GeolCarp_Vol60_No5_397

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA, OCTOBER 2009, 60, 5, 397—417 doi: 10.2478/v10096-009-0029-9

Eocene-Oligocene sedimentation in the external areas of the

Moldavide Basin (Marginal Folds Nappe, Eastern

Carpathians, Romania): sedimentological, paleontological

and petrographic approaches

CRINA MICLĂU

, FRANCESCO LOIACONO

, DIEGO PUGLISI

and DORIN SORIN BACIU

Department of Geology, “Al. I. Cuza” University of Ia i, Carol I Boulevard 20A, 700505 Ia i, Romania; crina_miclaus@yahoo.co.uk;

dsbaciu@clicknet.ro

Dipartimento di Geologia e Geofisica, University of Bari, Via E. Orabona 4, 70125 Bari, Italy; loiacono@geo.uniba.it

Dipartimento di Scienze Geologiche, University of Catania, Corso Italia 55, 95129 Catania, Italy; dpuglisi@unict.it

(Manuscript received July 18, 2008; accepted in revised form March 26, 2009)

Abstract: The Marginal Folds Nappe is one of the most external tectonic units of the Moldavide Nappe System (East-
ern Carpathians), formed by Cretaceous to Tertiary flysch and molasse deposits, piled up during the Miocene closure of
the East Carpathian Flysch basin, cropping out in several tectonic half-windows, the Bistri a half-window being one of
them. The deposits of this tectonic unit were accumulated in anoxic-oxic-anoxic conditions, in a forebulge depozone
(sensu DeCelles & Giles 1996), and consist of a pelitic background sporadically interrupted by coarse-grained events.
During  the  Late  Eocene  the  sedimentation  registered  a  transition  from  calcareous  (Doamna  Limestones)  to  pelitic
(Bisericani Beds) grading to Globigerina Marls at the Eocene-Oligocene boundary, and upward during the Oligocene in
deposits rich in organic matter (Lower Menilites, Bituminous Marls, Lower and Upper Dysodilic Shales) with coarse-
grained interlayers. Seven facies associations were recognized, and interpreted as depositional systems of shallow to
deeper water on a ramp-type margin. Two mixed depositional systems of turbidite-like facies association separated by
a thick pelitic interval (Bituminous Marls) have been recognized. They were supplied by a “green schists” source area
of  Central  Dobrogea  type.  The  petrography  of  the  sandstone  beds  shows  an  excellent  compositional  uniformity
(quartzarenite-like  rocks),  probably  representing  a  first  cycle  detritus  derived  from  low  rank  metamorphic  sources,
connected with the forebulge relief developed on such a basement. The sedimentation was controlled mainly by differ-
ent subsidence of blocks created by extensional tectonic affecting the ramp-type margin of the forebulge depozone.

Key words: Eocene—Oligocene, Eastern Carpathians, Romania, Moldavide Basin, Marginal Folds Nappe, paleogeography,
petrography, sedimentology.

Introduction and objectives

In Central Europe, the Carpathian Mountains join the Alps
with the Balkan and Rhodopean Chains, including remnants
of Tethyan oceanic crust and of its continental margins,
namely the internal Austro-Bihorean and the external Euro-
pean ones. Both were strongly deformed by Cretaceous and
Miocene tectonic events (Săndulescu 1988).

Two important sectors can be recognized in the Eastern

Carpathians  according  to  their  compressional  periods:  the
Dacides  (Median  and  External,  respectively)  deformed  in
Cretaceous  tectogeneses,  and  the  Moldavide  Nappe  System
deformed in Miocene tectogeneses (Săndulescu 1984, 1988).
The  Median  Dacides  are  formed  by  crystalline  basement
nappes with their Mesozoic sedimentary cover, whereas the
External  Dacides  are  formed  by  nappes  originating  from  a
marginal  trough  within  European  margin,  and  mainly  con-
sisting  of  Jurassic  to  Cretaceous  flysch  deposits  with  some
basic and ultrabasic volcanic rocks (Săndulescu 1975, 1980,
1984).  These  latter  rocks  prove  that  the  External  Dacides
represent  the  second  ophiolitic  suture  of  Carpathians  of  in-
traplate type, besides the main Tethyan suture known in the

Romanian Carpathians as the Transylvanides (Săndulescu
1980, 1984).

The Moldavide Nappe System mainly consists of Creta-

ceous to Tertiary flysch and molasse nappes (Bancilă 1958;
Ionesi 1971; Săndulescu 1975, 1980, 1984; tefănescu et al.
1979; Debelmas et al. 1980; Grasu et al. 1988).

As a consequence of tectonic loading related to Early-Late

Cretaceous shortenings of the Median Dacides and the internal
part  of  the  External  Dacides,  a  first  forebulge,  the  so-called
Perimoldavian  Cordillera,  was  developed  (Bădescu  2005).
The  Moldavidian  Realm  was  located  in  the  backbulge  depo-
zone  of  the  foreland  basin  system.  By  the  end  of  the  Creta-
ceous  the  External  Dacides  were  completely  deformed,  their
nappes being overthrusted over the Moldavidian Realm inter-
nal margin (Bădescu 2005). Consequently, the entire East Car-
pathian  foreland  basin  systems  migrated  outward.  This  stage
of  development  was  called  by  Grasu  et  al.  (1999)  “the  old
foreland  basin”  of  the  Eastern  Carpathians.  The  Moldavide
Nappe  System  is  linked  to  the  Miocene  tectogeneses  and  to
the closure of the Moldavide Basin when the East Carpathian
foreland  basin  systems  achieved  their  present  configuration,
called by Grasu et al. (1999) “the new foreland basin”.

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MICLĂU , LOIACONO, PUGLISI and BACIU

In the Eastern Carpathians, the Moldavide Nappe System

includes  an  inner  group  of  units  represented  by  the  Convo-
lute  Flysch  (or  Teleajen)  Nappe,  Macla  and  Audia  Nappes
consisting  mainly  of  Cretaceous  flysch  (Săndulescu  1975,
1984; Grasu et al. 1988). The outer group is represented by
the Tarcău Nappe and the Marginal Folds Nappe (or Vrancea
Nappe), consisting of Cretaceous to earliest Miocene flysch
deposits,  and  the  Subcarpathian  Nappe,  comprising  Paleo-

Fig. 1. Geological sketch map of the Bistri a half-window with the location of the studied logs and lithostratigraphic column of the Marginal Folds
Nappe between the Bistri a and Tazlău Rivers (based on Micu 1976, 1983, and Grasu et al. 1988): S – Sărata Beds; L – Lep a Beds; PU – Pi-
atra Uscată Beds; JM – Jgheabu Mare Beds; D – Doamna Limestones; B – Bisericani Beds (where rgs = red and green shales, ggm = green-
ish-grey mudstones, and gm+L = Globigerina Marls and Lucăce ti Sandstones); LM – Lower Menilites (Lm+F+cm = Lingure ti Marls,
Fierăstrău Sandstones and compact Menilites); BM – Bituminous Marls; LDS – Lower Dysodiles; GK – Kliwa Sandstones; UDSM – Upper
Dysodiles and Menilites; GS – Gura oimului Beds; f – faults.

gene flysch but mainly Early to Middle Miocene molasse
successions (Săndulescu 1975, 1984, 1994; Grasu et al.
1988).

The Marginal Folds Nappe, object of this study, is struc-

turally  interposed  between  the  Tarcău  and  Subcarpathian
Nappes which are placed inward and outward, respectively.
The  sedimentary  succession  of  this  tectonic  unit  at  the
Eocene-Oligocene  boundary  is  mainly  characterized  by  a

399

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

thick  pelitic  succession  (Bisericani  Beds),  grading  upward
into deposits known in the Romanian geological literature as
the Lower Menilites and Bituminous Marls, followed by Low-
er  Dysodiles  (Dumitrescu  1952;  Băncilă  1958;  Ionesi  1971;
Grasu  et  al.  1988;  Săndulescu  &  Micu  1989;  Grasu  et  al.
2007),  locally  interlayered  with  arenaceous  beds  (Lucăce ti,
Fierăstrău and Kliwa Sandstones; Fig. 1).

