The Sub-Cambrian Peneplain in southern Norway: its geological significance and its implications for post-Caledonian faulting, uplift and denudation

Abstract

The Sub-Cambrian Peneplain in southern Norway formed in the Cryogenian–early Cambrian. It was transgressed in the Cambrian–early Ordovician, and subsequently broken up by Caledonian thrusting, post-Caledonian normal faulting and regional uplift. In southern Norway the Sub-Cambrian Peneplain is generally expressed as an angular unconformity or nonconformity surface with no apparent deep weathering. In some localities the basement is characterized by a weathered top. Furthermore, the basement may have a mineralized top in some cases. The peneplain is commonly overlain by in situ regolith, and/or Cryogenian glacial diamictite, Lower–Middle Cambrian siliciclastic sediments, Lower–Upper Cambrian black shale or Lower Ordovician limestone. It has commonly mildly tectonized contacts, but occasionally displays contacts that have been completely destroyed by Caledonian thrusting and reworked into fault rocks. Tracing the peneplain across southern Norway reveals a fault-affected and fault-delineated plateau with a sloping eastern margin. Onshore cumulative offsets record vertical movements of > 2000 m. A 1–5° dip below Caledonian nappes suggests a flexural component related to tectonic overburden. As the oldest identifiable and dateable surface covering much of Scandinavia the peneplain constitutes the reference surface for studies of the younger regional morphotectonic evolution. Its shape supports the interpretation that Cenozoic uplift combined with faulting, not smooth flexural doming, caused the Southern Scandes high in South Norway.

The U–Pb age of the Finse batholith, a composite bimodal Sveconorwegian intrusion

“…The basement was eventually uplifted, eroded down, forming a regolith which is locally preserved as a zone of weathering and alteration a few metres thick, with typical rustiness, and the local development of a basal conglomerate (Goldschmidt, 1912;Gabrielsen et al, 2015).…”

Tectonic, sedimentary and diagenetic controls on sediment maturity of lower Cambrian quartz arenite from southwestern Baltica

“…During early Cambrian time, Baltica was located around 35–60° south (Torsvik & Cocks, ,), in an estimated warm temperate to moderately humid climate (Dreyer, ). By this time, the Scandinavian part of Baltica was a relatively flat surface termed the Sub‐Cambrian Peneplain (Gabrielsen, Nystuen, Jarsve, & Lundmark, ). The peneplainization resulted from denudation of the 0.90–1.20 Ga Sveconorwegian–Grenvillian Orogen, and generated large amounts of sediment available for deposition.…”

“…These deposits are now a part of the Caledonian Osen‐Røa Nappe Complex. The Ringsaker Member also occurs in autochthonous position beneath the Caledonian nappe cover, directly on the Sub‐Cambrian Peneplain (Elvsborg & Nystuen, ; Gabrielsen et al, ).…”

Crustal structure of the Ruby Mountains metamorphic core complex, Nevada, from passive seismic imaging

“…"Moho offsets" and "mantle shear zones" have previously been interpreted beneath the North Sea as due to post-Caledonian Devonian crustal collapse (the "paired shear zone" model of Fossen et al, 2014) that is linked to core-complex formation, overprinted by Permo-Triassic rift formation (the "decoupled stretching" model of Klemperer, 1988). Marine deep-seismic reflection profiles along the Norwegian margin show an "intramantle bundle of reflections" and "crust/Moho offsets" that span ~20-30 km at the Moho and extend ~10 km below the Moho (Gabrielsen et al, 2015), similar to the scale of our crustal welt defined by converters m1 and m2. Other possible examples are minor crustal roots at the margins of the Dabie Shan core complex, eastern China (Yuan et al, 2003) and the Nyainqentanglha core complex, eastern Tibet (Tian et al, 2015).…”