Diverse and well-preserved Toarcian radiolarians have been recovered
from a succession of organic-rich shale with intercalations of siliceous
limestone. The succession is located at the Slovenian-Italian border in
the Julian Alps and was deposited on a subsided block pertaining to the
south Tethyan passive continental margin. Twenty spumellarian and 17
nassellarian genera were found in total. Thirty-six taxa were identified
to species level and one new species, Bistarkum mangartense n. sp., is
described. The assemblages show a high predominance of spumellarians
over nassellarians. Spongy spumellarians, especially Orbiculiforma ?,
are markedly abundant. Pantanelliidae are generally rare but reach a
pronounced peak of 13% in one stratigraphic level. Among nassellarians,
Parahsuum is the most abundant but members belonging to Syringocapsidae
are scarce to absent. In addition to paleolatitude and water column
depth, ecological conditions accompanying the early Toarcian global
anoxic event may have to a considerable extent determined the specific
taxonomic composition of these radiolarian faunas. (C) 2003 Elsevier
B.V. All rights reserved.