Styrian Basin Research Articles

Volcaniclastic events in coral reef and seagrass environments: evidence for disturbance and recovery (Middle Miocene, Styrian Basin, Austria)

Volcanic disturbances and ecosystem recovery at sites of neritic carbonate production are rarely documented, neither in the recent nor past geological record. Herein, we present a Middle Miocene (ca 14.5 Ma) shallow-marine carbonate record from the Styrian Basin (Austria) that shows recurrent breakdowns of the carbonate producers (i.e., coralline red algae and zooxanthellate corals) in response to ashfalls from nearby volcanic island sources. These volcanic events are preserved as distinct marl layers with idiomorphic biotite crystals and volcaniclasts that mantle the former seafloor topography. The pyroclastic sediments suffocated the carbonate producers in coral reef and seagrass environments. A subsequent turbid, eutrophic phase caused by the redistribution, suspension, and dissolution of volcaniclastics is characterized by the spreading of suspension-feeding biota, coralline algae, and the larger benthic foraminifer Planostegina. During this stage, rapidly consolidated pyroclastic deposits acted as hard grounds for attached-living bivalves. The fact that the facies below and above the studied ashbeds are almost identical suggests that volcaniclastic events had no long-lasting effects on the structure of the carbonate-producing benthic communities. Although Miocene shallow-water carbonate systems of the circum-Mediterranean region are well known and situated in one of the geodynamically most active regions worldwide, this study is the first that exams the impact of volcanic sedimentation events on shallow marine ecosystems.

The cricetid rodents from Gratkorn (Austria, Styria): a benchmark locality for the continental Sarmatian sensu stricto (late Middle Miocene) in the Central Paratethys

The cricetid rodents from Gratkorn (Austria, Styria): a benchmark locality for the continental Sarmatiansensu stricto(late Middle Miocene) in the Central ParatethysThe recent discovery of a terrestrial vertebrate assemblage in the clay pit St. Stefan at Gratkorn (Austria, Styrian Basin) is of major importance for our understanding of the evolution of late Middle Miocene mammal assemblages in the Paratethys realm. The cricetid rodent assemblage includes four species:Megacricetodon minutusDaxner, 1967,Democricetodonsp. nov. (sensuKälin & Engesser 2001),Eumyarionsp., and "Cricetodon" fandlisp. nov. The latter species belongs to the "Cricetodon" fandli-C. klariankaeHír, 2007 lineage, which allows for a long-distance correlation with other late Middle Miocene/earliest Late Miocene European localities. The biostratigraphic conclusions drawn from the study of the fossils from Gratkorn concurs with the age estimates based on regional geology, paleomagnetic measurements, and the gastropod-based biostratigraphy at the base of the Late Sarmatians. str.(late Serravallian, latest Volhynian), around 12-12.2 Ma (Chron C5An.1n) ago.

Eruptive and sedimentary evolution of the Pliocene Grad Volcanic Field, North-east Slovenia

Middle to Upper Pliocene (~ 3 Ma) Grad Volcanic Field (SW Pannonian basin system) encompasses an area of about 3 km 2, of which some 1.7 km 2 belong to the outcropping volcanics. Pyroclastic and syn-eruptively reworked volcaniclastic deposits are the most widespread in occurrence. Remains of an autobrecciated lava flow, a residual neck and their peperites are partially reworked by a large debris flow. Volcanic activity occurred in a continental depositional environment dominated by alluvial fan and braided river systems. Streams draining from the north-west to the south-east were infilling a rapidly subsiding Radgona Depression. The style of volcanic activity was mainly explosive and was reinforced by hydrovolcanic processes. Three volcanic centres probably existed, and they migrated spatially and temporally from the north to the south over a distance of some 5.6 km. The rocks of the northernmost volcanic centre are fairly eroded and contain abundant, up to 10 cm sized lherzolite xenoliths. The largest crater developed about 2.5 km to the south. From an early maar stage, a tuff-cone, and subsequently, a tuff-ring evolved. The crater was filled with eroded pyroclastic material and stream load. A new vent became active some 500 m to the south. Initial stage was mainly magmatic and produced pyroclastic flow and fall deposits. Late-stage eruptions were predominantly hydrovolcanic (phreatomagmatic and phreatic), and built up a small tuff-cone having some 300 m in diameter. Trachybasaltic and subordinate basanitic magmas erupting in the Grad Volcanic Field are geochemically distinguishable from the neighbouring occurrences in the South Styrian Basin and the South Burgenland Swell. Relatively lower abundance of TiO 2, MgO, Sc, V and Cu, and higher abundance of MnO, P 2O 5, Zn, Sr, Zr, Hf, Nb, Ba, Ta and U indicate somewhat different source and/or evolutionary pattern.

