Abstract This large format (11 × 17 inch) all color outcrop atlas and field guide was produced for the SEPM Research Conference held in Chile in February, 2009. It contains a wealth of information on the world class deep water outcrops of the Cretaceous of the Magallanes Basin in the Ultima Esperanza District, Chilean Patagonia. This book covers the significant outcrops in the region the Punta Barrosa Formation, CerroToro Fm., and the Tres Pasos Fm.

Abstract This road log follows a clockwise circuit around the Ultima Esperanza region starting and ending in Puerto Natales, highlighting the majority of the outcrop locations shown in this document. The satellite map (A) and the simplified geologic map (B) show the outcrop locations and road. Road log is in kilometers.

Abstract The Magallanes Basin SEPM Field Conference, February 2009, showcases outcrops of Cretaceous deep-water clastic strata exposed in the Ultima Esperanza District of southernmost Chile from Puerto Natales northward to Torres del Paine National Park. Why travel to the ‘end of the Earth’ to see these deep-water deposits? We believe that the deep-water succession in the Magallanes Basin of Chilean Patagonia is destined to join a select set of outcrop systems such as the Tanqua Karoo of South Africa (e.g., Wickens and Bouma, 2000 ; Johnson et al., 2001 ) and Brushy Canyon Formation of west Texas (e.g., Beaubouef et al., 1999 ; Gardner et al., 2003 ) as a world-class outcrop analog for buried, petroliferous deep-water systems. Magallanes Basin outcrops are notable for several key features: (1) Involvement in a latest Cretaceous – early Tertiary fold-thrust belt, providing nearly continuous down-depositional-dip 2-D outcrops for ~100 km, with local 3-D exposures provided by folding and topography; (2) Deep excavation and many bare-rock surfaces created by Late Cenozoic glaciation; (3) Contrasting styles of deep-water systems stratigraphically stacked during basin evolution, from unconfined and/or weakly-confined turbidite systems through highly-confined channelized systems through progradational failure-dominated delta slope with numerous channels and sand-filled mini-basins. The variability of the Magallanes Basin fill over a relatively small area makes the exposures of the Ultima Esperanza District worthy of the attention of the international sedimentologic community. But it has not always been so. Cretaceous outcrops in the Magallanes Basin of the Ultima Esperanza District

Abstract The Magallanes Basin is a retroarc foreland basin ( Suarez and Pettigrew, 1976 ; Dalziel, 1981 ; Wilson, 1991 : Fildani and Hessler, 2005 ) and the sedimentary sequence preserved in the Andean fold-thrust belt reflects the early extensional phase of basin evolution and the subsequent contractile phase with eventual uplift associated with Andean orogenesis ( Figs. i.1 and i.2 ). In the latest Jurassic, extension associated with the initial breakup of southern Gondwana ( Bruhn, et al., 1978 ; Gust, et al., 1985 ; Pankurst, et al., 2000 ; Calderón et al., 2007 ) culminated in the development of an oceanic backarc basin referred to as the Rocas Verdes Basin ( Katz, 1963 ). Ophiolitic rocks exposed in the Cordillera Sarmiento, south and west of Parque Nacional Torres del Paine, represent the obducted remains of the floor of this backarc basin ( Wilson, 1991 ; Fildani and Hessler, 2005 ; Calderón et al., 2007 ). Compression associated with the onset of the Andean orogeny resulted in rapid uplift along the western basin margin and concurrent foreland subsidence. A deep-water depositional phase, caused by flexural loading of obducted ophiolitic blocks over the attenuated crust, is marked by the turbidites of the Punta Barrosa Formation ( Fig. i.1 ). The overlying shale-rich Upper Cretaceous Cerro Toro Formation represents the climax of deep-water sedimentation. Conglomerate-filled channel systems (channel belt up to 8 km wide) within the Cerro Toro Formation developed along much

Abstract The effect of inherited attenuated crust from the closure of the predecessor backarc basin led to a relatively narrow orogenic belt during the Magallanes foreland development and a short distance from arc to foredeep. The attenuated crust heritage also provided continuous basinal subsidence (contributed to by fold-thrust belt loading and ophiolitic block obduction),which permitted long-lived (>20 my) deep-marine deposition and accumulation of >4000 m of turbiditic sediment that filled the basin axially in a north to south direction ( Figs. ii.1A and C ). Three distinct formations that reflect three distinct phases of deep-water deposition with different stacking patterns are featured in this document: the Punta Barrosa Formation, the Cerro Toro Formation, and the Tres Pasos Formation. These three formations were deposited with contrasting stratigraphic architectures that we relate to two general factors: (1) variability in amount and type of source material (i.e., changes in provenance and/or staging area) and (2) variations in the basin shape throught time. Changes in the source and staging areas are represented by clear sedimentological differences, including the sandstone-and mudstone-dominated Punta Barrosa Formation with banded slurry beds, the conglomeratic channel-fill deposits of the Cerro Toro Formation, and the sandstone packages and mudstone-rich mass transport deposits of the Tres Pasos Formation slope system ( Figs. ii.1B and C ; see following page). Basin morphology controls the general lay-out of depositional systems (e.g., channel dimensions, degree of confinement, dispersal patterns, etc.), which influences the distribution of sediment and resultant stacking patterns. We suggest

