Pannonian (late Miocene) ostracod fauna from Pécs-Danitzpuszta in Southern Hungary

The large outcrop at Pécs-Danitzpuszta, southern Hungary, exposes a 65-meter-thick succession of calcareous marls, clay marls and calcareous sands that were deposited during the early history of Lake Pannon, a vast, Caspian-type lake in Central Europe in the late Miocene. Within the framework of the complex stratigraphic investigation of this succession, well preserved, relatively diverse benthic ostracod assemblages containing 39 taxa were recovered from 29 samples (16 samples were barren). Palaeoecological interpretation of the ostracod genera suggests that deposition took place in a low-energy environment, in the shallow sublittoral zone of Lake Pannon, in pliohaline (9–16‰ salinity) water. The entire succession was divided into four interval zones based on the first occurrences of assumedly useful marker fossils: Hemicytheria lorentheyi Zone (from sample D29), Hemicytheria tenuistriata Zone (from sample D17), Propontoniella candeo Zone (from sample D115) and Amplocypris abscissa Zone (from sample D209). Based on comparison to the Beočin section 150 km to the SE, where a lithologically and stratigraphically similar section was dated magnetostratigraphically by an international team, we tentatively assume that the Pannonian marl succession of the Pécs-Danitzpuszta outcrop represents the time interval of 11.6 to ca. 10 Ma.

Middle Miocene (Badenian) macroinvertebrates from Pécs-Danitzpuszta (Mecsek Mts, SW Hungary)

This paper examines Badenian (middle Miocene) macroinvertebrates – corals and molluscs – from the Pécs-Danitzpuszta sand pit (Mecsek Mts, SW Hungary) in order to extend our knowledge on Miocene normal marine deposits of the Mecsek region. Corals occur reworked in the upper Miocene sand that was deposited in the brackish Lake Pannon, and presumably originate either from the middle Badenian Pécsszabolcs or the upper Badenian Rákos Member of the Lajta Formation. A total of seven taxa were identified. These taxa suggest subtropical conditions and a lack of coral reefs in the Badenian. Molluscs were found in situ in the upper Badenian Szilágy Clay Marl Member of the Baden Formation and the Rákos Member of the Lajta Formation. They dominantly consist of bivalves and represent benthic assemblages typical of the middle Miocene Central Paratethys.

Structural features in the Miocene sediments of the Pécs-Danitzpuszta sand pit (SW Hungary)

The Pécs-Danitzpuszta sand pit in southern Hungary exposes middle and upper Miocene (Badenian to Pannonian/Langhian to Tortonian) sediments along the mountain front fault zone of the Mecsek Mts and preserves an essential record of tectonic events during and after the early late Miocene, which are not exposed elsewhere in the region. In this paper we present structural observations recorded over 20 years of work, date the deformation events with mollusk biostratigraphy and make inferences on the structural evolution of the area. At the beginning of the time interval between 10.2–10.0 Ma, NNW–SSE (to NW–SE) extension created normal faults and negative flower structures. These show that extension-related fault activity lasted here up to the late Miocene. Shortly thereafter, still in the early part of the time interval between 10.2–10.0 Ma, N–S to NNW–SSE compression ensued and dominated the area ever since. Deformations under this stress field included reverse faulting in the Pannonian marls and sands, folding of the whole succession, with bedding-plane slip and shearingelated block rotation in the already deposited middle and upper Miocene marl layers and continuously changing bedding dips and southward thickening layers in the Pannonian sands. Lake level changes of Lake Pannon must have played a role in the formation of an angular unconformity within the sands besides compression. The compressional event can be explained by the Africa (Adria) – Europe convergence, but cannot be correlated regionally; it pre-dates basin inversion-related events reported from the region so far.

Sarmatian and Pannonian mollusks from Pécs-Danitzpuszta, southern Hungary: a unique local faunal succession

