This is the accepted version of the article: Matamales Andreu, Rafel; Peñalver, Enrique; Mujal, Eudald; [et al.]. «Early-Middle Triassic fluvial ecosystems of Mallorca (Balearic Islands) : Biotic communities and environmental evolution in the equatorial western peri-Tethys». Earth-Science Reviews, (August 2021), art. 103783. DOI 10.1016/j.earscirev.2021.103783 This version is available at https://ddd.uab.cat/record/248973 under the terms of the license 1 Early–Middle Triassic fluvial ecosystems of Mallorca (Balearic Islands): biotic 2 communities and environmental evolution in the equatorial western peri-Tethys 3 4 5 Rafel Matamales-Andreua,b*, Enrique Peñalverc, Eudald Mujala,d, Oriol Omse, Frank Scholzef, 6 Josep Juárezb, Àngel Galobarta,g & Josep Fortunya 7 8 a 9 Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Edifici 10 ICTA-ICP, c/ Columnes s/n, Campus de la UAB, 08193 Cerdanyola del Vallès, Barcelona, 11 Spain. 12 b 13 Museu Balear de Ciències Naturals, ctra. Palma-Port de Sóller km 30, 07100 Sóller, Mallorca, 14 Illes Balears, Spain. 15 c 16 Instituto Geológico y Minero de España (Museo Geominero), CSIC, c/ Cirilo Amorós 42, 17 46004 València, València, Spain. 18 d 19 Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, 70191 Stuttgart, Germany. 20 21 e Departament de Geologia, Universitat Autònoma de Barcelona, av. de l’Eix Central s/n, 22 Campus de la UAB, 08193 Cerdanyola del Vallès, Barcelona, Spain. 23 f 24 Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, 07749 Jena, 25 Germany. 26 g 27 Museu de la Conca Dellà, c/ del Museu 4, 25650 Isona i Conca Dellà, Lleida, Spain. 28 29 *Corresponding author: rafel.matamales@icp.cat 30 31 32 1 33 Abstract 34 During the Early–Middle Triassic, the biosphere was recovering from the most severe mass 35 extinction event of multicellular life, in the Permian–Triassic transition. Continental basins 36 corresponding to present-day Mallorca (Balearic Islands, western Mediterranean) were located 37 in the equatorial region of the supercontinent Pangaea, in the western peri-Tethys. Its recorded 38 stratigraphic succession can be divided in four alluvial/fluvial formations, formally described 39 here: Punta Roja Formation, Estellencs Formation, Pedra Alta Formation and Son Serralta 40 Formation. Based on an exhaustive review of all available literature and new stratigraphic and 41 palaeontological data, an upper Olenekian–lower Anisian interval is proposed for the whole 42 succession. The richest fossil assemblage is that of Estellencs Formation, with abundant 43 invertebrate and vertebrate trace fossils, and remains of plants, arthropods and rare fishes, which 44 together represent a lotic/riverine ecosystem with a relatively complex food web. Plants and 45 insects show strong biogeographical affinities with those of the Vosges, in central Europe; clam 46 shrimps are similar to those of central Europe and Asia; and tetrapod tracks are also reminiscent 47 to those of Eurasia and North America. Ultimately, integration of all these data provides a 48 comprehensive and multidisciplinary characterisation of one of the oldest Triassic ecosystems 49 of equatorial Pangaea, providing new insights to understand the evolution of 50 palaeoenvironments of Iberian Plate, an area that has historically suffered from severe 51 undersampling. 52 53 Key-words: Olenekian, Anisian, clam shrimps, insects, tetrapod tracks, central Pangaea 54 55 56 1. Introduction 57 The Triassic is a key period in the history of life, as its ecosystems were recovering from the 58 most critical mass extinction event in the Phanerozoic, in the Permian–Triassic transition 59 (Erwin, 1994; Benton, 2008; Romano et al., 2020). Although the former complexity of the 60 ecosystems was eventually restored, its floras and, especially, its faunas, had experienced 61 profound turnovers (still not fully understood in the terrestrial realm), leading to more typically 62 Mesozoic assemblages (Retallack et al., 1996; Labandeira, 2005; Benton & Newell, 2014; 63 Romano et al., 2020). Those organisms lived and evolved under a megamonsoonal regime 64 caused by the Pangaean supercontinental configuration, characterised by a marked seasonality, 65 with alternating arid seasons and heavy rainfalls (Parrish, 1993; Zeng et al., 2019). 66 In the western peri-Tethys, initial Triassic sedimentation resulted in the Buntsandstein 67 continental red-bed facies, usually overlaying a hiatus in the form of an unconformity, and 68 representing semi-arid to arid climates (Durand, 2006; Bourquin et al., 2011; Mujal et al., 2016, 2 69 2017a, 2017b; López-Gómez et al., 2019a). In the case of Iberia, those sediments were 70 deposited into half-graben basins that opened as a result of the relaxation of the Variscan orogen 71 and subsequent fragmentation of the supercontinent (Bourquin et al., 2011; Frizon de Lamotte 72 et al., 2015) in the intra-Pangaean dextral megashear zone (e.g., Irving, 2004). During the 73 Olenekian, semi-arid climates have been inferred in most of the sections because of the 74 development of wadi and erg systems in the central part of Iberia (Marzo, 1986; Soria et al., 75 2011; López-Gómez et al., 2012, 2019a; Galán-Abellán et al., 2013a). Conversely, during the 76 early Anisian, the ecosystems flourished under more humid climates, recognised because of the 77 meandering style of the rivers and other geochemical and palaeopedological proxies (Borruel- 78 Abadía et al., 2014, 2015), with a biotic diversity that evidences the richness of the ecosystems 79 of palaeoequatorial Pangaea. Typical of this stage are plant assemblages composed of horsetails, 80 ferns, conifers, spores and pollen (e.g., Diez et al., 2005, 2010 and references therein). In some 81 cases, arthropod fossils, including both traces (e.g., Mujal et al., 2018a) and body fossils 82 (Aristov & Zessin, 2009; Béthoux et al., 2009), are also locally abundant. Tetrapod fossils 83 usually appear in the form of ichnites (e.g., Fortuny et al., 2011a and references therein; Mujal 84 et al., 2016, 2017b), but bone remains have been occasionally reported as well (Fortuny et al., 85 2011a, 2011b, 2014; Ezcurra et al., 2017). 