GEOLOGICA CARPATHICA, 50, 3, BRATISLAVA, JUNE 1999
LATE CRETACEOUS ISOLATED PLATFORM EVOLUTION
IN THE BAKONY MOUNTAINS (HUNGARY)
Geological Research Group of the Hungarian Academy of Sciences, Eötvös Loránd University, Múzeum krt. 4/A,
1088 Budapest, Hungary; firstname.lastname@example.org
(Manuscript received July 3, 1998; accepted in revised form March 17, 1999)
Abstract: Upper Cretaceous rudist platform and slope deposits were studied in the Bakony Mountains. During the
TuronianEarly Senonian tectogenesis an articulated basin came into being in the area of the Bakony; depressions and
highs were formed roughly parallel with the structural strike of the mountain. Inundation of the highs led to the
evolution of carbonate platforms. The studied platform was located in the inner part of the basin separating a southern
and a northern sub-basin. Facies studies revealed that the architecture and evolution of the southern and the northern
slope of the asymmetrical platform were fundamentally different. A steep erosional slope bounded the platform to the
south with lithoclast accumulation at the toe of the slope, whereas a gentle accretional slope was developed north-
ward. Evolution of the platform and the slopes was controlled mainly by two 3
-order relative sea level changes on
which higher order oscillation of the sea level was superimposed.
Key words: Transdanubian Range, Bakony Mountains, Upper Cretaceous, carbonate platform, foreslope, megabreccia,
During the Senonian, in the western part of the Transdanubian
Range structural unit, a large basin came into being and was
filled by continental and marine sediments. The mid-Creta-
ceous (AptianEarly Albian) and Late Cretaceous (Turonian
Coniacian) tectogenetic events led to the formation of the rath-
er complicated structural pattern of the basement of the basin
(Császár & Haas 1984). As a net result of tectonic movements
and subaerial erosion, highs and elongated depressions (sub-
basins) came into existence, roughly parallel with the structur-
al strike of the unit. In addition to the tectonically-forced in-
crease of accommodation, evolution of the basin was
controlled for a long time by the initial topography (Haas
1983). Unequal subsidence of the structural unit led to trans-
gression affecting the western part of the unit in the Santonian.
Fluvial-lacustrine-paludal sedimentation was initiated in the
depressions whereas the paleohighs were inundated only dur-
ing a subsequent stage of the relative sea level rise in the Cam-
panian, when carbonate platforms evolved on their top. Fur-
ther relative sea level changes resulted in progradation and
retrogradation of the carbonate platforms, before their final
drowning in the Late Campanian.
In the Northern Bakony Mountains, outcrops, quarries, and
boreholes exposed sequences deposited on platforms and ba-
sins as well as on slopes between platforms and basins. Stud-
ies of these slope sequences revealed that the northern and
southern slopes of the paleohigh in the central part of the Se-
nonian basin (it is referred in the present paper as the Ugod
High or the Ugod platform) show significantly different devel-
opment. The primary aim of the present paper is to describe
the characteristic features of the slope facies and explain the
cause of the differences mentioned above. Attempts were also
made to understand the role of sea-level changes in the history
of the evolution of the basin, also taking into account the fact
that sea-level changes left traces in the foreslope and platform
In the early part of the Alpine evolutionary stage, from the
Late Paleozoic to the Early Tertiary, the structural units (ter-
ranes) making up the basement of the Pannonian Basin were
located far from their present-day setting and far from each
other. The Bakony Mountains as a part of the Transdanubian
Range Unit was located somewhere between the Upper Aus-
troalpine and the South Alpine realms (Kovács 1982; Kovács
& Kázmér 1985; Haas et al. 1994). In the middle and Late
Cretaceous, collisions of the Adriatic microplate and other mi-
croplates in the southern foreland of the European plate may
have led to squeezing out of the Transdanubian Range Unit
and the initiation of its large scale eastward displacement. The
reconstructed paleogeographic setting of the study area in the
Senonian is presented in Fig. 1 based on works of Ziegler
(1988), Haas et al. (1990), Csontos et al. (1992), Dercourt et
al. (1993), Wagreich & Faupl (1994).
Senonian formations hundreds of metres in thick occur in
the western part of the Transdanubian Range Unit, i.e. in
the Bakony Mountains and in the basement of the Kisalföld
(Small Plain) and the North Zala Basin (Fig. 2). Late Cen-
omanian-Turonian collision (Pre-Gosau phase) led to uplift
and intense erosion in the Transdanubian Range Unit. This
was followed by subsidence from the Santonian to the next
collision event in the Paleocene (Laramian phase), resulting
in a typical tectonically-forced transgressionregression
depositional cycle. The major lithostratigraphic units of the
Senonian cycle and their stratigraphic position and relation-
ships are shown in Fig. 3. Their basic features are described
Bauxites. In certain areas of the Bakony Mountains bauxitic
sediments occur at the base of the Senonian cycle. Bauxites
were deposited in karstic depressions of the bedrocks, under
subaerial conditions, in some cases in fluviatile-lacustrine en-
vironments (Mindszenty et al. 1984; Haas 1984; Juhász 1990).
