Carnian clastic-carbonate succession from the Slovenian Basin (Southern Alps)

The Slovenian Basin (the eastern Southern Alps, Slovenia) formed during the Middle Triassic and lasted until the end of the Mesozoic. The oldest succession belongs to the Ladinian volcanic- and clastics-dominated Pseudozilian Formation, followed by the Carnian Amphiclina Formation, composed of shale, sandstone, subordinately conglomerate and bedded limestone. Several sections were documented by Skaberne et al. (2024) in the southern part of the Tolmin Nappe (subunit of the Southern Alps), but only one succession was logged from more northern parts of the Tolmin Nappe (Gale et al., 2017). Consequently, little is known about Carnian paleotopography of the basin. To augment current knowledge on the lateral differences within the Amphiclina Formation, a succession was logged on the Martinj Vrh hill, structurally situated in the middle part of the Tolmin Nappe. The entire succession is 47.3 m long and ends at the transition to the Norian-Rhaetian Bača Dolomite Formation. According to conodont data, this stratigraphic boundary corresponds to the Carnian-Norian boundary. The rocks were analysed using optical microscopy, XRD, and μ-EDRF. The outcrop consists of bedded fine-, medium- and coarse-grained sandstone, marlstone, mud-supported conglomeratic breccia, conglomeratic breccia with carbonate cement, and bedded limestone with occasional occurrences of dolomite. Parallel and cross-lamination, load casts, ball and flame structures, scour structures, slumps and synsedimentary faults are present. Limestone is mudstone-wackestone with radiolaria, filament and bioclastic wackestone, echinoderm-intraclastic packstone, filament-peloidal packstone-grainstone, intraclastic-peloid packstone-grainstone, peloidal grainstone, and rudstone. Position within the basinal area cannot be directly determined, although the sedimentary structures suggest that sedimentation took place on the basin slope. Comparison with previously published logs shows that sedimentation within the basin greatly varied and that no clear distinction can be drawn between different parts of the Tolmin Nappe. This is probably due to complex internal topography of the basin.

Gale et. al. 2017: Characterization of silicified fossil assemblage from upper Carnian "Amphiclina beds" at Crngrob (central Slovenia). Geologija, No. 60/1, pp. 61–75.

Skaberne et. al. 2024: Middle Triassic deeper-marine volcano-sedimentary successions in western Slovenia. Geologija, No. 67/1, pp. 71–103.