Lower Miocene to Quaternary Diatom Biostratigraphy of Leg 57, off Northeastern Japan, Deep Sea Drilling Project

Abstract

Sediments recovered during Leg 57 provide a nearly complete lower Miocene to Holocene composite reference section for diatoms in the northwestern Pacific. High-and middle-latitude diatoms dominate the assemblages; however, because of the influence of the warm-water Kuroshio Current, low-latitude diatoms are consistently present in low abundance. Low-latitude diatom datums tied to paleomagnetic stratigraphy in the equatorial Pacific show little or no displacement in time at the 40°N latitude of the Leg 57 sites. Both highand low-latitude diatom zones are recognizable in the upper Miocene to Quaternary of Sites 438 and 440 and thus allow the first direct detailed correlation of these zonations for the upper Miocene. Eleven new subzones, which offer refinement of the existing high-latitude diatom zonation of the North Pacific, are proposed. In addition, the base of the Denticula lauta Zone is defined, and a new zone, the Actinocyclus ingens Zone, is proposed for the upper lower Miocene.A late Miocene hiatus spanning the interval from about 5.6 to 6.7 m.y.B.P. is identified at Sites 438 and 440. Correlative hiatuses occur throughout the middle-and high-latitude North Pacific both on the continental slopes and in the ocean basins. Onshore in California, this interval corresponds with an increase in the rate of sediment accumulation associated with the transition from laminated diatomites to overlying, more massive diatomaceous mudstones. These latest Miocene sedimentologic events apparently are related to a global cooling event.

The Stratigraphy of Neogene Silicoflagellates from the Norwegian Sea, ODP Leg 104

“…Locker and Martini (1985) directly correlated the range of Neonaviculopsis with the upper NNllb to within NN12. This zone is also correlative to the Denticulopsis hustedtii Zone, Subzone b of the North Pa cific diatom zonation (Barron, 1985). Based upon correlation of the Bachmannocena diodon nodosa zone to the diatom zona tion of Leg 104 (Ciesielski, et al, unpublished), this zone en compasses the middle upper Miocene.…”

Explanatory Notes

“…to the F0 of N. koizumii. The N. kamtschatica Zone is divided into subzone a and subzone interval b-c by the FO of T. oestrupii, as was proposed by Barron (1980). A third modification to the Akiba (1985) zonation uses the LO of Rocella gelida as the marker species for the base of the Thalassiosira spinosa Zone, rather than the FO of T. spinosa, based on F. Akiba's observation (pers.…”

“…Cande and Kent (1992). Notes: Sources for calibration: (1) Koizumi and Tanimura, 1985;(2) (3) Koizumi, 1992;(4) Barron, 1980;(5) Gersonde and Burckle, 1990;(6) Harwood and Maruyama, 1992; (7) Baldauf and Barron, 1991; (8) Bodén, in press; (9) new calibration from Site 884 magnetostratigraphy. LO = last occurrence; LCO = last common occurrence; FO = first occurrence; FCO = first common occurrence.…”

Site 799

“…A similar assemblage was reported from DSDP Site 302 (Ling, 1975), the only known such occurrence from submarine sediments of the Sea of Japan, and its age is considered within the "Denticula (= Neodenticula) kamtshatica" (diatom) Zone of Koizumi (1975). The top of this diatom zone is defined by the initial appearance of Neodenticula koizumii, which has been placed near the bottom of the Gauss Chron at 3.36 to 3.7 Ma (Koizumi, 1975;Koizumi and Tanimura, 1985), or between the "b" and "c" subchrons of Gilbert Chron, which has been estimated at 4.2 Ma in the northwestern Pacific (Barron, 1980). Therefore, these two occurrences can be considered as time-correlative.…”