The Gerecse Hills, which represent the northwesternmost part of the Mesozoic-Palaeogene Transdanubian Range, are surrounded by an Upper Miocene -Pliocene (Pannonian) lacustrine to fluvial sedimentary cover to the west and to the north: namely, towards the Danube -Kisalföld Basin of Slovakia and Hungary. The oldest reports on fossil molluscs from these sediments were published almost 150 years ago. A systematic mapping of the area by geologists of the Geological and Geophysical Institute of Hungary during the last decades revealed a number of natural and artificial outcrops of fossiliferous Lake Pannon sediments. The present study is based on the molluscs collected from these outcrops, and the sedimentological description and interpretation of the embedding sequences.The Upper Miocene deposits near the Gerecse Hills comprise one transgressive-regressive cycle. In the brickyard claypits of Tata, located in the western foreland of the Gerecse Hills, the transgressive limb is represented by the Szák Formation. This formation starts with a thin transgressive lag and consists of homogeneous, bioturbated, bluish-grey clay and argillaceous marl, deposited from suspension in quiet offshore conditions. Characteristic mollusc species include large dreissenids (Congeria czjzeki, C. partschi, C. ungulacaprae), a wide variety of cockles (Lymnocardium tegulatum, L. triangulatocostatum, L. majeri, L. apertum, L. aff. brunnense, L. aff. rogenhoferi, "Pontalmyra" otiophora, Paradacna sp.), and deep-water-adapted pulmonate snails (Valenciennius reussi, Radix kobelti, Gyraulus sp.). This fauna lived in a nutrient-rich and well-oxygenated deep sublittoral environment, at a water depth of several tens of metres.Probably the same transgressive event is reflected in the Vályus-kút outcrop (Tardos), in the central part of the hills at 375 m above sea level, where a small patch of Lake Pannon sediments escaped subsequent erosion. In this sequence, lignite-bearing black clay and variegated clays with freshwater and terrestrial molluscs (Theodoxus radmanesti, Melanopsis sturi sturi, M. sturi tortispina, Planorbidae sp., Unionidae sp., Valvata oecsensis, V. obtusaeformis, Oxychilus procellarius) are overlain by clay and silt with Congeria czjzeki, Lymnocardium majeri, and other brackish species. This superposition indicates flooding of paludal areas, deepening, and the development of an intense connection with the sublittoral offshore environment of Lake Pannon.A third -and highly atypical -type of lower contact of Pannonian sediments was discovered in one of the northern valleys of the Gerecse Hills (Iván-halála Valley, Dunaszentmiklós). A poorly-sorted conglomerate consisting of cobbleand boulder-sized clasts with a sandy-clayey matrix overlies directly a Cretaceous sandstone. Imbrication of the clasts indicates a N to S transport direction i.e. from the open lake towards the dry land. The matrix contains abundant mollusc fauna, including articulated valves of Congeria aff. simulans turgida, Dreissenomya (Sinucongeria) arcuata, Pa...

The Neogene Transylvanian Basin (TB), enclosed between the eastern and southern Carpathians and the Apuseni Mountains in Romania, is a significant natural gas province with a long production history. In order to improve the (bio) stratigraphic resolution, correlations and dating in the several 100-m-thick upper Miocene (Pannonian) succession of the basin, the largest and most fossiliferous outcrop at Guşteriţa (northeastern part of Sibiu) was investigated and set as a reference section for the Congeria banatica zone in the entire TB. Grey, laminated and massive silty marl, deposited in the deep-water environment of Lake Pannon, was exposed in the ~55-m-high outcrop. The uppermost 25 m of the section was sampled in high resolution (sampling per metres) for macro- and microfossils, including palynology; for authigenic 10Be/9Be dating and for magnetostratigraphy; in addition, macrofossils and samples for authigenic 10Be/9Be isotopic measurements were collected from the lower part of the section as well. The studied sedimentary record belongs to the profundal C. banatica mollusc assemblage zone. The upper 25 m can be correlated to the Hemicytheria tenuistriata and Propontoniella candeo ostracod biozones, the uppermost part of the Spiniferites oblongus, the entire Pontiadinium pecsvaradense and the lowermost part of the Spiniferites hennersdorfensis organic-walled microplankton zones. All samples contained endemic Pannonian calcareous nannofossils, representing the Noelaerhabdus bozinovicae zone. Nine samples were analysed for authigenic 10Be/9Be isotopic measurements. The calculated age data of six samples provided a weighted mean value of 10.42 ± 0.39 Ma. However, three samples within the section exhibited higher isotopic ratios and yielded younger apparent ages. A nearly twofold change in the initial 10Be/9Be ratio is a possible reason for the higher measured isotopic ratios of these samples. Magnetostratigraphic samples showed normal polarity for the entire upper part of the outcrop and can be correlated with the C5n.2n polarity chron (11.056–9.984 Ma, ATNTS2012), which is in agreement with the biostratigraphic data. Based on these newly obtained data and correlation of the biozones with other parts of the Pannonian Basin System, the Guşteriţa section represents the ~ 11.0–10.5 Ma interval, and it is a key section for correlation of mollusc, ostracod, dinoflagellate and calcareous nannoplankton biostratigraphic records within this time interval.

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Sedimentary successions exposed at basin margins as a result of late-stage inversion, uplift and erosion usually represent only a limited portion of the entire basin fill; thus, they are highly incomplete records of basin evolution. Small satellite basins, however, might have the potential of recording more complete histories. The late Miocene sedimentary history of the Șimleu Basin, a north-eastern satellite of the vast Pannonian Basin, was investigated through the study of large outcrops and correlative well-logs. A full transgressive–regressive cycle is reconstructed, which formed within a ca. 1 million-year time frame (10.6–9.6 Ma). The transgressive phase is represented by coarse-grained deltas overlain by deep-water lacustrine marls. Onset of the regressive phase is indicated by sandy turbidite lobes and channels, followed by slope shales, and topped by stacked deltaic lobes and fluvial deposits. The deep- to shallow-water sedimentary facies are similar to those deposited in the central, deep part of the Pannonian Basin. The Șimleu Basin is thus a close and almost complete outcrop analogue of the Pannonian Basin’s lacustrine sedimentary record known mainly from subsurface data, such as well-logs, cores and seismic sections from the basin interior. This study demonstrates that deposits of small satellite basins may reflect the whole sequence of processes that shaped the major basin, although at a smaller spatial and temporal scale.