Deep-Sea Record of Impact Apparently Unrelated to Mass Extinction in the Late Triassic

Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic

Tetsuji Onouea,1, Honami Satoa, Tomoki Nakamurab, Takaaki Noguchic, Yoshihiro Hidakad, Naoki Shiraid, Mitsuru Ebiharad, Takahito Osawae, Yuichi Hatsukawae, Yosuke Tohe, Mitsuo Koizumie, Hideo Haradae, Michael J. Orchardf, and Munetomo Nedachig

aDepartment of Earth and Environmental Sciences, Kagoshima University, Kagoshima 890-0065, Japan; bDepartment of Earth and Planetary Material Sciences, Tohoku University, Miyagi 980-8578, Japan; cDepartment of Science, Ibaraki University, Mito 310-8512, Japan; dDepartment of Chemistry, Tokyo Metropolitan University, Tokyo 192-0397, Japan; eQuantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1195, Japan; fGeological Survey of Canada, Vancouver, BC, Canada V6B 5J3; and gDivision of Instrumental Analysis, Frontier Science Research Center, Kagoshima University, Kagoshima 890-0065, Japan

Edited by Dennis V. Kent, Rutgers University/Lamont-Doherty Earth Observatory, Palisades, NY, and approved October 3, 2012 (received for review June 4, 2012) The 34-million-year (My) interval of the Late Triassic is marked by microspherules, nickel (Ni)-rich magnetite, and a platinum group the formation of several large impact structures on Earth. Late element (PGE) anomaly, all of which suggest an extraterrestrial Triassic impact events have been considered a factor in biotic impact event (2, 13). A previous paleomagnetic study of the extinction events in the Late Triassic (e.g., end-Triassic extinction Sakahogi locality indicated that the bedded chert accumulated at event), but this scenario remains controversial because of a lack of low latitudes (3.9° ± 3.3° N or S) within a deep Paleo-Pacific stratigraphic records of ejecta deposits. Here, we report evidence (Panthalassa) basin (14, 15). We examine the high-resolution for an impact event (platinum group elements anomaly with biostratigraphy of microfossils across the impact event horizon nickel-rich magnetite and microspherules) from the middle Norian and discuss the relationship between the impact and extinction (Upper Triassic) deep-sea sediment in Japan. This includes anom- events in the Late Triassic deep-sea sediments. alously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridium- Impact Ejecta Layer enriched ejecta layers of the Late Triassic may be found on a global Evidence of a Late Triassic impact event was discovered as scale. The ejecta deposit is constrained by microfossils that suggest a PGE anomaly from a claystone layer in an Upper Triassic correlation with the 215.5-Mya, 100-km-wide Manicouagan impact bedded chert succession of the Sakahogi locality, Inuyama area, crater in Canada. Our analysis of radiolarians shows no evidence of Central Japan (SI Appendix, Fig. S1). The claystone layer, which a mass extinction event across the impact event horizon, and no we call the “Sakahogi ejecta layer,” contains microspherules, Ni- contemporaneous faunal turnover is seen in other marine plank- rich magnetite, and a high abundance of PGEs, ranges in thickness tons. However, such an event has been reported among marine from 4 to 5 cm, and extends laterally for at least 90 m at Sakahogi. faunas and terrestrial tetrapods and floras in North America. We, We distinguish lower and upper sedimentary sublayers within therefore, suggest that the Manicouagan impact triggered the the claystone (SI Appendix, Fig. S3). The lower sublayer (∼8-mm- extinction of terrestrial and marine organisms near the impact site thick) contains 10–15% (by rock volume) microspherules in but not within the pelagic marine realm. a matrix of clay minerals (mainly illite), cryptocrystalline quartz, and hematite. Our preliminary investigation reveals that this chert | Panthalassa | Mino Terrane | pelagic sediments sublayer contains many small euhedral to subhedral crystals of oxidized Ni-rich magnetite (16). Geochemical mapping using he discoveries of an iridium-enriched clay layer at the Cre- a scanning X-ray analytical microscope also reveals a high con- Ttaceous/Paleogene (K/Pg) boundary and the 65-million-year centration of nickel (SI Appendix, Fig. S4). The upper sublayer of (My)-old Chicxulub impact structure in Mexico have revealed the claystone is composed of undisturbed sediments of clay (illite) the global environmental damage such impacts can cause and and cryptocrystalline quartz containing radiolarians, siliceous their association with mass extinction events (1, 2). Analysis of sponge spicules, and conodonts. the K/Pg event has led to the assumption that other large ex- The geochemical signals of the extraterrestrial impact are traterrestrial impacts also contributed to mass extinction events recorded in the lower sublayer of the claystone. Anomalies in over the past 250 million years (3, 4). The Late Triassic, 236–201 iridium and other PGEs in the lower sublayer were identified million years ago (Mya), is marked by several large impact cra- based on analyses of nine claystone and two chert samples by ters (5): the 100-km Manicouagan and the 40-km Saint Martin instrumental neutron activation analysis (INAA) and inductively structures in Canada; the 25-km Rochechouart structure in coupled plasma–mass spectrometry (ICP–MS). The anomalously France; the 10-km Paasselkä structure in Finland; and the 9-km high abundances of iridium, which is limited to the lower sub- Red Wing structure in the United States (Fig. 1). Previous layer (Fig. 2), is defined by concentrations of up to 41.5 parts per researchers suggested that these Late Triassic impact craters billion (ppb), much greater than the background level of ∼0.2 could have resulted in the end-Triassic extinction event (6, 7) or earlier extinctions at the Norian/Rhaetian or Carnian/Norian boundaries (8, 9). To understand the causal link between the Author contributions: T. Onoue, H.S., T. Nakamura, T. Noguchi, M.E., T. Osawa, and Late Triassic extinctions and the impact events, it is necessary to Y. Hatsukawa designed research; T. Onoue, H.S., T. Nakamura, T. Noguchi, Y. Hidaka, N.S., M.E., T. Osawa, Y. Hatsukawa, Y.T., M.K., H.H., M.J.O., and M.N. performed research; precisely date the age of crater formation and locate the geologic T. Nakamura contributed new reagents/analytic tools; T. Onoue, H.S., T. Nakamura, record of the impact ejecta layer within a well age-constrained T. Noguchi, Y. Hidaka, N.S., M.E., T. Osawa, Y. Hatsukawa, Y.T., M.K., H.H., M.J.O., stratigraphic sequence. Although the ages of the Late Triassic and M.N. analyzed data; and T. Onoue and H.S. wrote the paper. impact events have been constrained by radioisotopic dating (SI The authors declare no conflict of interest. Appendix, Table S1), deposits containing their ejecta are known This article is a PNAS Direct Submission. only from a nonmarine sequence in southwestern Britain (10–12). 1To whom correspondence should be addressed. E-mail: [email protected]. Here, we report that Upper Triassic deep-sea sediment (bedded This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. chert) at Sakahogi in the Inuyama area, Central Japan, contains 1073/pnas.1209486109/-/DCSupplemental.

