Evaluation of Upper Triassic – Lower Jurassic breccia/conglomerate-bearing beds described from boreholes in the vicinity of the town of Komló

Abstract

Various type of coarse-grained rock fragments are known in the Upper Triassic to Lower Jurassic formations of the
Mecsek Mountains. This paper deals with the study of the conglomerate- and breccia-bearing beds located around Komló
in the Eastern Mecsek. In the study area plenty of boreholes have been drilled for coal prospecting and these provide a lot
of data about the detrital beds. The aim of the paper is to (i) introduce the Upper Triassic and Lower Jurassic formations
(ii) prepare isopach maps for the formations and also for the bundles of breccia/conglomerate-bearing beds (iii)
characterise the distribution of the rock types and their relative frequency and (iv) draw conclusions from the evaluation
of these data from palaeogeographic and evolutionary history points of view.
Major results:
— There are for blocks that subsided faster than the average. It means that the study area was fractured during the
sedimentation of these formations.
— The thick occurrences of the conglomerate/breccia beds are perfect indications of the one time river- and delta
beds, albeit the small size of the study area and the secondary erosion makes it difficult to follow the direction and size of
the river- and delta bed.
— The areas of the greatest thicknesses correlate well with the largest thicknesses of the conglomerate/breccia
occurrences. This confirms the correctness of the statement above. This tendency is true for the Karolinavölgy Sandstone
and the Mecsek Coal Formations.
— The Vasas Marl Formation contains only a few coarse-grained rock fragments, which is the consequence of the
continuous change of the sedimentary environment. The stream gradient decreased and then the fluvial sedimentation
was replaced first by a largely paludal environment, and then a shallow marine one. During this history the coarse-grained
rock fragments were replaced by finer-grained ones and coarser-grained fragments are found only in the delta
environment.
— The predominant rock-type of the conglomerate and breccia is quartz, but occasionally intraformational sedimentary
rocks, Triassic limestones and dolomites can also be found in an enriched form. The quartz (granitoid and metamorphites)
has its origins in the granitic rocks to the north, while the Middle Triassic limestone and dolomite are from the south, as is
stated by E. NAGY (1969).