Sato et al. Progress in Earth and Planetary Science (2020) 7:61 Progress in Earth and https://doi.org/10.1186/s40645-020-00371-x Planetary Science RESEARCH ARTICLE Open Access Biotic and environmental changes in the Panthalassa Ocean across the Norian (Late Triassic) impact event Honami Sato1,2* , Yutaro Takaya1,2,3,4, Kazutaka Yasukawa1,4,5, Koichiro Fujinaga1,4, Tetsuji Onoue6 and Yasuhiro Kato1,2,4,5 Abstract Stratigraphic records of impact ejecta preserved in a pelagic deep-sea setting occur within Upper Triassic successions of the subduction-generated accretionary complexes of central Japan. A significant biotic turnover in radiolarians occurred during the ~ 300 kyr time interval after the impact event, which is characterized by a remarkable reduction in the burial flux of radiolarian silica. However, the nature of the environmental conditions at this time remains unclear. To investigate the environmental changes that triggered a decline in radiolarian burial flux after the impact event, geochemical proxies (major, trace, and rare earth elements) were applied to the middle–upper Norian (Upper Triassic) bedded chert succession of the Mino Belt, central Japan. A progressive environmental deterioration is evident from (1) a post-impact shutdown of burial flux of primary and silica- and apatite-secreting organisms; and (2) a subsequent abrupt increase in chemical weathering associated with a sustained reduction in the burial flux of radiolarian silica. No significant redox changes were observed across the impact event. The continental weathering proxies suggest a transient increase in weathering intensity occurred during the decline of radiolarian burial flux, likely in response to a short-term warm and humid period. Our results delineate a remarkable record of progressive environmental changes in the Panthalassa Ocean after this large impact event. Keywords: Late Triassic, Norian, Bedded chert, Impact event, Environmental changes, Radiolaria 1 Introduction studies of the Triassic bedded chert succession in the An Upper Triassic (Norian) impact event has been Sakahogi section suggest that these sediments accumu- inferred from anomalous concentrations of platinum- lated in a pelagic, open-ocean setting within a low- to group elements (PGEs) and a negative osmium (Os) mid-latitudinal zone of the Panthalassa Ocean (Uno isotope excursion, in addition to occurrences of micro- et al. 2015) (Fig. 2). The late middle Norian age of the spherules and Ni-rich magnetite, in a claystone layer in claystone layer (Onoue et al. 2016a; Yamashita et al. an Upper Triassic bedded chert succession in the Saka- 2018) suggests that the PGE anomalies originate from an hogi section, central Japan (Onoue et al. 2012; Sato et al. extraterrestrial source, related to an impact event that 2013; Sato et al. 2016) (Fig. 1). Previous paleomagnetic formed the 90 km-diameter Manicouagan crater in Canada at 215.5 Ma (Clutson et al. 2018) (Fig. 2). Studies * Correspondence: [email protected] of PGEs and Os isotopes have revealed that the anomal- 1Ocean Resources Research Center for Next Generation, Chiba Institute of ously high PGE abundances in the lower sublayer Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan 2 claystone resulted from a large chondritic impactor with Submarine Resources Research Center, Research Institute for Marine – Resources Utilization, Japan Agency for Marine-Earth Science and a diameter of 3.3 7.8 km (Sato et al. 2013; Sato et al. Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan 2016). Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Sato et al. Progress in Earth and Planetary Science (2020) 7:61 Page 2 of 24 Fig. 1 Map showing the study area. a, b Geographic maps of the study area in the Inuyama area, Mino Belt, central Japan. c The Sakahogi section along the middle reaches of Kiso River Onoue et al. (2016a) showed that extinctions of middle paleontological and geochemical data also revealed that Norian radiolarian species occurred in a stepwise fashion two paleoenvironmental events occurred during the ini- in the ~ 1 Myr interval above the ejecta horizon, which tial phase of the radiolarian turnover interval. The first was associated with the radiation of late Norian event (E1) involved post-impact shutdown of primary radiolarians (Fig. 3a). Furthermore, high-resolution productivity reflected by a remarkable decline in the 60 Manicouagan (90 km) 215.5 Ma 30 This study Lagonegro