Algae as depth indicators in the Silurian of the Oslo region

Specimens of Girvanellu sp. are described for the first time from the Oslo region, Norway. The specimens discussed here occur in Lower Llandoverian biomicrites in the central part of the Oslo region (Bærum/Asker). The distinct association between Girvanella sp. and other faunal elements in the succession provides important new information on the depth ranges of Lcwer Silurian brachiopod communities.     

The environmental significance of algae in the mi Llandovery succession of the central Oslo Region

Girvanella , micritization phenomena and the dasycladacean alga Cyclocrinites are found in the middle Llandovery succession of the central Oslo Region. Both Girvanella and micritization phenomena occur in carbonate-dominated sequences where sedimentary structures and associated faunas suggest depositional environments above normal wave base. In contrast, Cyclocrinites occurs in shale-dominated sequences where other evidence suggests quiet, deep-water environments. We suggest that Cyclocrinites would not normally be preserved in situ in its life environment in relatively turbulent shallow waters. Preservation most commonly resulted from post mortem transport into low-energy muddy environments devoid of in situ algal activity. The resultant fossil is a flattened cast of this originally spherical alga.