Journal of Earth Science  2018, Vol. 29 Issue (4): 837-853   PDF    
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Nitrogen and Carbon Isotope Data of Olenekian to Anisian Deposits from Kamenushka/South Primorye, Far-Eastern Russia and Their Palaeoenvironmental Significance
Yuri D Zakharov1, Micha Horacek2,3, Alexander M Popov1, Liana G Bondarenko1    
1. Far Eastern Geological Institute of Russian Academy of Sciences(Far Eastern Branch), Stoletiya Prospect 159, Vladivostok 690022, Russia;
2. BLT Wieselburg, Research Center HBLFA Francisco-Josephinum, Wieselburg 3250, Austria;
3. Institute of Lithospheric Research, Vienna University, Vienna 1090, Austria
ABSTRACT: The Kamenushka Formation, exposed in the northern part of South Primorye (Kamenushka-1 and Kamenushka-2 sections), is one of the few localities in the world with richly fossiliferous Lower-Upper Olenekian sedimentary successions. Lower to Middle Triassic ammonoid-, brachiopod-and conodont-bearing silty-clayey deposits of the Kamenushka-1 and Kamenushka-2 sections have been isotope-geochemically investigated in detail. As a result, these sections, together with the previously investigated Abrek Section, exposed in the southern part of South Primorye, provide almost complete 15Norg- and 13Corg- records for the Lower Triassic of this region. Nine N-isotope intervals and the five negative C-isotope excursions, reflecting, apparently, unstable climatic and hydrological conditions, have been distinguished in the Lower Triassic of South Primorye. On the basis of the new C-isotope data the Mesohedenstroemia bosphorensis Zone (upper part), Shimanskyites shimanskyi and Neocolumbites insignis zones of South Primorye are correlated now with the Lower Smithian part of the Yinkeng Formation, the Upper Smithian part of the Helongshan Formation and the Middle Spathian part of the Nanlinghu Formation in South China, respectively, as has been observed in the Abrek, Kamenushka-2, West Pingdingshan and Majiashan sections.
KEY WORDS: Triassic    N-and C-isotopes    palaeoclimatology    bio-and chemostratigraphy    Pri-morye    Russia    

0 INTRODUCTION

The results on 13Corg and 13Ccarb investigations of the Lower Triassic for many regions are well known (e.g., Wignall et al., 2015, 1998; Algeo et al., 2014, 2008; Song et al., 2014, 2013; Zakharov et al., 2014; Dustira et al., 2013; Takahashi et al., 2013, 2010; Hermann et al., 2011, 2010; Horacek et al., 2010a, b, 2009, 2007a, b, c; Luo et al., 2011; Korte and Kozur, 2010; Korte et al., 2010; Kaiho et al., 2009, 2001; Grasby and Beauchamp, 2008; Nakrem et al., 2008; Galfetti et al., 2007; Tong et al., 2004; Baud et al., 1989; Holser and Magaritz, 1987). However, 15Norg records from the Lower Triassic are restricted mainly to some data from Arctic Canada (Smith Creek Section in the Svedrup Basin; Grasby et al., 2016, 2015) and South China (e.g., Algeo et al., 2014; Saitoh et al., 2014; Yin et al., 2012).

Recently, we increased the significance of one of the Lower Triassic sections in South Primorye (Abrek) (Zakharov et al., 2018) by demonstrating of N-isotope data, showing correlation with O-isotope data, obtained from Induan and Early Olenekian conodonts of the Nammal Section in the Salt Range, Pakistan (Romano et al., 2013).

This paper focuses on detailed 15Norg and 13Corg investigation of both the Lower and the Upper Olenekian of the Lower Triassic in Kamenushka River Basin, South Primorye (Fig. 1), to fill a gap in our knowledge on isotopic change of the upper part of the Olenekian in this region in order to assist the correlation of Lower Triassic sections of South Primorye with other isotopic studied sections.

1 GEOLOGICAL SETTING AND STRATIGRAPHY

The main areas of investigations are the Bureya-Jiamusi-Khanka superterrane (including Kamenushka River Basin) and a cratonic fragment (the Sergeevka terrane) obducted into a Jurassic accretionary wedge (Isozaki et al., 2017; Golozubov, 2006; Kemkin, 2006; Khanchuk et al., 1995). These study areas are located between the Sino-Korean Craton to the south and the Sikhote-Alin fold belt to the east (Khanchuk et al., 1995). The major part of the Sikhote-Alin orogenic belt is occupied by Jurassic to Cretaceous accretionary complexes and arc-related volcano-sedimentary rocks of the Samarka, Taukha, Zhuravlevka, Kiselevka and Kema belts (Isozaki et al., 2017; Khanchuk et al., 2016). The common age spectra of detrital zircons of the Palaeozoic sandstones in South Primorye and NE-SW Japan (Isozaki et al., 2017) support the concept of "Greater South China" (Isozaki et al., 2014) that is comprised of conterminous South China to extend to Japan/Primorye, which is consistent with the mutual similarities recognised in Late Paleozoic, including latest Changhsingian, marine fauna (Isozaki et al., 2014; Zakharov et al., 1997; Zakharov, 1994).

The principle biostratigraphic framework for Middle to Lower Triassic zonal boundary intervals in South Primorye were constrained by ammonoid and conodont fossils. Early and Middle Triassic ammonoids in this region were firstly collected by Margaritov V P and Ivanov D I, who made geologic reconnaissance work for the construction of the military outpost Vladivostok and the Trans-Siberian railroad in the 1880s. On the initiative of Karpinsky A P, President of the Russian Academy of Sciences, the Induan, Olenekian and Anisian ammonoids, collected in some of the sections (e.g., Schmidt, Zhitkov, Ayax and Tri Kamnya), were forwarded to C. Diener (Vienna University), who described them in 1895 (Diener, 1895). Later, further monographs (e.g., Shigeta et al., 2009; Zakharov, 1978, 1968; Kiparisova, 1961) were published on this topic. In addition Early Triassic conodonts of South Primorye had been investigated by Buryi (1979) and Bondarenko et al., (2015, 2013).