A giant termite from the Late Miocene of Styria, Austria (Isoptera)

A giant termite is described and figured from the Late Miocene of the Styrian Basin in southeastern Austria. Gyatermes styriensis gen. n. et sp. n. is represented by a relatively complete forewing, with basal scale. The fossil approximates in size the largest of all termites today and is the largest fossil termite on record. The presence of this species in the Late Miocene fauna of Europe indicates that climatic conditions were appropriate for the persistence of species and colonies requiring relatively stable, warm conditions. The genus is primitive in overall features but shares some similarity with the dampwood termites.

Miocene emplacement and rapid cooling of the Pohorje pluton at the Alpine-Pannonian-Dinaridic junction, Slovenia

New laser ablation-inductive coupled plasma-mass spectrometry U-Pb analyses on oscillatory-zoned zircon imply Early Miocene crystallization (18.64±0.11 Ma) of the Pohorje pluton at the southeastern margin of the Eastern Alps (northern Slovenia). Inherited zircon cores indicate two crustal sources: a late Variscan magmatic population (∼270–290 Ma), and an early Neoproterozoic one (850–900 Ma) with juvenile Hf isotope composition close to that of depleted mantle. Initial ∈Hf of Miocene zircon points to an additional, more juvenile source component of the Miocene magma, which could be either a juvenile Phanerozoic crust or the Miocene mantle. The new U-Pb isotope age of the Pohorje pluton seriously questions its attribution to the Oligocene age ‘Periadriatic” intrusions. The new data imply a temporal coincidence with 19–15 Ma magmatism in the Pannonian Basin system, more specifically in the Styrian Basin. K-Ar mineral- and whole rock ages from the pluton itself and cogenetic shallow intrusive dacitic rocks (∼18–16 Ma), as well as zircon fission track data (17.7–15.6 Ma) gave late Early to early Middle Miocene ages, indicating rapid cooling of the pluton within about 3 Million years. Medium-grade Austroalpine metamorphics north and south of the pluton were reheated and subsequently cooled together. Outcrop-and micro scale structures record deformation of the Pohorje pluton and few related mafic and dacitic dykes under greenschist facies conditions. Part of the solidstate fabrics indicate E-W oriented stretching and vertical thinning, while steeply dipping foliation and NW-SE trending lineation are also present. The E-W oriented lineation is parallel to the direction of subsequent brittle extension, which resulted in normal faulting and tilting of the earlier ductile fabric at around the Early/Middle Miocene boundary; normal faulting was combined with strike-slip faulting. Renewed N-S compression may be related to late Miocene to Quaternary dextral faulting in the area. The documented syn-cooling extensional structures and part of the strike-slip faults can be interpreted as being related to lateral extrusion of the Eastern Alps and/or to back-arc rifting in the Pannonian Basin.

Fault slip analysis in the Koralm Massif (Eastern Alps) and consequences for the final uplift of “cold spots” in Miocene times

The Paleogene and Neogene evolution of Austroalpine basement units east of the Tauern Window is characterised by the formation of two major sets of faults: (1) ESE–WNW- to E–W-trending faults, associated with ENE- and NNW-trending conjugate structures and (2) N–S to NNE-SSW striking structures, mainly acting as high-angle normal faults, often associated with E-dipping low-angle normal faults along the western margin of the Styrian Basin.Together with the stratigraphic evolution of the Styrian and Lavanttal Basins and the related subsidence histories a tectonic evolution may be reconstructed for this part of the Eastern Alps. In the southern part of the Koralm Massif, WNW-trending fractures were activated as dextral strike-slip faults, associated with the evolution of WNW-trending troughs filled up with coarse block debris. W- to WNW-trending fractures were reactivated as normal faults, indicating N–S extension. It is assumed that these phases resulted in subsidence and block debris sedimentation in Karpatian and Badenian times (ca. 17–13 Ma).In the Western Styrian Basin no Sarmatian (13–11.5 Ma) sediments are observed; Pannonian (11.5 to 7.1 Ma) sediments are restricted to the Eastern Styrian Basin. This indicates, that the Koralm basement and the Western Styrian Basin were affected by post-Sarmatian uplift, coinciding with a re-activation of N-trending normal faults along the eastern margin of the Koralm Massif. Therefore, we suggest that the final uplift of the Koralm Complex, partly together with the Western Styrian Basin, occurred during the early Pannonian (at approximately 10 Ma). The elevation of clastic deposits indicates that the Koralm Complex was elevated by approximately 800 m during this phase, associated with an additional phase of E–W-directed extension accommodated by N–S striking normal faults.

