Cyrtospirifer

Abstract: The new trench Z−17 situated in the Debnik anticline (Cracow Region, southern Poland) exposed strata representing the Frasnian–Famennian boundary interval. The latest Frasnian crisis interval is characterized by the fauna of Ryocarhynchus tumidus interval consisting of the nominal species, Barroisella campbelli, Biernatella polonica, and representives of Lingulipora, Athyris, ?Retichonetes, Longispina, Cyrtospirifer and Warrenella. The first brachiopods that appears imme− diately above the F–F boundary in the survival interval include the unidentified rhipidomellid, Praewaagenoconcha cf. speciosa, and Pampoecilorhynchus geniculatus sp. nov. The fauna in the succeeding layer is dominated by P. geniculatus and Cyrtospirifer minor. The earliest Famennian repopulation assemblage consists of representatives of Barroisella, ?Rhyssochonetes, Praewaagenoconcha, Nigerinoplica, Schizophoria, unidentified rhipidomellid, Pampoecilorhynchus geniculatus sp. nov., Chapinella striata sp. nov., Crinisarina angelicoides, and Cyrtospirifer minor. Low diversity and low frequency brachiopod assemblages consisting of stunted specimens characterize the succeeding brachiopod intervals spanning the remainder of the Palmatolepis triangularis Zone. Basinal dysoxia prevailed in the region for the duration of Pa. triangularis Zone. Resumption of aerobic bottom−water conditions is marked by the appearance of brachiopods of the Dmitria gibbosa interval (Pa. crepida Zone). Resumption of favorable environmental conditions during the recovery in− terval is marked by an increase in brachiopod diversity recording the beginning of a strong post−extinction re− diversification of the fauna.

Abstract: The northwest part of the Three Forks sheet, mapped by Peale (1896), has been remapped. The Pebbly limestones (Cambrian) of Peale9s section could not be identified. The contact of the Dry Creek shales with the overlying Jefferson limestone represents a hiatus involving the Ordovician, Silurian, and Lower Devonian. The Jefferson is correlated with the Devils Gate of Nevada; upper Middle Devonian age is indicated in the lower beds by Spirifer cf. S. engelmanni (Spirifer argentarius zone, Devils Gate), and the base of the Upper Devonian is marked by the occurrence of Phillipsastraea , 175 feet above the base of the formation. Sixty feet of yellow sandstone overlying the Cyrtospirifer zone of the Three Forks shale (Upper Devonian), and previously included in that formation, contains a Lower Carboniferous Syringothyris fauna (Kinderhook) and is lithologically a recognizable unit. The name Sappington sandstone is here proposed. The Belt is not present in the southern part of the area but is represented by 4000 feet of conglomerate, arkosic sandstone, and micaceous shale in the northern part. A relatively steep shore line is indicated, and the section probably is the near-shore facies of one or more of the formations distinguishable farther north. The Belt shore line is marked by an east-west zone of Laramide high-angle thrusting, including the Jefferson Canyon fault, with an apparent throw of approximately 12,000 feet. The faulting was probably controlled by the declivity in the basement surface, which in turn was localized by a zone of weakness within the basement. North of the Jefferson Canyon fault, the structures conform to those of the Northern Rockies in their orientation and plainsward thrusting. South of it, the trends are west and northwest, and thrusting and overturning are to the southwest. This conforms to the general structural pattern of southern Montana and is not explainable by local resolution of east-northeastward Laramide stresses.

Abstract: Study of the shell features of Givetian and Frasnian spiriferid brachiopods attributed to the genus Cyrtospirifer shows that the type species C. verneuili has micro-ornament consisting of fine concentric growth lines, radial capillae, with microspines arising from some capillae, spine bases appear to extend into the primary shell layer. Its dorsal interior features a pseudoseptum supporting the cardinalia. Micro-ornament of Cyrtospirifer varies widely and is a useful criterion for characterization of species of the genus. Most Frasnian species retained in the genus have micropustulate shells. Two late Givetian and Frasnian phylogenetic species groups of Cyrtospirifer are recognized based on similarities of shell form and external and internal shell features. Species of the verneuili- syringothyriformis group have transverse alate shells, and are the most abundant and widespread group in Frasnian deposits worldwide. The verneuiliformis group includes the oldest known species of Cyrtospirifer with narrow hinges and more inflated ventral valves where shell width is close to or equal to length. The oldest Cyrtospirifer originated in western Europe during the late Givetian, and subsequently migrated at different times during the Frasnian into other shelf areas of Eurasia, North America and China. The initial migration of Cyrtospirifer into tropical and subtropical shelf settings in North America coincided with the middle Frasnian eustatic sea level rise of Devonian Transgressive-Regressive (T-R) cycle IIc of Johnson and others. A second late Frasnian dispersal from western Canada to subtropical carbonate and clastic shelves in the southwestern and central U.S. coincided with the initial sea level rise of T-R cycle IId of Johnson and others. The Frasnian species Cyrtospirifer glaucus Crickmay, 1952a (middle Frasnian of western Canada) is the type species for Regelia Crickmay, 1952b, and is considered a valid genus, and is not a synonym of C. chemungensis (Conrad, 1842) as previously interpreted by some authors. Regelia differs from Cyrtospirifer in the absence of a delthyrial plate, complete in-filling of the delthyrial cavity by secondary shell material, its simpler rod-like teeth, and its fewer medial sinal shell plications. Species of Regelia are restricted to the middle to late Frasnian of North America.