As the almost 200-year palaeontological research revealed, the geographical distribution of various fossil mollusk faunas in deposits of the late Neogene Lake Pannon displays a regular pattern. The lake basin was filled by lateral accretion of sediments, resulting in condensed sedimentary successions in the distal parts of the basin and successively younger shallow-water deposits from the margins towards the basin center. Exposed intra-basin basement highs, however, broke this strict pattern when they acted as sediment sources during the lake’s lifetime. The Mecsek Mts in southern Hungary was such an island in Lake Pannon during the early late Miocene. Deposition of the 200 m thick Sarmatian–Pannonian sedimentary succession in Pécs-Danitzpuszta at the foot of the Mecsek Mts was thus controlled by local tectonic and sedimentary processes, resulting in a unique succession of facies and mollusk faunas. A typical, restricted marine Sarmatian fauna is followed by a distinct freshwater or oligohaline interval, which, according to micropalaeontological evidence, still belongs to the Sarmatian. Although poor preservation of fossils does not allow firm conclusions, it seems that freshwater Sarmatian snails were the ancestors of the brackish-water-adapted early Pannonian pulmonate snail taxa. The successive “Sarmatian-type” dwarfed cockle fauna is similar to those widely reported from the Sarmatian–Pannonian boundary in various parts of the Pannonian Basin; however, a thorough taxonomic study of its species is still lacking. The bulk of the sedimentary succession corresponds to the sublittoral to profundal “white marls,” which are widespread in the southern Pannonian Basin. In Croatia and Serbia, they are divided into the Lymnocardium praeponticum or Radix croatica Zone (11.6–11.4 Ma) below, and the Congeria banatica Zone (11.4–9.7 Ma) above; this division can be applied to the Pécs-Danitzpuszta succession as well. Sedimentation of the calcareous marl, however, ceased at Pécs-Danitzpuszta at about 10.5–10.2 Ma ago (during the younger part of the Lymnocardium schedelianum Chron), when silt was deposited with a diverse sublittoral mollusk fauna. Similar faunas are known from the Vienna Basin, southern Banat, and other marginal parts of the Pannonian Basin System, but not from Croatia and Serbia, where deposition of the deep-water white marls continued during this time. Finally, the Pécs-Danitzpuszta succession was capped with a thick, coarse-grained sand series that contains mollusk molds and casts representing a typical littoral assemblage. This littoral fauna is well-known from easternmost Austria, northern Serbia, and northwestern Romania, but never directly from above the sublittoral L. schedelianum Zone. The fauna is characteristic for the upper part of the Lymnocardium conjungens Zone and has an inferred age of ca. 10.2–10.0 Ma. The Pécs-Danitzpuszta succession thus allows to establish the chronostratigraphic relationship between mollusk faunas that have not been observed in one succession nor in close proximity to each other in other parts of the Pannonian Basin.

Dinoflagellate cysts from the Pannonian (late Miocene) "white marls" in Pécs-Danitzpuszta, southern Hungary

Dinoflagellate-cyst based biostratigraphy is an important tool in the stratigraphical subdivision and correlation of the Neogene Lake Pannon deposits. A total of 66 palynological samples were investigated from the Pannonian (upper Miocene) marl succession exposed in the Pécs-Danitzpuszta sand pit in order to evaluate the biostratigraphical assignment and constrain the age of the strata. Earlier attempts to recover dinoflagellate cysts from this important reference section had failed. In our material, six samples contained well-preserved palynomorphs. One sample from the lower part of the succession (D25) contained a probably reworked middle Miocene assemblage. Samples from the middle segment of the succession (D3, D2, D1) indicate the Pontiadinium pecsvaradensis Zone (ca. 10.8 to 10.6 Ma). Samples from the top of the marl (D219, D221) did not give additional stratigraphic information (P. pecsvaradensis Zone or younger). The palynofacies of samples D3 to D221 indicates a relatively distal, calm, occasionally oxygen-deficient, probably deep depositional environment.

Calcareous nannofossils from the middle/upper Miocene succession of Pécs-Danitzpuszta, southern Hungary: cosmopolitan Paratethys and endemic Lake Pannon assemblages

Quantitative analyses on calcareous nannofossils were carried out on 109 middle/late Miocene (Sarmatian/ Pannonian) samples from the section at Pécs-Danitzpuszta sand pit (Hungary). The lower part of the section, which can be assigned to the Sarmatian, contains normal marine low-diversity assemblages dominated by Calcidiscus leptoporus, Reticulofenestra pseudoumbilicus, Sphenolithus moriformis and Syracosphaera spp. accompanied by didemnid ascidian spicules (Perforocalcinela fusiformis). The middle/late Miocene (Sarmatian/Pannonian) boundary is characterized by the last occurrences of normal marine calcareous nannofossils. The upper part of the section (Pannonian) can be subdivided into intervals characterized by monospecific endemic nannofossils Isolithus spp. and ascidians, respectively. A short interval with common endemic coccoliths belonging to the family Noelaerhabdaceae (Bekelithella echinata, Noelaerhabdus bozinovicae, N. jerkovici, Praenoelaerhabdus banatensis) in the upper part of the profile was also documented. The drastic change in nannofossil assemblages at the Sarmatian/Pannonian boundary is a result of paleoenvironmental stress caused by the isolation of the Central Paratethys from the Eastern Paratethys.

