DIFFERENTIATION OF NEOTECTONIC MOVEMENTS IN WESTERN S0RKAPP LAND (SPITSBERGEN) ON THE GROUND OF PHOTOINTERPRETATION

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1 Ryszard Szczęsny Institute of Geology Warsaw University X X Polar Symposium Lublin, 1993 DIFFERENTIATION OF NEOTECTONIC MOVEMENTS IN WESTERN S0RKAPP LAND (SPITSBERGEN) ON THE GROUND OF PHOTOINTERPRETATION Deglaciation after the Vistulian = Wiirm = Weichsel = Sorkapp Land Glaciation (Lindner, Marks and Pękala 1987) generated intensive uplift of whole Svalbard archipelago, due to glacioisostatic rebound of the earth crust. Raised marine beaches are the evidence of vertical land and sea movements in the past. Rate and range of these movements are intensively studied and adequate schemes are constructed (Grosswald et. al. 1967, Boultonet al. 1982). According to above mentioned interpretations Svalbard is raising almost en-block, stronger eastwards than the westwards. But these schemes are based on a few, separated measuring points only, so they seem to be simplyfied. Structure of pre-quaternary rocks is not taken into consideration there. Geologic investigations show that especially western part of Spitsbergen has a specific block structure formed in the Palaeocene during the Spitsbergenian Phase" (Flood, Nagy and Winsnes 1971, Birkenmajer 1972). In author's opinion Holocene vertical land movements are concentrated along the main dislocations. It is confirmed by geophysic measurements which indicate that areas of contemporary seismic activity correspond to the main fault zones (Chan and Mitchell 1985, Panasenko, Kremenetskaya and Aranovich 1989). Existence of separated blocks in the bedrock should induce their independent vertical movements. Author's investigations were carried out in the western part of Sorkapp Land. Bedrock is cut by system of dislocations of WNW-ESE and NE-SW directions there (Fig. 1). Because of scarcity of absolute datings of raised marine beaches, author decided to test another method for reconstruction of vertical movements of the individual blocks. Different rate of raising should differentiate superficial processes, e.g. rate of dissecting of raised marine beaches by glacial rivers. In order to verify this principle detailed analysis of Norwegian air photos in a scale of 1:50,000 was made (see Szczęsny 1991). It was completed by several morphological profiles prepared with a use of stereoplotter Topocart В (see Figs 2, 3, 4). Measurements were made between the Gasbreen and Olsokbreen (see Fig. 1). This part of the coast was divided into the 3 parts of different lithology of bedrock and structure of raised 441

2 marine beaches. The northern part Kulmstranda is composed of Carboniferous sandstones covered by the Quaternary marine shingle forming 7 raised marine beaches at altitudes from 3 to 100 m a.s.l. (Klysz and Lindner 1981). In the western part (Breinesflya) of the same composition, 8 raised marine beaches at altitudes from 3 to 75 m a.s.l. were distinguished (Ostaficzuk, Lindner and Marks 1982, 1986). The southern part Bjornbeinflyene is quite different. Marine terraces are cut within the Ordovician limestones and Triassic siltstones (Szczęsny, Lindner and Marks 1987). Only 4 terraces at altitudes from 5 to 26 m a.s.l. were distinguished there. Within the each part the biggest permanent rivers were selected and their longitudinal profiles were prepared. These profiles were connected with morphological ones across the raised marine beaches, located close to the rivers (Figs 2, 3, 4). If studied area is raising steadily in time, rate of dissection of marine beaches increases with their altitude (like on profile E-F on Fig. 2) and is similar along the all coast. Compared profiles show that dissection of successive raised marine beaches is different for the individual rivers. Dissection of marine beaches of the same altitude is incomparable as well. On this ground sectors of different character of dissection were distinguished. They seem to be connected with periods of varying tectonic activity of the bedrock. Interpreted vertical movements were divided into the 3 grades: intensive raising, moderate raising and stagnation. The last grade could also include periodic subsidence. In the northern part of studied area beaches above 25 m a.s.l. were moderately raised while the lower beaches were raised much more intensively (see Fig. 2). In the western part (Fig. 3) beaches above 35 m a.s.l. seem to be moderately raised. Then, up to forming of the beach 15 m a.s.l. uplift went out. The lowest beaches from 3 to 15 m a.s.l. were moderately raised again. Exceptional is area close to the Vinda (profile M-N), where more intensive raising of the lowest beaches is observed. The most differentiated movements are observed in the southern part, where bedrock is fractured into several small blocks (see Fig. 1). After the forming of terraces above 15 m a.s.l. distinct differentiation of raising rate is observed. The most intensive raising was in vicinity of Bjornbeinbekken and Luktvassebekken, while close to the Vitkovskibekken and Hilmarbekken raising was only moderate (Fig. 4). Results of above interpretation were compared with a map of tectonic dislocations (Fig. 1). Clear connection between structure of the bedrock and differentiation of vertical movements was distinguished. Independent reaction of individual blocks at decreasing load of glacier ice is distinct. On this ground contemporary active fault zones could be also shown. Presented analysis would be also completed by field investigations. Field442

