Architecture of a Deep-water Levee Avulsion, Silla Ojo Mesa, Parque Nacional Torres del Paine, Chile

Abstract

Extensive outcrops of coarse-grained channel to fine-grained levee deposits of the Campanian Cerro Torro Formation are present throughout the Torres del Paine National Park in southern chile (Figure 1; Fildani et al, chapter 33, this volume). The outcrop panel in Figure 2 represents part of one face of a nearly continuous exposure mapped in this paper that is present on all four faces of a mesa within the Silla Ojo Syncline (Figure 1). The depositional architectures consist predominantly of sheetlike, tabular elements comprising interbedded sandstone and shale bedsets, onlapping older levee deposits (described by Barton et al., chapter 39, this volume). Isolated channel elements and scour features are also present. The vertically stacked, tabular architectural elements observed in the outcrop panel are interpreted to represent a phase of partially confined to unconfined deposition outboard of a major levee avulsion site, analogous in many respects to the avulsion deposits described by Hiscott et al. (1979). Overlying and truncating the tabular elements of the avulsion deposits is a thick, multistory channelized conglomerate (Figure 2) with internally organized and chaotic bedding and impressive debris flow deposits. A similar vertical facies transition from levee to avulsion to channel deposists is also described by O’Byrne et al. (chapter 30, this volume) and Arnott (chapter 29, this volume) from the Isaac Formation, Canada.