GeolCarp_Vol53_No3_159

GEOLOGICA CARPATHICA,53,3,BRATISLAVA, JUNE 2002

159 — 178

ORIGIN AND EVOLUTION OF LATE TRIASSIC BACKPLATFORM

AND INTRAPLATFORM BASINS IN THE TRANSDANUBIAN RANGE,

HUNGARY

JÁNOS HAAS

Geological Research Group of the Hungarian Academy of Sciences, Eötvös Loránd University, Pázmány Péter sétány 1/c, 1117 Budapest,

Hungary; haas@ludens.elte.hu

(Manuscript received May 21, 2001; accepted in revised form December 13, 2001)

Abstract:  The  setting  and  facies  distribution  of  the  Upper  Triassic  basin  formations  in  the  Transdanubian  Range  of
Hungary  clearly  reflects  the  paleo-geodynamic  evolution  of  the  northwestern  termination  of  the  Neo-Tethys  margin.
Westward  propagation  of  the  Neo-Tethys  continued  during  the  Middle  Triassic.  By  the  Late  Triassic  large  carbonate
platforms (Dachstein-type platforms) developed on the continental margin of the newly formed oceanic branch. Progres-
sive rifting led to downfaulting of the external (ocean-ward) margin of the platforms and formation of narrow intraplatform
basins roughly parallel to the platform margin since the Carnian. Some of these basins were already filled up and reoccu-
pied by carbonate platforms in the Triassic but some of  them persisted  until  the  Jurassic.  Initiation of  opening  of the
Ligurian-Penninic ocean-branch resulted in rifting and formation of new extensional basins in the Late Norian. In this
way a large basin-system came into being (Kössen Basin) behind the platforms, so that the previous continent-encroach-
ing platform became an isolated platform. The basins were filled up with terrigenous clay and platform-derived carbon-
ate mud by the Late Rhaetian, giving rise to progradation of the platforms onto the former basins. Coeval rifting of the
Neo-Tethys and the Ligurian-Penninic branches led to disintegration and step-by-step drowning of the Dachstein plat-
form system in the Early Jurassic. Although the evolution of the studied basins was mainly tectonically controlled, their
architecture and depositional pattern were influenced by several other factors: climate, sea-level changes and the general
paleogeographic  setting.

Key words: Transdanubian Range, Upper Triassic, intraplatform basin, carbonate slope, facies analysis.

Introduction

The Upper Triassic of the Transdanubian Range (TR), Hunga-
ry is made up of platform carbonates and intraplatform basin
deposits. Neo-Tethys rifting in the late Anisian—Ladinian re-
sulted in the formation of relatively large basins in the central
part of the TR. Increased terrigenous influx and shedding of
carbonate  mud  led  to  filling  up  of  these  basins  by  the  latest
Carnian. The leveled topography made possible the formation
of  an  extremely  extensive  carbonate  platform  system
(Dachstein-type platform). At the same time new basins were
formed in the northeastern part of the TR Unit, and some of
them persisted until the Jurassic. During the Norian new ba-
sins  were  formed  both  on  the  northeastern  and  southwestern
sides of the TR Unit.

According to the recent paleogeographical reconstructions

the TR Unit was a part of the Neo-Tethys passive margin in
the  Late  Triassic  (Dercourt  et  al.  1993;  Haas  et  al.  1995a;
Vörös 2000). It may have been located between the South Al-
pine and the Upper Austroalpine realms (Haas et al. 1995a). In
the  Northern  Calcareous  Alps  (Upper  Austroalpine  unit),
backstepping of the platform margin and formation of narrow
basins near the offshore margin were explained by thinning of
the continental crust due to rifting of the Tethys (Lein 1985,
1987) or Neo-Tethys according to the present-day nomencla-
ture. In the Southern Alps, in Lombardy and also in the Car-
nian  Fore-Alps,  formation  of  intraplatform  basins  in  the  late
Norian was attributed to incipient rifting of the Ligurian-Pied-

mont ocean branch (Jadoul et al. 1992; Carulli et al. 1998). On
the basis of studies of the tensional features of the Late Trias-
sic basins in the Carnian Fore-Alps, Cozzi (2000) emphasized
the role of the westward propagation of the Neo-Tethys in the
Southern Alps as well.

The TR Unit has got good potential for the comparative

study of various intraplatform basins and analysis of their orig-
inal  relationships  because  it  represents  an  almost  complete
cross-section of the Neo-Tethys paleomargin and it was affect-
ed only by relatively slight tectonic deformation during the Al-
pine Orogeny.  In  the  last  decade,  detailed  studies  have  been
carried  out  to  detect  the  stratigraphy  and  sedimentological
characteristics  of  the  basins.  Majority  of  the  results  of  these
studies has been published, mainly in Hungarian (Csővár Ba-
sin – Haas et al. 1995b; Hármashatár-hegy Basin – Haas et
al. 2000; Kössen Basin – Haas 1993). These results are only
briefly summarized, occasionally updated and complemented
here, highlighting data on the facies evolution.

The aim of the present paper is to summarize the character-

istics and compare the evolutionary history of the Late Triassic
intraplatform basins in the area of the TR and to consider their
evolution within the structural frame of the region.

Paleogeographical and stratigraphic setting

The Transdanubian Range is located in northwestern Hun-

gary, traversing northern Transdanubia in a NE—SW direction

160 HAAS

(Fig. 1). The mountain range is made up predominantly of Tri-
assic formations which also constitute the basement of Tertia-
ry basins SW and NE of the mountains (Fig. 1). According to
recent geodynamic concepts, the TR Unit broke away from its
original location probably in the Late Cretaceous and as a re-
sult of multi-phase dislocations joined with other lithosphere

Fig. 2. Paleogeographical sketch-map of the western Neo-Tethys
and reconstructed location of the Transdanubian Range Unit in the
Norian.

