Katian (Upper Ordovician) Radiolarians from the Malongulli Formation, Lachlan Fold Belt, New South Wales Australia, and the Hanson Creek Formation, Nevada USA
Radiolarians from limestone in the Malongulli Formation, New South Wales are re-examined and compared to faunas from the Hanson Creek Formation, Nevada, and demonstrate that a distinct fauna dominated by entactinarians, inaniguttids and haplotaeniatumiids was widely distributed during the Upper Ordovician. Both the Malongullli and Hanson Creek formations are mixed shale and carbonate representing distal shelf to slope facies. The Malongulli has been previously shown to contain a fauna dominated by Kalimnasphaera maculosa, Stigmosphaerostylus subulata, and palaeoscenidiids we assign to Palaeoephippium octaramosum. In addition, we recognize a significant haplotaeniatumiid component, including Haplotaeniatum spongia, and two new species of Haplotaeniatum. Other significant components are Secuicollacta ornata, Inanigutta complanata, and Protoceratoikiscum chinocrystallum. Etymalbaillilla yennienii is rare and reported for the first time outside of China. Malongulli limestones were dated previously by conodonts and graptolites as Katian (middle Upper Ordovician). Conodonts are assigned to the O. velicuspis Zone of the N. American mid-continent, and graptolites from below the limestone to the D. kirki Zone. The Hanson Creek fauna is slightly younger, also Katian (D. ornatus graptolite Zone), and is strikingly similar to the Malongulli fauna sharing 7 of the 12 Malongulli species and likewise dominated by K. maculosa, E. subulata and P. octaramosum. Secuicollacta and haplotaeniatumiids are common and P. chinocrystallum is rare. Hanson Creek radiolarians have unusual preservation in that the internal structures of spherical forms are not silicified, which has hampered previous identification work. This assemblage is also recognized in radiolarian chert. K. maculosa, E. subulata, P. chinocrystallum, and S. ornata occur in more poorly preserved basinal facies rocks in the Lachlan Fold Belt of New South Wales and in the Vinini Formation in central Nevada. Improved chronostratigraphic correlation combined with this investigation provides a solid picture of the middle Katian radiolarian assemblages and their use in biostratigraphy.