Stratigraphic and Provenance Variations in the Early Evolution Of

Home , Deseado Massif, Golfo San Jorge Basin, Magallanes Basin, Volcanic arc

Sediment routing in a collisional foreland basin, Patagonian Andes Stratigraphic and provenance variations in the early evolution of the Magallanes-Austral foreland basin: Implications for the role of longitudinal versus transverse sediment dispersal during arc-continent collision

Matthew A. Malkowski1,†, Theresa M. Schwartz2, Glenn R. Sharman3, Zachary T. Sickmann1, and Stephan A. Graham1 1Department of Geological Sciences, Stanford University, Stanford, California 94305, USA 2Department of Geology, Allegheny College, Meadville, Pennsylvania 16335, USA 3Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas 78758, USA

ABSTRACT deep-water strata. Time-transgressive prov et al., 1992; Janecke et al., 2000; De Ruig and enance variations continue southward (along Hubbard, 2006; Hubbard et al., 2008; Lawton Resolving the role of longitudinal versus strike), where lithostratigraphic equivalents et al., 2014; Szwarc et al., 2014). These stud- transverse sediment dispersal in ancient in the Ultima Esperanza and Fuegian sectors ies emphasize that although dispersal patterns sedimentary basins is paramount for under of the basin contain a mix of arc and pre- may be locally influenced by regional topogra- standing filling history and the timing of Jurassic metamorphic basement sources and phy, basin-scale sediment routing is tectonically source area exhumation. The southern Pata a paucity of Jurassic ages. We interpret these controlled. These tectonic controls can include: gonian Andes provide a unique opportunity along-strike provenance variations to be the longitudinal transport forced by a forebulge for constraining these relationships because result of significant local sediment contribu drainage divide (e.g., Burbank, 1992; DeCelles, Upper Cretaceous shallow- and deep-marine tions from transverse sources. The influence 2012), thrust sheet loading and structural con- strata that record the longitudinal filling of transverse tributaries during the early finement of narrow basin geometries (Puig history of the Magallanes-Austral foreland history of the Magallanes-Austral foreland defàbregas et al., 1992; De Ruig and Hubbard, basin are exposed along a 500+ km outcrop basin suggests that the diachronous onset 2006; Hubbard et al., 2008), sequential colli- belt. New stratigraphic, sedimentologic, and of coarse clastic deposition in the basin was sion of obliquely aligned margins (cf. Graham facies analyses of the Cenomanian-aged Lago likely due to the progressive delivery (and ini et al., 1975), and inherited crustal and structural Viedma Formation indicate a protracted tiation) of more locally derived coarse clastic components of preceding tectonic regimes (cf. phase of a dominantly shoreface and fore sediment. We attribute this to southward- Romans et al., 2010; Fosdick et al., 2014). shore depositional setting at the northern end progressing thrust-belt development associ Although basin-scale longitudinal dispersal of the basin (Austral basin sector), whereas ated with progressive north to south collision systems have been inferred for numerous ancient 200 km to the south, age-equivalent strata (or suturing) of the parautochthonous Pata systems, limited spatial context due to tectonic of the Punta Barrosa Formation are char gonian arc with attenuated continental crust overprinting or incomplete and discontinuous acterized by southward-flowing deep-water of South America. outcrop preservation has left significant uncer- fan systems. New sandstone compositional tainty about how these systems initiated and data from both formations are rich in inter INTRODUCTION evolved. It is particularly difficult to constrain mediate volcanic grains and suggest an un the relative significance of transverse tributaries dissected to transitional volcanic arc source. Longitudinal (i.e., axial) transport systems to these larger-scale longitudinal drainage net- However, detrital zircon populations from have long been identified as important modes works without this spatial context (Fig. 1). This the shallow-marine Lago Viedma Formation of sediment dispersal patterns along convergent study aims to better understand the fundamental are dominated by arc sources (126–75 Ma), plate margins (Eisbacher et al., 1974; Graham relationships among tectonics, basin evolution, whereas deep-water strata of the Punta Bar et al., 1975). Large-scale (hundreds of kilome and sediment dispersal along convergent mar- rosa Formation contain much greater abun ters) orogen-parallel drainages can be ob- gins by assessing orogen-parallel variations in dances of Jurassic (199–161 Ma) and preserved in modern tectonic settings, such as the depositional facies, timing of deposition, and Jurassic (>200 Ma) ages. This indicates that Hikurangi Trough (Lewis, 1994), South China sediment provenance during the early evolution deep-water fan systems were not linked to a Sea (Hsiung and Yu, 2011), and the Ganges of a widely recognized longitudinal sediment shelfal sediment dispersal system by a simple foreland (Burbank, 1992), and they are inferred dispersal system, permitted by excellent outcrop northward point-source model, despite con for a range of depositional settings in the ancient preservation in the Magallanes-Austral Basin. sistent southward-directed paleocurrents in record (e.g., Appalachian-Ouachita system, The Magallanes-Austral Basin in southern Pata Austrian Molasse Basin, Magallanes-Austral gonia (Fig. 2) is a well-preserved example of an ancient longitudinal sediment dispersal system †Present address: U.S. Geological Survey, 2885 Basin of southern Patagonia, North American Mission Street, Santa Cruz, California 95060, USA; Sevier foreland basin, South Pyrenean foreland that initiated and filled diachronously from north e-mail: matthew.malkowski@gmail.com. basin; Graham et al., 1975; Puigdefàbregas to south in deep- to shallow-marine environ-

GSA Bulletin; March/April 2017; v. 129; no. 3/4; p. 349–371; doi: 10.1130/B31549.1; 17 figures; 2 tables; Data Repository item 2016319; published online 3 November 2016.

A arc rift basin (the Rocas Verdes Basin) followed by a successor retroarc foreland basin (Magal point-source lanes-Austral Basin; Fig. 3). The Jurassic–Early sediment staging Cretaceous Rocas Verdes Basin opened in a backarc extensional setting associated with the breakup of Gondwana (Katz, 1963; Dalziel et al., 1974; de Wit and Stern, 1981; Biddle et al., 1986; Wilson, 1991). Lithospheric exten- basinwarbasinward sion is recorded through bimodal volcanism, underfilled progradation deep-water basin including widespread silicic volcanism of the El Quemado complex, Ibañez Formation, and Tobífera Formation of western Patagonia and B mafic to intermediate volcanism associated with the Sarmiento, Capitán Aracena, Carlos III, and Tortuga ophiolite complexes (Fig. 2; Saunders et al., 1979; Pankhurst et al., 2000; Calderón et al., 2007, 2013). Rifting and seafloor spreading initiated at the southern end of the basin system and propagated northward through line-source tributaries time (Stern and de Wit, 2003; Malkowski et al., underfilled 2016). This resulted in an extensional gradient deep-water basin defined by a wider and more-evolved ocean ba- Figure 1. Schematic illustrations of deep-water longitudinal (orogen- sin to the south and a narrower basin with transi- parallel) depositional systems. These end-member models highlight tional to continental crust at the northern margin contrasting modes of sediment transport in systems characterized (de Wit and Stern, 1981; Mukasa and Dalziel, by: (A) simple basinward progradation from a single point source 1996; Stern and de Wit, 2003; Malkowski et al., (e.g., a delta), and (B) progressive basinward input of detritus from 2016). Stratigraphy of the Rocas Verdes Basin transverse tributaries. primarily consists of intermediate to silicic volcaniclastic units of the El Quemado complex and Tobifera Formation and black shale of the ments (Bernhardt et al., 2012; Malkowski et al., sition and the early development of a deep-water Rio Mayer and Zapata Formations in Argentina 2015). Despite this constraint, questions about foreland basin. Data from this study combined and Chile, respectively (Fig. 3; Wilson, 1991; the timing and nature of sediment dispersal in with previous work document along-strike (oro- Fildani and Hessler, 2005; Calderón et al., 2007; the basin remain unresolved. For instance, was gen-parallel) variations in facies, timing of depo Richiano et al., 2015). the diachronous nature of sediment delivery sition, and sediment sources that suggest that the The transition from backarc extension to governed by tectonic forces (e.g., progressive early evolution of the Magallanes-Austral Basin compression and subsequent foreland basin de- southward thrusting and exhumation) or by sedi- was characterized by an incompletely integrated velopment is represented by the Punta Barrosa mentary drivers such as southward-prograding longitudinal transport system, which also in- Formation and its lithostratigraphic equivalents, depositional systems from a northerly point cluded significant contributions from trans- which mark the onset of deep-marine coarse source? Was the basin filled by a simple longitu- verse sources. Provenance trends from fluvial clastic deposition (Fig. 3; Wilson, 1991; Fildani dinal sediment influx over time, as paleocurrent and shallow-marine systems that characterize et al., 2003; Fildani and Hessler, 2005; Mal- data suggest, or was there appreciable sediment the early evolution of the basin in the northern kowski et al., 2015). South of ~50°S, continued contribution from nonaxial (transverse) sources sector were part of a larger (continental-scale) development of the foreland basin produced (Fig. 1)? Overall, this pattern of basin filling longitudinal drainage, whereas age-equivalent a belt of deep-marine axial channel deposits (diachronous and longitudinal) is similar to other “downdip” deep-marine systems were sourced that distributed sediment from north to south basins (e.g., Austrian Molasse Basin, South by locally derived arc and thrust-belt detritus. (Cerro Toro Formation; Winn and Dott, 1979; Pyrenean foreland basin, Great Valley forearc, Finally, we suggest that orogen-parallel varia- Crane and Lowe, 2008; Hubbard et al., 2008; etc.), meaning that many of these questions are tions such as the north-south diachronous initia- Jobe et al., 2010; Bernhardt et al., 2012). The not unique to the Magallanes-Austral Basin. tion of coarse clastic deposition, the distribution overlying Alta Vista and Tres Pasos Formations This study focuses on two Cenomanian- of shallow- to deep-marine depositional facies record continued southward paleodispersal with aged formations that record spatial variations (shelf-to-basin paleogeography), and variations the progradation of high-relief slope clinoforms in depositional setting (shallow-marine shelf to in provenance signatures support an oblique arc- and turbidite channel facies (Shultz et al., 2005; deep-marine fan systems) during the early evo- continent collisional model for the early evolu- Armitage et al., 2009; Romans et al., 2009; lution of foreland basin sedimentation in the tion of the Patagonian Andes. Hubbard et al., 2010; Fig. 3). In the Austral Magallanes-Austral Basin. We utilize both U-Pb basin sector (~49°S–50°S), deep-marine facies detrital zircon geochronology and sandstone GEOLOGIC BACKGROUND transition upward to shallow- and marginal- petrography to compare: (1) the provenance of marine successions of the Lago Viedma and age-equivalent shelfal and basinal units, and The Jurassic–Cretaceous tectonic evolution Mata Amarilla Formations as early as Ceno- (2) sediment source areas for facies-equivalent of southern Patagonia consists of a two-part his- manian time (Riccardi and Urreta, 1988; Arbe, units that record the onset of coarse clastic depo- tory, which includes the development of a back- 2002; Varela et al., 2012; this study), whereas

350 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

South 70°W 65°W Legend: 40°SAmerica A B EAMC DM Patagonian RVB structure Tertiary NPM 48°S batholith high (-1000 m) (sedimentary) Atlantic Naz. Pl.

Ocean MAB Upper Cretaceous ld (sedimentary) e Figure 4 Lower Cretaceous (sedimentary) Scotia Pl. Ant. Pl. Ophiolite complex RV B

tagonia ice fi LV Figure 3A Upper Jurassic Weddell Pa (volcaniclastic) Sea Ant. DYMC Middle Jurassic (volcanic) Austral Sector LA Paleozoic basement 45°S Gastre Figure 3B (metasedimentary) Fault Zone DZ samples Golfo San Jorge Basin This study Previous studies DM Figure 3C Sarmiento Complex Dung B Argentina Ri

eness Chico Early Jurassic volcanics Chile Rio Chico Dungeness (188–168 Ma) Ult. Esp. Sector Arch – Magallanes– 50°S Austral Basin Mid Jurassic volcanics (178–152 Ma) Figure 3D

Argentina Arch Malvinas Chile Basin

Capitán Aracena Fuegian Sector and Carlos III CDMC 200 kms Complexes N Tortuga 55°S 0 100 km Complex 56°S 75°W 70°W 65°W 75°W 70°W

Figure 2. (A) Generalized map of southern South America showing the location of the Magallanes-Austral Basin relative to regional sources of sediment and major tectonic features in Patagonia. Pl.—Plateau. (B) Geologic map of the modern foreland fold-and-thrust belt with locations of detrital zircon (DZ) samples from early foreland basin deposits (this study; Fildani et al., 2003; McAtamney et al., 2011; Mal kowski et al., 2015). Black bars correspond to the locations of schematic stratigraphic columns shown in Figure 3. Black box delineates the study area in the Austral basin sector, shown in Figure 4. CDMC—Cordillera Darwin metamorphic complex; DM—Deseado Massif; DYMC—Duque de York metamorphic complex; EAMC—East Andes metamorphic complex; LA—Lago Argentino; LV—Lago Viedma; NPM—North Patagonia Massif; Ult. Esp.—Ultima Esperanza; RVB—Rocas Verdes Basin. this major facies transition does not occur in belt, near Puesto El Alamo (Fig. 4), has been with age-equivalent, deep-marine strata lo- the Ultima Esperanza basin sector until the interpreted as an overall upward-coarsening cated to the south (Punta Barrosa Formation; Campanian–Maastrichtian Dorotea Formation succession of deltaic and fluvial deposits (Arbe, Malkowski et al., 2015). In total, we present a (Covault et al., 2009; Schwartz and Graham, 2002; Canessa et al., 2005). Age-equivalent 1-km-thick section of stratigraphy measured at 2015; Schwartz et al., 2016; Figs. 2 and 3). The (Cenomanian–Coniacian) strata near the eastern the decimeter scale to document major vertical Lago Viedma Formation is exposed along an end of Lago Viedma are referred to as the Mata changes in depositional facies determined by ~35-km-long outcrop belt north of Lago Viedma Amarilla Formation (Varela et al., 2012). bedding geometry and stacking patterns, sedi- and east of the town of El Chalten, Argentina mentary structures, grain-size variation, fossils, (Fig. 4). Previous workers have assigned a late SEDIMENTOLOGY AND and ichnofacies (Fig. 5). Albian to late Cenomanian age on the basis of STRATIGRAPHY OF THE LAGO ammonite fauna (Riccardi and Urreta, 1988; VIEDMA FORMATION Stratigraphic Characteristics Aguirre-Urreta, 2002). The Lago Viedma For- and Lithofacies mation conformably overlies the Lower Creta- The following sections include descriptions ceous Rio Mayer Formation and is overlain by and interpretations of the sedimentology and The Lago Viedma Formation consists of the Turonian (?) Puesto El Alamo Formation stratigraphy of the Lago Viedma Formation at fine- to medium-grained sandstone and gravel (Fig. 3; Arbe, 2002; Canessa et al., 2005). Stra- Cerro Pyrámide (Fig. 4), which provide im- conglomerate (Fig. 5). Overall, the succession tigraphy along the eastern end of the outcrop portant context for understanding relationships coarsens upward from ~200 m of thinly inter-

Geological Society of America Bulletin, v. 129, no. 3/4 351 Malkowski et al.

A LAGO VIEDMA, ARGENTINA B LAGO ARGENTINO, ARGENTINA C ULTIMA ESPERANZA, CHILE D CORDILLERA DARWIN, CHILE

L. Cerro Cuchilla/ L. L. L. La Irene/ Man Aike Fms. Ricallosa Fms. Dorotea Fm. PA PA PA PA Hiatus Dorotea/Pari Aike/ Shallow marine Cerro Fortaleza Fms. Cardiel Fm. Deep marine La Anita Fm. Tres Pasos Fm. Hiatus Alta Vista Fm.