Fig. 1. A – Location of the study area in Europe and B – within Hungary. C – Upper Triassic formations in the Transdanubian Range
Unit and location of the studied basins.

fragments (terranes) reaching its present-day setting during the
Tertiary  (Majoros  1980;  Kázmér  1984;  Kázmér  &  Kovács
1985; Balla 1988; Csontos et al. 1992; Haas et al. 1995a). The
reconstruction  of  the  original  setting  of  the  present-day  TR
Unit  (i.e.  prior  to  the  major  orogenic  movements)  is  based
mainly on fitting of the Late Permian to Triassic facies zones
(Haas et al. 1995a; Haas & Budai 1995). According to these
reconstructions the TR Unit was located at the western termi-
nation of the Neo-Tethys between the South Alpine and Drau-
zug—Upper  Austroalpine  realms  (Fig.  2).  For  the  entire  Late
Permian—early  Late  Triassic  interval,  a  segment  of  the  Neo-
Tethys margin, the present-day TR Unit, shows a definite fa-
cies polarity: its northeastern part represents the seaward side
(which was located closer to the Neo-Tethys Basin), whereas
its southwestern part represents the landward one. This setting
was significantly modified in the latest Triassic—Jurassic due
to rifting of the Ligurian-Penninic ocean branch.

In the Late Permian continental red beds (fluvial-lacustrine

formations)  were  deposited  in  the  southwestern  part  of  the
area of the TR Unit, whereas evaporitic dolomites of shallow
lagoonal cyclic subtidal—sabkha facies formed in its northeast-
ern part. Transgression in the earliest Triassic (subsequent to
the Permian/Triassic boundary event) led to inundation of the
whole  area  leading  to  a  shallow  ramp  setting.  On  the  ramp
mixed siliciclastic—carbonate deposition took place in the Ear-
ly  Triassic,  which  was  followed  by  prevalence  of  carbonate
deposition in the early Middle Triassic (Early Anisian). In the
Middle Anisian Neo-Tethys rifting led to the formation of ex-
tensional basins in the central part of the TR (Bakony—Balaton

LATE TRIASSIC BACKPLATFORM AND INTRAPLATFORM BASINS 161

Highland  area)  whereas  on  the  relatively  elevated  blocks,
small isolated carbonate platforms developed coevally. Dep-
osition of volcanic tuffs from a distal source initiated in the
latest Anisian and repeated at several times till the beginning
of  the  Carnian.  In  the  Ladinian,  coeval  deposition  of  con-
densed  pelagic  limestone  in  the  basins  and  shallow  marine
carbonates on the platforms continued, with progradation of
the  platforms  during  the  sea-level  highstands.  The  segment
of the Neo-Tethys margin, represented by the southwestern
part of the TR (Bakony—Balaton Highland area), was affect-
ed by intense terrigenous influx in the early Carnian, result-
ing  in  gradual  filling  of  the  basins  by  the  late  Carnian  (see
the stratigraphic chart for the Upper Triassic – Fig. 3). On
the other hand, in the northeastern part of the area of the TR
(Gerecse Mts, Buda Mts, and Danube E-side blocks) contin-
uation of the Neo-Tethys rifting led to disintegration of the
Ladinian platforms and establishment of new extensional in-
traplatform basins in the Carnian. One of them, the Zsámbék
Basin (Gerecse Mts) was also affected by an intense terrige-
nous influx and filled up by the Late Carnian (Haas 1994). In
contrast, the basins in the northeastern part of the TR were
not reached by terrigenous material and thus persisted for a
long time: the Hármashatár-hegy Basin (Buda Mts) at least
until  the  Rhaetian,  and  the  Csővár  Basin  (Danube  E-side
blocks) also into the early Jurassic. As a consequence of the
filling up of the larger basins in the inner part of the TR seg-
ment of the Neo-Tethys margin, an extremely leveled topog-
raphy came into existence by the Late Carnian. A short-term
subaerial exposure in some parts of the area may also have

contributed  to  the  levelling  of  the  surface  (Haas  &  Budai
1999).  Due  to  the  levelled  topography,  transgression  at  the
beginning of the Late Tuvalian led to the formation of a huge
platform  system  (Dachstein-type  platforms).  In  the  inner
platform,  cyclic  peritidal  successions  were  deposited  and
pervasively dolomitized under semiarid climatic conditions.
In  the  segmented  outer  platform,  shallow  subtidal  oncoidal
limestone was formed. At the beginning of the Late Norian,
initiation of the rifting of the Ligurian-Penninic ocean basin
led to formation of large extensional basins (Kössen-type ba-
sins) in the southwestern part of the TR. Filling of these basins
by fine terrigenous siliciclastics and platform derived carbon-
ates was completed by the late Rhaetian. It was followed by
fast  progradation  of  the  platform.  Penecontemporaneously  a
small intraplatform basin was established in the area of the Pi-
lis Mts (Fekete-hegy Basin) in the northeastern part of the TR,
and filled up by carbonates prior to the Rhaetian.

Facies characteristics and evolution of the basins

The Csővár Basin

In North Hungary, east of the Danube, small outcrops of the

Mesozoic basement occur in fault-bounded, uplifted blocks,
which also belong to the TR Unit. They are made up of Upper
Triassic platform carbonates as a rule. However, one of them,
the Csővár Block, along with platform facies, also contains co-
eval slope and basin facies (Figs. 1, 2).

Fig. 3. Stratigraphic chart for the Upper Triassic of the Transdanubian Range. Abbreviations: F – Feketehegy Formation, D – Dachstein
Limestone, M – Mátyáshegy Formation, Cs – Csővár Formation.

162 HAAS

The cherty carbonate sequence was first reported by Szabó

(1860) who tentatively classified it as Liassic. Vadász (1910)
correlated the succession with the “Raibl Beds” and assigned
it to the Carnian. A revision of this chronostratigraphic assign-
ment  was  suggested  by  Kozur  &  Mostler  (1973)  who  found
Upper Norian microfossils in the Pokol-völgy quarry. Detre et
al.  (1988)  determined  Upper  Norian  ammonoids,  Kozur  &
Mock (1991) and Haas et al. (1997) reported Rhaetian macro-
and  microfossils  from  the  same  quarry.  Kozur  (1993)  found
Hettangian and Sinemurian radiolarian fauna in samples taken
from the Vár-hegy (Castle Hill). A preliminary report on the
biostratigraphy  of  the  Triassic/Jurassic  boundary  section  on
the Vár-hegy was published by Pálfy & Dosztály (1999).

In the northwestern part of the Csővár Block, thick-bedded

Upper Carnian-Norian oncoidal limestone, that is the oncoidal
facies of the Dachstein Limestone with bioconstructed patch-
reefs (Nézsa Member) crops out. In a few outcrops, rudstones
and floatstones representing the foreslope facies of the reef
also occur.

