EAGE Basin Research (2013) 25, 638–658, doi: 10.1111/bre.12025 Late Quaternary stratigraphy, sedimentology and geochemistry of an underfilled lake basin in the Puna plateau (northwest Argentina) Michael M. McGlue,* Andrew S. Cohen,† Geoffrey S. Ellis* and Andrew L. Kowler† *Central Energy Resources Science Center, U. S. Geological Survey, Denver, CO, USA †Department of Geosciences, The University of Arizona, Tucson, AZ, USA

ABSTRACT Depositional models of ancient lakes in thin-skinned retroarc foreland basins rarely benefit from appropriate Quaternary analogues. To address this, we present new stratigraphic, sedimentological and geochemical analyses of four radiocarbon-dated sediment cores from the Pozuelos Basin (PB; northwest Argentina) that capture the evolution of this low-accommodation Puna basin over the past ca. 43 cal kyr. Strata from the PB are interpreted as accumulations of a highly variable, underfilled lake system represented by lake-plain/littoral, profundal, palustrine, saline lake and playa facies associations. The vertical stacking of facies is asymmetric, with transgressive and thin organic-rich highstand deposits underlying thicker, organic-poor regressive deposits. The major controls on depositional architecture and basin palaeogeography are tectonics and climate. Accommodation space was derived from piggyback basin-forming flexural subsidence and Miocene-Quaternary nor- mal faulting associated with incorporation of the basin into the Andean hinterland. Sediment and water supply was modulated by variability in the South American summer monsoon, and perennial lake deposits correlate in time with several well-known late Pleistocene wet periods on the Alti- plano/Puna plateau. Our results shed new light on lake expansion–contraction dynamics in the PB in particular and provide a deeper understanding of Puna basin lakes in general.

INTRODUCTION that cause loading, flexure, and sediment-starved depres- sions to develop (e.g. Carroll et al., 2006). Modern lakes occur in a wide variety of tectonic settings, The formation of lakes in thin-skinned forelands, how- and sediments recovered from such basins prove valuable ever, is more complicated. In these orogens, topographic in geological and palaeoenvironmental research. Unlike closure in the proximal foredeep is hindered by erosion of lakes formed by glacial or fluvial processes, tectonic lakes the thrust belt, as high rates of sediment accumulation typically persist on the landscape for  104 years, often (  10À1 mm yearÀ1; Sinha & Friend, 1994) balance or producing thick depositional sequences that can archive overwhelm available accommodation space. Accordingly, climatic, biological, and surficial processes with high reso- lakes are scarce in these settings and usually exist only lution (Olsen, 1990; Colman et al., 1995; Gierlowski- when the watershed geology is carbonate-rich, thereby Kordesch & Park, 2004; McGlue et al., 2008). Despite favouring rivers with low ratios of bedload to dissolved many decades of study, major gaps exist in our under- load (e.g. Drummond et al., 1996; Zaleha, 2006). In con- standing of several types of modern tectonic lakes, partic- trast, lake formation is more likely in the hinterland ularly those associated with retroarc foreland basin regions of a thin-skinned foreland system, as these higher systems (DeCelles & Guiles, 1996). Lake formation is rel- and drier environments may lack the ability to transport atively well understood in thick-skinned forelands, and significant sediment loads. Climate is critical to topo- data concerning ancient lakes exist in great abundance for graphic closure and lake type in these intracontinental set- these basins (e.g. Eocene Green River Formation of wes- tings, due to its effect on sediment and water supply, tern North America; Eugster & Hardie, 1975; Smith which helps to govern interactions between lake level and et al., 2003). In this setting, lakes may form as erosion- the basin sill (Carroll & Bohacs, 1999). This is especially resistant basement blocks rising along steep reverse faults true along mountain fronts such as the Andes, where ris- ing air masses lose much moisture at low elevations. Indeed, lakes and wetlands are conspicuous compo- nents of high-altitude basins in the thin-skinned central Correspondence: Michael M. McGlue, Central Energy Resources Science Center, U. S. Geological Survey, P.O. Box Andes, providing vital habitat for a wide range of endemic 25046, M.S. 977, Denver, CO 80225, USA. E-mail: mmcglue@ species and a key resource base for local human popula- usgs.gov tions (Caziani et al., 2001; Nunez~ et al., 2002). Yet, from

© 2013 The Authors 638 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems the perspective of basin analysis, many of these modern BACKGROUND deposystems are understudied. This knowledge deficit 2 limits the full use of lacustrine deposits in explorations of The PB is an NNE-oriented, elongate (ca. 2750 km ) pig- ° ° ancient tectonic and climatic change in retroarc foreland gyback basin at ca. 22 S, 66 W. West-verging thrust settings. sheets carrying siliciclastic and volcanic Ordovician rocks To address this gap, we studied four sediment cores bound the flat-floored basin (Fig. 1a). Relief between the from Laguna de los Pozuelos (LP) (Gangui, 1998). This basin floor (ca. 3663 m a.s.l.) and flanking ranges exceeds < playa-lake occupies the centre of the Pozuelos Basin (PB), 450 m, but the basin spill point is 40 m above the mod- a piggyback basin in the Puna plateau of northwest Argen- ern playa-lake (Fig. 1b). Seismic stratigraphic analysis tina (Fig. 1). Radiocarbon-dated cores from LP provide and regional correlations suggest that PB formation and an excellent opportunity to characterize the stratigraphy, synorogenic sedimentation began in the Oligocene, with sedimentology, and geochemistry of an underexplored maximum subsidence occurring near the eastern-margin class of thin-skinned retroarc foreland basin lakes. Fur- thrust faults (Gangui, 1998). The basin is tectonically thermore, sediments from LP provide the chance to assess complex and the most recent deformation is associated climate change in the Puna and its northern equivalent, with normal faulting and volcanism (Cladouhos et al., the Altiplano. Notably, palaeoclimate proxy records are 1994). Neogene ignimbrites are widespread along the spatially complex and sometimes conflicting from the high basin’s eastern flank, whereas small exposures of Creta- Andean plateau (Betancourt et al., 2000; Bobst et al., ceous nonmarine sediments crop out near the southern 2001; Latorre et al., 2002; Godfrey et al., 2003; Fritz end of the basin. Miocene nonmarine carbonates, evapor- et al., 2004; Chepstow-Lusty et al., 2005; Maldonado ites, and tuff (i.e. Cara Cara Formation; Cladouhos et al., 1994) cropout along the eastern basin margin (Fig. 1a). et al., 2005; Placzek et al., 2006; Nester et al.,2007; À1 Quade et al., 2008; Blard et al., 2011). Prior actualistic Total precipitation in the PB is ca. 320 mm year and analyses of LP sediments (McGlue et al.,2012a)were monthly mean air temperatures range between 3 and ° used to guide interpretations of these cores, and we pres- 13 C (Legates & Willmott, 1990a, b). Rainfall, derived ent herein new insights into the facies architecture almost entirely from eastern sources, is strongly seasonal, with about 70% of the yearly total occurring during the and palaeogeography of the PB from ca. 43 cal ka BP to present. austral summer. Climate in the region is governed by the

(a) (b) (c)

Fig. 1. (a) Simplified geological map and cross-section of the Pozuelos Basin (PB). Cross-section location is marked by a dashed line. Extensional lineaments (dotted lines) are from Caffe et al. (2002). LP, Laguna de los Pozuelos. SR, Sierra de Rinconada. SC, Sierra de Cochinoca. SQ, Sierra de Quichagua. T, Tertiary. M, Miocene. O, Ordovician. K, Cretaceous. Q, Quaternary. GP, Group. (b) Shuttle Radar Topography Mission digital elevation model of the PB illustrating the elongate basin shape and its spill-point, located ca. 35 m above the basin floor. (c) Approximate location of the sediment cores discussed in the text, referenced to a recent shoreline of LP. Inset map shows the position of the basin in South America.

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 639 M.M. McGlue et al.