19134–19139 | PNAS | November 20, 2012 | vol. 109 | no. 47 www.pnas.org/cgi/doi/10.1073/pnas.1209486109 Downloaded by guest on September 24, 2021 AB Age Stage/ Ejecta P(10km) (Myr) FZ Impact crater 228.7 ± 3 Myr Substage deposit Hettangian 0B SW Britain 200 0A

8D 30 Rhaetian

8C 8B 210 Upper 8A 7 6B Middle Japan 6A 220 Lower Impact site

Ejecta deposit 5B Land 230 Carnian 5A Shelf Deep water 4B

Fig. 1. Late Triassic paleogeography and age of impact craters and ejecta deposits. (A) Approximate locations of five impact craters and ejecta sites plotted on a Late Triassic paleogeographic map modified from the original figure in ref. 5. The hatched area indicates the inferred depositional area of the bedded chert from the Mino Terrane in the low-latitudinal zone of the Panthalassa Ocean (14). See B for abbreviations for the craters and ejecta sites. (B) Radio- isotopic and stratigraphic ages of the five impact craters based on the timescale proposed by ref. 27. Triassic radiolarian fossil zones (FZ) are from ref. 45. Note that the age of the ejecta deposit is constrained by conodonts and radiolarians (base of the 6B fossil zone) and is, therefore, given without an error range. The blue shading in the fossil zone column indicates the total age range of the section shown in Fig. 5.

