Leo Szewczyk
email: leo.szewczyk@mines-paristech.fr

Emmanuelle Vennin

Jean-David Moreau

Georges Gand

Michel Verolet

Nicolas Klee

Emmanuel Fara

TRACKING DINOSAURS IN COARSE-GRAINED SEDIMENTS FROM THE UPPER TRIASSIC OF ARDÈCHE (SOUTHEASTERN FRANCE)

Keywords: dinosaur tracks, preservation, abandoned channel, Triassic, Geopark

Coarse

-grained sediments deposited in high-energy environments are usually considered as unfavorable to the preservation of fossil tracks. Here we report on dinosaur footprints showing a good physical preservation despite being found in coarse-grained sandstones of alluvial origin from the Upper Triassic of Ardèche, southeastern France. The ichnoassemblage, dominated by Grallator isp., raises questions about the processes leading to the formation and preservation of tracks in coarse-grained sediments. The track-bearing surface is a medium-to coarse-grained quartz arenite that is microconglomeratic locally. The average grain size ranges from 0.2 to 2 mm and numerous pebbles are present. It is overlain by a succession of thin, intercalated layers of clays and silts, themselves covered by a mix of silts and coarse-grained sandstones. We interpret this succession as a progressive decrease in energy due to a meandering channel migration culminating in channel abandonment, followed by channel reactivation and infill by coarse-grained sediments. Sedimentological and taphonomic observations indicate that the trackmakers walked on the layer of silts and clays and their passage deformed the underlying coarse-grained sands, forming transmitted undertracks. The fine-grained layer helped record the pedal anatomy of the trackmakers and contributed to protecting the transmitted undertracks from destruction just after their formation. Overall, this suggests that the fossil footprints were preserved by abiotic processes only, the main factor being the lithological contrast between successive sedimentary layers. The exceptional preservation of tracks in coarsegrained deposits contrasts sharply with the prevailing models involving fine-grained sediments and microbial mats present in low-energy environments. This unusual phenomenon may have been relatively frequent in the Upper Triassic sandstones in Ardèche.

INTRODUCTION

The formation and preservation of fossil tracks involve numerous biotic and abiotic processes.

The substrate properties controlling track formation (or track registration, sensu [START_REF] Marchetti | Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present[END_REF]) include the nature of the lithology and the grain size of the surface trampled [START_REF] Laporte | Tracks and substrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya[END_REF]Allen 1997;Alcalá et al. 2014;[START_REF] Pérez-Lorente | Dinosaur footprints & trackways of La Rioja[END_REF], the sediment water saturation (Allen 1997; [START_REF] Gatesy | Three-dimensional preservation of foot movement in Triassic theropod dinosaurs[END_REF]Milàn andBromley 2006, 2008;[START_REF] Jackson | Laboratory controlled simulations of dinosaur footprint in sand: a key to understanding vertebrate tracks formation and preservation[END_REF][START_REF] Jackson | Range of experimental dinosaur (Hypsilophodon foxii) Footprint due to variation in sand consistency: how wet was the track?[END_REF], the lithological contrast between the different sedimentary layers deformed by the trackmaker [START_REF] Laporte | Tracks and substrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya[END_REF][START_REF] Paik | Dinosaur track-bearing deposits in the Cretaceous Jindong Formation, Korea: occurrence, palaeoenvironments and preservation[END_REF][START_REF] Falkingham | The Goldilocks effect: preservation bias in vertebrate track assemblages[END_REF][START_REF] Da Silva | Footprints of large theropod dinosaurs and implications on the age of Triassic biotas from Southern Brazil[END_REF][START_REF] Pérez-Lorente | Dinosaur footprints & trackways of La Rioja[END_REF] and, potentially, the presence of microbial mats [START_REF] Marty | Formation and taphonomy of human footprints in microbial mats of present-day tidal-flat environments: implication for the study of fossil footprints: Ichnos[END_REF][START_REF] Carmona | The role of microbial mats in the preservation of bird footprints: a case study from the mesotidal Bahia Blanca estuary (Argentina)[END_REF][START_REF] Carmona | Microbially induced sedimentary structures in Neogene tidal flats from Argentina: Paleoenvironmental, stratigraphis and taphonomic implications: Palaeogeography[END_REF][START_REF] Cariou | Dinosaur track record on a shallow carbonate-dominated ramp (Loulle section[END_REF][START_REF] Carvahlo | Preservation of dinosaur tracks induced by microbial mats in the Sousa Basin (Lower Cretaceous)[END_REF][START_REF] Prescott | Microbial mats and ichnofauna of a fluvial-tidal channel in the lower Pennsylvanian Joggins Formation[END_REF]. The shape, size and depth of the tracks are also controlled by factors linked to the trackmaker, such as anatomy, weight, speed, gait, behavior and, more generally, the force applied on the sediment by the animal [START_REF] Heyler | Piste de tétrapodes permiens dans la région de Lodève Hérault : Mémoire du Muséum national d[END_REF]Allen 1997;[START_REF] Falkingham | The Goldilocks effect: preservation bias in vertebrate track assemblages[END_REF][START_REF] Gatesy | Neither bones nor feet: track morphological variation and 'preservation quality[END_REF][START_REF] Marchetti | Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present[END_REF].

The preservation of tracks reflects the balance between various processes that enhance or reduce the likelihood of the tracks being preserved [START_REF] Cohen | Modern vertebrate track taphonomy at Lake Manyara, Tanzania[END_REF][START_REF] Carmona | The role of microbial mats in the preservation of bird footprints: a case study from the mesotidal Bahia Blanca estuary (Argentina)[END_REF]).

After their formation, tracks usually have an estimated lifespan of hours or days at most, depending on the substrate on which they are formed [START_REF] Cohen | Modern vertebrate track taphonomy at Lake Manyara, Tanzania[END_REF][START_REF] Marty | Formation and taphonomy of human footprints in microbial mats of present-day tidal-flat environments: implication for the study of fossil footprints: Ichnos[END_REF][START_REF] Carmona | The role of microbial mats in the preservation of bird footprints: a case study from the mesotidal Bahia Blanca estuary (Argentina)[END_REF]). The processes impacting on whether tracks are preserved include their being infilled or buried [START_REF] Paik | Dinosaur track-bearing deposits in the Cretaceous Jindong Formation, Korea: occurrence, palaeoenvironments and preservation[END_REF][START_REF] Romano | Jurassic dinosaur tracks and trackways of the Cleveland Basin, Yorkshire: preservation, diversity and distribution[END_REF][START_REF] Milàn | Preservation and erosion of theropod tracks in eolian deposits: examples from the Middle Jurassic Entrada Sandstone[END_REF][START_REF] Huerta | Exceptional preservation processes of 3D dinosaur footprint casts in Costalomo (Lower Cretaceous, Cameros Basin[END_REF]Xing et al. 2015a, b), early cementation induced by microbial mats [START_REF] Scott | Preservation and paleoenvironmental significance of a footprinted surface on the Sandai Plain[END_REF][START_REF] Carmona | The role of microbial mats in the preservation of bird footprints: a case study from the mesotidal Bahia Blanca estuary (Argentina)[END_REF], substrate desiccation [START_REF] Cohen | Modern vertebrate track taphonomy at Lake Manyara, Tanzania[END_REF]Allen 1997), little or no reworking [START_REF] Maples | Paleoecological and Sedimentological Significance of Bioturbated Crinoid Calyces[END_REF]; precipitation of evaporites [START_REF] Cohen | Modern vertebrate track taphonomy at Lake Manyara, Tanzania[END_REF][START_REF] Scott | Taphonomic controls on animals tracks at saline, alkaline Lake Bogoria, Kenya Rift valley: impact of salt efflorescence and clay mineralogy[END_REF]Alcalá et al. 2014), fluids circulation and pedogenesis [START_REF] Paik | Dinosaur track-bearing deposits in the Cretaceous Jindong Formation, Korea: occurrence, palaeoenvironments and preservation[END_REF][START_REF] Phillips | Sequence stratigraphic controls on synsedimentary cementation and preservation of dinosaur tracks: Example from the lower Cretaceous, (Upper Albian) Dakota Formation[END_REF]Tunik et al. 2009;[START_REF] Pazos | Paleoenvironmental framework of dinosaur tracksites and other ichnofossils in Early Cretaceous mixed siliciclastic-carbonate deposits in the Neuquén Basin, northern Patagonia[END_REF][START_REF] Cariou | Dinosaur track record on a shallow carbonate-dominated ramp (Loulle section[END_REF]. Depending on local conditions, a single process can induce the long term preservation of tracks or on the contrary accelerate their degradation (Allen 1997;[START_REF] Scott | Taphonomic controls on animals tracks at saline, alkaline Lake Bogoria, Kenya Rift valley: impact of salt efflorescence and clay mineralogy[END_REF].