South American summer monsoon (SASM; Zhou & Lau, vation, and provenance. Total organic carbon (TOC), total 13 â 1998). As with most of the Puna plateau, the El Nino-~ nitrogen and d COM were measured on a Costech Southern Oscillation (ENSO) phenomenon and North (Costech Analytical Technologies Inc., Valencia, CA, Atlantic sea surface temperatures modulate patterns of USA)elemental analyser coupled to a continuous-flow gas- precipitation over the PB (Garreaud et al., 2009). Rain- ratio mass spectrometer (Finnigan Delta PlusXLâ; fall, topography, and soil moisture gradients control vege- Thermo Fisher Scientific Inc., Waltham, MA, USA). To tation in the basin, which is a mixture of C3 and C4 remove carbonate minerals that could influence isotope grasses, shrubs, succulents, and macrophytes (Bonaven- values, samples were pretreated at room temperature for tura et al., 1995; McGlue et al., 2012a). several hours using 1M HCl, then washed four times in de Laguna de los Pozuelos is hydrologically closed, mak- ionized water and air dried. Samples were combusted in ing it sensitive to changes in effective precipitation (P-E; the elemental analyser. Standardization was based on acet- Teller & Last, 1990). The surface area of LP fluctuates anilide for elemental concentration, NBS-22 and USGS- 13 annually, and several lines of evidence indicate that it can 24 for d COM. Precision was better than Æ0.09 for 2 13 exceed ca. 135 km during years with above average pre- d COM based on repeated internal standards. Atomic C/ cipitation (e.g. Mirande & Tracanna, 2009). Conversely, N ratios were corrected for contributions of inorganic intervals of prolonged drought commonly lead to its des- nitrogen following the procedure outlined by Talbot iccation. The playa-lake floor is flat when LP is filled and (2001). Total inorganic carbon (TIC) and biogenic silica the maximum water depth is ca. 1.5 m. Weak southeast- (BiSi) analyses were conducted at LacCore. Weight per- erly summer winds and stronger westerly winter winds cent of TIC was determined using a UIC Inc.â (Joliet, IL, prevent LP from developing persistent stratification. LP USA) total carbon coulometer and provided quantitative is fed by both groundwater and a small surface water constraints on carbonate content. Analytical precision drainage network (Igarzabal, 1978). The Rıos Cincel and associated with this analysis was ca. 0.20%. BiSi analyses Chico are more permanent and form small axial deltas at utilized multiple extractions of hot alkaline digestions fol- the southern end of LP, whereas the Rıo Santa Catalina is lowing a modified protocol designed by Demaster (1979). ephemeral and forms a seasonally subaerial, terminal splay Reported values had an analytical precision of  1.0%. complex north of LP (Fig. 1c; McGlue et al., 2012a). Rock-Eval pyrolysis was conducted on select de-calcified Numerous ephemeral streams form alluvial fans along samples (n=20) from deep intervals in the cores at the Uni- LP’s lateral margins. versity of Houston, to help discriminate the source of OM and infer environmental conditions during deposition (Espit- alie et al., 1977; Katz, 1983). METHODS Due to the importance of age control for interpreting stratigraphy and palaeoclimate, the geochronology of Sediment cores were collected from the PB using a modi- Quaternary lake sediments from the Puna and Altiplano fied split-spoon sampler attached to a gasoline-powered has been the subject of much research (Geyh et al., hammering device (Fig. 1c and Table S1). PVC liners 1999; Sylvestre et al., 1999). Potential pitfalls associated allowed incremental core sections to be collected by repeat with the radiocarbon dating of different organic materi- drives into the open borehole. Recovery per drive varied als in Andean lakes were summarized in detail by Geyh (30–100%), most likely in response to vertical changes in et al. (1999) and Placzek et al. (2006). Briefly, samples water content and sediment density. Individual core sec- may be affected by the introduction of 14C-depleted tions were sealed in the field, then shipped to LacCore water into lake surface waters from various carbon reser- (University of Minnesota) and subsequently analysed for voirs, producing old apparent ages. Alternatively, physical properties using a GEOTEK multi-sensor scan- sources of carbon in equilibrium with the atmosphere at ner. Magnetic susceptibility, gamma-ray attenuation, any given time can contaminate older sediments, result- lithostratigraphic markers, and radiocarbon data were ing in spuriously young apparent ages. used to: (1) differentiate between intact stratigraphy and As with many lakes in high-altitude arid catchments, sediments collapsed from the sides of the borehole; (2) terrestrial organic materials are exceedingly rare in LP. vertically correlate the intact stratigraphy; and (3) create Thus, the initial approach for establishing the chronology composite stratigraphic logs for each borehole. at LP focused on dating <63-lm sediment OM, primarily Facies analysis was conducted on freshly split core sur- using a low-temperature combustion technique (McGee- faces. Particle sizes were estimated using a grain size card, hin et al., 2001). This procedure minimizes the potential and sedimentary components were assessed using a combi- for older, clay-bound carbon to influence the age determi- nation of smear slides, ca. 125-lm sieved residues, and nation. Moreover, samples were exposed to an acid-base- powder X-ray diffraction. Shortly after core splitting, dis- acid pretreatment to remove any carbonate or humic acid crete sediment samples (2–3cm3) were collected every ca. that could complicate age determinations. In all, 23 sedi- 12–15 cm and freeze–dried prior to further analysis. Ele- ment samples were dated using this method (Table S2). In mental and stable isotopic analyses of sedimentary organic addition, we dated seeds of the macrophyte Ruppia matter (OM) were conducted at the University of Arizona (n = 4), which grow in LP today and are also preserved in (UA) to provide insights into biomass production, preser- sediment cores. Carbon extraction and 14C analysis were

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Fig. 2. Age models with error envelopes (light gray) for cores 2A, 3A, 4A and 6A. Organic matter dates used in the interpolation appear as black diamonds, whereas excluded dates appear as white diamonds. Ruppia dates appear as gray diamonds. Inset maps show the location of cores with respect to a recent shoreline of Laguna de los Pozuelos. Note slower sedimentation rates between ca. 19 and 3 cal ka BP, interpreted as evidence of maximum lowstand conditions. carried out at the UA – Accelerator Mass Spectrometer aquatic floras assimilate only dissolved inorganic carbon Facility. Conversion of 14C ages to median calendar ages (DIC) and not carbon from the atmospheric reservoir. utilized the INTCAL09 calibration curve and the program The water and sediment chemistry of LP suggests that CALIB 6.0 (http://calib.qub.ac.uk/calib; Reimer et al., discharge from deep aquifers makes negligible contribu- 2009). Sediment samples that returned ‘post-bomb’ 14C tions to the playa-lake’s hydrologic balance (McGlue ages were calibrated using the Southern Hemisphere rou- et al., 2012a). Furthermore, minimal exchange of ground- tine (Hua & Barbetti, 2004) in the program CALIBomb water DIC with 14C-dead inorganic carbon from Miocene (http://calib.qub.ac.uk/CALIBomb). An age-depth carbonates on the eastern PB margin is likely in the mod- model was developed for each of the sediment cores using ern system (Fig. 1a). Therefore, we conclude that at pres- a simple linear interpolation (Fig. 2). ent, DIC is most strongly influenced by dilute runoff and shallow groundwater sources. If deep palaeolakes occupied the PB and experienced RESULTS prolonged intervals of water column stratification, then Radiocarbon geochronology the DIC in these palaeoenvironments could have been out of equilibrium with atmospheric CO2. A similar situation A seed collected from a living Ruppia plant in 2006 would occur if greater than modern contributions from returned a post-bomb age, which calibrated to 1959–1961 14C-depleted groundwater flowed into the basin. To or 1983–1986 CE (Table S2). These dates constrain reser- assess the extent of these potential 14C-reservoir effects, voir effects within modern LP to <50 years, because we employed paired dating on palaeo-Ruppia and coevally

