Taxonomic Studies of Upper Jurassic (Tithonian) Radiolaria from the Taman Formation, East-central Mexico

Yang Qun

pp. 1-164, in English

Abstract:

The upper Tithonian Radiolaria (Upper Jurassic; Zone 4) of the Taman Formation represent a highly abundant and diversified fauna of outer neritic to bathyal environment. Thirteen families (one new), forty-four genera (seven new), and one hundred and seventy-two species level taxa (forty-nine new) are documented herein. Biostratigraphically important taxa present in this assemblage include Acanthocircus dicranocanthos, Vallupus hopsoni, Bivallupus, Parvicingula excelsa, and Perispyridium. The distinctive Jurassic “marker” Perispyridium rapidly decreases in abundance towards the top of Subzone 4 beta and does not occur in Subzone 4 alpha. Curiously, the Taman radiolarian fauna is poor in Mirifusus and completely lacks Ristola altissima, R. procera, Eucyrtidiellum ptyctum, and Sethocapsa (?) cetia, which are common, distinctive upper Tithonian elements elsewhere. This radiolarian fauna is associated with ammonites, calpionellids, and pectenacids. It includes the Kossmatia-Durangites assemblage and the lower part of Substeueroceras-Proniceras assemblage of Imlay (1980). Furthermore, the base of Zone 4 corresponds closely to the first occurrence of hyaline calpionellids. The radiolarian assemblage is correlated with radiolarian faunas in other areas, such as the Cape Verde Basin (East Atlantic) and Oman. Additionally, a new genus (Loopus, Family Pseudodictyomitridae), described here in from the Taman, bridges the correlation of Tithonian between North American and Japan.

Subfamilies Tetraditryminae Baumgartner and Higumastrinae Baumgartner are treated herein as synonyms on the basis of their internal test structure. Two new genera (Neoparonaella and Pseudohigumastra) of the Family Hagiastridae and one new genus (Tetriastrum) of Spumellariina family incertae sedis are erected herein.

The Acaeniotylidae, n. fam., is established herein to include a unique group of Radiolaria represented by the well-known genus Acaeniotyle Foreman. The new family is characterized by having a tubercular cortical shell, a latticed medullary shell and a number (varying among genera) of secondary spines on the test surface. Three new genera (Acastea, Acusten and Praeconosphaera) of this family are erected herein, and Genus Aceaniotyle Foreman is emended.

The following families are common in the Taman (Zone 4): Acaeniotylidae, n. fam., Hagiastridae, Patulibracchiidae, Hsuidae, Parvivaccidae, Parasaturnalidae (Acanthocircus), Epitingiidae (Perispyridium), Archaeodictyomitridae, Pseudodictyomitriidae, Syringocapsidae, Xiphostylidae, and Ultranaporidae (Napora).

Paleobiogeographically, the upper Tithonian Taman faunas described herein belong to the Northern Tethyan Province of Pessagno et al. (1987a), because of the common occurrence of both Pantanelliidae and Parvicingula and the lack of Ristola.

Keywords: Radiolaria, Upper Jurassic, east-central Mexico, Taman Formation

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