In the northeastern part of the Netherlands and in the neighbouring part of Germany Lower-Pleistocene fluviatile sediments contain numerous erratic Ordivician silicified limestones from deposits in the Baltic Sea or the Bothnian Golf. In this paper the author describes the cyclocrinitid algae in this erratics. In the Middle-Ordovician stages C3-D1 Coelosphaeridium sphaericum (Kjerulf 1865) (=C. cyclocrinophilum Roemer 1885) occurs together with Mastopora concava Eichwald 1840, Apidium krausei (Kiesow 1893) and occasionally with Cyclocrinites porosus Stolley 1896. The younger Cyclocrinites spaskii has only been found in the lavenderblue silicifications, which are rare in this region. Apidium krausei (Kiesow 1893) is the most frequent alga, but has been neglected in the Dutch literature and in the Dutch collections. A short view of three preservation-types is followed by the report of a new type of preservation. Regularly empty casts show three-dimensionally the inner structure, i.c. parts of the walls of the mainax as well as the laterals and their pattern of ramification. The original organic material of the walls has been silicified and shows now the fragile skeleton. A number of specimens are in the Geological Institute in Oslo for further examination by dr. N. Spjeldnaes and dr.M.H.Nitecki. In the Upper-Ordovician silicified öjlemyrlimestone the author reports the occurrence of Apidium rotundum Høeg 1932 and Apidium sp.,cf. A.sororis Stolley 1896.

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Grondboor & Hamer

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Nederlandse Geologische Vereniging

F. Rhebergen. (1994). Ordovicische algen I. Cyclocrinieten. Grondboor & Hamer, 48(6), 97–107.