Field studies 2020: Chukotka Field Party

From 07.07.2020 to 25.09.2020 specialists of the Northeast sector of the Department of Regional Geology and Mineral Resources of Eastern Regions of Russia, FGBU VSEGEI, and invited specialists from the FGBUN Geological Institute, RAS, and the FGBUN Shirshov Institute of Oceanology, RAS, carried out field studies for Sheet R-60 under the task of FGBU VSEGEI “Creation of sets of the State Geological Map at a scale of 1:1,000,000 for a group of sheets of the Russian Federation in 2019-2021 (P-49, S-55 , 56, Q-57, R-59, R-60, L-55 (with K-55 flap), L-56”.

The purpose of the work was to create a set of the State Geological Map at a scale of 1:1,000,000, sheets R-59, R-60. Spatial boundaries are as follows: the Russian Federation, the Far Eastern Federal District, the Chukotka Autonomous District, the Iultinsky District - the Egvekinot urban district, sheet R-60.

The field studies were performed by the Chukotka Field Party of the North-East Sector, Department of Regional Geology and Mineral Resources of Eastern Regions of Russia, FGBU VSEGEI, at five prospects: Oleptyn, Veletkinai, Pyrkatagin, North and South Moltykan. Members of the field party: K.N. Mazurkevich, head of the party (FGBU VSEGEI), M.V. Luchitskaya, leading geologist, doctor of geological and mineralogical sciences (FGBUN Geological Institute, RAS (Moscow), N.V. Tsukanov, leading geologist, Ph.D. (FGBUN Shirshov Institute of Oceanology, RAS (Moscow), I.V. Zhigmanovsky, 1st category geologist (FGBU VSEGEI), N.O. Penzin, 2nd category geologist (FGBU VSEGEI), D.V. Bushueva, geologist (FGBU VSEGEI), M.V. Ivanov, technician geologist (FGBU VSEGEI) and seasonal workers: V.S. Kolyuka, V.V. Zagoskin, V.N. Tagin.

The field studies were carried out by groups consisting of two persons. The total length of transfers directly to the field study areas, between temporary camps and back was 2,100 km. GAZ-71 caterpillar trucks and Ural vehicles were used for transportation.

Transportation chart of the Chukotka Field Party during field studies

The field party studied the structural composition and made sampling for determining the absolute age of the gabbroids of the Early Mesozoic Anyui gabbro-dolerite complex. Gabbroid massifs were studied in the Pyrkatagin and Velitkenai prospects.

Gabbroid outcrops of the Anyui Complex (Pyrkatagin Prospect)

One of the largest plutons within the Chukchi Fold Area, the Velitkenai Massif, was also studied.

Granitoids of the Velitkenai Massif

At the Velitkenai Prospect, the Chukotka Field Party studied the metamorphic complex of rocks of the Velitkenai Massif and their interrelationships. The detailed study and sampling to determine the absolute age, as well as the investigation of the nature of contacts with the host rock will make it possible to confirm or deny the possibility of identifying the oldest Early Proterozoic formations in this area, which were not previously distinguished.

Metamorphic rocks of the Velitkenai Massif

Early Cretaceous sections of the Olkhovka Fm. (К1ol) were studied in detail. Deposits of the Olkhovka Fm. can be used as reference deposits for this area. In neighboring areas, the upper parts of the section of the Olkhovka Fm. were examined; however, in the area of Sheet R-60, the lower parts of the section, represented by conglomerate containing pebbles of intrusive rocks were mapped. The sections of the Olkhovka Fm. were studied in detail as well as their contacts with underlying and overlying sediments. Sampling was carried out for absolute age, which determination would make it possible to determine the age of the formations eroded at the time of the origination of the lower part of the Olkhovka Formation section.

The Olkhovka Formation sections were studied within the Velitkenai and Oleptyn prospects.

Bedrock outcrops of the Olkhovka Fm. (K1ol) on the right side of the Alapyrtyn (Oleptyn)

The main task at the Severny and Yuzhny Moltykan prospects, the Moltykan Massif, was to study the composition, structure, and interrelationship of various rock varieties. The contacts of the massif with the Triassic host rocks and overlying Late Cretaceous rocks were also examined.

Moltykan Massif

Age, composition, structural control, boundaries and areas of granitoids of the Ichuveem Complex of small Cretaceous intrusions were studied at the South Moltykan and Oleptyn prospects as part of the geological task.

At the Pyrkatagin and Velitkenai prospects, the work was aimed at updating the age, composition and tectonic position of the Paleozoic stratified formations of the Chaun SFZ within the Kuulsky Uplift of the Chukchi Fold Area. At the Oleptyn Prospect, our group updated the age, composition, geology and relationship of Triassic and Jurassic deposits within the Chaun SFZ.

When studying the age, genesis, distribution and relationship of Cenozoic formations, the structural and textural features and stratigraphic position of the glacial complex, the sediments of which filled in the trough valleys of the area, were updated; the structure and granulometric composition of alluvial strata were specified.

The Chukotka Party completed more than 250 km geological routes at a scale of 1:50,000 for studying pre-Quaternary deposits, more than 160 km of geological routes at a scale of 1:200,000 for studying Quaternary formations and geomorphological observations, 3,000 m of cross-sections were described, more than 3000 m of special-purpose geological studies on pre-Quaternary sediments and Quaternary formations were carried out.