How post-Caledonian burial, exhumation and peneplanation shaped the scenery of Fennoscandia

The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides limited documentation of the post-Caledonian history. But a more complete understanding can be obtained by also considering evidence of rocks that were formerly present but have since been removed (‘missing section’).

We report apatite fission-track data and associated thermal history constraints in 331 samples of Precambrian basement, Phanerozoic sediments and igneous rocks from outcrops and boreholes (up to 6 km depth) from Norway, Sweden and Finland, which define multiple episodes of cooling over the last billion years.

We are therefore able to establish a post-Caledonian history of Fennoscandia involving repeated episodes of kilometer-scale burial and exhumation with key episodes of exhumation beginning during late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene. The effects of these episodes are documented in the stratigraphic record and as prominent peneplains. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasizing the tectonic nature of the history.

Results from Finland record events also recognized in Norway and Sweden (though less pronounced) and are thus not consistent with long-term cratonic stability. We interpret the lack of preserved Phanerozoic sedimentary cover in Finland to be due to complete removal during multiple episodes of denudation. For example, our results show that about 2 km of Cambrian to Middle Triassic sediments covered the Sub-Cambrian Peneplain in southern Finland prior to the onset of Middle Triassic exhumation. In southern Scandinavia, Miocene exhumation led to formation of a peneplain which in Pliocene times was uplifted and dissected, producing the modern landscape, also by exhuming older peneplains from below their protective cover rocks.

The Carboniferous to Cretaceous exhumation episodes affected Fennoscandia as well as East Greenland, however, post-breakup episodes affected the conjugate margins of the NE Atlantic differently. Whereas Neogene uplift began in the early Miocene in Fennoscandia, it began in the late Miocene in Greenland. Pliocene uplift affected both margins at about the same time. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.

 

References

Bonow & Japsen, 2021, Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic. GEUS Bulletin.

Green et al., 2022a, Episodic kilometre-scale burial and exhumation and the importance of missing section. Earth-Science Reviews.

Green et al., 2022b, The post-Caledonian thermo-tectonic evolution of Fennoscandia. Gondwana Research.

Japsen & Chalmers, 2022, The Norwegian mountains: the result of multiple episodes of uplift and subsidence. Geology Today. https://doi.org/10.1111/gto.12377

Japsen et al., 2018, Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces. Journal of the Geological Society, London.

Japsen et al., 2021, Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic. GEUS Bulletin.

Lidmar-Bergström et al., 2013, Stratigraphic landscape analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence. Global and Planetary Change.