|Résumé||(disponible en anglais seulement)|
The Late Cretaceous uintacrinid crinoid genus Marsupites is recognized widely around the globe, including the US Western Interior and Gulf Coast region,
northern and eastern Europe, North Africa, India and Madagascar, and Australia, and is now accepted as an index fossil for the uppermost Santonian Stage, with the last appearance (extinction) of the genus denoting the boundary of the Santonian with
the Campanian. However, uintacrinids in general, and Marsupites in particular, have never before been recognized in the vast North Pacific region, including Japan, Sakhalin, Koryak, Alaska, British Columbia, and California, as well as the Pacific
coast of South America.
Thanks to the efforts of the amateur collecting community, a large number of examples of the genus Marsupites have now been found in strata of the Upper Cretaceous Nanaimo Group, exposed on southeastern Vancouver Island,
British Columbia, Canada. We have documented all occurrences of these fossils known to us and determined their precise geographic and stratigraphic settings. We recognize two distinct species of Marsupites present in the Nanaimo Group succession,
Marsupites testudinarius (von Schlotheim 1820) and M. lamberti Besairie 1936, the former recognized widely around the globe, the latter known previously only from Madagascar. Fossils associated with Marsupites in the Nanaimo Group are commonly found
in the upper part of the Eubostrychoceras elongatum Zone of the group and include the ammonites Eupachydiscus haradai and Amapondella sp. cf. amapondense, as well as the inoceramid bivalves Sphenoceramus elegans, S. orientalis, and S. sachalinensis.
The zonal index Eubostrychoceras elongatum is noted at several localities immediately subjacent to the first occurrence of Marsupites. Strata overlying those containing Marsupites are characterized by occurrences of the ammonites Pseudoschloenbachia
umbulazi and Canadoceras mysticum.
We propose the new biostratigraphic zone of Marsupites testudinarius for uppermost Santonian strata of the Nanaimo Group, succeeding the Eubostrychoceras elongatum Zone and beneath the lowest Campanian
Pseudoschloenbachi umbulazi Zone. This zonation places all of the Eubostrychoceras elongatum Zone in the upper Santonian, and the earliest occurrences of the sphenoceramid bivalves Sphenoceramus elegans, S. orientalis, and S. sachalinensis firmly
within the uppermost Santonian. These bivalves constituted the bulk of the Sphenoceramus schmidti Zone of previous workers (e.g., Jeletzky, 1970; Ward, 1978); S. schmidti sensu stricto in the Nanaimo Group is known only from younger strata of the
lower Campanian. The bivalves S. elegans, S. orientalis, and S. sachalinensis are also known from strata of northern California, the Japanese Islands, and Sakhalin Island and Koryakia, East Russia, where the genus Marsupites has not yet been found,
and all those strata can now be correlated with the uppermost Santonian stage as well.
|Sommaire||(Résumé en langage clair et simple, non publié)|
Les auteurs présentent ce document sur les nouveaux résultats scientifiques du 12e symposium de paléontologie de la Colombie-Britannique. Les
auteurs ont identifié un type de fossile particulier dans les roches crétacées de l'île de Vancouver, datant d'environ 84 millions d'années, ce qui indique un intervalle de temps géologique très précis et se retrouve dans de nombreux endroits du
globe, mais jamais auparavant. Région Pacifique. En utilisant ce fossile, les auteurs peuvent maintenant corréler précisément les roches qui le contiennent avec celles d'Europe, d'Afrique et d'Asie.