GeolCarp_Vol57_No1_15

GEOLOGICA CARPATHICA, FEBRUARY 2006, 57, 1, 15—27

www.geologicacarpathica.sk

Late Aptian—Early Albian syn-tectonic facies-pattern of the

Tata Limestone Formation (Transdanubian Range, Hungary)

TAMÁS POCSAI and LÁSZLÓ CSONTOS

Eötvös University, Department of Geology, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary; csontos@ludens.elte.hu

(Manuscript received November 2, 2004; accepted in revised form June 16, 2005)

Abstract: The Upper Aptian to Lower Albian Tata Limestone Formation consisting of brown-grey bioclastic crinoidal
limestone presumably represents the first unconformable formation, which recorded early deformation events of the
Alpine cycle. The base of the Tata Limestone is affected by erosional features accompanied by significant breccia bodies.
Reconstruction of the paleomorphology of the basin bottom supported by paleoecological (e.g. water depth) data shows
(in the recent orientation) at least five northwest—southeast trending zones with significant erosional features and accom-
panied by coarse-grained graded breccia in a more clayey matrix (e.g. Cseh-1 borehole). These elevations were uplifted
above deeper basins filled with crinoidal limestone. The geometry of the uplifted units is asymmetrical, anticline-like and
the deeper depressions have a syncline-like structure. According to previous works to the anticline-like morphology of
the uplifted zones and to the transport direction of the coarse breccia clasts, these uplifted units were possibly formed by
thrusting, in a compressional regime. The differences in the thickness of the crinoidal limestone and the breccia interbeds
show synsedimentary character of these movements. In the borehole Cseh-1, large limestone fragments appear already
in the Sümeg Marl Formation and they are present throughout all the Tata Limestone sequence. This fact indicates that
the tectonic movements started in the Barremian and continued during the whole Aptian.

Key words: Aptian—Albian, Carpathians, Transdanubian Range, tectonic model, syn-tectonic sedimentation, bioclastic
limestone, scarp breccia.

Introduction

The  Transdanubian  Range  is  located  in  Hungary,  in  the
heart  of  the  Pannonian  Basin  and  is  made  of  gentle  hills
(600 m  elevation;  Fig. 1).  It  nevertheless  provides  nice  ex-
posures  of  Paleozoic  to  Miocene  successions,  which  were
traditionally  related  to  the  Austroalpine  or  South  Alpine
structural  units  (Kázmér  &  Kovács  1985;  Császár  et  al.
1998).  This  unit  is  now  regarded  as  an  Upper  Austroalpine
nappe  (Tari  1994;  Fodor  et  al.  2003).

The Mesozoic successions are conformable until the

mid-Late  Albian.  At  the  basis  of  a  Munieria-bearing  marl
and  rudistid  limestone  (Tés  and  Zirc  Formations)  angular
unconformity  is  observed  (Fig. 2a)  (Császár  1986).  How-
ever,  a  lower  formation,  named  “Aptian  crinoids  lime-
stone”  or  the  Tata  Formation  (Fülöp  1976)  also  shows
very  gentle  unconformity  towards  lower  horizons  (Császár
et  al.  1998).  This  is  mainly  manifested  as  hiatuses  or  dis-
solved  surfaces  and  no  pronounced  angular  unconformi-
ty  was  described  so  far.  Our  main  goal  was  to  investigate
this  unconformity  and  the  overlying  Tata  Formation,  in
order  to  demonstrate  pre-  or  syn-depositional  tectonic  ac-
tivity  and  to  better  constraint  the  start  of  the  Cretaceous
structural  events.

Main characters of the Tata Formation

The Tata Limestone Formation is one of the most easi-

ly recognized members of the Cretaceous sequence in the

Transdanubian  Range.  The  bulk  of  it  consists  of  brown
to  grey,  fine-  to  coarse-grained  crinoidal  limestones.  In
some  places  brachiopod  or  ammonite-rich  coquina  is
found  at  its  base;  otherwise  the  formation  is  very  poor  in
macrofossils.  Based  on  paleontological  investigations
(Bodrogi  1994;  Görög  1996;  Fogarasi  2001;  Szíves
2001;  Bodrogi  &  Fogarasi  2002),  the  age  of  the  Tata
Limestone  is  Late  Aptian  to  Early  Albian  (Fig. 2b).  The
base  of  the  formation  seems  to  be  a  time-transgressive
surface:  in  western  zones  it  could  be  Late  Aptian,  in  east-
ern  outcrops  it  is  proven  to  be  Early  Albian  (Szives
2001).  In  eastern  areas  (at  Olaszfalu,  Eperkés  Hill  and
Tata  Kálvária  Hill)  some  small  pockets  at  the  unconfor-
mity  may  yield  Middle  Aptian  fauna  as  well  (Somody
1987;  Szives  2001).  In  western  zones  (Sümeg  and  envi-
rons)  the  sedimentation  was  continuous  from  the  under-
lying  pelitic,  glauconitic  Sümeg  Marl,  the  age  of  which
is  Barremian  to  Early  Aptian  (Haas  et  al.  1984).  In  the
central  area  of  the  Transdanubian  Range,  the  Tata  Lime-
stone  conformably  overlies  a  crinoidal  limestone  of  Val-
anginian  (Barremian?)  age,  which  is  a  heteropic  facies  to
the  Sümeg  Marl  (Borzavár  Formation).  In  the  other  areas
the  basis  of  the  formation  is  erosional,  at  some  places  the
erosion  surface  cuts  down  to  Jurassic  rocks  or  even  deep-
er  (Fig. 2b).  In  some  places  the  biodetrital  limestone
overlies  directly  the  Upper  Triassic  Dachstein  Limestone.
It  is  remarkable  that  there  is  a  major  hiatus  even  at  places
surrounded  by  Sümeg  Marl  exposures.

