Correlation of upper Miocene–Pliocene Lake Pannon deposits across the Drava Basin, Croatia and Hungary

Upper Miocene to Pliocene (Pannonian) sediments of the Pannonian Basin System accumulated in the brackish Lake Pannon and the fluvial feeder systems, between 11.6-2.6 Ma. Their stratigraphic subdivision has been problematic for a long time due to the laterally prograding architecture of the basin fill and the historically independently evolving stratigraphic schemes of the neighbouring countries. We correlated the lithostratigraphic units of the Lake Pannon deposits between Hungary and Croatia in the Drava Basin, using lithological, sedimentological and palaeontological data from boreholes and outcrops, and seismic correlation. The Croatica and Medvedski breg formations in Croatia correspond to the Endrőd Fm. in Hungary, comprising shallow to deep water, open lacustrine, calcareous to argillaceous marls. The Andraševec fm. in Croatia corresponds to the Szolnok and Algyő Fms. in Hungary, consisting of sandstones and siltstones of turbidite systems and of clay marls deposited on the shelf-break slope. The Nova Gradiška fm. in Croatia is an equivalent of the Újfalu Fm. in Hungary, built up of a variety of lithologies, including sand, silt, clay and huminitic clay, deposited in deltaic environments. The Pluska fm. in Croatia corresponds to the Zagyva Fm. in Hungary, consisting of variegated clays, silts, sands and lignites, deposited in alluvial and fluvial environments. Coarse-grained (sand, gravel) basal layers are assigned to the Kálla and Békés Fms. and the Sveti Matej member of the Croatica fm. Coarse-grained intercalations within the deep-water marls belong to the Dorozsma Member of the Endrőd Fm. in Hungary, and to the Bačun member of the Medvedski breg fm. in Croatia. Sediment transport and lateral accretion of the shelf edge in the Drava Basin took place from the N, NW, and W, to the S, SE, and E, respectively. According to the biostratigraphic and chronostratigraphic analyses, the oldest shelf-break slopes in the Mura Basin are more than 8 Ma old, whereas the youngest ones in the southeasternmost part of the Drava Basin may be Pliocene in age (younger than 5.3 Ma). Thus, the 180 km long and at least 700 m deep Drava Basin was transformed into a fluvial plain during the last 3.5 million years of the Miocene.</p

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

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)

Towards a high-resolution chronostratigraphy and geochronology for the Pannonian Stage : Significance of the Paks cores (Central Pannonian Basin)

A new stratigraphic standard for the open lacustrine to deltaic Pannonian Stage is emerging from the combinedsedimentological, lithostratigraphical, sequence stratigraphical, biostratigraphical, seismic stratigraphical, geo chrono -logical, and magnetostratigraphical investigations of 6 long drill cores. These were drilled by Paks II Nuclear Power PlantPlc. as a preparatory step for the construction of a new power plant near the city of Paks, Central Pannonian Basin,between 2015 and 2016. The boreholes are in a distance of 8–12 km from each other, and five of them fully penetrated thelocal Pannonian sequence in a thickness of 390 to 662 m. Each core includes offshore clay marl deposited far fromsediment entry points (Endrőd Fm), heterolithic, sandy siltstones of a <200 m high shelf-margin slope (Algyő Fm), andseveral stacked deltaic deposits from prodelta silts to sandy mouth bars, heterolithics, lignite and sandy channel-fills ofthe delta plain (Újfalu Fm). Magnetostratigraphic investigations from two cores and authigenic 10Be/9Be dating from twoothers were combined by means of seismic correlation between the boreholes, and thus they provide a solid geo -chronological and chronostratigraphic basis for the interpretation of the sedimentological and palaeontological recordsof the cores. The continuous representation of the earliest Pannonian (11.6–9.1 Ma) in the cores needs furtherpalaeontological investigation, as both magnetostratigraphy and authigenic 10Be/9Be dating failed to give reliable agedata from the basal, condensed calcareous marls. The 9.1 to 6.5 Ma interval, however, is represented in the cores by various lithologies and abundant and sometimes excellently preserved fossils. In the deltaic succession, 10 sedimentarysequences were correlated between the cores; as their duration is not more than 200 kyr each, they can be regarded as 4th-order sequences. The palaeontological record of the cores shows a very good agreement with the formerly establishedbiochronostratigraphical system. The cores provide an insight into the evolution of the sedimentary environment and thebiota of Lake Pannon between 9.1 and 6.5 Ma with a so far unprecedented temporal and spatial resolution

Towards a High-Resolution Chronostratigraphy and Geochronology for the Pannonian Stage: Significance of the Paks Cores (Central Pannonian Basin) = A paksi fúrómagok szerepe a pannóniai emelet nagy felbontású időrétegtanának és geokronológiájának kifejlesztésében

