In the early days of magnetostratigraphy, a few piston cores notably E13-17 [ Hays and Opdyke, 1967] and RC 12-66 [ Foster and Opdyke, 1970] recorded the entire Plio-Pleistocene geomagnetic polarity record. The development of the hydraulic piston corer (HPC) and advanced piston corer (APC) by the Deep Sea Drilling Project (DSDP) led to higher sedimentation rate records of Plio-Pleistocene polarity chrons. Notable among the Plio-Pleistocene biomagnetostratigraphies recovered by HPC/APC are those from DSDP Leg 68 in the Caribbean [ Kent and Spariosu, 1983] and DSDP Leg 94 in the North Atlantic [ Weaver and Clement, 1986]. Apart from their value for biomagnetostratigraphic correlations, the Plio-Pleistocene magnetostratigraphies from DSDP Leg 94 were important for two additional reasons. Firstly, they resulted in the documentation of two short duration normal polarity subchrons within the Matuyama Chron (Gilsa and Cobb Mountain subchrons) which had not previously been adequately recorded in sediments [ Clement and Kent, 1987]. Secondly, the correlation of oxygen isotope records to Leg 94 Plio-Pleistocene magnetostratigraphies resulted in a first attempt to astronomically tune the pre-Brunhes part of the GPTS [ Ruddiman et al., 1989; Raymo et al., 1989].
The Plio-Pleistocene stages in most geological timescales are derived from stratotype sections located in Italy [see Rio et al., 1991]. Correlation of these stratotype sections to marine sequences outside the Mediterranean is complicated by provinciality of Mediterranean flora and fauna, and by changes in lithofacies in the stratotype sections. Magnetostratigraphies in the stratotype region provide the potential means of global correlation. Biomagnetostratigraphic correlations in the Mediterranean have been accomplished for the Mediterranean Plio-Pleistocene [ Langereis and Hilgen, 1991, and references therein] and for part of the Mediterranean Late Miocene [ Langereis et al., 1984; Krijgsman et al., 1994].
Biomagnetostratigraphic correlations are not well established for the Miocene partly due to the high reversal rate which makes polarity pattern correlations difficult at pelagic sedimentation rates. Over 20 years ago, piston cores from the central Pacific led to the correlation of siliceous fossil zones to sediments as old as early Miocene [ Opdyke et al., 1974; Theyer and Hammond, 1974], however these cores contained numerous hiatuses inhibiting unequivocal correlation to the oceanic magnetic anomaly record. Apart from the Upper Miocene magnetostratigraphy from Crete [ Langereis et al., 1984], the best quality Miocene magnetostratigraphic records are HPC/APC cores from North Atlantic [ Clement and Robinson, 1986], South Atlantic [ Tauxe et al., 1983; Poore et al., 1984], Indian Ocean [ Schneider and Kent, 1990; Backman et al., 1990] and Pacific Ocean [ Schneider et al., 1994]. Biomagnetostratigraphic correlations in the Miocene, particularly in the early late and middle Miocene, remain poorly constrained [see Miller et al., 1994] due to the combination of high reversal frequency and widespread hiatuses in deep sea sections. For the Late Miocene, the Leg 138 results from the eastern equatorial Pacific [ Schneider et al., 1994] are particularly important, in large part due to core correlation from multiple holes leading to complete composite sections.
Italian land sections and South Atlantic deep-sea cores have played the major role in correlations of micropaleontological zonations to the GPTS for the Paleogene [ Lowrie et al., 1982; Poore et al., 1984; Napoleone et al., 1983; Aubry et al., 1986, Speiss, 1990] and Late Cretaceous [ Alvarez et al., 1977; Monechi and Theirstein, 1985; Channell and Medizza, 1981; Poore et al., 1984]. Direct correlation of the GPTS to European Upper Cretaceous ammonite zones which define stage boundaries has not been achieved, however, the C33r/C33n polarity chron boundary has been correlated to ammonite biostratigraphy in Wyoming [ Hicks et al., 1994].