Csehbánya Formation. It is made up by an alternation of
variegated clays, clay-marls, marls, silts, sands, and gravels
and in minor quantities dark grey clays with thin coal seams.
In some areas, the alternation of the lithofacies types shows
definite meter-scale cyclicity (alluvial cycles). In the eastern
part of the basin, the Csehbánya Formation directly overlies
the pre-Senonian basement, or locally rests on bauxites. It ex-
ceeds 200 m in thickness. Proceeding to the west in the central
depression, the Csehbánya Formation is about 100 m thick,
overlying the Ajka Coal, and further to the west it pinches out.
Channel and flood plain deposits of the Csehbánya Formation
were deposited in fluvial and delta plain environments (Jocha-
Ajka Coal Formation. It consists of an alternation of brown
coal beds and dark grey to brownish-grey carbonaceous to
argillaceous or lighter-shaded marly and silty lithofacies with
mollusc coquina interlayers. The thickness of the formation
may exceed 100 m. The Ajka Coal was formed in fresh- or
brackish-water mangrove swamps. Coal-capped shallowing-
upward cycles reflect a high-frequency sea-level oscillations
(Góczán et al. 1986; Haas et al. 1992).
Jákó Marl Formation. It is constituted by grey marl and
silty marl. Coquina layers are abundant and typical. The lower
part of the unit (Csingervölgy Marl Member) is characterized
by clay-marl to marl lithotypes and by storm coquinas of
brackish-water molluscs and solitary corals. Marl, calcareous
marl and silty marl rock-types prevail in the upper member of
the formation, showing an upward increase in the carbonate
content. Pycnodonta or Exogyra abound in some layers,
though sequences poor in megafossils also occur. The thick-
ness of the formation is usually 60 to 80 m but exceeds even
100 m in some places. The lower member has a uniform thick-
ness of 10 to 20 m while the thickness of the upper member is
much more variable. Deposition of the lower member took
place in a shallow marine, locally slightly brackish-water la-
goonal environment, whereas the upper member may have
been deposited in a normal salinity neritic environment, show-
ing an upward deepening trend (Haas 1983).
Ugod Limestone Formation. It is made up of light-coloured
bioclastic limestones composed to a considerable extent of
shell fragments of rudists. Calcarenites are the most common
rock types but calcirudites are not infrequent either. Rudist
bioherms or biostromes, locally with hermatypic corals, hy-
drozoans and red algae also occur. In some areas wackestones
or mudstones poor in megafossils but locally rich in benthic
foraminifers are known. The formation attains a maximum of
200 m in thickness in the Bakony (it may exceed 300 m in the
Zala Basin). The Ugod Limestone was formed on carbonate
platforms. Various rock types of the formation represent differ-
ent shallow subtidal environments of the platforms (inner plat-
form, platform margin, and proximal foreslope) (Haas 1979;
Haas & Pálfalvi 1989).
Polány Marl Formation. It is made up of grey marl, sandy,
silty marl, calcareous marl and argillaceous limestone lithofa-
cies. The lower part of the formation is of higher carbonate
content. Flaser bedding and bioturbation are characteristic fea-
tures. In some areas, also in the lower part of the sequence,
limestone bodies containing lithoclasts of the Ugod Limestone
and also calcarenite interlayers are known to occur (Jákóhegy
Fig. 1. Paleogeographic setting of the Transdanubian Range Unit
in the Campanian. Abbreviations: LOM Lombardy, DOL
Dolomites, DR Drauzug, JU Julian Alps, TR Transdanu-
bian Range, MT Mid-Transdanubian Unit, BÜ Bük Unit,
I.W. CARP Inner West Carpathians.
Fig. 2. Extension of the Senonian and distribution of the Campa-
nian formations in the Transdanubian Range Unit.
Fig. 3. Lithostratigraphic chart of the Senonian in the Transdanubi-
an Range. Abbreviations: JB Jákóhegyi Breccia, bx bauxites.
LATE CRETACEOUS ISOLATED PLATFORM 243
Breccia Member Nagy 1957). In the higher parts of the for-
mation, the carbonate content decreases, the amount of clay
and silt increases and sandstone interlayers appear (Ganna
Siltstone Member). The maximum thickness of the formation
may attain 800 m; the original thickness, however, is known
nowhere due to subsequent erosion. The depositional environ-
ment of the Polány Marl extended from the toe-of-slope of the
rudist platforms to the shallow bathyal basin as regards the
lower member, and was a deep bathyal basin during the depo-
sition of the upper member (Haas 1983).
In the present paper the platform (or trend of platforms) lo-
cated on the central high in the north-eastern part of the basin
is discussed. Extension of the Senonian formations, outcrops
and locality of the most important borehole sections are dis-
played in Fig. 4. A conceptual cross-section running through
the study area is shown in Fig. 5.
