Geomorphological Evolution of the Podgorski Karst, SW Slovenia: Contribution of Magnetostratigraphic Research of the Črnotiče II Site with Marifugia sp.

Povzetek

Proučena je bil 9 m visoka sekvenca jamskih sedimentov Črnotiče II. V spodnjem delu grade profi l ciklično urejene plasti fluvialnih sedimentov (konglomerati, peski, melji in gline), v zgornjem pa laminirane ali pasovite plasti melja in gline. Oba dela profi la loči dobro izražena prekinitev, ki je povezana z močno erozijo v spodnjem delu profi la in tektonskimi premiki . Fluvialna zapolnitev je prekrita s kaotično blokovno brečo z rdečim ilovnatim matriksom – porušenim stropom. Na enem delu sten votline so številne drobne cevke, ki pripadajo polihetnim črvom. Podobne so cevkam recentnega jamskega cevkarja Marifugia cavatica. Oba dela profi la imata normalno polariteto, v vsakem pa je tudi kratka reverzna ekskurzija. Iz pridobljenih magnetostratigrafskih podatkov lahko sklepamo, da so se sedimenti odlagali v Gaussovi (2,5 do 3,6 Ma) ali kateri drugi dolgi dobi z normalno polariteto. Profi l Črnotiče II je bil odložen v zelo kratkem času. Planota Podgorskega krasa je od miocena doživela komplicirano geomorfološko evolucijo, ki so jo povzročili tektonski dvig, nagibanje in rotacija ozemlja.Več obdobjem razvoja freatičnih in epifreatičnih jam je sledil nastanek vadoznih brezen, zapolnjevanje jam, denudacija in uravnavanje površja.

The sequence of interior cave facies 9 m high is composed of cyclically arranged fl uvial sediments (conglomerates, sands, silts, clays) in the lower part and by laminated to banded silts to clays in the upper part. Both parts are separated by pronounced unconformity associated with deep erosion of the lower part of the profi le and tectonic tilting. The fi ll is covered by chaotic fl owstone boulder breccia with red loamy matrix. One segment of the cavity wall was covered by tiny tubes of polychates worms comparable to recent fresh-water Marifugia cavatica. Both profi les show normal magnetozone with only one narrow reverse excursion in each. The correlation of the obtained magnetostratigraphy log can indicate the Gauss chron (ca 2.5 to 3.6 Ma) or the other long normal chron. Črnotiče II site was fi lled in a substantially short time. Gemorphological evolution of the Podgorski karst plateau (Classical Karst, Karst Edge) since Miocene underwent complicated development with distinct phases of repeating phreatic speleogenesis (horizontal caves), vadose evolution (drawdown shafts), filling, fossilisation, exhumation, block tilting and rotation, uplift and planation.