Architecture and sedimentary evolution of the Ladinian Kobilji curek Basin of the External Dinarids (Rute Plateau, central Slovenia)

The largest Mesozoic paleogeographic perturbation of the present-day Alpine-Dinaric transition zone occurred in the Ladinian. The entire area was subjected to intense tectonic extension related to the rifting of the Neotethys Ocean. The most intense subsidence occurred in the central part of this segment of the continental margin, and the area remained deep-marine (called the Slovenian Basin) until the end of the Mesozoic. To the south, extension also resulted in differentiation, but the predominant paleoenvironments were either continental (often emerged areas) or shallow-marine. Locally, however, small-scale, short-lasting, deep-marine environment also developed. Herein we present the study of the Kobilji curek Basin in the Rute Plateau (central Slovenia, 25 km south of Ljubljana), where the the Ladinian platform to basin transition has recently been studied in detail. The study includes sedimentological analysis, biostratigraphy, mineralogical analysis, and detailed mapping. In the studied area, following Ladinian facies were outlined: F1 - deep marine (volcano)clastic rocks (bentonitic clays, tuffitic sandstone, tuffs), F2 - hemipelagic limestone (micritic and filament limestone), F3 - resedimented limestone (breccia and calcarenite), and F4 - shallow marine carbonates (bioclastic limestone and dolomite) (for details see Kocjančič et al, this volume). The base is Anisian dolomite and the top Carnian clastites. In contract, the highly variable Ladinian facies merge both laterally and vertically. Detailed geological mapping revealed that the area can be divided into four tectonic blocks with characteristic sequences, separated by roughly N-S and E-W trending paleofaults. In the NW tectonic block (B1), the most basinal succession is outcropping with two intervals of platform carbonates, while the sequence in the SE block (B4) is entirely characterized by platform carbonates. In the transition blocks (B2 and B3), platform carbonates predominate with minor basinal intervals. The entire Ladinian succession shows five major subsidence pulses followed by partial or twice also complete platform progradation. The first subsidence is documented exclusively in B2 and B3 (F1 and F2), followed by platform progradation (F4). During the second subsidence, the major paleofault between B1 and B2 is activated. This pulse is evident in B1 as a fairly thick basinal succession (F1) containing carbonate resediments (F3) in the upper part, indicating distant platform progradation. This pulse is also seen in B2 as thin deep marine limestone (F2 and F3), again followed by platform carbonates (F4). The third pulse is seen in B1 as coarse resediments (F3) followed by general platform progradation (F4), and in B2 as thin deep marine carbonates (F2 and F3) followed by platform carbonates (F4). This platform progradation seals the paleofault between B1 and B2. The fourth pulse is uniform in blocks B1 and B2 and consists of a continuous basinal interval (F1 and F2) followed by a final rapid platform progradation (F4). The fifth subsidence is uniform in B1, B2, and B3 and begins with hemipelagic limestone (F2) followed by (volcano)clastic rocks (F1) with some felsic extrusive rocks. In B4, this pulse either did not occur or the rocks were eroded during regional emersion in the early Carnian.