Muriel Vidal
email: mvidal@univ-brest.fr

Alfredo Loi
email: alfloi@unica.it

Marie-Pierre Dabard
email: marie-pierre.dabard@univ-rennes1.fr

Arnaud Botquelen

A Palaeozoic open shelf benthic assemblage in a protected marine environment

Keywords: Barrier-lagoon environments, taphonomy, facies analysis, Katian (Ordovician), Armorican Massif

A Late Ordovician benthic assemblage containing trilobites (Colpocoryphe, Onnia) and diploporid echinoderms (Aristocystites) taxa that are usually typical of open shelf environments is preserved in protected marine settings in the lower part of the Kermeur Formation (Armorican Massif, NW France). A facies analysis carried out on the Veryac'h section (Crozon Peninsula) allows identification of four sedimentary facies (SF), ranging from the bay/lagoon domain (SF1 and SF2) to the back-barrier (SF3) and barrier (SF4) domains. A benthic fauna comprising trilobites, brachiopods and diploporids is found in the SF1 and SF2.

.

Introduction

Numerous studies have been carried out on Ordovician shelf successions belonging to the northern Gondwana margin in order to explain the relationships between benthic fauna distributions and related depositional environments. Results from these studies have led to the recognition of "biofacies" or benthic associations along an open shelf profile, especially for trilobites (Fortey andOwens, 1978, 1987;[START_REF] Henry | Un biofaciès à Trilobites Homalonotidae dans l'Ordovicien de la marge nord-gondwanienne: implications paléobiologiques et paléogéographiques[END_REF][START_REF] Vidal | Le modèle des biofaciès à trilobites: un test dans l'Ordovicien inférieur de l'Anti-Atlas, Maroc[END_REF][START_REF] Zhiyi | Llanvirn-early Caradoc trilobite biofacies of western Hubei and Hunan, China[END_REF], 2003;[START_REF] Turvey | Early Ordovician (Arenig) trilobite palaeoecology and palaeobiogeography of the South China plate[END_REF] and brachiopods [START_REF] Villas | Braquiópodos del Ordovícico medio y superior de las Cadenas Ibéricas Orientales[END_REF][START_REF] Villas | New Caradoc brachiopods from the Iberian Chains (Northeastern Spain) and their stratigraphic significance[END_REF][START_REF] Villas | Caradoc through Ashgill brachiopods from the Central-Iberian zone (central Spain)[END_REF][START_REF] Havlíček | Climatic changes and development of benthic communities through the mediterranean Ordovician[END_REF][START_REF] Havlíček | Upper Ordovician brachiopod assemblages of the Carnic Alps, Middle Carinthia and Sardinia[END_REF]. These biofacies are valuable tools for palaeogeographic reconstructions [START_REF] Fortey | The Arenig Series in South Wales: Stratigraphy and Palaeontology. I. The Arenig Series in South Wales[END_REF][START_REF] Henry | Paléoenvironnements et dynamique de faunes de trilobites dans l'Ordovicien (Llanvirn supérieur-Caradoc basal) du Massif Armoricain (France)[END_REF][START_REF] Henry | Stratification thermique probable des eaux marines sur la marge gondwanienne (Massif Armoricain) pendant l'Ordovicien (Llanvirn): Implications paléogéographiques[END_REF][START_REF] Fortey | Palaeontological evidence bearing on global Ordovician-Silurian continental reconstructions[END_REF].

The present work shows that, in some particular contexts, benthic taxa that are generally associated with open shelf environments can also be associated with marine protected depositional settings. The Upper Ordovician succession studied here is located on the Crozon Peninsula (Armorican Massif, western France). Sediments were laid down during the sea-level rise following the major sea-level fall recorded in the foliaceus graptolite zone (Sandbian-Katian boundary; [START_REF] Webby | Stratigraphic framework and time slices[END_REF]. This regressive event is recognized in several areas of the northern Gondwana Domain, from the Armorican Massif [START_REF] Robardet | Evolution géodynamique du Nord-Est du Massif armoricain au Paléozoique[END_REF] to the Iberian Domain (Portugal: [START_REF] Henry | Chitinozoaires, Ostracodes et Trilobites de l'Ordovicien du Portugal (serra de Buçaco) et du Massif Armoricain: essai de comparaison et signification paléogéographique[END_REF][START_REF] Paris | Les Chitinozoaires de la Formation de Louredo, Ordovicien supérieur du synclinal de Buçaco (Portugal)[END_REF][START_REF] Paris | Les Chitinozoaires dans le Paléozoïque du Sud-Ouest de l'Europe[END_REF]Spain: Villas, 1992), as well as the Algerian Sahara and central Morocco [START_REF] Videt | Biostratigraphical calibration of third-order Ordovician sequences of the northern Gondwana Platform[END_REF] and other palaeogeographic domains such as Baltoscandia [START_REF] Nielsen | Ordovician Sea Level Changes: A Baltoscandian Perspective[END_REF] and Laurentia (Turinian-Chatfieldian boundary: [START_REF] Ross | Ordovician sea-level fluctuations[END_REF]. In the northern Gondwana Domain, the fall and successive rise of the sea-level coincided with a decline in the endemicity of benthic fauna and the arrival of taxa from Avalonia, Laurentia and Baltica (Havlíčcek, 1989;[START_REF] Cocks | Biogeography of Ordovician and Silurian faunas[END_REF][START_REF] Young | Ordovician sedimentary facies and faunas of Southwest Europe: palaeogeographic and tectonic implications[END_REF]. In the Armorican Massif, the transgressive phase led to the deposition of nearshore successions yielding a poorly diversified benthic fauna [START_REF] Robardet | Ordovician, Silurian and Devonian of the Medio-North-Armorican Domain[END_REF].

The aims of the present study are to (1) identify the depositional environments of these successions, (2) investigate the origin, either autochthonous or allochthonous, of the benthic taxa, and (3) understand the mode of settlement of organisms during the transgressive phase.

The analysed successions comprise the upper part of the Postolonnec Formation (Sandbian) and the lower part of the Kermeur Formation (Katian). An integrated approach involving facies analyses combined with palaeontological and taphonomic observations (e.g., faunal content and preservation mode) is carried out.

