Occurrence of gas hydrate in the Chukchi plateau, Arctic

<p>The Arctic MArine Geoscience Expedition (AMAGE) program led by the Korea Polar Research Institute (KOPRI) is a multidisciplinary undertaking to investigate the geological environment and methane release phenomena in the Arctic seas. The icebreaking research vessel (IBRV) Araon has carried out three expeditions in the Chukchi Plateau (CP) and the East Siberian Seas in 2016, 2018 and 2019. In the first 2016 expedition, a chain of topographic mounds (with the height of several tens meters and the width of hundreds meters) was identified by subbottom profiler and multibeam bathymetric survey in the western continental slope of the CP. Gas hydrate samples were first retrieved in the Araon Mound-6 among the mound structures in the CP and ESS areas during the expedition. The detailed morphology and subsurface structures of the mounds were mapped from the subsequent expeditions in 2018 and 2019. More gas hydrate samples were obtained in the Araon Mound-3 and Araon Mound-6 in these expeditions. To examine gas hydrate occurrence conditions, we conducted geophysical surveys including seismic (sparker in 2018 and multi-channel in 2019) and heat flow methods during these expeditions. The seismic profiles obtained using two seismic methods show very well-developed bottom simulating reflectors (BSRs) which are widespread on the western slope of the study area. The BSR depths detected on the seismic profiles are well coincided with the depths of the lower boundary of the gas hydrate stability zone calculated from the geothermal gradient of heat flow measurement.</p><p>Arctic gas hydrates are considered to be vulnerable to the ongoing rapid Arctic warming. The AMAGE program will provide comprehensive understanding on poorly-known gas hydrate in the Arctic in the various research fields of geology, geophysics, geochemistry, biogeoscience, and oceanography.</p>

Seaward Dipping Reflectors Sequences (SDRs) mapping in the field of the Mendeleev Rise

<p>The report focuses on the strata of the Mendeleev Rise and adjacent Podvodnikov Basin, Makarov Basin, Toll Basin, and North Chukchi Basin together with Lomonosov Ridge and Chukchi Plateau. Eleven 2-D seismic profiles with a total length of 7540 km were interpreted. The uplifts within the study area are represented by asymmetric raised blocks of the crust with strongly rugged by half-graben structures. We found semi-continuous, from moderate to bright high-amplitude gently dipping reflectors similar to SDRs inside some half-grabens. The SDRs complexes distribute only in half-grabens. A few wedges with several kilometers thick can be distinguished here. The lower boundary of SDRs does not clearly trace. The relationship with underlying complexes is uncertain.  SDRs top is bright enough and interpreted as an angular unconformity, that is progressively onlapped by overlying sediments. Top of SDRs probably coincides with rift-postrift boundary age of 110-100 Ma.  We traced the distribution and direction of SDRs and made a map. SDRs dip from the central axis of Mendeleev Ridge in opposite directions – toward to Toll and Podvodnikov basins. In the central part of Podvodnikov and Toll basins are recognized small raised blocks of continental crust to which anti-directional SDRs converge. The nature of this rises can be explained by tectonic uplift. Thus, SDRs complexes dip symmetrically in two directions from the Mendeleev Rise. Two-directional SDRs also occur in conjugate Podvodnikov and Toll basins. They dip from the Mendeleev Rise and from the Lomonosov Terrace and the Chukchi Plateau, respectively. The SDRs occur on the hyperextension continental crust complex and accompany magmatism on volcanic passive margin (VPM). We propose that the Mendeleev Rise was formed as two-directional VPM, and the Lomonosov Terrace and the Chukchi Plateau also was formed as one-directional VPM. The Mendeleev Rise was formed simultaneously with Podvodnikov, Toll and North Chukchi basins ca. 125-100 Ma because of extensional tectonics. We also assume that the Makarov Basin (with obvious half-graben structures) could form simultaneously with the Nautilus Basin. This work was supported by RFBR grants (18-05-70011 and 18-05-00495).</p>

The rises of the Amerasia basin, arctic ocean, and possible equivalents in the Atlantic ocean

Main positive morphostructures of the Amerasia Basin, the Lomonosov Ridge, Alpha Ridge, Mendeleev Rise, Chukchi Plateau and Northwind Ridge, have been considered from geomorphological, geological and geophysical aspects. Time and Depth seismic sections have been provided up to the Moho discontinuity from the Lomonosov Ridge and its junction with the Greenland and East-Siberian shelves. Time and Depth seismic sections of the Mendeleev-Alpha rises and Chukchi Plateau are presented too. The sections were set up based on seismic surveys: deep seismic sounding and multichannel seismic reflection. Some similarities have been reflected for the foregoing land structure depth sections and typical sections of the continental crust. Brief geological and geophysical data have been presented for the positive morphostructures of the Atlantic Ocean such as the Rockall and Vring plateaus, the continental nature of which is established beyond all doubt. Genesis of positive morphostructures in the northern Atlantic Ocean and the Arctic Ocean has been connected with processes of continental rifting and concomitant intraplate magmatism.

Mineralogical characteristic of quaternary sediments (sand fraction) from the southern extremity of the Chukchi plateau, Arctic ocean

The data on mineralogical analysis of fine sand fractions in sediments accumulated in the southern part of the Chukchi Plateau during the Quaternary are presented. The associations and downcore distribution of the rock-forming and accessory minerals in relation to other characteristics are considered. The established climatically controlled mineralogical features, i. e. periodicity of warmings and coolings, can be used in solving a number of genetic problems, stratigraphic subdivision of sediments and paleoreconstructions.