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The Rajmahal Traps were discovered in the Panagarh area, West Bengal, during the exploration for coal resources. A Gondwana succession was found beneath the traps, consisting of the Early Cretaceous Intratrappean Rajmahal Formation, the Early Triassic Panchet Formation and the Late Permian coal-bearing Raniganj Formation. The present palynological study was aimed at confirming the age of the Panchet Formation. As a result of this study it has been found that Jurassic sediments are also included in the Panchet Formation. The study has revealed that the Panchet Formation, defined on a lithological basis, is a time-transgressive unit extending from the Early Triassic to the Late Jurassic, with a phase of non-deposition between the Middle Triassic and Middle Jurassic. 相似文献
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Summary This paper endeavours to evolve a method of simultaneous determination of astronomic latitude, azimuth and longitude from
observations of a star-pair near their times of east and west elongations and a south star near its time of meridian transit.
The star-pair of observation being within a short distance of elongation, either east or west, their motion in azimuth then
is extremely slow and the small error in time has therefore insignificant effect on their azimuth, and in addition, the south
star with its azimuth known from observations of the previous star-pair, being very fast-moving, the method is especially
suitable for determining the astronomic latitude, azimuth and longitude by observing only the time and horizontal angees between
them, and also a reference mark for ensuring the orientation of the horizontal circle side by side. 相似文献
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J. C. Bhattacharji 《Journal of Geodesy》1980,54(2):225-233
The Everest spheroid, 1830, in general use in the Survey of India, was finally oriented in an arbitrary manner at the Indian
geodetic datum in 1840; while the international spheroid, 1924, in use for scientific purposes; was locally fitted to the
Indian geoid in 1927. An attempt is here made to obtain the initial values for the Indian geodetic datum in absolute terms
on GRS 67 by least-square solution technique, making use of the available astro-geodetic data in India, and the corresponding
generalised gravimetric values at the considered astro-geodetic points, as derived from the mean gravity anomalies over1°×1° squares of latitude and longitude in and around the Indian sub-continent, and over5° equal area blocks covering the rest of the earth’s surface. The values obtained independently by gravimetric method, were
also considered before actual finalization of the results of the present determination. 相似文献
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Somdev Bhattacharji Rajesh Sharma Nilanjan Chatterjee 《Journal of Earth System Science》2004,113(4):771-784
The western continental margin and the intraplate Narmada-Tapti rifts are primarily covered by Deccan flood basalts. Three-dimensional
gravity modeling of +70mgal Bouguer gravity highs extending in the north-south direction along the western continental margin
rift indicates the presence of a subsurface high density, mafic-ultramafic type, elongated, roughly ellipsoidal body. It is
approximately 12.0 ±1.2 km thick with its upper surface at an approximate depth of 6.0 ±0.6 km, and its average density is
{dy2935} kg/m3. Calculated dimension of the high density body in the upper crust is 300 ±30 km in length and 25 ±2.5 to 40 ±4 km in width.
Three-dimensional gravity modeling of +10mgal to -30mgal Bouguer gravity highs along the intraplate Narmada-Tapti rift indicates
the presence of eight small isolated high density mafic bodies with an average density of {dy2961} kg/m3. These mafic bodies are convex upward and their top surface is estimated at an average depth of 6.5 ±0.6 (between 6 and 8km).
These isolated mafic bodies have an average length of 23.8 ±2.4km and width of 15.9 ±1.5km. Estimated average thickness of
these mafic bodies is 12.4±1.2km. The difference in shape, length and width of these high density mafic bodies along the western
continental margin and the intraplate Narmada-Tapti rifts suggests that the migration and concentration of high density magma
in the upper lithosphere was much more dominant along the western continental margin rift. Based on the three-dimensional
gravity modeling, it is conjectured that the emplacement of large, ellipsoidal high density mafic bodies along the western
continental margin and small, isolated mafic bodies along the Narmada-Tapti rift are related to lineament-reactivation and
subsequent rifting due to interaction of hot mantle plume with the lithospheric weaknesses (lineaments) along the path of
Indian plate motion over the Réunion hotspot. Mafic bodies formed in the upper lithosphere as magma chambers along the western
continental margin and the intraplate Narmada-Tapti rifts at estimated depths between 6 and 8 km from the surface (consistent
with geological, petrological and geochemical models) appear to be the major reservoirs for Deccan flood basalt volcanism
at approximately 65 Ma. 相似文献
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The discovery of traps in the subsurface Mesozoic succession of the Panagarh area, West Bengal, has drawn attention to their correlation with the traps in the Rajmahal Basin, Bihar. The objective of this paper is to assess the palynological dating of the intertrappean beds with the help of sequential first appearances of the stratigraphically important spore species Cicatricosisporites australiensis, Aquitriradites spinulosus, and Foraminisporis wonthaggiensis. C. australiensis, along with the first appearance of A. spinulosus, denotes the earliest Berriasian. This association is significant for recognition of the Jurassic/Cretaceous boundary. The lowest occurrence of F. wonthaggiensis indicates deposits of Berriasian–Valanginian age. The data on which these observations are based have been obtained from the intertrappean beds of the Rajmahal Formation in six boreholes: PGD-1A, 2, 4, 6, 8 and 9A. Further palynological studies on boreholes PGD-4, 8 and 9A have indicated the approximate time-span for the duration of volcanic activity in the Panagarh area. This seems to have been initiated in the early Berriasian and continued into the Hauterivian, which is earlier than the volcanism associated with the Rajmahal traps in the Rajmahal Basin. 相似文献
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