Cerro Matrero/

Mata ACEOUS ACEOUS ACEOUS

Cerro Toro Fm. ACEOUS Amarilla Cerro Toro Fm. Escarpada Fms. Fm. (Lago Sofia Deep marine Shallow marine conglomerate) Puesto El U. CRET U. CRET U. CRET

Alamo Fm. U. CRET Latorre/ Upper La Paciencia Fms. Punta Barrosa * Punta Barrosa Magallanes–Austral foreland basi n Lago Viedma Fm. Fm. < 89 Ma Fm. (equiv.?) < 92 Ma ~ 98 Ma Zapata/Yahgan/ ~115 Ma Rio Mayer Onset of coarse Canal Bertrand/ Zapata Fm. Lower La Fm. clastic deposition rdes Rio Mayer Fm. Paciencia Fms. L. CRE T. L. CRE T. L. CRE T. L. CRE T.

Springhill Fm. Springhill/ Springhill Fm. Springhill Fm. Rio Jackson Fms. Rocas Ve El Quemado El Quemado Tobifera Fm. Tobifera Fm. backarc basi n U. JUR. U. JUR. U. JUR. U. JUR. Complex Complex (Sarmiento OC) (Tortuga OC)

Pre-Jurassic Pre-Jurassic Pre-Jurassic Pre-Jurassic metasedimentary metasedimentary metasedimentary metasedimentary basement basement basement basement N * Informal use of nomenclature - identifies equivalent facies S

LEGEND

Ophiolitic rocks Micritic limestone/mudstone Mudstone Interbedded sandstone and (basalt, gabbro, sheeted dickes) conglomerate (shallow marine) Channelized Metasedimentary rocks Felsic volcanic rocks Sandstone Sandstone and conglomerate units (deep marine) Figure 3. Generalized, along-strike (N-S) stratigraphic correlations of units in the Patagonia fold-and-thrust belt (modified from Mal kowski et al., 2015). Dark-gray shaded region corresponds to deep-water depositional systems, and light-gray shaded region corresponds to shallow- and nonmarine depositional systems Stratigraphic columns are representative of: (A) the region just north of Lago Viedma (near El Chalten) in Argentina, modified after Arbe (2002); (B) the region just north of Lago Argentino in Argentina, modified after Kraemer and Riccardi (1997); (C) the Ultima Esperanza district of southern Chile, modified after Wilson (1991), Fildani and Hessler (2005), and Romans et al. (2010); and (D) the Cordillera Darwin region in Chile, modified after McAtamney et al. (2011). OC—ophiolite complex; U—Upper; L—Lower; Jur—Jurassic; Cret—Cretaceous; Pal—Paleozoic. bedded sandstone and mudstone to massive erosion and basal scour. Individual beds com- turbidites are commonly associated with deep- and cross-bedded sandstone and gravel up to monly show normal grading and contain planar water environments (e.g., Arnott, 2010), we 800 m thick (Fig. 5). At the regional outcrop lamination and ripple cross-lamination. Thicker prefer a relatively shallow-marine (shelfal) in- scale, packages of stratigraphy show little lat- beds (30–150 cm) of medium- to coarse-grained terpretation given the relationship to overlying eral heterogeneity, and individual packages sandstone contain planar laminations and dis lithofacies (discussed below). can be traced for kilometers across the well- articulated fossil fragments. Nondescript biotur- exposed mountainside (Fig. 6). We divide the bation is common within this lithofacies. LF-2: Massive Siltstone and Lago Viedma Formation into seven lithofacies Interpretation. Individual beds are inter- Fine‑Grained Sandstone that we use to constrain the environment of preted as sedimentation units deposited by low- Description. Lithofacies 2 consists of silt- deposition preserved by these deposits, and at density turbidity currents (Bouma, 1962). Nor- stone to fine-grained sandstone with occasional a broader scale, the regional paleogeography. mally graded beds reflect suspension settling intervals of medium- to coarse-grained sand- Descriptions and interpretations of these litho- during waning flow conditions. Within beds, stone. Bed thicknesses range from 20 to 100 cm facies are described in the following paragraphs massive sandstone intervals (Ta), planar- (Tb) but are more commonly 20–40 cm thick. Both and are summarized in Table 1. and ripple-laminated intervals (Tc), as well as individual beds and bedsets of LF-2 appear

capping mudstone portions (Td) correspond to tabular and continuous at the scale of the out- LF-1: Thin-Bedded Sandstone and Mudstone internal Bouma divisions (Bouma, 1962). Disar- crop. Much of this section is poorly exposed Description. Thin-bedded sandstone and ticulated fossil fragments and shell hash concre- and appears crudely bedded and/or structureless mudstone facies compose the lower ~200 m tions are interpreted as evidence for high-energy (Fig. 7C). Sedimentary structures include planar of the stratigraphy, which consists of thin (5– conditions associated with turbulent flows. We laminations, flame structures, and low-angle 20 cm) beds of fine-grained sandstone, siltstone, interpret LF-1 to represent an offshore marine cross-bedding. Concretions around bivalves and mudstone (Figs. 7A and 7B). Beds are lat- setting such as an outer shelf and/or prodelta and gastropod hash are common. Evidence for erally continuous and rarely show evidence of environment, below storm wave base. Although bioturbation is pervasive within LF-2, and often

352 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

difficult to identify, but includes Ophiomorpha, N Cerro Fitz Roy 73°00′W various 72°30′W N=112 Skolithos, and borings in woody debris that may LP33 Klv be Teredolites. Klv Interpretation. We interpret LF-2 to rep- El Chalten resent a lower shoreface to offshore shallow- Cerro Pyrámide Puesto marine depositional setting in water depths be- Pmet El Alamo low storm wave base. The well-sorted nature of Jeq Cund Vi this lithofacies is a result of preferential seaward edma Glacie Krm 49°30′S movement of finer-grained particles by asym- r Kpa metric oscillation (Clifton, 2006). Although spe- Pmet cific ichnofacies are difficult to determine, we speculate that the massive, crumbly appearance Ea. Los and poor preservation of primary depositional Patagonia Hermanos Ice Field features are the result of pervasive bioturba- Lago Viedma tion and low sedimentation rates (MacEachern LH157 et al., 2010).

LF-3: Amalgamated Cross-Bedded Sandstone Explanation Kpb-Kctav and Conglomerate with Hummocky and

r sole marks N=46 deep-water Glacier/ice Swaley Cross-Stratified Sandstone slope facies Description. Lithofacies 3 consists of amal- Qal (undif.) Quaternary alluvium gamated, interstratified assemblages of cross- RG164 ripples Cenozoic Basalt bedded fine- to medium-grained sandstone and Upsala Glacie N=10 gravel conglomerate. Individual sandstone and Krm n Cenozoic clastics

o i Cund t (undif.) a i conglomerate beds are commonly 10–40 cm t s n n 50°00′S u thick, and amalgamated successions are 50– a Dorotea & Calafate P Kdc r

- T Fms. (undif.) Jeq r 200 cm thick. Internally, beds thicknesses are a e s Cerro Toro & Alta y

o Kctav laterally variable (displaying pinch-swell geom- a r Vista Fms. (undif.)

r M

a etries, scour, and erosive bases), but at the out-

o B

i Kpa R Puesto El Alamo Fm. Krm crop scale, amalgamated successions are later- CH05 Klv Lago Viedma Fm. ally continuous with even thicknesses. Common structures observed in sandstone units include Kpb Punta Barrosa Fm. (and equivs.) planar, low-angle crossbedding, wave ripples, planar (horizontal) laminations, and swaley and Krm Lago Argentino Krm sole marks Rio Mayer Fm. hummocky cross-stratification (Figs. 7D, 7E, N=11 and 8). Gravelly units are commonly massive to Jeq El Quemado Complex normally graded and exhibit planar cross-bed- Pmet Paleozoic metasedimentary ding. Both sandstone and conglomerate units Jeq ripples Magallanes show evidence of basal scour, but these occur- N=18 U-Pb detrital zircon sample Peninsula (this study) rences are more common in gravelly units (Figs. Kctav U-Pb interbedded ash sample 7F and 8). Zones of fossil concretions, similar to (Malkowski et al., 2015) MP97 those mentioned above, are observed within the 50°30′S erito Morenor MP96 P Glacie Paleocurrent summary coarser, cross-bedded units. Interpretation. Deposits associated with 015 020 sole marks LF-3 are interpreted as the deposits of high- N=147 Kilometers a energy storm events in a shallow-marine sys- Argentin tem between storm and fair-weather wave base. Brazo Sur Patagonia Chile Coarse-grained, gravelly successions correspond Cund Ice Field ripples LTA83 to deposition in the upper to middle shoreface, N=89 Kctav Kdc whereas beds characterized by fine- to medium- Kctav grained sandstone with abundant hummocky and Tres Cerro Toro Fm. Pasos Fm. swaley cross-bedding represent a more distal setting (middle to lower shoreface). Individual beds Figure 4. Geologic map of the Austral basin sector. Sedimentologic and stratigraphic record successive changes in flow conditions observations and interpretations of the Lago Viedma Formation come from Cerro during storm events. Erosive bases (scour), sus- Pyrámide. Detrital zircon sample locations from deep-water facies correspond to the lo pension settling (graded gravel), and cross-strati cations of ash beds reported in Malkowski et al. (2015). Measured stratigraphic section fied gravel conglomerates correspond to the ini- in Figure 5 corresponds to the same location as the detrital zircon samples near Cerro tial high-energy conditions in which combined Pyrámide. Map details are modified after Meilan and Maza (1994), Kosmal and Spiker flow (unidirectional and oscillatory currents) mann (2001), Ghiglione et al. (2009), and Malkowski et al. (2015). Ea.—Estancia. processes were active (e.g., Cheel and Leckie,

Geological Society of America Bulletin, v. 129, no. 3/4 353 Malkowski et al.

CP150 945 burrows (Thal.) EXPLANATION Puesto El Alamo Formation? Lithology gravelly ss CP154 PC-7 mudstone 1000 PC-6 940 LF4 PC-7 8 meter-scale beach siltstone PC-6 LF6 n=10 tangential foreshore sandstone n=10 foresets conglomerate 935 6 carbonaceous clastic 900 PC-3 PC-2 crossbedded sandstone PC-2 PC-1 PC-5 and conglomerate upper 930 LF5 PC-1 4 shoreface gravel lenses n=7 LF7 n=21 n=12 internal channelization 800 CP72 925 2 Grain Size CP147 & CP148 LF3 covered Transgressive LF5 shoreface Embayment cl sl fs ms cs p LF7 0 cl - clay 920 poorly exposed m cl sl fs ms sl - silt PC-4 fs - fine sand 700 ms - medium sand cs - coarse sand p - pebble LF5 n=12 915 LF4

Sedimentary Structures CP146 EXPLANATION LF4 Mudstone 600 (continued) rip-up clasts PC-A 910 Hummocky/Swaley PC-B Samples cross-stratification PC-A (Oph. & Thal.) Detrital zircon PC-B n=6 1 m cover Planar laminations (U-Pb geochronology) n=8 905 Thin Section Cross-stratification (Petrography) 500 heavy mineral (beach) placer LF6 Burrowing/bioturbation Paleocurrents CP45 Fossil-hash concretion 900 Trough cross- m cl sl fs mscs p stratification Plant material LF4 PC-D CP68 3.0 Bivalves PC-D Planar cross- 400 stratification 2.0 n=21 Gastropods LF3 1.0 Lithofacies Petrified logs/trees LF1: Thin-bedded 0 sandstone and mudstone m cl sl fs mscs p 300 1.2 LF2: Massive siltstone and fine-grained sandstone CP43 0.8 LF3: Amalgamated cross- LF3 bedded sandstone and ~200-300 m 0.4 conglomerate w/ hummocky covered and swaley cross-stratified 200 Igneous sill 200 0 sandstone m cl sl fs ms cs p 1.0 LF4: Massive to cross- bedded conglomerate (continuation of se 0.8 LF2 LF5: Planar and Ta-Td tangentially cross-bedded sandstone 0.6 100 100 LF6: Planar and ct horizontally laminated ion) 0.4 LF1 sandstone LF1 0.2 LF7: Carbonaceous and CP09b CP37a siliceous siltstone and fine- grained sandstone 0 0 0.0 cl sl fs ms cs p cl sl fs ms cs p m cl sl fs ms Figure 5. Measured stratigraphy from the Lago Viedma Formation at Cerro Pyramide. The entire Lago Viedma Formation section, including covered intervals, is shown schematically. See Figure 4 for locations of detrital zircon samples and measured stratigraphy from Cerro Pyrámide. More detailed “call outs” of individual lithofacies (LF-1, -3, -4, -5, -6) are displayed in higher resolution in order to highlight detailed sedimentological features (see text for lithofacies descriptions). Ichnofossils include Thalassinoides (Thal.)

and Ophiomorpha (Oph.); ss—sandstone; PC—paleocurrent measurements; Ta–Td—internal Bouma divisions (Bouma, 1962).

354 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

1.5 km A LOOKING EAST

shoreface inner shelf outer shelf to slope lower 200 m CP09b

B LOOKING NORTH

CP150 Puesto El Formation (? Alamo ) ?

CP72 Dominan Shore

face tly

Transgressive Embayment

CP68

CP43 Dominantly Shoreface

Figure 6. Photopanoramas of the Lago Viedma Formation exposed at Cerro Pyrámide that highlight the exposure quality and lateral continuity of stratigraphic units. (A) View to the east showing the regional extent and outcrop expression of the Lago Viedma Formation. (B) View to the north from Cerro Pyrámide showing the lateral continuity of stratigraphy. In general, color variations in the strata cor respond to lithofacies changes. Subvertical, crosscutting units are intrusive dikes of unknown age (Cenozoic?).

1992; Fig. 8). In coarser-grained units, massive multiple events and/or that their proximity to the glomerate are continuous at the outcrop extent and cross-bedded conglomerate transitions up- shoreline was maintained in a zone where storm with basal irregularities due to scour and erosion ward to wave ripple and planar laminated sand- energy was greatest. (Figs. 7G and 7H). Units are commonly planar stone, which represents waning storm energy and tangentially cross-bedded or appear mas- and oscillatory flow (Cheel and Leckie, 1992; LF-4: Massive to Cross-Bedded Conglomerate sive. Some successions of LF-4 contain abun- Plint, 2010). Likewise, hummocky and swaley Description. Massive and cross-bedded con- dant petrified logs, up to 70 cm in diameter. With cross-bedding observed in finer-grained sand- glomerate facies include very coarse-grained the exception of isolated occurrences of Ophio- stone beds is interpreted to reflect dominantly sandstone to gravelly, clast-supported conglom- morpha, bioturbation is rarely observed in LF-4. oscillatory flow conditions (Dumas and Arnott, erate. Clast diameters are 1–3 cm, but range up to Interpretation. Lithofacies 4 is interpreted to 2006). The amalgamation of multiple storm beds 5 cm. Units of LF-4 are commonly amalgamated represent a high-energy, shallow-marine depo- indicates that storms were strong enough to par- and occur in 1–5-m-thick intervals, but range up sitional setting such as the upper shoreface of tially erode previous storm deposits and preserve to 20 m thick. Successions of amalgamated con- a storm-affected, and probably steep, shoreline

Geological Society of America Bulletin, v. 129, no. 3/4 355 Malkowski et al.

