Oleg Mandic

Oligocene-Miocene basin evolution in SE Anatolia, Turkey: constraints on the closure of the eastern Tethys gateway

Abstract The Oligocene–Miocene was a time characterized by major climate changes as well as changing plate configurations. The Middle Miocene Climate Transition (17 to 11 Ma) may even have been triggered by a plate tectonic event: the closure of the eastern Tethys gateway, the marine connection between the Mediterranean and Indian Ocean. To address this idea, we focus on the evolution of Oligocene and Miocene foreland basins in the southernmost part of Turkey, the most likely candidates to have formed this gateway. In addition, we take the geodynamic evolution of the Arabian–Eurasian collision into account. The Muş and Elazığ basins, located to the north of the Bitlis–Zagros suture zone, were most likely connected during the Oligocene. The deepening of both basins is biostratigraphically dated by us to occur during the Rupelian (Early Oligocene). Deep marine conditions (between 350 and 750 m) prevailed until the Chattian (Late Oligocene), when the basins shoaled rapidly to subtidal/intertidal environment in tropical to subtropical conditions, as indicated by the macrofossil assemblages. We conclude that the emergence of this basin during the Chattian severely restricted the marine connection between an eastern (Indian Ocean) and western (Mediterranean) marine domain. If a connection persisted it was likely located south of the Bitlis–Zagros suture zone. The Kahramanmaraş basin, located on the northern Arabian promontory south of the Bitlis–Zagros suture zone, was a foreland basin during the Middle and Late Miocene, possibly linked to the Hatay basin to the west and the Lice basin to the east. Our data indicates that this foreland basin experienced shallow marine conditions during the Langhian, followed by a rapid deepening during Langhian/Serravallian and prevailing deep marine conditions (between 350 and 750 m) until the early Tortonian. We have dated the youngest sediments underneath a subduction-related thrust at c. 11 Ma and suggest that this corresponds to the end of underthrusting in the Kahramanmaraş region, i.e. the end of subduction of Arabia. This age coincides in time with the onset of eastern Anatolian volcanism, uplift of the East Anatolian Accretionary Complex, and the onset of the North and East Anatolian Fault Zones accommodating westward escape tectonics of Anatolia. After c. 11 Ma, the foreland basin south of the Bitlis formed not (or no longer) a deep marine connection along the northern margin of Arabia between the Mediterranean Sea and the Indian Ocean. We finally conclude that a causal link between gateway closure and global climate change to a cooler mode, recorded in the Mi3b event (δ18O increase) dated at 13.82 Ma, cannot be supported.

The muddy bottom of Lake Pannon – a challenge for dreissenid settlement (Late Miocene; Bivalvia)

Abstract The Late Miocene dreissenids of Lake Pannon – a long existing eastern-central European lake – bear witness to two very different modes of life, which allowed these bivalves to successfully settle in what appears to be an inhospitable environment. One guild is restricted to the genera Mytilopsis Conrad, 1858 and Sinucongeria Lorenthey, 1894 . These representatives are extreme r-strategists which tend to produce temporal boom-and-bust populations during ‘time windows’ of improved ecological conditions. These opportunities are interpreted here to correlate with cyclic shifts in the epilimnion/hypolimnion relation and the corresponding oxygenation of bottom waters, events which are probably triggered by low-frequency orbital forcing. The second guild is composed solely of Congeria Partsch, 1836. The paradox of the proliferation of a single species, characterised by extreme size and weight, in a muddy, oxygen-deficient lake environment avoided by nearly all other molluscs points to a ‘hidden’ mechanism not accessible to other species. We tentatively link this mechanism with chemosymbiosis. Functional morphology in interplay with a highly sulphidic, over-saturated interstitial water support an interpretation of the large Congeria subglobosa as a successful ‘H2S pump’ model.

