GeolCarp_Vol48_No3_193

GEOLOGICA CARPATHICA, 48, 3, BRATISLAVA, JUNE 1997

193–203

PALEOGENE SEDIMENTS BELOW THE BASE OF A MESOZOIC NAPPE

IN THE HUMENSKÉ VRCHY MTS. (PODSKALKA BOREHOLE):

STRATIGRAPHIC CONSTRAINTS FOR TERTIARY THRUST TECTONICS

JÁN SOTÁK

, JOZEF MICHALÍK

, DANIELA REHÁKOVÁ

and BOHUMÍL HAMRŠMÍD

Geological Institute, Slovak Academy of Sciences Bratislava, Branch: Severná 5,

974 01 Banská Bystrica, Slovak Republic

Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 842 26 Bratislava, Slovak Republic

Moravian Oil Company, Sadová 4, 695 30 Hodonín, Czech Republic

(Manuscript received December 12, 1996; accepted in revised form March 18, 1997)

Abstract

: The footwall unit below the Mesozoic nappe complex of the Humenské vrchy Mts. has been reached by the

MLS-1 Podskalka borehole. The lowermost (1769–1833 m) sandstone/claystone formation in this borehole it is con-
strained to be Late Cretaceous? but rather Paleogene in age (according to the youngest nannofossils). The hangingwall
of these sediments consists of the Krížna Nappe complex which comprises formations from Middle Triassic up to
Albian in age. The observations from the MLS-1 borehole point to the underthrusting of the externally seated flysch
units beneath the collisional edge of the Centrocarpathian plate. The Paleogene formations may be attributed to the
same unit which being deeply underplated, buried, and than exhumed in the East Slovak Basin floor (Iňačovce-
Krichevo Unit). The Paleogene formations of this unit suffered sub-greenschist metamorphism and they are over-
lapped by ultrabasic thrust slices (Zbudza-1 borehole).

Key words

: Western Carpathians, Tertiary thrust tectonics, suture zone, Mesozoic biostratigraphy, litostratigraphy.

Introduction

The Humenské vrchy Mts. represent the easternmost moun-
tain range of the Western Carpathians, formed by the Central
Carpathian nappe pile (Fig. 1). Three tectonic units were
distinguished here by Mahe (1986): the Strážske Unit with
Tatric affinities, the Staré Unit similar to the Veporic Ve ký
Bok Unit and the Humenné Unit compared with the Vysoká
Unit of the Fatric Krížna Nappe system. The structure of the
Humenské vrchy Mts. was significantly affected by younger
tectonic deformation, namely by the slicing of nappe com-
plexes and south-vergent reverse faulting (Mahe 1983,
1986; Jacko jun. & Schmidt 1994).

The close neighborhood of the Humenské vrchy Mts. with

the Pieniny Klippen Belt and their overprinting by young
collisional tectonics predetermines this mountain range for
study of relations between Central and Outer Carpathians.
The structural MLS-1 Podskalka borehole was projected
with this aim, and, in particular, with the aim to verify
possible allochthonous position of the Mesozoic units of the
Humenské vrchy Mts. However, the interpretation of Kull-
manová & Mahe et al. (1975), despite of the find of Juras-
sic peculiar facies (dark marlstones and sandy limestones
with ostracods) below the base of the Triassic complexes of
the Krížna Nappe, did not fully confirmed this assumption.
The problem of allochthonity of the Humenské vrchy Mts.
structure became topical in the context of new findings from
the East Slovak Basin floor, where the Mesozoic nappe rem-
nants directly overlay the metamorphic rocks of the
Iňačovce-Krichevo Unit (Soták et al. 1993a,b). Under these
stimuli, we subjected the whole Podskalka borehole log to a

new reinterpretation. It resulted in a proof of Late Cretace-
ous? or likely Paleogene sediments in the lowest known
structural level of the Humenské vrchy Mts.

Geological characteristics of the Podskalka

MLS-1 borehole log

The lithostratigraphy and structure of the Mesozoic com-

plexes in the Podskalka borehole was firstly described by
Kullmanová & Mahe et al. (1975). These authors distin-
guished two partial digitations of the Humenné Unit in the
borehole profile.

The upper digitation, penetrated by the interval of 20.6 to

810.0 m, is built up by Upper Triassic up to Cenomanian for-
mations. The thickest part of the upper digitation consists of
Upper Albian to Lower Cenomanian marly shales (Poruba
Formation, 20.6–466.0 m). Below them, Barremian-Aptian
limestones

of Urgonian type (466.0–512.8 m) and marly

limestones (512.8–619.0 m)

with Lower Cretaceous ammo-

nites occur. The lowest part of the Lower Cretaceous se-
quence is formed by Berriasian calpionellid limestones
(619.0–623.8 m). Jurassic members of the upper digitation
represented by Tithonian calpionellid limestones (623.0–
638.0 m), Kimmeridgian Saccocoma and Protoglobuligerina
limestones (638.0–648.5 m), Middle Jurassic crinoidal lime-
stones (648.5–657.0 m) and Liassic sandy crinoidal lime-
stones (657.0–807.8 m) remind the Vysoká type sequence.
The base of the sequence forming the upper digitation is
formed by variegated Keuper shales and laminated sand-
stones (807.8–810.0 m). This upper interval of the Podskalka

194 SOTÁK et al.

borehole is comparable with the the Uhliská slice of the Hu-
menské vrchy Mts. structure (Mahe 1986).

