6 – Facies interpretation - Sedimentology, biostratigraphy and diagenesis of Upper Triassic sha

Based on a detailed description, each facies can be related to a precise depositional environment. Hereafter, facies are interpreted in term of position within the carbonate system based on significant organisms, sedimentary structures and mud content. Note that a diagenetic study of these limestone units, supported by stable isotopes and REE analyses, is in progress and can light up new clues to better precise the following interpretations. The diversity of facies related to sampled outcrops is presented on Table 2.

6.1 – Lagoonal environment – F1 & F2

F1 and F2 are dominated by carbonate mud, involutinid foraminifers and megalodontid bivalves. The latter are isolated or form plurimetric–sized bioherms (Fig. 4G). This association is typical of quiet protected subtidal shallow environments: megalodontids have been widely reported in such environments from tropical Tethyan and Panthalassa domains (e.g., Bernecker,

FaciesSamplesLocalitiesBiotic content/foraminifer assembalgeOther clasts/sedimentary featuresFacies interpretation F1 Oncoid-microbial mudstone to wackestone GP132, GP139, GP142, GP147-GP149, GP177, GP181, GP183, GP185B, GP187,GP188A-C, GP189 Verkhnii-Rudnik Quarry Verkhnii-Rudnik Valley Sakharnaya Mountain Partizansky Sadovy Mine

Cayeuxia sp., Baccanella floriformis, megalodontids / ?Trocosiphonia sp., indet. foraminifers Oncoids, cyanoids, microbial peloids, radial ooids / Voids, fenestral structures, geopetal inflinings, burrows

Lagoon F2 Involutinid-Megalodontid wackestone to rudstone

GP113B, GP114A, GP114B, GP121, GP124, GP126, GP133, GP165B-GP169B, GP171, GP174, GP180, GP186A, GP186B, GP193-GP195, GP197-GP200, GP206A-C, GP210 Verkhnii-Rudnik Quarry Niznii-Rudnik Mine Sakharnaya Quarry Sakharnaya Mountain Partizansky Vokzalnaya Massif Karyernaya

Megalodontids, other bivalves, gastropods and green algae debris, echinoderms, indet. calcimicrobes / Aulotrotus sp., Parvalamella friedli, Aulosina oberhauseri, Trochosiphonia josephi, Triasina hantkeni, indet. foraminifers Rare oncoids / Burrows, rare stromatactis filled with geopetal infilling

Lagoon F3 Peloidal-Bioclastic packstone to grainstone

GP115A-C, GP123, GP125, GP130, GP131, GP133, GP134, GP135A, GP135B, GP140, GP143A, GP143B, GP150A, GP150B, GP151-GP153, GP156, GP161, GP165A, GP168, GP169A, GP169B, GP172A, GP172B, GP173, GP175, GP176, GP178A-GP179B, GP182, GP184, GP196, GP199, GP200 Verkhnii-Rudnik Quarry Verkhnii-Rudnik Valley Rudnik-Nikolaevsky Quarry Niznii-Rudnik Mine Sakharnaya Quarry Sakharnaya Mountain Partizansky Vokzalnaya Massif Karyernaya

Echinoderms, shell debris, green algae (dasycladecean), serpulid colonies, ostracods, indet. calcimicrobes, Baccanella floriformis, Plexoramea ceribriformis, Parafavreina(rare) / Agathammina austroalpina, ?Duostominidae, indet. Miliolids, indet. Textulariidae, encrusting foraminifer, Aulotortus tumidus, Parvalamella sp., Trochosiphonia josephi, "Trochammina" jaunensis, indet. foraminifers Peloids (microbial, fecal pellets, reworked mud grains, micritized grains), concentric and radial ooids (rare), coated grains, intraclasts, aggregate and compound grains, oncoids (rare) / Stromatactis, perforated shells, burrows

