Sedimentary Geology, 62 (1989) 59-77 59 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands Detrital and authigenic feldspars in Permian and early Triassic sandstones, Eastern Alps (Austria) KARL KRAINER 1 and CHRISTOPH SPOTL 2 1 Universitiit Innsbruck, InstitutJ'~r Geologie und Paliiontologie, Innrain 52, 6020 Innsbruck (Austria) 2 Universitiit Bern, lnstitutfiir Geologie, BaltzerstraBe 1, 3012 Bern (Switzerland) Received June 21, 1988; revised version accepted October 10, 1988 Abstract Krainer, K. and SpiStl, C., 1989. Detrital and authigenic feldspars in Permian and early Triassic sandstones, Eastern Alps (Austria). Sediment. Geol., 62: 59-77. Detrital and authigenic feldspars of Permian and early Triassic (Scythian) sandstones of the Eastern Alps (Austria) have been investigated using thin section microscopy, cathodohiminenscence (CL), X-ray diffraction and electron microprobe. Sandstones of Permian alluvial sequences are low in detrital feldspars due to strong weathering and diagenetic alteration. Within early Permian sandstones detrital feldspar type is strongly dependent on the source rock. Late Permian sandstones of all sections investigated are very tow in detrital feldspars, most of which are alkali varieties. Early Triassic sandstones are characterized by a better degree of sorting and rounding and higher feldspar contents, especially in the marine environment (subarkoses to arkoses). Alkali-feldspar dominates by far in all sections of the Alpine Buntsandstein Formation (Drau Range, Gurktal Nappe and Northern Calcareous Alps). In the Werfen Formation of the Drau Range and Gurktal Nappe alkali-feldspars also dominate, whereas albites are the most common detrital feldspars in the Northern Calcareous Alps due to different source rocks. Despite the fact that late Permian (Gr'rden Formation) and early Triassic sandstones (Alpine Buntsandstein and Werfen Formations) are derived from reworking of intra-Permian rhyolitic volcanics to a great extent containing sanidines, it is evident from X-ray diffraction and CL investigations that detrital alkali-feldspars within these units are not of volcanic but of metamorphic origin, being microchnes with bright blue CL. Sanidines of intra-Permian volcanics, as being very unstable due to their structural state, appear to have been completely destroyed during weathering and diagenesis. Authigenic feldspar overgrowths (almost pure potassium feldspars) frequently occur in Scythian sandstones of the Drau Range and Gurktal Nappe, particularly in the marine environment. Compared to the detrital cores anthigenic feldspar overgrowths are characterized by different optical orientation, chemical differences in minor and trace elements and absence of CL. Dissolution of volcanic sanidine, volcanic rock fragments, plagioclases and other unstable silicate minerals increased the concentration of pore waters for A1, Si and K, leading to the precipitation of diagenetically formed K-feldspar overgrowths in sandstones of marine origin. Introduction Only over about the last two decades have sedimentary petrologists undertaken detailed mineralogical investigations of feldspars, one of the most important constituents in siliciclastic 0037-0738/89/$03.50 © 1989 Elsevier Science Publishers B.V. rocks. By means of XRD, EMPA, CL and SEM feldspar grains and cements were analysed with regard to chemical composition, structural state, weathering features, host rock provenance and diagenetic alteration and modification. Helmold (1985) briefly summarized the relatively small