--> Abstract: The Topography and Landscapes of the Scandinavian passive Margin: What Caused Them and How Old Are They?, by Per Terje Osmundsen; #90177 (2013)

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The Topography and Landscapes of the Scandinavian passive Margin: What Caused Them and How Old Are They?

Per Terje Osmundsen

Scandinavia and Greenland were the sources for very substantial amounts of sediments from the Mesozoic to present day, but our understanding of how Scandinavia's topography and landscape evolved through this time is poorly known. The uncertainty related to the age of formation of relict surfaces has led some to question whether Cenozoic uplift is necessary to explain the topographic and landscape evolution of the margin. Also, topographic steps and landscape contrasts observed across tectonic lineaments require explanation: do they represent an exhumed, rift-age topography or a fault-related topography that was generated later? The crustal thinning gradient, or taper, of the crystalline crust appears to control the long-term landscape evolution and topographic evolution. The sharper the taper, the higher is the coastal escarpment, and the greater its degree of asymmetry. This relationship is valid for many glaciated and non-glaciated passive margins. At the sharply tapering Møre margin, low-angle normal faults facilitated tectonic excision of 3/4 or more of the crystalline crust. Onshore, the reactivated Møre-Trøndelag Fault Complex (MTFC) and important faults in the Lofoten-Troms regions generated up to >1.5 km high topographic envelopes consistent with normal fault displacement gradients. Mesozoic activity along the these faults is evidenced by both K-Ar dating of unconsolidated fault products and by jumps in apatite fission-track data. They document Triassic, Jurassic, Cretaceous and probably later activity. Some of the faults were active after the main phase of Late Jurassic-Early Cretaceous faulting, favouring a phase of post-rift topographic rejuvenation. These ages bring the rifted margin onshore NO, and highlight the gap in knowledge of its onshore history between the Paleozoic and the Quaternary. Post-rift onshore normal faulting is a phenomenon that Scandinavia shares with other passive margins. In SE Brasil normal faults bound inland Cenozoic half-graben basins and a low-relief peneplain was tilted and uplifted to high elevations. In Scandinavia, the patterns of topography and drainage related to formation and rejuvenation of the margin were modified and in some cases enhanced during the Quaternary glaciations, sometimes producing dramatic landscape contrasts across the reactivated faults. In particular, larger river hinterland valleys became incised along trends parallel to the slip direction recorded along a very distinct population of reactivated faults along the margin. A number of critical questions arise from these relationships, such as how old are the faults and how old are the drainage patterns that appear to be related to them?

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013