No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Oligocene–Miocene age of aridity in the Atacama Desert revealed by exposure dating of erosion-sensitive landforms
Abstract
The age of onset of hyperaridity in the Atacama Desert, Chile, which is
needed to validate geological and climatological concepts, has been
heretofore uncertain. Measurement of cosmogenic 21Ne in
clasts from erosion-sensitive sediment surfaces in northern Chile shows
that these surfaces have been barely affected by erosion since 25 Ma.
Surface exposure ages of sediment clasts give replicate values at 25,
20, and 14 Ma and individual values at 37 and 9 Ma. Predominantly
hyperarid conditions are required to preserve these oldest continuously
exposed surfaces on Earth. Our findings are compatible with the
hypothesis that the onset of aridity in the Atacama Desert could be the
reason for, rather than the consequence of, uplift of the high Andes.
... The fact that such processes can be identified in the hyperarid core of the Atacama Desert is linked to spatially widespread and persisting hyperarid conditions since at least the Early Miocene (Dunai et al., 2005;Evenstar et al. 2009;Jordan et al., 2014;Evenstar et al., 2017;Ritter et al., 2018, Ritter et al. 2022. Sporadic precipitation events have favoured extremely low erosion rates (Kober et al., 2007;Placzek et al., 2010Placzek et al., , 2014Starke et al., 2017;Mohren et al., 2020a, Ritter et al. 2023) resulting in long-term surface preservation (Dunai et al., 2005;70 Nishiizumi et al., 2005;Kober et al., 2007, Evenstar, et al., 2017Ritter et al. 2019Ritter et al. , 2022 and the accumulation of landscape-draping calcium sulphate-rich soil by atmospheric deposition (Ericksen, 1981(Ericksen, , 1983Rech et al., 2003;Michalski et al., 2004;Ewing et al., 2006;Wang et al., 2014Wang et al., , 2015Rech et al., 2019). ...
... The fact that such processes can be identified in the hyperarid core of the Atacama Desert is linked to spatially widespread and persisting hyperarid conditions since at least the Early Miocene (Dunai et al., 2005;Evenstar et al. 2009;Jordan et al., 2014;Evenstar et al., 2017;Ritter et al., 2018, Ritter et al. 2022. Sporadic precipitation events have favoured extremely low erosion rates (Kober et al., 2007;Placzek et al., 2010Placzek et al., , 2014Starke et al., 2017;Mohren et al., 2020a, Ritter et al. 2023) resulting in long-term surface preservation (Dunai et al., 2005;70 Nishiizumi et al., 2005;Kober et al., 2007, Evenstar, et al., 2017Ritter et al. 2019Ritter et al. , 2022 and the accumulation of landscape-draping calcium sulphate-rich soil by atmospheric deposition (Ericksen, 1981(Ericksen, , 1983Rech et al., 2003;Michalski et al., 2004;Ewing et al., 2006;Wang et al., 2014Wang et al., , 2015Rech et al., 2019). However, hyperaridity in the Atacama Desert is repeatedly interrupted by wetter but still (hyper-)arid conditions (e.g. ...
... However, hyperaridity in the Atacama Desert is repeatedly interrupted by wetter but still (hyper-)arid conditions (e.g. Dunai et al. 2005;Jordan et al. 2014;Evenstar et al. 2017;Ritter et al., 2018, 2019, Diederich et al. 2020Medialdea et al. 2020;75 Ritter et al. 2022, Wennrich et al., 2024, which appear to provide sufficient moisture to 'activate' salt dynamics in evaporite-bearing deposits (e.g. Buck et al., 2006;Howell et al., 2006;Howell, 2009;Wang et al., 2015;Rech et al. 2019). ...
While the formation of periglacial wedges and polygonal patterned grounds has been extensively studied and many of the processes involved have been understood, knowledge on the formation of similar post-sedimentary features found in arid to hyperarid environments remains largely rudimentary. Our contribution to fill this gap is the investigation of a network of vertically laminated calcium sulphate-rich wedges in the subsurface of the Aroma fan in the northern Atacama Desert. The subsurface wedges are characterised by high anhydrite contents and hence differ from the wedge and polygon structures of other study sites in the Atacama Desert, which appear to have been predominantly formed by thermal contraction or desiccation processes. By contrast, haloturbation mechanisms are thought to be a main driver of wedge formation at the Aroma fan site. Haloturbation requires moisture input, and hence Aroma fan wedge formation is likely to be associated with meteoric water received from sporadic rain events and episodes of arid climate characterised by slightly wetter conditions than prevailing at present. The polygonal patterned ground is covered by a stratigraphically younger gypsum-dominated surface crust cover. The presence of the surface crust could indicate an environmental change towards drier conditions, which favoured surface accumulation of calcium sulphate and other salts by means of atmospheric deposition. Such a climatic shift could have caused a deceleration of haloturbation and other wedge formation processes in the subsurface, although modern sediment conveyance from the surface towards its interior still appears to occur along cracks within the crust. In order to gain comprehensive insights into the complex mechanisms involved in wedge formation and formation rates, the establishment of a geochronological framework directly obtained from wedge and crust material remains indispensable. The temporal resolution of wedge growth stored within the succession of vertical laminae promises a high potential for the calcium sulphate wedges to be used as palaeoclimate archives, potentially helping to unravel wedge and polygonal patterned ground formation in other water-limited environments, such as Mars.
