BIOSTRATIGRAPHIC REVISION OF HUNGARYS DEEPEST BOREHOLE 475
GEOLOGICA CARPATHICA, 55, 6, BRATISLAVA, DECEMBER 2004
BIOSTRATIGRAPHIC REVISION OF THE HÓD-I WELL:
HUNGARYS DEEPEST BOREHOLE FAILED TO REACH THE BASE
OF THE UPPER MIOCENE PANNONIAN STAGE
, MÁRIA SÜTÕ-SZENTAI
and IMRE MAGYAR
MOL Hungarian Oil and Gas Co., Batthyány u. 45, 1039 Budapest, Hungary; firstname.lastname@example.org; email@example.com
Natural History Collection of Komló, Városház tér 1, 7300 Komló, Hungary; firstname.lastname@example.org
(Manuscript received May 26, 2003; accepted in revised form December 16, 2003)
Abstract: Hungarys deepest borehole, Hód-I, was drilled in 196971 SE of the town of Hódmezõvásárhely, in order to
explore one of the thickest Neogene basin fills of the entire Pannonian Basin (the Makó Trough). The final depth of the
well was 5842.5 m. According to earlier analyses of 45 core samples taken from the borehole, the lowermost 700 m was
thought to belong to the Middle Miocene (Badenian and, possibly, Sarmatian Stages), whereas the overlying part was
believed to belong to the Upper Miocene (deposits of Lake Pannon, Pannonian Stage), Pliocene, and Quaternary. In
order to establish a more precise position of the Neogene stage boundaries, we carried out micropaleontological investi-
gations on the 4100 to 5823 m interval (cores 25 to 45). Ostracods have been prepared by solution of the samples in
acetic acid. Dinoflagellates were investigated in palynological preparations and in petrographic thin sections. It was
found that core 34 (50705074 m), earlier thought to represent the base of the Pannonian Stage, in fact belongs to the
younger part of the Lake Pannon sequence (Spiniferites validus Zone). Downwards to the base of the borehole, the
Spiniferites paradoxus, Pontiadinium pecsvaradensis, and Spiniferites bentorii oblongus Zones were found, all belong-
ing to the Pannonian. Accordingly, ostracods indicated the younger part of the Upper Miocene lacustrine sequence for
the upper samples of the investigated interval, and older Upper Miocene down to core 44. Thus, the drilling failed to
reach the base of the Pannonian Stage. The huge thickness (>6 km) of the postrift sediments above the relatively thin
synrift stages (Badenian and ?Sarmatian) in the Makó Trough corroborates the notion that simple rifting models are not
sufficient to adequately describe basin evolution in the central part of the Pannonian Basin.
Key words: Upper Miocene, Pannonian Basin, Lake Pannon, biostratigraphy, Ostracoda, Dinoflagellata.
Prior to the recognition of basin-centred gas plays in the late
1990s, the central, deepest parts of sedimentary basins were
rarely probed by drilling. State-owned oil companies, espe-
cially under the circumstances of a planned economy, how-
ever, may be governed by other factors than strictly commer-
cial ones in their decisions. The borehole Hódmezõvásárhely-I
(Hód-I) was drilled by the Hungarian Oil and Gas Trust in
196971 in order to explore the stratigraphic, sedimentologi-
cal, tectonic, petroleum geological and organic geochemical
conditions in one of the deepest Neogene subbasins of the en-
tire Pannonian Basin. The Makó (or Makó-Hódmezõvá-
sárhely) Trough is a northwestsoutheast trending, slightly
asymmetric extensional graben in southeast Hungary (Grow et
al. 1994; Fig. 1). It was formed in the Middle Miocene as a re-
sult of metamorphic core complex style extension (Tari et al.
1997, 1999; Fig. 2) and subsequently filled with more than
6000 m of Neogene and Quaternary sedimentary rocks (Mat-
tick et al. 1985, 1988; Bérczi & Phillips 1985; Bérczi 1988).
The well is located some 10 km SE of the town of Hód-
mezõvásárhely, close to the axis of the trough (Gajdos et al.
1983; Fig. 1).
