GEOLOGICA CARPATHICA, 53, 2, BRATISLAVA, APRIL 2002
65 — 69
TYPICAL CLAY MINERAL ASSOCIATIONS FROM GEOLOGICAL
FORMATIONS IN HUNGARY
A REVIEW OF RECENT INVESTIGATIONS
Hungarian Institute of Geology, Stefánia út 14, H-1143 Budapest, Hungary; firstname.lastname@example.org
(Manuscript received October 4, 2001; accepted in December 13, 2001)
Abstract: In this review some typical formations are listed according to tectonic units and in a stratigraphic order.
Results achieved in the last years are specially emphasized. In the Mecsek Mts Middle Triassic marly dolomites contain
corrensite. There is only illite and some illite/smectite depending on diagenetic grade in the Liassic limestones. In the
Toarcian manganese ores at Úrkút (Trandanubian Range) typical chemical sedimentation and diagenesis produced an
assemblage of celadonite and nontronite. In the Lower Cretaceous sandstones and marls of Gerecse Mts a corrensite-rich
association could be derived from ophiolitic sources. In thick clastic detrital sequences of Paleogene and Neogene basins
mixed-layer illite/smectites display diagenetic transition toward illite depending on depth, temperature, rate of subsid-
ence and subsequent tectonism. In Pliocene and Quaternary basaltic craters of W Transdanubia bentonites consist of
iron-rich beidellites. Red clays contain disordered kaolinite-bearing and a smectite(+vermiculite)-bearing units. At Visonta
high charge beidellites were found. Paleontological and mineralogical records agree well in the fresh and paleosol layers
of loess. In the clay fraction of Recent soils, chernozems are characterized by illite, brown forest soils, humic gleys and
salt affected soils by more smectite-rich associations.
Key words: Hungary, diagenesis, paleosols, loess, carbonate rocks, claystones, red clays, clay minerals.
Clay minerals are important and characteristic components of
most geological formations of Hungary. Systematic investiga-
tions carried out in the last 30—40 years have shown that sedi-
mentary and volcanogenic formations bear typical clay miner-
als depending on their conditions of formation and secondary
modifications such as diagenesis or hydrothermal alteration.
The actual state of knowledge on clay minerals in Hungarian
sedimentary rocks was summarized by the present author sev-
eral times (Viczián 1975, 1987, 1995). For details of the classi-
fication of clay minerals in Hungarian rocks we refer to these
former review articles. The present review mainly considers
the results of the last few years. The most important new data
will be arranged according to regional geological units, in a
stratigraphic order. The geological units and localities men-
tioned in the paper are shown on Fig. 1. The present paper
does not review the clay mineral researches carried out on in-
cipient (or very low-grade) metamorphic formations of Hun-
gary. In this respect the author refers to the recent overviews of
Lelkes-Felvári et al. (1996) and Árkai (2001). Because of the
wealth of the new investigations only very brief descriptions
will be given.
Materials and methods
In most cases clay mineralogical analysis was carried out as
part of a normal petrographic analysis of rock samples collect-
ed in connection with geological mapping or other geological
research projects. The most frequently used analytical meth-
ods were X-ray diffraction, thermal and chemical analysis. In
some cases petrographic and electron microscopy, IR spectros-
copy and determination of K/Ar ages were also used.
Paleozoic and Mesozoic formations
Mecsek Mts (southern Transdanubia)
Lower Carboniferous granitoid rocks as possible candidates
for repository site of low- to medium-level radioactive waste
in the Eastern Mecsek area are intersected by various types of
fissures filled by carbonate and clay minerals (vermiculite-like
Mg>Ca montmorillonite, palygorskite and illite). The miner-
als were formed in a Mg-rich hydrothermal environment
(Kovács-Pálffy et al. 2000a). K/Ar ages measured on illites in-
dicate that formation of the fissure filling took place during the
In the last years a formerly virtually unknown Upper Per-
mian formation, the Boda Claystone Fm attracted much in-
terest as a possible repository site of high-level radioactive
waste (Árkai et al. 2000). Its main clay minerals proved to be
much illite-muscovite and less chlorite. The peculiarity of
the formation is the low quartz and extremely high authigen-
ic albite and high hematite contents, which are the result of
sedimentation in highly alkaline and oxidative lakes under
semi-arid to arid climatic conditions. The degree of diagene-
sis is high, close to the boundary of the anchizone due to
thermal effects culminating in the Lower Jurassic period.