... The Atacama Desert, located between Southern Peru (15°S) and Northern Chile (30°S), is one of the driest environments in the world (precipitation <10 mm year À1 ; Goudie et al., 2002;Houston & Hartley, 2003;Pfeiffer et al., 2021). These arid to hyperarid conditions result from the reduced precipitation and the evapotranspiration capabilities of its surfaces (Boy et al., 2022;Dunai et al., 2005;Pfeiffer et al., 2021). In the El Médano DCA, the meteorological conditions and geological stability of Atacama surfaces led to the preservation of about up to 170 meteorites with a mass >10 g km À2 after pairing (Hutzler et al., 2016), with a mean terrestrial age of 710 ky (Drouard et al., 2019). ...
... In the case of Atacama Desert chondrites, the mean H/L ratio is even higher (1.4 AE 0.05), but it fluctuates notably among DCAs (see Table 1). Drouard et al. (2019) suggested that H chondrites dominated the flux between 1.2 and 0.4 Ma, and due to the long-standing preservation of Atacama surfaces (Dunai et al., 2005), the H/L values in Atacama DCAs integrated past variations of extraterrestrial material flux on Earth. It should however be noted that the H/L parameter could be strongly modified by (i) the pairing process of meteorite showers and (ii) local fragmentation during weathering (Ashley & Velbel, 2000;Kouvatsis & Hofmann, 2020). ...
... The Atacama chondrites make up the oldest collection of non-fossil meteorites with a mean terrestrial age of 710 ka (Drouard et al., 2019). Although our morphogenetic classification of Atacama DCAs is based on present-day climatic conditions, the Atacama surfaces are characterized by a long-standing hyperaridity, possibly during the last 10 Ma (Clarke, 2006;Dunai et al., 2005;Rech et al., 2006). In this sense, the weathering degree of Atacama meteorites could (i) integrate the past climatic conditions in the Atacama Desert, which, while still arid, could have episodically been more humid than today or (ii) mainly represents the initial climatic conditions at the time of the meteorite landing and then be only affected by local factors such as sporadic rainfall events or daily coastal fog influences. ...
In the last 15 years, more than 2700 meteorites have been recovered and officially classified from the Atacama Desert. Although the number of meteorites collected in the Atacama has risen, the physical and climatic properties of the dense collection areas (DCAs) have not been fully characterized. In this article, we compiled the published data of all classified meteorites found in the Atacama Desert to (i) describe the distribution by meteorite groups, (ii) compare the weathering degree of chondrites among different Atacama DCAs and other hot and cold deserts, and (iii) determine the preservation conditions of chondrites in the main Atacama DCAs in relation with the local climatic conditions. The 35 DCAs so far identified in the Atacama Desert are located in three main morphotectonic units: The Coastal Range (CR), Central Depression (CD), and Pre‐Andean Range/Basement. A comparison with reported weathering data from other cold and hot deserts indicates that the mean terrestrial weathering of Atacama chondrites (W1–2), displays less alteration than other hot deserts (W2–3) and resembles the weathering distribution of the Antarctic meteorites (W1–2). The highest abundance of Atacama chondrites with low weathering (≤W2) is localized in the CD (78.8%, N = 1435), which is protected from the coastal fog influence and seasonal rainfalls and displays the oldest surfaces in the Atacama Desert. The morphogenetic classification based on present‐day temperatures and precipitations of the main Atacama DCAs reveals similar regional/subregional climatic conditions in the most productive areas and a truly productive surface for meteorite recovery between 5% and 58% of the quadrangles formally defined for each Atacama DCA. Our morphogenetic classification lacks consideration of some meteorological parameters such as the coastal fog, so it cannot fully explain the differences in weathering patterns among CR chondrites. Future studies of chondrite preservation in the Atacama DCAs should consider other meteorological variables such as relative humidity, specific humidity, or dew point, in combination with exposure ages of meteorites and its surfaces.