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 641 M.M. McGlue et al. deposited sedimentary OM. A single Ruppia seed from playa-lake by sheet floods and wind (Hardie et al., 1978), core 2A (depth 434 cm) returned a 14C age younger than but laminations have been disrupted by bioturbation that of coeval OM, suggesting either a reworked origin of (McGlue et al., 2012a). Polygonal cracks are common on the OM or a reservoir effect influencing the apparent age the PB floor today, and observed mudcracks are attributed of the seed. In contrast, OM from depth 526.5 cm yielded to desiccation. Although the sediments of many playa- a date several thousand years younger than Ruppia seeds lakes consist of evaporites, mixed siliciclastic-carbonate from depths 540 and 434 cm (Table S2). We interpret the playas similar to LP may develop where runoff and stand- OM age at depth 526.5 cm as spurious, most likely due to ing water permeate into deeper aquifers (e.g. Turnbridge, laboratory contamination; it was excluded from the age 1984; Chivas et al., 1986). Alternatively, flooding may model. As reversals do not occur in the other cores dissolve soluble evaporites on a seasonal basis (Smoot & (Fig. 2), we favour an age model for core 2A that excludes Lowenstein, 1991). Diatoms, particularly Cocconeis pla- the two anomalies, employing the Ruppia date at 434 cm centula, Nitzschia hungarica and Navicula sp., represented in place of its paired OM counterpart. Additional support the dominant source of BiSi within this facies (Maidana for this interpretation is provided by the concordance of et al., 1998). core 2A’s resultant chronostratigraphy with those derived for the other cores. Because our data do not permit quan- Facies B – weakly stratified clayey sand tification of possible reservoir effects within individual stratigraphic units, we do not apply a reservoir correction This facies consisted of ungraded, crudely bedded (cm- and report calibrated ages with the caveat that these val- scale) to massive, red-brown, very fine- to medium- ues may represent maximum ages. grained clayey sands with rare vertical cracks (Fig. 3a). Our oldest record (ca. 43 cal ka BP) comes from core Diatoms were present in minor abundances. The average 3A, whereas the lowermost dated samples from the other TOC, TIC and BiSi concentrations were 1.4, 0.2 and cores are slightly younger (ca. 37–38 cal ka BP; Fig. 2). 2.2 wt.% respectively. Framework grains were moderate The ages of core tops across the PB are highly variable, to well-sorted and consisted of quartz, muscovite, and ranging from 1966 CE to ca. 1 cal ka BP. We interpret plagioclase feldspar. Beds were ca. 15–20 cm thick and nonmodern ages to indicate eolian deflation and bioturba- exhibited sharp (change over <1 mm), weakly erosive tion of the basin floor, which may have been subaerially basal contacts. exposed at different times in the late Holocene. Support- ing text on radiocarbon-derived sedimentation rates is Interpretation located in the online archive (Fig. S1). Facies B is attributed to subaerial sheetfloods on the Facies analysis extant Rıo Santa Catalina terminal splay complex (McGlue et al., 2012a). Stratification was produced by Thirteen facies types were recognized in the analysis upper flow regime, plane bed conditions during sand (Fig. 3 and Table S3). These facies were laterally contin- deposition (Fedo & Cooper, 1990; Horton & Schmitt, uous and could be identified in all of the cores across the 1996). Waning (decelerating) flows of flood events proba- nearly 5-km span of the study site, except where noted. bly provided the source of clays (Fisher et al., 2008). Ter- minal splay sedimentation occurs where unconfined Facies A – massive clay floods enter a closed basin, but do not significantly raise playa-lake levels (e.g. Lang et al., 2004; Fisher et al., This facies consisted of ungraded, massive, red-brown 2008). Vertical cracks are attributed to subaerial exposure clay with up to ca. 20% dispersed quartz and mica silt and desiccation of the terminal splay complex. The head- (Fig. 3a). Mudcracks were present at the tops of beds. waters of the Rıo Santa Catalina reside in the Sierra de Minor abundances of ostracodes, diatoms, and inorganic Rinconada (western PB margin; Fig. 1a), which means carbonates (low-Mg calcite and aragonite) were also pres- that detrital grains were recycled from Ordovician marine ent. The average TOC, TIC, and BiSi concentrations sandstones and shale. were 0.8, 0.5, and 2.3 wt.% respectively. Beds were ca. 10–35 cm thick and they exhibited nonerosional, indis- –  Facies C massiveoxide-richsiltyclaywith tinct basal contacts (transition over 1 cm). silt laminae and irregular silt pods This facies consisted of ungraded, massive, tan silty clay Interpretation with Fe-oxide mottles (Fig. 3b). Tilted or flat laminations Facies A is attributed to suspension sedimentation in the (0.5–3 mm thick) or thin (1–3 mm) jagged–edged pods of extant playa-lake, LP (Igarzabal, 1978; McGlue et al., silt were scattered throughout (Fig. 3b). Mudcracks were 2012a). Playa waters were well-oxygenated due to wind rare and filled with fine sand or mud. Whole and frag- mixing, which accounts for oxidized sediment colours mented ostracodes were common, and XRD scans and poor OM preservation, as reflected in low TOC con- detected traces of halite. The average TOC, TIC and BiSi tent (Cohen, 2003). Siliciclastic grains were carried to the concentrations were 0.4, 0.4 and 2.8 wt.% respectively.

© 2013 The Authors 642 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

Fig. 3. Sediment core photographs from the Pozuelos Basin, illustrating the major facies encountered in the study area. Cores are ca. 3.5 cm wide and tops are to the right. (a) Massive red clay (Facies A) and weakly stratified clayey sand (Facies B) of the playa facies association (Unit I). Facies B bedding, most likely produced by sheetfloods, has been disrupted by the coring process. (b) Massive oxide-rich tan clay (Facies C) of the saline lake facies association (top Unit II), with arrows marking the location of tilted and flat lami- nae. This facies is interpreted as the maximum lowstand in the stratigraphic framework. (c) Massive black pyrite-rich mud (Facies D) of the saline lake facies association (basal Unit II), with arrow marking a burrow-like oxidation feature. (d) Massive green silty clay (Facies E) of the palustrine facies association (Unit III), with arrow marking the location of dispersed pebbles. (e) Laminated diatom ooze (Facies F1), showing an example of the sharp contact with underlying transgressive deposits. (F) Laminated diatom ooze (Facies F2). Arrow marks thick laminations comprised of calcified Chara debris and ostracodes. (g) Laminated to thinly bedded OM-rich silty clay (Facies G), a sublittoral deposit from core 2A. These sediments are coeval to Facies F, suggesting shoaling in the direction of the core site. (h) Mottled clays (Facies H), with crudely laminated and disrupted beds of macrophyte debris marked by an arrow. (i) Thinly interbedded green sand and clay (Facies I2; marked by arrow), most likely produced by sheetfloods. (j) Normally graded and massive sands from core 3A. (k) Normally graded, matrix-supported gravel and coarse sand (Facies M) overlying Facies L from core 3A.

Beds were ca. 45–90 cm thick and exhibited diffuse to sure and desiccation of the basin floor (Plummer & Go- indistinct (transition over 1 mm to 3–4 cm) contacts that stin, 1981; Smoot, 1983; Demicco & Gierlowski- lacked erosion. Kordesch, 1986). Silt laminae were comprised of rounded quartz and highly refractory micas that suggest eolian processes helped to shape this environment (e.g. Keen & Interpretation Shane, 1990; Rosen, 1994). The paucity of fine sedimen- Facies C is attributed to deposition and reworking in a tary structures, massive bedding, and jagged-edged silt dry mudflat. Colour, Fe-oxides, mudcracks and low TOC pods are interpreted as evidence that bioturbation has all point towards very shallow water, oxidizing conditions, altered primary depositional textures. This type of mostly likely with prolonged intervals of subaerial expo- reworking, primarily accomplished by waterbirds, is

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 643 M.M. McGlue et al. common on LP’s fringing mudflats today (McGlue et al., strata of shallow, well-oxygenated lakes marked by low 2012a). Alternatively, these pods may have accumulated gradient floors (Galloway & Hobday, 1996; Blair & in the cavities of thin efflorescent salt crusts, which is con- McPherson, 2008). Formation of carbonate stem casts fol- sistent with the presence of halite. lows CO2 uptake by Chara during photosynthesis, which requires shallow water in a lake’s photic zone (Anadon Facies D – massive pyrite-rich mud et al., 2002). Dispersed pebbles near the base of Facies E are interpreted to reflect rare deposition by gravity flows This facies consisted of ungraded, massive, black pyr- during storms, as alternative mechanisms like ice or bio- ite-rich mud with minor diatoms (Fig. 3c). Rare cal- logical rafting (Bennett et al., 1996) were much less likely cite laminae (1–2 mm thick) were also encountered. in this environment. Pyrite occurred as fine framboidal aggregates, in some cases filling the interior cavities of pennate diatoms. Facies F – laminated diatom ooze The average TOC, TIC and BiSi concentrations were 1.0, 0.9 and 2.4 wt.% respectively. Dolomite and This facies consisted of thinly or thickly laminated halite were detected on XRD scans in this facies. Beds (up to 5–6 mm), dark green-brown diatom ooze were ca. 40–75 cm thick and basal contacts were (Fig. 3e, f). Two variants of this facies were observed. indistinct. Facies F1 consisted of thinly laminated ooze that was characterized by high diatom diversity (Fig. 3e). Facies F consisted of ooze with intermittent thick lamina- Interpretation 2 tions of calcified charophyte debris, ostracodes, and Facies D is attributed to deposition by suspension fall- pyrite-encrusted macrophyte fragments (Fig. 3f). The out in a perennial saline lake. Authigenic calcite lami- average TOC, TIC and BiSi concentrations were 2.3, nae suggest a lake whose bottom periodically escaped 0.7 and 5.3 wt.% respectively. Traces of halite were reworking by waves and bioturbation. Facies D shares also detected on XRD scans. Beds were typically a number of similarities with the Pleistocene saline 20–45 cm thick and were encountered in the axis of lake facies of the Badwater Basin (Death Valley, Cali- the basin (cores 4A, 3A and 6A). Basal contacts were fornia, United States), including (1) rapid (hours to planar and sharp. days) oxidation of black muds to a gray-green colour; (2) the presence of burrow-like oxidation features Interpretation (Fig. 3c); (3) carbonate laminae; and (4) low average TOC (Roberts et al., 1994). Low TOC may be the The variants of Facies F are attributed to deposition by result of bacterial oxidation of OM in the presence of suspension fallout in the profundal zone of a perennial sulphate, which also helps to explain the abundance of lake. Broadly similar diatom-rich laminites have been pyrite (Potter et al., 2005). Evaporative loss of lake identified as open lacustrine (below the photic zone) water is indicated by the presence of dolomite and deposits in a number of other intermontane basins (Fritz halite, but the dominance of detrital sediment suggests et al., 2004; Rigsby et al., 2005). Facies F1 was defined by that this lake was sustained by surface inflows (e.g. fine planar laminations and high TOC, which suggest a Smoot & Lowenstein, 1991; Rosen, 1994). low-energy profundal zone that escaped wave reworking. Highly reduced sediment colours point to oxygen-defi- Facies E – massive silty clay cient waters that may have been influenced by seasonal water-column stratification (e.g. Katz, 1995). We inter- This facies consisted of ungraded, massive, green silty pret deltaic processes to have influenced the development clay. Ostracodes, diatoms, calcified Chara stems, and dis- of Facies F2, with wave action assisting in the concentra- seminated macrophyte debris were minor to abundant in tion of biogenic debris. Facies E. Rare outsized (2–3 cm) sedimentary rock clasts were encountered in this facies at core site 2A (Fig. 3d). Facies G – laminated to thinly bedded OM- The average TOC, TIC and BiSi concentrations were rich silty clay 0.8, 0.8 and 3.4 wt.% respectively. Beds were ca. 65–250 cm thick and exhibited diffuse to indistinct (tran- This facies consisted of laminated to thinly bedded (up to sition between ca. 1 and 40 mm) basal contacts that lacked 5 cm), brown and green silty clay (Fig. 3g). Fragments of erosion. aquatic macrophytes (Ruppia sp. and Najas sp.)andCha- ra were the principal constituents of brown laminae, whereas green laminae and thin beds consisted of silty Interpretation clay with diatoms. The average TOC, TIC, and BiSi con- Facies E is attributed to deposition by suspension fallout centrations were 2.1, 1.2 and 1.5 wt.% respectively. Beds in the littoral zone of a perennial lake. This interpretation ranged from ca. 24 to 70 cm thick and were exclusively is supported by the presence of massive bedding and cal- found in core 2A, on the western basin margin. Basal con- careous microbenthos, which are common features in the tacts were planar and sharp.