Abstract The Tres Pasos Formation is a continental margin-scale progradational mudstone- to siltstone-rich slope succession. The lower part of this formation is characterized by an architecturally variable suite of sandstone-rich channel and sheet elements punctuated by mudstone-rich mass transport deposits. Sandstone-rich sedimentary bodies comprise massive sandstone (mostly high-density turbidity current deposits; S1 and S3 sensu Lowe, 1982 ), intrabasinal mudstone-clast conglomerates, and various finer-grained turbidite facies (i.e., Bouma divisions; Bouma, 1962 ). The sandstone bodies exhibit a highly-variable internal architecture, including complex scour-and-fill features and lateral facies changes. Large-scale mudstone-dominated mass transport deposits (MTDs) typically contain mud-matrix supported debris flow deposits mixed with slide/slump blocks of variable sizes and are common between sandstone packages. The upper part of the Tres Pasos Formation is dominated by turbiditic mudstone and siltstone, hemipelagic mudstone, and sparse scours filled with coarse-grained pebbly material interpreted as by-pass conduits.

Abstract Three different outcrops, presented along depositional dip, are featured in this fieldguide from the Punta Barrosa Formation. The outcrops are relatively close to each other and their location is highlighted by the yellow areas on map at left. The Punta Barrosa Formation represents the early filling phase of the Magallanes foreland basin, consisting of the early, relatively unconfined flows that reached the basin floor. An architecturally variable suite of sandstone-rich channel and sheet elements are present within the formation. Mudstone-rich intervals are also extensive. The photos below show the best preserved sheet-like deposits of the upper Punta Barrosa Formation that will be visited at Outcrop #1 (Marina’s Cliff) and Outcrop #3 (Park Headquarter’s Cliff). The conformable relationship from the sandstone-dominated upper Punta Barrosa Formation to the mudstone-dominated Cerro Toro Formation is transitional and exposed in the National Park. Various sheet elements are present within the shale-dominated formation but sandy channels have also been observed.

Abstract Outcrop accessibility: easy Outcrop Coordinates: 51.2284°S, 72.9526°W Refer to outcrop 1 on location map

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, sensu Lowe 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

Abstract Outcrop accessibility: easy Outcrop Coordinates: 51.1786°S, 72.9618°W Refer to outcrop 3 on location map The Headquarters section ( Fig. 3.1A ), located within a few hundred meters of the Torres del Paine Park Headquarters, is one of the most accessible outcrops of the upper Punta Barrosa Formation. Stratigraphically, it sits directly below the first mudstone considered as part of the Cerro Toro Formation. This outcrop does not offer the same lateral continuity of exposure as the Marina’s cliff sections, but it presents an interesting packaging of slurry beds (S1) capped by amalgamated thick-bedded conventional turbidites. In the lower part of the section, the stratigraphic packaging consists of an alternation of thin-bedded fine-grained turbidite packets with more resistant and massive slurry-bed packets. Thin-bedded turbidites include T c,d,e intervals ranging in thickness from a few centimeters to a maximum of a few tens of centimeters. Slurry bed packets display well-developed meso- and macro-banding. No other sedimentary structures have been observed beyond rare climbing ripples in some of the fine-grained tops of sedimentation units. The lowest bed of the lowest slurry flow package is characterized by a superb example of multi-banding ( Fig. 3.1B ). It shows fourteen bands defined by dark and light coloration, and it is capped by a 5 cm thick ripple-laminated, fine-grained sandstone interval probably related to more typical turbiditic sedimentation. The top of the stratigraphic succession is capped by amalgamated, thick-bedded high-density turbidity current deposits stacked offset of one another (compensational stacking).

