In September 2020, the Department of Regional Geoecology and Marine Geology carried out field studies in the East Siberian Sea within the confines of the Russian Federation, Sheets S55-56 (Far Eastern Federal District of the Russian Federation).
The Polar Party consisted of 9 specialists: I.A. Neevin (head of the party), A.Yu. Sergeev (chief geologist), A.V. Shmanyak (leading geologist), L.M. Budanov (1st category geophysicist), V.I. Khorikov (1st category geologist), F.A. Leontiev (1st category geologist), E.S. Nosevich (1st category geologist), A.A. Moskovtsev (1st category geophysicist), A.V. Chekulaev (1st category geophysicist).
In accordance with the Fieldwork Program, main geological tasks of field studies consisted in detailed investigation of geological features of the territories, including:
- identification and tracing of limits of Quaternary cover seismostratigraphic units – seismic sequences;
- correlation of seismostratigraphic units with stratigraphic-genetic units on land;
- identification of Late Pleistocene loess-ice features (Yedoma Formation) and a complex of Holocene polygenic features, which are bone-bearing reservoirs of the first and subsequent generations, and assessing the prospects of coastal-marine areas for fossil mammoth bone;
- establishing limits and areas of lithological (granulometric) types of bottom sediments, determining their petrology and genotype using bottom sampling.
All the studies were performed from the rented research vessel Kapitan Voronin. The ice situation in the study area allowed the planned studies to be fulfilled. Despite difficult hydrometeorological conditions (wind speed ranged from 9 to 17 m/s, wave height from 0.2 to 2.5 m), the work program was overfulfilled one-and-a-half times.
R/V Kapitan Voronin in the port of Tiksi
Physical and geological map of fieldwork area
The work was made along the system of regional rectilinear profiles of great length, at a speed of 4.5-5.5 knots. Simultaneously (in one passage of the vessel) 3 different types of geophysical and hydrographic methods were performed, namely:
• bathymetric survey with a multi-beam echosounder (MBE);
• side-scan sonar (SSS);
• Continuous seismoacoustic profiling (CSP) was performed using three seismoacoustic instrumentation systems designed for seismic operations of high and ultra-high resolution in water areas when studying the structure of the bottom and bottom sediments. Depending on specific geological conditions, two types of radiation sources were used: the high-frequency sparker with a central frequency of the sounding signal of 530 Hz and a low-frequency sparker with a central frequency of 270 Hz; at the same time, recording was also made in a multifrequency mode (at frequencies of 6, 10, and 100 kHz simultaneously) with a high-frequency parametric profiler mounted on a boom.
Results of geophysical methods
Sampling bottom sediments. The sampling of bottom sediments was carried out for granulometric and mineralogical analysis and other types of analytical studies, as well as to verify and interpret the SSS and CSP data using grab buckets, box corers and gravity direct-flow corers.
Underwater video observation
Underwater video observation was performed using remotely operated underwater vehicles and an ultra-high-resolution camera for verifying and interpreting data of the SSS and sampling, to establish the limits and areas of granulometric types of bottom sediments and to determine their petrology and genotype. An AC-ROV 100 underwater television and a camera with flashlights mounted on a bucket were used.
Equipment used for underwater survey: a - AC-ROV 100 underwater television; b - Sony high-resolution camera, mounted on the box-corrector
Main results of the field studies:
1. Volumetric indicators in terms of the length of the profiles of continuous seismoacoustic profiling and side-scan sonar envisaged by the Fieldwork Program have been fully completed.
2. Volumetric indicators in terms of the number of sampling stations, video profiling stations and the planned number of samples were fully accomplished.
3. For the first time, primary geophysical data (CSP) were obtained for the water part of Sheets S55-56, which make it possible to identify and trace the limits of seismostratigraphic units of the Quaternary cover – seismic sequences for correlation with stratigraphic-genetic units on land and the subsequent compilation of sheet-by-sheet maps of Quaternary formations, as well as to identify areas of Late Pleistocene loess-ice features (Yedoma Formation) and a complex of Holocene polygenic features that are bone-bearing reservoirs.
4. Bottom sediment cores were taken (22 columns with a total length of 16 m 48 cm) and sedimentation material was obtained for subsequent laboratory studies (granulometric, geochemical, mineralogical, micropaleontological analysis, absolute dating) for determining the genesis and age of Quaternary sediments. 5. Surface bottom sediments were sampled for further laboratory studies and materials of underwater videorecording were obtained for establishing limits and areas of lithological (granulometric) types of bottom sediments and their petrography and genotype.