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K/Ar geochronology of igneous amphibole phenocrysts in Miocene to Pliocene volcaniclastics, Styrian Basin, Austria

Bojar H. P., Bojar A. V., Hałas S., Wójtowicz A.

Geological Quarterly

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2013

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Vol. 57, No. 3

405–-416

EN

We present fifteen new K/Ar ages on amphibole phenocrysts of Neogene volcaniclastic rocks from the Styrian Basin, Austria. The westernmost sub-basin of the Pannonian Basin is the Styrian Basin, which hosts a large number of phreatomagmatic tuff occurrences beside Middle Miocene shield volcanoes and Pliocene effusive alkaline volcanic rocks. The investigated tuffs contain the well-known mantle xenoliths and frequent amphibole and pyroxene phenocrysts. The new K/Ar ages indicate that the Late Miocene phreatomagmatic volcanism started in Pontian (7.51 Ma) and ended in Romanian (2.73 Ma) times. The complete interval of the youngest volcanism in the Styrian Basin covers 5.8 Ma, similar to the volcanism of the western part of the Pannonian Basin and the Nógrád/Novohrad area (West Carpathians). The dated volcanic occurrences display NNW–SSE oriented arrays which are approximately parallel to the Auersbach basinal high zone. The new data indicate that the Late Miocene to Pliocene volcanism of the Styrian Basin is synchronous with the onset of a regional compressional event and eastward tilting of the Styrian basin fill.

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Middle Miocene zeolite-bearing turbidites, Abrămuţ Basin (Pannonian Basin), NW Romania

Bojar A. V., Barbu V., Bojar H. P.

Geological Quarterly

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2012

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Vol. 56, No 2

261-268

EN

Detailed lithostratigraphic data from a borehole in the Abrămuţ Basin, located in the northwestern part of Romania, has revealed the presence of turbiditic deposits containing several layers with tuff/tuffaceous materials in the lower Badenian. The age of these deposits is determined by the presence of the foraminifera Praeorbulina glomerosa and Orbulina suturalis. Detailed quantitative and qualitative X-ray diffraction data (XRD) on 10 different tuff layers situated at depths between 2450 and 2640 m show a mineralogical association comprising analcime, quartz, volcanic glass, smectite, mica, calcite, K-feldspar, glass and minor quantity of chlorite and albite. The presence of analcime suggests that the albite isograd for the interval studied has been never reached and the maximum temperatures have been lower than c. 125degrees C since the early Badenian.

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Stable isotopic and mineralogical investigations of an arid Quaternary lacustrine palaeoenvironment, Western Qaidam, China

Bojar A. V., Rieser A., Neubauer F., Bojar H. P., Genser J., Liu Y., Ge X. H.

Geological Quarterly

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2005

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Vol. 49, No. 2

173-184

EN

Stable isotope analyses on carbonates from lake evaporites collected from the non-marine western Qaidam basin yield a positive excursion from Pliocene to Quaternary times. At Dafeng Shan, the Quaternary sequences are composed of alternating layers of celestine/dolomite and aragonite/calcite/barite with distinct isotopic compositions. The sequence described at Dafeng Shan formed in a low energy, hypersaline lacustrine environment as indicated by the microstructures and evaporitic minerals as well as by the absence of lithoclasts. The peloids, ooids and oncoids described are related to microbialactivities in saline lake. The oxygen isotopic composition of the carbonates vary between +34.4 and +39.8‰ (SMOW), representing the heaviest values measured until now. The δ18 O and the δ34 S isotopic composition of the celestine range between 20.1 to 22.3‰ (SMOW) and +19 to +22‰ (CDT) respectively, suggesting sulfur recycling via sulfide oxidation. The carbon isotopic compositions of the carbonates show a large negative excursion of up to -30‰. The microstructures, mineralogy and isotopic compositions as well as the geological context suggest oxidation of methane from a deep source.

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Palaeoenvironmental interpretation of dinosaur- and mammal-bearing continental Maastrichtian deposits, Hateg basin, Romania

Bojar A. V., Grigorescu D., Ottner F., Csiki Z.

Geological Quarterly

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2005

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Vol. 49, No. 2

205--222

EN

The Hateg basin, South Carpathians, Romania, contains a thick sequence of Maastrichtian continental deposits from which a rich dinosaur and mammal fauna is known. Field data as well as mineralogical and stable isotope analyses from three representative profiles were integrated in order to reconstruct environmental conditions during Maastrichtian time. Tustea quarry is characterized by the presence of well drained calcisols, with smectite (montmorillonite) as the main clay component. Along the profile, the δ18 O and δ13 C isotopic compositions of calcretes show a small variation, of up to 0.9‰. The profile along the Barbat Valley shows preponderantly calcisols, the main clay mineral being smectite, with subordinate illite and chlorite. The oxygen isotopic compositions of calcretes are ~0.5‰ lighter than those from Tustea. The soils are interpreted as having formed under more humid conditions and they are similar to those situated at the bottom of the sequence developed along Sibisel Valley. The abundant smectite from the Tustea and Barbat Valley depos its, as well the presence of good developed soils, reflects palaeoenvironmental conditions predominantly controlled by climate. Preliminary magnetostratigraphic data along the Sibisel Valley section indicate that sedimentation started at the end of chron C32n. All other palaeomagnetic sites distributed up stream, as far as the upper limit of this formation, have only reversed polarity and the corresponding time interval is probably chron C31r. Along this valley, the sequence shows a general coarsening upward trend. The palaeosol type changes from calcisol- to vertisol-dominated sequences. The soils are moderate to weakly developed. The mineralogical composition of the clay fraction also changes, from smectite- to illite and chlorite-dominated. These features points to wards unstable tectonic conditions and higher uplift rates of the surrounding area within chron C31r. To wards the top of the sequence, the oxygen and carbon isotopic composition of calcretes be come 1 and ~2‰ lighter, respectively. These changes indicate a transition from generally semi-arid to wards more humid and possible cooler conditions and correlate with the world wide trend for chron 31r.

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Lateglacial-Middle Holocene stable isotope records in two coeval stalagmites from the Bihor Mountains, NW Romania

Tamaş T., Onac B. P., Bojar A. V.

Geological Quarterly

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2005

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Vol. 49, No. 2

185-194

EN

Oxygen and carbon stable isotope records of two stalagmites from NW Romania provide a continuous climatic record between 14.8 and 5.6 ka BP. The chronology is established by 21 TIMS uranium series ages. Uncertain ties in the isotope chronology range between ±20 and ±100 yr. The δ18 O values are positively correlated with temperature, whereas δ13 C fluctuations suggest changes in soil CO2 production. Lateglacial deposition of both stalagmites started at ~14.8 ka BP. The delta 18 O records subsequently show a slow decline in temperatures until 12.6 ka BP. Three warmer periods with increased soil productivity occurred at 14.5-13.9 ka BP, 13.6-13.2 ka BP, and 12.9-12.6 ka BP. Lower delta 18 O and high δ13 C values between 12.6 and 11.4 (11.7) ka BP in dicate a cold and dry climate during the Younger Dryas (GS-1). During the Early Holocene, three short cold intervals are marked on the δ 18 O profiles at 11.0-10.6, 10.5-10.2 and 9.4-9.1 ka BP. For the remainder of the Holocene sequence, the δ18 O records show less variation between 9 and 7.8 ka BP and gradual warming from 7.6-5.6 ka BP. The speleothem records correlate with the Green land ice core records and with other proxies through out Europe and the North Atlantic region.