The Devonian–Carboniferous Boundary In

The Devonian–Carboniferous boundary in the stratotype area (SE Montagne Noire, France) Raimund Feist, Jean-Jacques Cornée, Carlo Corradini, Sven Hartenfels, Markus Aretz, Catherine Girard

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Raimund Feist, Jean-Jacques Cornée, Carlo Corradini, Sven Hartenfels, Markus Aretz, et al.. The Devonian–Carboniferous boundary in the stratotype area (SE Montagne Noire, France). Palaeobiodi- versity and Palaeoenvironments, Springer Verlag, 2020, 10.1007/s12549-019-00402-6. hal-03005525

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The Devonian-Carboniferous boundary in the stratotype area (SE 1 2 3 Montagne Noire, France) 4 5 6 1* 2 3 4 7 Raimund Feist • Jean-Jacques Cornée • Carlo Corradini • Sven Hartenfels • Markus 8 Aretz5 • Catherine Girard1 9 10 11 12 1 ISEM, UMR 5554, CNRS, IRD, Université Montpellier, Montpellier, France 13 14 2 Géosciences Montpellier, CNRS-Université de Montpellier-Université des Antilles, 15 16 Pointe à Pitre, (FWI), France 17 3 18 Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Cagliari, Italy 19 4 20 Institut of Geology and Mineralogy, University of Cologne, Cologne, Germany 21 5 Géosciences Environnement Toulouse, UPS, CNRS, IRD, avenue Edouard Belin, 22 23 Toulouse (France) 24 25 26 27 * Corresponding author : [email protected] 28 29 30 31 Abstract 32 33 Sections with continuous sedimentation across the Devonian-Carboniferous (D-C) boundary 34 35 in the Montagne Noire allow to build a virtual transect from shoreline to deep basin. 36 Nearshore facies characterise the D-C boundary stratotype and neighbouring sections at La 37 38 Serre in the Cabrières klippen domain and offshore facies are present at the Col de Tribes and 39 40 Puech de la Suque sections in the Mont Peyroux nappe domain. Both domains exhibit 41 42 equivalents of the Hangenberg Black Shale (HBS). At La Serre, an initial regressive trend is 43 44 indicated by the presence of oculated trilobites in the topmost pre-HBS Wocklumeria 45 Limestones. Above the HBS level, regressive depositional conditions characterise oolitic 46 47 deposits that comprise lithic erosional flows with an admixture of transported shallow-water 48 49 biotas. Maximum regression is recognised with the deposition of coarse breccias and local 50 51 features of emergence prior to the first appearance of Protognathodus kockeli. The oolites are 52 53 superseded by the transgression of outer shelf deposits. In the nappe domain, the HBS is 54 55 intercalated in outer ramp nodular limestones, and it exhibits detrital elements pointing to its 56 regressive nature. The regressive trend culminates than reverses when post-HBS carbonate 57 58 sedimentation resumes. Protognathodus kockeli appears in the post HBS carbonates. 59 60 Associated oculated trilobites indicate shallower bathymetric conditions than those of the pre- 61 62 63 1 64 65 HBS Wocklumeria Limestones. Thereafter, replacement of sighted trilobites by blind ones and 1 2 the protognathodid biofacies by facies dominated by siphonodellids indicate a deepening 3 trend. The near- and off-shore sites of the D-C transition permit correlation of short-term 4 5 bathymetric fluctuations with faunal turnovers and entries of biostratigraphic markers. 6 7 8 9 Keywords Devonian-Carboniferous boundary • Montagne Noire • biostratigraphy • 10 11 sedimentary dynamics • bathymetric trends • near-shore – off-shore correlation 12 13 14 15 16 Introduction 17 18 19 20 Palaeozoic rocks of the Montagne Noire, at the external margin of the southern French 21 Massif Central, underwent a complex poly-phased Variscan deformation that resulted in a 22 23 piling of large-scale, south-facing recumbent folds emplaced during the latest Viséan (e.g. 24 25 Arthaud 1970; Echtler 1990). Synorogenic flysch sedimentation comprises gravitational 26 27 mass-flows with large, up to kilometric-sized olistolitic blocks of various pre-tectonic ages 28 29 (Cabrières klippen, “Ecailles de Cabrières”) (Engel et al. 1978). The rocks were affected by 30 31 syntectonic metamorphism with decreasing intensity in the highest parts of the nappe pile, 32 Hence, the south-eastern inverted portions of the Mont Peyroux nappe, including the 33 34 Cabrières klippen (Fig. 1), are composed of highly fossiliferous sedimentary rocks with only 35 36 locally very low-grade metamorphic overprint (conodont Colour Alteration Index between 2 37 38 and 4, Wiederer et al. 2002). This allows facies analyses and investigations on fine-scaled bio- 39 40 and chemostratigraphy to be conducted in good conditions of preservation. 41 42 During Devonian through early Carboniferous times the nappe successions exhibit an 43 almost continuous carbonate succession that was deposited on a low-angle, flat ramp. After 44 45 deposition in coastal environments related to the initial Devonian transgression on an eroded 46 47 early Palaeozoic hinterland (Feist 1985), the depositional conditions subsequently changed 48 49 with an increase in both depth and distance from the shore. In the Mont Peyroux nappe, the 50 51 Devonian-Carboniferous transition is located in a succession of outer ramp nodular limestones 52 (“supragriottes”, Boyer et al. 1968), which contain a Hangenberg Shale horizon of a few 53 54 decimetres in thickness. Conversely, contemporaneous environmental conditions were 55 56 different in the source area from where the erratic Cabrières klippen originated including the 57 58 La Serre olistolite where the D-C boundary stratotype was defined (Paproth et al. 1991). In 59 60 this area the uppermost Devonian exhibits increasingly strong influence from a near-by 61 62 63 2 64 65 shallow shoal or even emerged land that resulted in dominantly mixed carbonate and 1 2 siliciclastic near-shore sedimentation at the Devonian-Carboniferous transition. Consequently, 3 two domains, near-shore Cabrières klippen and off-shore nappe successions, are represented 4 5 in the south-eastern Montagne Noire (Fig. 1). Description and comparison of these two 6 7 domains using biostratigraphical and sedimentological markers to evaluate the currently 8 9 debated D-C boundary definition is the purpose of this contribution. 10 11 12 13 14 Cabrières klippen 15 16 Sections spanning the Devonian-Carboniferous boundary in different blocks among 17 18 the Cabrières klippen were first compared by Engel et al. (1980-81, fig. 6). While in most 19 20 cases late Tournaisian strata conformably overstepped various levels of the Famennian lower 21 and middle Griotte formations, a complete Devonian through early Carboniferous succession 22 23 is exclusively exposed at La Serre. At this site, local facies of the late Famennian through 24 25 early Tournaisian Griotte Group (Feist 1985; Korn and Feist 2007), including transitional 26 27 beds across the D-C boundary, were subsequently investigated in trenched sections (Feist and 28 29 Flajs 1987a, b; Flajs and Feist 1988; Kaiser 2009; Cifer et al. 2017; updates herein). 30 31 La Serre E’ D-C boundary stratotype section 32 33 The GSSP for the base of the Carboniferous is defined in trench LS-E’ (Fig. 2a) on the 34 35 southern slope of La Serre Hill at about 125 m S of the top 252 and 500 m to the E of La 36 37 Rouquette farmhouse, ca. 2.5 km S of Cabrières (Paproth et al. 1991; Feist et al. 2000). Many 38 39 studies were conducted at the La Serre D-C stratotype section concerning conodonts (Engel et 40 41 al. 1980-81, Feist and Flajs 1987a; Flajs and Feist 1988; Girard 1994; Kaiser 2009), 42 ammonoids (Becker and Weyer 2004; Korn and Feist 2007), ostracods (Casier et al. 2002), 43 44 trilobites (Flajs and Feist 1988; Brauckmann et al. 1993; Feist and Petersen 1995), 45 46 brachiopods (Legrand-Blain & Martinez-Chacon 1988), corals (Semenoff-Tian-Chansky 47 48 1988), fish (Derycke et al. 1995), and foraminifera and algae (Vachard 1988). In addition, 49 50 detailed data on microfacies (Flajs and Feist 1988; Casier et al. 2002), isotope and element 51 52 geochemistry (Brand and Legrand-Blain 1993, 2004; Buggisch & Joachimski 2006; Bábek et 53 al. 2016) are available. 