86 The present work focuses on the Lower–Middle Triassic Buntsandstein facies of Mallorca, with 87 outcrops located in a limited coastal area between Cala d’Estellencs and Punta de son Serralta 88 (Estellencs, Mallorca, western Mediterranean). Its aim is to provide an accurate 89 palaeoecological reconstruction integrating environmental, botanical, entomological and 90 ichnological data. For that reason, the stratigraphy and sedimentology of all the outcrops are 91 revised, formally defining lithostratigraphic units, namely, formations, in order to clear previous 92 inaccuracies and misconceptions. This also makes it possible to infer the specific depositional 93 palaeoenvironments represented in their rocks, as well as their evolution through time. 94 Moreover, all the previous works on fossil plants and spores/pollen are reviewed, and the 95 arthropod assemblages and invertebrate and vertebrate ichnoassemblages are studied in detail 96 for the first time. These data are useful for the study of the palaeoenvironmental and 97 palaeobiogeographical developments of ecosystems recorded in the formations of Mallorca in 98 the context of the western peri-Tethys, and, therefore, the importance of the present work lies 99 not only in the improvement of the regional knowledge on the continental Triassic 100 lithostratigraphic units and palaeoecosystems, but also in contextualising these data in a broader 101 framework for palaeoequatorial Pangaea. 102 103 104 2. Geographical and geological context 3 105 Mallorca, the largest of the Balearic Islands (western Mediterranean) (Figure 1A), is a northeast 106 extension of the Betic orogen, tectonically structured in a series of grabens and horsts by 107 northeast-southwest faults of late Miocene age (Vera et al., 2004). The oldest rocks that crop 108 out on the island, as part of the lowermost unit of the Serra de Tramuntana, have been assigned 109 to the Carboniferous marine Culm facies (Rodríguez-Perea & Ramos, 1984; Ramos & 110 Rodríguez-Perea, 1985; Calafat, 1988). Above them and by means of a mechanical contact, 111 Permian rocks appear, recording the sedimentation in continental environments such as alluvial 112 fans, rivers and floodplains. Those palaeoenvironments persist in the Lower–Middle Triassic, 113 with red-beds that appear in a group of very localised and precipitous outcrops along the 114 northern coast of the island (Figure 1A–B), which are the object of the present study. 115 In the Early–Middle Triassic, Mallorca was part of a continental basin located in the western 116 Tethyan domain of central Pangaea (Scotese, 2014; Scotese & Schettino, 2017), where the 117 Variscan belt, uplifted during the Palaeozoic (e.g., Edel et al., 2018), still constituted a major 118 geographical feature. The sediments resulting from its erosion ended up in the grabens of rifts 119 that had started to open all over the western peri-Tethys (present-day western Europe and 120 northern Africa), due to the extensional tectonic regime that prevailed until the late Mesozoic 121 (Arche & López-Gómez, 1996; Hounslow & Ruffell, 2006; McCann et al., 2006; Stampfli & 122 Hochard, 2009; Frizon de Lamotte et al., 2015). In the case of Iberia, which was right in the 123 midst of the intra-Pangaean dextral megashear zone (e.g., Irving, 2004), such basins followed a 124 general northwest-southeast trend, and contained river systems flowing towards the southeast 125 (Borruel-Abadía et al., 2015; López-Gómez et al., 2019a). The Basque-Cantabrian and 126 Pyrenean basins were an exception, as there the rivers had variable palaeocurrent directions 127 (Nagtegaal, 1969; Robles & Llompart, 1987; Borruel-Abadía et al., 2015; Gretter et al., 2015; 128 López-Gómez et al., 2019b), probably pointing to the endorheic character of those basins. Six 129 main basins (each with several sub-basins) were opened in the Iberian area: the Basque- 130 Cantabrian Basin, the Pyrenean Basin, the Catalan Basin, the Iberian Basin (with the Castilian 131 and Aragonese branches) and the basins of Mallorca and Menorca. Those of the present-day 132 Balearic Islands record the most distal deposits of the Iberian area and, specifically on Mallorca, 133 the successions are well exposed and are very rich in fossil plants and animals. 134 The inaccessibility of the sections of Mallorca had so far precluded their correct 135 characterisation. Over time, several informal lithostratigraphic divisions had been proposed 136 (Supplementary Text 1; Supplementary Table 1), resulting in a plethora of disagreeing 137 approaches that had never been properly collated. The present work provides a detailed study of 138 all the sections of the island (Figure 1C) and formal definitions for each of the lithostratigraphic 139 units to avoid ambiguity in future studies. 140 4 141 142 3. Material and methods 143 3.1. Stratigraphy and sedimentology 144 For the stratigraphic and sedimentological study, four stratigraphic sections have been measured 145 bed by bed to a minimum resolution of 1 cm of bed thickness. Covered and semi-covered 146 intervals have been measured using a Jacobs staff. Most zones of complicate access due to the 147 steepness of the outcrops have been reached using climbing gear. They all have been logged in 148 detail (in 1:25 scale) (presented in Supplementary Logs in 1:40 scale). Those have been named, 149 from southwest to northeast: ‘Pedra Alta’ (18.5 m), ‘Punta Negra’ (103.5 m), ‘Punta Roja’ 150 (126.5 m, including a repeated stretch of 14 m) and ‘Tenassa de sa Tanca’ (47.5 m) (Figure 1B). 