... Desert systems are a case of such extreme environments requiring specialized adaptations and the driest desert ecosystem on Earth, the Atacama Desert, is found along the Peruvian-Chilean coast (Dunai et al., 2005). In particular the northern Chilean and southern Peruvian coastal region is characterized by a hyperarid climate defined by <25 mm of annual precipitation. ...
... The Atacama Desert is among the oldest ecosystems spanning a history of several millions of years and therefore provides a unique setting to study biological processes of adaptation and speciation. The formation of the Atacama Desert started in the Early Miocene, 15-20 million years ago or even earlier (Dunai et al., 2005;Hartley and Rice, 2005;Ritter et al., 2018), and therefore exceeds the age of origin of any plant species growing there. Distribution range and dimensions of the desert system along the Chilean-Peruvian coast changed throughout its existence and plant species adapted to these extreme conditions must have followed these patterns by migration or local/regional adaptation, extinction and de novo formation and speciation. ...
... Therefore, range dynamics might also indicate that the "tillandsiales" formations may not be very old (in geological terms) same as their growth adaptation to survive in arid/ hyperarid environments and to have sand as their main substrate. Furthermore, considering that the most arid core of the South American western desert occurs in Chile and dates back possibly up to 35 mya (Dunai et al., 2005), the aridification of the desert has been further accentuated with the transition from semi-arid to hyper-arid about 3 mya (Dunai et al., 2005). The emergence of the Peruvian-Chilean desert is known to be the result of three fundamental events: the presence of the cold Humboldt current, a low thermal inversion layer defined by the Humboldt current and the trade winds, which move the low altitude clouds towards the continent (Houston and Hartley, 2003). ...
Epiarenic (sand-growing) Tillandsia vegetation in the hyperarid and arid region of the Chilean-Peruvian Atacama Desert represents an extreme case of adaptation in plant species-poor ecosystems. The involved species exist at the limit of terrestrial life and form mono/oligo-specific and very characteristic structures within the landscape. Covering thousands of square kilometers they represent the major carbon sink in the hyperarid Atacama core. The various Tillandsia species and respective vegetation may have evolved and adapted independently to this extreme environment. The most abundant vicariant diploid species are T. landbeckii in Chile and T. purpurea in Peru. Spatio-temporally varying distribution range overlaps may have caused potentially adaptive gene flow between different species leading to present day gene pools. Using species distribution modelling we explored the idea that from Last Glacial Maximum (LGM) onwards both species shifted their distribution ranges, which resulted in the formation of varying suture zones from Peru towards northern Chile. We further explored genetic data from a Tillandsia loma vegetation in Southern Peru with three sympatrically growing species exemplifying inter-species gene flow crossing even ploidy levels. This mechanism highlights a strategy to evolve and adapt more rapidly to environmental changes in extreme arid and hyperarid habitats and provides an opportunity for Tillandsia populations to efficiently conserve new genotypes via subsequent clonal propagation.
... The paleo-climate history along the Atacama Desert shows a first onset of hyperarid conditions during the Oligocene in the Coastal Cordillera of the northern Atacama Desert (Dunai et al., 2005;Ritter et al., 2018. Fig. 2C). ...
... The Pacific Paleosurface ( Fig. 2A), which stretches for over 1200 km along the forearc region in northern Chile and southern Peru would have been preserved due to the mid-late Miocene increasing aridity (e.g., Galli-Olivier, 1967;Alpers and Brimhall, 1988;Farías et al., 2005;Hoke et al., 2007;Cooper et al., 2016;Evenstar et al., 2017). Moreover, cosmogenic nuclide exposure dating from the Pacific Paleosurface supports evidence for a dominantly hyperarid climate since at least 25 Ma, which switched episodically to relatively more humid (but still arid) conditions at 17-16 Ma, 12-11 Ma, 8-7 Ma and 5-3 Ma (Dunai et al., 2005;Jordan et al., 2014;Evenstar et al., 2009. The Pacific Paleosurface is not a single paleosurface but a mosaic of smaller surfaces that were formed by aggradational and degradational processes over >19 million years (Evenstar et al., 2017). ...
... The exceptional preservation of pediplains in the Atacama Desert was thought to be due to regional arid climate conditions which have persisted since the Mid Miocene (e.g., Bouzari and Clark, 2002;Hall et al., 2008;Cooper et al., 2016;Rech et al., 2006Rech et al., , 2010Rech et al., , 2019 or even earlier from the Late Oligocene (e.g., Dunai et al., 2005;Evenstar et al., 2009Evenstar et al., , 2017. We propose that the onset of the hyperarid condition in the Mid Miocene allowed for the development of a stable surface in the Eastern-CD and Precordillera at the Salado Canyon latitude. ...
