Changes of the lignite seam architecture - A case study from Polish lignite deposits

The architecture of a lignite seam is not only of great cognitive importance, but it is also important for the planning and exploitation of lignite. Therefore, this paper presents the factors that had or could have an impact on the deformation of lignite seams. All the currently extracted lignite seams in Poland of the Early and Middle Miocene age have been considered. Their development, as indicated by the thickness from a few to nearly 250 m, was controlled by intensive subsidence during deposition of the peat reaching a maximum of more than 700 m. Most cases that are theoretically possible were supported by data from boreholes and observations in existing opencast mines. Both surfaces bounding the lignite seam, that is, bottom and roof, were taken into account. The following factors could impact on the formation of the bottom of the lignite seam: the paleotopography before the development of peat mires and syn- and post-depositional tectonics. On the other hand, the roof of the lignite seam could be deformed by such geological processes as: the post-depositional tectonics, post-depositional erosion and compaction. The causes of changes in the bottom of the lignite seam deformations are relatively easy to explain. In contrast, the causes of the roof of the lignite seam irregularities are still poorly understood. In the latter case, often overlooked or underestimated, is the impact of compaction with maximum sizes ranging up to 450 m. In fact, the compaction of peat/lignite often plays a major role in the folding of the roof of the lignite seam. (C) 2013 Elsevier B.V. All rights reserved.