Petrography and metamorphism of the lower Gondwana (Permian) coal of Rangit Valley, eastern Himalays, India
TL;DR: A triangular outlier of coal-bearing lower Gondwana rocks comprises a tectonic window within the Precambrian metamorphic terrain of the Rangit Valley, in the eastern Himalays of India as discussed by the authors.
About: This article is published in International Journal of Coal Geology.The article was published on 1997-09-01. It has received 11 citations till now. The article focuses on the topics: Coal & Coal mining.
Citations
More filters
TL;DR: In this article, the nitrogen functionalities present within the chemical framework of the bituminous coal samples from the Raniganj and the Jharia Basins and anthracite A samples of the fold-thrust belts of the Sikkim Himalayas as well as to document the metamorphic transformations of these nitrogenous moieties with the advent in the degree of the coalification.
11 citations
01 Jan 2011
9 citations
TL;DR: In this article, the authors have studied the geochemical signature of tectonically induced higher-ranked coals in Indian coal using stable isotope ratio of organic carbon (δ13C) analysis.
Abstract: Higher ranked Permian and Cenozoic coals are reported in tectonically affected regions of northeast India. The geochemical signature of the tectonically induced higher-ranked coals has not been studied carefully, although such coals' hydrocarbon potential is assessed using parameters, such as kerogen maturity. Notably, published data of stable isotope ratio of organic carbon (δ13C) analysis in Indian coal is rare, and only a few researchers attempted to study the δ13C signature of tectonically affected coals. We have studied the δ13C and kerogen maturity parameters in the Permian sub-bituminous coal from Arunachal Pradesh, Permian Anthracite from Sikkim, Late Oligocene bituminous coal from Tirap and Ledo Open Cast Projects in Assam, Eocene lignites from Umarsar, Matanomadh and Panandhro and Upper Eocene to Oligocene lignite from the Tadkeshwar lignite mines in Gujarat, and Mio-Pliocene lignite from Neyveli lignite mine in Tamil Nadu. The results are compared with the published data to understand the tectonic effect on the kerogen character and δ13C signature of coal. Cenozoic lignites, not affected by thrusting, are mainly composed of mixed type-II to III (oil–gas prone) and/or type-III kerogen (gas prone). Low Tmax (maximum pyrolysis temperature) values of the lignites further indicate the thermally immature character of the kerogen. In contrast, tectonically affected Cenozoic sub-bituminous coals show higher maturity of kerogen. Permian coals, affected by the shear stress of the Main Boundary Thrust (MBT), show type-IV (inert) and post-mature character of kerogen. The study reflects that tectonic activities strongly influence kerogen maturity. Enriched δ13C values of Permian coals compared to the younger Cenozoic coals are attributed to the enrichment of the heavier carbon isotope during coalification. Tectonically driven alteration of coal is evidenced by the enriched δ13C values of the thrust-affected coals. Nonetheless, an overall C3 plant source of the coal organic matter irrespective of the age, rank and tectonic history is reflected by the δ13C values (–21‰ to –27‰). The stable isotope composition further assigns an angiosperm source to the Cenozoic coals and a gymnosperm source to the Permian coals. The results indicate that kerogen maturity and δ13C of coal reflect the influence of tectonic activities, although the stable isotope source signature of coal remains unaffected.
3 citations
TL;DR: In this paper , the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins, as well as the anthracite samples from Himalayan fold-thrust belts of Sikkim, India.
Abstract: Abstract The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins, as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim, India. The SiO 2 content (48.05 wt% to 65.09 wt% and 35.92 wt% to 50.11 wt% in the bituminous and anthracite samples, respectively) and the ratio of Al 2 O 3 /TiO 2 (6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples) reveal the intermediate igneous source rock composition of the minerals. The ratio of the K 2 O/Al 2 O 3 in the ash yield of the bituminous coal samples (0.03 to 0.09) may suggest the presence of kaolinite mixed with montmorillonite, while its range in the ash yield of the anthracite samples (0.16 to 0.27) may imply the presence of illite mixed with kaolinite. The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions. The plot of the bituminous coal samples in the A–CN–K diagram depicts the traditional weathering trend of parent rocks, but the anthracite samples plot near the illite field and are a bit offset from the weathering trend. This may imply the plausible influences of the potassium-metasomatism at post coalification stages, which is further supported by high K 2 O/Na 2 O ratio (29.88–80.13). The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of illite in the anthracite samples substantiating the effect of the epigenetic potassium-metasomatism. The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.
1 citations
30 Apr 2022
TL;DR: In this article , the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins, as well as the anthracite samples from Himalayan fold-thrust belts of Sikkim, India.
Abstract: Abstract The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins, as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim, India. The SiO 2 content (48.05 wt% to 65.09 wt% and 35.92 wt% to 50.11 wt% in the bituminous and anthracite samples, respectively) and the ratio of Al 2 O 3 /TiO 2 (6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples) reveal the intermediate igneous source rock composition of the minerals. The ratio of the K 2 O/Al 2 O 3 in the ash yield of the bituminous coal samples (0.03 to 0.09) may suggest the presence of kaolinite mixed with montmorillonite, while its range in the ash yield of the anthracite samples (0.16 to 0.27) may imply the presence of illite mixed with kaolinite. The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions. The plot of the bituminous coal samples in the A–CN–K diagram depicts the traditional weathering trend of parent rocks, but the anthracite samples plot near the illite field and are a bit offset from the weathering trend. This may imply the plausible influences of the potassium-metasomatism at post coalification stages, which is further supported by high K 2 O/Na 2 O ratio (29.88–80.13). The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of illite in the anthracite samples substantiating the effect of the epigenetic potassium-metasomatism. The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.
