The Takamatsu Plain, located in the northeast part of Shikoku Island, is one of several large plains around the Seto Inland Sea. The late Quaternary sediments in this plain are important to the discussion of the Seto Inland Sea through the Quaternary. In this paper, these formations in the Takamatsu Plain are described in terms of lithology, volcanic ash, molluscan fossils, and ¹⁴C dating in detail. The Holocene relative sea level change in the Takamatsu Plain is also discussed based on these data.
The late Quaternary sediments in the Takamatsu Plain are divided into the Kotogawa Formation and the Takamatsu Formation. The Kotogawa Formation is subdivided into two members: Ban-cho gravels as alluvial deposits before Würm II, and Fukuoka-cho muds as marsh deposits during Würm II. The Takamatsu Formation is also subdivided into four members: Hamano-cho sandy gravels, Nishiuchi-machi mulls, Nishiuchi-machi sands as marine sediments, and Nishiuchi-machi gravels as flood sediments.
The relative sea level change is estimated based on ¹⁴C ages and paleo-depths obtained from analyses of some molluscan assemblages. According to the relative sea level change curve, about 5, 800yrs BP the sea level is supposed to have been higher than at present in Takamastu.
The delta of the Kotogawa river originated by covering Hamano-cho sandy gravels. The bottom set beds of the delta around Nishiuchi-machi and Hamano-cho area were formed about 4, 000yrs BP. The foreset beds were deposited between 4, 000 and 3, 600yrs BP, and then the topset beds covered these beds after 3, 600yrs BP.

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The Stratigraphy, lithofacies, and petrologic character of the Plio-Pleistocene volcanic ash layers were clarified in a 1, 700m core drilled at Uozakihama, Higashinada-ku, Kobe City, in the northern part of the Osaka sedimentary basin. The chemical compositions of volcanic glass shards from major volcanic ash layers were measured. The volcanic ash layers were correlated with previously known tephras based on stratigraphic, lithologic, and chemical characteristics. The lithostratigraphic, division of the sediments in the core can be correlated to the Neogene to Quaternary sequences exposed in or deposited under the Osaka Basin.
The Higashinada 1, 700m core consists of two sedimentary units, K1-L and K1-U, which unconformably overlie basement rocks (Granodiorite). The K1-L unit from depths 1, 545.7 to 691.8m is mainly composed of silt, sand, and gravel beds of freshwater origin, which intercalates the K1-1382 volcanic ash layer that can be correlated to the Asashiro volcanic ash. This unit is correlated to the Miyakojima Formation, which lies beneath the Osaka Plain, corresponding to the lowermost part of the Osaka Group and the lower half of the lower part of the group.
The K1-U unit conformably overlies the K1-L, and is correlated to the Tanaka Formation, which is correlative with the upper half of the lower part of the Osaka Group and the terrace deposits. This unit comprises alternating beds of terrestrial silt, sand, and gravel with 19 marine clay beds and 31 volcanic ash layers. The volcanic beds of the K1-648, K1-566, K1-537, K1-488, K1-486, K1-444, K1-422, K1-351, K1-348/K1-347.4, K1-245, K1-223, K1-175, K1-141, K1-101, and K1-26 are equivalent with the Yellow II/III, Pink, Komyoike III, Yamada III, Azuki, Sayama, Imakuma II, Hacchoike I, Hacchoike II, Kasuri, Minatojima I, Naruohama IV, Handa, one of the beds from the Koshienhama III to Koshienhama IV, and Heian-jingu volcanic ash layers, respectively. Further correlation can be assessed: K1-223 with the Ks 5 volcanic ash in the Kasamori Formation of the Kazusa Group at the Boso Peninsula, K1-175 with the BT 72 volcanic ash in the Takashima-oki boring core, and K1-171 with the Kakuto tephra layer. On the basis of this tephra correlation, 19 marine clay beds of the K1-U are equivalents of the Ma-1, Ma0, Ma0.5, Ma1, Ma1.3, Ma1.5, Ma2, Ma3, Ma4, Ma5, Ma6, Ma7, Ma8, Ma9, Ma10, Ma11(1), Ma11(2), Ma11(3), and Ma12, in ascending stratigraphic order.

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Late Quaternary strath terraces younger than 50ka were investigated in the Shitada (Ikarashi River) and Tochio (Kariyada River) regions, central eastern margin of the Niigata Basin, in order to clarify their chronology and implications to neotectonic movements. The terraces were classified based on geomorphologic configuration and tephro-stratigraphic relation between marker tephra horizons and the terraces. Six tephra horizons (ST 1-ST 6) were found in the loam and black soil, which overlie terrace deposits. ST 4 is correlated with the widespread tephra As-K (13ka), ST 5 with AT (25ka) and ST 6 with Dkp (50ka). The terraces are in chronologic order Sh-D, Sh-C, Sh-B, Sh-A₃, Sh-A₂ and Sh-A₁ terraces for the Shitada region and To-D, To-C, To-B, To-A₄, To-A₃, To-A₂ and To-A₁ terraces for the Tochio region.
The presence of strath terraces since the post-glacial transgression indicates that intermittent local and/or regional uplift initiated terrace development. Same aged terraces had different relative heights from the present riverbed across NNE-SSW and NW-SE trending active faults. These discontinuities cannot be simply explained by tilting due to active folding. We propose that the NNE-SSW and NW-SE trending fault systems have been active as the result of block segmentation, which characterize the uplift movement of the Shitada and Tochio regions since 50ka.

