Early Pleistocene plant biostratigraphy of the Shobudani Formation, southwest Japan, with reference to extinction of plants.

Abstract

Plant macrofossil assemblages from the Shobudani Formation in the northern part of Hashimoto City, Wakayama Prefecture, are described. 221 taxa including 21 extinct plants are identified. Six assemblage zones, SB-I to SB-VI in ascending order, are established. The zones SB-II and SB-V are characterized by the occurrence of the members belonging to subarctic and cool-temperate elements indicative of a cool climate. The zones SB-I, SB-III, SB-IV and SB-VI are characterized by the occurrence of the members belonging to warm-temperate and/or subtropical elements associated with some cool-temperate elements, suggesting warm climatic conditions. The coexistence of the members attributed to both subtropical and cool-temperate elements in the zone SB-III suspects warm winters and cool summers. A scarcity of the members belonging to the cool-temperate elements associated with common subtropical and warmtemperate elements in the zone SB-VI indicates warmer summer conditions than in the zone SB-III. Based on the mode of the occurrence of fossil plants, the Shobudani Formation is thought to be early Pleistocene in age. The late early-Pleistocene extinction of Cyclocarya paliurus, Pterocarya aff. stenoptera, and Picea koribai is assumed to a lowering of the winter temperatures. In respect to the extinction of Metasequoia glyptostroboides from the area, a warming of the summer climate and a change in topography together with repeated changes in overall climatic deterioration are suspected.

Neogene Palynology of Holes 794A, 795A, and 797B in the Sea of Japan: Stratigraphic and Paleoenvironmental Implications of the Preliminary Results

“…Over the next 2 m.y., the very large and frequent changes in forest composition reconstructed from pollen assemblages from Holes 794A, 795A, and 797B (Figs. 3-5 and 8) correspond to forest dynamics inferred from changes in pollen and floral assemblages throughout Japan (Tai, 1973;Igarashi, 1976;Hase and Hatanaka, 1984;Igarashi et al, 1988;Hayashida and Yokoyama, 1989;Yahata et al, 1989;Momohara et al, 1990).…”

Late Pliocene Plant Biostratigraphy of the Lowermost Part of the Osaka Group, Southwest Japan, with Reference to Extinction of Plants.

“…The differences in the matrix seem to be influenced by depositional conditions, as mentioned in Momohara et al (1990). One is interbedded within stratified sands or sandy silt, and the other is unstratified and laterally well continued peaty silt.…”

“…Characteristically, many plants belonging to the cool-temperate elements occurred with the subtropical and warm-temperate elements. The coexistence of plants attributed to both subtropical and cool-temperate elements in the fossil assemblages has often been recorded from the Plio-Pleistocene strata (e. g., Miki, 1948;Minaki et at., 1981;Momohara et al, 1990). These authors assumed that these plants may have occurred among nearby vegetation under mild oceanic conditions.…”

“…These changes, combined with a change in climate, should have led to extermination of the Tertiary elements. Momohara et al (1990) discussed the cause of the late early-Pleistocene plant extinctions in the Shobudani Formation, located to the south of the Izumi Range. The authors considered that the topographical change and climatic change together caused the extinction of plants including Metasequoia glyptostroboides.…”

Preliminary Results of High-Resolution Pollen Analyses of Selected Pleistocene Intervals from Holes 798A, 798B, and 798C

“…Changes in seasonality are implicit in the shifting compositions of vegetation. For example, the cooccurrence of warm temperate and cool temperate elements in early Pleistocene macrofossil assemblages from southwest Japan has been interpreted as evidence of warm winters and cool summers (Momohara et al, 1990).…”