DISCUSSION AND CONCLUSIONS

Site 1149 is located on a positive magnetic anomaly (Plank, Ludden, Escutia, et al., 2000). Two alternative models of the oceanic magnetic lineations of this part of the Pacific plate were supposed, one identifying the positive anomaly at Site 1149 as Chron M12 and the other as Chron M11 (Plank, Ludden, Escutia et al., 2000; Nakanishi et al., 1992). In Hole 1149B, a sharp ¹³C positive peak (3-3.5) was identified in Cores 185-1149B-23R and 22R, and it was dated as late Valanginian by means of the radiolarian UAZ 95 18 (Fig. F2). In the Tethyan land sections, UAZ 95 18 is also coincident with maximum values of ¹³C (Jud, 1994; Baumgartner et al., 1995b). The upper Valanginian positive peak was correlated to Chron M11 (Channel et al., 1993) (Fig. F2). Because at Site 1149 the upper Valanginian ¹³C positive peak is situated in Cores 185-1149B-23R and 22R (Fig. F2), the magnetostratigraphic correlation of the basement with Chron M11 can be excluded. In Hole 1149D, at the direct contact with basalt, a radiolarian assemblage assignable to UAZ 95 16 was recovered. In the Tethyan land sections, the UAZ 95 16 was correlated with magnetic polarity zone interval M14 to M12. The radiolarian data together with the shape of ¹³C curve (Fig. F2) strongly supports, therefore, the magnetostratigraphic correlation of Site 1149 with Chron M12.

The upper Valanginian ¹³C positive peak recorded in Hole 1149B is coincident with high concentrations of barium in sediments and high abundances of Pantanellium in radiolarian assemblages. Barium is an indicator of high biogenic input (Lea and Boyle, 1990; Von Breymann et al., 1992; Klump et al., 2000). The observed positive correlation between abundance of Pantanellium and barium proves that certain paleoecological effects are highly influencing the faunal assemblages and that Pantanellium can be considered as a marker of high primary productivity conditions. The Pantanellids were mentioned as indicators of upwelling conditions by Baumgartner (1987). High abundances of the taxa Pantanellium squinaboli squinaboli have also been observed in Zones E2 and F1 from the Bosso section (central Italy) by Jud (1994). Zones E2 and F1 (Jud, 1994) correspond to UAZ 17 and 18 (Baumgartner et al., 1995b) and are correlatable with the upper Valanginian positive excursion.

The upper Valanginian carbon isotope event was very well documented as almost in the Tethyan and Atlantic domains. It was attributed to perturbation of the global carbon cycle and collapse of carbonate production in a scenario of intensified greenhouse conditions (Weissert and Lini, 1991; Weissert et al., 1998; Wortmann and Weissert, 2000). In such a scenario, an acceleration of the water cycle may have provoked an increase of weathering on the continents and input of nutrients in the basins, inducing eutrophication and a crisis of carbonate production (Weissert et al., 1998). The data from Leg 185 show that the upper Valanginian carbon positive excursion seems to mirror eutrophic conditions also in the northwestern Pacific setting (distal during the Cretaceous from detrital input from continents). Such an "oceanic eutrophication" may be linked to extensive volcanism. The late Valanginian ¹³C positive excursion is confirmed as a global event, probably linked to high primary productivity.