54 55 56 The section displays the upper part of the local facies of the Montagne Noire Griotte 57 58 Group straddling the D-C boundary (Figs. 2a, 3). The exposed base of the section, below Bed 59 64, comprises well bedded, compact, grey-beige platy calcilutites with intercalated 60 61 62 63 3 64 65 calcisiltites. The former are organized into dm-thick beds with horizontal to oblique plane 1 2 bedding, convolutes and ripple-marks at their top. As such they are interpreted as fine- 3 grained, distal turbidites. The facies becomes predominantly nodular towards the top (Beds 4 5 64-67), and terminates with a layer of dissociated micritic limestone nodules in a clayey 6 7 matrix (Bed 68). These contain a few poorly preserved iron-oxide coated Wocklumeria sp., 8 9 giant (up to 5mm long) leperditiid-like ostracods and numerous, often fragmented small 10 11 trilobites. The varied association of the latter is dominated by sighted taxa, phacopids 12 13 (Omegops) and proetids (Pseudowaribole) (Fig. 4), whereas blind forms characterizing the 14 deeper off-shore domain such as Helioproetus are rare, and in particular, Dianops and 15 16 Chaunoproetus are missing. This may indicate a near-shore (inner ramp to lagoonal?), photic 17 18 environment that recalls the shallow shelf paleoenvironment of the Velbert area (NW Rhenish 19 20 Slate Mts) (Michels 1986). Topmost nodules of Bed 68 contain rich conodont faunas with the 21 22 last Bispathodus costatus, Bi. ultimus ultimus, representatives of the Palmatolepis gracilis 23 24 group and Pseudopolygnathus marburgensis trigonicus of the Bi. ultimus Zone. Though early 25 protognathids are missing, the presence of Siphonodella praesulcata recorded by Kaiser 26 27 (2009) may indicate the higher part of this zone. 28 29 The topmost Wocklumeria yielding nodular limestones are superseded by thin cm- 30 31 thick, greyish shale that tends to be squeezed out locally by gravity slide parallel to bedding, 32 33 but it is well represented in neighbouring sections (trench C and F, Fig. 5). This compressed 34 35 level (between Beds 68 and 69) is thought to be equivalent to the Hangenberg Black Shale 36 37 (HBS). It is overlain by well-bedded, graded biodetrital oolitic limestones with reworked 38 39 and/or transported bio- and litho-clasts. This 3.5 m thick package can be divided into the 40 lower (Beds 70-81) and upper (84-97) calcoolitic units. These are separated by the 41 42 intercalation of 80 cm-thick clayey, sandy and conglomeratic levels (Beds 82-83) with oolites 43 44 and reworked upper Famennian blocks and pebbles: the intermediate siliciclastic-calcareous 45 46 unit (Flajs and Feist 1988). The lower calcoolitic unit displays normal or inversely graded 47 48 bedding and its upper part contains oolitic lime breccias. The lower part of the upper 49 50 calcoolitic unit displays lime lithic oolitic grainstones with hummocky cross stratification, 51 changing upwards into fine-grained bioclastic wackestone to mudstone. The clayey interval 52 53 between the oolitic units comprises matrix supported grains, and dm-sized reworked 54 55 Famennian boulders that display microkarst features on the surface. 56 57 The lithic-oolitic coarse-grained limestones are interpreted as being deposited in a 58 59 shallow, high energy depositional setting in the inner ramp (upper shoreface) (Wright and 60 61 62 63 4 64 65 Burchette 1992; Merzeraud 2017). The clayey-conglomeratic beds of the intercalated 1 2 siliciclastic-calcareous unit are interpreted as mass-flow deposits in the inner ramp, with an 3 erosional surface at the bottom and boulders issued from an emergent area. To sum up, from 4 5 faunal content and facies analysis, these sediments were deposited in an oscillating upper 6 7 littoral shoreface, foreshore, and lagoon depositional environments, with interbedded debris 8 9 flows. Consequently, these rocks indicate a major regression representing the time equivalent 10 11 of the regressive phase of the Hangenberg Event, probably equivalent to the Hangenberg 12 13 Sandstone (HSS) at Drewer, Rhenish Slate Mts. (Kaiser 2009; Becker et al. 2016). 14 15 The upper oolitic unit is overlain by grey pyrite-rich calcilutites with few oolites, rich 16 17 in brachiopods and trilobites, and microsparitic crinoidal limestones (Beds 98-100). Above 18 19 Bed 100 the facies change abruptly into nodular fine-grained marly limestones that make up 20 the topmost portion of the Montagne Noire Griotte Group. This 1.5 m-thick succession is best 21 22 exposed 20 m to the W of LS-E’ in an auxiliary trench (“LS-E”). These limestones yielded 23 24 few goniatites and deep-water anthozoans (Becker and Weyer 2004), smooth ostracods, and 25 26 blind trilobites including Liobolina that indicate a deeper offshore, lower ramp environment. 27 28 The GSSP of the D-C boundary is located within the upper calcoolitic unit, between 29 30 beds 88 and 89 (Fig. 2a) after the decision and ratification of ICS/IUGS in 1990, following 31 32 the proposal of the relevant International D-C boundary Working Group (Paproth et al. 1991). 33 34 The decision was based on the first occurrence of Siphonodella sulcata, but since the 35 beginning this decision encountered criticisms due to difficulties to interpret intermediate 36 37 morphotypes between Si. praesulcata and Si. sulcata (Ji et al. 1989, p. 72; Ziegler & 38 39 Sandberg 1996). Since the presence of Si. sulcata is recognized in Bed 84b (Kaiser 2009) the 40 41 position of the GSSP is currently called into question. With regard to the problem of 42 43 controversial assignments of early siphonodellids, the potential using protognathodids as a 44 45 tool to define the D-C boundary has currently gained interest (Corradini et al. 2016). In this 46 context, the successive appearance of index forms of this group in section LS-E’ is of utmost 47 48 importance. 49 50 51 Early protognathodids, i.e. Protognathodus collinsoni and Pr. meischneri, are present 52 throughout the succession after their entry in Bed 70. Protognathodus kockeli occurs at the 53 54 base of the upper oolitic unit (Bed 84a) defining the onset of the Pr. kockeli Zone above the 55 56 levels of maximum regression (top Bed 81). This correlates with sections in the Rhenish Slate 57 58 Mountains where Pr. kockeli invariably enters above the regression of the Hangenberg 59 60 Sandstone (Becker et al. 2016). Protognathodus kuehni enters in the middle of the upper 61 62 63 5 64 65 oolitic unit (Bed 93) shortly above the GSSP. Early and late protognathodids occur 1 2 abundantly among many reworked Late Devonian conodonts in Beds 98-100. The Si. 3 bransoni Zone starts in Bed 98 with the entry of Si. bransoni (Fig. 6). Thus, the Pr. kockeli/Si. 4 5 bransoni zonal boundary coincides with the top of the calcoolitic units. 6 7 8 Among macrofaunal biostratigraphical markers at the D-C boundary ammonoids are 9 virtually absent with the exception of a single specimen of Acutimitoceras intermedium in 10 11 Bed 90 characterizing the basal Carboniferous. Trilobites are absent in the lower calcoolitic 12 13 units and appear sporadically in the siliciclastic debris-flow unit (Beds 82-83) with poorly 14 15 preserved fragments of Pudoproetus sp. and ?Mirabole sp. The former usually does not 16 17 appear prior to the entry of Protognathodus kockeli and this might questionably indicate an 18 19 extension of the Pr. kockeli Zone below Bed 84a. Trilobites are relatively abundant in the 20 upper calcoolitic unit (Feist in Flajs and Feist 1988). New collections indicate that 21 22 Pudoproetus mediterraneus and Brachymetopus germanicus are present as early as Bed 84. 23 24 Conversely, Belgibole abruptirhachis, a worldwide marker of the kockeli Zone (Yuan and 25 26 Xiang 1998) has not been found below Bed 89 and Winterbergia (?Eowinterbergia) cf. 27 28 funirepa occurs later in Beds 90-92. Instead of a late entry of these two index taxa at La Serre, 29 30 their absence in Bed 84 might result from sampling bias rather than from facies control. 31 32 La Serre C and F sections 33 34 La Serre trench C (LS-C) and trench F (LS-F) sections are situated respectively 100 m 35 36 east and 150 m west of the present Global Stratotype Section and Point (GSSP) (Fig. 5). 37 38 Though different in thickness, these sections exhibit a rather similar succession. 39 40 The section LS-C (Fig. 5e) exposes a similar succession than that of the section LS-E’, 41 42 but indicates a slightly more distal deposition. In contrast to the stratotype section, the 43 44 Hangenberg Black Shale (HBS) equivalent (Bed 54k) is well-developed (30 cm thick) below 45 46 the regressive lower calcoolitic unit (Beds 54l to 55g) (Cifer 2016; Cifer et al. 2017). 