ALBERT

Description: Project 74-4/683 - Proceeding and Generalization of Materials of Parametric Drilling on Arctic Islands (Nagurskaya and Severnaya parametric drill holes on the Franz Josef Land Archipelago). Reasons for drilling: 1. Study of the geological-geophysical section from the first deep drill hole on the Franz Josef Land Archipelago for providing reliable referencing of geophysical materials, for establishing structure of the sedimentary cover, rock properties and composition. 2. Obtaining information for stratification of the section and its allocation with geophysical sections. Technical results: The hole has penetrated the section of 3204 m and stopped in Neoproterozoic (Ediacaran) deposits. Scientific results: 1. The hole has crossed terrigenous and carbonaceous sedimentary rocks, metamorphic formations, and magmatic intrusive and effusive rocks. Besides, the hole has crossed a series of steeply dipping high amplitude disjunctive dislocations. 2. Stratigraphic sequence (based on different faunal groups, leaf flora, sporen, pollen) of the section has been carried out. 3. Two rock complexes have been defined in the section. From surface up to 1895 m there occurs a platform mantle composed of Triassic and Carboniferous carbonaceous-terrigenous rocks and Cretaceous terrigenous-volcanogenic rocks. This platform mantle is underlain by a folded basement 〉1309 m thick composed of Neoproterozoic shales and quartzites. 4. The platform mantle rocks lay almost horizontally in the followed sequence (from down to up): Early Carboniferous sandy-silt deposits of a paralic coal-bearing formation (155 m), Upper Carboniferous biogenic limestones (83 m), Early and Middle Triassic shallow marine silty-clayey deposits (1375 m), Early Cretaceous sedimentary-volcanogenic formation composed of blanket basalts with layers of clays and coaly argillites (283 m). 5. Neoproterozoic (Ediacaran) basement rocks dip at angles of 20-750. Quartz-sericitic microschists predominate in the lower part, microquartzites - in the upper part. These rocks belong to the greenschist facies of regional metamorphism. 6. The hole has crossed 21 intrusive bodies from 4 to 160 m thick along the borehole. Both steeply dipping dikes and layered bodies occur, mostly in the basement rocks. The followed rock types of the trapp formation occur: microdolerites (dolerites), gabbro-dolerites, quartz gabbro-dolerites, and taxitic gabbro-dolerites. Magma intruded in two phases: Late Triassic - Early Jurassic (between 205 and 190 myr BP) and Early Cretaceous (between 130 and 100 myr BP). 7. Accumulation of homogeneous Early Triassic silty-clayey deposits was in different conditions. Lower horizons (interval 1500-1600 m) accumulated in a marine basin with normal salinity in a quiet tectonic environment and slow compensate accumulation of clay sediments in reduced conditions. Upper horizons (500-1500 m) accumulated with high sedimentation rates in a marine basin with disturbed salinity in reduced conditions.