Pediplains are classically identified as flat landscape surfaces in arid regions linked to tectonic quiescence, whereas deep incision of a pediplain is attributed to tectonic uplift. In the Atacama Desert, pediplains are generally used as morphotectonic markers to define the chronology of episodes of Late Cenozoic Andean uplift from their erosion and incision patterns and timings. The Atacama Pediplain (AP) extends over >12,000 km² (26° to 28°S Lat) through the Central Depression and Precordillera of the southern Atacama Desert. In this study we perform geomorphologic and stratigraphic observations on the AP in the Salado Canyon area, combining new geochronological results derived from ⁴⁰Ar/³⁹Ar biotite ages from volcanic layers interbedded within the alluvial deposits, and ²¹Ne exposure ages on quartz-clasts on alluvial plains, to determine the chronology of the AP evolution. Results show that the evolution of the AP is a long-term and continuous process (from >20 to ~2.3 Ma) of alluvial deposition and subsequent alluvial plain formation developed by interplay between the climate variability of the Atacama Desert and Andean uplift. The AP alluvial deposition occurred in two spatially and temporally separated episodes of alluvial backfilling: 1) shortly before ~20.14 Ma and to prior to ~9.4 Ma, a timespan that allows for the drainage capture of the eastern Precordillera, and considerable landscape rearrangement; 2) post ~9.4 Ma, with a re-positioning of alluvial backfilling from the Precordillera towards the Central Depression. This occurs after the Mid Miocene onset of the hyperarid conditions in the Central Depression and is more likely due to late Miocene surface uplift. Exposure ages reveal the cessation of basin-scale deposition and the abandonment of the alluvial plains during ~5.24 to ~3.8 Ma linked to the incision of Salado Canyon. Subsequent climate conditions modulated the surfaces by the development of lag deposits until ~2.69 to ~2.3 Ma when hyperarid conditions reach a threshold that limits surficial activity. Additionally, the drainage capture of the Precordillera by headwards erosion of the Salado Canyon explains marked deep incision depth of this canyon without the need for an increase in surface uplift or a change in climate conditions. The AP is not a general marker of a single climatic or tectonic event/period but a composite paleosurface formed by a complex concatenation of extrinsic and intrinsic geomorphic processes over more than ~17 myr.
... The low complexity and high aridity of these deserts provide a unique setting to study plant adaptation and survival strategies, shedding light on the fundamental mechanisms of adaptation and the limits of life on Earth (Stebbins, 1952). The Atacama Desert, with its prolonged hyperaridity (Dunai et al., 2005;Ritter et al., 2019b;Evenstar et al., 2017), sparse vegetation (Rundel et al., 1991) and complex landscape dynamics, stands out as an exceptional study site to investigate the interplay between evolutionary processes, landscape dynamics and plant responses . ...
... However, these current climatic conditions have not been stable since the suggested Oligocene-Miocene onset of hyperaridity in parts of the desert and subsequent expansion of these conditions throughout the Atacama Desert (Dunai et al., 2005; et al., 2017), predominant hyperarid conditions exhibit also variability which reflect global trends of the paleoclimate throughout the Miocene (Zachos et al., 2001;Edwards et al., 2010;Ritter et al., 2018). Several palaeoclimatic models (Houston, 2006), as well as paleoclimate records (e.g., Ritter et al., 2019;Diederich et al., 2020;Medialdea et al., 2020;Jordan et al., 2014;Jordan et al., 2022;Ritter et al., 2022) have shown that during the Pleistocene and Pliocene, pluvial phases repeatedly interrupted the hyper-arid conditions. ...
... However, this is still controversial. First, there is no agreement on the onset of hyperaridity, with evidence ranging from ~25 Ma (Dunai et al., 2005) to 1.5 Ma ago (Reich et al., 2009). Second, climate simulations show conflicting results for precipitation changes as topography is reduced in the Atacama Desert (Sepulchre et al., 2009;Ehlers and Poulsen, 2009;Garreaud et al., 2010). ...
... This pattern of drying is supported by various studies. The earliest estimates of the Atacama hyperaridity onset (~25 Ma) considered the absence of major erosion by taking samples next to the coast (i.e., the Coastal Cordillera, Dunai et al., 2005). When studies used evidence in the interior of the desert and the precordillera (supergene mineralization) the onset of the hyperaridity is placed between 19 and 13 Ma (Rech et al., 2006;Sillitoe and McKee, 1996). ...