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Interpretation trations of TOC, TIC and BiSi were 0.2, 0.5 and 1.9 wt.% respectively. Beds were <10 cm thick and the Facies G is attributed to deposition by suspension fall- nature of the contacts with underlying units is unknown. out in the sub littoral zone of a perennial lake. Preser- vation of laminations suggests a low-energy lake floor, possibly influenced by wave action but deep enough to Interpretation escape flamingo bioturbation (upper limit of ca. Facies I is attributed to deposition by sheetfloods associ- 50 cm; Mascitti & Castanera,~ 2006). Abundant silt and 1 ated with the transition to a subaqueous delta, due to the macrophyte fragments, as well as the relatively high interfingering of sand with diatom-rich silty clays. In this TIC content, imply a contrast in water depth between case, sedimentation was likely rapid as distal sheetfloods Facies G and the laterally equivalent Facies F, which became inundated by rapidly rising lake levels at a low is interpreted as a shoaling of the lake floor towards point in the basin (Smoot, 1985). Facies I is also attrib- the location of core 2A (Fig. 1c). 2 uted to deposition by sheetfloods in a more proximal sub- aerial distributary environment (Hampton & Horton, Facies H – mottled clays 2007). Interbedded sand and muds are common deposits that form as unconfined floods spread out over alluvial This facies consisted of massive, mottled dark green- plains (Gierlowski-Kordesch & Rust, 1994). The abun- olive-brown clays with variably abundant macrophyte, dance of volcanic rock fragments in Facies I accounts for diatom, and calcified Chara debris (Fig. 3h). In some 2 the sub-equal percentages of quartz and andesine detected cases, biogenic and inorganic components were crudely by XRD. The most likely source of these sediments was interbedded, but disrupted fabrics were most common. erosion of the eastern PB margin, where Ordovician and The average concentrations of TOC, TIC and BiSi were Miocene volcanic arc lithologies are exposed in the Sierra 1.7, 0.8, and 4.6 wt.% respectively. Beds in cores 2A and de Cochinoca (Fig. 1a). 6A were ca. 44–70 cm thick and basal contacts lacked ero- sion and were diffuse to indistinct (transition over 1 mm to 3–4 cm). Facies J – massive sands This facies consisted of massive, ungraded to poorly Interpretation inversely graded, green, moderate to well sorted, fine- to Facies H is attributed to deposition by suspension fallout coarse-grained sands with a few granule clasts encoun- at the margin of a perennial lake. Mottling suggests that tered near the top of the bed (Fig. 3j). The basal contact the environment was marked by variable water saturation was planar and weakly erosional. The bed of Facies J was and interaction of iron with oxygenated or reduced pore ca. 42 cm thick and present in core 3A. waters (Freytet & Verrecchia, 2002; Lindbo et al., 2010). Although clear evidence of pedogenesis is absent, mottles Interpretation may reflect root traces and the macrophyte remains could signify the presence of a supra-littoral wetland (e.g. Li- Facies J is attributed to deposition by hyperconcentrated utkus & Ashley, 2003). Elevated concentrations of BiSi flows or sheetfloods associated with a subaerial deltaic and TOC suggest relatively high productivity for this environment. Rapid deposition of sand from turbulent environment. Lake-margin wetlands identified in the rock suspension precluded the development of bedforms record often preserve diatom-rich sediments, due to the (Smith, 1986; Horton & Schmitt, 1996). Facies J overlies prevalence of organic acids and low pH levels during interbedded matrix-and clast-supported gravels, which deposition (Deocampo & Ashley, 1999). may reflect deposition from the dilute, waning stage of floods (Pierson & Costa, 1987). Smoot (1983) documented similar, massive-bedded sheetflood sandstones associated Facies I – thinly interbedded sand and silty with a closed-basin lake in the western USA. The coarse- clay fraction mineralogy of Facies J is similar to Facies I2, Two variants of Facies I were encountered in this study. suggesting a common provenance within the Sierra de Cochinoca. Facies I1 consisted of thinly interbedded packages of dark brown sand (0.5–2 cm) and green silty clay with diatoms. Facies I1 exhibited very fine- to medium-grained sands Facies K – normally graded sands and wavy bedding, and was present at the base of Core 6A. Facies I2, found at the base of Core 4A, exhibited dark This facies consisted of normally graded, unstratified, green, very fine- to coarse-grained sands interbedded with green, poor to well-sorted fine to very coarse sands with silty clay. Sedimentary structures were absent from Facies dispersed gravel typical near the base (Fig. 3j). Sedimen- – I2. XRD scans determined that the framework grains were tary structures were absent. Beds were ca. 15 25 cm thick comprised of quartz, volcanic rock fragments (dominantly and present in cores 3A and 4A. Basal contacts were irreg- plagioclase feldspar) and muscovite. The average concen- ular and erosional.

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 645 M.M. McGlue et al.

