yield was estimated by comparing the monthly net volume of water removed from the aquifer, with the volume of aquifer de-saturated, based on monthly water level data. The estimated specific yield ranges from 0.0019 in May to 0.0173 in November with an average value of 0.0093. A correlation of the groundwater levels with the detailed geology suggests that the higher specific yield value (0.017) corresponds to dewatering of the weathered zone within the shallow aquifer. The specific yield of the massive basalt immediately below the weathered zone varies from 0.0089 to 0.0103. The underlying vesicular basalt, which is dissected by sheet joints, has a relatively higher specific yield (0.0121). The massive basalt, which forms the base of the shallow aquifer system, has a lower specific yield from 0.0019 to 0.0022.

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Résumé Le débit spécifique est un paramètre essentiel pour tout plan de gestion des eaux souterraines. Les analyses volumétriques, dans le cadre des bilans hydriques des eaux en dehors des mois de mousson, ont été entreprises pour un bassin-versant typique de la province basaltique du Deccan. Le bassin-versant du Torla Odha couvre une superficie de 22 km², et alimente l’affluent du troisième ordre de la rivière Bhima, qui coule vers l’Ouest. La pluviométrie annuelle atteint 643 mm. Toute la demande en eau es assurée par des puits foncés pénétrant dans l’aquifère phréatique. Le débit spécifique a été estimé en comparant le volume net mensuel d’eau captée dans l’aquifère, avec le volume de l’aquifère dé-saturé, basé sur les données des niveaux piézométriques mensuels. Le débit spécifique estimé s’étend entre 0,0019 en Mai et 0.173 en Novembre; la moyenne se situe à 0,0093. Une corrélation entre les niveaux des eaux souterraines et la géologie, suggère que les débits spécifiques les plus importants (0,017) correspondent aux zones altérées de l’aquifère phréatique. Le débit spécifique du massif basaltique, immédiatement sous la zone altérée, varie entre 0,0089 et 0,0103. Le basalte vésiculaire, situé juste en dessous et traversé par des diaclases parallèles, possède un débit spécifique sensiblement plus élevé (0,0121). Le basalte massif, qui forme la base de l’aquifère phréatique, possède un débit spécifique moins important, compris entre 0,0019 et 0,0022.

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Resumen El rendimiento específico es un parámetro esencial para cualquier plan de manejo de aguas subterráneas. Se ha llevado a cabo el análisis volumétrico, en el entorno de balance de aguas subterráneas, para los meses sin monzón de una cuenca típica de la provincia de basaltos Deccan. La cuenca Rorla Odha cubre un área de 22 km² en un tributario de tercer orden del Río Bhima que fluye al oeste. La cuenca capta una lluvia anual normal de 643 mm. La totalidad de la demanda de agua es abastecida por pozos manuales que penetran un acuífero somero. Se estimó el rendimiento específico al comparar el volumen neto mensual de agua removido del acuífero con el volumen de agua de-saturado estimado a partir de datos de niveles de agua mensuales. Los valores estimados de rendimiento específico varían de 0.0019 en mayo a 0.0173 en noviembre con un valor promedio de 0.0093. La correlación de niveles de agua subterránea con la geología de detalle sugieren que el valor más alto (0.017) de rendimiento específico corresponden con el desaguado de la zona de intemperismo dentro del acuífero somero. El rendimiento específico del basalto masivo que se encuentra inmediatamente debajo de la zona de intemperismo varía de 0.0089 a 0.0103. El basalto vesicular subyacente, el cual está disectado por fracturas laminares, tiene un rendimiento específico relativamente más alto (0.0121). El basalto masivo, que forma la base del sistema de acuífero somero, tiene un rendimiento específico más bajo el cual varía de 0.0019 a 0.0022. Palabras clave: basalto Deccan. India. Rendimiento específico. Recarga de agua subterránea. Balance hídrico.