ppb (SI Appendix, Table S2). The magnitude of this concentra- carbonaceous chondrite) at four stratigraphic levels in the study tion is comparable to that measured at K/Pg sites (17), suggesting section. In the lower sublayer, the concentrations of all of these that the iridium-enriched ejecta layers of the Late Triassic may elements are well above the background values in the underlying be found in sites worldwide (18). Anomalies in other PGEs are and overlying levels, and are enriched by up to three orders of also seen in the lower sublayer of the claystone (Fig. 2). Fig. 3 magnitude compared with average terrestrial crustal abundances shows the average elemental abundances of PGEs (relative to CI (19). The PGE anomaly was conﬁrmed by an additional analysis of

Distribution of PGEs (ppb) Sample Species ranges of radiolarian fossils RZ CZ Age No. 0 10 20 30 40 (NH-) 53.0 ata 52.4 dent bi 6B a EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES dolell gon i p

52.3 E 52.2 Ejecta layer c 52.1 si

51.2 Trias 51.0 everi tes s w nana

cm ta .

20 Middle Norian stu Upper cf byx pe nova ula r a i a r bu Chert p ps ro se cam s a u c E. p

Os (ICP-MS) 6A / ono ul latus Corum regium a o icho

(INAA) t odoce cf. anape Ir P Jap ria

10 er S Capnodoce sarisa n Capnodoce ruesti T Syringocapsa batodes Xiphosphaera fistulata Capnodoce extenta chosphaera cf. de Capnodoce crystallina Ir (ICP-MS) ap u post C

Ru (ICP-MS) E. Capn 0 Pt (ICP-MS) 50.2

Fig. 2. PGE abundances and biostratigraphy of radiolarians from the middle Norian section (Sakahogi) in Japan. Solid squares beside the lithologic section indicate the occurrence of conodonts and radiolarians in cherts and claystones. The radiolarian ranges are used to constrain the age of the ejecta deposit. Radiolarian (RZ) and conodont (CZ) zones are from refs. 45 and 22, respectively. See SI Appendix, Tables S2 and S3 for PGE data.

Onoue et al. PNAS | November 20, 2012 | vol. 109 | no. 47 | 19135 Downloaded by guest on September 24, 2021 1 relevance to the extinction events at the end-Triassic and Nor- ian/Rhaetian boundaries (7, 23, 24). K/Pg boundary Our biostratigraphic analysis suggests that there was no mass s 10-1 extinction of radiolarians across the impact event horizon. Fig. 5 ce n

a shows biostratigraphic ranges of 147 species in 62 genera of d Norian ejecta deposit radiolarians from 331 horizones; the collection intensity was 10-2 uniform without any sampling gaps (SI Appendix, Fig. S2). A

Eabun signiﬁcant faunal turnover is observed ∼1 m above the impact ejecta horizon in the upper middle Norian. Given that the av- Norian deep-sea deposit 10-3 erage sedimentation rate of the middle Norian chert succession, zed PG i

al estimated from the measured thickness and the time interval of m its deposition (SI Appendix, Fig. S2), is 1.0 mm per thousand years, NH-52.2 (ejecta deposit) nor