Environmental changes and diversification ofCyprideis in the Late Miocene of the Styrian Basin (Lake Pannon, Austria)

The turnover from the Sarmatian Paratethys Sea into Lake Pannon around 11.6 Ma seriously impacted aquatic biota like ostracods and triggered their adaptation to the changed environments. One survivor of this ecological switch is certainly the genusCyprideis, which is well known for its radiation in Lake Pannon. A high-resolution micropalaeontological investigation of a transgressive-regressive sedimentary cycle just above the Middle/Late Miocene boundary focused on the taxonomy of the foundCyprideis species. Species-diagnostic characters were evaluated applying qualitative as well as lineal and geometric morphometric analyses. These examinations led to the introduction of two new ostracod species (Cyprideis kapfensteinensisGross n. sp. andCyprideis mataschensisGross n. sp.), which diverge only indistinctly in outline, but are undoubtedly separated by their size and hinge structure along with considerable differences in number of posteroventral spines. We conclude that these co-occurring species were two sympatric species, which were probably adapted to different microhabitats.C. kapfensteinensis is only recognised in the interval at the peak of the transgression, which corresponds to the maximum deepening of the lake in this area and with meso-/polyhaline conditions. In contrast,C. mataschensis seems to be a more euryplastic species because it appears well before this event and is also recorded in the regressive prodelta sediments up section.

A limnic ostracod fauna from the surroundings of the Central Paratethys (Late Middle Miocene/Early Late Miocene; Styrian Basin; Austria)

Aquatic biota of the marine Middle Miocene Paratethys and the Late Miocene Pannonian Lake, a long-lived lake in Central and Eastern Europe, are well known. However, knowledge of the marginal freshwater environments is still rather poor. Recently, a thin-shelled ostracod fauna was discovered in Late Sarmatian to Early Pannonian sediments of a clay pit at the northern margin of the Styrian Basin (St. Stefan, N Graz). 11 taxa are described taxonomically of which some are left in open nomenclature due to insufficient preservation: Vestalenula cylindrica (Straub, 1952), Paracandona cf. euplectella (Robertson, 1889), Candona ( Camptocypria) gratkornensis n. sp., Candona (?) sp., cf. Candonopsis arida Sieber (1905), ? Cypria sp., Cyclocypris nitida Sieber (1905), cf. Bradleystrandesia reticulata (Zaddach, 1844), Stenocypris sp., ? Cypridopsis sp., “Striate ostracod sp.”. The ostracod associations point to a shallow, sometimes richly vegetated, limnic environment. Indications of a “warm”, maybe subtropical climate are suggested by the occurrences of Vestalenula, cf. Candonopsis, ? Cypridopsis and Stenocypris. The ostracod fauna indicates a freshwater environment, detached from the marine Sarmatian Sea and respectively from the brackish Pannonian Lake and provides hereby an insight into the palaeohabitats of the surrounding wetlands.

Isotopic evidence for the origin of an acid sulphate alteration, Styrian basin, Austria

AbstractThe Gossendorf volcanic body is the only one in the Styrian basin that shows extensive hydrothermal alteration. K‐Ar dating of primary volcanic biotite and alteration products (alunite) suggests that the emplacement of the volcanic body and hydrothermal alteration took place synchronously, 15 Ma ago. The stable isotope compositions of the alteration products such as opal, barite, pyrite and alunite combined with crystallographia investigations indicate temperatures between 150 and 200 °C for the formation of the alteration zones. The calculated stable isotopic compositions of the parent fluid, responsible for the alteration, show an exogene marine component, which interacted with the host rock. Sulphur isotopic compositions of sulphur, sulphides and sulphates indicate disequilibrium, and progressive oxidation. This fact, combined with the mineral zonation of the alteration zone, reflects not only change in the pH but also change in the fO2 of the ascending fluids.