151 The logs have been synthesised (1:1160 scale) and correlated in Figure 1C. The datum to 152 correlate Pedra Alta (PI) and Punta Negra (PN) logs is the top of the green/pink interval in the 153 upper part of Estellencs Formation. The datum to correlate Punta Negra and Punta Roja (PR) 154 logs is the boundary between Estellencs Formation and Pedra Alta Formation, that is, the 155 change of colour from dominant red to dominant white/blue/green. The datum to correlate Punta 156 Negra and Tenassa de sa Tanca (TT) logs is the boundary between Son Serralta Formation and 157 the Muschelkalk marine facies. The recognised sedimentary lithofacies have been classified 158 according to Miall (1977, 1985, 2006) and Postma (1990), with additional support of more 159 specific works such as Shanley et al. (1992), Mack et al. (1993), Gómez-Gras & Alonso-Zarza 160 (2003) and Shiers et al. (2018) (Table 1). Architectural elements have been classified according 161 to Miall (1985, 2006) (Table 2). 162 163 3.2. Tetrapod tracks 164 The specimens of tetrapod tracks, which were left in the field, were assigned numbers 165 depending on their position in the stratigraphic logs. The ones under the code PN-7.6?-[slab 166 number]-[ichnite number] were found ex situ near the metre 7.6 of Punta Negra log and may 167 belong to that bed. PN-7.6-[slab number]-[ichnite number] were the only ones found in situ 168 there. PN-14.6-[slab number]-[ichnite number] and PN-14.7-[slab number]-[ichnite number] 169 were found in situ in an unequivocal lateral equivalent of the metres 14.6 and 14.7, respectively, 170 of Punta Negra log but at Platja de sa Marina, where no log was confected. All studied tetrapod 171 tracks are preserved as concave epireliefs. In some cases, the natural cast is also preserved as a 172 convex hyporelief (providing the same information as the studied epireliefs), although it is 173 usually eroded because it is proportionally finer-grained. 5 174 In order to study the tetrapod footprints, the layers of rock covering them were removed, and the 175 exposed surface was recorded in a digital 3D model. Photogrammetry was made mostly 176 following the procedure explained by Mujal et al. (2020), using Agisoft Photoscan standard 177 version 1.1.4. (http://www.agisoft.com) to create the mesh and the texture, MeshLab version 178 2016.12 (http://meshlab.sourceforge.net) to align, scale and measure the mesh, and ParaView 179 version 4.1.0 64-bit (http://www.paraview.org) to create the false colour-coded depth maps with 180 contours. The main descriptive parameters of each footprint (Leonardi, 1987; Hasiotis et al., 181 2007) were measured on schematic diagrams, using the software ImageJ version 1.52d 182 (https://imagej.nih.gov/ij), and are here presented in Supplementary Table 2. No trackway 183 measurements were taken given the fragmentary nature of all the specimens. 184 185 3.3. Fossil arthropods and fishes 186 The present research is based on three different collections. The most important one is the 187 historical Tomeu Sáez collection (Binissalem, Mallorca, Balearic Islands, Spain), which had 188 been studied by Calafat & Sáez (1987) and Calafat (1988). It contains over 60 compression 189 fossils of animals (30 insects, about 30 clam shrimps and a fish) in 10 slabs (A–J). All these 190 specimens have been identified using the acronym TS-[slab letter]-[specimen number] and were 191 obtained in the early 1980s from a single lutitic horizon rich in arthropods of Pedra Alta section 192 (ca. metre 4.75 of the log presented in Supplementary Logs; T. Sáez, pers. comm., 2020). 193 Specimens of a same slab have been correlatively numbered. 194 The second collection is that of Museu Balear de Ciències Naturals (Sóller, Mallorca, Balearic 195 Islands, Spain). It includes one insect specimen under the acronym MBCN[specimen number] 196 from a lutitic horizon of Pedra Alta section (ca. metre 7.55 of the log presented in 197 Supplementary Logs). 198 The third collection of ca. 100 slabs with clam shrimps (“conchostracans”) and insects has been 199 sampled for the present work with permission of Consell de Mallorca (file numbers 305/2019 200 and 52/2021), and are deposited in Museu de Mallorca (Palma, Mallorca, Balearic Islands, 201 Spain) with the acronym DA21/[campaign number]-[horizon number]-[specimen number]. 202 Those were collected from four different stratigraphic levels: a few clam shrimps are from a 203 lutitic horizon of Punta Roja section (metre 86.5 of Punta Roja log presented in Supplementary 204 Logs); all insects (n = 120) and most clam shrimps were sampled from a lutitic bed of Pedra 205 Alta section (ca. metre 7.20–7.30 of Pedra Alta log presented in Supplementary Logs); and 206 several more clam shrimps were collected from lutitic horizons of Punta Negra section (metre 207 39.5 and 82.0 of Punta Negra log presented in Supplementary Logs). Parts/counterparts are 6 208 identified with a number “1”/“2” following the museum collection number. Different specimens 209 on a same rock slab have been identified with correlative letters. 210 Photographs of clam shrimps were taken using a LEICA MZ12 stereo-microscope with a WILD 211 drawing mirror tube, and a BRESSER MikroCamII digital camera. Insects from Tomeu Sáez 212 collection were photographed using a single-lens reflex camera Canon EOS 40D and a digital 213 camera Olympus SC30 attached to an Olympus SZ61-TR stereomicroscope; some of its 214 specimens were wet with alcohol to be photographed enhancing the contrast of the 215 carbonaceous parts. Specimens housed at Museu de Sóller and at Museu de Mallorca were 216 photographed using a digital camera Olympus Camedia MODEL N.C5050 ZOOM attached to 217 an Olympus SZX9 stereomicroscope. 218 Clam shrimp measurements and terminology follow Scholze & Schneider (2015). Mayfly 219 morphological terminology follows that of Sinitshenkova et al. (2005) and Bashkuev et al. 220 (2012); body lengths of the mayfly nymphs were measured up to the base of cerci and 221 paracercus. Abbreviations for the wing venation are as follows: CuA: anterior cubitus, CuP: 222 posterior cubitus, M: media, MA: media anterior, R: radius, Rs: radial sector, Sc: subcosta. 