The drilling had been planned to penetrate the entire Neo-
gene fill and to hit the Paleozoic metamorphic basement be-
fore reaching its final depth of 6000 m. The following unbro-
ken stratigraphic column was expected above the crystalline
basement: Lower Miocene (and possibly Paleogene), 1300 m;
Middle Miocene (including two Central Paratethyan regional
stages, the marine Badenian and the restricted marine Sarma-
tian), 600 m; Upper Miocene (comprising deposits of the
brackish Lake Pannon and the adjacent fluvial plains, and syn-
onymized in this study with the Pannonian Stage), 2600 m;
Pliocene (predominantly fluvial and freshwater lacustrine sed-
iments), 700 m; Quaternary, 700 m. Each of the three Miocene
stages mentioned above has a characteristic fossil fauna and
flora, so in most cases they are easily distinguishable by pale-
ontological investigations (Table 1).
Although the drilling was abandoned due to technic prob-
lems at 5842.5 m without reaching the base of the Neogene
formations, it is still the deepest well ever drilled in Hungary.
Information obtained from this well is commonly referred to
in sedimentological, geochemical, mineralogical, structural
geological and geophysical studies (e.g. Szemethy 1977; Sza-
lay & Szentgyörgyi 1979, 1988; Sajgó 1980; Kõrössy 1981;
Gajdos et al. 1983; Bérczi & Phillips 1985; Sajgó et al. 1988;
Bérczi 1988; Dövényi & Horváth 1988; Horváth et al. 1988;
Mattick et al. 1985, 1988; Royden & Dövényi 1988; Szalay
1988; Hámor-Vidó & Viczián 1993; Clayton et al. 1994; van
Balen et al. 1999).
The Neogene sequence of the well has been sampled with
45 cores, numbered in descending order (Fig. 3). The samples
were subjected to routine biostratigraphic investigations
(Csongrádi et al. 1971). According to these investigations,
476 SZUROMI-KORECZ, SÜTÕ-SZENTAI and MAGYAR
Fig. 1. Thickness of the Neogene basin fill in the central Pannonian Basin with location of Hód-I well (asterisk) in the NWSE trending ex-
tensional Makó Trough. V-pattern indicates Neogene volcanics at the surface. Location of the seismic profile presented in Fig. 2 is also in-
Fig. 2. Line drawing of a seismic profile across the Algyõ High, Makó Trough, Battonya-Pusztaföldvár High, and Békés Basin. Location of
the profile in Fig. 1. According to the interpretation of Tari et al. (1999), the Makó Trough formed as the mass of the Battonya-Pusztaföldvár
High slid eastwards from above the emerging Algyõ metamorphic core in the Middle Miocene (from Tari et al. 1999, modified).
BIOSTRATIGRAPHIC REVISION OF HUNGARYS DEEPEST BOREHOLE 477
Table 1: The Middle and Upper Miocene regional stages of the Central Paratethys: their ages (according to Vakarcs et al. 1999 and Magyar
et al. 1999a) prevailing depositional environments, and characteristic fossils.
core 34 belonged to the Pannonian Stage, since it contained
the endemic Lake Pannon bivalve Paradacna abichi (R.
Hörnes), whereas core 35 already represented the marine Bad-
enian Stage with the appearance of planktonic foraminifers
(Fig. 3). Badenian foraminifers were washed from cores 35 to
45, together with a few ostracod fragments which were too
poorly preserved for determination. Thin sections, mostly
made of hard sandstone layers, showed an increasing amount
of marine fossils indicating Badenian age from core 35 down-
wards; these included planktonic and benthic foraminifers and
fragments of red algae and echinoderms (Fig. 3). The majority
of the foraminifers were small, poorly preserved, and had py-
ritic incrustations. Palynological investigations had also been
carried out on several samples of this interval, but yielded no
conclusive biostratigraphic results. Although it was a widely
held view that there was no significant hiatus in the Neogene
sequence of the basin, the restricted marine Sarmatian Stage,
sandwiched between the marine Badenian and the lacustrine
Pannonian, was not identified in the borehole. The boundary
between the Middle Miocene and the Pannonian was
marked at the top of core 35, at 5167 m. The final well report
did not even mention the apparent absence of the Sarmatian
The conviction that the Sarmatian Stage must be present in
the well was strong. Royden & Dövényi (1988), for example,
re-evaluated the stratigraphy of the well (on unknown
grounds) so that the upper 160 m of the earlier Badenian
represented the Sarmatian. To clarify the position of Neogene
stage boundaries, Báldi-Beke (1995) investigated nannoplank-
ton from cores 33 to 45. Only a few samples yielded strati-
graphically interpretable fossils. Typical Badenian associa-
tions with Sphenolithus heteromorphus Deflandre,
Sphenolithus aff. moriformis (Brönnimann et Stradner), etc.,
were found in cores 44 and 43; an impoverished Badenian(?)