3 works should focus on geodetic measurements, especially on precise levelling across the potentially active fault zones. Sampling of all raised marine beaches (on every block) for absolute dating should be also done. Such complex investigations would create the basis for full and reliable interpretation of differentiation of neotectonic movements generated by glacioisostasy. REFERENCES Birkenmajer K., 1972: Tertiary history of Spitsbergen and continental drift. Acta Geol. Polon., 22: Birkenmajer K., 1978: Cambrian succesion in South Spitsbergen. Studia Geo). Polon., 59:7-47. Boulton G. S., Baldwin С. Т., Peacock J. D., McCabe A. M., Miller G., Jarvis J., Horsfield В., Worsley P., Eyles N.. Chroston P. N.. Day Т. E., Gobbard P., Hare P. E., and Brunn V., 1982: A glacio-isostatic fades model and amino acid stratigraphy for the Late Quaternary events in Spitsbergen and the Arctic. Nature, 289, Chan W. W. and Mitchell B. J., 1985: Intraplate earthquakes in northern Svalbard. Tectonophysics 114, Flood В., Nagy J. and Winsnes T. S., 1971: Geological map of Svalbard 1:500,000, sheet 1G, Spitsbergen, southern part. Norsk Polarinstitutt Skr. 154A. GrosswaldM. G., Devirtis A.L., DobkinaE. I. and Semevsky D. V., 1967: Earth crust uplift and the age of glaciation stages in the Spitsbergen area. Geochemistry 1, Klysz P. and Lindner L., 1981: Development of glaciers on the southern coast of Hornsund in Spitsbergen, during the Wtirm (Vistulian) Glaciation. Acta Geol. Polon., 31: Lindner L., Marks L. and Pękala К., 1987: Quaternary chronostratigraphy of South Spitsbergen. Polar Res. 5 n.s Lindner L., Marks L. and Szczęsny R., 1986: Late Quaternary tectonics in western Sorkapp Land, Spitsbergen. Acta Geol. Polon., 36: Osląficzuk S., Lindner L. and Marks L., 1982: Photogeological map of the Bungebreen forefield (West Spitsbergen), scale 1 : 10,000. Państw. Przeds. Wyd. Kart., Warszawa. Ostaficzuk S., Lindner L. and Marks L., 1986: Photogeological map of the Slaklidalen region (Serkapp Land, Spitsbergen), scale 1 : 10,000. Wyd. Geol., Warszawa. Panasenko G. D., Kremenetskaya E.O. and Aranovich Z. /., 1989: Earthquake on Spitsbergen. Ac. of Sci. of the USSR Moscow, 81 pp. Szczęsny R., 1991: Quaternary landforms and deposits in southern Spitsbergen on the ground of photointerpretation. Pol. Polar. Res. 12/3, Szczęsny R., Lindner L. and Marks L., 1987: Photogeological map of the Hilmarfjellet region (Sorkapp Land, Spitsbergen), scale 1: Wyd. Geol. Warszawa. WendorffM., 1985: Geology of Palffyodden area (NW Sorkapp Land) course and some results of investigations in Zesz. Nauk. UJ, 756, Prace Geogr., 63: Address of the author: dr Ryszard Szczęsny, Institute of Geology, Warsaw University, Żwirki i Wigury 93, Warsaw, Poland 443

