|
|
|
|
|
|
|
|
CGG-02 Subglacial environments: Processes, sediments, landforms, modelling and experiments
|
|
|
|
Radar stratigraphy of the glaciotectonically deformed deposits in Isoniemi area, Haukipudas, Finland
|
|
|
|
Antti Pasanen, University of Oulu (Finland)
|
|
|
|
The Oulu region is situated in a crucial area, considering the behaviour of the Scandinavian Ice Sheet during the Weichselian Stage. The 25 km2 Virpiniemi-Isoniemi glaciofluvial complex is still relatively unknown despite the large-scale exploitation of sand and gravel in the last few decades. The Isoniemi glaciofluvial complex is the westernmost part of the Pudasjärvi end-moraine zone, which is thought to represent the Early Weichselian ice limit.
The sedimentary deposits in Isoniemi area were studied using Ground Penetrating Radar (GPR) in autumn 2005 and spring 2006. The GPR data was interpreted using the principles of radar stratigraphy.
The preliminary interpretation of the GPR data shows five distinct radar facies and two major radar surfaces. The lowermost radar facies consists of wavy and chaotic reflections with cross-cutting radar surfaces. It was interpreted to represent glaciotectonically deformed glaciofluvial deposits. Above it a radar facies consisting of weak amplitude chaotic reflections could be identified in places. The radar facies was interpreted to represent till deposits. The GPR data suggests that in the proximal side of the area the till may be thrusted close to the modern ground surface, whereas in the distal side the till deposits are laterally continuous. A radar surface consisting of concave high amplitude reflection was identified mainly in the distal side of the area. It was interpreted to represent a glaciofluvial erosion surface and a palaeochannel which reaches a maximum depth of approximately 15 metres and maximum width of 300 metres. Within the palaeochannel two radar facies were interpreted. The lowermost facies consists of concave reflections which were interpreted to represent channel fill deposits whereas the uppermost facies consists of eastward dipping reflections with an apparent dip angle of approximately 30°. The uppermost radar facies were interpreted to represent a glaciofluvial fan-delta deposited adjacent to the ice-margin. On top of all the other radar facies a radar surface consisting of horizontal and continuous reflection was identified. It was interpreted to represent an erosion surface of the littoral phase. Above it a radar facies consisting of horizontal and slightly dipping towards the west (seawards) and east reflections was identified. The radar facies was interpreted to represent redeposition of the earlier sediments in the littoral phase. The preliminary data suggests that the deformation of the glaciofluvial sediments were more intense in the proximal side of the area than in the distal side. Also in the proximal side of the area the till deposits can be older than the last glaciation in the area whereas in the distal side the till was probably deposited during the last glaciation. The three east-west orientated glaciofluvial channels cut in to the earlier sediments were found next to each other approximately 1km apart suggesting a multiple tunnel system at the ice margin.
|
|
|
|
|
|
|
|
|