The top of the formation is either a marked unconfor-

mity, or a facies transition. The more unconformable

POCSAI and CSONTOS

parts  are  found  in  the  west,  while  the  facies  transition  is  lo-
cated  in  the  east.  Here  the  Tata  Formation  passes  laterally
to  a  rudistid  patch  reef  (Környe  Formation)  and  further  to
the  east  to  dark  basinal  silt  (Vértessomló  Formation)
(Császár  1986;  Mindszenty  et  al.  2001).  Both  of  these  for-
mations  have  an  Early  to  Middle  Albian  age  (Görög  1996;
Bodrogi  &  Fogarasi  2002).  In  other  places  to  the  west  (at
the  Bakony  Mts,  except  Sümeg  and  environs)  the  Tata
Limestone  is  covered  by  dark  brackish,  shallow  marine
marls  (Tés  Formation).  Mindszenty  et  al.  (2001)  suggested
that  the  facies  belts  moved  to  the  west  during  Middle—Late
Albian,  due  to  a  forebulge  and  fold-thrust  propagation.

There is always a significant extraclast content in the

formation.  This  is  eventually  manifested  as  spectacular
breccias  near  the  base  of  the  formation.  The  extraclasts
originated  from  older  members  of  the  Mesozoic  se-
quence.  The  average  size  of  these  detrital  limestone  frag-
ments  is  different  in  each  outcrop:  at  some  places  they
are  coarse-grained  (with  boulder  sized  limestone  frag-
ments),  making  up  thick  breccia  bodies.  At  other  places
the  extraclasts  are  represented  by  only  some  well  sorted
and  well  rounded,  sand-grain  sized  limestone  fragments
in  the  crinoidal  matrix.  The  coarser  members  were  inter-
preted  so  far  as  shallow  marine  transgressive  basal  brec-
cias  (Fülöp  1976).

Fig. 1. Location of the Aptian-Albian Tata Limestone (Transdanubian Range, N Hungary).

Lelkes (1981, 1983) made a detailed microfacies study of

the  formation.  He  described  three  main  microfacies  types.
According  to  him  the  deepest  environment  (100 m)  pro-
duced  a  sponge-bearing,  micritic  limestone  (“A”-type).  This
was  observed  at  two  distal  places.  The  bulk  of  the  formation
was  ranged  to  a  medium-grained,  well  sorted,  cross-bedded,
hummocky  bedded  bioclastic  grainstone  with  extraclasts
(“B”-type)  deposited  in  shallow  and  medium  depth
(30—100 m).  The  shallowest  (10—30 m),  coarse-grained
heavily  recrystallized  grainstone  with  minor  extraclasts
(“C”-type)  was  also  described  from  a  couple  of  exposures.

Methodology

Our main interests were to map the erosional features

at  the  base  of  the  Tata  Limestone,  to  locate  the  signifi-
cant  breccia  bodies  at  the  base  of  the  formation  and  to
try  to  collect  some  paleoecological  data  to  reconstruct
the  paleomorphology  and  paleo-water  depth  of  the  sedi-
mentary  basin.  Conventional  methods  were  used  to  reach
this  goal:  macroscopic,  and  microscopic  description  was
made  from  the  chosen  sections.  Thin  section  study  was
done  to  describe  the  microfacies  and  the  foraminiferal
communities  of  the  crinoid  limestone.

