Fazies-Analyse der zyklischen Dachstein-Kalke (Ober-Trias) des Bakony-Gebirges, Ungarn

Abstract

The cyclic development of the lower Dachstein Limestones (Norian) was studied in a 410 m thick sequence intersected by the borehole Porva Po-89 in the northern Bakony Mountains. Deviations from the ideal Lofer cyclothems described by FISCHER (1964) were found for a considerable part of the total of 138 cycles. Because of very slight erosion of the regressive member of the cyclothems (algal mat bed, B′) the basic formula of the Hungarian Lofer cyclothems is d-ABCB′-d (see Fig. 1/1). Intracyclic anomalies, minor internal unconformities, or erosion may be responsible for the lack of members; most often member A is absent or strongly reduced. No megacycles comparable with those in the Northern Alps have been found. The environmental interpretation is based on macroscopic and microscopic facies criteria (see Figs. 1 and 2) and on the comparison with Recent carbonates. The rocks of member A were formed within the supratidal zone and perhaps in the uppermost part of the intertidal zone. Member B was deposited within different parts of the intertidal zone. Carbonates of member C were formed within a shallow, subtidal lagoonal environment. The cyclicity of peritidal sedimentation seems to have been caused not by world-wide eustatic changes in sea-level but rather by minor climatic changes which might have been responsible for slightly changing rates of accumulation and evaporation.