Abstract Five Tres Pasos Formation outcrops, presented along depositional dip, are featured in this fieldguide. The outcrop belt is traced in orange on the satellite image at left. The Tres Pasos Formation is highlighted on the stratigraphic column at the lower left; it consists of continental margin-scale slope deposits that represent the filling phase of the Magallanes foreland basin. An architecturally variable suite of sandstone-rich channel and sheet elements are present within the formation. Mudstone-rich mass transport deposits are also extensive. The photos in the lower right contrast the relatively shalier northern Tres Pasos outcrops (e.g., Cerro Divisadero) with the more sandstone-rich southern outcrops (e.g., Picana-Figueroa). One outcrop from the overlying Dorotea Formation is also included in this fieldguide. The conformable relationship from the shale-dominated upper Tres Pasos Formation to the shallow-marine and deltaic deposits of the Dorotea Formation is documented at Cerro Escondido.

Abstract Outcrop accessibility: very difficult - Overview accessibility: easy Outcrop Coordinates: 50.8166°S, 72.6947°W Refer to outcrop 11 on location map Outcrops of the Tres Pasos and Dorotea formations in northern Ultima Esperanza District highlighted in this field guide ( outcrops 10 , 12 , and 15 ) are remote and extremely difficult to access. One way to appreciate the general characterstics of the strata is from a distance along a dirt road on the west side of the north-south flowing Rio Zamora, which has carved a canyon into the Tres Pasos Formation and upper Cerro Toro Formation. From within the boundaries of Parque Nacional Torres del Paine, take the road to “Laguna Azul” and continue heading north ( Fig. 11.1A ) (note: at the time of publication, this road went through private land with unlocked gates; please always respect private land and communicate your intentions to stay on road and view outcrops from afar). The outcrops are on the other side of Rio Zamora from this road; do not attempt to cross the river. From north to south, the outcrop belt straddles three mountains: Cerro Divisadero, Cerro Mirador, and Sierra Contreras. Abundant paleocurrent data from the Tres Pasos Formation in this area indicate that basinward was to the south-southeast ( Shultz et al., 2005 ; Romans et al., 2008 ). The transect displayed in this river canyon is therefore generally parallel to depositional dip, providing an opportunity to see a dip-parallel slope cross-section. Some east-west tributary

Abstract Outcrop accessibility: difficult Outcrop Coordinates: 50.8859°S, 72.6545°W Refer to outcrop 12 on location map At Sierra Contreras, deep-water slope depositional relationships between fine-grained mass transport deposits (MTDs) and overlying turbiditic sandstones can be assessed. The lateral continuity of sandstone-rich reservoir-scale bodies was dominantly controlled by original seafloor topography, related to the morphology of underlying MTDs. Overlying sandstone beds pinch-out and lap onto the relative topographic highs of the MTDs. Turbidite architecture evolves to more laterally continuous, sheet-like deposits as a result of depositional smoothing of MTD relief and diminished confinement ( Shultz et al., 2005 ; Armitage et al., in press). Small-scale MTD topography, characterized by several meters of vertical relief, was associated with local pockets of accommodation where sands were ponded. These small-scale surface irregularities are inferred to have been associated with the rugose tops of viscous MTDs. Meso-scale MTD topography (10 to several 10s of meters relief) was created by coherent rafted sandstone blocks resting on top of, or within the upper portion of MTD deposits; it is onlapped by overlying sandstone beds. This topography can laterally compartmentalize significant packages of sandstone. The largest scale of topography identified (several hundred meters horizontally and vertically) resulted from individual mass-wasting events (e.g., outsized block emplacement) creating topographic relief at the time of deposition. Topographic features at this scale can laterally divide large-scale sediment gravity flow pathways, leading to significant compartmentalization of sandstone bodies. The size and abundance of rafted blocks in MTDs increases vertically in the outcrop suggesting

