1. The part of the earth's crust surrounded by three large pre-Paleozoic platforms (the eastern European, middle Siberian, and Greenland-Canadian) is the Arctic basin, and the presence of these 3 platforms was the initial basis for the origin and development of the Arctic Ocean. The existence of these platforms and their surrounding fold belts created conditions favorable for sedimentary accumulation in the inner regions of the ocean.

2. The various sedimentary frameworks in different parts of the ocean show the different types of tectonic movements that affected the area, and indicate specifically the history of reconstruction of the former continental features into oceanic ones.

3. Oceanic margins--the regions of the present shelf--represent, according to tectonic data, vast parageosynclinal basins nearly of isometric shape, composed of thick sedimentary layers of different ages and structures. In a west-east direction one may observe the successive rejuvenation of the sedimentary cover and the progressive decrease in the degree of consolidation of the cover sediments.

4. The sedimentary framework of the eastern sector of the inner Arctic Ocean basin differs from that of the western sector. A double stage structure of the sedimentary sequence is typical for the eastern sector of the Arctic Ocean basin. Unconsolidated sediments with seismic velocity values of 1.6-2.5 km/sec are everywhere underlain by consolidated rocks with velocity values of about 3.5-4.5 km/sec. In the western Arctic basin, the unconsolidated sediments overlie either relict folded basement with seismic velocity values of 5.0-6.0 km/sec, or basaltic basement with seismic velocity values of 6.3-6.7 km/sec.

5. In large arched uplifts, the thickness of unconsolidated

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sediments is much less than that in the adjacent troughs, but in most places, the thickness of the rocks comprising the second stage is identical for both troughs and orogenically uplifted areas. The last fact suggests that the large vertical movements of the inner Arctic Ocean occurred mainly in late Mesozoic-Cenozoic time. It was during this time that the present morphometric form of the Arctic Ocean basin was created.

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