In the southeastern part of the block, thin-bedded, cherty do-

lomite  and  limestone  (Csővár  Limestone  Formation)  are  ex-
posed  in  a  quarry  and  outcrops.  The  field  observations  were
complemented by core data. Core Csv-1 exposed an approxi-
mately 600 m-thick part of the Csővár Formation, representing
the  Upper  Carnian—Lower  Rhaetian  interval  (Haas  et  al.
1995). In the borehole, above a major low-angle fault, cherty
dolomite (Pokolvölgy Dolomite Member – Carnian) was en-
countered  in  a  thickness  of  100  m.  It  was  followed  by  thin-
bedded, laminated, locally cherty limestone of basin and toe-

Lithofacies type

Description

Interpreted depositional setting

Lithoclastic–bioclastic (Lb)

Fine calcirudite– coarse calcarenite gr, p
Crinoid and mollusc fragments

proximal toe-of-slope

Oncoidal–grapestone (On)

Coarse calcarenite gr, p, w
Brachiopods, molluscs, ostracodes

proximal toe-of-slope

Redeposited bioclastic wackestone (Rb)

Coarse calcarenite w
Crinoids, benthic foraminifers,
microproblematicums, ostracodes

proximal toe-of-slope

Proximal turbidite (Pt)

Coarse calcarenite p
Crinoids, molluscs, bethic foraminifers,
microbial crust fagments

toe-of-slope

Distal turbidite (Dt)

Fine calcarenite,
peloidal p, and sponge spicule w alternate
crinoids, molluscs, ostracodes, sponge
spicules, radiolarians

distal toe-of-slope–basin

Very distal turbidite (Vt)

Laminitic: calcisilt and calcilutite alternate, w
Filaments, radiolarians

basin

Sponge spicule facies (S)

Calcisilt, calcilutite w
Sponge spicules, crinoids, filaments,
radiolarians

basin

Filament facies (F)

Calcisilt, calcilutite w
Filaments, radiolarians, echinoderm fragments

basin

Radiolarian facies (R)

Calcisilt, calcilutite w
Radiolarians, sponge spicules
Filaments, echinoderm fragments

basin

Condensed radiolarian facies (Ra)

Calcisilt, p
Radiolarians (very abundant), sponge spicules
echinoderm fragments

deep basin

Table 1: Lithofacies types of the Csővár Formation. Abbreviations: gr – grainstone, p – packstone, w – wackestone.

of-slope facies. The upper part of the Csővár Formation (Rha-
etian) is exposed in the Pokol-völgy quarry (Haas et al. 1995)
and outcrops on the steep southwestern slope of the Vár-hegy.
The Triassic/Jurassic boundary can be drawn within the
Csővár Formation (Pálfy & Dosztály 1999). As to their sedi-
mentological features, there is no significant difference be-
tween the Upper Triassic and the Hettangian part of the forma-
tion. The probably Sinemurian (Kozur 1993) cherty limestone
layers, cropping out at the top of the Vár-hegy, are of deeper
basin facies.

The characteristics of the distinguished lithofacies types of

the Csővár Formation are summarized in Table 1 and Fig. 4.
The results of facies analysis of core Csv-1 were presented by
Haas et al. (1995). In this paper only the uppermost (Upper
Norian—Lower Rhaetian) segment of the core section is pre-
sented (Fig. 5) for the sake of comparison with the time-equiv-
alent basinal sections in the TR. Sections of the Pokol-völgy
quarry and the Vár-hegy trench are shown in Figs. 6 and 7, re-
spectively.

The sedimentological features and fossil assemblage of the

Csővár Formation point to a toe-of-slope depositional environ-
ment, as well as slope to basin transitional zone. This paleo-
environmental  setting  is  indicated  by  gravity-flow  deposits
(debris-flow  deposits,  graded,  allodapic  limestone  etc.)  and
frequent  occurrence  of  remnants  of  platform  biota,  together
with  typical  pelagic  fossil  elements  (Haas  et  al.  1995).  The
major facies units can be characterized as follows:

Carbonate platform – Platform carbonates, coeval with the

Csővár Formation (Upper Carnian—Norian) are known in the

164 HAAS

vicinity of the study area (see Fig. 2). The nearest occurrence
of coeval platform carbonates, which can be classified as
Dachstein Limestone Formation, is located northwest of the
Pokol-völgy quarry, at a distance of 2 km. Patch-reef and on-
coidal facies occur, indicating the marginal zone of a carbon-
ate platform.

Slope – Rudstone and floatstone consisting of coarse detri-

tus of reefal limestone.

Proximal toe-of-slope – Debris-flow deposits, that is litho-

clasts of various size and rudite—calcarenite-sized bioclast in
mudstone—wackestone matrix characterize this depositional
zone (Fig. 8).

Distal toe-of-slope – Predominance of turbiditic deposition

characterizes this depositional environment. Above erosional
surfaces (locally erosional channels), allodapic limestone,
showing features of the classic Bouma sequence, are visible,
alternating with laminitic limestone, that is fine-grained tur-
bidites, deposited from low-density turbidity currents.

Pelagic basin – In the inner basin, relatively far from the

slope, pelagic oozes (filament or radiolarian oozes) were de-

Fig. 5. Lithology, microfacies types and facies interpretation of the
uppermost part of Csv-1 core. Abbreviations: M – mudstone, W –
wackestone, P – packstone, G – grainstone, DF – debris flow de-
posit (debrite); Rb – Redeposited bioclastic facies, Rc – crinoidal
grainstone, Dt – distal turbidite, Vt – very distal turbidite, F –
filament facies, R – radiolorian facies; Pl – carbonate platform,
S – slope, T – toe-of-slope, B – basin.

Fig. 6. Lithology, microfacies types and facies interpretation of a
composite section in the Pokolvölgy quarry. For legend and expla-
nation of abbreviations see Fig. 5.

LATE TRIASSIC BACKPLATFORM AND INTRAPLATFORM BASINS 165

posited as a rule. Fine lamination, that is, alternation of cal-
cisilt and mudstone laminae, is common. It can be interpreted
as a very distal, low-density turbidite. Calcarenitic turbidites
are rare and very thin (mm-thick).

