Albian - Cenomanian resedimented limestone in the Lower ﻿flyschoid Formation of the Mt. Mrzli Vrh Area (Tolmin region, NW Slovenia)

Boštjan Rožič

doi:10.5474/geologija.2005.017

Abstract

The Lower flyschoid formation of the Slovenian Basin is characterized by marl, shale and subordinate chert, interbedded with micritic limestone and resedimented carbonates. In the upper part of the formation marly and micritic limestones commonly prevail. The maximum range of the formation is Albian to Turonian. Contact with underlying successions is always erosional and the formation usually overlies upper Tithonian to Neocomian Biancone limestone. In the Mt. Mrzli vrh area, the formation is composed of upper Albian to lower Cenomanian resedimented limestone and upper Cenomanian to Turonian shale and marl, marly limestone and cherts. It directly overlies Lower Jurassic basinal succession or Upper Triassic platform dolomite. In this study resedimented carbonates of the formation were analyzed. A two km2 area was mapped and an 80m thick Mt. Grmuč section was studied in detail. This section consists of micritic limestone and abundant breccia and calcarenite. Whereas the calcarenite is predominantly composed of platform-derived material, the breccia consists of slope-to-basin intraclasts and various extraclasts of older platform and basin deposits. The analyzed facies association indicates a lower slope depositional environment. A correlation with other successions of the Lower flyschoid formation reveals that resedimented carbonates are the thickest and most abundant in the Tolmin region, that paleogeographically corresponds to the western part of the Slovenian Basin. Intense Albian - Cenomanian tectonic activity is inferable regionally, from platform as well as basinal successions, and is thought to have been the major factor causing and controlling the carbonate gravity-flows sedimentation in the Slovenian Basin. The Mt. Mrzli vrh area is important for paleotopographic reconstruction because it links the central Slovenian Basin with the margin of the Dinaric Carbonate Platform. The observed lateral facies distribution, the composition of lithoclasts and variable degree of erosion between the Lower flyschoid formation and underlying beds indicate a steep, fault-bounded slope, along which older platform and basinal succession were eroded.

Highlights

The Lower flyschoid formation of the Slovenian Basin is characterized by marl, shale and subordinate chert, interbedded with micritic limestone and resedimented carbonates
A correlation with other successions of the Lower flyschoid formation reveals that resedimented carbonates are the thickest and most abundant in the Tolmin region, that paleogeographically corresponds to the westem part of the Slovenian Basin
The structureless megabeds of clast-supported breccias are interpreted as debrisflow deposits

Summary

Introduction

The Mt. Grmuč section is located in the Mt. Mrzli vrh area in the foothills of the Julian Alps north of Tolmin in north-westem Slovenia (Fig 1.). The Mt. Mrzli vrh area is characterized by Upper Triassic shallowwater massive dolomite overlain by the Jurassic to Cretaceous succession of the 10km 1 b. Mt.Grmuc section a N\Tolmin Austria 1^7 2 " Slovenia. This paleogeographic unit formed at the end of the Triassic and beginning of the Jurassic and was placed between the Julian Carbonate Platform to the north and the Dinaric Carbonate Platform to the south. In the Early Jurassic the Julian Carbonate Platform subsided, while the Dinaric Carbonate Platform remained shallow throughout the entire Mesozoic (Buser, 1989)

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