Interpretation matrix accounted for >60% of the deposit. Beds of in core 3A were ca. 3–15 cm thick and basal contacts were none- Facies K is attributed to deposition by hyperconcentrated rosive and planar to sub-planar (tilted). flows or sheetfloods associated with a subaerial deltaic environment. In the case of channelized hyperconcentrat- ed stream flows, sedimentation from turbulent suspension Interpretation produced the normal grading, but dispersive pressure Facies M is attributed to deposition by subaerial pseudo- and buoyancy generated by the high clast concentration plastic debris flows associated with a subaerial deltaic or prevented bedform development (Smith, 1986). Deposits alluvial fan environment. The cohesion of the fine- similar to Facies K are also described for sheetfloods, grained matrix was the primary grain-support mecha- where grading and poor sorting reflect decelerating, high- nism, but buoyancy and elevated pore pressure played a concentration unconfined flows (Smoot, 1983; Smoot & role in supporting larger clasts (e.g. Lowe, 1982). Very Lowenstein, 1991).The abundance of volcanic rock frag- coarse-grained, thickly bedded, matrix-supported con- ments accounts for the green colour and elevated plagio- glomerates often represent onshore debris flow lobes asso- clase (andesine) content of these sands. ciated with lacustrine fan deltas (McPherson et al., 1987; Blair & McPherson, 2008). However, several authors have Facies L – normally graded clast-supported documented fine-grained, thinly bedded matrix-sup- gravels ported conglomerates in fan deltas, believed to be derived from dilute debris flows with low matrix strength and dis- This facies consisted of normally graded, green, poor to persive pressure (Schultz, 1984; Horton & Schmitt, moderately sorted, clast-supported very fine to fine gravel 1996). (Fig. 3k). Outsized coarse pebble clasts (>2 cm) were found near the bases of these deposits. A muddy sand matrix accounted for 10–35% of these deposits and distri- Lithostratigraphy and facies associations bution normal grading (both clasts and matrix fine Five lithostratigraphic units (V–I, old to young) are pres- upward) was common. XRD scans indicated that quartz, ent in the PB cores (Figs. 4 and 5). The vertical succes- plagioclase (andesine in cores 3A and 4A; albite in core sion of facies associations is: lake-plain/littoral (Unit V); 2A), and muscovite were the dominant framework grains profundal (Unit IV); palustrine (Unit III); saline lake – in Facies L. Beds were ca. 5 60 cm thick and basal con- (Unit II); and playa (Unit I). Units V through II are inter- tacts were planar and nonerosive. preted as a lake expansion–contraction cycle, similar to those that have been described for underfilled lake basins Interpretation (e.g. Pietras & Carroll, 2006). This cycle occurred from ca. 43 to 3 cal ka BP and was deposited under variable P-E Facies L is attributed to deposition by hyperconcentrated conditions. Unit I represents the inception of a new cycle flows or sheetfloods associated with a subaerial deltaic that began after ca. 3 cal ka BP and was deposited under environment. Sediment was transported in hyperconcen- negative P-E conditions, similar to the modern climate. trated flows by a combination of turbulence, grain disper- sive pressure and buoyancy (Smith, 1986). Such flows may have originated from torrential floods that incorpo- Lake-plain/littoral association (Unit V) rated water and sediment along their paths (Sohn et al., This association marks an interval of basin flooding and 1999). Although traction-produced sedimentary struc- transgression that began prior to ca. 43 cal ka BP. Its tures were not apparent, the normal grading and matrix thickness is ca. 5 to 135 cm and includes Facies I, J, K, L abundance may have been produced by clast interactions and M. These facies are interpreted to represent a delta in a turbulent cohesionless flow (Horton & Schmitt, that entered the PB along its eastern margin. Beds thin 1996). Facies L in cores 3A and 4A have similar frame- and sediments become finer grained towards the core 6A work mineralogy to Facies I, J and K; in these cores, this site, near the centre of the PB (Fig. 1c). Most of the sedi- facies is likely to be made up of sediments derived from mentological characteristics of Unit V indicate deposition Sierra de Cochinoca (Fig. 1a). In contrast, Facies L in in the onshore portion of the delta by sheetfloods, hyper- core 2A appears to be derived from the Sierra de Rincona- concentrated stream flows and debris flows. The general da, based on the presence of Na-feldspars. absence of interbedded fine-grained lake sediments sup- ports this interpretation (Fig. 5; Horton & Schmitt, Facies M – normally graded matrix- 1996). By contrast, interbedded sand and diatom-rich supported gravels silty clay (Facies I1) reflects distal sheetflood deposition interacting with rising lake waters (Fig. 4b). The inter- This facies consisted of normally graded, green, poor to pretation of delta type is constrained by the spatial distri- moderately sorted, matrix-supported coarse sand to fine bution and number (n=4) of cores in the dataset, which gravel that lacked internal stratification (Fig. 3k). Coarse- does not permit a thorough evaluation of delta architec- tail normal grading was typical in Facies M. A muddy ture (i.e. sheets versus channels). Additionally, the narrow

© 2013 The Authors 646 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems

(a)

(b)

Fig. 4. (a) Stratigraphy of core 2A. (b) Stratigraphy of core 6A. 14C, radiocarbon age, presented as median calendar year before pres- ent. C, clay. Si, silt. Sa, sand. G, gravel. TIC, total inorganic carbon. BiSi, biogenic silica. TOC, total organic carbon. width of the cores could preclude the full expression of deposits from both gravity flows and sheetfloods, which is structures like climbing ripples, which clearly indicate consistent with Facies M, I2, J and K. However, Smoot & decelerating flows and are typical in sheetflooding envi- Lowenstein (1991) noted that identifying fan deltas in ronments. closed basins is problematic because of the potential for Sheet, ‘Gilbert-type’, birdfoot-type or fan deltas are rapid lake level fluctuations and wave reworking of sub- commonly associated with perennial lakes in closed aerial alluvial fan sediments. Evidence of shoreline depos- basins, and in some cases, deltas with combined charac- its are absent in Unit V, which suggest that either the teristics have been documented (Smoot & Lowenstein, onshore–offshore transition was not captured in the cores, 1991). Most available data support either a sheet or fan or that beach deposits were poorly developed. Poorly delta interpretation for Unit V. McPherson et al. (1987) developed shorelines are characteristic of basins with explained that coarse-grained fan deltas usually exhibit gently sloping, uniform floors where sheet deltas are

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 647 M.M. McGlue et al.

(a)

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Fig. 5. (a) Stratigraphy of core 3A. (b) Stratigraphy of core 4A. 14C, radiocarbon age, presented as median calendar year before pres- ent. C, clay. Si, silt. Sa, sand. G, gravel. TIC, total inorganic carbon. BiSi, biogenic silica. TOC, total organic carbon. common (Gierlowski-Kordesch & Rust, 1994). Thinly presence of well-preserved Ruppia seeds and pyrite sug- bedded, graded sands and gravels (Facies J and L respec- gests a shallow subaqueous depositional environment. tively) are common where unconfined sheetfloods enter closed basins (Smoot, 1983). Regardless of delta type, Profundal association (Unit IV) Unit V deposits clearly indicate significant surface water inflows to the PB, which suggest more positive P-E than This association marks a short-lived episode of lake-level modern. highstand from ca. 43–36 cal ka BP. Its thickness is ca. 25 Sediment mineralogy suggests that a lateral river(s) to 120 cm and includes Facies E, F1/F2, and G. Profun- draining the Ca-plagioclase-rich, andesitic and dacitic dal association deposits are separated from underlying lavas of the Sierra de Cochinoca fed this ancient delta Unit V beds by sharp contacts, suggesting rapid lateral (Fig. 1a; Caffe et al., 2002). Facies L encountered at the lake expansion. An offshore, relatively deep lacustrine base of core 2A is also interpreted as a delta, which environment was interpreted based on the presence of entered the PB on its western margin, with sediment sup- fine-grained laminated ooze. The southerly deepening ply from the Sierra de Rinconada (Fig. 1a). Here, the bathymetric trend implied by the lake-plain/littoral facies