Basin evolution is summarized in Fig. 9. The Upper Car-

nian—Norian succession encountered in the Csv-1 core shows
a fairly clear trend. In the lower part of the succession, the pre-
dominance of the basin facies is characteristic, whereas distal
toe-of-slope facies prevails upward, thus suggesting platform
progradation. Within this long-term trend, short-term facies
changes can also be seen. These may reflect sea-level changes.
An increasing amount of microfossils of platform-interior ori-
gin probably indicates highstand intervals (high-stand shed-
ding – Reijmer & Everaars 1991; Reijmer et al. 1992; Schla-
ger et al. 1994).

Fig. 8. Debrite intercalation in a distal turbidite succession. Large
plasticlasts and lithoclasts occur in the debrite bed. Pokolvölgy
quarry, Csővár.

In the early part of the Rhaetian, represented by the basal

layers of the Pokol-völgy quarry a remarkable facies change
could be recognized. Appearance of a large amount of larger
plant fragments (among them an imprint of a pine-cone – J.
Oravecz pers. comm.) and sporomorphs of continental plants
(Haas et al. 1995), suggests a significant sea-level drop, when
large parts of the former platforms may have been subaerially
exposed and restriction of the intraplatform basin increased
(Fig. 9).

The appearance of proximal toe-of-slope facies in the higher

part of the quarry can be bound to sea-level rise, when reefs
(bioherms) were formed on the upper slope, whereas a large
part of the neighbouring platform remained probably emerged,
thus providing a relatively large amount of sporomorphs of
continental plants for the basin. This model can also explain
why the inner-platform foraminifers are missing in the Rha-
etian part of the Csővár Formation.

According to the study of the Vár-hegy section, an upward-

deepening trend characterizes the latest Rhaetian. The distal
turbidites are followed by laminitic layers, that is very distal
turbidites and then filament wackestones of basin facies. A
thin debris-flow layer was found at the T/J boundary interval,
which was determined by ammonites (Pálfy & Dosztály 2000)
and conodonts (Pálfy et al. 2001). This was followed by distal
turbidites and pelagic basin facies, which probably already be-
long to the Jurassic.

The Hármashatár-hegy Basin

In the Buda Mountains, Upper Triassic cherty dolomite and

limestone of basin facies have been known since the 19th cen-

Fig. 7. Lithology, microfacies types and facies interpretation of
the Vár-hegy trench. For legend see Fig. 5, for explanation of ab-
breviation see Table 1.

166 HAAS

tury (Hofmann 1871). On the basis of a few fossils, they were
classified  into  the  Middle—Upper  Carnian  (Schafarzik  1902;
Lőrenthey  1907).  In  the  same  area,  thick-bedded  dolomites
with Upper Carnian molluscs and without chert were also en-
countered.  Accordingly,  the  concept  of  coeval  shallow  and
deep marine Late Triassic facies already emerged in the 1920s.
The juxtaposition of the significantly different facies was ex-
plained by Horusitzky (1943, 1959) by a nappe structure. On
the other hand, Wein (1977) attributed the facies differences to
the  paleogeographical  setting,  assuming  subparallel  basins
separated by submarine highs. In 1993, Kozur & Mock report-
ed Carnian—Rhaetian age data from the cherty basin facies in
the  Hármashatár-hegy  Range.  In  1992,  a  core  boring  (Vh-1)
penetrated a 200 m-thick succession of the Upper Triassic ba-
sin and slope facies, which provided data of outstanding im-
portance from both stratigraphic and sedimentological points
of view. Detailed analyses of the core samples and new con-
cepts on carbonate platform and foreslope evolution inspired a
comprehensive  re-evaluation  of  the  existing  data  and  the  re-
sults of the new studies (Haas et al. 2000).

The geological setting of the Upper Triassic basin and plat-

form facies is shown in Fig. 10. Cherty basin facies occur in
two ranges, in the southwestern and northeastern side of the
Buda Mts, respectively. They are separated by coeval platform
facies. The time/space relationship of the basin and platform
formations are presented in Fig. 3.

The lithology, chronostratigraphic subdivision and results of

petrographic and microfacies studies, as well as facies inter-
pretation of core Vh-1, which exposed the Upper Norian—Rha-
etian part of the Mátyáshegy Formation are shown in Fig. 11.
The characteristic facies types recognized in the core section
are presented in Table 2 and Figs. 12, 13.

A general depositional model for the Late Norian—Rha-

etian part of the Mátyáshegy Formation based mainly on the
studies of the microfacies and organic matter in core Vh-1, is
shown  in  Fig.  14.  A  high-productivity  intraplatform  basin,
partially  separated  from  the  open  sea  by  isolated  platforms
and  islands,  was  the  site  of  deposition.  From  the  ambient
platform, bioclasts and lithoclasts were transported into the
basin and deposited at the toe of the slope. The semi-consoli-
dated sediments were commonly affected by synsedimentary
deformation.

The main facies units can be characterized as follows:
Carbonate platform – Platform carbonates (Fődolomit =

Hauptdolomit and oncoidal Dachstein Limestone), of the same
age of the Mátyáshegy Formation (Upper Carnian—Rhaetian)
are known in the neighborhood of the outcrops of basinal de-
posits. Near to the paleomargin of the platform, peculiar fossil
assemblages (e.g. ammonites in platform facies) occur.

Proximal toe-of-slope – Polymict and monomict breccia

represent the talus of the steep slope, whereas debrites char-
acterize the more gentle outer part of the toe-of-slope fan.

Lithofacies type

Description

Interpreted depositional setting

Sedimentary breccia (Br)

Monomict or polymict intraformational
breccia

lower slope

Redeposited bioclastic (Rb)

Calcisilt – coarse calcarenite, w
Crinoids, Tubiphytes, benthic foraminifers
+ lithoclasts

proximal toe-of-slope

Distal turbidite (Dt)

Graded fine calcarenite, peloidal, bioclastic
gr and peloidal p–w alternate

distal toe-of-slope–basin

Peloidal wackestone (Pw)

Calcisilt w, peloids, bioclasts
Filaments, ostracodes, echinoiderm
fragments, radiolarians, algal cysts, sponge
spicules

basin (hemipelagic deposit)

Sponge spicule facies (S)

Calcisilt, calcilutite w
Radiolarians, algal cysts, ostracodes,
filaments, phytoclasts

basin

Radiolarian facies (R)

Calcisilt, calcilutite w, p
Radiolarians (molds — very abundant),
sponge spicules, filaments, ostracodes

basin

Algal cyst facies (Ac)

Calcisilt, calcilutite w, p
Cysts of Tasmanites-type algae (very
abundant), ostracodes, phytoclasts

basin

Homogenous mudtstone–wackestone (Ho)

Calcilutite m, w
Phytoclasts, filaments, ostracodes, algal
cysts

basin

Laminitic (La)

Alternation of microsparite and fine
phytoclastic, organic rich laminae
Algal cysts, ostracodes, echinoderm
fragments (rare)

oxygen-depleted basin

Silty marl (Sm)

Argillaceous mudstone with significant
amount of siliciclastic silt, laminitic
Globular molds, sponge spicules, ostracodes

oxygen-depleted basin with terrigenous
input

Table 2: Lithofacies types of the Mátyáshegy Formation in the Vh-1 core.