47 Conodonts and trilobites recorded below the HBS are the same as in LS-E’ 68 indicating the 48 49 presence of the higher part of the Bispathodus ultimus Zone. Whereas only reworked 50 51 conodonts were found in the calcoolitic and siliciclastic units, the presence of the Si. bransoni 52 53 Zone is established in the superseding yellow nodular limestones (Bed 58u), based on 54 55 lithology. The uppermost strata of the Montagne Noire Griotte Group, i.e. the yellow nodular 56 57 limestone above the oolites, are topped by a recurrent oolitic bed with reworked bioclasts with 58 plant remains. This bed yielded a rich and divers siphonodellid association including 59 60 Siphonodella quadruplicata and Si. crenulata (Engel et al. 1980-81, fig. 6). This bed is 61 62 63 6 64 65 superseded by black marls and chert bearing shales with numerous compressed plant remains 1 2 (Galtier et al. 1987). These rocks are considered representing a particular facies of the 3 Lydiennes Formation (basal St. Nazaire Group, Korn and Feist 2007). 4 5 6 The section LS-F (Fig 5a) has a 20 cm-thick HBS horizon (Bed 18) with numerous 7 8 phytoclasts of terrestrial origin (R. Brocke, det.). It is superseded by three carbonate units and 9 two clayey beds with Famennian reworked boulders (Bed 22) or oolitic boulders (Bed 25). 10 11 The lower carbonate unit (Beds 19-21) comprises fine-grained and bioclastic platy beds and 12 13 dm-thick oolitic beds above. The top of Bed 21 with Protognathodus collinsoni (Fig. 6) 14 15 displays karst erosional gullies, which indicate of a local subaerial surface (Fig. 5a). The 16 17 intermediate siliciclastic units (Beds 22 and 25) are much thicker (ca 2.5 m) then in trench 18 LS-E’, and the intercalated calcoolitic unit (Beds 23-24) is questionably emplaced by gravity 19 20 slide. The uppermost oolitic unit (Beds 26 to 28) is rich with accumulations of large-sized, 21 22 dissociated brachiopod shells and fewer remains of oculated trilobites including Belgibole 23 24 abruptirhachis. Rare cases of reworked Omegops occur as intraclasts. Above Bed 28, the 25 26 uppermost coarse-grained oolitic unit changes into micritic, grey cephalopod limestones 27 28 superseded by siliceous shales (lydites). The succession from Beds 18 to 28 is interpreted as a 29 slightly more proximal setting than LS-C and LS-E. 30 31 32 33 34 Geochemistry 35 36 Though caution is warrated in the investigation of almost entirely reworked and/or 37 38 transported materials, studies on carbon and oxygen isotopes have been conducted on oolitic 39 40 limestones at La Serre LS-E’ by Buggisch and Joachimski (2006) and on brachiopod shells by 41 42 Brand et al. (2004) for the succession across the D-C boundary. Temperatures found by Brand 43 44 et al. (2004) are not well constrained, but suggest a cooling peaked near the D-C boundary. 45 Strontium isotope studies on unaltered brachiopod shells at La Serre E’ reflect changes in 46 47 continental weathering patterns and are congruent with data obtained by Bábek et al. (2016). 48 49 Elevated percentage of detrital proxies was interpreted as an increase of siliciclastic input, 50 51 which possibly reflects records of a glacio-eustatic sea-level drop. Furthermore, the cooling 52 53 indicated by the positive oxygen isotope peak preceding the carbon cycle perturbation, as 54 indicated by a peak in carbon isotopes, record global carbon cycle perturbations prior to the 55 56 D-C boundary (Bábek et al. 2016, Kaiser et al. 2008). 57 58 59 60 61 62 63 7 64 65 Mont Peyroux nappe domain 1 2 The Devonian-Carboniferous transition in the nappes is characterized by distal ramp 3 4 settings of uniform grey nodular cephalopod limestones (Montagne Noire Griottes Group, 5 6 Korn and Feist 2007) in which a pluri-decimetres thick Hangenberg Shale is invariably inter- 7 bedded. At Mont Peyroux, the Col de Tribes and Puech de la Suque sections have been 8 9 studied in detail, whereas at Pic de Bissous only preliminary data are available to date (Korn 10 11 and Feist 2007; Aretz et al. 2016). 12 13 14 15 Col des Tribes section 16 17 The Col des Tribes section (Figs. 2b, 7) is situated about 2 km N of Causses-et-Veyran 18 19 and about 1.5 km to the SSW of the Puech de la Suque section. This section displays a 20 21 complete inverted succession from upper Frasnian (approximately Lower Kellwasser horizon) 22 23 to the Tournaisian (Lydiennes Formation) (Girard et al. 2014). This section is rather similar to 24 25 the Puech de la Suque, but is depositionally in a slightly more proximal position with regard 26 27 to its geographical position on the inverted limb of the Mont Peyroux nappe. At Col des 28 Tribes, previous studies across the D-C boundary beds concerned ammonoids (Price and 29 30 House 1984; Becker and Weyer 2004; Korn 2005), actinopterygian fishes (Gauchey et al. 31 32 2014), as well as conodonts and carbonate microfacies (Girard et al. 2014). 33 34 The Devonian-Carboniferous boundary interval starts with cephalopod-rich mudstone 35 36 to wackestone beds (Beds CT70 to CT70-3 of Girard et al. 2014) with reduced eyed 37 38 (Haasproetus) and blind (Chaunoproetus) trilobites (Fig. 8), ostracods, bivalves, brachiopods, 39 40 crinoids, and filaments (pelagic bivalves) deposited in an outer platform setting. This 2.8 m- 41 42 thick package can be attributed to the late Famennian Bispathodus ultimus Zone (Girard et al. 43 2014). It is superseded by 0.5 m of dark shales (between Beds CT70.3 and DC1) comprising a 44 45 thin inter-bed of dolomitized yellowish limestone. The shale interval is overlain by 3 m of 46 47 thick wackestone- to packstone-beds with poorly preserved ammonoids (Levels DC1 to 48 49 CT75). In the lower meter of these limestones, ammonoids are associated with crinoidal 50 51 remains. Blind trilobites (Liobolina) occur at the top beds (upper part of level CT75) 52 53 preceding the black bedded cherts (“Lydiennes Formation”) of the St. Nazaire Group. 54 55 56 57 The Beds DC2 and DC3 just above the Hangenberg Shale equivalent contain 58 59 Protognathodus kockeli. The Si. sulcata Zone is present in levels DC4 and DC5 (Fig. 6). The 60 61 62 63 8 64 65 Si. bransoni Zone is recognized in level DC6 (equivalent of the level CT70-7 in Girard et al 1 2 2014). Above, the base of the Si. duplicata Zone has been discriminated in Bed DC13. Bed 3 CT72 belongs to the Si. jii Zone due to the first occurrence of Siphonodella cooperi. The Si. 4 5 sandbergi Zone is defined by the occurrence of Pseudopolygnathus triangulus triangulus, 6 7 and then the Si. quadruplicata Zone is recognized just before the black chert deposits in level 8 9 CT75. 10 11 12 13 Puech de La Suque section 14 15 16 The Puech de la Suque (PS) section (Figs. 2c, 9) is situated along a vineyard track on 17 18 the eastern and south-eastern slope of Puech de la Suque hill about 2.2 km SE of Saint 19 Nazaire-de-Ladarez. The overturned section exposes a continuous succession of upper 20 21 Famennian to mid-Tournaisian strata belonging to the Montagne Noire Griotte Group and St. 22 23 Nazaire Group (Korn and Feist 2007). The Devonian-Carboniferous boundary transition is 24 25 situated in the upper part of the Montagne Noire Griotte Group (“supragriottes” Boyer et al 26 27 1968). It was studied for conodonts (Boyer et al. 1968; Girard 1994; Kaiser et al. 2009), 28 ostracods (Lethiers and Feist 1990, Casier et al. 2001), ammonoids (Korn and Feist 2007), 29 30 sedimentology (Michel 1971, Casier et al. 2001) and geochemistry (Kaiser et al. 2008; Bábek 31 32 et al. 2016, Fačevicová et al. 2016). 33 34 The investigated topmost limestone succession of the Montagne Noire 35 Wocklumeria 36 Griotte Group (Beds PS85 to PS90) consists of bedded, nodular dm-thick micritic limestones 37 38 with dominant cephalopods and filaments (pelagic bivalves), blind trilobites (Chaunoproetus) 39 40 and predominantly Thuringian-type ostracods (Casier et al. 2001) that indicate a quiet off- 41 42 shore environment below the photic zone. The topmost Bed 90 (of Girard 1994) is rich in 43 44 Wocklumeria denckmanni and conodonts including Bispathodus costatus, Bi. ultimus, 45 representatives of the Palmatolepis gracilis group and Si. praesulcata of the Bispathodus 46 47 ultimus Zone. No early protognathodids occur. The top of Bed PS90 displays iron coatings. It 48 49 is overlain by 5 cm of yellowish shale with few calcareous iron-coated nodules, followed up 50 51 by 1 cm of thick stripped shale, then by 26 cm of dark shale (Fig. 10), which is thought to be 52 53 equivalent to the Hangenberg Black Shale horizon (HBS) of the pelagic realm. We 54 55 determined the mineralogy of the HBS and quantified their components by X-ray diffraction 56 at the University of Montpellier using Philips X'Pert PRO MPD diffractometer and 57 58 PANalytical X'Pert HighScore Plus version 3.0.5 software; each sample was analysed during 59 60 1 h between 5 and 60° Theta, with a 0.033° Theta step. The presence of organic matter and 61 62 63 9 64 65 oxidised pyrite between