223 224 225 4. Stratigraphy and sedimentology 226 Formal units have hitherto never been defined for the Lower–Middle Triassic red-beds of 227 Mallorca. Several works (Cuevas-López, 1958a, 1958b; Pomar-Gomà, 1979; Martí et al., 1985; 228 Ramos et al., 1985; Calafat, 1986, 1987, 1988; Rodríguez-Perea et al., 1987; Barnolas, 1991a, 229 1991b; Gómez-Gras, 1992, 1993; Ramos, 1995) provided informal classifications of the 230 different units (Supplementary Table 1), and other reviews upgraded them to formations without 231 any formal description (Arche et al., 2002; López-Gómez et al., 2002, 2019a; Vera et al., 2004; 232 Bourquin et al., 2007, 2011; Cassinis et al., 2012). This situation, as well as some 233 miscorrelations between units (see Supplementary Text 1 and Supplementary Table 1), required 234 a formal description of the lithostratigraphic units of the Buntsandstein facies of Mallorca. 235 Whenever possible, however, the first name used for each of the units has been preserved. 236 Descriptions and interpretations of all the lithofacies and architectural elements are here 237 presented in Table 1 and Table 2. 238 239 4.1. Punta Roja Formation 7 240 This formation (Figure 2A) can be identified in the field because of the abundance of medium- 241 grained sandstone beds, which are often tabular and show abundant planar cross-bedding. Those 242 sandstones are white or pink in colour, and near the base of the unit they show a very distinct 243 alternation of white and pink laminae. Red lutites are extremely rare in the lower part of the 244 formation, and they become progressively more abundant towards the top. 245 4.1.1. Location and boundaries 246 A small part of Punta Roja Formation crops out at Cala d’Estellencs and southwest of Pedra 247 Alta (Figure 1B). The most complete outcrop is at Punta Roja and, although it lacks its base, up 248 to 53 m have been measured until its boundary with Estellencs Formation. The Punta Roja 249 outcrop (Figure 1B) is herein formally designated as the stratotype of Punta Roja Formation. Its 250 lower boundary cannot be observed, and its upper boundary with Estellencs Formation is 251 transitional, characterised by the change of colour from pink to red, the presence of thick lutitic 252 beds and a switch from dominant planar cross-bedding to dominant trough cross-bedding and 253 ripple lamination. 254 4.1.2. Lithological features and palaeontological content 255 The lithofacies (Figure 3, Table 1) and architectural elements (Table 2) present in Punta Roja 256 Formation are reduced to a few dominant types, the rest being quantitatively less important. 257 Breccias (lithofacies type Gt) are rare, and are composed of intraformational clasts and 258 carbonate nodules, appearing as isolated beds among sandstone deposits in the uppermost part 259 of the formation, both in the base of sandstone packs and intercalated between lutites. 260 Sandstones are clearly dominant, especially in the lower part. The lower half of the formation is 261 essentially made up of medium-grained sandstones of lithofacies type Sp, whereas lithofacies 262 type St (Figure 3I) appears more frequently towards the top of the formation. Lithofacies of 263 types Sl and Sh also appear abundantly in the upper part of the formation, together with 264 lithofacies type Sr, Ss, Sm and Sb, which are rarer. Lutite lithofacies (types Fl and Fm) are more 265 frequent towards the upper part of the formation and they are often associated with lithofacies 266 type P, which displays abundant carbonate nodules (diameter between 0.5–3 cm) and 267 rhizocretions. The dominant architectural element is SB, with sporadic intercalations of the 268 elements LS and FF towards the upper part. 269 4.1.3. Interpretation 270 In this formation, lithofacies type Gt represents reworked floodplain deposits (as the clasts are 271 always soft pebbles and carbonate nodules) in the basal lag of some channels and in the 272 floodplain, similarly to the cases described by Gómez-Gras & Alonso-Zarza (2003). Regarding 273 sandstone deposits, lithofacies type Sp corresponds to transverse fluvial bar deposits, St 8 274 represents megaripple deposits formed under lower flow regime conditions, Sl and Sh 275 correspond to events of sediment deposition under higher flow regimes, Sr was formed by 276 waning flows, and Ss corresponds to the infill of scours. Moreover, lithofacies type Sm probably 277 corresponds to events of rapid deposition or to beds reworked by bioturbation, similarly to Sb, 278 which possesses abundant burrowing. Lutite lithofacies (types Fl and Fm) correspond to 279 overbank and floodplain fine-grained deposition, and lithofacies type P can be interpreted as 280 palaeosols, which in this case would correspond to Calcisols given the abundance of carbonate 281 nodules and lack of gleyed patches (Mack et al., 1993). Architectural element SB represents 282 shallow channel-fill assemblages, whereas LS and FF correspond to sheetflood deposits and 283 floodplain fines, respectively. 284 This formation represents a shallow perennial braided river in the sense of Miall (2006), 285 because of the dominance of architectural element SB, made up of lithofacies type Sp, 286 corresponding to transverse bar deposits. Calafat (1988) suggested an aeolian origin for this 287 unit, because of the overall lack of fine sediments and the well-sorted sands. Indeed, in thin 288 sections, those sandstones do have a relatively consistent grain size distribution (medium- 289 grained sands), yet mica flakes are very abundant. In aeolian contexts, such minerals are usually 290 blown away by the wind (e.g., Glennie, 1970), thus making it more probable for Punta Roja 291 Formation to be of mixed aeolian–fluvial origin. Specifically, it would correspond to river 292 deposits that reworked aeolian dune fields, hence the well-sorted sand grains. The palaeocurrent 293 direction, based on field measurements (n = 20), had a dominant direction towards the 294 southwest, with little dispersion (see ‘7. Discussion’). Towards the top of the formation, the 295 transition towards meandering rivers with associated floodplain deposits can be observed 296 because of the overall increase of the relative abundance of lutites. This formation has not been 297 confidently dated because of its lack of fossil content, however, here it is assumed to be of 298 upper Olenekian (Spathian) age, based on the age of the overlying units and correlation with 299 lithologically similar formations of Iberia (see ‘7. Discussion’ and Supplementary Table 3), 300 altough a younger age, i.e., lower Anisian (lowermost Aegean), cannot be completely ruled out 301 for its upper part. 302 303 304 4.2. Estellencs Formation 305 This formation (Figure 2B–C) can be identified in the field because of the abundance of very 306 fine- and fine-grained sandstones with dominant trough cross-bedding and ripple lamination, 307 interbedded with abundant lutites. Both the sandstones and the lutites are of a bright red colour. 