Bioestratigrafía de la Formación Barranca Final, Neógeno de la Cuenca del Colorado, Argentina

Abstract

Dinoflagellate cysts from the Barranca Final Formation type section are diverse and well preserved. The assemblages are dominated by the arder Gonyaulacales, with subordinate Peridiniales represented only by protoperidiniaceans. Based on selected dinoflagellate cyst events, and in accordance with the foraminiferal data, we suggest a Middle to Late Miocene age for the section. LnbyrinthodiniulI1 truncatum subsp. truncaium Piasecki ranges from la test Early Miocene or early Middle Miocene through Late Miocene and Selenopemphix dionneacvstn Head et ni. has its range base within the Middle Miocene. The occurrences of these species together with the presence of Bngontedinium canacoense (Wall) Reid confirms an age not older than Middle Miocene for the bottom of the section. The low representation of oceanic species, such as lmpagidinium spp., the presence of Nenunosphaeropsis rigida Wrenn (inner to outer? neritic), the di verse representation of protoperidinacean species (inner neritic), and the abundance of euryhaline forms. particularly specimens of the Cperculcdinium centrocarpum/isvaeímnum complex, Tubercutodinium vnncl1l1lpol1e Wall and Lingulodinium hemicustum McMinn, reflect estuarine to inner neritic conditions for the lower part of the section. Tuberculodinium vnnenl11pone and Lingulodinium machaerophorum (Deflandre y Cookson) Wall suggest warm temperate to tropical conditions. Upwards, the assemblages are characterized by an increased terrigenous influx together with the apparent disappearance of most dinocyst taxa. Within the generally estuarine palaeoenvironment, the occurrence of oceanic to neritic markers coinciding with a glauconitic section, suggests a marine flooding surface.