Late Quaternary evolution of the sedimentary environment in Modrejce near Most na Soči (Soča Valley, Julian Alps)

Petra Jamšek Rupnik,Manja Žebre,Giovanni Monegato

doi:10.5474/geologija.2020.022

Abstract

Geomorphological and geological mapping have long been used to study the glacial history of the Slovenian Alps, but many uncertainties remain regarding the time and extent of Pleistocene glaciations there. Glacial landforms and undisturbed glacial deposits are rare in the areas of the former glacier terminus, especially in the Soča Valley, where large discrepancies in the interpretation of the extent of the former Soča Glacier have been reported. Early studies proved inconclusive as to whether one or two glaciations extended into the Soča Valley as far as Most na Soči. In order to answer this question, the Quaternary sedimentary succession and landforms in the Modrejce Valley near Most na Soči were investigated. New geological and geomorphological field data allow the interpretation of the sedimentary environment and the stratigraphic relationships between different units. In response to glacial dynamics, the sedimentation developed from glaciofluvial and glaciolacustrine to fully glacial environments, followed by slope deposition. At higher altitudes lateral moraines are preserved, while the staircase-like slope below has been carved into older glacial, glaciofluvial and glaciolacustrine deposits by glacial and post-glacial processes, including fluvial erosion and slope dynamics. We conclude that the succession studied here was deposited over the course of two different glacial advances – LGM and pre-LGM. Our study thus suggests that the Soča Glacier extended as far as the area of Most na Soči twice over the course of the late Quaternary.

Highlights

The glacial history of the southeastern Alps covers multiple glaciations, which were first established by Penk & Brückner (1901–1909)
In the Alps, deposits related to older glaciations are difficult to date (e.g., Dehnert et al, 2012; Lowick et al, 2015; Rades et al, 2016) and their relative chronologies are inferred through their stratigraphic relationship with the alluvial-coastal stratigraphy (Fontana et al, 2010) or through analysis of their boundaries, which are sometimes characterized by paleosoils or peat layers (Gianotti et al, 2015)
The glacial history of the Slovenian territory has been studied since the late 19th century, many uncertainties remain about the timing and extent of Pleistocene glaciations in the Slovenian Alps (Bavec & Verbič, 2011; Ferk et al, 2017)

Summary

Introduction

The glacial history of the southeastern Alps covers multiple glaciations, which were first established by Penk & Brückner (1901–1909). The glacial history of the Slovenian territory has been studied since the late 19th century, many uncertainties remain about the timing and extent of Pleistocene glaciations in the Slovenian Alps (Bavec & Verbič, 2011; Ferk et al, 2017) This is especially true for the Soča mountain basin, where spatially incomplete records on landforms and lack of geochronological data still do not allow us to make any thorough reconstructions of former ice limits. Using geological and geomorphological mapping and sedimentological analysis we investigated the landforms and deposits, interpreted their sedimentary environments, and established their relative chronological relationships This enabled us to reconstruct the late Quaternary sedimentary evolution of this area in relationship to glacial advances and slope dynamics

Methods

Findings

Conclusions