9 308 In the upper part of the formation, there is an intercalation of coarser deposits (breccias and 309 medium-grained sandstones) that are pink, white or green. 310 4.2.1. Location and boundaries 311 Estellencs Formation crops out completely at Cala d’Estellencs and at Punta Roja. Smaller 312 outcrops can be observed in a roadcut near Cala d’Estellencs, between Pedra Alta and Punta 313 Negra and at Platja de sa Marina (Figure 1B). At Punta Roja, where this formation is well 314 accessible and crops out completely, 55 m have been measured. The Punta Roja outcrop is 315 herein formally designated as the stratotype of Estellencs Formation. Its lower boundary is 316 gradual and its upper boundary is sharp. Its upper boundary with Pedra Alta Formation is 317 characterised by the change of dominant colour from red to green/blue/white, the almost 318 complete absence of red lutites and the dominant planar cross-bedding. 319 4.2.2. Lithological features and palaeontological content 320 The lithofacies (Figure 3, Table 1) and architectural elements (Table 2) present in this formation 321 are quite varied, consisting mostly of lutite and sandstone types. Breccias (lithofacies type Gt) 322 are not frequent, and they appear as isolated events scouring underlying lutites or sandstones, 323 both in the base of sandstone packs or as isolated beds in the lutite intervals. They show crude 324 trough lamination, and are composed of intraformational clasts (mudstones, sandstones) and 325 reworked calcretes. The sandstone lithofacies of types Sh, Sp, Ss, St and Sm (Figure 3D, H) are 326 also rare except for the stretch between metres 18–27 of Punta Negra log and its lateral 327 equivalent: Pedra Alta log (Figure 1C). The sandstone lithofacies of types Sl and Sr (Figure 3G) 328 are by far the most abundant, usually in the form of thin, very fine- to fine-grained, tabular beds, 329 although they can also be part of sequences showing clear lateral accretion, especially at the 330 base of the formation. On the top of the beds, wrinkle structures (Porada & Bouougri, 2007) are 331 sometimes well visible. Lithofacies type Sb is characterised by profuse burrowing and is usually 332 found associated to lithofacies of types Sl and Sr. Lithofacies type P (Figure 3O) contains 333 abundant carbonate nodules (diameter between 0.5 and 3 cm) and often root traces and gleyed 334 patches as well. Lutite lithofacies (types Fl and Fm, Figure 3M, N) often appear over lithofacies 335 of types Sl/Sr and form relatively thick packs. The dominant architectural elements are LV/CS 336 and FF, and sporadically LA can also be observed. 337 4.2.3. Interpretation 338 In this formation, lithofacies type Gt represents high-energy deposits reworking floodplains, 339 produced by occasional events of heavy rains or as the basal lags of channels, similarly to the 340 case described in the Permian of Menorca (Gómez-Gras & Alonso-Zarza, 2003). Sandstone 341 lithofacies of types Sh, Sp, Ss, St and Sm correspond to bedforms of major river channels under 10 342 different flow regimes (see ‘4.3. Pedra Alta Formation’). Lithofacies of types Sl and Sr are 343 interpreted as the result of the waning flows in major sheetfloods, as overbank deposits over the 344 floodplains or as point bar deposits of meandering channels. The wrinkle structures that appear 345 on the top of some beds of these lithofacies types were probably formed by microbial mats 346 (Porada & Bouougri, 2007), which favour the preservation of small tetrapod ichnites (Carmona 347 et al., 2011). Lithofacies of types Sb and P are nothing but the reworking of the other types 348 mentioned above and, specifically, lithofacies type P can be interpreted to correspond to vertic 349 Calcisols when small carbonate nodules and gleyed patches are present, whereas Calcisols can 350 be inferred when there are only carbonate nodules, generally larger (Mack et al., 1993). 351 Lithofacies of types Fl and Fm correspond to deposition of low-energetic to still waters in 352 environments such as the uppermost part of crevasse splays and playa lakes (in the sense of 353 Briere, 2000). Architectural elements LV/CS and FF represent the floodplain 354 palaeoenvironment, whereas LA corresponds to point bars of meandering channel deposits. 355 The lower half of this formation corresponds to meandering river channels with conspicuous 356 lateral accretion. Towards the upper part, interbedded floodplain deposits, including crevasse 357 splays, start to appear more frequently. However, the stretch between metres 18–27 of Punta 358 Negra log, metres 103–112 of Punta Roja log and the whole Pedra Alta log represent a 359 relatively higher energy pulse with sedimentary environments comparable to those of Pedra 360 Alta Formation (see ‘4.3. Pedra Alta Formation’). The palaeocurrents measured in this 361 formation (n = 13) show a wide dispersion but with a general trend towards the southeast (see 362 ‘7. Discussion’). The palynoassemblages of this formation made it possible to date it as lower 363 Anisian, probably lower Aegean, because the base of the overlying formation is of upper? 364 Aegean age (see ‘4.3. Pedra Alta Formation’, ‘7. Discussion’ and Supplementary Table 3). 