A major extinction of intermediate‐water (500–1000 m) benthic foraminiferal species coincided with a major decrease in δ13C (2.8‰) of terrestrial organic matter (n‐C29 alkane) and δ34S (20‰) of whole rock sulfide in a continuous siltstone sequence in the Tawanui Section (46°S paleolatitude) along the Akitio River, southeastern North Island, New Zealand, in the middle part of the uppermost Paleocene nannofossil zone (CP8). The benthic extinction (25% of species) occurred over ∼3 kyr at ∼55.5 Ma. Increases in kaolinite/illite and kaolinite/smectite ratios and in terrestrial organic carbon percentages started ∼3 kyr before the major benthic extinctions, lasted over ∼40 kyr, and probably reflect warmer climate and increased rainfall. The productivity of planktonic foraminifera and calcareous nannoplankton decreased ∼3 kyr prior to the major extinctions and recovered at the time of benthic extinctions. These events that started ∼3 kyr before the extinction can be best explained by warming, increased rainfall, reduced salinity of surface waters, and increased influence of warm saline deep water (WSDW). Benthic foraminiferal oxygen indices indicate a strong decrease in dissolved oxygen levels within the intermediate water from low oxic (1.5–3.0 mL/L O2) to suboxic (0.3–1.5 mL/L O2) conditions coinciding with the benthic extinctions. Increases in total organic carbon (TOC) and in the hydrocarbon‐generating potential of kerogen (measured as the hydrogen index (HI)) agree with the interpretation of decreased dissolved oxygen levels of the intermediate water. The lowest oxygen conditions lasted ∼40 kyr and coincided with a decrease in calcareous benthic foraminiferal productivity, highest TOC levels, and lowest δ13C of terrestrial organic carbon. Dominant formation of WSDW or sluggish intermediate‐water circulation caused by warming and high rainfall in high‐latitude areas most likely led to the ∼3‐kyr time lag between events on land and in surface waters preceeding the extinction and the development of dysaerobia in the sea, coinciding with the major benthic extinction and decrease in δ13C and δ34S in New Zealand. Global warming of deep and intermediate waters may have caused decomposition of methane hydrate in sediments, resulting in a strongly decreased δ13C of marine carbonates, promoting dysaerobia in the ocean, and warming global climate by increased methane concentrations in the atmosphere. Upwelling of WSDW, occurring soon after it became dominant in high‐latitude areas, is likely responsible for the recovery of normal salinity and the concomitant recovery of planktonic foraminifera and calcareous nannoplankton productivity in high‐latitude surface waters. Minor benthic foraminiferal extinctions (9% of species) occurred ∼40 kyr after the major extinctions, lasted ≤ ∼6 kyr, and coincided with the initiation of environmental recovery.

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At Site 582, DSDP Leg 87, turbidites ~ 560 m thick were recovered from the floor of the Nankai Trough. A turbidite bed is typically composed of three subdivisions: a lower graded sand unit, an upper massive silt unit, and an uppermost Chondrites burrowed silt unit. The turbidites intercalate with bluish gray hemipelagic mud which apparently accumulated below the calcite compensation depth. In order to investigate the nature and provenance of the turbidites, we studied the grain orientation, based on magnetic fabric measurements and thin-section grain counting, and grain size, using a photo-extinction settling tube and detrital modal analysis.The following results were obtained: (1) grain orientation analysis indicates that the turbidity current transport parallels the trench axis, predominantly from the northeast; (2) Nankai Trough turbidites generally decrease in grain size to the southwest; (3) turbidite sands include skeletal remains indicative of fresh-water and shallow-marine environments; and (4) turbidites contain abundant volcanic components, and their composition is analogous to the sediments of the Fuji River-Suruga Bay area. Considering other evidence, such as physiography and geometry of trench fill, we conclude that the turbidites of Site 582 as well as Site 583 were derived predominantly from the mouth of Fuji River and were transported through the Suruga Trough to the Nankai Trough, a distance of some 700 km. This turbidite transport system has tectonic implications: (1) the filling of the Nankai Trough is the direct consequence of the Izu collision in Pliocene-Pleistocene times; (2) the accretion of trench fill at the trench inner slope observed in the Nankai Trough is controlled by collision tectonics; and (3) each event of turbidite deposition may be related to a Tokai mega-earthquake.

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Shipboard and shore-based investigation on siliceous and calcareous microfossil biostratigraphy, magneto-stratigraphy and tephrostratigraphy identified numerous datum events from the sedimentary sequences of Sites 1150 and 1151 drilled on the forearc basin of northern Japan by the Ocean Drilling Program Leg 186. Some 83 datum events were selected to construct new age-depth models for the sites. Based on the reliable magnetostratigraphy from the Pleistocene to the Upper Miocene, which were correlated to the standard geomagnetic polarity timescale, and on excellent records of diatom and radiolarian biostratigraphy throughout the sequences, the shipboard age model was revised. Major revisions referred to stratigraphic position of the Miocene-Pliocene boundary that has been shifted more than 200 m downward in each sequence. The age-depth relations of the forearc sites represent drastic changes in the sedimentation rate-extremely high (40 cm/ k.y. on average) in the Early Pliocene and low (less than 2 cm/k.y. on average) in the Middle Miocene-and several hiatuses exist throughout the sequence. The drastic changes can be related mostly to changes in diatom sedimentation and the tectonics of the Japanese Island Arc. Local ages for some foraminiferal, calcareous nannofossil and radiolarian bioevents are estimated from the age-depth models at each site. These newly calibrated bioevents and biozones as well as established diatom biostratigraphy are incorporated into the updated magneto-biochronologic timescale, which will contribute to an improvement in biochronologic accuracy of Neogene sediments in northern Japan and adjacent areas.

The Middle America Trench SE of Acapulco is flanked by a steep canyon-incised slope and narrow shelf, showing one of a variety of sedimentary facies patterns possible at convergent margins. Piston and drill cores from this region define eight facies belts including: (1) a pelagic facies of brown clay, (2) an outer slope mud facies, (3) a trench sand facies, (4) a foraminiferan-free facies on the lower slope, (5) a foraminiferanbearing facies on the mid-slope, (6) a laminated mud facies on the upper slope, (7) a shelf facies of sand and mud, and (8) a canyon facies of sand and gravel. The superposition of trench and lower slope sediment during accretion results in a fining upward sequence reflecting a gradual uplift of the seafloor through the trench sediment-plume. The lower limit of the foraminiferan-bearing facies is defined by the absence of in situ calcareous foraminiferans and is controlled by the calcite compensation depth. The upper slope laminated mud facies probably reflects the depth range of the oxygen minimum zone.In the Leg 66 area sedimentation rates are high in the trench and on the outer and lower slope, decrease on the mid-slope, and increase again on the shelf. On the inner shelf, waves and currents concentrate sand which funnels through a prominent submarine canyon, bypassing the mud-dominated slope and accumulating in the trench. A terrigenous sediment-plume generated by trench turbidity flow causes accelerated sediment accumulation to about 500 m above and 40 km seaward of the trench. The volume of material transported by the trench sediment-plume is five or six times greater than that moved by the shelf sediment-plume which supplies detritus to the shelf, upper slope and mid-slope environments.

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