Glacial and rocky-shore dynamics of the Karlebotn monadnocks: late Neoproterozoic of northern Norway

Abstract

Located near the village of Karlebotn in East Finnmark, Norway, a cluster of six gneissic monadnocks is unconformably surrounded by weakly metamorphosed sandstone strata of late Neoproterozoic age in the Smalfjord Formation. Differentiated by faults, the monadnocks were further sculpted by a glacier that flowed through a coastal valley concordant with the present-day Varangerfjorden. The largest of the monadnocks is 337 m long and 167 m wide. There remains ample evidence of glacial activity associated with this feature. Relict lodgement tillites are preserved on the west side of the monadnock, flowtillites on the steep surfaces of the north and southwest sides, and a small esker directly on top. The valley was later inundated due to glacial eustacy, and the Karlebotn monadnocks became an archipelago in a shallow estuary of a broad fjord. Interpretation of exposed versus sheltered rocky shores on opposite sides of the largest monadnock island is supported by mineralogical variations in basal strata along the unconformity and evidence of paleocurrents. Greater water energy was concentrated on the southeast side, where a small sandy beach developed. Water energy must have been minimal on the north side because of a general lack of reworking and winnowing of till when the rocky shore was inundated.