Based upon comparison of ammonoid assemblages discovered from the main Lower Triassic sections in South Primorye (Fig. 1), eight biozones were defined (e.g., Zakharov et al., 2016; Zakharov and Moussavi Abnavi, 2013). The Induan in South Primorye consists of the following two zones: (1) Tompophiceras ussuriense and (2) Gyronites subdharmus. The Olenekian consists of the following six zones (and beds): (3) Mesohedenstroemia bosphorensis (Ussuriflemingites abrekensis and Euflemingites prynadai beds); (4) Anasibirites nevolini; (5) Shimanskyites shimanskyi; (6) Tirolites-Amphistephanites (Bajarunia dagysi and Tirolites ussuriensis beds); (7) Neocolumbites insignis; (8) Subfengshanites multiformis; (9) Prohungarites beds.

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Figure 1. Location of the examined sections in South Primorye, Russian Far East: 1. Kamenushka; 2. Shmidt; 3. Zhitkov; 4. Ayax; 5. Konechnyj; 6. Tobizin; 7. Atlasov; 8. Tri Kamnya; 9. Golyj; 10. Abrek.

Two nearby sections (Kamenushka-1 and Kamenushka-2) rich in ammonoid and brachiopod fossils represent an excellent record of the Lower–Upper Olenekian deposits which were deposited in a marine deeper water environs. No indications of sedimentary breaks have been found in these two studied sections. Observed-ranges of ammonoids across the Olenekian interval are summarized in Fig. 2.

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Figure 2. Temporal ranges of OlenekianEarliest Anisian ammonoids from the Kamenushka River Basin. Abbreviations:?Gyron. subd., ?Gyronites subdharmus; Mesoh. b., Mesohedenstroemia bosphorensis; Anas. nevol., Anasibirites nevolini; Shim. shiman., Shimanskyites shimanskyi; Tirolites-Amphisteph., Tirolites- Amphistephanites.

Fossils from the two studied sections (Kamenushka-1 and Kamenushka-2; Fig. 3), have been studied in detail (e.g., Popov and Zakharov, 2017; Smyshlyaeva and Zakharov, 2017; Zakharov and Smyshlyaeva, 2016; Zakharov et al., 2016). Their descriptions are not included in this paper. However, the description of the Kamenushka-1 and Kamenushka-2 sections is given for the first time.

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Figure 3. The Kamenushka-1 and Kamenushka-2 sections (plan), South Primorye.
1.1 Description of the Kamenushka-1 Section

The Kamenushka-1 Section is situated 6.5 km SSE of the village of Kondratenovka, along a gas pipeline. Its geographic coordinates are: latitude 43°36'11.8"N; longitude 132°10'16.8"E of Greenwich. The section is exposed of the Lazurnaya, Kamenushka and Karazin formations. Herein (in both the Kamenushka-1 and the Kamenushka-2 sections), the numbers in the brackets correspond to the samples taken for the C- and N-isotope measurements. The Kamenushka-1 Section is composed of the following Lower and Middle Triassic lithological and biostratigraphical combination (in descending order).

1.1.1 Lower Anisian

(1) Leiophyllites pradyumna and Ussuriphyllites amurensis zones

Member 27: More than 28.0 m of dark grey striped and spotted sandy siltstone and mudstone intercalated with grey, fine-grained sandstone (K-431). The unit is characterised by rare ammonoid finds: Hollandites sp. and Leiophyllites sp. These fossils support the Early Anisian Age of Member 27 (likely Leiophyllites pradyumna Zone).

Member 26: 6.0 m of thin intercalation of dark grey siltstone and grey, fine grained sandstone (K-420, K-425 and K-430).

Closed interval corresponding to more than 50 m in thickness.

1.1.2 Olenekian

(1) Neocolumbites insignis Zone

Member 24: About 8 m of dark grey siltstone and mudstone with interbeds of grey fine grained sandstone, lenses of calcareous sandstone-coquina and concretions of calcareous marl (K-410 and K-415, taken from the upper part of Member 24). The following fossils were found in this member: abundant brachiopods, preliminarily identified as rhynchonellids (e.g., Piarorhynchella tazawai Popov), terebratulids (Bittnerithyris margaritovi (Bittner)), spiriferinids (Lepismatina sp.) and athyridids (e.g., Hustedtiella planicosta Dagys); rare bivalve molluscs, abundant gastropods; rare nautilids and abundant ammonoids (Pseudosageceras longilobatum Kiparisova, Cordillerites sp., Ussurijuvenites sp., Inyoceras singularis Zakharov et Smyshlyaeva, Jeanbesseiceras sp. nov., Yvesgalleticeras proximus Zakharov et Smyshlyaeva, Tirolites opiparus Zakharov et Smyshlyaeva, Koninckitoides popovi (Kummel), Nordophiceratoides praecox Zakharov et Smyshlyaeva, Goricanites sp.) and conodonts Neospathodus sp. A, Neospathodus sp. B (Popov and Zakharov, 2017; Zakharov and Smyshlyaeva, 2016).

Members 21–23: 11.0 m of dark grey siltstone with numerous lenses of calcareous sandstone-coquina (K-379, K-384, and K-389 from Member 21; K-390 and K-393 from Member 22; K-394 and K-399 from Member 23). The units contain a diverse fossil assembage: rare brachiopods, identified as rhynchonellids (Piarorhynchella tazawai Popov), terebratulids (Bittnerithyris margaritovi (Bittner)), spiriferinids (Lepismatina sp.); rare bivalve molluscs, abundant gastropods, rare nautilids and abundant ammonoids (e.g., Inyoceras singularis Zakharov et Smyshlyaeva and Yvesgalleticeras proximus Zakharov et Smyshlyaeva).

Members 19–20: About 7.0 m of dark grey sandy siltstone with rare lenses of calcareous sandstone-coquina (K-369, K-373, K-375 and K-376, K-378, respectively). Members 19–20 are characterised by some brachiopods (Bittnerithyris margaritovi (Bittner)), and ammonoids Ussurijuvenites sp. and Koninckitoides popovi (Kummel).

Members 17–18: 20.5 m of dark grey siltstone with lenses of calcareous sandstone-coquina and concretions of calcareous-marl (K-333, K-338, K-342 and K-343, K-348, K-351, K-356, K-361, K-367, respectively). Members 17–18 yield the rare nautilids and ammonoids Yvesgalleticeras proximus Zakharov et Smyshlyaeva and Koninckitoides popovi (Kummel).