Influence of Size-sorting on Diversity Estimates from Tempestitic Shell Beds in the Middle Miocene of Austria

Abstract Paleontological data frequently are extracted from genetically and stratigraphically complex shell beds. It is therefore important to recognize taphonomic biases that can lead to major errors in paleoecological interpretations (e.g., on ancient local biodiversity). The strong influence of transport-related shell-size sorting on diversity estimates from single samples was studied in a transect of the middle Miocene Grund Formation (Lower Austria), which contains allochthonous, psammitic event beds with channel structures, sharp erosional bases, and graded bedding. These event beds are interpreted as proximal tempestites, and contain densely packed, polytaxic molluscan assemblages. The faunal composition and taphonomic features of shells indicate that transport occurred from wave- or current-agitated nearshore habitats into a pelitic, inner-shelf environment. The different skeletal concentrations contain a highly diverse molluscan fauna with 130 species identified from more than 4200 individuals. Although the quantitatively most-important species are the same in standardized samples from five different shell beds, species richness differs significantly among the three samples from the base of the transect and the two samples from its top. Diversity depends on size-sorting and therefore reflects the transport history of the individual tempestites, not the species richness of the original paleocommunity. Poorly sorted samples (indicating relatively minor transport) approximate the diversity of single samples of that environment better than well-sorted samples (which indicate stronger transport). Diversities of shelly assemblages from parautochthonous and allochthonous assemblages cannot be compared directly. Even comparisons among tempestites are problematic because transport intensity governs diversity. The intensity of any taphonomic process, however, is difficult to predict without detailed investigations. The use of samples from taphonomically complex shell beds for diversity comparisons can bias results, especially on the fine-scale level of local diversity patterns. Studies at such fine scales of resolution should consider the taphonomic framework of assemblages, which is necessary to recognize the dominant taphonomic factors and their intensities.

Revised Middle Miocene datum for initial marine flooding of North Croatian Basins (Pannonian Basin System, Central Paratethys)The Pannonian Basin System (PBS) originated during the Early Miocene as a result of extensional processes between the Alpine-Carp

The Pannonian Basin System (PBS) originated during the Early Miocene as a result of extensional processes between the Alpine-Carpathian and the Dinaride Orogenic Belts. The Paratethys Sea flooded the new basins successively during the Karpatian (late Burdigalian, Early Miocene) and the Early Badenian (middle Langhian, Middle Miocene). The North Croatian Basins (NCB) occupied the south-western margin of the PBS and the Central Paratethys Sea. Their initial marine flooding has until now been dated as Karpatian in age. The transgression into the NCB invaded a lacustrine environment therein, representing the northern prolongation of the vast Dinaride Lake System extending southwards as far as the Adriatic Plate. We reinvestigate two sections from opposite margins of the NBS - from Mt. Medvednica on the west and from Mt. Požeska on the east - including corresponding lowermost marine Miocene deposits to critically examine the Karpatian datum. Our new biostratigraphic data – integrating calcareous nannoplankton, planktic and benthic foraminifera, diatom and mollusk records – have substantially revised the previous interpretation. The presence of a calcareous nannoplankton assemblage of the NN5 Zone and the planktic and benthic foraminifera of the regional Lower Lagenidae Zone now place the transgression into the main Early Badenian transgressive pulse of the Central Paratethys. Consequently, the initial marine transgression correlates accurately with the middle part of the Early Badenian, which is more than 2 m.y. younger than the previously inferred datum and at least 1 m.y. younger than the lower boundary of the Badenian and the Middle Miocene, respectively. Finally, the basal lacustrine infill of the NCB, previously dated as Ottnangian (middle Burdigalian, Early Miocene) and continuously grading into marine deposits, has to be reconsidered as Early Badenian as well.

THE STRATIGRAPHIC AND SEDIMENTOLOGIC FRAMEWORK OF FINE-SCALE FAUNAL REPLACEMENTS IN THE MIDDLE MIOCENE OF THE VIENNA BASIN (AUSTRIA)