The lower digitation was penetrated by the interval 810.0–

1725.4 m of the MLS-1 borehole. It consists of Middle Trias-
sic dolomites with interlayers of grey micritic limestones and
cherty limestones resembling the Reifling Limestone (1217–
1725.4 m). Upper Triassic strata are composed of variegated
shales and dolomites of the Keuper Formation (838.0–1217
m) and of the Rhaetian Fatra Formation limestones with bi-
valves, brachiopods and corals (810.0–838.0 m). Thick lime-
stone-dolomite complex of the lower digitation is exposed by
the Krivoštianka Ridge.

The interval 1739.3–1833.1 m, where the Liassic forma-

tion with an uncommon character is the most noteworthy part
of the MLS-1 borehole log. It is separated from the overlying
limestone-dolomite complex by a horizon of Keuper shales
and sandstones (1725.4–1739.3 m). The formation consists
of dark grey to black marly shales, calcareous sandstones and

organodetritic limestones with ostracods Ognoconcha and
bivalves Plagiostoma cf. punctatum Sowerby, Parallelodon
sp., Pseudolimea

sp. and others. Apart from ostracods and

bivalves, the formation was also attributed to the Lower Ju-
rassic by the sporomorphs Leiotriletes cf. braevilaesuratus
Kedves-Simoncsics, Concavisporites martoni De Jersey,
Sphaeripollenites

cf. subgranulatus Couper, Foveosporis cf.

irregularis

Tralau and others. The lithology of this formation

differs from other Liassic formations in the higher intervals
of the Podskalka borehole log in having more pelitic cha-
racter and darker colouring, abundant ostracods and sporo-
morphs, while intercalations of crinoidal, crinoidal-sandy
and cherty limestones are less frequent. According to Kull-
manová & Mahe et al. (1975), the finding of this Liassic for-
mation below the Triassic carbonate complex is an remark-
able argument speaking in favour of the allochthonous
concept of the Humenské vrchy Mts. nappe structure. Later
Mahe (1986) correlated this formation with younger mem-
bers of the Strážske Unit, cropping out from below the
Gutenstein limestones of the Krížna Unit along the Krivoš-
tianka Fault.

Results of a new revision of the Podskalka

MLS-1 borehole log

Several important contributions to the lithostratigraphy

and microfacies of the Mesozoic formations (Fig. 2) have
been obtained by a new supplementary detailed study of the
Podskalka borehole log.

The sediments from the interval 20.6–466.0 m represent

the Albian–Cenomanian formations of the Humenné Unit
(Jasenov Succession). Their mostly marly character corre-
sponds to the Homôlka Marlstone Member of the Poruba
Formation (Jablonský in Samuel et al. 1988), in which in-
tervals of flysch sedimentation also appear with the deve-
lopment of hieroglyphs (Senkovci Member). The Middle
Cretaceous sediments of the Jasenov Succession also com-
prise bodies of polymict conglomerates, which probably be-
long to the Ludrová Member. Another possible interpretation
of the Middle Cretaceous formation from the Podskalka
borehole was given by Ondra et al. (1990). These authors
pointed to the petrophysical and lithofacies affinity of these
sediments with the Cretaceous formations of the Klippen
Belt. Similarly, Ivan & Sýkora (1993) pointed to the proximi-
ty of source areas of the Cretaceous conglomerates from
both Jasenov and the Klippen Belt. They see similarity
mainly in the presence of pebbles of glaucophanic rocks. The
Jasenov conglomerates are also rich in pebbles of Urgonian
limestones with abundance of dasycladacean algae and orbi-
tolinid foraminifers (Soták & Mišík 1993).

Fig. 1.

Geological sketch-map of the Humenské vrchy Mts. and

adjacent areas simplified according to Mahe (1971, 1986), Roth
(1956), Jacko jun. & Schmidt (1994) and others. 1 — Staré Unit;
2

— Strážske Unit; 3 — Humenné Unit (sole part — T, J

); 4 —

Humenné Unit (cover part — T

, J, K

1-2

); 5 — Upper Cretaceous

formations of the Pieniny Klippen Belt; 6 — Kyjov Beds, 7 —
Magura Unit; 8 — Neogene sediments of the East Slovak Basin;
9

— Central Carpathian Paleogene; 10 — neovulcanites; 11 — re-

verse faults; 12 — fault tectonics of the Pieniny Klippen Belt.

Fig. 2.

Geological profile of the MLS-1 Podskalka borehole with

lithostratigraphic subdivision and structural interpretation of drilled
sequences. Krp — Keuper Fm., Fts — Fatra Fm., Trs — Trlenská
Fm and Kopienec Fm, Czs — Tegernsee Fm, Ons — Padlá voda
Fm, Ptv — Pseudothurmannia Beds, Phs — Bohatá Fm. The distri-
bution of index microfossils is shown on the right side.

