345 Silurian Radiolarian Zonation for the Caballos Novaculite, West Texas

Silurian radiolarian zonation for the Caballos novaculite, Marathon Basin, west Texas - BAP #345

This paper presents a local biozonation for Silurian radiolarians recovered from the Caballos Novaculite, Marathon uplift, Texas. Six measured sections representing 25-30 m of strata from the western half of the uplift have yielded abundant and moderately well-preserved radiolarian assemblages that can be subdivided into six biozones. The Rotasphaerid Superzone (Ro), contains the four oldest zones 1, 2, 3, and 4, and is defined by the first and last appearances of the superfamily Rotasphaeracea. The base of this superzone has not yet been determined in the Marathon uplift. All taxa chosen for this biozonation are commonly occurring, distinctive, robust forms that can be correlated from section to section, thereby meeting the criteria for establishing a practical and widely applicable biostratigraphic scheme.

Three conodont assemblages co-occur with the radiolarians and show the youngest zone to be no younger than Pridolian (Late Silurian). The oldest zone, Zone 1, is at least as old as Ludlovian and may be as old as Wenlockian (Early Silurian). Further chronostratigraphic calibration is needed to constrain the ages of these radiolarian zones better. 

Taxa from the Ro Superzone bear strong resemblance to Silurian radiolarian assemblages from the Canadian Archipelago and Southern Urals, and are identical to forms described from the Fusalfanus osobudaniensis through Stylosphaera? sp. C assemblages from the Fukuji Area, Gifu Prefecture, Japan. Several taxa in the lower part of Zone 6, above the Ro Superzone, are identical to those in the Devoniglansus unicus assemblage from the Kurosegawa Tectonic Zone, southwest Japan. The widespread geographic distribution of these assemblages suggests that it may be possible to generate a global radiolarian biozonation for the Silurian period. 

Various biostratigraphically useful Silurian radiolarians are described in this paper. One new superfamily, three new families, six new genera, and 28 new species are described. The new superfamily Rotasphaeracea includes the new families Rotasphaeridae and Pseudorotasphaeridae. Within the Rotasphaeridae are the genera Rotosphaera, n. gen. containing R. beckwithensis, n. sp., R. delicata, n. sp., R. marathonesis, n. sp., R. nude, n. sp., R. quadrata, n. sp., and R. robertsorum, n. sp., and Secuicollacta Nazarov and Ormiston, containing S. cassa? Nazarov and Ormiston, S. foliaspinella, n. sp., S. solara, n. sp., and S. (?) platyspina, n. sp. Within the Pseudorotasphaeridae is Pseudorotasphaera, n. gen., containing P. communa, n. sp., P. hispida, n. sp., P. lanceolata, n. sp., P. (?) robustispina, n. sp., and P. (?) rotunda, n. sp. The new family Paleoactinosphaeridae contains Stylactinosphaera, n. gen., with S. prima, n. sp., and Paleoactinosphaera, n. gen. containing P. antica, n. sp., P. asymmetrica, n. sp., P. barricki, n. sp., P. (?) crucispina, n. sp., P. elegantissima, n. sp., and P. (?) ocaspina, n. sp. Other new taxa described are Pseudospongoprunum (?) tauversi n. sp., Praespongocoelia n. gen., containing P. fusiforma, n. sp. and P. parva Furutani, Bipylospongia, n. gen. containing B. rudosa, n. sp., Stylosphaera (?) magnaspina, n. sp., Oriundogutta (?)  kingi, n. sp., Oriundogutta (?) varispina, n. sp., and Zadrappolus lunaris, n. sp. Systematic revisions of the following taxa are also included: Genus Secuicollacta Nazarov and Ormiston and its type species. Secuicollacta cassa, Family Inaniguttidae Nazarov and Ormiston and its genera Inanigutta Nazarov and Ormiston, Inanihella Nazarov and Ormiston, Fusalfanus Furutani, Zadrappolus Furutani, and Oriundogutta Nazarov and Ormiston, in addition to Spongocoelia parvus Furutani, Fusalfanus osobudaniensis Furutani, and Pseudospongoprunum, Wakamatus et al.