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  • Author or Editor: Andor Barabás x
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The Jakabhegy Sandstone Formation, known for a long time at surface in the western part of the Mecsek Mts, SE Transdanubia, was encountered by several boreholes in the second half of the 20th century in a large part of SE Transdanubia, during exploration for uranium ore in the Upper Permian formations in its subcrop. The formation is made up of five informal lithologic units, from the base upward the "main conglomerate", the "gravelly sandstone", the "pale sandstone" with "conglomerate 2" at its base, then the "red-brown siltstone and sandstone" and at the top the "variegated sandstone" (units "a, b, c, d, e"). Grain size becomes finer upsection, the grains are medium-rounded, and sorting generally improves upward. Planar cross-bedding of varying size is characteristic. The Jakabhegy Sandstone Formation occurs in two types of development. In the case of complete development, all the lithologic units are present, but the lower two ("a+b") do not overlap the Late Permian-Early Triassic Kővágószőlős Sandstone Formation. The case in which the formation is only built up of units "c+d+e" is called incomplete development. In both cases erosional unconformity and hiatus occur between the formation and its underlying unit, while showing continuous transition toward its cover, the Patacs Siltstone Formation. On the basis of the sedimentological features the main conglomerate and the gravelly sandstone ("a+b") were deposited in fluvial facies, "c" in wave-dominated, and "d" and "e" in tide-dominated delta facies. In the clast composition of the Jakabhegy Sandstone, the quartz predominates, the amount of K-feldspars is much smaller and plagioclase is almost completely absent. The rock debris is derived from metamorphic, acidic volcanic and plutonic rocks. According to the quartz/feldspar ratio, the most mature sandstone layers can be found in the central beds of unit "c" and appear in incomplete development at the base of the sequence, locally in quartz arenite quality. The fossil content of the Jakabhegy Sandstone consists almost exclusively of microflora found in the gray layers of the two upper units ("d+e"). According to the palynological investigation, unit "d" and the lower part of unit "e" represent the Spathian substage of the Olenekian stage, while the upper part of "e" already belongs to the Lower Anisian. Downsection, microflora-free red sediments are encountered down to the layers below the upper member of the underlying formation. In the microflora found in these lowest levels, Lower Triassic spores appear with dramatic suddenness and in remarkable quantity, alongside decrease in the amount of Upper Permian pollen.

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