Taxonomy and biostratigraphy of the fossil resting spore morpho-genera of the marine diatom genus Chaetoceros Ehrenberg 海生珪藻Chaetoceros属の休眠胞子化石の分類・生層序学的研究

博士論文

The fossil resting spores of marine diatom genus Chaetoceros were investigated by detailed LM and SEM observations in order to reveal its taxonomy, using the samples of Deep Sea Drilling and on-land section from the middle Eocene through the Quaternary. In addition, the stratigraphic significance of these species is discussed. Moreover, the stratigraphic changes of fossil resting spore diversity, abundance and valve size were investigated in order to understand past productivity and paleoenvironmental changes in upwelling regions. Thirteen fossil Chaetoceros resting spore morpho-genera including nine new ones, with 85 species including 53 new species, 6 new varieties and 12 new combinations areidentified and described. As a result of identification, many staratigraphically shortranging species can potentially serve as additional useful biostratigraphic markers to improve resolution of the diatom biostratigraphy of North Pacific and Atlantic Ocean. Moreover, because of the dissolution-resistant nature of these robust resting spore species, their stratigraphic utility is potentially great, especially in sediments containing poorly preserved diatoms where the more delicate forms have been destroyed. Moreover, four resting spore events are recognized in the Eocene/ Oligocene boundary (Event EO), the Oligocene/ Miocene boundary (Event OM), late Miocene (Event LM) and late Pliocene (Event LP): (1) The Event EO is characterized by the explosive diversification in both generic and specific levels, drastic increase in abundance, and sudden decrease of valve size. (2) Event OM is defined by the two-fold increase in species diversity. (3) Events LM and LP are identified by the mass occurrences of resting spores in late Miocene and in the interval from late Pliocene to Recent, respectively. The changes of diversities of genera and species, and abundance and valve size of resting spore may indicate enhanced productivity. ･･･

2003

Includes bibliographical references