Basin (central Japan) Black Bear Ridge (British Columbia) (southern Italy) Petrified Forest National Park Tethys (Arizona, USA) 0 Norian paleolatitude of deposition range: 0.3 14.4 N (Ando et al., 2001, Uno et al., 2015) Panthalassa 30 60 Fig. 2 The paleogeography in the Late Triassic. Approximate location of the Manicouagan crater and the inferred depositional area of the bedded chert in the Mino Belt in low-latitude zones of the Panthalassa Ocean (Uno et al. 2015). The red circles represent the approximate paleo-locations of the Late Triassic sites. The orange arrows are the simulated surface winds from Kutzbach and Gallimore (1989) Sato et al. Progress in Earth and Planetary Science (2020) 7:61 Page 3 of 24 Sampled bed (NHR-) 101 99 MAR radiolarian 98 -2 -1 Radiolarian species range PGE concentrations (ppb) 97 silica (g cm kyr ) 96 94 95 -28 -27 -26 -25 -24 -23 0.020.06 0.10 0.14 Sampled bed 0204060 92 NHR42 91 90 89 88 87 86 85 84 82 80 81 NH52-R7 76 75 74 72 71 NH52-R6 70 69 67 66 65 64 NH52-R5 59 57 NH52-R4 56 55 54 53 NH52-R3 52 50 51 49 48 47 46 E2 NH52-R2 44 43 42 E1 Os Ejecta horizon 40 Ir 39 38 37 Ru 36 Pt 34 33 Rh 32 31 NHR40 Pd 30 0 0.02 0.06 0.10 0204060 Radiolarian chert (red/gray) MAR sponge Spicular chert Claystone silica (g cm-2 kyr-1) Fig. 3 Biostratigraphy and chemostratigraphy of the bedded cherts in the Sakahogi section (Onoue et al. 2016a;Satoetal.2016). a Stratigraphic profiles of organic carbon isotopes, mass accumulation rates of biogenic silica, and radiolarian biostratigraphy. The mass accumulation rate of biogenic silica was estimated by assuming a constant sedimentation rate of 1.1–1.6mmkyr−1 in the middle–upper Norian chert succession (Onoue et al. 2016a),whichisanalternativetoa previous model assuming different sedimentation rates between chert and claystone (Hori et al. 1993). b Stratigraphic profiles of PGE concentrations in the claystones of the studied section. NH52-R2 indicates the lower sublayer of claystone (ejecta layer) with microspherules and Ni-rich magnetite amount of biogenic silica. The second event (E2) was geochemistry of the cherts has been extensively studied characterized by a large and sustained reduction in the in the context of the depositional environment and glo- burial flux of radiolarian silica and the proliferation of bal environmental change (e.g., Murray et al. 1992; Hori siliceous sponges. This E2 event lasted until ~ 300 kyr et al. 1993; Murray 1994; Kato et al. 2002; Takiguchi after the impact. Although the relatively long period of et al. 2006; Hori et al. 2007). The stratigraphic variations the E2 interval (~ 300 kyr after the impact) largely ex- of major and trace elements in Triassic bedded cherts cludes the possibility that the decline was triggered by from Japanese accretionary complexes are widely used as instantaneous environmental stresses (e.g., extended proxies to trace changes in (1) hinterland components, darkness, global cooling, or acid rain) that would have (2) degree of chemical weathering in hinterland regions, been caused by a bolide impact, the primary cause of (3) paleoproductivity, and (4) oceanic redox conditions. this decline remains uncertain. In this study, we assessed temporal variations in the In this study, we examined variations in the composi- compositions of major, trace, and rare earth elements tions of major, trace, and rare earth elements (REE) in (REE) in the Triassic bedded cherts to investigate the bi- bedded cherts in the Sakahogi section to identify the en- otic responses to environmental changes that occurred vironmental changes responsible for the decline in radio- after the impact event in the Panthalassa Ocean. larian burial flux after the middle Norian impact event. The bedded cherts were composed originally of biogenic 2 Geological setting and stratigraphy silica, apatite, barite, clastic lithogenic materials, and hy- The Mino Belt consists of Jurassic accretionary com- drogenous materials such as Fe–Mn oxides. The plexes in central Japan. The accretionary complexes in Sato et al. Progress in Earth and Planetary Science (2020) 7:61 Page 4 of 24 the Mino Belt consist of two coherent units (i.e., the occurs in upper middle Norian bedded chert. Given that Samondake and Kamiaso units) and five melange units the average sedimentation rate of the middle Norian (i.e., the Sakamoto-toge, Funafuseyama, Kuze, Nabi, and chert, estimated from the measured thickness of the Kanayama units).