Sequence and correlation of Tremadoc graptolite assemblages
Title:
Sequence and correlation of Tremadoc graptolite assemblages
Author:
Cooper, R. A.
Appeared in:
Alcheringa
Paging:
Volume 3 (1979) nr. 1 pages 7-19
Year:
1979
Contents:
Five successive events can be widely recognized in the Tremadoc to early Arenig graptolite sequences of the world: 1, appearance of Dictyonema flabelliforme s.l. at the base; 2, appearance of Anisograptus; 3, appearance of Clonograptus and/or Adelograptus; 4, appearance of Temnograptus, Kiaerograptus, large Clonograptus and Tetragraptus; and 5, appearance of Tetragraptus approximatus at the base of the Arenig. The five events are used as a basis for distinguishing 5 successive graptolite assemblages and for correlating Tremadoc sequences. The most precisely and confidently correlated horizon is that of event 5, the appearance of T. approximatus; the next best is that based on event 4. Derivation of the biradiate Anisograptids, Clonograptus, and Adelograptus, from their presumed ancestor, Dictyonema flabelliforme, now appears to have passed through a stratigraphically, if not phyletically, intermediate stage represented by the triradiate Anisograptus, Triograptus and Bryograptus.
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