A new stratigraphic standard for the open lacustrine to deltaic Pannonian Stage is emerging from the combined sedimentological, lithostratigraphical, sequence stratigraphical, biostratigraphical, seismic stratigraphical, geochronological, and magnetostratigraphical investigations of 6 long drill cores. These were drilled by Paks II Nuclear Power Plant Plc. as a preparatory step for the construction of a new power plant near the city of Paks, Central Pannonian Basin, between 2015 and 2016. The boreholes are in a distance of 8–12 km from each other, and five of them fully penetrated the local Pannonian sequence in a thickness of 390 to 662 m. Each core includes offshore clay marl deposited far from sediment entry points (Endrőd Fm), heterolithic, sandy siltstones of a <200 m high shelf-margin slope (Algyő Fm), and several stacked deltaic deposits from prodelta silts to sandy mouth bars, heterolithics, lignite and sandy channel-fills of the delta plain (Újfalu Fm). Magnetostratigraphic investigations from two cores and authigenic 10Be/9Be dating from two others were combined by means of seismic correlation between the boreholes, and thus they provide a solid geochronological and chronostratigraphic basis for the interpretation of the sedimentological and palaeontological records of the cores. The continuous representation of the earliest Pannonian (11.6–9.1 Ma) in the cores needs further palaeontological investigation, as both magnetostratigraphy and authigenic 10Be/9Be dating failed to give reliable age data from the basal, condensed calcareous marls. The 9.1 to 6.5 Ma interval, however, is represented in the cores by various lithologies and abundant and sometimes excellently preserved fossils. In the deltaic succession, 10 sedimentary sequences were correlated between the cores; as their duration is not more than 200 kyr each, they can be regarded as 4th-order sequences. The palaeontological record of the cores shows a very good agreement with the formerly established biochronostratigraphical system. The cores provide an insight into the evolution of the sedimentary environment and the biota of Lake Pannon between 9.1 and 6.5 Ma with a so far unprecedented temporal and spatial resolution. A pannóniai emelet kutatásában kivételes lehetőségként jelent meg, és kiemelkedő jelentőséggel bír a paksi atomerőmű bővítési folyamata során fúrt kőzetmagok sokoldalú rétegtani vizsgálata. A Paks II Atomerőmű Zrt. által 2015 és 2016 folyamán fúratott 6 magból 5 teljes (390 és 662 m közötti) vastagságban, folyamatos magmintavétellel harántolta a helybeli pannóniai képződményeket. A fúrások Paks környékén, egymástól 8–12 km távolságra mélyültek. Mindegyik fúrás a folyótorkolatoktól távol, nyílt és aránylag mély vízben képződött márgák (Endrődi Formáció), a 200 méternél nem magasabb selfperemi lejtőn lerakódott homokos kőzetliszt (Algyői Formáció), és a delta előtéri kőzetlisztből, torkolati zátonyok homokjából, deltasíksági lignitből és homokos csatornakitöltésekből álló deltaképződmények (Újfalui Formáció) egymásutánját tárta fel. Két fúrómagból mágnesrétegtani, két másikból pedig autigén 10Be/9Be korhatározási módszerrel nyertünk korokat, majd a fúrások közötti szeizmikus korreláció megteremtésével kialakítottunk egy, a fúrómagok szedimentológiai és paleontológiai jellemzőitől független időrétegtani és geokronológiai keretet. A szarmatától kezdődő folyamatos üledékképződésnek és a legidősebb (11,6–9,1 millió éves) pannóniai rétegek összefüggő jelenlétének a bizonyítására további mikropaleontológiai vizsgálatokra lesz szükség, mert jelenleg sem a mágnesrétegtani, sem az autigén 10Be/9Be korhatározási módszer nem alkalmas a kondenzált mészmárga üledékek korolására. A 9,1 és 6,5 millió évek közötti intervallumot ezzel szemben változatos litológia és — sok esetben kivételesen jó megtartású — ősmaradványanyag képviseli a fúrómagokban. A delta üledékekben legalább 10 üledékes szekvenciát lehetett azonosítani és korrelálni; mivel ezek időtartama egyenként legfeljebb 200 ezer év lehetett, negyedrendű szekvenciáknak tekinthetők. A fúrómagokban azonosított biozónák korhatárai igen jó egyezést mutatnak az eddig használt biokronosztratigráfiai rendszerrel, lényegében megerősítik és néhány helyen pontosítják azt. A paksi PAET fúrómagok eddig soha nem látott részletességű képet nyújtanak a Pannon-tó üledékes környezeteinek és élővilágának fejlődéséről a 9,1 és 6,5 millió év közötti intervallumban