Three Polish Antarctic Geodynamical Expeditions in 1979/80, 1984/85 and 1987/88 undertook seismic investigations in West Antarctica. Seismic measurements, including multichannel seismic reflection and deep seismic soundings, were carried out in the region of the west coast of the Antarctic Peninsula, between Antarctic Sound and Adelaide Island, Bransfield Strait, South Shetland Islands and South Shetland Trench along several lines with a total length of about 5000 km. Selected crustal sections and one and two-dimensional models of the crust for this area are discussed in detail. The thickness of the crust ranges from 30-33 km in the South Shetland Islands to 38—45 km near the coast of the Antarctic Peninsula. The crustal structure beneath the through of Bransfield Strait is highly anomalous; a seismic discontinuity with velocities of 7.0—7.2 km/s was found at a depth of 10 to 15 km, and a second discontinuity with velocities of about 7.6 km/s was found at a depth of 20—25 km. A seismic inhomogeneity along the Deception-Penguin-Bridgeman volcanic line has also been found. A scheme for the geotectonic division and a geodynamical model of the area are discussed. On the base of all experimental seismic data, it will be possible to construct a continuous geotraverse from Elephant Island, across Bransfield Strait, up to Adelaide Island with a total length of about 1100 km. Crustal section and seismic models along the northern segment of the geotraverse from the King George Island to the Palmer Archipelago are discussed in detail here.
The lithospheric transect South Shetland Islands (SSI) — Antarctic Peninsula (AP) includes: the Shetland Trench (subductional) and the adjacent portion of the SE Pacific oceanic crust; the South Shetland Microplate (younger magmatic arc superimposed on continental crust); the Bransfield Rift and Platform (younger back-arc basin); the Trinity Horst (older magmatic arc superimposed on continental crust); the Gustav Rift (Late Cenozoic) and James Ross Platform (older back-arc basin). Deep seismic sounding allowed to trace the Moho discontinuity at about 30 km under South Shetlands and at 38—42 km in the northern part of Antarctic Peninsula (Trinity Horst), under typical continental crust. Modified crust was recognized under Bransfield Strait. Geological interpretation based on deep seismic refraction and multichannel reflection soundings, and surface geological data, is presented.
The results of the detailed seismoacoustic profilling (CSP, boomar) are presented. The investigation has been carried out in February 1985 and 1988 during two Geodynamical Expeditions organized by the Institute of Geophysics of the Polish Academy of Sciences. The boomar penetration of the caldera floor went down to 150 msec. Four seismoacoustic units of volcanic formations have been determined. The unit A corresponds to pre-caldera series and occurred only in the border part of the flooded caldera. The unit contains mainly pyroclastic rocks (consolidated agglomerates and tuffs) and probably some intercalations of lavas. The units B, C and D fill up the caldera bottom and correspond to post-caldera series. The units are composed of pyroclastic rocks, containing also materials redeposited by lahars, glaciers, landwaters and by wind. The units C and D (the youngest one) were certainly deposited under water. All the units are cut by numerous faults, vents and other types of intrusions. The larger faults, en echelon type, are situated around the bottom and form a ring-fracture. Caldera was formed by succesive stages of collapsing. This process is not finished yet and volcanic activity is still alive (especially in the western part of the flooded caldera).
Seismic refraction studies on Central Spitsbergen have shown that there is the fault systems with north-south strike directions, which divide the crust into western, central and eastern blocks. Thickness of the crust in this area varies from 35 to 40 km. Interpretation and modelling of seismic refraction data indicate that the Moho boundary beneath the Central Spitsbergen Basin is a complicated transition zone between crust and upper mantle with the thickness of about 5 km.
An analysis of seismic shocks from the Heer Land and the Nordaustlandet was made (shocks recorded by the Hornsund seismological station). Kinematic models and synthetic seismograms were constructed. A system of horizontal discontinuities located in the upper mantle was assumed. A good agreement between observational data from the seismograms and theoretical results was obtained.
On the ground of results obtained by the seismoacoustic profiling carried out in 1985 and primary examination of core samples the following main seismoacoustic units are distinguished and characterized: unit A — bedrock, unit B — till and/or compacted glaciomarine deposit, unit C — glaciomarine ice-front deposit, unit D — glaciomarine mud. These results enabled to present the distribution of seismoacoustic units along the fiord and its extension on the shelf, as well as to determine a relation of bottom structures to Late Vistulian(?) deglaciation and the action of Holocene tributary glaciers, probably during the Little Ice Age. The position of marginal structures corresponding to local retreat stages of the glacier front is also presented.
The Slyngfjellet Conglomerate which occurs at the base of the Upper Proterozoic Sofiebogen Group in South Spitsbergen had formed predominantly as a debris-flow deposit, with subordinate contribution by fluvial and probably lacustrine sediments. There is no evidence for glacial conditions at the time of formation of the conglomerate, the latter being much older than the latest Proterozoic Varangian glaciation tillites elsewhere in Svalbard. The Slyngfjellet Conglomerate originally filled buried valleys eroded by rivers in block-faulted and uplifted western margin of the Mid-Proterozoic Torellian Basin.