© 2013 The Authors 648 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems association is borne out by the presence of profundal Saline lake association (Unit II) Facies F2 at the base of core 6A. This facies suggests that in addition to suspension settling, wave activity influ- This association marks a continued regressive phase from enced sediment accumulation in this palaeolake. Time- ca. 23 to 3 cal ka BP. Its thickness ranges from ca. 95 to equivalent, interbedded Facies G and Facies E at the core 180 cm and includes Facies C and D. Saline lake associa- 2A site are interpreted as a sublittoral environment of tion deposits are separated from the underlying Unit III deposition, situated several km west of the deepest zone beds by indistinct contacts. The depositional environ- of the palaeolake (Fig. 4a). The presence of thick lamina- ments represented in this association include a perennial tions and thin beds in Facies G provides additional sup- saline lake and dry mudflats, suggesting that evaporation port for shoaling towards the western PB margin, as (declining and negative P-E) played an increasingly variations in laminae texture are known to accompany important role in Unit II time. changes in water depth in other lake systems (Smoot, Basal sediments in Unit II relate to the presence of a 1991). perennial saline lake and mark the final appearance of a Expansion of a relatively large palaeolake in the PB palaeolake in the PB (ca. 26–19 cal ka BP). We interpret may have promoted water column stratification and that this lake was smaller and held more saline waters than reducing conditions on the lake floor, which is consistent the palaeolake represented by the underlying profundal with the preservation of fine laminations in Facies F1 and and palustrine facies association (Units IV and III). Nev- elevated TOC in most of the Unit IV facies types (Katz, ertheless, the massive pyrite-rich silty clays of Facies D 1995; Cohen, 2003). Widespread bottom-water anoxia are characteristic of a saline lake where relatively fresh appears unlikely for this palaeolake, however, due to the surface waters were important to basin hydrology and abundance of in situ benthic invertebrate fossils in Facies sedimentation (Smoot & Lowenstein, 1991). Authigenic E, F2 and G. In concert with carbonates, traces of halite calcite precipitation was common in this saline lake, as identified in profundal oozes suggest that the lake’s revealed by discrete laminae and peaks in TIC (Figs. 4 hydrology was closed during the deposition of Unit IV. and 5). By contrast, most of the carbonate of the profun- The presence of a large palaeolake suggests more positive dal and palustrine facies associations is derived from P-E than modern during the deposition of Unit IV. ostracodes and Chara. Halite and dolomite were detected in XRD scans, but not on smear slides, which suggest to Palustrine association (Unit III) us that palaeolake waters were relatively dilute. This con- dition is not unusual, however, as perennial saline lakes This association is interpreted to reflect shoreline retreat are known to exist for thousands of years without precipi- from ca. 37–23 cal ka BP. Its thickness ranges from ca. 70 tating evaporites (Smoot & Lowenstein, 1991; Roberts to 260 cm and includes Facies E and H. Palustrine associ- et al., 1994) ation deposits are separated from the underlying Unit IV The transition from Facies D to Facies C marks a beds by gradational contacts, suggesting gradual contrac- major palaeoenvironmental change in Unit II time. Maxi- tion of the lake under climate conditions marked by mum lowstand conditions in the PB are inferred from declining P-E. The palustrine environment encompasses Facies C, which exhibits the slowest sedimentation rates both permanently and seasonally inundated areas (Freytet in the record (Fig. 2). The most likely depositional envi- & Verrecchia, 2002; Pietras & Carroll, 2006). In low ronment for Facies C is a dry mudflat. This mudflat accommodation, low gradient deposystems like the PB, developed due to the desiccation of the perennial saline the palustrine environment is highly sensitive to fluctua- lake (Facies D) as climate became more arid and surface tions in P-E, as minor changes in inflows can expose broad and groundwater inflows to the basin were diminished. areas of the basin floor. Facies C exhibits desiccation cracks, tilted silt laminae, A palustrine origin for Facies E is implied by abundant and very low TOC, which are features that are consistent ostracodes and macrophyte OM, which indicate the pres- with subaerial exposure and deflation of lake beds (Smoot ence of a shallow, well-oxygenated, photic zone that was & Lowenstein, 1991). Traces of halite are likewise present conducive to benthic organisms and plant growth. Mas- in Facies C, and may have formed by evaporative pump- sive bedding features in Facies E were likely produced by ing of groundwater along the mudflat margins. bioturbation and wave mixing. Adjacent lake plain envi- ronments likely supplied the ‘floating’ pebbles (Fig. 3d) to Facies E during intense storms that produced gravity Playa association (Unit I) flows that entered the lake. A shoreline wetland is indi- This association marks the inception of a transgression cated by the mottled clays (Facies H) and massive green and new lake cycle in the PB that began after ca. 3 cal ka silty clays (Facies E) in cores 6A and 2A. Facies H, which BP. Its thickness ranges from ca. 16 to 54 cm and includes is characterized by mottling, thick laminations, and cru- Facies A and B. Playa association deposits are separated dely bedded macrophyte debris, is similar to sediments from the underlying saline lake facies association by sharp that have been linked to fluctuating, shallow lake environ- to indistinct contacts, suggesting an abrupt expansion of ments in other Andean basins (Rigsby et al., 2005). the lake surface. Depositional environments represented

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 649 M.M. McGlue et al. in Unit I include the extant playa-lake and terminal splay (a) complex of the Rıo Santa Catalina. Effective precipitation is interpreted to be similar to modern for Unit I, which strongly contrasts with the climate that accompanied the transgression of Unit V. Today, the Rıo Santa Catalina maintains an axial flow path in the PB (Fig. 1c), and the fine-grained deposits of its terminal splay (interbedded Facies A and B) reflect the geology of the western basin margin. This depositional configuration is much different from the coarse-grained delta of Unit V, whose mineralogy and colour indicate palaeoflow from the eastern basin margin. Today, sum- mer rainfall produces sheetfloods on the Rıo Santa Cata- (b) lina (Facies B) that rarely interact with the extant playa- lake, whereas flooding and P-E is interpreted to have been much higher during Unit V time. The playa-lake was described in detail elsewhere (McGlue et al., 2012a), but the massive clays of Facies A share a number of character- istics with disrupted playa mudstones observed in other closed basins (Turnbridge, 1984; Gore, 1989).

Organic matter geochemistry Bohacs et al. (2000) explained that basin type strongly controls organic enrichment in lacustrine rocks, which is a function of OM production, destruction, and dilution. (c) For the late Quaternary sediments of the PB, we exam- ined bulk OM geochemistry (Fig. 6a, b) and Rock Eval datasets (Fig. 6c), to assess the importance of each of these major controls. Production in lake basins refers to the primary produc- tivity by plants, which can grow within the lake itself (autochthonous) or in the lake’s watershed (allochtho- nous), requiring transport by wind or water prior to sedi- mentation. Commonly cited controls on productivity in lake basins include solar energy, water chemistry and nutrient availability (Passey et al., 2010). The production of OM is relatively high in Unit IV, where profundal facies average 2.3 wt.% TOC (Fig. 6a and Table S3). Fig. 6. Bulk organic matter (OM) geochemistry from the Pozu- – Hydrogen index (HI) values for Facies F and G (profun- elos Basin. (a) Total organic carbon (TOC) total organic nitro- dal and adjacent sub littoral deposits) range from 92 to gen (TON) crossplot. Note elevated TOC concentrations of À1 profundal Facies F. (b) Carbon to nitrogen ratio (C/N) – carbon 287 mg HC g TOC (Fig. 6c). In concert with micro- 13 isotope (d COM) crossplot. Note broad C/N and enriched scopic observations, these Rock Eval data suggest autoch- 13 d COM values, interpreted as reflecting destructive processes thonous production from a mixture of algae and due to shallow bathymetry in all palaeolake environments. Note macrophytes (i.e. Type II kerogens) in a late Pleistocene that symbols are the same for panel A. (c) Rock Eval modified lake that was likely larger than modern LP (Fig. 6c). The van Krevelen diagram. HI, hydrogen index. OI, oxygen index. 13 enriched d COM values for Unit IV (Fig. 6b) are attrib- Poor preservation of OM supports the interpretation of basin uted to the DIC-pool of the lake water, which was proba- underfilling in the late Quaternary. bly influenced by the kinetic effects of evaporation and À 13 algal utilization of HCO3 as a carbon source for photo- tinct cloud on the left side of the C/N – d COM cross- synthesis (Meyers & Teranes, 2001). The absence of plot, mostly likely signifying high diatom productivity in higher plant remains on smear slides suggests that trans- the wetland environment (Fig. 6b). In the saline lake and ported terrestrial vegetation contributed very little to the playa facies associations, accumulations of OM are gener- sedimentary OM of Unit IV, which is consistent with ally low (Fig. 6a) and production appears to be dominated observations from other underfilled lakes (Bohacs et al., by macrophytes, which are known to be isotopically 2000). Mottled clays (Facies H) of the palustrine associa- enriched in the PB (Fig. 6b; McGlue et al., 2012a). tion also produce TOC peaks (Fig. 4) and mean HI values Destruction refers to removal of OM prior to or during of 240 mg HC gÀ1 TOC (Fig. 6c). Facies H creates a dis- sedimentation, typically by inorganic oxidation,