The stratigraphic succession sampled and logged in the

Bistri a half-window (sensu Băncilă 1958), near the town of
Piatra Neam (Fig. 1), shows the entire sedimentary succes-
sion of the Marginal Folds Nappe with an excellent exposure
of the middle to upper portions, where it is possible to ob-
serve the transition to the Lower Menilites.

Above these “menilite facies”, the section shows a mainly

pelitic interval (Bituminous Marls) evolving into the Lower
Dysodilic Shales. These include the Kliwa Sandstones which
due to their small thickness, less than 15 m, cannot be distin-
guished as a formation like in the Tarcău Nappe, where they
reach  hundreds  of  meters.  At  the  top,  the  Upper  Dysodilic
Shales  and  the  Upper  Menilites  close  the  flysch  sedimenta-
tion, while the Gura  oimului Beds seem to mark the begin-
ning of the molassic deposition.

Equivalent successions have recently been studied in the

more  internal  Tarcău  Nappe  from  the  sedimentological  and
petrographic points of view (Gigliuto et al. 2004; Puglisi et
al. 2006;  Miclău   et  al.  2007)  in  order  to  determine the pa-
leogeographic  context  of  the  deposition  of  the  arenaceous
turbidites mainly associated with the Lower Oligocene Low-
er Menilite Formation and the overlying Bituminous Marls.

Thus, the aim of this paper is to collect new interdiscipli-

nary stratigraphic and petrographic data in a more external
sector of the Moldavide Basin (Marginal Folds Nappe) in or-
der to (1) characterize the sedimentary facies and the clastic
provenance and (2) to hypothesize a paleogeographic scenario
for this portion of the basin, also supported by the compari-
son with the more internal successions.

Finally, accordingly to previous authors (Săndulescu

1972, 1984, 1988), the Paleocene-Oligocene flysch deposits
have been compared within the Ukrainian and Romanian
Carpathians, emphasizing a close similarity among the Ski-
ba/Boryslav-Pokuttya Nappes (Ukraine) and the Tarcău/
Marginal Folds Nappes (Romania).

So, the results of this study might also improve the knowl-

edge of the external areas of the Moldavide Basin and they
can probably also provide useful information for a more ex-
tensive paleogeographic reconstruction.

Stratigraphic setting

The Nechit River 1, 2 and oimu Sections were logged in

the  Bistri a  half-window,  belonging  to  the  Marginal  Folds
Nappe,  the  outermost  tectonic  flysch  unit  of  the  Moldavide
Nappe System. The deposits which crop out in this area are
mainly Eocene—Early Miocene in age and correspond, from
the bottom to the top, to the following formations, according
to  the  Romanian  geological  literature:  Jgheabu  Mare  Beds,
Doamna  Limestone,  Bisericani  Beds,  Globigerina  Marls,
Lower Menilites, Bituminous Marls, Lower Dysodilic Shales

and Kliwa Sandstones, Upper Dysodilic Shales and Meni-
lites, Gura oimului Beds (Fig. 1).

The flysch deposits involved in Moldavide units were ac-

cumulated in a foreland-type basin system (sensu DeCelles
& Giles 1996). The Marginal Folds Nappe sedimentation
area was located on the cratonic side of this basin, probably
on the internal part of the forebulge depozone.

The physiography of such a basin margin is usually of

ramp  type,  without  significant  change  in  water  depth  from
shallow  to  much  deeper  water  (Van  Wagoner  et  al.  1990).
Local  fault-controlled  uplifts and  depocentres, rather than a
smooth  flexural  profile,  might  develop  on  the  forebulge  in
foreland  basin  systems.  Extensional  fault  systems  are  com-
mon  on  potential  forebulge  uplifting  area,  both  related  to
tensional stresses caused by forebulge migration, and to old-
er  structure  reactivation  (references  in  DeCelles  &  Giles
1996). The forebulge of the foreland basin system might be
both an important source area of sediment, and a site of sedi-
ment accumulation.

Our paper concerns the deposits extending from the Biser-

icani Beds to the Upper Dysodilic Shales and Menilites.

Facies analysis

Facies analyses have been carried out in the field, collect-

ing  data  on  lithology,  grain  size,  sedimentary  structures,
sand : mud  ratio,  bed  thickness,  fining  and  thinning  upward
(FThU)  and  coarsening  and  thickening  upward  (CTkU)  cy-
cles  in  three  different  sections  (Figs. 2,  4,  5).  Seven  facies
associations (FA) have been distinguished and interpreted in
terms  of  sedimentary  environments,  parts  of  depositional
systems, according to criteria and models proposed by Mutti
& Ricci Lucchi (1972, 1975), Pickering et al. (1989), Mutti
(1992), Mutti et al. (1996, 2000, 2003, 2007).

1. Greenish-grey pelites with slumps facies association

of mud-rich slope apron system corresponds, according to
Ionesi (1971), to the middle part of the Bisericani Beds, and
consists of around 300 m of greenish-grey mudstones, main-
ly unstructured, with sporadic thin- to medium-bedded sand-
stones  (10  to  40 cm  thick),  locally  strongly  deformed  in
antiforms (10 m high) or flat lying folds (Fig. 3b) and cut by
sandstone  injections  (Fig. 3a).  Some  pebbly  mudstones  and
block-bearing mud flows can be also found. Some bioturbat-
ed  levels  (Chondrites)  were  also  noticed,  especially  in  the

oimu Section.

The lithologic uniformity and the absence of sedimentary

structures can be considered a result of the high frequency of
slumps, enhanced by some folded sandstone interlayers as
can be noticed in the Nechit River 1 Section. These, mainly
derived by rotational slumps, can be related to the F

2.1

facies

of Pickering et al. (1989) and their abundance might testify
the slope instability.

The significant thickness of this facies association (about

300 m) might prove that these deposits were sedimented on
upper slope where the influence of sediment plumes carried
by hypo- and mesopycnal currents is usually considered very
important (Galloway 1998) and induces slope active progra-
dation and aggradation (Fig. 4).

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MICLĂU , LOIACONO, PUGLISI and BACIU

Fig. 2. Nechit River 1 Section: facies associations and environmental interpretation (Late Eocene—Early Miocene). The legend shown is also
the legend for Figs. 4, and 5. I – sedimentary structures; II – Bouma sequences; III – ThU and TkU sequences; IV – sandstone bed thick-
nesses; V – Pickering et al. (1989) facies. 1 – plan parallel lamination; 2 – cross-lamination; 3 – undulated lamination; 4 – normal
grading; 5 – lenticular bedding; 6 – convolute lamination; 7 – flute and tool casts; 8 – load casts; 9 – mud intraclasts; 10 – thinning up-
ward sequences; 11 – thickening upward sequences; 12 – bioturbation; 13 – debrites; 14 – Kliwa + Kliwa-type sandstones; 15 – bitumi-
nous marls; 16 – brown marls; 17 – black shales (dysodilic shales); 18 – greenish-grey mudstone; 19 – whitish marls; 20 – black cherts
and shales; E—O b – Eocene-Oligocene boundary; O – Oligocene.

401

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

Fig. 3. Sand injections (a) and flat-lying folds (b) in greenish-grey mudstone of the Bisericani Beds ( oimu River Section and Nechit Riv-
er 1 Section, respectively). Menilite intraclasts within the Bituminous Marls in the Nechit River 2 (c) and 1 (d) Sections.