365 366 4.3. Pedra Alta Formation 367 This formation (Figure 2B–C) can be identified in the field because of the abundance of 368 medium-grained sandstone beds, which are of a clear colour (white, yellowish, bluish, pink), 369 intercalated with intervals of blue or green lutites. The dominant sedimentary structures in the 370 sandstones are planar or trough cross-bedding, whereas the lutites frequently have planoparallel 371 lamination. 372 4.3.1. Location and boundaries 373 Pedra Alta Formation crops out completely between Pedra Alta and Punta Negra, and at Platja 374 de sa Marina. It can also partially be observed at a roadcut near Cala d’Estellencs, at Cala 375 d’Estellencs and at Tenassa de sa Tanca (Figure 1B). The outcrop located in the precipitous 11 376 ravine between Pedra Alta and Punta Negra (Punta Negra log) is herein formally designated as 377 the stratotype for Pedra Alta Formation, where 44 m have been measured. Both its lower and 378 upper boundaries are sharp but apparently not erosive. Its upper boundary with Son Serralta 379 Formation is characterised by the change of dominant colour from green/blue/white to red and 380 the appearance of thick beds of red lutites. 381 4.3.2. Lithological features and palaeontological content 382 The lithofacies (Figure 3, Table 1) and architectural elements (Table 2) present in this formation 383 are somewhat constant, with sequences with a lower part made up of sandstones (sometimes 384 with basal breccias as well) and an upper part made by lutites. Breccias (lithofacies type Gt, 385 Figure 3A) are exclusively composed of intraformational clasts (sandstones and lutites, 386 sometimes also with carbonised remains of large woody debris), and possess crude trough 387 cross-bedding. The sandstone lithofacies of types Sp and St (Figure 3F) are rather abundant and 388 are usually constituted by medium-grained sandstones with planar or through cross-bedding, 389 respectively. Over them, lithofacies of types Sl or Sr (Figure 3E) appear, usually in very fine- to 390 fine-grained sandstones grading to the lutite lithofacies. Very fine-grained sandstone lithofacies 391 type Sh and horizontally laminated lithofacies type Fl with abundant remains of plants, 392 arthropods and, rarely, fishes constitute the top of the sequences, sometimes with lithofacies 393 type Fm as well. The dominant architectural element is SB, but FF also appears between the 394 sandy bedforms. 395 4.3.3. Interpretation 396 In this formation, lithofacies type Gt represents the basal lags of major channel deposits. 397 Lithofacies of types Sp and St correspond to linguoid and/or transverse bars and sand dunes 398 migrating on the channel floor, and those of types Sl/Sr were deposited during waning currents 399 in channel top sequences. Lithofacies of types Sh (very fine-grained) and Fl have been 400 interpreted as fine sediments deposited during intervals of low energy flow, and lithofacies type 401 Fm corresponds to deposition in periods of still waters in abandoned channels or backswamps. 402 Architectural element SB represents channel-floor dune fields and top-bar assemblages, whereas 403 element FF was formed by the deposition of fine sediments in abandoned channels or 404 backswamps. 405 This formation represents several sequences of a sheetflood distal braided river (as defined by 406 Miall, 2006), consisting in superimposed flood cycles with abundant bedforms without 407 associated floodplain deposits (the element FF corresponds to the infill of the channels during 408 low water stage). Linguoid and transverse bars amount to more than half of sandstone elements, 409 deposited during flood stage. Over them and fining upwards, low angle cross-bedded and ripple- 410 laminated beds appear, as a result of the waning of the flow after the main flood events. The 12 411 sequences often end with greenish or red lutite deposits, either laminated or apparently massive. 412 They represent pools with still to very low energetic flows (Coleman, 1969; Williams & Rust, 413 1969; Miall, 1977, 2006), isolated in abandoned channels among the remnants of megaripples 414 (similar to those described in the Upper Cretaceous of the southern Pyrenees by Vila et al., 415 2013) or backswamps (similar to those described for the Lower Triassic of the Central European 416 Basin by Kustatscher et al., 2014). The variety of colours of the lutites can result from 417 pedogenetic alteration or water circulation during diagenetic processes, but in some specific 418 beds it can also be explained by the height of the water table in the time of sediment deposition, 419 since the fossil content varies greatly from red lutites to green lutites, being by far more 420 abundant in the latter. Thus, lutites that were sedimented in well-drained areas underwent 421 oxidation and became red, whereas the green/grey/blue lutites were deposited below the water 422 table. Similar environments were inferred for the clay levels of the Middle Triassic Grès à 423 Voltzia of the Vosges (Gall, 1971) and the Solling Formation (Kustatscher et al., 2014), both in 424 the Central European Basin. This accounts for the very high preservation potential of plant 425 remains, clam shrimps, insects and, rarely, scales and very small fishes in the fossiliferous 426 horizons of the studied sections. The palaeocurrents measured in this formation (n = 23) show a 427 wide dispersion but with a general trend towards the southeast (see ‘7. Discussion’). This 428 formation was dated as Aegean (lower Anisian), probably upper Aegean, by Diez (2000) and 429 Diez et al. (2005, 2010) based on the study of spores and pollen (see ‘7. Discussion’ and 430 Supplementary Table 3). 431 432 4.4. Son Serralta Formation 433 This formation (Figure 2C–D) can be identified in the field because of the absolute dominance 434 of fine sediments and lack of thick sandstone elements. The most abundant lithologies are red 435 very fine- to fine-grained sandstones and red lutites. Sporadically and especially towards the 436 top, intercalations of greenish lutites become progressively more abundant. 