Relation between the mineralogical composition and fades of the sedimentary formation of the Northern and North-eastern Cserhát Mts. (Hungary)

The lithostratigraphic mapping of the mainly Tertiary, detrital surficial sedimentary formations of the northern and eastern Cserhát Mts. served as basis for the reconstruction of the sediment accumulation environments. The basis for the fades analyses was the grain-size distribution study by log-probability diagrams. The derived grain-size distribution curves show clearly the distinct fractions of the differently transported (rolled, saltated or suspended) grains. The diagram indicate the size ranges of the grain populations. The literature on sediment transport gives equations for the relationship of grain-size and water movement, velocity and the depositional boundary-velocity can be calculated from the size of the differently transported grain populations. These values give one of the most important quantitative characteristic of the former environment. Analyzing the data regionally, the changes in the accumulation terrain can be traced. The method enabled also a more reasonable evaluation of the heavy mineral studies. From the specific gravity — grain-size equation for rolled sediment transport made possible to count the size of the light minerals transported and deposited together with the heavy mineral associations of 0.1 to 0.2 mm size and different density. On the basis of the fact, that the light fraction constitutes the main quantity of the rock, this calculation gives what size of rolled grain population serves as basis for the comparison of heavy mineral frequency of the given.rock. Those beds, which were deposited from these rolled grains of calculated size range can be easily assigned from the log-probability grain distribution diagrams. The heavy mineral data, which were evaluated regionally by this method, are in good agreement with the results having been derived from facies and environmental reconstruction on the basis of grain-size distributions'