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In order to detect the effects of thermally altered obsidian on lithic assemblage, prominent morphological characteristics of obsidian artifacts, which include crazing and breakages, were classified in examining a Meboshigawa 2 assemblage at a late upper Paleolithic site in Hokkaido, northern Japan.
Observations made using a light microscope discerned six prominent morphological characteristics: crazing like a fingerprint, squamous crazing, tiny cracks, vesiculation, breakage with flat surface, and breakage with irregular surface. All specimens could fall into one of 33 categories in terms of the sets of the above characteristics. The frequency of relationships between these characteristics in each specimen indicated that some of them may have significant impact on their formation.
Only tiny cracks and breakage with irregular surface were compatible with the results of laboratory experiments, and formation of those tiny cracks is constrained by temperature and duration of heating. Hence, tiny cracks on the surfaces of obsidian artifacts should be criteria for detecting thermal alteration of obsidian.
Based on the ratio of tiny cracks in the assemblage, I propose implications for manufacturing context, using and discarding the context of obsidian artifacts in terms of the relationship between the process of lithic assemblage formation and the use of fire.

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Accurate radiocarbon (¹⁴C) and carbon isotope measurements of fossil bones require complete removal of all exogenous carbon. XAD-2 chromatography was used to eliminate the foreign organic matter from bones. The fossil bones used in the experiment were animal bone fragments collected at the Awazu submarine archeological site. The bone samples were demineralized with 0.8M HCl at 4°C, and the acid-insoluble residue was concentrated by centrifugation and lyophilized. The demineralized bone powder was hydrolysed with 6M HCl at 110°C. Solid components were removed by centrifugation before the filtered hydrolysate was passed through the XAD-2 resin used for removal of fulvic acids. In addition, the gelatin extraction method of decalcification in a cellulose tube with 1.2M HCl, followed by heating at 90°C in water was used for the same species to compare the ability of the two methods to remove organic contaminants.
The purified hydrolysates obtained from XAD-2 chromatography have more positive δ¹³C values and older ¹⁴C ages than gelatin collagens extracted from hot water. The difference tends to become greater for poorly preserved fossil bones containing less than 0.7% collageneous materials. The fulvic phases give apparently younger ages and significantly more negative δ¹³C values than bone organic carbon. Furthermore, the XAD-treated hydrolysates of gelatin collagens give the same ¹⁴C ages (older than those of gelatin collagens) as the XAD-purified hydrolysates. The result indicates that the gelatin extraction method is sufficient for ¹⁴C dating on well-preserved bones, but insufficient on poorly preserved bones, because hot-water extraction does not totally remove exogenous organic carbon. Therefore, XAD-2 resin is recommended for accurate ¹⁴C and carbon isotope measurements.

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The Miyada Formation was originally described by Aoki (1925) to include the marine strata distributed on the Miyada Plateau of the southern part of the Miura Peninsula. This Formation unconformably overlies the Miocene Miura Group and is overlain by upper Pleistocene strata. The formation, which consists mainly of sand, is well known to yield a large number of molluscan fossils. Okumura et al. (1979) reported 253 species of molluscan fossils from the Miyada Formation.
Recently, the authors determined the geological ages of the Miyada Formation by the Electron Spin Resonance-method (ESR). These ages show 513, 000±63, 000 years (lower part of the Miyada Formation, using the shell of Glycymeris yessoensis) and 325, 000±40, 000 years (Upper part of the Miyada Formation, using the shell of Felaniella usta). The authors considered that these ages of the Miyada Formation are not contradictory those identified by the former studies, e. g. 300, 000-370, 000 years of age (Ohmura, 1991) and 400, 000 years of age (Yamada et al., 1983). The Miyada Formation is possibly correlative with the Zizodo Formation and the Yabu Formations of the Simosa Group developed in the Boso Peninsula. This correlation was based on the ESR and Fission Track methods and a comparison of the characteristics of the molluscan fauna in the two areas.

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Two turbidite layers of earthquake origin were found in a sediment core collected from the Rishiri Trough, west of Rebun Island, northernmost part of Hokkaido, Japan. Radiocarbon age determinations using planktonic foraminiferal tests in hemipelagic mud indicated that the depositional ages of each turbidite were 2, 300 ¹⁴C yrs BP and 5, 500 ¹⁴C yrs BP, respectively. Therefore, the recurrence interval of the large earthquakes forming the turbidites in this area was estimated to be around 3, 200 years. This interval is longer than that around the Okushiri Ridge (around 1, 000 years), west of Hokkaido near the hypocenter of the 1993 Hokkaido-nansei-oki Earthquake, or that in northern Sakhalin (more than 2, 000 years).

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