Calcareous nannofossils in Neogene sediments of ODP Leg 117 holes

Calcareous nannofossils were studied in 574 Neogene samples recovered from eight sites drilled in block-faulted basins on the continental margin of Oman. This portion of the Arabian Sea experiences seasonal upwelling associated with the southwest monsoon. Not surprisingly, some of the more typical Neogene warm-water nannoplankton are either missing entirely or are extremely rare in these sediments. Coccolithus pelagicus, a typical cold-water indicator, is extremely abundant in many samples of late Pliocene to early Pleistocene age. These intervals correspond to periods of Northern Hemisphere glaciation. Reworked Late Cretaceous and Cenozoic nannofossils are found in a majority of the samples. They were probably carried from the Arabian Peninsula or the continent of Africa on strong southwest summer winds. Ages for the various nannofossil events were calculated by projecting the nannofossil datums onto the magnetostratigraphic scale for Sites 724, 727, and 728. These are the first ages for the various nannofossil datums derived from Oman Margin sediments. The following ages have been calculated for these nannofossil events: FAD Emiliania huxleyi, 0.23 Ma; LAD Pseudoemiliania lacunosa, 0.38 Ma; FAD Helicosphaera inversa, 0.42 Ma; top of acme of Reticulofenestra sp. A, 0.70 Ma; FAD Gephyrocapsaparallela, 0.85 Ma; LAD Gephyrocapsa spp. (large), 1.07 Ma; LAD Helicosphaera sellii, 1.34 Ma; LAD Calcidiscus macintyrei, 1.47 Ma; FAD Gephyrocapsa oceanica, 1.53 Ma; FAD Gephyrocapsa caribbeanica, 1.80 Ma; LAD Discoaster brouweri, 2.03 Ma; LAD Discoasterpentaradiatus, 2.31 Ma; LAD Discoaster surculus, 2.42; LAD Discoaster tamalis, 2.77 Ma; LAD Sphenolithus abies, 3.44 Ma; and LAD Reticulofenestra pseudoumbilica, 3.44 Ma.

Calcareous nannofossil abundance and datums of ODP Leg 189 sites

Quaternary sediments were recovered at all five sites drilled during Ocean Drilling Program (ODP) Leg 189 in the Tasmanian Gateway. Two of these sites lie north of the present-day Subtropical Front (STF), and three sites lie south of the STF. Quaternary sediments recovered at Sites 1168, 1170, 1171, and 1172 were studied in detail to determine the calcareous nannofossil biostratigraphy and construct an age model for these sediments. The Pliocene/Pleistocene boundary was identified by the last occurrence (LO) of Discoaster brouweri at Site 1172 and approximated by the LO of Calcidiscus macintyrei at the other sites because of a lack of discoasterids. A hiatus encompassing the entire Helicosphaera sellii Zone was tentatively identified at Sites 1168 and 1172 by the coincident LOs of C. macintyrei and H. sellii. Similar hiatuses have been noted at ODP Site 1127 on the Great Australian Bight, Deep Sea Drilling Project Site 282 off the Tasman subcontinent, and ODP Site 1165 in Prydz Bay, Antarctica.

Calcareous nannofossils in Pliocene and Quaternary sediments of ODP Leg 117 holes

A total of 21 calcareous nannofossil datums was found in the upper Pliocene and Quaternary sediments recovered from the ocean floor of the North Atlantic during DSDP Leg 94. These datums were correlated to magnetostratigraphy, and ages were estimated by interpolation between magnetic reversals. Calcareous nannofossil assemblages from 549 samples recovered during ODP Leg 117 were studied in order to estimate the age of the sediments of Sites 720, 721, 722, and 731 drilled at the Indus Fan and the Owen Ridge in the Arabian Sea, Indian Ocean. We also showed that the datums above mentioned can be traced into the Indian Ocean. Two new species, namely Helicosphaera omanica and Reticulofenestra ampla, are described.

Distribution of calcareous nannofossils in the Miocene interval of DSDP Hole 94-608 in the north Atlantic (Fig. 1)

DSDP North Atlantic Site 608 yielded an excellent Miocene pelagic section which affords a further opportunity for elucidating the chronology of the calcareous nannofossil succession in the framework of magnetostratigraphic control. Most of the conventional (zonal) markers have been documented for this site and some of the earlier results are confirmed and refined. In addition several unconventional and less known markers have been added. The first two are the highest (last) occurrence of Sphenolithus delphix and Sphenolithus capricornutus at 23.6 Ma, which is immediately above the Oligocene-Miocene boundary as identified by the last occurrence of Reticulofenestra bisecta at 23.7 Ma. The next unconventional datum is the highest (last) occurrence of Ilselithina fusa at 22.8 Ma, which is also the highest (last) occurrence of Helicosphaera recta. Calcidiscus tropicus' lowest (first) occurrence is at 19.5 Ma, which is also the lowest occurrence of Sphenolithus belemnos, and Calcidiscus leptoporus' lowest (first) occurrence coincides with that of Sphenolithus heteromorphus at 18.5 Ma. Sphenolithus dissimilis' highest (last) occurrence is at 18.2 Ma and the Calcidiscus premacintyrei lowest (first) and highest (last) occurrences are, respectively, at 17.7 and 11.7 Ma. Discoaster braarudii occurs from 11.6 to 11.3 Ma and its highest (last) occurrence corresponds to that of Cyclicargolithus floridanus. Minylitha convallis occurs from 9.0 to 6.9 Ma. Within the range of Minylitha, at 8.0 Ma, a major shift occurs in reticulofenestrid placoliths from dominantly large (Reticulofenestra pseudoumbilicus) and medium size (Reticulofenestra minutula) species below to significant numbers of very small species (Dictyococcites productus and Gephyrocapsa) above. This is interpreted to be a major, though perhaps seasonal, change of productivity of the North Atlantic at Site 608. A new genus and species Cryptococcolithus takayamae, is described and a variety, Reticulofenestra pseudoumbilicus var. amplus is identified.