Taphonomic studies show that some combinations of processes have a greater potential for track formation and preservation than others. For example, fine-grained sediments combined with a 10 to 20% water saturation appears optimal for tracks' formation [START_REF] Laporte | Tracks and substrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya[END_REF]Allen 1997;[START_REF] Jackson | Laboratory controlled simulations of dinosaur footprint in sand: a key to understanding vertebrate tracks formation and preservation[END_REF][START_REF] Jackson | Range of experimental dinosaur (Hypsilophodon foxii) Footprint due to variation in sand consistency: how wet was the track?[END_REF]Alcalá et al. 2014;[START_REF] Pérez-Lorente | Dinosaur footprints & trackways of La Rioja[END_REF]. Also, the combination of fine-grained sediments and non-mineralized microbial mats that stabilize the sediments [START_REF] Decho | Exopolymer microdomains as a structuring agent for heterogeneity within microbial biofilms[END_REF][START_REF] Noffke | Extensive microbial mats and their influence on the erosional and depositional dynamics of a siliciclastic cold water environment[END_REF]Schreiber et al. 2007;[START_REF] Dai | Microbially-induced sedimentary wrinkle structures and possible impact of microbial mats for the enhanced preservation of dinosaur tracks from the Lower Cretaceous Jiaguan Formation near Qijiang[END_REF][START_REF] Davies | Resolving MISS conceptions and misconceptions: A geological approach to sedimentary surface textures generated by microbial and abiotic processes[END_REF], is considered as one of the most important factors. However, these mats seem to develop only in low-energy environments such as lakes, lagoons or tidal-flats [START_REF] Noffke | Environmental requirements for microbial mat formation in recent tidal systems[END_REF][START_REF] Gerdes | Microbial signatures in peritidal siliclastic sediments: a catalogue[END_REF][START_REF] Porada | Wrinkle structures -a critical review[END_REF][START_REF] Marty | Formation and taphonomy of human footprints in microbial mats of present-day tidal-flat environments: implication for the study of fossil footprints: Ichnos[END_REF][START_REF] Bouton | External controls on the distribution, fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon[END_REF][START_REF] Prieto-Barajas | Microbial mat ecosystems: Structure types, functional diversity, and biotechnological application[END_REF]. Their fossil analogs, the Microbially Induced Sedimentary Structures (MISS, [START_REF] Noffke | Microbially Induced Sedimentary Structures: A new category within the classification of primary sedimentary structures[END_REF], are principally found in finely grained sediments [START_REF] Porada | Wrinkle structures -a critical review[END_REF][START_REF] Sheldon | Microbially induced sedimentary structures in the ca. 1100 Ma terrestrial midcontinent rift of North Africa[END_REF]Souza Carvahlo et al. 2013;[START_REF] Davies | Resolving MISS conceptions and misconceptions: A geological approach to sedimentary surface textures generated by microbial and abiotic processes[END_REF], although some MISS can occasionally occur in medium-to coarse-grained sandstones [START_REF] Prave | Life on land in the Proterozoic: Evidence from the Torridonian rocks of northwest Scotland[END_REF][START_REF] Schieber | Atlas of Microbial Mat Features Preserved within the Siliciclastic Rock Record[END_REF][START_REF] Carvahlo | Preservation of dinosaur tracks induced by microbial mats in the Sousa Basin (Lower Cretaceous)[END_REF][START_REF] Prescott | Microbial mats and ichnofauna of a fluvial-tidal channel in the lower Pennsylvanian Joggins Formation[END_REF]Wilmeth et al. 2014;Tu et al. 2016).

Overall, the major role played by fine-grained sediments in track formation and preservation has led many authors to suggest that coarse-grained sediments are extremely unlikely to host vertebrate fossil tracks (e.g., [START_REF] Laporte | Tracks and substrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya[END_REF]Allen 1997;[START_REF] Carvahlo | Dinosaur footprints from Northeastern Brazil: Taphonomy and environmental setting: Ichnos[END_REF][START_REF] Carvahlo | Preservation of dinosaur tracks induced by microbial mats in the Sousa Basin (Lower Cretaceous)[END_REF]Alcalá et al. 2014;[START_REF] Pérez-Lorente | Dinosaur footprints & trackways of La Rioja[END_REF]. Although this is intuitive and generally correct, researchers usually do not indicate precisely what grain size is associated with the descripted 'coarse' sediments, relative to grain size scales for clastic sediments (Wentworth 1922). Although grain size can be coarse in several sedimentary contexts (alluvial/fluvial systems), specific track-bearing layers are nearly always finer grained (Tucker and Burchette 1977;[START_REF] Lockley | The paleoenvironmental context, preservation and paleoecological significance of dinosaur tracksites in the western USA[END_REF][START_REF] Carvahlo | Dinosaur footprints from Northeastern Brazil: Taphonomy and environmental setting: Ichnos[END_REF]) and preferentially preserved in mud-dominated floodplain sedimentary facies [START_REF] Buatois | Ichnology: Organism-Substrate Interactions in Space and Time[END_REF]. In rare exceptions tracks made in fine-grained sediments can be filled by coarse grains (up to 1 cm of diameter) that form convex hyporeliefs in sheet-flood deposits (Tucker and Burchette 1977;[START_REF] Moreau | Biometric morphometric approaches on Lower Hettangian dinosaur footprints from the Rodez Strait[END_REF]).

We report here on an exceptional dinosaur tracksite characterized by abundant footprints preserved in coarse-grained (0.2 to 2 mm) fluvial sandstones from the Upper Triassic of Ardèche (south-eastern France). This range of grain size is larger than those reported in other cases of tracks found in "coarse" sediments [START_REF] Courel | Une nouvelle espèce Coelurosaurichnus grancieri du Trias de l'Ardèche[END_REF][START_REF] Milàn | Preservation and erosion of theropod tracks in eolian deposits: examples from the Middle Jurassic Entrada Sandstone[END_REF][START_REF] Seiler | A wet interdune dinosaur trampled surface in the Jurassic Navajo Sandstone, Coyote Buttes, Arizona: Rare preservation of multiple tracks types and tail traces[END_REF][START_REF] Jackson | Range of experimental dinosaur (Hypsilophodon foxii) Footprint due to variation in sand consistency: how wet was the track?[END_REF]Xing et al. 2015b). Our aim is to identify the biosedimentary processes that contributed to form and preserve tracks in this coarse-grained substrate. We describe the associated facies, sedimentary context and specific layers involved in the tracks' formation, to generate an ichnotaphonomical model.

GEOLOGICAL CONTEXT

The Triassic deposits from the Ardèche region are known worldwide for their remarkable ichnological abundance and richness [START_REF] Blanc | Empreintes de pas sur le grès d'Ailhon (Ardèche)[END_REF][START_REF] Montenat | Empreintes de pas de reptiles dans le Trias moyen du plateau du Daüs près d'Aubenas (Ardèche)[END_REF][START_REF] Finelle | Contribution à l'étude du Trias de la bordure cévenole. Stratigraphie, Sédimentologie[END_REF][START_REF] Cula | Les Grés de la série inférieure du Trias ardéchois. Essai de dynamique sédimentaire, environnements fluviatiles à sursalés[END_REF][START_REF] Gand | Les pistes dinosauroïdes du Trias moyen français : interprétation et réévaluation de la nomenclature[END_REF][START_REF] Gand | Les traces de pas d'amphibiens, de dinosaures et autres reptiles du[END_REF]Klein and Haubold 2007: Fig 11). These deposits are exposed along the southeastern border of the Massif Central, on the western edge of the subalpine basin [START_REF] Courel | Données nouvelles sur le Trias cévenol : chronologie, sédimentologie, implications métallogéniques[END_REF][START_REF] Courel | Sequence stratigraphy along a Triassic transect on the western peritethyan margin in Ardèche (SE France Basin): Correlations with subalpine and germanic realms[END_REF][START_REF] Razin | Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine basin during the Triassic and Jurassic[END_REF]. They form a 50 km long, 2 to 6 km wide strip of continental detrital sedimentary rocks with a NE-SW orientation (Fig. 1A). These deposits, dated palynologically (Tradispora, Cameroporites secatus) [START_REF] Rouire | Notice explicative, carte géologique de la France (1/250000[END_REF][START_REF] Elmi | Notice explicative, carte géologique de la France (1/50000)[END_REF][START_REF] Poli | Stratigraphie séquentielle haute-résolution, modèles de dépôt et géométrie 2D-3D des séquences triasiques de la marge théthysienne ardéchoise[END_REF], have an uncomfortable contact with the Upper Paleozoic rocks and the Hercynian basement of the Massif Central. The oldest Triassic deposits correspond to the "Formation Arkosique et Conglomératique" (Fig. 1b). They are Middle Triassic (Anisian-Ladinian) in age and contain fluvial conglomerates and sandstones with ventifacts [START_REF] Durand | The problem of the transition from the Permian to the Triassic Series in southeastern France: comparison with other Peritethyan regions[END_REF]. These deposits are interpreted as having formed in braided rivers and lagoonal environments [START_REF] Courel | Trias in Synthèse géologique du Sud-Est de la France[END_REF][START_REF] Poli | Bordure cévenole de Valence à Lodève : Groupe Français du Trias[END_REF][START_REF] Elmi | Notice explicative, carte géologique de la France (1/50000)[END_REF]. Locally, they yield halite pseudomorphs, desiccation cracks and vertebrates tracks, implying an arid climate (Evans 1911;[START_REF] Bourquin | Lower Triassic sequence stratigraphy of the western part of the Germanic Basin (west of Black Forest): Fluvial system evolution through time and space[END_REF][START_REF] Bourquin | The Permian-Triassic boundary and Lower Triassic sedimentation in western European basins: an overview[END_REF]. The fossil vertebrate tracks and trackways document pseudosuchian-dominated faunas typical of the Middle Triassic [START_REF] Demathieu | Les empreintes de pas fossiles des grès triasiques de la mine de Largentière (Ardèche)[END_REF][START_REF] Courel | Une ichnofaune reptilienne remarquable dans les grès triasiques de Largentière[END_REF][START_REF] Gand | Les pistes dinosauroïdes du Trias moyen français : interprétation et réévaluation de la nomenclature[END_REF][START_REF] Gand | Les traces de pas d'amphibiens, de dinosaures et autres reptiles du[END_REF].

