Geological settings and the history of the Eperjes Hill, Olaszfalu, Bakony Mountains

Abstract

Sedimentology and the structural build-up of the Mesozoic sequence of the Eperjes Hill at Olaszfalu has been
interpreted in different ways in the past. The results of our latest research answer some of the questions about geology,
sedimentology and geological history of the Eperjes Hill and its adjacent areas. The major findings of the paper are
summarized below:
— The study gives new details about the ammonite stratigraphy of the Eperjes Hill. The presence of several new
ammonite zones has been proven from the Kimmeridgian and Lower Tithonian, based on abundant and well-preserved
fossil remnants.
— The left-lateral strike-slip fault, running in a north–south direction on the middle part of the western slope of the
Eperjes Hill separates an incomplete Jurassic sequence of slope facies (starting with the Hettangian Kardosrét Limestone
and finishing with the Tithonian Hierlatz type Szentivánhegy Limestone) from a non-Hierlatz-type Upper Jurassic
succession consisting of large blocks of Upper Triassic Dachstein Limestone, Lower Jurassic Kardosrét Limestone and
Hierlatz Limestone.
— The Middle Jurassic rifting of the Ligurian Ocean can be considered as the root cause of the mega-breccia found
to the east of the strike-slip fault, and this is in contrast to other opinions with respect to compression and thrust faulting.
Therefore, the breccia is classified as scarp breccia. The phenomenon can be well correlated with the mega crevasses of
Csóka Hill at Mór, the Middle Jurassic breccias of the Wildenstein Valley of the Karavanken, and several other breccias
of the Southern Alps and other regions of the Mediterranean.
— Although a Middle Jurassic matrix has not been found anywhere on the surface among breccia bodies there are no
sedimentary structures in the Upper Jurassic matrix indicates rock fall into unconsolidated mud or on consolidated rocks. The
lime mud between the blocks shows characteristics of having been deposited after the formation of the breccia. This is an
indication that the poor late Middle Jurassic sediment supply was not sufficient to fill the large gaps between the giant blocks.
— The Lókút Radiolarite of late Middle Jurassic to early Late Jurassic age has been shown to be present on the top of
the Eperjes Hill in a borehole, and the extent of the Aptian Tata Limestone has been delineated eastwards. The occurrence
of the Lókút Radiolarite in the basement also excludes both the olistostrome-type sedimentation and the breccia
formation caused by nappe structure or thrust faulting.
— There is no explanation for the thick and complete deep water Jurassic sedimentation on the Som Hill within the
submarine Ámos High. Further study is needed in connection with the Telegdi Roth Line which is considered as a
horizontal and at the same time vertical displacement zone. The question also can be raised whether the Ámos Hill was
part of the nearby submarine high at all.
— New data, together with some earlier indications, proved that the Late Jurassic somewhat lacunose sedimentation
was followed by an ephemeral sedimentation in the Early Cretaceous and this produced a small, coral- and worm colonybearing lenses as seen on the Eperjes Hill. The sedimentation became more or less continuous only by the end of the Late
Aptian, or perhaps at the beginning of the Early Albian.
— The area became land during the Early Albian when the Tata Limestone (possibly together with the underlying,
very thin and spotty Jurassic rocks) was completely eroded from the eastern continuation of the Eperjes Hill.
— A global (at least 150 metres) eustatic sea level change which took place in two phases ended the formation of the
Urgonian carbonate platform during the Late Albian and the sedimentation continued with hemipelagic marl (Pénzeskút
Marl Fm).