TABLE 1. SUMMARY OF DESCRIPTIONS AND INTERPRETATIONS OF LITHOFACIES Sedimentary structures Interpreted depositional Lithofacies Grain size Bed thickness Bed geometry and notable features Interpreted deposition process(es) environment LF1: Thin- Mudstone, Typically Tabular, Graded (normal) Deposition by low-density turbidity Distal offshore marine setting bedded siltstone, and 5–20 cm, even, and bedding, ripple cross- currents; graded beds reflect below storm wave base; sandstone fine-grained range continuous laminations, planar suspension settling during waning may also reflect an outer- and mudstone sandstone, w/ 2–40 cm laminations, flame flow conditions; planar and ripple shelf, prodelta environment medium- to structures, bioturbation laminations represent internal coarse-grained (nondescript) divisions of low-density turbidites sandstone (Bouma, 1962) LF2: Massive Siltstone to Typically Tabular, Massive, crumbly, Preferential seaward movement Lower shoreface to offshore siltstone and fine-grained 20–40 cm, even, and pervasively bioturbated of finer-grained particles by environment; below storm fine-grained sandstone w/ up to meter- continuous (nondescript), outcrops asymmetric oscillation (Clifton, wave base with ideal sandstone medium- to scale (difficult often poorly exposed 2006); primary depositional fabric conditions for bioturbation coarse-grained to discern rarely preserved sandstone bedding) LF3: Fine- to medium- Individual Successions Erosive bases; massive or Event-beds (storms) w/ initial high- Coarse-grained storm beds Amalgamated grained sandstone/ are laterally normally graded lower energy (erosive) conditions during deposited in a shallow- cross-bedded sandstone conglomerate continuous at intervals; low-angle combined flow; suspension settling marine (upper to middle sandstone and interbedded and units are outcrop scale, cross-stratification; and cross-stratification of gravel shoreface) setting, likely conglomerate amalgamated 10–30 cm, w/ internal planar cross-bedding, during combined flow; wave ripple between fair weather and w/ hummocky w/ gravel amalgamated irregularities planar laminations; bed forms and planar laminated storm wave base; intervals and swaley conglomerate successions (e.g., pinch- wave ripples; swaley sandstone result from waning with a greater abundance cross-stratified typically swell, erosive and hummocky oscillatory flow and hummocky/ of hummocky/swaley cross- sandstone 50–200 cm bases) cross-stratification in swaley bed forms associated with bedding are associated sandstone intervals fine- to medium-grained sandstone; with slightly more distal the effects of near-bottom setting (middle to lower unidirectional current are greater shoreface) than gravel-rich shoreward, resulting in basinward intervals sediment transport (Cheel and Leckie, 1992; Dumas and Arnott, 2006; Plint, 2010) LF4: Massive to Very coarse Amalgamated Tabular at Massive to planar and Well-sorted gravel accumulations Shallow-marine, upper cross-bedded sandstone successions outcrop extent tangential cross- associated w/ asymmetric shoreface; along a high- conglomerate to gravelly are commonly w/ some bedding (sometimes oscillation and preferential energy, storm-affected clast-supported 1–5 m and lenticular faint cross-bedding), landward segregation of coarser shoreline (may also reflect conglomerate, range up to (pinch-swell) petrified logs (up to grain sizes; gravel bed forms are a steep shoreline) clast diameters 20 m units, erosive 50 cm in diameter) the result of high-energy (waves 1–3 cm, up to bases and storms) unidirectional flow 5 cm and/or longshore flow along bar- trough system (Clifton, 2006) LF5: Planar and Fine- to medium- Amalgamated Amalgamated Planar and tangential Bed forms are the result of Shallow-marine, upper tangentially grained succession successions cross-bedded unidirectional flow associated with shoreface, possibly high- cross-bedded sandstone, are commonly exhibit even sandstone w/ trough longshore and rip currents along energy storm-affected sandstone w/ some 1–5 m, range thickness cross-stratification the shoreface (Clifton et al., 1971; nonbarred shoreline coarse-grained from 20 cm to at extent of Clifton, 2006; Plint, 2010) and/or longshore bar- sandstone 12 m outcrop trough system w/ rip and scattered channels pebbles LF6: Planar- Fine- to medium- Intervals range Tabular, Planar and horizontally Deposited under upper-flow- Coastal marine, beach laminated grained from 20 cm even, and laminated, fine- to regime conditions produced by foreshore (swash zone) sandstone sandstone up to 300 cm continuous medium-grained wave swash on the foreshore; and perhaps as distal as sandstone including accumulation of heavy minerals uppermost shoreface laterally continuous resulted from winnowing (and heavy mineral placer seaward transport) of lighter sand deposits grains (Clifton, 1969, 2006; Plint, 2010) LF7: Siltstone and Bedding not Regionally Massive to laminated with Deposition in a low-energy setting Backshore, coastal plain, Carbonaceous very fine- to discernible correlatable abundant plant debris by accumulation and suspension and/or lagoon deposition and siliceous fine-grained (massive, and horizon, even settling of silt, sand, and organic setting siltstone and sandstone bioturbated) thickness material fine-grained sandstone

environment (e.g., Schwartz and Birkemeier, grained bar-trough system (Hart and Plint, stone with minor coarse-grained sandstone and 2004; Clifton, 2006). Thick, well-sorted accu- 1995; Clifton, 2006; Plint, 2010; Schwartz and scattered pebbles (Fig. 7I). Amalgamated suc- mulations of amalgamated gravel conglomerate Birkemeier, 2004). cessions of LF-5 are commonly 1–5 m thick, but along the shoreline resulted from asymmetric range from 20 cm to 12 m and show even, con- oscillation and preferential landward segrega- LF-5: Planar and Tangentially tinuous thicknesses at the extent of the outcrop. tion of coarser grain sizes. Planar and tangen- Cross‑Bedded Sandstone Tangentially cross-bedded units show trough tially cross-bedded units reflect high-energy Description. Lithofacies 5 is characterized cross-stratification. Bioturbation is common (wave- and storm-influenced) unidirectional by amalgamated units of planar and tangentially in LF-5 and includes Ophiomorpha, Diplocra- flow and/or longshore flow along a coarse- cross-bedded, fine- to medium-grained sand- terion, Rosselia, Skolithos, and Macaronichnus.

356 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

A B C

~3m

D E F

~40cm

G H I

A ~20m

J K L

~1m ~3m

Figure 7. Outcrop photos of the Lago Viedma Formation from Cerro Pyrámide. (A) Thin-bedded and tabular turbidites representing LF-1. (B) Bed-scale photo of LF-1 showing grading, bioturbation, and foundering of coarse-grained bases into fine-grained tops; scale is 16 cm. (C) Example of LF-2 highlighting the recessive nature of outcrop exposures; person for scale. (D) Low-angle (swaley) cross-bedding inter bedded with cross-stratified gravel lenses typical of LF-3; scale is 16 cm. (E) Swaley, cross-stratified, fine- to medium-grained sandstone of LF-3; scale is 16 cm. (F) Example of erosive sole marks (grooves and flutes) on base of storm beds. (G–H) Thick (~20 m) succession of mas sive and cross-bedded gravel conglomerate (LF-4); person for scale in G. (I) Cross-stratified medium- to coarse-grained sandstone typical of LF-5; arm/hand for scale. (J) Black, fine-grained magnetite sandstone (~1 m thick) representing a heavy mineral beach placer (LF-6). (K) South-southeast–dipping clinoforms of beach placer deposits (dark, inclined bands). (L) Siltstone and fine-grained sandstone with plant debris, which is characteristic of LF-7.

Geological Society of America Bulletin, v. 129, no. 3/4 357 Malkowski et al.

A B

30 U O

U O 0 cm cl ssl f ms cs p

LEGEND 50 C Current conditions

U unidirectional 40

SB-3 O oscillating assymetrically 30 U O oscillating erosive base

20 SB-2 Sedimentary structures U O horizontal lamination wavy lamination 10

SB-1 wave ripples

U O cross bedding 0 cm cl ssl f ms cs p Figure 8. Outcrop examples and interpretations of storm deposits. (A) Swaley cross-stratification in a fine- to medium-grained sandstone. (B) Outcrop photo and line-drawing interpretation of a coarse-grained storm bed or possibly two amalgamated beds (dashed line indicates possible bed break). (C) Outcrop photo and line-drawing interpretation of amalgamated, coarse-grained storm beds (SB-1, SB-2, and SB-3). Scale in all photos is 16 cm. Schematic interpretations and current conditions are based on Cheel and Leckie (1992). Grain-size legend same as Figure 5.

Interpretation. Planar and tangentially cross- eral placer sands form large-scale, inclined sets discernible because it weathers recessively and bedded sandstone facies are interpreted to that dip toward the southeast (Fig. 7K). is covered by loose sediment. Overall, this unit represent a shallow-marine, upper shoreface Interpretation. Lithofacies 6 represents a is massive (structureless) with rare laminated depositional setting, which could include a coastal marine depositional setting in the swash beds. It contains abundant plant and woody high-energy, storm-affected nonbarred shore- zone of the beach foreshore and/or perhaps as debris (Fig. 7L). line and/or a longshore bar-trough system with distal as the uppermost shoreface. Subhorizontal Interpretation. Massive carbonaceous and rip channels (e.g., Clifton, 2006). Preserved bed to low-angle planar-laminated sandstone is de- siliceous siltstone and sandstone facies reflect forms reflect unidirectional flow associated with fined by textural variations due to segregation of deposition in a low-energy environment, which longshore currents and rip channels along the grain size and density produced by wave swash was likely dominated by suspension settling of shoreface (Fig. 8; Clifton et al., 1971; Clifton, along the foreshore (Clifton, 1969). The accu- silt, fine-grained sand, and organic material. We 2006; Plint, 2010). mulation of heavy minerals results from con- interpret LF-7 to represent a backshore deposi- tinuous, density-driven winnowing in the swash tional setting such as a coastal plain or lagoon LF-6: Planar-Laminated Sandstone zone, resulting in seaward transport of lighter environment. Description. Planar-laminated sandstone fa- sand grains (Clifton, 1969, 2006; Plint, 2010). cies consist of fine- to medium-grained sand- Large-scale, inclined sets of heavy mineral Interpretation of Depositional Environment stone and commonly occur in amalgamated in- placers (e.g., Fig. 7K) represent beach clino- tervals that range from 20 cm to 300 cm. These forms, which reveal southeastward progradation The Lago Viedma Formation along Cerro successions of planar-laminated sandstone of a (transient?) beach-shoreface environment. Pyrámide is interpreted to represent a shallow- are tabular and continuous at the extent of the to marginal-marine depositional setting influ- outcrop. In some intervals, LF-6 is composed LF-7: Carbonaceous and Siliceous Siltstone enced, if not dominated, by wave and storm ac- of heavy mineral placer sands that consist of and Fine-Grained Sandstone tivity. Overall, the succession is progradational, magnetite (Fig. 7J). Internally, lamina sets range Description. Lithofacies 7 is characterized beginning with outer shelf or prodelta (distal from subhorizontal to shallowly inclined (up to by brown, carbonaceous and siliceous siltstone offshore) deposits (LF-1–LF-2) that transi- ~5°). In some exposures, the dark, heavy min- and fine-grained sandstone. Bedding is rarely tion upward into stacked successions of beach

358 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes foreshore and shoreface deposits (LF-3–LF-6). Q The thick (800+ m) succession of stacked upper Austral Sector - Lago Viedma Fm. (n=9) shoreface and foreshore deposits suggests long- Austral Sector - Punta Barrosa Fm. equivs. (n=8) term shoreline stasis with subtle fluctuations in Qm base level, accompanied by rapid subsidence. Recycled A major transgressive event is recorded near Orogenic the middle of the section (700–800 m; Fig. 5). Here, strata transition upward from foreshore Recycled and beach-related medium- to coarse-grained Orogenic sandstone to siltstone and fine-grained sandstone associated with a coastal plain or lagoonal setting (LF-7). BU Although previous workers have suggested Dissected Mixed both tidal and fluvial influence for the upper arc Lago Viedma Formation 10–20 km southeast of Transitional the study area (e.g., Arbe, 2002; Canessa et al., arc Undissected Dissected 2005), we observed little evidence that supports arc arc a significant tidal or fluvial influence at Cerro F L Pyrámide. The presence of large (up to 70-cm- Transitional diameter) petrified logs and cobble-sized con- arc glomerate likely suggest nearby input from a fluvial source. A possible indication of primary FLUndissected t fluvial deposition comes from an isolated oc- arc currence of a 10 m section of internally chan- Figure 9. Ternary diagrams displaying the relative abundance of framework grains in sand nelized and cross-bedded sandstone and gravel stone from the Lago Viedma Formation and Punta Barrosa Formation within the Austral conglomerate that occurs at ~800 m (Fig. 5). basin sector. The Lago Viedma Formation shows greater compositional variability, but sam However, these channelized units are rare, and ples from both units commonly plot within a magmatic arc provenance field. Q—quartz, there are no indications of distributary mouth F—feldspar, L—lithic rock fragments, Qm—monocrystalline quartz, Lt—total lithics bar deposits in the section. The sheet-like geom (lithic rock fragments + polycrystalline quartz). BU—basement uplift. etry of these stratigraphic “packages” likely re- flects a broad foreshore depositional setting that was off-axis from a delta and that was reworked by waves and storms. Consequently, it is dif- rent data is available in Appendix 1.1 In short, and eight were collected from lithostratigraphic ficult to infer how closely these deposits were interpreted paleoflow is variable throughout equivalents of the Punta Barrosa Formation ex- related to a fluvial-deltaic system. the section, but measurements yield predomi- posed in the Austral basin sector (Figs. 2 and 4). nantly northeast to south-southeast paleocur- Standard petrographic thin sections were cut and Paleocurrents rents, consistent with previous studies (Fig. 4; stained for plagioclase and potassium feldspar Canessa et al., 2005). Given the complexity of and then were analyzed according to the modi- One of the characteristic features of wave- and the currents in coastal marine systems, such an fied Gazzi-Dickinson point-counting method storm-influenced nearshore/shoreface systems array of interpreted paleoflow directions could (Dickinson, 1970; Ingersoll et al., 1984). Modal is that they consist of complex water circulation yield both east-west– and north-south–trending compositions were determined by identifying systems that may yield a variety of current di- shorelines. However, the presence of southeast- 400 grains from each thin section. A summary rections that require careful consideration (e.g., dipping heavy mineral beach clinoforms (Fig. of the raw and recalculated point-count data is Clifton, 2006; Plint, 2010). These include long- 7K) suggests a paleoshoreline that was oriented available in Appendix 2 (see footnote 1). shore currents that parallel the coast, rip currents southwest-northeast. The bulk modal composition of sandstone that move seaward, landward-oriented wave from the Lago Viedma and Punta Barrosa For- currents, and the combined effects of unidirec- PROVENANCE mations in the Austral sector is characterized tional and oscillatory currents that occur during by quartz (Q) and lithic fragments (L) with storms. Previous work from nearby exposures Sandstone Petrography secondary amounts of feldspar (F) (Fig. 9). of the Lago Viedma Formation noted predomi- The total quartz composition consists of mono- nantly southward-oriented paleocurrents at the Sandstone compositional and petrographic crystalline quartz (Qm) with minor amounts of base of the section and northeast to southeast data were obtained from 17 samples in order to microcrystalline quartz (chert) and polycrystal- paleocurrents in the upper part of formation constrain detrital source areas (e.g., Dickinson line quartz (Lt = total lithics [lithic rock frag- (Canessa et al., 2005). and Suczek, 1979; Dickinson et al., 1983). Of ments + polycrystalline quartz]). Feldspar (F) We present ~112 new paleocurrent measure- the 17 samples, nine were collected from the is common and consists mostly of plagioclase ments from the Lago Viedma Formation that Lago Viedma Formation at Cerro Pyrámide, with rare occurrences (1 or 2 grains per sample) were collected from planar and trough cross- of potassium feldspar. The lithic component of 1 bedded sandstone and gravel conglomerate. GSA Data Repository item 2016319, Appendi- the Lago Viedma and Punta Barrosa Formations ces 1–3, raw data and methods, is available at http:// Interpreted flow directions are shown in Figure www.geosociety.org/pubs/ft2016.htm or by request consists of volcanic grains (Lv) with minor oc- 5, and a more detailed summary of paleocur- to editing@geosociety.org. currences of sedimentary lithic (Ls) and meta-