Beds Hjb2 and HB1 probably indicates momentarily dysoxic 1 2 conditions. Thin-sections and X-ray analysis of the silty greyish to black shales, devoid of 3 carbonates, reveal the presence of detrital quartz and muscovite grains that make up to 80% of 4 5 the whole rock as well as berlinite grains, a high temperature mineral (Fig. 10). The 6 7 allochthonous origin of the sand indicates erosion of distant emergent areas, and emphasises 8 9 the regressive nature of this level. Using the maximum and minimum amounts of quartz and 10 11 muscovite (easily transportable), two minor regressive/transgressive cycles can be interpreted 12 13 from Beds PS 89 to Hjt1. Neither conodonts nor spores were found in the shales and among 14 scarce cephalopod remains poorly preserved and undeterminable pyritic protoconchs of 15 16 ammonoids occur. Besides the bearing of innumerable dissociated bivalves, preliminary study 17 18 reveals the presence of rare scolecodonts and acritarchs (R. Brocke, det.). The shales are 19 20 topped by 10 cm of silty, yellowish decalcified mudstone (Fig. 2a: star) with numerous 21 22 bivalves and filaments (pelagic bivalves), in which a specimen of Bispathodus stabilis ssp., a 23 24 few specimens of the Polygnathus communis group, and indeterminable ramiform conodonts 25 were found. The shales are superseded by the reappearance of carbonate sedimentation with 2 26 27 m of grey-yellowish, nodular, dm-thick bedded mudstone to wackestone. At the base, nodules 28 29 of biomicritic limestones (Bed PS10a, Fig. 2c) in shaly matrix yielded the first 30 31 Protognathodus kockeli and partly silicified ostracods, bivalves, filaments (pelagic bivalves) 32 33 and abundant goniatites (Acutimitoceras subbilobatum, A. intermedium). In the body- 34 35 chambers of the latter oculated juvenile trilobites (Belgibole abruptirhachis and Winterbergia 36 (?Eowinterbergia) funirepa) are abundant (Fig. 8). The exclusively normally oculated nature 37 38 of the trilobites points to level-bottom conditions within the photic zone and a minimum in 39 40 paleobathymetry. Protognathodus kockeli enters in Bed PS10a (Bed numbers from Girard, 41 42 1994) (Fig. 6). Bed PS 11 yielded Gattendorfia subinvoluta in a fine-grained matrix with 43 44 crinoid ossicles and trilobite remains. Above the base of the Protognathodus kockeli Zone, 45 enters the succession in Bed PS 11 (Bed 12a of Kaiser 2009), 46 Siphonodella sulcata Si. 47 bransoni in Bed 13, Si. duplicata in Bed 15, Si. jii in Bed 17, Pseudopolygnathus triangulus 48 49 triangulus indicating the base of the Si. sandbergi Zone in Bed 23, and Si. quadruplicata in 50 51 Bed 25. This nodular limestone succession corresponds to the Hangenberg Limestone of the 52 53 Rhenish Slate Mountains. It progressively changes upwards into shales with fewer and fewer 54 55 limestone nodules of late early Tournaisian age. Abundant silicified trilobite remains and 56 ostracodes occur in the highest limestone nodules (Bed 28) preceding the black bedded cherts 57 58 of the St. Nazaire Group (Lerosey-Aubril 2005, Lethiers and Feist 1990). In these beds, 59 60 predominance of ostracodes of Thuringian eco-type and blind trilobite individuals such as 61 62 63 10 64 65 Liobolina (Fig. 8) indicate bottom conditions below the photic zone while siphonodellids 1 2 dominate the conodont associations (Girard 1994). 3 Due to diagenetic overprinting, δ13C values at Puech de la Suque are not available 4 5 (Buggisch and Joachimski 2006), but the analyses of major and trace elements by Bábek et al. 6 7 (2016) provided the same trends as those observed at La Serre LS-E’ section, assuming a 8 9 rapid sea-level drop at the Hangenberg Event. For both areas, analyses of organic carbon 10 11 (TOC) do not reveal characteristic lithological features for black shales and very little or no 12 13 evidence for water dysoxia/anoxia (Kaiser et al. 2008; Bábek et al. 2016), as found at Puech 14 de la Suque where only 1 cm of stripped shales occur. 15 16 17 18 19 Bathymetric trends and nearshore – offshore correlations 20 21 According to the model of Engel et al. (1980-81) the Cabrières sedimentary klippen 22 23 were intercalated, after gravity transport, into higher parts of the flysch succession [Laurens 24 25 Flysch Group of Korn and Feist (2007), Laurens-Cabrières Group of Vachard et al. (2017)] 26 that composes the normal limb of the Mont Peyroux nappe. The recumbent fold nappes, such 27 28 as the Mont Peyroux nappe, and the concomitant syntectonic sedimentary transport with 29 30 gravitational flows of exotic blocks, such as the Cabrières klippen, were emplaced with the 31 32 same north (internal) to south (external) polarity (Engel 1984). Thus, a southward directed 33 34 movement of nappe emplacements (e.g. Arthaud 1970; Echtler 1990) implies that the source 35 36 area of the exotic Cabrières klippen, including La Serre, has to be farther to the north than the 37 site from where the nappes originated. This model is supported by sedimentary and biofacies 38 39 criteria that indicate shallower depositional conditions of the Devonian-Lower Carboniferous 40 41 succession in the klippen that were closer to the shoreline (Feist and Echtler 1994) than the 42 43 nappes. 44 45 46 At La Serre sea-level fluctuations across the D-C boundary levels were previously 47 48 interpreted by Flajs and Feist (1988) and Casier et al. (2002) based on section LS-E’. These 49 50 interpretations are refined herein based on new data and observations from section LS-E’ and 51 52 the adjacent sections LS-C and LS-F. In the upper part of the Famennian, preceding the HBS 53 54 horizon, the water depth decreases, with depositional environments changing from outer to 55 56 mid ramp (LS-E’, Beds 56-67; LS-C, Beds 52-54; LS-F, Beds1-17) to inner ramp setting of 57 the lower carbonate/oolitic units. This regressive trend is also indicated by the presence of 58 59 predominantly oculated trilobites and leperditiid-like ostracods that characterise nearshore 60 61 62 63 11 64 65 environments in LS-E’ Bed 68 (= equivalents of the upper Wocklumeria Limestones). The 1 2 onset of oolitic sedimentation marks a pronounced regression that culminates in the 3 deposition of lime breccias (LS-E’ 80-81 and LS-C 55f-g) and in a local emergence (above 4 5 Bed 21 in trench LS-F), below the debris flow deposits. Noticeably, the correlation between 6 7 the three investigated sections (Fig. 11) at La Serre show that this emergence surface is 8 9 erosional westwards as several beds of the lower calcoolitic unit of section E’ are missing in 10 11 section F. The existence of an emergence surface is also indicated by 1) Devonian boulders 12 13 with karst phenomena in the debris flows at La Serre E’ and C, indicative of neighbouring 14 emerged areas, 2) evidence of erosional hardgrounds and hiatuses in sections of other 15 16 Cabrières klippen (e.g. Tourière, Engel et al. 1980-81: fig. 6) and 3) by the overwhelming 17 18 percentage of reworked late Frasnian (ancyrodellids) to Famennian conodonts in calcoolitic 19 20 units, indicative of the removal of at least 50 meters of Late Devonian outer-shelf carbonate 21 22 deposits (Feist 1985). Above the lower carbonate/calcoolitic unit a transgressive trend occurs 23 24 with first the deposition of the debris flow in inner ramp setting, then the deposition of 25 carbonate units. At the onset of the upper oolitic unit Protognathodus kockeli appears (Bed 26 27 LS-E’ 84). This transgressive trend, progressively developed in succeeding beds with lithic- 28 29 oolitic deposits of shoreface to mid-ramp environments changes upwards into nodular 30 31 mudstones of the outer ramp (offshore). 