Stratigraphy and deformation history of the Jurassic coal bearing series in the Eastern Mecsek (Hungary)

Abstract

Abstract Based on integrated interpretation of well-log and core data of 60 fully cored deep drillings and 2D seismic profiles, sequence stratigraphic and structural development models have been elaborated for the “Maza-South–Varalja-South” coal exploration site and for the Northern Imbricates, Eastern Mecsek, SW Hungary. Twenty four mostly coal capped parasequences and 4 sequences have been identified in the deltaic series of the coal bearing formation. Coal seams of high sulfur content are related to early transgressive systems tracts, while those with low sulfur content and great thickness are associated to late transgressive systems tracts. The sequences were traced on seismic profiles and mapped by subsurface methods. The structural reconstruction indicates that an open, almost symmetric, southward plunging anticline was formed in the Maza-South–Varalja-South area striking practically north–south. This anticline has a gradual transition westward, into another open, almost symmetric, westward plunging anticline. Related to the Cretaceous–Paleogene brittle deformation a set of thrusts with northern vergence were formed as the result of an in sequence thrust wedge development causing shortening of 13%. The Northern Imbricates has been re-interpreted as the result of the Neogene activity of this thrust wedge development; its Miocene development represents an in sequence thrust and a series of out of sequence backthrusts causing shortening of 22.5%. This multi-phase compressive deformation history caused the significant (34%) increase of the coal resources in the study area. However, it also resulted in strong structural fragmentation and multiple coal seams in the coal bearing formation increasing the costs of underground mining and the risks of underground coal gasification.