- -4 ∼ I 10 NH-52.3 this turnover occurred 1 My after the impact event. Only one C NH-52.1 species became extinct at the ejecta horizon and the extinction Upper continental crust NH-52.4 rate of radiolarians (extinct species divided by total species at the 10-5 same level) is estimated to be about 5% at the horizon. High- Os Ir Ru Pt Rh Pd resolution radiolarian biostratigraphy across the impact ejecta Fig. 3. CI chondrite–normalized PGE patterns of middle Norian samples at layer also indicates that, of the 13 radiolarian species identiﬁed Sakahogi. Stratigraphic levels of samples are shown in Fig. 2. The concen- below this horizon, only one species, Trialatus robustus, disappears trations of CI chondrites are from ref. 20. PGE patterns of the upper conti- at the horizon (Fig. 2). The extinction of the genus Trialatus nental crust (19) and K/Pg boundary sediments (17) are shown for comparison. appears to have occurred synchronously across several regions in See SI Appendix, Table S3 for data. the middle Norian (SI Appendix, SI Text), meaning its last occurrence may be a good time indicator for the ejecta deposit. the second sample (NH-52R2) from the lower sublayer in the Discussion Sakahogi locality (SI Appendix,TableS3). Because PGEs are highly depleted in the Earth’s crust relative to solar abundances (19, 20), A biostratigraphic analysis of radiolarians and conodonts reveals the PGE anomaly reported here may have resulted from the ac- that the ejecta deposit is embedded in the upper middle Norian. cretion of a signiﬁcant amount of siderophile elements from a large Recent magnetostratigraphic studies linked to conodont bio- – projectile. However, additional sampling for PGEs is needed to stratigraphy (25 27) suggest that the stratigraphic position of the further test the origin of the projectile and to estimate its size. Sakahogi ejecta layer can be correlated with paleomagnetic The discovery of microspherules and Ni-rich magnetite asso- chron PM9 to PM10 at the Pizzo Mondello section in Sicily (26) ciated with the PGEs anomalies in the lower sublayer also sug- and with SB-9 at the Silická Brezová section in Slovakia (25). gests an impact event (2, 13, 21), although they are affected by Although no radiometric age data are available, the magneto- secondary processes, including low-grade regional metamor- stratigraphic ages from these Norian sections have been assigned – phism of the study area [conditions below those of the prehnite– an age range of 216 212 Mya (SI Appendix, Fig. S7) based on the pumpellyite facies (15)], which altered their chemical composition. correlation with the astronomically tuned geomagnetic polarity Microspherules were only found in the lower sublayer and have time scale (Newark-APTS of refs. 28–30). These ages would never been reported in the Triassic bedded chert succession of the seem to consistent with the dating of an impact ejecta layer in Inuyama area. The microspherules in the lower sublayer are dark southwestern Britain that has yielded a diagenetic age (from green to dark gray and range in size from 200 to 300 μm(Fig.4A). Synchrotron X-ray diffraction analysis indicates that the microspherules are pseudomorphs of clinochlore-rich chlorite (SI Ap- pendix,Fig.S5). These microspherules preserve a pseudomorphic internal texture that comprises dendrites and spherulites radiating from the surface into the microspherules (Fig. 4B). Some microspherules contain a high proportion of small, euhedral to subhedral crystals of oxidized Ni-rich magnetite (Fig. 4C). The Ni-rich magnetite grains are 5–20 μm in size and commonly have skeletal or octahedral morphologies (Fig. 4D). Electron microprobe analysis shows large variations in the concentrations of Al, Fe, Cr, Ni, and Zn among the magnetite grains, along with minor amounts of Mg, Ti, and Mn (SI Appendix,TableS4). These magnetite grains are distinguished from typical igneous magnetite by high contents + of Ni and Fe3 and relatively low concentrations of Ti. Age and Biostratigraphy The depositional age of the claystone is constrained by radiolarians and conodonts (SI Appendix, Table S6 and Fig. S6). A detailed discussion of their biostratigraphy in the Sakahogi locality is given in SI Appendix, SI Text. The claystone layer lies between pelagic Fig. 4. Microspherules and Ni-rich magnetite from a Norian ejecta deposit chert layers of the radiolarian zones TR6A and TR6B and is cor- in Japan. (A) Photomicrographs of microspherules from the ejecta deposit. μ related with the upper middle Norian. A biostratigraphic analysis Plane-polarized light. (Scale bar: 500 m.) (B) Microspherule showing the of conodonts also reveals that the ejecta deposit is embedded in the inward-radiating growth form of clinochlore pseudomorphs. (Scale bar: 100 μm.) (C) Scanning electron micrographs (backscattered mode) of a polished upper middle Norian (base of the Epigondolella bidentata zone of section of microspherule from the ejecta deposit. Ni-rich magnetite (bright ref. 22). This age indicates that the impact event occurred well grains) commonly occur as skeletal grains. (Scale bar: 100 μm.) (D) Close-up before the Rhaetian interval (Epigondolella mosheri and Mis- view of the microspherule in C illustrating skeletal crystal morphologies of ikella posthernsteini conodont zones), and, therefore, it has no Ni-rich magnetite in the microspherule. (Scale bar: 20 μm.)

