Outcrop 2. Punta Barrosa Formation Sheet Complex, Rio Serrano Section (New Roadcut)

Abstract Outcrop accessibility: easy Outcrop Coordinates: 51.2177°S, 72.9606°W Refer to outcrop 2 on location map A recently excavated roadcut at the Rio Serrano bridge (Fig. 2.1A), located just south of the Rio Serrano, is an easily accessible outcrop of the upper Punta Barrosa Formation. Stratigraphically positioned at the same level as the Marina’s Cliff outcrops (from which it is visible), this outcrop offers good lateral continuity of tabular architecture with few clear examples of scouring and amalgamation. Individual sandstone packets (elements) are almost entirely composed of slurry-beds with some intebedded packets of conventional fine-grained turbidites and mudstone (S4 and S6). The slurry-beds in the roadcut exposure display a beautiful array of internal banding (micro-, meso-, and macro-banding, sensuLowe and Guy, 2000), consisting of bands of mud-rich (dark) and cleaner (light) sandstone within individual beds. Band thickness varies throughout beds, both laterally and vertically (B). Few beds evolve from meso-banding at the base into micro-banding at top (C). Water escape features are present throughout the beds, commonly as vertically oriented sheets in pale bands (D), sheared sheets in dark bands (D), and throughout massive beds (E; photo slightly higher in measured section). We interpret the slurry-beds to be the result of relatively rapid load fallout from turbidity currents, causing mud entrapment within sand falling out of suspension. The banding is interpreted in a similar way to the process described by Sylvester & Lowe (2004), whereby during rapid sedimentation, the high proportion of mud