437 4.4.1. Location and boundaries 438 Son Serralta Formation crops out completely at Tenassa de sa Tanca, between Pedra Alta and 439 Punta Negra, and at Platja de sa Marina (Figura 1B). Of those three, the most accessible outcrop 440 is at Tenassa de sa Tanca, which is herein formally designated as the stratotype of this 441 formation, with a measured thickness of 22 m. Both its lower and upper boundaries are sharp. 442 Its upper boundary is characterised by the onset of carbonate shallow marine sedimentation (M- 443 1 unit of the Muschelkalk facies; e.g., Matamales-Andreu et al., in press). 444 4.4.2. Lithological features and palaeontological content 13 445 The lithofacies (Figure 3, Table 1) and architectural elements (Table 2) present in this formation 446 are few and quite constant throughout, with very fine to fine-grained sandstone lithofacies 447 representing about a half of the whole sequence. At its base, the most abundant lithofacies is 448 type Sr that, together with type Sl, form tabular deposits of very fine- to fine-grained 449 sandstones. The lithofacies of types St and Sp are also constituted by very fine- to fine-grained 450 sandstones, and are relatively less abundant and have usually less lateral continuity. The lutite 451 lithofacies (types Fl, Fm) appear over the sandstone beds and form intervals that are thicker 452 towards the top of the unit. Very typical of this formation are the yellowish massive sandstones 453 (herein classified in lithofacies type Sm, Figure 3I) that appear as channelled or irregular beds 454 isolated among the lutites, and the presence of interlayered sand/mud bedding (lithofacies type 455 Si, Figure 3L), forming packs of up to 60 cm of thickness, which are usually deformed and 456 affected by desiccation cracks. The dominant architectural elements are LV/CS and FF, whereas 457 the element LA appears in the middle part of the formation. 458 4.4.3. Interpretation 459 In this formation, lithofacies of types Sr and Sl represent crevasse splay deposits, and lithofacies 460 of types St and Sp correspond to small fluvial channel deposits. Lutite lithofacies such as type Fl 461 and type Fm have been interpreted as the result of deposition of suspended fine sediments on 462 the floodplain. Moreover, there are two lithofacies that are typical of this formation and 463 common in tidal environments. In the middle part, there appear irregular or channelled beds of 464 yellowish, massive sandstones isolated among the lutites (herein classified as a particular kind 465 of lithofacies type Sm). Some of them show clear lateral accretion sets separated by lutite drapes 466 (Figure 3I), corresponding to inclined heterolithic point bars of tidal creeks (e.g., Ghinassi et al., 467 2021). In the middle and upper part of the formation, sandstone beds are arranged in very thin 468 layers alternating with lutites (lithofacies type Si), which is another typical (albeit not exclusive) 469 trait of tidally-influenced environments, especially mixed-flats and mud-flats (e.g., Nio & Yang, 470 1991; Davis, 2012; Shiers et al., 2018). Architectural elements LV/CS and FF represent the 471 floodplain palaeoenvironment, whereas element LA corresponds to small tidal creek deposits. 472 This formation represents the transition between the continental environments of the three 473 underlying units to a marine environment such as the overlying Muschelkalk facies shallow 474 platform carbonates (Calafat, 1988; Gómez-Gras, 1993; Ramos, 1995; Matamales-Andreu et al., 475 in press), and thus representing a local expression of the so-called Röt facies. The lower part of 476 Son Serralta Formation still shows a great amount of fluvial influence, with relatively thin 477 sandstone beds with ripples representing crevasse splay deposits over the lutitic floodplain, 478 similarly to the lower and middle parts of Estellencs Formation (see ‘4.2. Estellencs 479 Formation’). In the middle and upper parts of Son Serralta Formation, there appear inclined 14 480 heterolithic point bars that conform tidal-influence criterion for red-bed successions (see 481 Ghinassi et al., 2021). Some intervals of this portion of the formation also display interlayered 482 sand/mud bedding, which is very typical (albeit not exclusive) of tidal environments (e.g., Nio 483 & Yang, 1991; Davis, 2012; Shiers et al., 2018). Moreover, from this formation, Ramos (1995) 484 reported the presence of tepee/pseudo-anticline structures, which are indicative of marine 485 influence, appearing together with other structures such as wave ripples, flaser bedding and 486 evaporite solution breccias, which are also common in such settings. The few palaeocurrents 487 measured (n = 2) have not been considered representative, and therefore no palaeocurrent data 488 are available, although the same trend towards the southeast is probably followed, similarly to 489 the underlying units. This formation was dated as Anisian by Calafat (1988), just 12 m below 490 the boundary with the Muschelkalk facies, which was confirmed by subsequent works such as 491 Diez (2000) and Diez et al. (2005, 2010) (see Supplementary Table 3). Given that the base of 492 the underlying Pedra Alta Formation is of upper? Aegean age (see ‘4.3. Pedra Alta Formation’), 493 this formation could belong to either the uppermost Aegean (lower Anisian) or even the 494 Bithynian (lower part of the middle Anisian) (see ‘7. Discussion’ and Supplementary Table 3). 495 496 497 5. Systematic palaeoichnology 498 5.1. Invertebrate ichnofossils 499 Ichnogenus Gordia Emmons, 1844 500 Gordia isp. 501 Figure 4A 502 Studied material: One specimen, left in the field. From Punta Negra section (metre 9.00), 503 middle part of Estellencs Formation, Aegean. 504 Description: Horizontal trace preserved in convex hyporelief, consisting in a loosely winding, 505 unbranched burrow, thin and with a somewhat irregular wall. The preserved trace appears to 506 make a loop that would cross over itself. The fill is the same as the surrounding matrix (very 507 fine-grained sandstone). 