32 33 Regarding bathymetry, the nappe-sections Col des Tribes and Puech de la Suque are 34 35 clearly in a more distal position than the sections at La Serre. The latest pre-Hangenberg 36 Griotte limestones of the Bispathodus ultimus Zone, in particular, are homogenously 37 38 biomicritic, nodular and devoid of shallow-water biotas. The extremely rich content of 39 40 clymenids (Wocklumeria) in the last beds preceding the HBS level indicates a pelagic outer 41 42 platform environment where no regressive trend is discernable. In particular, the presence of 43 44 blind and reduced eyed trilobites, such as Chaunoproetus, Haasproetus and Struveproetus 45 (Fig. 8), emphasizes level-bottom habitats that remained below light penetration, and this 46 47 contrasts with equivalent levels at La Serre. This contrast is interpreted as a result of water 48 49 depth below the photic zone in the Mont Peyroux nappe sections where the record of the 50 51 regression remained cryptic. However, based on detrital influxes, the regressive trend 52 53 becomes obvious as outer platform (Wocklumeria Limestone) environments change to a mid- 54 55 platform setting during deposition of the Hangenberg Shale above Bed Hjb2. The maximum 56 regression is supposed to correlate at the top of the yellow mudstone above the HBS, within a 57 58 level between Hjt2 and PS10a (Fig. 10) prior to the entry of Protognathodus kockeli (Beds 59 60 DC2 at Col des Tribes and PS10a at Puech de La Suque). This extremely condensed level 61 62 63 12 64 65 between the yellow mudstone and the first limestone nodules with Protognathodus kockeli 1 2 must correspond, arguably, to the emergence level at La Serre (top Bed 21 in LS-F). Above, a 3 transgressive trend developed from mid platform to outer platform settings during the early 4 5 Tournaisian part of the Montagne Noire Griotte Group, succeeded by a basinal, poorly 6 7 oxygenated setting of the Lydiennes Formation. 8 9 The correlation of near-shore sections at La Serre and off-shore sections of the Mont 10 11 Peyroux nappe are based on sedimentological, geochemical, palaeoecological and 12 13 biostratigraphical criteria. In this regard the palinspastic position of the Devonian- 14 15 Carboniferous transition in both areas can be comparably placed on a proximal-distal transect: 16 17 the La Serre olistolite in a near-shore situation under direct influence of coarse erosional input 18 from the close-by source area and, on the other hand, the Puech de la Suque and Col de Tribe 19 20 nappe sections were in a distal outer shelf position with fine-grained, long-distance detrital 21 22 input (Fig. 11). The distance between both sites remains unknown; however Engel et al. 23 24 (1980-81) demonstrated that both are intimately linked to the same tectono-sedimentary 25 26 complex of the Mont Peyroux nappe and, as such, their source areas may not have been 27 28 separated by considerable distances. 29 30 31 32 Conclusions and perspectives 33 34 The Montagne Noire offers the unique opportunity to compare and potentially 35 36 correlate condensed distal basinal settings with contemporaneous near-shore carbonates that, 37 38 following the HBS level, stood under direct influence of an emerged hinterland. As such the 39 latter reflect sea-level variations corresponding to the degree of intensity and nature of detrital 40 41 input from the near by source area. Regardless of the overwhelming percentage of reworked 42 43 conodonts in these near-shore sediments, the first appearances of index forms such as 44 45 Protognathodus kockeli, Pr. kuehni, and Siphonodella bransoni allow the succession to be 46 47 dated. The top of the lower calcoolitic unit and the intermediate siliciclastic unit bear evidence 48 49 of maximum regression which can be correlated with the top of the yellow organo-detrital 50 mudstones that superseds the HBS in the outer-shelf sections of the nappe domain. In the 51 52 latter, the maximum regression occurred at the end of the HBS shale deposits and slightly 53 54 before the onset of the post-event carbonate sedimentation that yield the first Protognathodus 55 56 kockeli. The reappearance of outer ramp griotte limestones may initially correspond to 57 58 shallower bathymetric conditions than those of pre-Hangenberg times, as indicated by the 59 60 presence of trilobites exclusively with large eyes. This initially relatively shallower period 61 62 63 13 64 65 might correspond to the time-interval of the upper oolitic unit at La Serre. Thereafter, from 1 2 the beginning of the Siphonodella bransoni Zone onwards, transgressive trends lead to sub- 3 photic zone deep water conditions in both areas with blind trilobites and the increase of 4 5 siphonodellids. The correlation of bathymetric trends between both sites is of utmost 6 7 importance in the search to locate the turnover between the Hangenberg regression and the 8 9 onset of the post-Hangenberg transgression, a crucial criterium in the debate to redefine the 10 11 D-C boundary. Ongoing work focuses on search for sections in intermediate position between 12 13 proximal and distal sites on the transect La Serre – Puech de la Suque. It is speculated that in 14 such intermediate, mid-ramp sites fine-grained carbonate sedimentation resumes, superseding 15 16 the HBS level beyond reach of coarse detrital input. Such post-HBS carbonates would be 17 18 contemporaneous with the condensed yellow mudstones at the top of the HBS at Puech de la 19 20 Suque. The SE Montagne Noire constitutes a great potential for recovering such sites. 21 22 23 24 The D-C boundary sections of the Montagne Noire emphasise the importance of the 25 Hangenberg Event affecting marine biotas in both near- and off-shore domains. As in the 26 27 Rhenish Slate Mountains and Carnic Alps for example, the biotic turnover is particularly 28 29 marked in the outer shelf domain; it seems the same in the near-shore domain of La Serre, 30 31 though the evidence is obscured by reworking processes during deposition of detrital input. 32 33 As elsewhere, the Hangenberg Event in the Montagne Noire is characterised mainly by 34 35 eustatic perturbations, notably regressive trends in the topmost Wocklumeria Limestones and 36 during the HBS and HSS, followed up by a global transgression above. Among level-bottom 37 38 biotas with light receptors, trilobites are most sensitive to changing conditions in the degree of 39 40 light penetration to their habitats. With the onset of the HBS regression they lost all lower- 41 42 rank taxa (genera and species) and none of them survived the crisis. The taxonomic 43 44 origination rate following the HBS/HSS regression in both domains is outstanding, leading to 45 evolutionary lineages after the explosion of and that characterise 46 Pudoproetus Winterbergia 47 the early Carboniferous radiation. As such, the position of the D-C boundary at the base of the 48 49 post-event transgression is favoured, as it coincides with a marked faunal overturn that 50 51 permits tracing a time-line from shore to off-shore domains. 52 53 54 55 Acknowledgements 56 57 We are greatly indebted to the owner of “la Rouquette” farm, Maryse Boisgontier for her kind 58 59 permission to investigate on her ground at La Serre, to Dieter Korn (Berlin), Rainer Brocke 60 61 62 63 14 64 65 (Frankfurt) and Bruno Milhau (Lille) for determining ammonoids, palynomorphs and 1 2 ostracods, respectively. We thank Claudia Spalletta (Bologna) and Jeff Over (Geneseo, NY) 3 for their insightful comments on the manuscript. Sandra Kaiser (Stuttgart) provided 4 5 information on conodonts of her own collections from LS-E’ and PS, and helpfully 6 7 contributed to the discussion on biostratigraphical significance of index taxa. Anne-Lise 8 9 Charruault and Suzanne Jiquel (Montpellier) helped efficiently in the field. We thank B. 10 11 Fraisse who performed the RX diffraction analysis (Réseau de Rayons X et Gamma Z, 12 13 Ressource technologique de l'Université de Montpellier) and Doriane Delmas and Christophe 14 Nevado for performing thin slices of rock-samples. The research was supported by the ANR 15 16 Project ECODEV (ANR-13-BSV7-005) and the Projet Marcon (Labex CeMEB). This is 17 18 contribution ISEM 2019-072. 19 20 21 22 The authors declare that they have no conflict of interest. 23 24 This article does not contain any studies with human participants or animals performed by any 25 of the authors. 26 27 28 29 References 30 31 Aretz, M. (2016). The Kulm Facies of the Montagne Noire (Mississippian, southern France). 32 33 Geologica Belgica, 19, 69–80. 34 35 Aretz, M., Corradini, C., Cornée, J.-J., Feist, R., & Girard, C. (2016). A new look on the 36 37 Devonian – Carboniferous Boundary. Fieldguide to the DCB section in the SE Montagne 38 39 Noire. 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Oxford: Blackwell Science. 59 60 61 62 63 20 64 65 Yuan, J., & Xiang, L. (1998). Trilobite fauna at the Devonian-Carboniferous boundary in 1 2 South China (S-Guizhou and N-Guangxi). Special Publication 8, National Museum of 3 Natural Science, Taiwan, 1–281. 4 5 6 Ziegler W. (1959). Conodonten aus Devon und Karbon Südwesteuropas und Bemerkungen 7 8 zur bretonischen Faltung (Montagne Noire, Massiv v. Mouthoumet, Span. Pyrenäen). 9 Neues Jahrbuch für Geologie und Paläontologie. Monatshefte, 7, 289–309. 10 11 12 Ziegler, W. (1969). Eine neue Conodontenfauna aus dem höchsten Oberdevon. Fortschritte 13 Geologie von Rheinland und Westfalen, 17, 179–191. 