Reconstruction of the evolution of the Ugod platform and its
slopes requires exact stratigraphic correlation of the studied
sections. Boreholes in the neighbourhood of Magyarpolány
provided the best data for the southern sub-basin of the Senon-
ian basin, the Mp-42 and Mp-38 cores were studied most com-
prehensively from a biostratigraphic point of view. Nanno-
plankton and palynologic investigations were carried out on
both cores (Félegyházy 1985; Bodrogi & Fogarasi 1995; Bo-
drogi et al. 1998; Siegl-Farkas 1983; Siegl-Farkas & Wagreich
1996). According to the studies of Fogarasi on the Mp-42
core, the first nannofossils (represented by the species Calcu-
lithes obscurus) appear in the lower member of the Jákó Fm.
Lucinorhabdus cayeuxii (ssp. B) appears at the top of the Jákó
Fm. while the lower portion of the Polány Fm. is characterized
by Broinsonia parca constricta. The first appearance of the
species Ceratolithoides aculeus was found at the top of the
Jákóhegy Mbr. The youngest part of the succession is charac-
terized by Quadrum gothicum which appears near the top of
the lower member of the Polány Fm. Nannoplankton investi-
gations on the Mp-38 core were carried out by Bóna and Gál
(in Haas 1981) about 20 years ago. According to the re-evalua-
tion of their results by Fogarasi (pers. com.), Calculithes ob-
scurus also appears in the lower member of the Jákó Marl, but
together with Lucinorhabdus cayeuxii. However, nannofossil
correlation of the higher part of the succession is rather un-
On the basis of the palynological data (Bóna & Góczán in
Haas 1981; Siegl-Farkas 1983) in both cores, the boundary of
the palyno-zones D and E (for a definition of the zones see
Góczán 1964) can be drawn within the Jákó Marl, practically
at the boundary of the lower and upper members; the top of
zone E is located at the top of the Jákó Fm. The boundary of
zones E and G can be emplaced in the lower part of the Jákóh-
In the northern sub-basin palynological investigations on the
Pápa Pa-2 core carried out by Góczán (in Haas 1981) provided
a basis for the biostratigraphic correlation between the two
sub-basins. He found that the boundary of zones D and E is
also within the Jákó Fm. and that the E/F boundary is located
in the lower part of the Polány Fm., while zone G begins with-
in the lower member of the Polány Fm., about 60 m above its
base. These data constrain synchronous marine flooding in the
two sub-basins in zone D. The inundation of the Ugod High
may have begun at the end of zone E. This is also supported by
recognition of the E zone at the base of the Ugod Limestone
on Szár Hill at Ugod (Góczán in Haas 1981).
Based on nannofossils, Fogarasi (pers. com.) has drawn the
Santonian/Campanian boundary at the appearance of Broinso-
nia parca constricta, that is, in the basal part of the Polány Fm.
The chart of Haq et al. (1987) defines the boundary somewhat
deeper, in the topmost part of the Lucianorhabdus cayeuxii
Fig. 5. N-S cross-section of the Senonian Basin in the Bakony ar-
eas. (For location of the section (AB) see: Fig. 4).
Fig. 4. Outcrops and subcrops of the Senonian formations and lo-
cality of the most important borehole-sections in the Bakony area.
Zone. The higher part of the Polány Formation in the core Mp-
42 can be emplaced in the Campanian.
The Ugod platform
On Szár Hill (south of village Ugod see Fig. 4), Upper
Triassic carbonates are directly overlain by Campanian rudist
limestones of carbonate platform facies. According to core
data, a similar setting can be found in a 34 km wide zone un-
der the Tevel Hill (south of Tapolcafõ see Fig. 4) and prob-
ably also even further in a south-west direction (Haas 1979).
The thickness of the platform carbonates (Ugod Limestone)
exceeds 100 m. This elongated carbonate platform (or plat-
forms) trending southwestnortheast is referred to in the
present paper as the Ugod platform.
A complete succession of the Ugod Limestone was exposed
in the core Tapolcafõ-1 (Fig. 6 for detailed lithological de-
scriptions and results of microfacies analysis see Haas 1979).
The Senonian sequence begins with platform limestones, di-
rectly overlying the Upper Triassic Dachstein Limestone. A
lag-layer only a few meters thick, containing clasts of the un-
derlying formation was found at the base of the sequence
(Haas 1979). In the platform sequence (facies-type A) the fol-
lowing microfacies sub-types were distinguished by Haas &
ostracode-miliolinid biopelmicrite, wackestone (facies-
biomicrite, packstone with rudite, arenite and silt-sized
bioclasts of rudists (A2);
micritic biosparite, packstone-grainstone poorly win-
nowed grainstone. Medium to coarse calcarenite with frag-
ments of rudists, other molluscs, echinoderms, intraclasts and
foraminiferal biosparite, grainstone with large amount of
benthic foraminifers (A4);
biosparite, grainstone. Medium to coarse calcarenite-cal-
cirudite. It consists mainly of rudist fragments (A5).
The northern slope of the Ugod platform (neighbourhood
Sequences deposited on the northwestern slope of the Ugod
platform can be studied in the quarries located northwest of
Tevel Hill and in cores cut in the same area (Fig. 4).
