ABSTRACT: The aim of this report is to 1) to formally describe Austral and Subtropical Gyre Radiolaria recovered from ODP Hole
123-765C), 2) to compare them with published records of Southern Hemisphere “non-Tethyan” assemblages and 3) to discuss
radiolarian paleobiogeography of the Southern Hemisphere and its implications for global climate change during the Jurassic–Cretaceous
transition. The Tithonian to Aptian/early Albian radiolarian record recovered from Hole 765C, Cores -62R to -36R in the Argo
Abyssal Plain (AAP) is unique in its density of well-preserved samples and in its faunal contents. Radiolaria recovered from claystones
yielded the low diversity, ecologically tolerant “Crypto-Archaeo” Assemblage, (chiefly cryptocephalic and cryptothoracic nassellarians
and Archeodictyomitra spp.) interpreted herein as originated in the Subtropical Gyre (STG).
In contrast, assemblages extracted from radiolarite layers, interpreted as pelagic turbidites derived from the deeper Australian margin,
are dominated by Austral taxa. Neotethyan taxa are very rare to absent before the late Hauterivian/Barremian, when they gradually
gain in diversity and abundance. Described Austral and STG taxa include 10 families, of which Fusitanellidae n. fam. and Windaliinae
n. subfam. are new. Of 18 genera 7 are new (Nodosphaera, Praewindalia, Pachycingula, Archaeotanella, Morchella, Fusitanella,
Argofusus) and of 55 species 30 new ones are formally described and 14 new ones are left in open nomenclature. The southern hemisphere
Late Jurassic to Early Cretaceous radiolarian biogeography is defined from low- to high latitude: 1. the Neotethyan (NT) and 2.
the Central Panthalassan (CP) realms, 3. Eastern Boundary Current (EBC) realm, 4. the Subtropical Gyre (STG) and the Austral (A)
circum south-polar realm. Radiolarian biogeography and plate tectonic models support a scenario of palaeoceanographic and global climatic
change during the Jurassic–Cretaceous transition related to progressive Pangea break-up with the following consequences: 1. an
increased heat transfer to the Southern hemisphere which caused cooling of Neotethyan regions during the Late Tithonian dry event. 2.
Anorthward shift of the southern summer Intertropical Convenience Zone reduced the Neotethyan monsoon area and allowed the establishment
of a southern Neotethyan subtropical gyre documented by the “Crypo-Archaeo” Assemblage. 3. The south-polar West Wind
Drift may have forced a circum Antarctic-Australian cold current through the epicontinental rift between India and Antarctica-Australia
since the Berriasian (140 my), transporting Austral Radiolaria into the AAP where they accumulated in radiolarite layers.
Micropaleontology, vol.