The thickness of the examined interval of the Neocolumbites insignis is about 47 m.

(2) Tirolites-Amphistephanites and Shimanskyites shimanskyi zones

Members 13–16: These units include an interval of approximately 15 m, and consist of dark grey siltstone, sandy siltstone and mudstone interbedded with grey fine grained sandstone and contain rare concretions of calcareous marl and lenses of calcareous sandstone in the upper part (K-304 and K-307 from Member 13; K-308, K-313 and K-315 from Member 14; K-316 and K-321 from Member 15; K-324, K-329 and K-33 from Member 16), with poorly preserved fossils.

Members 11 (upper part) and 12: About 5 m of dark grey mudstone (K-296, K-300 and K-303 from Member 12). These members yield conodonts (Furnishius triserratus Clark, Hadrodontina sp.) and ostracodes.

Covered interval (10–15 m in thickness).

Members 10–11 (lower part): About 28 m of dark grey siltstone with interbeds of grey fine grained sandstone in the lower part and dark grey mudstone with numerous concretions of calcareous-marl. The units contain abundant ammonoids (Shimanskyites shimanskyi Zakharov et Smyshlyaeva, Arctoceras septentrionale (Diener), Prosphingitoides ovalis (Kiparisova) and ostracodes (Zakharov et al., 2016).

Covered interval (15–20 m in thickness).

1.1.3 Induan

?Gyronites subdharmus Zone

Member 5: 5.0 m of conglomerate of small pebbles and a layer of grey fine grained sandstone at the base.

Member 4: 20.0 m of conglomerate of large pebbles.

Member 3: 20.0 m of grey fine grained sandstone, with lenses of conglomerate.

Member 2: 20.0 m of grey fine grained sandstone.

Member 1: 30.0 m of grey fine grained sandstone, with rare lenses of conglomerate.

The total thickness of the examined Induan is 95 m. Lower Triassic basal conglomerate and sandstone in some other sections (e.g., Golyj and Tri Kamnya) are mainly characterised by ammonoids Gyronites subdharmus Kiparisova (Zakharov, 1978, 1968; Kiparisova, 1961).

1.2 Description of the Kamenushka-2 Section

The Kamenushka-2 Section is located along a new road, 100–140 m west of the Kamenushka-1 Section. It exposes the Induan Lazurnaya (upper part) and Olenekian Kamenushka formations. The Kamenushka-2 Section represents a unique and valuable record of the Lower–Middle Olenekian exposed in South Primorye. In descending order, the lithological and biostratigraphical combinations of its Lower Triassic deposits are as following.

(1) Neocolumbites insignis Zone

Member 24: About 41 m of dark grey sandy siltstone with interbeds of grey fine grained sandstone and concretions of calcareous marl (K-295, K-260, K-265, K-270, K-285, K-290). Member 24 contains brachiopods, identified as rhynchonellids (e.g., Piarorhynchella tazawai Popov), terebratulids (Bittnerithyris margaritovi (Bittner)) and spiriferinids (Lepismatina sp.); abundant gastropods; abundant ammonoids (Koninckitoides popovi (Kummel), Inyoceras singularis Zakharov et Smyshlyaeva, Nordophiceratoides praecox Zakharov et Smyshlyaeva, Koninckitoides solus Zakharov et Smyshlyaeva, Albanites vulgaris Zakharov et Smyshlyaeva and fish remains (Popov and Zakharov, 2017; Zakharov and Smyshlyaeva, 2016).

Member 23: 3.5 m of dark grey sandy siltstone lenses of grey fossil-rich calcareous sandstone-coquina (K-249, K-254). Member 23 yields brachiopods, identified as terebratulids (Bitnerithyris margaritovi (Bittner) and athyridids (Hustedtiella planicosta Dagys (Bed 961-11), and ammonoid Inyoceras singularis Zakharov et Smyshlyaeva.

Member 22: 2.0 m of dark grey sandy siltstone (K-245, K-248).

Member 21: 5.5 m of dark grey sandy siltstone with intercalated fossil-rich calcareous sandstone lenses (K-233, K-238, K-244). Member 21 contains diverse organic remains: abundant brachiopods, identified as rhynchonellids (Piarorhynchella tazawai Popov), terebratulids (Bittnerithyris margaritovi (Bittner), Heterelasma sp.), spiriferinids (Lepismatina sp.) and athyridids (Hustedtiella planicosta Dagys), rare bivalve molluscs, abundant gastropods, abundant ammonoids (Pseudosageceras longilobatum Kiparisova, Tirolites opiparus Zakharov et Smyshlyaeva, Kazakhstanites? sp., Nordophiceratoides praecox Zakharov et Smyshlyaeva, Khvalynites sp., Eodanubites sp., Palaeophyllites admirandus Zakharov et Smyshlyaeva) and fish teeth (Popov and Zakharov, 2017; Zakharov and Smyshlyaeva, 2016).

Member 20: 3.0 m of dark grey siltstone with lenses of calcareous sandstone-coquina (K-228, K-232).

Member 19: 4.0 m of dark grey sandy siltstone (K-219, K-224, K-227). Member 19 yields ammonoids Koninckitoides popovi (Kummel) and Nordophiceratoides praecox Zakharov et Smyshlyaeva and brachiopod Piarorhynchella tazawai Popov.

Member 18: 13.0 m of dark grey siltstone with lenses of calcareous sandstone-coquina (K-193, K-198, K-203, K-208, K-213, K-218). Member 18 contains diverse organic remains: brachiopods, identified as rhynchonellids (Piarorhynchella tazawai Popov), terebratulids (Bittnerithyris margaritovi (Bittner)), ammonoids Inyoceras singularis Zakharov et Smyshlyaeva, Tirolites opiparus Zakharov et Smyshlyaeva, Tirolites? sp., Koninckitoides popovi (Kummel), Albanites vulgaris Zakharov et Smyshlyaeva, Kamenushkaites acutus Zakharov et Smyshlyaeva (Popov and Zakharov, 2017; Zakharov and Smyshlyaeva, 2016).

