Mathias Harzhauser

Circum-Mediterranean Oligo–Miocene biogeographic evolution – the gastropods’ point of view

Based on studies in Iran (Qom Basin, Esfahan^Sirjan Basin, Zagros Mountains), in Turkey (Mut and Sivas basins), in the Mesohellenic Basin, and in northeastern Egypt, a new palaeobiogeographic concept for the Oligocene and Miocene in the circum-Mediterranean area with special emphasis on the distribution patterns of gastropod faunas is presented.A very strict biogeographic terminology is proposed to avoid the common fusion of geographic, faunistic and geodynamic terms in the palaeontologists’ jargon.Our main interest focuses on the affinities and the faunistic interactions between the early ‘Mediterranean’ and the early ‘Indo-Pacific’ regions during the Oligo^Miocene. Especially the role of the early Indo-Pacific faunas as the mythic centre of origination of Early Neogene European mollusc faunas, as often vaguely indicated in the literature, is critically evaluated.This leads to the establishment of a Mediterranean^Iranian Province and a Western Indian^Eastern African Province as palaeobiogeographic subunits of the Western Tethys Region during the Oligocene.Due to major geodynamic and related biogeographic changes in the Early Miocene the Western Tethys Region no longer existed and was replaced by the Proto-Mediterranean^Atlantic Region.For the area of the Paratethys the palaeobiogeographic unit Danubian Province, which includes the ProtoCaspian Subprovince, is proposed.Furthermore, the underrated transatlantic communication of the Oligo^Miocene nearshore mollusc faunas is demonstrated.Altogether this paper is a contribution to the discussion on the biogeographic concepts, classification and nomenclature in palaeontology as initiated by Westermann [Palaeogeogr.Palaeoclimatol.Palaeobiogeogr.158 (2000) 1^13; 163 (2000) 49^68]. @ 2002 Elsevier Science B. V.All rights reserved.

Sarmatian (Late Middle Miocene) gastropod assemblages of the Central Paratethys

SummaryA rather diverse gastropod fauna from Sarmatian deposits of the Austrian/Hungarian Eisenstadt-Sopron Basin was studied. The fauna derives from two layers of clay and silt within a siliciclastic section at St. Margarethen in Burgenland (Austria). These layers are interpreted as littoral mudflats which formed during the Sarmatian (Late Middle Miocene) along the western coast of the Central Paratethys. Strong shifts in the composition of the gastropod fauna, dominated by Potamididae (Cenogastropoda: Cerithioidea), within each layer indicate successions of limnic-fluvial to oligohaline, brackish-littoral, and marine-littoral environments. These shifts in facies are reflected by an alternational of thePotamides hartbergensis assemblage,Granulolabium bicinctum assemblage, and thePotamides disjunctus assemblage.The speciesJujubinus turriculus (Eichwald, 1850),Gibbula buchi (Dubois, 1831), andCylichnina elongata (Eichwald, 1830) are reported for the first time from the Sarmatian of the Paratethys.Mitrella agenta nov. sp. (Neogastropoda: Columbellidae) is introduced as a new species. These species might represent relics of the diverse Badenian fauna but could also prove a minor ingression of marine species from an adjacent bioprovince in the Late SarmatianMactra “Zone”.

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.

Palaeoenvironmental reconstructions by stable isotopes of Middle Miocene gastropods of the Central Paratethys