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跑马岗组时代涉及的若干重大问题   总被引：1，自引：0，他引：1  

李伟同  刘耕武  陈钦保  张清如 《地层学杂志》2002,26(4):286-288,292

湖北当阳新店—跑马岗剖面的跑马岗组跨白垩系与古近系 ,所含轮藻、介形类化石的丰富程度极为罕见。跑马岗组的时代问题与白垩系 -古近系界线及其陆相辅助层型的建立、印度德干玄武岩沉积夹层的时代、印度与亚洲大陆联合的时代和白垩系 -古近系界线事件起因假说等数个重大地学问题 ,以及江汉盆地深层油气资源评价密切相关 ,值得重视 ,尽早搞清  相似文献   

Gravity and magnetic signatures of volcanic plugs related to Deccan volcanism in Saurashtra, India and their physical and geochemical properties   总被引：1，自引：0，他引：1  

D.V. ChandrasekharD.C. Mishra  G.V.S. Poornachandra RaoJ. Mallikharjuna Rao 《Earth and Planetary Science Letters》2002,201(2):277-292

The Bouguer anomaly and the total intensity magnetic maps of Saurashtra have delineated six circular gravity highs and magnetic anomalies of 40-60 mGal (10⁻⁵m/s²) and 800-1000 nT, respectively. Three of them in western Saurashtra coincide with known volcanic plugs associated with Deccan Volcanic Province (DVP), while the other three in SE Saurashtra coincide with rather concealed plugs exposed partially. The DVP represents different phases of eruption during 65.5±2.5 Ma from the Reunion plume. The geochemical data of the exposed rock samples from these plugs exhibit a wide variation in source composition, which varies from ultramafic/mafic to felsic composition of volcanic plugs in western Saurashtra and an alkaline composition for those in SE Saurashtra. Detailed studies of granophyres and alkaline rocks from these volcanic plugs reveal a calc-alkaline differentiation trend and a continental tectonic setting of emplacement. The alkaline plugs of SE Saurashtra are associated with NE-SW oriented structural trends, related to the Gulf of Cambay and the Cambay rift basin along the track of the Reunion plume. This indicates a deeper source for these plugs compared to those in the western part and may represent the primary source magma. The Junagadh plug with well differentiated ring complexes in western Saurashtra shows well defined centers of magnetic anomaly while the magnetic anomalies due to other plugs are diffused though of the same amplitude. This implies that other plugs are also associated with mafic/ultramafic components, which may not be differentiated and may be present at subsurface levels. Paleomagnetic measurements on surface rock samples from DVP in Saurashtra suggest a susceptibility of 5.5×10⁻² SI units with an average Koenigsberger ratio (Q_n) of almost one and average direction of remanent magnetization of D=147.4° and I=+56.1°. The virtual geomagnetic pole (VGP) position computed from the mean direction of magnetization for the volcanic plugs and Deccan basalt of Saurashtra is 30°N and 74°W, which is close to the VGP position corresponding to the early phases of Deccan eruption. Modeling of gravity and magnetic anomalies along two representative profiles across Junagadh and Barda volcanic plugs suggest a bulk density of 2900 and 2880 kg/m³, respectively and susceptibility of 3.14×10⁻² SI units with a Q_n ratio of 0.56 which are within the range of their values obtained from laboratory measurements on exposed rock samples. The same order of gravity and magnetic anomalies observed over the volcanic plugs of Saurashtra indicates almost similar bulk physical properties for them. The inferred directions of magnetization from magnetic anomalies, however, are D=337° and 340° and I=−38° and −50° which represent the bulk direction of magnetization and also indicate a reversal of the magnetic field during the eruption of these plugs. Some of these plugs are associated with seismic activities of magnitude ≤4 at their contacts. Based on this analysis, other circular/semi-circular gravity highs of NW India can be qualitatively attributed to similar subsurface volcanic plugs.  相似文献   

Rivers, chemical weathering and Earth's climate   总被引：4，自引：0，他引：4  

Bernard Dupr  Cline Dessert  Priscia Oliva  Yves Goddris  Jrme Viers  Louis Franois  Romain Millot  Jrme Gaillardet 《Comptes Rendus Geoscience》2003,335(16):1141-1160

We detail the results of recent studies describing and quantifying the large-scale chemical weathering of the main types of continental silicate rocks: granites and basalts. These studies aim at establishing chemical weathering laws for these two lithologies, describing the dependence of chemical weathering on environmental parameters, such as climate and mechanical erosion. As shown within this contribution, such mathematical laws are of primary importance for numerical models calculating the evolution of the partial pressure of atmospheric CO₂ and the Earth climate at geological timescales. The major results can be summarized as follow: (1) weathering of continental basaltic lithologies accounts for about 30% of the total consumption of atmospheric CO₂ through weathering of continental silicate rocks. This is related to their high weatherability (about eight times greater than the granite weatherability); (2) a simple weathering law has been established for basaltic lithologies, giving the consumption of atmospheric CO₂ as a function of regional continental runoff, and mean annual regional temperature; (3) no such simple weathering law can be proposed for granitic lithologies, since the effect of temperature can only be identified for regions displaying high continental runoff; (4) a general law relating mechanical erosion and chemical weathering has been validated on small and large catchments. The consequences of these major advances on the climatic evolution of the Earth are discussed. Particularly, the impacts of the onset of the Deccan trapps and the Himalayan orogeny on the global carbon cycle are reinvestigated. To cite this article: B. Dupré et al., C. R. Geoscience 335 (2003).  相似文献   

