THE CLAY MINERALS OF THE BALBUENA SUBGROUP (MAASTRICHTIAN ?DANIAN) IN THE TRES CRUCES SUB-BASIN, JUJUY ARGENTINA

APARICIO GONZÁLEZ, PAMELA; AGNES IMPICCINI; DO CAMPO MARGARITA; CAYO, LUBÍN ERIC

Paraná Entre Ríos

Congreso; XVII Reunión Argentina de Sedimentología; 2021

Asociación Argentina de Sedimentología

This abstract presents the first results of a mineralogical study of pelites from the Balbuena Subgroup (Lecho-Yacoraite formations) taken from outcrops of Maimara section (23 ° 37´30.92 "S 65 ° 23´56.07" W Maimará, Jujuy), corresponding to the Tres Cruces sub-basin (Salfity y Marquillas, 1999) of the Salta Group in Eastern Cordillera.The deposits of the Balbuena Subgroup (Maastrichtian-Danian) lies uncomformably above the quartz sandstones of the Mesón Group (Middle ? Upper Cambrian), dipping towards to the west. The Lecho Formation is transitionally overlain by the Yacoraite Formation. In the Maimará section the Yacoraite Formation is 55 m in thickness, and the base of the Lecho Formation is composed of a fining-upward succession of matrix supported conglomerates and coarse to fine-grained sandstones. The conglomerate is composed for angular and poorly sorted fragments of rocks with a clearly provenance from the Mesón Group. These levels were interpreted as products of debris flows in an environment with laminate sparse water supply of alluvial fans. The Yacoraite Formation is composed of limestones, laminate pelites, calcareous sandstones and stromatolitic limestones with traces fossils and dinosaur tracks (Marquillas et al., 2005, Díaz-Martínez et al., 2016, Console et al. 2017).The analyzed samples correspond to two reddish and greenish pelite levels from the Yacoraite Formation. Clay minerals were identified using a Rigaku DMAX-2D diffractometer, employing Cu radiation, with a step size of 0.05º2θ and scanning speed of 0.01º/min, at 40 kV and 20 mA. The total rock powders were scanned from 3.0 to 65.2° 2θ, and clay fractions (< 2 μm) were scanned from 2.2 to 40.2° 2θ.The two pelitic levels are composed of quartz, feldspars, calcite and clays. The clay fraction of these levels are composed of illite/mica and kaolinite, where the second one is the most abundant in the greenish layers. The origin of illite/mica in these levels is probably detrital, coming from the Mesón Group as the clay fraction of the Campanario Formation is mainly composed of illite/mica. The kaolinite could be formed as an authigenic mineral by alteration of feldspars or detrital from the illite/mica fraction of the Mesón Group. This mineral forms under humid subtropical to tropical climates, where highly hydrolytic conditions prevail (Chamley, 1989). The presence of the kaolinite is common in rocks of the Cretaceous period where the palaeoclimatic global models that indicates higher average temperature and humidity, during that period compared to current climatic conditions (Bauluz, 2015).