Late Cretaceous to Pleistocene Archaeomonads, Ebridians, Endoskeletal Dinoflagellates, and Other Siliceous Microfossils from the Subantarctic Southwest Pacific, DSDP, Leg 29

Abstract

Late Cretaceous, late Eocene, and Neogene archaeomonads, ebridians, endoskeletal dinoflagellates, and some siliceous microfossils of uncertain affinity found in the siliceous sequences penetrated on DSDP Leg 29 are described and illustrated. As much as possible, their stratigraphic distribution on Leg 29 is indicated, discussed, and compared with other reports. Some new archaeomonads and two new ebridians are described. INTRODUCTIONRecently (Dumitrica, 1973), presented a thorough investigation of the Cenozoic endoskeletal dinoflagellates from the southwestern Pacific sediments cored during DSDP Leg 21. On DSDP Leg 29, in an area immediately to the south of Leg 21 (Figure 1), cored sediments range in age from Late Cretaceous to Pleistocene and contain siliceous spicules of endoskeletal dinoflagellates. The same sediments usually contain common to abundant diatoms, and often radiolarians (Petrushevskaya, this volume), as well as archaeomonads and ebridians. The latter were discussed by Ling (1973), from DSDP Leg 19 in the North Pacific. Dumitrica (1973) described and discussed the few genera and species of Actiniscidae and has given their stratigraphic distribution from the middle Oligocene to the middle Pleistocene. In this report, the siliceous spicules of the endoskeletal dinoflagellates of Late Cretaceous and late Eocene to Pleistocene age are illustrated on Plate 10, and their stratigraphic distribution is shown in Tables 1 to 3. On the same tables the distribution of the archaeomonads and ebridians illustrated on Plates 1 to 9 and 12 is also shown. In the following discussion each group is considered separately. Methods of StudyThe samples studied for this report were either smear slides prepared for coccolith investigations, or slides prepared from samples treated with diluted HC1, and then washed several times by centrifuging. In this manner, the very small forms could be observed. For some samples an extra slide was prepared from material washed through a 53µ sieve to permit an easier survey of the larger forms. Canada balsam was used as a mounting medium. ARCHAEOMONADSThe Archaeomonadaceae are a family of fossil marine chrysomonadins and probably have led a planktonic life in the photic zone of the oceans. During their life cycle the single cells formed cysts consisting of SiCh which may be considered as resting stages. The cysts have an opening of different size and form, which served as an escape tunnel for the protoplasmatic cell content. This was after the resting stage in the protective Siθ2 sphere was over (Stradner, 1971).Archaeomonads are known from the Late Cretaceous to the Miocene. So far no archaeomonads have been described from the Oligocene and the Pliocene (Tynan, 1971). It is therefore of special interest to note their occurrence in the Oligocene at Sites 278 and 280 and in the (?)Pliocene at Site 278. The siliceous Upper Cretaceous sequence penetrated at Site 275 yielded few to common archaeomonads. The most well known and common, Micrampulla parvula Hanna, has been descr...

Eocene to Pliocene Archaeomonads, Ebridians, and Endoskeletal Dinoflagellates from the Norwegian Sea, DSDP Leg 38

“…The form and size of the opening, as well as of the cyst, are used to distinguish genera and species. Archaeomonads occur from the Late Cretaceous through the Miocene and possibly Pliocene (Tynan, 1971;Perch-Nielsen, 1975).…”

“…Six new species are described from the late Eocene to early Oligocene. The late Eocene to early Oligocene (late Eocene and early Oligocene cannot be distinguished by silicoflagellates which were used for the age determination in most cases) archaeomonad assemblages are different and richer than those reported from the subantarctic southwest Pacific (Perch-Nielsen, 1975), although some species are in common.…”

“…Preservation varies from very poor to moderate. The assemblages include many of the forms found in the subantarctic southwest Pacific (Perch-Nielsen, 1975), but lack completely Micromarsupium and Craniopsis. On the other hand, Ammodochium complexum, A. novum, and Parebriopsis symmetrica are new species from the Eocene of the Norwegian Sea.…”

“…Previously, Dumitrica (1973) reported on ebridians and endoskeletal dinoflagellates from the southwestern Pacific (DSDP Leg 21), and Ling (1973, DSDP Leg 19) discussed ebridians from the North Pacific. It was therefore of great interest to study these groups from high northern latitude sites in the Atlantic and to compare the findings with the results from the high southern latitudes presented in Perch-Nielsen (1975).…”

Archaeomonads as Eocene and Oligocene Guide Fossils in Marine Sediments

“…Archaeomonads are known as fossils from the Late Cretaceous to Miocene, only recently having been reported from the Oligocene by Perch-Nielsen (1975). Tynan (1971), in a report on the known geologic occurrences of archaeomonads, noted that "there are no reported occurrences of the archaeomonads in the Oligocene."…”