A late Burdigalian gobiid fish,Gobius brevis (Agassiz, 1839), in the Upper Hydrobia Beds in the middle Upper Rhine Graben (W-Germany)

Gobius brevis (Agassiz, 1839) was hitherto exclusively based on articulated skeletons. It first appears in the late Early Miocene (late Burdigalian, Karpatian) and is widespread throughout the Middle Miocene. Its previously known zoogeographical distribution was the western Paratethys and the Styrian Basin in Austria. We here report on articulated skeletons ofG. brevis with otoliths in situ from a temporary outcrop at Edenkoben, located in the middle Upper Rhine Graben, Germany. The strata are assigned to the basal part of the Upper Hydrobia Beds. The otoliths in situ are identical with those ofGobius latiformis Reichenbacher, 1992, which is an otolith-based species occurring in the Karpatian and Middle Miocene of the western Paratethys; henceG. latiformis has to be regarded as a younger synonym ofG. brevis (Agassiz, 1839). The skeletons ofG. brevis from Edenkoben differ from other articulated freshwater or brackish water MioceneGobius species in the number of vertebrae, more elongate body shape, and number of fin rays. Also the otoliths ofG. brevis differ in their overall shape from these species. However, the in situ preserved otoliths ofG. brevis in the Edenkoben locality show a more primitive evolutionary stage than the Middle Miocene otoliths ofG. brevis (formerly described asG. latiformis). Thus, the gobiid fishes from Edenkoben belong to the oldest representatives ofG. brevis and must be late Burdigalian in age.Gobius brevis probably migrated into the middle Upper Rhine Graben from the Paratethys area.

Slab melt and intraplate metasomatism in Kapfenstein mantle xenoliths (Styrian Basin, Austria)

Anhydrous and amphibole-bearing mantle peridotite xenoliths from Kapfenstein (Styrian Basin) have been studied with the aim of understanding both the processes responsible for amphibole formation and the nature of metasomatizing agents which affected this portion of lithosphere. This area of the Pannonian Basin underwent a subduction event which was followed after about 15 Ma, by alkaline intraplate magmatism. Primary clinopyroxene (cpx1) in four-phase lherzolite xenoliths is characterized by LREE-depleted to slightly LREE-enriched patterns. LREE-depleted cpx1 have low Th and U contents and Zr (and Hf) anomalies varying from slightly negative to positive. LREE-enriched cpx have high Th and U contents and remarkable positive anomalies of Zr and Hf. Primary clinopyroxenes in amphibole-bearing lherzolites present a comparable compositional variation from LREE (and Th, U, Zr, Hf)-depleted type to LREE (and Th, U, Zr, Hf)-enriched type. LREE-depleted cpx1, with strong negative Zr and Ti anomalies, are also recognized in the peridotite matrix of a composite sample cut by a large amphibole vein. Textural and geochemical evidence indicates that amphibole disseminated within the matrix grew at the expense of primary spinel and clinopyroxene, mimicking the trace element patterns of the latter. As a consequence, the geochemical features of amphibole vary in relation to those of clinopyroxene, from enriched to depleted. On the other hand, the composition of vein amphibole in the composite xenolith compares well with amphibole megacrysts and microphenocrysts, suggesting that it represents a fractionation product of alkaline melt that passed through the lithosphere. Two kinds of metasomatism, superimposed on a slightly depleted lithospheric mantle, were identified. A slab-derived melt (proto-adakite?) metasomatic agent was responsible for the first enrichment in Th, U, Zr and Hf observed in clinopyroxene, whereas an alkaline within-plate metasomatic agent caused the formation of the Nb (and Ta)- rich disseminated amphibole. The final process was the alkaline magmatism, which was responsible for the formation of the large amphibole vein and megacrysts. It is proposed that the Nb-poor and Nb-rich amphiboles record the transition between the suprasubduction slab melt-related and the intraplate alkaline metasomatism. These geochemical features are consistent with a lithospheric portion enriched in slab melt components which was subsequently metasomatized by alkaline melt. Alternatively an asthenospheric uprising could have scavenged a previously slab melt-enriched region of the lithosphere.

