SOME QUESTIONS OF THE PLEISTOCENE SEDIMENTATION OF THE BARENTS SEA SHELF

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1 Gennadyi A. Tarasov Murmansk Marine Biological Institute Russian Academy of Sciences XX Polar Symposium Lublin, 1993 SOME QUESTIONS OF THE PLEISTOCENE SEDIMENTATION OF THE BARENTS SEA SHELF ABSTRACT On the basis of the investigations of the full sections of the Barents Sea Quaternary sediments exposed by the bores, the analysis of moraine-like clays formation is given. Their general distribution on the shelf is shown. Peculiarities of these lithological formations are the following: typical combination of heterogenity and high contents of clay particles; they are the main indices of high speed of terrigenous material supply. The presence on the shelf imposing cuts of different ages and peculiarities of moraine-like calys composition give grounds to assume the prevailing role of the subglacial waters of Pleistocene Glaciers in the Barents Sea sedimentogenesis. Great importance is given to the mainland and insular Pleistocene Glaciation, fluvioglacial processes from which a great quantity of loose material was removed from the land territories and accumulated on the shelf and in the ocean. INTRODUCTION Large scale geological-geophysical investigations carried out recently, marine drilling data and engineering-geological investigations under the drilling platforms in the Russian zone of the Barents Sea which were caused by necessity of oil-gas search gave completely new from all points of view information on the structure peculiarities of the Barents Sea Quaternary deposits. Practically everywhere full thickness of loose deposits constituting maximum 120 meters has been drilled. The majority of these bores revealed moraine-like formations (diamicton) which can be attributed to the Low-Middle Pleistocene complex of deposits absolute age of which according to the data of works by amino-acidic, uranium-thorium, thermoluminiscent methods is ka (Gritsenko, 1992). They are presented as dense ( g/cm 3, humidity to 15%) dark-grey deposits with scattered gravel material. Their distribution everywhere and thick layers testify to the continuity of the Quaternary sedimentation process on the Barents Sea shelf. But scientists are of quite different opinion in the questions concerning 453

the genesis of these layers. Some scientists connect these formations with basin-transgressive sedimentation, others consider them as formation of the glacier complex.

2 the genesis of these layers. Some scientists connect these formations with basin-transgressive sedimentation, others consider them as formation of the glacier complex. MATERIALS AND METHODS This paper is based on the investigations of more than 100 column samples up to 3 meters long carried out on board the Scientific Research Vessel Dalnye Zelentsy" (Murmansk Marine Biological Institute). Seven core samples of marine drilling wells carried out from board of the drilling ship Bavenit" (Fig. 1) (Arctic Marine Geotechnical Expedition AMIGE") and also during the field investigations by the author on the islands and archipelagos: Spitsbergen, Franz-Josef Land, Novaya Zemlya and the Kola Peninsula coast. The author was given the chance to examine the materials of acoustic-seismic profiling. These materials were kindly given to the author by I. I. Gritsenko and U. U. Bondarev. The author is thankful to them. PLEISTOCENE SEDIMENTATION PECULIARITIES Recently there have appeared many papers concerning Quaternary sediments formation structure in the Barents Sea; these papers are based on the investigations of marine drilling core samples (Gritsenko, Krapivner, 1989, Bondarev et al. 1990, Tarasov et al. 1991). The eastern part of the shelf in general is presented by more or less homogeneous layer of loose sediments excluding only the Pechorskomorskaya part which has more complicated stratigraphy. Well illustrated Figure 2 was drawn on the basis of the acoustic seismic profiling data (Gritsenko, Krapivner, 1989). We have shown (Tarasov et al. 1991) loose deposits structure on the eastern slope of the Central Height. Quaternary deposits of general thickness 29 meters are divided into Holocene (0-5 m) and Pleistocene (5-29 m) according to the lithological peculiarities. Pleistocene in fully is presented by the massive moraine-like clays with bottom stone material (up to 2.05%) inclusion. To have a better and more complete picture of the character of deposit components in the negative land forms we shall give the data concerning core of the bore 189 situated in the confines of the southern border of the Goose chute at the sea depth 130 m; that is a relatively narrow chute stretching to the north-west direction between the Goose and North-Kanin Plateau. Bore 189 The bore reveals Quaternary deposits section 45 m thick m greenish-grey fine sand with inclusions of scattered gravel (dresva) 454

$and organic remnants. In the granulometric composition peak falls to the large aleurite fraction (0.1-0.05 mm) with the content up to 38.5%. Next fraction is fine sand (0.25-0.1 mm) up to 23.4%.$

