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Abstract

Palaeomagnetic investigation of the Upper Carboniferous clastic Hyrnefjellet Formation from opposite limbs of the Hyrnefjellet Anticline in southern Spitsbergen (Svalbard Archipelago) uncovered two components of NRM. Direction C1 (D = 224.6°; I = –27.9°; κ = 22.40; α95% = 5.6°) is of prefolding origin and most probably of near-primary origin. High Tb spectra above 575°C indicate hematite as the carrier of C1. Acquisition of the C1 component may be related to an early diagenetic crystallization of hematite, not excluding a detrital origin of the NRM. A paleopole calculated for the C1 component (F = 23.3°N; L= 147.7°E) falls into the Late Devonian–Early Carboniferous sector of APWP for Baltica. This result suggests that Svalbard remained in the present day orientation with respect to Baltica since the Carboniferous time. A second component with intermediate unblocking temperatures, determined in the Hyrnefjellet Formation deposits, is labelled C2. Its mean orientation for in situ position is D = 11.2°; I = 69.2° (κ = 44.05; α95% = 6.3°), thus being similar to Late Mesozoic directions for Baltica. After 100% tectonic correction for tilting of anticline limbs and axis, the C2 component orientation is D = 265.7°; I = 59.7°, thus being distant from any directions for Baltica. Detailed analysis suggest that the C2 component is most probably of synfolding origin, and it was formed during the Tertiary Alpine Tectonic Event.

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Authors and Affiliations

Krzysztof Michalski
Marek Lewandowski
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Abstract

Nine samples of basic (dolerite, gabbro) intrusions collected at Bellsund, South Spitsbergen, have been K−Ar dated. Three dates, between 87.8 and 102.9 Ma, obtained from dolerite sills which intrude Carboniferous and Permian deposits in Van Keulenfjorden point to a Cretaceous age of intrusive activity (Diabasodden Suite). The K−Ar dates obtained from dolerite and gabbro which intrude Upper Proterozoic metasedimentary terrane of Chamber− lindalen form two groups: the dates between 97.1 and 178.6 Ma point to a Mesozoic age of the intrusions (Diabasodden Suite); the dates from a tectonized gabbroid (280.9–402.0 Ma) might point to a Late Palaeozoic age of the intrusion. No K−Ar dates which would indicate a Proterozoic age of the basic intrusions were obtained

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Authors and Affiliations

Krzysztof Birkenmajer
Zoltán Pécskay
Krzysztof P. Krajewski
Marek W. Lorenc
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Abstract

The Szamotuły Graben covers the southernmost part of the Permo-Mesozoic Poznań–Szamotuły Fault Zone. Along this regional discontinuity there are several salt structures, including the Szamotuły diapir, over which an extensional graben formed in the Paleogene and Neogene. The graben is located north of Poznań in central- western Poland, and is NW–SE-trending, ~20 km long, 3–5.5 km wide, and up to 160 m deep. It is filled with Lower Oligocene and Neogene sediments, including relatively thick lignite seams. Data from boreholes allow the assignment of the graben-fill sediments to appropriate lithostratigraphic units. Furthermore, analysis of changes in the thickness of these units provides evidence for periods of accelerated graben subsidence or uplift relative to its flanks. As a result, two distinct stages of tectonic subsidence and one inversion in the Paleogene–Neogene evolution of the Szamotuły Graben have been distinguished. Thus, relatively significant subsidence occurred in the Early Oligocene and the middle Early–earliest Mid-Miocene, while slight inversion took place in the middle part of the Mid-Miocene.

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Authors and Affiliations

Marek Widera
Wojciech Stawikowski
Grzegorz Uścinowicz

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