Estimation of environmental paleogradient values based on presence/absence data: a case study using benthic foraminifera for paleodepth estimation

A two-step procedure for estimating paleogradient values based on the presence/absence of variates (e.g., species, chemical elements, and traits) is presented. The first step requires information about the general (basic) distributions of variates along the gradient. Using species as variates, fundamental ecological niches corresponding to the gradient represent these general distributions. The second step involves a transfer equation, which is the arithmetic mean of location parameters of variates weighted by their dispersion parameters. This procedure strengthens variates with narrow dispersions, yielding more information about the location at the gradient than variates with wide dispersion. The method proposed here does not require information about frequencies; solely the presence of variates is sufficient. Objective criteria are used to eliminate non-overlapping variates along the gradient (e.g., species whose distributions do not overlap in living individuals but are mixed in samples of empty tests). This is important in estimating paleogradients because mixing of non-overlapping variates is a common effect due to post-mortem transport, bioturbation, or sediment reworking. The new method is calibrated for depth estimation using living symbiont-bearing benthic foraminifera and empty tests from the NW Pacific, and living smaller benthic foraminifera from the shelf and continental slope of Senegal. This approach is then successfully applied for paleodepth estimation of a lower to middle Miocene transect in the Styrian Basin (Austria), where plankton/benthos ratios of foraminifera yield poor depth estimations.

Composition and evolution of lithosphere beneath the Carpathian–Pannonian Region: a review

Our knowledge of the lithosphere beneath the Carpathian–Pannonian Region (CPR) has been greatly improved through petrologic, geochemical and isotopic studies of upper mantle xenoliths hosted by Neogene–Quaternary alkali basalts. These basalts occur at the edge of the Intra-Carpathian Basin System (Styrian Basin, Nógrád-Gömör and Eastern Transylvanian Basin) and its central portion (Little Hungarian Plain, Bakony-Balaton Highland). The xenoliths are mostly spinel lherzolites, accompanied by subordinate pyroxenites, websterites, wehrlites, harzburgites and dunites. The peridotites represent residual mantle material showing textural and geochemical evidence for a complex history of melting and recrystallization, irrespective of location within the region. The lithospheric mantle is more deformed in the center of the studied area than towards the edges. The deformation may be attributed to a combination of extension and asthenospheric upwelling in the late Tertiary, which strongly affected the central part of CPR subcontinental lithosphere. The peridotite xenoliths studied show bulk compositions in the following range: 35–48 wt.% MgO, 0.5–4.0 wt.% CaO and 0.2–4.5 wt.% Al 2O 3 with no significant differences in regard to their geographical location. On the other hand, mineral compositions, particularly of clinopyroxene, vary according to xenolith texture. Clinopyroxenes from less deformed xenoliths show higher contents of ‘basaltic’ major elements compared to the more deformed xenoliths. However, clinopyroxenes in more deformed xenoliths are relatively enriched in strongly incompatible trace elements such as light rare earth elements (LREE). Modal metasomatic products occur as both hydrous phases, including pargasitic and kearsutitic amphiboles and minor phlogopitic micas, and anhydrous phases — mostly clinopyroxene and orthopyroxene. Vein material is dominated by the two latter phases but may also include amphibole. Amphibole mostly occurs as interstitial phases, however, and is more common than phlogopite. Most metasomatized peridotites show chemical and (sometimes) textural evidence for re-equilibration between metasomatic and non-metasomatic phases. However, amphiboles in pyroxenites are sometimes enriched in K, Fe and LREE. The presence of partially crystallized melt pockets (related to amphiboles and clinopyroxenes) in both peridotites and pyroxenites is an indication of decompression melting and, rarely, incipient partial melting triggered by migrating hydrous melts or fluids. Metasomatic contaminants may be ascribed to contemporaneous subduction beneath the Carpathian–Pannonian Region between the Eocene and Miocene. Sulfide inclusions are more abundant in protogranular and porphyroclastic xenoliths relative to equigranular types. In mantle lithologies, sulfide bleb compositions vary between pentlandite and pyrrhotite correlating with the chemistry and texture of the host xenoliths. While sulfides in peridotites are relatively rich in Ni, those in clinopyroxene-rich xenoliths are notably Fe-rich.

