Journal of Alpine Geology, 54: 379-404, Wien 2012 Permian-Triassic-Boundary and Lower Triassic in the Dolomites, Southern Alps (Italy) By RAINER BRANDNER, MICHA HORACEK & LORENZ KEIM† With 21 figures Field Trip Guide 29th IAS Meeting of Sedimentology Schladming/Austria Addresses of the authors: RAINER BRANDNER Universität Innsbruck Institut für Geologie & Paläontologie Innrain 52 6020 Innsbruck Austria E-mail: [email protected] MICHA HORACEK BLT Wieselburg Lehr-und Forschungszentrum Francisco Josephinum Rottenhauser Straße 1 3250 Wieselburg Austria E-mail address: [email protected] Journal of Alpine Geology 54 S. 379-404 Wien 2012 379 BRANDNER, HORACEK & KEIM: Permian-Triassic boundary and Lower Triassic in the Dolomites, Southern Alps (Italy) LORENZ KEIM Amt für Geologie & Baustoffprüfung/ Ufficio Geologia e prove materiali Autonome Provinz Bozen - Südtirol/Provincia Autonoma di Bolzano-Alto Adige Eggentalerstr. 48/ Via Val d’Ega 48 I-39053 Kardaun/Cardano Italy Lorenz Keim died during a cross country ski tour in a snow avalanche at the Stallersattel (South Tirol, Italy) on February 4, 2012. He just turned 43, was married and had three little boys. In the last years he worked at the Geological Survey as field geologist, as coordinator of geological maps and was involved in reconnaissance studies for the Brenner Base Tunnel on the South Tyrolean side. As excellent geologist he leaves a big hole in the Tyrolean geology. He is painfully missed. Content Abstract........................................................................................................................................................................380 1. Topics and area of the Field Trip.................................................................................................................................381 2. Introduction and geological setting of the Dolomites...................................................................................................382 3. The Field Trip............................................................................................................................................................384 3.1. The Pufels/Bulla road section: from the Permian-Triassic Boundary (PTB) to the Induan-Olenekian Boundary (IOB)......................................................................................................................384 3.1.1 Outcrop 1: Permian/Triassic Boundary......................................................................................................388 3.1.2 Outcrop 2: Supratidal/subtidal facies.........................................................................................................393 3.1.3 Outcrop 3: Siliciclastic input, climate signal..............................................................................................394 3.2. Seis/Siusi section and the attempt of PTB high-resolution global correlation by carbon isotope investigation........395 3.3. Tramin/Termeno section - end Permian coastline and transgression....................................................................398 Acknowledgements............................................................................................................................................................402 References.......................................................................................................................................................................402 Abstract exceptionally long lasting recovery period for reefal buildups in the whole Tethys area, the first appearance of The field trip focuses on the sedimentary response of the reef building organisms was found in the lower Middle end Permian mass extinction and the time of recovery in Triassic nearby in the Olang/Valdaora Dolomites the whole Lower Triassic. Along some type sections, i.e. (BECHSTÄDT & BRANDNER 1970). the parastratotype section of Bulla/Pufels in the Gröden The lack of reefal buildups and binding organisms may valley, the Seis/Siusi section further to the southwest and have caused the extreme mobility of loose carbonate and the Tramin/Termeno section south of Bolzano/Bozen, we siliciclastic sediment piles, which have been removed will have a good opportunity to study facies developments repeatedly by storm-dominated high energy events. This in the inner and outer ramp position. Detailed magneto- generated a storm-dominated stratification pattern that and chemostratigraphy enable correlations of cycles and characterises the specific Werfen facies. Applying the sequences along the wide ramp. This should provoke a concept of proximality of storm effects (AIGNER 1985), i.e. discussion on eustatic sea-level changes and climatic the basinward decrease of storm-waves and storm-induced