Pannonian ostracods from the southwestern Transylvanian basin

Pannonian (Late Miocene) ostracods were investigated from 7 outcrops, exposing deep-water lacustrine sediments along the western margin of the Transylvanian Basin. Sedimentological patterns in the outcrops indicate deposition in sublittoral to profundal environments where fine-grained, suspension fall-out sediments are intercalated with various types of mass transport deposits, most commonly turbidites. The ostracod fauna, consisting of 30 taxa, is dominated by endemic species of the brackish Lake Pannon. The assemblages indicate a mixture of deep-water (sublittoral to profundal) species, such as Paratethyan Candoninae, and shallow-water (littoral) species, belonging to Cyprideis, Loxoconcha, Amnicythere and Hemicytheria. The mixed character of the assemblages is most probably a consequence of the reworking of littoral specimens into deeper environments, a phenomenon also observed in the molluscan fauna from some of the investigated outcrops. Alternatively, some endemic and extinct species of the littoral genera might have adapted to the deep-water environment. A significant decrease in the abundance and diversity of ostracods from west to east is interpreted reflecting increasingly distal environments. The ostracod fauna indicates the Hemicytheria hungarica (2 outcrops), Hemicytheria tenuistriata (3 outcrops), and Propontoniella candeo Zones (2 outcrops) of the lower Pannonian Slavonian Substage.</p

Turbidites as Indicators of Paleotopography, Upper Miocene Lake Pannon, Western Mecsek Mountains (Hungary)

The floor of Lake Pannon covering the Pannonian Basin in the Late Miocene had considerable relief, including both deep sub-basins, like the Drava Basin, and basement highs, like the Mecsek Mts, in close proximity. The several km thick lacustrine succession in the Drava Basin includes profundal marls, basin-center turbidites, overlain by shales of basin-margin slopes, coarsening-upward deltaic successions and alluvial deposits. Along the margin of the Mecsek Mts locally derived shoreface sands and deltaic deposits from further away have been mapped so far on the surface. Recent field studies at the transition between the two areas revealed a succession that does not fit into either of these environments. A series of sandstone a few meters thick occurs above laminated to bioturbated clayey siltstone. The sandstone show normal grading, plane lamination, flat erosional surfaces, soft-sediment deformations (load and water-escape structures) and sharp-based beds with small reverse faults and folds. These indicate rapid deposition from turbidity currents and their deformation as slumps on an inclined surface. These beds are far too thick and may reveal much larger volumes of mass wasting than is expected on the 20–30 m high delta slopes; however, regional seismic lines also exclude outcropping of deep-basin turbidites. We suggest that slopes with transitional size (less than 100 m high) may have developed on the flank of the Mecsek as a consequence of lake-level rise. Although these slopes were smaller than the usually several hundred meter high clinoforms in the deep basins, they could still provide large enough inertia for gravity flows. This interpretation is supported by the occurrence of sublittoral mollusc assemblages in the vicinity, indicating several tens of meters of water depth. Fossils suggest that sedimentation in this area started about 8 Ma ago

Balatoni nagyfelbontású (egycsatornás) szeizmikus szelvények szedimentológiai, sztratigráfiai értelmezése és korrelációja a Balaton környékén felszínen kibukkanó üledékekkel = Sedimentological and stratigraphical interpretation of ultrahigh-resolution (single-channel) seismic profiles acquired on the Lake Balaton and their correlation with outcrop data

