Palaeoclimate and ecology of the Oligo–Miocene sequences of the East Mátra Mts (North Hungary) — Tracing the effects of the Antarctic Oligo–Miocene ice sheet changes in the Paratethys

Abstract

Boreholes deepened mostly in the1970’s in the exploration area of the Recsk copper mine with continuous coring
were examined. Some of these cores transected especially thick Oligocene–Miocene sequence. The aim of the present
study is not related to ore exploration, but to review the Oligocene – Lower Miocene sedimentary sequence from other
aspects never adressed before. Such are the palaeoecological interpretation of already published faunal lists, especially
in relation to global climate and eustatic sea level changes. Five cores of 1200 m length of Oligocene–Miocene age were
chosen deepened in the 70’s, studied by the same author at the time of drilling. Collecting macrofauna and sampling were
carried out at the drill-site by the Department of Physical and Historical Geology at the Eötvös University. Further
macroscopic studies of the cores to accomplish the earlier description noted at the drill site were carried out at the Eötvös
University. This included the taxonomic determination of the fossil material by depth intervals, finding its relative age
and its ecological and palaeogeographic interpretation. Our results were found feasible at the time by other experts and
the gist of our results were published in several short publications at the time. The conclusions reached at the time are still
true, but can be improved and our new focus on palaeoclimate can contribute accomplishing new results.
New contributions to understand better this Oligocene–Miocene sequence:
— The age of the Kiscell Clay Formation was cross correlated and in accordance with our previous results were found
to belong to the NP 24 nannozone. The NP 21–22 zone is the time of the formation of the Recsk Andesite as proved by
LESS and BÁLDI-BEKE (recently published in LESS et al. 2008).
— The Lower part of the Oligocene (NP 21–22–23 zones) called Tard Clay is missing in this territory.
— The infraoligocene denudation known from Transdanubia since TELEGDI-ROTH (1927) has never been found from
the Northern Midmountains, even where the phenomenon is clearly recognizable. It is supposed, that the Tard Clay
Formation was forming through the NP 21–22 zones (34.5–31.5 Ma) in this area, but most likely in relation to the volcanic
activity it was eroded in the NP 23 chronozone. This is supported by the nearby occurrence of Tard Clay Formation layers
deposited under deep anoxic conditions (in Bükkszék, Fedémes, Eger, westward in the South Cserhát, in Őrbottyán,
Cinkota and in the Buda Hills).
The duration of the NP 23 zone is 1.5 Ma, providing long enough time to erode the ascended Tard Clay, Buda Marl
Formations and the whole Eocene and partly or totally the Palaeogene volcanite formation exposed on land. The total
erosion of the Tard Clay and Buda Marl Formations is especially feasible due to its negligable thickness of about ten,
twenty metres or of a maximum100 m thickness. In the NP 23 zone, where the sequence is continuous the intercalation
of shallow or freshwater deposits testifies for the great scale global sea level drop TB1.1. of the great Oligocene
regression. A rough palaeowater depth estimation for the lowermost two levels of the Tard Clay is of 700 m, while in the
upper part following the great regression of NP 23 is shallowed to 130–300 m.
— The erosion of the Tard Clay Formation is indicated in Miskolc–8 core, where a mass of reworked foraminifera and
nannoplankton from Tard Clay occures (BÁLDI & SZTANÓ 2000).
— After this main sea level drop a small scale eustatic sea level rise occured leading to the deposition of the NP 24
Kiscell Clay Formation. The start of this sea level rise resulted the clastic sedimentation of the so called Pálbükk Member
of varying thickness. These clasts are of local origins (andesite, tuff, angular clasts, red clay, limestone) confirming the
presence of nearby land. The Kiscell Clay Formation is 200 m thick in the vicinity of Parád and Recsk, and at several
levels at regular intervals intercalated by thin glauconitic layers with shallower shelf origin fossils like the large
foraminifers as Nummulites and small Lepidocyclinids. It is believed that these intercalations are not reworked but
autochtonous. The homogeneous clay of Kiscell Clay Formation intercalating with the glauconitic sandstone is most
likely the result of astronomical forcing of the 100 000 years MILANKOVITCH (1930) cycles.— The thick schlier overlying the Kiscell Clay starts with glauconite-bearing layers belonging to the NP 25 nannozone. The glauconitic layers at the base are similar to the intercalations of the Kiscell Clay with rich fossil fauna (Corbula
gibba, Chlamys biarritzensis). The bivalve Chlamys biarritzensis occurring in the same level in the glauconitic sandstone
at Novaj and at other places also.
— Altogether there are three intercalations of the Pétervására Sandstone in the Szécsény Schlier. The schlier always
appears in homogenous thick layers due to its high sedimentation rate (20 cm/1000 year). This rate of sedimentation is
similar to the Kiscell Clay, on the other hand the glauconitic sandstones have an extremely slow sedimentation rate of 5
cm/1000year.
— The detailed study of the cyclity of the variable sedimentary units of this area is to be persued in a later future
research.