The Upper Triassic is represented by the "Formation Argilo-Carbonatée", the "Formation Bariolée d'Ucel" and the "Grès Roux" (Fig. 1B). The "Formation Argilo-Carbonatée", dated from the Ladinian-Carnian, is composed of two black argillite units interbedded with massive dolomite beds, interpreted as having been deposited in a lagoonal setting [START_REF] Courel | Données nouvelles sur le Trias cévenol : chronologie, sédimentologie, implications métallogéniques[END_REF][START_REF] Courel | Trias in Synthèse géologique du Sud-Est de la France[END_REF][START_REF] Poli | Bordure cévenole de Valence à Lodève : Groupe Français du Trias[END_REF][START_REF] Elmi | Notice explicative, carte géologique de la France (1/50000)[END_REF][START_REF] Razin | Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine basin during the Triassic and Jurassic[END_REF]. The Carnian-Norian "Formation Bariolée d'Ucel" contains sandstones, microconglomerates and some argillite layers that formed in a fluvial environment [START_REF] Poli | Bordure cévenole de Valence à Lodève : Groupe Français du Trias[END_REF][START_REF] Razin | Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine basin during the Triassic and Jurassic[END_REF][START_REF] Courel | Sequence stratigraphy along a Triassic transect on the western peritethyan margin in Ardèche (SE France Basin): Correlations with subalpine and germanic realms[END_REF]. The sandstone beds of the "Formation Bariolée d'Ucel" yield the tracks studied here. The ichnofauna is dinosaur-dominated and has been studied extensively [START_REF] Courel | Les empreintes de pas fossiles dans le Trias de la bordure est et nord-est du Massif Central[END_REF], 1976, 2000;[START_REF] Demathieu | Les empreintes de pas fossiles des grès triasiques de la mine de Largentière (Ardèche)[END_REF][START_REF] Gand | Les traces de pas d'amphibiens, de dinosaures et autres reptiles du[END_REF]). The Rhaetian "Formation de la Croix Blanche" contains sandstones with flaser bedding and bivalves, and was deposited in a tidally influenced marine environment [START_REF] Reineck | Classification and origin of flaser and lenticular bedding[END_REF][START_REF] Elmi | Le Lias inférieur et moyen entre Aubenas et Privas (Ardèche): Travaux du laboratoire géologique de Lyon[END_REF][START_REF] Elmi | Notice explicative, carte géologique de la France (1/50000)[END_REF][START_REF] Courel | Sequence stratigraphy along a Triassic transect on the western peritethyan margin in Ardèche (SE France Basin): Correlations with subalpine and germanic realms[END_REF]. These deposits mark the beginning of a marine transgression that continued until the Early Jurassic [START_REF] Elmi | Notice explicative, carte géologique de la France (1/50000)[END_REF][START_REF] Razin | Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine basin during the Triassic and Jurassic[END_REF].

The site studied here is in the town of Ucel in the Ardèche department, southeastern France.

Discovered by one of us (M.V.) in 2007, this site was only briefly mentioned once in Gand et al. (2007, p.22) under the local name "La Bourzède" (misspelled "La Burzède"). It is now a new referenced geosite within the Monts d'Ardèche UNESCO Global Geopark, and is more appropriately called "Le Sartre". [START_REF] Gand | Les traces de pas d'amphibiens, de dinosaures et autres reptiles du[END_REF] provided a preliminary report on footprints assigned to Grallator isp. and to Otozoum grandcombensis. The site is currently being extended for public access. A detailed ichnotaxonomic analysis of the tracks from Le Sartre is on-going and will be described in detail elsewhere. At present, the ichnoassemblage is composed of more than 300 tracks among which footprints of Grallator isp. dominate.

MATERIAL AND METHODS

The sedimentary facies described and depositional settings inferred are based on observations made at Le Sartre together with data obtained from the macroscopic and microscopic study of 10 lithological samples. For the purpose of facies description and taphonomical observations, six thin sections were made in substrate and track samples prior observation with an AZ100 Nikon optical microscope. We use [START_REF] Dott | Wacke, graywacke and matrix -What approach to immature sandstone classification?[END_REF] In this paper, the track-bearing surface refers to the level on which tracks are visible today.

The tracks, however, can be true tracks, undertracks or overtracks [START_REF] Hitchcock | Ichnology of New England. A report on the sandstone of the Connecticut Valley, especially its fossil footmarks[END_REF][START_REF] Lockley | Tracking dinosaurs: a new look at an ancient world[END_REF]Allen 1997;[START_REF] Marty | Formation and taphonomy of human footprints in microbial mats of present-day tidal-flat environments: implication for the study of fossil footprints: Ichnos[END_REF][START_REF] Pérez-Lorente | Dinosaur footprints & trackways of La Rioja[END_REF][START_REF] Marty | Dinosaur Track Terminology: A Glossary of Terms[END_REF]. The tracking surface is the layer on which the contact between the substrate and the animal's foot occurred (e.g. Pérez-Lorente 2015; [START_REF] Falkingham | Dinosaur tracks: The next steps[END_REF].

FACIES AND DEPOSITIONAL ENVIRONMENTS OF LE SARTRE

At Le Sartre, the track-bearing surface is 50 m long and 4-to 8-m-wide and is located on top of a 7 m thick, coarse siliciclastic unit (Unit 1) that dips gently towards the SSE (Fig. 2A-B).

This unit is subdivided into two parts. The basal part is 5.5 m thick, massive and made of meter-scale wide amalgamated sandstone channels amongst which decimeter-scale clayey layers intercalate. The upper part is 1.5 m thick and made of conglomeratic layered sheet-like deposits (Fig. 2B-C). A second unit (Unit 2) starts with a 50 cm thick interval of clay-and siltstones that is overlain by a 3 m thick succession composed of meter-scale wide amalgamated sandstone channels (Fig. 2C).Five facies associations are identified in these two units and presented in Figure 3. They are numbered relative to increasing flow energy. Unit 1 is composed of three facies associations (Fa1, Fa4 and Fa5). Facies association Fa1 consists of argillite-rich lenticular deposits. It contains fine siltstones with a few mm-sized quartz grains organized in discontinuous mm-thick layers. Fa1 is locally incised by channel-shaped sandstone bodies (Fa5) and characterized by horizontally-aligned calcareous concretions (Fig. 2C). Fa5 is composed of grain-supported coarse-grained sandstones to microconglomerates forming 0.5-to 2-m-thick, 10-to 20-m-wide aggrading amalgamated lenticular bodies with erosive bases (Fig. 2B-C). They are locally interlayered with conglomerates made of pebbles up to several cm in diameter, forming 10-to 30-cm-thick matrix-supported intervals. The lenticular bodies can show faint cross-bedding and current ripples and are arranged into upward-fining successions. This Fa5 interval is overlain by 10-to 20-cm-thick, continuous tabular and stacked sandstones beds assigned to Fa4 (Fig. 2 B-C). These sandstones beds are aggrading and each of them are grain-supported with a fining-upwards trend, from 0.2 to 5 mm, with some cm-sized pebbles. The last 4 or 5 beds show a retrograding pattern indicated by successive pluri-cm scale thick lobes (Fig. 4A-B). Each lobe shows a decreasing grain size following the flow direction. Footprints associated with desiccation cracks are observed on top of this sedimentary succession, at the surface of the lobes.