Célunk a Balaton holocén iszapja alatt és a környékén felszínen található pannóniai összlet őskörnyezeti és integrált sztratigráfiai értelmezése volt. Következtetéseink terepi szedimentológiai, paleontológiai észleléseken, fúrási adatokon, geoelektromos és földradar méréseken, kísérleti terepi gammaszelvényeken, valamint ultra-nagyfelbontású, kb. 25 m behatolású, vizi szeizmikus szelvények értelmezésén alapulnak. A Pannon-tó "Bakonyi-félsziget" alkotta peremén, a tó kialakulásának transzgressziv fázisában a parthomlok erősen mozgatott vízében fövenypartokon, öblökben és jelentős üledékbehozatalt jelző, ám lokális anyagból épülő Gilbert-deltákon ülepedett a Kállai Homok. Ezzel egyidőben a hullámbázis alatti mélységű nyíltvízben Száki Agyagmárga halmozódott fel. A tó fejlődésének regresszív szakaszában ettől jelentősen eltérő őskörnyezet alakult ki. Az Alpok-Kárpátok felöl érkező üledékkel a Kisalföld medencéjének feltöltése után, a Dunántúli-középhegység sekély vízzel borított öve is feltöltődött, kiterjedt deltasíkság formájában. Gazdag és változatos nyíltvizi faunával jellemezhető homok-aleurit a deltaelőtér hullámbázisnál alig mélyebb vizében Somlói Formációként ülepedett. A delta torkolatok előreépülésével a síkságon öblök képződtek, melyek rétegsorát a rövid idejű, néhány méteres tószintváltozások és a gyakori torkolat-áthelyeződések során kialakuló, ősmaradványtartalommal párhuzamosan változó aleurit-finomhomok-huminites agyag ciklusok épitik fel (Tihanyi Formáció). | The objective was paleoenvironmental and integrated stratigraphical interpretation of the Late Miocene Lake Pannon deposits that underlie the Holocene mud of Lake Balaton and are exposed in the vicinity of that lake. Conclusions are based on sedimentological and paleontological observations in the field, well data analysis, geoelectric and GPR measurements, pilot studies of gamma ray in outcrops, and ultra-high resolution seismic images. The sedimentary history of Lake Pannon along the southern margin of the Bakony peninsula was controlled first by transgression, then by intense regression. During the transgressive interval, sand and gravel (Kálla Fm) were deposited in Gilbert-type deltas built from local sediment sources, and in the strongly agitated shoreface to foreshore of embayments. At the same time, the Szák Claymarl was deposited in sublittoral environments. By the second phase, however, the paleogeography had considerably changed. Sediments originating from the Alps and Carpathians filled the Kisalföld basin and then levelled the shallow basins of the Transdanubian Range by deltaic deposits. In the prodelta, below the wave base, silt and sand of the Somló Fm were deposited. This environment was characterized by rich and diverse brackish-water fauna. The interdistributary bays of the deltaplain were filled by cyclic repetition of silt-fine sand-huminitic clay, controlled by high-frequency, low-amplitude lake level changes and frequent channel avulsions (Tihany Fm)

A Tihanyi Formáció a Balaton környékén: típusszelvény, képződési körülmények, rétegtani jellemzés.

Revisiting the Tihany, Fehérpart section, overviewing archive data, comparison with successions of nearby wells, well-logs, stratigraphic data and results of the high-resolution seismic surveys on Lake Balaton resulted a coherent picture on the depositional environment, age, stratigraphic correlation and palaeogeographic connections of the Tihany Formation. In addition to former analyses of grain-size distributions, carbonate and clay content, the sedimentary structures were investigated, a pilot study of gamma-ray measurements on the field was carried out and several orders of cyclicity were demonstrated. Besides previous palaeontological studies new fossils were collected, determined and magnetic polarity of the rocks were measured. The Tihany, Fehérpart section is correlated with the Spiniferites tihanyensis dinoflagellate, the MN11 micromammal and the Limnocardium decorum sublittoral mollusc biozones. It shows normal magnetic polarity. It is underlain by open lacustrine, reverse polarity shales of the Congeria praerhomboidea zone, and is overlain by layers indicative of the Prosodacnomya zone. The latter is well definied by the radiometric age (7.9 Ma) of the overlying volcano sedimentary suite. Therefore the Fehérpart section was deposited either 8.1–8.0 Ma (C4An.2n) or 8.3–8.2 Ma (C4Ar.1n chron) ago. The Tihany Formation was deposited in a variety of palaeoenvironments related to deltas entering Lake Pannon. It is built up of parasequences, i.e. shallowing up successions from below wave base to lake level generated by sediment accumulation. Parasequences were formed on the delta front or in inter-distributary bays to delta-plain swamps and distributary channels. Beyond the high frequency lake-level and partly autocyclic environmental fluctuations, most likely climatically induced fourth-order lake-level changes of about 15–30 m amplitude occurred, resulting in minor transgressions followed by repeated progradation of deltaic lobes. Although the Tihany (as well as the very alike Somló) Formation is found along the rim of the hills currently, during its origin it was deposited in the same way as the Újfalu Formation known only from the subsurface of deep basins. The dynamics of deltaic settings feeding to Lake Pannon can be understood by studying the Tihany Formation in outcrops. The only difference among the two formations might be in the number of overlying delta cycles and their thickness. Both numbers were determined by rate of subsidence smaller at basement highs where Tihany Formation accumulated than at basin areas where Újfalu Formation was definied. It is suggested here to include Tihany (and Somló) beds as members of the Újfalu Formation. Fourth-order sequence boundaries were recognized between the overlying progradational deltaic bodies. In the vicinity of Tihany no evidences of lake-level drops were revealed, but elsewhere small incised-valley fills point to minor lake-level drops. Overall regression interrupted by transgressive events continued on the study area until the shelf edge of Lake Pannon shifted as far to the south as 50-60 km, i.e. at about 8 Ma ago. Since then flooding events became rare and small in amplitude, then the area became a terrestrial plain. Fluvial deposits are not known from the direct vicinity, but travertines formed in small freshwater ponds fed by karst springs. The transition from lacustrine to terrestrial palaeoenvironments is part of the overall normal regression as a result of high sediment input to Lake Pannon. Large incised valleys or other evidences of recurring terrestrial conditions which could be related to third-order sequence boundaries mappable all over the Pannonian Basin were identified neither in Tihany nor in Újfalu Formations