Palaeomagnetism and magnetostratigraphy of the Permian–Triassic northwest central Siberian Trap Basalts     

E.L. Gurevitch  C. Heunemann  V. Rad'ko  M. Westphal  V. Bachtadse  J.P. Pozzi  H. Feinberg 《Tectonophysics》2004,379(1-4):211-226

A detailed palaeomagnetic and magnetostratigraphic study of the Permian–Triassic Siberian Trap Basalts (STB) in the Noril'sk and Abagalakh regions in northwest Central Siberia is presented. Thermal (TH) and alternating field (AF) demagnetisation techniques have been used and yielded characteristic magnetisation directions. The natural remanent magnetisation of both surface and subsurface samples is characterised by a single component in most cases. Occasionally, a viscous overprint can be identified which is easily removed by TH or AF demagnetisation.The resulting average mean direction after tectonic correction for the 95 flows sampled in outcrops is D=93.7°, I=74.7° with k=19 and α₉₅=3.3°. The corresponding pole position is 56.2°N, 146.0°E.Unoriented samples from four boreholes cores in the same regions have also been studied. They confirm the reversed–normal succession found in outcrops. The fact that only one reversal of the Earth's magnetic field has been recorded in the traps can be taken as evidence for a rather short time span for the major eruptive episode in this region. However, there is evidence elsewhere that the whole volcanic activity associated with the emplacement of the STB was much longer and lasted several million years.  相似文献   

The anatomy of Continental Flood Basalt Provinces: geological constraints on the processes and products of flood volcanism   总被引：2，自引：0，他引：2  

Dougal A. Jerram  Mike Widdowson   《Lithos》2005,79(3-4):385-405

The internal architecture of the immense volumes of eruptive products in Continental Flood Basalt Provinces (CFBPs) provides vital clues, through the constraint of a chrono-stratigraphic framework, to the origins of major intraplate melting events. This work presents close examination of the internal facies architecture and structure, duration of volcanism, epeirogenetic uplift associated with CFBPs, and the potential environmental impacts of three intensely studied CFBPs (the Parana-Etendeka, Deccan Traps and North Atlantic Igneous Province). Such a combination of key volcanological, stratigraphic and chronologic observations can reveal how a CFBP is constructed spatially and temporally to provide crucial geological constraints regarding their development.

Using this approach, a typical model can be generated, on the basis of the three selected CFBPs, that describes three main phases of flood basalt volcanism. These phases are recognized in Phanerozoic CFBPs globally. At the inception of CFBP volcanism, relatively low-volume transitional-alkaline eruptions are forcibly erupted into exposed cratonic basement lithologies, sediments, and in some cases, water. Distribution of initial volcanism is strongly controlled by the arrangement of pre-existing topography, the presence of water bodies and local sedimentary systems, but is primarily controlled by existing lithospheric and crustal weaknesses and concurrent regional stress patterns. The main phase of volcanism is typically characterised by a culmination of repeated episodes of large volume tholeiitic flows that predominantly generate large tabular flows and flow fields from a number of spatially restricted eruption sites and fissures. These tabular flows build a thick lava flow stratigraphy in a relatively short period of time (c. 1–5 Ma). With the overall duration of flood volcanism lasting 5–10 Ma (the main phase accounting for less than half the overall eruptive time in each specific case). This main phase or ‘acme’ of volcanism accounts for much of the CFBP eruptive volume, indicating that eruption rates are extremely variable over the whole duration of the CFBP. During the waning phase of flood volcanism, the volume of eruptions rapidly decrease and more widely distributed localised centres of eruption begin to develop. These late-stage eruptions are commonly associated with increasing silica content and highly explosive eruptive products. Posteruptive modification is characterised by continued episodes of regional uplift, associated erosion, and often the persistence of a lower-volume mantle melting anomaly in the offshore parts of those CFBPs at volcanic rifted margins.  相似文献   