Geological context

In the Armorican Massif (Fig. 1), the lower Palaeozoic terrains are subdivided into two palaeobiogeographic units: the Medio-North Armorican Domain (MNAD) and the South Armorican Domain (SAD). In the MNAD, several transgressive-regressive cycles occurred in the Ordovician [START_REF] Paris | Ordovician sedimentary rocks of France[END_REF][START_REF] Paris | Chitinozoan-based calibration of Early-Mid Ordovician transgressive events on northern Gondwana[END_REF][START_REF] Dabard | Evolution de la plateforme paléozoïque centre-armoricaine de l'Ordovicien au Dévonien. 12ème Congrès Français de Sédimentologie, Rennes[END_REF]. The first transgressive phase began in the Floian (Early Ordovician) with the deposition of continental and/or coastal plain facies, and then several cycles succeeded each other in the overlying silty clayey formations until the late Sandbian regressive phase. In the Crozon Peninsula (Fig. 2), the Floian is characterized by thick sandstones of the Grès Armoricain Formation that were deposited in nearshore settings [START_REF] Durand | Le Grès Armoricain. Sédimentologie -Traces fossiles -Milieux de dépôt[END_REF]. These sandstones are overlain by silty-clayey shelf facies of the Postolonnec Formation, which is Dapingian to Sandbian in age [START_REF] Paris | The Ordovician chitinozoan biozones of the Northern Gondwana Domain[END_REF]. Then, the clastic sedimentation continued into the Katian with micaceous sandstones, quartz-arenites and mudstones of the Kermeur Formation (90 to 450 m thick; [START_REF] Plusquellec | Notice explicative de la feuille de Châteaulin, Carte géologique de la France 1/50000[END_REF]. In the studied area, this formation is overlain by the Cosquer Formation, dated as Hirnantian [START_REF] Bourahrouh | Chitinozoaires et palynomorphes de l'Ordovicien supérieur nordgondwanien: impact de la glaciation ashgillienne[END_REF], and interpreted as glacio-marine deposits [START_REF] Hamoumi | Les Schistes du Cosquer (Ordovicien supérieur, Massif armoricain occidental) : une formation glacio-marine marine à la périphérie d'un inlandsis ordovicien[END_REF]. The Postolonnec, Kermeur and Cosquer formations were deposited under stable platform conditions and were affected by weak deformation [START_REF] Rolet | L'évolution géodynamique dévono-carbonifère de l'extrémité occidentale de la chaîne hercynienne d'Europe sur le transect Armorique-Cornwall[END_REF][START_REF] Darboux | Evolution tectonosédimentaire et structuration synmétamorphe des zones externes du segment hercynien ouest-européen : le modèle du Domaine Centre-Armoricain occidental[END_REF] and low-grade metamorphism [START_REF] Paradis | Le métamorphisme hercynien dans le domaine centre armoricain occidental: essai de caractérisation par l'étude des phyllites des formations grèsopélitiques[END_REF] during the Late Devonian-Early Carboniferous.

The diversity of the benthic fauna is variable in these Ordovician sediments. The Postolonnec Formation yields numerous and well-known macrofossil assemblages (Mélou and Plusquellec, 1975a) comprising trilobites [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF], brachiopods [START_REF] Botquelen | Caradoc brachiopods from the Armorican Massif (Northwestern France)[END_REF], bivalves [START_REF] Babin | Mollusques Bivalves et Céphalopodes du Paléozoïque Armoricain[END_REF], ostracods (Vannier, 1986a(Vannier, , 1986b)), graptolites [START_REF] Philippot | Les Graptolites du Massif Armoricain[END_REF][START_REF] Henry | L'apport de Graptolites de la Zone à G. teretiusculus dans la datation de faunes benthiques lusitano-armoricaines[END_REF], echinoderms [START_REF] Chauvel | Recherches sur les Cystoïdes et les Carpoïdes Armoricains[END_REF][START_REF] Chauvel | Sur la présence de Phlyctocystis Chauvel, 1966, échinoderme Cystoïde, dans l'Ordovicien de la Presqu'île de Crozon (Finistère)[END_REF] and gastropods. This diversity is reduced to only a few species in the overlying Kermeur Formation, including brachiopods and trilobites (trinucleids and dalmanitids; [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF] that are reported only from the upper part of the formation. The lower part is characterized by abundant bioturbation with few brachiopods and echinoderm plates (Mélou and Plusquellec, 1975a, 1975b[START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF]. New material sampled by the authors reveals a higher benthic diversity than previously known.

Stratigraphic context

The upper part of the Postolonnec Formation (Fig. 3) consists of clayey silty facies containing sandy beds with hummocky cross-stratifications or siliceous and/or phosphatic concretion-bearing beds and shellbeds. It was deposited in a shelf environment dominated by storm wave action, between the median part of the inner shelf and the outer shelf [START_REF] Loi | Les nodules silico-alumineux: une expression de la condensation sédimentaire sur une plateforme distale[END_REF][START_REF] Loi | Controls of sea level fluctuations on the formation of Ordovician siliceous nodules in terrigenous offshore environments[END_REF][START_REF] Dabard | Relationship between phosphogenesis and sequence architecture: Sequence stratigraphy and biostratigraphy in the Middle Ordovician of the Armorican Massif (NW France)[END_REF]. The bioturbation structures are small and primarily represented by Planolites. Macrofaunas are either randomly dispersed in the clayey siltstones or concentrated in shellbeds. Two types of shellbeds sensu [START_REF] Botquelen | Formation et signification paléo-environnementale des concentrations coquillières: exemples de l'Ordovicien de Sardaigne et du Dévonien du Massif Armoricain[END_REF] can be distinguished: (1) type A, 1 to 5 mm thick, lenticular and made up of a single coquina level; and (2) type B, up to 20 cm thick, continuous and composed of several superposed and amalgamated coquina levels. Trilobites (Marrolithus bureaui) and chitinozoans (Lagenochitina ponceti, L. deunffi and L. dalbyensis biozones; [START_REF] Paris | The Ordovician chitinozoan biozones of the Northern Gondwana Domain[END_REF][START_REF] Paris | Ordovician sedimentary rocks of France[END_REF] yield a Sandbian age for the upper part of the Postolonnec Formation.

