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Palaeoecology of the Hiraiso Formation (Miyagi Prefecture, Japan) and implications for the recovery following the end-Permian mass extinction - PubMed

  • ️Sat Jan 01 2022

Palaeoecology of the Hiraiso Formation (Miyagi Prefecture, Japan) and implications for the recovery following the end-Permian mass extinction

William J Foster et al. PeerJ. 2022.

Abstract

The Hiraiso Formation of northeast Japan represents an important and under-explored archive of Early Triassic marine ecosystems. Here, we present a palaeoecological analysis of its benthic faunas in order to explore the temporal and spatial variations of diversity, ecological structure and taxonomic composition. In addition, we utilise redox proxies to make inferences about the redox state of the depositional environments. We then use this data to explore the pace of recovery in the Early Triassic, and the habitable zone hypothesis, where wave aerated marine environments are thought to represent an oxygenated refuge. The age of the Hiraiso Formation is equivocal due to the lack of key biostratigraphical index fossils, but new ammonoid finds in this study support an early Spathian age. The ichnofossils from the Hiraiso Formation show an onshore-offshore trend with high diversity and relatively large faunas in offshore transition settings and a low diversity of small ichnofossils in basinal settings. The body fossils do not, however, record either spatial or temporal changes, because the shell beds represent allochthonous assemblages due to wave reworking. The dominance of small burrow sizes, presence of key taxa including Thalassinoides, Rhizocorallium and Holocrinus, presence of complex trace fossils, and both erect and deep infaunal tiering organisms suggests that the benthic fauna represents an advanced stage of ecological recovery for the Early Triassic, but not full recovery. The ecological state suggests a similar level of ecological complexity to late Griesbachian and Spathian communities elsewhere, with the Spathian marking a globally important stage of recovery following the mass extinction. The onshore-offshore distribution of the benthic faunas supports the habitable zone hypothesis. This gradient is, however, also consistent with onshore-offshore ecological gradients known to be controlled by oxygen gradients in modern tropical and subtropical settings. This suggests that the habitable zone is not an oxygenated refuge that is only restricted to anoxic events. The lack of observed full recovery is likely a consequence of a persistent oxygen-limitation (dysoxic conditions), hot Early Triassic temperatures and the lack of a steep temperature/water-depth gradient within the habitable zone.

Keywords: Anoxia; End-Permian extinction; Recovery; Spathian; Trace fossils.

© 2022 Foster et al.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. A summary map of the basement geology of Japan showing the terranes that have sedimentary sequences that include Triassic rocks, with an inset map showing the palaeogeographic location of the South Kitakami terrane during the Triassic (red circle).

Ch, Chichubu terrane, Ks, Kurosegawa terrane, Sa, Sangun terrane, Mz, Maizuru terrane, Jo, Joetsu terrane, Nk, North Kitakami-Oshima terrane, Id, Idonnappu terrane. Modified from Wallis et al. (2020). TTL, Tanakura Fault. ISTL, Itoigawa-Shizuoka Fault. Blue lines represent plate boundaries. Palaeogeographic map after Blakey (2012).

Figure 2
Figure 2. Locality map for the Kamiwarizaki and Hiraiso Coast sections, Miyagi Prefecture, Japan.

(A) Inset showing the location of the different sections in relation to Motoyoshi and Kesennuma in Miyagi prefecture. (B) Shows the location of the investigated section at Kamiwarizaki (highlighted in blue with a K). (C) Shows the location of the investigated sections on the Hiraiso Coast (highlighted in blue). Only the major fault lines are shown following Kashiyama & Oji (2004).

Figure 3
Figure 3. Field photographs showing the nature of the exposures along the Hiraiso Coast and at Kamiwarizaki.

(A) Upper Permian Toyoma Formation, Maehama Fishing Port. Hammer for scale. (B) Lower Triassic Hiraiso Formation, Hiraiso Coast, Maekawara Fishing Port. (C) Lower Triassic Hiraiso Formation, Kamiwarizaki, Kotaki Fishing Port. Person for scale. (D) Transition between the Hiraiso (exposure on the right) and Osawa Formation (exposure of the left), Akaushi Fishing Port.

Figure 4
Figure 4. Schematic diagram showing a transect of the depositional environments of the Hiraiso Formation.

Estimated bathymetric ranges of the lithofacies is shown below the schematic. Depositional schematic modified from Kamada & Kawamura (1988).

Figure 5
Figure 5. Ammonoids identified from the Hiraiso Formation.

(A–C) Koninckitoides aff. posterius, specimen NMNS PM35937, Hiraiso Formation, early Spathian; (C) suture line of NMNS PM35937 at H = 19 mm; (D–H) Proptychitidae gen. et sp. indet., specimen NMNS PM35938, Hiraiso Formation, early Spathian; (H) suture line of NMNS PM35938 at H = 9 mm. Scale bars: 10 mm (A and B, D–G), 5 mm (C and H).

Figure 6
Figure 6. Examples of the ichnogenera identified from the different bedding surfaces in the field.

