petrographic descriptions were estimated from thin sections. Radiometric age data were classified by the Geologic Time Scale of the ICS (2018/08) ( Cohen et al., 2013 , updated). K/Ar geochronology For the purpose of K/Ar age determination, the least
Variscan basement components of the central Tauern Window, Eastern Alps (Austria): constraints from new single zircon U-Pb geochronology. - Int. Journ. of Earth Sciences, accepted for publication.
Fast neutron irradiation of potassium-bearing minerals produces artificial39Ar. Mass spectrometric measurement of the39Ar/40Ar ratio allows to calculate a geological age. Stepwise degassing of the sample yields insight into its history. As an example, analysis of a single hornblende from the Valtellina (Italian Alps) reveals an unexpected pre-Alpine history of that region.
The results of seven
Ar analyses and two K/Ar analyses of mineral
separates of metamorphic rocks from the Transdanubian part (west of the Danube
River) of the Tisza Mega-Unit is presented, and a review of the
geochronological data available in the literature is given. Investigated rocks
come from boreholes and include amphibolite facies rocks, mainly containing
garnet, staurolite, kyanite, andalusite and sillimanite as index minerals. The
investigated area covers 120 × 85 km in Transdanubia, including all tectonic
units distinguished by previous authors. The
spectra of the muscovites yielded fairly well-established plateau ages ranging
from 307 Ma-312 Ma in all units. Similar muscovite Ar/Ar cooling ages of ca 310
Ma were obtained from other parts of Tisza Mega-unit east of the Danube, e.g.
from the kyanite-sillimanite-bearing metapelites of the Villány-Bihar Subunit
(Great Plain; Lelkes-Felvári et al. 2003).
Sediment cores were collected at the Cananeia-Iguape Estuary and thelevels of 210Pb, 226Ra and 137Cs were measuredby gamma-ray spectrometry. The total 210Pb levels in sedimentsvaried from 13.5 to 122.5 Bq . kg —1 , for 226Raranged from 2.4 to 28 Bq . kg —1 and for 137Csfrom 0.28 to 6.1 Bq . kg —1 . Sedimentation rates were calculatedfrom the slope of the excess 210Pb profile in the core. The valuesobtained varied from 5 to 10 mm . y—1 , depending on thesediment deposition inputs in the local of sampling.
Instrumental analysis methods for 210Pb, 226Raand 137Cs by gamma-spectrometry in sediments, as well as the sedimentationrates in cores collected from Brazilian coastal region are presented. Samplinglocations have covered the Cananeia-Iguape estuary and the continental shelfof southern Sao Paulo State. Values for 210Pb ranged from 122.5to 14.3 Bq . kg —1 for estuarine sediments and from 195.5to 23.6 Bq . kg –1 at the continental shelf. For 226Ra thevalues obtained in sediments varied from 15.2 to 2.3 Bq . kg —1 in the estuary and from 30.1 to 16.1 Bq . kg —1 atthe continental shelf. Sedimentation rates are variable, ranging from 0.53to 0.98 cm . y —1 in estuary sediments and from 0.18 to 0.40cm . y —1 at the continental shelf.
A sediment core was taken to determine if sediment accumulation rates could be conducted using 240+239Pu signatures in the coastal mangrove mudflats of southeastern Brazil. The results from this study show that 240+239Pu fallout activities are sufficient and well preserved in the coastal sediments of this region. Sediment accumulation rates
determined from the 240+239Pu signatures were 4.4 mm/year and 4.1 from 210Pb (CIC) method. A sediment mixing coefficient rate was calculated using chlorophyll-a profile (9.5 cm2).
Berggren, W. A., D. V. Kent, C. C. Swisher III, M.-P. Aubry 1995: A revised Cenozoic geochronology and chronostratigraphy. - In: W. Berggren A., D.V Kent, M.-P. Aubry, J. Hardenbol (Eds): Geochronology, time
L air , G. J. , Z ehetner , F. , H rachowitz , M. , F ranz , N. , M aringer , F.-J. & G erzabek , M. H. , 2009 . Dating of soil layers in a young floodplain using iron oxide crystal-llinity . Quaternary Geochronology . 4 . 260 – 266