Orsolya Sztanó

Tertiary Subsurface Facies, Source Rocks and Hydrocarbon Reservoirs in the SW Part of the Pannonian Basin (Northern Croatia and South-Western Hungary)

The Neogene sedimentary successions of the Drava, Sava and Slavonija–Srijem depressions in the SW part of the Pannonian Basin Systemare built up of three 2nd order megacycles separated by four majorerosional unconformities. The first megacycle contains terrestrial tomarine syn-rift and early post-rift sediments of Early to Mid-Mioceneage. The second is built up of Late Miocene Lake Pannon deposits,while the third contains those sediments which were deposited inthe remnants of Lake Pannon and in the subsequent fluvial systems,in areas of continuous subsidence associated with basin inversionfrom the Pliocene onwards. Most of the petroleum source rocks andreservoir rocks are of Miocene age and were formed during the firstand second depositional megacycle. Conditions for the accumulationand preservation of large quantities of marine and terrigenousorganic matter were most favourable during the Badenian, Sarmatianand Early Pannonian, in deep basin settings, partly associated withrifting. The generation of hydrocarbons was promoted by relativelyhigh geothermal gradients during the initial and subsequent thermalsubsidence. Various sedimentary environments produced depositswith good reservoir characteristics: e.g. fault-related talus breccia(mainly Lower Miocene), reefs (mainly Badenian), coastal, shallowmarine (Karpatian, Badenian) and deltaic (Pannonian–Pontian) sandbodies or turbiditic sand lobes (mainly Pannonian). The hydrocarbon(HC) migration paths were often provided by the major unconformitiesbounding the three megacycles, as well as by faults, particularlyaround the basement highs.

Preferred Clast Orientation in Volcaniclastic Mass-Flow Deposits: Application of a New Photo-Statistical Method

A photo-statistical method has been developed to quantify the strength of directional clast fabric in various types of volcaniclastic mass-flow deposits. Fabric strength (R) is defined as the resultant vec- tor length of clast alignment computed from clast angles visible on a vertical outcrop face. R can be obtained from photographs of an ex- posure via image analysis and statistical assessment with regard to clast number and direction of exposure face vs. paleoflow. Relative to tra- ditional, manual field measurements, the photo-statistical method gives reproducible quantitative results that are independent of subjective clast selection. On average, one hundred and fifty clasts are the mini- mum number necessary to obtain reliable R values. For determining the strength of directional fabric, it is more accurate to measure ran- domly collected clasts than only the most elongated ones (normally the practice during manual measurements), because more elongated clasts display a stronger fabric. Clast size generally does not influence clast alignment. R values obtained from lower or upper portions of vertical exposure faces may show significant differences if pronounced imbri- cation is developed in the lower part of the beds passing upward to purely bed-parallel clast alignment. Bimodality caused by the coexis- tence of imbricated and bed-parallel clasts tends to reduce R values. The studied examples include (1) near-vent breccias, (2) block-and- ash flow deposits, and (3) mostly cohesive volcaniclastic debris-flow deposits from 49 selected exposures (24 in Hungary, 6 in France, 4 in Japan, 3 in New Zealand, 2 in Indonesia, and 1 in the U.S.A., Argen- tina, Chile, Turkey, and Romania, each). Near-vent breccias show a relatively weak fabric (R

Palaeogeographic significance of tidal deposits: an example from an early Miocene Paratethys embayment, Northern Hungary

Abstract Tide-influenced deposits can be used in palaeogeographic reconstructions because they are good indicators of open marine connections. An example is presented from the Eggenburgian (late Aquitanian-early Burdigalian) of the North Hungarian Bay. This bay was part of an inland sea, the Paratethys. Tide-influenced deposits prove that tidal motions in the North Hungarian Bay were locally amplified. This required a free propagation of tidal waves from the open ocean through the Paratethys into this embayment. Since all seaways towards the Mediterranean were closed during the early Eggenburgian, the only connection between the North Hungarian Bay and open marine waters, which allowed the transmission of tidal waves was the outlet towards the East Slovakian Basin in the northeast. The presence of tide-influenced deposits in the North Hungarian Bay implies that tidal waves entered the Eastern Paratethys from the east through a wide passage. Other examples of Lower Miocene tide-influenced deposits in the Mediterranean and Paratethian regions are reported from different periods. In these cases amplification of tidal motions in various embayments and straits also occurred because of the local basin morphology. It is demonstrated that significant palaeogeographic changes during the Early Miocene resulted in changes of current pathways and related shifts of loci of tide-influenced deposition.

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

Abstract 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.

