Facies analysis of Ladinian and Carnian beds in the area of Rute Plateau (External Dinarides, Central Slovenia)

Abstract

<p>The Rute Plateau is a region located 25 km south of Ljubljana. Structurally, it belongs to the External Dinarides, which form an extensive fold and thrust belt. The study area is located in the eastern part of the Hrušica Nappe in a very complex tectonic area between two major NW-SE fault zones.<br />The peculiarity of the Rute Plateau consists in a varied succession of sedimentary and volcanoclastic rocks of Ladinian and Carnian age, while the whole area is divided into different tectonic blocks with local differences in stratigraphic evolution. The reason for these deformations and the variability of the paleotopography lies in the Middle Triassic extensional phase, which completely disintegrated the uniform Slovenian carbonate platform at the end of the Anisian age (for details see Rožič et al., this volume). Subsequently, the Ladinian strata of the External Dinarids reveals, that deep marine sediments in this area were deposited in small basins or tectonic depressions, while carbonate deposition continued on higher or relatively less subsided tectonic blocks (isolated platforms). During the Ladinian, tectonic movements were also accompanied by volcanic activity. <br />Six sedimentological sections were logged in the studied area, and the Ladinian strata were divided into four different facies: F1 - deep marine (volcano)clastic rocks, F2 - hemipelagic limestone, F3 - resedimented limestones and F4 - shallow marine carbonates. Each of these Ladinian facies is characteristic of a particular sedimentary environment and is indicated from the most distal sedimentary environment (F1) to the most proximal carbonate platform environment (F4). Facies F1 consists of greenish to light ochre bentonitic clays, tuffitic sandstone, pelitic tuffs, and subordinate felsic extrusive rocks. Facies F2 consists of laminated black micritic limestone (mudstone to wackestone) with horizons of bioclastic packstone rich in filaments, limestone rich in organic residue and interbedded with dark chert laminas and marlstone. In facies F3 we find up to 30 cm thick beds of calcarenites, limestone breccias often with large olistoliths, graded and laminated calciturbidites - mostly packstone, grainstone and rudstone beds with rare chert laminas and nodules. Finally, facies F4 consists largely of massive, light grey calcimicrobial and dasycladacean limestone with horizons or lenses of white bioclasts and intraclasts derived from reefs. The last two facies are commonly dolomitized.<br />At the end of the early Carnian, the entire region was subjected to the regional emersion phase when deposition of clastic sediments began. It is characterized by facies F5 - red clastic sediments consisting mainly of sandstone with quartz grains and carbonate lithoclasts and conglomerate. Within all these facies, we were able to determine 28 different microfacies, which, based on their composition, further elucidate sedimentation in different paleoenvironments.</p>