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191.
Evidence of lacustrine sedimentation in the Upper Permian Bijori Formation, Satpura Gondwana basin: Palaeogeographic and tectonic implications 总被引:1,自引:0,他引:1
The Upper Permian Bijori Formation of the Satpura Gondwana basin comprising fineto coarse-grained sandstone, carbonaceous
shale/mudstone and thin coal bands was previously interpreted as the deposits of meandering rivers. The present study documents
abundance of wave ripples, hummocky and swaley cross-stratification and combined flow bedforms in the Bijori Formation, suggesting
that a significant part of the formation was deposited in a wave-agitated environment. Evidence of near-emergent depositional
conditions provided by repeated occurrence of rootlet beds and hydromorphic paleosols, local flooding surfaces denoting rapid
fluctuation of water level, occurrences of temnospondyl vertebrate fossils, and absence of tidal signatures and marine fossils
suggest a lacustrine rather than marine depositional regime. Five facies associations recognised within the Bijori Formation
are inferred to represent fluvial channels and associated floodplains (FA1), lake shorelines (FA2), subaqueous distributary
channels and associated levees (FA3), waveand storm-affected delta front (FA4), and open lacustrine/lower shoreface (FA5)
deposits. The planoconcave fluvial channel-fill sandbodies with unidirectional cross-beds are clearly distinguishable from
the delta front bars that show a convexo-plan or bi-convex sandbody geometry and dominance of wave and combined flow bedforms.
Some of the distributary channels record interaction of fluvial and wave-dominated basinal processes. Major distributary sandbodies
show a north to northwest flow direction while wave-affected delta front sandbodies show very complex flow patterns reflecting
interaction between fluvial discharge and wave processes. Wave ripple crest trends show that the lake shoreline had an overall
east-northeast to west-southwest orientation. The lack of documented contemporaneous lacustrine or marine sediments in the
Satpura Gondwana basin posed a major problem of basin-scale palaeogeographic reconstruction. The existence of Bijori lake
solves the problem and the lake is inferred to have acted as repository for the contemporaneous alluvial drainage. Development
of the large Bijori lake body implies generation of accommodation space exceeding the rate of sediment supplied and thus represents
locus of high tectonic subsidence. Transition of fluvial sediments with red mudstone and calcareous soil profile in the lower
part of the succession to carbonaceous shale and coal-bearing lacustrine sediments in the upper part, denote a change from
a warm semi-arid climate with seasonal rainfall to a more humid one. 相似文献
192.
Anant Parekh Abhijit Sarkar M. Ravichandran 《Journal of the Indian Society of Remote Sensing》2005,33(1):121-126
Multi-channel Scanning Microwave Radiometer (MSMR) onboard 1RS P4 (Oceansat I) measured Brightness Temperature data of the
different bands are found sensitive to the surface and the overlying atmosphere to different degrees. A judicious combination
of multi-channel data can provide such oceanic/atmospheric parameters as surface wind speed, sea surface temperature, water
vapour in the marine atmosphere, etc. This paper highlights results obtained in relation to surface wind speed. Co-location
and concurrence of several ocean data buoys in the Arabian Sea with MSMR observations allowed empirical construction of D-matrix
coefficients for surface wind speed. With both MSMR and the Arabian Sea buoys functioning for the period of one and a half
year (June, 1999 to December, 2000) without interruptions provided a large database. All channels are found to exhibit moderate
sensitivity to surface wind speed. MSMR data in the immediate vicinity (within 150 km) of the buoy locations and within a
time window of one hour were used. A multi-channel linear equation for surface wind speed was subsequently derived. The equation
was subjected to tests with independent data set for the period January - June 2001 over the Arabian Sea and found to be moderately
accurate. The empirical equation is expected to be useful for regional applications over the Arabian Sea and over regions
closer to west coasts, which might have been flagged out in the operational geophysical data stream. An interesting subset
of data revealed the wind signatures of the May 2001 cyclone in the Arabian Sea. 相似文献
193.
The statistical behaviour of the sudden enhancement in signal strength (SES) in relation to solar X-ray flares has been studied for the near east-west propagation of 40 kHz radio waves from Sanwa (36°11’N; 139°51’E) in Japan to Calcutta (22°34’N; 88°24’E) over a long distance path of 5100 km for a period of two years. The period has been divided into four phases - P1, P2, P3 and P4, according to the position of the overhead sun. The change in signal strength during X-ray flares is dependent on the solar zenith angle and climatic conditions. The statistical modal values of the time lag of the SES peak with respect to that solar X-ray flare is found to increase as solar zenith angle increases. The relative rates of increase and decrease of the signal strength (RRISS and RRDSS respectively) have been evaluated for a number of SES which are related to large X-ray flares. Their characteristics have also been investigated. The modal values of the relaxation time have been found to be highly correlated with climatic conditions like temperature and humidity of the propagation path. 相似文献
194.