→

196 SOTÁK et al.

The Lower Cretaceous succession of the Podskalka bore-

hole is similar to a marginal Fatric (Vysoká or Havran) suc-
cession comprising the Bohatá Limestone (466–470.6 m),
marlstones of the Mráznica Formation (512.8–619.0 m) with
an interval belonging to the Pseudothurmannia Beds (470.6–
512.8 m), and hemipelagic limestones of the Osnica/Padlá
Voda Formation (619–630 m). The latter mentioned formation
contains Berriasian and Early Valanginian microfossils of the
Calpionella, Calpionellopsis and Calpionellites Zones. Bio-
micrites with subordinate clay admixture contain Calpionella
alpina

Lorenz, Calpionella elliptica Cadisch, Tintinnopsella

carpathica

(Murg. & Filip.), Tintinnopsella longa (Colom),

Calpionellopsis simplex

(Colom), Calpionellopsis oblonga

(Cadisch), Remaniella fillipescui Pop, Remaniella ferasini
(Catalano), Remaniella cadischiana (Colom), Lorenziella
hungarica

Knauer, Lorenziella plicata Remane, Calpionellites

darderi

(Colom), aptychi, crinoids, bivalves, ostracods, glob-

ochaetes, radiolarians and calcareous dinoflagellates (Pl. I:
Figs. 1–2).

The Upper Jurassic sediments are reduced to the interval

of 630–646 m in the borehole log. Stratigraphic condensa-
tion mainly of the Upper Tithonian Brevis Subzone interval
(630–641 m) is responsible for small thickness of the for-
mation. Pale limestones with stylolites dominated by clay
infiling, but also brownish and red nodular limestones are
typical lithofacies. Calpionellid association consists of
Crassicollaria brevis

Remane, Crassicollaria massutiniana

(Colom), Crassicollaria parvula Remane, Calpionella alpi-
na

Lorenz and Tintinnopsella carpathica carpathica (Murg.

& Filip.). The limestones also contain juvenile ammonites, ap-
tychi, globochaetes, radiolarians and crinoids. Pale micritic
limestones of the “majolica” facies with microplankton be-
longing to the early Late Tithonian of the Remanei Subzone
(641–643 m). Organodetrital wackestone contain calpionel-
lids Crassicollaria intermedia (Durand Delga) and Crassi-
collaria massutiniana

(Colom), less frequently also Crassi-

collaria parvula

Remane and Calpionella alpina Lorenz,

aptychi, radiolarians, foraminifers, ostracods, globochaetes,
dinocysts and crinoids. At a depth of 643.8 m, microfossils
of the early Late Tithonian Praetintinopsella Zone were re-
corded micritic limestones. Below them, up to a depth of
646 m, brownish-grey micritic limestones with Saccocoma–
Globochaete and radiolarian–Globochaete microfacies occur.
Parastomiosphaera malmica

(Borza), Cadosina parvula

Nagy, Cadosina fusca fusca Wanner, Protoglobuligerina sp.
and others microfossils co-occurring with abundant Saccoco-
ma

sp. and Globochaete alpina Lombard pointing their

Kimmeridgian–Early Tithonian age.

Crinoidal packestones (Pl. I: Fig. 3) represent the Lower

and Middle Jurassic strata in the structure of the upper digi-
tation. Besides of them, ostracodal limestones of the same
type as those found below the limestone-dolomite complex at
a depth of 1747 to 1769 m (Pl. I: Fig. 4) were also recorded
here (780.5–795.5 m). The peculiar character of these ostra-
codal limestones compared with another Liassic lithofacies
of the Krížna Unit, is therefore not so unique as emphasized
by Kullmanová & Mahe et al. (1975). The fact that we also
recorded them in Prešov-1 borehole in the strata overlying
above the Fatra Formation (2845–2850 m) also testifies to

the assignment of the ostracod limestones to the Liassic Tat-
ric or Fatric sequence.

The complex fold-slice structure in the Podskalka boreho-

le is also documented by a repetition of the Rhaethian Fatra
Formation. It forms the interval 767–835 m and another one
at a depth of 1723–1747 m below the Middle Triassic lime-
stone-dolomite complex. The upper slice consists of dark-
grey detrital and muddy limestones. The detrital limestones
have a biosparruditic structure formed mainly by black coat-
ed molluscs shells, crinoid ossicles, micro-gastropods, algal
nodules formed by Girvanella filaments, punctate brachio-
pod shells and other allochems. The muddy limestones have
the character of foraminiferal biomicrites with numerous
tests of Tetrataxis inflata Kristan, Tetrataxis nanus Kristan &
Tollmann, Duotaxis metula Kristan and others (Pl. I: Fig. 5).
The Rhaetian limestones from the underside of the Middle
Triassic carbonate complex are also represented by biospar-
rudites and foraminiferal biomicrites. However, the associa-
tions of foraminifers are formed almost exclusively by small
forms of “Glomospira” and “Glomospirella” only, which
were described from the Fatra Formation by Michalík et al.
(1979) and emended by Zaninetti et al. (1986) as the cummu-
lative taxon of Agathammina inconstans (Pl. I: Fig. 6).