flora with Cyclococcolithus rotula (Kamptner), Cyclococco-
lithus leptoporus (Murray et Blackman), Cyclicargolithus
floridanus (Roth et Hay), etc., in cores 40 and 42; and an asso-
ciation of eurytopic species, such as Coccolithus pelagicus
Wallich, Reticulofenestra pseudoumbilica (Gartner), etc., in
core 35 (Fig. 3). Báldi-Beke (1995) thought that the latter
might have represented the Sarmatian Stage, although she as-
serted that this stage has no diagnostic nannoflora. Several
years later Kollányi (2000) published her results on Pannonian
nannoplankton investigations from various boreholes. She
concluded that many species, which inhabited brackish waters
in the Badenian and Sarmatian ages, survived into the Pannon-
ian, and, consequently, the Badenian/Sarmatian and Sarma-
tian/Pannonian boundaries cannot be readily marked by nan-
noflora (although endemic Pannonian species do exist).
This was when we launched our search for the Sarmatian
Stage in the Hód-I well, invoking new methods of micropale-
ontological preparation. Our investigations led to an unexpect-
ed result: the Sarmatian Stage is missing from the explored
succession, because the drilling failed to reach the bottom of
the Pannonian Stage.
For micropaleontological investigations we sampled the
lower third of the Hód-I well, from core 25 downward
(Fig. 3). There was no recovery from cores 29 and 31, and we
had access to only a small chunk of core 42. In each core, the
most fine-grained intervals available were sampled and sandy
layers rejected. Where quality and recovery of the core al-
lowed, we collected larger amounts of sediments (500
1000 g) for treatment with acetic acid.
Preparation of ostracods
Our investigation marks the first time that acetic acid treat-
ment has been applied to Pannonian rocks in order to obtain
calcitic fossils from them. The samples were broken into small
pieces and bathed in concentrated solution of acetic acid (96%
) until the sediment was entirely soaked and disinte-
grated (about two weeks). Acetic acid dissolves cement of the
rock faster than it does the crystalline CaCO
of the fossil
shells. With this method, we were able to free intact ostracod
shells even from the hardest sample. Traditional preparation
with peroxide of hydrogen from the same samples yielded
Pannonian ca. 12.0 Ma
Sarmatian ca. 13.7 Ma
ca. 16.5 Ma
normal marine normal marine echinoids, red algae
478 SZUROMI-KORECZ, SÜTÕ-SZENTAI and MAGYAR
Fig. 3. Stratigraphic column of the lower section of well Hód-I, showing the results of earlier biostratigraphic investigations (Csongrádi et
al. 1971; Báldi-Beke 1995; left side) and the results of our study (right side). Symbols of Badenian (marine) fossils are grey-filled, those of
Pannonian are empty.
only a few indeterminable fragments, so we soon abandoned
the latter method altogether.
Preparation of dinoflagellates
In addition to traditional palynological preparations, di-
noflagellates were also observed in normal (30 µm thick) pet-
rographical thin sections. During the first description of the
Hód-I core samples thirty years ago, paleontologist J. Kõváry
(in Csongrádi et al. 1971) recorded dinoflagellates in a thin
section from core 35. This thin section was reexamined now,
and a rich association of determinable dinoflagellates was rec-
ognized in it. Encouraged by this success, we systematically
investigated both old and freshly made thin sections of each
BIOSTRATIGRAPHIC REVISION OF HUNGARYS DEEPEST BOREHOLE 479
sample. Dinoflagellates have been found in many of the sec-
tions. Their size varied, however, and they were not always as
conspicuous as in the first section where they could be easily
recognized with 100 times magnification.
