Etage 5 i Asker ved Kristiania. Studier over den norske Mellemsilur

Abstract

Forkortet: The present work gives the results of the author's researches in the Middle Silurian (Stage 5) in Asker, which lies nearly 10 miles SW from Oslo, on the west side of the head of the Oslofjord. In the first place the Facies and the tract which they characterise in this district are described; the two lower subdivisions, 5 a and 5 b of the Middle Silurian, are described separately. For each of these there are first given accurate descriptions of all observed sec- tions, next a general survey (see pages 5-37). The Second section treats of the changes of the facies, and of the Middle Silurian upheaval in the Norwegian Silurian ocean (pages 37-55). The various reasons are given that show that the great change of facies from Stage 4 through Middle Silurian to Upper Silurian partly with distinct shore deposits like pebble beds and breccia can only be explained by an uplifting of a great part of the sea-bottom above the sea level in Middle-Silurian time, caused by a crumpling of the earth's crust, a period of mountain-chain formation. The principal evidence of this lies in the composition of the conglomerate in Asker and in the Oslo district, and in some of the sections pointed out by the author in Asker where 5 b lies directly upon the lower part of 5 a Rhabdoporella-limestone by which a concealed uncorformity is demonstrated.