19136 | www.pnas.org/cgi/doi/10.1073/pnas.1209486109 Onoue et al. Downloaded by guest on September 24, 2021 Age RZ Species ranges of radiolarians in Inuyama area )

0B 40 Hettangian Hett.

Jura. (m) 0A

201 (Mya Rhaetian 8D ian t 35 Rhae 8C Rhaetian 30

209.8 Norian 8B 8A

Upper Norian 20 7 .8 11

2 Ejecta horizon 6B Upper Triassi c Middle Nor. 16.4

6A 10

Norian Lower Nor. 6.6 2

22 Carnian 5B Carnian 0 01020 30 40 50 60 70 80 90 100 110 120 130 140

Fig. 5. Stratigraphic ranges of Late Triassic radiolarian species in Inuyama area projected onto the composite section. Species numbers are shown on the x axes. For an explanation of radiolarian taxon ranges, see SI Appendix, Table S5. Radiolarian zone (RZ) is from ref. 45.

authigenic K-feldspar) of 214 ± 2.5 My (11), although the the Manicouagan impact (8) could have produced the PGE- recalculated age of 216.7 My for the British ejecta layer using the enriched ejecta layer in Japan, the pelagic Paleo-Pacific paleo- method of Renne and coworkers (31, 32) is slightly outside position of the ejecta deposit suggests that impact ejecta layers the range of 216–212 Mya. However, the 40Ar/39Ar age of the will be found at other middle Norian sites worldwide. Sites at British ejecta layer has yet to be confirmed by a second analysis, which the ejecta horizon might be found include pelagic lime- and the preferred age of ∼214 My is based on a plateau age that stone sequences of the Pizzo Mondello in Sicily (26) and Black includes only slightly more than 50% of the gas released (11). Bear Ridge in British Columbia (22) and the nonmarine sequence Accurate age dating of the ejecta layer, coupled with an im- of the Newark Supergroup at the eastern margin of North proved understanding of the correlation of the radioisotopic ages America (28–30). The application of an event-stratigraphic ap- with the magnetobiostratigraphy of the Norian stage (25–27), proach (13) at such sections is required to confirm the distribution would be required to precisely compare the ages between the of the Manicouagan ejecta. It is also important to determine ejecta layers of Japan and southwest Britain. The mineral as- whether the absolute age of these middle Norian sections corre- EARTH, ATMOSPHERIC,

semblage of the spherules from the Sakahogi locality differ from lates with the 215.5-Mya Manicouagan impact. AND PLANETARY SCIENCES those of hollow illitic and glauconitic spherules reported from Because the middle Norian is now known to contain evidence southwestern Britain (10, 11). However, in many cases, impact of an impact event, an analysis of the extinction patterns of spherules in ejecta deposits are devitrified and altered to clays marine and terrestrial biotas at a more regional scale might be resulting in loss of original chemical composition (33). There- the next step in investigating the nature of extinction and bi- fore, the difference in spherule composition between Japan and ological turnover events at ejecta horizons. Marine microfossils southwest Britain spherules does not rule out the possibility of have been thought to be one of the broad taxonomic groups most the same impact origin for these spherules. effected by the Chicxulub impact event at the K/Pg boundary (2, Based on recent radioisotopic ages for Late Triassic impact 35). Our analysis of radiolarians does not show a mass extinction structures, there are two candidate impacts that may have pro- event across the impact ejecta layer (Fig. 5). Along with radio- duced the ejecta found in the Sakahogi deposit: the 100-km larians, dinoflagellates and calcareous nannoplanktons are the Manicouagan structure in northeastern Canada [dated at 215.5 dominant marine plankton in the Late Triassic ocean (36, 37). Mya (34)] and the 9-km Red Wing structure in North Dakota, On a generic level, a survey of Upper Triassic dinoflagellate cyst United States (dated at 200 ± 25 Mya; SI Appendix, Table S1). and calcareous nannoplankton assemblages shows neither a mass We suggest that the Manicouagan impact structure is the source extinction nor a marked decline across the impact event horizon of the Sakahogi ejecta deposit, because (i) the age of the Man- (SI Appendix, Fig. S8). The record of their floral change in the icouagan crater formation is consistent with the age of the ejecta Late Triassic has been established at the species level in several deposit and (ii) the Manicouagan impact was large enough to regions (36, 37), and the record shows that there was no ex- produce a global distribution of ballistic ejecta within ∼30° tinction event around the impact event horizon. Therefore, we paleolatitude of the crater.* If the projectile and target rocks of suggest that many groups of marine planktons survived the Manicouagan impact event. Other marine fossil records to date support the absence of globally synchronous mass extinctions in *Wrobel KE, Schultz PH, Thirty-Fourth Annual Lunar and Planetary Science Conference, the middle Norian (38, 39). However, late middle Norian marine March 17–21, 2003, Houston, TX, abstr 1190. extinctions have been reported at the genus and/or species level

