中生代珪藻化石研究の諸相 : 首長竜とともに生きた珪藻たち [in Japanese] Current studies on the Mesozoic diatom fossils [in Japanese]
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This paper gives a perspective on the current studies of the Mesozoic diatoms with their evolution and the paleoenvironmental changes. As known, diatoms have taken one of the most important roles in the food web/carbon cycle on the earth during the Cenozoic, however, the origin of the diatoms has been on discussion. Though no direct evidence by fossil record is obtained, it is estimated to be back to the latest Permian-early Jurassic, based on the molecular clock and the oldest fossil record from Germany. Exceptionally, well-preserved assemblages were found from the Aptian-Albian marine sediments of the Ocean Drilling Program Site 693, the Weddell Sea, Antarctic. As inferred from the frustular morphology of the fossil assemblages, diatoms at the earlier stage took a physio-ecological strategy of forming resting spores to protect themselves against severe environmental changes, such as desiccation and unstable salinity/nutrient availability in the littoral zones. Fossil records of the diatoms from the Cenomanian-Turonian, the age of the oceanic crisis (mid-Cretaceous Oceanic Annoxic Event 2), are almost absent. Remarkable diversification in morphology with various ultrastructures recognized also in the modern taxa and colonization into new habitats as plankton in the Campanian-Maastrichtian shows that the vast sedimentation of pelagic diatomaceous oozes started mainly in higher latitude in the age. Diatoms succeeded to survive the Cretaceous/Paleogene boundary associated with the mass extinction of several organisms. Recently, Cretaceous (latest Santonian-earliest Campanian) diatom fossils were recovered from methane seepage-inducing authigenetic carbonate rocks in the Teshio-Nakagawa area, northern Japan, nevertheless the records from the Mesozoic are quite few across the country. These Cretaceous assemblages are the most well-preserved among those from the eastern Asian regions, and thus will promisingly provide the detailed Cretaceous algal biogeography and evolution of the diatoms.
Fossils 96(0), 15-28, 2014
Palaeontological Society of Japan