Nearshore articulate crinoid from the Albian of Alberta, Canada (Early Cretaceous, Echinodermata)

During the middle Albian, a southward incursion of the Boreal Ocean flooded northern Alberta and adjacent British Columbia, forming a large embayment known as the Hulcross Sea. Marine mudstones of the Hulcross Formation and Harmon Member of the Peace River Formation record transgression, whereas sandstones of the Cadotte Member of the Peace River Formation record shoreline regression to the north. Abundant hummocky and swaley lamination in the Cadotte sandstone attest to the influence of storms on a shallow shelf. The Cadotte sandstone undergoes a lateral facies change from mud-free shoreface sandstone in the south to heterolithic offshore facies in the north. An articulated crinoid was found within a hummocky sandstone bed about 15 km seaward (north) of the shoreface-shelf facies transition. The articulated state of the crinoid indicates that it was buried very rapidly, and never exhumed. The arms through 20 mm of the column are preserved, but because the details of the aboral cup are not well preserved, this specimen must be left in open nomenclature. The elliptical columnals with a concave latus in the distal portion of the preserved column ally this specimen to the Bourgueticrinida, although with details of the aboral cup lacking and other characters atypical for Mesozoic bourgueticrinids, the Canadian specimen is placed in Bathycrinidae indeterminate. The oldest previously recorded bathycrinids were from the Upper Cretaceous (Maastrichtian), thus this report extends their range to the Lower Cretaceous (Albian). Durant l'Albien moyen, une incursion vers le sud de l'ocean Boreal a inonde le nord de l'Alberta et de la Colombie-Britannique, formant une grande echancrure appelee mer de Hulcross. Des mudstones marins de la Formation de Hulcross et du membre de Harmon de la Formation de Peace River font etat d'une transgression, alors que les gres du membre de Cadotte de la Formation de Peace River documentent une regression du littoral au nord. L'abondance de laminas bosselees et en gouttieres dans le gres de Cadotte temoigne de l'action des tempetes sur un milieu de plate-forme peu profond. Cette unite presente un changement lateral de facies, passant d'un gres d'avant-plage sans argiles au sud a un facies extracotier heterolithique au nord. Un crinoide articule a ete trouve dans un lit de gres bossele a environ 15 km au large (au nord) de la transition entre le facies d'avant-place et celui de plate-forme. La nature articulee du crinoide indique qu'il a ete enseveli tres rapidement et n' a jamais ete exhume. Bien que les bras soient preserves sur 20 mm du pedoncule, ce specimen doit etre laisse en nomenclature ouverte etant donne la pietre conservation des details du calice. Les articles elliptiques avec une plaque laterale concave dans la portion distale du pedoncule preserve allient ce specimen aux Bourgueticrinides, mais etant donne l'absence de details du calice et la presence d'autres caracteres non typiques des bourgueticrinides mesozoiques, le specimen canadien est affecte aux Bathycrinides indetermines. Les bathycrinides les plus anciens recenses anterieurement etant du Cretace superieur (Maastrichtien), la presente etude repousse les limites de leur repartition jusqu'au Cretace inferieur (Albien). [Traduit par la Redaction]
Introduction Cretaceous stalked crinoids are relatively rare fossils, especially from North America. Meyer and Macurda (1977) argued that stalked crinoids became restricted to deep-water habitats by the Late Cretaceous; and [...]