Traditional palynological preparations from cores 25 to 33
yielded only black, amorphous fragments and a few, poorly
preserved sporomorphs. Samples from cores 34 to 45, howev-
er, contained dinoflagellates.
Results of paleontological investigations
Thin sections from cores 28 and 34 contained dinoflagellate
associations including the species Spiniferites validus, indi-
cating the Spiniferites validus Zone (Table 2, Figs. 3, 4). This
zone belongs to the upper part of the Lake Pannon sequence;
core 34 was thus far too young to represent the base of the
Pannonian, as the stratigraphic position of the core had been
interpreted originally (Fig. 3).
Samples from the top of core 35 (35a) yielded Spiniferites
paradoxus in both thin sections and palynological prepara-
tions, indicating the Spiniferites paradoxus Zone (Table 2,
Fig. 3); dinoflagellates from this sample are depicted in
Figs. 5 and 6AC. Thin sections from deeper parts of the core
(35b) contained Pontiadinium pecsvaradensis, indicating the
Pontiadinium pecsvaradensis Zone (Table 2, Fig. 3). The
boundary between the paradoxus and pecsvaradensis Zones
is thus interpreted to run within core 35.
Palynological preparations from cores 37 and 44 gave di-
noflagellate associations that indicate the Spiniferites bentorii
oblongus Zone. In accordance with these results, thin sections
Table 2: Dinoflagellates from cores of well Hód-I. For depth intervals of cores, see Fig. 3.
Spiniferites balcanicus (Baltes)
Spiniferites validus Sütõ-Szentai
Spiniferites maisensis Sütõ-Szentai
Spiniferites bentorii (Rossignol)
Spiniferites bentorii pannonicus Sütõ-Szentai
Spiniferites bentorii oblongus Sütõ-Szentai
Spiniferites bentorii coniunctus Sütõ-Szentai
Spiniferites paradoxus (Cookson et Eisenack) Sarjeant
cf. Pontiadinium sp.
Pontiadinium obesum Sütõ-Szentai
Pontiadinium pecsvaradensis Sütõ-Szentai
Pontiadinium inequicornutum (Baltes)
Gonyaulax digitalis (Pouchet)
Romanodinium areolatum Baltes
Nematosphaeropsis balcombiana (Deflandre et Cookson)
Millioudodinium pelagicum Sütõ-Szentai
Chytroeisphaeridia cariacoense Wall
of cores 36, 37, 40, 44, and 45 also yielded fossils belonging
to the oblongus Zone (Table 2, Figs. 3, 6D).
The two lowermost dinoflagellate zones of the Pannonian
Stage, that is the Mecsekia ultima and the Spiniferites bentorii
pannonicus Zones, have not been identified in the core sam-
ples; the well did not reach the base of the Pannonian Stage.
The interval between cores 25 and 35 yielded relatively
poorly preserved and low-diversity ostracod associations (Ta-
ble 3; Fig. 3). This fauna consisted of various subgenera of
the genus Candona, such as Hastacandona, Caspiolla,
Bakunella, and Thaminocypris. Only a single specimen from
core 25 could be identified on the species level: Candona
(Bakunella) dorsoarcuata. According to Krstiæ (1972) and
Sokaæ (1990), this species is characteristic of the Pontian
(corresponding to the upper part of the Lake Pannon se-
quence, latest Miocene).
Samples from the deeper part of the well (cores 36 to 44)
responded more favourably to solution in acetic acid, and
yielded better preserved and richer associations (Table 3;
Fig. 7AG). The fauna is dominated again by Candona: C.