Kullmanová & Mahe et al. (1975) placed the main tectonic

boundary between the lower and upper digitation at the
depth of 807.8 to 810 m. This boundary should be indicated
by a horizon of red-brown micaceous sandstones, which the
authors attributed to the Keuper Formation. The sandstones
are overlain by lower Liassic Kopienec Formation, sandy-
crinoidal limestones and underlain by the Rhaetian Fatra
Formation. These relations show that the sandstones are part
of the Rhaetian-Liassic sequence and not a tectonically in-
serted slice of Keuper rocks. Their “Keuper” appearance is
not decisive, since sandstones of the Schattwald Beds occur-
ring at the base of the Liassic Kopienec Formation in the Tat-
ric and Krížna Units also have a similar lithological charac-
ter, with redish brown colour, well developed lamination and
a high concentration of detritic mica. In such a case, the
Rhaetian-Liassic sequence not interrupted at the interval of
807.8–810 m, but continues from the Fatra Formation through
the Schattwald Beds to the Kopienec Formation proper.

However, the fundamental importance for the geological

interpretation of the Podskalka borehole and the whole struc-
ture of the Humenské vrchy Mts. comes from the finding of
the Late Cretaceous? but rather Paleogene sediments in the
lowermost borehole intervals (1769–1833.1 m).

Plate I:

Microfacies and microfauna of the Mesozoic formations

in the Podskalka MLS-1 borehole. Fig. 1 — Berriasian limestone
with Calpionellopsis simplex (Colom) and Tintinnopsella carpath-
ica

(Murg. & Filip.), 627.3 m, magnif. 20

; Fig. 2 — Berriasian

limestone with Remaniella fillipescui Pop, Calpionella elliptica
Cadisch and Lorenziella plicata Remane, 624.5 m, magnif. 20

;

Fig. 3

— Liassic organodetrital limestone with crinoid ossicles,

784 m, magnif. 7

; Fig. 4 — Liassic biosparitic limestones with

abundance of ostracods, 780.5 m, magnif. 45

; Fig. 5 — Rhaetian

microbiosparitic limestone rich in foraminiferal fauna of Tetra-
taxidae

(T. inflata Kristan and Duotaxis metula Kristan), 812.5 m,

magnif. 20

; Fig. 6 — Rhaetian foraminiferal limestone with Aga-

thammina inconstans

(Michalík et al.).

→

198 SOTÁK et al.

The lithology and stratigraphic constraints

of the sediments from below the base

of the Mesozoic nappe complex

The deepest interval of the Podskalka borehole log is formed

by sandstone-claystone beds. The upper part of this interval has
a pelitic character (1779–1806 m), while in the lower part, ho-
mogeneous sandstones become dominant (1806–1833.1 m).

The grain size of the sandstones is variable. Prevalence of

siliciclastic components is characteristic of the fine-grained
types of sandstones, while lithic grains make up a larger pro-
portion of the coarse grained sandstones. The content of lith-
ic components (mainly carbonates) clearly distinguishes
these sandstones from Keuper and Liassic sandstones from
the hanging wall units. They are also specific by a higher
content of polycrystalline quartz, fragments of phyllitic
rocks, skeletal detritus of organisms and presence of spinel
grains (in contrast, the older sandstones have a monotonous
composition with dominance of plutonite detritus, monocrys-
talline quartz and feldspars including microcline). Carbonate
detritus of the underlying sandstones is composed of mainly
dolomites and dolomitic limestones, while clasts of calpi-
onellid and filamentous limestones are less abundant. They
also contain clasts of crypto-crystalline silicites, radiolarites,
vitrophyric volcanites and occasionally serpentinites. The
bioclastic content of the sandstones is composed of rare alga
fragments, crinoid particles and foraminiferal tests (Textula-
ria, Miliolina

and Rotalia). The sandstones have a quartzose-

clayey matrix which is partly recrystallized to phyllosilicate
cement. The associations of accessory minerals are formed
by zircon, spinel and rutile. Oval structures with colloidal in-
fill, clusters of framboidal pyrite and apparently also idio-
morphic crystals of tourmaline are authigenic in origin.

Dark calcareous claystones of the underlying formation

are distinguished from the claystones of both the Fatra and
Kopienec Formations mainly by their increased mica con-
tent, which clearly documents a change in the mechanisms of
their deposition. The concentration of detritic mica is clearly
a result of the hydrodynamic separation of currents in turbid-
ite environment. Under microscope, the claystones have a
microschlieren texture given by the preferred orientation of
fine mica leaflets (microlites). The structure of the clay-
stones is aleuropelitic, the silt admixture being dispersed in
the clayey material or graded into laminae. At the base of the
graded siltstone laminae, signs of current erosion can fre-
quently be observed. The claystones are impregnated with a
dark earthy substance and framboidal pyrite. X-ray powder
diffraction analysis of whole rock preparations revealed the
following composition of the claystones: Qz, I, Ch, Pg (prob-
ably albite) and carbonates. The fine fractions of claystones
(< 2 µm) are formed by illite and chlorite. Cross sections of
foraminifers are clearly outlined in the aleuropelitic material
of the shales: the smaller tests regularly filled with pyrite,
while the tests of the larger forms are not pyritized.