Epigenetic alteration in fractured rocks may have produced
minor amounts of expandable phases. Hydraulic properties
are highly affected by the quality of clay minerals (Kesserű
Former mineralogical investigations (Viczián 1992, 1993a)
have shown that Middle Triassic rocks of the Mecsek Mts.
bear clay minerals similar to analogous formations in the Ger-
man Triassic Basin. Formations comparable to the Röt Mem-
ber contain Mg-chlorite and corrensite and formations similar
to the Muschelkalk contain only illite and authigenic K-feld-
spar. Recently the study of another bore hole profile con-
firmed the repartition of the clay minerals and the existence of
the mineralogical correlation between the Mecsek Mts and the
German-type Triassic (Viczián 2000a).
Substantial development has been achieved in the study of
Lower and Middle Jurassic marly carbonate rocks overlying
the Liassic black coal deposits. In barren rocks of the coal
highly diagenetic illite and kaolinite are the dominant phases.
Grading upwards kaolinite decreases and the expandability of
illite/smectite increases as a combined effect of paleogeo-
graphical conditions of deposition in a deepening sea and de-
creasing overburden pressure during postdepositional alter-
ation. An excellent analysis of the details of the paleo-
geographical factors, cyclic deposition and interrelation with
organic matter was given by Raucsik (1999) and Raucsik &
Bakony and Gerecse Mts (Transdanubian Range)
In the year 2000 a monographic work has been published by
Polgári et al. discussing the conditions of formation of the
Toarcian manganese ores at Úrkút, Southern Bakony Mts.
From the point of view of clay mineralogy the most important
question is the formation of the so-called Radiolarian marl
member in which typical chemical sedimentation and diagene-
sis produced an assemblage of celadonite and nontronite.
These minerals were correctly identified for the first time by
Kaeding et al. (1983). The celadonite was formerly regarded
as glauconite. X-ray and IR analyses carried out by Pápay in
1985 are published in the book of Polgári et al. (2000) proving
the real celadonitic nature of this mineral. Samples of the
Úrkút material were also investigated by B. A. Sakharov, who
has found celadonite-1M with 20 % nontronite type interlayers
and nontronite (published by Varentsov et al. 1988).
Recently Weiszburg and his students were able to make ex-
act chemical determination of the Úrkút celadonite on careful-
ly separated samples. The ordered structure was proved by
Dódony by electron diffraction (Mizák et al. 2000; Weiszburg
et al. 2001). K/Ar ages indicate the diagenetic formation of the
celadonite in the Middle to Upper Jurassic (Polgári et al.
In the Lower Cretaceous marl and sandstone series of the
Gerecse Mts substantial components are mixed-layer chlorite/
smectite/vermiculite minerals (Viczián & Kovács-Pálffy
1997). The mineralogy of these formations has interesting
geotectonic implications. In accordance with petrographic
analyses (Árgyelán 1996) these minerals may be attributed to
redeposited ophiolitic material. In the Bersek Marl and Lábat-
lan Sandstone Fms regular interstratifications (corrensites)
occur. In the overlying conglomerate and marl formations,
Fig. 1. Sketch map showing the geographical names occurring in the paper (after Császár 1997, modified).
CLAY MINERAL ASSOCIATIONS FROM GEOLOGICAL FORMATIONS IN HUNGARY 67
however, only irregular interstratifications may be found.
Regular interstratifications point to heating up to slightly
above 100 °C, which seems to be restricted only to the two for-
Until the first half of the ‘90s, in connection with the hydro-
carbon prospection, extensive studies were carried out on the
diagenetic transition of mixed-layer illite/smectites towards il-
lite in clastic detrital sediments of the Neogene Pannonian Ba-
sin. The smectite proportion in I/S proved to be an important
diagenetic indicator. Summarizing publications have shown
the effect of depth, temperature, rate of subsidence and subse-
quent tectonism as well as the importance of source material
on the transition. Correlation with the vitrinite reflection was
established. Comparison with the East Slovak and Vienna Ba-
sins was done (Hámor-Vidó & Viczián 1993; Franců et al.
