Mid-oceanic shallow-water carbonates of the Panthalassa domain: new microfacies data from the Sambosan Accretionary Complex, Shikoku Island, Japan

Abstract

During the Late Triassic, carbonate platforms expanded on continental shelves and island arcs. They have been studied in detail in the Tethys realm but coeval mid-oceanic shallow-water environments of the Panthalassa domain have received less attention. To fill this gap, we investigated the Upper Triassic limestone of the Sambosan Accretionary Complex (SAC), southwest Japan. A comprehensive sampling of the Upper Triassic limestone has been performed in 16 localities at Shikoku Island. Eight microfacies, ranging from pelagic to lagoonal settings, were identified, including two microfacies that are described in the SAC for the first time. Quantitative microfacies analysis assesses the composition of the SAC limestone and its biostratigraphy is refined. Finally, a speculative depositional model of the SAC carbonate platforms is proposed based on modern and ancient analogues. Instead of a true atoll-type platform with well-defined facies belts as suggested by previous studies, this new model suggests that the typical Sambosan platform was more probably a carbonate bank with submerged margins and a mosaic of microfacies in the platform interior. Special attention is given to the factors that have probably controlled the carbonate sedimentation at the top of the seamount(s)

Sedimentology and biostratigraphy of the upper Triassic carbonates from the Shiriya cape, North Kitakami Belt, Japan

“…The size and shape of the recrystallized specimens were compared with analogous and synchronous microfacies to support this identification (Chablais, Martini, & Onoue, 2010; Peybernes, Chablais, Onoue, & Martini, 2016; Peyrotty, Rigaud, et al, 2020; Rigaud et al, 2012). Large echinoderms, gastropods and rare ostracods, embedded in dark micrite, also occur.…”

“…Conglomerates are of high interest in accretionary contexts, since limestone clasts embedded in polygenic conglomerates are usually much better preserved than the surrounding limestone slabs, representing essential sampling targets (Peybernes, 2016). Limestone clasts in a few conglomerates were sampled (Figure 2, orange stars).…”

“…As documented by multiple studies conducted over the past 15 years, the Triassic Panthalassa met all the environmental conditions for the development of numerous shallow‐water carbonate systems (Chablais, Martini, & Onoue, 2010; Chablais, Martini, Samankassou, et al, 2010; Chablais, Onoue, & Martini, 2010; Chablais et al, 2011; Del Piero, Rigaud, Peybernes, et al, 2022; Fucelli et al, 2021; Heerwagen & Martini, 2020; Khalil et al, 2018; Martindale et al, 2015; Onoue et al, 2009; Peybernes et al, 2015; Peybernes, Chablais, Onoue, Escarguel, & Martini, 2016; Peybernes, Chablais, Onoue, & Martini, 2016; Peybernes et al, 2020; Peyrotty, Rigaud, et al, 2020; Peyrotty, Brigaud, & Martini, 2020; Peyrotty, Ueda, et al, 2020; Rigaud et al, 2010, 2012, 2016; Rigaud, Vachard, & Martini, 2015; Rigaud, Martini, & Rettori, 2013; Rigaud, Blau, et al, 2013; Rigaud, Martini, & Vachard, 2015; Rigaud & Martini, 2016; Sano et al, 2012; Senowbari‐Daryan et al, 2010; Zonneveld et al, 2007). The remnants of those systems occur today in the Circum‐Pacific area, either in accretionary complexes (i.e., Philippines, Japan, Russian Far East) or on accreted terranes (USA, Canada, Mexico) (Figure 1).…”

“…Their sedimentological, biostratigraphical and diagenetical investigations shed light on the development, evolution and demise of shallow‐water carbonate systems out of Tethyan domain (Figure 1). Accordingly, these studies provided new perspectives about ecology, environmental conditions, fauna dispersion within the immense Panthalassa Ocean (Bucur et al, 2020; Chablais, Martini, & Onoue, 2010; Chablais, Martini, Samankassou, et al, 2010; Chablais, Onoue, & Martini, 2010; Chablais et al, 2011; Del Piero et al, 2020; Del Piero, Rigaud, & Martini, 2022; Del Piero, Rigaud, Peybernes, et al, 2022; Forel et al, 2022; Peybernes et al, 2015; Peybernes, Chablais, Onoue, Escarguel, & Martini, 2016; Peybernes, Chablais, Onoue, & Martini, 2016; Peybernes et al, 2020; Peyrotty, Rigaud, et al, 2020; Peyrotty, Brigaud, & Martini, 2020; Peyrotty, Ueda, et al, 2020; Rigaud et al, 2010, 2012, 2016; Rigaud, Martini, & Rettori, 2013; Rigaud, Blau, et al, 2013; Rigaud, Vachard, & Martini, 2015; Rigaud, Martini, & Vachard, 2015). Although the majority of these Panthalassan relics have been studied, some outcrops are still under‐explored regarding petrography and sedimentology.…”

Microbial-, fusulinid limestones with large gastropods and calcareous algae: an unusual facies from the Early Permian Khao Khad Formation of Central Thailand

“…Flügel 2004). Gastropods are also considered to be tolerant to high temperature and salinity variations which point to at least some or temporary environmental restriction (Wagner and Van der Togt 1973;Tucker and Wright 1990;Riegl et al 2010;Peybernes et al 2016). Intraclasts, some of them quite large and yielding also large gastropods, indicate resedimentation and a considerable topography and finally proximate deposition.…”