Nanoplancton Calcareo

Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 160

8. CALCAREOUS NANNOFOSSIL QUANTITATIVE BIOSTRATIGRAPHY OF HOLES 969E AND 963B (EASTERN MEDITERRANEAN)1
Enrico Di Stefano2

ABSTRACT The distribution patterns of the selected biostratigraphically useful calcareous nannofossils were analyzed inthe Pliocene– Pleistocene sequences of Holes 969E and 963B drilled during Ocean Drilling Program Leg 160 (Eastern Mediterranean). Quantitative methods were used to verify the reliability of the sequence of calcareous nannofossil events detected during ODP Leg 107, Site 653 in the Western Mediterranean. In the Mediterranean record, just above the base of the Zanclean, the Reticulofenestrapseudoumbilicus paracme interval can be used to improve biostratigraphic resolution in the basal Pliocene record. At the base of the sequence of Hole 969E only the uppermost part of the Reticulofenestra pseudoumbilicus paracme was identified. It is concluded, therefore, that a short segment is not present at the local base of the Pliocene.

INTRODUCTION
A calcareous nannofossil biostratigraphic schemefor the Mediterranean Pliocene–Pleistocene record was proposed by Raffi and Rio (1979) with reference to Deep Sea Drilling Project (DSDP) Leg 13 Site 132. Rio et al. (1990) revised this scheme after detailed analysis of Leg 107 Site 653, which reoccupied Site 132. Essentially based on the sequence of extinction levels of Discoaster taxa during the Pliocene (only the MNN12/13 and MNN14−15/MNN16azonal boundaries are defined by nonasterolith markers) and on the evolution of the Gephyrocapsa complex in the Pleistocene (Fig. 1), this zonal scheme for the Western Mediterranean has been widely accepted and used in several studies (Di Stefano and Sprovieri, 1990; Channell et al.,1992; Di Stefano et al., 1993; Castradori, 1993). The detailed analysis of calcareous nannofossils from thePliocene–Pleistocene sequence of Hole 969E provided the opportunity to apply this zonal scheme to an Eastern Mediterranean geologic section, to compare the calcareous nannofossil evolution in these two different Mediterranean sub-basins. Hole 963B was drilled seaward of the Sicilian Capo Rossello land section (Fig. 2). The recovered sequence encompasses the stratigraphic interval between the uppermost leveloutcropping at Capo Rossello, referable to the first occurrence (FO) of large Gephyrocapsa (Di Stefano et al., 1993) and the Holocene. This hole is therefore important for reporting the sequence of bioevents that can be only sporadically identified, and only for the upper part of the lower Pleistocene, in outcropping sections along the southern coast of Sicily (Di Stefano et al., 1991).

cordingto the estimated sediment accumulation rate (see the following), a time interval of ~35 k.y. is represented per 70 cm of core. The underlying upper Messinian Unit II is represented by ~2 m of calcareous silty clay that was not included in this study. Hole 963B is located in the Strait of Sicily (Fig. 2), on the unstable foreland of North Africa, close to the deformation front of the Gela Nappe. Thesediments of the single recognized sedimentary unit are nannofossil ooze, with minor intercalations of silt, volcanic ash, and clay intervals. Samples examined totalled 253. Two samples from each section were studied with a maximum sample spacing of about 70 cm. As reported subsequently, this sample spacing covers a time interval of ~9 k.y. in lower Pleistocene sediments and ~3 k.y. in the middlePleistocene through Holocene sediments.

METHODS
Smear slides for light microscope analyses were prepared according to standard techniques. The scanning electron microscope (SEM) was used only to investigate the Emiliania huxleyi FO according to the methodology introduced by Thierstein et al. (1977). The same unprocessed material that was used to prepare smear slides was smeared on a SEM...