GEOLOGICAL HETEROGENEITY OF A SEDIMENTARY COVER OF THE PECHORA PLATE ACCORDING TO HYDROMAGNETIC SURVEY

In August–September, 2018 in the Pechora Sea during the 38th flight of NIS “Academician Nikolay Strakhov” complex geologic-geophysical researches were conducted. Magnetic survey was carried out along with seismic profiling where as the radiator of elastic fluctuations the electrospark Sparker radiator was used. The group of a sea magnetometry was faced by a problem of mapping of the top layer of a sedimentary cover, including allocation of zones of development of thin deposits, buried paleochannels, zones of jointing and geological explosive violations. Hydromagnetic survey and interpretation of the received materials was as a result executed that allowed to estimate spectral structure of the abnormal magnetic field (AMF) and to allocate three frequency components to which there corresponds the deep range of sources of the field. Leaning on the received estimates of depths, and comparing them to the description of wells, also temporary bindings for the allocated deep ranges of sources of magnetic field were defined. High-frequency component, there corresponds the arrangement of sources of AMF in the topmost part of a section. The top edges of sources lie in the range of depths from 35 to 70 m that possibly correspond to deposits of pleystotsenovy age. It is possible that the thin deposits created during the last Valdai freezing can be sources of these high-frequency anomalies. The second deep range is created by sources of AMF the top edges of which are located in the range of depths of 260–510 m that possibly corresponds to stratigrafichesky range from top Yura to the lower chalk. The third, the deep range of bedding of the top edges of sources of AMF allocated by authors is determined by the most low-frequency part of a range and according to authors reflects the late Devonian stage of activization of magmatism.

3‐D tomographic seismic inversion of a paleochannel system in central New South Wales, Australia

Buried paleochannels are of significant interest for understanding hydrological mechanisms and their potential as alluvial gold deposits. Seismic tomographic methods are a suitable solution for resolving the vertical and horizontal structure of such features. We assess a method for seismic 3‐D tomographic inversion from refraction arrivals with reflection control over a suspected paleochannel adjacent to the Wyalong gold fields in the Lachlan fold belt of central New South Wales, Australia. A standard multichannel engineering seismic recording and cable–receiver system was used on a 3‐D field geometry of multiple linear arrays. More than 3000 P‐wave first‐arrival traveltime values were inverted using a regularized inversion scheme for which simplified 2‐D models served as initial velocity–depth models for the complete 3‐D inversion. Seismic reflection arrivals provided additional depth estimates to the bedrock and compensated for a lack of refraction phases at that depth. Correlating the 3‐D seismic velocity–depth data with existing drillhole and nonseismic geophysical data resulted in a detailed structural and compositional interpretation of the paleochannel and the incised regolith. The model suggests the presence of a system of deposits from meandering channels overlying a metasedimentary bedrock formation. The general paleodrainage deposit is relatively conductive in electromagnetic surveys, indicating a potential saline storage or transport mechanism.