Abstract Fine-scale paleocommunity dynamics were studied in a short (∼16 m) section in the Middle Miocene (Badenian Stage) of the Central Paratethys, which consists of siliciclastic, pelitic, and sandy-to-gravely shallow-water deposits. Two basal, coarsening- and shallowing-upward parasequences of a late highstand systems tract are separated by a third-order sequence boundary from the deepening-upward basal part of a transgressive systems tract at the top of the section. Benthic faunas in this succession are primarily autochthonous and storm-influenced, level-bottom assemblages, but a distinct oyster-vermetid boundstone occurs near the base of the transgressive systems tract. Additionally, three tempestitic shell beds were included, which were found out of sequence in an associated basinal setting; their faunal content relates them closely to the fine-grained deepest parts of the transgressive systems tract. Ordination of species and samples using detrended correspondence analysis and analysis of similarity suggest that two basic benthic assemblages can be distinguished. The oyster-vermetid boundstone is tied to a unique set of environmental conditions and indicates a major environmental change at the sequence boundary. The faunal assemblage in the boundstone shows a weak gradient into the pelitic (deeper and quiet-water) level-bottom assemblage, which in turn is characterized by strong overlaps with the fauna of sandy (shallower and more agitated) habitats. Therefore it is concluded that the benthic assemblages in the studied section belong to the same basic metacommunity, which was not seriously affected by the strong facies changes at the sequence boundary and at the flooding surfaces. Moreover, the species in the studied benthic assemblages reacted to changes in the environment by habitat tracking.

Fossil evidence for chemoautotrophic bacterial symbiosis in the thyasirid bivalve thyasira michelottii from the middle Miocene (Badenium) of Austria

Many modern thyasirid bivalves are known to engage with chemoautotrophic bacteria in symbiosis, which can be inferred from the specialized feeding and digestive systems of these bivalves, as well as from stable carbon isotope ratios of their soft tissues. Fossil evidence for this life habit consists largely of facies criteria and bio‐geochemical markers. Further evidence for chemosymbiosis is found in the characteristic burrow‐systems of these bivalves, by which sulfide is obtained to sustain the symbiotic bacteria. These burrows were previously known only from observations made in aquaria. Such a burrow is described here for the first time in a fossil thyasirid bivalve. Thyasira michelottii (R. Hörnes, 1875) burrowed in sandy sediment in an anterior‐up position, approximately 5–10 cm below the surface, to which it was connected by an inhalant tube. It also produced a prominent posterio‐ventral tunnel, extending up to 300 mm into the sediment. Like modern thyasirids, this animal lacked an exhalant tube. By comparison with the ecology of modern thyasirid bivalves, we suppose that oxygen was obtained by active ventilation through the inhalant tube and that the prominent posterio‐ventral tunnel reflects search by the probing, vermiform foot for short‐lived pockets of sulfidic material in an otherwise low‐sulfide environment. The monospecific occurrence of Thyasira and the paleogeographic setting indicate dysaerobic, warm water conditions. A short distance to the coast and the occurrence of proximal tempestites suggest an inner shelf setting, prone to occasional disturbance by storms.

Pectinid coquinas and their palaeoenvironmental implications — examples from the early Miocene of northeastern Egypt

Abstract The Early Miocene (Burdigalian) section at Gebel Gharra (SW Suez, Egypt) represents a mixed carbonate/siliciclastic regime and is composed of a series of fining- and deepening-upward sequences. Mass occurrences of scutellid echinoids and pectinid bivalves are remarkable features within this section. Five pectinid horizons, occurring in two superpositioned fining-upward sequences, are qualitatively and quantitatively studied in detail. The taxonomic composition of respective pectinid accumulations clearly support a deepening-upward interpretation with decreasing pectinid diversity, decreasing convexity, shell thickness, and sculpturing. The taphonomic parameters of the pectinid beds, in combination with the study of co-occurring biota and frequency and density of shell encrustations and bioerosion, clearly point to different mechanisms for shell accumulations, namely as ‘composite concentrations’ and ‘reworked event-concentrations’.

