Sedimentary facies and biofacies of theTorinosuLimestone in theTorinosu area,KochiPrefecture,Japan

Abstract

The Torinosu Limestone represents carbonate platform deposits in a foreland basin, the sedimentary setting of which is highly different from those of well‐known Late Jurassic reefs in the western Tethys that developed on shelf areas of continental margins and intra‐Tethyan platforms. Sedimentological and paleontological analyses were conducted on a 55.5 m‐thick Upper Jurassic–Lower Cretaceous (Tithonian–Berriasian) carbonate sequence (Torinosu Limestone) at the Eastern Hitotsubuchi Quarry, Kochi Prefecture, Southwest Japan. The carbonate sequence is composed of two sections that are separated by a subaerial exposure surface. Two and three depositional units have been defined in the lower and upper sections, respectively, based on changes in lithology and the biotic composition of the carbonates; they are numbered from 1 to 5, in ascending order. Calcified demosponges (stromatoporoids and a chaetetid Chaetetopsis crinita) are abundant in three units (2, 3, and 5), in which microencrusters (mostly Lithocodium aggregatum and Bacinella irregularis) and microbialites are also common to abundant. Although most of them are para‐allochthonous, in‐situ branching stromatoporoids are found on and above the subaerial exposure surface (unit 3). Corals are less common, poorly diverse, and primarily represented by the family Microsolenidae. Siliciclastic grains occur in all units, but they are particularly common in units 1 and 4. The co‐occurrence of the Lithocodium–Bacinella association, which is typical of oligotrophic or moderately mesotrophic shallow‐water environments, with microsolenids, which are indicative of high nutrient levels and/or low‐light intensity due to high turbidity, suggests repeated changes in nutrient levels associated with terrigenous input. Based on lithology, biotic composition, and succession, we infer that sea‐level changes and related terrigenous input controlled the sedimentary environment of the studied carbonate sequence.

A Lower Valanginian coral fauna from the South Iberian Palaeomargin (Internal Prebetic, SE Spain)

“…The large limestone blocks in the area of Štramberk (Czech Republic) are clearly dated as Tithonian to Early Berriasian (Vašíček et al, 1994;Skupien, 2016, 2019). The same situation presents the Torinosu Limestone; its assignation to the Tithonian was tentative (e.g., Eguchi, 1951), and it includes older as well as younger sediments (Löser and Mori, 2002;Kakizaki et al, 2012;Ohga et al, 2013). Tithonian and lower Berriasian shallow marine sediments with corals crop-out transitionally in the Crimea area (Arkadiev et al, 2018).…”

大分県東部・四浦半島に分布する後期ジュラ紀の礁性石灰岩の堆積環境と厚歯二枚貝の産状

“…Kano et al, 2006 e.g. Kano, 1988;Kano andJiju, 1995 Shiraishi andKano, 2004;Ohga et al, 2013Kano, 1988Kano and Jiju, 1995 Figs. 6A, 7 50-100 m e.g.…”

Carbon isotope stratigraphy of Torinosu‐type limestone in the western Paleo‐Pacific and its implication to paleoceanography in the Late Jurassic and earliest Cretaceous

“…; Ohga et al . ). The age of the limestone has been broadly determined as the Kimmeridgean to the Berriasian, based on fossil assemblages of surrounding mudstone, such as radiolarian (e.g.…”

“…Tamura 1960;Kano 1988). The limestone generally contains shallow-marine carbonate components such as bioclastics, ooids, and oncoids (Morino 1993;Kano & Jiju 1995;Kiyama & Iryu 1998;Ohga & Iryu 2004;Kakizaki & Kano 2009), and yields abundant reef-building organisms such as stromatoporoids, hermatypic corals, rudists, and microencrusters (Tamura 1961a;Mori 1963;Kano 1988;Morino 1993;Shiraishi & Kano 2004;Shiraishi & Yoshidomi 2005;Sano et al 2007Sano et al , 2008Sano & Skelton 2010;Kakizaki et al 2011;Ohga et al 2013). The age of the limestone has been broadly determined as the Kimmeridgean to the Berriasian, based on fossil assemblages of surrounding mudstone, such as radiolarian (e.g.…”