Seismic geomorphology of cretaceous megaslides offshore Namibia (Orange Basin): Insights into segmentation and degradation of gravity-driven linked systems     

《Marine and Petroleum Geology》2016

This study applies modern seismic geomorphology techniques to deep-water collapse features in the Orange Basin (Namibian margin, Southwest Africa) in order to provide unprecedented insights into the segmentation and degradation processes of gravity-driven linked systems. The seismic analysis was carried out using a high-quality, depth-migrated 3D volume that images the Upper Cretaceous post-rift succession of the basin, where two buried collapse features with strongly contrasting seismic expression are observed. The lower Megaslide Complex is a typical margin-scale, extensional-contractional gravity-driven linked system that deformed at least 2 km of post-rift section. The complex is laterally segmented into scoop-shaped megaslides up to 20 km wide that extend downdip for distances in excess of 30 km. The megaslides comprise extensional headwall fault systems with associated 3D rollover structures and thrust imbricates at their toes. Lateral segmentation occurs along sidewall fault systems which, in the proximal part of the megaslides, exhibit oblique extensional motion and define horst structures up to 6 km wide between individual megaslides. In the toe areas, reverse slip along these same sidewall faults, creates lateral ramps with hanging wall thrust-related folds up to 2 km wide. Headwall rollover anticlines, sidewall horsts and ramp anticlines may represent novel traps for hydrocarbon exploration on the Namibian margin.The Megaslide Complex is unconformably overlain by few hundreds of metres of highly contorted strata which define an upper Slump Complex. Combined seismic attributes and detailed seismic facies analysis allowed mapping of headscarps, thrust imbrications and longitudinal shear zones within the Slump Complex that indicate a dominantly downslope movement of a number of coalesced collapse systems. Spatial and stratal relationships between these shallow failures and the underlying megaslides suggest that the Slump Complex was likely triggered by the development of topography created by the activation of the main structural elements of the lower Megaslide Complex.This study reveals that gravity-driven linked systems undergo lateral segmentation during their evolution, and that their upper section can become unstable, favouring the initiation of a number of shallow failures that produce widespread degradation of the underlying megaslide structures. Gravity-driven linked systems along other margins are likely to share similar processes of segmentation and degradation, implying that the megaslide-related, hydrocarbon trapping structures discovered in the Namibian margin may be common elsewhere, making megaslides an attractive element of deep-water exploration along other gravitationally unstable margins.  相似文献   

Tracking temporal palynofloral changes close to Cretaceous-Paleogene boundary in Deccan volcanic associated sediments of eastern part of central Deccan volcanic province     

《世界地质(英文版)》2016,(4):205-215

Deccan volcanic sequences( DVS) in the central Deccan volcanic province( CDVP) are designated as Sahyadri Group having ~ 500 m thick lava pile associated with multiple sedimentary beds at different stratigraphic levels. In the eastern part of CDVP between the latitude 19 °55 '--20 °25 ' N and the longitudes 78 °15 '--78 °30 ' E,palynological investigation of the intertrappean sedimentary beds at five stratigraphic levels was carried out. The study was basically aimed for tracking the floral and environmental changes across the Deccan transition. The resulting finds indicate that the intertrappean sediments at the lowest stratigraphic level between the earliest lava flows are characterized by presence of marker Maastrichtian palynomorphs- Gabonisporis vigourouxii,Aquilapollenites bengalensis,Azolla cretacea and Farabeipollis associated with triporate and tricolpate pollen grains,phytoliths of Oryzeae of Poaceae family and peridinoid dinoflagellate cysts. The increasing volcanism deteriorated the existing flora as evident by absence of pollen-spores and presence of only structured biodegraded organic matter,fungal spores,acritarchs and algal( Botryococcus) remains in the sediments of higher-up in the sequence. For chronostratigraphic constraints on the lava flows magnetic polarity of the flows bracketing the intertrappean beds was investigated. The results indicated presence of N-R-N-R magnetic polarity in the basal lava pile that are interpreted as representing the magnetochron C30 N to C28 R( Maastrichtian-Paleogene). The floral change begins with the onset of volcanism in the chron C30 N and floral deterioration is observed in C29 N with increasing volcanism and it is only in the chron C28 R( Danian) that some evidence of recovery of flora is recorded. The current study shows that in eastern part of CDVP the post Cretaceous-Paleogene boundary eruptions represent the main phase of eruptions that triggered deterioration of the flora.  相似文献