170 HAAS

Fig. 13. Organic-rich laminitic calcareous marl (laminitic facies).
Core Vh-1, 128.9. Scale bar: 2 cm.

The early evolution of the Hármashatár-hegy Basin is poor-

ly known. During the Julian (Kozur & Mock 1993) above the
former platform (Budaörs Dolomite) a relatively shallow basin
came into being where platy dolomite was formed. There are
no biostratigraphic data for the Late Carnian—Early Norian in-
terval, but survival of the basin can be assumed. Cherty dolo-
mite and limestone of pelagic basin facies make up the pre-
dominant part of the Hármashatár-hegy Range. On the basis of
the study of core Vh-1 a more detailed evolutionary history
could be presented for the Late Norian—Rhaetian interval (for
details see: Haas et al. 2000).

Laminitic dolomite, rich in organic material, locally with

microlayers rich in radiolarians or cysts of Tasmanites-type al-
gae, is the most characteristic rock type in the Upper Norian
part of the succession. It may have been formed in a restricted
basin of layered water mass. The high-productivity upper wa-
ter layer must have been rich in nutrients, whereas decay of or-
ganic material led to oxygen depletion in the lower water lay-
er. Establishment of nutrient-rich surface water conditions can
be explained by upwelling. The nutrient-rich water may have
reached the restricted basin via intraplatform channels. At the
water/sediment interface, anoxic conditions came into exist-
ence providing ideal condition for anaerobic bacteria activity.

Fig. 14. Sedimentological model for the Hármashatár-hegy Basin.
Size of O

symbols refers to the oxygen content of the water. For ex-

planation of the abbreviations see Table 2.

The microbial sulphate reduction, removing the inhibitor sul-
phate  from  the  system,  allowed  the  dolomite  to  precipitate
(microbial  dolomite  model  –  Vasconcelos  &  McKenzie
1998).  Synsedimentary  microfaults,  fractures,  slump  struc-
tures  and  sedimentary  breccia  are  common  in  the  lower  and
middle parts of the core section. They indicate sliding of the
more or less consolidated sediments on a gentle slope.

The upper part of the core section is practically free of dolo-

mite. It may reflect more humid climatic conditions, that is
less effective water layering in the basin. Increasing kaolinite
content and interlayers rich in silt-sized siliciclastics also sug-
gest increasing humidity. The predominance of the laminitic
microfacies does not change, but graded distal turbidite layers
appear and basin facies with sponge spicules, radiolarians and
Tasmanites-type algal cysts are also common.

The Fekete-hegy Basin

In a small area in the Pilis Mts, in the northeastern part of

the TR, a dark grey, thin-bedded dolomite and limestone se-
quence crops out (Fig. 2). It probably overlies the Fődolomit
(Hauptdolomit)—Dachstein Limestone transitional unit, al-
though their boundary is not exposed, and it is conformably
overlain by the Dachstein Limestone (Fig. 3).

Stache (1866) first reported the occurrence of dark, thin-

bedded limestone, rich in bivalves. Schafarzik (1884) de-
scribed it as a fossil-rich segment of the Dachstein Limestone.
Lóczy sen. (1913) considered it to belong to the “Kössen
Beds”. Oravecz (1961) proposed the name “Feketehegy Beds”
(which was later modified to Feketehegy Formation) and clari-
fied the stratigraphic setting of the formation.

The lower part of the 400 to 500 m-thick formation is made

up of dark grey, thin-bedded dolomite. Upsection it grades to
brownish  grey  or  dark  grey,  thin-bedded  limestone  (peloidal
mudstone and skeletal wackestone). Intercalations of thicker,
graded lithoclastic—bioclastic and ooidic—oncoidal calcarenite
beds and cross-bedded mollusc coquinas are common. In the
mudstone—wackestone  layers,  along  with  ostracods  and
sponge  spicules,  a  monospecific  conodont  fauna  Metapolyg-
natus slovakensis (Kozur) indicating the boundary of the Mid-
dle  and  Upper  Norian  was  found  (Budai  &  Kovács  1986;
Kovács & Nagy 1989). The coquina beds are characterized by
the  massive  occurrence  of  bivalves  (Avicula,  Halobia,  Myo-
concha,  Gervilleia,  Myophoria,  etc.  –  Fig.  15)  and  gastro-
pods (Euomphalus, Worthemia, Noritopsis, Coelostylina, etc.).
Ammonoids (Rhabdoceras suessi Mojs., Arcestes, Paraplac-
ites, Megaphyllites) also occur (Oravecz 1961, 1987). The oc-
currence of Rhabdoceras suessi Mojs. proves the Sevatian age
of the upper part of the formation.

The Feketehegy Formation was deposited in a small, re-

stricted intraplatform basin (Fekete-hegy Basin) which proba-
bly began forming in the Middle Norian. Restricted conditions
of the basin are also evidenced by the monospecific conodont
fauna. The sedimentological features of the succession point to
a gentle slope (ramp) between the basin and the ambient plat-
form. The ooid and oncoid grains and some of the bioclasts are
of platform margin—inner ramp origin. The coquinas and the
graded calcarenite beds are probably storm layers, which were
formed on the mid-ramp, that is above the storm wave-base.

LATE TRIASSIC BACKPLATFORM AND INTRAPLATFORM BASINS 171

Fig. 15. Bivalve (Avicula) coquina in the Feketehegy Formation. Fekete-hegy key section. Scale bar: 2 cm.

The relatively shallow basin was filled up by the latest Norian
giving rise to extension of the platform system (Dachstein
Limestone) onto the area of the former basin.

The Kössen Basin

In the southwestern part of the TR Unit (South Bakony,

Keszthely Mts, North Zala Basin) platy dolomite (Rezi Dolo-
mite) and dark shale (Kössen Formation) of restricted basin fa-
cies represent the Late Norian to Early—Middle Rhaetian inter-
val.