(Thaminocypris), C. (Thyphlocypris), C. (Cryptocandona),
and C. (Lineocypris). Apart from Candona, specimens of
Amplocypris sp., Hungarocypris sp., and Xestoleberis sp.
occurred. The following taxa could be determined on the
species level (all from cores 39 to 41): Candona (Typhlocyp-
ris) alpherovi, Candona (Typhlocypris) cf. fossulata, Can-
dona (Thaminocypris) cf. improba, Candona (Lineocypris)
According to Krstiæ (1972, 1985), these species indicate the
lower part of the Lake Pannon sequence (Slavonian Sub-
480 SZUROMI-KORECZ, SÜTÕ-SZENTAI and MAGYAR
Fig. 4. A Spiniferites validus SütõSzentai, 1982. Thin section
from core 28 (45384546 m). B Pontiadinium sp. (Dinoflagel-
lata form 29). Thin section from core 34 (50705074 m). C
Spiniferites validus (a process). Thin section from core 34
(50705074 m). All scale bars = 10 µm.
stage), more precisely the Hemicytheria tenuistriata Zone.
Fossils characteristic of the basal Pannonian ostracod bio-
zones of Krstiæ (1985), however, have not been found. Core
45 did not yield ostracods.
In 1971, core 35 was considered to indicate the top of the
Badenian Stage because some planktonic foraminifers were
found in the washing residue. We found planktonic foramini-
fers (Globigerina (?) sp.) as high as core 33 (Fig. 3). The
amount of reworked marine (Badenian) fossils increases from
here towards the bottom of the borehole. They include worn
specimens of planktonic and benthic foraminifers (Fig. 7H),
red algae, and echinoids, and usually appear in coarse-
grained, sandy layers.
In addition to micropaleontological investigations, we care-
fully searched for shells of molluscs, but with poor success.
Only in core 25 we found poorly preserved specimens of
Pontalmyra otiophora (Brusina), Dreissenomya digitifera(?)
(Andrusov), and Valenciennius sp., indicating a typical deep-
water association of Lake Pannon (Magyar 1995). The fossils
are small in size, partly because they are fragmentary, partly
because they represent juvenile individuals; their determina-
tion is therefore somewhat uncertain.
Lithospheric extension and formation of the Pannonian Ba-
sin system is thought to have started in the early Middle Mio-
cene (Badenian) or somewhat earlier, in the late Early Mio-
cene (Ottnangian and Karpatian ages). Various rifting
models were proposed for the different basin types. The pe-
ripheral basins, such as the Vienna and Transcarpathian Ba-
BIOSTRATIGRAPHIC REVISION OF HUNGARYS DEEPEST BOREHOLE 481
Fig. 5. Dinoflagellates in thin sections from core 35a (51675183 m, upper part). A Impagidinium sp. (Dinoflagellata form 72). B
Spiniferites balcanicus (Baltes, 1971) Sütõ-Szentai, 2000. C Spiniferites bentorii (Rossignol, 1964) Wall et Dale, 1970 ssp. coniunctus
Sütõ-Szentai, 1990. D Spiniferites paradoxus (Cookson et Eisenack, 1968) Sarjeant, 1970.
C. (Hastacandona) sp.
C. (Caspiolla) sp.
C. (?Caspiolla) sp.
C. (Thaminocypris) sp.
C. (?Thaminocypris) sp.
C. (Thaminocypris) cf. improbus Krstiæ
C. (Typhlocypris) sp.
C. (Typhlocypris) cf. alpherovi (Schneider)
C. (Typhlocypris) cf. fossulata Pokorný
C. (Zalanyiella) sp.
C. (Lineocypris) sp.
C. (Lineocypris) cf. dorsobrevis Krstiæ
C. (Pseudocandona) sp.
C. (Cryptocandona) sp.
C. (Bakunella) cf. dorsoarcuata Zalányi
Table 3: Ostracods from cores of well Hód-I. For depth intervals of cores, see Fig. 3.
