Puzzling magnetic anomaly in the Barun-Khal valley (Olkhon region, western Gisbaikalia)

Abstract

The Brun-Khal valley is in the Olkhon region, northwest of the village of Chernorud. Since the end of the 70s. the valley and its surroundings has been studied with geophysical methods. During magnetic survey in the central part of the valley, some round-shaped magnetic anomalies were mapped the nature of which remains unclear. Especially unusual is a negative magnetic anomaly with an amplitude of more than 1200 nT and a width of about 50m. According to the simulation, the anomaly is caused by a vertical, negatively magnetized rod or a thin cylinder, the upper and lower edges of which are located at a depth of 17m and 50m, respectively. Presumably, the anomaly is due to a stock of igneous rocks that intruded into host rocks when the polarity of the geomagnetic field was negative.