The quarries and the upper part of core T-1 exposed rock
types showing intermediate features between the Ugod and
Polány Formations; to be precise the intertonguing zone of the
two formations is exposed. The typical microfacies types of
the transitional interval are as follows:
Biomicrite (packstone) with arenite-sized rudist frag-
ments and large amounts of calcisphaerulids (E1);
Biomicrite (packstone) with predominantly silt-sized
bioclasts. It is rich in calcisphaerulids and a few planktonic
foraminifers also occur (E2).
Comparison of the Senonian sequence of the T-1 core with
that of core Tfõ-4 (see Fig. 6; description in Haas & Pálfalvi
1989), drilled at about 500 m distance from core T-1, roughly
perpendicularly to the strike of the paleohigh, makes it possi-
ble to establish the following tendencies:
the Ugod Limestone shows a definite trend of thinning
northwestward i.e. moving away from the core of the platform;
thin interlayers of foreslope facies appear in the lower
part of the Ugod Limestone, in core Tfõ-4.
the thickness of the first thicker pelagic interval appear-
ing above the Ugod Limestone is approximately equal in the
two cores but upsection the proportion of the pelagic intervals
is much higher in core Tfõ-4.
the calcirudite facies is completely missing in the transi-
tional unit in core Tfõ-4.
The Senonian sequence of the sub-basin north of the Ugod
platform is known from the borehole Pápa Pa-2 (Figs. 4, 5),
drilled about 5 km to the north of borehole T-1. In borehole Pa-
2, overlying the Triassic formations, a typical basinal succes-
sion was exposed: the Csehbánya Formation (120 m) at the
base is overlain by the Jákó Marl (60 m) which passes upward
into the Polány Marl.
The southern slope of the Ugod platform (neighbourhood
South of the Ugod platform, the Senonian formations are ex-
posed by a few outcrops and cored wells near Magyarpolány.
According to the core data, the Senonian sequences are under-
lain by Jurassic-Lower Cretaceous formations. At the base of
the Senonian succession, overlying a few meter-thick terrestri-
al interval, the 50100 m thick Ajka Coal Formation occurs. It
is covered by the terrestrial Csehbánya Formation, 50150 m
in thickness. The transgressional marine sequence begins with
the brackish lower member of the Jákó Formation which is
followed by the normal saline upper member of the Jákó For-
Fig. 6. Simplified lithofacies column of cores T-1 and Tfõ-4 and
their facies interpretation. Abbreviations: TST transgressive
systems tract; HST highstand systems tract.
LATE CRETACEOUS ISOLATED PLATFORM 245
mation. With an upward-increasing carbonate content, the
Jákó Marl gradually progresses into the lower member of the
Polány Marl, consisting mainly of calcareous marl. In the
300350 m thick lower member, the Jákóhegy Breccia, a 30
100 m thick lithoclastic limestone intercalation appears. Up-
section the lower member passes gradually up into the more
argillaceous and silty upper member (Ganna Siltstone).
The Jákóhegy Breccia in the Magyarpolány-38 core
The first lithoclastic interlayer in the lower member of the
Polány Marl appears at 406 m in core Mp-38 (for location see
Fig. 4). Upsection the frequency of the lithoclastic layers and
proportion and size of the clasts increase. The lower boundary
of the Jákóhegy Member was drawn at the horizon where the
lithoclasts begin to occur continuously (Fig. 7). The upper
boundary of the member is sharp. Above 270 m the lithoclasts
abruptly disappear. In the lithoclastic layers, the proportion of
the clasts is 5090 % (Pl. I: Figs. 23). Mud-supported texture
characterizes the lithoclastic interlayers of the Polány Marl
and the lower and uppermost part of the Jákóhegy Breccia,
whereas grain-supported texture prevails in the middle part of
the Jákóhegy Member. Microstylolitic grain contacts are com-
mon in the latter interval. The size of the lithoclasts is between
0.1 and 10 cm. The maximum grain size was also found in the
middle part of the Jákóhegy Member. The roundness of the
clasts is highly variable. Angular grains are predominant, but
well-rounded ones occur as well. The petrographic data of the
lithoclastic intervals are summarized in Fig. 8.
A detailed microscopic study was carried out on the litho-
clastic layers to investigate the microfacies characteristics of
the lithoclasts and their matrix. The diagenetic features of the
Fig. 7. Lithologic column, lithostratigraphy and relative sea-level
curve of Core Mp-38. For legend see Fig. 9. Abbreviations: LST
lowstand systems tract, TST transgressive systems tract; HST
highstand systems tract.
Fig. 8. Megascopic data, and microfacies-types of the lithoclasts in
the lithoclastic interval of Core Mp-38. Legend (for Figs. 8, 9, 10):
1. limestone, 2. argillaceous limestone, 3. calcareous marl, 4. litho-
clasts, 5. plastoclasts, 6. rudite-size bioclasts, 7. nodules, 8. biotur-
bation, 9. Polány Formation, 10. Jákóhegy Breccia Member.