Integrated stratigraphy of the Sarmatian (Upper Middle Miocene) in the western Central Paratethys

The Vienna Basin and the Styrian Basin have been cornerstones for the definition and description of the Central Euro-pean Sarmatian Stage. New inter-and intrabasin correlations of well-logs and surface outcrops reveal a rather uniform development of depositional systems in all considered basins, which excludes local autocyclic processes as the sole trigger. The lithostratigraphy of these basins is critically summarized and the Wolfsthal Member is introduced as a new lithostratigraphic unit. The more than 1000-m-thick Sarmatian basin-fill is recorded in geophysical logs by a characteristic succession of serrated funnel-to bell-shaped curves separated by shale-line intervals. The correlative floodings are well preserved in marginal settings and accessible in surface outcrops. Slight falls of the relative sea-level are also reflected in the littoral zone by erosive surfaces, caliche formation and progradation of fluvial facies. The stratigraphic position and duration of the Sarmatian suggests a relation to the 3 rd order cycle TB. 2.6. Internally, two 4 th order cycles are depicted. An exact correlation with Mediterranean standard stages and the "Haq-cycles" is difficult due to the endemic marine fauna that flourished in the nearly land-locked Paratethys Sea during the Sarmatian. This obstacle may be overcome by a first cautious calibration of the sedimentary sequence with astronomical target curves. Hence, the 400-Ka eccentricity component might have triggered the 4 th order cycles, with the maximum flooding surfaces coinciding with the maxima of that band. An overall trend from a pelitic-siliciclastic Lower Sarmatian 4th order cycle towards an oolitic Upper Sarmatian 4 th order cycle could be forced by the inflection of the 2.35-Ma component. The tentative calibration requires a new positioning of the Badenian/Sarmatian boundary close to 12.7 Ma, which would fit excellently to the glacio-eustatic isotope event MSI-3. The coincidence of the final retreat of the sea from the Molasse Basin with a major phase of progradation of alluvial fans into the Styrian and the Vienna Basins suggests a pulse of uplift in the eastern Alpine region at 12.1-12.3 Ma.

Middle Miocene seasonal temperature changes in the Styrian basin, Austria, as recorded by the isotopic composition of pectinid and brachiopod shells

Using the isotope record on pectinid and brachiopod shells, we reconstructed Middle Miocene palaeotemperatures for a shelf environment in the Styrian basin, Austria. Bivalve shells of Macrochlamys sp., collected from different horizons of the Lower Badenian Leitha limestone, show δ 18O values in the range of −3 to 0‰ (PeeDee Belemnite). The large intrashell variability of 3‰ indicates significant seawater temperature fluctuation. The results suggest that despite the high geographical latitude (ca. 40°N), the climate in southern Austria was warm (subtropical) with a pronounced seasonality at that time. In contrast, the δ 18O isotopic composition of a pectinid ( Flabellipecten sp.) and an indeterminate terebratulid brachiopod, from the siliciclastic deposits overlying the Leitha limestone, ranges between 0 and −1‰. This indicates cooler mean annual temperatures and reduced seasonal variations. A 39Ar/ 40Ar age on fresh volcanic biotites shows a value of 14.2±0.1 Ma. The tuffs containing the biotites are located below the layer containing the terebratulid and the Flabellipecten sp. The stable isotope and radiogenic data suggest that the drop in temperature is in direct relationship with the East Antarctic Ice Sheet expansion, which started at ca. 14 Ma. Due to the variation in temperature, the subtropical fauna in the Retznei quarry disappeared during the Early Miocene and the biogenic limestones were replaced by clastic sediments. The δ 18O isotopic profiles from three pectinids collected from the Leitha limestone indicate that these grew within ca. 1.5 years. Growth interruptions occurred during the warm season because during this period the pectinids very likely used their energy for the growth and maturation of gonads. Carbon isotopic compositions vary between 0 and 2‰. Statistical tests show that for some of the analyzed shells, the cyclicity of the δ 13C profiles may be explained by the temperature-dependent fractionation between air CO 2 and dissolved bicarbonate.

