Study of paleochannels by means of gravimetric observations

Abstract

RUS Investigation of ancient river valleys – paleochannels – is of particular relevance for the territory of St. Petersburg and the Leningrad region due to a poor stability of rocky soils here and the subsequent high risk of structural damage during the construction of multi-storey buildings. In addition, paleochannels in the region constitute a source of renewable drinking water owing to a significant capacity of sandy sediments. The mapping and estimation of the capacity of such reservoirs may be useful for the selection and monitoring during operation of water sources feeding the nearest settlements (Sestroretsk, Solnechnoye, etc.). Since the density of the enclosing rocks is higher than that of incising sediments, paleochannels constitute areas having a relatively high thickness of low-density sediments, over which negative gravimetric anomalies can be expected. At the first stage of the study, observations along a single profile crossing the assumed position of the paleochannel under study were performed. The study was conducted using a high-precision gravimeter Autograv CG-5 with geodesic tracking. The research confirmed the efficiency of gravity survey for solving the research tasks, as well as for performing areal gravimetric observations combined with shallow seismic surveys. The anomaly above the incision under study was approximately 1 mGa. The study revealed the presence of tectonic disruptions under the paleochannel, vertically displaced respective to the underlying sediments not inherited by the modern relief. Observations, processing and interpretation of the data were performed with the participation of students from the St. Petersburg Mining University in the framework of elective classes.