Silurian Bryozoans which grew in the shade

A study is made of bryozoan faunas which grew on the underside of coral and stromatoporoid heads, and in other shade-biotopes from the Silurian of Gotland. An analysis is made of the faunal associations, and the stability of these association in the geological record. Comparison with recent analoges are introduced in order to analyse the physiological and ecologic parameters involved in these rather special biotopes. Some possibilities for using the shade-biotopes as palaeoecological indicators of depth, turbidity and silting conditions are suggested, and it is also noted that the recent shade-bryozoans may be useful as indicators of ecological change, especially pollution.Étude des faunes de bryozoaires croissant sur la partie inférieure des coraux et des stromatopores et dans d'autres biotopes ombragés du Silurien du Gotland. Analyse des associations fauniques et de leur stabilité durant les temps géologiques. Comparaison avec des faunes récentes pour analyser les paramètres physiologiques et écologiques impliqués dans ces biotopes très spéciaux. Possibilité d'employer ces biotopes comme des indicateurs paléoécologiques de profondeur, turbidité et envasement ; les bryozoaires "d'ombre" actuels peuvent être utilisés comme indicateurs de changements écologiques, spécialement de pollution.Spjeldnæs Nils. Silurian Bryozoans which grew in the shade. In: Documents des Laboratoires de Géologie de la Faculté des Sciences de Lyon. Hors série n°3, 1975. Bryozoa 1974 – Proceedings of the third Conference International Bryozoology Association – Lyon (fasc. 2) pp. 415-424

Late Ordovician trace fossils from offshore to shallow water mixed Siliciclastic and carbonate facies in the Ringerike Area, Oslo Region, Norway

Upper Ordovician (Rawtheyan-Hirnantian) deposits in the Ringerike area contain 21 ichnogenera of burrows and two ichnogenera of borings. These deposits consist of a lower siliciclastic part and an upper part dominated by carbonates and mixed clastic-carbonate deposits. Sedimentological and geochemical investigations combined with an ichnological analysis in the lower siliciclastic part point to a shallowing from a transitional-offshore partly dysoxic zone to an oxic delta front/upper shoreface facies. The trace fossils belong to the proximal, archetypal, and distal Cruziana ichnofacies. The upper part of the sequence comprises a complex pattern involving patch reefs interfingering with shallow marine deposits of sandstones and crinoidal limestones in the southern area and carbonate mud banks to the north. The carbonate mud banks were subaerially exposed with the development of local coastlines. The overlying transgressive sediments, consisting of sandstones and carbonates, contain an offshore to transitional trace fossil assemblage