Basin-scale paleobiogeography and paleoecology: an example from Karpatian (Latest Burdigalian) benthic and planktonic foraminifera and calcareous nannofossils from the Central Paratethys

We present the paleobiogeography and ecology of benthic and planktonic foraminifera and calcareous nannoplankton during the Karpatian (Latest Burdigalian) in the Austrian part of the Central Paratethys. Results are based on quantitative data of assemblages from the Molasse and Styrian Basins. Our data suggest that, although adjacent, the two basins underwent different paleoceanographic evolution during the Karpatian. Dysoxic bottom waters characterized the Molasse Basin, together with reducing environments, which produced the formation of pyritized levels. In the Styrian Basin, intense volcanic activity enriched surface waters in nutrient and produced strong primary productivity. Reduced planktonic foraminiferal abundance and dominance of agglutinated benthic forms in the Styrian Basin can be attributed to paleoceanographic conditions. The planktonic-depleted assemblages bias the paleodepth estimation by 100P(P + B) in the Styrian Basin and new tools for assessing paleodepth are needed. This study shows that paleobiogeography of foraminifera and calcareous nannoplankton is strictly related to local ecological conditions in enclosed basins and demonstrates that quantitative ecological studies are the best way to monitor the biogeographic evolution of enclosed basins.

Parameters determining the carbon isotopic composition of coal and fossil wood in the Early Miocene Oberdorf lignite seam (Styrian Basin, Austria)

Petrographical and geochemical data of gelified and ungelified fossil wood from the Early Miocene Oberdorf lignite seam (Styrian Basin, Austria) provide evidence that the early diagenetic, aerobic degradation of wood by fungi may be followed by further decomposition under reducing conditions by the activity of anaerobic bacteria. Based on the molecular compositions of terpenoid hydrocarbons, the wood fragments in the lignite are identified as gymnosperms. This result is corroborated by the mean isotopic composition ( δ 13C=-24.2‰) of the macrofossils. The isotopic difference between fossil wood and extracted cellulose of most samples (3.9–2.5‰) is higher than in modern trees, which can be explained by the smaller effect of 13C discrimination during decomposition of cellulose when compared with wood. The mean carbon isotope values found for gymnosperms and coals (−24.2‰ and –24.7‰, respectively) confirm the results from biomarker analyses indicating that the peat-forming vegetation of the Oberdorf seam was dominated by gymnosperm taxa. Minor variation in the relative contributions of gymnosperms and angiosperms to coal deposition is of negligible influence on the isotopic composition of the coals. Cross-correlations between δ 13C of the coals, soluble organic matter yield, and the proportions of liptinite macerals of higher-plant origin imply that the carbon isotopic composition may be affected by the contents of plant lipids because of their δ 13C values ranging from 5 to 10‰ less than whole-plant tissue values. An isotopic shift of the coals towards more negative values due to the activity of prokaryotes (i.e. anaerobic bacteria) in organic matter degradation is proposed. The results obtained from the Early Miocene Oberdorf lignite indicate that the carbon isotope ratios of the coals are primarily affected by varying contributions of different parts of whole-plant tissue, due to their different isotopic and molecular compositions (e.g. epicuticular leaf waxes, resins, wood) and their different decay-resistance against the early diagenetic changes involved in organic matter decomposition. Carbon cycling during anoxic decomposition of plant-derived organic matter is assumed to affect the δ 13C values of coal. δ 13C values of wood and extracted cellulose are affected only to a minor extent.

Organic geochemistry of the Lower Miocene Oberdorf lignite (Styrian Basin, Austria): its relation to petrography, palynology and the palaeoenvironment