An exceptional surface occurrence: the middle to upper Miocene succession of Pécs-Danitzpuszta (SW Hungary)

The Pécs-Danitzpuszta sand pit is the most important outcrop of the oldest Pannonian (upper Miocene, Tortonian) deposits in southern Hungary. A trench excavated in 2018 exposed Lake Pannon deposits and underlying Paratethys strata down to the upper Badenian (Serravallian), and together with the sand pit they make up a continuous sedimentary succession with a true thickness of ~220 metres. Due to tectonic deformation, middle Miocene deposits and carbonates in the lowermost Pannonian are overturned. Layers become vertical close to the marl-sand boundary, then the dip changes to normal, with continuously decreasing dip angles. The exposed succession starts with 5 m of upper Badenian (13.8-12.6 Ma old) calcareous marls and sandy limestones with sublittoral, then littoral molluscs, which were deposited in the normal salinity seawaters of the Central Paratethys. The overlying 8 m of sand, silt, sandy breccia and conglomerate are fossil-free,; only the lowermost silt layer contains reworked Badenian microfauna. This unit probably accumulated from gravity-driven flows in a fan-like, probably terrestrial depositional setting. The next 7.5 m of frequently alternating thin-bedded limestones, marls and clays with sublittoral biota represent rapid transgression. Foraminifers, ostracods, molluscs and calcareous nannoplankton indicate late Sarmatian, then Pannonian age for this interval. However, the locations of the boundaries indicated by the various groups are not are not consistent, making the position of the Sarmatian/Pannonian boundary uncertain. The Sarmatian beds with marine fossils still accumulated in the Paratethys, between ~12.1–11.6 Ma, under varying salinities due among others to temporary freshwater input. The Pannonian strata already represent sediments of the brackish Lake Pannon. Above these beds, uniform calcareous marl becomes dominant with some clay layers and graded or structureless conglomerate to sandstone interbeds. The deposition of the overall 64- m- thick Pannonian calcareous marl section took place in the open, probably few -hundred -metres -deep water of the lake between ~11.62 and 10.5–10.2 Ma. It may represent a rare, well-exposed surface occurrence of the Endrőd Formation which is known from thousands of wells in the Pannonian Basin. Above this section, a 6-7 -m- thick transitional interval of silty marls and sands is followed by ~140 m of limonitic, pebbly sands. They have poor to moderate sorting and rounding, metre -thick beds with transitional boundaries and abundant fossils and clasts reworked from older Miocene units. Their accumulation took place between 10.2-10.5 and 9.6 Ma by gravity flows connected to deep-water portions of fan deltas.

A diverse Miocene fish assemblage (Chondrichthyes and Osteichthyes) from the Pécs-Danitzpuszta sand pit (Mecsek Mts, Hungary)

Chondrichthyans and osteichthyans are widely reported from marine sediments of the Central Paratethys, not only by sporadic occurrences, but also by complex, diverse fish assemblages. Here we present a rich fish fauna from the upper Miocene (Pannonian, Tortonian) lacustrine sediments exposed in the Pécs-Danitzpuszta sand pit, in the SW Pannonian Basin. Altogether 22 227 specimens were investigated, and they could be classified into 17 chondrichthyan and 16 osteichthyan taxa. Among the chondrichthyans Odontaspididae (55.51%) and Myliobatidae (14.4%) are the most abundant, while the bony fishes are dominated by the Sparidae (77.07%). The limonitic, yellow, coarse-grained, gravelly sands yielded an extremely large amount of isolated fish fossils. A considerable part of the vertebrate material of the sands is likely reworked from older, middle Miocene (Badenian and Sarmatian, i.e. Langhian and Serravallian) sediments. The late Miocene calcareous marls underlying the sands also yielded a variety of fish remains. From these remains, associated and articulated latid bones are coeval with the sediment and suggest freshwater and brackish conditions in the area, in accord with other biotic data. Other, isolated fossils, namely teeth, otoliths, cycloid scales and jaw elements of Gadidae, Gobiidae, Sparidae and Latidae could be reworked and thus have a very limited paleoecological significance. Based on habitat preferences of extant relatives, all chondrichthyans and most osteichthyan taxa found in the sands must be of Badenian origin. The abundant remains allow for some conclusions on the environmental conditions during the Badenian. They refer to a shallow, coastal environment with tropical-subtropical climate with connection to more open water habitats. Remains of some osteichthyan taxa were found in coprolites, showing that these taxa were part of the food chain as prey items. Sirenian ribs and odontocete limb bones bearing tooth marks refer to trophic relations between marine mammals and large sized macropredatory sharks. The Pécs-Danitzpuszta record of shark-attributed bite marks on bones of marine mammals is the second of the Badenian of the Central Paratethys. Acipenserids and latids of the sands, linked to brackish and/or freshwater environments, could originate from any Miocene stratigraphic units.