246 PLATE I
Plate II: Microfacies type A (lithoclasts). Fig. 1. Rudist-bearing biomicrite (packstone) Core Mp-38, 315.0 m. Fig. 2. Biopelsparite (grain-
stone) Core Mp-38, 345.0 m. Fig. 3. Biointramicrite (packstone) Core Mp-38, 330.0 m. Fig. 4. Pore filling drusy sparite cement Core Mp-
38, 330.0 m.
Plate I: Fig. 1. Outcrop of the Jákóhegy Breccia on the top of Jákó Hill (stratotype-section). Fig. 2. The Jákóhegy Breccia in core Mp-
38, 329.3 m. Fig. 3. The Jákóhegy Breccia in core Mp-38, 308.3 m. Fig. 4. The Jákóhegy Breccia in core Dv-3, 629.5 m.
PLATE II 247
quency of type D is significant (22 %) while types B, C and F
are poorly represented (46 %) (Pl. IV: Figs. 34, Pl. V: Figs.
In many cases, signs of cementation and other early diage-
netic features could be recognized in the lithoclasts, mainly
in type A, but occasionally also in types B and C. The inter-
particle pores are filled with equant sparry calcite as a rule;
drusy mosaic and syntaxial overgrowths are common. The
biomolds are generally filled by coarse sparite. In two B-type
lithoclasts, vug pores were observed. In two A-type litho-
clasts, isopachous fibrous rims were visible around the
grains; in another sample, fibrous sparite lined the biomoldic
Fig. 9. Petrography, microfacies-types and facies interpretation of
the matrix in the lithoclastic interval of Core Mp-38. For legend see:
Fig. 8. Abbreviations: M mudstone, W wackestone, P
packstone, G grainstone; S silt-size, A arenite-size, R
rudite-size; Gl Globotruncana, He Heterohelix, plF other
planktic forams, Ca Calcisphaerulids, bF benthic forams, Ech.
echinoderms, Ost. ostracods, Mol. molluscs, Rud.rudists.
Table 1: Relationships between the microfacies types of the litho-
clasts and the host-rocks (matrix) of the lithoclasts.
lithoclasts were also studied. The results are shown in Fig. 9.
On the basis of this analysis microfacies-types were defined.
Most of the types were recognized in both the matrix and the
lithoclasts, but certain types appeared only in the matrix or in
The defined microfacies types are as follows:
A/ Packstone-grainstone with arenite-size particles (Pl. II:
Figs.14). It contains a large amount of shell fragments of rud-
ists and other thick-shelled molluscs and echinoderm frag-
ments. Benthic foraminifers and occasionally algae (Pieninia)
also occur. A few calcisphaerulids may also be present. This
type was recognized only in lithoclasts.
B/ Wackestone, packstone, less frequently grainstone, cal-
carenite (Pl. III: Figs. 12). It is characterized by a predomi-
nance of mollusc shell fragments and echinoderm elements.
Benthic foraminifers are generally present, but in a small
quantity as a rule. This type is fairly common in the lithoclasts
and it also occurs in the matrix, but rarely.
C/ Wackestone, packstone, less frequently grainstone, with
arenite-size or locally silt-size particles (Pl. III: Fig. 3). Echin-
oderm fragments are predominant and benthic foraminifers are
generally also present. It is frequent as material of lithoclasts,
but infrequent in the matrix.
D/ Wackestone, packstone with silt-size particles, prevail-
ingly of echinoderm origin (Pl. III: Fig. 4). A few calcisphaer-
ulids are present as a rule. This type is common as both matrix
E/ Packstone, wackestone with silt-size particles of mollusc
and echinoderm origin (Pl. IV: Fig. 1). It is characterized by
the large number of calcisphaerulids. This type is common in
the lithoclasts (21 %), and the most frequent as matrix (64 %).
F/ Mudstone, wackestone (Pl. IV: Fig. 2). Planktonic fora-
minifers (including the globotruncanids) are common. Other
fossil elements are scarce. This microfacies was not found in
lithoclasts, and is also rare as matrix of lithoclasts. It is typical
in the intervals where the lithoclasts are absent.
The relations of the microfacies of the lithoclasts and the
matrix are shown on Table 1, on the basis of analysis of 118
thin sections. According to these data, microfacies A is the
most frequent in the lithoclasts (31 %), while types B, C and E
are present in about equal proportion (1417 %). In the matrix,
microfacies type E is definitely predominant (64 %), the fre-
Plate III: Microfacies type B (lithoclasts). Fig. 1. Poorly winnowed biosparite with drusy mosaic cement, Core Mp-38, 292.8 m. Fig. 2.
Biomicrite (packstone), Core Mp-38, 304.0 m. Fig. 3. Microfacies type C (matrix), fine calcarenite-calcisilt packstone, Core Mp-38,
304.0 m. Fig. 4. Microfacies type D (matrix), calcisilt packstone, Core Mp-38, 269.7 m.
PLATE III 249
250 PLATE IV
LATE CRETACEOUS ISOLATED PLATFORM 251
Fig. 10. The Jákóhegy Breccia in core-sections in the neighbour-
hood of Magyarpolány. For legend see: Fig. 8.
