326 Jurassic Nassellariina (Radiolaria) from North American geologic terranes

Much of the western part of the Cordilleran Region of North America is characterized by geologic terranes which originated at low latitudes and were displaced to higher latitudes during the Late Paleozoic and Mesozoic. Many of these terranes such as the Wrangellia terrane have been displaced hundreds or even thousands of kilometers from lower, near-equatorial latitudes to their present positions. The magnitude of the tectonic complexity of the western Cordilleran Region is immense. Obviously, paleontologists must consider the displaced terrane problem in their attempts to compile meaningful biostratigraphic zonations and zoogeographic reconstructions for the Mesozoic of this region and indeed, the entire Circum -Pacific margin.

The potential utility of Radiolaria in Mesozoic biostratigraphic and paleo-oceanographic studies and in geology in general is enormous. Radiolarian zonal schemes now rival those of the ammonites in parts of the Jurassic and Cretaceous. Furthermore, even though the study of Jurassic Radiolaria is still in its infancy, it is now apparent that at least for the Middle and Upper Jurassic, Radiolaria can be utilized to differentiate the Tethyan Realm from the Boreal Realm and to subdivide each of these faunal realms into provinces. On the basis of simple criteria we subdivide the Tethyan Realm into: (1) A Central Tethyan Province characterized by the presence of Ristola Pessagno and Whalen, 1982, the absence of Parvicingula Pessagno, 1977a, and high pantanelliid diversity; and (2) a Northern Tethyan Province, characterized by common Parvicingula and high pantanelhid diversity. The radiolarian assemblage of the Boreal Realm during the Middle and Late Jurassic is characterized by the presence of abundant Parvicingula and by low pantanelliid diversity. The Boreal Realm is in turn subdivided into a Southern Boreal Province where pantanelliids still persist and a Northern Boreal Province where pantanelliids appear to be absent.

Using these simple criteria together with megafossil and paleomagnetic data (where available), we have been able to chart the course of various displaced terranes from low to higher latitudes during the course of Jurassic time. In the terranes of the Blue Mountains Province of eastern Oregon, both the radiolarian and ammonite assemblages reflect a change from Tethyan (Northern Tethyan Province) to Boreal (Southern Boreal Province) during the late Bathonian/Callovian. The first or final appearances of many taxa occurring in the late Bajocian — Bathonian— Callovian may, in fact, be paleolatitudinally controlled and may not reflect their total range in Boreal or Tethyan strata.

Most of the taxa included in the Systematic Paleontology herein are described from geologic terranes that have been displaced from low (Tethyan) latitudes to higher (Boreal) latitudes during Jurassic times. Two new genera {Farcus, n. gen., and Rolumbus, n. gen.) and thirty-four new species {Farcus asperoensis, n. sp., F. graylockensis, n. sp., Rolumbus gastili, n. sp., R. hamiltoni, n. sp., R. halseyensis, n: sp., R. mirus, n. sp., R. venustus, n. sp., Hilarisirex inflatus, n. sp., H. oregonensis, n. sp., Jacus reiferensis, n. sp., J.(?) sandspitensis, n. sp., Napora antelopensis, n. sp., N. baumgartneri, n. sp., N. bearensis, n. sp., N. bona, n. sp., N. boneti, n. sp., N. browni, n. sp., N. burckhardti, n. sp., N. cerromesaensis, n. sp., N. cosmica, n. sp., N. fructuosa, n. sp., N. (?) graybayensis, n. sp., N. heimi, n. sp., N. horrida, n. sp., N. insolita, n. sp., N. izeensis, n. sp., N. maritima, n. sp., N. mitrata, n. sp., N. moctezumaensis, n. sp., N. morganensis, n. sp., N. opaca, n. sp., N. tumultuosa, n. sp., N. turgida, n. sp., and N. vegaensis, n. sp.) have been described among the nassellarian families Farcidae, n. fam., Hilarisiregidae Takemura and Nakaseko, 1982, and Ultranaporidae Pessagno, 1977b. In an effort to formulate a more phylogenetic classification for these families and their included genera, we have stressed test construction as the primary basis for their definition.

Many of the species and genera figured in this report are distinctive and short ranging; as a result, they should prove useful in compiling a detailed radiolarian zonation for the Jurassic. Range zone data are presented for all taxa. Where known, the distribution of taxa within the Tethyan and Boreal realms is indicated in the text and text-figures.
   

Year published: 1986