The importance of water vapor in arid and hyperarid regions motivates a comparative study in the Atacama and Namib deserts, a natural laboratory to test the role of topography in present-day climate. Based on ERA5 reanalysis evaluated by satellite and ground-based instruments, we focus on the climatological water vapor seasonal cycle and interannual variability offshore the deserts, distinguishing between the free troposphere (FT) and the marine boundary layer (MBL) moisture. In the Namib, moisture variability is strongly controlled by air mass transport. For example, between austral fall and winter, an easterly continental warm and cloud-free air mass settles over the coast, reducing the MBL height to a few hundred meters and decreasing humidity. In summer, the easterly winds are also present, bringing moisture from the center of the continent to the FT of the Namib, along with clouds and rainfall. This feature is intensified during the cold phase of ENSO (La Niña). In contrast, the Andean Cordillera blocks any air mass exchange between the continent and the MBL, allowing the development of stable southerly winds along the coast that transport cold air over warmer waters due to the early westward turn of the Humboldt Current. This induces a strong coupling between SST and MBL moisture, which is enhanced by a permanent stratocumulus cloud cover. In addition, the FT remains drier than the Namib for most of the year due to the predominance of westerly dry air in the region. ENSO is not correlated with the MBL moisture offshore Atacama, and it is the local SST that plays a major role in modulating interannual moisture variability. Only in winter, ENSO seems to impact the FT by increasing the moisture transport from the mid-latitudes during the warm phase (El Niño). We hypothesize that the differences in moisture seasonality and its controlling mechanisms are strongly related to differences in topography and the resulting circulation patterns. Furthermore, similar moisture transport and variability may have been part of a Paleo-Atacama when its topography was similar to the present-day Namib Desert.
... Dunai et al., 2005;Evenstar et al., 2017;Kober et al., 2007;Mohren et al., 2020;C. Placzek et al., 2014;C. ...
... Being spatially isolated from other larger sedimentation systems, the Coastal Cordillera between 19° and 23°S experienced the evolution of aridity without being significantly influenced by allochthonous climate signals, as is the case for landscapes in the Central Depression. Several studies have already indicated that predominantly arid to hyperarid conditions in this part of the Atacama Desert have prevailed at least since the Early Miocene (Dunai et al., 2005;Evenstar et al., 2017;Ritter et al., 2018Ritter et al., , 2022. Reasons for this persistent aridity are manifold. ...
The Atacama Desert is one of the driest and oldest deserts on Earth, with extremely low precipitation rates (<2 mm/yr). Mostly abiotic hyperarid environmental conditions prevail, and surface processes act at extremely low rates over the long‐term. To gain knowledge about the rate of surface processes and age of landscapes in desert environments, terrestrial cosmogenic nuclide derived erosion rate estimates can be used. Within the Huara Intrusive Complex, situated in the hyperarid core of the Atacama Desert, basin‐averaged bedrock erosion rates from channel sediments are extremely low, that is, less than 1 m/Myr. Such low rates indicate that fluvial processes operate very slowly or are almost absent. Bedrock erosion rates of channel knickpoints, however, reveal one to two orders of magnitude higher erosion rates (2–12 m/Myr). Erosion rates are remarkably low when compared to the steep surrounding topography. Tectonic uplift creates higher gravitational potentials for surface processes, controlling the overall erosion rate capacity. However, erosion itself is taking place by local precipitation capable of exceeding thresholds for surface activity. In the Atacama Desert, this happens only due to rare severe precipitation events, explaining the extremely low erosion rates. The efficiency of these events is modulated by local intrinsic processes and conditions, such as high infiltration capacities of Atacama soils and/or large channel boulder accumulations. Due to the virtual absence of these precipitation events capable of erosion, the landscape appears to be in hibernation.
... This feature is observed over 700-1000 km along the coastal area and is thought to be relatively young (6-3 Ma) and presently active (Armijo and Thiele, 1990;González et al., 2003;Contreras-Reyes et al., 2012, Fig. 1). The coastal scarp has been interpreted as the surface expression of an extensional fault (Armijo and Thiele, 1990;Paskoff, 1980), a paleo-cliff line (Mortimer and Saric, 1972), a relic of long-term uplift process that has been maintained by the extremely small denudation rate of the Atacama Desert (Dunai et al., 2005, Fig. 1) and a secondary effect of angle variation along the dip of the subduction interface (Armijo and Thiele, 1990;Contreras-Reyes et al., 2012). While the long-term stress regime along the coastal area of northern Chile is predominantly extensional (Armijo and Thiele, 1990;Delouis et al., 1998;Hartley et al., 2000), there is also evidence for a relatively recent (since late Miocene) regional uplift (e.g. ...
... Armijo and Thiele, 1990;Hartley and Jolley, 1995;Delouis et al., 1998;Clift and Hartley, 2007;Allmendinger and González, 2010;Armijo et al., 2015;Melnick, 2016). This uplift created a barrier for the westward draining sedimentary systems, thereby retaining Miocene and younger sediments within the Longitudinal Valley (Delouis et al., 1998;Hartley et al., 2000;Wörner et al., 2002;Dunai et al., 2005). There is still discussion on the causes, timing and mechanism for the uplift, which may Fig. 2. Bathymetric map of the study area. ...