These facies associations record mainly the vertical transition from a possibly high-sinuosity fluvial system (FA5) to its disconnection stage, during which the last bedload deposits were made (FA4). The fluvial system developed upon the floodplain, indicated by the presence of argillites with calcareous root concretions corresponding to paleosols and occasional small-scale quartz layers interpreted as flooding events (Wolman and Leopold 1957;[START_REF] Miall | A review of the braided-river depositional environment[END_REF][START_REF] Miall | Lithofacies types and vertical profile models in braided river deposits: a summary[END_REF][START_REF] Cant | Development of a facies model for sandy braided river sedimentation: comparison of the South Saskatchewan river and the Battery Point Formation[END_REF][START_REF] Cant | Fluvial process and facies sequence in the sandy braided South Saskatchewan river[END_REF][START_REF] Ramos | Evolution of Buntsandstein Fluvial Sedimentation in the Northwest Iberian Ranges (Central Spain)[END_REF][START_REF] Kraus | Eocene hydromorphic paleosols: significance for interpreting ancient floodplain processes[END_REF]. The aggrading to prograding channel beds and sandbars are interpreted as an active, possibly highsinuosity fluvial system [START_REF] Fisk | Fine grained alluvial deposits and their effects on Mississippi River activity: Mississippi River Commission[END_REF]Allen 1964;[START_REF] Cant | Development of a braided-fluvial facies model for the Devonian Battery Point Sandstone[END_REF][START_REF] Ramos | Evolution of Buntsandstein Fluvial Sedimentation in the Northwest Iberian Ranges (Central Spain)[END_REF][START_REF] Plint | Sedimentary facies analysis: a tribute to the research and teaching of Harold G. Reading: Special publication of the International Association of Sedimentologists[END_REF][START_REF] Miall | The Geology of Fluvial Deposits[END_REF]. The continuous aggrading tabular stacked sandstone beds and the retrograding pattern observed towards its top indicate a reduction of the flow energy (Ashley 1990) that led to channel abandonment (Allen 1964(Allen , 1965;;[START_REF] Cant | Development of a braided-fluvial facies model for the Devonian Battery Point Sandstone[END_REF][START_REF] Plint | Sedimentary facies analysis: a tribute to the research and teaching of Harold G. Reading: Special publication of the International Association of Sedimentologists[END_REF][START_REF] Miall | The Geology of Fluvial Deposits[END_REF][START_REF] Collinson | Sedimentary structures[END_REF] as indicated here by the presence of desiccation cracks. Each retrograding lobe and its composition indicate a weaken flow energy in paleocurrents that were flowing towards the ENE (Fig. 4A-B).

Unit 2 is composed of two facies associations (Fa2 and Fa3). Facies association Fa2 is subdivided into siltstones to medium-grained sandstones (Fa2a) and thin claystones (Fa2b).

Fa2a contains 2-to 20-cm-thick, continuous tabular or lenticular siltstone layers showing desiccation cracks, rare halite pseudomorphs and current ripples. Scarce mm-thick discontinuous layers of fine-to medium-grained sandstones are intercalated in these siltstones. Fa2b is characterized by several 1-5 cm thick discontinuous clay drapes with desiccation cracks (Fig. 5B). This facies association is surmounted by facies association Fa3, which is also subdivided into two facies (Fa3a and Fa3b). Fa3a is formed by 5-to 25-cmthick, 10-to 30-m-wide prograding siltstone to coarse-grained sandstone sets (Fig. 5A-B).

The sets show occasional erosive bases and fining-upward successions. Fa3b contains continuous, 5-to 20-cm-thick claystones that underline prograding sets with rare desiccation cracks.

Unit 2 records a floodplain depositional environment (Fa2b and Fa3b) in which an abandoned channel was reactivated, as indicated by the presence of successive prograding sandy channels (Fa2a and Fa3a). The claystone and siltstone deposits with small current ripples and desiccation cracks (Fig. 5B) indicate recurrent emersion and flooding episodes, respectively.

The presence of claystones indicates low-energy conditions in the abandoned channel,

showing its transition to an abandoned stage (Fig. 3). The progradation of the sets is indicative of channel reactivation (Wolman and Leopold 1957;Allen 1964Allen , 1965;;[START_REF] Plint | Sedimentary facies analysis: a tribute to the research and teaching of Harold G. Reading: Special publication of the International Association of Sedimentologists[END_REF].

ICHNOTAPHONOMY

Following the recent extension of the track-bearing surface, it currently displays two areas.

The first, called the 'weathered area' hereafter, is dark and has been exposed and weathered over many decades. The second, called the 'fresh area', is light in color and has been exposed only since April 2019 only (Fig. 4A-B). The former displays the coarse-grained (0.2 to 2 mm) sediment track-bearing surface (Fa4), whereas the latter shows this surface locally covered by patches of silts and clays (Fa2) (Fig. 6A). The entire surface yields abundant tridactyl footprints of Grallator isp. (Fig. 2A,4B) and comprise a typical Late Triassic Grallator ichnocoenosis (sensu Hunt andLucas 2006, 2007;[START_REF] Buatois | Ichnology: Organism-Substrate Interactions in Space and Time[END_REF]. The tridactyl morphology of Grallator isp. is used here as a template for assessing ichnotaphonomic features and the morphological variability of the footprints. The latter are all preserved as concave epireliefs. Despite the coarseness of the sediment, the track-bearing surface occasionally yields some footprints showing complete digit impressions, claw marks, digital pads and well-defined imprint walls (Fig. 6B-D). The occurrence of such imprints in the weathered area shows that long-term erosion did not alter their quality (Fig. 6B-D).

The fresh area preserves more ichnotaphonomic and sedimentological features. A first generation of desiccation cracks occurs on top of the coarse-grained sandstones, T lined by a thin layer of clays and filled by silts (Fig. 6G). These desiccation cracks do not affect the underlying sandstones. They can be found all around the tracks but are erased within them (Fig. 6H), indicating that the animals walked over this first generation of desiccation cracks.

The thin clay-and siltstones were deformed in the footprints and displaced laterally, resulting in mm-scale displacement rims (Fig. 6H, 7A left). In some instances, these fine-grained sediments were locally injected into the underlying coarse-grained sediments. All these footprints and the surrounding sediment are covered by a new duet of clay-and siltstone layers that draped and sealed the whole surface. The entire surface was affected later by a new generation of desiccation cracks that were filled by silts and fine-grained sands, some of which formed in the overtracks (Fig. 7B). Some of these desiccation cracks are so deep that they affect the underlying coarse-grained sandstones at a depth of up to 1 cm. Although sedimentation continued, no tracks were found in the subsequent layers.

These observations on the layers and sedimentary structures provide a relative chronology that help locate the tracking surface. It is bracketed by the two sets of successive clay-and siltstones and by the two generations of desiccation cracks. The animals walked over the first set of fine-grained sediments in which they left their footprints. When preserved, these are therefore true tracks (Fig. 7A left). This implies that most of the tracks observed in the coarsegrained sandstones (Fig. 6B-D) are in fact transmitted undertracks, although a few could be penetrative undertracks. Both the thinness of the first set of clay-and siltstones and the clay injections only observed in the bottom of some tracks indicate that the latter can be interpreted as unsealed penetrative tracks (Fig. 7C).

Could this inference have been made from the weathered area only? In the absence of the fine-grained layers and their associated sedimentary structures, there is still evidence for their role in the track formation processes. The evidence consists of flaked clay coatings forming very small patches in some footprints, particularly at the digit tips and joints (Fig. 6E-F). At the bottom of some tracks, clay injections in the sandstones show the displacement of quartz grains by the clays, inducing a lack of cohesion between quartz grains (Fig. 7D-E). Lateral to the tracks, when clays are observed in the sandstones, they only infill small pores of an undisturbed sediment. Although inconspicuous on the weathered area, these observations confirm that at least one claystone layer overlaid the coarse-grained sandstones before being trampled.

DISCUSSION

The combined sedimentological and ichnotaphonomical observations allow us to propose a model involving several phases for track formation and preservation at the ichnosite of Le Sartre (Fig. 8). The first phases involves the deposition of the retrograding lobes corresponding to what became an abandoned channel at the top of Unit 1 (Fig. 8A-B). Each of these lobes tends to show a lateral decrease in grain size towards the ENE. After a decrease in flow energy indicated by the retrogradation pattern (Fig. 8B), the abandoned channel was covered by a clay layer corresponding to the base of Unit 2 (Fig. C). The base of Unit 2 shows several flooding and emersion episodes (Fig. 8C-F). During the emersion of the first clay layer, desiccation cracks were generated (Fig. 8D) and filled by silts during the following flooding event (Fig. 8E). Both the clay and silt layers were formed under water, respectively at low and moderate flow energy. As these deposits covered all the lobes, despite the more recent lobes being topographically higher, the water depth must have been at least several decimeters. The activity by the dinosaurs was recorded on top of the silt (Fig. 8F), deforming the clay and silt layer (Fig. 7A left) and erasing the first generation of desiccation cracks (Fig. 6H). It shows that the sediments of both the base of Unit 2 and the top of Unit 1 were soft and cohesive at that time. The collapsed walls of some tracks (Fig. 7C) and a sliding trace (Fig. 7F) located on the distal part of one of the lobes suggest that the sediment was unevenly cohesive across the site when the animal walked in the channel. The following phases recorded a new increase and a decrease in water level marked by the deposition of clayey sediments, and then another flooding with deposition of silty sediments (Fig. 8G-I). An episode of emergence between the clayey and silt deposits was marked by deeper desiccation cracks that affected the top of Unit 1 (Fig. 8H), and some of the tracks (Fig. 7B).