Greenish-grey pelites with slump facies association in-

cluding Facies D

1.2

; D

2.2

; D

2.3

; F

2.1

in Pickering et al. (1989)

terminology, are attributed to distal turbidites and hemipe-
lagites in an underfed system of mud rich slope apron envi-
ronment (on the basis of the sand : pelite ratio and vertical
trend). The mud rich slope apron environment is also indicat-
ed by very frequent slump deposits. In the uppermost part of
the FA a progradational trend indicated by CTkU cycles can
be noticed. It is important to underline that this slope had to be
rather a local feature of the bed topography controlled by the
extensional faults associated with the forebulge depozone.

2. Black shales with bedded cherts and sandstones fa-

cies  association  of  shallow  channels,  corresponding  to
Lower  Menilites,  consists  of  alternating  quartz-rich  sand-
stones (about 40 % in the association column), black shales,
brown  marls  and  siltstones,  greenish-grey  pelites  and  thin-
bedded menilite s.s. (black cherts; 15—16 % in the column).
Sandstones,  usually  thick-bedded  and/or  amalgamated,
(0.02—0.6 m), with flute/tool or load casts on sole, wavy tops
and internal structures such as plane-parallel and cross-lami-
nations,  are  organized  in  two  fining-  and  thinning-upward

sequences (ThU) in the Nechit River 1 Section. The same se-
quences can be recognized in the oimu River Section,
where the sandstone beds (Fierăstrău Sandstone) are up to
2 m thick, and in the Nechit River 2 Section (Fig. 5).

The menilite s.s. beds are mm—cm thick, very finely lami-

nated  and,  locally,  inter-bedded  with  brown  marls  and  grey
pelites. This facies association, very diversified in lithology,
characterizes  only  the  Nechit  River 1  and  2  Sections  but  is
absent  in  the  oimu  River  Section,  and  corresponds  to  the
Lower Menilites.

The facies association is referred to C, D, E (channel, in-

ter-channel  or  levee)  and  to  G  (pelagites,  organic  and
chemogenic  sediments)  facies  of  Pickering  et  al.  (1989).
This FA suggests an increase of clastic input due to a progra-
dational trend (such as that noticed in all three logs), contem-
poraneous  to  a  significant  supply  of  pelagic  sediments
(mainly Nechit River 1 and 2 Sections).

The fining- and thinning-upward sequences (FU/ThU), are

frequently interpreted as channel deposits, but in this specif-
ic case, due to their small thickness, seem to be linked to
some distal and shallow channels.

402

MICLĂU , LOIACONO, PUGLISI and BACIU

Fig. 4. oimu River Section: facies associations and environmental interpretation (Late Eocene—Oligocene). The same key as for Fig. 2.

403

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

3. Bituminous marls facies association of anoxic shelf,

ranges in thickness from about 10 m (Nechit River 1 and

oimu Sections) to 50 m (Nechit River 2 Section, Tazlău Riv-

er, near the homonymous village, and Văleni village on the
Bistri a River; Fig. 1), and consists of very fine laminated limy
clays and marls, rich in organic matter (TOC = 3.54—10.04 %
after Grasu et al. 1988), with cross-laminated thin interlayers
(mm to dm; Figs. 6b, 7a, and 7b) of sandstones. At the bot-
tom, large intraclasts of menilite s.s. lying parallel to the
stratification can be noticed (Figs. 3c,d, and 6a).

In this facies association, sedimentary structures very sim-

ilar  to  swaley  and  hummocky  cross-stratification  (SCS  and
HCS;  Fig. 8a),  together  with  parallel  and  low  angle  cross-
bedding, and wavy (Fig. 7a) and lenticular (Fig. 6b) bedding
are  recognized.  Some  sandy  injections  as  dykes,  sills  and
ptygmatic  structures  of  decimetric  dimensions  are  sporadi-
cally present (Nechit River 2 Section; Fig. 8b).

This facies association, which corresponds to the Bituminous

Marls, is deposited from two different processes: fallout from
suspension, as their fine lamination proves, and on this back-
ground,  cyclical  deposition  of  coarse  material.  The  fine  sand-
stone  interlayers  (like  those  in  Tazlău  or  Nechit 2  Section;
Figs. 1,  7)  can  be  attributed  to  storms  or  floods  which  devel-
oped hyperpycnal flows or turbidite currents moving downslope.

The HCS-like structures (Fig. 8a), which seems to be of

scour-drape  type,  together  with  swaley  cross-stratification
are usually interpreted as indicating storm conditions in shelf
environment  above  the  storm  wave  base  (Cheel  &  Leckie
1993). Anyway such hummocky morphology can also be de-
veloped  by  hyperpycnal  flows  as  “flood-generated  delta
front  lobes”  (Mutti  et  al.  2000).  At  the  Tazlău  observation
point  (Figs. 1,  7)  within  the  Bituminous  Marls,  centimetric
interlayers of sandstones showing wave ripple cross-lamina-
tion, have also been noticed (Fig. 7b).

The bituminous marls facies association shows the fea-

tures of a distal shelf, either fed during storms or fed by hy-
perpycnal  flows  from  shoreline  sources  during  possible
floods.  The  shallow  sedimentation  conditions  are  also
proved  by  the  existence  of  very  well  preserved  flatfish  like
Scophthalmus which will be described later in the paper.

4. Sandstone and conglomerate facies association of

channels with levee, mainly consists of sandstones, matrix-
and clast-supported conglomerates, and, subordinately, of
bituminous pelites of dysodilic shale-type. It corresponds
more or less to the coarser lower part of the Lower Dysodilic
Shales with Kliwa Sandstones.

Clast-supported thick-bedded conglomerates (up to 4 m

thick; Fig. 9a), mainly composed of “green schist” clasts (up to
0.8 m in diameter), subrounded and rounded white limestone,
and intraclasts of dysodilic shales (Fig. 9b), show a large scale
(meters to tens of meters wide) lenticular geometry with erosive
bases, locally with large sole casts. These conglomerates are fre-
quently associated with slided blocks, consisting of dysodilic
shales and thin-bedded Kliwa-type sandstones.

The matrix-supported conglomerates show finer “green

schist” clasts (3—5 cm diameter) floating in a Kliwa-type aren-
aceous sandstone matrix or sandy dysodilic shale matrix.

Sandstones of this association show different characteris-

tics: (a) thick and composite beds (up to 4 m thick), crudely

Fig. 5. Nechit River 2 Section: facies associations and environmental
interpretation (Late Eocene—Oligocene). The same key as for Fig. 2.
1 – hummocky and swaley like cross-stratification; 2 – sandstones
(Kliwa and Kliwa like); 3 – debrite with mud intraclastst and/or
green schist clasts; 4 – dark grey pelite; 5 – sand injections;
MRSA – mud-rich slope apron; Pb – Priabonian.

404

MICLĂU , LOIACONO, PUGLISI and BACIU

Fig. 6. a – Contact between menilites and Bituminous Marls (Nechit River 2 Section). b – Cross-laminated sandstones with load casts
and flame (mm to cm thick) interlayered in Bituminous Marls, proving the rapid influx of coarse materials.

Fig. 7. a – Sandstones with wavy and lenticular bedding interlayered within the Bituminous Marls at Tazlău. b – Detail of the internal
structure of sandstone beds (wave ripple cross-lamination) in white rectangle.

Fig. 8. a – Hummocky- and swaley-like cross-stratification (HCS and SCS, respectively) in bituminous marls at the Nechit River 2 Sec-
tion. b – Dyke (d), sill (s) and ptygmatic structures (p) within the Bituminous Marls in the Nechit River 2 Section.