changes. The sections are located in the beautiful, world currents, we tried to interpret relative sea-level changes famous landscape of the Dolomites (UNESCO World from the stratigraphic record. Proximal and distal Heritage). tempestite layers are arranged in shallowing-upward cycles The shallow marine sediments of the topmost Bellerophon (parasequences) but also in deepening-upward cycles Fm. and Werfen Fm. were deposited on a very gentle, NW depending on their position within the depositional - SE extending ramp with a coastal plain environment of sequences. However, numbers of cycles and cycle stacking the upper Gröden Fm. in the west and a shallow marine, patterns vary from section to section according to the dif- mid and outer ramp environment of the Bellerophon Fm. ferent ramp morphology. Thus the main control seems to in the east. The PTB mass extinction of carbonate be the ratio between accommodation space and sediment producing organisms prevented the evolution of a rimmed supply, which follows the variable position of the base level shelf area for the whole Lower Triassic. After the (see base level concept from WHEELER 1964). Variations of 380 Journal of Alpine Geology, 54: 379-404, Wien 2012 the base level determine the geometry of progradational, producing organisms prevented the evolution of a rimmed aggradational and retrogradational stacking patterns of the shelf area for the whole Lower Triassic. cycles. The base level, however, does not automatically The lack of reefal buildups and binding organisms may correspond to sea level. Therefore until now it was not have caused the extreme mobility of loose carbonate and possible to proof true eustatic sea level changes within the siliciclastic sediment piles, which have been removed Lower Triassic. repeatedly by storm-dominated high energy events. This generated a storm-dominated stratification pattern that characterises the specific Werfen facies. Applying the concept of proximality of storm effects (AIGNER 1985), i.e. 1. Topics and area of the Field Trip the basinward decrease of storm-waves and storm-induced currents, we tried to interpret relative sea level changes The field trip focuses on the sedimentary response of the from the stratigraphic record. Proximal and distal end Permian mass extinction and the time of recovery in tempestite layers are arranged in shallowing-upward cycles the whole Lower Triassic. Along three type sections, i.e. (parasequences) but also in deepening-upward cycles the parastratotype section of Bulla/Pufels in the Gröden depending on their position within the depositional valley, the Seis/Siusi section at the foot of the Schlern/ sequences. However, numbers of cycles and cycle stacking Sciliar mountain and the Tramin/Termeno section south patterns vary from section to section according to the dif- of Bolzano/Bozen (Fig. 1), we will have a good opportunity ferent ramp morphology. Thus the main control seems to to study facies developments in the inner and outer ramp be the ratio between accommodation space and sediment position. Detailed magneto- and chemostratigraphy enable supply, which follows the variable position of the base level correlations of cycles and sequences along the wide ramp. (see base level concept from WHEELER 1964). Variations of This should provoke a discussion on eustatic sea level the base level determine the geometry of progradational, changes and climatic changes. Both sections are located aggradational and retrogradational stacking patterns of the in the beautiful, world famous landscape of the Dolomites cycles. The base level, however, does not automatically (UNESCO World Heritage). correspond to sea level. Therefore until now it was not The shallow marine sediments of the topmost Bellerophon possible to proof true eustatic sea-level changes within the Fm. and Werfen Fm. were deposited on a very gentle, NW Lower Triassic. - SE extending ramp with a coastal plain environment of End Permian and Early Triassic high-resolution the upper Gröden Fm. in the west and a shallow marine, stratigraphy allow now detailed correlations of mid and outer ramp environment of the Bellerophon Fm. lithostratigraphic units along the gentle ramp, indicating in the east. The PTB mass extinction of carbonate the different timing of the onset of sedimentation of several Fig. 1: Overview map of the excursion area in the western Do- lomites (N- Italy) with the field trip stops: Pufels/Bulla (stop 1), Seis/ Siusi (stop 2), Tramin/Termeno (stop 3). The dashed line marks the coastline of the Bellerophon-Sea in the uppermost Permian. 381 BRANDNER, HORACEK & KEIM: Permian-Triassic boundary and Lower Triassic in the Dolomites, Southern Alps (Italy) Werfen members on the gentle ramp. BRANDNER & KEIM (2011). According to Lower