The Permian–Triassic boundary interval in the Rosengarten/Catinaccio Massif

Abstract (en):

The Laurinswand section in the Rosengarten/Catinaccio Massif (Dolomites, Southern Alps, Italy) covers the Permian–Triassic boundary in a proximal marine setting. The section has been studied for palynology, ostracods and carbonate microfacies. Five microfacies types are defined for the carbonates of the Bellerophon Formation (Changhsingian) in this section. Ostracod assemblages from the upper Bellerophon Formation show a moderate to high diversity and mostly indicate normal marine conditions, with some samples from the upper Casera Razzo Member being dominated by eurytopic forms. The ostracod fauna follows transgressive-regressive trends with low diverse assemblages occurring in the regressive parts. These trends are also reflected in the microfacies and can be assigned to three sequences. Palynological assemblages are dominated by phytoclasts, which is typical for proximal marine environments. Sporomorphs are represented predominantly by bisaccate and asaccate pollen grains and are mostly minor components of the palynofacies. Other minor, but consistent components in the Bellerophon Formation are acritarchs, Reduviasporonites and unidentified possible algae or fungi. The latter are particularly abundant in samples with ostracod faunas indicating restricted conditions. The Werfen Formation (uppermost Permian to Lower Triassic) yielded quantitatively poor palynological assemblages, with one sample from the Tesero Member showing a notable increase in spores and spore tetrads. This is indicative of the socalled “spore spike”, a well-known signal from this interval. One sample from the overlying Mazzin Member demonstrated a high relative abundance of Reduviasporonites, which may be related to mass occurrences of this taxon in the Tesero Member at Tesero and at other localities near the Permian–Triassic boundary. Such a mass occurrence normally pre-dates the spore spike, whereas at the Laurinswand, the former post-dates the latter considerably.