405

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

graded,  with  large  undulated  amalgamation  surfaces,  some-
times  with  thin  plane-parallel  stratified  and  cross-laminated
tops,  locally  associated  with  conglomerates  with  “green
schist” clasts (Fig. 9e); (b) simple centimetre- to decimetre-
sized beds, parallel flat-based or slightly undulated with tool
casts, wavy tops with parallel to low angle cross-laminations
(Fig. 9d); (c) simple, very thin-bedded and lenticular strata;
(d)  thick-bedded,  laminated  sandstones  with  water  escape

structures (Fig. 9c); and (e) thick sandstone beds crudely
horizontal laminated with small floating clasts (Fig. 9c) rest-
ing on sandstone with convolute laminae.

This facies association re-groups all Walker’s (1992) “facies”

belonging to the turbidite family (i.e. massive sandstones, clas-
sical turbidites, pebbly sandstones and conglomerates). Accord-
ing to Pickering et al. (1989) the F

2.1

, C

2.1

, C

2.2

, C

2.4

, A

1.4

and

2.7

facies can be distinguished. FThU sequences are also fre-

Fig. 9. Clast-supported conglomerates and thick-bedded sandstones (a), locally with “green schist” and limestone clasts (b) cut in dysodilic
shales in the Nechit River 1 Section. (c) Sharp contact between parallel laminated sandstones with water escape structures and massive
sandstones

(Nechit River 1 Section), (d, f) simple flat base and wavy top sandstone beds interlayers in the Dysodilic Shales (Nechit River 1

and 2 Sections), and (e) thick and composite sandstone beds (Nechit River 1 Section).

406

MICLĂU , LOIACONO, PUGLISI and BACIU

quent and this may justify the interpretation of these deposits as
channel fills. This facies association indicates the proximal part
of a turbiditic system (facies A, B, C and intercalated D) com-
posed of coarse bodies, up to 10 m thick, organized in FThU se-
quences, attributed to debris or sandy cyclic flows more or less
channelized (Nechit River 1 Section).

The thick, composite sandstone beds might also be inter-

preted as type-A mixed system of Mutti et al. (2003). As the
latter authors showed, the mixed systems might be difficult
to distinguish from the basinal turbidites if the sediments are
not framed in their stratigraphic and structural setting.

The source area of the above described coarse deposits

was a “green schist” basement and its sedimentary cover of
limestone probably of platform type containing nummulites.
Such “exotic” clasts were described by many authors in Cre-
taceous to Late Miocene flysch and molasse deposits of ex-
ternal nappes of Moldavides since the early years of 20

century (Zuber 1902; Simionescu 1909; Mrazec 1910; Mur-
goci 1929; Băncilă 1958; and later by Ionesi 1971; Anastasiu
1984, 1986; Săndulescu 1984; Grasu et al. 1988, 1999, 2002,
2007). Their source area is considered to be Central Dobro-
gea although there are not many papers concerning the petro-
graphic-mineralogical comparison of source area rocks and
the resedimented “green schist” clasts except Simionescu

(1908) and Anastasiu (1984, 1986). Central Dobrogea is an
uplifted block of East Moesia located in south-east Romania.

The dominance of FThU sequences may indicate a deep-

ening basin which also explains the episodic character of the
gravity flows deriving from an unstable margin of the basin.
This is a clue for the subsident trend of the basin, the main
extensional tectonics (normal faults, growth faults) of the ba-
sin margin, and collapsing processes. A very important proof
of extensional tectonics is the presence of a large bituminous
marl  olistolith  (in  Nechit  River 1  Section;  Fig. 2)  in  the  fa-
cies  association  column.  The  active  tectonic  subsidence  be-
gan, in fact earlier, since the bituminous marl sedimentation.
This is proved by important differences of thicknesses from
proximal (around 50 m thick in Nechit River 2 Section, and
Tazlău or Văleni observation points) to distal (15—20 m thick
in the Nechit 1, and  oimu Sections) studied sections. In or-
der to explain this, we can suppose a marginal block delimit-
ed  by  normal  faults  producing  adjacent  areas  with  active
syn-sedimentary uplift or subsidence.

5. Arenaceous-pelitic facies association of depositional

lobes partly corresponds to the upper part of the Lower Dys-
odilic Shales with Kliwa Sandstones (Figs. 10a,b) and partly
to the Upper Dysodilic Shales. Sandstone beds show irregular
scoured bases (Fig. 10a), locally with sole casts and wavy tops

Fig. 10. a – Sandstones with irregular base and wavy top with black shale interlayers. b – Arenaceous-pelitic facies association (deposi-
tional lobe) within the Upper Dysodilic Shales (bituminous pelitic facies association) in the oimu River Section. c – Deformed deposits
(slump) of bituminous pelitic facies association in the Nechit River 1 Section. d – Thin intelayers of bentonitic shale in bituminous pelitic
facies association (Nechit River 1 Section).

407

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

with  decimeter-sized  current  ripple.  Parallel-  and  cross-lami-
nations, normal grading and weakly undulated amalgamation
surfaces are the most frequent internal structures. This facies
association  always  follows  channel  fill  deposits  (sandstone
and  conglomerate  facies  association).  It  consists  of  T

, T

turbidites or C

2.2

facies of Pickering et al. (1989).

Facies belonging to this association can be interpreted as

depositional lobes due to the absence of significant erosive
surfaces at the base of sandstone layers. The sand : mud ratio

≈ 1 might suggest that this facies association can be referred
to the intermediate part of a turbiditic system.

6. Bituminous pelites with slumps and debrites facies as-

sociation of fringe fans, corresponds with the upper part of the
Upper  Dysodilic  Shales,  and  mainly  consists  of  decimeter-  to
meter-thick pelites of dysodilic shale-type, very rich in organic
matter.  These  deposits,  frequently  deformed  (Nechit  River 1
Section; Fig. 10c), are associated with paraconglomerates with
“green  schist”  clasts  and,  locally,  to  thin  beds  of  bentonitic

Fig. 11. a – Bioturbated sandstones (Thalassinoides) of whitish marl with debrite facies association in  oimu River. b – Highly bioturbated pel-
itic interlayers replaced by burrow fills (Thalassinoides) in whitish marl with debrite facies association in the  oimu River. c – Debrite with
brown marl intraclasts and green schist clasts in Globigerina Marls s.s. in  oimu River. d – Thick lamination in Globigerina Marls s.s. in the

oimu River.

408

MICLĂU , LOIACONO, PUGLISI and BACIU

shales  (up  to  1 cm;  Fig. 10d)  and  to  thin-bedded  sandstones
with planar to weakly erosive bases (with sole casts). The thin
sandstone  layers  show  wavy  tops,  plane-parallel  and  cross-
laminations.  They  might  have  sheet  or  lenticular  (0.5—1 m
wide) geometry, and tend to disappear upward in succession.

The facies belonging to this association may represent a

distal turbiditic system, and show a deepening upwards trend
of the whole facies succession. They were sedimented into a
subsident basin. Sandstone beds show the characteristics of
T

and T

or of C

2.3

facies. The small amount of sandstones

upwards in the column might be the result either of supply-
ing channel avulsion, or of a decreasing supply of coarse ma-
terial. The deformed deposits are slump type which involves
a slope of the basin floor. Based on these facts we can sup-
pose that the deposits were sedimented on the distal turbidit-
ic system but located at the base of a local slope.

7. Whitish marl with debrite facies association of oxic

shelf, recognized in oimu River, Nechit River 2, and Ne-
chit 1 River Sections. In this facies association the well
known Globigerina Marls are included.

It consists of (1) decimetric, highly bioturbated sandstone

beds (Fig. 11a), intelayered with pelites almost entirely replaced
by horizontal to sub-horizontal anastomosed sandy filled bur-
rows of Thalassinoides (Fig. 11b); (2) whitish, thick-laminated

and  also  bioturbated  (e.g.  Chondrites)  Globigerina  Marls  s.s.
(representing the upper part of the Bisericani Beds according to
Ionesi  1971;  Figs. 11c,d,  12a),  showing  sub-vertical  and  hori-
zontal  sand-filled  burrows  (possible  Skolithos);  (3)  debrites
( > 1 m  thick;  Figs. 11d,  12c)  with  brown  mud  intraclasts  and
“green schist” clasts; (4) thick-bedded Kliwa-type quartzareni-
tes (i.e. Lucăce ti Sandstones) with sharp bases and thin parallel
laminated tops; (5) grey quartzarenites; and (6) brown marls.

