Silicioflagellates and Ebridians

Silicioflagellates and ebridians are unicellular, flagellate marine algae. The former are autotrophic and the latter heterotrophic. The silicioflagellate skeleton consists of a network of hollow opaline rods of ring like geometrical arrangement which is preserved in latest Cretaceous to recent marine sediments. They are similar in size to diatoms (20 - 100 µm) and are biostratigraphically useful in samples in which diatoms are abundant. They are quite variable and readily influenced by environment, a fact reflected in the provinciality of several silsilicioflaellate zonations. Some 25 Cenozoic zones/ subzones of regional utility ha been recognised, with finest resolution in the Pleistocene (1my) and Eocene (3 - 5 my). Known temperature preferances of living species facilitate paleotemperature interpretation of fossil assemblages. Ebridians produce a solid opaline skeleton of triradial or tetraxial semmetry, tens of micrometres in size, which is preserved in low abundance in deep-sea sediments. Ebridians occur from Paleocene to Recent, with greatest abundance and diversity during Eocene to Miocene time. They are commonly observed in diatom and silicioflagellate preparations and have been successfully used in sub-Epoch stratigraphic division with resolution similar to silicioflagellate.