THE CARBONIFEROUS FAUNAS OF THE HUARACO FORMATION AT CORDILLERA DEL VIENTO, NEUQUÉN BASIN

TABOADA, ARTURO CÉSAR; PAGANI MARÍA A; LIMARINO CARLOS O

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

New faunal assemblages were recently identified in outcrops of the Huaraco Formation surrounding the Andacollo locality at western flank of the Cordillera del Viento, Neuquén, Argentina. The Huaraco Formation of 700 m of maximum thickness is constrained between ca. 327 Ma (Serpukhovian) from rhyolites intercalated in the underlying Arroyo del Torreón Formation and ca. 288 Ma (Artinskian) from the overlying Huinganco Plutovolcanic Complex. The Huaraco Formation is mainly composed of shales, mudstones and fine- to medium- grained sandstones together with very scarce levels of coarse-grained sandstones and conglomerates. The stratigraphic analysis of the unit allowed recognizing four depositional sequences (DS), bounded by different types of incision surfaces, in which several transgressive-regressive cycles were found. Three main fossil-bearing intervals were located in the upper half of the sequence, the lower one included in the lower part of the DS 3, while the rest corresponds to the middle-upper part of the DS3 and the lower DS4. The lower assemblage is a low diverse brachiopod-dominant assemblage characterized by the plentiful occurrence of the brachiopod Linipalus sp. nov. associated with Neochonetes granulifer (Owen), Leiorhynchus sp., Reticularia sp., Orbiculoidea sp. and scarce Nuculidae bivalves. This association has some common elements with the warm-temperate Marginovatia-Maemia fauna from western Argentina of late Bashkirian-early Moscovian age, indicating the influence of warmer ocean currents southward reaching the Neuquén Basin. The second fossil-bearing horizon has coquinoid occurrences of Tivertonia jachalensis (Amos), scarce other brachiopods such as Rhynchopora sp., Orbiculoidea sp., Lanipustula patagoniensis (Simanauskas), more diverse bivalves such as Phestia sp., Palaeolima sp., Nuculopsis sp., Palaeoneilo sp., Streblopteria sp. and Sueroa sp., and the gastropod Glabrocingulum Thomas. Stratigraphically close, a third and uppermost fossiliferous horizon bears monospecific remains of Septosyringothyris sp. Most elements from these two last horizons were previously recognized in northern basins of western Argentina (San Rafael, Calingasta-Uspallata and Río Blanco basins) as taxa belonging to the temperate Tivertonia-Streptorhynchus fauna constrained to a Moscovian age. Its low diversity or impoverished expression in the Neuquén Basin could be interpreted as a cold-temperate faunal assemblage and related to the incoming of colder ocean currents from lower latitudes, where the psychrophilic Lanipustula patagoniensis thrived during the Serpukhovian-Moscovian time-span, represented by its record throughout the stratigraphic interval of ca. 1000 m thickness in the Pampa de Tepuel Formation, Tepuel-Genoa Basin, southern Patagonia. The Huaraco?s faunal assemblages enrich the known paleobiogeographic scenario offering potential links to far-field faunas along the southwestern margin of Gondwana.