(Table 2) Correlation of Mi zones with hiatuses in ODP Site 181-1124

Results from Ocean Drilling Program sites 1121-1124 show the Eastern New Zealand Oceanic Sedimentary System (ENZOSS) evolved in response to: (1) the inception of the circum-Antarctic circulation, (2) orbital and nonorbital regulation of the global thermohaline flow, and (3) development of the New Zealand plate boundary. ENZOSS began in the early Oligocene following opening of the Tasmanian gateway and inception of the ancestral Antarctic Circumpolar Current (ACC) and SW Pacific Deep Western Boundary Current (DWBC). Widespread erosion, marked by the Marshall Paraconformity, was followed by extensive drift formation in the late Oligocene- early Miocene. Alternating nannofossil chalk and nannofossil-rich mud deposited in response to 41-kyr orbital regulation of the abyssal circulation, with the mudstones representing times of increased inflow of corrosive southernsource waters. Drift deposition at the deepest sites was interrupted by bouts of erosion coincident with Mi 1-5 isotopic events signifying expansions of the East Antarctic Ice Sheet and enhanced bottom water formation. By late Miocene times, the basic ENZOSS was established. South of Bounty Trough, the energetic ACC instigated an erosional/low depositional regime. To the north, where the DWBC prevailed, orbitally regulated drift deposition continued. Increased convergence at the New Zealand plate boundary enhanced the terrigenous supply, but little of this sediment reached the deep ENZOSS as the three main sediment conduits - Solander, Bounty and Hikurangi channels - had not fully developed. The Plio-Pleistocene heralded a change from a carbonate- to terrigenous-dominant supply caused by interception of the DWBC by the three channels (~1.6 Ma for Bounty and Hikurangi, time of Solander interception unknown). The Solander and Bounty fans, and Hikurangi Fan-drift systems formed, and drifts downstream of those systems, received terrigenous detritus. Supply increased with accelerating uplift along the plate boundary, but delivery to the DWBC was regulated by eustatic fluctuations of sea level. Times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased (Bounty, Solander), or reduced (Hikurangi) in highstands. In glacial times, sediment was entrained by a DWBC invigorated by an increased input of Antarctic bottom water. The ACC also accelerated under strengthened glacial winds. Thus, glacials were times of optimum sediment supply to ENZOSS depocentres where depositional rates were 2-3 times more than interglacial rates.

Geochemistry and mineralogy of ultramafic rocks from conical seamount

The Mariana arc-trench system, the easternmost of a series of backarc basins and intervening remnant arcs that form the eastern edge of the Philippine Sea Plate, is a well-known example of an intraoceanic convergence zone. Its evolution has been studied by numerous investigators over nearly two decades (e.g., Kang, 1971; Uyeda and Kanamori, 1979; LaTraille and Hussong, 1980; Fryer and Hussong, 1981; Mrosowski et al., 1982; Hussong and Uyeda, 1981; Bloomer and Hawkins, 1983; Karig and Ranken, 1983; McCabe and Uyeda, 1983; Hsui and Youngquist, 1985; Fryer and Fryer, 1987; Johnson and Fryer, 1988; Johnson and Fryer, 1989; Johnson et al., 1991). The Mariana forearc has undergone extensive vertical uplift and subsidence in response to seamount collision, to tensional and rotational fracturing associated with adjustments to plate subduction, and to changes in the configuration of the arc (Hussong and Uyeda, 1981; Fryer et al., 1985). Serpentine seamounts, up to 2500 m high and 30 km in diameter, occur in a broad zone along the outer-arc high (Fryer et al., 1985; Fryer and Fryer, 1987). These seamounts may be horsts of serpentinized ultramafic rocks or may have been formed by the extrusion of serpentine muds. Conical Seamount, one of these serpentine seamounts, is located within this broad zone of forearc seamounts, about 80 km from the trench axis, at about 19°30'N. The seamount is approximately 20 km in diameter and rises 1500 m above the surrounding seafloor. Alvin submersible, R/V Sonne bottom photography, seismic reflection, and SeaMARC II studies indicate that the surface of this seamount is composed of unconsolidated serpentine muds that contain clasts of serpentinized ultramafic and metamorphosed mafic rocks, and authigenic carbonate and silicate minerals (Saboda et al., 1987; Haggerty, 1987; Fryer et al., 1990; Saboda, 1991). During Leg 125, three sites were drilled (two flank sites and one summit site) on Conical Seamount to investigate the origin and evolution of the seamount. Site 778 (19°29.93'N, 146°39.94'E) is located in the midflank region of the southern quadrant of Conical Seamount at a depth of 3913.7 meters below sea level (mbsl) (Fig. 2). This site is located in the center of a major region of serpentine flows (Fryer et al., 1985, 1990). Site 779 (19°30.75'N, 146°41.75'E), about 3.5 km northeast of Site 778, is located approximately in the midflank region of the southeast quadrant of Conical Seamount, at a depth of 3947.2 mbsl. This area is mantled by a pelagic sediment cover, overlying exposures of unconsolidated serpentine muds that contain serpentinized clasts of mafic and ultramafic rocks (Fryer et al., 1985, 1990). Site 780 (19°32.5'N, 146°39.2'E) is located on the western side of Conical Seamount near the summit, at a depth of 3083.4 mbsl. This area is only partly sediment covered and lies near active venting fields where chimney structures are forming (Fryer et al., 1990).

Accumulation rates and grain sizes of eolian dust in sediments of the Intertropical Convergence Zone in the northeast Pacific

A 328 cm-long piston core (KODOS 02-01-02) collected from the northeast equatorial Pacific at 16°12'N, 125°59'W was investigated for eolian mass fluxes and grain sizes to test these proxies as a tool for the paleo-position of the Intertropical Convergence Zone (ITCZ). The eolian mass fluxes of the lower interval below 250 cm (15.5-7.6 Ma) are very uniform at 5 +/- 1 mg/cm**2/kyr, while those of the upper interval above 250 cm (from 7.6 Ma) are over 2 times higher than the lower interval at 12 +/- 1 mg/cm**2/kyr. The median grain size of the eolian dusts in the lower interval increases from 8.4 Phi to 8.0 Phi downward, while that of the upper interval varies in a narrow range from 8.8 Phi to 8.6 Phi. The determined values compare well in magnitude to those of central Pacific sediments for the upper interval and equatorial and southeast Pacific sediments for the lower interval. This result suggests a possibility that the study site had been under the influence of southeast trade winds at its earlier depositional period due to the northerly position of the ITCZ, and subsequently of the northeast trade winds for a later period when the upper sediments were deposited. This interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to Central/South America for the lower interval and to Asia for the upper interval. This study suggests that the distinct differences in eolian mass flux and grain size observed across the ITCZ can be used to trace the paleo-latitude of the ITCZ.