14 15 Ziegler, W. & Leuteritz, K. (1970). Alter, Fazies und Paläogeographie der Oberdevon / 16 17 Unterkarbon-Schichtenfolge an der Seiler bei Iserlohn. Fortschritte Geologie von 18 19 Rheinland und Westfalen, 17, 679-732 20 21 Ziegler W., & Sandberg, C.A. (1996) Reflexions on Frasnian and Famennian Stage boundary 22 23 decisions as a guide to future deliberations. Newsletters on Stratigraphy, 33, 157–180. 24 25 26 27 28 29 Figure captions 30 31 32 33 Fig.1. Geological map of Devonian and early Carboniferous deposits in the south-eastern 34 35 Montagne Noire (Mont Peyroux nappe and klippen of Cabrières) after Engel et al. (1980-81). 36 37 a: location of the Montagne Noire (France); b: situation of Devonian-lower Tournaisian in the 38 39 nappes and Cabrières klippen of the southern Montagne Noire; c: location of D-C boundary 40 41 sections: La Serre (GSSP), Puech de la Suque, Col des Tribes, Pic de Bissous. 42 Lithostratigraphic terms after Korn and Feist (2007). Modified from Aretz (2016). 43 44 45 46 Fig. 2. Field views: a. Trenched stratotype section E’ at La Serre. The GSSP of the D-C 47 48 boundary was ratified at the base of Bed 89 within the upper oolitic unit. b. Inverted DCB 49 50 section at Col des Tribes. The excavation corresponds to the Hangenberg Shale interval. c. 51 52 Inverted Hangenberg Black Shale (HBS) equivalent topped by yellow mudstone (star) at 53 Puech de la Suque; Bed PS 9 = Bed 90 in Girard (1994), and on Figure 6 (this study); first 54 55 Protognathodus kockeli in superseding limestone nodules (Bed PS 10a). Scale: the hammer is 56 57 40 cm long. 58 59 60 61 62 63 21 64 65 Fig. 3. a-d: carbonate microfacies of the pre-HBS latest Famennian limestone and the post- 1 2 HBS lower and upper oolitic units in the stratotype section La Serre E’ (described in Flajs and 3 Feist (1988) and Casier et al. (2002)); a: calcisiltite; b-c: coarse-grained lithic oolitic 4 5 grainstone; d: oolitic wackestone to packstone with brachiopods-oolites are tangential to 6 7 radial. Right: log of the section and ranges of important conodont species. Legend: Oo: oolite, 8 9 Br: brachiopod, Ex: extraclast, Ech: echinoid. Abbreviations: ac.: aculeatus; c.: communis; g.: 10 11 gracilis; p.: purus. Green line: the D-C Boundary, dotted lines: base of conodont zones. 12 13 Conodont Zones after Corradini et al. (2017). 14 15 16 Fig. 4 Significant oculated trilobites in topmost Wocklumeria Limestones of the stratotype 17 18 section LS-E’, Bed 68 at La Serre. Deposit: Collections of Montpellier University (UM-IP). 19 20 a–c Omegops accipitrinus (Phillips, 1841), (a) fragmentary cephalon UM-IP 839, dorsal view, 21 22 (b) fragmentary cephalon UM-IP 840, lateral view, (c) pygidium UM-IP 841, dorsal view. d–e 23 24 Rabienops wedekindi (Richter and Richter, 1926), (d) cephalon, dorsal view, (e) pygidium, 25 dorsal view. f–h Pseudowaribole sp. A aff. macrops Yuan, 1988 in Yuan and Xiang, 1998, (f) 26 27 incomplete cranidium UM-IP 842, dorsal view, (g) juvenile cranidium UM-IP 843, dorsal 28 29 view, (h) incomplete librigena UM-IP 844, dorsal view. i–j Pseudowaribole conifera Richter 30 31 and Richter, 1926, (i) incomplete cranidium UM-IP 845, dorsal view, (j) pygidium UM-IP 32 33 846, dorsal view. k Waribole warsteinensis Richter and Richter, 1926, pygidium UM-IP 847, 34 35 dorsal view. Scale bars correspond to 0.5 mm. 36 37 38 Fig. 5. Facies and depositional environment in section La Serre F and C. a-d (LS-F): a: 39 40 lithostratigraphic succession. b: cm-bedded limestone of the lower calcoolitic unit. c: 41 42 erosional surface, plane view; arrow indicates dissolution of Bed 21. d: erosional surface, 43 44 perpendicular view; arrow indicates dissolution of Bed 21. e: (LS-C): lithostratigraphic 45 succession; numbering of beds is from Cifer et al. (2017). 46 47 48 49 Fig. 6. Stratigraphically significant conodonts from the base of the Carboniferous. The 50 51 material is stored in the collections of Montpellier University (UM CND). a: Protognathodus 52 53 kockeli (Bischoff, 1957), upper view of element UM CND 1 (Col des Tribes, level DC2); b: 54 55 Protognathodus kockeli (Bischoff, 1957) transitional form to Pr. kuehni Ziegler and Leuteritz, 56 1970, upper view of element UM CND 2 (Puech de la Suque, PS10A); c: Siphonodella 57 58 bransoni Ji, 1985, upper view of element UM CND 3 (Puech de la Suque, PS13); d-e: 59 60 ?Siphonodella cf. bransoni (LSE' 98), d: upper view of element UM CND 4, e: lower view of 61 62 63 22 64 65 element UM CND 4; f: Protognathodus kuehni Ziegler and Leuteritz, 1970, upper view of 1 2 element UM CND 5 (Col des Tribes, DC4); g: Protognathodus collinsoni Ziegler, 1969, 3 upper view of element UM CND 6 (La Serre trench F, LSF21); h: Protognathodus collinsoni 4 5 Ziegler, 1969, transitional form to Pr. kockeli Bischoff, 1957 upper view of element UM 6 7 CND 7 (La Serre trench F, LSF21), i-j: Siphonodella bransoni Ji, 1985 i: upper view of 8 9 element UM CND 8, j: lower view of element UM CND 8 (La Serre E’, LSE' 98) 10 11 12 13 Fig. 7. Devonian-Carboniferous transition at Col des Tribes section. Left: carbonate 14 microfacies: wackestones with cephalopods, crinoids and benthic ostracods. Right: log of the 15 16 section and distribution of conodont species. Green line: the D-C Boundary, dotted lines: base 17 18 of conodont zones. Conodont zones after Becker et al. (2016b) and Corradini et al. (2017). 19 20 Legend: Ech: echinoid, G: ammonoid; T: trilobite; Ob: benthic ostracod. Abbreviations: Bi.: 21 22 Bispathodus, Br.: Branmehla, Pa.: Palmatolepis, Po.: Polygnathus, Pr.: Protognathodus, Ps.: 23 24 Pseudopolygnathus, Si.: Siphonodella, com.: communis, gr.: gracilis, HBS: Hangenberg 25 Shale. 26 27 28 29 Fig. 8. Stratigraphically and palaeoecologically significant blind and reduced-eyed trilobites 30 31 in topmost Wocklumeria Limestones at Col des Tribes (e) and Puech de la Suque (b-d), 32 33 oculated trilobites from the Pr. kockeli Zone at Puech de la Suque (f-k), blind trilobite from 34 35 the Si. quadruplicata Zone at Puech de la Suque (a) and Col des Tribes. Deposit: Collections 36 of Montpellier University (UM-IP). a Liobolina sp., cephalo-thorax with displaced librigena 37 38 UM-IP 848, b–c Struveproetus ocellatus Feist in Feist et al., 2000, (b) cephalon UM-IP 849, 39 40 lateral view, (c) dorsal view, d Chaunoproetus palensis (Richter, 1913), pygidium UM-IP 41 42 850, dorsal view, (e) Haasproetus cf. aprickensis (Feist in Feist et al., 2000), incomplete 43 44 pygidium UM-IP 851, dorsal view, f–h Winterbergia (?Eowinterbergia) funirepa Feist in 45 Flajs and Feist, 1988, (f) librigena UM-IP 852, dorsal view, (g) cranidium UM-IP 853, dorsal 46 47 view, (h) pygidium UM-IP 854, dorsal view, i–k Belgibole abruptirhachis (Richter and 48 49 Richter, 1951), (i) fragmentary cranidium UM-IP 855, dorsal view, (j) librigena UM-IP 856, 50 51 dorsal view, (k) juvenile pygidium UM-IP 857, dorsal view. Scale bars correspond to 0.5 mm. 52 53 54 55 Fig. 9. Devonian-Carboniferous transition at Puech de la Suque section. Left: carbonate 56 microfacies. Right: log of the section and distribution of conodont species. Green line: the D- 57 58 C Boundary, dotted lines: base of conodont zones. Conodont zones after Becker et al. (2016b) 59 60 and Corradini et al. (2017). Legend: F: filament, G: ammonoid, B: brachiopod; Ob: benthic 61 62 63 23 64 65 ostracod; T: trilobite. Abbreviations: Bi.: Bispathodus, Br.: Branmehla, M.: Mehlina, Pa.: 1 2 Palmatolepis, Po.: Polygnathus, Pr.: Protognathodus, Ps.: Pseudopolygnathus, Si.: 3 Siphonodella, ac.: aculeatus, c.: communis, gr.: gracilis, m.: marburgensis, p.: purus, tr.: 4 5 triangulus. HBS: Hangenberg Shale. 6 7 8 9 Fig. 10. X-ray analysis of the Hangenberg Black Shale (HBS) equivalent at Puech de la Suque 10 11 section. The undulated surface at top of bed PS90 is locally coated by iron hydroxydes. This 12 13 surface probably results in post depositional fluid circulations and dissolutions because of 14 contrasting lithologies (limestones / shales) in the inverted and compacted succession. 15 16 T/R: transgression/regression. HBS: Hangenberg Black Shale equivalent. 17 18 19 20 Fig. 11. Facies- and conodont-based correlations of D-C boundary sections from near-shore 21 22 (klippen of Cabrières) to distal off-shore (nappes) environments. The red line indicates the 23 24 end of the maximum regression. (a), a virtual coastal to basinal transect with HBS level in 25 black (b) (after Flajs and Feist 1988, updated). Abbreviations: Bi.: Bispathodus, Pr.: 26 27 Protognathodus, Ps.: Pseudopolygnathus, Si.: Siphonodella, tr.: triangulus. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 24 64 65 Figure 1