Onoue et al. PNAS | November 20, 2012 | vol. 109 | no. 47 | 19137 Downloaded by guest on September 24, 2021 in ammonoids, bivalves, and conodonts from western North Materials and Methods America (40). It is possible that the Manicouagan impact may For whole-rock analyses of PGEs, eleven samples were powdered in an agate have triggered the extinctions of these marine faunas, at least in mortar. Veins and strongly recrystallized zones were avoided to minimize the western North America, but this will require further biostrati- effects of diagenetic or metamorphic overprinting. PGE abundances were graphic study at middle Norian sites globally. determined using inductively coupled plasma–mass spectrometry combined Terrestrial records of Late Triassic vertebrates and plants have with a nickel sulfide fire assay (SI Appendix, SI Materials and Methods). been well studied in the Chinle Formation of the Petrified Forest Iridium was measured using a neutron activation technique. Powder samples were enclosed in small pure quartz vials and irradiated for 48 h in the JRR-3 National Park in southwestern United States. Recent magneto- reactor at the Japan Atomic Energy Agency (Ibaraki, Japan). Iridium was stratigraphic and radioisotopic studies of the Chinle Formation quantified with a gamma–gamma spectrometer detecting the 468- to 316- suggest that a faunal turnover of terrestrial tetrapods, including keV γ-ray coincidence resulting from the decay of 192Ir. the disappearance of herbivorous dicynodonts, occurred in the We handpicked microspherules from the crushed rock powders (<500-μm middle Norian (41–43). This turnover may coincide with a floral grain size) of the ejecta deposit under a binocular microscope. To investigate turnover in North America deduced from palynology studies the mineral composition of individual microspherules, synchrotron X-ray (41, 42, 44). The depositional site of the Chinle Formation is diffraction analysis was performed using a Gandolfi camera with synchro- relatively close to the Manicouagan crater (within ∼3,500 km), tron X rays of 2.165-Å wavelength at the High Energy Accelerator Research raising the possibility that the effects of the impact [e.g., acid rain Organization (Tsukuba, Japan). After this analysis, microspherules were fi mounted in epoxy, sectioned, and polished to reveal their internal texture and wild re on a regional scale (35)] triggered a catastrophic using a field-emission scanning electron microscope. Chemical compositions disruption of the terrestrial ecosystems in North America (42). of Ni-rich magnetite were determined by electron microprobe with an However, it is uncertain whether the igneous and metamorphic electron acceleration voltage of 15 keV and a beam current of 10 nA. Details target rocks of Manicouagan impact (8) could have produced of our sample preparation and analytical methods can be found in SI Appendix, catastrophic environmental effects (35), and a lack of age data SI Materials and Methods. prevents confirmation of the concurrence of the Manicouagan impact and floral and faunal turnovers in North America (41, ACKNOWLEDGMENTS. We thank C. Yasuda for assistance in the field; the 43). Detailed studies of terrestrial sections in the middle Norian High Energy Accelerator Research Organization (KEK) for synchrotron X-ray diffraction analysis; and the Japan Atomic Energy Agency (JAEA) for are needed to determine whether the biotic turnover of terres- instrumental neutron activation analysis. This work was supported by the trial biotas at this time was caused by the Manicouagan impact. Japan Society for the Promotion of Science.

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