MORAINE COMPLEXES AND CERTAIN QUESTIONS CONCERNING PALEOECOLOGY OF THE TRESKELEN REGION IN THE HORN SUND FIORD (W. SPITSBERGEN).

Transcription

1 G. A. Tarasov, S. G. Denisenko, G. G. Matishov, I. A. Pogodina Murmansk Marine Biological Institute of the Russian Academy of Sciences Wyprawy Geograficzne na Spitsbergen UMCS, Lublin 1992 MORAINE COMPLEXES AND CERTAIN QUESTIONS CONCERNING PALEOECOLOGY OF THE TRESKELEN REGION IN THE HORN SUND FIORD (W. SPITSBERGEN). Material for this investigation was collected in June-July 1991 during the 49th voyage of the R/V Pomor" to the final part of the Hornsund Fiord. Moraine complexes of Treskelen Peninsula and moraine ridges above they sea level in the vicinity of the Storbeen Glacier (Fig. 1) were investigated. All those parallel ridges form a chain of moraine massifs left by a glacier in the last hundred years. The surface of the moraines is characterized by undulated-hilly relief with amplitudes of height changes 2-3 m. The altitude decreases from west to east beginning from 40 m (moraine No. 1) to 15 m (the last moraine). They are covered with one type of material, dark-gray in colour, which is built of various clay-sand particles with a great amount of stone material. A deep part of the moraines contains also sharp parts of rocks of different sizes and various degrees of rounding. Traces of ice scratches can be found on large rock boulders (Fig. 2). Afine grained part of the moraine massif looks like a concrete mass. Sometimes, especially on steep slopes, due to its consistency, the mass flows down. It is deposited on the submarine slope of Treskelen, down to the depth of 60 m. Numerous foraminifers and a grea amount of bivalvians (Fig. 3) can be found in moraines. Apart from them, there are also very well preserved red calcareous algae of Lithothamnion genus. Groups of bryozoans Celleporina ventricosa, Cellepora sp., Porella princeps, Porella minuta, Microporella ciliata have been found on shells of Chlamys islandica (moraine No. 1). Paleofaunal complex of bivalve molluscs in sediment of the moraine No. 1 is represented by the following forms (beginning from the most important ones): Chlamys islandica, Hiatella arctica, Mya truncata, Elliptica elliptica, Tridonta borealis. Chlamys islandica, Mya truncata, Tridonta borealis v. placenta, Elliptica elliptica can be found in sediments of the moraine No. 2. Chlamys islandica, Elliptica elliptica, Mya truncata, Astarte crenata in moraine No. 3 and Hiatella arctica in the moraine No. 4. Radiocarbon dating of shells of Chlamys islandica from the moraine No. 1 given the age 8380 ±80 years (GIN 7083), and from the moraine No ± 200 (GIN 7084). The samples taken from the moraine No. 1 in location 5, 20, 40 m a.s.l. contained a large number of benthos foraminifers (Fig. 4). Plankton forms also appeared there. The following foraminifers have 89

2 also been found in the complex: Elpidium clavatum, Cassidulina reniforme, Astrononion gallowayi, Cibicides lobatulus. Their shelters were very well preserved. Such forms are typical for arctic shelf complexes. Shallow water types Protelphidium orbiculare, Elphidium bartletti, and another type Nónion labradoricum (up to 5.3%) have also been found in the samples collected in localities 5 to 20 m a.s.l. In the layer No. 2 in the submarine part of the Treskelen slope, at the depth 60 m the amount of foraminifers decreases (Fig. 5). The dominating species are Cibicides lobatulus, Cassidulina reniforme, Elphidium clavatum, Astrononion gallowayi. There are also sand forms Spiroplectamina biformis there. A slightly different picture can be observed in the lower layer of bottom sediments No. 3, collected 200 m from the front of the Hans Glacier at the depth 50 m (Fig. 5). Here, most of foraminifers are juvenile forms, which are difficult to be recognized. The most popular are Cassidulina reniforme. The number of shelters varies from 180 to 200 m pieces, the highest amount is at the level 55 cm. A cross section Bel-1 (Bellsund Fiord) is quite similar, but the most common is Elphidium clavatum and a bit less common Cassidulina reniforme. Such taxonomic similarity of paleofaunal complex of bivalve molluscs in all the moraines proves their identical biocoenic occurrence. Formation of foraminifers complexes which can be found in moraines took place in normal marine conditions. The glaciers Stor and HoriTentered thefiord not more thenfive times in the last ten thousands years. The glaciers deposited sediments on the bottom during their movements, moved and also deposited material from upper layers on rock blocks situated across the fiord. Obviously, each time during movements the glaciers formed moraines. The oldest one is moraine No. 1 which means that previously the glaciers were much larger. 90

3 Fig. 1. Location of moraines and places where samples were collected in the Hornsund Fiord. 91

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6 СП tva С ^ О О m above sea level ««С о» ГО со о Q.u,Lnq.uelocuUna sp. PatelUna corrugata CLblcld.es lobatulus Buccella friglda NorxLonella auricula f/onionelllna labradorica Astrononion pallo way С &lph.ictiella arctica Sbphidium subarcticum Slphidlum bartletti Glphidlum orbiculare- &lph.icuum clairatum CassCdulina reniforme Islanaiella helenae Islandiella norerossi Trifarina fluens Sta.inforth.La loeblichl BolLvina. pseudopunctata PobymorphLnldae spp. bentalina Lttai Lagena sp. Lagena apiopleura Lagena strtato punctata OolLna costatcc Oolina melo Fissurina marginata FCssurina serrata Fissurina sp. Number of ben.th.lc specimens per 100 g of dry sediment -с о N> го "О r^ -с Number of species 4. Distribution of foraminifers in sediments of moraine No. 1.

7 I F itl-lllsm Но- 3 Г Mm) Иг-ИЮ ml Core number (water depth) / - A Weight percentage of ^ ^ V. seltre fraction > 0.05 mm, V» a «H ^ -t о о о О о о «Л ««И S 3 в М 0 0^ е»- Sample. depth In em ООО Adtreotryma Heephax scottll т п в TrochammlnoUa. glomtrata Spiroptoctammlna biformls sp. - qutneuclocullna ebpcrella advena т Pateulna cormoata stauteri КозаМпа ClbiciŁes lobatulus Ruecetla зрр. ttonlonellina trlglda iabradorica Astrononion Mel on is ta.rlita.nuj eiphietium ga.lleura.yi tlphidium subarcticum Ca.33iCLuJ.ina cla.tratu.rn reniformt Stain lslandiella helenae - Bolivina fort/ii sp. a lotblic/ti Labena Polirm orph graciluma in iclat spp. Indefinite FiSsurina зр. и v. мм «к Neogloboquadrina /feoglotoquadrma pachyderma pachyderma sen. dex. >гг \ Number of benthic specimens per 100 g of dry sediment ^ о number of species Л Ла «М о л a faunal dominance, */«Fig. 5. Distribution of foraminifers in bottom sediments in Hornsund and BelJsund Fiords. 95