Abstract Outcrop accessibility: moderate Outcrop Coordinates: 51.1537°S, 72.4725°W Refer to outcrop 13 on location map Limited exposures of sandstone are present in the Tres Pasos Formation between Sierra Contreras and Laguna Figueroa; an important exception is a 60 m thick succession dominated by coarse-grained turbiditic units at El Chingue Bluff. The stratigraphic section is characterized by an upward coarsening of grain size, and the vertical progression of facies indicating increasing energy. The top of the bluff is defined by the thick sandstone package; beds at the base of this sandstone package are truncated by a normal fault at the southern end of the outcrop, and lap out towards the north onto the tilted hanging wall. Stratal thickening and thinning across the fault, and unfaulted overlying deposits, have led to the interpretation that the fault was active during sand deposition (a growth fault), and that it created accommodation space for the partially ponded sand body ( Shultz and Hubbard, 2005 ). This, and other growth faults in the underlying strata, have contributed to the development of an intraslope minibasin model for deposition. The sandstone package is overlain by a thick succession of mass transport deposits, recording the progradation of the slope across the area. Sandstone dikes are extensive, paralleling growth fault planes. Shultz (2004) has speculated that these dikes were injected downwards, sourced from the coarse sandstone present in the top of the measured section.

Abstract Outcrop accessibility: easy to moderate Outcrop Coordinates: 51.3696°S, 72.4210°W Refer to outcrop 14 on location map A thick sandstone package (~350 m) characterizes the Tres Pasos Formation outcrop between Laguna Figueroa and Arroyo Picana along the Puerto Natales-Cerro Castillo highway ( Fig. 14.1 ). Overlying this sandstone package is a succession of mudstone-dominated strata on the order of 1000 m thick. Sierra Dorotea is capped by deltaic deposits of the Dorotea Formation. In the satellite image presented in Figure 14.1 , the northern part of Sierra Dorotea, Cerro Sol and Cerro Cazador are featured. The interpreted stratigraphic architecture consists of large-scale slope surfaces (Chingue, Figueroa, and Puma) building southward (the image is oriented along depositional dip). Sandstones of the Tres Pasos Formation at Laguna Figueroa are interpreted as base-of-slope deposits. Conversely, the corresponding topset units are attributed to the shallow-marine Dorotea Formation. Individual slope surfaces are locally identified as resistant ridges in the satellite image (surface length ~30–35 km; surface stratigraphic relief ~1600 m; slope angle ~2.5–3 degrees). A schematic diagram of the architecture in the region is presented in Figure 14.3 , incorporating the location of the El Chingue Bluff slope minibasin fill within the regional context ( Outcrop 13 ). Architectural elements along the lower part of slope surfaces include mud clast-filled bypass channels, channelized sheets and sandstone-filled channels, featured on the following pages.

Abstract Outcrops of the Upper Cretaceous (Campanian-Maastrichtian) Tres Pasos Formation at Cerro Divisadero, southern chile, expose a >500-m (>1640-ft)-thick succession of clastic deep-water deposits. The Tres Pasos Formation represents the upper portion of a 5000-m (16,400-ft)-thick deep-water succession recording sedimentation in the narrow (<10 km [<6.2 mi]) foredeep of the Magallanes basin. Facies, local paleocurrent data, and regional context from previous work indicate these strata record the southward progradation of a deep-marine slope. The Tres Pasos Formation at Cerro Divisadero consists of four discrete sandstone-rich units (20–50 m [65–150 ft] thick) interbedded with mudstone-rich intervals of comparable thickness. Two of these units are presented here. Paleocurrent information indicates the outcrop is oriented parallel to depositional dip although arroyos provide local three-dimensionality. The lower sandstone element (C1) is 40–50-m (130–150-ft)-thick and continuous for >2 km (>1.2 mi) parallel to depositional dip. The cliff-face exposure documented here is a representative example of the facies associations and internal architecture. This element is subdivided into two components based primarily on bedding geometry and degree of sandstone bed amalgamation, and separated by thin-bed element Tl. The lower subelement (C1a) has a basal erosional surface, complex internal scouring, and a high sandstone-shale-ratio because of amalgamation of sedimentation units. The upper subelement (C1b) is characterized by wedge-shaped to tabular bedsets and decreased sandstone amalgamation and distinct compensational stacking. The overlying channelform element (C2) is thinner (5–20 m [15–65 ft] thick) and more lenticular than C1. Lower subelement (C2a) has a basal erosional surface and an onlapping heterolithic fill