POCSAI and CSONTOS

Jurassic—Lower  Cretaceous  white  micrites  (Biancone)  are
conformably  covered  by  grey,  glauconitic  sandy  marl  and
silt  with  coalified  plant  remains:  the  Sümeg  Marl  (Fig. 3).
This  formation  of  Barremian—Early  Aptian  age  (Haas  et  al.
1984)  contains  variable  size  clasts  derived  from  the  Upper
Jurassic—Lower  Cretaceous  succession.  In  some  intervals
breccia  layers  are  observed.  These  are  grain  supported,  fin-
ing  upwards  and  have  a  pelitic  matrix  (Fig. 4).  High  in  the
well  Middle  Jurassic  radiolarite  is  also  present  among  the
clasts.  At  441 m  the  first  crinoidal  limestone  interlayer  oc-
curs  within  the  extraclast-bearing  grey,  micro-bedded
marl.  Further  upwards  more  and  more  crinoid-bearing  marl
follows.  Several  other  breccia  horizons  with  glauconitic
clasts  and  crinoid-rich  glauconitic  matrix  are  found  in  this
part  of  the  well.  These  are  normally  graded,  grain-support-
ed  breccias  with  the  crinoid  content  increasing  upward  in
each  breccia  horizon.  The  extraclasts  are  dominated  by
whitish  limestones  and  cherts.  The  lower  limit  of  the  Tata
Formation  is  interpreted  at  the  first  occurrence  of  the
crinoidal  limestone.  Both  the  Sümeg  Marl  and  the  Tata
Formation  are  deeper  basinal  sediments  with  several  grain-
supported,  normally  graded,  resedimented  breccia  hori-
zons.  It  seems  the  extraclastic  input  decreases  upwards  and
leaves  the  place  to  increasing  crinoid-input.

Fig. 3. Stratigraphic section of the well Csehbánya-1, only the
Lower Cretaceous succession is shown.

The Hajag exposure (Gombás puszta) is located 3 km

from  the  former  well  (Appendix).  This  exposure  on  a  steep
hill-side  covers  a  5 m  thin  and  condensed  Jurassic  succes-
sion  (Fig. 5)  (Fülöp  1964).  The  basal  Tata  Beds  lie  on  Upper
Jurassic,  or  Lower  Jurassic  strata.  Although  the  transition  is
within  a  short  distance,  no  visible  angular  unconformity  is

Fig. 4. Graded breccia sample from the Csehbánya-1 well,
396—398 m interval, with a chert fragment of 2 cm in diameter
in the middle of the core.

Fig. 5. Section at Gombás puszta.

LATE APTIAN—EARLY ALBIAN SYN-TECTONIC FACIES-PATTERN (HUNGARY)

seen  between  Jurassic  and  Upper  Aptian  beds.  The  base  of
the  Tata  Formation  is  made  of  a  0.5 m  thick  breccia  layer  of
nodular  appearance.  The  clasts  are  derived  from  older  for-
mations  and  from  the  Tata  Formation  itself.  This  horizon  is
covered  by  well-layered  crinoidal  limestone  with  extra-
clasts  of  2—3 mm  in  size.  Centres  of  crinoid  fragments  are
frequently  coloured  in  black.  This  might  indicate  an  organ-
ic-rich  or  reductive  environment.  These  layers  quickly  pass
to  the  typical,  coarse-grained  crinoidal  limestone  with
cross-stratification  without  recognizable  extraclasts.  In  thin
sections  a  lot  of  bioclasts  other  than  crinoid-ossicles  are  rec-
ognized.  There  are  frequent  and  relatively  big  (0.5—1 cm)
fragments  of  corals,  brachiopods  and  these  are  bio-eroded
(Fig. 6).  The  coarse-grained  crinoidal  grainstone  frequently
contains  dissolved  grains,  filled  by  coarse  sparitic  cement.
This  latter  was  produced  at  two  time  intervals:  first  a  thin,
radial,  submarine  cement  was  formed,  then  a  coarse-grained
shallow  burial  cement  filled  the  voids.  All  clasts  are  well
rounded  and  sorted.  The  absence  of  micrite  suggests  a  well-
agitated  environment.  The  high  percentage  of  shallow  water
fauna  as  well  as  bio-erosion  suggests  the  upper  part  of  the
photic  zone  with  a  maximum  of  15 m  water  depth.  It  is  in-
teresting  to  note  that  further  to  the  east  2 km  from  this  shal-
low  facies  exposure  another  well  (Hárskút-2)  found  the
Barremian—Aptian  Sümeg  Marl,  and  then  the  Tata  Forma-
tion  as  a  sponge  spicule  bearing  micrite  (Appendix).  Nei-
ther  the  marl,  nor  the  Tata  Limestone  contains  extraclasts  or
breccias.  The  transition  between  the  marl  and  limestone  ap-
pears  gradual.  Lelkes  (1983)  described  his  deepest  microfa-
cies  in  the  Hárskút-2  well.  Higher  in  the  well  the  Tata
Limestone  becomes  progressively  more  crinoidal  and  has
shallower  marine  facies.