The problem of selecting the optimum operating frequency of a scatterometer, used for remote sensing of sea surface wind speed
has been addressed by applying the criteria of maximum sensitivity of backscattering coefficient to wind speed as well as
its correlation with wind speed. The backscattering coefficient values for sea surface were computed by the two-scale scattering
theory. To compute the atmospheric transmittance, 753 clear sky atmospheres over Indian Ocean were used. While the correlation
coefficient was uniform (0.94) throughout the frequency range of 1 to 30GHz, only frequencies above 5GHz were found sensitive
enough to yield a wind speed accuracy of ±2msec−1 and better, the accuracy improving with frequency. 相似文献
195.
The paper deals with the relationship between the sea surface wind speed (U) and the backscattering coefficient (σ0) for microwave frequencies and quasi specular range of angles. Valenzuela’s effective reflection coefficient based on the theory of scattering of electromagnetic waves from rought dielectric surfaces has been introduced in the expression of backscattering coefficient and the final result compared with the σ0-U relationship derived fromSEASAT scatterometer and concurrent sea truth data. 相似文献
196.
197.
Applying the method of ‘statistical linear regression’, atomspheric water vapour over oceanic areas has been estimated from
the 19GHz and 22 GHz data of the satellite microwave radiometer (SAMIR) system onboard the Bhaskara II satellite. In the absence of any simultaneousin situ measurements on water vapour over ocean, theSAMIR-derived water vapour data have been compared with like data from theNOAA-7 satellite. It is suggested that a positive bias seen in theSAMIR data could be due to calibration errors in the basic data. In view of the observed bias, the original regression equation
is modified and then used to obtain water vapour distributions over ocean for winter and south-west monsoon seasons usingSAMIR data of several orbits. 相似文献
198.
Results of investigations of local earthquakes in the region of the Main Central Thrust (MCT) in the Kumaon Himalaya, between and adjacent to the valleys of the Bhagirathi and Yamuna rivers, are presented. Records of over 250 earthquakes were analysed and the following facts emerged:
- 1. (1) Earthquakes in the Himalayas occur in specific areas and belts. One such belt has been identified in the region under investigation, hypocentral estimates being more reliable for earthquakes occurring in the middle segment approximately 70 km long of this belt, crossing the Yamuna river between the villages of Barkot and Syanachatti.
- 2. (2) All but a few epicentres in this middle segment, lie to the southwest of the surface trace of the MCT in a zone with a width of 10–30 km.
- 3. (3) Most of the earthquakes in this segment occur at depths of less than 10 km below the ground surface, the maximum estimated depth being 32 km.
199.
D. P. Kanungo S. Sarkar G. S. Mehrotra 《Journal of the Indian Society of Remote Sensing》1995,23(4):201-210
A geostatistical analysis of the remotely-sensed lineament fabric data associated with the North Almora Thrust of Garhwal Himalaya has been carried out The analysis of data provided 18 major orientations of the lineament density girdles. Further statistical treatment of these derived lineaments using the method of analysts of directional data indicates that the lineaments can be classified into genetic groups. The result indicates that the North Almora Thrust and Kaliasaur Fault are not genetically related and occurred in separate phases of tectonic activities. The results also show that the Alaknanda river is flowing through a tectonically-controlled valley. The study suggests the suitability of statistical methods in lineament-fabric-data analysis for tectonic interpretations. 相似文献
200.
The Vindhyan sedimentary succession in central India spans a wide time bracket from the Paleoproterozoic to the Neoproterozoic
period. Chronostratigraphic significance of stable carbon and oxygen isotope ratios of the carbonate phase in Vindhyan sediments
has been discussed in some recent studies. However, the subtle controls of facies variation, depositional setting and post-depositional
diagenesis on stable isotope compositions are not yet clearly understood. The Vindhyan Supergroup hosts four carbonate units,
exhibiting a wide variability in depositional processes and paleogeography. A detailed facies-specific carbon and oxygen isotope
study of the carbonate units was undertaken by us to investigate the effect of these processes and to identify the least altered
isotope values. It is seen that both carbon and oxygen isotope compositions have been affected by early meteoric water diagenesis.
The effect of diagenetic alteration is, however, more pronounced in case of oxygen isotopes than carbon isotopes. Stable isotope
compositions remained insensitive to facies only when sediments accumulated in a shallow shelf setting without being exposed.
Major alteration of original isotope ratios was observed in case of shallow marine carbonates, which became exposed to meteoric
fluids during early diagenetic stage. Duration of exposure possibly determined the magnitude of alteration and shift from
the original values. Moreover, dolomitization is found to be accompanied by appreciable alteration of isotope compositions
in some of the carbonates. The present study suggests that variations in sediment depositional settings, in particular the
possibility of subaerial exposure, need to be considered while extracting chronostratigraphic significance from δ13C data. 相似文献