Physical properties of the drill core from the El'gygytgyn impact structure, NE Russia


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The El'gygytgyn impact structure in northeast Russia was drilled in 2008/2009. The 3.5 Ma old structure has a rim-to-rim diameter of 18 km and is the only known impact structure that has been formed on a siliceous volcanic target. The petrophysical, rock- and paleomagnetic properties, including attempted reorientation of samples, along the El'gygytgyn drill core were analyzed. Physical properties, such as bulk density, porosity, seismic velocity, and electrical conductivity, clearly showed the propagation of shock and the associated fracturing. The grain density, however, was probably influenced by the postimpact hydrothermal activity and/or the distribution of impact melt. The highest values of electrical conductivity coincided with higher concentrations of particular metals as indicated by Raschke et al. (2012a). The rock- and paleomagnetic investigations showed iron-titanium oxides with varying oxidation/reduction states as the main magnetic fraction in the core samples and indicated them as carriers for remanent magnetization. With few exceptions, most samples showed normal polarity of characteristic remanent magnetization and confirmed that the impact occurred after the Gauss/Gilbert (approximately 3.596 Ma) reversal. Shallower inclinations than that expected for a 3.5 Ma dipole field were probably due to impact-related block movements and/or compaction.