Az alföldi pannóniai s.l. képződmények ásványi összetétele II. - A pannóniai s.l. homokok és homokkövek ásványi összetétel változásának tendenciái és földtani jelentőségük

Sedimentological as well as seismic and sequence stratigrapic studies show that during the LateMiocene - Pliocene (Pannonian s.l.) the main sediment input into Lake Pannon in the area of today' sHungarian Plain came from the NW and NE and subordinately from SE directions. Sediments werecarried along by large fluvial and deltaic systems into the lake. The characteristics of the mineralogicalcomposition and origin of sediments transported from different directions were studied on the basis ofthe heavy mineral data of 868 sand and sandstone samples from 53 boreholes, also using statisticalmethods. During the interpretation the studied samples were identified in terms of depositional facies,depositional cycles, and lithostratigraphic units. The detailed results of the work can be seen in THAMOBozso et al. 2006. As a conclusion of this earlier detailed study, in this paper it is possible to highlightmajor tendencies in the mineralogical composition of the sediments.Different kinds of tendencies have been recognized and these have different backgrounds. There arethe characteristic differencies between the NW and NE sediment input of the basin. Sands which camefrom the NW and reached the middle and southern parts of the Hungarian Plain, have significantlymore minerals deriving from metamorphic rocks, while in sands which originated from the NE andwhich reached the Bekes Basin, are characterised by the dominance of volcanic rocks. There is a minorsediment source from the SE from the Apuseni Mountains. The average amount of chlorite graduallyincreases from fluvial sands, through delta and basin-slope sediments to the deep-basinal turbiditesandstones. This is in contrast to garnet, volcanic pyroxenes and amphiboles, the respective frequenciesof which gradually decrease with water depth as well as distance from the source area. These tendencieswere caused by the selective sorting of minerals during transport and sedimentation and the changingof source rocks. The maturity of the studied sands and sandstones primarily depends on the distancefrom their source areas. There are characteristic vertical changes in the mineralogical composition of thesedimentary succession. These changes are connected to depositional cycles rather than vertical facieschanges. The closer the minerals are to the source area, the stronger the changes are. The mostconsiderable changes are connected to tectonically controlled 3rd order sequence boundaries, especiallyin those cases when they indicate a considerable hiatus. In the NE area, close to the sediment source,even the 4th order cycles clearly show changes in the mineralogical composition.