Sedimentation continued, eventually transitioning from a low-energy floodplain environment to a new active channel dynamic (Fig. 5) and the ichnosite was buried further down. Today the exposed full outcrop shows erosion-resistant transmitted undertracks set in the coarsegrained sandstones on the top of Unit 1 together with erosion-prone true tracks and partiallyfilled tracks at the base of Unit 2 (Fig. 8J). As of November 2019, only a few (fast deteriorating) true tracks and some overtracks are left on the fresh area.

Overall this model is built invoking only abiotic parameters unlike models that infer a crucial role of microbial mats in the formation and preservation of tracks, as found in many other tracksites worldwide (e.g. [START_REF] Carmona | The role of microbial mats in the preservation of bird footprints: a case study from the mesotidal Bahia Blanca estuary (Argentina)[END_REF][START_REF] Carmona | Microbially induced sedimentary structures in Neogene tidal flats from Argentina: Paleoenvironmental, stratigraphis and taphonomic implications: Palaeogeography[END_REF][START_REF] Carvahlo | Preservation of dinosaur tracks induced by microbial mats in the Sousa Basin (Lower Cretaceous)[END_REF][START_REF] Cariou | Dinosaur track record on a shallow carbonate-dominated ramp (Loulle section[END_REF][START_REF] Prescott | Microbial mats and ichnofauna of a fluvial-tidal channel in the lower Pennsylvanian Joggins Formation[END_REF][START_REF] Dai | Microbially-induced sedimentary wrinkle structures and possible impact of microbial mats for the enhanced preservation of dinosaur tracks from the Lower Cretaceous Jiaguan Formation near Qijiang[END_REF][START_REF] Davies | Resolving MISS conceptions and misconceptions: A geological approach to sedimentary surface textures generated by microbial and abiotic processes[END_REF]. These biotic models rely on the fact that microbial mats increase the cohesiveness of the substrates on which they grow and protect the tracks after their formation by preventing their being eroded in the short-term (e.g., [START_REF] Cuadrado | Identification of microbially induced sedimentarystructures over a tidal flat[END_REF]. The presence of clayey and silty layers represents an alternative mechanism that favors the formation and preservation of tracks, when placed over competent coarse-grained sediments. Therefore, it seems that this specific lithological superposition is sufficient for the formation and preservation of tracks. As shown here, the coarse-grained sediments (>1-2 mm) observed on the top of Unit 1 were cohesive enough to prevent the disappearance of the tracks thanks to the presence of clay-and siltstones layers. The sedimentation following trackway formation, dominated by fine grains, favored preservation of the tracks. Such an abiotic scenario, invoking contrasts in sediment grain size and rheology, has been proposed previously based field observations and analogic experiments [START_REF] Laporte | Tracks and substrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya[END_REF]Allen 1997;[START_REF] Paik | Dinosaur track-bearing deposits in the Cretaceous Jindong Formation, Korea: occurrence, palaeoenvironments and preservation[END_REF][START_REF] Milàn | The impact of sediment consistency on tracks and undertracks morphology: experiments with Emu tracks in layered cement: Ichnos[END_REF][START_REF] Rainforth | Swimming theropod? A new investigation of unusual theropod footprints from Dinosaur State Park[END_REF][START_REF] Buatois | Ichnology: Organism-Substrate Interactions in Space and Time[END_REF][START_REF] Falkingham | The Goldilocks effect: preservation bias in vertebrate track assemblages[END_REF][START_REF] Da Silva | Footprints of large theropod dinosaurs and implications on the age of Triassic biotas from Southern Brazil[END_REF][START_REF] Milner | Dinosaur swim track assemblages: characteristics, contexts, and ichnofacies implications[END_REF]. However, to our knowledge, the outcome of these scenarios is the formation and preservation of tracks in fine-grained sediments only and mainly in overbank intervals (particularly in floodplains) within a fluvial succession [START_REF] Maples | Paleoecological and Sedimentological Significance of Bioturbated Crinoid Calyces[END_REF][START_REF] Buatois | Permian nonmarine invertebrate trace fossils from southern Patagonia, Argentina: Ichnologic signatures of substrate consolidation and colonization sequences[END_REF]). In addition, [START_REF] Lockley | The paleoenvironmental context, preservation and paleoecological significance of dinosaur tracksites in the western USA[END_REF] and [START_REF] Buatois | Ichnology: Organism-Substrate Interactions in Space and Time[END_REF] illustrated the formation of densely tracked surfaces impressed on a muddy substrate, and cast by sand, during a subsequent flooding event. Clearly, the occurrence of footprints showing a good physical preservation in coarse-grained sediments results from an unusual combination of factors and makes Le Sartre a remarkable ichnosite. It shows that grain size can on occasion be rejected as being an adequate predictor of preservation quality for vertebrate fossil tracks, and also that microbially-driven processes may not be invariably involved in track preservation. The implication of microbial mats is a hypothesis that cannot be entirely rejected, but there is currently no evidence for it.

It is, of course, unlikely that tracks would be routinely formed and preserved in coarsegrained sediments deposited by high-energy events within dynamic environments. The intuitive notion, however, that such environments are less favorable may lead to an a priori bias during ichnological prospection. In this regard, this situation is somehow reminiscent of earlier debates on the preservation of tracks in eolian deposits [START_REF] Mckeever | Trackway preservation in eolian sandstones from the Permian of Scotland[END_REF]. There are nonetheless some instances of tracks found in "coarse" sediments throughout the world [START_REF] Milàn | Preservation and erosion of theropod tracks in eolian deposits: examples from the Middle Jurassic Entrada Sandstone[END_REF][START_REF] Seiler | A wet interdune dinosaur trampled surface in the Jurassic Navajo Sandstone, Coyote Buttes, Arizona: Rare preservation of multiple tracks types and tail traces[END_REF][START_REF] Jackson | Range of experimental dinosaur (Hypsilophodon foxii) Footprint due to variation in sand consistency: how wet was the track?[END_REF]Xing et al. 2015b) and in the Ardèche region [START_REF] Courel | Une nouvelle espèce Coelurosaurichnus grancieri du Trias de l'Ardèche[END_REF]. In these cases, however, the grain sizes reported for the track-bearing surfaces (fine-to medium-grained sands) are smaller than those observed at Le Sartre (medium-grained sand to microconglomerate, >0.2-2 mm, with some pebbles up to several centimetres; Fig. 3).

Beyond the general acceptance that tracks can be formed only exceptionally in coarse sediments, most authors agree that in such cases the fidelity in which the tracks replicate pedal anatomy should be low [START_REF] Laporte | Tracks and substrate reworking by terrestrial vertebrates in Quaternary sediments of Kenya[END_REF][START_REF] Lockley | The paleoenvironmental context, preservation and paleoecological significance of dinosaur tracksites in the western USA[END_REF]Allen 1997;[START_REF] Carvahlo | Dinosaur footprints from Northeastern Brazil: Taphonomy and environmental setting: Ichnos[END_REF][START_REF] Gatesy | Neither bones nor feet: track morphological variation and 'preservation quality[END_REF], or even that the limited cohesiveness of the substrate makes it impossible to preserve anatomical features such as digit length, digital pads and claw marks (Alcalá et al. 2014;[START_REF] Pérez-Lorente | Dinosaur footprints & trackways of La Rioja[END_REF]. Regardless of grain size, the high number of factors that control track formation and, the complex interactions among them imply that some tracks will never, or barely, show any anatomical details, even immediately following their formation. [START_REF] Gatesy | Neither bones nor feet: track morphological variation and 'preservation quality[END_REF] showed that although such tracks provide almost no information about their maker's anatomy, their morphology could really be in the exact state and shape in which they were formed. In that perspective, the recent critical reviews on terminology and preservation scales by [START_REF] Belvedere | A numerical scale for quantifying the quality of preservation of vertebrate tracks[END_REF], [START_REF] Gatesy | Neither bones nor feet: track morphological variation and 'preservation quality[END_REF], [START_REF] Marchetti | Can undertracks show higher morphologic quality than surface tracks? Remarks on large amphibian tracks from the early Permian of France[END_REF] and [START_REF] Marchetti | Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present[END_REF] represent much-awaited contributions for clarifying communication among vertebrate ichnologists.

