Análisis de facies y estratigráfico secuencial de la Formación Bardas Blancas (Toarciano inferior-Bajociano inferior), Cuenca Neuquina

BRESSAN, G.S.; KIETZMANN, D.A.; PALMA, R.M.

Trelew

Simposio; V Simposio Argentino del Jurásico y sus Límites; 2013

Strata of the Bardas Blancas Formation (lower Toarcian-lower Bajocian) are exposed in northern Neuquén Basin. Five sections have been studied in this work. Shoreface to offshore deposits predominate in four of the section studied exhibiting a high abundance of hummocky cross-stratified, horizontally bedded and massive sandstones, as well as massive and laminated mudstones. Shell beds and trace fossils of the mixed Skolithos-Cruziana ichnofacies appear in sandstone beds, being related with storm event deposition. Gravel deposits are frequent in only one of these sections, with planar cross-stratified, normal graded and massive orthoconglomerates characterizing fan deltas interstratified with shoreface facies. A fifth outcrop exhibiting planar cross-stratified orthoconglomerates, pebbly sandstones with low-angle stratification and massive mudstones have been interpreted as fluvial channel deposits and overbank facies. The analysis of the vertical distribution of facies and the recognition of stratigraphic surfaces in two sections in Potimalal river area let recognized four transgressive-regressive sequences. Stacking patterns show a retrogradational arrangement of facies related with a widespread transgressive period. Forced regressive events are recognized in the regressive intervals. Comparison of vertical distribution of facies also shows differences in thickness in the lower interval among the sections studied. This would be related with a control in the sedimentary deposition by the half graben structures result of the relief generated by the extensional regime of the rifting stage which act in the basin during the Rhaetian–Pliensbachian. Lateral variation of facies let recognize the deepening of the basin through the southwest.