Jurassic radiolarians from 220 samples in Queen Charlotte Islands, B.C.,
Williston Lake, B.C., east-central Oregon, Baja California Sur, southern
Spain, Austria, Slovenia, Turkey, Oman, Japan and Argentina were studied
in order to construct global zonation for the Pliensbachian, Toarcian
and Aalenian stages. Well-preserved faunas from continuous stratigraphic
sections in Queen Charlotte Islands provide the most detailed record for
this time interval, and all collections are tied to North American
ammonite zones or assemblages. Collections from nearly all other areas
lack independent dating except for early Toarcian carbon-isotope dating
in Slovenia and late Aalenian ammonites in Spain.
A database of 197 widely distributed updated taxonomic species was used
to construct a Unitary Association (UA) zonation for the interval. A
global sequence of 41 UAs was obtained for the top of the Sinemurian to
the base of the Bajocian. The first and the last UAs represent the Late
Sinemurian and the Early Bajocian respectively. The remaining 39 UAs
were merged into nine zones (four Early Pliensbachian, one Late
Pliensbachian, one Early Toarcian, one Middle-Late Toarcian, and two
Aalenian) according to prominent radiolarian faunal breaks and ammonite
data. The new zones are the Canutus tip pen - Katroma clara Zone (latest
Sinemurian/earliest Pliensbachian); Zartus mostleri - Pseudoristola
megaglobosa, Hsuum mulleri - Trillus elkhornensis and Gigi fustis -
Lantus sixi zones (Early Pliensbachian); Eucyrtidiellum nagaiae -
Praeparvicingula tlellensis Zone (Late Pliensbachian); Napora relica -
Eucyrtidiellum disparile Zone (Early Toarcian); Elodium pessagnoi -
Hexasaturnalis hexagonus Zone (Middle and Late Toarcian); Higumastra
transversa - Napora nipponica Zone (early Aalenian); and Mirifusus
proavus - Transhsuum hisuikyoense Zone (late Aalenian). These zones can
be correlated worldwide and link previously established UA zonations for
the Hettangian-Sinemurian and the Middle to Upper Jurassic. The new
zonation allows high-resolution dating in the studied interval and
provides a solid basis for analyzing faunal turnovers and the
paleobiogeography of Jurassic radiolarians. (C) 2010 Elsevier B.V. All
rights reserved.