The Kermeur Formation overlies the Postolonnec Formation without apparent angular discordance at the outcrop scale. The lower bounding surface is sharp and erosional. It is overlain by a conglomeratic unit, 40 to 70 cm thick, containing numerous ferruginous (Fe) oolites and phosphatic (P) pebbles [START_REF] Deunff | Microfossiles planctoniques du Primaire armoricain. I. Ordovicien du Véryac'h (presqu'île de Crozon)[END_REF][START_REF] Henry | Chitinozoaires, Ostracodes et Trilobites de l'Ordovicien du Portugal (serra de Buçaco) et du Massif Armoricain: essai de comparaison et signification paléogéographique[END_REF][START_REF] Paris | Les Chitinozoaires dans le Paléozoïque du Sud-Ouest de l'Europe[END_REF]. The chitinozoans present in the conglomerate matrix belong to the Euconochitina tanvillensis biozone [START_REF] Paris | Les Chitinozoaires dans le Paléozoïque du Sud-Ouest de l'Europe[END_REF][START_REF] Bourahrouh | Chitinozoaires et palynomorphes de l'Ordovicien supérieur nordgondwanien: impact de la glaciation ashgillienne[END_REF] from the lower Katian [START_REF] Webby | Stratigraphic framework and time slices[END_REF].

Different chitinozoan assemblages of Sandbian age have been observed in the P-pebbles [START_REF] Henry | Chitinozoaires, Ostracodes et Trilobites de l'Ordovicien du Portugal (serra de Buçaco) et du Massif Armoricain: essai de comparaison et signification paléogéographique[END_REF][START_REF] Paris | Les Chitinozoaires dans le Paléozoïque du Sud-Ouest de l'Europe[END_REF]; some belong to the L. deunffi biozone and others to the L. dalbyensis biozone. These microfauna data indicate a partial reworking of the upper part of the Postolonnec Formation linked to the late Sandbian-early Katian sea-level fall [START_REF] Paris | Palaeozoic in Western Brittany (Outline of the Armorican geological history and geological itinerary in the Crozon Peninsula)[END_REF].

Material and Methods

The Postolonnec and Kermeur formations crop out in the Crozon Peninsula along the Mort-Anglaise, Veryac'h and Poul sections (Fig. 1). This study was carried out at the Veryac'h beach, where these formations are both continuous and exposed in the sea-cliff. The high quality of exposure allows a facies analysis to be performed, including logging at the 1/40 scale. At the same time, palaeontological material was collected in the Kermeur Formation by excavation favoured by recent cliff-slides. Although macrofossils are rare and scattered in these facies, about 90 specimens were collected. The diversity of the collected samples is similar to that obtained by amateurs over a period of a several years (M. Le Duff, personal communication, 2005). All specimens are housed in collections at the Geology Department at Brest University (prefix LPB), France. As most of the collected taxa have been previously described by [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF] and [START_REF] Botquelen | Caradoc brachiopods from the Armorican Massif (Northwestern France)[END_REF], only a few species are briefly discussed here at the end of this paper.

Facies analysis

Five sedimentary facies, SF0 to SF4, occur in the lower part of the Kermeur Formation.

Description

SF0: the basal conglomeratic facies contains Fe-oolites (mainly chamosite) and phosphatic pebbles (P-pebbles) in a bioturbated clay-sandy matrix made up of detrital quartz grains (150 to 250 µm in size) and phyllosilicates. The size of the Fe-oolites varies between 250 and 700 µm. They are deformed with a maximum elongation direction parallel to the bedding and some of them are broken. The P-pebbles, 0.1 to 2 cm in size, show an ovoid shape and display various compositions; some consist of microcrystalline apatite with detrital silt-sized grains of quartz and phyllosilicates and others contain coquinas with P-cement. SF1: this bioturbated facies overlies SF0. It consists of beds with a constant thickness of approximately 1 m, made up of fine-to medium-grained clayey sandstones of a dark-grey colour ("dirty" sandstone); the argillaceous matrix makes up about 50% of the rock [START_REF] Hamoumi | Analyse sédimentologique des formations de l'Ordovicien Supérieur en Presqu'île de[END_REF]. These sandstones are rich in quartz and contain micas and organic matter.

They are intensely bioturbated and the primary sedimentary structures have been destroyed.

The bioturbation is less abundant in places, which leads to the preservation of some sandy layers (Fig. 4 A), 1 to 3 cm thick with flaser bedding, and some thin layers of black mudstone (approximately 1 cm thick). The well-diversified trace fossils are large (up to 3 cm in diameter). Most of them belong to the ethological categories of domichnia and equilibrichnia, (e.g., Bifungites and Arenicolites; Mélou and Plusquellec, 1975b), as well as some spiral systems (Fig. 4 B). In this facies, the fauna is scattered and scarce with the occurrence of some trilobites, diploporid echinoderms and very rarely, brachiopods. Some trilobite exoskeletons and diploporid thecae that are still articulated are preserved (see part 6.1). SF2: this facies forms beds, 0.5 to 1 m thick, made up of intensively bioturbated sandy mudstones. The matrix (about 60% of the total rock) and organic matter are more abundant here than in SF1. Locally, the bioturbation is less abundant and primary structures can be observed. They are represented by thin (a few centimetres thick) black mudstones layers (Fig. 4 D) that can extend laterally over several decimetres and also by roughly laminated clayeysandy beds with diffuse basal and top surfaces. Flaser bedding also occurs. The bioturbation, which is less diversified than in SF1, is dominated by numerous equilibrichnia structures (Teichichnus, 0.1 to 1 cm in width) that are distributed along the stratification (Fig. 4 C). This facies yields brachiopods, diploporids and only a few trilobite sclerites. Although the fauna is generally disarticulated and scattered, some rare lenticular shellbeds, made up of a single coquina layer, are present. SF3: the bioturbated heterolithic facies is made up of well-sorted fine-to mediumgrained sandy beds, several centimetres to 1 dm thick, that alternate with lenticular to flaser bedding (Figs. 5 A,C,D,E,F,G). The sandy beds show planar to subhorizontal laminations with very flattened hummocky cross-stratification (HCS) locally. The basal surface of the sandy beds is slightly erosive (Figs. 5 B,C) and preserves the crawling structures produced in the underlying clay. Locally, weakly incised gutters and furrows are observed (Fig. 5 B). 2D current ripples (with a wavelength of several centimetres to 1 dm) and wave ripples (sometimes at the top of the sandy beds with HCS) are present in the lenticular to flaser bedding (Figs. 5 A,D,E). Current ripples showing opposite palaeocurrent directions (e.g., F). This facies is devoid of body fossils. SF4: this sandstone facies consists of medium-to coarse-grained and well-sorted quartz-arenite beds (1 dm to 1 m thick) with planar and low-angle laminations (Figs. 6 A,B).