Back-reef, open-lagoon F4 Mollusc-calcimicrobe packstone to grainstone

GP116-GP120, GP127, GP144, GP145A-GP145B, GP192, GP196, GP205 Verkhnii-Rudnik Quarry Verkhnii-Rudnik Valley Primorsky Massif Vokzalnaya Massif Karyernaya Plexoramea Cerebriformis, Cayeuxia sp., Garwoodia sp., ?Hedstromia sp., echinoderms, ostracods, rareTubiphytessp. and serpulids colonies Debris of: green algae, sponges, corals, Megalodonts, gastropods / "Trochammina" alpina, ?Duostominidae, Variostominidae, Endotriada sp., indet. Miliolids

Aggregate and coumpond grains, coated grains, intraclasts, oncoids, peloids / Voids, stromatactis and fenestral structures, large isopaquous and blocky cements, geopetal infilling

Back-reef, open-lagoon F5 Sponge-coral boundstoneGP113A, GP136-GP138, GP141, GP150A, GP154, GP155, GP157

Verkhnii-Rudnik Quarry Verkhnii-Rudnik Valley Rudnik-Nikolaevsky Quarry Indet. phaceloid and solitary corals, indet. calcareous sponges, chaetetid sponges, indet. encrusting sponges, gastropods, Radiomura cautica, Girvanella-like calcimicrobes, Microtubus communis, Baccanella floriformis, Uvanella, various indet. microbial laminations, rare brachipods and green algae / Indet. foraminifers, indet. Miliolids, encrusting foraminifers

Rare radial ooids / Large ispaquous and blocky cements, reef cavitiesReef, bioherm F6 Ooid-bioclastic grainstone

GP115D, GP128, GP129, GP168, GP169A, GP183A, GP185A, GP190, GP201-GP204, GP208 Verkhnii-Rudnik Quarry Sakharnaya Quarry Partizansky Sadovy Mine Karyernaya

Undetermined branched calcimicrobes, echinoderms, gastropods, green algae / ?Duostominidae, Variostomatidae Rounded or tangential ooids (concentric, distorted, micritized, compound), peloids, rare large oncoids / Large firbous isopaquous and blocky cements

Shoal, sand bar F7 Laminated mudstone-wackestone and graded packstone-grainstone

GP122A-GP122D, GP158-160, GP163-GP164C Verkhnii-Rudnik Quarry Rudnik-Nikolaevsky Quarry Niznii-Rudnik Mine Debris of: corals, sponges, bivalve shells, echinoderms / _ Lithified limestone clasts / Flame structures, differantial compaction, gradingUpper to middle slope F8 Radiolarian-filament mudstone to wackestoneGP166, GP191Niznii-Rudnik Mine Primorsky Massif

Filaments, radiolarians, echinoderms, brachipods, ostracods / _ Ooids, oncoids, lithified limestone clasts / _Lower slope to basin

Table 2 – Facies content, associated localities and environmental interpretations.

41 6.1 – Lagoonal environment – F1 & F2

Haas et al., 1998; Martini et al., 1997; Onoue et al., 2009; Pomoni–Papaioannou, 2008;

Peybernes et al., 2016b; Tamura, 1983; Yancey & Stankey, 1999; Yao et al., 2007). Some green algae debris and rare calcimicrobes also occur, confirming deposition within the upper photic zone. Gastropods and thin–walled involutinids, locally very abundant, are known to be adapted to the high temperatures and hypersalinity of a restricted lagoon (Tucker & Wright, 1990). In addition, rare pyrite minerals associated with dark plurimetric sized areas (Fig. 3C) have been observed, suggesting a replacement of organic matter by pyrite in a reducing environment (Hudson, 1992). Microbial features (cyanoids, stromatactis structures, microbial peloids) associated with small (200 µm in diameter) radial ooids are also well represented in F1 (Fig.