© 2013 The Authors 650 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems photo-oxidation, microbial respiration or ingestion by organic enrichment just above the shoreline/transgressive metazoans (Bohacs et al., 2000). Destructive processes package (Bohacs et al., 2000); and (5) strongly coupled are interpreted to be the most significant influence on accumulation rates and lake levels, such that highstand organic sedimentation in the low accommodation PB. deposits display the highest sedimentation rates (Bohacs This is especially true late in Unit II, as very low sedi- et al., 2000). Pietras & Carroll (2006) pointed out that the mentation rates and frequent subaerial exposure limited vertical stacking of disparate facies in Wilkins Peak cycles the preservation of OM in the dry mudflat environment do not readily conform to Walther’s law of facies succes- (average TOC = 0.4 wt.%). During Unit I time, the sion, making a strict sequence stratigraphic interpretation playa-lake’s shallow bathymetry and polymixis conspired a challenge. The low sedimentation rates, silt laminae, to limit the preservation of mixed algal/macrophyte OM low TOC concentrations, and diagenetically altered OM 13 (McGlue et al., 2012a). The C/N – d COM crossplot exhibited by the dry mudflat deposits of Unit II (Facies and relatively high oxygen index values indicate that oxi- C) provide clear evidence of subaerial exposure and ero- dation may have affected the larger palaeolakes repre- sion; this is the best candidate for a sequence boundary in sented by Unit IV, III, and II strata (Fig. 6b, c). For the PB record. example, the diagenetic loss of labile nitrogen could help Notably, Type II OM is present in the PB, which con- produce the broad range of C/N values exhibited by these trasts with the Type I OM that more commonly accumu- facies associations, as terrestrial vegetation makes very lates in underfilled basins (Fig. 6c). This is believed to be limited contributions to the sedimentary OM (Meyers & linked to the dearth of accommodation space in the basin, Teranes, 2001). The heavy impact of oxidation is attrib- which led all palaeolakes to remain relatively shallow. uted to the relatively shallow bathymetry and limited Whereas many underfilled basins are hypersaline, the sal- accommodation space inferred for all of the Pleistocene- ine-alkaline waters of palaeolakes in the PB allowed both Holocene palaeolake environments in the PB. macrophytes and diatoms to flourish. This interpretation Dilution refers to the reduction in the concentration of is also supported by sediment mineralogy, as alkaline OM in sediments due to deposition of siliciclastic or bio- earth carbonates are present throughout Units IV-I, genic (e.g. diatom silica or shell carbonate) materials. Si- whereas halite is only present in traces. These data sug- liciclastic dilution is not a common process in the gest that groundwater discharge from saline aquifers did depocentres of underfilled lake basins, as lake expansion not control hydrology in the PB during the late Quater- during highstands constrains transport and deposition of nary. Rather, fluctuating P-E and surface water inflows coarse siliciclastic detritus to the basin margins (Smoot, appear to have been most important to palaeolake hydro- 1983; Pietras & Carroll, 2006). Relatively high TOC val- chemistry. ues in laminated diatom oozes (Facies F) argues against significant biogenic dilution during highstands. Dilution Climate is most apparent in our cores at the muddy tops of Unit V deltaic deposits. Organic carbon concentrations for these Today, the landscape of the Puna plateau is marked by sediments (Facies I, J and L) never exceed 0.3 wt% internally drained basins, dry valleys, ephemeral playa- (Figs 4 and 5). lakes, and salt flats, which reflect the arid climate. Precipi- tation at the PB falls in the austral summer, and due to its latitude, Amazonian sources should play a key role in the DISCUSSION moisture balance (Garreaud et al., 2009). Our palaeogeo- Depositional history and palaeogeography graphical reconstruction posits that palaeolakes larger than modern LP occupied the basin during the late Pleis- Several lines of evidence suggest that during the past ca. tocene (Fig. 7). To sustain large lakes, most researchers 43 cal kyr, water levels in the PB remained below the have suggested that large swings in P-E are necessary spill-point elevation, resulting in basin underfilling (Hastenrath & Kutzbach, 1985). Others favour variability (Fig. 7). Underfilled lake basins form where rates of in air temperature and glacial meltwater controls on lake accommodation continually exceed the rate of sediment levels, which modelling has shown may be valid in certain plus water fill (Carroll & Bohacs, 1999). The cyclic strata locales on the southern Altiplano (e.g. Blodgett et al., of the Wilkins Peak Formation (Green River Basin; Pie- 1997). tras & Carroll, 2006), which represent lake expansion–- Several decades of research suggest that during the late contraction dynamics, are perhaps the best studied Pleistocene, a series of palaeolakes existed on the Alti- underfilled lake deposits. Quaternary PB strata share a plano (<250 km northwest of the PB; Fig. S2). The exis- number of similarities with these Wilkins Peak cycles, tence of palaeolakes Tauca (ca. 18–14 cal ka BP) and including (1) asymmetric facies stacking patterns, with Coipasa (ca. 13–11 cal ka BP) is almost universally agreed thin transgressive facies overlain by thicker regressive upon, as data for these lakes exist in both drill core stratig- intervals (Pietras et al., 2003); (2) scale, with cycles up to raphy (Baker et al., 2001a, b) and shoreline records (Plac- ca. 5–6 m thick (Pietras & Carroll, 2006); (3) abundant zek et al., 2006). The presence, extent and timing of other sedimentary evidence of evaporation and desiccation palaeolakes are the topic of ongoing debate. Placzek et al. (Carroll & Bohacs, 1999); (4) low overall TOC, with peak (2006) argued for a deep paleolake, Ouki, from ca.

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 651 M.M. McGlue et al.

(a) (b)

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(e) (f)

Fig. 7. Palaeogeographical sketch maps of the Pozuelos Basin (PB) from ca. 43 ka – present illustrating pervasive basin underfilling. Lakes appear blue (darker hues signify greater relative water depths), and the basin landscape appears green (positive P-E) or brown (negative P-E). (a) A shallow playa-lake with intermittent axial streams and fringing mudflat environments has existed since ca. 3 cal ka BP. Note that the Rıo Santa Catalina forms a fine-grained terminal splay near the northern end of the playa-lake. (b) A dry mudflat, formed by subaerial exposure and eolian deflation of lake beds, likely during the early-middle Holocene. If Tauca and Coipasa aged palaeolakes existed in the PB, evidence of them is missing. (c) A saline lake occupied the PB from ca. 26 to 19 cal ka BP, which broadly correlates with the Sajsi lake cycle (Placzek et al., 2006; Blard et al., 2011). (d) From ca. 37 to 23 cal ka BP, a shallow paleolake occupied the basin and produced thick regressive deposits in our cores. (e) A deeper paleolake existed in the PB from ca. 43 to 37 cal ka BP. Based on the present age model, maximum lake expansion correlates in time with the Minchin highstand and Heinrich event 4, identified in other records from the Altiplano (Baker et al., 2001b; Fritz et al., 2004; Kanner et al., 2012). (f) Stacked coarse siliciclastic units indicate the presence of a delta in the PB prior to ca. 43 cal ka BP. The mineralogy of deltaic deposits suggests palaeo- flow from the east.

120–98 cal ka BP and several shallow palaeolakes, Salinas lake known as Minchin, which is believed to have occu- (ca. 95–80 cal ka BP), Inca Huasi (ca. 46 cal ka BP), and pied the Uyuni Basin from ca. 46 to 36 cal ka BP (Baker Sajsi (ca. 24–21 cal ka BP), on the basis of shoreline stra- et al., 2001b; Fritz et al., 2004; Chepstow-Lusty et al., tigraphy, radiocarbon and U/Th data. More recently, 2005). The Sajsi palaeolake is not typically differentiated Blard et al. (2011) reported that the Sajsi palaeolake in drill core strata and the age assigned to the Tauca pal- was moderately deep and refined its chronology to ca. aeolake spans ca. 26–15 cal ka BP, whereas evidence of the 25–19 cal ka BP, coincident with the global Last Glacial large Ouki palaeolake and indeed, large lakes in general Maximum. By contrast, interpretations of drill core stra- are absent prior to ca. 50 cal ka BP (Fritz et al., 2004, tigraphy have focused on the deep Tauca and an older 2012).