1 citations
References
More filters
TL;DR: In this paper, it is shown that the temperature on the fault plane can reach the melting temperature for short periods if the slip is sufficiently large and the displacement required to produce melting depends on the magnitude of the regional stress and also on the friction stress.
Abstract: Summary For simple models of the movement on a fault during an earthquake the temperature on the fault plane is shown to reach the melting temperature for short periods if the slip is sufficiently large. The displacement required to produce melting depends on the magnitude of the regional stress and also on the friction stress. If both stresses are one kilobar melting can occur for displacements as small as one millimetre. If, however, both stresses are ten bars melting is impossible for any observed displacement. It is estimated that the width of the melted zone could be between 2 mm and lcm. Melting on fault planes during earthquakes is not in disagreement with geological and geophysical observations, and suggests a new explanation for some mylonites. Melting may be important because the molten film rock formed on the fault may act as a lubricant and in the case of large earthquakes allow the release of almost all the elastic strain in the region of the shock. This would provide an important constraint in estimating the state of stress along a fault.
346 citations
Book•
01 Jan 1981
TL;DR: The main aim of Organic Maturation Studies and Fossil Fuel Exploration is to provide a platform for current research, developments, applications and discussion on organic maturation of sedimentary organic matter presented against the ever increasing requirements of petroleum exploration as discussed by the authors.
Abstract: Petroleum exploration is an expensive and increasingly difficult but necessary operation. It requires the use of sophisticated technology and an understanding of the various chemical and geological processes involved in the generation of petroleum from the accumulated organic matter in the source rocks, via organic maturation and migration to the ultimate accumulation of hydrocarbons in the reservoir rocks. During the last decade there has been particular progress made in the study of hydrocarbon source rocks, orqanic maturation and the generation, occurrence and properties of petroleum. These advances and applications are reflected in the present volume. The main aim of Organic Maturation Studies and Fossil Fuel Exploration is to provide a platform for current research, developments, applications and discussion on organic maturation of sedimentary organic matter presented against the ever increasing requirements of petroleum exploration. The book contains papers by geologists, geochemists, chemists and palvnologists, presented at an international symposium held at the University of Cambridge in July 1980. An interdisciplinary approach was adopted and the book contains papers by acknowledged acadernic and industrial experts concerned with organic maturation and petroleum exploration.
163 citations
TL;DR: In this article, the authors measured the levels of organic maturation below and within shear zones of thrust faults in the Rocky Mountains and revealed no general thermal metamorphism that can be attributed to faulting, with the exception of very localized areas.
86 citations
TL;DR: The anisotropic reflectance fabric of coal is used as a finite strain marker in the structural analysis of deformed strata in the Broad Top Coal Field of central Pennsylvania.
Abstract: The anisotropic “reflectance fabric” of coal is used as a finite strain marker in the structural analysis of deformed strata in the Broad Top Coal Field of central Pennsylvania. Oriented blocks of coal were collected at various field locations. The reflectances of three orthogonal surfaces were used to estimate the magnitudes and orientations of the three principal reflectance axes. Broad Top coals are shown to have three principal reflectance values, in contrast with most bituminous coals, which have only two. Reflectance values can be represented by a biaxial indicatrix that may be either prolate or oblate. The oblate indicatrices, showing flattening in the bedding plane, are associated with gently deformed strata. The prolate indicatrices, elongated parallel to the fold axes (N32°E), are associated with more intensely folded strata and show the influence of strong lateral compression superimposed upon gravitational loading. The reflectance indicatrices maintain a constant spatial orientation, regardless of the inclination of the enveloping bedding. The minimum principal reflectance axis plunges steeply toward the west, indicating that during deformation the direction of maximum compression was plunging toward the northwest. These results suggest that in the Broad Top field maximum coalification and, therefore, maximum burial were penecontemporaneous with the later stages of deformation, postdating most of the folding.
71 citations
TL;DR: The radiometric dating of the emplacement of the thrust plates by the K-Ar method has been studied in this paper, with ages ranging from 72 to 56 m.p.y.
Abstract: Mesozoic sedimentary rocks overridden by thrust plates in the disturbed belt of northwestern Montana have been metamorphosed by burial beneath these plates. Bentonite in the Cretaceous section has been converted to potash bentonite by this metamorphism, allowing radiometric dating of the emplacement of the thrust plates by the K-Ar method. Ages determined thus far range from 72 to 56 m.y. B.P. The oldest ages coincide with estimates for the beginning of thrusting from stratigraphic and structural evidence. Field evidence does not allow a reliable estimate for the end of thrusting. Thus, the younger ages, which indicate completion of thrusting at the end of Paleocene time, represent additional data of interest to the structural history of the disturbed belt.
69 citations