Detailed sampling of the Upper Triassic atoll-type carbonates of the
Sambosan Accretionary Complex throughout Southwest Japan yielded highly
abundant and diversified porcelaneous, microgranular, agglutinated and
hyaline foraminifers of Carnian-Rhaetian age, as well as some
microproblematica and ostracods. The foraminiferal assemblages were
collected from shallow-water carbonates originated upon volcanic
seamounts surrounded by deep-water radiolarian chert in a mid-open
oceanic realm of the Panthalassan Ocean during Triassic time. Because
most studies of the Upper Triassic microfauna come from the former
Tethys, counterparts of the Panthalassan Ocean are pivotal to decipher
the micropalaeontological biodiversity of the western circum Pacific, as
well as to evaluate the distribution patterns of organisms and their
evolution trends throughout the Tethys and Panthalassa. This study
reports on 42 genera and 60 species whose associations can be used as
sedimentary facies indicators of carbonate buildup environments.
Japanese specimens show a strong Tethyan affinity, and especially with
the Peri- and Southern Tethyan forms. A palaeobiogeographic distribution
analysis using a large foraminiferal database is led, in order to
evaluate the extraordinary spreading of these Upper Triassic
foraminifers between the Neo-Tethys and the Panthalassa. Data are
finally integrated in a new plate tectonic model, where six faunistic
provinces are defined, each containing a characteristic foraminiferal
assemblage. This map provides for the first time a useful and visual
synthesis of the Upper Triassic foraminifer palaeobiogeographic
distribution.