Ordovician sponges from west-central and east-central Alaska and western Yukon Territory, Canada

Abstract

Moderate collections of fossil sponges have been recovered over a several-year period from a few scattered localities in west-central and east-central Alaska, and from westernmost Yukon Territory of Canada. Two fragments of the demosponge agelasiid cliefdenellid, <i>Cliefdenella alaskaensis</i> Stock, 1981, and mostly small unidentifiable additional fragments were recovered from a limestone debris flow bed in the White Mountain area, McGrath A-4 Quadrangle in west-central Alaska. Fragments of the agelasiid actinomorph girtyocoeliids <i>Girtyocoeliana epiporata</i> (Rigby & Potter, 1986) and <i>Girtyocoelia minima</i> n. sp., plus a specimen of the vaceletid colospongiid <i>Corymbospongia amplia</i> Rigby, Karl, Blodgett & Baichtal, 2005, were collected from probable Ashgillian age beds in the Livengood B-5 Quadrangle in east-central Alaska. A more extensive suite of corymbospongiids, including <i>Corymbospongia betella</i> Rigby, Potter & Blodgett, 1988, <i>C. mica</i> Rigby & Potter, 1986, and <i>C.</i>(?) <i>perforata</i> Rigby & Potter, 1986, along with the vaceletiid colospongiids <i>Pseudo-imperatoria minima</i>? (Rigby & Potter, 1986), and <i>Pseudoimperatoria media</i> (Rigby & Potter, 1986), and with the heteractinid <i>Nucha naucum</i>? Pickett & Jell, 1983, were recovered from uppermost part of the Jones Ridge Limestone (Ashgillian), on the south flank of Jones Ridge, in the Sheep Mountain Quadrangle, in westernmost Yukon Territory, Canada. The fossil sponges from the McGrath A-4 and Livengood B-5 quadrangles were recovered from attached Siberian terranes, and those from the Sheep Mountain Quadrangle were recovered from an allochthonous Laurentian terrane in the Yukon Territory

The first sphinctozoan-bearing reef from an Ordovician back-arc basin

“…In contrast to the high-energy stromatolite-sphinctozoan reefs from the Late Silurian, this case represents a low-energy and Rigby 1999;Carrera and Botting 2008). Sphinctozoan occurrences are known from eastern Australia (New South Wales), Alaska, California, northwestern China, and Kazakhstan, with a more than twofold increase in biodiversity at the genus and species levels compared with the Cambrian (Senowbari-Daryan and García-Bellido 2002; Carrera and Rigby 2004;Rigby et al 2008a). Some Ordovician sphinctozoans might stem from reefal deposits but these are not well described (Senowbari-Daryan and Rigby 2011).…”