40Ar/39Ar dating of Miocene tuffs from the Styrian part of the Pannonian Basin: An attempt to refine the basin stratigraphy (original) (raw)
In this study we present new 40 Ar/ 39 Ar age data obtained from volcaniclastic material intercalated within shallow-marine to neritic sediments of the Styrian part of the Miocene Paratethyan Sea, which allow a better control of the sedimentation. At Retznei quarry, a volcaniclastic layer has been deposited in erosional patches above a consolidated rhodolite limestone ("Leitha Limestone") of the siliciclastic/marine Badenian Weissenegg Formation. Ar-release plots of a biotite bulk-grain concentrate (30 grains) and a concentrate of three sanidine crystals (0.5-1 mm) display fairly flat release-patterns with minor fluctuation in the low-energy gas-release steps. From the statistical point of view the biotite concentrate yielded a high-precision plateau age of 14.21 ± 0.07 Ma, the three sanidine crystals yielded a plateau age of 14.39 ± 0.12 Ma. The radiometric ages obtained match the biostratigraphic record (Upper Lagenide Zone). A drill-core recovered from the well Hörmsdorf, exposes several sand-dominated horizons and two layers of crystal tuff, of the Karpatian Eibiswald Formation. Ar-analyses of one single biotite grain (> 1 mm) from the hanging-wall, another biotite single-grain from the lower tuff both display slightly disturbed Ar-release spectra. However Ar-plateau ages of 15.08 ± 0.09 Ma and 15.22 ± 0.17 Ma, respectively, have been obtained. Volcaniclastic rocks from Pöls are intercalated within the Florian Formation, for which previous authors suggested a Early Badenian age (16.4-ca. 15 Ma according to . A concentrate of two clear sanidine crystals (0.5-1.0 mm), yielded a perfect Ar-plateau recording an age of 15.75 ± 0.17 Ma, which is more precise than previously published K-Ar results.
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