482 SZUROMI-KORECZ, SÜTÕ-SZENTAI and MAGYAR
sins, seem to have obeyed the model of uniform lithospheric
stretching (Sclater et al. 1980). The thermal subsidence of
most parts of the Pannonian Basin system can be satisfactorily
explained by mid-Miocene regional rifting and subsequent
cooling of the lithosphere (Tari et al. 1999). In the deep sub-
basins of the central Pannonian Basin, including the Makó
Trough, however, unrealistically excessive stretching would
have been required to cause the observed thermal subsidence
(Sclater et al. 1980). Additional subcrustal thinning (Horváth
et al. 1988) and intraplate stress associated with a recent com-
pressional inversion of the Pannonian Basin (Horváth & Clo-
etingh 1996) were considered as possible explanations for this
subsidence anomaly. Tari et al. (1999) suggested that basin
evolution in the area started with a metamorphic core complex
extension in the Karpatian as the modern Battonya-Pusz-
taföldvár High slid eastwards from above the modern Algyõ
High along a NE-dipping detachment fault (Figs. 1, 2). This
initial stage was followed by a wide rift style extension in the
Badenian and eventually by local rifting (narrow rift style)
that extended well into the Sarmatian and Pannonian (Tari et
al. 1997, 1999). However, our results indicate that old
Fig. 6. A Spiniferites bentorii (Rossignol, 1964) Wall et Dale, 1970 ssp. pan-
nonicus Sütõ-Szentai, 1986. Thin section from core 35a (51675183 m, upper
part). BC Spiniferites bentorii (Rossignol, 1964) Wall et Dale, 1970. Thin
section from core 35a (51675183 m, upper part). D Gonyaulax digitale
(Pouchet, 1883) Kofoid, 1911. Thin section from core 36 (5250.0
5267.0 m). All scale bars = 10 µm.
(though not basal) Pannonian strata are not tilted
and thus apparently were not affected by exten-
sion. We also found that the postrift sedimentary
cover is even thicker here than was thought be-
fore; future models have to accomodate a >6 km
postrift sedimentary pile in the centre of the Makó
The statement that thin synrift sediments have
been deposited in locations of the Pannonian Ba-
sin situated far from the Carpathian thrust belt and,
consequently, far from sediment sources (Royden
1988; Grow et al. 1994), applies particularly well
to the Makó Trough. Supposing an unbroken sedi-
mentary cycle beginning as early as the Badenian,
the Badenian and Sarmatian Stages as well as the
two lowermost Pannonian dinoflagellate zones
must exist in the <800 m gap between the meta-
morphic basement and the bottom of the Hód-I
well (Fig. 2). This arrangement allows only rela-
tively thin synextensional Badenian and Sarma-
tian sediments to be present in the axis of the
trough (although tilted synrift strata may be some-
what thicker to the east, in the Middle Miocene
axis of the basin; Fig. 2). Thus, the Makó Trough
was probably a starved basin during the Middle
Sediment supply from outside the basin was
scarce even during the Early Pannonian. The in-
vestigated interval of Hód-I was interpreted by
Bérczi (1988) as a superposition of three main fa-
cies, such as coarse-grained basal turbidites,
deep-basin fine-grained sediments, and distal
prodelta sediments. The lower part of the well
contains a quantity of reworked Badenian fossils
and pebbly horizons (Fig. 3). This is in accord
with the sedimentological interpretation of Bérczi
(1988), who thought that the >300 m basal series
in Hód-I consisted of sediment gravity flow de-
posits. Patchy occurrences of the Badenian and Sarmatian
Stages (erosional fragments?) have been explored by drillings
on the eastern flank of the Makó Trough, whereas they are not
known on the western flank. Heavy reworking of Badenian
sediments indicates steep slope morphology.
The original goal of the study, that of determining Sarma-
tian boundaries, was not achieved; however, Pannonian bio-
zones were identified in the Hód-I sequence. Chronostrati-
graphic interpretation of these biozones, according to Magyar
et al. (1999a), is given in Table 4. The thickness of the bio-
zones (Table 4) reflects various stages of sedimentation. The
Spiniferites bentorii oblongus Zone is at least 600 m thick in
the Hód-I well, whereas it rarely exceeds 100 m in other areas
of the Pannonian Basin. During the deposition of this zone,
the shoreline of Lake Pannon ran close to the margins of the
Pannonian Basin (Magyar et al. 1999b), thus no significant
fluvial sediment transport could reach the Makó Trough from
the basin margins. The sources of the anomalously thick sedi-
ment pile in the Makó Trough must have been the surround-
ing highs (islands), as indicated by the high ratio of reworked
material in these deposits.