Geological Society of America Bulletin, v. 129, no. 3/4 359 Malkowski et al. morphic lithic (Lm) grains. Volcanic fragments TABLE 2. LOCATIONS OF DETRITAL ZIRCON SAMPLES (DATUM: WGS84) are mafic to intermediate with fine-grained Lat Long. Age Matching ash age ± 2σ Sample ID (°S) (°W) (Ma)Formation (sample ID) groundmass. The Q-F-L and Qm-F-Lt modal CP09b 49°20.799 72°46.319CenomanianLago Viedman/a compositions are more variable in the Lago CP41 49°20.002 72°47.614CenomanianLago Viedman/a Viedma Formation than Punta Barrosa equiva- CP37a 49°20.570 72°47.236CenomanianLago Viedman/a CP43 49°20.576 72°47.063CenomanianLago Viedman/a lent units within the Austral sector, due to varia- CP68 49°20.709 72°47.000CenomanianLago Viedman/a tions between the relative abundances of quartz CP72 49°20.734 72°46.788CenomanianLago Viedman/a and lithic fragments (Fig. 9). CP150 49°20.931 72°46.324Cenomanian– Lago Viedma– n/a Turonian(?) Puesto El Alamo Compositional data suggest that the Lago LTA83 50°41.602 72°58.864CenomanianPunta Barrosa (equiv.)98.1± 1.3 (LTA84) Viedma and Punta Barrosa Formations in the MP96 50°28.993 72°58.819CenomanianPunta Barrosa (equiv.)95.6± 1.4 (MP94) MP97 50°29.181 72°57.566CenomanianPunta Barrosa (equiv.)96.8± 1.6 (MP48) Austral sector were derived from intermediate CH05-19 50°09.753 72°48.852CenomanianPunta Barrosa (equiv.)96.5± 1.4 (CH06) volcanic rocks. The overall abundance of inter- RG164 49°58.205 72°48.535CenomanianPunta Barrosa (equiv.)92.3± 1.7 (RG163) mediate lithic volcanic grains and the relative LH157 49°41.004 72°49.935CenomanianPunta Barrosa (equiv.)100.3 ± 2.7 (LH158) proportion of plagioclase feldspar to potassium Note: WGS84—World Geodetic System 1984. n/a—not applicable. feldspar are consistent with an andesitic volcanic arc source. However, source areas also contrib- uted lesser amounts of quartz and feldspar. A and yield age trends similar to each other, with Pre-Jurassic Metamorphic Complexes comparison of these data with the provenance relative probability age peaks at 114–111 Ma, Devonian–Triassic metamorphic complexes fields of Dickinson et al. (1983) shows that 14 104–100 Ma, and 96–93 Ma (Fig. 10). The present throughout the Patagonian Andes include of the 17 samples plot within the undissected uppermost sample from Cerro Pyrámide Devonian–Permian metamorphosed turbidites or transitional magmatic arc fields, whereas the (CP150) is the one exception to this trend, as it of the Eastern Andean metamorphic complex, remaining three fall within the recycled oro- is dominated by Jurassic ages (56%) and has a higher-grade metamorphic rocks of the Main gen category (Fig. 9). Compositional variation minor Cretaceous component (16%). Range metamorphic complex, mid- to late Paleo- within the Lago Viedma Formation may reflect zoic units of the Cordillera Darwin metamorphic variable source terranes; however, this may also Punta Barrosa Formation (and Equivalents) complex, and Triassic metasedimentary rocks be the result of secondary, compositional sorting Detrital zircon samples from Cenomanian- of the Chonos and Duque de York metamorphic processes, which are common within shallow- aged deep-water units of the Punta Barrosa complexes (Fig. 11; Faúndez et al., 2002; Hervé marine environments. Formation consist of variable proportions of et al., 2003, 2010). Each of these complexes is pre-Jurassic (>200 Ma), Early–Middle Jurassic distinguished by its location, metamorphic grade, Detrital Zircon Geochronology (199–161 Ma), and Cretaceous (145–90 Ma) inferred depositional age, provenance, and proto ages (Fig. 10). All samples contain Cretaceous- lith (Hervé et al., 2003, 2008). In addition to meta- In total, 13 sandstone samples were col- aged grains; however, the Cretaceous popula- morphic complexes exposed along the thrust belt, lected and analyzed from Cenomanian- tion is relatively small (14%) in sample RG164 Paleozoic meta-igneous and metasedimentary aged units within the Austral sector of the compared to the others (Fig. 10). There is an of rocks underlie the North Patagonia and Deseado Magallanes-Austral Basin for U-Pb detrital abundance (25%–40%) of Early–Middle Ju- Massifs (e.g., Pankhurst et al., 2006; Chernicoff zircon geochronology and yielded 1176 new rassic ages (199–161 Ma) in samples LH157, et al., 2013; Moreira et al., 2013; Fig. 11). single-grain ages (Table 2; Fig. 10). Seven of RG164, and MP97. Samples LH157, LTA83, Paleozoic–Triassic metamorphic complexes these samples were collected from the Lago and MP97 consist mostly of Cretaceous grains associated with the Andean convergent mar- Viedma Formation at Cerro Pyrámide, and six (54%, 56%, and 36%, respectively), whereas gin likely represent the major sources for Pre- were from stratigraphic/facies equivalents of pre-Jurassic ages represent the most abundant cambrian and Paleozoic zircon grains in the the Punta Barrosa Formation (Fig. 4) and are population in samples RG164 (46%), CH05 Magallanes–Austral Basin. Figure 11A shows companion samples to ashes reported in Mal- (71%), and MP96 (57%). a summary of detrital zircon age spectra from kowski et al. (2015). Additionally, we report metasedimentary complexes south of 48°S. De- 67 new grain ages from three previously pub- Potential Source Terranes trital zircon age spectra from the aforementioned lished samples from the Punta Barrosa Forma- complexes show a prominent age peak between tion in the Ultima Esperanza District of Chile The primary source terranes for Upper Cre- 310 and 260 Ma that is best developed in the (Fildani et al., 2003). U-Pb analyses were taceous siliciclastic units of the Magallanes- Main Range metamorphic complex, Chonos conducted using laser ablation–inductively Austral Basin include pre-Jurassic metamorphic metamorphic complex, and Duque de York coupled plasma–mass spectrometry (LA-ICP- complexes, Jurassic volcanic and volcaniclastic metamorphic complex (Fig. 11). Additional age MS) and reduced at the Arizona LaserChron rocks, and latest Jurassic and Cretaceous vol peaks occur at 410–350 Ma (Devonian–Lower Center following methods described in Ap- canic and magmatic components of the Pata- Mississippian), 550–450 Ma (Cambrian–Ordo- pendix 3 (see footnote 1). gonia arc/batholith system (Fig. 2). Previous vician), and 1200–900 Ma (Proterozoic). Zircon detrital zircon studies suggest that sediment in older than 1200 Ma is found in low abundances Lago Viedma Formation the Magallanes-Austral Basin was primarily (3%–10%) within each metamorphic complex Samples from the Lago Viedma Formation derived from the north and/or west during Cre- (Fig. 11). at Cerro Pyrámide consist of Cretaceous-aged taceous time (e.g., Fildani et al., 2003; Romans grains (ca. 145–90 Ma) with minor Jurassic and et al., 2010; McAtamney et al., 2011; Bernhardt Jurassic Rift Volcanics Paleozoic age populations (Fig. 10). Samples et al., 2012; Malkowski et al., 2015). The fol- Regional Jurassic rifting during the breakup CP09b, CP41, CP37a, CP43, CP68, and CP72 lowing sections discuss each of these source of Gondwana produced large volumes of consist mostly of Cretaceous ages (78%–94%) areas in more detail. plume-related silicic magmatism referred to

360 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

A 25 180 15 CP150 (n=104/108) 96 5 93 114 20 CP72 (n=88/89) 10

20 104 113 15

) CP68 (n=76/78) 10 5 112 16 12 CP43 (n=95/96) 8 4 100 6 4

Frequency (# of grains CP37a (n=26/27) 2

100 25 111 CP41 (n=91/96) 15 5 101 35 25 111 CP09b (n=95/95) 15 5

B 14 113 102 DA: 100.3 ± 2.7 10 179 LH157 (n=100/104) 6 2

14 182 DA: 92.3 ± 1.7 10 RG164 (n=85/102) 6 2 ) 93 118 4 CH05-CH19 (n=66/107) DA: 96.5 ± 1.4 142 2

12 110 123 DA: 98.1 ± 1.3 8 140 LTA83 (n=83/90) 4 Frequency (# of grains 116 DA: 95.6 ± 1.5 6 98 125 MP96 (n=74/97) 4 178 2

12 95 DA: 96.8 ± 1.6 8 143 180 MP97 (n=82/87) 4

50 100 200 300 400 500 600 Age (Ma) Figure 10. U-Pb detrital zircon results from the Lago Viedma Formation (A) and the Punta Barrosa Formation (B) from the Austral sector of the basin. Data are shown as histograms and probability density plots. N—number of ages shown/number of total ages; DA—depositional age determined by interbedded U-Pb ash ages (Malkowski et al., 2015).

Geological Society of America Bulletin, v. 129, no. 3/4 361 Malkowski et al.

A 278 C Patagonia Arc/Batholith Rocks MRMC 40°S 70°W 65°W Main Range NPM A magmatic arc system has occupied the Metamorphic Complex Chubut Group western margin of Patagonia since Late Juras- (n = 67) samples sic time, as recorded by the southern Patagonia 277 CMC batholith (Hervé et al., 2007). Arc volcanism be- Chonos Metamorphic Complex gan as early as ca. 157 Ma and is thought to have (n = 215) occurred in pulses, which include 157–145 Ma

532 EAMC (J), 144–137 Ma (K1), 136–127 Ma (K2), and 287 Eastern Andean 126–75 Ma (K3) (Fig. 12; Hervé et al., 2007). Metamorphic Complex 1040 MRMC For the purposes of this study, we divided the (n = 478) Golfo San Cretaceous arc age populations into two groups 273 CMC

Relative probability DYMC Jorge Basin (144–127 Ma and 126–75 Ma) by combining Duque de York RB & RT 200 kms the K1 and K2 pulses defined by Hervé et al., Metamorphic Complex samples DM (n = 167) 2007 (Fig. 12). This was done to simplify the EAMC ? 404 Mid Jurassic volcanics number of populations and because the K1 and CDMC (178–152 Ma) K2 age populations represent a small proportion 266 Cordillera Darwin DYMC of detrital ages. 1028 Metamorphic Complex (n = 569) Early Jurassic volcanics (188–168 Ma) 0 500 1000 1500 2000 2500 3000 Summary and Interpretation of Age (Ma) DZ samples without Regional Provenance Trends B 180 199–161 Ma ages A comparison of sandstone compositional Chubut Group Malvinas (n = 171) DZ samples with data from this study with lithostratigraphic 199–161 MaBasi agesn 105 equivalents of the Punta Barrosa Formation Sediment routing 121 Rio Tarde and in the Ultima Esperanza basin sector and the 179 Rio Belgrano Fms. Latorre and upper La Paciencia Formations in CDMC Early Mid Non- Relative probability (n = 152 of 191) 55°S Jur. Jur. Jur. the Fuegian sector (Fildani and Hessler, 2005; 50 100 150 200 250 300 350 75°W 70°W grains 65grains°W grains McAtamney et al., 2011) shows that each of Age (Ma) the basin sectors has a distinguishable sand- Figure 11. (A) U-Pb detrital zircon (DZ) age spectra from Paleozoic metasedimentary (base stone composition (Fig. 13). Sandstone from ment) rocks of southern Patagonia. Gray bars represent common peak age populations of the Punta Barrosa Formation in the Ultima 1200–900 Ma, 550–450 Ma, 410–350 Ma, and 310–260 Ma. (B) U-Pb detrital zircon ages Esperanza sector contains greater abundances from Aptian–Albian strata north of the study area, which also have a significant proportion of quartz and plagioclase feldspar and plots of early Jurassic (ca. 180 Ma) zircon. (C) Map of southern Patagonia highlighting regional within the transitional to dissected arc and re- Early–Middle Jurassic detrital zircon sources and interpreted paleodispersal patterns in the cycled orogen provenance fields (Fig. 13). In Magallanes-Austral Basin. Note that Early to Middle Jurassic zircon is absent in samples contrast, sandstone from the Fuegian sector of south of the Austral basin sector (~50°S). DM—Deseado Massif; NPM—North Patagonia the Magallanes-Austral Basin is enriched in Massif; RB—Rio Belgrano, RT—Rio Tarde. feldspar grains compared to lithostratigraphi- cally equivalent units in the Ultima Esperanza and Austral sectors. Sandstone compositional as the Chon Aike silicic large igneous prov- extending the V3 phase into earliest Early data plotted on the Q-F-L ternary diagram sug- ince (Gust et al., 1985; Pankhurst et al., 1998, Cretaceous time. gest a progressive, albeit subtle, north to south 2000). Associated Jurassic volcanic and vol- The Early Jurassic volcanic pulse (V1) is pattern of arc dissection between early foreland caniclastic rocks are present throughout the perhaps the most diagnostic of these mag- basin deposits from each sector (Fig. 13). Patagonia region and have different names, matic phases, as these ages (ca. 188–178 Ma) We divided the detrital zircon U-Pb age dis- including the Marifil, Chon Aike, Ibañez, El are only known to be present in the Marifil tributions into five age populations that reflect Quemado, and Tobifera Formations (Figs. 2 Formation, which crops out along the North the age ranges of the previously discussed po- and 3; Pankhurst et al., 1998). Ages of vol- Patagonia Massif (Figs. 2 and 11). Recent tential source terranes (Fig. 14): (1) pre-Jurassic canic rocks associated with the Chon Aike studies have suggested that Marifil volcanics ages between 3500 and 200 Ma, (2) Early to large igneous province range from ca. 190 were a primary source for Aptian–Albian flu- Middle Jurassic ages between 199 and 161 Ma, to 150 Ma, but magmatism is inferred to vial deposits of the Chubut Group and the Río (3) Late Jurassic ages between 160 and 145 Ma, have been episodic (Pankhurst et al., 2000). Belgrano–Río Tarde Formations, which are (4) Early Cretaceous ages between 144 and Based on a suite of compiled geochronology located north and south of the Golfo San Jorge 127 Ma, and (5) Early to Late Cretaceous ages data, Pankhurst et al. (2000) proposed three Basin, respectively (Fig. 11; Ghiglione et al., between 126 and 75 Ma. Precambrian-aged zir- major pulses of Jurassic magmatic activity: 2015; Navarro et al., 2015). Although Chon con grains are present, but they are rare (~8% of V1 (188–178 Ma), V2 (172–162 Ma), and V3 Aike volcanism is thought to have migrated all ages; ranging from 2% to 15%). Pre-Jurassic (157–153 Ma). However, more recent work in westward through time, Middle to Upper Ju- ages are interpreted to be derived from Paleozoic the Ultima Esperanza District of Chile sug- rassic volcanic rocks are more broadly dis- metamorphic rocks exposed within the thrust gests that rift volcanism in this region contin- tributed throughout central and southern Pata belt and along the Deseado and North Patagonia ued until ca. 142 Ma (Calderón et al., 2007), gonia (Figs. 2 and 11). Massifs (Fig. 11). Jurassic ages are derived from

362 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

Rifting Compared to the Lago Viedma Formation, Arc magmatism Magmatic pulses K3 K2 K1 J (Herve et al., 2007) detrital zircon samples from Cenomanian-aged Peak magmatism 120–70 Ma (Bruce et al., 1991) deep-water units of the Punta Barrosa Formation 0 50 100 150 200 yield greater variability in source areas. Samples 0 LH157 and LTA83 consist of arc-derived grains, 2 whereas Paleozoic basement sources repre- 4 sent the most abundant population in samples 6 RG164, CH05, MP97, and MP96 (Fig. 11). The 8 SPB Ages robust population of Early to Middle Jurassic n = 164 10 (199–161 Ma) zircon suggests that the paleo drainage network extended north to the North- 12 ern Patagonian Massif (~600 km northeast; Fig. 14 99 11). This population is absent in facies-equiva- 500 1400 lent strata in the Ultima Esperanza and Fuegian basin sectors. Therefore, deep-water slope and

400 fan deposits within the Austral sector were also 1200 sourced, in part, by sediment dispersal systems