Geometry of the Jákóhegy Breccia body
Outcrops of the Jákóhegy Breccia are known on Ség Hill, on
Tevel Hill and on Jákó Hill west of Bakonyjákó (Fig. 4; Pl. I:
Fig. 1). The Jákóhegy Member is also encountered in some
boreholes in the neighbourhood of Magyarpolány and further
SW in the core Devecser-3 (Fig. 4; Pl. I). The core data of the
Magyarpolány area also provided some information on the ge-
ometry of the Jákóhegy Breccia. Figs. 10 and 11 show the fea-
tures and thickness of the Polány Formation and within it the
Jákóhegy Member as found in these cores. In the 3.5 km-long
cross-section connecting the cores Mp-42Mp-44Mp-41 sig-
nificant southeastward thinning of the Jákóhegy Member is
clearly visible. In the north-south cross-section between the
cores Mp-40 and Mp-44 marked thinning is also evident.
These trends suggest the southward or southeastward dipping
of the slope. The differences in the thickness of the member
are much less along the profile between cores Mp-42 and Mp-
38 (also in a north-south direction). It can be explained either
by a change in the orientation of the paleoslope or by subse-
quent tectonic displacements.
General facies model
On the basis of the study of the surface exposures and cores
in the neighbourhood of Tapolcafõ and Magyarpolány a gener-
al facies model can be set up for the time when the transgres-
sion reached the top level of the paleohigh (Ugod High) be-
tween the southern and northern sub-basins (Fig. 12). The
paleohigh was probably bordered by normal faults and it might
have been slightly tilted to the north. Inundation of this high
led to the formation of a 58 km wide isolated carbonate plat-
form with a steep southern slope and a much gentler northern
one. On the platform rudist limestones were formed, on the
northern slope redeposited bioclasts of platform origin and at
the foot of the southern slope lithoclastic sediments were de-
posited. The difference in the material of the foreslope depos-
its also indicates an intense lithification along the southern
platform margin, which did not occur on the opposite margin.
Based on the features of the cements, meteoric diagenesis can
be assumed, which may have affected the more elevated
southern rim during the high-frequency lowstand intervals.
Along an idealized north-south cross-section the following
paleo-environments and sub-environments could be distin-
Low-angle accretional slope (microfacies E1, E2)
Along the northern margin of the Ugod platform a wide gen-
tle slope (23
) can be reconstructed. On the distal part of the
slope, carbonate silt (E1) was deposited. The platform may
have been the source of some part of the calcisilt. However, al-
gae producing calcisphaeres (the other major component of the
Plate IV: Fig. 1. Microfacies type E (matrix), wackestone with Calcisphaerulides, Core Mp-38, 383.0 m. Fig. 2. Microfacies type F
(matrix), wackestone with planktic Foraminifera, Core Mp-38, 378.0 m. Fig. 3. Rudist shell fragment in F-type matrix, Core Mp-38,
283.0 m. Fig. 4. Lithoclast of type E in B-type matrix, Core Mp-38, 291.0 m.
silt-sized carbonate) probably lived on the slope. In the proxi-
mal part of the slope arenite-sized bioclasts, mainly fragments
of rudists (E2), were accumulated together with in-situ depos-
Rudist platform (microfacies A5-1 and A)
Within the rudist platform, the following environments
could be reconstructed on the basis of the study of the cores at
Outer platform high-energy carbonate sand shoal envi-
ronment with accumulation of abraded fragments of rudists
(A5) or benthic foraminifers (A4). The poorly winnowed
grainstone microfacies type (A4) may have been deposited in
the transitional zone between the outer and inner platform en-
252 PLATE V
LATE CRETACEOUS ISOLATED PLATFORM 253
For an environmental reconstruction of the southern part of
the platform only the lithoclasts of the Jákóhegy Breccia pro-
vided data. In the marginal zone, a medium to high-energy car-
bonate sand shoal environment may have existed (microfacies
A), similar to that on the northern margin. Meteoric cement in
the lithoclasts indicates the early lithification of the carbonate
Plate V: Fig. 1. Lithoclast of type A in E-type matrix, Core Mp-38, 303.0 m. Fig. 2. Lithoclast of type B in E-type matrix, Core Mp-38,
341.5 m. Fig. 3. Lithoclast of microfacies type A in D-type matrix, Core Mp-38, 324.0 m. Fig. 4. Lithoclast of type B in E-type matrix,
Core Mp-38, 321.0 m.
Fig. 11. Cross-sections through the core-sections which penetrated the Jákóhegy Breccia in the neighbourhood of Magyarpolány. Loca-
tion of the section is shown on the insert-map. Legend of the map: 1. outcrops of the Polány Formation. Abbreviations: J Jákó Fm., P
Polány Fm., JB Jákóhegy Breccia.
Fig. 12. General facies model for the Ugod High and the surrounding basins in the Campanian.
Inner platform medium to low-energy environment (A2)
with accumulation of fragments of rudists and other shallow
marine biota. Bioerosion may have played an important role in
the fragmentation of the skeletons.