Porosity Development Controlled by Deep-Burial Diagenetic Process in Lacustrine Sandstones Deposited in a Back-Arc Basin (Makó Trough, Pannonian Basin, Hungary)

Deeply buried Pannonian (Upper Miocene) siliciclastic deposits show evidence of secondary porosity development via dissolution processes at a late stage of diagenesis. This is demonstrated by detailed petrographic (optical, cathodoluminescence, fluorescence, and scanning electron microscopy) as well as elemental and stable isotope geochemical investigations of lacustrine deposits from the Makó Trough, the deepest depression within the extensional Pannonian back-arc basin. The analyses were carried out on core samples from six wells located in various positions from centre to margins of the trough. The paragenetic sequence of three formations was reconstructed with special emphasis on sandstone beds in a depth interval between ca. 2700 and 5500 m. The three formations consist, from bottom to top, of (1) open-water marls of the Endrőd Formation, which is a hydrocarbon source rock with locally derived coarse clastics and (2) a confined and (3) an unconfined turbidite system (respectively, the Szolnok and the Algyő Formation). In the sandstones, detrital grains consist of quartz, feldspar, and mica, as well as sedimentary and metamorphic rock fragments. The quartz content is high in the upper, unconfined turbidite formation (Algyő), whereas feldspars and rock fragments are more widespread in the lower formations (Szolnok and Endrőd). Eogenetic minerals are framboidal pyrite, calcite, and clay minerals. Mesogenetic minerals are ankerite, ferroan calcite, albite, quartz, illite, chlorite, and solid bituminous organic matter. Eogenetic finely crystalline calcite yielded δ13CV−PDB values from 1.4 to 0.7‰ and δ18OV−PDB values from –6.0 to –7.4‰, respectively. Mesogenetic ferroan calcite yielded δ13CV−PDB values from 2.6 to –1.2‰ and δ18OV−PDB values from –8.3 to –14.0‰, respectively. In the upper part of the turbidite systems, remnants of the migrated organic matter are preserved along pressure dissolution surfaces. All these features indicate that compaction and mineral precipitations resulted in tightly cemented sandstones prior to hydrocarbon migration. Interconnected, secondary, open porosity is associated with pyrite, kaolinite/dickite, and postdates of the late-stage calcite cement. This indicates that dissolution processes took place in the deep burial realm in an extraformational fluid-dominated diagenetic system. The findings of this study add a unique insight to the previously proposed hydrological model of the Pannonian Basin and describe the complex interactions between the basinal deposits and the basement blocks

Late Miocene sedimentary record of the Danube / Kisalföld Basin: interregional correlation of depositional systems, stratigraphy and structural evolution