Member 17: 8.0 m of greenish grey mudstone with thin (3 mm) layers of sandy siltstone, lenses of calcareous sandstone-coquina and concretions of calcareous marl (K-177, K-182, K-187, K-192). Member 17 yields rhynchonellid brachiopods (Piarorhynchella tazawai Popov), abundant gastropods, abundant ammonoids (Inyoceras singularis Zakharov et Smyshlyaeva, Yvesgalleticeras proximus Zakharov et Smyshlyaeva, Koninckitoides popovi (Kummel), Bajarunia magna Zakharov et Smyshlyaeva, Palaeophyllites admirandus Zakharov et Smyshlyaeva).

The thickness of the examined interval of the Neocolumbites insignis Zone (Inyoceras singularis Beds) in the Kamenushka-2 Section is no less than 80.0 m.

(2) Tirolites-Amphistephanites Zone

Member 16: 4.5 m of intercalation of dark grey siltstone and greenish grey fine grained, calcareous sandstone (K-168, K-174, K-176). Member 16 yields the ammonoids Albanites vulgaris Zakharov et Smyshlyaeva and Nordophiceratoides praecox Zakharov et Smyshlyaeva.

Member 15: 4.0 m of thin intercalations of dark grey mudstone and grey fine grained sandstone, with numerous lenses of calcareous sandstone-coquina and concretions of calcareous marl (K-161, K-167).

Member 14: 5.0 m of dark grey mudstone with rare, thin (4 cm) layers of grey sandy siltstone and rare concretions of calcareous marl with terebratulid brachiopods (e.g., Bittnerithyris margaritovi (Bittner)) (K-150, K-155, K-160).

Member 13: About 4.0 m of dark grey siltstone and mudstone with interbeds of grey fine grained sandstone (K-147, K-149).

Member 12: 27.5 m of dark grey mudstone with numerous concretions of calcareous-marl (K-102, K-107, K-112, K-117, K-122, K-127, K-132, K-137, K-142, K-146). Member 12 contains diverse organic remains: brachiopods, identified as rhynchonellids (Piarorhynchella tazawai Popov), terebratulids (Bittnerithyris margaritovi (Bittner)), spiriferinids (Lepismatina sp.), rare bivalve and, nautilid molluscs, abundant ammonoids (Jeanbesseiceras explicatum Zakharov et Smyshlyaeva, Tirolites? sp., Koninckitoides popovi (Kummel), Koninckitoides solus Zakharov et Smyshlyaeva, Bajarunia magna Zakharov et Smyshlyaeva, Albanites vulgaris Zakharov et Smyshlyaeva, Nordophiceratoides praecox Zakharov et Smyshlyaeva), ostracodes and conodonts (Popov and Zakharov, 2017; Zakharov and Smyshlyaeva, 2016).

The thickness of the examined interval of the Tirolites-Amphistephanites (Bajarunia magna Beds) in the Kamenushka-2 Section is 45.0 m.

(3) Shimanskyites shimanskyi Zone

Member 11: 9.0 m of dark grey mudstone and siltstone with numerous concretions of calcareous-marl (K-83, K-88, K-93, K-98, K101 from the southern block and K-58, K-63, K-68 from the northern block). Member 11 yields brachiopods (Piarorhynchella tazawai Popov, Bittnerithyris margaritovi (Bittner), Lepismatina sp.), ammonoids (Ussuriidae gen. et sp. indet., Parussuria sp., Pseudosageceras longilobatum Kiparisova, Ussuriaspenites sp., Kamenushkaites sp., Xenoceltites? subvariocostatus Zakharov et Smyshlyaeva, Shimanskyites shimanskyi Zakharov et Smyshlyaeva, Arctoceras subhydaspis (Kiparisova), Churkites syaskoi Zakharov et Shigeta, Anasibirites simanenkoi Zakharov et Smyshlyaeva, Monneticeras kalinkini Zakharov et Smyshlyaeva, Mianwaliites ziminu Zakharov et Smyshlyaeva, Hemiprionites klugi Brayard et Bucher, Nyalamites? sp., Ussurijuvenites sp., Owenites carpenteri Smith, Prionites markevichi Zakharov et Smyshlyaeva, Prionites subtuberculatus Zakharov et Smyshlyaeva, Radioprionites abrekensis Shigeta et Zakharov, Juvenites sp.), nautiloids (Trematoceras sp.), ostracodes and conodonts (Furnishius triserratus Clark, Hadrodontina sp. and Neospathodus sp.) (Zakharov et al., 2016).

(4) Anasibirites nevolini Zone

Member 10: 11.5 m of dark grey mudstone and bandy siltstone with interbeds of fine-grained sandstone and numerous concretions of calcareous-marl (K-73, K-78, K-82 from the southern block and K-34, K-39, K-44, K-49, K-54, K-57 from the northern block).

The unit contains diversed organic remains: abundant ammonoids (Pseudosageceras sp., Prosphingitoides ovalis (Kiparisova), Owenites koekeni Hyatt et Smith, Arctoceras subhydaspis (Kiparisova), Arctoceras septentrionale (Diener), Churkites cf. syaskoi Zakharov et Shigeta, Anasibirites cf. nevolini Burij et Zharnikova., Prionites markevichi Zakharov et Smyshlyaeva, Xenoceltites? subvariocostatus Zakharov et Smyshlyaeva, Mianwaliites zimini Zakharov et Smyshlyaeva), ostacodes and conodonts (Furnishius triserratus Clark, Hadrodontina sp.) (Zakharov et al., 2016).

Position of a tectonic fault (the upper part of the Mesohedenstroemia bosphorensis Zone in this section is absent).

(5) Mesohedenstroemia bosphorensis Zone (lower part)

Member 9: 12.5 m of thin intercalations of dark grey siltstone and grey fine grained sandstone, with rare concretions of calcareous-marl (K-10, K-15, K-20, K-25, K-33 from the northern block, which has been subjected to folding and faulting).

Member 9 yields bivalves (Bakevellia exporecta Gordon), ammonoids (Pseudosageceras sp., Arctoceras septentrionale (Diener), Balchaeceras subevolvens (Zakharov), Ussurijuvenites artyomensis Smyshlyaeva et Zakharov) (Zakharov et al., 2016).