In the southwestern part of the Southern Bakony and also in

the Keszthely Mts, already in 1913 Lóczy sen. distinguished
the platy dolomite from the bedded Fődolomit (= Hauptdolo-
mit). Noszky (1958) referred to it as “Kössen Dolomite” be-
cause it contained a “Kössen-type” fossil assemblage. Bohn
(1979) defined it as Rezi Dolomite Formation.

The 150 to 300 m-thick Rezi Dolomite conformably over-

lays the Fődolomit. It is made up of platy, laminated dolomite
with lithoclastic—bioclastic interlayers and slump structures.
Mollusc coquinas are common mainly in the upper part of the
formation. In the Keszthely Mts a thick-bedded dasycladacean
dolomite intercalation (150—170 m in thickness) occurs in the
middle part of the formation, which can be interpreted as a
tongue of the Fődolomit.

In the lower part of the succession conodonts indicating the

boundary between the Middle and Upper Norian were found
(Budai & Kovács 1986).

The Kössen Formation overlays the Rezi Dolomite and ex-

tends over it northeastward, interfingering with the Dachstein
Limestone.

The term “Kössen Beds” was introduced by Oppel (1854) in

the Northern Calcareous Alps. Böckh (1872) applied the term
in the TR. Later on, the term of Kössen Beds was used with
many different meanings, both in the TR and the Northern
Calcareous Alps. At present it is applied to dark, shaly—calcar-
eous sequences deposited in restricted, oxygen-depleted basins
(Kuss 1983; Haas 1993). In the Southern Alps (Lombardy) the

Riva di Solto Shale and the cyclic Zu Limestone shows close
facies relationships with the Kössen Formation (Stefani &
Goldfiery 1989).

In the Zala Basin, in the southwestern part of the TR Unit,

the approximately 500 m-thick Kössen Formation is made up
predominantly of shale. It is overlain by Upper Rhaetian-Het-
tangian platform limestone.

In the Keszthely Mts the thickness of the formation may

have reached 300 m, but its topmost part has been eroded. This
succession  is  exposed  in  the  core  Rezi-1  (Fig.  16).  Above  a
thin  transitional  interval  (consisting  of  dolomite,  limestone
and  shale),  the  Kössen  Formation  begins  with  alternating  li-
thoclastic—bioclastic slope deposits and laminitic restricted ba-
sin facies. On the basis of sporomorphs, the Norian/Rhaetian
boundary could be recognized in this interval (Góczán 1987).
Upsection it is overlain by monotonous shale of inner basin fa-
cies.

Northeast of this area, in the westernmost part of the South

Bakony, the Kössen Formation is made up of cyclic alternation
of carbonate and shale intervals (Fig. 17). According to the fa-
cies studies, the carbonate beds were formed in shallow sub-
tidal, the shale layers in deeper subtidal environments (Haas
1993). Further northeastward, the shale layers pinch out within
the Dachstein Limestone (Fig. 18).

A general depositional model for the Kössen Basin in the

TR Unit is shown in Fig. 19. The main stages and controlling
factors of the basin evolution can be summarized as follows.

The Kössen Basin, that is the site of deposition of the Rezi

and Kössen Formations, began forming at the end of the Mid-
dle Norian as a result of extensional tectonics that led to disin-
tegration of the previously existing large carbonate platform.
In the early stage of the evolution of the basin, platy dolomites
(Rezi Dolomite) were formed. Intercalation of platform dolo-
mite into the platy basin succession indicates progradation of
the platform facies during highstanding sea-level, which was
followed by a new transgression. An intense, climate-induced
terrigenous influx led to shale deposition in the latest Norian.
As a consequence, in the inner part of the 100 to 150 m-deep

LATE TRIASSIC BACKPLATFORM AND INTRAPLATFORM BASINS 173

Sedimentological analysis of the sections revealed that sea-

level changes significantly controlled the features of the suc-
cession (Haas 1993; Haas & Budai 1995, 1999). In the area of
the Keszthely Mts, the toe-of-slope facies in the lower part of
the Kössen Formation is overlain by a laminitic deeper basin
facies reflecting sea-level rise in the early Rhaetian. At the cli-
max of the transgression, the clayey basin facies extended over
the upper slope and even some parts of the platform. This was
followed by regression in the highstand interval when the
Dachstein Platform re-occupied a large part of the former ba-
sin. This third order cycle is superimposed by higher order
(probably 4

and 5

order) transgression-regression cycles. It

is clearly demonstrated in the cyclic successions of the wide
gentle slope (ramp) between the Dachstein Platform and the
Kössen Basin.

Facies relationships and summary of Late Triassic

basin evolution

In the TR Unit, segmentation of the practically undifferenti-

ated ramp began in the Middle Anisian. It was attributed to the
Neo-Tethys rifting (Budai & Vörös 1992, 1993; Haas & Budai
1995). It is worth mentioning that this rifting affected the cen-
tral part of the TR (Balaton Highland) whereas in the north-

eastern part of the TR a large carbonate platform came into ex-
istence in the Ladinian.

Segmentation of the Budaörs Platform was initiated in the

Early  Carnian  (Julian).  The  Zsámbék  Basin  (basement  of  a
Tertiary basin W of the Buda Mts and the southwestern part of
the  Buda  Mts—Sas-hegy  Range)  and  the  Hármashatár-hegy
Basin  (northeastern  part  of  the  Buda  Mts—Hármashatár-hegy
Range) began forming at this time and most probably the evo-
lution of the Csővár Basin also began at the same time.

The Zsámbék Basin was affected by intense influx of fine

siliciclastics (“Reingraben Event” – Lein 1987) leading to
the complete filling of the basin by the latest Carnian (Late
Tuvalian) and establishment of carbonate platform condi-
tions (deposition of the Fődolomit Formation) in the area of
the former basin (Haas 1994; Góczán & Oravecz-Scheffer
1996).

In contrast, the Hármashatár-hegy Basin and the Csővár Ba-

sin received only poor terrigenous siliciclastic influx and fault-
controlled steep slopes did not favour platform progradation.
Therefore these intraplatform basins persisted for a long time.

A tectonically tranquil interval occurred during the latest

Carnian to middle Norian, giving rise to the complete building
up of the Dachstein platform-system. In the Csővár Basin,
slow and small-scale progradation of the platform took place
coevally (Haas 1997).

