The Proterozoic (1.85 Ga) Alvestorp Conglomerate, Bergslagen, Central Sweden

摘要

The Alvestorp conglomerates, deposited in an alluvial fan setting, form part of the Svecofennian orogenic belt in west Bergslagen, south central Sweden and are estimated to be as old as c. 1.85 Ga. Reaching a thickness of one kilometre, their architecture and form suggest an alluvial origin. Along sections, massive conglomerates often grade into pebbly mudstones and greenschist facies slates, while pure slates with dolomite concretions and olistolites occur in dark slatey mudstones on the eastern shore of lake Brunnsjon. Inner fan trenches are filled with massive, clast-supported conglomerates that contain more than 80 percent epiclastic tuffaceous material. The Alvestorp conglomerate is therefore classified as the product of a Proterozoic stream-flow channel and debris flow, or alluvial fan. The Grythyttan Basin to the north originated by extension after the first of two orogenic stages of Bergslagen.