Abstract Two thick turbidite sandstone units collectively form the basal Tres Pasos Formation sandstone exposed on the west face of the Sierra Contreras mountain range, Ultima Esperanza, chile ( Figures 1 , 2 ). Both sandstone units overlie and interact with thick mass-transport complexes (MTCs). These units are generically interpreted to represent infill of accommodation produced by slope failure, and may represent submarine fans, channel-fill units, crevasse-splay units, or units representing channel capture by slope failure. Extensive exposure of both coarse- and fine-grained strata make the Tres Pasos Formation an important analog system for hydrocarbon reservoirs in mud-rich, structurally complex, slope environments. This spectacular outcrop underscores the importance of slope failure on the preservation and stratigraphic architecture of deep-water sandstones.

Abstract The Tres Pasos Formation, Magallanes Basin, Chile, represents the deposit of a submarine slope depositional system. The formation is approximately 1500 m thick where exposed in the Ultima Esperanza district of southernmost Chile. It is characterized by a basal turbiditic sandstone unit up to 200 m thick that shows a north-to-south, proximal-to-distal facies evolution from turbidite channel-fill complexes to sheet-like sandstone units. This unit is interpreted as having been deposited at or near the base of slope. Overlying the basal sandstone unit is approximately 500 m of amalgamated mass transport complexes, fine-grained strata, and channelized and non-channelized turbidity current deposits, collectively comprising the middle part of the formation. Mass transport complexes exert a primary control on the character and grain size of turbidite sandstone bodies in the basal and middle part of the formation. In the southern part of the study area, a 300 m thick coarse-grained unit interpreted as a turbidite channel-fill complex partially replaces the middle part. The upper part of the formation is approximately 500 m thick and consists primarily of fine-grained strata. Failure scarps and thin turbidite channel-fill units are present in this upper part, interpreted as upper slope deposits.

Abstract Outcrop accessibility: extremely difficult Outcrop Coordinates: 50.7048°S, 72.7361°W Refer to outcrop 10 on location map The Tres Pasos Formation (1000–1500 m thick) records the transition from bathyal water depths of the upper part of the Cerro Toro Formation to the shallow-marine and deltaic facies of the overlying Dorotea Formation. The lower part of the Tres Pasos Formation exposed at Cerro Divisadero (600 m thick) is the northernmost (most landward) of the Tres Pasos outcrop locations in this guidebook. Four sandstone-rich packages that range in thickness from 20 to 80 m are recognized and mapped across a ~3 km long outcrop transect. The north-south trending outcrop is generally parallel to depositional dip (basinward to the south), although ridge-and-gully topography provides three-dimensionality at a smaller scale (10s to 100s of meters). The four sandstone-rich units are separated by intervals of shale and siltstone tens of meters thick. Unit 1 is partially covered and minor post-depositional structure (reverse faults and associated drag folds) disrupt detailed architectural characterization of Unit 4. Units 2 and 3 are, therefore, the focus of the panels in this guidebook. Refer to Romans et al. (2008) for detailed presentation and interpretation of the Tres Pasos Formation at Cerro Divisadero.

Abstract Outcrop accessibility: extremely difficult Outcrop Coordinates: 50.7309°S, 72.6324°W Refer to outcrop 15 on location map The stratigraphic section at Cerro Escondido contains the most complete exposure of the Dorotea Formation in the Ultima Esperanza District ( Fig. 15.1 ). Cerro Escondido is located south of the Argentina-Chile border on an anticline between the Rio de las Chinas and the Rio Zamora (refer to outcrop location map). The contact between the Tres Pasos and Dorotea formations had not been formally mapped at Cerro Escondido, and we define it as the first contact between turbidites of the Tres Pasos Formation and overlying shallow-marine hummocky-cross stratified sandstone of the Dorotea Formation ( Fig. 15.1 ). Greater than 300 m of stratigraphy are exposed across >800 m of the Cerro Escondido outcrop ( Fig. 15.1 ). Two stratigraphic sections were recorded at cm-scale resolution (295 m thick in the east and 197 m thick in the west; Fig. 15.1C ).