4A), suggesting moreover a very calm and stagnant environment with very low water circulation (Carozzi, 1961; Conley, 1977). Involutinids are common in a wide range of environments from shoal to lagoon (Chablais et al., 2010c, 2011; Gazdzicki, 1983; Gazdzicki

& Reid, 1983; Peybernes et al., 2015; Piller, 1978). However, Parvalamella friedli, very common in the Dalnegorsk limestone, has also been widely described in similar restricted environments of Panthalassa (Rigaud et al., 2012, 2013a). Occasionally, F2 is associated to a laminated debris–rich packstone (Fig. 4B) characteristic of a connection with the open part of the carbonate system, at the pace of a tidal channel (see Little Bahama Bank, Reeder & Rankey, 2008; Andros Island, Bahamas, Rankey, 2007; Enewetak Atoll, Atkinson et al., 1981). The laminated debris–rich packstone can also be related to punctual events, such as storms or strong tides. The infilling of burrows is always represented by high–energy facies (F3 or F6B) indicating common variations in the depositional energy, evolving from quiet to more open environments (Fig. 9). Such variations are well defined in the field in Partizansky and Karyernaya outcrops. In these two areas, F1 and F2 are the dominant facies, locally intercalated with F3 and F6B showing a sudden change from subtidal (lagoonal) to intertidal (shoal) environment followed by a progressive evolution back to F1/F2 (Fig. 9). In Karyernaya outcrop, this evolution is well marked on the quarry walls, suggesting that the original facies succession has been partly preserved. From the eastern part of the quarry to the western part, facies are first dominated by F1 and F2 and then progressively marked by burrows filled with F6B facies

42 to the west. Facies are then abruptly marked by F6B (the contact between F1/F2 and F6B is not visible on the field), progressively evolving back to F1/F2 finally characterized by burrows filled by F6B facies to the westernmost part of the quarry. Note that the burrows are always filled by F6B in the Karyernaya area, indicating the possible polarity of the succession. This evolution of the carbonate system through time could be due to 1) minor sea–level variations, possibly controlled by tectonic (relative variations) or orbital (eustatic variations) factors, as widely reported in the Dachstein limestone (see Lofer Cycles, Cozzi et al., 2005; Enos &

Samankassou, 1998; Hass et al., 2007; Satterley & Brandner, 1995) contemporary to Dalnegorsk limestone or 2) shoal migration (Major et al., 1996), F3 and F6B being interpreted as open–lagoon and shoal environments. Note that our field observations are coherent with a sudden change with a sharp lower contact between F6B and F1/F2 which is possibly not cons–

Fig. 9 – Different facies observed in the Dalnegorsk limestone. A. F2, Involutinid–Megalodontid (white arrow) rudstone. Yellow arrow: gastropod. B. Dark unevenly shaped burrows, within F2. C. F1, Oncoidal wackestone. Yellow arrows: oncoids. D. Recrystallized megalodontid in life position. E. F6B, dominated by large oncoids. F. Polished surface of F6B, composed of ooids and oncoids. G. F6B, oolitic grainstone. H.

Polished surface of F6B composed only of ooids. Note the presence of well delimited recrystallized zone (?dissolved bioclasts, ?burrows, yellow arrow). I. Burrows in lagoonal deposit (F1/F2), filled by shoal facies (F6B). J. Polished surface of burrows (dark zones) filled by oolitic facies. The facies around burrows is composed of mud. Scale bars: A, C, E, G, I 5 mm; F, H, J 1 cm.

–istent with progressive eustatic changes linked to orbital factors. Those variations are well defined in the field at Partizansky and Karyernaya outcrops. Indeed, in these two areas F1 and F2 are the dominant facies, locally intercalated with F3 and F6B showing a sudden change from subtidal (lagoonal) to intertidal (shoal) environment followed by a progressive evolution back to F1/F2 (Fig. 9). Further investigations might be needed to precisely define the controls of this facies changes and a possible cyclicity in the evolution of the carbonate system (Fig. 9). F1 and F2, well represented in the field, are typical of lagoonal environments, with probable complex morphology represented by restricted reducing parts and other more open areas punctuated by megalodontid bioherms.