3 and organic remnants. In the granulometric composition peak falls to the large aleurite fraction ( mm) with the content up to 38.5%. Next fraction is fine sand ( mm) up to 23.4%. General size composition is as follows: gravel 1-0.2%, sand 32.4%, aleurite 53.1%, pelite 14,05% m grey, fine silt, homogeneous, without visible inclusions. The prevailed fraction is a subcolloid component less than mm 22.5%. Coarse silt quantity is a bit less 21.0%. In general the aleurite content is about 40%, clay particles 38.15%. The contact between horizons is smooth m grey clay with spots of hydrotroilite, sticky, small debrises of lime shells can be seen. Deposits are characterized by the regular one peak histogram with the peak on the subcolloid fraction ( %, average 49%). The amount of sand is less than 1% m dark-grey moraine-like clay (suglinock) with many black flow rolls of the lithified clay and small debrises of angled particles, aleurite, scattered shell debrises. There can be noticed a high content of clay particles ( %) and their quantity in the section is more or less equally distributed. In the moraine-like clays percent of sand (up to 10.1%) is much greater than in the horizon laying higher. In the sands, particles of the fine fraction are mainly distinguished and the sum of the coarse and medium size compostions does not exceed 1%. In the interval of the bore m the colour of the moraine-like clay changes into light grey without changes in the granulometric composition. According to the mineralogical composition of the bore rocks the percent output of the heavy fraction is not great ( %) (Fig. 3). Autigenic minerals prevails, in the moraine-like clays their content is up to 98.7%, average 79.3%. Siderite is present here at high concentrations (92.9%). Content of pyrites in the bore section fluctuates from 0.2% to 20.2%, its high quantity is shown in the upper layer of the moraine-like clays horizon. In the clay rocks terrigenous minerals are distributed more or less equally though in some intervals concentrations can be noticed. It is typical for moraine-like clays (bore interval %) to have minimum mineral contents, very often they are found as separate grains or are even absent. Hornblende ( %) minerals of the epidote group ( %), garnet ( %), black ore minerals ( %) are present in clays in high concentrations. Apatite, zirconium, staurolite, leucoxene are present in smaller concentrations. Other minerals are found as separate grains. As far as chemical composition is concerned there exists a distinguishable difference between sediments in the horizons represented by the clays (bore interval m) and moraine-like clays (bore interval m) (Fig. 4). In the clay there can by clearly seen high contents of oxides C 0 2 ( %), F e ( %), MgO ( %), R ( %), A ( %). Water soluble salts are distributed in the same manner, the same refers to some microelements Mn ( %), Ti ( %), Ni ( %), 455

CO (0.001-0.002%) (Fig. 5). But increase in the content of С org. (up to 2.36%), CaO (23.52%), C a C 0 3 (32.32%), amorphous silica (up to 18.

4 CO ( %) (Fig. 5). But increase in the content of С org. (up to 2.36%), CaO (23.52%), C a C 0 3 (32.32%), amorphous silica (up to 18.89%) can be pointed out in the bore section from the top to the bottom, the maximum content are the sediments represented by moraine-like clays. The structure of Quaternary deposits in other bores is almost the same but they have different thickness in different parts of the shelf. In general combination of heterogeneity and high contents of clay particles is typical for them. This fact points to the high speed of terrigenous material supply. The question under what circumstances sedimentation of this thick complex occurred and what processes took place is still not clear. Analyses of shelf bottom geomorphology can be here additional factors. DISCUSSION Examples discussed in the paper give a basis for the conclusion that massive moraine-like formations on the Barents Sea shelf should be considered sediments, accumulation of which is fully and completely connected with glacier front retreat. Four processes dominate the formation: (1) low density (hypopycnal) overflows, (2) high density (hyperpycnal) underflow, (3) sediments gravity flows, (4) ice rafting (Edwards 1986). But determining and dominating role is played by high-density subglacial waters which are formed in the basal zone of the glacier due to the entering of the meltwater from the surface along the cracks and glaciers channels. Ice melting is the result of the Earth inner heat, ice melting near the glacier basement is a result of strong pressure. As a result of the subglacial water erosion flow valleys are formed, their cuts are several meters deep, one kilometer wide and several hundred kilometers long. Geomorphology peculiarities of the valley glaciers on the Barents Sea shelf have been studied in detaild by G. G. Matishov (1984). He gave a detailed analysis of the underwater valleys structure, he pointed out that almost all underwater fiords, marginal and transversal chutes have been timed to the old-structural-erosional shelf cut. During the glacier period glaciers and glacial meltwater widened and deepened already existing big cuts in the sea bottom surface. During other periods of glacier front retreat underwater valleys already formed were the directions of high-density flow of sediment material passing. The material was taken out far from the front to the shelf boundaries and into the deep-water basins beyond the Barents Sea. During the final fiord phase of glaciation underwater valleys owing to the enormous quantity of sediments either smoothed orfilled compeletely depending on the bottom relief topography. Fig. 7 shows a typical cut revealed by seismic acoustic profiling in the roof of the basic rocks, in the region of Murmansk Height, similar of other cuts are often 456

