Sedimentology and Architecture of a Partially Contained Deposit, Cerro Solitario, Magallanes Basin, Chilean Patagonia

Abstract

The depositional styles of sediment gravity currents depend, in part, on the relationship of flow magnitude to the scale of topographically controlled containment and range from unconfined lobes to fully contained deposits. Determining the degree of containment is important for understanding depositional processes, land to ocean sediment transfer and subsurface reservoir characterization/prediction. Depositional models of the fully contained (commonly referred to as 'ponded') end member have been developed (e.g. fill-and-spill model). However, fully contained deposits represent only a portion of deepwater deposits and little work has been done identifying and examining the degree of containment of the more complex, partially contained deposits in outcrop. Here, I document the sedimentological facies and stratigraphic architecture of the Zorrillo Unit, a partially contained system exposed at Cerro Solitario within the Upper Cretaceous Tres Pasos Formation of the Magallanes Basin. The evolution of partial containment at this outcrop is expressed as: 1) bypass in the proximal zone and flow stripping in the distal zone, 2) backstepping and blanketing of the outcrop, followed by 3) renewed bypass. The partially contained system at Cerro Solitario deviates from the widely used fill-and-spill model due to subtle relief. This record of infilling provides insight into the overall evolution of the depositional system. Within the Magallanes Basin, the partially contained and linked depocenters along the Chingue Clinoform represent the dying breaths of the Cerro Toro axial conglomerate channel system as the canyon-fed point source collapsed and choked off the sediment routing system out to the distal basin.