147 linked to regional drainages from as far as the Deseado and North Patagonia Massifs (Fig. 11). 1000 300 75 Unlike the results of the Lago Viedma Forma- U-Pb DZ Ages tion, there is no systematic spatial or temporal 800 200 n = 4414 relationship between the samples that do and

(6606) do not have a significant proportion of Early– Middle Jurassic ages. This may be a reflection 600 180 100 17 of deep-water deposits that are at the terminus Frequency 39 of a sediment dispersal system, which are likely 400 to have more integrated provenance signatures compared to higher-order shallow-marine and 283 0 50 100 150 200 fluvial systems (cf. Ingersoll, 1990). Late Cretaceous–modern 200 464 DZ ages from the MAB In summary, sandstone compositional data 371 520 n = 6490 (6606) and detrital zircon geochronology indicate that the Lago Viedma Formation is an arc-derived 0 0 200 400 600 800 1000 1200 1400 unit (Figs. 13 and 14). The Punta Barrosa For- Age (Ma) mation from the Austral sector yields sandstone compositions that are also arc-derived, Figure 12. Compilation of detrital zircon (DZ) ages from Upper Cretaceous (Cenoma but it shows greater variation in detrital zircon nian) and younger deposits within the Magallanes-Austral Basin (MAB) compared with source regions, including significant contribu- published ages from the South Patagonia Batholith (SPB). Note that the peak age popu tions from Lower to Middle Jurassic volcanics lation (ca. 99 Ma) in the detrital zircon data corresponds to a decline in the frequency and Paleozoic grains recycled from metasedi- of batholith ages, indicating an apparent “lull” in magmatic activity or an underrepre mentary rocks within the thrust belt (Figs. 13 sented age population of the batholith. In contrast, peak detrital populations at ca. 147 and 14). Provenance data from the Punta Bar- and 17 Ma correlate well with apparent pulses of magmatism. J, K1, K2, and K3 mag rosa Formation in the Ultima Esperanza sector matic pulses/episodes are from Hervé et al. (2007). Peak magmatism from 120 to 70 Ma show a mix of dissected arc and recycled orogen is after Bruce et al. (1991). U-Pb and K-Ar ages from the South Patagonia Batholith are sources, which is corroborated by detrital zircon from: Halpern (1973); Hervé et al. (1984); Suarez et al. (1987); Bruce et al. (1991); and populations that consist of arc-derived ages and Hervé et al. (2007). Compiled detrital zircon U-Pb ages are from: Fildani et al. (2003); recycled grains from Paleozoic metamorphic Barbeau et al. (2009); Romans et al. (2010); McAtamney et al. (2011); Bernhardt et al. complexes (Figs. 13 and 14; Fildani et al., 2003; (2012); Fosdick et al. (2014); Pepper et al. (2016); Schwartz et al. (2016); and this study. Fildani and Hessler, 2005). Sandstone compositions from the Fuegian basin sector are signifi- cantly different from the other basin sectors; they volcanic and volcaniclastic units associated with nificant provenance shift that suggests drainage are dominantly composed of feldspar, and the the Chon Aike large igneous province exposed reorganization from dominantly arc-derived lithic component consists of recycled sedimen- throughout Patagonia. Finally, Cretaceous-aged (westward) to north- or northeast-derived tary grains (Fig. 13; McAtamney et al., 2011). grains are linked to sources in the Patagonia arc sources. Because sample CP150 comes from However, detrital zircon ages are arc-derived and batholith system along the western margin the uppermost portion of the section on Cerro with secondary contributions from recycled of Patagonia. Pyrámide and contains Turonian-aged zircon, it Paleozoic metasedimentary basement sources The abundance of Cretaceous-aged grains in may represent the lowermost Puesto El Alamo (Fig. 14; McAtamney et al., 2011). Regional, the Lago Viedma Formation indicates that the Formation, which corresponds to a major shift shelf-to-basin comparisons of provenance data arc was the primary detrital source for zircon. in paleocurrent direction and a transition to tidal for the Lago Viedma and Punta Barrosa Forma- The uppermost sample (CP150) records a sig- facies (Canessa et al., 2005). tions show that (1) sediment dispersal systems

Geological Society of America Bulletin, v. 129, no. 3/4 363 Malkowski et al.

N Austral Sector - Lago Viedma Fm. Chile (Wilson, 1991; Fildani and Hessler, 2005; Q Cen. Austral Sector - Punta Barrosa Fm. equivs. Romans et al., 2011), and a minimum thickness Tur. Ult. Esp. Sector - Punta Barrosa Fm. of 300 m is constrained by the most continuous section identified to date that occurs near Brazo S Con. Fuegian Sector - Latorre / U. La Paciencia Fms. Sur (Fig. 4; Malkowski et al., 2015). Although Recycled the variation in sediment caliber (and thickness) Orogenic Qm may in part be explained by their relative po- sition in the depositional setting (i.e., proximal Recycled vs. distal), we speculate that this is also a result Orogenic of sediment sequestration (especially coarser- grained material) on a subsiding shelf. Conse- quently, a southward-prograding depositional BU system that is highlighted in the younger basin Dissected arc fill (Santonian–Maastrichtian units) was not yet Mixed a characteristic feature during the early evolu- Transitional tion of the basin. Furthermore, evidence for a arc Undissected Dissected relatively disconnected depositional system is arc arc also supported by the provenance discrepancies F L discussed in the following.

Transitional Linking Sandstone Provenance from arc Shelf to Deep Basin: Elucidating the Role of Longitudinal versus Transverse FLt Undissected Dispersal Systems arc Figure 13. Comparison of sandstone modal compositions from the Lago Viedma Forma Sandstone modal compositions and detrital tion and Punta Barrosa Formation and regional facies equivalents highlighting north-south zircon signatures in the shallow-marine deposits variability in compositional trends. Provenance fields are from Dickinson et al. (1983). of the Lago Viedma Formation are arc-derived, Sandstone compositional data from the Punta Barrosa Formation in the Ultima Esperanza whereas age-equivalent deep-water slope and (Ult. Esp.) District are from Fildani and Hessler (2005), and data from the facies-equivalent fan deposits to the south consist of mixed de- Latorre and upper La Paciencia Formations are from McAtamney et al. (2011). Polygons trital zircon populations that include arc-derived reflect the standard deviation of point-count results for each sample set. Qm-F-Lt data are grains, Early Jurassic volcanic sources, and not available from the Fuegian sector. Cen.—Cenomanian, Tur.—Turonian, Con.—Conia pre-Jurassic metamorphic basement sources. cian, Q—quartz, F—feldspar, L—lithic rock fragments, Qm—monocrystalline quartz, Lt— The presence of Early–Middle Jurassic zircon total lithics (lithic rock fragments + polycrystalline quartz). BU—basement uplift. (199–161 Ma) in shallow- and deep-water deposits is an indicator that the fluvial systems that transported sediment to this basin extended as were not homogenized between the Austral and cycle, we speculate that numerous smaller-scale far northeast as the North Patagonia or Deseado Ultima Esperanza sectors, (2) shelfal deposits cycles of progradation and retrogradation could Massifs (Fig. 11). However, the presence of arc had a more limited source area than age-equiva- be identified by more detailed study. Such an ac- and recycled orogen signatures in modal sand- lent basinal units, and (3) there is more variation cumulation of shoreface deposits suggests that stone compositions and the abundance of Cre- within and between samples in the deep-water subsidence was sufficient to balance sediment taceous and Paleozoic zircon ages also suggest portions of the basin, suggesting mixing of supply such that shallow-marine deposits were that the deep-water slope and fan deposits of multiple sediment dispersal systems. aggrading rather than prograding. We interpret the Austral basin sector were sourced by tribu this subsidence as a response to foreland flexure taries from the west (Patagonia arc and Eastern DISCUSSION due to loading by the fold-and-thrust belt. Andean metamorphic complex). It is also pos- In contrast, less than 100 km to the south, sible that the Early Jurassic ages were derived Accommodation and Sediment Supply the age-equivalent Punta Barrosa Formation from uplifted and recycled Aptian–Albian strata consists of mudstone and fine- to medium- to the north, which are rich in this population The Lago Viedma Formation at Cerro grained sandstone deposited within slope and (Ghiglione et al., 2015). Pyrámide consists of ~1 km of sandstone and basin-floor deep-water fans (Malkowski et al., In contrast to the Austral sector, Turonian conglomerate deposited along a high-energy, 2015). These strata lack the abundant coarse to Coniacian deep-water strata that record the coarse-grained coastline (cf. Clifton, 2006). sandstone and conglomerate that dominate the onset of coarse clastic deposition in the Ultima The persistence of shallow-marine foreshore shelfal Lago Viedma Formation to the north. Esperanza and Fuegian basin sectors possess and shoreface deposits throughout most of the Although true thickness is difficult to determine distinguishable sandstone compositions and section (800+ m) suggests little variation in with confidence due to thrust-belt deformation, lack the Jurassic ages that represent the Deseado relative sea level or gross depositional environ- the stratigraphic thickness of the Punta Barrosa and North Patagonian Massifs. Instead, they ment, with the exception of a single transgres- Formation is likely much less than that of the were sourced by Patagonia arc rocks and the sive episode (Fig. 5). Although the stratigraphic Lago Viedma Formation. A maximum thickness Paleozoic metamorphic complexes (e.g., East- package represents an overall progradational of ~1000 m is documented near Cerro Ferrier in ern Andean metamorphic complex and Duque

364 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

CP150 (n=108)

CP72 (n=89)

CP68 (n=78)

Austral Sector CP43 (n=96)

CP37a (n=27) edma Fm. - CP41 (n=96) Lago Vi

LENT CP09b (n=95) VA AGE EQUI LH157 (n=104)

Figure 14. Relative probabil RG164 (n=102) ity plots and proportions (pie Austral Sector charts) of detrital zircon ages CH05-CH19 (n=107) from the Lago Viedma For mation and deep-water, coarse MP97 (n=87) clastic deposits of the Punta Barrosa Formation and facies- MP96 (n=97) equivalent units. Samples from the Austral sector show sig LTA83 (n=90) nificantly different zircon age Punta Barrosa Fm. (equivs.) - populations in age-equivalent 50 100 200 3004Age (Ma) 00 500600 (Cenomanian) shallow- and deep-marine strata (top two PB 3-5-3 (n=85) panels). In addition, there is significant along-strike varia

tion in zircon age populations LENT from lithostratigraphic equiva PB 01-04 (n=29) lents (bottom three panels). See text for data references. PB 2-21-3 (n=75) CIES EQUI VA FA PB 2-6-4 (n=32)

PB 3-11-3 (n=66) Punta Barrosa Fm. - Ultima Esperanza Sector

Patagonia arc/batholith: 0993 (n=98) L Cret: 126–75 Ma E. Cret: 144–127 Ma 0998D (n=85)

Chon Aike volcanism: L. Jur: 157–145 Ma 09116 (n=45) E.-M. Jur: 200–157 Ma

0864A (n=84) Other sources: Pre-Jur: 3500–200 Ma 0850 (n=84) Latorre and La Paciencia Fms. - Fuegian Sector 50 100 200 3004Age (Ma) 00 500 600

Geological Society of America Bulletin, v. 129, no. 3/4 365 Malkowski et al. de York metamorphic complex) within the fold- the Zagros foreland fold-and-thrust belt (e.g., Along-Strike Variations in Basin and-thrust belt (Fig. 11; Fildani et al., 2003; Bahroudi and Koyi, 2004). If so, this implies and Thrust-Belt Evolution McAtamney et al., 2011). This indicates that that these transform fault systems were active a simple, north-to-south longitudinal model during the early (Cenomanian) evolution of Several recent studies have highlighted the may not be appropriate. Rather, data from the the Magallanes-Austral foreland basin system, existence of progressive along-strike (north- Austral basin sector suggest a more complex and may have influenced sediment dispersal south) variations in the structural and strati- paleodispersal pattern that includes at least two pathways. graphic evolution of the Magallanes-Austral dispersal systems: (1) the Lago Viedma For- Basin and its predecessor, the Rocas Verdes mation drainage and longshore drift system, Comparison of Batholith Ages with Basin (e.g., Stern and de Wit, 2003; Ghiglione which was arc-derived; and (2) a fluvial system Arc‑Derived Detrital Age Populations et al., 2009; McAtamney et al., 2011; Betka linking the northern Magallanes-Austral Basin et al., 2015; Malkowski et al., 2015, 2016). For to the northeast massifs that delivered Early– Study of ancient volcanic arc systems is ham- instance, the Rocas Verdes Basin likely opened Middle Jurassic zircon to the basin (Fig. 11). pered by variable preservation of the volcanic by “unzipping” via progressive south-to-north Source area variability is also supported by the carapace. Thus, the detrital record preserved rifting (Mukasa and Dalziel, 1996; Stern and ca. 100 Ma slope deposits near Estancia Los within arc-adjacent basins provides a valuable, de Wit, 2003; Malkowski et al., 2016). Addi- Hermanos (Fig. 4), which are older than the time-integrated archive of the long-term evolu- tionally, there is a progressive north-to-south Lago Viedma shoreface sands and yet contain tion of magmatic activity within volcanic arcs increase in the amount of estimated shortening the Early–Middle Jurassic age peak. Thus, out- (e.g., Barth et al., 2013; Sharman et al., 2015). accommodated in the thrust belt from the Aus- of-plane (transverse) and extraregional sedi- In general, the span of detrital ages within the tral sector to the Fuegian sector (Betka et al., ment contributions played a significant role in Magallanes-Austral Basin matches the distribu- 2015). Similarly, the early evolution of the fore- the Austral sector of the basin. tion of batholith ages (Fig. 12). However, one of land basin was characterized by a southward Another obstacle to a longitudinal model is the more striking results of this comparison is progressive onset of deep-marine coarse-clastic the lack of Early–Middle Jurassic ages in the that the peak age population (ca. 99 Ma) from deposition, initiating in Albian time near El oldest sandstone units south of the Magallanes the detrital ages of the Magallanes-Austral Ba- Chalten (~49°S) and perhaps as late as Santo- Peninsula (Fig. 4). The paucity of this age sin corresponds to a relative magmatic lull in the nian–Campanian time in the Fuegian sector population suggests the following interpreta- igneous age population of the South Patagonia (~55°S; Fig. 3; Malkowski et al., 2015). Finally, tions: (1) Deep-water fan systems south of the Batholith. Other detrital peaks (147 and 17 Ma) results from this study highlight both spatial Magallanes Peninsula were sourced by west- correlate well with apparent pulses in magma- and temporal variability in provenance trends ward tributaries that did not tap Lower–Middle tism (Fig. 12). Although numerous factors could from strata representing the early evolution of Jurassic sources; (2) the Jurassic population was contribute to a discrepancy in age populations the foreland basin. These results emphasize the diluted through time and space by westward (e.g., variations in zircon fertility, lack of ages relative importance of transverse sediment sup- tributaries; or (3) Jurassic source rocks were no from inaccessible batholith exposures, sam- ply and demonstrate that a simple longitudinal longer available later in time. Given that Early– pling bias, etc.), the disparity in age frequen- dispersal system cannot account for variations Middle Jurassic volcanic rocks are still in place cies could indicate that (1) the age range of the in provenance, sediment accumulation, and tim- today, and that, to our knowledge, there is no batholith is poorly constrained, and more data ing of deposition during the earliest phases of other independent evidence for major drainage are needed to elucidate its true range, or (2) ca. the basin (Malkowski et al., 2015; this study). reorganization in the northernmost Austral basin 100 Ma batholith rocks have been preferentially In turn, we posit that the diachronous onset sector at this time, we prefer one of the first two exhumed, eroded, and preserved in the sedimen- of coarse-clastic deposition was more likely models. That is, westward transverse tributaries tary record. Bruce et al. (1991) suggested that associated with progressive changes in local were either the only source or were abundant to magmatism associated with the South Patagonia sediment supply and thrust-belt evolution rather the point of diluting any extraregional (Jurassic- Batholith peaked between 120 and 70 Ma. How- than protracted progradation (Figs. 15 and 16). aged) provenance signals. In either case, these ever, Hervé et al. (2007) challenged this asser- Sand was delivered to deep-water depositional interpretations further exemplify the importance tion based on a new suite of data and the notion systems by more proximal thrust-belt sources of transverse tributaries during the early evolu- that the previously published K-Ar and Ar-Ar to the west (i.e., a line source), which fed into tion of the foreland basin. ages may have been influenced (i.e., partially south- to southeast-flowing deep-marine fan The observed provenance trends may also be reset) by more recent tectonism. Of the ~4000 systems (Figs. 15 and 16), akin to sediment dis- due, at least in part, to fault-controlled basin seg- detrital zircon U-Pb ages that are younger than persal in the modern Golo Fan east of Corsica mentation. Previous studies have highlighted to 160 Ma, 67% are between 120 and 70 Ma (Fig. (e.g., Gervais et al., 2004; Deptuck et al., 2008). presence of large, east-west–oriented, transform 12). Thus, the available detrital data support the To account for these variations, we prefer faults along Lago Viedma and Lago Argentino hypothesis by Bruce et al. (1991), i.e., that mag- an oblique arc-continent collisional model that in Argentina and near Torres del Paine, in Chile matism peaked between 120 and 70 Ma. Given includes earlier exhumation (and thrust belt ini- (Ghiglione et al., 2009; Likerman et al., 2013). that the Patagonian arc was such a significant tiation) in the Austral basin sector, which was These transform faults are thought to have de- sediment source for the Magallanes-Austral facilitated by the geometry of the predecessor veloped during the Jurassic rift phase of the ba- Basin, we suggest that the apparent mismatch Rocas Verdes Basin (Fig. 16). This basin mor- sin and were reactivated during the subsequent in zircon age frequencies between the basin fill phology resulted from a narrower and relatively compressional regime (Likerman et al., 2013; and arc sources emphasizes the importance of short-lived rift basin in the north and a wider Ghiglione et al., 2014a). Thus, along-strike continued efforts to better understand the evolu- and deeper basin, floored by oceanic crust, to variations in provenance signatures may also tion of the South Patagonia arc system and the the south (Stern and de Wit, 2003; Malkowski be the result of basin segmentation by large- adjacent Rocas Verdes and Magallanes-Austral et al., 2016). During subsequent closure of scale transform faults such as that observed in Basin systems. the basin, this geometry permitted an earlier,