Inner platform lagoon very low-energy, protected envi-
ronment (A1) with low-diversity biota.
sand, most probably during the short-term subaerial exposure
Steep erosional slope with depositional terraces (microfacies
An abundance of lithoclasts in the southern foreland of the
Ugod platform indicates a steep erosional slope bounding the
platform to the south. However, the fact that in addition to the
platform facies (A) various microfacies types of the foreslope
were also found in the lithoclasts suggests that as a result of
the pre-depositional and syn-depositional tectonic activity, ter-
races could have formed on the slope where accumulation of
sediments may have occurred. Consolidated or semi-consoli-
dated sediments of these terraces may also have subject to
clastification and reworking.
The echinoderm-mollusc calcarenite (microfacies B) and
the echinoderm calcarenite-calcisilt (C) microfacies were
probably deposited under shallow marine conditions, but be-
low the euphotic zone. A certain part of the bioclasts was
transported from the platform, but the other part (e.g. majority
of the crinoids) may have lived on the slope terrace. The rela-
tively elevated position of this environment is also indicated
by the fact that this facies is fairly common in the lithoclasts.
At the toe of the slope a large amount of lithoclasts of varied
origin were deposited mainly by rockfall. Periplatform taluses
were formed. The intraparticle pores of the grain-supported
breccia were filled mainly by echinoderm calcisilt mud (mi-
crofacies D) which may also have been deposited on the top of
the taluses during quiet periods. This interpretation is also sup-
ported by the observation that this microfacies type is common
both in the lithoclasts and in the matrix of the lithoclasts.
Debris was deposited in the more distal part of the toe-of-
slope environment. Slump structures are also common. Mol-
lusc-echinoderm silt with a large amount of calcisphaerulids
(microfacies E) is the characteristic matrix. However, this mi-
crofacies-type also appears in the lithoclasts. This moderately
deep, pelagic environment may have been very similar to that
of the distal zone of the northern slope (E1).
Hemipelagic basin (microfacies F)
Relatively deep (shallow bathyal) hemipelagic basin. The
pelagic nature of the depositional environment is indicated by
the almost exclusively planktonic biota. Its distant location
from the coeval platforms is also supported by the fact that
bioclasts and lithoclasts of platform origin did not reach this
environment as a rule. However, the high carbonate content of
the deposited mud may have originated partly from the sur-
Cyclicity was recognized in the studied successions of both
the northern and southern slopes. It was very obvious and easi-
ly recognizable in the cored sections at Tapolcafõ. In the core
T-1 the field observations already revealed the cyclic alterna-
tion of three basic lithotypes in the approximately 100 m-thick
transitional unit above the typical Ugod Limestone (Haas
1979). It was also confirmed by the microfacies analysis: skel-
etal (rudist) calcirudite-coarse calcarenites (A5) and fine to
medium rudist-echinoderm calcarenites (A3) alternate with
calcisphaerulitic fine calcarenite-calcisilt layers (E1, E2).
In the Tfõ-4 core, in the lower part of the Ugod Limestone
the calcisphaere facies appeared in two horizons. Then, fol-
lowing a thick platform limestone interval, the microfacies
types E1 and E2 prevail in the transitional unit (Haas & Pál-
falvi 1989). They are punctuated by the intercalations of fine
to medium calcarenites (A3). The facies successions and their
relationships in the two cores together with the interpretation
of their cyclicity are shown in Fig. 6.
On the basis of the facies analysis, two 3
sea-level cycles, superimposed on 4
- and probably 5
ones, could be recognized in the studied successions. Sea-level
rise at the beginning of the first 3
-order cycle led to the inun-
dation of the Ugod High, colonization of the platform biota
and initiation of the carbonate factory on the top of the paleo-
high. The early evolutionary stage of the platform was fol-
lowed by a significant platform progradation during the high-
stand stage of the cycle. The low angle of the northern slope
may have favoured rapid progradation. The first cycle may
have ended with a sea-level drop which probably resulted in
the subaerial exposure of the top of the platform and conse-
quently reduced shedding and slope accretion.
The next sea-level rise led to the back stepping of the plat-
form. It resulted in the appearance of the deeper slope facies
above the platform and upper slope facies. It was followed by
a highstand progradation, superimposed however on 4
-order oscillations (retrogradations and progradations) prior
to the final drowning.
In the Magyarpolány Mp-38 core, recognition of the cy-
clicity was more difficult. However, on the basis of the mi-
crofacies analysis the cyclic alternation of the depositional
facies could be detected (Fig. 9). Within the lower member
of the Polány Formation two 3
-order cycles could also be
interpreted. The first cycle was initiated by a sea-level rise,
the same one which resulted in the establishment of the car-
bonate factory on the Ugod High. This event is probably re-
flected in the significant increase of the carbonate content in
the deepening-upward basinal succession in the transitional
interval between the Jákó and Polány Formations. Although
both rises and falls of relative sea-level may result in mega-
breccia formation and according to the available data the
lowstand periods were generally more favourable for the
megabreccia accumulation (Spence & Tucker 1997), the
Jákóhegy Breccia was probably formed in the highstand
stage of the first cycle. Positive correlation between the
amount of lithoclasts and the amount of sand-size bioclasts
of platform origin appear to support this interpretation (see
Fig. 9); since shedding of the platform bioclasts was proba-
bly more intense in the highstand periods when the platform
was covered by shallow sea (Droxler & Schlager 1985). The
first debris flow deposits may have formed during the early
highstand. This was followed by basinward extension of the
toe-of-slope megabreccia aprons (Jákóhegy Member) during
the late highstand. The top of the Jákóhegy Breccia marks
the end of the first 3
LATE CRETACEOUS ISOLATED PLATFORM 255
Traces of high-frequency cyclicity were also detectable.