The beds contain numerous concave scours, draped by thin silty to fine-grained sandy beds, with a lateral extension from 1 to several metres (Figs. 6 B,C). Swaley cross-stratification (SCS) is observed locally (Fig. 6 D). The top surfaces of the sandy beds are flat and smooth, but wave ripples (wavelength of about 1 dm) occur within some sub-circular depressions (about 1 to 3 m in diameter; Fig. 5 H). At the outcrop scale, some beds pass laterally into layers with a flattened HCS belonging to SF3 (Fig. 6 C). Bioturbation (mainly Skolithos) is very sparsely developed. This facies is devoid of body fossils.

Interpretation

The P-pebbles of SF0 were provided from the underlying deposits. The late Sandbian sea-level fall led to a partial emergence of the shelf as well as the erosion of the nodulebearing clayey siltstones occurring in the upper part of the Postolonnec Formation. During this regressive phase, the P-nodules were concentrated by winnowing and made up of pebbles of lag deposits. Then, during the transgressive phase, these pebbles were integrated into the first Katian sediments.

In SF1 and SF2, the sandy fraction is relatively abundant (the mean values range from 40 to 50%), however no storm-related structures (e.g., HCS, silty laminae, coquina storm bed; [START_REF] Aigner | Storm Depositional Systems[END_REF][START_REF] Botquelen | Formation et signification paléo-environnementale des concentrations coquillières: exemples de l'Ordovicien de Sardaigne et du Dévonien du Massif Armoricain[END_REF] have been observed in the rare non-bioturbated intervals. Rather, the mudstone layers and flaser bedding in these intervals reflect alternating periods of quiescence and low-energy currents. Furthermore, some skeletons (carapaces or thecae) preserved in SF1 are still articulated or slightly dislocated (see part 6.1). These characteristics, together with the intense bioturbation affecting the deposits as a whole, are incompatible with sudden supply of sediments, yet imply low depositional rates with regular inputs. All these features argue against storm-dominated sedimentation in an open shelf setting, as can be observed in the underlying Postolonnec Formation [START_REF] Dabard | Relationship between phosphogenesis and sequence architecture: Sequence stratigraphy and biostratigraphy in the Middle Ordovician of the Armorican Massif (NW France)[END_REF].

Instead, they suggest a restricted environment, protected from storm influences, where sandy inputs are related to unidirectional currents or fair-weather waves.

HCS and SCS occurring in SF3 and SF4 are structures related to storm wave action [START_REF] Leckie | Storm-and tide-dominated shorelines in Cretaceous Moosebar-Lower Gates interval-outcrop equivalents of deep basin gas trap in western Canada[END_REF][START_REF] Aigner | Storm Depositional Systems[END_REF][START_REF] Brenchley | Proximal and distal hummocky cross-stratified facies on a wide Ordovician shelf in Iberia[END_REF]. SCS (SF4) have only been described from shoreface environments [START_REF] Leckie | Storm-and tide-dominated shorelines in Cretaceous Moosebar-Lower Gates interval-outcrop equivalents of deep basin gas trap in western Canada[END_REF], whereas HCS (SF3) occur in spillover lobes in coastal lagoons [START_REF] Shirai | Sedimentary successions formed by fifth-order glacio-eustatic cycles in the Middle to Upper Quaternary formations of the Oga Peninsula, Northeast Japan[END_REF], open-coast tidal flats [START_REF] Yang | Sedimentation on a wave-dominated, opencoast tidal flat, southwestern Korean: summer tidal flat-winter shoreface[END_REF][START_REF] Yang | Transgressive sedimentation and stratigraphic evolution of a wave-dominated macrotidal coast, western Korea[END_REF] and on open storm-wave-dominated shelves from the shoreface to the median part of the inner shelf [START_REF] Dott | Hummocky stratification: Significance of its variable bedding sequences[END_REF][START_REF] Aigner | Storm Depositional Systems[END_REF][START_REF] Guillocheau | Zonation des dépôts de tempêtes en milieu de plate-forme: le modèle des plates-formes nord-gondwanienne et armoricaine à l'Ordovicien et au Dévonien[END_REF]. In SF3, the wave ripples at the top of the sandy beds with HCS rule out inner shelf settings and are in agreement with nearshore settings. On the other hand, the occurrence of 2D ripples in lenticular to flaser beddings (SF3) and the preservation of clay drapes within current ripples imply alternations of periods of current activity and periods of quiescence.

Such features are generally associated with environments submitted to tidal and/or fair-weather wave processes [START_REF] Reineck | Classification and origin of flaser and lenticular bedding[END_REF][START_REF] Sultan | Depositional environments at a Palaeoproterozoic continental margin, Västervik Basin, SE Sweden[END_REF][START_REF] Billeaud | Preservation potential of highstand coastal sedimentary bodies in a macrotidal basin: example from the Bay of Mont-Saint-Michel, NW France[END_REF]. A tidal influence is consistent with the opposite current directions (Figs. 5 E) observed in SF3. Moreover, it explains the preservation of wave ripples in sub-circular depressions (SF4), which can be interpreted as puddles linked to a tidally-driven emergence in a shoreface barrier. In these two facies, the association of storm-related structures with tidalrelated structures suggests a barrier context (e.g., [START_REF] Boyd | Classification of clastic coastal depositional environments[END_REF][START_REF] Dalrymple | Estuarine facies models: conceptual basis and stratigraphic implications[END_REF][START_REF] Cattaneo | Transgressive deposits: a review of their variability[END_REF], where SF4 is interpreted as a barrier facies and SF3 as a backbarrier facies (see the model in Fig. 7). The sandy beds, with planar and subhorizontal laminations and very flattened HCS associated with small wave ripples (SF3), represent deposits laid down when storm waves cut through and spilled over the barrier. These last processes are emphasized in SF4 by concave scours draped by silt and fine-grained sand (Fig. 6 B). SF1 and SF2, deposited in an environment protected from storm influences, thus correspond to bay/lagoon deposits (e.g., [START_REF] Maccarthy | Transgressive facies in the South Munster Basin, Ireland[END_REF][START_REF] Plint | Sharp-based shoreface sequences and 'offshore bars' in the Cardium Formation of Alberta: their relationship to relative changes in sea level[END_REF]. In these facies, sandy particles were supplied by continental areas (fluviatile system) and barriers (spillover lobes) and were secondarily reworked by low-energy currents in the lagoon. The central location of SF2 in the protected setting is supported by (1) the higher clay/sand ratio, which is consistent with an environment far from a direct continental influence and (2) the occurrence of disarticulated shells and rare lenticular shellbeds, which provide evidence of winnowings on the bottom. The lack of evidence for restrictive conditions (e.g., hypersaline or anoxic conditions) suggests extensive connections with an open marine environment, probably linked to the discontinuity of the barrier and/or to submerged barrier portions. No indication of depth (e.g., desiccation marks, wave ripples) has been found in SF1 and SF2. Bioturbation occurring in the successive facies (SF1: Bifungites, Arenicolites; SF2: Teichichnus; SF3 and SF4: Skolithos) is consistent with such depositional settings (e.g., marine lagoons and open bays; [START_REF] Ekdale | Ichnology: The Use of Trace Fossils in Sedimentology and Stratigraphy[END_REF][START_REF] Frey | Ichnofacies and bathymetry: a passive relationship[END_REF][START_REF] Mangano | Ichnology of Carboniferous tide-influenced environments and tidal flat variability in the North American Midcontinent[END_REF][START_REF] Maceachern | The Ichnofacies Paradigm: A fifty-Year Retrospective[END_REF].