Various marginal marine environments in the Central Paratethys: Late Badenian and Sarmatian (middle Miocene) marine and non-marine microfossils from Pécs-Danitzpuszta, southern Hungary

The middle Miocene foraminifera and ostracod record of the Central Paratethys usually reflects stable normal marine epositional environments for the Badenian and more patchy, less stable restricted marine environments for the Sarmatian. A 17 m thick outcrop at Pécs-Danitzpuszta, Mecsek Mts, SW Hungary exposed an upper Badenian to Pannonian succession where foraminifers and ostracods document significant environmental changes. The basal layers of the section contain micro- and macrofossils indicating normal marine, shallow, warm, well-oxygenated habitat with relatively high-energy conditions and algal vegetation on the bottom, and represent the upper Badenian (13.82 to 12.65 Ma). The marine deposits are followed by coarse sandstone, breccia and siltstone layers barren of microfossils but containing rhizoliths. The sediments were probably subaerially exposed for some time. The following marine inundation, marked by the appearance of clays and limestones as well as fossils, was dated to the late Sarmatian (ca. 12 to 11.6 Ma) on the basis of the restricted marine microfossil assemblages from the upper part of the succession (Porosononion granosum Zone, Aurila notata Zone). This community is characterized by exclusively eurytopic forms indicating an unstable and vegetated marginal marine environment with fluctuations in salinity, as well as oxygen and food availability. Within the 5 m thick upper Sarmatian marine interval, a unique fresh- to oligohaline fauna characterizes a few layers in less than 1 m thickness. This fauna consists of highly euryhaline foraminifera and freshwater to oligohaline ostracod assemblages, indicating a temporary salinity reduction to 5–10 ‰. No similar freshwater fauna has been reported from the Sarmatian of the Central Partethys so far. The eventual disappearance of the foraminifera from the paleontological record coupled with a complete turnover in the ostracod fauna indicates the transition from the marginal marine Sarmatian Sea to the brackish Lake Pannon, marking the Sarmatian/Pannonian boundary (11.6 Ma).

Anyakőzet-tulajdonságok és termikus átalakulások a Kösseni Formációban

Az olaj-anyakőzet korrelációk eredményei szerint a Nagylengyelben felfedezett nehéz-olajat a Kösseni Formáció generálta. A Rock-Eval adatok és a szerves kén-szén atomarányok alapján a Kösseni Formáció alsó része a Rezi-1 fúrásban magas szénhidrogén-potenciálú és a kénben dús, IIS típusú kerogén jelenlétét mutatja. Felhasználva a Bak-Nova árokban lévő Kösseni Formáció eltemetődési történetét és a IIS típusú kerogénnek megfelelő kinetikai konstansokat, a nehéz-olaj képződése a felsőkréta időszakban, 70°C hőmérsékleten ért véget. Az olaj ilyen korai képződése a kénben dús, IIS típusú kerogén jelenlétének köszönhető. A nehéz-olajnak a túlnyomás által létrehozott primer migrációja egybeesik a nehéz-olajban lévő aszfaltének bomlása kezdetével. A Kösseni Formáció felrepedése a pórusokban jelen lévő olaj térfogat-növekedése miatt előállt nyomásnövekedésnek köszönhető, ami az aszfaltén-bomlás következménye. A Kösseni Formáció kerogénjének termikus átalakulása gáz-képződéssel zárul a legalább 1.3 % vitrinitreflexiónak megfelelő magasabb termikus érettségi szinteken.