The exposure on the top of the Som-hegy (Appendix)

shows  the  contact  of  the  Upper  Jurassic—Lower  Cretaceous
and  the  Tata  Limestone.  In  a  trench  (Fülöp  1964)  the  pinkish
white,  marly  micrite  (Biancone,  possibly  of  a  Valanginian
age)  is  encrusted  by  an  undulated  and  ferruginous-manganif-
erous  surface  (Fig. 7).  This  typical  hard-ground  is  covered  by
apparently  conformable  beds  of  the  Tata  Limestone.  The  bas-
al  beds  are  made  of  a  weakly  lithified  clastic  layer  with  red
clay  matrix.  Several  types  of  fragments  encrusted  by  fer-

Fig. 6. Gastropod fragment with micritic encrustation in early di-
agenetic cement. (Hajag Mountain, Gombás-Puszta exposure).

Fig. 7. Section at Som-hegy.

ruginous  surface  and  fossils  (mainly  shark  teeth)  were
found  floating  in  the  matrix.  The  carbonate  content  in-
creases  in  the  next  10 cm  bed,  with  pinkish  micritic  ma-
trix.  This  bed  also  contains  encrusted  red  and  green
pebbles  and  glauconite  grains.  The  higher  beds  are  lack-
ing  in  encrusted  ferruginous  clasts,  but  contain  greenish
clay  pebbles,  carbonate  and  radiolarite  clasts  with  green-
ish  clay  coating.  The  next  laminated  clay  layer  is  covered
by  crinoidal  limestone  with  very  frequent  extraclast  peb-
bles.  These  extraclasts  of  variable  size  are  persistent  higher

POCSAI and CSONTOS

upwards (Fig. 8). At about 75 m horizontal distance from
the base, a huge (20

×30 m) Lower Jurassic thick bedded

limestone  block  occurs  within  the  formation.  This  block,
formerly  interpreted  as  a  horst,  has  no  root  and  is  not  ex-
posed  in  a  very  near  undercutting  cave  (Fig. 9).  Therefore

Fig. 8. Breccia at Som-hegy.

Fig. 9. Map of Som-hegy, after Császár (1982), modified.

it  is  interpreted  as  an  olistolith.  There  was  no  grain  size
change  neither  in  eastern,  nor  in  western  directions.  500 m
further  to  the  NE  the  Tata  Limestone  is  a  crinoidal,  well
bedded  limestone  with  practically  no  extraclast  (only  mm
size  clasts  occur).  Unfortunately,  the  transition  between
the  thick  breccia  and  the  extraclast-free  outcrops  is  not  ex-
posed  properly.

In thin section, the basal grainstone beds contain a great

amount  of  bio-  and  extraclasts.  Beside  crinoid  ossicles,  ag-
glutinated  benthic  foraminifers  (Verneuillinoides)  are
present  in  a  great  number.  These  fossils  are  characteristic
for  the  inner  shelf  to  shallow  bathyal  environments  and
are  not  present  in  littoral  or  lagoonal  environments  (Van
den  Akker  2000).  The  clasts  are  strongly  bio-eroded  with
bacterial  dissolution  marks.  They  are  frequently  impreg-
nated  by  ferrous  solutions.  In  some  cases  silicification  also
occurs.  The  clasts  are  dominantly  Lower  Cretaceous—Up-
per  Jurassic  whitish,  pinkish  micrites,  but  cherts,  radiolar-
ite  clasts  also  occur.  Less  frequently  weakly  rounded  and
angular  quartz  forms  the  core  of  ferruginous  nodules.
These  quartz  clasts  show  an  undulating  extinction  and  are
probably  of  metamorphic  origin.  The  crinoids  are  re-
worked,  transported  and  sorted.  Higher  in  the  section
(0.5 m  from  the  unconformity)  a  biomicrite  packstone—

LATE APTIAN—EARLY ALBIAN SYN-TECTONIC FACIES-PATTERN (HUNGARY)

grainstone  is  found.  The  sparitic  cement  suggests  early  di-
agenetic  cementation  and  rapid  sedimentation  (Mindszen-
ty,  pers.  comm.).  This  pinkish  layer  contains  extraclasts
without  bio-erosional  marks  and  with  glauconite  coatings
on  them.  Their  material  is  derived  from  the  Lower  Creta-
ceous  Biancone  and  underlying  Upper  and  Middle  Juras-
sic  ammonitico  rosso  type  micritic  limestones.  The
foraminiferal  assemblage  is  characterized  by  both  plank-
tonic  and  benthic  forms  (Fig. 10).

In the basal beds the plankton-benthos content is 40—50 %

versus  60—50 %.  Higher  up  in  the  section  (0.5 m  from  the
basis)  it  raises  to  60—70 %  versus  40—30 %.  On  the  basis  of
the  plankton-benthos  content,  the  depositional  depth  in
the  basal  bed  (van  Marle  et  al.  1987)  would  correspond  to
150—250 m.  (The  recent  ratio  and  depth  relation  may  not
be  directly  applicable  to  Cretaceous  assemblages.)  Higher
up  the  water  depth  should  dramatically  increase  to  a  mini-
mum  of  200,  but  possibly  400 m.  Such  a  dramatic  increase
is  unlikely;  therefore  we  suppose  that  the  basal  beds  (like
the  others)  were  redeposited  from  a  shallower  area.  In  fact
the  sedimentology  would  correspond  much  more  to  a
slope  and  deeper  basin,  than  a  shallower  shelf  environ-
ment.  It  is  interesting  to  note  that  300 m  SE  from  this  ex-
posure,  on  the  hillside,  Tata  Limestone  overlies  directly
the  Lower  Jurassic  massive,  thick  bedded  formations.
Therefore  the  source  of  the  redeposited  extraclasts  may  be
in  this  southeastern  region.  The  area  is  affected  by  younger
strike  slip  tectonics  (Sasvári  2003),  therefore  this  conclu-
sion  should  be  taken  with  care.