The highest abundance of foraminifers was observed in

the claystone interval of 1784–1794 m. They are represented
almost exclusively by planktonic forms. So far the more de-
tailed systematic assignment of the foraminifers from thin
section studies, only is possible since they have not been suc-

cessfully obtained from washing of claystones. However, as
already clear from cross sections, calcareous, perforated and
trochospiral tests occur here belonging mostly to the repre-
sentatives of the Upper Cretaceous foraminiferal plankton. It
has been proved that foraminifers from the globotruncanid
group are present here. Their closer determination was pos-
sible for the species Kassabiana falsocalcarata (Kerdany &
Abdelsalam), Globotruncanita calcarata (Cushman), Globo-
truncanella havanensis

(Voorwijk), Rugoglobigerina cf. rug-

osa

(Plummer), Globotuncana cf. arca (Cushman) and

Globotruncana

sp. Apart from the Upper Cretaceous glo-

botruncanid foraminifers, cross-sections of the Globigerina
and Globorotalia- like tests, which could be Paleogene fora-
minifers, were identified in the thin sections as well. These
are the species Subbotina triloculinoides (Plummer), Moro-
zovella pseudobulloides

(Plummer) and Praemuranica aff.

inconstans

Subbotina. The rotalid foraminifers Kathina cf.

selveri

Smout should also be a Paleogene species. It is not

possible to unambiguously determine the age of the forma-
tion from the interval 1769–1833.1 m on the base of above
mentioned foraminiferal association. However, the presence
of planktonic foraminifers excludes the assumption of the
Early Jurassic age of the formation (Kullmanová & Mahe et
al. 1975). The Upper Cretaceous planktonic species (Maas-
trichtian) were mostly identified here. However, stratig-
raphic evidence of the Upper Cretaceous foraminifers does
not have to be valuable, because the presence of some youn-
ger forms points out to recyclicity. Therefore the age of the
formation can also be a younger — Paleogene.

The study of nannoplankton also contributed to the age

determination of the formation from the interval 1769–1833.1 m.
The distribution of nannoplankton in the borehole profile is as
follows (the Eocene forms are denoted by asterisk):

1774–1779 m: Watznaueria barnesae (Black) Perch-Niel-

sen, Lithraphidites carniolensis Deflandre, Eiffellithus turri-
seiffeli

(Deflandre) and Dictyococcites bisectus* (Hay et al.).

The association contains Lower and Middle Cretaceous spe-
cies and Upper Eocene coccoliths.

1784–1789 m, sample No. 175: Watznaueria barnesae

(Black) Perch-Nielsen, Nannoconus cf. steinmannii Kampt-
ner, Lithraphidites carniolensis Deflandre, Cycla-
gelosphaera deflandrei

(Manivit) Roth, Lotharingius sp.,

Discorhabdulus

sp., Staurolithites crux (Deflandre) Caratini.

In this interval, nannoplankton association is poor, but repre-
sented by Jurassic and Lower Cretaceous species.

1784–1789 m, sample No. 175-B: Watznaueria barnesae

(Black) Perch-Nielsen, Eiffellithus turriseiffeli (Deflandre)
Reinhardt, Zeugrhabdotus embergerii (Noel) Perch-Nielsen,

Plate II:

Planktonic foraminifers in the Late Cretaceous? or likely

Paleogene sediments from the base of the Mesozoic nappe com-
plexes in the Podskalka MLS-1 borehole (1769–1806 m). Fig. 1
— Kassabiana falsocalcarata (Kerdany & Abdelsalam), 1784–
1789 m, magnif. 38

; Figs. 2–4 — Globotruncanita calcarata

(Cushman), 1784–1789 m, magnif. 38

; Fig. 5 — Rugoglobigeri-

cf. rugosa (Plummer), 1792–1799 m; magnif. 38

; Fig. 6 —

Globotruncanella hanavanensis

(Voorwijk); 1781–1785 m, mag-

nif. 38

; Fig. 7 — Globotruncana cf. arca (Cushman), 1792–1799 m,

magnif. 38

; Fig. 8 — Morozovella sp., 1784–1789 m, magnif. 38

→

200 SOTÁK et al.

Coccolithus pelagicus

* (Wallich) Schiller, Tranolithus mani-

festus

Stover, Helicosphaera bramlettei* (Müller) Jafar &

Martini, Biscutum constans (Gorka) Black, Rhagodiscus an-
gustus

(Stradner), Lotharingius hauffii Gün & Zweili,

Lithraphidites carniolensis

Deflandre, Dictyococcites bisec-

tus

* (Hay et al.) Bukry & Percival, Gartnerago obliquum

(Stradner) Reinhardt, Polycostella beckmannii Thierstein
and Cyclagelosphaera margerelii Noel. This nannoplankton
association consists of Jurassic, Lower and middle Cretaceous
forms and species from the Middle and Upper Eocene.