4 ZRÓŻNICOWANIE TEMPA RUCHÓW NEOTEKTONICZNYCH W ZACHODNIM S0RKAPP LAND (SPITSBERGEN) W ŚWIETLE ANALIZY FOTOINTERPRETACYJNEJ Streszczenie W artykule przedstawiono próbę oceny zróżnicowania tempa ruchów tektonicznych powodowanych glacjoizostazją w zachodniej części Sorkapp Land (Spitsbergen). Z racji na blokową budowę podłoża przedczwartorzędowego (fig. 1) należy spodziewać się niezależnej reakcji odpowiadających im fragmentów wybrzeża na odciążanie a co za tym idzie różnicowania niektórych zachodzących tam procesów powierzchniowych. Na podstawie pomiarów wykonanych na zdjęciach lotniczych określono stopień rozcięcia wyniesionych teras morskich przez stałe rzeki glacjalne (fig. 2, 3, 4). Głębokości wcięć erozyjnych nie wykazują bezpośredniego związku z wysokością teras i są różne na poszczególnych profilach. Wydaje się, że przyczyną tego zjawiska jest nierównomierne, tak w czasie jak i w przestrzeni, dźwiganie zachodniego wybrzeża Sorkapp Land. Porównanie uzyskanych wyników z mapą sieci nieciągłości tektonicznych wskazuje na istnienie wyraźnego związku pomiędzy budową podłoża a zróżnicowaniem głębokości rozcięć teras. Największe zróżnicowanie stwierdzono w południowej części badanego terenu (fig. 4), gdzie podłoże przedczwartorzędowe jest wyjątkowo silnie spękane (fig. 1). W celu ostatecznego zweryfikowania przyjętych założeń konieczne jest pobranie prób w celu określenia wieku poszczególnych wyniesionych teras morskich na każdym z bloków oraz przeprowadzenie precyzyjnych pomiarów geodezyjnych dla określenia tempa przemieszczeń stref tektonicznych podejrzanych o współczesną mobilność. Praca zrealizowana w ramach badań własnych Instytutu Geologii Podstawowej UW. 444

5 Fig. 1. Map of dislocations in western Sorkapp Land, adopted from: Flood, Nagy and Winsnes 1971, Birkenmajer 1978, Wendorff 1985, Lindner, Marks and Szczęsny 1986 and Szczęsny, Lindner and Marks 1987:1 ice-free areas, 2 glaciers, 3 lakes, 4 shoreline, 5 overthrusts, 6 inclined faults, 7 vertical faults, 8 profile lines, 9 grades of activity of vertical movements: intensive raising, moderate raising, stagnation 445

6 Fig. 2. Morphological profiles across the Kulmstranda: 1 morphological profiles across raised marine beaches, 2 longitudinal profiles of rivers, 3 grades of activity of vertical movements: intensive raising, moderate raising, stagnation

7 Fig. 3. Morphological profiles across the Breinesflya (for explanations see Fig. 2)

8 oo m a.sl SW w 0 ^itkovskibekken ( ) P m a.s l U Hilmorfaekken (*) U mas.l mc.il. 20 Ю 250m Fig. 4. Morphological profiles across the Olsokflyene (for explanations see Fig. 2)