The Borzavár exposure (Appendix) shows a Valangin-

ian—Lower  Barremian  crinoidal  limestone  and  the  Tata
Limestone,  with  no  apparent  unconformity.  The  lower
crinoidal  limestone  is  covered  by  a  thin  clay  horizon  and
the  cross-bedded,  crinoidal  Tata  Limestone.  The  foresets
of  the  cross-beds  were  measured  in  this  latter  and  a  domi-
nant  NE—SW  transport  was  found.  A  secondary  NW—SE
transport  was  also  recorded  (Fig. 11).  With  the  naked  eye
the  medium-grained  crinoid  sand  apparently  contains  no
extraclasts.  In  thin  sections  the  clasts  are  dominated  by

crinoid  ossicles,  which  are  reworked.  The  grainstone  ce-
ment  is  syntaxial.  Bryozoan  and  brachiopod  fragments
also  occur.  The  foraminiferal  assemblage  is  dominated  by
reworked,  thick-shelled  lenticulinas  and  by  some  aggluti-
nated  forms.  No  planktonic  form  was  found.  Sometimes
sponge  spicules  are  dissolved  to  form  chert  nodules.  In
thin  sections  a  lot  of  sand  grains  proved  to  be  extraclasts
(30 %).  Most  of  these  are  undeterminable  micritic  grains,
but  some  are  certainly  derived  from  Lower  Jurassic  on-
coidic  limestone  and  Middle  Jurassic  pelagic  Bositra
limestone.  The  clasts  were  sorted  and  deposited  parallel  to
the  cross-bedding  laminae.  The  above  described  sedimen-
tological  features  speak  in  favour  of  a  shallow,  well  agitated
marine  environment.  The  oxygenation  of  the  environment
was  good  (as  indicated  by  the  presence  of  Lenticulina),  the
sedimentary  rate  being  relatively  high.  The  extraclasts  are
probably  rounded  by  wave  activity.

The Vértessomló exposure is a small trench along a forest

road  (Appendix,  Fig. 12).  The  Tata  Limestone  covers  a
Tithonian—Berriasian  pinkish  limestone.  The  basal  bed
contains  a  60 cm  thick  coarse  breccia  with  6—8 cm  clasts  in
pelitic-sandy  matrix.  The  clasts  are  mostly  composed  of  the
uppermost  Jurassic  and  lowermost  Cretaceous  carbonates.
This  bed  is  overlain  by  weakly  cemented  sandy-calcareous
silt  with  calcareous  nodules.  Then  a  stronger  cemented

Fig. 10. Thin section with crinoid fragments and planktonic fora-
minifera, Som-hegy.

Fig. 11. Rose diagram of measured cross-bedding foreset lamel-
lae. Dark signs indicate direction of sediment transport.

POCSAI and CSONTOS

marly  limestone  comes  with  frequent  crinoids.  Higher  the
succession  continues  as  an  alternation  of  sandy  siltstone
and  crinoidal  limestone  layers.  In  thin  section,  the
poorly

cemented

nodular

layer

was

biomicritic

wackestone.  The  bioclasts  are  mostly  echinoderm
fragments,  but  foraminifers  and  mollusc  shell  fragments
are  also  frequent.  The  foraminiferal  fauna  is  dominated
by  Lenticulina  (30—40 %),  while  the  rest  contained
mono-,  bi-,  triserial  forms.  There  were  no  planktonic
elements  observed.  The  mollusc  shells  are  oriented
parallel  to  layering  and  show  a  weak  grading.  Some  of
the  clastic  quartz  grains  show  undulating  extinction  in
crossed  nicols.  The  sample  immediately  above  this  layer
shows  the  presence  of  glauconite  as  individual  grains  or
as  infill  in  foraminifers  (Fig. 13).  The  rock  is  a  packstone
with  mainly  echinoderms  as  clasts.  Contrasting  the
former  layer,  this  one  has  a  very  high  (70 %)  planktonic
foraminiferal  proportion.  This  content  indicates  several
100 m  water  depth.  The  apparent  contradiction  between
shallow  and  deep  water  may  be  resolved  by  considering
the  signs  of  redeposition  in  the  lower  bed.  The  breccia
elements  may  have  been  derived  from  shallow  water

Fig. 13. Thin section with crinoid fragments and planktonic fora-
minifers. Dark grains are glauconite infills, Vértessomló.

environment, but were redeposited in deeper water basin
facies. The rest of the formation is also a deep basin
deposit.

