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Medientyp:
E-Artikel
Titel:
Lower Ordovician (Zone D) Faunules from the Williston Basin, Montana
Beteiligte:
Lochman, Christina
Erschienen:
Society of Economic Paleontologists and Mineralogists and the Paleontological Society, 1965
Erschienen in:
Journal of Paleontology, 39 (1965) 3, Seite 466-486
Sprache:
Englisch
ISSN:
1937-2337;
0022-3360
Entstehung:
Anmerkungen:
Beschreibung:
Two cores from the subsurface Deadwood Formation in the Williston Basin have furnished trilobites which can be referred to the Lower Ordovician Zone D; and the zone may also be present in a third core, but strictly diagnostic trilobites were not recovered from this material. The faunules show an association of Kainella, Apatokephalus and Lloydia (Leiostegium) with genera of Hystricuridae, Nanorthis, Apheoorthis and several gastropod genera. This is a typical Zone D assemblage of the Cordilleran craton seaways. In the Southwest Richey #32-33B core the limestone pebble conglomerates carrying the shelly facies faunules are overlain by a 32-foot unit of dark green glauconitic pyritic micaceous shales. Near its base planktonic graptolites, represented by Dictyonema flabelliforme aff. subspecies norvegicum Kjerulf, make their first appearance in this region. In the succeeding shales other graptolite genera characteristic of Tremadoc or early Arenig zones were found. The hystricurid, Glabretina andrewsi, and the graptolite, Mastigograptus macrotheca n. subspecies montanensis are described.