hrvatski

Magnetske sferule otkrivene u kršu Hrvatske

While investigating magnetic susceptibility in sediments of the whole Kupa River drainage basin (Croatia, Slovenia, Bosnia and Herzegovina) two interesting anomalies have been discovered. The first one was in lower course of Mrežnica River ; it is of anthropogenic origin, caused by coal ash and slag disposal directly into river. The second observed anomaly was in karstic sinking Dobra River, which is assumed to be of natural origin. Magnetic particles in Dobra River sediments were investigated in details (Frančišković-Bilinski et al., 2014), to suggest the possible origin of magnetic particles in the river sediments within the Dinaric karst region, which to our knowledge was not exposed to metal manufacturing processes. Sediments were collected near the channel bank (from the top layer) at 16 representative stations distributed along the length of the Dobra River (110 km). Sediments were air-dried and passed through 2 mm and 63 μm sieves, and analyzed for magnetic susceptibility (and Curie temperature), isothermal remanent magnetism (IRM), stereo-microscopy of separated magnetic grains, mineralogical analysis (using X-ray diffraction), and chemical analysis (using inductively coupled plasma–mass spectrometry). Increased magnetic susceptibility and IRM values, as well as extremely interesting magnetic spherules, were observed mostly in the sediments of the Upper Dobra, especially at sampling point D-9 just before the river sinks in abyss in Ogulin. It seems that none of those particles have passed through karstic underground, as they have not been found in Lower Dobra River. Thermomagnetic curves show a distinctive Curie-point of magnetite at 580 °C. Additional transformation observed at 520–560 °C derives from titanomagnetite. There was no significant correlation between magnetic susceptibility and Fe. Magnetic particles from the Dobra River sediments contain pyroxene, plagioclase, hematite and quartz, in addition to magnetite. White spherules within magnetic grains are also present. The major constituent of five separated magnetic spherules is Fe ; the minor constituents are Al, Ca, Mg and Si, and there are numerous trace elements (Ba, Cr, K, Mn, Na, Ni, Ti and V). The ratio Ni/Fe versus Cr/Fe suggests that the magnetic spherules are impactites. Those impactites could either be formed by a shock event caused by a meteorite impact or by volcanic processes. The presence of magnetic spherules in the fluvial sediments of the Upper Dobra River represents a new and exciting finding and deserves further field work and laboratory research to prove either an ancient meteorite impact or existing of volcanic activity in the past in this region.

Dinarski krš; Hrvatska; krška rijeka ponornica Dobra; magnetske sferule; impaktiti

nije evidentirano

engleski

Magnetic spherules discovered in Croatian karst

While investigating magnetic susceptibility in sediments of the whole Kupa River drainage basin (Croatia, Slovenia, Bosnia and Herzegovina) two interesting anomalies have been discovered. The first one was in lower course of Mrežnica River ; it is of anthropogenic origin, caused by coal ash and slag disposal directly into river. The second observed anomaly was in karstic sinking Dobra River, which is assumed to be of natural origin. Magnetic particles in Dobra River sediments were investigated in details (Frančišković-Bilinski et al., 2014), to suggest the possible origin of magnetic particles in the river sediments within the Dinaric karst region, which to our knowledge was not exposed to metal manufacturing processes. Sediments were collected near the channel bank (from the top layer) at 16 representative stations distributed along the length of the Dobra River (110 km). Sediments were air-dried and passed through 2 mm and 63 μm sieves, and analyzed for magnetic susceptibility (and Curie temperature), isothermal remanent magnetism (IRM), stereo-microscopy of separated magnetic grains, mineralogical analysis (using X-ray diffraction), and chemical analysis (using inductively coupled plasma–mass spectrometry). Increased magnetic susceptibility and IRM values, as well as extremely interesting magnetic spherules, were observed mostly in the sediments of the Upper Dobra, especially at sampling point D-9 just before the river sinks in abyss in Ogulin. It seems that none of those particles have passed through karstic underground, as they have not been found in Lower Dobra River. Thermomagnetic curves show a distinctive Curie-point of magnetite at 580 °C. Additional transformation observed at 520–560 °C derives from titanomagnetite. There was no significant correlation between magnetic susceptibility and Fe. Magnetic particles from the Dobra River sediments contain pyroxene, plagioclase, hematite and quartz, in addition to magnetite. White spherules within magnetic grains are also present. The major constituent of five separated magnetic spherules is Fe ; the minor constituents are Al, Ca, Mg and Si, and there are numerous trace elements (Ba, Cr, K, Mn, Na, Ni, Ti and V). The ratio Ni/Fe versus Cr/Fe suggests that the magnetic spherules are impactites. Those impactites could either be formed by a shock event caused by a meteorite impact or by volcanic processes. The presence of magnetic spherules in the fluvial sediments of the Upper Dobra River represents a new and exciting finding and deserves further field work and laboratory research to prove either an ancient meteorite impact or existing of volcanic activity in the past in this region.

Dinaric karst; Croatia; karstic sinking Dobra River; magnetic spherules; impactites

nije evidentirano