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A rich assemblage of Lower Cretaceous (lower Albian) siliceous microfossils was recovered at ODP Site 693 on the Weddell Sea margin of East Antarctica during Leg 113. This assemblage includes marine diatoms, silicoflagellates, radiolarians, Chrysophycean cysts, and endoskeletal dinoflagellates that are extraordinarily well preserved and in most cases, radiolarians excluded, represent the oldest known well-preserved assemblages of these groups. This chapter describes and illustrates Lower Cretaceous diatom resting spores, Chrysophycean cysts, and an endoskeletal dinoflagellate from Holes 693A and 693 B. Six new diatom genera and 20 new species of probable diatom resting spores are presented here, in addition to 10 apparently new Chrysophycean cyst taxa and one endoskeletal dinoflagellate species. Diatom assemblages reported here and in the preceding chapter on vegetative forms (Part 1) suggest: (1) that diatoms were a complex, diverse, and widespread group by late Early Cretaceous time; (2) that diversities are high enough to anticipate the construction of a useful biostratigraphic zonation as more data become available; (3) that there is a considerable difference between assemblages in these Albian sediments and younger Senonian diatomites known around the world; (4) that both resting spore formation and the ability to form chains are ancient features of the diatoms; and (5) that diatom distribution in the Early Cretaceous may have been restricted to continental margins and interior seas, areas where resting spore formation is most common. Because these assemblages are the oldest, well-preserved diatom and chrysophycean floras known, this chapter concludes with a brief review and discussion on the origin of the diatoms, addressing both the role of resting spores and postulated links to Chrysophycean flagellates.

proceedings of the ocean drilling program

Lower Cretaceous Diatoms from ODP Leg 113 Site 693 (Weddell Sea). Part 2: Resting Spores|Chrysophycean Cysts|an Endoskeletal Dinoflagellate|Notes on the Origin of Diatoms