Anna I. Antoshkina (1) and Constance M. Soja (2)
Late Silurian reconstruction indicated by migration of reef biota between Alaska, Baltica (Urals), and Siberia (Salair)

Keywords
Late Silurian, reef biota, Alaska, Baltica, Siberia, paleo-Uralian sea

Abstract
During the Late Silurian, reefs with similar frame-building biotas formed along the margins of the Uralian Seaway in areas that include present-day southeastern Alaska, the Ural Mountains, and the Salair Ridge in southwestern Siberia. The Uralian reefs grew at a passive platform margin, Alaskan and Salairian reefs originated in island arcs. The unique feature of these Ludlovian reefs is the framework structures that were built by microbial communities associated with atypical Silurian reef-related metazoans: sphinctozoan sponges (aphrosalpingids) and a problematic hydroid, Fistulella. The unusual but highly similar reef biotas imply that the paleo-Uralian sea during the Ludlow was partially enclosed, narrow, and subequatorial. In the Paleo-Asian Ocean, the Salair island arc may have been welded to the Siberian continental margin after the Early Caledonian orogeny, but other evidence suggests Salair persisted as an arc system until the Carboniferous. The microbial-sponge-hydroid reefs in Salair suggest a marine connection to similar reef communities of the Urals and Alaska evolving along the margins of the Uralian Seaway during the Late Silurian.

Author info
1) Institute of Geology, Komi Science Centre, Ural Branch, Russian Academy of Sciences, 54 Pervomayskaya Street, 167982, Syktyvkar, Russia; Antoshkina@geo.komisc.ru 2) Department of Geology, Colgate University, 13 Oak Drive, Hamilton, NY, 13346 USA; csoja@mail.colgate.edu

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