366 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

Figure 15. Cenomanian–Turonian Collision–Suturing–Exhumation Cenomanian-Turonian Piedra Clavada Fm paleogeographic reconstruction (100–89 Ma) o shallows marine - fluvial based on new results from this ggo FFmm LagoLLaaag a F Mata 1 mma study combined with those of Mal ededdm Amarilla Fm kowski et al. (2015). This work em ViV edmae Fm. A phasizes the relative importance of transverse sources within the 2 PPuntunta B northern basin sector rather than BBarrosaarrosa Fm a simple longitudinal drainage sys 3 tem fed by a northerly point source C (Fig. 1). Dashed lines indicate the underfilled approximate locations of previ deep-water basin ously proposed transform fault systems, highlighting their poten tial influence on sediment routing 1 El Chalten, Argentina 2 Argentina/Chile Border 3 Ultima Esperanza, Chile systems (see text for discussion and references). A Lago Viedma Transform (?) B Lago Argentino Transform (?) C Torres del Paine Transform (?)

oblique collision or suturing at the northern end ABLate Jurassic to late Early Cretaceous early Early Cretaceous (Aptian–Albian) of the system between the parautochthonous arc-continent ‘collision’ Opening arc terrane (Jurassic–Early Cretaceous arc and South Atlantic Ocean Paleozoic metamorphic rocks) and continen- South So tal South America (Fig. 16); in contrast, in the u

(attenuated crust) America - Gondwana Fuegian sector, an entire ocean basin (hundreds America (attenuated

agonia t of kilometers wide) needed to close before a similar “collisional” event occurred. South of

nous Pa 50°S, progressive southward closure of the o Rocas Verdes Basin resulted in both the obduction of ophiolite complexes as well as westward Rocas Verdes ? cr

arautochth underthrusting of oceanic and continental crust Parautochthonous Patagonia backarc basin us P t) (Klepeis et al., 2010; Calderón et al., 2013). ? volcanic arc on Paleozoic basement Closure of the Rocas Verdes Basin and subse- Closure of Rocas Verdes Basin quent development of a successor foreland fold- and-thrust belt during arc-continent collision late Early Cretaceous to early Late Late Cretaceous CDCretaceous (Albian–Cenomanian) (Cenomanian–Turonian) resulted in southward progressive suturing, exhumation, and sediment delivery to the foredeep

South

South (Fig. 16; cf. Graham et al., 1975). We further suggest that the Jurassic–Creta-

ia southward America (attenuated crust) propagating A merica ceous tectonic evolution preserved in the south- thrust belt

agon ‘suturing’ t ern Patagonian Andes is analogous to modern

(attenuated crust) tectonic settings observed along the western

nous Pacific margin (Fig. 17). That is, opening of the

o Obducted ophiolite Rocas Verdes Basin in a backarc setting is like complexes

tochth that of the modern Sea of Japan, which includes

u Magallanes deep-water basins floored by oceanic crust that transition Para basin along strike to more attenuated continental crust Parautochthonous Patagonia

? Obducted ophiolite (Fig. 17; Dalziel et al., 1974; Ingle, 1992; Fildani complexes and Hessler, 2005; Malkowski et al., 2016). Dur- ing the Miocene, the Japanese arc system rifted Figure 16. Schematic diagram of the Cretaceous tectonic evolution of the Patagonian Andes. away from Korea by continental rift volcanism (A) Late Jurassic–Early Cretaceous northward progressive rifting in the predecessor Rocas induced by backarc spreading, which culmi- Verdes backarc basin yielding a wider ocean basin in the south and narrow (and shallower) nated in basaltic seafloor magmatism (Pouclet basin in the north; (B) oblique Aptian–Albian collision initiation at the northern end of the et al., 1994). Incipient closure of the Sea of basin between the parautochthonous Patagonia terrane and attenuated continental crust Japan began as recently as Pliocene–Pleistocene of South America; (C) Albian–Cenomanian progressive southward suturing and initia time and is therefore only in the initial stages tion of coarse clastic deposition and foreland basin establishment in the Austral basin sec of basin transition (e.g., Taira, 2001). Thus, an tor (~49°S); (D) continued southward suturing and coarse clastic deposition, reaching the additional analogue for the foreland basin stage Ultima Esperanza basin sector (~51°S) by Cenomanian–Turonian time. of the Magallanes-Austral Basin is found near

Geological Society of America Bulletin, v. 129, no. 3/4 367 Malkowski et al.

cannot be characterized by any one “classic” ba- A Amur Plate sin type (see discussion in Romans et al., 2010); however, it does represent an excellent example of a “successor” foreland basin (Eisbacher Russia et al., 1974; Graham et al., 1993; Fosdick et al., n 2014; Malkowski et al., 2015). Given that there

N. Korea are numerous examples of ancient and modern Sea of Japan e Figure 17. Modern tectonic successor foreland basin systems, the tectonic backarc ocean basi Pacific Ocean analogues corresponding to and stratigraphic evolution of the Magallanes- m the multiphase basin evolution Austral Basin is not unique or enigmatic; rather, incipient closur ench we argue the only unique aspect of this system S. Korea Tr preserved in the southern Pata is that it is well preserved. Pacific Plate gonian Andes. (A) The Ceno Japan arc syste apan J zoic evolution of the Sea of 1200km Japan is analogous to opening CONCLUSIONS of the Late Jurassic–Early Cre B 1200km Sedimentologic, stratigraphic, and prov- ent ough taceous Rocas Verdes backarc n Tr enance data from early coarse-clastic deposits wa basin, and (B) oblique collision -contin c collisio of the Magallanes-Austral Basin provide novel Ar Okina between the Taiwan-Luzon arc China chh insights into the Cenomanian–Turonian depo- ennch system with the Asian continent TTrree u T sitional history, paleogeography, and tectonic n ky is analogous to the oblique arc- yuyuk iwa RyukRyR y evolution of the Patagonian Andes. The Late Ta continent collisional proposed in this study. Cretaceous (Cenomanian) Lago Viedma Forma- sediment tion is interpreted as a succession of mostly near- Philippine Sea dispersal shore and shoreface deposits along a wave- and storm-influenced shoreline. Sandstone compositions from the Lago Viedma Formation consist

South China Sea n Luzon of intermediate lithic volcanic grains and plot h

Trench c within the undissected to transitional arc prov-

ren T enance fields. These results are corroborated East Luzo

Manila by detrital zircon age populations of mostly Cretaceous-aged grains, sourced by the Andean arc. Age-equivalent strata representing the deep- the South China, Sea where collision between 2010; Calderón et al., 2013), placing the early water portion of the Austral basin sector are also the Taiwan–Luzon arc system and continental evolution of the southern Magallanes-Austral arc-derived (compositionally), but they yield Asia forms the uplifted island of Taiwan (Fig. Basin into a peripheral foreland setting. Second, variable detrital zircon age proportions that in- 17). This system consists of a foreland fold-and- there is a concurrent reversal in subduction po- clude Early Jurassic and pre-Jurassic grains, thrust belt at the northern end and transitions larity north of Taiwan, which is kinematically which were likely sourced from the North Pata southward to a relatively sediment-starved rem- linked with the southward-oblique collision gonian Massif and Paleozoic metasedimentary nant ocean basin in the South China Sea where between Taiwan and China (e.g., Suppe, 1984). rocks. Variations in provenance trends between collision has not yet occurred (Ingersoll et al., Although a similar geodynamic response is age-equivalent units suggest that the deep-water 1995). Although supply is limited, sediment is not widely recognized for regions north of the depositional systems that represent the early fill derived from the uplifted suture and dispersed Magallanes-Austral Basin, there is recent evi- of the Magallanes-Austral Basin were not fed axially to the south where young turbidite sys- dence for northeast-southwest extension in the by a single, shallow-marine point source to the tems (e.g., deep-water canyons and channels) Golfo San Jorge Basin during Late Cretaceous north, but rather by sources that contained more are beginning to develop (Teng, 1990; Huang and Paleogene time (Foix et al., 2012). Early Jurassic and Paleozoic ages, which may et al., 1992; Ingersoll et al., 1995; Hsiung et al., Finally, one might predict that continued con- include sources from the northeast (e.g., North 2015). We recognize that there are some critical vergent margin evolution of both the Japan and Patagonia Massif) and Paleozoic rocks to the distinctions between the proposed models for Taiwan systems could yield foreland fold-and- west associated with the Eastern Andean meta- the Magallanes-Austral Basin and the current thrust belt systems with many similar character- morphic complex. Turonian–Coniacian deep- setting of the South China Sea and Taiwan arc istics to that of the Magallanes-Austral Basin, water deposits that record the onset of foreland system. For instance, eastward-verging thrusts such as thick successions of deep-water strata, basin sedimentation in the central and southern along western Taiwan and subduction along the along-strike variations in kinematic shortening, parts of the Magallanes-Austral Basin (Ultima Manila Trench place the Taiwan foreland in a obduction of variable ophiolitic complexes, and Esperanza and Fuegian sectors) yield detrital zir- peripheral foreland basin setting, whereas the diachronous and longitudinal depositional sys- con provenance signatures that can be explained Magallanes-Austral Basin is generally charac- tems. Despite the abundance of backarc ocean by local (westward) sources in the fold-and- terized as a retroarc foreland basin. However, as basins along the western Pacific margin, tec- thrust belt. Distinguishable provenance trends previously mentioned, recent work has shown tonic and sedimentary analogues of such sys- may also have been facilitated by segregation evidence to support westward underthrusting, tems are rare in the rock record because their of depocenters associated with reactivated east- albeit short-lived, of oceanic and continental preservation potential is low (Ingersoll, 2011). west transform faults along Lago Viedma, Lago crust beneath the Patagonian arc (Klepeis et al., The Magallanes–Austral foreland basin system Argentino, and near Torres del Paine, Chile.