P, Planolites, Ta, Taenidium, Te, Teichichnus, Rh, Rhizocorallium, Ca, Catenichnus, Sk, Skolithos, Ar, Arenicolites, Di, Diplocraterion, Th, Thalassinoides, Ch, Chondrites. Scale bar = 1 cm. Camera lens cap diameter = 5 cm.

Figure 7
Figure 7. Cluster analysis of the trace fossils from bedding planes from the Hiraiso Formation, Miyagi Prefecture, Japan.

Five different ichnological communities were qualitatively recognised based on the cluster analysis separated by dashed lines. The lithofacies each sample comes from is labelled. Facies Hd was subdivided into Hd (lower) and Hd (upper) based on log heights.

Figure 8
Figure 8. Jitter plot showing burrow diameters for each ichnospecies measured in the Hiraiso Formation.

The squares indicate the median size for each ichnospecies.

Figure 9
Figure 9. Jitter plot of burrow diameters of the most abundant ichnogenera across the different lithofacies.

The median diameters for each ichnospecies are shown as squares for each lithofacies.

Figure 10
Figure 10. Examples of the different ichnofabrics recognised in this study.

(A) Unbioturbated, laminated ichnofabric. (B) Unbioturbated, massive ichnofabric. (C) Vertical indeterminate traces (cf. Lingulichnus) ichnofabric. (D) Teichichnus ichnofabric. (E) Rhizocorallium-Chondrites ichnofabric. (F) Rhizocorallium ichnofabric. (G) Chondrites-Teichichnus ichnofabric. (H) Chondrites-Rhizocorallium ichnofabric. (I) Chondrites ichnofabric. Scale bar = 1 cm.

Figure 11
Figure 11. Ichnological data collected from the ichnofabric analysis between the different lithofacies.

(A) Ichnodiversity. (B) Ichnofabric Index (bioturbation). (C) Ichnofabric. (D) Burrow Depths. Note: burrow depths frequently extended beyond the sample size. These depths also do not account for sediment compaction.

Figure 12
Figure 12. Histograms of the geometric median shell size of bivalve specimens from the Hiraiso Formation.

(A) Bedding plane at 6.8 m in section 1a. (B) Bedding plane at 18.6 m in section 2. Histogram bin width is 1 mm.

Figure 13
Figure 13. Cluster analysis of the bioclasts from polished slab samples from the Hiraiso Formation, Miyagi Prefecture, Japan.

The cluster analysis together with the SIMPROF test identified 9 groups (labelled a–i) of samples that are statistically distinct. The different groups have been interpreted as different biofacies.

Figure 14
Figure 14. Cross plot of redox indices V/Cr and Th/U.

The ranges for V/Cr and Th/U are from Jones & Manning (1994) and Twitchett & Wignall (1996), respectively.

Figure A1
Figure A1. Measured sections of the Hiraiso Formation along the Hiraiso Coastline, Miyagi Prefecture, Japan.

Ichnofabric Index (II) after Droser & Bottjer (1986). Grain size scale: C, clay; S, siltstone; VF, very fine sand; F, fine sand. Colour in the lithology column refers to the rock colour observed. Seds, sedimentary structures. The GPS coordinates for the base of each log are also shown.

Figure A2
Figure A2. Measured sections of the Hiraiso Formation along the Hiraiso Coastline, Miyagi Prefecture, Japan.

Ichnofabric Index (II) after Droser & Bottjer (1986). Grain size scale: C, clay; S, siltstone; VF, very fine sand; F, fine sand. Colour in the lithology column refers to the rock colour observed. Seds, sedimentary structures. For the logged sections 2–5 the composite log height is given. The GPS coordinates for the base of each log are also shown.

Figure A3
Figure A3. Measured sections of the Hiraiso Formation along the Hiraiso Coastline and Kamiwarizaki, Miyagi Prefecture, Japan.

Ichnofabric Index (II) after Droser & Bottjer (1986). Grain size scale: C, clay; S, siltstone; VF, very fine sand; F, fine sand. Colour in the lithology columnrefers to the rock colour observed. Seds, sedimentary structures. For the logged sections 2–5 the composite log height is given. The GPS coordinates for the base of each log are also shown.

Figure A4
Figure A4. Measured sections of the Hiraiso Formation along the Hiraiso Coastline and Kamiwarizaki, Miyagi Prefecture, Japan.

Ichnofabric Index (II) after Droser & Bottjer (1986). Grainsize scale: C, clay; S, siltstone; VF, very fine sand; F, fine sand. Colour in the lithology column refers to the rock colour observed. Seds = sedimentary structures. For the logged sections 2–5 the composite log height is given. The GPS coordinates for the base of each log are also shown.

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This study was funded by a British Council and JSPS Summer Programme grant to William Foster in 2014, Nagoya University Museum funded subsequent fieldwork for William Foster in 2016, Amanda Godbold was funded by the Mitacs-JSPS Summer Program grant, and Richard Twitchett was funded by the NERC grant (NE/I005641/2). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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