Multi‐approach characterization of shallow‐water carbonates off Minamitorishima and their depositional settings/history

Abstract

Sedimentological, geochemical, and chronological analyses were carried out on 19 carbonate rock samples collected from the submarine slope to the west of Minamitorishima (Marcus Island) located near the western margin of the Pacific Plate.Four groups of carbonate rocks were distinguished: mollusk-rich carbonates, coral-rich carbonates, foraminiferal-nannofossil packstone, and mudstone/wackestone. The mollusk-rich carbonates are characterized by dominance of bivalve (including rudist) and gastropod shells. Skeletal grains are extensively bioeroded, some with thick micrite envelopes. Sr isotope ratios ( 87 Sr/ 86 Sr) and Mesorbitolina ex gr. texana (large benthic foraminifer) indicate that the shallow-water carbonates were deposited in the late Aptianearly Albian (~122-111 Ma). The coral-rich carbonates are characterized by abundant scleractinian corals and nongeniculate coralline algae associated with encrusting acervulinid foraminifers. The biotic composition indicates that the carbonates were deposited in a coral reef setting during the Oligocene-Miocene. Geochemical data show that the coral-rich carbonate were dolomitized at 6.8-9.5 Ma (Tortonian-Messinian) and that normal seawater is the likely parent fluid. The foraminiferal-nannofossil packstone is semi-consolidated foraminiferal-nannofossil ooze, deposited in the Pleistocene (0.99-0.45 Ma). The mudstone/wackestone is marked by absence of macrofossils and is phosphatized: its age and depositional environment could not be assessed. The Cretaceous mollusk-rich carbonates are distributed to shallower depths than expected following standard seafloor subsidence, clearly showing that Minamitorishima has undergone not continuous thermal subsidence but significant episodic uplifts probably by Eocene volcanism.

Editorial for the thematic issue, “Orogens, ophiolites, and oceans: A snapshot of Earth's tectonic evolution”

“…The Paleogene volcanic activity might have locally overprinted Early to mid‐Cretaceous volcanic edifices, at least on the Ogasawara Plateau and the Minamitorishima volcanic edifice. The presence of Cretaceous reefal limestone reported by Aftabuzzaman et al (2021) strongly supports this scenario. As reported by Miyata et al (2020), such seamount‐capping carbonates that were deposited on the Pacific Plate prior to its subduction can provide highly valuable records that allow comprehensive geological interpretations to be made of the Izu–Bonin–Mariana forearcs.…”

“…The three papers by Miyata et al (2020), Aftabuzzaman et al (2021), and Hirano et al (2021) address the topic of seamounts. Miyata et al (2020) examine shallow‐water carbonates collected from the eastern slope of Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes.…”

“…Thus, the eastern section of this seamount is interpreted as an accretionary wedge. Aftabuzzaman et al (2021) present sedimentological, geochemical, and chronological analyses on carbonate rock samples collected from the western slope of Minamitorishima (Marcus Island) and determine the history of this seamount as follows. After deposition of the Cretaceous shallow‐water carbonates, including the mollusk‐rich limestone, Minamitorishima was inundated, and its top was covered with a pelagic cap.…”

Fine‐scale chemostratigraphy of cross‐sectioned hydrogenous ferromanganese nodules from the western North Pacific

“…All seamounts in this area are grouped in the West Pacific Seamount Province (WPSP; Koppers et al, 2003;Sager et al, 1993). Seamounts in this region including Minamitorishima Island were formed by the Early-Middle-Cretaceous hotspot volcanism (Aftabuzzaman et al, 2021;Koppers et al, 2003); however, Minamitorishima Island is thought to be overprinted by Paleogene volcanism (Hirano et al, 2021). The oceanic basement below these seamounts, the Cretaceous Pacific Plate, formed between 165 and 157 Ma (Müller et al, 2008;Nakanishi et al, 1989).…”

Topography, sedimentology, and biochronology of carbonate deposits on seamounts in the JA area, northwestern Pacific Ocean

“…4.2.9 | JA22 Seamount (Butakov Guyot) (Sager et al, 1993) and144 (Premoli Silva et al, 1993), and on Minamitorishima Island (Aftabuzzaman et al, 2021).…”