Search

International audience; The Permian-Triassic Boundary is an important interval, intensely studied to clarify climatic, biotic andenvironmental conditions. Continental sedimentation of the studied interval, upper F2/F3/lower F4 and upperT2/T3/lower T4 units, respectively in the High Atlas of Marrakech and Argana Valley spans from late Permian,dated from vertebrates, to Middle Triassic. It records all changes in the depositional environments undertectonic and climatic control. The sedimentological study aimed to characterize the Permian-Triassic transitionby a sedimentological outcrop analysis, to recognize sedimentary facies, facies associations, to reconstitute thedepositional history and the palaeogeography evolution from the end of the Permian to the beginning of theTriassic siliciclastic succession. Finally, from depositional sequences we propose stratigraphic correlation atthe scale of Morocco basins and the western Peri-Tethyan domain. The late Permian (upper F2/upper T2 units)facies association represents fluvial fans in a dry alluvial plain. The Early Triassic F3 /T3, dated from foodprints, and F4a/T4a units rest unconformably on the Permian strata, and consist of (i) arid alluvial fans, (ii)aeolian deposits, (iii) palustrine-lacustrine deposits, (iv) floodplain, (v) meandering river and (vi) braided river.The Anisian F4b/T4b units represent axial fluvial plain of high sinuosity rivers. The dynamics of alluvial fan,fluvio-lacustrine, eolian deposits, the synsedimentary tectonic and the baselevel fluctuations will be taken intoconsideration during the filling of the sedimentary basins to constrain the stratigraphic cycles. The evolutionof early Triassic environments constitutes a major stratigraphic cycle with retrogradational and progradationaltrends, and is bounded by surfaces correlated at the scale of Morocco basins. The Anisian units arecharacterized by floodplain and meandering river deposits, and represent the beginning of another stratigraphiccycle. The stratigraphic cycle can be discussed at the scale of western Peri-Tethyan domain

International audience; The Late Triassic Irohalen Mudstone is 500 m in thickness and is laterally continuous in outcrop withinArgana valley, Western High Atlas, Morocco. This mudstone-dominated unit rests conformably on the Agelgalsandstone and represents the upper part of the Timezgadiouine Formation. It comprises two fining-upward andcoarsening-upward alluvial plain sequences that are accumulated under semi-arid climate. The two sequencesare represented by (1) Lower Irohalen Mudstone and (2) Upper Irohalen Mudstone. It is composedpredominantly of floodplain siliciclastic mudstones with interbedded proximal crevasse splay sandstones thatevolve laterally into extensive floodplain siliciclastic mudstone, ephemeral lacustrine carbonate mudstonesand distal crevasse splay siltstones. Channel sandstones and levee siltstones are also present. The lowerIrohalen Mudstone has yielded a low diversity and abundant invertebrate and vertebrate ichnofossils. Theinvertebrate ichnofossil assemblages include Scoyenia, Cruziana, Rusophycus, Taenidium and Fuersichnus.The vertebrate ichnofossils consist of the lacertoide ichnogenus Rhynchosauroides, the dinosaurianichnogenus Grallator, and the chirotherian ichnogenus Brachychirotherium. The purpose of this contributionis to describe the facies and associations of facies constituting the lower Irohalen Mudstone and to review thesevertebrate and invertebrate ichnofossils and discuss their occurrence in a sedimentological andpaleoenvironmental context.

18 pages; National audience

Arthropitys bistriata (Cotta) Goeppert, 1864 (Fig. 4 B-D, F, G) We attribute a number of stems showing a wide range of sizes and of secondary xylem thickness to this species. The small stem (Fig. 4B) has a diameter of 19 × 5 mm including the cortex; it shows a small development of secondary xylem (0.5 mm thick, i.e. about 15 tracheids); 62 primary xylem strands with carinal canals (80 µm in diameter) are surrounding the pith at 0.7 mm intervals (Fig. 4F). Secondary xylem wedges are separated by interfascicular rays that are 5-6 cells wide. The outer sclerenchymatous cortex is well preserved as well as groups of large cells in the inner cortex (arrow, Fig. 4F). This young stem shows the beginning of development of secondary xylem. In its general organization, small amount of secondary xylem and cortex anatomy, it is very similar to specimens of A. bistriata var. augustodunensis from Autun illustrated by Renault (1893: pl. 46, fig. 7; pl. 47, figs 1, 2). Other observed specimens belonged to older parts of plants, with a wood thickness ranging from 1 to 60 mm, but generally the cortex is missing. For example the stem (Fig. 4C) has a wood of 10 mm thick; it represents probably one third of the original woody cylinder.About 30 primary xylem strands are visible; carinal canals are 100 to 250 µm in diameter, their preservation may be excellent (Fig. 4G) and sometimes there is no lacuna (arrow, Fig. 4C). The average distance between carinal canals is 1 mm, it may be up to 2 mm in stems with wood several centimetres thick. In transverse section, interfascicular rays are less than 1 mm wide, made of 5 to 8 parenchymatous cells, and they are generally visible through the whole secondary xylem. The secondary xylem wedges consist of rays and tracheids showing an initial quick increase of their diameter from 30 to 70 µm (Figs 4F, G). Some specimens consist of a single fragment of wood including a portion of the pith and a few primary xylem strands. The observed maximum wood thickness of 60 mm suggests an (Cotta) Goeppert; B, incomplete transverse section of a young stem showing a little development of secondary xylem (SAR40C1T03); C, partial transverse section of an older stem with thick secondary xylem and well-marked interfasciculary rays (SAR58C1B01); D, radial longitudinal section in the secondary xylem showing scalariform pitting of tracheids and high ray cells on the left (SAR51BL01); F, detail of the stem (B) showing two primary xylem strands with circular carinal canals, one interfascicular ray, small development of secondary xylem, cluster of large cells (arrow) in inner cortex and sclerenchymatous outer cortex; G, detail of one primary xylem strand and secondary xylem wedge of a stem with thick wood (SAR51A01). Scale bars: A-C, 1 mm; E-G, 0.5 mm; D, 100 μm. original stem diameter of at least 15 cm if we include the pith and cortex. This corresponds to some specimens of A. bistriata illustrated by Renault (1893: pl. 44, figs 1, 2) as well as original specimens of the species described by Cotta (1832). In all the observed stems the secondary xylem tracheids show scalariform thickening to pitting on their radial walls (Fig. 4D). All the features recognized in these specimens suggest that they belong to Arthropitys bistriata. However,the original material of this species was decorticated and Cotta’s diagnosis did not include cortical features or information on young stems such as that presented by Renault (1893 -1896) for A. bistriata var. augustodunensis. There is also a strong presumption that the very small stems attributed to A. renaultii belong to the same plant.Detailed comparison of this material is out of the scope of the present paper., Published as part of Galtier, Jean, Ronchi, Ausonio & Broutin, Jean, 2011, Early Permian silicified floras from the Perdasdefogu Basin (SE Sardinia): comparison and bio-chronostratigraphic correlation with the floras of the Autun Basin (Massif central, France), pp. 43-69 in Geodiversitas 33 (1) on pages 50-52, DOI: 10.5252/g2011n1a4, http://zenodo.org/record/4596948, {"references":["RENAULT B. 1893 - 1896. - Bassin houiller et permien d'Autun et d'Epinac. IV. Flore fossile: Atlas (1893); Texte (1896). Etude des Gites mineraux de la France. Imprimerie Nationale, Paris, 578 p.","COTTA B. 1832. - Die Dendrolithen in Beziehung auf ihren inneren Bau. Arnoldische Buchhandlung, Leipzig and Dresden, 89 p."]}