6.2 – Back–reef/Open lagoon environment – F3 & F4

F3 is dominated by well–sorted peloidal packstone to grainstone, associated with dasycladacean green algae and autochthonous calcimicrobes (Fig. 5). This association is typical of open–lagoon environments, within the upper photic zone, characterized by regular changes in water energy, above the Fair Weather Wave Base (FWWB). F3 can be found as mud–rich packstone to grainstone, indicating a depositional setting characterized by very variable water energy. Peloids are mainly represented by fecal pellets or reworked micritized ooids, common in this facies and indicating a close link with open–marine environments (F6B). Shells, echinoderms and other bioclasts are coated by a micritic rim, related to algal–fungi activity forming constructive and destructive cortoids, characteristic of stable shallow–water environments (up to 20 m deep, Swinchatt, 1969), with a low sedimentation rate. As observed in the lagoonal environment, burrows are also filled by F6B, confirming changes in the platform settings through time, related to probable minor relative sea–level variations or shoal migrations. F3 is locally associated with coral–sponge bioherms (F5), interpreted locally as plurimetric–sized isolated bioconstructions developed in an open–lagoon environment. On the other hand, F4 is characterized by abundant calcimicrobes with a loose packing represented by large voids, stromatactis and fenestral structures filled with sparry cement (Fig. 5C). This facies

44 has always been found associated with reef patterns (F5) and is interpreted herein as typical of peri–reef environments, dominated by microbial patterns in a relatively open marine setting.

Stromatactis likely formed after the decay of skeletons of free reef–building organisms. Note that this facies is well known in similar Panthalassan environments of the same age (Chablais et al., 2010b; Kiessling & Flügel, 2000; Peybernes et al., 2016b). The large isopachous and blocky cement and the absence of mud indicate a rapid cementation in an active circulating water environment confirming the previous interpretation. F3 and F4 are the most represented facies, corresponding to a transitional zonation from protected to open environments, a transition widely represented in the studied system.

6.3 – Reef/Bioherms – F5

F5 is characterized by framebuilders (mostly sponges and corals) associated with various microbial crusts and microproblematica, and delimiting reefal cavities (Fig. 6). The described association in this facies is interpreted as diagnostic of reef environments. Similar assemblages are widely reported from Upper Triassic platform margins in the Tethys (Bernecker, 2005; Flügel & Senowbari–Daryan, 2001) and Panthalassa (Chablais et al. 2010c, Onoue et al., 2009; Peybernes et al., 2015; Martindale et al., 2012). However, poor preservation and diversity in organisms (Fig. 6) do not allow us to make specific comparison with these coeval systems. Reefal cavities are filled with large isopachous and blocky sparry cement (Fig.

6B), indicating a rapid cementation in an open environment with active circulating water.

According to field observation, F5 occurs locally as pluri–metric patches associated with F3.

The samples related to these structures are defined as coral–sponge boundstone but are devoid of reefal cavities and large microbial crusts, and mostly dominated by mud (Fig. 6E). Those facies have been characterized as localized pluri–metric bioherms within the protected part of the system (back–reef, open–lagoon) as described in recent systems (see Glover Reef Atoll, Belize, Wallace & Schafersman, 1977; Rasdhoo Atoll, Maldives, Parker & Gischler, 2011). F5 is a poorly represented facies in the Dalnegorsk limestone and no proper reefal deposits have been observed in the field (i.e., large continuous coral–sponges rudstone/framestone). It is therefore highly unlikely that this reefal facies, represented by slight framebuilders, was developed along the windward side of the carbonate platform, subject to high–energy waves and currents. Based on these observations, we can suggest that the external part of the platform, especially the windward side, was not dominated by framebuilders (no strong and continuous reef barrier), but represented mostly by shoals whereas the leeward side was also characterized by shoals, but probably alternating with small (patch) reefs and tidal channels.

