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Soja, C.M., 1985

Paleonotologic, paleoecologic, and sedimentologic studies of Lower Devonian facies, Kasaan and Wadleigh islands, southeastern Alaska

Bibliographic Reference

Soja, C.M., 1985, Paleonotologic, paleoecologic, and sedimentologic studies of Lower Devonian facies, Kasaan and Wadleigh islands, southeastern Alaska: University of Oregon, Eugene, Ph.D. dissertation, 666 p., illust.


This study of Late Early Devonian (Emsian) faunas from Kasaan and Wadleigh Islands in southeastern Alaska involves the systematic description, discussion, and illustration of 31 species and subspecies of brachiopod genera. Sixteen of these species are new taxa assigned to the genera Gypidula, Ancillotoechia, ?Sibiritoechia, Protathyris, Leptathyris, Cyrtinaella, Howellella, Amoenospirifer, Howittia, ?Eoreticularia, Reticulariopsis, and Micidus; the remaining two species represent new genera not previously described. Species belonging to the genera Lingula, Schizophoria, Mesodouvillina, ?Cymostrophia, ?Brachyprion, ?Eoschuchertella, Xenogypa, ?Trigonirhynchia, Anatrypa, Spinatrypa, and Crurithyris are also identified in these faunas. The fossils under study occur in rocks that are included in the Alexander Terrane, which comprises a predominantly Paleozoic sedimentary sequence and local occurrences of volcanic flows and intrusive igneous rocks. A petrographic analysis shows that carbonate facies representing, in ascending order, restricted nearshore subtidal sediments, offshore stromatoporoid banks, an open lagoon, and restricted lagoonal ponds form the Lower Devonian sequence of limestones on Kasaan Island. On Wadleigh Island, a cosmopolitan brachiopod fauna occurs in open shelf sediments. These open shelf deposits are interbedded with stromatoporoid-rich sediments representing offshore subtidal conditions and with Amphipora packstones, which are interpreted as restricted shelf deposits. Uralian, rather than North American, affinities were ascribed to the Emsian, shallow-shelf faunas from Kasaan Island by Kindle (1907). A comparison undertaken herein indicates that there is no biogeographic affinity between the brachiopods from Kasaan Island and assemblages in the circum-Pacific region, nor between the Kasaan Island and Uralian faunas. This dissertation indicates that the Kasaan Island brachiopods are a mixture of endemic genera and of taxa that occur in western North America, Europe, Australia, and northeastern USSR at relatively earlier or later times. This association of taxa may represent an endemic enclave within the Cordilleran Region. The development of relatively isolated faunas in southeastern Alaska may be related to the paleotectonic setting of southeastern Alaska, which is believed to represent an accretionary island-arc complex.

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