Member 8: 2.5 m of dark grey mudstone with numerous concretions of calcareous-marl (K-6, K-9), containing poor preserved ammonoids (e.g., Arctoceras? sp.).

Member 7: 1.0 m of thin intercalations of dark grey siltstone and grey fine grained sandstone (K-3, K-4).

Member 6: 0.5 m of dark grey mudstone with rare concretions of calcareous-marl, yielding small bivalve molluscs (K-1, K-2). The total thickness of the examined interval of the Olenekian in the section is about 167 m.

1.3 Induan

?Gyronites subdharmus Zone

Members 4 and 5: About 25 m of conglomerate with interbeds of grey fine grained sandstone. The total thickness of the examined interval of the Induan–Olenekian deposits in the Kamenushka-2 Section is about 192 m.

2 MATERIAL AND METHODS

Material was collected with care taken to avoid mudstone intervals with visible diagenetic features. From 425 samples of Olenekian and Anisian mudstone from the Kamenushka-1 and Kamenushka-2 sections, 116 samples, taken in sampling interval of approximately 1–3 m, were analyzed using a Flash EA (Thermo, Bremen/Germany), connected via a CONFLO Ⅳ (Thermo, Bremen/Germany) to a Delta advantage mass-spectrometer (Thermo, Bremen/ Germany) in Wieselburg/ Austria (HBLFA Francisco-Josephinum). Bulk sediment material was decarbonated by placing the samples in glasses on a heated surface (58–60 ℃) and addition and frequent replacement of HCl (10% v/v), until decarbonation was completed. Completion of decarbonation was checked by occurrence of bubbles after addition of HCl. Maximum decarbonation time was several weeks.

The results are reported in the conventional-notation in permil (‰) relative to the international V-PDB (Vienna PeeDee) and N-air standards for carbon and nitrogen, respectively. Reproducibility of replicate standards are better than ±0.2‰ for carbon and ±1‰ for nitrogen (because of low content of the latter in the samples).

3 RESULTS AND DISCUSSION

The detailed N- and C-isotope investigation of the Kamenushka-1 and Kamenushka-2 sections and data from the earlier investigated the Abrek Section (Zakharov et al., 2018), have revealed that nine N-isotope intervals, indicated as Ⅰ–Ⅸ, and some C-isotope excursions can be recognised in the Lower Triassic of this region (Figs. 46).

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Figure 4. The Kamenushka-1 Section: Upper Olenekian–Lowest Anisian C- and N-isotope data. Abbreviations: Tirolites-Amphist, Tirolites-Amphistephanites; Us. Amurensis-Lei. pr., Ussuriphyllites amurensis-Leiophyllites pradyumna; Hollandites-Leioph., Hollandites-Leiophyllites; Kam.-1. Kamenushka-1; Kam-2 (s. bl.). Kamenushka-2 (southern block).
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Figure 5. The Kamenushka-2 Section: Lower–Upper Olenekian C- and N-isotope data. Abbreviations: M. bos. (l.p.), Mesohedenstroemia bosphorensis (lower part); Anas. n., Anasibirites nevolini; Shim. s., Shimanskyites shimanskyi; Ar. s.-Bal. s., Arctoceras septentrionale–Balhaeceras subevolvens; Kam-2 (n.bl.). Kamenushka-2 (northern block); Kam-2 (s.bl.). Kamenushka-2 (southern block); Kam-1. Kamenushka-1. Other designations as in Fig. 4.
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Figure 6. Correlation of Lower Triassic layers in South Primorye (Abrek and Kamenushka) and Salt Range, Pakistan (Nammal) based on N- and O-isotope and palaeotemperature data. Abbreviations: Tompoph.u., Tompophiceras ussuriensis; Gyr.s., Gyronites subdharmus; P.k, Pseudoaspidites aff. kvansianus. ?A., ?Anasibirites nevolini; An.n., Anasibirites nevolini; S.s., Shimanskyites shimanskyi; Tirolites-Amphisteph., Tirolites-Amphistephanites; Ch., Changhsingian; Lo. Lower; Temp.in (and N.i.i.). palaeotemperature interval (and N-isotope interval).

Interval Ⅰ corresponds to the lower part of Induan layers of Tompophiceras ussuriense-Pseudoproptychites hiemalis in the Abrek Section, which is characterised by frequent alternation of negative (up to -4‰) and positive (up to +2.2‰) δ15N values.

Interval Ⅱ, corresponding mainly to the upper Induan Gyronites subdharmus Zone and the lower part of the Lower Olenekian Mesohedenstroemia bosphorensis Zone in the Abrek Section, is mainly characterised by positive δ15N values (up to +8‰).

Interval Ⅲ, covering the middle part of the Lower Olenekian Mesohedenstroemia bosphorensis Zone in the Abrek Section, is characterised by predominantly negative δ15N values (up to -5.8‰).

Intervals Ⅳ and Ⅴ, corresponding to the upper part of the Mesohedenstroemia bosphorensis Zone in the Abrek Section, are characterised by frequent alternation of negative (up to -2.1‰) and positive (up to +1.8‰) δ15N values and predominantly positive δ15N values (up to +1.0‰), respectively.

However, there is, apparently, only the lowermost part of N-isotope interval Ⅴ in the Abrek Section (Fig. 6). In the Kamenushka-2 Section, the possible continuation of this interval, also characterised by predominantly positive δ15N values, seems to be extending into the lower part of the Upper Olenekian Tirolites-Amphistephanites Zone. Therefore, the Kamenushka-2 Section provides more complete record on interval Ⅴ.

In contrast with the Abrek Section (Zakharov et al., 2018), the Induan strata of the Kamenushka-2 Section is represented by conglomerate and sandstone, which rock types are usually unsuitable for isotopic investigation. The Lower Olenekian sequences, known in the northern block of the Kamenushka-2 Section (Arctoceras septentrionale-Balchaeceras subevolvens beds) are mainly characterised by positive δ15N values (up to +1.51‰; samples K-1, K-2, K-3, K-4, K-6, K-9, K-10, K-15, K-20, K-25, K-30, K-33).