The paper presents descriptions and illustrations of Anthracoporella spectabilis Pia (Dasycladaceae) and Palaeoaplisina laminaeformis Krotov (Hydrozoa) from the Treskelodden Formation (Lower Permian, Sakmarian) of the Hornsund area (Treskelen, Urnetoppen), and Chaetetes arcticus sp. n. (Demospongiae) from the „Wordiekammen Limestone" (Pernio — Carboniferous) of the Isfjorden area of the southern and central part of Spitsbergen. A. spectabilis and P. laminaeformis common in the Hornsund area are also known from the northern Ural Mts. and Timan.
In Northwestern and Central Spitsbergen geomorphological and botanical data were collected on slope deposits associated with infrequent meteorological events. In hillslope debris flows triggered by heavy rainfall, compact volumes of debris range from 1 to 600 m3 . Recurrence intervals of major episodes are tentatively estimated from lichenometry at 80 to 500 years. Such debris flows are widespread in Spitsbergen and induce conspicuous geomorphological effects. Nevertheless, typical levees and lobes are small-sized because of the thinness of permafrost and they rarely survive more than one century. In contrast, catastrophic slush avalanches mobilize 1300 to 7000 m3 of rock debris every 500 years, forming long boulder tongues and fans. Such accumulations can been observed in much more restricted sites. In Central Spitsbergen at least three generations of slush avalanche deposits have been identified and lichenometry suggests that such boulder tongues survive for at least 2000 years. So the geomorphic impact of sporadic slush avalanches appears much more important than the effects of recurrent spring snow avalanches which do not generate original and long-lasting landforms. Botanical studies show that investigations of saxicolous lichen communities allow more reliable chronological reconstructions than observations of phanerogamic and bryophytic vegetation cover. Rhizocarpon diameters are partly interpreted from growth curves from Baffin Island and North Alaska. The results will be refined when a curve is published for Spitsbergen. Nevertheless, recurrence intervals proposed here seem to be consistent and are fruitfully compared with previous evaluations from Swedish Lappland and Colorado.
Studies of Quaternary sediments of South Spitsbergen (Hornsund, Bellsund and northern Billefjorden regions) focus on their occurrence, origin and chronostratigraphy. Methods and results of geological mapping are described. Glacial, glaciofluvial, glaciolacustrine and aeolian sedimentary environments, rock glaciers, taluses and raised marine beaches are presented. Mutual relations of these sediments as well as their radiocarbon and thermoluminescence datings made chronostratigraphy of Late Quaternary glacial episodes possible. Results of preliminary neotectonic studies are also presented, the same as works on periglacial phenomena, chemical weathering and tundra vegetation. Key significance of the studies for the Quaternary evolution of the Arctic and for better recognition of geodynamic phenomena of Pleistocene glaciations in Poland (Tatra and Sudeten Mts included) is underlined.
Field mapping and analysis of air photos enabled to prepare a photogeological map of Treskelen-Hyrnefjellet-Kruseryggen area in scale of 1:10,000. Slope, glacial and nival landforms and sediments, and ten raised marine beaches were distinguished. Morphogenetic evolution of the area is also presented, with discussion of probable glacier advances and land uplift during the Late Pleistocene and the Holocene.
Photogeological map of of Treskelen-Hyrnefjellet-Kruseryggen area, Wedel Jarlsberg Land, Spitsbergen.
Scale 1 : 10,000
The contents of copper, manganese, zinc, lead and cadmium have been determined in plants of the Spitsbergen tundra, collected at Calypsostranda, Lyellstranda and Chamberlindalen in 1987. Five species of vascular plants, four species of mosses and fourteen species of lichens have been investigated. Manganese content in all the studied plants falls in the physiological limits of this element. Appreciable concentrations of copper, and zinc exceeding the physiological concentrations of these elements and presence of lead and cadmium have been shown for many plants.
Permanent renewal of measurements of phenomena occuring on Earth sufrace — the main task of geodesy and cartography — is the important element of geodynamic studies of the Arctic and Antarctic regions. Insitute of Geodesy and Cartography participates in the program of research led by Polish Academy of Sciences for over 10 years, using conventional geodetic methods, as well as new types of data, acquired from satellite observations and through remote sensing techniques. This activity is evidenced by setting-up astronomical main points close to Hornsund Station in 1958, as well as at Arctowski Station in 1976, where cyclic astronomical and satellite measurements were performed on these points. Geodynamic test site was organized in the Hornsund Region. As a result of these works numerous topographic and thematic maps were produced and many scientific publications were prepared by Institute specialists.
Freedom of research is one of the fundamental principles upon which the Antarctic Treaty System (ATS) was founded. Its scope is defined by the limitations imposed by relevant legal rules. They provide among other for prohibition of scientific investigation of military character and declare that no activities — including research — shall constitute a basis for territorial claims in Antarctica. Of particular importance are limitation;' imposed on freedom of research for the benefit of environmental protection. But, contrary to some views, most scholars consider that the freedom of research and the protection of the environment and ecosystems in Antarctica are equally important principles central to the whole ATS. They are inter-dependent and neither one should be attributed priority over the other. In the best interest of science, Antarctic research needs to be controlled to the necessary minimum of environmental impact and risk.
Aby subskrybować czasopismo wpisz swój adres e-mail:
*Pola oznaczone gwiazdką są obowiązkowe do wypełnienia i zaznaczenia. Aby subskrybować czasopismo musisz wyrazić zgodę na przetwarzanie danych osobowych.