Investigation of Middle and Lower Jurassic Radiolaria from the Neuquen Basin of west-central Argentina.

摘要

This report is the first study on South American Lower to Middle Jurassic Radiolaria. The radiolarian faunas were recovered from several Formations on well-exposed sections of Neuquen Basin, central-west Argentina. Profiles bearing samples with Radiolarian are described in the text. Five new genera are proposed: Domoella, Tetractoma, Cialia, Reija, and Butchus. At the species level twenty seven new ones are described: Archaeocenosphaera lapaensis, Archaeocenosphaera neuquensis, Ares lapaensis, Bernoullius lapaensis, Bernoullius musacchioi, Bernoullius patagoniensis, Bistarkum musacchioi, Butchus lapaensis, Cialia lapaensis, Citriduma lapaensis, Citriduma patagoniensis, Danubea patagoniensis, Droltus lapaensis, Emiluvia (?) neuquensis, Katroma lapaensis, Niagotum andinus, Niagotum neuquensis, Orbiculiforma patagonica, Paliandromeda lapaensis, Pantanellium australis, Paronaella patagoniensis, Patulibracchium lapaensis, Patulibracchium lapaensis, Perispyridium neuquensis, Protoperispyridium neuquensis, Pseudopantanellium lapaensis, Pseudopantanellium neuquensis, Reija lapaensis, Sontonaella lapaensis, Sontonaella lisa, Tetractoma lapaensis, and Thurstonia patagoniensis.; A first attempt to outline a Lower-Middle Jurassic Radiolarian Biostratigraphic Scheme for South America is presented herein. The basic units are ten preliminary radiolarian associations, with the occurrence dated by ammonite zones. The Lower Jurassic has three Associations: J1-A (Pliensbachian), J1-B, (Lower Toarcian) and J1-C (Middle Toarcian). Liassic faunas show strong Tethyan affinities with many species in common with those described by Pessagno and his study group in the Queen Charlotte Islands (British Columbia), east-central Oregon, and Turkey. Hettangian and Sinemurian strata have not yielded radiolaria yet. The Middle Jurassic includes seven Associations: J2-A, B (uppermost Aalenian-lowermost Bajocian), J2-B (lower Bajocian), J2-C (lower Bathonian). The upper Bathonian, comprise three Associations, J2-D, J2-E, and J2-F, while the last Association J2-G is dated as lowermost lower Callovian to middle lower Callovian. A high degree of endemism is present on these last three associations, particularly in the upper Bathonian.; The above mentioned associations (informal biostratigraphic units) will be refined after further investigation on other Jurassic Basins of South America.