The sub-Caledonian unconformity on Hjelmsøy - new evidence of primary basement/cover relations in the Finnmarkian nappe sequence.

Abstract

A new and important occurence of a primary stratigraphic unconfomity beneath tha Caledonian cover in allochthon of the Finnmarkian segment of the North Norwegian Caledonides is described. This unconformity, on the island of Hjelmsøy, is excellently although only locally preserved as a geological accident. The basal lithology above the unconformity is an orthoquartzite. This is overlapped by meta-arkoses containing clasts of the crystalline basement rocks. The effests of Caledonian tectonothermal processes produce a structural and tectural convergence of both members along the cover\/basement interface, which may blur the precise contant. The Caledonian structural and metamorphic development og Hjelmsøy is also briefly discussed, as is the regional significance of the unconformity.