508 Remarks: The studied ichnofossil differs from similar unspecialised freshwater grazing traces of 509 the Mermia ichnofacies (Buatois & Mángano, 1998) such as Cochlichnus, Helminthoidichnites, 510 Helminthopsis or Mermia, because of its irregular winding course and the fact that the trace 511 crosses over itself (Hofmann & Patel, 1989; Han & Pickerill, 1995; Gaigalas & Uchman, 2004; 512 Uchman et al., 2009; Getty et al., 2017). The ichnogenus Gordia occurs in marine and 15 513 continental facies from the Precambrian to the Holocene (Pickerill & Peel, 1991), and, in the 514 case of freshwater environments, the probable trackmakers were insect larvae (Gaigalas & 515 Uchman, 2004; Minter et al., 2007). 516 517 Ichnogenus Skolithos Haldeman, 1840 518 Skolithos isp. 519 Figure 4B 520 Studied material: Many specimens, left in the field. From Punta Negra (metre 8.00) and Punta 521 Roja (metre 81.00) sections, among others, middle part of Estellencs Formation, Aegean. 522 Description: Subvertical, straight to slightly curved, unbranched burrows of circular section. 523 The fill is massive; it usually corresponds to the sediment of the overlying bed (very fine- 524 grained sandstone). 525 Remarks: The ichnogenus Skolithos occurs in marine and continental facies from the 526 Precambrian to the Holocene (Fillion & Pickerill, 1990), and, in the case of freshwater 527 environments, the probable trackmakers were insect larvae (Bromley & Asgaard, 1979; 528 Ratcliffe & Fagerstrom, 1980; Fitzgerald & Barrett, 1986). In continental deposits, it usually 529 appears in the Scoyenia ichnofacies (Buatois & Mángano, 1998). 530 531 Ichnogenus Taenidium Heer, 1877 532 Taenidium barretti (Bradshaw, 1981) 533 Taenidium isp. cf. T. barretti 534 Figure 4C 535 Studied material: Many specimens, left in the field. From Punta Roja section (metre 81.00), 536 among others, middle part of Estellencs Formation, Aegean. 537 Description: Variably oriented (usually horizontal but vertical sections also observed), 538 unwalled, sinuous to winding, unbranched burrows of circular section. They have a meniscate 539 backfill with a similar sediment to that of the surrounding matrix (fine-grained sandstone). 540 Menisci are short, arcuate and closely spaced. 541 Remarks: Ichnotaxonomy of meinscate backfilled traces is somewhat contentious (e.g., Minter 542 et al., 2007; Smith et al., 2008; Díez-Canseco et al., 2016) and it is beyond the scope of the 16 543 present work to provide a systematic review of such ichnotaxa. The specimens studied herein 544 are comparable to those illustrated by Minter et al. (2007) under the identification of T. barretti. 545 Those traces have been interpreted to be produced by arthropods, probably coleopterans 546 (Baucon et al., 2014), which would aestivate in the moist sediment during the dry season 547 (Minter et al., 2007). In continental deposits, this ichnogenus usually appears in the Scoyenia 548 ichnofacies (Buatois & Mángano, 1998). 549 550 Ichnogenera Rusophycus Hall, 1852, Cruziana d’Orbigny, 1842, and Diplichnites Dawson, 551 1873 552 Diplichnites gouldi (Gevers in Gevers, Frakes, Edwards et Marzolf, 1971) 553 Rusophycus isp. - Cruziana isp. - Diplichnites isp. cf. D. gouldi 554 Figure 4D 555 Studied material: Two specimens, left in the field. From Punta Negra section (on an ex situ 556 block, probably from metre 6.00), middle part of Estellencs Formation, Aegean. 557 Description: Positive hyporelief of a compound trace with three different ichnotaxa in fine- 558 grained sandstone. The part corresponding to Rusophycus is a weakly bilobate mound, with a 559 longitudinal, very smoothed ridge. The part corresponding to Cruziana originates from the 560 central part of the anterior margin of the Rusophycus, and corresponds to a chevronate (V- 561 shaped) trace with more or less symmetric lobes on each side of its longitudinal axis. Finally, 562 Diplichnites isp. cf. D. gouldi appears connected to the open part of the V of the chevrons. The 563 parts corresponding to Diplichnites isp. cf. D. gouldi consist of two parallel trace series of 564 circular to tear-shaped, regularly spaced impressions. In the more completely preserved areas, 565 the impressions form a V shape with two smaller imprints located outwards and anteriorly, and 566 two larger imprints located inwards and posteriorly. 567 Remarks: The studied specimens represent the traces left by three different behaviours of a same 568 organism, recording its movement from a resting position in the sediment (Rusophycus), to 569 crawling to get out of it (Cruziana), to walking over it (Diplichnites isp. cf. D. gouldi). Such 570 behaviour, expressed in the same ichnotaxa, is well known from Palaeozoic trilobites (e.g., 571 Crimes, 1970), but it has also been reported in younger deposits (e.g., Bromley & Asgaard, 572 1979; Minter et al., 2007; Hminna et al., 2020), meaning that the potential producers of these 573 ichnofossil are disparate (see Hammersburg et al., 2018, for a review of the possible producers 574 of these three ichnogenera). In the case of the traces studied here, the most likely producer was a 575 notostracan crustacean, similarly to the cases described by Bromley & Asgaard (1979), Minter 17 576 et al. (2007) and Gand et al. (2008). In continental deposits, these traces usually appear in the 577 Scoyenia ichnofacies (Buatois & Mángano, 1998). 578 579 5.2. Tetrapod tracks 580 Ichnogenus Rhynchosauroides Maidwell, 1911 581 Rhynchosauroides isp. 1 582 Figure 5A–B; Supplementary Table 2 583 Studied material: PN-7.6?-01 (gypsum cast made in the 1980s of a right manus undertrack). PN- 584 14.7-01 (left manus undertrack and a partially preserved probable left pes undertrack, left in the 585 field). From Punta Negra section and its lateral equivalent at Platja de sa Marina, middle part of 586 Estellencs Formation, Aegean. 587 Description: Manus track semiplantigrade to plantigrade, pentadactyl, with the base of the digits 588 III–IV being the deepest imprinted zone. The imprints of the digits I–IV end in pointed tips and 589 can be slightly curved inwards. The imprint of digit V also possesses a pointed tip and is 590 slightly curved outwards. The length of the digit impressions can be ordered as follows: 591 I