Sedimentología de la formación Carrizal (Triásico) en el Depocentro Marayes - El Carrizal, provincia de San Juan, República Argentina

the carrizal formation is one of the triassic units of the marayes - el carrizal rift located in the eastern san juan province, argentina (figs. 1, 2). the facies analysis and the architectural study of the carrizal formation (table 1) allowed recognising two facies associations. facies association 1 corresponds to the arroyo seco member (fig. 3), and facies association 2 to the rickard member (fig. 4). the arroyo seco member (figs. 3, 5) comprises vertical stacked channel belt conglomerates, associated with sandstones, gravelly sandstones and scarce mudrocks. channel belt conglomerates are composed of extraformational rounded to subangular pebbles of gneiss, migmatite, schist, granitoid, anphibolite and quartz derived from the local crystalline basement. these deposits are encased in amalgamated lenticular beds composed of sandstones, gravelly sandstones and fine-grained conglomerates, in which trough cross-bedding is the most conspicuous sedimentary structure (fig. 6). thin and laterally continuous fine- and medium-grained sandstones and mudstones are less common. a monotypic corystospermaceae forest with 38 stems resting in live position was identified in one of the basal levels of the arroyo seco member (fig. 6). the deposits of this facies association are essentially the result of bedload accumulation in a braided fluvial system (cf. smith, 1970; miall, 1978; bluck, 1979; steel and thompson, 1983; ramos et al., 1986; smith, 1990; bristow and best, 1993; bristow, 1993b), characterised by marked changes in discharge and sediment supply. the rickard member (fig. 4) consists of discrete conglomerate channel fill deposits cut into laterally extensive tabular deposits (sandstones, heterolithic intervals, mudstones, coal beds). three sub-associations are recognised. the first sub-association is composed of discrete thick and lenticular conglomerate beds showing a well defined imbrication structure, and composed of subangular to rounded pebbles and cobbles derived from