The inheritance of a Mesozoic landscape in western Scandinavia

Abstract

In-situ weathered bedrock, saprolite, is locally found in Scandinavia, where it is commonly thought to represent pre-Pleistocene weathering possibly associated with landscape formation. The age of weathering, however, remains loosely constrained, which has an impact on existing geological and landscape evolution models and morphotectonic correlations. Here we provide new geochronological evidence that some of the low-altitude basement landforms on- and offshore southwestern Scandinavia are a rejuvenated geomorphological relic from Mesozoic times. K-Ar dating of authigenic, syn-weathering illite from saprolitic remnants constrains original basement exposure in the Late Triassic (221.3±7.0–206.2±4.2 Ma) through deep weathering in a warm climate and subsequent partial mobilization of the saprolitic mantle into the overlying sediment cascade system. The data support the bulk geomorphological development of west Scandinavia coastal basement rocks during the Mesozoic and later, long-lasting relative tectonic stability. Pleistocene glaciations played an additional geomorphological role, selectively stripping the landscape from the Mesozoic overburden and carving glacial landforms down to Plio–Pleistocene times. Saprolite K-Ar dating offers unprecedented possibilities to study past weathering and landscape evolution processes.

Complex Bedrock Fracture Patterns: A Multipronged Approach to Resolve Their Evolution in Space and Time

“…The ages of the coarser grain size fractions likely still represent mixed ages affected by various contents of protolithic K-bearing phases. The ages of the finest fractions remain maximum ages, but they are the best absolute chronological constraint of the last recorded slip event, as indicated by the steadily growing regional database, which is very consistent Fredin et al, 2017;Ksienzyk et al, 2016;Torgersen et al, 2015;Viola et al, 2016 7d-7i).…”

“…The ages of the coarser grain size fractions likely still represent mixed ages affected by various contents of protolithic K‐bearing phases. The ages of the finest fractions remain maximum ages, but they are the best absolute chronological constraint of the last recorded slip event, as indicated by the steadily growing regional database, which is very consistent (Fossen et al, ; Fredin et al, ; Ksienzyk et al, ; Torgersen et al, ; Viola et al, ). The dated fault gouges yield therefore a Middle Triassic age (245 ± 6 Ma, TSC‐66), Early Jurassic ages (185 ± 4 Ma, TSC‐28 and 183 ± 8 Ma, TSC‐65), and a Late Jurassic age (162 ± 5 Ma, TSC‐8), with both the Early Jurassic ages being identical within error (Table and Figures d–i).…”

“…At 39 localities within the RGD we also observed the results of processes other than faulting leading to the physical disintegration and decomposition of the rock, while the magmatic texture of the RGD remains preserved (see also Viola et al, ). We interpret this as resulting from fluid‐induced alteration, which can stem from hydrothermal fluids or from weathering (e.g., Fredin et al, ). Fluid‐induced alteration is restricted to the RGD and was found in predominantly steep, mainly N‐S striking fractures and faults (Figure j).…”

Fractured basement play development on the UK and Norwegian rifted margins

“…Permo-Triassic rifting, which culminated in the north-south-trending graben geometry of the Northern North Sea and Norwegian North Sea (Evans 2003;Sajjad 2013), was also associated with a warm and dry climate that lasted into the Late Triassic. Throughout this period, peneplanation and associated deep basement weathering (Lidmar-Bergström 1993;Olesen et al 2013) occurred in Norway, as well as over a wide area of Scandanavia (Fredin et al 2017). Triassic exposure and continental weathering products have been inferred to have affected the Rona play through the presence of aphanocrystalline hematite recorded 300 m (true vertical depth) below the basement unconformity , and from the presence and character of Triassic sediments which onlap the northern flank of the Rona Ridge at Lancaster (Fig.…”

“…In stark contrast to Rona, basement saprolites are very well developed across Scandinavia (Gunterberg 2013;Riber et al 2015;Fredin et al 2017), with most of the cores evaluated from the Utsira High showing signs of post-crystallization alteration (Riber et al 2015). Whilst the exact process of diagenetic alterations cannot be established for all well penetrations, it is evident that, from Late Triassic time, the basement was subaerially exposed and deep weathering took place.…”