Stratigraphic evolution

The sharp-based contact and reworking of the underlying deposits characterize the transition between the Postolonnec and Kermeur formations. The lack of regressive facies is in agreement with a rapid and/or forced regression that led to the emersion and erosion of a segment of the shelf. Then, the first transgressive deposits were laid down during the Katian (E. tanvillensis biozone) on a flat surface inherited from the Sandbian shelf (the transgressive surface, TS in Fig. 8). This type of gently sloping shoreface-shelf profile allows the formation of coastal barriers (e.g., [START_REF] Beets | Holocene tidal back-barrier development at decelerating sea-level rise: a 5 millennia record, exposed in the western Netherlands[END_REF][START_REF] Dillenburg | Barrier evolution and placer formation at Bujuru southern Brazil[END_REF][START_REF] Loi | The Late Ordovician glacioeustatic record from a high-latitude storm-dominated shelf succession: The Bou Ingarf section (Anti-Atlas, Southern Morocco)[END_REF], which are built up from wave transport and sand accumulation along the coastline. In the Kermeur Formation, the basal transgressive deposits are represented by the bioturbated SF0, SF1 and SF2 laid down on a bay/lagoon setting. The superposition of back-barrier (SF3) and barrier sediments (SF4) indicates a landward barrier migration. This vertical facies evolution, from protected marine to open marine environments, is integrated into a transgressive evolution associated with a long-term sea-level rise (e.g., [START_REF] Heward | A review of wave-dominated clastic shoreline deposits[END_REF][START_REF] Maccarthy | Transgressive facies in the South Munster Basin, Ireland[END_REF][START_REF] Plint | Sharp-based shoreface sequences and 'offshore bars' in the Cardium Formation of Alberta: their relationship to relative changes in sea level[END_REF][START_REF] Swift | Sedimentation on continental margins, IV: lithofacies and depositional systems[END_REF][START_REF] Cattaneo | Transgressive deposits: a review of their variability[END_REF][START_REF] Yang | Transgressive sedimentation and stratigraphic evolution of a wave-dominated macrotidal coast, western Korea[END_REF]. Higher up in the formation, several oscillations between protected marine and shoreface barrier environments can be identified (Fig. 3), gradually leading to an open marine environment later in the Katian (Belonechitina robusta biozone; [START_REF] Gorini | Evoluzione stratigrafica pre-hirnantiana della Formazione di Kermeur (Massiccio Armoricano)[END_REF].

Faunal assemblages and taphofacies

Description

In the lower part of the Kermeur Formation, fossils are only present in SF1 and SF2.

Two different taphofacies are recognized, TF1 and TF2. TF1: preserved in SF1, the fossil assemblage of this taphofacies (Fig. 9 A) includes trilobites, diploporids (echinoderms) and very rarely, brachiopods. The trilobites are assigned to Colpocoryphe grandis, Onnia seunesi ?, Zeliskella (Zeliskella) sp., Phacopidina sp. and Eccoptochile sp. The diploporids are assigned to Aristocystites sp., and the brachiopods to Drabovia pentagonomya (see below for systematic assignments; [START_REF] Botquelen | Caradoc brachiopods from the Armorican Massif (Northwestern France)[END_REF] for the brachiopods). The bioclasts are isolated and randomly dispersed throughout the thickness interval of SF1, without any ordered arrangement in the bedding plane and unrelated to sedimentary events. In this taphofacies, two different preservation stages (or taphonomic grades) for the fossils are distinguished, denoted as TF1a and TF1b, accounting for 60% and 40% of the material, respectively (out of a total of 46 specimens).

In the first grade (Fig. 9 A, TF1a), skeletons belonging to three taxonomic groups are preserved with different skeletal parts that are still articulated, each of them occurring as a single species. The trilobites include numerous complete exoskeletons and in situ exuviae (most of the specimens identified as moults correspond to a joined thorax and pygidium with overturned librigenae in the immediate vicinity; Figs. 10 A,B); this material is all assigned to Colpocoryphe grandis. The diploporids (Fig. 11), identified as Aristocystites sp., are preserved as scattered but complete thecae and a few isolated thecal plates. The brachiopods are represented by very scarce articulated Drabovia pentagonomya valves. These fossils are all preserved as internal and external moulds, without abrasion or bioerosion marks.

The second grade of this taphofacies (Fig. 9 A,TF1b) is characterized by a high degree of shell disarticulation, which are nevertheless always randomly dispersed; most of the material is composed of trilobite exoskeleton fragments, including trinucleids (Onnia seunesi ?, Figs. 10 E-H) and dalmanitids (Zeliskella (Zeliskella) sp., Fig. 10 G L-M). These taxa are preserved only as isolated exoskeletal parts, and some specimens were broken before burial.

