Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 14. 1989. (Budapest, 1989)

SEDIMENTOLOGICAL OBSERVATIONS In my sedimentological studies, the basal Middle Eocene formations and the limestone sequences furnished data valuable for a sedimentological model. Basal formations This group of formation is called the Darvastó Formation in the southwestern, and the Dorog Formation in the northeastern part of the TCR. In the carbonaceous clays of the Darvastó Formation we have found a considerable amount of tiny cristals of gypsum. A part of them has a diagenetic origin by the decay of pyrite, the other part (clear, bright needles), however, must have been formed by evaporation. This means that the lagoons where these sediments have been deposited, became hypersaline from time to time (KECSKEMÉTI and VÖRÖS 1975), which implies an arid climate. The coarse terrigenous elastics of the Darvastó Formation (gravels, conglomerates) are not true "basal conglomerates" but they form intercalations within or above the variegated and carbonaceous clays. The thickness of these conglomerate bodies changes between 0.25 to 7.5 m_ thickening northwestwards. The thickness is less than a half meter in the line of Darvastó - Bálimba - Kislód, and reaches several metres in the line of Csabrendok (Cr-2) Magyarpolány (Mp-4). The material of the well-sorted and well-rounded pebbles differs from the neighbouring basement rocks: in the case of Cretaceous basement the pebbles are mainly dolomitic, in the case of Upper Triassic dolomite basement the majority of the pebbles is quartzitic. The detritus coming from the Mesu^oic rocks of the TCR (Triassic carbonates and cherts, Jurassic radiolarites) is surprisingly subordinate. The material of the above mentioned dolomite pebbles has no relation to the TCR; it is a strongly recrystallized, aequigranular dolosparite. The source area of these pebbles can be sought in the north, in some of the metamorphosed Alpine terrains. In the northwestern area - as evidenced by the studies in the Oroszlány-Pusztavám district - the coarse detritus appearing in the basal part of the Dorog Formation shows a different picture. These gravels can not be regarded as "basal conglomerates" either, but they point to a neighbouring source area. Here, the basement is consisted of Triassic and Jurassic carbonate and siliceous rocks and, correspondingly, the majority of the pebbles is Triassic carbonate or Jurassic chert (sponge spiculite). The comparison of several borehole sequences suggests that the detritus was carried from the northwest (and not from the southerly lying Vértes Hills which was suspected as emerged land and source area by earlier authors). The important brown-coal (lignite) bearing strata of the Oroszlány-Pusztavám district were not studied in detail, but the enormous accumulation of the detrital plant material needs a very rich and dense vegetation in the background, which implies a humid climate. Some general conclusions drawn from the study of the basal formations: (1) The pebble material was not produced by local abrasion along the sea-shore, but a shorter or longer fluviatile transport can be supposed. (2) The material of the pebbles; the diminution of the grain-size and the thinning out of conglomerate bodies toward the SE point to a northwestern source area. No signs of thé southern margin of the Middle Eocene basin can be recorded, considerable terrestrial background and a near shoreline is suspected only in the northwest. (3) A regional climatic change during the four million years passed between the two steps of transgression can be the cause of the different development of the southwestern and the northeastern areas of the TCR. Arid climate at the beginning of the Lutetian caused local evaporation and hindered the development of a rich vegetation. Humid climate at the end of the Lutetian supported a dense land vegetation and enhanced the production and transport of terrigenous detrital material. Limestone sequences Extensive limestone sequences were studied in the southwestern area only. The rather uniform limestone complex was called "Hauptnummulitenkalk" traditionally; its recently