Multi-Scale Stratigraphic and Geochronologic Investigations of Late Cretaceous Sediment-Routing Systems, Magallanes Basin, Chile

Abstract

The deposits of deep-water depositional systems preserve evidence for sedimentary processes linked to prolonged off-continent sediment transfer, and may inform continental evolution in cases where deposits are dynamically linked to orogenesis. Though investigations of the evolution of deep-water environments have been undertaken by previous workers, deciphering the nature of processes that impact the development of deep-water stratigraphic architecture, as well as the time scales over which they occur, remains a topic of current research. This thesis addresses numerous hypotheses related to the evolution of deep-water systems via a series of stratigraphic and geochronologic investigations of Upper Cretaceous stratigraphic units of the Magallanes Basin (Chile). Objectives of this thesis were to: (1) elucidate the role of fundamental sediment transfer processes (i.e., erosion, bypass, deposition) in the development of deep-water slope deposit architecture; (2) constrain the evolutionary timing of the deep-water stratigraphic intervals in the basin; and (3) investigate the influence of Andean orogenesis on the evolution of the Magallanes Basin across deep geologic time. Stratigraphic architecture was characterized for all Upper Cretaceous units in the basin-fill succession (Punta Barrosa, Cerro Toro, Tres Pasos, and Dorotea formations) at a variety of scales. Investigation of slope channel systems of the Tres Pasos Formation revealed that the downslope changes in channel fill and stacking patterns are principally controlled by the degree of coarse-grained sediment bypass that occurs at a given point in the system. This information is valuable for predictions of sandstone proportion in deep-water systems, and may assist with future petroleum exploration efforts. Consideration of depositional ages derived from geochronologic analyses (U-Pb zircon and Sr isotope ages) alongside stratigraphic data provided temporal constraints on the evolution of all stratigraphic units, and fostered development of a new chronostratigraphic framework for the basin. Analysis of chronostratigraphic data alongside evidence for Andean uplift and deformation demonstrated that changes in basin-fill architecture are principally related to changes in rock uplift and deformation style in the orogen. These results may help elucidate the development of stratigraphic architecture in other analogous orogen-adjacent basins worldwide.