a Montagne Noire b c Pic de Bissous

Lodève Pic de Castres Bissous

Cabrières St Pons La Serre Mont Peyroux Péret Minervois 0 10 20 km nappes Cabrières klippes Vailhan La Serre

Laurens

Nazaire -de -Ladarez Gabian Laurens-Flysch Group: Puech de la Suque Viséan limestone / flysch

St Nazaire Group: Tournaisian lydites / limestone

N Devonian / lowermost Col des Tribes 2 km Carboniferous limestones Figure 2

D/C 89 88 73 72 HBS

68 a

9 70-3

HBS HBS

10a 10b1 10b2

71 b c Figure 3 Beds Facies Deposi. T/R Conodont distribution LA SERRE E' m environ. cycles Zones Nodular limestone Mid to outer ramp 5 100 Lithic bioclastic, Si. Faci es 99 Fine-grained, trilobites Inner to d 98 mid ramp bransoni Bioclastic limestone, oolites Lagoonal 97 96 95 94 Lithic oolitic grainstone, Inner ramp 93 brachiopods, crinoids 92 91 90 Br 89 Oolithic packstone Lagoonal 88 T 4 87 Lithic oolitic grainstone sulcata Si.

86 kockeli Pr. 85 Tempesti tes DCB Oo 84 b a c Laminated packstone, Ex microbreccia, ooids, 83 some clay, micritic boulders

Oo Debris fl ow 3 82 Br 81b Oolithic microbreccia Inner ramp Ex 81a Breccia 80 Littoral 79 78 Poorly structured 77 lithic oolite and b 76 fii nely bedded lithic oolite 75 R 74 with bioclasts 73 2 Tempesti tes? 72

Ech ultimus Bi. 71 70 69 Ech 68 Greyish bioclastic, nodular Oo 67 66 Greyish mudstone a 65 1 Calcisiltite, 64 plane beding, 63 convolutes, Turbi di tes ripple-marks 62 Mid to 61 outer ramp Greyish mudstone, 60 nodular 59 58 Calcisiltite 57 Palmatolepis g. expansa g. Palmatolepis communis c. Polygnathus inornatus Polygnathus gracilis g. Palmatolepis sigmoidalis g. Palmatolepis symmetricus Polygnathus obliquicostatus Polygnathus marburgensis Ps. trigonicus gonioclymeniae g. Palmatolepis collinsoni Protognathodus meischneri Protognathodus purus p. Polygnathus kockeli Protognathodus kuehni Protognathodus subplanus p. Polygnathus Pseudopolygnatusprimus Bispathodus costatus Bispathodus Branmehlainornata Branmehlasuprema bispathodus Bispathodus vulgaris stabilis Bispathodus anteposicornis ac. Bispathodus spinulicostatus Bispathodus stabilis stabilis Bispathodus Bispathodusultimus aculeatus Bispathodusac. Mehlina strigosa Mehlina 0 56 Siphonodellapraesulcata Siphonodellasulcata Siphonodellabransoni Figure 4 Click here to access/download;Figure;Fig.4_trilos.jpg Figure 5 LA SERRE F LA SERRE C

