Old red sedimentation in the buelandet-vaerlandet devonian district,western norway

A preserved maximum thickness of 3,400 m of Devonian breccia, conglomerate, and sandstone of the Buelandet-Vaerlandet Formation crop out in the Buelandet-Vaerlandet district. The sedimentary rocks rest unconformably on Cambro-Silurian greenschist. Fragments of Psilophyton sp. found in the upper part of the stratigraphic sequence suggest an Early Devonian or early Middle Devonian age. The strictly continental sediments were deposited in a structurally formed half-graben by streams draining a complex crystalline source area to the north. This depositional basin was one of six separate Devonian basins located in the area of the former eugeosynclinal portion of the Caledonian geosyncline. The initial tectonism, resulting in the formation of Devonian grabens, was later followed by folding and faulting of the sedimentary basins during the Svalbardian disturbance. The tectono-sedimentologic environment of the Buelandet-Vaerlandet district is thought to have been similar to that of the Triassic Newark basins of the North American Appalachian Mountains.The oldest member of the here-named Buelandet-Vaerlandet Formation, the Melvaer Breccia, consists of angular, chaotically arranged greenschist fragments deposited as mudflows, sheetfloods and talus accumulations on the surfaces of alluvial fans. The intermediate Vaeroy Conglomerate consists of polymict alluvial fanglomerates deposited by braided distributaries of major streams that cut deep canyons into the northerly provenance area. The youngest unit is the Sörlandet Sandstone Member, a green arkosic deposit of larger braided streams, with local gravel bars preserved. Textural, fabric and paleocurrent data indicate a facies gradation southward along the paleoslope from breccia to sandstone. Tectonic uplift of the source area contemporaneous with fan sedimentation is suggested by the thickness and coarseness of fanglomerates. Rapid deposition in upperflow regime conditions, and a temperate or humid climate are indicated.