The intercalations of the pelagic facies F poor in particles of
platform origin may indicate the short-term lowstand inter-
vals whereas layers rich in platform derived bioclasts and
also in lithoclasts correspond to the highstand stages.
The second 3
-order cycle is made up of pelagic carbon-
ates; rudite to arenite-sized grains are missing (Fig. 9). This
means that due to retrogradation of the platform only the silt
or lutite-sized carbonate mud may have reached the internal
part of the intraplatform basins. However, the high carbonate
content of the basin sediments indicates survival of the plat-
forms in the immediate neighbourhood. The end of the sec-
ond cycle is indicated by a significant change in the litholo-
gy, in the form of the remarkable increase in the clay and
siliciclastic silt content (Fig. 9).
-order cycles (sequences) recognized in the studied
successions could also be applied for stratigraphic correla-
tion of the basin, slope and platform sections. In the section
of the Mp-38 core representing the southern slope of the plat-
form, from the upper part of the Jákó Fm. (top of palyno-
zone E) to the base of the Ganna Mbr., two sequences were
recognized. Similarly, two sequences were found in the cores
at Tapolcafõ, representing the northern side of the platform
and its northern foreslope, where deposition of the Ugod Fm.
probably began in palyno-zone E.
Summary of platform and slope evolution
By the early Senonian, as a combined effect of the pre-Se-
nonian structural evolution and denudation, a WSWENE
trending elongated, asymmetrical high had come into being,
leading to separation of a southern and a northern sub-basin
within the Transdanubian Range Unit. The Ugod High may
have been bounded by steep multiple faults to the south. In
contrast, a gentle slope came into existence on the northern
side of the Ugod High. The difference in the altitude of the top
of the high and the bottom of the depression may have been
about 120150 m. Filling up of the basins may have com-
menced in the Santonian. In the first evolutionary stage, a flu-
vial environment came into being in the northern sub-basin
(Csehbánya Formation) and fluvial, lacustrine and paludal
deposition occurred in the southern one (Csehbánya and Ajka
Formations). It was followed by an abrupt facies change in the
second stage, at the end of the Santonian, which led to the in-
undation of the basin and the establishment of shallow neritic
brackish-water conditions in both sub-basins (lower member
of the Jákó Marl). At this evolutionary stage, the difference in
the altitude of the top of the high and the bottom of the shallow
sea may have been about 2050 m. Subsequently, the relative
sea level rise continued. It is clearly reflected in the fundamen-
tal change in the biota upsection in the Jákó Formation.
It is highly probable that the rising sea level reached the
top of the Ugod High at the very end of the Santonian, when
the transitional layers between the Jákó and the Polány For-
mations were deposited in the basin (Fig. 13). The definite
trend of upward-increasing carbonate content within the Jákó
Marl may indicate the initiation of the euphotic carbonate
production on the surrounding platforms.
The tectonically pre-formed, steep but articulated southern
slope was transformed into a steep erosional slope whereas
on the more gentle northern side an accretional submarine
slope came into being. At the toe of the steep slope, litho-
clastic fans were formed, while on the low-angle slope, bio-
clasts (mainly of platform origin) were accumulated.
During the highstand of the next significant (3
level cycle a rapid progradation of the platform may have
taken place on the northern slope, while the lithoclastic fans
at the toe of the southern slope prograded toward the inner
part of the southern sub-basin. Controlled by higher order sea
level oscillations, however, the intensity of the bioclastic and
lithoclastic influx from the platform fluctuated.
The transgression at the base of the next 3
-order cycle led
to a significant reduction in the extension of the platform. It
is reflected in retrogradation and significant back stepping of
the facies zones on the northern slope and cessation of the li-
thoclast and rudite to arenite-size bioclast accumulation at
least in the inner part of the southern sub-basin.
The next sea level rise and the coeval increase of the fine
terrigenous influx may have caused the final drowning of the
Ugod platform and also of the other rudist platforms in the
Fig. 13. Stages of evolution of the Ugod High and the surrounding ba-
sins during the SantonianCampanian interval. Abbreviations: TST
transgressive systems tract; HST highstand systems tract.
Senonian basin of the Transdanubian Range, in the middle
part of the Campanian.
Acknowledgments: The investigations providing the basis
of the present paper were carried out by the author at the
Hungarian Geological Institute. The work was also support-
ed by the Hungarian Academy of Sciences. The author is in-
debted to Attila Fogarasi (Budapest) for the discussions on
the biostratigraphy. J. Michalík, M. Wagreich, A. Galácz are
gratefully acknowledged for comments and suggestions that
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