Elsevier

Precambrian Research

Volume 352, January 2021, 106000
Precambrian Research

Ultra-slow cratonic denudation in Finland since 1.5 Ga indicated by tiered unconformities and impact structures

https://doi.org/10.1016/j.precamres.2020.106000Get rights and content
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Highlights

  • Erosion history reconstructed for craton in southern Finland since 1.5 Ga.

  • Tiered unconformities and impact structures indicate erosion at <2.5 m/Ma.

  • Low-temperature thermochronology overestimates former sedimentary cover thickness.

  • Persistence of Phanerozoic fracture coatings, Palaeogene groundwater and microbiomes.

  • Cratonic regime has tectonic stability, prolonged shallow burial and ultra-slow erosion.

Abstract

The Earth’s cratons are traditionally regarded as tectonically stable cores that were episodically buried by thin sedimentary covers. Cratonic crust in southern Finland holds seven post-1.7 Ga tiered unconformities, with remnants of former sedimentary covers. We use the geometries of the tiered unconformities, along with previously dated impact structures and kimberlite and carbonatite pipes, to reconstruct the erosion and burial history of the craton and to derive estimates of depths of erosion in basement and former sedimentary rocks. The close vertical spacing (<200 m) of the unconformities and the survival of small (D ≤ 5 km) Neoproterozoic and Early Palaeozoic impact structures indicate minor later erosion. Average erosion rates (<2.5 m/Ma) in basement and cover are amongst the lowest reported on Earth. Ultra-slow erosion has allowed the persistence in basement fractures of Phanerozoic fracture coatings and Palaeogene groundwater and microbiomes. Maximum thicknesses of foreland basin sediments in Finland during the Sveconorwegian and Caledonide orogenies are estimated as ~1.0 km and <0.68–1.0 km, respectively. Estimated losses of sedimentary cover derived from apatite fission track thermochronology are higher by factors of at least 2 to 4. A dynamic epeirogenic history of the craton in Finland, with kilometre-scale burial and exhumation, proposed in recent thermochronological models is not supported by other geological proxies. Ultra-slow erosion rates in southern Finland reflect long term tectonic stability and burial of the craton surface for a total of ~1.0 Ga beneath generally thin sedimentary cover.

Keywords

Craton
Unconformity
Impact structure
Denudation
Thermochronology
Finland

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