This interval Ⅴ, corresponds to members 10–12 (Anasibirites nevolini, Shimanskyites shimanskyi and Tirolites-Amphistephanites (lower part) zones), which is characterised mainly by positive δ15N values. δ15N data ranges from -0.81‰ to +1.49‰, with a mean of +0.33‰ (the samples K-73, K-78, K-82, K-83, K-88, K-93, K-98, K-101, K-102, K-107, K-112, K-117, K-122, K-127, K-132, K-137, K-142, K-146 from the southern block, and K-34, K-39, K-44, K-49, K-54, K-57, K-58, K-63, K-68 from the northern block of the Kamenushka-2 Section and the samples K-295, K-300, K-303 from the southern block of the Kamenushka-1 Section). The maximal δ15N value was measured from the Anasibirites nevolini-Shimanskyites shimanskyi boundary beds (Sample K-58). This interval is characterised by comparatively variable δ13Corg values, ranging from -26.9‰ to -23.3‰, with the three carbon isotope minimum. The first of them (-26.1‰) is located near the boundary between the Anasibirites nevolini and Shimanskyites shimanskyi zones (Sample K-83), two others (-26.9‰ and -25.8‰) are located in the middle part of Member 12 (samples K-117 and K-127, respectively) of the Tirolites-Amphistephanites Zone.

Interval Ⅵ, corresponding to members 13–17 (the upper part of the Tirolites-Amphistephanites Zone and lowest part of the Neocolumbites insignis Zone), is characterised by significantly fluctuating δ15N values, from -1.83‰ to +1.31‰, with a mean of +0.05‰ (the samples K-147, K-149, K-150, K-155, K-160, K-168, K-174, K-176, K-177, K-182, K-187, K-192 from the southern block of the Kamenushka-2 Section and the samples K-304, K-307, K-308, K-313, K-315, K-316, K-321, K-323, K-324, K-329, K-332, K-333, K-338, K-342 from the southern block of the Kamenushka-1 Section). The minimal δ15N value (-1.83‰) was discovered at Tirolites-Amphistephanites- Neocolumbites insignis boundary beds (Sample K-176).

The δ13Corg values of interval Ⅵ are somewhat higher and less variable, ranging from -24.3‰ to -23.9‰, with lack of any distinct excursions.

Interval Ⅶ, corresponding to Member 18 of the Neocolumbites insignis Zone, is characterised by mainly positive, weakly fluctuating δ15N values ranging from -0.52‰ to +1.60‰, with a mean +0.41‰ (the samples K-193, K-198, K-203, K-208, K-213, K-218 from the southern block of the Kamenushka-2 Section and the samples K-343, K-348, K-351, K-356, K-361, K-367 from the southern block of the Kamenushka-1 Section).

The interval Ⅶ is also characterised by less variable δ13Corg values, ranging from -25.0‰ to -23.9‰, with a small positive excursion (δ13Corg = -23.9‰) in the lower part of Member 18 (Sample K-198).

Interval Ⅷ, corresponding to members 19–23 and the lower part of Member 24 of Neocolumbites insignis Zone, is characterised by predominantly positive, significantly fluctuating δ15N values, ranging from -0.45‰ to +2.60‰, with a mean +0.88‰, with the two positive excursions (the samples K-219, K-224, K-226, K-227, K-228, K-232, K-233, K-238, K-244, K-248, K-249, K-254, K-255 from the southern block of the Kamenushka-2 Section and the samples K-368, K-373, K-375, K-376, K-378, K-379, K-384, K-389, K-390, K-393, K-304, K-399, K-410, K-415 from the southern block of the Kamenushka-1 Section). The maximal δ15N value (+ 2.60‰) was discovered at the base of Member 21 (Sample K-233).

This interval is also characterised by quite stable δ13Corg values, ranging from -25.3‰ to -24.0‰.

Interval Ⅸ, corresponding to the main part of members 24 of the Neocolumbites insignis Zone, is characterised by predominantly positive δ15N values, ranging from -0.62‰ to +1.69‰, with a mean +0.73‰ (the samples K-260, K-265, K-270, K-275, K-280, K-285, K-290 from the southern block of the Kamenushka-2 Section, the Sample K-415 from the southern block of the Kamenushka-1 Section). The maximal value (+1.69‰) was discovered at the middle part of Member 24 (Sample K-275).

The Late Olenekian interval Ⅸ exhibits a significant decrease in the δ13Corg values (down to -27.4‰ in the middle part of Member 24 (Sample K-270), closed to -26.7‰, obtained from the Sample K-430, which was taken from Member 27 of Early Anisian Age (Fig. 4).

3.1 N-Isotope Records

Nitrogen is one of the most common elements of the solar system, the main component of air on Earth (in the form of diatomic molecules N2). Nitrogen is a chemical element absolutely necessary for the existence of living organisms. It is a major component of biomass and is required for photosyntesis (Robinson et al., 2012). The main part of the molecular nitrogen of air is fixed precisely biotically (Bauersachs et al., 2009), by certain types of cyanobacteria (diazotrophic cyanobacteria–other phytoplankton representatives do not possess such abilities). As a result, ammonium compounds (NH4+) and ammonia (NH3), products that are well assimilated by plants, are formed. The combined nitrogen is transmitted along the food chain to herbivores and carnivores, and, being oxidized to nitrate (NO3-) and nitrite (NO2-), it enters the sea and fresh water bodies in a dissolved form. The tissues of the dead organisms undergo the three main processes: ammonification (decomposition with the release of ammonium), anammox (anaerobic ammonium oxidation) and denitrification (reduction of nitrate to nitrite and further to nitrogen gaseous oxides and molecules) (Glud et al., 2009), which largely compensate for the loss of nitrogen in the atmosphere. However, the fundamental aspects of the nitrogen cycle in the atmosphere, investigated with the N-isotopic method, still require further in-depth study (Sigman et al., 2009).

Studies of the isotope composition of nitrates in the modern subtropics of the northern Pacific showed that relatively low values of δ15NO3- (1‰–3‰) are typical for depths from 100 to 500 m, and steadily high values (4.5‰–5.5‰) for depths exceeding 1 000 m (Altabet et al., 2005). A similar dependence of the N-isotopic composition of matter on the depths of the ocean is also shown on the example of modern corals from low, middle and high latitudes (Wang et al., 2015).

