Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 62. (Budapest 1970)

Szabó, I. ; Ravasz, Cs.: Investigation of the Middle Triassic volcanics of the Transdanubian Central Mountains, Hungary

As a result oi the completion of numerous artificial exposures such as exploratory trenches, shafts, and boreholes in recent years, the sequence under consideration could be explored in fuller detail. Consequently, the role of the individual rock types in local sequences, the qualitative changes of the volcanic material and its thickness have become better known than before. Beside discussion of the stratigraphie role of pyroclastic matter, the present paper is primarily concerned with its petrographical nature and mineralogical composition. The mineralogical and petrographical analyses have been extended to all of the tuffs and tuffaceous rocks so far discovered in the various horizons. In the territory of the Transdanubian Central Mountains the tuffaceous rocks are wide-spread throughout the Middle Triassic profiles (Fig. 1). The tuff and tuffaceous layers within the sequences largely vary in thickness (Fig. 2). At present, rocks of volcanic origin are known to occur in the upper member of the Anisian and in the Lower Ladinian strata. According to their types of occurrence, three characteristic (I—III) areas have been investigated in comparatively fuller detail. The most complete and, at the same time, the most varied profil is known to occur near Pccsely-Aszóíő (I) (Fig. 3). Here a tuffaceous formation can be encountered between the Upper Anisian yellow, bedded limestones and the Megyehegy dolomite. It can be identified with the Paraceratites trinodosus Florizon of the Upper Anisian on the basis of both its stratigraphie position and its varied ammonite fauna. The sequence is petrographically variable, the changes in the amount of pyroclastics and carbonates being traceable even to the naked eye. The lower part of the sequence is often "bentonitized". The tuffaceous formation is overlain, locally through intercalation of dolomitic limestones, by yellow, thick-bedded limestones. With their abundant representatives of Ptychites, they are referred to the Trinodosus beds. The Lower Ladinian tuffaceous sequence begins with cherty radiolarites containing siliceous shales and can be characterized by the index fossil Protrachyceras reitzi. The intercalated cherty-siliceous big. 2. Settlement of the tui'faceous horizons within the Upper Anisian and Lower Ladinian area (I-III). — 1. Ladinian dolomite. 2. Cherty limestone. — 3. Limestone. — 4. Cherty dolomite. — 5. Megyehegy dolomite. — 6. Cherty limestone. - 7. Radiolaiite. — 8. Quartzose shale. - 9. Tui'faceous clay. — 10. Tuff.