Reconstructing the large-scale sediment delivery systems during the Early Cretaceous in the Neuquén Basin (Argentina)

Abstract

One of the most challenging aspects when analyzing the stratigraphic architectures ofancient basins is to constrain the extent and dynamics of the sedimentary systems involvedin its record. Especially when considering clastic delivery systems in a source-to-sinkapproach, it is important to evaluate how large the transfer systems from the continent tothe basin were and the volume of sediment that had been transferred through these systemsin order to define the drainage length and catchment size that are key when trying to buildrealistic palaeogeographic reconstructions.The Neuquén Basin, developed in the SWmargin of Gondwana during the Mesozoic, evolved as a shallow, large embaymentconnected to the proto-Pacific Ocean through gaps in a volcanic arc, and limited by cratonicareas to the northeast and southeast. Despite that the amount of clastic input to the marinebasin changed through the basin´s history, large-scale fluvial systems sourced from theeast/southeast were commonly developed as the main delivery systems of large volumes ofclastic material. Even when the record of these delivery systems in the Neuquén Basin iswell known in the stratigraphy and has been widely described in the literature, detail on thelarge-scale reconstruction of these systems, as well as on the relationship betweencatchment areas and the extension and evolution of the fluvial/deltaic systems is still sparseand far from integrated at a basin scale. The combination of outcrop and subsurface data,together with highly reliable chrono/biostratigraphic constrains, was used to build a highresolution Sequence stratigraphic scheme for the late Valanginian-early Hauterivian of theNeuquén Basin. The record of this period shows the development of a fluvial/deltaic systemthat sourced large volumes of clastic material from the east, with different degrees ofstorm/wave reworking within the basin. Through detailed definition of different hierarchies ofsequences, the extent of the fluvial/delta plain environment could be reconstructed atdifferent stages in order to understand the evolution of the delta plain, as well as the relativeimportance of fluvial processes versus waves and storms influence. Based on these datathe evolution of this deltaic system can be divided in three stages with a differentcombination of rate of progradation (basinward extent of the delta plain), location of the mainentry point/s and relative proportion of fluvial and marine processes. A quantification of thevolume of clastic material delivered by these systems can then be contrasted withpalaeohydrological estimates at these different stages of evolution, which gives key data toconstrain the potential size of corresponding catchments. The large-scale reconstruction ofthe delivery systems, the estimation of the length of the drainage, and a preliminary analysisof detrital zircons in the studied sediments open new perspectives on the role of theNeuquén Basin in the paleogeography of SW Gondwana during the Early Cretaceous.