The Danube / Kisalföld Basin is the north-western sub-basin of the Pannonian Basin System. The lithostratigraphic subdivision of the several-km-thick Upper Miocene to Pliocene sedimentary succession related to Lake Pannon has been developed independently in Slovakia and Hungary. A study of the sedimentary formations across the entire basin led us to claim that these formations are identical or similar between the two basin parts to such an extent that their correlation is indeed a matter of nomenclature only. Nemčiňany corresponds to the Kálla Formation, representing locally derived coarse clastics along the basin margins (11– 9.5 Ma). The deep lacustrine sediments are collectively designated the Ivanka Formation in Slovakia, while in Hungary they are subdivided into Szák (fine-grained transgressive deposits above basement highs, 10.5 – 8.9 Ma), Endrőd (deep lacustrine marls, 11.6 –10 Ma), Szolnok (turbidites, 10.5 – 9.2 Ma) and Algyő Formations (fine-grained slope deposits, 10 – 9 Ma). The Beladice Formation represents shallow lacustrine deltaic deposits, fully corresponding to Újfalu (10.5 – 8.7 Ma). The overlying fluvial deposits are the Volkovce and Zagyva Formations (10 – 6 Ma). The synoptic description and characterization of these sediments offer a basin-wide insight into the development of the basin during the Late Miocene. The turbidite systems, the slope, the overlying deltaic and fluvial systems are all genetically related and are coeval at any time slice after the regression of Lake Pannon initiated about 10 Ma ago. All these formations get younger towards the S, SE as the progradation of the shelf-slope went on. The basin got filled up to lake level by 8.7 Ma, since then fluvial deposition dominated

A Vértes és előtereinek szerkezetfejlődése és annak kapcsolata a kainozoos üledékképződéssel és ősföldrajzzal = Structural evolution if the Vértes Hills including their forelands and the relationship with Cenozoic sedimentation and paleogeography

A Vértes kainozos szerkezetfejlődésében 6 fázis elemeit és azoknak az üledékképződéshez és felszínfejlődéshez való kapcsolatát vizsgáltuk. Az eocén üledékképződés (Ny)ÉNy-(K)DK-i összenyomás és merőleges húzás hatására ment végbe. Az enyhe gyűrődés következtében ÉK-DNy-i csapású hátak és medencék jöttek létre. Előbbieken karbonátos, utóbbiakban pelites rétegsorok rakódtak le. A karbonátos üledékképződés változó jellegű rámpákon ment végbe, melyek tükrözik a kismértékű deformációt, a karbonátproduktivitást és a globális vízszintesést. Az oligocénben a Móri-peremvető működött, ami nagy vastagságú összlet lerakódását tette lehetővé. A vértesi törmelékes sorozat képződése a kiscelli végén kezdődhetett. A kora-miocénben működő K-Ny-i jobbos és ÉNy-DK-i balos eltolódásokat ismertünk fel. A kora-, középső-miocén szin-rift fázis normálvetőihez a szarmatától társult szintektonikus üledékképződés. Az úgynevezett poszt-rift fázisban számos normálvető és eltolódás jött létre ill. reaktiválódott, melyek meghatározták a késő-pannon árkokat, transztenziós medencéket. A pliocéntől kitakaródó Vértesről hegylábfelszínek mentén pusztult le a miocén és paleogén fedőüledék. A negyedidőszaki vetők mozgása kibillentette a hegylábfelszíneket és módosította a vízrajzot, deformálta a kvarter üledékeket. A felszínalakulást erős szélerózió kísérte. | We investigated 6 Cenozoic deformation phase and their relationship to sedimentation, basin formation and landscape evolution. The Eocene sedimentation was controlled by (W)NW-SE compression and perpendicular tension. The gentle folding resulted in the formation of NE-trending ridges and basins. Shallow marine carbonate sedimentation occurred on ridges, while deeper basins were marked by pelitic successions. Carbonate sedimentation occurred on ramps with varying style, reflecting the gentle deformation, carbonate productivity and global eustatic sea level changes. The Oligocene activity of the Mór Fault permitted the deposition of a thick clastic succession, which started to form in the late Kiscellian. We recognized E-W striking dextral and NW-SE striking sinistral strike-slip faults of early Miocene age. The late Early to Middle Miocene syn-rift phase was associated with sedimentation only from the Sarmatian. The post-rift phase is marked by numerous normal and strike-slip faults, which controlled the evolution of late Miocene syn-sedimentary grabens and transtensional basins. The Miocene and Palaeogene sedimentary cover of the Vértes was eroded along pediment surfaces from the Pliocene onset of exhumation. The Quaternary slip of reactivated faults resulted in tilting of the pediment surfaces, sediment deformation and deflection of the drainage pattern. Landscape evolution was strongly influenced by wind erosion