368 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

Numerous systematic, along-strike variations eds., Facies Models 4: St. John’s, Newfoundland, Geo- Clifton, H.E., 2006, A reexamination of facies models for logical Association of Canada, p. 295–322. clastic shorelines, in Posamentier, H.W., and Walker, characterize the structural and stratigraphic evo- Bahroudi, A., and Koyi, H.A., 2004, Tectono-sedimentary R.G., eds., Facies Models Revisited: Society for Sedi- lution of the southern Patagonian Andes. Fore- framework of the Gachsaran Formation in the Zagros mentary Geology (SEPM) Special Publication 84, land fold-and-thrust belt variations in kinematic foreland basin: Marine and Petroleum Geology, v. 21, 293 p. no. 10, p. 1295–1310, doi:10.1016/j.marpetgeo.2004 Clifton, H.E., Hunter, R.E., and Phillips, R.L., 1971, Deposi- shortening, diachronous initiation of coarse .09.001. tional structures and processes in the non-barred high- clastic deposition, and the provenance of early Barbeau, D.L., Olivero, E.B., Swanson-Hysell, N.L., Zahid, energy nearshore: Journal of Sedimentary Research, K.M., Murray, K.E., and Gehrels, G.E., 2009, Detrital- v. 41, no. 3, p. 651–670. foreland sedimentation can be explained by an zircon geochronology of the eastern Magallanes fore- Covault, J.A., Romans, B.W., and Graham, S.A., 2009, Out- arc-continent collision model along obliquely land basin: Implications for Eocene kinematics of the crop expression of a continental-margin-scale shelf- aligned margins. Collision and suturing between northern Scotia Arc and Drake Passage: Earth and edge delta from the Cretaceous Magallanes Basin, Planetary Science Letters, v. 284, no. 3–4, p. 489–503, Chile: Journal of Sedimentary Research, v. 79, p. 523– a parautochthonous Patagonia arc terrane and doi:10.1016/j.epsl.2009.05.014. 539, doi:10 .2110 /jsr .2009 .053 . attenuated continental crust of South America Barth, A.P., Wooden, J.L., Jacobson, C.E., and Economos, Crane, W.H., and Lowe, D.R., 2008, Architecture and evolu- initiated near the northern terminus of the basin R.C., 2013, Detrital zircon as a proxy for tracking the tion of the Paine channel complex, Cerro Toro Forma- magmatic arc system: The California arc example: Geol tion (Upper Cretaceous), Silla syncline, Magallanes and migrated southward through time. In doing ogy, v. 41, no. 2, p. 223–226, doi:10.1130/G33619.1. Basin, Chile: Sedimentology, v. 55, p. 979–1009, doi: so, southward progressive suturing (including Bernhardt, A., Jobe, Z., Grove, M., and Lowe, D., 2012, 10.1111/j.1365-3091.2007.00933.x. Paleogeog raphy and diachronous infill and of an an- Dalziel, I.W.D., de Wit, M.J., and Palmer, K.F., 1974, Fossil thrust faulting and uplift) resulted in the diach cient deep-marine foreland basin, Upper Cretaceous marginal basin in the southern Andes: Nature, v. 250, ronous initiation of coarse clastic deposition Cerro Toro Formation, Magallanes Basin: Basin Re- p. 291–294, doi:10.1038/250291a0. from locally derived sources. Prior to collision, search, v. 23, p. 1–26. DeCelles, P.G., 2012, Foreland basin systems revisited: Betka, P., Klepeis, K., and Mosher, S., 2015, Along-strike Variations in response to tectonic settings, in Busby, oblique arc-continent alignment was facilitated variation in crustal shortening and kinematic evolu- C., and Azor, A., eds., Tectonics of Sedimentary Ba- by a north-south gradient in the extent of rift- tion of the base of a retroarc fold-and-thrust belt: sins: Recent Advances: Chichester, UK, John Wiley & ing during the predecessor Rocas Verdes Basin Magallanes, Chile 53°S–54°S: Geological Society of Sons, Ltd., doi:10.1002/9781444347166.ch20. America Bulletin, v. 127, no. 7–8, p. 1108–1134, doi: Deptuck, M.E., Piper, D.J.W., Savoye, B., and Gervais, A., phase. Thus, the southern Patagonian Andes 10.1130/B31130.1. 2008, Dimensions and architecture of late Pleisto- highlight the transitional nature of convergent Biddle, K.T., Uliana, M.A., Mitchum, R.M., Jr., Fitzgerald, cene submarine lobes off the northern margin of East M.G., and Wright, R.C., 1986, The stratigraphic Corsica: Sedimentology, v. 55, no. 4, p. 869–898, doi: margin basins with the preservation of multiple and structural evolution of the central and eastern 10.1111/j.1365-3091.2007.00926.x. basin phases through Jurassic–Cenozoic time. Magallanes Basin, southern South America, in Allen, De Ruig, M.J., and Hubbard, S.M., 2006, Seismic facies P.A., and Homewood, P., eds., Foreland Basins: Inter- and reservoir characteristics of a deep-marine channel ACKNOWLEDGMENTS national Association of Sedimentologists Special Pub- belt in the Molasse foreland basin, Puchkirchen For- lication 8, p. 41–61, doi:10.1002/9781444303810.ch2. mation, Austria: American Association of Petroleum Funding for this research was provided by the Bouma, A.H., 1962, Sedimentology of Some Flysch Depos- Geologists Bulletin, v. 90, p. 735–752, doi:10 .1306 industrial affiliates of the Stanford Project On Deep- its: Amsterdam, Elsevier, 168 p. /10210505018. water Depositional Systems (SPODDS) and by sup- Bruce, R.M., Nelson, E.P., Weaver, S.G., and Lux, D.R., de Wit, M.J., and Stern, C.R., 1981, Variations in the degree 1991, Temporal and spatial variations in the southern of crustal extension during formation of a back-arc port from the McGee and Leverson graduate research Patagonian batholith; constraints on magmatic arc de- basin: Tectonophysics, v. 72, p. 229–260, doi:10 .1016 grants. We are grateful for the long-standing coopera- velopment, in Harmon, R.S., and Rapela, C.W., eds., /0040-1951(81)90240-7. tion from the owners and managers of the Estancias Andean Magmatism and its Tectonic Setting: Geologi- Dickinson, W.R., 1970, Relations of andesites, granites, and Nibepo Aike, La Quinta, Los Hermanos, Canigo, and cal Society of America Special Paper 265, p. 1–12, doi: derivative sandstones to arc-trench tectonics: Reviews San Jose, as well as the administration of the Parque 10.1130/SPE265-p1, doi:10.1130/SPE265-p1. of Geophysics, v. 8, no. 4, p. 813–860, doi:10 .1029 Nacional Los Glaciares of Argentina for providing Burbank, D.W., 1992, Causes of recent Himalayan uplift /RG008i004p00813. access to these outcrops. We thank Corey Steimel, deduced from deposited patterns in the Ganges basin: Dickinson, W.R., and Suczek, C.A., 1979, Plate tectonics Marcos Calo, and Mariano Valdez for their help with Nature, v. 357, p. 680–683, doi:10.1038/357680a0. and sandstone compositions: American Association of Calderón, M., Fildani, A., Hervé, F., Fanning, C.M., Weis Petroleum Geologists Bulletin, v. 63, p. 2164–2182. field work and Trevor Dumitru for assistance with logel, A., and Cordani, U., 2007, Late Jurassic bimodal Dickinson, W.R., Beard, L.S., Brakenridge, G.R., Erja- heavy mineral separations. Thanks also go to Nadja magmatism in the northern sea-floor remnant of the vec, J.L., Ferguson, R.C., Inman, K.R., Knepp, R.A., Drabon, George Gehrels, Mark Pecha, and the Ari- Rocas Verdes basin, southern Patagonian Andes: Jour- Lindberg, F.A., and Ryberg, P.T., 1983, Provenance of zona LaserChron staff members for their help with nal of the Geological Society London, v. 164, p. 1011– North American Phanerozoic sandstones in relation to geochronology analyses. This work has benefited 1022, doi:10.1144/0016-76492006-102. tectonic setting: Geological Society of America Bulle- greatly from insights and conversations with Ed Clif- Calderón, M., Prades, C.F., Herve, F., Avendaño, V., Fan- tin, v. 94, p. 222–235, doi:10.1130/0016-7606(1983)94 ton, Andrea Fildani, Julie Fosdick, Marty Grove, and ning, C.M., Massonne, H.J., Theye, T., and Simonetti, <222:PONAPS>2.0.CO;2. Brian Romans. We thank Stephen Johnston, John A., 2013, Petrological vestiges of the Late Jurassic– Dumas, S., and Arnott, R.W.C., 2006, Origin of hummocky Early Cretaceous transition from rift to back-arc ba- and swaley cross-stratification—The controlling influ- Wakabayashi, and an anonymous reviewer for their sin in southernmost Chile: New age and geochemical ence of unidirectional current strength and aggradation insightful comments and suggestions toward improv- data from the Capitán Aracena, Carlos III, and Tortuga rate: Geology, v. 34, no. 12, p. 1073–1076, doi:10 .1130 ing the quality and clarity of this manuscript. ophiolitic complexes: Geochemical Journal, v. 47, /G22930A.1. no. 2, p. 201–217, doi:10.2343/geochemj.2.0235. Eisbacher, G.A., Carrigy, M.A., and Campbell, R.B., 1974, REFERENCES CITED Canessa, N.D., Poiré, D.G., and Doyle, P., 2005, Estrati- Paleodrainage pattern and late-orogenic basins of the grafía de las unidades cretácicas de la margen norte del Canadian Cordillera, in Dickinson, W.R., ed., Tecton- Aguirre-Urreta, M.B., 2002, Inverbrados del Cretácico Infe- Lago Viedma, entre el Cerro Pirámides y la Estancia ics and Sedimentation: Society for Sedimentary Geol- rior, in Haller, M.J., ed., Geología y Recursos Naturales Santa Margarita, Provincia de Santa Cruz, República ogy (SEPM) Special Publication 22, p. 143–166, doi: de Santa Cruz, Relatorio del 15th Congreso Geológico Argentina: La Plata, Actas del XVI Congreso Geo 10.2110/pec.74.22.0143. Argentino: Buenos Aires, El Calafate, p. 439–459. lógico Argentino, v. 16, p. 157–164. Faúndez, V., Hervé, F., and Lacassie, J.P., 2002, Provenance Arbe, H.A., 2002, Análisis estratigráfico del Cretácico de Cheel, R.J., and Leckie, D.A., 1992, Coarse-grained storm and depositional setting of pre–Late Jurassic turbidite la cuenca Austral (Stratigraphic analysis of the Creta- beds of the Upper Cretaceous Chungo Member (Wapiabi complexes in Patagonia, Chile: New Zealand Journal ceous of the Austral Basin), in Haller, M.J., ed., Geo Formation), southern Alberta, Canada: Journal of Sedi- of Geology and Geophysics, v. 45, no. 4, p. 411–425, logía y Recursos Naturales de Santa Cruz, Relatario del mentary Research, v. 62, no. 6, p. 933–945. doi:10.1080/00288306.2002.9514982. 15th Congreso Geológico Argentino: Buenos Aires, El Chernicoff, C.J., Zappettini, E.O., Santos, J.O., McNaugh- Fildani, A., and Hessler, A.M., 2005, Stratigraphic record Calafate, p. 103–128. ton, N.J., and Belousova, E., 2013, Combined U-Pb across a retroarc basin inversion: Rocas Verdes– Armitage, D.A., Romans, B.W., Covault, J.A., and Graham, SHRIMP and Hf isotope study of the late Paleozoic Magallanes Basin, Patagonian Andes, Chile: Geologi- S.A., 2009, The influence of mass transport deposit Yaminué complex, Rio Negro Province, Argentina: Im- cal Society of America Bulletin, v. 117, p. 1596–1614, topography on the evolution of turbidite architecture: plications for the origin and evolution of the Patagonia doi:10.1130/B25708.1. The Sierra Contreras, Tres Pasos Formation (Creta- composite terrane: Geoscience Frontiers, v. 4, no. 1, Fildani, A., Cope, T.D., Graham, S.A., and Wooden, J.L., ceous), southern Chile: Journal of Sedimentary Re- p. 37–56, doi:10.1016/j.gsf.2012.06.003. 2003, Initiation of the Magallanes foreland basin: Tim- search, v. 79, p. 287–301, doi:10.2110/jsr.2009.035. Clifton, H.E., 1969, Beach lamination: Nature and origin: ing of the southernmost Patagonian Andes orogeny re- Arnott, R.W.C., 2010, Deep-marine sediments and sedimen- Marine Geology, v. 7, p. 553–559, doi:10 .1016/0025 vised by detrital zircon provenance analysis: Geology, tary systems, in James, N.P., and Dalrymple, R.W., -3227(69)90023-1. v. 31, p. 1081–1084, doi:10.1130/G20016.1.

Geological Society of America Bulletin, v. 129, no. 3/4 369 Malkowski et al.

