Evolution of the facies development of the Knurów deposit (USCB) based on the microlithotypes analysis

Abstract

This paper presents the first attempt to reconstruct the facies development of the entire Carboniferous coal deposit with an area of 38.50 km2, in the western part of the Upper Silesian Coal Basin based on microscopic microlithotype analysis. For this purpose, eight coal seams in the Knurów deposit were sampled. Samples were taken from all stratigraphic series of exploited seams and exploratory boreholes. This paper reconstructs the transition of environments between eight coal seams extracted in the active Knurów coking coal mine in the Upper Silesian Coal Basin, using microlithotype analysis of the whole seam basis on the fifty coal samples. Facies diagrams proposed in the literature by other researchers were used to reconstruct the depositional environments. The dominant microlithotypes in the coking coal of the Knurów deposit are vitrite (in the range from 19.96 vol% for coal seam No. 504 to 42.96 vol% for coal seam No. 355) and duroclarite (in the range from 20,57 vol% for coal seam No. 410 to 33,65 vol% for coal seam No. 405/1). The distribution of the samples indicates two dominant peat-forming environments. These are telmatic reed moor rich in duroclarite and telmatic forest moor rich in vitrite. This indicates a transitional environment between forest swamp and herbaceous swamp. Thus, the deposit evolved from the paralic to limnic facies. The formation of the river delta caused the progradation of terrestrial environments into the sea and the formation of extensive mires fed mainly by groundwater connected to the river system. Over time, the deposit changed from a reed facies to a forest facies. Periodically, the mires were flooded with waters formed in the proximal lacustrine delta by rising water levels or delta subsidence. The remnants of this phenomenon are interbeds in coal seams resembling macroscopic sapropelic coal rich in the clay matters and gelinite. These are layers containing vitrite in the range of 52.99–59.06 vol% and mineral matter in the amount of 19.76–34.59 vol%. The evolution of the basin proceeded from the paralic to limnic stage. The main factor determining the evolution of the mire was the existing river system with periodically variable activity and intensity.