Some differences can be noticed in the Nechit River 1 Sec-

tion, where this facies association consists mainly of whitish
mudstone thin (1—5 cm) or lenticular bedded, with plane-par-
allel lamination enhanced by an alternation of light and
brown laminae. The feature difference might be the result of
proximal (Nechit River 2 Section) to distal (Nechit River 1
Section) facies variation.

The prevalence of horizontal—sub-horizontal burrows indi-

cate  intervals  of  low  energy  levels  associated  with  pelites
sedimentation, well oxygenated basin bottom and abundance
of  deposited  food  (MacEarchen  et  al.  2007).  The  sandstone
interlayers are also intensely bioturbated by postdepositional
animal  activities  proving  their  periodic  sedimentation  on  a
background of low energy conditions. Upwards in facies as-
sociation  column,  the  sedimentation  becomes  muddier,  and
characterized  mainly  by  whitish  marls  with  Chondrites

Fig. 12. Horizontal (a) and vertical (b) burrow fills (Skolithos?) in Globigerina Marls s.s. in the Nechit River 2 Section; sharp contact be-
tween debrite with brown marl intraclasts and whitish marls (Globigerina Marl s.s.) in the Nechit River 2 Section (c); debrite with brown
marl intraclasts and green schist clasts in muddy matrix in the Nechit River 2 Section (d).

409

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

which might announce a decrease of oxygenation levels be-
fore the establishment of anoxia condition.

The above described characteristics seem to indicate shal-

low-water conditions, where the proximal debrites (Nechit 2
Section) can prove the instability of sediment sources. The
highly bioturbated sandstones possibly supplied by a sandy
coast system might also indicate a proximal offshore above
the storm wave base.

Depositional systems and sedimentary evolution

The study of the logs (Figs. 2, 4, and 5) based on the sedi-

mentary facies analysis, points out the vertical organization
of the FA and the lateral correlations in the context of an area
belonging to the external flysch basin of the Eastern Car-
pathians, during the Eocene—Oligocene time. Based on
above described and interpreted facies association we recog-
nized 5 depositional systems.

1. Mud rich slope apron – Both in the Nechit River 1

and  oimu Sections the very thick greenish-grey mudstones
(corresponding to Bisericani Beds) suggest a mud-rich slope
apron  system,  characterized  by  hemipelagites  and  thin  tur-
bidite  sandstones  of  facies  D.  This  slope  apron  might  be
rather  a  local  feature  of  the  forebulge  depozone  (Fig. 13b).
The frequent slump deposits indicate an unstable slope most
likely  controlled  by  the  extensional  marginal  faults  and  the
consequent subsidence trend in the adjacent sub-basins. Fa-
cies characters suggest a mud dominated sedimentation. Up-

Fig. 13. A rough 3D paleogeographic interpretation of the Late Eocene-Oligocene depositional systems of studied sections within the Bistri a
half-window (Marginal Folds Nappe – Eastern Carpathians). a – The position of the studied area in the foreland basin systems (the italics
indicate the depositional systems defined by Mutti et al. (2003) for foreland basins; the underlined italics are their equivalents on forebulge de-
pozone). b – The position of Late Eocene facies associations in a sub-basin of the forebulge depozone. c – The position of Oligocene facies
associations in a subsident sub-basin of the forebulge depozone; 1 – deposits of foreland basin systems; 2 – deposits older than Late Eocene.

wards in the visible stratigraphic intervals (between 0—19 m,
145—170 m,  and  315—330 m  in  the  Nechit  River 2,  Nechit
River,  and  oimu  Sections,  respectively)  an  enrichment  in
sand can be noticed, together with significant changes in grain
size, and increasing of the sand : mud ratio. All these charac-
ters suggest a more proximal sandy system proved also by the
observed  ichnofauna  of  the  whitish  marl  with  debrite  facies
association ( oimu and Nechit River 2 Sections; Figs. 4, 5).

2. Oxic shelf depositional system – The upward increase of

sands  in  the  column,  which  is  better  manifested  in  the  oimu
Section, suggests a shallowing upward trend of the system. As
we have shown above, the features of whitish marl with debrite
facies  association  (corresponding  to  Globigerina  Marls  and
Lucăce ti Sandstone) indicate a shallow-water depositional sys-
tem  (Fig. 13a),  while  the  sharp  contact  between  greenish-grey
mudstone and the bioturbated sandstones, visible especially in
the  oimu Section, seem to prove a regression.

3. Lower turbiditic system – In all three analysed logs,

an important change of the sedimentation background is reg-
istered,  from  pelite  deposited  in  oxic  conditions  (greenish-
grey  pelite  and  whitish  marls)  to  pelite  deposited  in  anoxic
conditions  (black-shale  like  deposits  such  as  dysodilic
shales,  black  cherts,  brown  and  bituminous  marls).  On  this
background,  an  increasing  sand  input  also  occurred  (black
shale  with  bedded  cherts  and  sandstone  facies  association).
Some authors (Ionesi 1971, 1981; Dicea & Dicea 1980; Io-
nesi & Florea 1981, 1982; Ionesi & Meszaros 1989) consider
that the Eocene-Oligocene boundary is placed in this strati-
graphic  interval,  based  on  NP21—NP22  taxa,  while  others

410

MICLĂU , LOIACONO, PUGLISI and BACIU

(Martini & Lebenzon 1971; Lebenzon 1973; Dicea & Dicea
1976; Micu & Ghe a 1986) consider that it is inside the well-
known Globigerina Marls belonging to what we have called
whitish  marl  with  debrite  facies  association.  According  to
Belayouni et al. (2009) some levels in Lucăce ti Sandstones
contain  latest  Rupelian  foraminifers  belonging  to  N1/P20
Zone of Blow (1969). The anoxia may be a result of increas-
ing sediment supply which consequently increased the pres-
ervation of organic matter. Anoxic conditions may also have
been  favoured  by  increasing  biological  productivity  linked
to changes in the physical and chemical conditions of the sea
water (C-organic and CO

content). This event, in turn, may

be explained by controls such as: 1) the geographical isola-
tion of the Paratethys basin from the Mediterranean one after
the  collision  between  Africa  and  Eurasia  plates  during  the
Oligocene (Rögl 1999); 2) the global climatic changes which
began  in  the  Middle  Eocene  (Pomerol  &  Premoli-Silva
1986; Soták et al. 2002); 3) the relative sea-level fluctuations
of  different  amplitude,  tectonically  controlled.  Channelized
sandy deposits occurring in the studied sections (black shale
with  bedded  cherts  and  sandstone  facies  association)  might
be  related  to  a  rich  sand  shoreface  and/or  deltaic  system
drowned because of tectonic controlled sub-basin subsidence
(Fig. 13b).

4. Anoxic shelf depositional system – corresponds to an

important  stratigraphic  marker  recognized  in  all  the  studied
sections  –  the  Bituminous  Marls.  Its  lower  boundary  is
sharp and erosional in the sections where it is exposed (Ne-
chit River 1, and Nechit River 2 Sections). The correspond-
ing  deposits  are  much  thicker  ( > 50 m)  in  proximal  section
(Nechit  River 2  Section)  than  in  distal  one  (around  10 m  in
the Nechit River 1 Section). This different thicknesses might
be the result of sedimentation on different blocks, some sup-
porting  active  subsidence  controlled  by  gravitational  faults
(such  is  Nechit  River 2  Section;  Fig. 13c),  others  being  up-
lifted (Nechit River 1, and  oimu Sections; Fig. 13c). Such a
vicinity of subsiding and uplifting blocks caused the instabil-
ity of unconsolidated deposits proved by menilite intraclasts
inside the bituminous marls or the shear plane at the base of
the bituminous marl facies association (Fig. 3c,d).