1792–1794 m, sample No. 177: Nannoconus steinmanni

Kamptner, Cyclagelosphaera margerelii Noel, Watznaueria
barnesae

(Black) Perch-Nielsen, Lithraphidetes carniolensis

Deflandre, Lotharingius cf. hauffi Grün & Zweili, Cycla-
gelosphaera deflanderei

(Manivit) Roth and Cyclicargolithus

floridanus

* (Roth & Hay) Bukry. The association contains

some Lower Cretaceous species and Eocene coccoliths.

1792–1794 m, sample No. 177-B: Watznaueria barnesae

(Black) Perch-Nielsen, Rhagodiscus angustus (Stradner) Re-
inhardt, Eiffellithus sp., Zeugrhabdotus embergerii (Noel)
Perch-Nielsen, Eprolithus antiquus Perch-Nielsen, Micran-
tolithus hoschulzii

(Reinhardt) Thierstein, Lithraphidites

carniolensis

Deflandre and Cyclagelosphaera margerelii

Noel. The identified species belong to the Lower and Middle
Cretaceous nannofossils (Hauterivian–Aptian).

1798–1800 m: Watznaueria barnesae (Black) Perch-Nielsen,

Rhagodiscus asper

(Stradner) Reinhardt, Lotharingius vela-

tus

Bown & Cooper, Zeugrhabdotus embergerii (Noel)

Perch-Nielsen, Nannoconus sp., Eiffellithus turriseiffelii
(Deflandre) Reinhardt, Cyclagelosphaera deflandrei (Manivit)
Roth and Cyclicargolithus floridanus* (Roth & Hay) Bukry.
In the sample, Jurassic and Lower Cretaceous nannofossils are
associated with Middle to Upper Eocene species.

The associations of nannoplankton in the claystones from

the interval 1769–1833.1 m are formed mostly by a mixture
of Jurassic, Lower and middle Cretaceous species. Apart
from these clearly redeposited nannofossils, the species
Dictyococcites bisectus

(Hay et al.), Coccolithus pelagicus

(Wallich), Helicosphaera bramlettei (Müller) and
Cyclicargolithus floridanus

(Roth & Hay) were also found in

the associations. These species are known from the upper
part of the Middle and Upper Eocene (zones NP 17–NP 19).
The nannofossils from the claystones are apparently de-
formed and recrystallized. The youngest elements in the as-
sociation also show these effects, which reduces the possibil-
ity of their contamination. Therefore, the occurrence of the
youngest elements of the nannoplankton, which date the
claystones to the Eocene, should be decisive for their strati-
graphic assignment.

Tectonic reinterpretation of the Podskalka

MLS-1 borehole

The Mesozoic formations in the Podskalka borehole show

a fold-nappe structure with partial digitations, internal dis-
conformities, stratigraphic repetitions, tectonic selection for
thrust detachements etc. (Fig. 2).

The upper section of the Podskalka borehole is formed by

cover part of the Humenné Unit having a structure of recum-
bent digitation. Lower Cretaceous, Jurassic and Rhaetian for-
mations occur in its normal limb. The fold closure of the digi-
tation structure occur in the underlying Keuper sediments
(774 m), in which the detachment plane is based. In the over-
turned limb of the digitation, younger stratigraphic members
are squeezed out, and only a synclinal bend with a comprimed
sequence of Fatra and Trlenská Formation occurs beneath the
Keuper sediments (“connective syncline”). At a depth of 835–
836.5 m, a disturbed zone occurs dividing the cover digitation
from the lower sole digitation of the Humenné Unit. It is based
in the Keuper sediments of sole digitation, the core of which is
built by a rigid limestone-dolomite complex at a depth of
1217–1723 m. The asymmetrical structure of the lower sole
digitation is documented by the reduced sequence of Keuper,
Fatra and Trlenská Formation sediments below the limestone-
dolomite complex at the depth of 1723–1769 m.

The main tectonic division in the Podskalka borehole oc-

cur at a depth of 1769 m, at the contact between the alloch-
thonous Mesozoic units and the underlying sediments. This
division is not very significant structurally. It is shown only
by the increased mechanical deformation in the top wall
Rhaetian limestones (1723–1747 m) and the more moderate
inclination of the underlying formation (15 to 20

). However

the presence of a structural boundary here is provable by the
significant discontinuity between the top wall Rhaetian–
Liassic formation and the flat wall Late Cretaceous? or likely
Paleogene formation.