Beds Facies Deposi. e environ. a m Blackish siliceous shale with plant debris Basin T/R Beds Facies Deposi. Oobioclastic limestone environ. cycles m 7 Bedded «lydites»- Outer Basin ramp Irregular surface to 59b coated by clay Nodular limestone 59a Lithic, bioclastic basin 58zd oolitic limestone 58z - zc 58y Thin-bedded 58v - x bioclastic limestone 6 6 58u d Oobioclastic limestone E W Mid to Nodular limestone changing upward into 58t3 Outer mudstone outer ramp 28 ramp 58t 2 58t1 T Lithic oolitic grainstone, Bedding 27 brachiopods, crinoids 58e-s 5 5 58d Cephalopod limestone 58 a-c Thin-bedded wackest. Sandy grainstone 26 57d Coarse-grained packstone, Bedded bioclastic Inner 57c and oolitic to mid microbreccia, ooids, 57b 25 some clay, grainstone ramp oolitic boulders 57a Tempesti tes ? 4 4 Debris flow Inner c ramp 56f-o Quartz, W E calcite, 56e magnetite, 24 Debris flow Oolitic limestone 56b sodalite, berlinite, muscovite Inner Dark clay ramp 23 Oolitic and bioclastic Fine grained limestone 3 laminated packstone, 3 microbreccia, ooids, 56a some clay, 55g micritic boulders Clay rich breccia with 22 Famennian boulders Breccia 55f Normally graded Debris fl ow grainstone to 55e packstone, plane Subaerial erosionnal surface bedding, 21 oolites, extraclasts R b 2 Bioclastic and oolitic 2 55d 20 c Turbi di tes ? Mid limestone b 55 ramp/ Thin bedded lithic Inner 55a1-3 slope ramp 54n oobioclastic limestone 19 Undulated cm bedded bioclastic limestone 54m Grainstone to packstone, plane bedding, oolites, Bedding 18 54l extraclasts Black shale HBS Quartz, 17 Greyish bioclastic, HBS Weathered calcite, 16 nodular 54k dark berlinite, 1 15 1 14 Grayish mudstone silty shale muscovite 13 54J Grayish mudstone, 12 Calcisiltite Turbi di tes 54 c 11 nodular, silty biocl. top 10 Mid to 54a 9 Grayish mudstone Outer 8 outer c ramp b Calcisiltite ramp 67 Calcisiltite 53 5 a 4 Grayish mudstone, 3 Grayish mudstone, 2 nodular 52d3 nodular 0 1 0 52d2 Figure 6

abcde

f g hi j Figure 7 Beds Facies Deposi. T/R Conodont distribution Zones environ.cycles

COL DES TRIBES m Crinoids

Cm bedded cherts (black “lydites”) Si. quadru 5 -plicata Si. sulcata Si. Si. bransoni Si. duplicata Si. Si. quadruplicata Si. Si. praesulcata Si. Si. cooperi Si. Pr. kockeli Pr. Bi stabilis ssp. stabilis Bi Ps. triangulus triangulus triangulus Ps. Ps. primus Ps. purus Polygnathus subplanus Polygnathus purus Polygnathus purus meischneri Protognathodus carina com. Po. Pr. collinsoni Pr. kuehni Pr. Po. com. communis com. Po. inornatus Po. primus Ps. CT75

Ob Greyish wackestone Si. sandbergi G with goniatites, flaments,i trilobites, 1 mm benthic ostracods, with subordinate crinoids, CT74 brachiopods and entomozoans

CT 73 Si. jii

C C CT 72.1 4 CT 72 ? DC 19 DC 18 CT 71.2 1 mm DC 17 Outer Si. duplicata DC 16 ramp DC 15 CT 71.1 DC 14 DC 13 CT 71

DC 12 dentatus com. Po. DC 11 DC 10 T Si. bransoni DC 9 DC 8 DC 7 CT 70.7 DC 6 DC 5 Si. sulcata DC 4 CT 70.6 DC 3 Pr. kockeli DC2 CT 70.5 G DC 1 CT 70.4 Blackish, weathered silty clay, HBS one recrystallized ? ? 3 limestone bed 1 mm CT 70.3 Bi. aculeatus Bi. Br. inornata Br. costatus Bi. Bi. spinulicostaus Bi. Br. suprema Br. ultimus Bi.

Ob gracilis gr. Pa. C Bi. ultimus CT 70.2 Outer Greyish wackestone ramp with goniatites, T some fi lament, 1 mm slight increase in trilobites, crinoids and brachiopods in the upper part 1

CT 70.1

CT 70 New 0 Figure 8 Click here to access/download;Figure;Fig.8_trilos.jpg Figure 9 T/R Facies Log Samples Deposi. Conodont distribution numbers environ. cycles Zones

PUECH de la SUQUE after m Girard (1994) Po. c. communis c. Po. dentatus c. Po. inornatus Po. primusprimus Ps. Po. longiposticus Po. Ps. marginatus Ps. Bi. ac. aculeatus ac. Bi. ssp. stabilis Bi. inornata Br. spinulicostatus Bi. symmetricus Po. carina c. Po. collinsoni Pr. meischneri Pr. kockeli Pr. purus p. Po. subpurus p. Po. multistriatus Ps. kuehni Pr. Si. quadruplicata Si. M. strigosa M. Si. carinthiaca Si. cooperi Si. obsoleta Si. sandbergi Si. Si.. praesulcata Si.. sulcata Si. bransoni Si. duplicata Si. jii Si. Ps. tr. inaequalis tr. Ps. Facies triangulus tr. Ps. PS14 5 PS28

Shales and PS27B calcareous Basin nodules Si.

1mm quadruplicata PS27A PS10B 4

1mm PS26

PS25 PS24 Si. sandbergi PS23 Nodular, argillaceous limestone, goniatites, PS22 3 trilobites 10 A PS21

PS20 Si. jii PS19 F PS18 Crinoidal wackestone Outer PS17 with brachiopods, 2 PS16 trilobites ramp Si. duplicata HJ t2 PS15 PS13-14 Si. bransoni G Greyish wackestone PS12 with goniatites Si. sulcata Ob PS11 Crinoidal wackestone T b2 Pr. kockeli b1 PS10 Yellowish silty clay with B a calcareous nodules Yellowish silty clay Mid- G B HBS outer Blackish silty clay R 1mm 1 Yellowish silty clay ramp PS90 PS90PS90 PS89 PS88 PS87 G Bi. ultimus PS86 Greyish wackestone with goniatites, some PS85 filaments, trilobites Outer and brachiopods ramp in the upper part 0 Bi. ultimus Bi. Bi. costatus Bi. Br. suprema Br.

PS81 gracilis gr. Pa. Pa. gr. expansa gr. Pa. Ps. m. trigonicus m. Ps. Pa. gr. gonioclym. gr. Pa. Figure 10

Thin sections, Samples Semi quantitative Relative T/R cycles natural light estimate from sea level RX analysis QUARTZ MUSCOVITE HEMATITEMAGNETITEGOETHITEBERLINITECALCITE BRUCITE DANALITESPINELCORINDON

cm PS 11 - +

55 10 B2 T3 10 B1 10 A Normally oculated trilobites kockeli HJ t2 R3 HJ t1 1 mm HB8 HB7 Silty claystone (quartz: light dots) HB6 T2 HB5 HBS HB4 Oxydized pyrite HB3 HB2 R2 HB1 T1 1mm HJ b2 HJ b1 R1 Stripped shale (organic 0 matter: dark; calcite: light) Wockl um SK9 = PS 90 PS 89 Percentages 10A 70/80 % 60/70% 50/60% 40/50% 30/40% 20/30% 10/20% Present/10% Trends: Decrease Increase Figure 11

North TOURIERES LA SERRE COL DES TRIBES South a PUECH DE LA SUQUE b Emergent and tectonized late Frasnian and Famennian La Serre F pelagic limestones Subaerial unconformity m Debris flow, early transgression 7 Sea level Earliest Tournaisian oolitic limestone, transgression Fair weather Earliest Tournaisian wave base nodular limestones 6 La Serre C Storm wave Oolitic base limestone, Pre HBS Famennian limestones end regression, Decalcifi ed local emergence marlstones 5 Si. quadruplicata Hangenberg La Serre E' Shale

4 Si. bransoni Col des Tribes Puech de m Si. bransoni la Suque Pr. kuehni 3 Pr. kockeli/ Si. sulcata Pr. collinsoni Si. quadruplicata

2 Max. regression Si. quadruplicata Pr. collinsoni Ps. tr. triangulus Ps. tr. triangulus

1 Si. jii T Si. duplicata Si. jii Pr. collinsoni ? Si. duplicata Si. bransoni Si. bransoni 0 Bi. ultimus Pr. kuehni/Si. sulcata Si. sulcata 1 Si. praesulcata Pr. kockeli Pr. kockeli 1 Hangenberg Si. praesulcata Shale R Bi. ultimus 0 Si. praesulcata 0 Klippen of Cabrières Basinal lydites Calcareous turbidite Mont Peyroux Nappe Long term 1 Bi. ultimus Off shore limestone Silty shale T/R cycle Shallow water Debris fl ow Si. praesulcata limestone 0