Charcoal particles in sediments have been examined to clarify fire history such as forest fire history. To reconstruct fire history since 17,000 cal BP in central Japan, we quantified microscopic and macroscopic charcoal particles in the sediments from Sonenuma Swamp located in Shiga Prefecture. The abundance of microscopic and macroscopic charcoal particles fluctuated differently. In sediments from 7.6 to 6.8 m deep (corresponding to 13,000–10,000 cal BP), microscopic charcoal particles abounded continuously. In sediments less than 7.0 m deep (after ca.10,000 cal BP), macroscopic charcoal particles often showed sudden increase. Thus, fires seem to have been extensive and frequent between 13,000 and 10,000 cal BP and local and occasional after 10,000 cal BP. Previous studies indicated that frequent fires occurred from terminal Pleistocene to incipient Holocene, and this study and studies in adjacent areas show that the fires were extensive at least in the Kinki district. Reflectance measurements of charcoal particles showed that charcoal particles in sediments at 300 cm deep (ca. 4000 cal BP) were formed at a high temperature (ca. 500°C), suggesting their probable formation through combustion of trees.
Fossil woods are abundant in the Cretaceous Yezo Group in Hokkaido, Japan. From 144 dicotyledonous wood samples, 14 species representing 10 genera were identified. All 14 species and four (Castanoradix, Frutecoxylon, Nishidaxylon, Sabiaceoxylon) of the 10 genera were new. Five genera (Icacinoxylon, Magnoliaceoxylon, Paraphyllanthoxylon, Plataninium and Ulminium) were already known from the Cretaceous and Tertiary, and one (Hamamelidoxylon) was known only from the Tertiary. Two specimens of Icacinoxylon kokubunii from the Albian (Lower Cretaceous) were the oldest records of dicotyledonous wood in Japan. The species distribution by age was: Albian: one species; Cenomanian: four species in four genera; Turonian: 10 species in eight genera; Coniacian: seven species in six genera; Santonian: eight species in seven genera. The study extended our knowledge of wood structural diversity among the early dicotyledons in the mid-Cretaceous in the northern hemisphere.