These sedimentary features indicate a basin margin affect-

ed by tectonic deformations and consequent gravitational
collapses, which may have produced a source of coarse ma-
terial, which sometimes supplied the muddy shelf system via
storm induced hyperpycnal flows or turbiditic currents in-
duced by floods or storms. The shallow sedimentation condi-
tions are also suggested by the existence of the extremely well
preserved flatfish as we have shown above. The sandy dykes
present in the marls may prove both the fast mud deposition
and the mobility of quicksands during bottom shocks.

5. Upper turbiditic system – The contact of FA 4 with

FA 3 is sharp in the Nechit River 1 Section, the only section
where it is exposed. The facies associations 4, 5 and 6 indi-
cate  a  deepening  trend  in  the  basin  evolution  in  the  Nechit
River 1  Section.  A  gradual  deepening  and  distal  characters
of the turbidite system can also be noticed in the  oimu Sec-
tion, and this is testified by the vertical succession of sand-
stone  lobes,  fringe  fan,  and  black  shale  deposits  referred  to
basin plain although the proximal part of this system is not

exposed. This deepening might be tectonically controlled by
the local subsidence of the block which hosted the analysed
area (Fig. 13b). An important proof of this is the presence of
the  bituminous  marl  (identical  with  FA 3  of  anoxic  shelf)
olistolith  re-sedimented  within  deposits  of  upper  turbiditic
system.  In  Săndulescu  &  Micu’s  (1989)  opinion  the  Lower
Dysodilic Shales and Kliwa Sandstones (our FA 4, and 5) to-
gether  with  the  Bituminous  Marls  were  sedimented  in  deep
water conditions, while the Upper Dysodilic Shale (our FA 6)
were  sedimented  on  a  shelf  (Dysodilic  Marginal  Shelf)  by-
passed  by  submarine  channels  which  fed  the  Tarcău  Realm
with coarse materials (Upper Kliwa Sandstones).

According to Mutti et al. (1996, 2000, 2003), such a coarse

type of turbidites, usually associated with debrites, may be the
products of hyperpycnal flows formed in delta systems during
catastrophic flood events, and able to carry sand or gravel over
tens  of  kilometers,  depositing  them  as  marginal  turbidites.
These authors have introduced the concept of “mixed deposi-
tional systems” made up of turbidite-like facies and facies as-
sociations formed at relatively shallow depths (seaward edges
of flood-dominated deltaic systems), but it is still difficult to
identify processes, environment and water depth (Mutti et al.
2003) based only on limited exposures such are those analy-
sed here. A possible argument for the relatively shallow-water
condition of the upper turbiditic system is the presence of ich-
nofauna of  Thalassinoides in the lobes of the  oimu Section
(Fig. 5).  The  instability  of  the  channels  in  this  system  is
proved  by  their  recurrence  in  the  sedimentary  successions
(FA 4)  in  alternation  with  the  lobes  (FA 5)  occurring  in  the
proximal part. Upwards in the succession of the upper turbid-
itic system the sand : mud ratio decreases, proving the deepen-
ing of the basin. Such a deepening was possibly controlled by
extensional tectonics affecting the forebulge depozone which
was retreating.

Mutti et al. (2003) recognized the “mixed depositional

systems”  in  wedge-top  basins,  actively  fed  by  deltaic  sys-
tems.  We  consider  that  such  systems  may  also  develop  on
forebulge  depozone  of  foreland  basin  systems  especially
during  their  underfilled  stage  of  development  (Crampton  &
Allen 1995) when the forebulge may have a prominent relief
drained by rivers. This had to be the case of the Moldavidian
Basin forebulge if we take into consideration the continuous
supply  of  “exotic”  clasts  from  the  Early  Cretaceous  to  the
Early  Miocene  climax.  For  the  Early  Miocene  Grasu  et  al.
(1999) described a fan-delta characterized by very coarse to
coarse  deposits  (Alma u  Conglomerates  and  Sandstones  on
Cuejdiu River northward of Piatra Neam ), consisting mainly
of “green schist”, white limestone, and even some pegmatite,
which  prograded  in  shallow-waters.  The  clasts  can  have
meters  in  diameter  suggesting  a  short  transport  from  their
source  area.  Their  main  sedimentation  processes  were  non-
cohesive and cohesive debris flows and high-density turbid-
itic  currents.  Such  fan-deltaic  systems  could  also  have  fed
the forebulge marginal basin during the Eocene—Oligocene.

All these elements suggest a ramp-type basin margin char-

acterized by collapsed or uplifted blocks controlled by nor-
mal faults where both source area and depocentres with rapid
basinward transition to deeper water system (subsident re-
gime) evolved (Fig. 13).

411

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

Petrography and provenance

Petrographic study of the Eocene-Oligocene arena-

ceous samples associated with the Lower Menilites in
the oimu River Section is focused on recognizing
the gross composition of the sandstones, the textural
characters of the grains and detecting the provenance
of the detrital supply.

This study has been carried out by means of modal

point counting in thin section, performed according to
the criteria suggested by Gazzi (1966), Dickinson
(1970) and by Gazzi et al. (1973), in order to minimize
the dependence of the rock composition on grain size.

The detrital framework of the analysed rocks is

characterized by a dominant non-carbonate extrabasi-
nal  fraction,  made  up  of  abundant  quartz,  low  per-
centages  of  feldspars  and  traces  of  lithic  fragments,
mixed with a conspicuous presence of a non-carbon-
ate intrabasinal fraction, mainly represented by glauc-
onite  grains  (14.5 %  maximum)  and  by  a  very  low
content of opaque minerals.

Quartz is undoubtedly the most abundant mineral in

all  the  analysed  sandstones.  According  to  the  Basu’s
et al. (1975) criteria, modified by Basu (1985), the de-
trital quartz has been distinguished into monocrystal-
line  and  polycrystalline  quartz  grains,  each  of  them
subdivided  into  two  populations:  monocrystalline
quartz grains of low and high undulosity (

≤5° or >5°

The analysed sandstones are usually medium- to fine-grained, thus respecting the conventional criteria to collect the data concerning the undula-

tory extinction and the polycrystallinity of the detrital quartz grains mainly from the medium sand-size fraction (0.25—0.50 mm; Basu et al. 1975;
Young 1976).

Fig. 14. Quartz-Feldspars-Lithic Fragments ternary plot showing the com-
position of the Lucăce ti and Fierăstrău Sandstones and other arenites asso-
ciated with the Lower Menilite Formation.

apparent angle of extinction, measured with a flat-stage) and
polycrystalline quartz grains with few or many subgrains (

≤4

or > 4, number of crystal units contained within each grain)

Monocrystalline quartz grains are more abundant than the

polycrystalline varieties and, in particular, the monocrystal-
line grains with high undulosity and the polycrystalline
quartz grains with many subgrains (Qm’’ and Qp’’ in Ta-
ble 1, respectively) are the more representative varieties.

These kinds of quartz (Qm’’ and Qp’’) are indicative of

low-grade metamorphic sources and, usually, they show a
very low stability pointing to selective destruction by me-
chanical agencies during prolonged transport and, of course,
during successive sedimentary cycles (Blatt & Christie 1963;
Basu 1985).

Thus, the abundance of Qm’’ and Qp’’ and the scarcity of

feldspar grains should be indicative of sediment sources pre-
dominantly composed of low-grade metamorphic rocks and,
in any case, they point to exclusion of conspicuous contribu-
tions from plutonic and/or high grade metamorphic source
(Fig. 14).