Long-term ecosystem stability in an Early Miocene estuary

The question of ecosystem stability is central to ecology and paleoecology and is of particular importance for estuaries, which are environmentally highly variable, considered as geologically short lived, and among the most degraded modern ecosystems of our planet. Understanding their ecological dynamics over geological time scales requires paleontological data in a sequence stratigraphic framework, which allows evaluation of paleocommunity dynamics in an environmental context. A 445-m-thick estuarine succession in a satellite basin of the Vienna Basin (Austria) shows continuous sedimentation over 700 k.y. and can be divided into two transgressive systems tracts and a highstand systems tract. In contrast to expectations, no major physical disturbances of the ecosystem involving abrupt changes in diversity and biofacies composition occurred at fl surfaces and at the sequence boundary. Accommodation space remained remarkably constant over the depositional history of the basin, and all changes between depositional environments were therefore more or less gradational. Biotic change along the studied succession can be described as a gradual faunal replacement in response to habitat tracking, a process also reported for some normal marine shelf environments. Benthic assemblages in the estuarine succession were strongly dominated by a few taxa and developed along two indirect gradients, water depth and hydrodynamic energy. These gradients show subtle long-term trends, corresponding to the sequence stratigraphic architecture. Tectonics affected the sequence architecture in this particular marginal marine setting: it controlled accommodation space and sedimentary input, and provided stable boundary conditions over hundreds of thousands of years. Our study demonstrates for the fi rst time that estuaries, which are under great environmental pressure today, are resilient to natural environmental perturbations and can persist over geological time scales.

Late Eocene palaeogeography of the proto-Paratethys Sea in Central Asia (NW China, southern Kyrgyzstan and SW Tajikistan)

Abstract The Cretaceous and Palaeogene sediments of the basins in Central Asia include the remnants of the easternmost extent of a vast shallow epicontinental sea, which extended across the Eurasian continent before it retreated westwards and eventually isolated as the Paratethys Sea. To improve understanding of its long-term palaeogeographical evolution, we complement the well-constrained chronological framework of the Tarim Basin in China with stratigraphic records of the sea retreat from the Fergana Basin and the Alai Valley Basin in southern Kyrgyzstan and the Afghan–Tajik Basin in SW Tajikistan. By lithostratigraphic analyses and identification of bivalve assemblages, this study establishes for the first time a clear and detailed regional correlation of Palaeogene marine strata across Central Asia, showing that the basins share a similar palaeogeographical evolution characterized by a long-term stepwise retreat punctuated by short-term shallow-marine incursions. Our correlation shows that the last two marine incursions recognized in the Tarim Basin can be traced westwards. The permanent disappearance of the sea from Central Asia probably occurred with limited diachroneity in the late Eocene, before the isolation of the Paratethys Sea, shifting the easternmost margin of the sea hundreds of kilometres westwards and probably significantly reducing moisture supply to the Asian interior.

Late Pleistocene climate history of the Baranja loess plateau – evidence from the Zmajevac loess-paleosol section (northeastern Croatia)

The Zmajevac loess-palaeosol succession (LPS) of the northeastern Baranja loess plateau is exposed along the southern slope of Bansko Brdo, on the western bank of the Danube River. The investigated 17.5-m-thick section shows 4 palaeosol, 1 loess-like and 6 loess horizons. Their integrative palaeoenvironmental analysis combines quantified dana from the mollusc record, magnetic susceptibility, grain-size, calcimetry and mineral abundances to reconstruct the pattern of regional palaeoclimate evolution. This result combined with infrared optically stimulated luminescence age est CLEAL imates by GALOVIC et al. (2009) enabled correlation of the depositional units to Middle to the Late Pleistocene Marine Isotope Stages (MIS) 6 to 2. Magnetic susceptibility measurements show strong peaks in the palaeosol horizons pointing to increased concentrations of pedogenic ferrimagnetic minerals. Sedimentological and mineralogical parameters are in good agreement with other Pannonian Basin LPS. Terrestrial gastropod palaeoecology based on 1705 specimens of 13 species counted from loess and loess-like horizons documents cyclic transitions between cryophilous to cold resistant and mesophilous to thermophilous assemblage types. Whereas Helicopsis striata, Arianta arbustorum and Chondrula tridens are common throughout the succession, the typical loess representatives Pupilla sp., Vallonia tenuilabris and Columella columella are abundant only in certain horizons. Nevertheless, species tolerating open and dry habitats are abundant throughout the succession. The faunal spectra for the samples prove the dominance of transitional palaeoecological assemblage types, whereas uniformly defined types are rare. One of these, the Columella columella assemblage from the base of the section proved to be indicative of the Penultimate Glacial Maximum.