Križna jama (SW Slovenia): Numerical-and correlated-ages from cave bear-bearing sediments

Povzetek

Križna jama is a large river cave located between Loško and Cerkniško poljes under Križna gora Mount in southern Slo­venia. It has been known since the mid-19thcentury due to numerous cave bear finds. The cave is filled by complicated sequences of cave fluvial and lacustrine sediments, whichare recently partly eroded. We studied two paleontological exca­vations and profiles in the Medvedji rov to contribute to the solution of dating of bone-bearing lithological horizons. The Križna jama I profile consists of alternation of speleothem lay­ers (flowstone sheets withsmall stalagmites, sometimes within situ cemented Ursus gr. spelaeus bones) and fine-grained silici­clastics often withbones of cave bear. It can be correlated withthe upper part of the Križna jama II profile, but witha slightly less preserved stratigraphic record. Radiocarbon and U-series dates clearly indicate two different ages of cave bear thanato­cenoses in the Križna jama I profile: those above flowstone crusts were dated to ca. 47–45 ka by radiocarbon dating; those included in speleothem layers and clay interbeds are older than 94 ka (U-series date). The details of internal lithology, low thicknesses of layers and the state of bone preservation exclude expected sandwiching of younger layers into eroded/washed spaces among flowstones. Numerical dating excludes re-depo­sition of bear bones from older assemblage to sediments above flowstones. According to the paleomagnetic parameters (pre­vailing normal polarization), the deposition took place within the Brunhes Chron (< 780 ka). There were discovered in total four short-lived reverse excursions of the magnetic field. Ac­cording to U-series data, the upper one (profile I) might be correlated withthe Blake excursion. The lower ones are older than ca 190 ka and can be correlated withsome of the Jamaica-Pringle Falls, Namaku, Calabrian Ridge, Portuguese margin or Calabrian Ridge 1 excursions. Sediments in studied profiles were deposited during the Last Glacial (Weichselian), Eemian interglacial, Saalian glacial and Holsteinian interglacial.