In summary, Drabovia occurs in both grades of this taphofacies, and Aristocystites and Colpocoryphe are mostly preserved as complete remains with different parts of their skeletons in articulated or slightly dislocated arrangements (Fig. 9 A; TF1a). Onnia, Phacopidina, Zeliskella and Eccoptochile are always disarticulated and/or fragmented (Fig. 9 A; TF1b). TF2: preserved in SF2, the faunal assemblage of this taphofacies (Fig. 9 B) consists mainly of brachiopod valves, diploporid thecal plates (Aristocystites sp.) and very rarely, trilobite sclerites (Calymenidae, consistent with Colpocoryphe grandis). The brachiopods include three species: Drabovia pentagonomya, which is clearly predominant, Tafilaltia destombesi and Triplesia cf. T. simplex. This taphofacies is characterized by the preservation of fossils as lenticular shell concentrations on a single bedding plane. The lateral extent of these lenses varies from 1 dm to 1 m and their thickness can reach 3 to 5 cm. These lenses have a slightly erosive basal surface and consist of either a single thin coquina layer or scattered shells in a silty-sandy matrix. Bioclasts are preserved as internal and external moulds. All the specimens are disarticulated with a fragmentation rate of about 40% (based on 44 specimens), showing slight differences from one species to another (only the valves for which more than one half of the specimen is preserved were taken into account). No erosion, bioerosion or abrasion mark was observed on these fossils; however, their preservation as internal and external moulds in medium-grained sandstones makes it difficult to observe these features.

Interpretation

In the first bioturbated facies (SF1), the two taphonomic grades are associated but show two different preservation stages: TF1a with complete skeletons in an articulated position and TF1b with disarticulated shells. Grade TF1a contains trilobite exuviae preserved in situ and shows a very low degree of disarticulation, even when the skeletons are composed of numerous easily disconnected skeletal parts or plates. The physical integrity of arthropod carapaces belonging to grade TF1a indicates that the sediments were not disturbed [START_REF] Plotnick | Taphonomy of a modern shrimp: implications for the arthropod fossil record[END_REF][START_REF] Speyer | Trilobite taphonomy: a basis for comparative studies of arthropod preservation, functional anatomy and behaviour[END_REF]. These features, along with the scattering of fossils in the sediments, provide strong evidence that these fossils are preserved in their life environment. The assemblage of this grade is made up of Colpocoryphe, a trilobite burrower with predator/scavenger feeding habits [START_REF] Hammann | Calymenacea (Trilobita) aus dem Ordovizium von Spanien; ihre Biostratigraphie, Ökologie und Systematik[END_REF]Fortey and Owens, 1999a), and Aristocystites, a recumbent suspension feeder [START_REF] Parsley | Aristocystites, a recumbent diploporid (Echinodermata) from the middle and late Ordovician of Bohemia, CSSR[END_REF]. After death, the pre-burial position of Colpocoryphe provided protection from disturbance and disarticulation. A similar taphonomic result is observed for Aristocystites, whose complete thecae occur in the same habitat. This diploporid displayed a reclining mode of life on the sea-floor and its preservation was probably favoured by regular sediment inputs.

Conversely, grade TF1b is characterized by shell disarticulation. This cannot be linked to storm reworking because the shells are scattered in the sediments and coquina storm beds have not been observed. Two hypotheses can be proposed to explain this grade. The first one considers the modes of life. The disarticulated exoskeletons belong to epibenthic trilobites, (Fortey andOwens, 1999a, 1999b) including Onnia, Phacopidina and Z. (Zeliskella), and very rarely, epifaunal brachiopod (Drabovia). The mode of life of these taxa exposes them to post-mortem disarticulation by scavengers, bioturbation and bacterial decomposition before burial. In some cases, the high proportion of disarticulation may be related to the morphology of the exoskeletons. For example, the distal tips of the trinucleid thoracic segments (such as in the genus Onnia) do not exhibit imbricated structures (Fortey and Owens, 1999b). These trinucleid morphological characteristics favour rapid disarticulation compared to other trilobite families. Thus, the two taphonomic grades (TF1a and TF1b) of the benthic assemblage in SF1 can be interpreted as being related to the different modes of life of the taxa. A second hypothesis can be proposed to explain the occurrence of these disarticulated and partially fragmented shells. They could be allochtonous and transported by currents from open marine settings. In that case, these shells would be distributed in both fossiliferous facies, yet they were not observed in SF2; their relative scarcity can explain the lack of data in this facies. In this second hypothesis, the benthic assemblage of TF1 corresponds to a composite assemblage with allochthonous and autochthonous species.

In TF2, the coquinas are disarticulated and accumulated in lenticular bodies with a slightly erosive basal surface. This arrangement can be related to type A-shellbeds, as described by [START_REF] Botquelen | Formation et signification paléo-environnementale des concentrations coquillières: exemples de l'Ordovicien de Sardaigne et du Dévonien du Massif Armoricain[END_REF], produced by the winnowing of the water-sediment interface that reworks the finer particles and leads to a concentration of shell debris. Two hypotheses can be proposed for TF2: 1) it corresponds to either a within-habitat timeaveraged assemblage (sensu [START_REF] Walker | The significance of fossil assemblages from fine-grained sediments: time average communities[END_REF][START_REF] Kidwell | Time-averaging in the marine fossil record: overview of strategies and uncertainties[END_REF], considering the evidence for a low energy setting in this facies, or 2) to a para-autochthonous to allochthonous assemblage, considering the high degree of disarticulated shells and their accumulation in lenticular bodies. It is difficult to assess the degree of transport, but the interpretation of SF2 is compatible with limited reworking. In this case, the fauna could have drifted from more open environments such as inlets.

There are other differences between the faunal assemblages of the two taphofacies. Some taxa, although occurring in TF2, are either absent from TF1 (Triplesia and Tafilaltia) or significantly less abundant (Drabovia). These differences argue for a different origin for these assemblages, such as two different biotopes. This is especially relevant for the brachiopods, the abundance of which in SF2 could be linked to the substrate composition. Indeed, the bioturbated sandy mudstones facies (SF2) could represent loose ground substrate, which is more favourable for epifaunal soft-substrate brachiopods than the bioturbated clayey sandstones facies (SF1). The latter facies is probably more closely comparable to soft ground in the terminology proposed by [START_REF] Goldring | Organisms and the substrate: response and effect[END_REF].

