Piston core record of Late Paleogene (31 Ma) to recent seafloor hydrothermal activity in the Southwest Pacific Basin

[1] A large diameter piston core containing 8.35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote Southwest Pacific Basin (31 42.1940S, 143 30 3310W; 5082 m water depth), providing unique insight into hydrothermal activity and eolian sedimentation there since the early Oligocene. A combination of fish-teeth Sr-isotope stratigraphy and INAA geochemical data reveals an exponentially decreasing hydrothermal flux 31 Ma to the present. Although hydrothermal sedimentation related to seafloor spreading explains this trend, a complex history of late Eocene/early Oligocene ridge jumps, propagating rifts and plate tectonic reorganization of South Pacific seafloor could have also played a role. A possible hiatus in deposition, as recorded by changes in core composition just below 2 m depth, is beyond the resolution of the fish teeth Sr isotope dating method employed here; however, the timing of this interval may be coincident with extinction of the Pacific-Farallon Ridge at 20 Ma. A low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth, consistent with dust-generating continental sources far to the west (Australia/New Zealand). This is the first long-term paleoceanographic record obtained from within the South Pacific ‘‘bare zone’ ’ (Rea et al., 2006), an anomalous region where Pacific seafloor has largely escaped sediment accumulation since the Late Cretaceous