One of the interesting characteristics of Le Sartre is that many tracks have a high fidelity to their morphology at the end of their registration. The tracks exhibit a high physical (P-) preservation sensu [START_REF] Marchetti | Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present[END_REF] (Fig. 7C; 7F) but also good M-preservation in some instances (presence of claw marks and digital pads; Fig. 6C). Another interesting characteristic of this site is that the first survey of the surface was made in 2016-2017 and two others in 2019 after the site extension. The tracks found after widening the site had not been exposed to weathering. This tracksite thus currently presents tracks in two states of preservation. The best preserved transmitted undertracks on the weathered part of the study surface still occur in a good state of physical preservation (Fig. 6B-C). While these remarkable transmitted undertracks admittedly do not meet the optimal criteria for ichnotaxonomy as proposed by [START_REF] Marchetti | Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present[END_REF], the walls are well defined, some digital pads are present, and a few claw marks and drag marks can be observed. One might therefore give these transmitted undertracks an M-preservation score of 2.0 according to [START_REF] Marchetti | Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present[END_REF] scale. This is unexpected considering the coarseness of the sediment in which they are set and the weathering they suffered. Some of the true tracks and transmitted undertracks found on the fresh part of the track-bearing surface can be attributed the same M-preservation score. While weathering has little effect on the score of transmitted undertracks, the rare true tracks show a low preservation potential, or P-preservation (Fig. 7A), as they are rapidly destroyed because the thin clay-and siltstones layers are easily eroded. This demonstrates once again that in sediments like the ones examined here true tracks tend to become fragile structures once unearthed [START_REF] Lockley | Did "Brontosaurus" ever swim out to sea? Evidence from brontosaur and other dinosaur footprints: Ichnos[END_REF][START_REF] Lockley | Tracking dinosaurs: a new look at an ancient world[END_REF][START_REF] Brand | Underprints of vertebrate and invertebrate trackways in the Permian Coconino Sandstone in Arizona: Ichnos[END_REF] and that they can disappear in a few weeks. However, the former presence of the true tracks is alluded to by the silt and clay injections preserved in the underlying sandstones and conglomerates that persist longer (and are still evident at present).

The dinosaur footprints from Le Sartre can also be discussed at the scale of the depositional sequence. As proposed by some authors (e.g. [START_REF] Buffard | Mise en évidence de deux niveaux bien individualisés à empreintes theromorphoïdes, lacertoïdes et crocodiloïdes dans le grès bigarré de Haute-Saône[END_REF]Tucker and Burchette 1977;[START_REF] Lockley | The paleoenvironmental context, preservation and paleoecological significance of dinosaur tracksites in the western USA[END_REF][START_REF] Reading | Sedimentary environments: processes, facies, and stratigraphy[END_REF], the formation and preservation of tracks in fluvial environments is preferentially observed on top of flood deposited successions in overbank settings or in abandoned or inactive channel deposits. Our observations are generally consistent with these conclusions as the tracks from Le Sartre are within a flooddeposited succession (Fig. 2C) in an abandoned channel (Unit 2, Fig. 3). Although clay drapes are considered to have played a role in the track preservation after they were formed, we show here that these drapes can also be involved in the processes responsible for tracks formation.

More precisely, true tracks are set in flood deposits, but the transmitted undertracks are set in coarse-grained sediments representing active channel deposits. [START_REF] Lockley | The paleoenvironmental context, preservation and paleoecological significance of dinosaur tracksites in the western USA[END_REF] mentioned rare examples of tracks from coarse-grained proximal fluvial deposits (with low preservation quality) and noted that tracks are much more frequently encountered in distal floodplain environments (see also [START_REF] Buatois | Ichnology: Organism-Substrate Interactions in Space and Time[END_REF]. At Le Sartre, the very abrupt change in sedimentary regime between the high-energy channel beds, the abandoned channel and the overbank settings allowed the formation and preservation of tracks in an environment considered hitherto by some authors as hostile to tracks formation (e.g., [START_REF] Carvahlo | Preservation of dinosaur tracks induced by microbial mats in the Sousa Basin (Lower Cretaceous)[END_REF].

CONCLUSION

The ichnosite of Le Sartre is outstanding as most of its dinosaur footprints are set in a substrate the grain size of which is above the range identified as being favourable to the formation and preservation of fossil tracks. The associated ichnotaphonomic model suggests that dinosaur footprints were preserved by abiotic processes only, the main factor being the lithological contrast between successive sedimentary layers. In turn, this is at odds with the most frequent models that rely heavily on fine-grained sediments, mostly muddy and microbial mats present in low-energy environments.

The tracks from Le Sartre were formed on the coarse-grained bed of an abandoned channel through clay-and siltstones that were being deposited during the channel filling stage. Most of the tracks are transmitted undertracks formed in coarse-grained sands deformed with the clay and silt layers on which the dinosaurs walked. The difference in competency and plasticity between sand, silt and clay influenced the tracks' formation and further drapings by clay and silts enabled their preservation. Weathering likely eroded true tracks over a few weeks, whereas the transmitted undertracks have proved to be more resistant at le Sartre.

Current investigations of the Upper Triassic sandstones from Ardèche suggest that such an unusual phenomenon might be present in other, nearby, localities. Some transmitted undertracks preserved in coarse-grained sediments retain sufficient key anatomical features and will lend themselves to at least generic-level ichnotaxonomic assignments in future works. mats in siliciclastic depositionnal systems through time: SEPM Journal of Sedimentary Research Special Publication, Tulsa, v. 101, p. 153-162, doi: 10.2110 Simplified geological map of the area based on the 1:50000 Aubenas geological map [START_REF] Kerrien | Carte géologique de la France (1/50000[END_REF]). B) Middle and Upper Triassic lithostratigraphic units for the Ucel area. Based on [START_REF] Rouire | Notice explicative, carte géologique de la France (1/250000[END_REF], Elmi et al. 1996[START_REF] Courel | Sequence stratigraphy along a Triassic transect on the western peritethyan margin in Ardèche (SE France Basin): Correlations with subalpine and germanic realms[END_REF].

  classification of sandstones, and Wentworth's (1922) grain size classification. After the first investigation by two of us (G.G. and M.V.) in 2007-2008, about 200 footprints were found during the first field session in 2016. Other field sessions were conducted after the exposed track-bearing surface was enlarged using heavy machinery in April and November 2019. The extension of the exposed surface revealed more than 100 additional tracks. These tracks were used to do a more detailed taphonomic study, as they have not been exposed to weathering before April 2019. The last survey was made in November 2019. All tracks were labelled and photographed, and photogrammetric reconstructions of the track were made using the Agisoft photoscan Professional software (v1.2.4). The 3D models and Digital Elevation Models (DEM) of the tracks presented in this study are available as Supplementary material.

  FIG. 1 -Geographical and geological context of the Le Sartre track-bearing locality. A)

FIG. 2 -

 2 FIG. 2 -Sedimentological setting of the Le Sartre outcrop. A) View of the track-bearing

  FIGURE 1

ACKNOWLEDGEMENTS

We are grateful to Peter Falkingham, Matteo Belvedere, Associate Editor XXX and Editor Patrick John Orr for their detailed and constructive comments that helped to improve the manuscript. We express our gratitude to the Parc Naturel Régional des Monts d'Ardèche (PNRMA)-Monts d'Ardèche UNSECO Global Geopark for facilitating our field investigations and for financial support. We acknowledge the Ucel Municipality for the permission to investigate the Le Sartre geosite and for making extension works possible. We also thank Suzanne Jiquel for her help with fossil casts and Pascal Taubaty for making the thin sections. This study is part of the scientific partnership between the PNRMA and the Biogéosciences laboratory for the study of Permo-Triassic trace fossils in Ardèche. BIBLIOGRAPHY ALCALÁ, L., PÉREZ-LORENTE, F., LUQUE, L., COBOS, A., ROYO-TORRES, R., MAMPEL, L., 2014, Preservation of dinosaur footprints in shallow intertidal deposits of the Jurassic-Cretaceous transition in the Iberian Range (Teruel, Spain): Ichnos, v. 21, p. 19-31, doi: 10.1080/10420940.2013.873721. ALLEN, J., R., L., 1964, Studies in fluviatile sedimentation: six cyclothems from the lower Old Red Sandstone, Anglowelsh Basin: Sedimentology, v. 3, p. 163-198. ALLEN, J., R., L., 1965, A review of the origin and characteristics of recent alluvial sediments: Sedimentology, v. 5, p. 89-191. ALLEN, J., R., L., 1997, Subfossil mammalian tracks (Flandrian) in the Severn Estuary, S. W. Britain: mechanics of formation, preservation and distribution: Philosophical Transactions of the Royal Society B: Biological Sciences, v. 352, p. 481-518, doi: 10.1098/rstb.1997.0035. ASHLEY, G.M, 1990, Classification of Large-Scale Subaqueous Bedforms: A New Look at an Old Problem-SEPM Bedforms and Bedding Structures: SEPM Journal of Sedimentary Research, v. 60, doi: 10.1306/212F9138-2B24-11D7-8648000102C1865D


Development of a Tool to Apply Chemical Fertilizer for Pineapple (Ananas comosus) Cultivation

Keywords: Applicator, Efficiency, Fertilizer, Pineapple, Tool I

Pineapple (Ananas comosus) is a heavy feeder and needs more nutrients to get an optimum yield. Fertilizer application is problematic in all Pineapple cultivations mainly due to two reasons. On the one hand, there are spiny and pointed leaves and on the other hand, the place where fertilization needs to be applied. The fertilizer should be applied to the base of the leaves and is a laborious and annoying practice, especially when done manually in commercial cultivation. Therefore, there is a necessity to develop a convenient technique to facilitate the fertilizer application. Hence, an experiment was conducted at the University of Colombo Institute for Agro-Technology and Rural Sciences, Hambantota, Sri Lanka to develop a simple tool to apply chemical fertilizer at the base of Pineapple leaves. The tool was developed using PVC pipes, nuts, bolts, rubber bands, a spring and glue. All these items were assembled in an orderly manner to develop a smart and a simple tool to achieve the purpose. The height of the tool can be adjusted by changing the fertilizer loading component. A questionnaire survey was conducted among the pineapple cultivators to evaluate the usefulness of the tool. The weight, height, safety, efficiency, cost and overall acceptability were evaluated using a fivepoint Likert scale. Further, the developed tool was compared with manual fertilizer application to monitor the time taken to apply fertilizers and the labour cost using 20 pineapple plants at the same age. The independent sample T-test was used to test the significance at 5% level. The tool placed the recommended amount of fertilizer/plant in two pushes (5.1 ± 0.19g) and covered 20 plants with an efficiency of 326.84 ± 2.46%. And efficiency of the cost involvement of the tool was 305.84 ± 3.58%. The farmer responses indicated that the tool was a simple, portable, smart and userfriendly tool with more advantages.

