The Castle Conglomerate Unit in the Poruba Member (Early Namurian, Mississippian) is a lithosome composed of coarse-grained sandstones and conglomerates. Its thickness, lithology and extensive area make it unique in the paralic sequence of the Ostrava Formation of the Upper Silesian Basin. The unit was studied on the basis of information from exploratory boreholes, mines and its outcrop at the type locality in the Lučina Valley in Silesian Ostrava. Locally, the unit attains a thickness of up to 115 m (average 24.4 m). Its present-day area is approximately 992 km 2 . The axis of the conglomerate facies (with character of interbeds) in the unit has a NNE-SSW alignment and coincides with the axis of the basin's maximum subsidence during the sedimentation of the Poruba Member. The maximum aggregate thickness of the conglomerate facies is 60 m; their present-day area of occurrence is approximately 480 km 2 . The Castle Conglomerate Unit represents deposits of a low-sinuosity river system. The upper part of the multistorey channel fill is characterised by channels filled with sand bedforms and occasional bars. Palaeocurrents show a low spread of vectors, primarily to the NNW. The lower part does not crop out; it is known, therefore, only from boreholes. The presence of the unit's coarse-grained clastics inside the basin filling, which is dominated by siltstone and medium-grained sandstone, indicates a major drop in the base level, which is interpreted here as a drop in the sea level. We correlate this event with the major glacio-eustatic sea level drop at 323 Ma that can be connected with the onset of glaciation interval C2 of the Late Paleozoic Ice Age. Because the resolution of available stratigraphic and geochronologic data is not currently sufficient, an alternative explanation of the tectonic origin cannot be ruled out of the discussion and may also be valid in regard to the active Variscan foreland. •
The Petøkovice Mem ber is the basal unit of the paralic suc ces sion of the Ostrava For ma tion of the Up per Silesian Ba sin. This mem ber is a valu able source of in for ma tion about the tran si tion from a ma rine ba sin filled with siliciclastic sed i ments into a paralic ba sin with the be gin ning of coal-bear ing sed i men ta tion. Mod els of: (1) the num ber of coal seams, (2) their to tal thickness, and (3) the coal con tent with re spect to the to tal thick ness of the suc ces sion were cre ated to de scribe and as sess the coal-bear ing ca pac ity of the Petøkovice Mem ber. The au thors pres ent mod els for coal seam thick nesses ex ceed ing ei ther 10 or 40 cm. The coal-bear ing ca pac ity of the Petøkovice Mem ber is very low. The av er age share of coal seams thicker than 0.1 m is 3%. The share of coal seams with a thick ness that ex ceeds 0.4 m is only 1.66%. More over, in large ar eas of the basin, in the N and NE parts, the coal-bear ing ca pac ity is close to zero, be cause coal seams of greater thick ness were de tected only lo cally there. Based on these mod els and on other geo log i cal data, it is ob vi ous that the on set of coal sed i men ta tion was grad ual and lim ited to par tic u lar sites show ing the great est sub si dence of the ba sin floor. In places where mi nor sub si dence took place, there were likely un fa vor able con di tions for ac cu mu la tion of or ganic mat ter.
The Young’s modulus and Poisson’s ratio, parameters reflecting the elastic response of a rock to stress, are the key parameters used in many engineering activities, such as hard coal mining and natural gas extraction. The objective of this paper was to present the results of complex laboratory measurements of the static and dynamic Young’s modulus and Poisson’s ratio for Upper Carboniferous hard coals from the Upper Silesian Coal Basin. The coals differed in geologic age (Mudstone Series—younger coals; Upper Silesian Sandstone Series—older coals) and petrographic structure (vitrain, clarain, and durain lithotype). Elastic parameters of the coals were determined following compression tests under a complex state of stress, as well as using the ultrasonic method in reservoir conditions. On this basis, linear functional dependences between parameters such as UCS, differential stress, confining pressure, strain rate, P- and S-wave velocities, and the static and dynamic Young’s modulus and Poisson’s ratio were determined. These dependences turned out to be linear, with strong and very strong correlation, as indicated by the high coefficients of determination, R2. These new results significantly broaden the knowledge of elastic properties of Carboniferous hard coals, especially in the field of geoengineering, underground coal gasification, and reservoir stimulation for coal bed methane extraction.
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