Discussion

The map constructed for the basal horizon of the Tata

Limestone  (Appendix  a,b,)  was  produced  using  available
well  data,  taking  into  account  Császár  &  Csereklei  (1982).
The  nature  of  the  basal  beds  is  indicated  as  coloured
squares  (exposures)  and  circles  (wells).  The  prominent
breccia  locations  are  marked  as  red  circles,  or  quadrangles.
Younger  structural  elements  were  simplified.  Since  the
present  day  topography  is  not  relevant  for  the  mid-Creta-
ceous  situation,  it  is  not  marked;  only  some  key  hills  or
settlements  are  indicated  for  orientation.  The  two  maps
show  the  two  main  exposure  areas  in  the  Bakony  and
Vértes  Foreland.

Both maps show northwest—southeast trending (recent

orientation)  uplifted  zones  with  significant  differential
erosion  at  the  base  of  the  Tata  Limestone.  There  are  indi-
cations  of  slight  folding  of  the  Tata  Formation  basement.
These  folds  are  best  seen  near  Zirc  and  southeast  of  Tata.
In  both  regions  small  wavelength  folds  can  be  constructed
based  on  well  and  exposure  data.  These  folds  have  a
NW-SE  axis,  very  similar  to  one  of  the  fold  sets  observed
in  the  Zirc  region.  The  longer  wavelength  anticlines  have
a  longer  NE  limb  and  a  shorter  SW  one.  This  is  especially
well  seen  in  the  Hajag  region  and  in  the  Vértes  Mountain,
which  is  interpreted  as  a  major  anticline.

It is remarkable that most breccia localities are found in

more  complete  Upper  Jurassic—Lower  Cretaceous  succes-
sions,  while  Tata  Limestone  without  breccias  may  cut
down  deep  into  the  Mesozoic  succession.  The  deep  ma-
rine  breccia  bodies  appear  to  be  localized  along  quick
changes  in  the  basement  lithology,  in  other  words  along
the  limits  of  main  pre-Tata  structures.  They  are  always  on
the  lower,  synclinal  part  and  never  on  the  anticlinal  part.

A series of cross-sections along relevant exposures was

constructed  (Figs. 14, 15).  These  sections  were  levelled  at
two  horizons:  at  the  base  of  Tata  and  at  the  top  of  Tata.
The  first  construction  stems  from  the  assumption  that  the
pre-Tata  erosion  created  a  peneplain.  This  might  not  be  a
valid  assumption,  since  in  several  key  locations,  hard-
grounds  were  found  at  the  base  of  Tata  and  deep  water
peneplanation  is  not  possible.  The  second  construction
stems  from  the  assumption  that  there  was  a  pre-Tata  paleo-
topography,  which  was  subsequently  filled  up.  We  ob-
serve  in  fact  a  shallowing  upwards  tendency  in  all
sections,  although  there  is  no  direct  sign  for  the  total  fill-
ing  up  of  the  basin.  Strong  facies  differences  suggest  the
existence  of  a  paleo-topography.  However,  it  is  quite  ob-
vious,  that  the  thickness  of  the  Tata  Formation  could  have
been  affected  by  later  erosion,  but  the  sedimentary  gap  be-
tween  this  formation  and  the  overlying  mid-Upper  Albian
marls  is  generally  small.  In  eastern  areas  there  is  no  gap
between  top  Tata  and  overlying  reefal  limestones  and  in-
terfingering  shales.  Therefore  we  consider  the  up-to-now

Fig. 12. Section of the Vértessomló road cut.

LATE APTIAN—EARLY ALBIAN SYN-TECTONIC FACIES-PATTERN (HUNGARY)

preserved thicknesses of Tata Limestone to reflect in a
way the original thicknesses.

On the maps (Appendix a,b,), as in both section types

(Figs. 14, 15)  the  pre-Tata  rock  units  form  a  folded  struc-
ture  beneath  the  unconformity.  The  sections  levelled  to
the  base  horizon  of  the  Tata  Limestone  do  not  explain,
however,  the  occurrence  of  breccia  bodies  and  the  ob-
served  facies  and  thickness  changes.  In  the  sections  lev-
elled  for  the  top  of  Tata  Formation,  the  folded  structures
remain  the  same  beneath  the  unconformity,  though  they
are  a  bit  accentuated.  In  these  sections  the  anticlines  be-
come  (paleo-)  topographic  highs,  while  the  synclines  be-
come  lows.