Abstract A series of Cerro Toro Formation outcrops, presented along depositional dip, are featured in this fieldguide. The outcrop belt of the conglomeratic member of the formation is traced in red on the satellite image at left; the interpreted paleogeographic position of the various outcrops featured in this fieldguide are highlighted in the schematic basin diagram presented below left ( Hubbard et al., 2008 ). Coarse-grained material of the Cerro Toro Formation is attributed to deposition in a foreland basin axial channel belt setting, with some outcrops proposed to record sedimentation in tributary conduits that fed the axial system. Levee deposits are recognized in outcrops associated with the axial channel belt (at outcrops 8 , 9 ), whereas previous workers have debated a channel-levee complex versus an incised channel origin for deposits in the tributary conduit (at outcrops 4 , 5 ). The conglomerate-rich portion of the formation has a stratigraphic thickness up to 1200 m; from north (paleogeographically proximal) to south (distal), an increase in amalgamation of channel bodies and complexes is notable. With a higher proportion of siltstone and shale present separating conglomeratic units in the north, the formation has succumbed to folding. The result is exceptional three-dimensional exposures of channel deposits in the vicinity of the Silla Syncline in the Torres del Paine National Park (see map at left and photo below). Further south in the Cordillera Manuel Señoret, amalgamated coarse-grained channel deposits are present in packages up to 600 m thick; these erosionally

Abstract Outcrop accessibility: easy Outcrop Coordinates: 51.1199°S, 72.9701°W Refer to outcrops 4 and 5 on location map The Silla Syncline is located within the Torres del Paine National Park east of Lago Pehoe and south of Lago Nordenskjöld. The Cerro Toro Formation in the area comprises more than 1100 m of deep-water strata within which Crane (2004) recognized and mapped three major coarse-grained channel complexes. These correspond to the informally named Pehoe, Paine and Nordenskjöld members, from oldest to youngest ( Figs. iii.1 , iii.2 ). The Pehoe channel complex, consists of two conglomerate units, Pehoe A and B, separated by a 100-m-thick sequence of thick-bedded sandstones and thin interbedded mudstone units (see outcrop #4). The Paine member is subdivided into the Paine A, Paine B, Laguna Negra debris flow deposit, and the Paine C (see outcrop #5). Paine C is the largest channel in the section with a width of 2.5 to 3 km and a minimum thickness of 200 m ( Figs. iii.1 , iii.3 and iii.4 ). The Nordenskjöld member is exposed as a near continuous, roughly circular outcrop in the axis of the syncline north of the park highway ( Fig. iii.3 ). This member is divided into two major subdivisions, Nordenskjöld A and Nordenskjöld B, separated by a thick debris flow deposit ( Figs. iii.1 and iii.4 ). The various channel complexes throughout the Silla Syncline section shifted locations as they were emplaced. The

Abstract Multiple models have been proposed to account for the origin of channel and out-of-channel deposits in the Cerro Toro Formation at the Silla Syncline. The complex stratigraphic relationship between coarse-grained channel, and fine-grained out-of-channel deposits has been a topic of considerable debate in the scientific literature. Winn and Dott (1979) , Beaubouef et al. (1996) , and Beaubouef (2004) propose aggradational channel-levee models for the channel complexes present in the Parque Nacional Torres del Paine ( Fig. iv.1A, B ). Conversely, Coleman (2000) , Crane (2004) , and Crane and Lowe (2008) have proposed variations on an evolutionary model that invokes erosional confinement of channel sediments in background Cerro Toro Formation mudstone ( Fig. iv.1C, D ). The high-energy axial portion of the best-exposed and most well studied channel complex (Paine C of Crane et al., 2008 ) is a minimum of 4 km wide and the Silla Syncline provides only an oblique cross-section through the complex ( Fig. iv.1D ). If the system is levee confined, the coeval levees must have added substantially to the cross-sectional width of the channel complex; post-depositional structures both east and west of the syncline limit the preserved width to only slightly more than the channel axis in most areas. As a result it is difficult to discern whether the erosional margins preserved in outcrop represent the edges of an incisional channel complex, or the eroded inner margins of extensive levees.

Abstract Outcrop accessibility: easy Outcrop Coordinates: 51.1199°S; 72.9701°W Refer to outcrop 4 on location map The Pehoe channel complex consists of two conglomerate units, Pehoe A and B (nomenclature of Crane, 2004 ), separated by a 100 m-thick sequence of thick-bedded sandstones and thinly interbedded mudstone units ( Fig.4.1A and B ). The Pehoe A member consists of the Pehoe A conglomerate and the Pehoe A thick-bedded sandstone and mudstone. The Pehoe B member is subdivided into the Pehoe B conglomerate and the associated Pehoe B mass transport deposits.