Turbidites as indicators of paleotopography, Upper Miocene Lake Pannon, Western Mecsek Mountains (Hungary)

Abstract 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.

Upper Oligocene marine fishes from nearshore deposits of the Central Paratethys (Máriahalom, Hungary)

A rich and diverse ichthyofauna is described from the upper Oligocene (Egerian) sands of Máriahalom, Hungary. The site is dominated by brackish molluscs that are preserved together with rare marine and terrestrial vertebrates. Based on the isolated elasmobranch and bony fish remains, eight sharks, four rays and seven teleost taxa were identified from Máriahalom. The ichthyofauna represents a nearshore marine subtropical community dominated by odontaspidid and carcharhinid sharks and by euryhaline durophagous sparids and by sciaenid teleost fishes. Epibenthic feeders were common, whereas piscivorous taxa included barracudas, billfishes and numerous sharks, including the macropredatory Otodus angustidens. Palaeontological, sedimentological and stratigraphical data indicates a tide-influenced and fluvial-influenced nearshore palaeoenvironment with brackish lagoons and normal marine littoral habitats. The remains of terrestrial, brackish and nearshore marine invertebrates and vertebrates accumulated in a tidal channel. The systematics of the ichthyofauna is consistent with the palaeogeography inferred from invertebrates, i.e. a Central Paratethys connected to the Mediterranean area during the Egerian.

Palaeobiology, palaeoecology and stratigraphic significance of the Late Miocene cockle Lymnocardium soproniense from Lake Pannon

Abstract Stratigraphic subdivision of the Upper Miocene deposits in the Pannonian Basin has been traditionally based on the endemic mollusc species of Lake Pannon. The cockle species Lymnocardium soproniense Vitális, apparently evolving through a sympatric speciation event in the sublittoral zone of Lake Pannon about 10.2-10.3 Ma, attained wide geographical distribution in the Pannonian basin and thus may serve as a good stratigraphic marker. Lymnocardium soproniense was one of the few large-sized cockles in Lake Pannon, most closely related to its ancestor, L. schedelianum (Fuchs), and to another descendant of the latter, L. variocostatum Vitális. According to the δ18O stable isotope record of its shells, the large size of L. soproniense was coupled with an extended life time of more than 10 years, probably reflecting a stable lake environment with increased resource availability and decreased predation. The species lived in quiet offshore conditions, below the storm wave base, where clay was deposited from suspension and the influence of currents was negligible. The base of the Lymnocardium soproniense Zone in the sublittoral deposits of Lake Pannon is defined by the first occurrence of the species, whereas the top of the zone is marked with the base of the overlying Congeria praerhomboidea Zone, defined by the FAD of C. praerhomboidea.

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.

Slope-toe Turbidite Systems Related to Aggradational - Progradational Sequences: Potential Stratigraphic Traps in the Makó Trough, Pannonian Basin, Hungary

Though the Mako Trough is best known as the location of major unconventional gas accumulations, the thick Neogene to Quaternary sedimentary successions may contain conventional HC resources as well. Structurally controlled traps are widespread on the neighbouring basement highs and not likely to occur in the basin interior. However, stratigraphic traps, untested so far, were identified in relation to the basin-filling progradational slope system. The style and pace of slope advancing are the key to understand sand delivery to and formation of potential reservoirs in the deep parts of the basin.

Tectonic Evolution and Burial History of the Makó trough, Hungary: Implications for the Exploration of Juvenile Unconventional Petroleum Systems in the Pannonian Basin

The Mako trough in Hungary is a sedimentary depression formed in the extensional Pannonian basin during the last 15-20 Ma. It represents a young HT/HP system with >6 km thick basin fill and has been recognized as the location of major unconventional hydrocarbon resources. Such accumulations are regarded as “unconventional” when economic production is only possible by means of some sort of stimulation technique, usually hydraulic fracturing. Hydrocarbons in this setting do not accumulate conventionally in structural or stratigraphic traps, but in pervasive cells. Due to the geological setting of the Mako trough, the hydrocarbon cell forms a relatively continuous zone marked by considerable internal lithological and petrophysical variability. Due to its novelty and complexity, the exploration of this unconventional resource demands the concurrent application of a wide range of geological and geophysical methods. Evaluation of such petroleum systems strongly rely on the reconstruction of the tectonosedimentary evolution of the host basin, the understanding of the subsidence, burial, thermal and maturation history, and the timing and mechanism of hydrocarbon generation and related abnormal pressure development. In this contribution, highlights are on the latest models for basin evolution and petroleum system development are presented.