Fig. 18. Relationship of the coeval Kössen and Dachstein Formations in the SW part of the Transdanubian Range, along a SW—NE section.

174 HAAS

At the end of the mid-Norian, extensional tectonics led to

formation of new basins in the area belonging to the SW part
of the present-day TR Unit. Consequently, the continent-en-
croaching Dachstein Platform was transformed into an isolat-
ed platform. This process, that is the initial stage of evolution
of the large Kössen Basin system, was roughly coeval with on-

set of the development of the small Fekete-hegy Basin (north-
eastern part of the TR). In the Hármashatár-hegy Basin, litho-
clastic intercalations in the Mátyáshegy Formation may indi-
cate tectonic rejuvenation of the basin-bounding fault system.
The back-stepping trend of the toe-of-slope facies zones in the
Csővár Basin can be explained by down-faulting of the plat-
form margin, roughly at the same time.

In the latest part of the Late Norian a significant change oc-

curred  in  the  sediment  deposition  of  the  Kössen  Basin.  Pure
carbonate (dolomite) deposition was replaced by deposition of
argillaceous sediments, probably reflecting a marked climatic
change.  More  arid  conditions  were  replaced  by  more  humid
ones,  leading  to  an  enhanced  terrigenous  siliciclastic  influx
(Haas 1994). In the Hármashatár-hegy Basin, the dolomite and
dolomitic  marl  are  substituted  by  limestone  and  silty  marl,
roughly in the same period (Haas et al. 2000).

The evolution of the Kössen Basin came to an end by rapid

progradation of the Dachstein Platform in the late Rhaetian. In
the area belonging to the southwestern part of the present-day
TR Unit, development of the carbonate platform system con-
tinued until the end of the Hettangian, whereas in the north-
eastern part of the TR Unit, disintegration, unequal subsidence
and drowning of the Dachstein Platform began at the end of
the Triassic.

The relationship of the Late Triassic facies and evolutionary

history  of  the  depositional  area  of  the  TR  Unit  can  be  ex-
plained by double rifting as a consequence of coeval westward
progression  of  the  Neo-Tethys  and  eastward  opening  of  the
Ligurian-Penninic ocean basins. Formation of the new exten-
sional basins in the northeastern part of the TR, that is near to
the margin of the Neo-Tethys shelf, can be attributed to Neo-
Tethys rifting. Segmentation of the wide continent margin was
interrupted in the latest Carnian. A new extensional period be-
gan at the end of the Middle Norian, affecting mainly the area
represented  by  the  southwestern  part  of  the  TR  Unit,  which

Fig. 20. Characteristic lithofacies of the Kössen Formation. A –
Organic rich laminite (calcareous marl) with a bioclastic slump in-
terlayer. Core Rezi-4, 105 m. B – Lithoclasts and plastoclasts in a
slump bed. Core Rezi-4, 50 m. Scale bar: 1 cm.

Fig. 19. Sedimentological model for the Early Rhaetian Kössen Basin. Size of O

symbols refers to the oxygen content of the water.

LATE TRIASSIC BACKPLATFORM AND INTRAPLATFORM BASINS 175

was originally located close to the later Ligurian ocean basin.
Therefore this process can be attributed to Ligurian-Penninic
rifting. Disintegration and drowning of the platforms resumed
at the very end of the Rhaetian in the northeastern part of the
TR, probably reflecting the rejuvenation of Neo-Tethys rift-
ing in this time. This was followed by the disruption of the
large platform in the southwestern part of the TR from the
Early Sinemurian on, which can be linked to Ligurian-Pen-
ninic rifting.

Facies and paleogeographical relationships outside

the TR Unit

Remnants of the huge Dachstein platform-system are well

known  in  the  Central  Western  Carpathians  (Michalík  1980,
1993;  Haas  et  al.  1995b),  Upper  Austroalpine  (Zankl  1967,
1971;  Tollmann  1976;  Fruth  &  Scherreiks  1982;  Haas  et  al.
1995a)  and  South  Alpine  units  (Bosellini  &  Hardie  1988;
Ogorelec  1999)  and  also  in  the  Dinarides  (Dimitrijevic  &
Dimitrijevic  1991),  that  is  in  various  segments  of  the  Neo-
Tethys passive margins.

The relationships of the segment of the Kössen Basin in the

TR  with  that  of  the  classic  Kössen  facies  area  in  the  Upper
Austroalpine realm appears to be plausible. Similarities with
the Riva di Solto Basin in the Southern Alps have also been
documented  (Haas  1993;  Haas  et  al.  1995;  Haas  &  Budai
1995). In the Hauptdolomit facies zone of the Northern Cal-
careous  Alps  (Bajuvaricum  and  parts  of  the  Tirolicum),  the
Kössen  Formation  conformably  overlies  the  Upper  Norian
Plattenkalk  (thin-bedded  dolomite  and  limestone)  which  is
similar to the Rezi Dolomite. Akin to the situation in the TR,
by  the  Late  Rhaetian,  large  parts  of  the  basin  were  filled  up
with shale and limestone, and the carbonate platforms were re-
established  (“Oberrhät”  Limestone).  In  the  Dachstein  Lime-
stone facies zone the Kössen Formation pinches out. It occurs
only in the most external part of the Tirolicum as a thin inter-
calation within the Dachstein Limestone (Golebiowsky 1990).

In Lombardy, the tectonic segmentation of the Dolomia

Principale  Platform led to the formation of smaller intraplat-
form basins, site of deposition of the Aralata Group, consisting
of organic-rich carbonates (Jadoul 1985; Jadoul et al. 1992).
This was followed by deposition of the Riva di Solto Shale, of
a much greater lateral extension. The facies change has been
attributed  to  a  significant  climatic  change  and  sea-level  rise
(Burchell et al. 1990). The Riva di Solto Shale is overlain by
the Zu Formation, consisting of shale-limestone cycles with a
shallowing upward facies trend. In the Late Rhaetian the plat-
form  carbonates  re-occupied  the  former  basin  (Conchodon
Dolomite).