Foix, N., Paredes, J.M., and Giacosa, R.E., 2012, Upper Cre- Hervé, M., Suárez, M., and Puig, A., 1984, The Patagonian Kraemer, P.E., and Riccardi, A.C., 1997, Estratigrafía de taceous–Paleocene extensional phase in the Golfo San batholith S of Tierra del Fuego, Chile: Timing and tec- la region comprendida entre los lagos Argentino y Jorge basin (Argentina): Growth-fault model, paleo- tonic implications: Journal of the Geological Society of Viedma (49°40′–50°10′ lat. S), Provincia de Santa seismicity and paleostress analysis: Journal of South London, v. 141, no. 5, p. 909–917, doi:10 .1144/gsjgs Cruz: Revista de la Asociación Geológica Argentina, American Earth Sciences, v. 33, no. 1, p. 110–118, doi: .141.5.0909. v. 52, p. 333–360. 10.1016/j.jsames.2011.07.005. Hsiung, K.H., and Yu, H.S., 2011, Morpho-sedimentary Lawton, T.F., Schellenbach, W.L., and Nugent, A.E., 2014, Fosdick, J.C., Graham, S.A., and Hilley, G.E., 2014, Influ- evidence for a canyon–channel–trench interconnection Late Cretaceous fluvial-megafan and axial-river sys- ence of attenuated lithosphere and sediment loading on along the Taiwan–Luzon plate margin, South China tems in the southern Cordilleran foreland basin: Drip flexure of the deep-water Magallanes retroarc foreland Sea: Geo-Marine Letters, v. 31, p. 215–226, doi:10 Tank Member of Straight Cliffs Formation and adja- basin, Southern Andes: Tectonics, v. 33, p. 2505–2525, .1007/s00367-010-0226-7. cent strata, southern Utah, USA: Journal of Sedimen- doi:10.1002/2014TC003684. Hsiung, K.H., Yu, H.S., and Su, M., 2015, Sedimentation in tary Research, v. 84, no. 5, p. 407–434, doi:10.2110 Gervais, A., Savoye, B., Piper, D.J., Mulder, T., Cremer, M., a remnant ocean basin off SW Taiwan with implication /jsr.2014.33. and Pichevin, L., 2004, Present morphology and depo- for closing of the northeastern South China Sea: Jour- Lewis, K.B., 1994, The 1500-km-long Hikurangi Channel: sitional architecture of a sandy confined submarine nal of the Geological Society of London, v. 172, no. 5, Trench-axis channel that escapes its trench, crosses system: The Golo turbidite system (eastern margin of p. 641–647, doi:10.1144/jgs2014-077. a plateau, and feeds a fan drift: Geo-Marine Letters, Corsica), in Lomas, S., and Joseph, P., eds., Confined Huang, C.Y., Shyu, C.T., Lin, S.B., Lee, T.Q., and Sheu, v. 14, p. 19–28, doi:10.1007/BF01204467. Turbidite Systems: Geological Society of London Spe- D.D., 1992, Marine geology in the arc-continent col- Likerman, J., Burlando, J.F., Cristallini, E.O., and Ghig cial Publication 222, p. 59–89, doi:10.1144/GSL.SP lision zone off southeastern Taiwan: Implications for lione, M.C., 2013, Along-strike structural variations in .2004.222.01.05. late Neogene evolution of the Coastal Range: Marine the southern Patagonian Andes: Insights from physical Ghiglione, M.C., Suarez, F., Ambrosio, A., Da Poian, G., Geology, v. 107, no. 3, p. 183–212, doi:10 .1016/0025 modeling: Tectonophysics, v. 590, p. 106–120, doi:10 Cristallini, E.O., Pizzio, M.F., and Reinoso, R.M., -3227(92)90167-G. .1016/j.tecto.2013.01.018. 2009, Structure and evolution of the Austral Basin Hubbard, S.M., Romans, B.W., and Graham, S.A., 2008, MacEachern, J.A., Pemberton, S.G., Gingras, M.K., and fold-thrust belt, southern Patagonian Andes: Revista de Deep-water foreland basin deposits of the Cerro Toro Bann, K.L., 2010, Ichnology and facies models, in la Asociación Geológica Argentina, v. 65, p. 215–226. Formation, Magallanes Basin, Chile: Architectural ele- James, M.P., and Dalrymple, R.W., eds., Facies Models Ghiglione, M.C., Likerman, J., Barberón, V., Beatriz ments of a sinuous basin axial channel belt: Sedimen- 4: St. John’s, Newfoundland, Geological Association Giambiagi, L., Aguirre-Urreta, B., and Suarez, F., tology, v. 55, p. 1333–1359, doi:10.1111/j.1365-3091 of Canada, GEOtext 6, p. 19–58. 2014a, Geodynamic context for the deposition of .2007.00948.x. Malkowski, M.A., Sharman, G.R., Graham, S.A., and coarse-grained deep-water axial channel systems in Hubbard, S.M., Fildani, A., Romans, B.W., Covault, J.A., Fildani, A., 2015, Characterisation and diachron- the Patagonian Andes: Basin Research, v. 26, no. 6, and McHargue, T.R., 2010, High-relief slope clino- ous initiation of coarse clastic deposition in the p. 726–745, doi:10.1111/bre.12061. form development: Insights from outcrop, Magallanes Magallanes-Austral foreland basin, Patagonian Andes: Ghiglione, M.C., Naipauer, M., Sue, C., Barberón, V., Va- Basin, Chile: Journal of Sedimentary Research, v. 80, Basin Research (in press), doi:10.1111/bre.12150. lencia, V., Aguirre-Urreta, B., and Ramos, V.A., 2015, no. 5, p. 357–375, doi:10.2110/jsr.2010.042. Malkowski, M.A., Grove, M., and Graham, S.A., 2016, Un- U-Pb zircon ages from the northern Austral basin and Ingersoll, R.V., 1990, Actualistic sandstone petrofacies: Dis- zipping the Patagonian Andes—Long-lived influence their correlation with the Early Cretaceous exhuma- criminating modern and ancient source rocks: Geol- of rifting history on foreland basin evolution: Litho- tion and volcanism of Patagonia: Cretaceous Research, ogy, v. 18, no. 8, p. 733–736, doi:10.1130/0091-7613 sphere, v. 8, no. 1, p. 23–28, doi:10.1130/L489.1. v. 55, p. 116–128, doi:10.1016/j.cretres.2015.02.006. (1990)018<0733:ASPDMA>2.3.CO;2. McAtamney, J., Klepeis, K., Mehrtens, C., Thomson, S., Graham, S.A., Dickinson, W.R., and Ingersoll, R.V., 1975, Ingersoll, R.V., 2011, Tectonics of sedimentary basins, with Betka, P., Rojas, L., and Snyder, S., 2011, Along-strike Himalayan-Bengal model for flysch dispersal in the revised nomenclature, in Busby, C., and Azor, A., eds., variability of back-arc basin collapse and the initiation Appalachian-Ouachita system: Geological Society of Tectonics of Sedimentary Basins: Recent Advances: of sedimentation in the Magallanes foreland basin, America Bulletin, v. 86, no. 3, p. 273–286, doi:10 .1130 Chichester, UK, John Wiley & Sons, Ltd., doi:10 .1002 southernmost Andes (53–54.5°S): Tectonics, v. 30, /0016-7606(1975)86<273:HMFFDI>2.0.CO;2. /9781444347166.ch1. no. 5, TC5001, doi:10.1029/2010TC002826. Graham, S.A., Hendrix, M.S., Wang, L.B., and Carroll, Ingersoll, R.V., Bullard, T.F., Ford, R.L., Grimm, J.P., Meilan, D., and Maza, A.E., 1994, Mapa Geologico de la A.R., 1993, Collisional successor basins of western Pickle, J.D., and Sares, S.W., 1984, The effect of grain Provincia de Santa Cruz Republica Argentina: San China: Impact of tectonic inheritance on sand compo- size on detrital modes: A test of the Gazzi-Dickinson Martin, Secretaria de Mineria Direccion Nacional del sition: Geological Society of America Bulletin, v. 105, point-counting method: Journal of Sedimentary Re- Servicio Geologico Argentino, scale 1:750,000. no. 3, p. 323–344, doi:10.1130/0016-7606(1993)105 search, v. 54, no. 1, p. 103–116. Moreira, P., Fernández, R., Hervé, F., Fanning, C.M., and <0323:CSBOWC>2.3.CO;2. Ingersoll, R.V., Graham, S.A., and Dickinson, W.R., 1995, Schalamuk, I.A., 2013, Detrital zircons U-Pb SHRIMP Gust, D.A., Biddle, K.T., Phelps, D.W., and Uliana, M.A., Remnant ocean basins, in Busby, C.J., and Ingersoll, ages and provenance of La Modesta Formation, Pata 1985, Associated Middle to Late Jurassic volcanism R.V., eds., Tectonics of Sedimentary Basins: Cam- gonia Argentina: Journal of South American Earth and extension in southern South America: Tectono- bridge, UK, Blackwell Science, p. 363–391. Sciences, v. 47, p. 32–46, doi:10.1016/j.jsames.2013 physics, v. 116, no. 3–4, p. 223–253, doi:10 .1016/0040 Ingle, J.C., 1992, Subsidence of the Japan Sea: Stratigraphic .05.010. -1951(85)90210-0. evidence from ODP sites and onshore sections, in Mukasa, S.B., and Dalziel, I.W., 1996, Southernmost Andes Halpern, M., 1973, Time of folding of the Yahgan Formation Tamaki, K., Suyehiro, K., Allan, J., McWilliams, M., and South Georgia Island, North Scotia Ridge: Zircon and age of the Tekenika beds, southern Chile, South et al., eds., Proceedings of the Ocean Drilling Program, U-Pb and muscovite 40Ar/39Ar age constraints on tec- America: Reply: Geological Society of America Bulle- Scientific Results Volume 127: College Station, Texas, tonic evolution of southwestern Gondwanaland: Jour- tin, v. 84, no. 3, p. 1113–1114, doi:10.1130/0016-7606 Ocean Drilling Program, p. 1197–1218. nal of South American Earth Sciences, v. 9, no. 5–6, (1973)84<1113:TOFOTY>2.0.CO;2. Janecke, S.U., VanDenburg, C.J., Blankenau, J.J., and p. 349–365, doi:10.1016/S0895-9811(96)00019-3. Hart, B.S., and Plint, A.G., 1995, Gravelly shoreface and M’gonigle, J.W., 2000, Long-distance longitudinal Navarro, E.L., Astini, R.A., Belousova, E., Guler, M.V., and beachface deposits, in Plint, A.G., ed., Sedimentary transport of gravel across the Cordilleran thrust belt of Gehrels, G., 2015, Detrital zircon geochronology and Facies Analysis: A Tribute to the Research and Teach- Montana and Idaho: Geology, v. 28, no. 5, p. 439–442, provenance of the Chubut Group in the northeast of ing of Harold G. Reading: Oxford, UK, Blackwell Pub- doi:10.1130/0091-7613(2000)28<439:LLTOGA>2.0 Patagonia, Argentina: Journal of South American Earth lishing Ltd., doi:10.1002/9781444304091.ch4. .CO;2. Sciences, v. 63, p. 149–161, doi:10.1016/j.jsames.2015 Hervé, F., Fanning, C., and Pankhurst, R., 2003, Detrital zir- Jobe, Z.R., Bernhardt, A., and Lowe, D.R., 2010, Facies and .07.006. con age patterns and provenance of the metamorphic architectural asymmetry in a conglomerate-rich sub- Pankhurst, R.J., Leat, P.T., Sruoga, P., Rapela, C.W., Márquez, complexes of southern Chile: Journal of South Ameri- marine channel fill, Cerro Toro Formation, Sierra del M., Storey, B.C., and Riley, T.R., 1998, The Chon Aike can Earth Sciences, v. 16, p. 107–123, doi:10.1016 Toro, Magallanes Basin, Chile: Journal of Sedimentary province of Patagonia and related rocks in West Ant- /S0895-9811(03)00022-1. Research, v. 80, p. 1085–1108, doi:10.2110/jsr.2010 arctica: A silicic large igneous province: Journal of Hervé, F., Pankhurst, R.J., Fanning, C.M., Calderón, M., .092. Volcanology and Geothermal Research, v. 81, no. 1–2, and Yaxley, G.M., 2007, The South Patagonian batho- Katz, H.R., 1963, Revision of Cretaceous stratigraphy in p. 113–136, doi:10.1016/S0377-0273(97)00070-X. lith: 150 my of granite magmatism on a plate margin: Patagonian Cordillera of Ultima Esperanza, Magallanes Pankhurst, R.J., Riley, T.R., Fanning, C.M., and Kelley, S.P., Lithos, v. 97, no. 3–4, p. 373–394, doi:10.1016/j.lithos Province, Chile: American Association of Petroleum 2000, Episodic silicic volcanism in Patagonia and the .2007.01.007. Geologists Bulletin, v. 47, p. 506–524. Antarctic Peninsula: Chronology of magmatism associ- Hervé, F., Calderón, M., and Faúndez, V., 2008, The meta- Klepeis, K.A., Betka, P., Clarke, G., Fanning, M., Hervé, ated with the break-up of Gondwana: Journal of Petrol- morphic complexes of the Patagonian and Fuegian An- F., Rohas, L., Mpodozis, C., and Thomson, S., 2010, ogy, v. 41, p. 605–625, doi:10.1093/petrology/41.5.605. des: Geologica Acta, v. 6, no. 1, p. 43–53. Continental underthrusting and obduction during the Pankhurst, R.J., Rapela, C.W., Fanning, C.M., and Márquez, Hervé, F., Fanning, C.M., Pankhurst, R.J., Mpodozis, C., Cretaceous closure of the Rocas Verdes rift basin, M., 2006, Gondwanide continental collision and the Klepeis, K., Calderón, M., and Thomson, S.N., 2010, Cordillera Darwin, Patagonian Andes: Tectonics, v. 29, origin of Patagonia: Earth-Science Reviews, v. 76, Detrital zircon SHRIMP U-Pb age study of the Cordi TC3014, doi:10.1029/2009TC002610. no. 3–4, p. 235–257, doi:10.1016/j.earscirev.2006.02 llera Darwin metamorphic complex of Tierra del Fuego: Kosmal, A., and Spikermann, J.P., 2001, Geología de la zona .001. Sedimentary sources and implications for the evolution del Cerro Fitz Roy, Provincia de Santa Cruz: Revista Pepper, M., Gehrels, G., Pullen, A., Ibanez-Mejia, M., of the Pacific margin of Gondwana: Journal of the Geo- del Museo Argentino de Ciencias Naturales, v. 3, no. 1, Ward, K.M., and Kapp, P., 2016, Magmatic history and logical Society of London, v. 167, no. 3, p. 555–568. p. 41–53, doi:10.22179/REVMACN.3.109. crustal genesis of western South America: Constraints

370 Geological Society of America Bulletin, v. 129, no. 3/4 Sediment routing in a collisional foreland basin, Patagonian Andes

from U-Pb ages and Hf isotopes of detrital zircons Basin, Chile: Marine and Petroleum Geology, v. 28, Geological Magazine, v. 124, no. 6, p. 569–575, doi:10 in modern rivers: Geosphere, v. 12, no. 5, p. 1532–1555, p. 612–628, doi:10.1016/j.marpetgeo.2010.05.002. .1017/S0016756800017398. doi:10.1130/GES01315.1. Saunders, A.D., Tarney, J., Stern, C.R., and Dalziel, I.W.D., Suppe, J., 1984, Kinematics of arc-continent collision, flip- Plint, A. G., 2010, Wave- and storm-dominated shoreline 1979, Geochemistry of Mesozoic marginal basin-floor ping of subduction, and back-arc spreading near Tai- and shallow-marine systems, in James, N.P., and igneous rocks from southern Chile: Geological Society wan: Memoir of the Geological Society of China, v. 6, Dalrymple, R.W., eds., Facies Models 4: St. John’s, of America Bulletin, v. 90, p. 237–258, doi:10 .1130 p. 21–33. Newfoundland, Geological Association of Canada, /0016-7606(1979)90<237:GOMMBF>2.0.CO;2. Szwarc, T.S., Johnson, C.L., Stright, L.E., and McFarlane, GEOText 6, p. 167–200. Schwartz, R.K., and Birkemeier, W.A., 2004, Sedimentol- C.M., 2014, Interactions between axial and transverse Pouclet, A., Lee, J.S., Vidal, P., Cousens, B., and Bellon, ogy and morphodynamics of a barrier island shoreface drainage systems in the Late Cretaceous Cordilleran H., 1994, Cretaceous to Cenozoic volcanism in South related to engineering concerns, Outer Banks, NC, foreland basin: Evidence from detrital zircons in the Korea and in the Sea of Japan: Magmatic constraints USA: Marine Geology, v. 211, p. 215–255, doi:10 Straight Cliffs Formation, southern Utah, USA: Geo- on the opening of the back-arc basin, in Smellie, J.D., .1016/j.margeo.2004.05.020. logical Society of America Bulletin (in press), doi:10 ed., Volcanism Associated with Extension at Consum- Schwartz, T.M., and Graham, S.A., 2015, Stratigraphic archi .1130/B31039.1. ing Plate Margins: Geological Society of London Spe- tecture of a tide-influenced shelf-edge delta, Upper Cre- Taira, A., 2001, Tectonic evolution of the Japanese island cial Publication 81, p. 169–191, doi:10.1144/GSL.SP taceous Dorotea Formation, Magallanes-Austral Basin, arc system: Annual Review of Earth and Planetary Sci- .1994.081.01.10. Patagonia: Sedimentology, v. 62, no. 4, p. 1039–1077, ences, v. 29, no. 1, p. 109–134, doi:10 .1146/annurev Puigdefàbregas, C., Muñoz, J.A., and Vergés, J., 1992, doi:10.1111/sed.12176. .earth.29.1.109. Thrusting and foreland basin evolution in the south- Schwartz, T.M., Fosdick, J.C., and Graham, S.A., 2016, Us- Teng, L.S., 1990, Geotectonic evolution of late Cenozoic ern Pyrenees, in McClay, K.R., eds., Thrust Tectonics: ing detrital zircon U-Pb ages to calculate Late Creta- arc-continent collision in Taiwan: Tectonophysics, Dordrecht, Netherlands, Springer, p. 247–254, doi:10 ceous sedimentation rates in the Magallanes-Austral v. 183, no. 1–4, p. 57–76, doi:10.1016/0040-1951 .1007/978-94-011-3066-0_22. basin, Patagonia: Basin Research (in press), doi:10 (90)90188-E. Riccardi, A.C., and Urreta, M.B., 1988, Bioestratigrafía del .1111/bre.12198. Varela, A.N., Poiré, D.G., Martin, T., Gerdes, A., Goin, Cenomaniano–Santoniano en la Patagonia Argentina: Sharman, G.R., Graham, S.A., Grove, M., Kimbrough, D.L., F.J., Gelfo, J.N., and Hoffmann, S., 2012, U-Pb zir- Santiago, Quinto Congreso Geologico Chileno, v. 2, and Wright, J.E., 2015, Detrital zircon provenance of con constraints on the age of the Cretaceous Mata p. 375–394. the Late Cretaceous–Eocene California forearc: Influ- Amarilla Formation, southern Patagonia, Argentina: Richiano, S., Varela, A.N., Gómez-Peral, L.E., Cereceda, ence of Laramide low-angle subduction on sediment Its relationship with the evolution of the Austral Basin: A., and Poiré, D.G., 2015, Composition of the Lower dispersal and paleogeography: Geological Society of Andean Geology, v. 39, no. 3, p. 359–379, doi:10.5027 Cretaceous source rock from the Austral Basin (Río America Bulletin, v. 127, no. 1–2, p. 38–60, doi:10 /andgeoV39n3-a01 . Mayer Formation, Patagonia, Argentina): Regional im- .1130/B31065.1. Wilson, T.J., 1991, Transition from back-arc to foreland plication for unconventional reservoirs in the Southern Shultz, M.R., Fildani, A., Cope, T.A., and Graham, S.A., basin development in the southernmost Andes: Strati- Andes: Marine and Petroleum Geology, v. 66, p. 764– 2005, Deposition and stratigraphic architecture of an graphic record from the Ultima Esperanza District, 790, doi:10.1016/j.marpetgeo.2015.07.018. outcropping ancient slope system: Tres Pasos forma- Chile: Geological Society of America Bulletin, v. 103, Romans, B.W., Hubbard, S.M., and Graham, S.A., 2009, tion, Magallanes Basin, southern Chile, in Hodgson, p. 98–111, doi:10 .1130 /0016 -7606 (1991)103 <0098: Stratigraphic evolution of an outcropping continental D.M., and Flint, S.S., eds., Submarine Slope Systems: TFBATF>2.3.CO;2. slope system, Tres Pasos formation at Cerro Divisa Processes and Products: Geological Society of London Winn, R.D., and Dott, R.H., Jr., 1979, Deep-water fan-chan- dero, Chile: Sedimentology, v. 56, p. 737–764, doi:10 Special Publication 244, p. 27–50, doi:10 .1144/GSL nel conglomerates of Late Cretaceous age, southern .1111/j.1365-3091.2008.00995.x. .SP.2005.244.01.03. Chile: Sedimentology, v. 26, p. 203–228, doi:10 .1111/j Romans, B.W., Fildani, A., Graham, S.A., Hubbard, S.M., and Stern, C.R., and de Wit, M.J., 2003, Rocas Verdes ophio .1365-3091.1979.tb00351.x. Covault, J.A., 2010, Importance of predecessor basin lites, southernmost South America: Remnants of pro- history on sedimentary fill of a retroarc foreland ba- gressive stages of development of oceanic-type crust Science Editor: David I. Schofield sin: Provenance analysis of the Cretaceous Magallanes in a continental margin back-arc basin, in Dilek, Y., Associate Editor: Wenjiao Xiao Basin, Chile: Basin Research, v. 22, p. 640–658, doi:10 and Robinson, P.T., eds., Ophiolites in Earth History: Manuscript Received 13 April 2016 .1111/j.1365-2117.2009.00443.x. Geological Society of London Special Publication 218, Revised Manuscript Received 4 August 2016 Romans, B.W., Fildani, A., Hubbard, S.M., Covault, J.A., p. 665–683, doi:10.1144/GSL.SP.2003.218.01.32. Manuscript Accepted 12 October 2016 Fosdick, J.C., and Graham, S.A., 2011, Evolution of Suarez, M., Herve, M., and Puig, A., 1987, Cretaceous deep-water stratigraphic architecture, Magallanes diapiric plutonism in the Southern Cordillera, Chile: Printed in the USA

Geological Society of America Bulletin, v. 129, no. 3/4 371