In the Oberdorf trough at the northwestern margin of the Styrian Basin (Austria), an up to 36-m thick Lower Miocene (Ottnangian) lignite seam occurs within the fluvial Köflach–Voitsberg Formation. Previous results indicate that the lignite originated in a topogenous mire within a wet-forest swamp palaeoenvironment. Differences in soluble organic matter (SOM) yield of borehole samples from the lignite seam are related to free lipids present in plant waxes or resins and the presence of thermally labile polymers indicated by the contents of liptinite macerals (i.e., resinite, suberinite, and liptodetrinite). The n-alkane distribution patterns are dominated by high-molecular weight lipids with marked odd over even predominance, originating from plant waxes. A contribution of algae to the even numbered short-chain lipids, observed in considerable amounts in the footwall sediments is proposed. Terpenoid biomarkers characteristic for conifers and angiosperms were detected, consistent with palynomorphic spectra which are dominated by forest swamp pollen (Taxodiaceae–Cupressaceae) and pollen from plants living in a mixed mesophytic forest. Excellent relationships between higher plant biomarker composition and palynologic data indicate that the organic geochemical results reflect the varying inputs of coniferales vs. angiosperms. The data further imply that cuparene may be used for taxonomical differentiation of coniferales families. Organic geochemical data provide evidence that the content of land plant-derived biomarkers is controlled by the input of resin-rich conifers. Concentrations of hopanoids, dominated by hop-17(21)-ene, generally increase towards the top of the lignite, a section characterised by high extents of aromatisation of triterpenoid biomarkers. The results suggest that the aromatisation of angiosperm-derived biomarkers may be governed by the activity of anaerobic rather than by aerobic bacteria. However, changes in the depositional environment and palynologic facies during peat formation probably influenced the origin and fate of angiosperm-derived triterpenoids. The results indicate how biomarker composition may contribute to the evaluation of environmental changes. Cross-correlations of organic geochemical parameters with palynological data and petrography-based facies indicators will provide further insights in the peat-forming vegetation and biogeochemical activities in the mire.

Syn- and post-collisional heat flow in the Cenozoic Eastern Alps

The heat flow evolution of a continental collisional zone is exemplified by the Eastern Alps. Heat flow maps for the syn-collision (Oligocene), syn-extrusion (Early/Middle Miocene), and post-extrusion (Late Miocene, Recent) stages are presented, and are discussed in relation to the orogenic evolution. Continental collision during Paleogene time was characterized by extremely low heat flow ( 150 mW/m2) a few hundred kilometers south of it. The former was a result of crustal thickening and of thermal blanketing due to rapid sedimentation and nappe stacking. The latter was caused by slab break-off and magmatic activity. The Early/Middle Miocene syn-extrusion stage was characterized by rapid exhumation of metamorphic core complexes (Tauern and Rechnitz Windows), and by magmatic activity (Styrian Basin). Both mechanisms caused extremely high heat flow (>200 mW/m2). In contrast, the orogenetic front remained cold. Thereafter, magmatic activity ended and uplift rates decreased. Thus, Late Miocene heat flow is characterized by low to moderately high values. Heat flow values >75 mW/m2 were restricted to the transition zone of the Pannonian Basin characterized by thinned crust, and to the Tauern Window area. Recent temperature data indicate a subtle post-Miocene increase in heat flow.

Thermal history of Tertiary basins in Slovenia (Alpine–Dinaride–Pannonian junction)

The transition zone between the Alps, the Dinarides, and the Pannonian Basin was affected by syn-collisional magmatism in Oligocene time and post-collisional lateral escape followed by extreme extension in early and middle Miocene times. Numeric heat flow models for sixteen sites and 650 vitrinite reflectance data from Paleogene and Neogene sediments were used to evaluate temporal and lateral heat flow variations related to these events.Oligocene. Oligocene (Smrekovec) volcanism is the main heat source for Paleogene sediments south of the Periadriatic Lineament. Vitrinite reflectance patterns suggest dextral displacement along the Donat Fault of the order of 50km. Coalification of Paleogene coal-bearing sequences south of the Pohorje is a result of the emplacement of the Oligocene Pohorje tonalite.Early/middle Miocene. Extremely elevated early/middle Miocene heat flow (>200mW/m2) occurred in the Styrian Basin, the Pohorje area, the Maribor–Radgona area, and along the Boč Anticline. It is partly a consequence of magmatic activity. However, no igneous rocks are known from the Maribor–Radgona area. A large shallow early Miocene pluton could explain the observed Miocene heat flow. Rapid uplift of hot basement rocks in the Pohorje/Kozjak region may have increased surface heat flow. Neither volcanic rocks nor metamorphic core complexes are known from the Boč area. The Ormož–Selnica Anticline was probably influenced by a middle Miocene heating event (∼150mW/m2). Coeval volcanism south of the anticline represents a potential heat source.Post-middle Miocene. The WSW–ENE-trending Ljutomer and Radgona Depressions are characterized by moderate Neogene heat flow (60–75mW/m2), whereas late Miocene to present-day heat flow in the Ormož–Selnica Anticline is 80–90mW/m2. A recent heat flow anomaly occurs in the Šomat-Benedikt area.