Entity

Time filter

Source Type


Nakazawa T.,Geological Survey of Japan | Ueno K.,Fukuoka University | Kawahata H.,University of Tokyo | Fujikawa M.,Akiyoshi dai Museum of Natural History
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

A Palaeoaplysina-microencruster reef community is recognized in the Gzhelian-Asselian interval of the Taishaku and Akiyoshi limestones in SW Japan, which represent accreted Panthalassan atoll carbonates. In a reef-core area of the atoll, the alga Palaeoaplysina acted as a framebuilder and was associated with various binders (e.g., Tubiphytes, Archaeolithoporella, cystoporate bryozoans, and microbialites) and sediment-bafflers such as fenestrate and cryptostomate bryozoans and phylloid algae. In a subtidal environment of the back-reef area, Palaeoaplysina and phylloid algae flourished as sediment-bafflers. A microbial community, including Tubiphytes and sessile foraminifers, was predominant in a very shallow, peritidal environment of the back-reef area.Palaeoaplysina was distributed mainly along the northern margin of Pangea and is regarded as a boreal element. During Gzhelian-Asselian time, its distribution extended to the tropical or subtropical Panthalassa Ocean due to global cooling. On the Akiyoshi atolls, the Palaeoaplysina-microencruster community was succeeded by a sponge-microencruster community in the late Early Permian. The timing of this biotic turnover is similar to that of a change in climate from icehouse to greenhouse conditions, and coincides with superplume activity beneath the mid-Panthalassa Ocean. © 2011 Elsevier B.V. Source


Nakazawa T.,Geological Survey of Japan | Ueno K.,Fukuoka University | Fujikawa M.,Akiyoshi dai Museum of Natural History
Geological Journal | Year: 2012

Middle Permian lagoonal bioherms are described from mid-Panthalassan atoll carbonates (Akiyoshi Limestone) the Akiyoshi accretionary complex, SW Japan. The bioherms are composed of frame-building sphinctozoan and inozoan sponges, together with encrusting organisms, including chaetetids, Shamovella, calcareous red algae, and other microbes. Of them, sphinctozoan sponges, Shamovella, and microbes (forming microbialites) are the most dominant. Chaetetids, which were predominant the Early Pennsylvanian but rapidly decreased the late Moscovian, are also common these bioherms. Archaeolithoporella and bryozoans are rare, probably due to the low-energy lagoonal environment. This sponge-microencruster community replaced the Gzhelian-Asselian Palaeoaplysina-microencruster community on the Akiyoshi atolls during the Sakmarian-Kubergandian interval. This drastic change the reef-building community type almost coincides with the rapid deglaciation of the Gondwanan ice sheet and superplume activity beneath the mid-Panthalassan ocean. The prosperity of calcareous sponges was possibly controlled by environmental factors such as warming and eutrophication after the Gondwanan glaciation. © 2012 John Wiley & Sons, Ltd. Source


Nakazawa T.,Geological Survey of Japan | Igawa T.,Geological Survey of Japan | Ueno K.,Fukuoka University | Fujikawa M.,Akiyoshi dai Museum of Natural History
Facies | Year: 2015

A Murgabian (Middle Permian) reef-core facies in the Akiyoshi Limestone, southwest Japan, which is of mid-Panthalassan atoll origin, is here described from a limestone slab. The reef-core facies is composed mainly of boundstone with submarine cement and matrix. The reef-building community is characterized by a high-diversity biota, including sponges (sphinctozoans, inozoans, and chaetetids), bryozoans (fistuliporids and cryptostomates), crinoids and various microencrusters (Tubiphytes, Archaeolithoporella, reticular and laminar microbialites, encrusting foraminifers and problematic laminar red algae). Among them, sphinctozoan sponges and microencrusters such as Tubiphytes and microbialites are the most abundant. This community is similar to a time-equivalent lagoonal mound (patch-reef) biota on the Akiyoshi atoll in terms of the dominant sponges, Tubiphytes and microbialites, but differs in the additional occurrence of bryozoans, Archaeolithoporella and encrusting foraminifers, which probably preferred higher-energy conditions in the reef-core environment. Among temporally changing reef-building communities on the Carboniferous–Permian Akiyoshi atolls, the sponge-dominated reefal community described here flourished on mid-Panthalassan atolls in a relatively stable warm-water environment during a Middle Permian post-deglacial period. © 2015, Springer-Verlag Berlin Heidelberg. Source


Yoshimura K.,Kyushu University | Kurisaki K.,Kyushu University | Okamoto T.,Japan Forestry and Forest Products Research Institute | Fujikawa M.,Akiyoshi dai Museum of Natural History | And 3 more authors.
ISIJ International | Year: 2014

At the Naganobori Copper-Mine site, Akiyoshi-dai, Yamaguchi, southwestern Japan, the mining of copper ores dates back from the end of the 7th century to the beginning of the 8th century. The copper ore smelting was considered to be performed near the mine. Although copper ores in the oxidizing zone should have been used in the early stages, but later the sulfide ores in the enriched and primary zones, it has not yet been clarified as to when the smelting of the sulfide ores was started. The environmental change information for the past two thousand years was extracted from two growing stalagmites in the Ogiri No. 4 pit. Their fluorescent annual microbanding information was used for dating. The sulfate concentration was almost constant from 100 to 1400 A.D., and then clearly increased, suggesting that the extensive smelting of the sulfide ores had started. The concentration gradually increased, reached a maximum in the early stages of the 1700s, and then increased again from 1900. The magnesium concentration changed, almost synchronizing with the sulfate concentration. The possible reduction of the biomass by acid rain or leaching of the magnesium ions from the soil was suggested. The records extracted were in good agreement with those partially extracted from ancient documents, ancient picture maps and topographical maps. The copper used for the Great Buddha of Nara casting has the high possibility of being smelted using copper ores from the oxidizing zone. Source


Nakazawa T.,Geological Survey of Japan | Ueno K.,Fukuoka University | Nonomura N.,Fukuoka University | Fujikawa M.,Akiyoshi dai Museum of Natural History
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Large oncoids (up to 14. cm) and microbialites are abundant in the Artinskian (Lower Permian) section of mid-Panthalassan Akiyoshi atoll carbonates. The oncoids and microbialites consist mainly of a tubular microproblematicum, girvanellid cyanobacterial filaments, microbial micrite crusts, and pore-filling sparry calcite cements. They are surrounded by intraclastic-bioclastic grainstone/rudstone, indicative of moderate- to slightly high-energy subtidal conditions. The microbial community was the primary boundstone-forming organisms on the Akiyoshi atoll during this time. It represents a transitional stage in a mid-Panthalassan reef succession between a cooler-water autotrophic Palaeoaplysina-microencruster community in the Gzhelian-Asselian and a warmer-water heterotrophic calcareous sponge-microencruster community in the Middle Permian. The flourishing mid-Panthalassan microbial community during the late Early Permian is related to enhanced alkalinity, increasing nutrient levels, elevated sea-surface temperatures, and the absence of major reef-building metazoans, which resulted from Gondwanan deglaciation, climatic changes, and a pulse of active volcanism. © 2014 Elsevier B.V. Source

Discover hidden collaborations