Upper Cretaceous Coccoliths from Texas and Europe
"Electron microscopy reveals a great range of crystallite ultrastructure patterns in the calcite scales of the unicellular marine algae, Coccolithophyceae. These tiny scales, called coccoliths, have been found as fossils in strata as old as 180 million years (Early Jurassic). During the Late Cretaceous, Coccolithophyceae were especially abundant, and their coccoliths were important rock-building constituents. The extensive chalk deposits representing this epoch contain not only large numbers of coccoliths but also a great variety of species. Electron microscopy of samples from this interval reveals fossils of 172 species of Coccolithophyceae. Of these, 94 species are new. Of the 48 genera represented, 11 are new: Amphizygus, Angulofenestrellithus, Bidiscus, Broinsonia, Costacentrum, Gartnerago, Heteromarginatus, Hexangulolithus, Percivalia, Similicoronilithus, and Vagalapilla. Special significance is attached to first occurrences, because reworking can extend stratigraphic ranges of these small (1-20 μ) fossils. Last occurrences of groups of species, while less reliable, can also be useful as auxiliary stratigraphic markers when critically evaluated. Two distribution tables are presented, one arranged by stratigraphic first occurrence and the other alphabetically. Samples examined from Texas were compared to samples from Europe. The bulk of the Santonian-Campanian coccolith floras, in both Texas and Europe, are composed of 41 long-ranging and abundant species. Santonian-age samples contain a total of 105 species; 53 of these appeared first during the Santonian. The succeeding Campanian samples contain 137 species of which 51 are not present in Santonian samples. The evolutionary diversity observed in groups of species with restricted ranges has made it possible to define four new coccolith assemblage zones for the Santonian and Campanian: Cyclagelosphaera? chronolitha Zone, Amphizygus minimus Zone, Zygodiscus macleodae Zone, and Prediscosphaera germ anica Zone."--Pg. 7.