45 6.4 – Shoal/sandbar – F6

F6 corresponds to a typical bioclastic and oolitic facies (Fig. 7) of a shoal or sandbar, controlled by fair weather waves and tidal influences (Hine, 1977). This facies is well known in modern tropical settings (Abu Dhabi, Friedman 1995, Lokier & Firorini 2016 ; Aitutaki Atoll, Cook Islands, Rankey & Reeder, 2009 ; Bahamas, Rankey & Reeder, 2011). Ooids are mostly of spherical concentric form, indicating high–energy conditions with open marine salinity (Flügel, 2004). Distorted shapes are also locally reported (Fig. 7C) and may indicate either a turbulent environment or be linked to the burial of uncemented ooids (Flügel, 2004). In the last case, distortions are clear indicator of high sedimentation rate with rapid burial and compaction.

But, ooids are partially micritized (micrite envelope), suggesting a long exposure with light at the water–sediment interface in a setting rich in cyanobacteria and related to a low sedimentation rate (Kendall & Alsharhan, 2011; Reid & Macintyre, 1998), supporting a turbulent environment. Note that ooids are locally totally homogenously micritized (not a rim) which may indicate the same early, more intense process or a later micritization during burial.

The lack of fossils is also typical of such oolitic open environments dominated by constant water flow favorable to their precipitation. Within F6B, some samples are peloid and oncoid–

rich, representing a more protected area, in contact with the shoal, but not subject to a strong wave action (back–shoal environment). F6 is also locally characterized by bioclastic grainstone (F6A, Fig. 7D), representative of high–energy environments and interpreted herein as immerged sandbars developed in intertidal, protected area. Bioclasts indeed include calcimicrobes, echinoderms and gastropods, abundant in open lagoon and lagoonal environments. No ooids were reported in this facies. No meniscus, bridging and gravitational cements or parallel laminations, typical of beachrock or emerged sandbar, have been observed in F6A. Duostominids found mostly in this facies (Fig. 7D) are common in such environments (Haas et al., 2010; Peybernes et al., 2016b). F6 is characterized by high–energy facies, deposited in shoals or sandbar, depending on the content. Due to the lack of continuous reef barrier and the huge amount of lagoonal facies observed in Dalnegorsk limestone, shoal are defined as the main relief acting as a barrier, protecting the lagoonal part from the open ocean, and probably migrating through time according to sea–level fluctuations and energy regimes (Fig. 9). The development of massive oolitic shoals, due to abrasion of oolitic sand, can produce a significant part of the high amount of carbonate mud deposited in the lagoon as recently demonstrated by Trower et al. (2019).

46 6.5 – Slope environment – F7

F7 is represented by laminated polygenic deposits (Fig. 8) interpreted as slope, turbiditic and debris–flow sediments. Centimetric grading deposits, composed of uncemented bioclasts, subrounded limestone clasts (lithified carbonate from the platform) and subrounded volcanic grains interpreted as altered volcanic fragments and tephras, characterize this facies and occur only in this depositional environment. The morphology and composition of this deposit clearly indicate regular sudden input of carbonate material from the platform within a deeper environment on the flanks of the system (Flügel, 2004). Flames (Fig. 8D) and convolutes structures confirm the rapid influx of material above a soft sediment, represented herein by homogeneous micrite. Volcanic grains suggest an erosion, reworking and transport of volcanic deposits possibly mainly concentrated within small channels or canyons along the slope of the system (Counts et al., 2018). Bioclasts, dominated by shallow–water organisms, attest to inputs from the active edge of the platform. Lithified clasts are interpreted as broken pieces of the early lithified part of the platform, to the favor of storms, strong swells, earthquakes, or gravitation–related flank collapses. Turbiditic inputs are intercalated with homogeneous muddy sediment (micrite), indicating a primarily quiet environment, below the fair– and probably storm–weather waves action. In the Niznii–Rudnik Mine (Loc. 4), F7 have been found in association with F8 confirming a deep setting along the middle to lower slope of the system.

The absence of wave ripples and hummocky or swaley cross stratifications reinforce the interpretation that these deposits cannot be related to storm deposit within the lagoon (Flügel, 2004).

