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

Geomorfoloske in geoloske raziskave zgodovine poledenitev v Slovenskem Alpskem prostoru imajo dolgo tradicijo, kljub temu pa se vedno ostaja vec nejasnosti o obsegu in casu pleistocenskih poledenitev v tem prostoru. Ledeniske geomorfne oblike in nepredelani ledeniski sedimenti so redko ohranjeni na obmocjih nekdanjih ledeniskih cel, kar se posebej velja za Posocje, za katero so bile porocane razlicne interpretacije obsega nekdanjega Soskega ledenika. Pretekle studije niso uspele ugotoviti, ali je ena ali morda vec poledenitev segalo tako dalec po Posocju, da je doseglo Most na Soci. Da bi raziskali to vprasanje, smo svojo studijo usmerili na kvartarno sedimentacijsko zaporedje in geomorfne oblike v Modrejcah pri Mostu na Soci. Novi terenski geoloski in geomorfoloski podatki omogocajo interpretacijo sedimentacijskega okolja in stratigrafskih odnosov med razlicnimi enotami. V povezavi z ledenisko dinamiko se je sedimentacijsko okolje razvilo iz glaciofluvialnega in glaciolakustricnega v ledeniskega, kateremu je sledilo odlaganje pobocnega materiala. Bocne morene so ohranjene na visjih legah, medtem ko je stopnicasto pobocje vrezano v starejse ledeniske, glaciofluvialne in glaciolakustricne sprijete sedimente. Vrezovanje je rezultat delovanja mlajsih ledeniskih procesov in procesov po umiku ledenika, kot so recna erozija in pobocna dinamika. Sklepamo, da je bilo preuceno sedimentacijsko zaporedje odlozeno med dvema razlicnima napredovalnima fazama; v zadnjem poledenitvenem visku in v enem izmed prejsnjih. Nasa studija tako nakazuje, da je Soski ledenik v poznejsem delu kvartarja dvakrat segal do obmocja Mosta na Soci.

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 Soca Valley, where large discrepancies in the interpretation of the extent of the former Soca Glacier have been reported. Early studies proved inconclusive as to whether one or two glaciations extended into the Soca Valley as far as Most na Soci. In order to answer this question, the Quaternary sedimentary succession and landforms in the Modrejce Valley near Most na Soci 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 Soca Glacier extended as far as the area of Most na Soci twice over the course of the late Quaternary.