1993; Viczián 1994; Mátyás 1994; Tanács & Viczián 1995;
Hillier et al. 1995).
The studies were later extended to the thick pelitic sequenc-
es of the North Hungarian Paleogene Basin (Viczián 1993b,
1996, 1997), however, a detailed publication on this subject is
Recently an excellent analysis of illite/smectite diagenesis
was carried out on the Pannonian sequence of the deepest Hun-
garian hydrocarbon exploration well Hód-I in a M.Sc. Thesis
of the Eötvös University, Budapest (Judik 2001).
In Hungary, clay mineralogy began with the study of the var-
ious products of alteration of the Tertiary volcanic rocks. One
of those classical minerals was “sarospatite”, a mixed-layer il-
lite/smectite from the locality Füzérradvány, Tokaj Mts (Vicz-
ián 1997, 2000b). After a period of stagnation in the study of
hydrothermal clays, some new progress seems to be starting.
Molnár (2000) developed a new model of the hydrothermal al-
teration in the Tokaj Mts based mainly on fluid inclusion stud-
ies. New mineralogical results of the study of bentonite depos-
its were included into the Ph.D. Thesis of Kovács-Pálffy
Pliocene and Quaternary
So called basaltic bentonites together with sediments rich in
Algal remnants were detected in lacustrine deposits formed in
crater lakes of Pliocene basaltic volcanoes in western Trans-
danubia (Viczián et al. 1992). Bentonites may contain up to
80—90 % smectite phases. The mineralogical nature of the
smectite has been determined as iron-rich beidellite (Juhász
1989). Partial data on the mineralogical properties of this Fe-
rich beidellite were published by Barna & Földvári (1992,
1996) and by Földvári (2000), however, a detailed mineralogi-
cal analysis is still missing.
In SE Transdanubia extensive areas are covered by the red
clay formation of Upper Pliocene—Lower Pleistocene age
(Tengelic Fm). Disordered kaolinites found in red clay depos-
its on the top of limestone surfaces in the Villány Hills were
studied by Bidló (1985). Recently by means of mineralogical
and geomorphological investigations the formation was subdi-
vided into a lower, kaolinite-rich part, formed in a warm, hu-
mid climate and an upper, smectite-rich part, which may be at-
tributed to climatic conditions at the boundary of savannah
and arid zones (Schweitzer & Szöőr 1997). On the surface of
the Mórágy Granite, biotites may have been weathered to
mixed-layer biotite/vermiculites during this latter period of
red clay formation (Kovács-Pálffy et al. 2000b).
Another Quaternary red clay formation is found in the
southern foothills of the Mátra Mts. Smectites in these red
clays found in the open pit works at Visonta have been deter-
mined by various treatments and Green-Kelly test as high
charge beidellites. The underlying grey clays are character-
ized by a mixture of low charge beidellite and montmorillo-
nite (Németh et al. 1999). It is supposed that the material of
the red clay is derived from the surface of the volcanic rocks
of the Mátra Mts, where similar red clays rich in smectites
were found (Berényi-Üveges et al. 2000).
The mineralogical composition of Quaternary loess and its
paleosol horizons has been the subject of many former stud-
ies. In a recent study mineralogy, geochemistry and paleontol-
ogy were compared in a loess profile in SE-Transdanubia. Un-
weathered loess contains well crystallized detrital clay
minerals, mainly illite and chlorite. In paleosol horizons clay
material is enriched due to dissolution of carbonates and is
dominated by smectite and, occasionally, vermiculite. Con-
clusions relating to paleoenvironmental conditions obtained
by various methods are in good agreement (Hum & Fényes
1995; Hum 2000).
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gary were determined by Varjú & Stefanovits (1979). Clay
mineralogy of salt-affected and meadow soils was studied by
Kapoor et al. (1986). According to these investigations, in the
clay fraction of chernozems, illite-dominated associations,
while in brown forest soils, humic gleys and salt affected
soils, assemblages enriched in smectites are typical. Salt af-
fected soils may contain high amounts of amorphous silica
(Szabolcs & Szendrei 1980). In Holocene alluvial sediments
of the SE Alföld area Kalmár et al. (1997) differentiated be-
tween inherited smectites and smectites of pedogenic origin.
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