Sequence boundary and related sedimentary and diagenetic facies formed on Middle Permian mid-oceanic carbonate platform: Core observation of Akiyoshi Limestone, Southwest Japan

Abstract

Detailed core observation of the Akiyoshi Limestone, Southwest Japan, reveals a sequence boundary and related sedimentary and diagenetic facies formed on a late Murgabian (Middle Permian) mid-oceanic carbonate platform. The sequence boundary lies upon karstified bioclastic grainstone and is overlain by peritidal lime-and dolo-mudstone. The karstified bioclastic grainstone, which had been affected by subaerial exposure and early diagenetic processes, is characterized by crystal silts, prismatic, bladed and dogtooth cements, blackened limestone features, and alveolar textures. The overlying peritidal limeand dolo-mudstone is 8 m thick and exhibits fenestrae, fissures, laminations, black pebbles, and low-diversity biota composed exclusively of ostracodes and calcispherids. The sequence boundary almost coincides with a major fusulinoidean biostratigraphic boundary. A sea-level fall in the late Murgabian resulted in a biotic turnover and formed the sequence boundary and the karst textures. The following relatively slow transgression resulted in the deposition of the thick transgressive peritidal unit.

An Early–Middle Guadalupian (Permian) isotopic record from a mid-oceanic carbonate buildup: Akiyoshi Limestone, Japan

“…apparently occurs at the top of the drilled core, whereas the youngest (Cd Z,) at the bottom. The first appearance horizons of the fusuline assemblages, the Pk Z., Ao Z., Ncr Z., Nf Z., and Cd Z. reported by Nakazawa and Ueno (2004), were confirmed in our study at 14, 34, 39, 61, and 74 m-level of the core, respectively.…”

“…Likewise, the similar trend was reported as a result of a late-stage burial diagenesis at elevated Table 1 Analytical results on carbon and oxygen isotopic compositions of limestone samples from the Kaerimizu core no.1 section. The fusuline zones reported by Nakazawa and Ueno (2004) are shown. The samples with two index taxa, i.e.…”

“…In particular, the Kaerimizu section in the northern Akiyoshi area (Fig. 1) exposes more than 10 fusuline zones of the Early to Middle Permian in sequence, as demonstrated by intense surface mapping and drilled core research (Ota et al, 1973;Ueno, 1992Ueno, , 1996Nakazawa and Ueno, 2004). Judging from the narrow age gap between the carbonate sedimentation and the tectonic accretion, the Akiyoshi paleo-seamount was Fig.…”

“…2). The fusuline zones used in this study is after Ota et al (1973) and Nakazawa and Ueno (2004), with a slight modification through our own microscopic studies helped by H. Igo who identified fusulines from the core samples. The Ns Z. is correlated with the Roadian at its Table 1).…”

“…For comparison, fusuline biozones by Ota (1977) and Nakazawa and Ueno (2004) were shown. Lithological description of the core samples is after Nakazawa and Ueno (2004): the dark gray part indicates lime-mudstone dominated facies, and the dotted part the grain-and pack-stone dominated facies, respectively. stratotype in Texas, whereas all other zones with the Wordian.…”