The presence of locally abundant epimetamorphic clasts in

several  stratigraphic  horizons  of  the  analysed  Eocene—Oli-
gocene  sedimentary  succession  (Lucăce ti  and  Fierăstrău
Sandstones, Bituminous Marls, Lower Dysodilic Shales with
Kliwa  Sandstones  interlayered),  mixed  with  predominant
subangular-to-subrounded  quartz  grains,  seems  to  support
this type of provenance (Fig. 15a).

In addition, this hypothesis of provenance seems to be in

agreement  with  Suttner’s  et  al.  (1981)  model,  which  suggests
that such kind of rocks are the only sources able to produce high
amounts of quartz grains as first cycle detritus under “a unique
combination of extreme conditions of climate, relief and sedi-
mentation”.  Such  conditions  of  climate,  in  particular,  seem  to
be realized during Oligocene times, just after the Eocene—Oli-
gocene transition global cooling, as documented by the values
of paleotemperature and precipitation which point to a subtropi-
cal-  and  paratropical-like  climate  recorded  at  the  Rupelian/
Chattian  boundary  (mean  annual  temperature/precipitation
ranging between 13—20 °C and 1.353—2.760 mm, respectively;
Givulescu  1997).  Anastasiu  (1986)  also  suggested  a  rather
chemical weathered material as source for the quartzarenites of
Kliwa  Sandstone  and  not  an  eolian  deposit  from  the  cratonic
area as Săndulescu & Micu (1989).

Finally, the presence of glauconite as the most representa-

tive mineral of a locally abundant non-carbonate intrabasinal
fraction must be noticed (Fig. 15b).

This mineral is usually supposed to be authigenic in origin

and formed in marine environments under reducing to slightly
oxidizing conditions on the continental shelf (Folk 1974; Pet-
tijhon 1975; Odin 1985; Kelly & Webb 1999; Hesselbo &
Huggett 2001). In the analysed rocks, it shows good round-
ness and grain size very similar to other detrital clasts. Round-
ness is an important textural characteristic indicative of highly
turbulent environments or also of prolonged transports and, in

412

MICLĂU , LOIACONO, PUGLISI and BACIU

Table 1:

Modal

point

counts

the

oimu

River

Section

sandstones

compa

red

with

the

Kliwa

Formation

and

the

“Moldovia

lithofacies”

artzarenite-like

sandstones

the

Tarcău

Nappe.

≤

Sym

e pa

s a

odal

Q = Q

+ Q

, w

her

l qua

zos

e gra

s in

ono

lli

e g

rains

d i

nto

’ = o

f l

und

ity

(

5°

) an

’’

of h

igh und

y (>

°) a

rse

-gra

fra

(i.

tal

quar

e g

rains

(

incl

udi

ert

) w

ch ha

ve b

een

ubd

’

= w

h f

ubg

s (

tal

its

per

rai

’’

= w

h m

any

ains

(

4 cr

tal

nits

r g

rain)

. Q

’,

’’,

’

’’

ve b

een

det

erm

rdi

e c

rit

eri

a s

ugges

ted

y B

u et a

l. (

1975

) an

d Ba

(198

;

F = P

+ K

, w

her

= to

tal

par

rains

, P

e an

ium

par

ing

rains

(

) or i

n c

rse

-gra

roc

k fra

);

L =

Lc +

, w

her

e fi

-gra

roc

k fra

, in

= v

can

, Ls

edim

ent

= ca

ona

, Lm

eta

and

sil

;

L +

, w

: Lt

l li

thi

c f

h un

le an

d qu

e);

M =

or ch

lori

gle gra

s (

);

glau

coni

gra

= o

the

r m

ine

l g

rains

, Mt

= s

ilic

; Cm

= car

; Sp

= s

rad

ic o

ccur

nce

, tr

= t

rac

≤

RO 6

RO 7

RO 8

RO 11

RO 19

σ x’

σ’

’

’’

’

’’

–

– – – – – – – –

–

÷9

–

– – – – – – – –

–

5÷

–

– – – – – – – –

–

– – – – – – – –

–

– – – – – –

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413

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

this case, on the basis of the above mentioned sedimentologi-
cal conjuncture, it appears to be closely related to the high hy-
drodynamism of a shallow marine-like environment.

The source area of these lithic fragments might be the

same  type  as  the  “green  schist”  clasts  re-sedimented  in  all
the  external  deposits  of  the  former  Moldavide  Basin  begin-
ning with Early Cretaceous, as we have shown above. Zuber
(1902) imagined this source area as an extension of the Cen-
tral  Dobrogea  chain  to  the  Przemyśl  region  (Poland)  which
apart the Flysch Basin from Podolian Continent (East Euro-
pean  Platform).  Since  then  most  geologists  referred  the
source area of “exotic” clasts to Central Dobrogea. Accord-
ing  to  Oaie  et  al.  (2005)  they  were  supplied  by  an  external
cratonic source area considered to be a belt of Neoproterozo-
ic—Lower  Cambrian  turbidites  lying  on  the  western  margin
of the East European Craton which is now almost completely
covered  by  East  Carpathian  nappes  (Oaie  et  al.  2005).  The
only places where these turbidites outcrop are in Central Do-
brogea,  an  uplifted  block  of  the  Moesian  Platform,  and  the
Malopolska  Massif  (in  Poland).  Anyway  as  we  have  shown
above,  the  “exotic”  clasts  supplied  by  the  “green  schists”
source  area  (Fig. 13)  also  include  metamorphics  and  pegma-
tites,  proving  its  rather  complex  constitution  from  the  petro-
graphic  point  of  view  (Anastasiu  1984,  1986;  Grasu  et  al.
1999).  Mirău ă  (1964)  showed  that  the  “green  elements”  re-
sedimented within flysch and molasses deposits are character-
ized  by  higher  metamorphic  rank  than  the  rocks  considered

Fig. 15. Thin sedimentary laminae mainly made up of subrounded quartzose grains (qz lamina), rare opaque minerals and occasional glauc-
onite (gl) within the Bituminous Marls (a, and b). Green schist clast (g—s clast) in the Fierăstrău Sandstone (c) and typical quartzarenites-
like products characterizing the Lucăce ti Sandstones (d).

their source area from Central Dobrogea. A possible explana-
tion for the petrographic variety of the “exotic” clasts would
be a deeper erosion of Central Dobrogea along the segment
which played the role of forebulge for the Moldavide Basin.

Paleontology and paleoecological implications

Fish, as fossils, are almost exclusively autochthonous and

thus best suited as direct indicators of aquatic vertebrate life
and vertebrate biodiversity in the past.

A significant Oligocene fish fauna has been collected from

the  Piatra  Neam   area,  located  in  the  Bistri a  half-window.
Most  of  the  type  specimens  as  well  as  numerous  additional
materials from this area have been collected from the Lower
Dysodilic  Shales  and  are  nowadays  deposited  in  the  pale-
ontological  collection  of  the  Natural  Sciences  Museum  of
Piatra Neam .

These fish are well preserved and the Lower Oligocene

collections contain specimens of more than 50 species repre-
senting  about  20  families.  The  most  important  species  in-
clude sardinas (Clupeidae), bristlemouth (Gonostomatidae),
hachetfish  (Sternoptychidae),  lightfish  (Photichthyidae),
lanternfish  (Myctophidae),  codlets  (Bregmacerotidae),  squir-
relfish  (Holocentridae),  dories  (Zeidae),  boarfishes  (Cap-
roidae),  shrimpfish  (Centriscidae),  bigeyes  (Priacanthidae),
sharksuckers (Echeneidae), jaks and pomparos (Carangidae),

414

MICLĂU , LOIACONO, PUGLISI and BACIU

pomfrets (Bramidae), snake mackerels (Gempylidae), cutlass-
fish (Trichiuridae), mackerels and tunas (Scombridae), drift-
fish (Nomeidae), lefteye fluoders (Bothidae), triplespines
(Triacanthidae).

