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Deep-sea ash records from Legs 127 and 128 in the Sea of Japan provide reliable data about the nature and composition of explosive volcanic activity of the surrounding area since the middle Miocene. Special attention is given to glass alteration and a determination of initial magmatic compositions. Barium accumulations are responsible for massive crystallization of barite and harmotome in some altered ash layers. The glasses are assigned to four compositional magmatic groups that correspond to various mediumand high-K andesite suites and to alkaline suites. Analyses of trace elements in selected ash layers distinguish two subgroups in the medium-K andesite suites (unenriched and moderately enriched in incompatible elements), one subgroup that corresponds to a K-andesite suite, and two alkaline subgroups of trachytic and phonolitic composition. Some Miocene ash layers exhibit compositions intermediate between the alkaline and the calc-alkaline suites. Compositions of coexisting minerals correlate with magmatic signatures: OPX and Aland Ti-poor CPX occur in the calc-alkaline ash layers, and Al-,Ti-, and Na-rich CPX, K-rich plagioclases, and Ti-rich biotites occur in the alkaline ash layers. INTRODUCTION Volcaniclastic material was recovered in lower Miocene to Quaternary sediments of the Japan Sea during Legs 127 and 128 (Fig. 1). Four sites were drilled during Leg 127, two to the east of the Japan Basin (Sites 795 and 796) and two within the Yamato Basin on its northeastern and western margins (Sites 794 and 797) (Tamaki, Pisciotto, Allan, et al., 1990). Two sites were drilled during Leg 128 at the Oki Ridge (Site 798) and at the Kita-Yamato Trough (Site 799). Moreover, Site 794 was revisited to drill deeper in the basement (Ingle, Suyehiro, von Breymann, et al., 1990). Recovery was excellent in Quaternary and Pliocene strata, less excellent, but satisfactory, in Miocene strata. The wide geographic spread of the sites provides an accurate record of the explosive volcanic activity of the Japan Sea region during middle Miocene to Quaternary time, with deposition of ash from the Japanese volcanic arc, from volcanic islands in the Japan Sea, and from the Korean volcanoes. VOLCANICLASTIC MATERIAL AT LEGS 127 AND 128 The volcaniclastic material consists mainly of discrete ash layers (0.1-20 cm thick) and dispersed glass shards of fallout deposition in all of the sedimentary sequences. The thickest deposits were recovered in Miocene strata, including a 27-m-thick pumice flow tuff at Site 799 and ash-fall and gravity-flow tuffs at Sites 794, 795, 796, and 797. Hyaloclastite tuffs were recovered at Sites 794 and 795, near the basaltic lavas of the basement. Lithological and petrographical aspects of ash layers are described in a parallel note on tephrochronology (Pouclet and Scott, this volume). Detailed investigations at Sites 798 and 799 provide the most accurate frequency of the volcanic activity. A total of nine volcanic 1 Tamaki, K., Suyehiro, K., Allan, J., McWilliams, M, et al., 1992. Proc. ODP, Sci. Results, 127/128, Pt. 2: College Station, TX (Ocean Drilling Program). 2 Géotectonique et Pétrologie, Faculté des Sciences, Université, BP 6759, 45067 Orleans Cedex 2, France. 3 Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-Ku, Tokyo 164, Japan. 4 Geological Institute, University of Tokyo, Hongo, Bunkyo-Ku, Tokyo 113, Japan. pulses are distinguished and numbered from youngest to oldest: VI, V2, and V3 in the Quaternary, V4 and V5 in the Pliocene, V6 in the late Miocene, V7 and V8 in the late middle Miocene, and V9 in the middle Miocene. The distinction of volcanic pulses is based on quiescence of explosive volcanic activity (no ash deposits), and on sharp variations of activities (expressed by number and thickness of ash layers). Similar volcanic phases can be recognized at Sites 794, 795,796, and 797. Table 1 indicates the number of sampled ash layers per volcanic phases at each site. Information about the distribution of ash layers has been drawn from Legs 127 and 128 Initial Reports volumes (Tamaki, Pisciotto, Allan, et al., 1990; Ingle, Suyehiro, von Breymann, et al., 1990). Samples selected for petrographic and geochemical studies are shown on the stratigraphic summary columns for the western (Sites 799, 797, and 798) and northeastern (Sites 794,796, and 795) parts of the Japan Sea (Fig. 2). Table 2 (back-pocket microfiche) presents the list of samples with their location and significant petrographical, chemical, and mineralogical features. Samples from Sites 799 and 798 have been numbered according to the Initial Reports volume's exhaustive list of ash layers (Ingle, Suyehiro, von Breymann, et al., 1990). Site 799 (Kita-Yamato Though) Holes were drilled in the southwestern middle part of the KitaYamato Trough. The deepest hole ended in lower middle Miocene terrigeneous sediments 1084 m below seafloor (mbsf), about 115 m above the acoustic basement. The nine volcanic pulses are well defined and were dated by using paleomagnetic polarity transitions and fossil data. The oldest volcanic event, V9, equated with the prominent 27-m-thick pumice flow tuff, has been dated about 12.5 Ma. It clearly indicates a major volcanic event linked to initial subsidence of the trough (Pouclet and Scott, this volume). A large selection of 90 samples of volcaniclastic material has been analyzed, along with three additional samples of sands from the hole's bottom, to determine their magmatic mineral content. Site 797 (Western Yamato Basin) Holes were drilled to the west of the Yamato Basin in Quaternary to middle or upper lower Miocene sediments. Drilling entered igneous basement from 554 mbsf to the hole's end (900.1 mbsf). The basement

Data Report: Geochemistry and Mineralogy of Ash Layers from Legs 127 and 128 in the Japan Sea