The Tata Limestone is generally thinner, where it over-

lies older Jurassic and Triassic formations above anti-
clines. Facies are shallow water type with frequent

cross-bedding.  Extraclasts  are  present  only  as  very  small,
rounded  fragments.  In  the  Vértes  area  the  thin  Tata  Forma-
tion  passes  into  a  reef  limestone  above  the  highs.  Sedi-
ment  transport  direction  measured  at  shallow  water  facies
cross-bedded  carbonate  sands  near  Borzavár  indicates  a
transport  from  NE  to  SW,  from  a  background  without  Tata
but  with  exposed  Triassic.

The thicker sequences cover an Upper Jurassic—Lower

Cretaceous  succession  with  less  or  no  hiatus  in  the  cores
of  synclines.  These  areas  with  less  erosion  are  interpreted
as  of  deeper  basinal  facies,  filled  with  thicker  crinoidal
limestone  and  marl.  At  the  margins  of  these  basins  there
are  often  coarse-grained,  graded  breccia  interbeds  in  a
more  clayey  matrix  (e.g.  Cseh-1  borehole).  According  to
detailed  sedimentological  studies,  the  breccias  are  all  sub-
marine,  slope  sediments.  These  breccia  bodies  originated

Fig. 14. Sections constructed across the Hajag area (Central Bakony Mts). a – levelled to the basal horizon of the Tata Limestone, b – lev-
elled to the top of the Tata limestone. Location of section marked in Appendix.

LATE APTIAN—EARLY ALBIAN SYN-TECTONIC FACIES-PATTERN (HUNGARY)

plains  the  observations  on  the  facies,  paleo-transport  and
breccia  occurrence.  This  in  turn  supposes  a  driving  force
to  create  such  a  syn-sedimentary  topography.  The  local-
ized  deep  water/slope  breccias  suggest  that  there  were
sudden  breaks,  or  steeper  slopes  in  topography.  Two  hy-
potheses  can  be  put  forward  to  explain  the  topographic
differences.  The  first  suggests  NW—SE  trending,  SW-dip-
ping  normal  faults,  the  second  suggests  NW—SE  trending,
mainly  NE-dipping  thrust  faults  (Fig. 16).  The  presence  of
folds  of  NW—SE  axial  trend  strongly  supports  the  second
possibility.  In  fact  the  thrust  faults  in  question  could  have
created  ramp  antiformal  and  foreland-hinterland-synfor-
mal  structures;  the  thrust  load  could  have  contributed  to
basin  formation.  Asymmetric  erosion  and  facies  differenc-
es  could  be  explained  by  tilted  normal  fault  blocks,  but
then  the  folds  remain  unexplained.  The  frontal  parts  of  the
tilted  blocks,  where  younger  formations  are  again  pre-
served,  are  not  impossible,  but  hard  to  explain  by  normal
fault  mechanism.

Borehole and outcrop data are spaced enough to enable

construction  of  a  variety  of  thrust  fault  directions.  Logi-
cally,  these  constructed  thrusts  should  be  parallel  to  one
of  the  potential  deformation  directions:  either  NW—SE  or
NE—SW,  as  also  seen  on  the  maps  of  the  Appendix.  It  is
suggested  that  the  thrust  faults  active  before/during  Ap-
tian  were  striking  NW—SE  and  not  in  a  perpendicular  di-
rection.  Besides  fold  data  (see  below,  Appendix),  there  is
an  additional  argument  in  the  Hajag  region  which  merits
attention.  The  northeastern  limb  of  the  Hajag  anticline  is
occupied  by  the  Sümeg  Marl,  the  youngest  formation  be-
fore  the  Tata  Formation.  However,  the  visible  NW-SE
strike  of  the  proven  extent  of  this  Sümeg  Marl  exposure  is
interrupted  by  a  NE—SW  tilted  structure.  There,  Aptian  is
also  eroded  away,  so  this  must  be  a  post-Aptian  structure.
The  NW—SE  trend  of  the  Sümeg  Marl  occurrences  would
be  much  better  explained  by  a  NW-SE  striking  thrust  fault,
than  by  a  perpendicular  (here  post-Aptian)  structure.

Fig. 16. Normal fault and thrust fault solutions to explain the syn-
depositional topography and facies variations. a – SW dipping
and rotated normal fault blocks, b – NE dipping thrust faults and
ramp anticlines.

Detailed tectonic studies in the neighbouring units of the

Transdanubian  Range  show  that  in  the  Barremian—Early  Al-
bian  time  interval  possibly  two  almost  orthogonal  folding
events  (Albert  2000)  occurred.  One  of  the  folding  phases
had  a  NW-SE  to  NNW-SSE  axial  direction  and  the  other
had  NE—SW  axial  direction.  Both  seem  to  be  covered  by  the
Middle—Late  Albian  unconformity  and  shallow  water  marls.
The  second  event  was  possibly  coupled  with  strike  slip  mo-
tions  (Mészáros  1983;  Kiss  et  al.  2001)  and  thrusts  (Sasvári
2003).  It  produced  long  wavelength  folds  dominating  the
structure  of  the  Transdanubian  Range.  The  first  event  pro-
duced  much  smaller  folds  and  coeval  thrusts  (Albert  2000).