The relationships of the Hármashatár-hegy and the Csővár

Basins beyond the TR are much less known. The Csővár For-
mation shows very close similarity to the Pötschen Limestone
(Schlager 1967), a characteristic Norian formation of the Hall-
statt facies unit of the Northern Calcareous Alps and the Inner
Western Carpathians. As far as the Rhaetian is concerned, the
predominantly carbonate lithology of the Csővár Formation
significantly differs from that of the contemporaneous Zlam-
bach Marl of the Hallstatt facies unit. In contrast, the Rhaetian

segment of the Mátyáshegy Formation is akin to the Zlambach
Formation in terms of its biofacies and lithofacies characteris-
tics. It is worth mentioning that toe-of-slope facies containing
detritus of the Dachstein Reef Limestone was also reported
from the Zlambach Marl in the Northern Calcareous Alps
(Janoschek & Matura 1980).

Detailed sedimentological investigations of the Pötschen

Limestone  section  in  the  Gosau  Valley  were  carried  out  by
Reijmer (1991). His studies revealed that the succession was
made up of calciturbidites containing mainly pelagic material,
that  is  planktonic  or  pseudo-planktonic  bioclasts  in  fine  car-
bonate  mud.  The  lithofacies  and  biofacies  in  the  Csv-1  core
show  features  very  similar  to  those  described  by  Reijmer
(1991) but due to the lack of continuous core detailed studies
of  the  facies  changes  and  cyclicity  could  not  be  carried  out.
Calciturbidites  in  the  Rhaetian  part  of  the  Csővár  Formation
show practically the same characteristics as were observed by
Reijmer (1991) in the Pötschen Limestone, with the exception
of debrite interbeds that were not reported in the studied sec-
tion of the Pötschen Limestone.

The Pötschen Limestone is also known in the Silica and Tor-

na  Nappe  (it  is  slightly  metamorphosed  in  the  latter  unit)  in
North Hungary (Aggtelek—Rudabánya Mts), as well as in Slo-
vakia. In the Silica Nappe it consists of grey, thin-bedded cher-
ty limestone with Halobia coquina interbeds. In the lower part
of the formation intraconglomeratic and allodapic crinoidal in-
tercalations are common (Balogh & Kovács 1981). The most
frequent radiolarian and radiolarian-filament microfacies rep-
resent basin facies, whereas crinoidal coquinas and intracon-
glomerates  indicate  toe-of-slope  depositional  environments.
The formation has been dated to the Tuvalian to Early—Middle
Norian mainly on the basis of conodonts (Kovács 1986). In the
Silica Nappe the Upper Norian—Rhaetian is represented by the
Zlambach  Marl  consisting  of  brownish-grey  marl  with  grey
limestone  interlayers.  Due  to  its  significantly  higher  terrige-
nous  content  this  part  of  the  sequence  differs  considerably
from the Rhaetian part of the Csővár Formation, but is akin to
the  Rhaetian  of  the  Mátyáshegy  Formation.  The  Zlambach
Marl is overlain by the Liassic “fleckenmergel” facies in the
territory of Slovakia.

In the Carnic Fore-Alps, in the eastern part of the Southern

Alps, Upper Triassic facies akin to those in the Buda Mts were
reported (Crauli et al. 1988; Cozzi & Podda 1998). Among the
carbonate platforms that made up the Norian Dolomia Princi-
pale and Rhaetian Dachstein Limestone, small intraplatform
basins occur. In the basins Norian cherty dolomite (Dolomia di
Forni) and Rhaetian to Liassic limestone were formed. The
platforms are bounded by N—S and NE—SW-trending synsedi-
mentary listric faults (Cozzi 2000). At the foot of the faults,
megabreccia was accumulated; further on, graded doloarenites
and in the inner part of the basins distal turbidites and mud-
stone facies were reported (Cozzi & Podda 1998).

In the Southern Karavanks (in a section between Mittagsko-

gel and Hahnkogel, Austria), a thick Upper Triassic intraplat-
form basin succession was investigated by Krystyn et al.
(1994) and the authors emphasized the similarity of this series
with the time-equivalent formations in the northeastern part of
the Transdanubian Range. The intraplatform basin in the
Southern Karavank region began to form at the Carnian/Nori-

176 HAAS

an boundary interval. The Lower and Middle Norian are repre-
sented by 200 m-thick cherty dolomite with slump structures,
sedimentary breccia and turbidites. This is followed by a 300
m-thick  pelagic  platy  limestone  formation  of  Late  Norian—
Rhaetian age. It consists of crinoidal and radiolarian turbidites
and  bioturbated  wackestones,  but  no  coarse  clastics  occur  in
the upper part of the succession. Just as in the Csővár Block, a
continuous  succession  of  deeper  basin  facies  represents  the
Rhaetian to Early Jurassic interval.

Conclusions

Due to Neo-Tethys rifting, extensional basins began forming

in the central part of the TR during the Middle Triassic. Some
of them persisted until the Late Carnian. A new rifting stage
was initiated in the Early Carnian, which resulted in the for-
mation of narrow intraplatform basins in the northeastern part
of the TR Unit.

In the late Norian, incipient rifting of the Ligurian-Penninic

Ocean led to formation of the Kössen Basin in the external belt
of the shelf that is in the southwestern part of the TR Unit.
Therefore, since that time a double rift system may have been
in operation.

Although formation of the basins was tectonically con-

trolled, their sedimentation pattern, facies characteristics, ar-
chitecture and evolution were influenced by various factors.
The most important of these are:

– the paleogeographical setting of the basins, that is their

relation to the continental hinterland (source area of the silici-
clastics) and the shallow marine (subtidal) carbonate factories.

– climate, which basically controlled the siliciclastic input

and also influenced the carbonate production and mode of di-
agenesis (e.g. dolomitization).

– sea-level changes which controlled the geometry of plat-

form carbonates and also determined the size and restriction of
the intraplatform basins. Signals of the 3

-order relative sea-

level changes are generally recognizable in the successions.
Higher order cyclicity was recognized in the successions
formed on the wide ramp between the Dachstein Platform and
the Kössen Basin.

Intraplatform basin successions akin to those in the TR are

known also in the Central Western Carpathians, Northern Cal-
careous Alps and Southern Alps, indicating a similar scenario
of basin evolution.

Acknowledgments: The author is indebted to M. Sacci, and
two anonymous referees for thoughtful reviews of the manu-
script and useful comments and suggestions. I thank H.M. Lie-
berman (Houston) for the linguistic corrections. This work
was supported by the Hungarian Research Fund (OTKA) by
projects T—034168 (Hetényi, M.) and T—02797 (Haas, J.).

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