BIOSTRATIGRAPHIC REVISION OF HUNGARYS DEEPEST BOREHOLE 483
Fig. 7. A Candona (Zalanyiella) sp. Core 38 (5405.55418.0 m). Lv, outside. B Candona (Hastacandona) sp. Core 40 (5468.0
5486.0 m). Rv, outside. C Candona (Thaminocypris) sp. Core 40 (5468.05486.0 m). Lv, outside. D Candona (Typhlocypris) cf. fos-
sulata Pokorný. Core 40 (5468.05486.0 m). Rv, outside. E Candona (Typhlocypris) cf. alpherovi (Schneider). Core 40 (5468.0
5486.0 m). Lv, outside. F Amplocypris sp. Core 41 (5486.05489.0 m). Rv, outside. G Candona (Thaminocypris) cf. improba Krstiæ.
Core 40 (5468.05486.0 m). Rv, outside. H Globigerina (?) sp. Core 40 (5468.05486.0 m). I A charophyte gyrogonite. Core 44
(5727.05738.0 m). All scale bars = 100 µm.
On the contrary, the Spiniferites paradoxus Zone, repre-
senting more than 1 million years, is surprisingly thin (less
than 100 m) in the Hód-I sequence. Coeval sediments in NW
Hungary may exceed 500 m, and have a strong transgressive
character in many parts of the Pannonian Basin (Sütõ-Szentai
1991; Szilaj et al. 1999). Seismic sequence stratigraphic stud-
ies also established a rising lake level for much of this interval
in various parts of the basin (Vakarcs et al. 1994; Sacchi et al.
484 SZUROMI-KORECZ, SÜTÕ-SZENTAI and MAGYAR
1999). According to Magyar et al. (1999b), Lake Pannon
reached its largest geographic extension at about the end of
this biochron. The rise of relative lake level and inundation of
vast areas in the basin margins as well as in the surrounding
highs may have caused a decrease in sediment supply and
sedimentation rate in the deep Makó Trough.
Preparation of ostracods with acetic acid and investigation
of dinoflagellates in thin sections revealed that the deepest
borehole in Hungary, Hód-I, failed to reach the base of the
Lake Pannon sediments (= Pannonian Stage, Upper Miocene)
in one of the deepest subbasins of the entire Pannonian Ba-
sin system. This subbasin, the Makó Trough, was considered
to be Middle Miocene in age; however, much of the basin is
filled with horizontal, relatively undisturbed Lake Pannon
sediments, whereas synrift sediments are relatively thin be-
tween the base of the well and the supposedly Paleozoic
metamorphic basement. The vast thickness of the postrift se-
quence indicates that mechanisms other than pure shear must
be invoked to assess basin evolution in the central Pannonian
In the beginning of Pannonian sedimentation, Middle Mio-
cene marine deposits and the metamorphic basement were
eroded and reworked probably by wave action in the
steep flanks of the basin and redeposited in the axis of the
trough (Spiniferites bentorii oblongus and Pontiadinium pecs-
varadensis Zones). Although a better understanding of paleo-
bathymetry would be crucial for structural evolution interpre-
tations, neither the lithology nor the fossils provide conclusive
evidence concerning the paleo-waterdepth of the Makó
Trough in the Early Pannonian. Later the rate of sedimenta-
tion decreased, probably due to a relative lake level rise (Spini-
ferites paradoxus Zone). Reworked Badenian fossils and peb-
ble layers disappear from the stratigraphic column of Hód-I
within the overlying Spiniferites validus Zone.
Acknowledgments: We thank our colleagues, Attila Fogara-
si, István Révész, and Éva Margitics-Sipõtz, at MOL Hungari-
an Oil and Gas Co., for supporting our work in various ways.
Györgyi Juhász is thanked for support from OTKA T035168.
We are also grateful to Dana H. Geary, Frank Horváth, Rado-
van Pipík, Natália Hudáèková, Johan E. Meulenkamp, and an
anonymous reviewer for their corrections and comments on
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