Discussion and conclusion

This study reveals a higher benthic diversity than that described by previous authors in the lower part of the Kermeur Formation, especially for trilobites, which have not been reported before. According to the benthic association models proposed for the Ordovician (Fortey andOwens, 1978, 1987;[START_REF] Henry | Paléoenvironnements et dynamique de faunes de trilobites dans l'Ordovicien (Llanvirn supérieur-Caradoc basal) du Massif Armoricain (France)[END_REF][START_REF] Vidal | Le modèle des biofaciès à trilobites: un test dans l'Ordovicien inférieur de l'Anti-Atlas, Maroc[END_REF], the taxonomic composition and diversity of the complete assemblage (TF1) implies open shelf settings. Assuming that this is a composite assemblage, the very low diversity of the autochthonous fraction (i.e., Colpocoryphe and Aristocystites) could be consistent with a nearshore assemblage [START_REF] Henry | Paléoenvironnements et dynamique de faunes de trilobites dans l'Ordovicien (Llanvirn supérieur-Caradoc basal) du Massif Armoricain (France)[END_REF][START_REF] Westrop | Trilobite alpha diversity and the reorganization of Ordovician benthic marine communities[END_REF][START_REF] Turvey | Early Ordovician (Arenig) trilobite palaeoecology and palaeobiogeography of the South China plate[END_REF][START_REF] Botting | Unravelling causal components of the Ordovician Radiation: the Builth Inlier (central Wales) as a case study[END_REF] but not with this taxonomic composition. In fact, the genus Colpocoryphe, which is numerically dominant in grade TF1a, usually occurs in relatively deep open shelf environments characterized by finegrained sediments [START_REF] Hammann | Calymenacea (Trilobita) aus dem Ordovizium von Spanien; ihre Biostratigraphie, Ökologie und Systematik[END_REF][START_REF] Vidal | Le modèle des biofaciès à trilobites: un test dans l'Ordovicien inférieur de l'Anti-Atlas, Maroc[END_REF]. Certain species with reduced eyes, such as Colpocoryphe taylorum or C. inopinata, were even adapted to the more distal environments of the outer shelf [START_REF] Fortey | The Arenig Series in South Wales: Stratigraphy and Palaeontology. I. The Arenig Series in South Wales[END_REF][START_REF] Henry | Paléoenvironnements et dynamique de faunes de trilobites dans l'Ordovicien (Llanvirn supérieur-Caradoc basal) du Massif Armoricain (France)[END_REF]. On the Crozon Peninsula, the species C. grandis is present in the upper part of the Postolonnec Formation [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF] in silty clayey facies that are related to a distal shelf environment (i.e., the median part of the inner shelf and the outer shelf; [START_REF] Dabard | Relationship between phosphogenesis and sequence architecture: Sequence stratigraphy and biostratigraphy in the Middle Ordovician of the Armorican Massif (NW France)[END_REF]. Moreover, these trilobites co-occur with Aristocystites, a diploporid echinoderm related to low-energy environments in some areas [START_REF] Parsley | Aristocystites, a recumbent diploporid (Echinodermata) from the middle and late Ordovician of Bohemia, CSSR[END_REF]. The other part of the assemblage (grade TF1b), which is either allochthonous or not according to the interpretation, is an epifaunal assemblage dominated by trinucleids (Onnia). This association with numerous trinucleids and dalmanitids is reminiscent of the assemblages described from either the upper part of the Postolonnec Formation (Crozonaspis chauveli faunizone, Veryac'h section in Henry, 1980, p. 232) or the upper part of the Kermeur Formation (Crozonaspis dujardini faunizone, Aber section, in Henry, 1980, p. 234). In both cases, the sedimentary facies yielding these assemblages are consistent with distal open shelf environments [START_REF] Loi | Controls of sea level fluctuations on the formation of Ordovician siliceous nodules in terrigenous offshore environments[END_REF][START_REF] Gorini | Evoluzione stratigrafica pre-hirnantiana della Formazione di Kermeur (Massiccio Armoricano)[END_REF]. The present study shows that, in the Kermeur Formation, these species are present in a bay/lagoon context. This paradox can be explained by a wider range of environmental tolerance (i.e., depth and granulometry) for these taxa, especially for Colpocoryphe and Aristocystites, and by environmental conditions that were probably similar to those of deeper open environments. In fact, during the early Katian transgression, the construction of a coastal barrier in neashore settings allowed the establishment of turbidity and hydrodynamic conditions that were close to those of deeper open-shelf environments. Moreover, if the barrier was discontinuous or partially submerged, the chemical conditions (i.e., salinity and oxygenation) in the protected area could be similar too. Thus, the formation of lagoon-barrier systems produced new ecological niches available for colonization by organisms accustomed to deeper shelf environments. This colonization may represent an example of offshore-onshore expansion, which is the inverse of the migration described in the onshore-offshore diversification model of Phanerozoic shelf communities [START_REF] Jablonski | Onshore-offshore patterns in the evolution of Phanerozoic shelf communities[END_REF][START_REF] Sepkovski | Diversification, faunal change, and community replacement during the Ordovician radiations[END_REF][START_REF] Sepkovski | Evolutionary faunas and the distribution of Paleozoic benthic communities in space and time[END_REF][START_REF] Sepkovski | A model of onshore-offshore change in faunal diversity[END_REF]. In this model, new species originate in shallow settings before spreading into deeper environments. Discussion: the large size of the specimens (8 to 10 cm in length on average, and up to 12 cm), the shape of the terminal axial piece of pygidium with lateral expansions, and the large but shallow vincular furrows on pygidial pleurae that become larger forwards, allow this material to be assigned to Colpocoryphe grandis (see [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF]. Colpocoryphe grandis occurs in the upper part of the Postolonnec Formation and in the lower part of the Kermeur Formation on the Crozon Peninsula, without apparent variation in morphology between these two different formations. In the Kermeur Formation, this taxon occurs as complete exoskeletons and exuviae scattered in SF1, and scarce disarticulated sclerites in lenticular shell concentrations of SF2.

Systematic palaeontology

Family Trinucleidae HAWLE andCORDA, 1847 Subfamily Marrolithinae HUGHES, 1971 Genus Onnia BANCROFT, 1933 Onnia seunesi ? (KERFORNE, 1900) Figs. 10 E,H Material: six cephala, preserved as incomplete internal and external moulds. LPB 14800 to LPB 14805. not possible. Although the internal mould of the pygidium (Fig. 10 J) is poorly preserved, its morphology is compatible with the species cited above. Zeliskella (Zeliskella) sp. occurs as scarce exoskeleton parts that are isolated and scattered in SF1.

Subfamily uncertain

Phacopidina BANCROFT, 1949 Phacopidina sp. Discussion: the glabellar furrows S2 and S3 are shallow and less marked than the S1 furrows; S2 furrows are concave backward in the shape of an arc; the S3 furrows are sinuous and convergent backward. These features, added to the shape of the glabella, the position and size of the eyes, as well as the course of the preocular suture -slightly in front but closely following the frontal lobe of the glabella -are consistent with the genus Phacopidina. This material is consistent with Phacopidina micheli (TROMELIN, 1877), Llanvirn-Lower Caradoc from the Armorican Massif [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF], but more material (especially pygidia) is needed to propose a reliable specific assignment. In the Kermeur Formation, Phacopidina sp. occurs as scarce exoskeleton parts that are isolated and scattered in SF1.