The Transdanubian Range is traditionally linked to the

Eastern  and  to  the  Southern  Alps  (Upper  Austroalpine
nappes).  Strong  genetic  links  exist  towards  the  Dinaric
platform  as  well.  Except  the  Southern  Alps,  all  of  these  re-
gions  are  characterized  by  widespread  shear  and  nappe
formation,  compressional  movements  in  the  pre-Middle
Albian  period.  WNW—ESE  trending  shortening  was  prov-
en  in  the  Graz  Paleozoic,  in  the  Gurktal  Paleozoic,  the
Greywacke-zone  of  the  Eastern  Alps  (e.g.  Ratschbacher
1986;  Neubauer  1987).  The  Dinaric  margin  underwent
NE-vergent  shear  followed  by  SW-vergent  shear  and  fold-
ing  prior  to  Albian  (Csontos  et  al.  2004).  In  both  places
120  to  100 Myr  metamorphism  indicates  an  Early  Creta-
ceous  nappe  stacking  episode  (Milovanović  1984;  Kralik
et  al.  1987;  Fritz  1988;  Belák  et  al.  1995).  The  different
shear  directions  all  parallelize  after  the  subsequent,  paleo-
magnetically  indicated  rotations  are  taken  into  account
(Márton  &  Fodor  1995;  Márton  et  al.  1999, 2002;  Csontos
et  al.  2004).  In  other  words,  the  whole  broader  region  is
characterized  by  compression  during  the  Early  Creta-
ceous,  therefore  the  presence  of  normal  faults  or  exten-
sional  systems  seems  unlikely.

Conclusions

The facies pattern, thickness changes, differential ero-

sion  and  the  scarp  breccias  suggest  a  syn-depositional
compressional  activity  through  the  whole  Tata  Limestone
depositional  area.  The  anticline-like  morphology  of  the
uplifted  zones  suggests  that  the  uplifted  units  were  created
by  thrusting,  in  a  compressional  regime  (Appendix  c).  The
differences  in  the  thickness  of  the  crinoidal  limestone  and
the  breccia  interbeds  show  that  these  movements  were
synsedimentary.  In  the  borehole  Cseh-1  the  coarse  lime-
stone  fragments  appear  already  in  the  Sümeg  Marl  Forma-
tion  and  they  are  present  in  the  whole  drilled  Tata
Limestone  sequence.  Thus,  the  tectonic  movements  must
have  started  in  the  Barremian—Early  Aptian  and  continued
through  the  Aptian,  or  Early  Albian.  The  Early  Albian  fa-
cies  transitions  in  the  eastern  Vértes  Mountains  also  sug-
gest  that  the  same  facies  pattern  and  depositional  logic  is
still  preserved.  Therefore  we  propose  a  longer,  Barremian-
Early  Albian  compressional  activity,  dominated  by  NE-SW
shortening.  Eventually,  at  the  end  of  the  Early  Albian,  an-
other  shortening  at  a  high  angle  may  have  occurred.  The
maximum  of  these  shortenings  could  be  located  in  the  Di-

POCSAI and CSONTOS

narides.  In  the  Late  Jurassic—Early  Cretaceous  widespread
ophiolite  obduction  occurred  there.  An  obducted  ophio-
lite  nappe  reached  the  northern  premises  of  the  Trans-
danubian  Range  by  the  Early  Cretaceous  (Császár  &
Bagoly-Árgyelán  1994;  Tari  1994, 1995;  Mindszenty  et
al.  2001).  The  advancing  nappe  could  have  created  the
stress  field  necessary  to  initiate  a  foreland-ward  propagat-
ing  thrust  system.  From  our  data  it  seems  that  this  system
is  as  early  as  Barremian  (if  not  earlier)  in  the  Transdanubian
Range.  Thrusting  might  have  occurred  in  distinct  epi-
sodes,  but  the  age  resolution  in  the  given  period  is  too  low
to  give  the  exact  time  periods  of  thrusting.

Acknowledgment:  This  work  was  performed  at  the  Depart-
ment  of  Physical  and  Historical  Geology  of  the  Eötvös
Loránd  University,  Budapest.  Á.  Görög  offered  essential
help  in  micropaleontological  determinations.  A.  Mindszen-
ty  helped  in  the  description  of  thin  sections.  We  would  also
like  to  thank  the  suggestions  of  G.  Császár  and  the  opportu-
nity  he  offered  to  study  drill  core  samples  at  the  Szépvízér
Core  Store  of  the  Hungarian  Geological  Institute.  The  re-
views of G. Császár, D. Plašienka and J. Michalík are grateful-
ly  acknowledged.  The  study  was  supported  by  Hungarian
OTKA  Science  Grants  No.  T  043760,  T  037510.

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