Stratigrafia e provenienza di formazioni cretaciche del Bacino di Neuquen, Argentina

During the Cretaceous, the Neuquén Basin evolved from an extencional back-arc to a retroarc foreland basin. In this study, we analyzed the petrography and the stratigraphy of the formations that mark this transition, in order to interpret the paleoenvironments in which the Rayoso Formation (Bajada del Agrio Group), the Candeleros, Huincul and Cerro Lisandro Formations were deposited; and to determine the sources of the sediments. Moreover, through petrographic analysis of the Candeleros and Huincul Formations we checked the presence of the Huincul High, a morpho-structural feature that would have divided the Neuquén Basin in two sub-basins. Through the field work we identified 14 lithofacies and 13 facies associations, which allowed to interpret that: the Rayoso Formation consists of fine and medium-grained sandstones interpreted as fluvial deposits interbedded with low energy alluvial and lacustrine deposits; the Candeleros Formation consists of coarse to fine grained sandstones and clast-supported conglomerate, interbedded in some cases with mudstones, deposited in a braided fluvial system, showing up section variations on the channels array and energy; Huincul Formation consists of cross-stritified coarse to medium grained sandstones and conglomerates that suggest a braided fluvial system; the Cerro Lisandro Fm. consists of laminated alluvial plain and massive mudstones interbedded with fine to medium-grained high sinuosity channel deposits. The modal petrographic analysis indicates that the sandstones are different in composition and provenance. In particular the feldspatic litharenites and the lithic feldarenites of the Rayoso and Barda Colorada Formations indicate a dissected arc and recycled orogen provenance whereas the Candeleros’s feldspatic litharenites suggest an undissected and transitional arc provenances. Instead, the lithic feldarenite of the Huincul and Cerro Lisandro Formations shows a more evolved composition, that indicates a dissected magmatic arc provenance. We interpret these provenance changes as due to a reorganization of the drainage system, mainly from the sources located on the East during the deposition of the Rayoso Fm., to convergent (both from East and West), probably due to the tectonic inversion, during the deposition of the Neuquén Group. In addition, on the basis of the different percentages of plutonic and metamorphic lithics in the samples from the North and from the South of the ridge, we believe that during the deposition of the Neuquén Group, the Huincul High was a morpho-structural feature that divided the drainage system