INTRODUCTION

One of the main commercial fruit crops grown in Sri Lanka is pineapple (Ananas comosus), which has a significant export market potential due to the country's ability to produce some of the best pineapples in the world. Due to a shortage of supplies and exportable quality, Sri Lanka, which ranks 34 th among countries that produce pineapple, is unable to meet the rising demand for the fruit on domestic and international markets [START_REF] Rupasinghe | Determinants for Contribution of Pineapple Growers for Export Volume in Gampaha District in Sri Lanka[END_REF]. Both in the lowlands and at higher altitude of up to 1,000 m above sea level, pineapples thrive in a temperature range of 18-32 0 C. Despite being a drought-tolerant crop, pineapples will still bear fruit in years with annual rainfall between 650 and 3,800 mm. The growth environment, cultivation methods, and variety all affect pineapple quality [START_REF] Hossain | World Pineapple Production: An Overview[END_REF]. Costa Rica, the Philippines, Netherland, USA, and Belgium were the top five pineapple exporters in the world in 2020. Total export quantity of 3.1 million tons in 2020, representing a 7.9 percent fall compared to 2019 [START_REF] Fao | Major Tropical Fruits Market Review[END_REF]. For pineapple, Sri Lanka's rank among global exporters was 36 and its market share in world pineapple market was 0.09 [START_REF] Silva | Consumption and dietary intake of fruits and vegetables in Sri Lanka with a focus on traditional and indigenous fruits and vegetables[END_REF].

Nitrogen and potassium fertilization greatly impact pineapple fruit yield, organoleptic, and sanitary quality [START_REF] Spironello | Pineapple yield and fruit quality effected by NPK fertilization in a tropical soil[END_REF]. Nitrogen is essential to maintain high growth rates, and pineapple response to N fertilization is strong, making it possible to produce high yields with short growing cycles. Potassium vital role in fruit quality [START_REF] Hepton | Cultural system. In The pineapple: Botany[END_REF], and plants and fruits require large quantities of K. The K/N ratio is also essential to yielding and organoleptic quality build-up. Although recommended fertilizer quantities vary according to the cultivar. As recommended by DOA Sri Lanka, fertilizers for pineapple plants should be applied on initially one month after planting and thereafter every 3-4 months after planting at the rate of urea -10g/ plant, TSP -5g to 7g/plant and MOP -15g/plant. Chemical fertilization thus represents a large part of total production costs.

Large-scale pineapple cultivation faces a challenge in fertilizer application. In Sri Lanka, manual application is the primary method of fertilizer application due to the difficulty of applying it to the leaf base. However, this method often causes hand injuries to farmers, which discourages them from using it. Therefore, there is a need to develop a simple tool to facilitate fertilizer application for pineapple farmers. An experiment was conducted with the aim of developing such a tool that could apply chemical fertilizers to the base of pineapple leaves and designing an efficient instrument for the precise application of fertilizer to pineapple plants, while ensuring the safety of farmers.

II. MATERIALS AND METHODS

A. Design Concept

The instrument we have developed allows for the targeted application of fertilizer to the base of pineapple plant leaves. The key components of this instrument include a 1.5-inch PVC fertilizer container, 1-inch PVC pipe, 0.75-inch PVC pipe, rubber band, fertilizer exhaust hole, spring, reducer, 45-degree barrier, and a fertilizer output PVC pipe. To use the instrument, fertilizer is loaded into the fertilizer container, which is then pushed into place and released. Subsequently, the fertilizer output hole opens, allowing the fertilizer to flow through the exhaust PVC pipe fixed at a 45-degree angle. This precise delivery method ensures that the fertilizer reaches the base of the pineapple leaves effectively. Once the fertilizer has been dispensed, the spring and rubber mechanism automatically return the fertilizer container to its original position, closing the fertilizer output hole securely. This instrument not only increases the efficiency of fertilizer application but also minimizes the risk of damage to farmers during the process.

An initial framework of the instrument (Figure 01) was designed using photoshop software (Coreldraw, 2019) to finalize the materials needed to develop the instrument.

B. Development of the Instrument

PVC pipes were selected with diameters of 1.5 inches and 0.75 inches, each measuring 80cm and 20cm in length, respectively (Figure 02). A hole with a diameter of 0.5 cm was drilled at the top end of the 1.5-inch PVC pipe, positioned 8cm from the top. A round wooden piece with a 6cm diameter was inserted into this hole until it reached the end of the pipe. To join the 1.5-inch and 0.75inch PVC pipes, a reducer was used, securely fixing them together (Figure 02a). Another component involved a single piece of 30cm-long PVC pipe with a 1-inch diameter. An end cap with a 1-inch diameter was affixed to the bottom end of this pipe. Additionally, a hole with a 0.5cm diameter was drilled 8cm from the top end of this PVC pipe. In close proximity to this hole, another hole measuring 0.5cm in width and 5cm in length was created, also positioned 8cm from the top. This pipe was then inserted into the 0.75-inch diameter PVC pipe. A screw was fastened to the round wooden piece inserted into the 1.5-inch PVC pipe, and a rubber band was attached to the top end of the instrument. Lastly, a 1-inch PVC pipe, measuring 20cm in length, was selected and cut at a 45-degree angle. This cut piece was then attached to a hole in the instrument. The final assembled tool is indicated in Figure 02b.

C. Working Principle

The rubber band is tightly fastened to the fixed piece, while the screw is connected to the movable piece. When the movable piece is pressed downward, it moves easily, but it returns to its original position with the aid of the rubber band. The open ends of both pieces meet together when the movable piece is pushed down. This action triggers the release of fertilizer, a process that occurs within seconds. The released fertilizer flows through the outlet end of the instrument, targeting the base of the pineapple crop. To utilize this tool effectively, fertilizer must be loaded into the fixed piece, which has a narrower PVC structure, creating the necessary pressure for the fertilizer to descend. By pushing the fertilizer container, minor pressure is applied to the long PVC pipes, facilitating the controlled release of the fertilizer.

D. Operation of the Tool

About 500 grams of fertilizer was filled through the top opening of the tool. The tool is equipped with a handle that allows for easy movement from one location to another. The tool was placed at a distance of 20 cm from the base of the pineapple crop. The end of the tool with the fertilizer was precisely positioned on the base leaf of the pineapple crop. The handle of the tool was pressed and did it for a second. During this brief period, the required amount of fertilizer was effectively applied to the base leaf of the pineapple crop (Figure 02d). This straightforward process facilitated the efficient and precise application of fertilizer to the base of the pineapple crop, ensuring optimal nourishment for healthy growth.

E. Evaluation of the Developed Tool

The weight and length of the tool were measured using scales. Acceptability of the developed tool for its weight, height, safety, handling ability, fertilizer efficiency, cost incurred for the tool and overall acceptability were evaluated five-point Likert scale (1 -Highly acceptable, 2 -Acceptable, 3 -Neutral, 4 -Not acceptable and 5 -Highly not acceptable). The collected data were statistically analyzed using SPSS version 25 and descriptive statistics were explained graphically.

Further, a field experiment was conducted to evaluate the time taken to apply fertilizers and the cost incurred for operation (Figure 02c). The land (1 acre) was divided into 4 parts (4 replicates) and the developed instrument was tested 20 times and average values were taken for comparison and substituted in equation 1. The above variables were measured separately the for manual method and using the tool. The collected data were statistically analyzed using an independent sample T-test at 5% significance level.

Then, time efficiency and cost efficiency were calculated for the tool as follows; Time efficiency was calculated by comparing time taken for fertilizer application using manual method and by using developed tool (E 1).

