Paleobiogeographic affinities of the Argentine Precordillera according its Late Palaeozoic brachiopod faunas

CISTERNA, G.A.; SIMANAUSKAS, T.; ARCHBOLD. N.W.

Sydney

Congreso; First International Palaeontological Congress; 2002

Distinctive Late Palaeozoic brachiopod faunas of Precordillera are found in the marine sequences of the Río Blanco and Calingasta-Uspallata basins and in the marine horizons from the west part of Paganzo basin. Fusulinids foraminiferans and conodonts are absent from these marine precordilleranian faunas hence the reliance for zonation and correlation purpose has been placed fundamentally on brachiopods with support from palynological data in some cases. Brachiopod genera considered for the paleobiogeographical analysis belong to four interval of time: Early Carboniferous (Tournaisian), characterized by its very low brachiopod diversity, includes brachiopods of the Protocanites scalabrinii-Azurduya chavelensis Zone (Chilenochonetes sp., Azurduya chavelensis (Amos), A. cingolanii sp. nov. and Pseudosyringothyris? sp.); Late Carboniferous (Namurian-Westphalian) interval includes the typical "Levipustula fauna" (Levipustula levis Maxwell, Kitakamithyris booralensis (Campbell), K. immensa (Campbell), Torynifer tigrensis Taboada and Cisterna, Spiriferellina octoplicata (Sowerby), Septosyringothyris keideli (Harrington), etc.), which appears in characteristic association with glacial sequences; Latest Carboniferous-Earliest Permian interval contains a particular assemblage composes by Micraphelia indianae Simanauskas and Cisterna, Tuberculatella peregrina (Reed), Aseptella aff. patriciae Simanauskas, Rhipidomella? sp. and Orbiculoidea sp; finally, the Early Permian (Late Asselian) interval includes fundamentally the brachiopods belonging to the Tivertonia jachalensis-Streptorhynchus inaequiornatus Biozone (Tivertonia jachalensis (Amos), Streptorhynchus inaequiornatus Leanza, Kochiproductus sp., Coronalosia argentinensis, Tupelosia paganzoensis, Costatumulus sp., Crurithyris? sp., Trigonotreta pericoensis (Leanza), Septosyringothyris sp. aff. S. jaguelensis Lech and Orbiculoidea sp.). The brachiopod affinities of Precordillera are studied by comparison with the biogeographical Late Palaeozoic units previously suggested by other authors and by cluster analysis, considering in this case only three interval of time (Late Carboniferous, Latest Carboniferous-Earliest Permian and Early Permian). For the Late Carboniferous Precordillera shows a high affinity value with the Austral realm, fundamentally by the presence of the Levipustula fauna elements in the Argentine Tepuel-Genoa basin and Eastern Australia. This fauna appears typically associated to glacial sequences related to the Namurian-Westphalian glacial event that affected the southwestern gondwanan margin. Contrasting with that happens in the other Carboniferous localities from the South Hemisphere, in where the brachiopod diversity decreases from the Early Carboniferous to Namurian, the Namurian Precordilleranian brachiopod faunas are most diversified in comparison with those from the Tournaisian sequences. However, the particularly low diversity of the Early Carboniferous brachiopod assemblages from Precordillera appears to respond to a local high-stress environment. During the Latest Carboniferous-Earliest Permian interval Precordillera loses affinity with the Austral realm. This interval is characterized by a very particular fauna with Tethyan and Boreal genera such as Micraphelia, Tuberculatella and Aseptella mixed together with endemic forms. To the Early Permian, probably latest Asselian, Precordillera shows the highest affinity with the Austral realm by the presence of typically core Gondwanan genera, i.e. Tivertonia, Coronalosia, Trigonotreta, Costatumulus, which are characteristic from the Permian sequences of Australia and India. However, other extragondwanic genera like Kochiproductus, Rhynchopora or Crurythyris would be linking Precordillera to the Tethyan and Boreal realms. Also, after the Late Carboniferous glacial episode Precordillera undergoes a climatic amelioration. Consequently, the Early Permian Precordilleranian brachiopod assemblages are characterized by typical cold water genera widely developed in the core Gondwanan realm, accompanied by a lesser percentage of genera such as Kochiproductus, Rhynchopora or Neochonetes, that suggest a warmer influence. All data compilation on world diversity through the Phanerozoic indicate that Late Palaeozoic diversity declined slightly from the Early Carboniferous to the Early Permian. However, Precordillera shows clearly an increase of the specific brachiopod diversity from the Carboniferous to the Permian. It is probably related with the strong climatic changes associated to the glacial episodes and to the paleogeographical evolution of the southwestern Gondwanan margin.