© 2013 The Authors 652 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems

A number of climatic hypotheses have been advanced and relevant to the PB seems to be associated with an inso- to explain rainfall variability on the Altiplano/Puna pla- lation minimum from ca. 8.0 to 4.0 cal ka BP (Mayle & teau. Some researchers favour variability in Southern Power, 2008). The impacts of reduced insolation and a Hemisphere insolation and its effect on the SASM as the northerly Intertropical Convergence Zone position on dominant control on lake hydrology (Baker et al., 2001a, monsoon precipitation were widely felt in tropical South b; Fritz et al., 2004; Hanselman et al., 2011). This group America, and expressed in proxy records from Amazonia, focuses on the correlation among maximum summertime the Pantanal, the Altiplano and mountain glaciers (Mayle insolation, increased interhemispheric meridional SST & Power, 2008; Burns, 2011; McGlue et al., 2012b). gradients, and evidence of lake expansion on the Alti- plano. North Atlantic SST gradients in particular are Te c t oni c s considered critical to moisture in the Amazon, the source region for precipitation in the central Andes (Baker et al., Two modes of tectonic deformation are important for 2001b). For example, cold SST anomalies and Heinrich lacustrine deposition in the PB. First, the formation of events (massive iceberg discharges prompting weak ther- the PB by thrust faulting and flexural subsidence controls mohaline circulation; Bond et al., 1992) in the Atlantic general aspects of basin geometry and the initial amount are correlated with evidence of wet conditions at Lake of accommodation space. The parallel bounding faults Titicaca and the Salar de Uyuni (Baker et al., 2001a; Fritz that make up the flanks of the PB constrain the size, depth et al., 2004; Blard et al., 2011). Additionally, a well-dated and hydrology of potential lake systems. The spacing speleothem record from Peru provides compelling evi- between the west-verging thrusts of the PB (<30 km) dence for linkages between Heinrich events and the inten- indicates that palaeolakes most likely exhibited a low sity of the SASM over the past ca. 50 cal kyr (Kanner width-to-depth ratio. These limnological conditions may et al., 2012). The alternative viewpoint favours variability have helped to promote water column stratification and in tropical SST gradients, especially in the Pacific (Plac- preservation of both fine laminations and OM during zek et al., 2006, 2009). This group focuses on modern lake-level highstands (Katz, 1995). For the PB, the NNE analogue data, which show: (1) increased precipitation on trend of boundary thrusts also limits the influence of east- the Altiplano accompanies the strengthened trade-winds erly winds on the basin floor, reducing the fetch of any of La Nin˜a events; and (2) humidity in the Chaco low- large palaeolake. Facies data suggest that the deepest pal- lands plays a role as a moisture source, particularly for the aeolake in the PB (ca. 43–37 cal ka BP; Fig. 7) may have southern Altiplano (Quade et al., 2008). been seasonally stratified, but placing constraints on the The radiocarbon-dated stratigraphic framework pre- surface elevation of this lake remains a challenge. If recent sented herein allows the PB to be placed in a regional pal- tectonic movements have not altered the basin margins, aeoenvironmental context. According to our current age then ca. 35 m of accommodation space is available to hold model, the deepest palaeolake existed in the PB from ca. a hydrologically closed lake in the PB, given its present 44–37 cal ka BP, roughly coeval with the appearance of day morphology (Fig. 1b). When hydroclimatic condi- the Minchin palaeolake in the Uyuni and Titicaca Basins tions allow this depth threshold to be crossed, spillover to (Baker et al., 2001a, b; Chepstow-Lusty et al., 2005). the northeast will occur and an open hydrologic system Similarly, water levels in the Salar de Hombre Muerto will form. We hypothesize that the observed asymmetric and the Rıo Desaguadero Valley are inferred to have been stratigraphy dominated by regressive deposits resulted higher during this time (Godfrey et al., 2003; Rigsby from lake levels remaining below the spill point elevation. et al., 2005). This time interval spans Heinrich event 4, A prominent shoreline would be expected at a level near which is very closely correlated with high precipitation the PB spill elevation, if palaeolakes had been persistently and a strong SASM observed in speleothem records from open (e.g. Placzek et al., 2009). Although lower elevation Peru (Kanner et al., 2012). palaeo-shorelines exist in the basin, such features have A saline palaeolake is interpreted to have occupied the not been discovered near ca. 3695 m a.s.l. PB from ca. 26 to 19 cal ka BP (Fig. 7). During this time, In the broadest sense, the Andes form a barrier to east- the Sajsi palaeolake occupied the Uyuni basin, and water ern moisture sources, which has important implications levels were higher in the Salar de Atacama (Bobst et al., for the sediment plus water availability for all basins on 2001; Blard et al., 2011). Evidence of large lakes that cor- the orogen. Very few natural lakes exist in the wedgetop relate in time with the Tauca and Coipasa phases is con- basins and valleys of the Andean foothills (elevations spicuously absent from the PB. Instead, these intervals,  1500 m), where precipitation is relatively high and and indeed all of the terminal Pleistocene and early Holo- dense Yungas evergreen forests are the norm. This is cene, are overprinted by evidence of basin floor desiccation because excess sediment plus water usually overwhelms and reworking associated with the dry mudflat (Facies C) available accommodation space in these settings, leading at the top of Unit II. Modification of the PB by wind is to at most the development of small (  1km2), shallow, clear in Facies C, and the OM geochemistry of these sedi- freshwater ponds or diffuse wetlands that accumulate thin ments is consistent with oxidation of previously deposited sapropels and clays. By contrast, large lake development lake sediments (Fig. 3b). Several intervals of aridity have is possible in basins high atop the arid orogen, due to the been inferred for the Altiplano/Puna, but most prominent preservation of accommodation space from sediment

© 2013 The Authors Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists 653 M.M. McGlue et al. starvation. Similar dynamics have also been observed in to follow eclogite root foundering in Cordilleran oro- Neogene Andean strata, which document the expansion genic systems (DeCelles et al., 2009). of palaeolakes when climatic (aridity) and tectonic (epi- sodic thrusting) conditions reduced sediment supply to the Bermejo Basin (Jordan et al., 2001). CONCLUSIONS Gangui (1998) noted that formation of the PB occurred during the Oligocene, and the mid-Miocene (ca. 14 Ma) (1) Five lithostratigraphic units (V–I; lake-plain/littoral, carbonate-evaporite sediments of the Cara Cara Forma- profundal, palustrine, saline lake, and playa facies tion described by Cladouhos et al. (1994) attest to the associations respectively) identified in radiocarbon- presence of another underfilled lake in the basin early in dated sediment cores record sedimentation in the PB its history. The geography of these outcrops, the geogra- over the past ca. 43 cal kyr. Pozuelos Basin facies are phy of these outcrops suggests that this Miocene palaeo- characterized by an asymmetric vertical stacking pat- lake may have been larger and deeper than the Quaternary tern, where thick regressive facies overlie relatively lakes identified in our core records. Seismic reflection data thin transgressive and highstand facies. The stratigra- suggest that sedimentation in the Miocene was syn-oro- phy reflects the expansion and contraction of palaeola- genic (Gangui, 1998), and thus the development of kes in an underfilled basin. Long-term (104 years) accommodation space, coupled with negative P-E, most sedimentation rates are relatively consistent among likely led to basin underfilling and large lake development. the PB cores, whereas short-term (102–104 years) The largest palaeolake in the PB (ca. 43–37 cal ka BP; rates are highly variable, which imply an incomplete Fig. 7) shares a number of similarities with late Oligo- stratigraphic record that is compatible with facies cene-early Miocene lake deposits mapped by Horton observations. (1998). In Bolivia, wedgetop basins formed by west- (2) Average TOC concentrations are highest in the pro- verging thrusts also evolved beginning in the Oligocene, fundal facies association (Unit IV), which suggests and mudstone-dominated lake beds with subordinate that the production and preservation of OM were carbonates and evaporites have been identified in some greatest during maximum lake expansion and P-E. of these systems (Horton, 1998). These small lakes Type II (mixed algal and macrophyte OM) kerogen formed when fault-related surface deformation was at a prevails throughout the late Quaternary PB record, minimum, and lake expansion most likely followed most likely a consequence of low accommodation reduced sediment supply and relatively dry climatic space and shallow bathymetry that characterized each conditions. of the palaeolake environments. Siliciclastic dilution The second type of tectonic control important for was minimal, but organic facies development may lake evolution in the PB is extension, as deformation have been impacted by oxidation during prolonged related to normal faulting could have impacted the regressive phases. amount of accommodation space available for lakes or (3) Late Quaternary lake dynamics and PB underfilling influenced hydrologic networks. Pliocene-Quaternary were controlled by both tectonics and climate. Cli- normal faults with variable offsets (up to ca. 5m)have mate, through its effect on P-E and sediment sup- been documented on the western side of the PB (Cla- ply, influenced the development of lakes of varying douhos et al., 1994). Aeromagnetic data have also character and water chemistry, some of which cor- revealed basin-crossing transtensional lineaments relate in time with well-known Pleistocene palaeo- (Fig. 1a) that have been linked to reactivation of thrust lakes in other basins on the Altiplano. The structures during Miocene volcanism on the PB’s structural configuration of the PB constrains the southern margin (Caffe et al., 2002). These extensional morphology and fetch of highstand lakes, poten- structures could have influenced the character of Qua- tially promoting water column stratification and ternary lakes in the PB through minor increases in development of laminated, organic-rich sediments basin floor gradient and accommodation space. Another during highstands. Accommodation space main- possibility is that extension is responsible for altering tained from piggyback basin-forming flexural subsi- groundwater flow paths, which could help explain the dence and new space created as the PB evolved in stark differences between Miocene and Quaternary lake the Andean hinterland (principally through normal sediments in the PB. Notably, groundwater discharge faulting) likewise impacted lake hydrology and features in the palaeolake strata of the past 43 cal kyr bathymetry. are absent, whereas the bedded evaporites of the Cara Cara Formation suggest that lake hydrology was sup- ported by groundwater in the Miocene. Horton (2012) noted that structural style and depositional patterns in ACKNOWLEDGEMENTS a piggyback basin may evolve as the orogen advances and the basin is incorporated into the hinterland This research was supported by the National Science region. This process could affect many Puna basins, Foundation (Award 0542993), American Chemical Soci- due to extension in the thrust-belt hinterland proposed ety (PRF grant 45910-AC8), ExxonMobil and small

© 2013 The Authors 654 Basin Research © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Puna basin lacustrine deposystems grants from Sigma Xi, GSA, and AAPG to the first millennial and orbital timescales on the Bolivian Altiplano. author. L. Lupo and R.G. Cortes of the Universidad Nac- Nature, 409, 698–701. ional de Jujuy provided coring equipment. E. Piovano BAKER, P., SELTZER, G., FRITZ, S., DUNBAR, R., GROVE, M., TA- and A. Kirschbaum arranged logistics and permitting. We PIA, P., CROSS, S., ROWE,H.&BRODA, J. (2001a) The history heartily thank J. Omarini, C. Gans, E. Gleason, M. Barri- of South American tropical precipitation for the past 25,000 years. Science, 291, 640–643. onuevo, M. Ayendez, D. Munoz,~ and the staff of PN BENNETT, M.R., DOYLE,P.&MATHER, A.E. (1996) Dropstones: Laguna de los Pozuelos for their assistance in the field. their origin and significance. Palaeogeogr. Palaeoclimatol. 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