The Brachiopod Fauna of the Arisaig Series (Silurian-Lower Devonian) of Nova Scotia

Citation

Harper, Charles Woods (1964) The Brachiopod Fauna of the Arisaig Series (Silurian-Lower Devonian) of Nova Scotia. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KYZC-7F43. https://resolver.caltech.edu/CaltechETD:etd-10152002-123526

Abstract

The Arisaig series comprises a very fossiliferous, fairly continuous sequence of strata of early Llandovery to Gedinnian age. The brachiopod species of the Arisaig series are described, identified generically, and compared with related species. Forty-five genera and eighty-two species are recognized. Seven new species, three new genera, and three new subgenera are proposed. A phylogeny is proposed for each of the following groups: the Rhipidomellidae, plagiorhynchids, leptostrophids, douvillinids, and the Pholidostrophiinae. Idiorthis is considered to be related to a proposed new genus of Silurian platyorthids. Shaleria(Telaeoshaleria) Williams is considered to be a pholidostrophid and is rejected as a subgenus of Shaleria Caster. Mclearnites Caster is considered to be closely related to Mesodouvillina Williams and not closely related to Shaleria. Pholidostrophia (Mesopholidostrophia) Williams and Lissostrophia(Mesolissostrophia) Williams are considered to be identical. Photochonetes Muir-Wood and Strophochonetes Muir-Wood are considered to be closely related, if not congeneric. Spirifer(Quadrifarius) Fuchs is redefined as a subgenus of Delthyria Dalman. The lowest formation in the Arisaig series, the Beechhill Cove Formation is considered to be of early Llandovery age, as is the Glencoe Brook Formation in Pictou Co., N.S. The three members of the Ross Brook which overlies it are middle Llandovery (or high early Llandovery), late Llandovery (C[subscript 3]-C[subscript 5]), and late Llandovery C[subscript 6] or low Wenlock in age respectively. The overlying French River Formation is considered to be late Llandovery (C[Subscript 6] or low Wenlock in age. The lower two members of the overlying McAdam Formation are considered to be Wenlock or Ludlow in age, the upper two, Ludlow in age. The overlying Moydart Formation is considered to be Ludlow in age, and the highest formation in the series, the Stonehouse Formation, is considered to be Gedinnian and possibly, in part, Skala in age. Many brachiopod groups which are common and widespread in beds of equivalent age elsewhere in the world are absent or virtually absent in the Arisaig series; the genera which are present are not endemic-most of them are common and widespread in beds of equivalent age elsewhere. This very possibly resulted from the presence of a barrier which prevented the larvae of some, but not all, groups from entering the area of Arisaig rocks; but the possibility that it resulted from certain factors in the depositional environment being unfavorable to the missing groups cannot be ruled out. Photographic materials on pp. 319-429 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.

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