Magnetostratigraphy and fold tests from Raika peina and Peina v Bortu caves (Classical Karst, Slovenia)

Clastic and chemogenic cave sediments were sampled and analyzed from Raika peina and Peina v Bortu caves of southwestern Slovenia. Samples were subjected to both thermal and alternating field demagnetization; specimens belonging to the same sample of the same layer produce identical results. Unblocking temperatures of 540 to 560A degrees C on average suggests magnetite as the principal carrier of magnetization. These directions also pass a reversals test indicating the demagnetization results are free of secondary overprints and have adequately averaged out paleosecular variation. Normally magnetized clays containing fauna belonging to the MN17 mammal biozone at a depth of similar to 4 m in Raika pecina cave indicate these clays were deposited at the beginning of the Olduvai subchron (1.95 Ma). Correlation with the Geomagnetic Polarity Time Scale (GPTS) indicates the base of the speleothems in Raika peina terminate in the upper part of subchron C2An.3n with numerous breaks in deposition, lasting up to 250 ka and more. Therefore rates of speleothem growth cannot be calculated. Fold tests on dome-like stalagmites of differing sizes and ages (Pleistocene, Pliocene) from the two caves indicate the domelike structures are primary.