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Definition of the Permian – Triassic boundary in Western Slovenia

The stratigraphy of the Permian-Triassic Boundary (PTB) beds has been intensively studied in many parts of the world for many years after the establishment of the Permian-Triassic Working Group (PTWG) in 1981. Stratigraphically most important species across the PTB belong to the conodonts of the Hindeodus-Isarcicella group. The Global Stratotype Section and Point (GSSP) of the PTB have been ratified by IUGS in 2001 (YIN et al. 2001). The first appearance datum (FAD) of the species Hindeodus parvus (Kozur & Pjatakova) of the Meishan section in South China marks the base of the Triassic System. The approved proposal clearly separates the event stratigraphic- and biostratigraphic boundaries and is of key importance not only for defining the GSSP of the basal Triassic boundary but also for study of the P/T mass extinction and recovery (WANG, 1999). Hindeodus parvus is the first globally distributed species that appears just above the minimum faunal diversity indicated by the minimum in δ13C (KOZUR 1996, KOZUR et al., 1996). Studies of the PTB interval were carried out in the Žiri area in the north-west part of the External Dinarides. In the paleogeographic sense Late Paleozoic and Early Triassic beds of the studied area were formed on extensive Slovenian Carbonate Platform which became established in the Late Permian, and remained stable until Late Anisian times (BUSER et al., 2008). Late Permian carbonates that are known also as »Žažar Fm« in Slovenia that represent equivalent of Bellerophon Fm. Above the Transitional beds that include P/T boundary is developed the Streaky limestone (KOLAR-JURKOVŠEK & JURKOVŠEK, 2007) and then follow oolithic-clastic Early Triassic succesion of beds. In the studied Late Permian-Early Triassic section Lukač six conodont zones have been recognized, these are in ascending order, the latest Changhsingian (uppermost Permian) praeparvus Zone, and Griesbachian (lowermost Triassic) parvus, lobata, isarcica, postparvus and anceps Zones. The FAD (first appearance datum) of H. parvus in the Transitional beds (sample L1) markes the base of the systemic boundary. On the basis of conodonts the Lukač section enables correlation with the sequences in Southern Alps and in other areas of the world. References: BUSER, S., KOLAR-JURKOVŠEK, T. & JURKOVŠEK, B. (2007): Triasni konodonti Slovenskega bazena. (Triassic conodonts of the Slovenian Basin). – Geologija 50/1, 19-28, Ljubljana. KOLAR-JURKOVŠEK, T. & JURKOVŠEK, B. (2007): First record of Hindeodus-Isarcicella population in Lower Triassic of Slovenia. – Palaeogeogr. palaeoclimatol. Palaeoecol. 252/1, 72-81, Amsterdam KOZUR, H. (1996): The Conodonts Hindeodus, Isarcicella and Sweetohindeodus in the uppermost Permian and lowermost Triassic. Geol. Croat. 49 (1), 81–115. KOZUR, H., RAMOVŠ, A., WANG, C.Y & ZAKHAROV, Y.D. (1996): The importance of Hindeodus parvus (Conodonta) for the definition of the Permian-Triassic boundary and evaluation of the proposed sections for a global stratotype section and point (GSSP) for the base of the Triassic, Geologija, 37-38 ; 173-213, Ljubljana WANG, C.Y. (1999): Conodont Mass Extinction and Recovery from Permian-Triassic Boundary Beds in the Meishan Sections, Zhejiang, China. Boll. Soc. Paleont. Ital. 37/2-3 (1998), 487-495, Modena. YIN, H., ZHANG, K., TONG, J., YANG, Z., & WU, S. (2001): The Global Stratotype Section and Point (GSSP) of the Permian–Triassic Boundary. Episodes 24, 102–114.

Permian-Triassic boundary; biostratigraphic dating; conodont zonation; Western Slovenia

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