Calcareous nannofossil stratigraphy, mass accumulation rates and bulk density of sediments from ODP Leg 173 sites

Drilling on the Iberia Abyssal Plain during Ocean Drilling Program Leg 173 allowed us to recover Upper Cretaceous through Paleocene sediments at Sites 1068 and 1069 and only upper Paleocene sediments at Site 1067, which expands considerably the Upper Cretaceous to Paleocene record for this region. Of these three sites, Site 1068 recovered uppermost Cretaceous sediments as well as the most complete Paleocene record, whereas Site 1067 yielded only uppermost Paleocene sediments (Zone CP8). Site 1069 provided a rather complete upper Campanian through Maastrichtian section but a discontinuous Paleocene record. After a detailed calcareous nannofossil biostratigraphy was documented in distribution charts, we calculated mass accumulation rates for Holes 1068A and 1069A. Sediments in Hole 1068A apparently record the final stages of burial of a high basement block by turbidity flows. Accumulation rates through the Upper Cretaceous indicate relatively high rates, 0.95 g/cm**2/k.y., but may be unreliable because of the lack of datum points and/or possible hiatuses. Accumulation rates in the Paleocene section of Hole 1068A fluctuated every few million years from lower (~0.35 g/cm**2/k.y.) to higher rates (~0.85 g/cm**2/k.y.) until the latest Paleocene, when rates increased to an average of ~2.0 g/cm**2/k.y. Mass accumulation rates for the Upper Cretaceous in Hole 1069A indicate a steady rate of ~0.60 g/cm**2/k.y. from 75 to 72 Ma. There may have been one or more hiatuses between 72 and 68 Ma (combined Zone CC24 through Subzone CC25b), as indicated by the very low accumulation rate of 0.15 g/cm**2/k.y. The Paleocene section of Hole 1069A does not show the same continuous record, which may result from fluctuations in the carbonate compensation depth and poor recovery (average = 40%). Zones CP4 and CP5 are missing within a barren interval; this and numerous other barren intervals affect the precision of the nannofossil zonation and calculation of mass accumulation rates. However, in spite of these missing zones, mass accumulation rates do not seem to indicate the presence of hiatuses as the rates for this barren interval average ~1.0 g/cm**2/k.y. This study set out to test the hypothesis that a reliable biostratigraphic record could be constructed from sediments derived from turbidity flows deposited below the carbonate compensation depth. As illustrated here, not only could a reliable biostratigraphic record be determined from these sediments, but sedimentation and mass accumulation rates could also be determined, allowing inferences to be drawn concerning the sedimentary history of this passive margin. The reliability of this record is confirmed by independent verification by the establishment of a magnetostratigraphy for the same cores.

(Table 1) Time series of ostracod population density off Bokniseck shore ('Hausgarten'), western Baltic Sea

Seasonal distributions of ostracode species from the Bay of Kiel, western Baltic Sea (Bokniseck, 'Hausgarten') were studied at seven observation stations located between 6 - 23.5 m water depth. During the period from December 1973 to March 1975, 175 samples were taken every two weeks from the sediment surface at each station. Environmental factors were measured simultaneously with sampling. Most of the ostracode species were present in all of the samples throughout the year; four species were found to be seasonal. On the other hand, the population densities of each of the examined ostracode species, as revealed by countings, indicate marked seasonal variations. These variations are attributed to changes in length rate and timing of the reproductive cycles of the different ostracode species, effected mainly by food supply. Maxima in the abundance of the ostracode species with short (1/2 - 1 month) life cycles, occurred simultaneously with peaks of food supply in spring and autumn, whereas the maxima abundance of ostracodes with longer (10 - 12 months) life cycles was delayed.