Palaeomagnetic Research of Cave Sediments in SW Slovenia

Abstract

Trije profili jamskih sedimentov (v fosilni jami blizu Divače, v Divaški jami in v Trhlovci) so bili preučeni na Krasu blizu Divače. Mineraloška analiza izpričuje relativno enotno sestavo lahke frakcije in kaže na glavni izvor v preperelih ostankih eocenskega fliša. Nekaj mineralov je produkt preparevanja (npr. gibbsit). Podrobna magnetostratigrafska raziskava treh profilov kaže na normalno in reverzno polarnost magnetocon in kaže na korelacijo med profiloma v Divaški jami in Trhlovci. Ozke normalne magnetocone verjetno sovpadajo z Jaramillo polarnostjo (0.90 do 0.97 Ma) v Matuyama epohi. Podatki kažejo na precejšnjo starost jame, v kateri je nastopilo zadnje obdobje zapolnjevanja pred 0,97 Ma in se končalo pred mejo med Brunhes/Matuyama, pred približno 0.73 Ma. Magnetostratigrafski podatki profila pri Divači so zabeležili dve ozki normalni magnetoconi v dolgi reverzni polarni coni, kar verjetno sovpada z Olduvai oz. Reunion (okrog 1.67 do 1.87 Ma) reverzne Matuyama epohe ali z normalnimi magnetoconami (okrog 3.8 d0 5.0 Ma) v reverzni Gilbert epohi. Podatki nakazujejo možnost, da je jama nastala v mesinski stopnji, za katero je značilen padec morske gladine in razvoj globokega krasa v Mediteranu.

Three profiles of caves sediments (Divača fossil cave, Divaška Jama and Trhlovca Cave) were studied in the Kras near Divača village. Mineralogical study proved relatively uniform mineral composition of the light fraction indicating the main source from weathered sediments of Eocene flysch. Some minerals are derived from weathering profiles and crusts (e.g. gibbsite). Detailed magnetostratigraphic investigations of three profiles defined normal and reverse polarity magnetozones and shows the correlation between the profiles in the Divaška Jama and Trhlovca Cave. The narrow normal magnetozones probably correlate with the Jaramillo polarity event (0.90 to 0.97 Ma) of the Matuyama epoch. Those data indicate the substantial age of cave in which the last phase of filling started before 0.97 Ma and finished before the Brunhes/Matuyama boundary, i.e. around 0.73 Ma. Magnetostratigraphic data of the Divača profile detected two narrow normal magnetozones in the long reverse polarity zone which probably correlate with Olduvai and Reunion polarity events (about 1.67 to 1.87 Ma) of reverse Matuyama epoch or with some of normal magnetozones (about 3.8 to 5.0 Ma) within reverse Gilbert epoch. Data indicate the possibility that the cave was originated during the Messinian period characteristic by sea-level fall and evolution of deep karst in the Mediterranean Basin.