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36. PLEISTOCENE and PLIOCENE FORAMINIFERA from the SEA of JAPAN, LEG 31, DEEP SEA DRILLING PROJECT James C

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36. PLEISTOCENE and PLIOCENE FORAMINIFERA from the SEA of JAPAN, LEG 31, DEEP SEA DRILLING PROJECT James C 36. PLEISTOCENE AND PLIOCENE FORAMINIFERA FROM THE SEA OF JAPAN, LEG 31, DEEP SEA DRILLING PROJECT James C. Ingle, Jr., Department of Geology, School of Earth Sciences Stanford University, Stanford, California ABSTRACT Pleistocene and Pliocene planktonic foraminiferal faunas found at Sites 299, 300, 301, and 302 in the Sea of Japan are dominated by Neogloboquadrina pachyderma and Globigerina bulloides s.l. in- cluding G. umbilicata. Minor accessory species include Globigerina quinqueloba, Globigerinita glutinata, G. uvula, and Globorotalia scitula. These species form a subarctic biofacies characteristic of up- per Pliocene through Recent deposits in much of the sea. Only sparse faunas were recovered at Sites 300, 301, and 302, but quantitative analysis of a fair to good Pleistocene sequence at Site 299 in the Toyama Channel clearly records significant planktonic foraminiferal events correlative with the initiation of severe cooling at 900,000 yr B.P. and a significant interglacial warming about 500,000 yr B.P. Unusual paleooceanographic and geochemical environments have been created in this sea during glacial maxima and minima due to un- usually shallow basin sills which, together with a relatively shallow calcium carbonate compensation depth (CCD), account for the vir- tual absence of calcareous foraminiferal assemblages from major portions of the sediments penetrated at Leg 31 sites in the Sea of Japan. INTRODUCTION from Leg 31 sites in the Sea of Japan (Figure 1, Tables 1 and 2). Moreover, the presence of significant amounts of The Sea of Japan represents one of the several ethane at Sites 299 and 301 and caving sand at Site 300 marginal basin complexes formed during Tertiary forced abandonment of these sites prior to penetration episodes of increased subduction and back-arc extension of Miocene sediments. Thus, the results of foraminif- in the western Pacific (Coleman, 1973). However, the eral analysis in the Sea of Japan are disappointing in Sea of Japan is bathymetrically and oceanographically terms of the original cruise objectives. Nevertheless, a more isolated than most of these seas including the adja- fair to good sequence of Pleistocene planktonic cent Sea of Okhotsk which formed during the same foraminifera was recovered at Site 299 (Figure 1) allow- Neogene tectonic pulse. A major objective of Leg 31 was ing quantitative biofacies analysis and providing a here- to probe the sedimentary and tectonic history of the Sea tofore unavailable record of major paleooceanographic of Japan with the expectation that study of temperature- variations during this period of climatic extremes. sensitive planktonic microfossils would reveal variations Pleistocene events are of special importance in the Sea of in the paleoclimatic and paleooceanographic history of Japan due to its unusual oceanographic and bathy- the Sea. In fact, studies of planktonic foraminifera from metric setting at a mid- to high-latitude position par- bathyal Neogene1 marine sediments exposed along the ticularly sensitive to climatic fluctuations. northwestern coast of Honshu have already demon- strated that significant variations in surface-water tem- Bathymetry and Oceanography perature have occurred within this area during the early The present unusual oceanographic environment of Miocene through Pleistocene period (Saito, 1963; Taka- the Sea of Japan has been summarized by Hidaka yanagi and Oba, 1966; Huzioka et al., 1970; Asano et (1966). Although over one-quarter of the sea is presently al., 1969; Saito and Maiya, 1973). These variations were deeper than 3000 meters (Figure 1), it is bathymetrically in response to the combined effects of paleoclimatic and topographically isolated from the adjacent Pacific events and tectonic adjustment of margins, sills, and Ocean by narrow straits and extremely shallow sills straits during evolution of the Sea (Minato et al., 1965). between Honshu and Hokkaido (130 m), Hokkaido and Unfortunately, calcareous foraminifera proved to be Sakhalin (55 m), Honshu and Korea (130 m),2 and sparse or absent in most of the sediments recovered 2Narrow channels in the Tsushima Straits reach depths of 250 'Neogene, as used in this report, includes the Miocene through meters (Ujiié, 1973), but were likely sediment filled during lower Pleistocene period. stands of sea level. 