Trilobites from the upper Lower to Middle Devonian Timrhanrhart Formation, Jbel Gara el Zguilma, southern Morocco (original) (raw)

2006, Trilobites from the upper Lower to Middle De) Timrhanrhart Formation, Jbel Gara el Zguilma, southern Morocco

Diverse and abundant trilobite faunas occur in several beds near the base of the section of the upper Emsian to Eifelian Timrhanrhart Formation exposed at Jbel Gara el Zguilma, south of Foum Zguid in Morocco. While trilobites occur throughout much of this section, they are exquisitely preserved and most diverse in the lowest (upper Emsian) portion. Several of the trilobite species are commercially available, but their taxonomy has never been formalized, and their field occurrence has not previously been described. Near the base of the section, two nodular argillaceous limestone beds contain highly diverse trilobite faunas, with many spectacular spiny forms. These include examples deviating from bilateral symmetry that are apparently unique in the Trilobita. Alpha diversity is high, with as many as 23 trilobite species in one bed. We suggest that these nodular beds represent thick, rapidly emplaced storm obrution deposits that underwent transport for a short distance before the trilobites came to rest in chaotic burial orientations. Calcareous nodule formation during early diagenesis protected the trilobites from compaction. Higher in the same section, in strata of Eifelian age, trilobite faunas are of lower diversity, and composed mainly of species of Phacops, Hollardops and Parahomalonotus, although one horizon has an alpha diversity of at least 9 species. Twenty three new species-level taxa include: Acastoides zguilmensis, Acastoides haddadi, Coltraneia effelesa, Cyphaspis agayuara, C. eberhardiei, C. hamidi, Diademaproetus mohamedi, Gerastos tuberculatus marocensis, Hollardops hassainorum, Kayserops tamnrherta, Koneprusia dahmani, Leonaspis haddanei, L. spinicurva, Parahomalonotus calvus, Phacops granulops, P. lebesus, P. smoothops, Psychopyge hammerorum, Scabriscutellum hammadi, S. lahceni, Tropidocoryphe amuri, Walliserops hammii, and W. tridens. Cyphaspis new species A is known only from a single cephalon. “Sculptoproetus” new species A and “S.” new species B are being named in another work that will appear in print after this work.