The stable isotopes of carbon and oxygen were used to provide information of mixing of marine and freshwater and subsequently used to determine palaeosalinities. In the Middle to Late Miocene St. Margarethen bZollhausQ section (Upper Sarmatian bMactra ZoneQ/Pannonian), a succession of three gastropod assemblages indicates changing environmental conditions from a limnic-fluviatile to littoral mudflat and a sublittoral marine environment. Several shells of the main representatives of the three assemblages [Potamides hartbergensis (Hilber), Granulolabium bicinctum (Brocchi), Potamides disjunctus (Sowerby)], and additionally shells of Lymnaea sp., a typical freshwater gastropod, and Pomatias conicus, a terrestrial gastropod, were taken for stable isotope analyses. Oxygen and carbon isotope data of the freshwater endmember are distinctively lower (dO~ 4.5x/dC~ 9x) than of the marine endmembers (dO~ 2.2x/dC~2.3x). In contrast to the expected intermediate isotopic composition between the freshwater and marine environment, the shells of supposed brackish environments have higher dO values than the shells of the marine environment. These higher dO values are explained by evaporation, which affected the protected areas of riverine to lacustrine environments and small pools on mudflats, formerly considered to be the habitats of the brackish assemblages. Thus, the oxygen and carbon isotope data extend the already existing palaeoenvironmental information. D 2004 Elsevier B.V. All rights reserved.

Early and Middle Miocene dinoflagellate cyst stratigraphy of the Central Paratethys, Central Europe

Marine organic-walled dinoflagellate cysts have been studied from the Early and Middle Miocene of the Central Paratethys in Austria (Vienna and eastern Alpine Foreland basins) and Hungary (Pannonian Basin), and compared with assemblages of similar age from the Atlantic Ocean and Mediterranean Sea. The presence of a diverse flora of 71 taxa, including such biostratigraphical markers as Apteodinium spiridoides, Cerebrocysta poulsenii, Cordosphaeridium cantharellus, Cribroperidinium tenuitabulatum, Exochosphaeridium insigne, Glaphyrocysta reticulosa s.l., Habibacysta tectata, Labyrinthodinium truncatum subsp. truncatum, Palaeocystodinium miocaenicum, and Unipontidinium aquaeductus, has allowed the establishment of five biozones that characterize the Ottnangian, Badenian and Sarmatian local stages (collectively equivalent to the mid-Burdigalian, upper Langhian and Serravallian stages). This is the first study to demonstrate the applicability of dinoflagellate cysts for detailed stratigraphic correlation and palaeoenvironmental interpretation in the Early and Middle Miocene of the Central Paratethys area.

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.

Integrated high-resolution stratigraphy of a Middle to Late Miocene sedimentary sequence in the central part of the Vienna Basin

Integrated high-resolution stratigraphy of a Middle to Late Miocene sedimentary sequence in the central part of the Vienna Basin In order to determine the relative contributions of tectonics and eustasy to the sedimentary infill of the Vienna Basin a high-resolution stratigraphic record of a Middle to Late Miocene sedimentary sequence was established for a well (Spannberg-21) in the central part of the Vienna Basin. The well is located on an intrabasinal high, the Spannberg Ridge, a location that is relatively protected from local depocentre shifts. Downhole magnetostratigraphic measurements and biostratigraphical analysis form the basis for the chronostratigraphic framework. Temporal gaps in the sedimentary sequence were quantified from seismic data, well correlations and high-resolution electrical borehole images. Stratigraphic control with this integrated approach was good in the Sarmatian and Pannonian, but difficult in the Badenian. The resulting sedimentation rates show an increase towards the Upper Sarmatian from 0.43 m/kyr to > 1.2 m/kyr, followed by a decrease to relatively constant values around 0.3 m/kyr in the Pannonian. The sequence reflects the creation of accommodation space during the pull-apart phase of the basin and the subsequent slowing of the tectonic activity. The retreat of the Paratethys from the North Alpine Foreland Basin during the Early Sarmatian temporarily increased the influx of coarsergrained sediment, but eventually the basin acted mostly as a by-pass zone of sediment towards the Pannonian Basin. At a finer scale, the sequence exhibits correlations with global eustasy indicators, notably during the Sarmatian, the time of greatest basin subsidence and full connectivity with the Paratethyan system. In the Pannonian the eustatic signals become weaker due to an increased isolation of the Vienna Basin from Lake Pannon.