On possible causes of Kargapolovo excursion failure in synchronous section of Polovinka dene from Central Kamchatkan depression

Abstract

Cover sandy loams (loess-like volcanogenic deposits) were paleomagnetically studied in Central Kamchatkan depression. 457 orientated samples were collected one by one every 10 cm vertically across the section from Kamchatka-river erosion of Polovinka dene (158°55'40"E, 54°54'40"N). There are 3 radiocarbon dating in this section. Average sedimentation rate was 1.5 mm/year. Estimated age of studied cover sandy loams is 33-55 Ka. We have tried to compare our resultant paleomagnetic angular records of paleosecular variation (PSV) with the data from well-known Kargapolovo section (Siberia), which is located 77° to the west of Polovinka dene on the same latitude and has the same age. A good correlation was identified between 34-39 Ka age parts of these sections in the shapes of the declination and inclination curves. The similarity was also revealed in the shapes of loops on the D-I stereograms. Such result can be explained by PSV generation from drifting of regional geomagnetic sources in Earth's core along the parallels. But our Polovinka PSV records have no geomagnetic excursion similar to currently accepted as global Kargapolovo one, that is located in the same time range. If we accept Polovinka PSV records synchronous to Kargapolovo geomagnetic excursion as conditioned we have to assume that global distribution of Lashamp-Kargapolovo-Yangiyul excursion is a failure. The lack of geomagnetic excursion in the Polovinka PSV records can be caused by:♦ wrong regime of magnetic cleaning for some layers, ♦ poor PSV record due to chemical remagnetization in thick layer of buried soil where this event could occur,♦ water erosion of some sediment layers. Suddenly a similarity was found between a piece of interested Polovinka record and PSV obtained by Averyanov & Melnikov on the lava section from Mutnovsky volcano crater (Kamchatka). On geological data this lava section is 10-26 Ka. But its agreeable place in Polovinka section is situated between layers with radiocarbon dating 38 and 55 Ka. This circumstance resulted in a new interpretation of missing of Kargapolovo excursion in Polovinka PSV records. This gives a hope that in Kamchatka the lost geomagnetic excursion will be find.