𝑇𝑖𝑚𝑒 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =

𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑓𝑜𝑟 𝑓𝑒𝑟𝑡𝑖𝑙𝑖𝑧𝑒𝑟 𝑎𝑝𝑝𝑙𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑢𝑠𝑖𝑛𝑔 𝑚𝑎𝑛𝑢𝑎𝑙 𝑚𝑒𝑡ℎ𝑜𝑑 𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑓𝑜𝑟 𝑓𝑒𝑟𝑡𝑖𝑙𝑖𝑧𝑒𝑟 𝑎𝑝𝑝𝑙𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑢𝑠𝑖𝑛𝑔 𝑑𝑒𝑣𝑒𝑙𝑜𝑝𝑒𝑑 𝑡𝑜𝑜𝑙

x 100 % ------E1

Cost for labour was used to calculate the efficiency and it was calculated by comparing cost incurred for fertilizer application using manual method and by using developed tool (E 2).

𝐶𝑜𝑠𝑡 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝐶𝑜𝑠𝑡 𝑖𝑛𝑐𝑢𝑟𝑟𝑒𝑑 𝑓𝑜𝑟 𝑓𝑒𝑟𝑡𝑖𝑙𝑖𝑧𝑒𝑟 𝑎𝑝𝑝𝑙𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑢𝑠𝑖𝑛𝑔 𝑚𝑎𝑛𝑢𝑎𝑙 𝑚𝑒𝑡ℎ𝑜𝑑 𝐶𝑜𝑠𝑡 𝑖𝑛𝑐𝑢𝑟𝑟𝑒𝑑 𝑓𝑜𝑟 𝑓𝑒𝑟𝑡𝑖𝑙𝑖𝑧𝑒𝑟 𝑎𝑝𝑝𝑙𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝑢𝑠𝑖𝑛𝑔 𝑑𝑒𝑣𝑒𝑙𝑜𝑝𝑒𝑑 𝑡𝑜𝑜𝑙

x 100 % ---E2

III. RESULTS AND DISCUSSION

A. Characteristics of the Developed Tool

The developed tool has been designed with specific attributes that make it particularly userfriendly for farmers. It weighs about 328 grams, which is remarkably light. This lightweight feature ensures that it can be carried and manipulated with ease by farmers regardless of their physical strength. Additionally, the tool's height is 1 meter, which falls within a practical range for ease of handling. This height is conducive to comfortable usage, allowing farmers to work with the tool without straining themselves or adopting uncomfortable postures. Height of the tool is adjustable by replacing the upper part (fertilizer loading component). The combination of its light weight and manageable height renders this tool highly convenient and accessible for all farmers, facilitating their agricultural tasks with efficiency and comfort.

B.

Acceptability of the Developed Tool Figure 03 indicates the user response for the developed tool. It was observed that the highest percentage (65%) of the respondents highly accepted the weight of the tool and the comparatively lowest percentage (35%) of the respondents accepted the weight of the tool. Further 55% of the respondents indicated that the height of the tool was highly acceptable and 35%. The lowest percentage (10%) of the respondents were neutral in tool height. Most of the respondents (75%) mentioned the safety of the tool is highly acceptable and 25% of the respondents were acceptable with the safety of the tool while handling.

Approximately 60% of the respondents expressed a high level of satisfaction with the instrument's handling ability, while the remaining respondents found the handling ability of the equipment satisfactory.

Approximately 70% of the participants indicated a strong acceptance of the fertilizer efficiency of the recently created instrument in comparison to manual application. 30% of the responders acknowledged the fertilizer efficiency of the instrument. 65% of respondents expressed a high level of satisfaction with the cost of the instrument, whereas 35% agreed with its pricing.

Ultimately, 60% of participants expressed a high level of satisfaction with the overall acceptance, while the remaining 40% indicated agreement (Table 01).

C. The Efficiency of Developed Tool

It was found that there were significant differences between the manual fertilizer application method and application using tool in terms of time required to apply fertilizers for 20 plants and labour cost (Table 2). It was found that approximately less time was consumed (39.3 seconds) to apply fertilizers for 20 plants using newly developed tool and 128.4 seconds consumed for the manual application. Furthermore, comparatively higher cost (1389.7) incurred for manual fertilizer application and lower cost (454.4 Rs.) was observed to apply fertilizers using tool. Further, it was revealed that, an average of 5.1 g was released from the developed tool in a single push. There was 326.84 % of time efficiency and 305.84 % cost efficiency on the fertilizer application using tool compared to the manual.

When it comes to the safety of agronomic practices, the use of machinery is essential, especially when chemicals are used. With manual fertilizer application, the farmer has to bend down to apply the fertilizer every time it is applied, which is laborious. Therefore, the better ergonomics is also a decisive advantage of the instrument. When using the fertilizer spreader Some regions still prefer manual application because they feel mechanical applicators waste fertilizer since they lack a speed feedback system to change the rate at which they apply the fertilizer. To satisfy crop nutrient needs, manual fertilizer application is frequently not tailed but rather maintained constant throughout time or over vast areas [START_REF] Xu | Methodology of fertilizer recommendation based on yield response and agronomic efficiency for rice in China[END_REF]. This contributes to fertilizer misuse, which runs counter to ecologically friendly agriculture and results in imbalanced, ineffective fertilization and low economic returns. In addition, excessive and improper fertilization results in low nutrient use efficiency [START_REF] Qin | Integrated nutrient: water and other agronomic options to enhance rice grain yield and N use efficiency in double-season rice crop[END_REF], which has an adverse effect on the environment by contributing to greenhouse gas emissions [START_REF] Feng | Impacts of cropping practices on yield-scaled greenhouse gas emissions from rice field in China: a meta-analysis[END_REF], land degradation, and freshwater pollution [START_REF] Guo | Significant acidification in major Chinese croplands[END_REF]Reidsma et al., 2013).

There should be consistency between doses administered at different times of fertilizer application. The goal of fertilizer application is to accelerate plant growth. Once the harvest schedule is established, there may still be plants that are not ready for harvest as uneven fertilization results in different harvest schedules for each tree [START_REF] Moreno | Agro-forestry management of Paulownia plantations and their impact on soil biological quality: The effects of fertilization and irrigation treatments[END_REF]. The problem of fertilization is one that many researchers in the agricultural industry are working to solve. Making a fertilizer spreader automation tool is a way to distribute fertilizer quickly, correctly and precisely. However, in actual application, this device is still ineffective due to its non-adjustable dosage, operational clogging, and inaccurate fertilizer dispensing dose. According to [START_REF] Jinfeng | Design and experiment of key components of side deep fertilization device for paddy field[END_REF], [START_REF] Yinyan | Analysis and experiment of fertilizing performance for precision fertilizer applicator in rice and wheat fields[END_REF][START_REF] Zhu | Influences of structure parameters of straight flute wheel on fertilizing performance of fertilizer apparatus[END_REF], the main disadvantage of using an applicator is that it has very little flexibility, stability, and dose, which has poor in uniformity and discharge rate.

IV. CONCLUSION

An innovative tool has been developed to address the challenges associated with fertilizer application in pineapple cultivation. The device was designed to be simple but effective and received positive feedback from farmers following a field evaluation that compared its performance to manual application methods.This validation highlights the tool's potential for improved efficiency in the field. However, further testing is required in different regions of the country before the tool can be successfully rolled out to pineapple farmers across the island.

Figure 01 :

 01 Figure 01: Initial framework of Developed Tool A. Fertilizer container (1.5 inch PVC pipe) B. 1 inch PVC pipe C. 0.75 inch PVC pipe D. Fertilizer exhaust hole (inside of the instrument) E. Spring (inside of the instrument) F. 45 degree barrier (inside of the instrument) G. Fertilizer output PVC pipe H. Rubber band I. Reducer J. Base K. Screw

Figure 02

 02 Figure 02: a) Parts of developed tool; b) Final view of developed tool; c) Field evaluation of developed tool; d) applying fertilizer at the leaf base of pineapple plants

Table 01 :

 01 Descriptive Statistics for Performances of the Tool

	Description	Mean SD
	Acceptability for the weight of the tool	1.35	0.49
	Acceptability for the height of the tool	1.55	0.69
	Acceptability for safety to the farmer	1.25	0.44
	when applying
	Acceptability for handling ability of the	1.40	0.50
	tool
	Acceptability for fertilizer efficiency of	1.30	0.47
	the tool
	Acceptability for the cost of the tool	1.35	0.49
	Overall acceptability	1.40	0.50
	Values represent the mean ± standard deviation
	of a 5 point Likert scale (1 -Highly
	acceptable; 5 -Highly not acceptable).

  , difficult bending positions are avoided. The operator, on the other hand, does not need to wear safety boots or overalls to avoid excessive contact with the fertilizer.

		HA A N NA HNA
		100%
		90%
		80%
	%	70%
	Respodent	30% 40% 50% 60%
		20%
		10%
		0%
		TW TH	S	AH	FE	TC	OA
				Variables

created

Table 02 :

 02 Time and Labour Cost Efficiency

	Values represent Mean ± Standard error of 4
	replicates. Each replications contained 20
	plants. P<0.05 is significant at 0.05 level.

Proceedings of Papers, 3 rd International Conference on Science and Technology Faculty of Technology, South Eastern University of Sri Lanka e-ISBN: 978-955-627-022-8

Parameter

Manual method