Discussion and conclusions

The reinterpretation of the Podskalka borehole brought

evidence of the presence of Late Cretaceous? or likely Pale-
ogene sediments in the base of the Mesozoic nappe complex-
es of the Humenské vrchy Mts. This is a further fact testify-
ing the allochthonity of the frontal parts of the Central
Carpathian nappe units, which, in western territory, has been
also proved by Soblahov-1 and Lubiná-1 boreholes (Kull-
manová 1978; Leško et al. 1978). Soblahov-1 Borehole pen-
etrated the formations of the Manín Unit, and in its basement
reached a slice system of Keuper sediments, of Jurassic sedi-
ments with black shalles lithology and Upper Cretaceous
Globotruncana-rich marls (Kullmanová 1978; Mahe 1981,
1988). The Liassic “black-shalles” formation belongs to the
sedimentary cover of the Tatric Inovec Unit (Kullmanová
1978), but in facies already approaches the “Bündnerschief-
er” lithology regarding to that from the Vahic/Penninic do-
main (Mahe 1988). However, the presence of deeply seated
and overthrusted Lower Campanian sediments in the Sobla-
hov-1 borehole convincingly documents the “post-Gosauian”
movements of the frontal parts of the Central Carpathians
nappes. Similar situation was also recorded in Lubiná-1
borehole, where the Eocene flysch formations of the Magura
Unit were reached in the basement of the Manín or Drietoma
Unit (Leško et al. 1978, 1982). According to Salaj &
Priechodská (1987), the Paleogene formations from the de-

PALEOGENE SEDIMENTS BELOW BASE OF A MESOZOIC NAPPE IN THE HUMENSKÉ VRCHY MTS. 201

epest intervals of Lubina-1 borehole (2607–3230 m) could
also belong to the Myjava Paleogene Group. Apart of bore-
hole occurrences, the underthrusted Upper Cretaceous sedi-
ments come to the surface in the Považský Inovec Mts.,
where they crop out from below the Tatric crystalline base-
ment nappe (Belice Unit — Plašienka et al. 1994). Consider-
ing the youngest member of outcropped sediments (Hranty
Beds — Campanian up to Maastrichtian), the Belice Unit
had been overthrusted by the Tatric basement nappe during
the latest Cretaceous–earliest Paleogene (Plašienka 1995).

The structure of the Humenské vrchy Mts. long ago led to

their allochthonous position being supposed. At the same ti-
me, it pointed mainly to intensive slice imbrication of the
nappe units of this mountain range (Kullmanová & Mahe et
al. 1975; Mahe 1986). However the most serious arguments
in favour of the allochthonity of their structure derive from
geophysical data. On the basis of interpretations of the gravi-
ty field, Pospíšil & Filo (1982) showed the possibility of a
gravitational shifting of the Mesozoic nappe complexes of
the Humenné vrchy Mts. onto the Klippen Belt and flysch
area. They think that the movement of the Mesozoic nappe
complexes into an allochthonous position was induced by the
ascension of a mantle diapir from the SW into the area of the

Iňačovce-Krichevo Unit. The extending of the Klippen Belt
and flysch units into the basement of the Humenné structure
is also interpreted in the geophysical profiles of Šútora et al.
(1990a,b). Hovever, the direct evidence for allochthonity of
the Humenné structure has been obtained from the Podskal-
ka borehole only.

The solution of the assignment of the Paleogene sedi-

ments from the underlier of the Mesozoic nappe complexes
in the Podskalka borehole gives several possibilities. Among
these, the least probable is their assignment to the Central
Carpathian Paleogene, which could have been inserted into
the deep structure of the Humenské vrchy Mts. in the course
of later backthrusting. The Central Carpathian Paleogene on
the northern edge of the Humenské vrchy Mts. is represented
by a basal sandstone-conglomerate formation and Sú ov type
conglomerates, the steep bedding of which points to the
strong influence of post-Paleogene deformation. Therefore,
the solution of the assignment of the basement unit is deter-
mined more by the relationship of the Mesozoic nappe com-
plexes of the Humenské vrchy Mts. to the reduced parts of
the Periklippen Zone and the more external flysch units.

A zone of intensive shortening and deformation of the Pa-

leogene flysch formations occurs at the contact of the Central

Fig. 3.

Geological cross-section from the northern margin of the East Slovak Basin, passing through the Humenské vrchy Mts. to the

Klippen Belt and Outer Flysch Carpathians. 1–4 Mesozoic units of the Humenské vrchy Mts. (Central Carpathian nappe system): 1 —
Humenné Unit — cover part; 2 — Humenné Unit — sole part, 3 — Staré Unit, 4 — Strážske Unit; 5–6 Pieniny Klippen Belt: 5 —
klippes with envelope of Púchov marls, 6 — Kyjov Beds; 7 — Magura Unit (detached and folded flysch sediments in the inner part of ac-
cretionary prism — out-of-sequence thrust); 8 — the Upper Cretaceous–Paleogene? formations beneath the Mesozoic nappe units of the
Humenské vrchy Mts.; 9–10 Iňačovce-Krichevo Unit (rock complexes subcreted from subducting slabs and underplated sediments of ex-
ternal terranes); 9 — metasedimentary formations (Upper Triassic variegated phyllites and marbly limestones, Jurassic and Cretaceous
formations of dark phyllitic schists, the Eocene metasediments with flysch lithology — EM, 10 — rocks derived from oceanic crust,
mainly serpentinites (SE); 11 — Dukla Unit; 12 — North European Platform, 13 — Central Carpathian Paleogene — Jasenov-type li-
thofacies; 14 — Neogene infill of the East Slovak Basin; 15 — neovulcanites.

