Microfacies and depositional setting of the Upper Triassic mid-oceanic atoll-type carbonates of the Sambosan Accretionary Complex (southern Kyushu, Japan)

Abstract

The Upper Triassic shallow-water limestones of the Sambosan Accretionary Complex are reconstructed as a remnant of a mid-oceanic atoll-type build-up upon a seamount in the Panthalassan Ocean. The Sambosan atolltype carbonates and its pedestal were accreted along with deep-water ribbon-chert and related siliceous rocks to the eastern margin of Asia during the Late Jurassic to Early Cretaceous. Studied limestones crop out in southern Kyushu Island, southwest Japan. Although the prevailing and intense deformation during the accretionary process prevents measurement of sections in stratigraphic successions, and sedimentary structures are poorly preserved, microfacies description and foraminifers analysis allow us to speculate the depositional setting of the Sambosan limestones. Seventeen microfacies are distinguished and several foraminifers of Tethyan affinity are identified. Foraminifers indicate a Late Carnian to Rhaetian age. The Tethyan affinity of the macro-and microfaunas suggests that the Sambosan seamount was located presumably in a low-to middle-latitudinal zone of the southern hemisphere during the Late Triassic.

Rhaetian foraminiferal assemblage from the Dachstein Limestone of Mt. Begunjščica (Košuta Unit, eastern Southern Alps)

“…Aulotortus friedli is known also from the Panthalassan Ocean (cHaBlais et al, 2010a(cHaBlais et al, , 2011riGaud et al, 2010). koeHn-zaninetti (1969) and later ciaraPica and zaninetti (1984b, 1985), which treat both species valid, cite the Ladinian to Carnian range for A. praegaschei and Norian to Rhaetian range for A. friedli.…”

“…HoHeneGGer & loBitzer, 1971;scHäfer & senowBari-daryan, 1978;senowBari-daryan, 1980;sadati, 1981;senowBari-daryan et al, 1982;wurm, 1982;zaninetti et al, 1982;kuss, 1983;matzner, 1986;kristan-tollmann, 1990 (flüGel, 1967;HoHeneGGer & loBitzer, 1971;scHäfer & senowBari-daryan, 1978;senowBari-daryan, 1980;senowBaridaryan et al, 1982); Norian and/or Rhaetian of Oman (Bernecker, 1996); Norian and Rhaetian of Sambosan Accretionary Complex, Japan (kristan-tollmann, 1990;cHaBlais et al, 2010b); Rhaetian of Carpathians (Gaz ª dzicki, 1974); Rhaetian of Northern Calcareous Alps, Austria (Gaz ª dzicki et al, 1979;scHäfer, 1979;matzner, 1986). VacHard and fontaine (1988) Material: Thin section 187A.…”

“…At the same time, spatial distributions on Mt. Begunj{~ica correspond to palaeoecological zonations established for reefs from the Northern Calcareous Alps (HoHeneGGer & loBitzer 1971;HoHeneGGer & Piller, 1975;scHäfer & senowBari-daryan, 1978;scHäfer, 1979;senowBari-daryan, 1980;flüGel, 1981;Piller, 1981;sadati, 1981;scHäfer & senowBari-daryan, 1981;kuss, 1983), Sici ly (senowBari-daryan et al, 1982;martini et al, 2007), Cyprus ), Oman (Bernecker, 2007, Seram in Indonesia (al-sHaBani et al, 1983;martini et al, 2004), Sulawesi in Indonesia (martini et al, 1997), from Sambosan Accretionary Complex in Japan (cHaBlais et al, 2010a(cHaBlais et al, , 2010b(cHaBlais et al, , 2011, and from the Palawan Block in Philippines (kiesslinG & flüGel, 2000). As typical markers of the central-reef area, we note K. fluegeli, A. perforatum, Tr.…”

“…"Sigmoilina" schaeferae favourized micritic substrate (Bernecker, 2005) of the central-reef area (HoHeneGGer & loBitzer, 1971;scHäfer & senowBari-daryan, 1978;wurm, 1982;senowBaridaryan et al, 1982;cHaBlais et al, 2010b) Material: Thin section 243B.…”

“…While reef-constructors from these reefs received considerable attention in the past studies, no such research has focused on associated organisms. Although benthic foraminifera are abundant in the Norian-Rhaetian reefs and can provide important additional information in recognizing peri-reef subenvironments (senowBari-daryan, 1980;sadati, 1981;flüGel, 1981;scHäfer & senowBari-daryan, 1981; senow- Bari-daryan et al, 1982;kristan-tollmann, 1986zamParelli et al, 1995;martini et al, 1997cHaBlais et al, 2010b), only few were mentioned by flüGel and ramoV{ (1961), turn{ek and ramoV{ (1987), ramoV{ and turn{ek (1991) and turn{ek and Bu ser (1991).…”