5 found. They are of different ages and formed in the basic rocks and in the Quaternary deposits. Thus, during the Quaternary sedimentogenesis in the Barents Sea high - density of underwater meltwaters were of great importance. They were characterized by the violent cycles connected with many years of climate warming up and flows stopping as a result of cooling. REFERENCES Edwards M., 1986: Glacial Environments. In: Sedimentary Environments and Fades. Oxford-London-Edinburgh Gritsenko I. /., 1992: Geology of Late Cenozoic sediments in the Barents Sea. Internationa] Conference on: The Oil and Gas Prospectivity of Barents - Kara Seas and Adjacent Areas. Murmansk, Gritsenko /. /., Krapivner R. В., 1989: Noveishie otlozhenija juzhno-barencevskogo regiona. Noveishie otlozhenija i paleogeografija severnykh morei. Apatity (in Russian). Matishov G. G., 1984: Dno okeana v lednikowyi period. Leningrad, Nauka. p. 176 (in Russian). Tarasov G. A., 1992: On Pleistocene underglacier (lows of thawing of the Last Glaciation in the Arctic Seas sedimentation. ICP 1Y. Kiel Tarasov G. A., Gricenko I. I., Matishov G. G., Pogodina I. A., 1991: Structure of the Quaternary incoherent deposits in the Central Eminence of the Barents Sea. Polar Session Arctic Environment Research. Lublin Address of the author: dr Gennadyi A. Tarasov, Murmansk Institute of Marine Biology, Institute of Russian Academy of Sciences, Vladimirska 17, Murmansk, Russia 457

76' 68 Fig. 1. Scheme of bores and profiles distribution Fig. 2. Seismic strati graphic sections (Gritsenko, Krapivner, 1989) on the profiles A and В (see Fig. 1).

6 76' 68 Fig. 1. Scheme of bores and profiles distribution Fig. 2. Seismic strati graphic sections (Gritsenko, Krapivner, 1989) on the profiles A and В (see Fig. 1). Seismic statigraphic complexes: 1 Upper Pleistocene-Holocene; 2 Upper Pleistocene; 3 Lower-middle Pleistocene; 4 Upper-middle Pleistocene; 5 before Cenozoic sediments; 6 lower Pliocene; 7 boundaries of complexes 458

$A aleurite; В heavy fraction output; С authigenic minerals; D siderite; E pyrites; F epidote$

7 Fig. 3. Main minerals distribution in the core 189 section. A aleurite; В heavy fraction output; С authigenic minerals; D siderite; E pyrites; F epidote group; H black ore; I garnets 459

Fig. 5. Microelements distribution in the core 189 section Fig. 6. Structure of Quaternary sediments section in the Porchnikha fiord, Murmansk coast.

8 Fig. 5. Microelements distribution in the core 189 section Fig. 6. Structure of Quaternary sediments section in the Porchnikha fiord, Murmansk coast. A bore section; В granulomere composition; С humidity; 1 sand-gravel materials; 2 finealeurite silts; 3 moraine-like clays; 4 pebble-gravel material; 5 sand; 6 aleurite; 7 pelite; 8 clay; 9 shells debris; 10 gravel; 11 pipes of worms; 12 solid rocks; 13 phormaniphera; 14 algae; 15 blow rolls. 460

ms ГК 80 100' l 81 i 8Z l 83 в' t Fig. 7.

9 ms ГК ' l 81 i 8Z l 83 в' t Fig. 7. Relief and cut peculiarities in the roofs of solid rocks in the region of Murmansk Height (Gritsenko, 1992). 461

FEATURES OF TERRIGEN1C MATERIAL TRANSPORT BY ICE IN POLAR SEDIMENTATION

FEATURES OF TERRIGEN1C MATERIAL TRANSPORT BY ICE IN POLAR SEDIMENTATION G. A. Tar aso v Murmansk Marine Biological Institute of the Russian Academy of Sciences Robert Spielhagen GEO MOR, Kiel Hannes Grobe Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven