Holocene activity of the Kuwana Fault was reconstructed based on 82 AMS ¹⁴C datings and on stepwise changes in the depositional rates of shallow marine sediments in four drilled cores. Depositional rates on the footwall and hanging wall are nearly equal during the interseismic period. Depositional rate on the footwall becomes markedly larger than that of the hanging wall just after the appearance of the vertical displacement of the fault. Six probable and one possible paleo-seismic events, including the last two historical earthquakes, were detected during the last 7, 000 years as stepwise changes of depositional rate on both sides of the fault.
Timing of faulting events was estimated from depositional curves of four drilling cores. Probable ages of seismic events are approximately 6, 200cal BP, 5, 700cal BP, 4, 000cal BP, 2, 100cal BP, AD 745, and AD 1586. Average recurrence interval of the Kuwana Fault calculated from these data is about 1, 000 years. Average vertical slip rate of the fault is at least 1mm/y during the last 7, 000 years.

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Middle Pleistocene sediments of Tarumi NT Cave (abbreviated to NT Cave) yield abundant and diversified vertebrate remains. Five excavations of the cave from 1992 to 1996 have revealed the morphology of the cave and the stratigraphic sequence and lithofacies of its sediments. Although the original cave had been severely destroyed by limestone quarrying before the first excavation was started, the cave seems to have originally been fissure-like, and extended in the NE-SW direction. The sediments in the cave are divided into three layers: Layers 1 to 3. Layer 3 is the original remain-bearing bed which has not been disturbed by quarrying. This layer consists mainly of brown mud with limestone breccia, and attains at least 5m in thickness. Mammalian remains are predominant in the vertebrate remains from the sediments. A preliminary taxonomic study of the remains has revealed the following characteristics of the mammalian assemblage of the cave. The assemblage contains considerable numbers of extinct species and forms exotic to present-day Japan, as well as a number of extant species. Forest dwellers are predominant in the assemblage, and a species now distributed in the high mountains of Honshu (Sorex shinto) is also abundant. A hedgehog (Erinaceus sp.) occurs in the assemblage, and voles exclusively comprise two extinct species (Clethrionomys japonicus and Microtus epiratticepoides). The faunal characters indicate that the sediments are dated to the middle Middle Pleistocene and were deposited under forest environments considerably colder than in the present Honshu.

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The refractive index of volcanic glass shards depends largely on its major element composition. The relationships among refractive index, specific refractivity, density, element dependent specific refractivity, and major element concentrations of examined dacitic to rhyolitic glasses demonstrate the systematic contribution of element concentration to the refractive index of glass.
The relationship between element concentrations and refractive index was examined by plotting data on oxide concentration-refractive index diagrams using EDS results from 102 tephra samples from the Kinki district and the Yatsugatake mountain range. Refractive index decreases in proportion to an increase of SiO₂. TiO₂, Al₂O₃, FeO^*, MgO, and CaO decrease with increasing SiO₂. Consequently, the relationship between these oxide concentrations and refractive index is a positive correlations. Alkali contents do not show any correlation with refractive index. Refractive index of glass shards is one of the useful methods of tephra identification and correlation. Major element compositions of the glass differ in some tephras, although the refractive indices are the same. Major element composition of tephra glasses can provide useful information for precise tephra correlation.

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The Tateno lava is the thickest lava flow distributed in the western part of post-caldera central cones of Aso Volcano, SW Japan. A pumice-fall deposit underlying the lava was identified, and it was correlated to Aso central cone pumice 4 (ACP4), one of the key tephra layers in and around Aso caldera. A noncarbonized root sample was discovered just below ACP4, and its ¹⁴C age was measured to determine the age of the eruption cycle producing ACP4 and the Tateno lava. The AMS ¹⁴C age was >43, 200yrs BP, which corresponded to >ca. 46cal ka. The age is consistent with a K-Ar age (51±5ka) for the Takanoobane lava, which occurs above the Tateno lava. In the western part of Aso central cones, two thick felsic lava flows, the Tateno lava (dacite) and the Takanoobane lava (rhyolite), were discharged at an interval of a few hundreds years around 50ka, and they accompanied precursor plinian pumice-fall deposits.

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Sedimentary processes accumulating and preserving terrestrial vertebrate fossil assemblages in a flood plain were examined from the middle Pleistocene Kiyokawa Formation in Chiba Prefecture, eastern Japan.
The flood-plain deposit is divided into three depositional units by lithology and fossil assemblages: A, B, and C Units. Unit A consists of massive mud with many plants remains from wash load by flooding. Unit B, which is composed of ill-sorted muddy sands or sandy muds, contains numerous wood debris, isolated terrestrial vertebrate remains, freshwater molluscan shells, and mudstone clasts. It may have been accumulated by a mudflow accompanying flooding. These fossil assemblages also indicate that these sediments come from a larger area than the stream channel. Unit C consists of massive muds and alternating layers of silts and fine-grained sands with in-situ freshwater bivalves and turtle remains. These fossils indicate that Unit C is a deposit of still water as a pond or shallow lake environment.

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The decolorization of humic acids from five different humic layers of ages from 8, 000 to 30, 000yrs BP by Coriolus consors IFO9078 was studied to understand the factors affecting the stability of humic substances in buried humic layers of the Holocene to late Pleistocene, which developed in weathered tephra beds called loam beds in Japan. After three weeks of incubation, the buried humic acids showed clear decolorization, but the magnitude of decolorization was lower than that of the humic acids from various Holocene surface soils in a previous study. Although the buried humic acids in this study were obtained from layers of different soil ages, the elemental compositions of all humic acids have similar highly dehydrated properties. These results suggest that the high resistance of the buried humic acids against microbial degradation may be due not only to the formation of humic-clay complex and the decline of microbial activity but also to the chemical properties of humic substances.

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[in Japanese]

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