| Research Abstract |
The investigators carried out field researches in the Maruyama Quarry and the Minami-dai Quarry in the Nishino-dai area of the Akiyoshi Limestone. About 700 thin sections of limestones and coral materials and 30 sheets of limestone slabs have been prepared and analyzed for the investigations on paleoecology and growth forms of reef building organisms. The results are as below :
1. Well-preserved reef facies zonation : lagoon facies zone, reef core facies zone, and fore reef slope facies zone, was recognized in the lower Upper Carboniferous part of the Minamidai area, based on distribution of the limestone rock types, the size and density of the reef frameworks, and growth forms of the frame-builders. The reef core facies zone was divided into five subfacies zones.
2. Among the subfacies zones, the reef front subfacies zone is characterized by the highest density of the reef-building organisms which have various growth forms. The relationships between basal planes of discoidal coral colonies and geopetal planes were confirmed that the reef slope was inclined about 30 to 40 degrees from the sea level.
3. The main reef builders in the early Late Carboniferous limestones fo the Akiyoshi Organic Reef Complex are rugose corals, Chaetetes, calcareous blue-green algae, tabulate corals, bryozoans, and encrusting foraminifers. Their distributions and various assemblages in the organic reef complex are discriminated. They have different growth forms and functional roles in the reef frameworks of the diffrent micro-environments, even in organisms belonging to the same taxon.
4. The Carboniferous part of the Akiyoshi Limestone includes paleokarst deposits, providing evidence of aerial exposure during regressive events. Some of transitional intervals between coral faunas coincide with these regressive events.
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