Summary Of The Traverse Group Stratigraphy In Michigan And Comparison Of Faunas

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ISBN 13 :
Total Pages : 120 pages
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Download or read book Brachiopods of the Traverse Group (Devonian) of Michigan written by and published by . This book was released on 1959 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The Traverse group, of middle and late Devonian age, comprises about 600 feet of limestone, argillaceous limestone, and calcareous shale along its belt of outcrop in the northern part of the southern peninsula of Michigan. The abundance and exquisite preservation of the invertebrate fauna make these beds one of the finest collecting grounds for Devonian fossils in North America, and many studies on the corals, mollusks, ostracods, and Bryozoa have been published. The present report begins the systematic study of Traverse brachiopods by an analysis of the superfamilies Dalmanellacea, Pentameracea, Strophomenacea, Orthotetacea, Chonetacea, and Productacea. Twenty-three genera, 98 species, and 11 subspecies are recognized. Fifty-four of the species are new. Five new genera (Sphenophragmus, Orthopleura, Oligorhachis, Helaspis, and Truncalosia) are proposed. Bivariate statistical techniques are employed as a means of characterizing the growth patterns of 70 species and subspecies. Unusually abundant and stratigraphically complete collections of several genera from the lower four formations of the Traverse group in the Thunder Bay region involve continuous variation between extreme morphologic types. This is interpreted as a record of endemic evolution rather than migration. Theoretical difficulties in the compartmentation of a biologic continuum, ordinarily not encountered because of the incomplete nature of the paleontologic record, are here met in fact. Significant differences are noted in the number of species of the genus Strophodonta found in different formations, with a maximum of taxonomic diversity and a minimum of morphologic variation characterizing collections from the Alpena limestone. This relationship is interpreted in terms of adaptive radiation into a diversity of habitats associated with Alpena reefs. Ranges of species in the sections exposed on the shores of Little Traverse Bay and Thunder Bay are established. Faunal evidence documents the correlation of the Gravel Point formation with the Alpena limestone and part of the Four Mile Dam formation and the correlation of the middle Petoskey formation with the Potter Farm formation. Although the proportion of cosmopolitan species is small, identification of Traverse forms in collections from Illinois, Ohio, Indiana, Ontario, Missouri, and New York contributes to the regional correlation of Traverse strata"--P. 351.