Family Cheiruridae SALTER, 1864

Subfamily Eccoptochilinae LANE, 1971 Genus Eccoptochile HAWLE and CORDA, 1847 Eccoptochile sp. Discussion: this pygidium, collected from the base of the Kermeur Formation, in SF1, is referred to Eccoptochile. The species of this genus described either in the Armorican Massif [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF] or Spain [START_REF] Hammann | Phacopina und Cheirurina (Trilobita) aus dem Ordovizium Spaniens[END_REF][START_REF] Hammann | Trilobiten aus dem oberen Caradoc der östlichen Sierra Morena (Spanien)[END_REF] are chiefly distinguished by their cephalic morphology, therefore a specific assignment is not possible from this single specimen. Discussion: on the external moulds, the thecae are ovoid in shape and more than 10 cm long.

Echinodermata

Class

The thecal plates are well sized (≥ 5 mm), relatively hexagonal in shape and more or less regularly arranged. They show dense vermicular openings but no tubercle is observed. These features indicate that the specimens from the base of the Kermeur Formation should be assigned to the genus Aristocystites, and are particularly reminiscent of A. bohemicus BARRANDE, 1887 (see [START_REF] Parsley | Aristocystites, a recumbent diploporid (Echinodermata) from the middle and late Ordovician of Bohemia, CSSR[END_REF]. Since neither holdfasts nor oral faces are observed on the collected specimens, the specific assignment remains uncertain. In the Kermeur Formation, Aristocystites sp. is preserved as complete thecae and isolated thecal plates scattered in the highly bioturbated SF1, and then only as thecal plates in lenticular shell concentrations of SF2 together with brachiopod valves. British stratigraphic stages (assigned from [START_REF] Paris | The Ordovician chitinozoan biozones of the Northern Gondwana Domain[END_REF][START_REF] Bourahrouh | Chitinozoaires et palynomorphes de l'Ordovicien supérieur nordgondwanien: impact de la glaciation ashgillienne[END_REF][START_REF] Webby | Stratigraphic framework and time slices[END_REF].

Figures captions

Fig. 5 E

 5 Fig. 5 E) and clay drapes within ripples (Figs. 5 A, D, E, G) are visible. Some wave ripples

;

  Phacopidina sp., Fig. 10 F), along with less abundant taxa such as Eccoptochile sp. (Fig. 10 I), as well as scarce brachiopod valves (Drabovia pentagonomya, Figs. 10

  Figs. 10 A-D Material: numerous specimens preserved as internal and external moulds,

Fig. 10 F

 10 Fig. 10 F

Fig. 10 I

 10 Fig. 10 I

Fig

  Fig.11 A-C

Fig. 1 .

 1 Fig. 1. Location of the Kermeur Formation outcrops in the Armorican Massif (Crozon

Fig. 2 .

 2 Fig. 2. Ordovician deposits in the Veryac'h section (Crozon Peninsula), with global and

Fig. 3 .

 3 Fig. 3. Lithostratigraphic column of the Veryac'h section, from the upper part of the

Fig. 4 .

 4 Fig. 4. Bioturbated clayey sandstone SF1 with some preserved sandy layers (arrows in A) and

Fig. 5 .

 5 Fig. 5. Bioturbated heterolithic SF3. General views (A and C) and details showing lenticular

Fig. 6 .

 6 Fig. 6. General view of the quartz-arenite SF4 (A) and details showing the concave scours in

Fig. 7 .Fig. 8 .

 78 Fig. 7. Depositional model for the lower part of the Kermeur Formation. Distribution of the

Fig. 9 .

 9 Fig. 9. Taxonomic and taphonomic composition of fauna from the lower part of the Kermeur

Fig. 10 .

 10 Fig. 10. Selected specimens from the lower part of the Kermeur Formation (SF1 and SF2),

Fig. 11 .

 11 Fig. 11. Aristocystites sp., diploporid from the lower part of the Kermeur Formation,

  Fig. 7

Acknowledgments

The authors are indebted to M. Robardet and Y. Plusquellec for helpful scientific discussions, to B. Dattilo and J. Botting for constructive comments on earlier version. The editorial work made by F. Surlyk greatly improved the manuscript. Dr. S. Mullin provided writing assistance. This work is a contribution to the ECLIPSE 2 programme (CNRS, France).

Discussion: in spite of the missing pygidium and thorax, the shape of the fringe and the position of the girder on the lower lamella allow this material to be assigned to the genus Onnia (see [START_REF] Ingham | A monograph of the upper Ordovician trilobites from the Cautley and Dent districts of Westmorland and Yorkshire[END_REF]: from the postero-lateral angle, the girder begins between the first and second row of pits, then curves inward and runs between the second and third row of pits.

Among the two Onnia species described from the Upper Ordovician of the Armorican Massif (see [START_REF] Lebrun | Les Onnia ordoviciens (Trinucleïdés, Trilobites) du Massif Armoricain[END_REF], O. seunesi is most closely related to material from the Kermeur Formation, as the latter shows an occipital spine. Nevertheless, the assignment to Onnia seunesi remains doubtful as all studied specimens are broken. They occur in sedimentary facies SF1 in the lower part of the Kermeur Formation, Veryac'h section.

Family Dalmanitidae VOGDES, 1890

Subfamily Zeliskellinae DELO, 1935 Genus Zeliskella DELO, 1935 Zeliskella (Zeliskella) DELO, 1935 Zeliskella (Zeliskella) sp. Discussion: the shape of the glabella (Fig. 10 G) and glabellar furrows (S2, S3), as well as the size and position of eyes, the pit on the frontal lobe of the glabella, the apparent lack of genal spines and tubercle on the occipital ring, are all characteristics shared with Z. (Zeliskella), particularly the slightly earlier species renaudae HENRY, 1980. Nevertheless, the posterior furrow of the cephalon stops laterally in the case of Z. renaudae (see [START_REF] Henry | Trilobites ordoviciens du Massif Armoricain[END_REF], whereas it continues on the free cheek of the single cephalon collected from the base of the Kermeur Formation. Considering this difference and the lack of some exoskeleton parts (particularly, the anterior part of the cephalon and the end-part of the pygidium), a specific assignment is