Coal seams of the Walbrzych formation, Intrasudetic Basin, Poland: inferences on changing depositional environment
ABSTRACT The petrological composition of coal seams of the Walbrzych Fm. was studied, and depositional conditions were reconstructed on the basis of both coal and clastic sediment analysis. Coal of this formation is of medium- to low-volatile bituminous rank; vitrinite reflectance Ro max ranges from 0.8 to 2.0% and volatile matter content from 29 to 16%.The coal seams of the Walbrzych Formation contain mainly banded coal; bright and dull lithotypes occur sporadically. The amount of banded and banded dull coals increases towards the top of the formation at the expense of banded bright coal. Consequently, vitrinite and vitrite content tends to decrease upwards. Peat deposition in the lower part of the Walbrzych Formation occurred predominantly in a telmatic forest zone. The mires were located between interdistributary channels on a delta plain, and they were probably ombrotrophic. In the upper part of the Walbrzych Formation, swamps were the primary sites of peat deposition. Abandoned channels were favoured as peat deposition sites for seams where increases in seam thickness are associated with increases in coarse clastic content below seams. Continuous peat deposition in overbank zones is postulated for seams wherein decreases in seam thickness are associated with increases in coarse clastic content. Where no relationship between seam thickness and coarse clastic content beneath the seam exists, the swamp may have encroached into overbank and channel zones rapidly. Changes in the environment of peat deposition may be related to tectonic activity along the basin margins during the Namurian.
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ABSTRACT: The petrographic and palynologic compositions of coal seams of the Żacler formation (Upper Carboniferous, Westphalian A) from northwestern and southeastern part of the Lower Silesian Coal Basin (LSCB) were examined. Coals studied are highly volatile bituminous coal, where Ro ranges from 0.91% to 1.09%. Seam 430 from the northwestern part of the basin contains high vitrinite percentage with rather low inertinite and liptinite contents, while percentage of mineral matter is variable. This petrographic composition is associated either with a predominance of Lycospora in miospore assemblage, or with a miospore assemblage of mixed character. The abundance of Lycospora reflects vegetation composed of the arborescent lycopsids while the mixed miospore assemblage is connected with diverse palaeoplant communities, namely, arborescent lycopsids, calamites and ferns. Seams 409 and 412/413 from the southeastern part of the LSCB are rich in inertinite and liptinite, while the vitrinite content is moderate. Their characteristic feature is the occurrence of a diagnostic crassisporinite (densosporinite). Amount of the mineral components in these coals is very low. Densosporites and related crassicingulate genera are main components of these miospore assemblages and were produced by herbaceous and/or sub-arborescent lycopsids. These petrographic and palynologic features were the basis for distinguishing three maceral–miospore associations: an arborescent lycopsid and mixed associations, occurring in the seam 430 and a herbaceous and/or sub-arborescent lycopsid association which was recorded in seams 409 and 412/413. The first two assemblages are interpreted as having been deposited in a planar rheotrophic mire, whereas the herbaceous and/or sub-arborescent lycopsid association is thought to have developed in an ombrotrophic, domed mire.International Journal of Coal Geology 07/1999; · 3.31 Impact Factor