Multiproxy analyses of the Triassic Agua de la Zorra Formation, Cuyana Basin, Argentina: Palynofacies, geochemistry, and biotic record

Abstract

The Triassic Agua de la Zorra Formation crops out in the Paramillos de Uspallata area(NW of Mendoza) and represents a deltaic-lacustrine system with volcanic activity aswell as episodic incursions of peperitic basalts. The succession is characterized bydistal lacustrine facies at base and top, with proximal shallow facies in the middlesection. The paleontological record includes invertebrates (spinicaudatans, insects),vertebrates (mainly fishs), tetrapod tracks and invertebrates traces, and plant remains(mainly referred to Umkomasiales). Kerogen in the distal facies is mostly terrigenous,with scarce amorphous and palynomorphs (disacates and microalgae). It shows avariable percentage of the total organic carbon content (between 0.2 and 4.6) withhydrogen and oxygen indices indicating a type III kerogen. In the shallow facies,kerogen is practically absent and the trace fossils reflect sporadic subaerial exposure.The palynological evidence indicates an oligotrophic lake and the low productivityrecorded was likely caused by dilution of the lake water by strong fluvial influence in anoverfilled lake basin type. The organic geochemistry data also suggests an overfilledlake basin and the inorganic geochemistry data support the development of anoxicconditions at the bottom of the paleolake. The spinicaudata valves occur in denselypacked beds that could have been driven by changes in the water physicochemicalparameters as a result of volcanic activity in the area. The volcanic activity in the areais a good explanation for variability in the biota diversity. However, the continuousrecord of plant remains through out the section seems to indicates that thepaleoenvironmental conditions in the surrounding terrestrial areas were stables.