... In the southern Central Andes (19 • to 27 • S) orographic effects promote a change from <500 mm/yr (assuming no topography) to 500-1000 mm/yr (Houston and Hartley, 2003) (Fig. 1A). This places the SZ at the higher end of semi-arid to dry subhumid climate conditions where erosion rates peak (West of the SZ the climate becomes increasingly arid to the AD which has one of the lowest erosional rates in the world (Dunai et al., 2005;Kober et al., 2007)). Whilst it is noted that precipitation rates vary from north to south across the Central Andes (see Fig. 2), the overall pattern is one of increased precipitation in the eastern foothills of the Andes due to enhanced orographic effects. ...
... This rapid decrease in erosion is detached from deformation rates which continue till the Late Miocene to present day ( Fig. 3B and E). For example, deformation continued after the Middle Miocene along the western edge of the Andes (Sáez et al., 1999;Wörner et al., 2002;Oncken et al., 2006;Charrier et al., 2013;van Zalinge et al., 2017) but, due to the low erosion rates associated with enhanced aridity (Dunai et al., 2005;Evenstar et al., 2017), this tectonic signature is preserved solely in the geomorphology. ...
The rise of large mountain ranges is considered to be driven by tectonics potentially coupled with climate driven-erosion, although the role of this coupling remains uncertain. The arid climate of the Central Andes allows us to strengthen our understanding of the relative roles of these processes in mountain range development globally. Here we compile estimates of exhumation, sedimentation, aridity and surface uplift across the Central Andes for the last 50 Ma. We aim to place constraints on the relative timing of rock uplift (displacement of rocks with respect to the geoid), exhumation (displacement of rocks with respect to the surface) and surface uplift (displacement of the earth's surface with respect to the geoid). We show that initial rock uplift of the Andes extends back at least 50 Myr. This rock uplift generated orographically driven precipitation on windward slopes leading to increased exhumation but limited preservation of surface uplift. Eastward propagation of the mountain range resulted in increasingly extreme orographic effects on the leeward side amplifying aridity, reducing exhumation and increasing preservation of surface uplift. Essentially, surface uplift shows a ∼5-10 Myr lag behind initial rock uplift as the Andes grow asymmetrically through time. We suggest that an eastward propagating pattern of exhumation, aridity and surface uplift with time, reconciles previous contradictory models of Andean uplift.
One Sentence Summary
Uplift of the Central Andes is reconstructed over the last 50 Myr and the precise relationship between roles of tectonics and climate established.
... The fluvial channels were the final spilling pathways across the scarp, before they were cut from their source area (Figs. 1,2). Fluvial channels are incised up to ~ 14 m into the crest of the thrust fault, indicating that initially incision kept pace with uplift. ...
... Since the areas to the west of the Andean fore slope are generally drier (e.g. [1][2][3][4], we also assume the study area was arid to hyperarid. During this time, intermittent locally-sourced precipitation events must have been capable of incising the channels into the flat alluvial fans without modifying the surface. ...
The Atacama Desert is the driest and oldest desert on Earth. Despite the abundance evidence for long-term landscape stability, there are subtle signs of localised fluvial erosion and deposition since the onset of hyperaridity in the rock record. In the dry core of the Atacama Desert, pluvial episodes allowed antecedent drainage to incise into uplifting fault scarps, which in turn generated sinuous to meandering channels. Incision of ancient alluvial fan surfaces occurred during intermittent fluvial periods, albeit without signs of surface erosion. Fluvial incision during predominantly hyperarid climate periods is evident from these channels in unconsolidated alluvium. The absence of dense vegetation to provide bank stability and strength led us to investigate the potential role of regionally ubiquitous CaSO4-rich surface cover. This has enabled the preservation of Miocene surfaces and we hypothesize that it provided the required bank stability by adding strength to the upper decimetre to meter of incised alluvium to allow high sinuosity of stream channels to form during pluvial episodes in the Quaternary.
... As a result, hyperarid conditions have developed and still currently prevail in the so-called Atacama Desert (e.g. Dunai et al., 2005). This context induces very low erosion rates (1-10 mm.ka −1 ; Madella et al., 2018 and references therein) which allows an exceptional preservation of landscapes over several millions of years (e.g. ...
... This context induces very low erosion rates (1-10 mm.ka −1 ; Madella et al., 2018 and references therein) which allows an exceptional preservation of landscapes over several millions of years (e.g. Dunai et al., 2005). Contrasting with these dominantly dry conditions, records of extreme erosional events, such as flash floods, debris flows or landslides linked to El Niño-La Niña oscillations (ENSO) have been reported during the late Pleistocene in Southern Peru (e.g. ...