693 45C 35< 35' PACIFIC SURFACE OCEAN CURRENTS CONTOURS IN FATHOMS 30c c C 30 130' I35 140' 145' 130' 135' 140' 145' Figure 1. Location map of the Sea of Japan area showing location of Leg 31 drilling sites; a second diagram illustrates the principal surface currents operating in the Japan Sea area and adjacent Pacific. PLEISTOCENE AND PLIOCENE FORAMINIFERA TABLE 1 geochemical ananysis of upper Pleistocene sediments Leg 31 Sea of Japan Site Data from the sea provide ample evidence that reducing con- Maximum ditions were indeed the rule during glacial episodes Depth Penetration (miyake et al., 1968; Ujiié and Ichikura, 1973). Below Sea Below Site Location Level (m) Sea Floor (m) Abundance and Preservation of Plio-Pleistocene Fora- minifera 299 39°29.69'N 2599 532 137°39.72'E The abrupt and almost total absence of calcareous benthonic and planktonic foraminifera within major 300 41°02.96'N 3427 117 136°06.30'E portions of the stratigraphic columns at Sites 299, 301, and 302 (Table 2) is in all likelihood a reflection of one 301 41°03.75'N 3520 497 or both of the Quaternary oceanographic extremes 134°02.86'E noted above. Sediments barren of foraminifera at these 302 40°20.13'N 2399 531.5 sites commonly contain framboidal pyrite indicative of 136°54.01'E the reducing bottom conditions envisioned for glacial Sakhalin and the Asian mainland (12 m) as noted by Niino et al. (1969). TABLE 2 Samples Barren of Foraminifera at Sites 299, 301, and 302 These shallow sills combine with a severe winter (Interval in cm) climate3 in the northern portions of the sea to produce an extremely cold, but highly oxygenated water mass. Site 299 Site 299 Site 301 Site 302 Some subtropical water enters the sea from the south as a branch of the Kuroshio Current termed the Tsushima 1-1,4547 19, CC 2-1,85-87 2-3, 50-52 Current (Figure 1), and contains a warm temperate- 1-2, 40-42 20-1,130-132 24, 30-32 24, 75-77 1-2,110-112 20-2, 70-72 2-5, 110-112 2-6, 80-82 subtropical planktonic biofacies (Ujiie, 1973). However, 1-3,14-16 20, CC 2-6, 109-111 3-6,130-132 the dominant highly oxygenated cold surface waters 1-5,110-112 21-1,55-57 2, CC 3,CC formed in the northern areas under severe winter con- 2-1, 140-142 21, CC 3-1,118-120 4-2, 100-102 ditions3 travel south as the Liman Current and ultimate- 24, 60-62 22-2, 4042 3,CC 44,125-127 ly sink. As they sink, they continually maintain a sill-full 3-3, 70-72 22-3, 50-52 4-2, 75-77 4,CC 34, 70-72 224, 4042 4,CC 5-2, 140-142 body of water exhibiting a uniform temperature of only 4-2, 35-37 22, CC 5-3, 34-36 54,100-102 0.2°C, an oxygen content of 5.3 ml/1, and a relatively 5-2, 87-89 23, CC 5, CC 5,CC low salinity of 34°/oo, thus creating an unusual sediment- 6-2, 55-57 24-1,113-115 7 (heat flow) 6,CC water interface capable of producing brown muds ("red 7-2, 50-52 24, CC 7,CC 7-2, 70-72 clay") at relatively shallow depths (Niino et al., 1969). 7-3, 48-50 25-1,4244 8-1,80-82 7-5, 50-52 The surface sediments also display unusually low 74, 96-98 25, CC 8,CC 7,CC 9-2, 55-57 26-1,85-87 9-1,133-135 8-2, 70-72 organic carbon values considering the high productivity 9-5, 25-27 26, CC 9,CC 8-5, 60-62 in the sea. In addition, Ujiié and Ichikura (1973) provide 10-2, 7-9 28-1,147-149 10-1,20-22 8,CC clear evidence of a relatively shallow CCD in the sea of 10-5, 30-32 28, CC 11-1,84-86 9-1,4042 about 1500 meters4 attesting to the aggressive nature of 10, CC 29-1,108-110 11, CC 9,CC the resident bottom water. 11-2,40-42 29, CC 12, CC 10-2, 70-72 114,4143 30-1,79-81 13-1,71-73 10-5, 70-72 Ujiié and Ichikura (1973) also emphasize the in- 11-5,13-15 30-3, 70-72 13, CC 10, CC escapable conclusion that eustatically lowered sea levels 11, CC 30-5, 32-34 14-1, 80-82 11-2,70-72 coincident with Plio-Pleistocene glacial maxima must 12-2,54-56 30, CC 14, CC 114,70-72 have completely isolated the Sea.5 All access through the 12-3,50-52 31-1,68-70 15-1,50-52 11, CC 124,13-15 31, CC 15-3, 80-82 12-1,90-92 present straits was undoubtedly severed when sea level 12-5,55-57 32-2, 4749 15, CC 12-3,70-72 dropped to -150 meters (Milliman and Emery, 1968) 13-3,127-129 32, CC 16-1,93-95 12, CC creating a truly unique environment ultimately produc- 134, 90-92 33-1,64-66 16, CC 13-1,100-102 ing reducing bottom conditions due to expansion and 13-5, 25-27 33, CC 16-1,93-95 13, CC duration of sea ice, loss of exchange with the Pacific, 13, CC 34-1,146-148 \1-1,4149 14-2, 70-72 144, 86-88 35-1,136-138 17, CC 14wt, 70-72 and sluggish bottom circulation.
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