During geological investigations in 2005—2006 an outcrop

was discovered on Pietricica Mountain, Piatra Neam , situated
in the second level of the Bituminous Marls, considered by Io-
nesi & Grasu (1993) to be an olistolith. Some interesting fish
fossils specimens, listed and described below, were collected
from Bituminous Marls cropping out near Piatra Neam al
Văleni (Fig. 1), and also from the above mentioned olistolith.

Order: Myctophiformes

Family: Myctophidae

Genus: Oligophus Ružena Gregorová, 1997

Oligophus moravicus (Paucă, 1931)

The most abundant fossil specimens from Bituminous

Marls (more than 10 very well preserved specimens,
Fig. 16a) belong to Oligophus moravicus (Paucă, 1931).

Typically, the recent species of myctophids are pelagic

fish of the open ocean. Most species are found in the upper
1000 m of the water column (mesopelagic). A few species
live deeper than 1000 m (bathypelagic). Some species are as-
sociated with continental and island slopes (pseudoceanic).

Daily vertical migrations from about 400 to 1000 m during

the day into the upper 200 m at night are common; some
species reach the surface (Craddock & Hartel 2002).

Order: Gadiformes

Family: Merluccidae

Genus: Palaeogadus Rath, 1859

Palaeogadus sp.

In the olistolith of Bituminous Marls only one specimen,

incomplete  of  Palaeogadus  sp.  (Fig. 16b)  has  been  discov-
ered. The recent species of the family Merluccidae are ben-
thopelagic  fish  living  on  the  shelf  and  upper  continental
slope,  from  shallow  coastal  waters  to  more  than  1000 m;
most  species,  if  not  all,  migrate  vertically  at  night  to  feed;
seasonal  onshore-offshore  migrations  have  also  been  docu-
mented (Iwamoto & Cohen 2002).

Order: Pleuronectiformes

Family: Scophthalmidae

Genus: Scophthalmus Rafinesque, 1810

Scophthalmus stamatini (Paucă, 1931)

Flatfish fossils are very rarely discovered. Baciu & Chanet

(2002) described the oldest known scophthalmid, Scophthal-
mus  stamatini  (Paucă,  1931),  from  the  Bituminous  Marls
(Lower Oligocene, Pietricica Mountain near Văleni; point V
on  Fig. 1).  Five  specimens  from  the  Bituminous  Marls  and
one from the olistolith of the Bituminous Marls resediment-
ed  in  Lower  Dysodilic  Shales  in  Pietricica  Mountain  expo-
sures,  very  well  preserved,  complete  and  undistorted  of

Fig. 16. a – Oligophus moravicus (Paucă, 1931). b – Palaeoga-
dus sp. c – Scophthalmus stamatini (Paucă, 1931).

Scophthalmus stamatini (Paucă, 1931), has been discovered
(Fig. 16c).

In the recent fauna, this family is represented by five gen-

era with about 18 species, distributed in the northern Atlan-
tic, Mediterranean and Black seas (Nelson 1994). Generally
these species inhabit sand to sand/silt or mud sediments in
relatively shallow-waters (less than 110 m); most abundant
from 1—2 m to, usually, less than 56 m (Munroe 2002).

Most of the fish fossil specimens from the Bituminous

Marls are undistorted and complete, proving the absence of

415

EOCENE-OLIGOCENE SEDIMENTATION OF THE MARGINAL FOLDS NAPPE (E CARPATHIANS, ROMANIA)

transport of the specimens over long distances. Gaudant
(1979) considers that it is possible to interpolate the ecologi-
cal characters between recent and fossil fish fauna until the
level of the family, so the presence of merluccids and scoph-
thalmids indicate that the depth of marine basin, at the level
of the Bituminous Marls had to be about 100 to 200 m.

Conclusions

The flysch deposits involved in the Moldavide units were

accumulated in a foreland-type basin system (Fig. 13a). The
Marginal Folds Nappe sedimentation area was located on the
internal part of the forebulge depozone.

The forebulge resulted after the tectonic loading of the cra-

tonic margin, possible of Moesian type as the “exotic” clasts
would indicate, as a consequence of the Late Cretaceous clo-
sure of the External Dacide trough, and overthrusting of its
nappes.  Its  outward  migration  could  cause  reactivation  of
older  faults  and/or  tensional  stresses  which,  in  turn,  could
determine  a  fragmentation  of  the  basin  margin  in  uplifted
and subsident blocks, hosting sub-basins. The forebulge was
partly emerged during the Oligocene and later when increas-
ing  quantities  of  “green  schists”  clasts  (meters  in  diameter)
were supplied into the marginal basin (Grasu et al. 1999).

A small area of the Marginal Folds Nappe exposed in the

Bistri a  half-window  (Eastern  Carpathians)  was  analysed
based on three successions logged on the Nechit River 1, Ne-
chit River 2, and  oimu River Sections. Seven facies associa-
tions  were  recognized  in  Upper  Eocene-Oligocene  deposits
(Bisericani  Beds,  Globigerina  Marls,  Lucăce ti  Sandstone,
Lower  Menilites  with  Fierăstrău  Sandstone,  Bituminous
Marls, Lower Dysodilic Shales with Kliwa Sandstone, Upper
Dysodilic Shales) based on lithology, sedimentary structures,
and  paleontological  content.  They  were  interpreted  as  repre-
senting – mud-rich slope deposits, oxic shelf, shallow chan-
nels,  anoxic  shelf,  channel-levee,  depositional  lobes,  and
fringe  fans  (Fig. 13b,c)  belonging  to  five  depositional  sys-
tems: 1) mud-rich slope apron, 2) oxic shelf, 3) lower turbidit-
ic system, 4) anoxic shelf, and 5) upper turbiditic system.

The different behaviour of these blocks might be the result

of the observed shallowing or deepening upward sedimenta-
ry trends. The sedimentation in shallow-water is proved first-
ly  by  the  coarseness  of  turbidites  which  are  interpreted  as
“mixed depositional system” according to Mutti et al. (2003)
terminology.  We  have  shown  that  these  mixed  depositional
systems  may  appear  not  only  on  the  active  margin  of  the
foreland  basin  system,  but  also  on  its  forebulge,  when  this
represents  an  important  source  of  coarse  material,  on  one
hand,  and  is  affected  by  deformations  and  collapses,  which
define local sub-basins connected to coarse material source,
probably of fan-delta type, on the other.

The presence of the two shelf depositional systems, one

oxic, and other anoxic, with highly bioturbated sandstones
and flatfish (Scophthalmus stamatini Paucă, 1931) prove
again the sedimentation rather in shallow-water conditions.

The source area was located entirely on the cratonic side of

the foreland basin as is proved by very frequent “green schists”
clasts, and by quartzarenite-type of sandstones (Lucăce ti, Fi-

erăstrău,  and  Kliwa  Sandstones).  The  source  area  for  “green
schists” clasts is considered to be a Central Dobrogea-type base-
ment,  and  its  sedimentary  cover,  which  played  the  forebulge
role.  The  quartzarenite  petrographic  characteristics  prove  a
provenance  from  low-grade  metamorphic  rocks  as  green
schists. Their high maturity might be a result of deep chemical
weathering  in  a  subtropical-  and  paratropical-like  climate  as
was the case during the Oligocene time in the studied area.

Acknowledgments: Financial support for this research was
provided by the Ministry of Education, Research and Youth
of  Romania  and  by  the  “Al.  I.  Cuza”  University  and  Re-
search  Ministry  of  Italy  as  grants  to  C.  Miclău   and  to  D.
Puglisi,  respectively.  The  authors  wish  to  thank  professors
Eugen  Grădinaru,  Doru  Bădescu  (University  of  Bucharest,
Romania), and Sergio Longhitano (University of Potenza, It-
aly)  as  well  as  an  anonymous  Referee,  whose  suggestions
strongly improved the manuscript.

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