Abstract Outcrop accessibility: easy Outcrop Coordinates: 51.1199°S; 72.9701°W Refer to outcrop 5 on location map The northwestern portion of the Paine C channel complex ( Fig. 5.1A ) is easily accessible from the Torres del Paine park highway. Exposures of the Paine C continue throughout the axis of the Silla Syncline from the park highway south to Laguna Negra ( Fig. 5.1B ). Stratigraphically, the Paine C lies directly above a regionally correlated mass transport complex informally named the Laguna Negra Debris Flow ( Fig. 5.1C ). The channels within the complex show overall paleoflow toward the southeast and south ( Figs. iii.5 and 5.1C ). The greatest preserved thickness of channel deposits trends southeast from section 11 to section 21 at the southeastern edge of the syncline ( Fig. 5.1B ). Given the orientation of the channel complex with respect to paleoflow, the limbs of the Silla Syncline expose a somewhat oblique cross-sectional view of the Paine C channel complex ( Fig. 5.1C ). Measured sections along the west limb of the syncline demonstrate that the Paine C thickens progressively to the south by the addition of sediment at the top of the section. A minimum of six stacked channel margins are present between the park highway and Lago Sarmiento Chico ( Fig. 5.1C ). Channel margins are identified by erosional surfaces which may or may not be mudstone draped and against which sandstones, conglomerates and interbedded sandstone and mudstone units onlap. The approximate locations of

Abstract Outcrop accessibility: N face - moderate; S face - extremely difficult Outcrop Coordinates: N face = 51.0781°S, 72.6999°W; S face = 51.1284°S, 72.6813°W Refer to outcrop 6 on location map Deposits of the Cerro Toro Formation on Sierra del Toro represent the most proximal axial channel belt deposits preserved in the Magallanes Basin outcrop belt, based on regional paleogeographic interpretations ( Scott, 1966 ; Hubbard, 2006 ; Hubbard et al., 2008b) . Scott (1966) provided the first description of conglomeratic deposits on Sierra del Toro; Winn and Dott (1979) interpreted this location as part of an elongate submarine fan that filled the basin axis from north to south. Cerro Toro Formation outcrops on Sierra del Toro include at least three conglomeratic units, each of which is interpreted to represent a submarine channel complex. These channel complexes were deposited within an axial channel belt ( Fig. 6.1A and 6.1B ). The units are hereby informally named, from oldest to youngest, the “Condor” ( Barton et al., 2008 ), “Guanaco”, and “Wildcat” channel complexes.

Abstract Outcrop accessibility: difficult Outcrop Coordinates: 51.0852°S, 72.6541°W Refer to outcrop 7 on location map The Wildcat channel complex is up to 5–6 km wide and 330 m thick, making it the largest exposed on Sierra del Toro. Hubbard and Shultz (2008) suggest that this channel complex is stratigraphically equivalent to the upper two-thirds of the conglomeratic portion of the Cerro Toro Formation at Cerro Castillo, located due south of Sierra del Toro adjacent to the south shore of Lago del Toro. A portion of the eastern Wildcat channel margin was characterized by Hubbard et al. (2008b) (outcrop featured in Fig. 7.2E , referred to as “Sarmiento Vista” by Hubbard et al., 2008b) . The eastern margin of the Wildcat channel complex is well exposed on the northeast face of the mountain, displaying 200 m of conglomeratic channel fill thinning until its final pinchout ( Figs. 7.1B and 7.2 ). This exposure allows for a direct correlation of beds along a ~3 km transect oblique to depositional strike (1.5 km when projected parallel to strike; Fig. 7.3 ). The slope of the margin averages approximately 7.5° over this distance, although it is partitioned into a steep ‘wall’ at its base, near the channel complex axis, and a shallower ramp nearer the final pinchout ( Fig. 7.3 ). As a result, the eastern margin is characterized by a “steerhorn” cross-sectional profile. Paleoflow measurements taken at the margin of the channel complex

Abstract Outcrop accessibility: variable Outcrop Coordinates: 51.4716°S, 72.6508°W Refer to outcrop 8 on location map Conglomeratic deposits of the Cerro Toro Formation attributed to deposition in a large-scale basin axial channel belt are well exposed in the Cordillera Manuel Señoret, north of Puerto Natales between Cueva del Milodon and Lago Toro. The conglomeratic succession is informally called the “Lago Sofia Member” because of the presence of Laguna Sofia in this area ( Scott, 1966 ). The large injectite complex that is the focus of Chapter 9 is present in the Cordillera Manuel Señoret on the south shore of Lago Sofia ( Fig. 8.1A ). The channel belt is characterized by low sinuousity, demonstrated with outcrop mapping and the collection of extensive paleocurrent data ( Fig. 8.1A ). Outcrop exposures of the channel belt margin are present on the north faces of Cerro Benitez and Cerro Mocho ( Fig. 8.1B, C ). Because of poor accessibility, the margin at Cerro Mocho cannot be easily visited. A levee interpretation for fine-grained material adjacent to the channel belt is based on a series of key observations: (i) paleocurrent measurements indicative of flow divergence (50° to 100°) measured from out-of-channel units as compared to those taken from inside the channel belt container; (ii) progressive thinning of sandstone beds away from the channel belt margin; (iii) evidence that the eroded channel margin was poorly indurated, including a stepped profile and injection of channel fill into out-of-channel strata; (iv) deposits that record slumping on the