It is of major importance for Earth surface sciences to reconstruct denudation rates in the most precise and accurate way. For this, it can be useful to test on the same setting methods based on different assumptions, such as those relying on geomorphological and geochemical observations. Here, we use an exceptionally suited setting in the Locumba catchment (southwestern Peruvian Andes) that offers the unique opportunity to compare denudation rates derived from in situ cosmogenic 3 He and 10 Be with a geomorphological sediment budget integrated over the last 18 ka. The sediment budget is estimated by determining the volume of sediment trapped in the Aricota lake that formed 18 ka ago after the occurrence of a giant rockslide dam. We reconstructed the topography of the Locumba valley before the dam emplacement and established that the captured sediment volume is 0.8 ± 0.1 km 3. Considering that the lake-water output is restricted to seepage through the dam and that overflow above the dam never occurred, this volume correctly represents the sediment flux integrated over the last 18 ka. Integrating this volume over the upstream catchment area (∼1500 km 2), we derived a corresponding mean erosion rate of 30 ± 9 mm.ka −1. Fluvial sediments feeding the Aricota lake were sampled to derive denudation rates from in-situ cosmogenic 10 Be in the silicates and from in-situ cosmogenic 3 He in the ferromagnesian minerals. Cosmogenic nuclide denudation rates from the main stream are 30 ± 2, 33 ± 2, 21 ± 1 and 82 ± 5 mm.ka −1 for the 10 Be-quartz, the 10 Be-feldspar, the 3 He-amphibole and 3 He-pyroxene, respectively. The consistency between the cosmogenic nuclide denudation rates derived from 10 Be in the silicates and the erosion rate derived from our sediment budget shows that the 10 Be accurately estimates of the sediment flux. Additionally, this work provides the first successful application of 10 Be-feldspar nuclide-mineral pair to derive catchment-mean denudation rate and demonstrate that 10 Be-feldspar can thus be a good alternative in catchments dominated by volcanic rocks with no quartz. The discrepancies observed between the denudation rates derived from the 3 He-amphibole and 3 He-pyroxene couples require further studies.
... The desert systems along the Peruvian-Chilean coast are regarded as the driest desert ecosystems on earth (Dunai et al., 2005). In particular the northern Chilean coastal region is characterized by arid and hyperarid climate. ...
... Aridity in the Atacama Desert is a long-term phenomenon throughout the Cenozoic and has been punctuated by wetter periods. The onset of the history of the Atacama Desert with its predominantly arid/hyperarid climate is placed into the Early Miocene 15-20 million years ago (Dunai et al., 2005) or potentially earlier (Hartley and Rice, 2005;Ritter et al., 2018). ...
Among the fascinating and highly specialized vascular plants in the hyperarid core of the Chilean and Peruvian Atacama Desert there are few Tillandsia species from the bromeliad family (Bromeliaceae). These grow epiarenically on bare sand without a functional root system, and in some rare cases they build up a monospecific and often the only landscape characterizing vegetation type, which is called Tillandsiales or Tillandsia loma. Tillandsia landbeckii is the dominating epiarenic species in Chile totally dependent on fog serving as the only water resource. Herein we elaborate on the hypothesis that migration and multiple colonization in concert with putative introgression from other Tillandsia species build up the present day phylogeographic distribution pattern and may contribute to the evolutionary dynamics and long-term success in hyperarid desert systems. Genomic analyses using GBS (genotyping-by-sequencing) data from the nuclear and plastid genome were conducted at the population level. A genome skimming approach was used to generate reference plastome data. The results indicate that both, multiple colonization and secondary contact of old gene pools and interspecies geneflow, contribute to present-day population genetic structure. Local-scale analysis also indicates that these past footprints of evolutionary history do contribute to present-day local adaptive potential of the species.
... Thus, it is rarely possible to accurately quantify the amount of cosmogenic 21 Ne produced since the LGM in the presence of a commonly substantially larger nucleogenic and atmospheric background. For this reason, cosmogenic 21 Ne exposure dating has been most applied to deposits with exposure ages of hundreds of thousands to millions of years (Dunai et al., 2005;Balter-Kenney et al., 2020;Spector and Balco, 2021). ...
