TRAZAS FOSILES DEL CARBONIFERO MEDIO-SUPERIOR DE LA PRECORDILLERA DE SAN JUAN: SU CORRELACION CON UN EVENTO GLACIAL

PERALTA, SILVIO H; MILANA, JUAN P.

Salta

Congreso; XIV Congreso Geológico Argentino; 1999

Asociación Geológica Argentina

ABSTRACT: Late Carboniferous deposits of the Argentine Precordillera are important because of thier relation with the world-wide Gondwanic glacial event. The record of marine trace fossil assemblages in the lowermost part of the Jejenes Formation (Earsten Precordillera), in the middle-lower part of the Guandacol Formation (Central Precordillera) and in the upper part of the Hoyada Verde Formation  (Western Precordillera) and associated marine shelly faunas and/or palynological assembblages, allows us to suggest a marine paleoenviroment. Morever taking into account sedimentological criteria, such as the occurrence of glacigenic structures and deposits, the ichnological assembblages recorded in the Late Carboniferous of the Precordillera, are assigned to the Cruziana ichnofacies whose development took place in cool to temperate conditions in shallow water paleoenviroment. In addition to the physical features previously mentioned Late Carboniferous ichnological assembblages include both epi and intrastratal crowling traces, ranging from simple to ornamented trails and track-ways consisting of individual podial imprints. Such assembblages are caracterized by low (Jejenes Formation) to moderate (Guandacol and Hoyada Verde Formation) diversity and moderate to high abundance, in opposite to the typical Seilachers Cruziana ichnofacies, characterized by generally high diversity and abundance. We assume that the low diversity of the ichnological assembblages recorded in the Argentine Precordillera, results from both climatic condition and moderate to high energy of the nearshore marine enviroment.