In connection with the selective absorption of substances with a light isotope 14N by phytoplankton this organic isotope is often enriched with organic substances deposited in modern seas in seasons of biological activity of phytoplankton. In the Sea of Japan, for example, such an isotopic effect demonstrating the relationship between the seasonal variability of phytoplankton productivity and the N-isotopic composition of precipitating organic particles is associated with phytoplankton, which develops at the end of autumn-early winter, and especially in spring, when the temperature of surface waters fluctuates from about 10 to 17 ℃ (Nakanishi and Minagawa, 2003).

In Junium and Arthur's (2007) opinion, the δ15N data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient-nitrogen poor, phosphorous replete waters during Late Mesozoic oceanic anoxic events (OAEs), when "black shale" facies were common. However, they consider that upwellings are not required for nitrogen fixation but they are necessary maintain the phosphate flux that is needed for long-term productivity and the consequent phosphate release. Cretaceous "black shales" are significantly depleted in 15N compared to modern "black shales" forming basins such as the Black Sea despite the important role of biological nitrogen fixation in both environments (Junium and Arthur, 2007).

Of particular interest to our research is the data on the N-isotopic composition of marine sediments deposited under greenhouse and glacial conditions (e.g., Algeo et al., 2014, 2008; Jenkyns et al., 2001; Altabet et al., 1995). They show the important role of the marine cycle of nitrogen in long-term climate change and give a general trend of higher 15N-values during times of cool climate (cool-house) and low 15N-values during warm period (hot-house). The high nitrogen isotope values are explained by increased denitrification in the water column, whereas low 15N-values are related to increase nitrogen fixation by cyanobacteria (e.g., Algeo et al., 2014; Luo et al., 2011).

Marine sedimentary organic matter can be diagenetically altered. However, Algeo et al. (2014) argued that organic matter diagenetic alteration usually only has a minor effect on the N-isotope ratio. Thus, marine sediments usually are regarded as quite robust, as published compound specific N-isotope offsets from the bulk ratio can dominantly be accounted to photosynthetic effects. Furthermore, deeper burial does not seem to significantly affect N-isotopes of marine sediments, as metamorphosed sediments show similar values as sediments that did not undergo deep burial. Therefore, it is concluded that marine sediments are a quite robust archive of seawater-fixed nitrogen (Algeo et al., 2014; Robinson et al., 2012; Higgins et al., 2010) and we follow this reasoning.

For the Kamenushka-1 and Kamenushka-2 sections, a rather distal shelf-slope is assumed and thus only a very minor influence of terrigenous organic matter on the sediment organic matter. Therefore, as terrigenous organic matter has a higher C : N ratio than marine organic matter, no significant influence on the N-isotope ratio is assumed.

According to Algeo et al. (2014), the Phanerozoic δ15Nsed curve has a strong relationship with first-order climate cycles, with low values occurring during the greenhouse climate modes (mid-Permian, mid-Jurassic and Cretaceous) and high values occurring during the icehouse climate modes (mid-Palaeozoic and Cenozoic). Cretaceous strata are strongly 15N-depleted (-4‰ to 0), whereas Carboniferous units are highly 15N-enriched (+6‰ to +14‰).

On the basis of data on the Induan and Lower Olenekian of the Abrek Section, reported by us earlier (Zakharov et al., 2018), intervals of the Lower Triassic, characterised by the lower (often negative) δ15N values, were found to be associated with warmer conditions (in comparison with intervals with the higher (positive) values).

The authors demonstrate this correlation between N-isotopes and seawater temperature for the entire Lower Triassic (Abrek and Kamenushka-2 sections). According to this correlation, the N-isotope record can be interpreted as showing fairly warm conditions prevailed in South Primorye in the Middle Induan followed by mainly cooler conditions during Late Induan–Olenekian and after that (the second part of the Mesohedenstroemia bosphorensis chron) again mainly warmer conditions. The first part of the Anasibirites nevolini chron is characterised by rather cooler conditions, followed by warmer ones during its second part. Subsequent cooler conditions during the Shimanskyites shimanskyi and Tirolites-Amphistephanites (lower part) chrons were followed, apparently, by warmer once. More or less stable cooler conditions during the Early Triassic took place, possibly, only during the Late Olenekian Neocolumbites insignis chron, which is in agreement with O-isotope palaeotemperature calculations, based on data from conodonts from the Nammal Section, Salt Range (Fig. 6).

Some workers mark a causal link between cooler conditions and increase in taxonomic diversity of marine fossils during the Early Triassic, because it was a time of mainly extreme warmth (e.g., Grigoryan et al., 2015; Schobben et al., 2014; Goudemand et al., 2013; Romano et al., 2013; Joachimski et al., 2012; Sun et al., 2012). If the hypothesis concerning interpretation of N-isotope data, recorded for South Primorye, is correct, it seems to be plausible to assume that the greatest increase in abundance and partly in taxonomic diversity of both ammonoids and brachiopods from the Upper Olenekian Neocolumbites insignis Zone of the Kamenushka-2 and Kamenushka-1 sections is also connected with cooler conditions of some N-isotope intervals (e.g., Ⅶ–Ⅸ; Fig. 6; see also description of members 17–24 in the "Geological setting and stratigraphy" section). Still, it needs to be noted and kept in mind that the low amounts of N in the samples also will account for some features identified in the sections, and the patterns thus need to be confirmed in other sections.

3.2 C-Isotope Records

Reasons according for the worldwide negative δ13C excursions, including that at the Permian-Triassic boundary, is still a topic at debate (e.g., Korte et al., 2010; Renne et al., 1995; Erwin, 1994; Baud et al., 1989; Gruszczyński et al., 1989; Holser and Magaritz, 1987). According to a well recognized version (e.g., Schobben et al., 2014; Sobolev et al., 2011; Korte et al., 2010; Horacek et al., 2007a, b, c; Chumakov, 2004; Isozaki, 1997; Renne et al., 1995), the global end-Permian negative C-isotope excursion has been provoked mainly by large imput of mantle-derived CO2 from the eruption of the Siberian traps. The most depleted δ13C values for the Permian-Triassic boundary have been documented in New Zealand by Krull et al. (2000), who hypothesized that methane release could have been in part responsible for the larger isotopic shift in southern high palaeolatitudes.