202 SOTÁK et al.

Carpathian Paleogene Basin and the Pieniny Klippen Belt in
Eastern Slovakia (Šambron-Kamenica Zone). The fold-and-
thrust deformation of this zone affected not only the Paleo-
gene flysch formations but also the Mesozoic basement com-
plexes (their tectonic slices in flysch sediments were
sometimes interpreted as intraformational carbonate bodies,
e.g. in the Plavnica 2 borehole). The significant intensity of
shortening probably led to the tectonic amputation of this
zone, while a part of the Paleogene formations in front of the
collisional edge of the Central Carpathian units could have
been pushed into their basement. A similar but much more
developed mechanism of collisional shortening and under-
thrusting affected the more external units of the Pieniny
Klippen Belt and flysch accretionary wedge. Therefore, the
Paleogene sediments in the basement of the Humenské vrchy
Mts. could also represent an underthrusted formations of the
Pieniny Klippen Belt or Magura Zone. The tendency for un-
derthrusting of the Klippen Belt and Magura Unit beneath
the Central Carpathian units could be also inferred from the
Hanušovce-1 borehole which was situated in the Pieniny
Klippen Belt at the northern edge of the Hanušovce Horst,
that is the western continuation of the Humenné elevation
(Leško et al. 1984). Hanušovce-1 borehole penetrated Upper
Cretaceous formations of the Pieniny Klippen Belt and at a
depth of 4000–6003 m reached the Magura Unit (Leško et al.
1984). From the situation in Hanušovce-1 borehole, a shal-
lower position could be assessed for the underthrusted units
in the elevation structure of the Humenské vrchy Mts., where
MLS-1 Podskalka borehole found them. However, from the
lithological properties of these sediments, it is not possible to
determine more closely their attribution to the external units,
since the characteristic horizons are lacking (e.g. variegated
pelites, menilite shales etc.). Flysch lithology, Upper Creta-
ceous redepositions and content of detrital spinels are com-
mon features of the Šambron Beds as well as of some Paleo-
gene formations of the Pieniny Klippen Belt and Magura
Unit (cf. Starobová 1962; Snopková 1990; Nemčok et al.
1977; Ďurkovič 1993 etc.). Therefore the Paleogene forma-
tions in the MLS-1 borehole do not have a closer specifica-
tion from the point of view of their identity with external
units. However the presence of these formations in the deep
structure of the Humenské vrchy Mts. does not correspond
only to a frontal overthrust of the Central Carpathian units,
but to a deeper underthrust of the external units into the base-
ment of the East Slovak Basin, where their metamorphic
equivalents occur (Fig. 3).

The basement of the East Slovak Basin is formed by the

Iňačovce-Krichevo Unit, which probably goes into the sub-
stratum of the Humenské vrchy Mts. (Leško et al. 1977). The
Iňačovce-Krichevo Unit is composed of the Mesozoic
metasedimentary and metaophiolitic rocks with Penninic
lithologies (calcareous phyllites, black phyllitic schists,
metaarenites, marbles, metaultramafites, metatuffites etc.).
The youngest formations of the Iňačovce-Krichevo Unit be-
come more flysch-like in character and belong to the Paleo-
gene (Soták et al. 1994). They also suffered the metamorphic
alteration under higher anchizone conditions up to lower epi-
zone (Soták et al. 1995; Biroň et al. 1995). This metamor-
phism probably occurred under the Central Carpathian units

nappe pile, since relicts of the nappes lie directly on the
metamorphic complexes of the Iňačovce-Krichevo Unit in
places (Hrušov-1 borehole). In this case, the metamorphosed
Paleogene sediments from the basement of the East Slovak
Basin would represent formations of the same unit as in the
Podskalka borehole, but from a deeper level of underplating
and accretion (10 km). The accretion-related structures of the
Iňačovce-Krichevo Unit are developed mostly as underplate
duplexes which were preferentially detached in the ductile
horizons of the ultrabasic rocks. Such duplex structures are
obvious since the metasedimentary Paleogene formations
were also overlapped by the ultrabasic thrust slices (e.g.
Zbudza-1 borehole, see Soták et al. 1993). The Paleogene se-
diments in the Podskalka borehole differ from those in the
Iňačovce-Krichevo Unit by the absence of metamorphism.
Therefore they may represent shallower parts of underthrust-
ed units incoming into subduction in the final step of the con-
vergence.

Acknowledgements:

The authors express their thanks to

RNDr. Jozef Salaj DrSc. for his help in determining the Up-
per Cretaceous planktonic foraminifers. RNDr. M. Rakús,
CSc., Prof. M. Mišík, DrSc., and Dr. G. Császár are ac-
knowledged for their critical reading and inspiring com-
ments. This work partly resulted from the Grant Project
No. 4077 financed by the Slovak Academy of Sciences and
from the results of IGCP 362 UNESCO Project.

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