La Formación Majaditas (Carbonífero), flanco occidental de la Precordillera sanjuanina: litoestratigrafia y facies

the majaditas formation (carboniferous) [amos and rolleri, 1965] is exposed along the western flank of the precodillera in the san juan province of western argentina (fig. 1). its exposures are flanked to the south and north by discontinuous outcrops of carboniferous deposits of similar age. the unit has been subdivided in six members (basal member, diamictítico member, rojo i member, areniscas y pelitas moteadas member, rojo ii member and superior member) [figs. 3 and 5]. nine facies were identified, namely: facies 1: deposits, confined to the basal part of the section (basal member), consist of clast-supported conglomerates and subordinate coarse- to medium- grained sandstones. clasts in the basal conglomerates display flow-parallel long axis orientation (fig. 7b), indicative of suspension rather than traction. the abundance of conglomerates and maximum clast size decrease up section. overall, the basal third of the section shows a clear fining-upward trend (fig. 6). these deposits were deposited by high-density gravity flows and tractional flows in a coarse-grained delta (fandelta) setting. facies 2: deposits are massive pebbly mudstones intercalated within the facies 1 deposits. the exposures are areally limited. some of the clasts show striations. based on contextual evidence, the pebbly mudstones may be interpreted as part of the spectrum of shallow gravity flows that dominate the basal part of the section. facies 3: is made up of laminated mudstones and interbedded lenticular diamictitites. dropstones, indicative of ice-rafted material, are present in the laminated mudstones. the lenticular bodies of diamictites show in some cases two distinct lithologies (pebbly mudstone and pebbly sandstone) with sharp contacts surrounded by variably deformed mudstones (fig. 9). facies 4: consists of thin-bedded, low-density turbidites with complete (ta-e) and base-cut (tb-e) bouma cycles. these facies deposits were locally affected by centimetric to decametric scale soft-s