6.6 – Pelagic environment – F8

F8 is a mud–dominated facies (Fig. 8E), related to a quiet environment. The occurrence of radiolarians and filaments (pelagic bivalve shells) is typical of deep, basinal open–marine environment. This facies has been widely described in pelagic settings from Triassic and Jurassic systems (Chablais et al., 2010b; Kuhry et al., 1976; Peybernes et al., 2016b; Vera &

Molina, 1998). Apart from radiolarians (recrystallized into calcite), F7 is composed only of carbonate bioclasts or mud, indicating a deposit above the ACD (Aragonite Compensation Depth) and CCD (Calcite Compensation Depth). Occasionally, shallow–water bioclasts occur (ooids, brachiopods), but not on the form of sudden input as described for F7. No sedimentary structures (e.g., laminations, grading, flames) have been observed in F8 and the shallow–water clasts (i.e., ooids, oncoids, brachiopods, echinoderms and ostracods) seem to be related to

47 gravitational transport of grains from the platform to deeper environment. Associated with F7, F8 is interpreted as lower slope to basinal facies set up on the ocean floor.

7 – Biostratigraphy

The Dalnegorsk limestone blocks are among the very rare occurrences of well–

preserved Upper Triassic shallow–water limestone from the Panthalassa Ocean. Thanks to their huge cropping volume, they represent a significant wealth of information to better constrain how and where carbonates were formed and evolved in the Panthalassan domain. It is therefore of the utmost importance to constrain the age of these deposits to compare our results with coeval systems and bring new, precise data for the paleogeographical knowledge of the Panthalassa Ocean. Paleontological revisions are also crucial for the understanding of marine life evolution during Late Triassic time and how organisms have colonized these carbonated niches across this huge ocean.

7.1 – General interpretations

The stratigraphy of the Dalnegorsk limestone, poorly constrained, is defined based on coral and conodont associations (Buryi, 1997a,b; Punina, 1997, 1999) (Table. 4, Fig. 11).

Recently, Vuks & Punina (2018) published a paper on Upper Triassic foraminifers of the Dalnegorsk limestone, with samples collected at the end of the 20^th century by T. Punina. The foraminiferal determinations proposed by Vuks & Punina (2018) are however unsatisfactory and as a result, their stratigraphic interpretation is unreliable. Most described foraminifers are not age significant. The only foraminifer that, according to them, would point to a Carnian age (i.e., ‘Pilamminella gemerica’ in pl. 2, figs. 2–3) is misidentified (relics of pores indicate that these forms are in fact micritized involutinids). See i) the sigmoidal coiling and total absence of the typical 90° change in plane of coiling and final planispiral stages that are characteristic of Pilamminella and ii) few relics of pores in fig. 2.2: upper median portion and fig. 2.3: upper left portion of the tests.

The biostratigraphy presented in the current work is based on foraminiferal associations and aims at refining previously proposed ages. Preservation of the sampled large frame builders, such as corals or sponges, does not permit proper identification for biostratigraphy.

Megalodontid bivalves, very common in our samples, have been widely identified in the Upper Triassic limestone units of similar settings of systems from Panthalassa (Chablais et al., 2010a;

48 Onoue et al., 2009; Peybernes et al., 2016b; Rigaud et al., 2015a; Senowbari–Daryan et al., 2010a; Tamura, 1983; Yancey & Stanley, 1999). However, due to their very long extension from Lower Devonian to Lower Jurassic, they cannot be used as accurate biostratigraphic markers. Occurrence of Plexoramea cerebriformis (Fig. 5F) (Anisian–Norian) and Microtubus communis (Fig. 6H) (Norian–Rhaetian) confirm a Triassic age. Other identified microproblematica, encrusted sponges and calcimicrobes extend beyond the Triassic.

7.2 – Foraminiferal associations and previous studies

Numerous age significant foraminifers have been found in the Dalnegorsk limestone

Dans le document Sedimentology, biostratigraphy and diagenesis of Upper Triassic shallow–water carbonates from Japan and Russian Far East: New investigations on the Panthalassa Ocean (Page 48-63)