Мурманская МИЛЯ. 2018 г. №4.

EXPLORATIONS 66 Results Such organizations as JSC MAGE, FSUE Atomflot, FSBI AARI, VNIIOkeanologia named after I.S. Gramberg, OOO Morgeonats, JSC Sevmorgeo, JSC GNINGI, Hydro-C Ltd., OOO Baltiysky Proyekt, Convers Avia Airline JSC took part in field works. JSC MAGE was responsible for the works arrangement and planning, technical support, general man­ agement and seismic survey performance. VNIIOkeanologia named after I.S. Gramberg took part in preparation and planning of the voyage and interpretation. The general scope of integrated hydro­ graphic and geophysical survey was over 10,000 km: CMP reflection using a 600 m streamer along with reflection and refraction sounding over 3,373.2 km; using 4,500 m streamer - 5,596.950 km; bottom relief sur­ veying along with gravity survey. Most of the work was performed in the ice with concentration of 9/10ths to 10/10ths up to 160 cm thick. At some lines ice thick­ ness reached 240 cm and ice ridges reached the height of 4 m. The icebreaker YAMAL of­ ten cleared the way for itself and after that it came back and cleared the way for the RV AKADEMIK FEDOROV. The data quality control confirms the va­ lidity of 2D CMP reflection data to fulfil the geological tasks. The acoustic basement sur­ face and reflectors in the sedimentary forma­ tion are steadily and continuously traced over the most sections. All reflectors are steadily traced against their classification established for the east Arctic seas [6-7, 9, 13]. During work performance for the first time there was shot a continuous seismic line AR1407 crossing all main structures of the Eurasian Basin: the Amundsen Basin, Gakkel Ridge, Nansen Basin. The results of the sur­ vey performed allowed creating an integrated stratigraphic model correlated to the data of ACEX IODP 302 well on the Lomonosov Ridge [6, 9, 11, 13, 14] and at the compari­ son of thinning zones of main sedimentary sequences near the surface of the acous­ tic basement (AB) with the location of linear magnetic anomalies (LMA) [3], determining the basement age. On the whole in accor­ dance with these principles three main un­ conformities can be traced in the basins of the Eurasian Basin (Fig. 1). The upper unconformity contacts with the acoustic basement surface in the envi­ ron of LMA 13 (33 mln.years, Oligocene) and on this ground is interpreted as the regional Fig. 1. The interpreted fragmen t of the reflection section AR 1407 (the Barents Sea shelf - the Lomonosov Ridge) Рис. 1. Интерпретированный фрагмент разреза МОВ-ОГТ AR 1407 (шельф Баренцева моря - хребет Ломоносова) pre-Miocene unconformity (RU). Coeval un­ conformity is identified on the Lomonosov Ridge and is equivalent to the main break or sedimentation arrest in the ACEX well sec­ tion. RU formation in the Eurasian Basin is probably associated with natural sedimenta­ tion energy, initiated by the discovery of the Fram Strait passage. The middle, most prominent unconformity is adjacent to the acoustic basement surface in the interval between LMA 24 (53 mln years, upper Paleocene) and LMA 20 (44 mln years, mid-Eocene). This unconformity is identified as the lower Eocene one (EoU). The lower unconformity contacts with the acoustic basement surface in the environ of LMA 24 (53 mln years, upper Paleocene) and on this ground is interpreted as the post- Campanian (pCU). Coeval (according to the ACEX data) unconformity is identified on the Lomonosov Ridge and is equivalent to the second continuous sedimentation break - 57-80 mln years. The formation of the post- Campanian unconformity is supposed to proceed the beginning of spreading in the Eurasian Basin. The unconformity is the roof of the upper Cretaceous sequence which has formed as a synrift on the continental crust in the rifting zone. The data acquired showed the asymmet­ ric structure of the Nansen and Amundsen basins basement against the modern axis of spreading on the Gakkel Ridge. Not only the shift southwards from the ridge axis of the MURMANSK MILE • 4-2018