However, the δ13Corg values of the most part of the Upper Olenekian interval in the Kamenushka-2 and Kamenushka-1 sections are not so depleted as in New Zealand (Fig. 7). The most prominent negative δ13Corg excursions in the Lower Triassic of South Primorye are found in the following levels: (1) the uppermost part of the Lower Olenekian Mesohedenstroemia bosphorensis Zone (up to -29‰ in the Abrek Section); (2) the uppermost part of the Lower Olenekian Anasibirites nevolini Zone (up to -26.1‰) of the Kamenushka-2 Section; (3) the lower part of the Upper Olenekian Tirolites-Amphistephanites Zone (up to -26.9‰) of both the Kamenushka-2 and the Kamenushka-1 sections and (4) the upper part of the Middle Olenekian Neocolumbites insignis Zone (up to about -28‰) of both the Kamenushka-2 and the Kamenushka-1 sections. C-isotope records documented from the Lower Triassic in South Primorye, might reflect possibly some cycles of sea level fluctuations during the Middle–Late Induan, Olenekian and Earliest Anisian times (Zakharov et al., 2018).

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Figure 7. Correlation of Lower Triassic layers in South Primorye (Abrek and Kamenushka) and Chaohu, South China (Western Pingdingshan and South Majiashan), based on C-isotope and palaeontological data. Abbreviations: Tomp.u., Tompophiceras ussuriensis; Gyr.s., Gyronites subdharmus; An.n., Anasibirites nevolini; Sh., Shimanskyites shimanskyi; Tirolites–Amphisteph., Tirolites–Amphistephanites; Helongsh., Helongshan; P.k, Pseudoaspidites aff. kvansianus.

Our isotopic data enable a regional and global geochemical correlation between Lower Triassic sections of South Primorye (Zakharov et al., 2018) and Lower Triassic sections from Chaohu, South China (Tong et al., 2004, see also Fig. 7).

There is no doubt that the negative δ13Corg excursion 2, presented in the uppermost part of the Mesohedenstroemia bosphorensis Zone in the Abrek Section (Fig. 7), corresponds to the negative δ13Ccarb excursion of the upper part of the Yinkeng Formation in the West Pingdingshan Section. This level in South China rather corresponds to the uppermost part of the Flemingites-Euflemingites Zone, than the lowermost part of the Anasibirites Zone in Tong et al.'s (2004) interpretation.

Upper Olenekian interval, located between excursions 4 and 5 in both the Kamenushka-1 and the Kamenushka-2 sections, as well as in the South Majiashan Section, are characterised by higher δ13C values. Taken into account these data, as well as position of the excursion 5 in the uppermost part of the Neocolumbites insignis Zone in South Primorye, the latter appears to be correlative in general with middle member of the Nanlinghu Formation (Fig. 7). However, as the Corg present in the samples can be of marine or terrigenous origin (with the latter possessing slightly higher carbon isotope values) the variations in δ13C can be to some extent explained by various amounts of terrigenous organic matter.

4 CONCLUSIONS

1. New N-isotope data are in agreement with the hypothesis (Zakharov et al., 2018), according to which intervals of the Lower Triassic, characterised by lower (negative) δ15N values are found to be associated with warmer conditions (in comparison with intervals with higher (positive) values), likely connected with the release large amount of N2O due to volcanic activity and warming.

2. N- and С-isotope data, obtained from both the Kamenushka-1 and Kamenushka-2 sections, as well as the Abrek Section in South Primorye, seem to be an evidence of unstable climatic and hydrological conditions of the Early Triassic.

3. It is known from the published data on δ18Osp composition of conodonts from the low and higher palaeolatitude areas (e.g., Salt Range) that extreme warm climate conditions were common for the Early Triassic. Our data of the δ15N composition of Lower Triassic mudstone from South Primorye show that the following somewhat cooler Early Triassic chrons, more favourable for biotic recovery, likely took place in South Primorye: (1) the Late Induan Gyronites subdharmus chron, (2) the beginning of the Early Olenekian (Early Smithian) Mesohedenstroemia bosphorensis chron, (3) the very end of the Early Olenekian Mesohedenstroemia bosphorensis chrone and the beginning of the Early Olenekian (Middle Smithian) Anasibirites nevolini chron, (4) the Early Olenekian (Late Smithian) Shimanskyites shimanskyi chron and the beginning of the Late Olenekian (Early Spathian) Tirolites-Amphistephanites chron, (5) the beginning of the Late Olenekian (Middle Spathian) Neocolumbites insignis chron, (6) the middle part of the Late Olenekian Neocolumbites insignis chron, (7) the end of the Late Olenekian Neocolumbites insignis chron. By and large this pattern is mainly in agreement with O-isotope palaeotemperature data from the Salt Range (Romano et al., 2013).

4. The most prominent Lower Triassic negative δ13Corg excursions of South Primorye, allowing correlation with corresponding Induan and Olenekian units of many Tethyan regions, including South China (Tong et al., 2004), fall on the following intervals, (1) the uppermost part of the Early Olenekian Mesohedenstroemia bosphorensis Zone), (2) the uppermost part of the Early Olenekian Anasibirites nevolini Zone, (3) the lower part of the Late Olenekian Tirolites-Amphistephanites Zone and (4) the upper part of the Upper Olenekian Neocolumbites insignis Zone.

ACKNOWLEDGMENTS

This research was funded by the grant RFBR 18-05-00023A. We gratefully acknowledge Prof. Jinnan Tong (China University of Geosdiences) for his unpublished information on 13Corg data from the Chaohu area, Doctor G. I. Guravskaya (FEGI, Vladivostok, Russia) for her consultation on Early Triassic conodonts and Doctor O. P. Smyshlyaeva (FEGI, Vladivostok, Russia) for her help in collection of fossils and anonymous reviewers for helpful comments that improved this manuscript. Processing of the samples by C. Panzenböck and isotope measurements by E. Riegler are thankfully acknowledged. The final publication is available at Springer via https://doi.org/10.1007/s12583-018-0792-6.


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