Lagerstätte

Plusieurs Lagerstätten à échinodermes ont été découverts au cours des dix dernières années dans l'Ordovicien supérieur de l'Anti-Atlas oriental (Tafilalt occidental, Maroc). Ces niveaux ont livré des assemblages particulièrement riches et diversifiés d'échinodermes. La préservation exceptionnelle de ces organismes témoigne d'un enfouissement rapide et in situ de communautés benthiques particulièrement denses constituées quasi-exclusivement d'échinodermes. Trois assemblages sont décrits : Bou Nemrou (Sandbien basal), piste de Jorf (Sandbien supérieur) et enfin, Tizi n'Mouri (Katien supérieur). L'intérêt scientifique majeur de ces faunes (implications paléoécologiques et paléogéographiques) est brièvement présenté. Enfin, la préservation de ces gisements, qui constituent un élément majeur du patrimoine paléontologique du Sud marocain, est abordée. Late Ordovician echinoderm Lagerstätten from the eastern Anti-Atlas (Morocco): an example of exceptional scientific heritage worthy of protection. Abstract. In the last ten years, several Late Ordovician echinoderm Lagerstätten have been discovered in the eastern Anti-Atlas (western Tafilalt) of Morocco. These levels have yielded extremely rich and diverse echinoderm assemblages. The exquisite preservation of most organisms suggests rapid and in-situ burial of large, particularly dense benthic communities largely dominated by echinoderms. Three « starfish beds » are briefly described: Bou Nemrou (earliest Sandbian), piste de Jorf (late Sandbian), and Tizi n'Mouri (late Katian). The major scientific relevance of these faunas is outlined herein (for example their palaeoecological and palaeogeographical implications). Finally, the conservation of these levels, which represent a major piece of the palaeontological heritage of southern Morocco, is discussed.

Documentation of non-or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification dynamics of metazoans during the early Palaeozoic. However, the fossil record of 'soft'-bodied metazoans is particularly scarce for this critical time interval, consisting of rare fossils found at a dozen or so localities worldwide. Here we report new occurrences of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. This locality had already yielded trilobites with phosphatised guts, with all specimens representing the same species and occurring within a 10-m-thick interval. Two stratigraphically higher horizons with soft-tissue preservation are reported herein; one has yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens. The ctenophore represents the first Furongian record of the phylum and the first reported occurrence of Burgess Shale-type preservation in the upper Cambrian of Laurentia. The aglaspidid belongs to a new species of Glypharthrus, and is atypical in having twelve trunk tergites and an anteriorly narrow 'tailspine'. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson. They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatitic) outer layer. The trilobite reveals previously unknown gut features, such as medial fusion of digestive glands, possibly related to enhanced capabilities for digestion , storage, or the assimilation of food. The new fossils demonstrate that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section may result in more abundant discoveries of exceptional fossils.

The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstätte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300 km to the southwest of Zagora. The palynological samples yielded acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The acritarchs can be assigned to the diagnostic messaoudensis-trifidum acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1–2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstätte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision.

Four distinct echinoderm Lagerstätten have recently been discovered in the Upper Ordovician of the eastern Anti-Atlas, Morocco. They have yielded hundreds of exquisitely preserved specimens. Their taphonomy and associated lithology both suggest rapid, in situ burial. Here we discuss the diverse range of assemblages represented and their significance to the diversity of echinoderms in the Lower Palaeozoic. The oldest assemblage (Izegguirene Formation, lowermost Caradoc) is dominated by eocrinoids, large ophi-uroids, and mitrate stylophorans associated with rare crinoids. It shows strong similarities with slightly older faunas described from the underlying Ouine-Inirne Formation (Llandeilian) in the Central Anti-Atlas. The second assemblage (lower part of the Lower Ktaoua Formation, lower-middle Caradoc) is composed of eocrinoids (Cardiocystites) and small ophiuroids (encrinasterid indet.). The third assemblage was collected in the upper part of the Lower Ktaoua Formation (lowermost Ashgill). This 'starfish' bed is dominated by ophiuroids and large solutes, associated with common diploporites and rhombiferans, and rare crinoids and mitrates. Finally, the youngest assemblage (lower part of Upper Tiouririne Formation, lower Ashgill) has yielded abundant remains of edrioasteroids and rhombiferans.