We report new cosmogenic 21Ne-in-quartz exposure ages from 18 samples on three distinct moraines deposited in the Lost Creek drainage, approximately 3–7 km down-valley from Lassen Peak in Lassen Volcanic National Park. Although measuring 21Ne in quartz is generally straightforward, accurate 21Ne exposure dating of deposits of late Pleistocene-age is rarely possible due to the significant quantities of non-cosmogenic 21Ne present in most lithologies. Young quartz-bearing volcanic rocks have been observed to be an exception. We take advantage of moraine boulders sourced from the ~28 ka dacite of Lassen Peak to generate a chronology of alpine deglaciation in Lassen Volcanic National Park. Ages from three distinct moraines are in stratigraphic order, ranging ~22–15 ka, and generally agree with other terminal and some recessional moraine ages across the Cascades and Sierra Nevada Range of the western United States. To date, these are among the youngest surfaces ever dated using cosmogenic 21Ne and provide a cost-effective proof-of-concept approach to dating moraines where applicable.
... Collections from sediments collected from old and stable surfaces in Antarctica and in the Atacama Desert exhibit the longest accumulation periods (>1 Myr [27,42,63,67,94]). In particular, these collections include thousands of micrometeorites larger than 200 µm [7,26,27,95,96], which are relatively rare in ice and snow collections due to the limited accumulation periods. ...
Micrometeorites are estimated to represent the main part of the present flux of extraterrestrial matter found on the Earth’s surface and provide valuable samples to probe the interplanetary medium. Here, we describe large and representative collections of micrometeorites currently available to the scientific community. These include Antarctic collections from surface ice and snow, as well as glacial sediments from the eroded top of nunataks—summits outcropping from the icesheet—and moraines. Collections extracted from deep-sea sediments (DSS) produced a large number of micrometeorites, in particular, iron-rich cosmic spherules that are rarer in other collections. Collections from the old and stable surface of the Atacama Desert show that finding large numbers of micrometeorites is not restricted to polar regions or DSS. The advent of rooftop collections marks an important step into involving citizen science in the study of micrometeorites, as well as providing potential sampling locations over all latitudes to explore the modern flux. We explore their strengths of the collections to address specific scientific questions and their potential weaknesses. The future of micrometeorite research will involve the finding of large fossil micrometeorite collections and benefit from recent advances in sampling cosmic dust directly from the air.
This article is part of the theme issue ‘Dust in the Solar System and beyond’.
... Ma, lo que indicaría que la hiperaridez en esta zona se estableció en esta época (Dunai et al., 2005). Sin embargo, existe controversia de cuando se estableció la hiperáridez ya que existen estudios que indican que el Mioceno Tardío se caracterizaba por aumento de las precipitaciones en la región central de los Andes (e.g Poulsen et al., 2010). ...
The Humboldt Current System (HCS) presents particular oceanographic conditions that make it the most productive ecosystem in the world. The origins of these conditions, however, are still unknown. Marine sediments indicate much warmer conditions in the eastern tropical Pacific during the Miocene and Pliocene, which lead to the Hypothesis of permanent El-Niño-like conditions. The modern East-West temperature gradient of the Pacific may have progressively grown with glacial conditions during the Early Pleistocene. How environmental conditions have evolved on the coast of Peru remain unclear. In the Miocene, the Andes were not as high as today, and a shallow epicontinental sea, protected from the open ocean by a mountain ridge, was present along the southern coast. This sedimentary basin, known today as the Pisco formation, has yielded one of the most extraordinary fossil record of marine vertebrate evolution. In this study, we collected fossil shells and shark teeth from the East Pisco Basin (EPB) from different sedimentary deposits from Late Miocene to Pleistocene, the ages of these deposits were determined by radiogenic dating and strontium isotopic stratigraphy. We compared the strontium isotopic signature between fossil shark teeth, which are indicators of open ocean oceanographic conditions, and mollusks as indicators of coastal conditions. Results shows for different ages an important connectivity between EPB and the oceanic waters, despite the barrier that the Coastal Cordillera could represent. However, for the Sacaco Chacra locality (Late Miocene) a considerable restriction did not allow complete mixing between the EPB and oceanic waters. Results shows for this locality a continental waters contribution would reach up to (~45%), affecting considerably the salinity of EPB. We analyzed the sclerochronology and the monthly variation δ18O and δ13C at high resolution in 19 shells for three ages. Mean δ18O indicate a cooling of the oceanic waters from Late Miocene to Pleistocene. High-resolution evaluation of δ18O and δ13C for Late Miocene (Sacaco Chacra locality) in 15 Anadara chilensis fossil shells would indicate El Niño events, with 2.9 years of frequency. Additionally, these El Niño events would cause flooding events in the EPB, showing that Peruvian south coast was not hyperarid for this time as it is currently known. My results represent the oldest direct record of El Niño activity.
... The Atacama Desert in northern Chile is known to be one of the oldest and driest deserts on Earth (e.g., Dunai et al., 2005). The extreme aridity is caused by coupled subtropical atmospheric subsidence, coastal upwelling of cold northward flowing Humboldt current and the temperature inversion created through this interaction (Houston and Hartley, 2003). ...
... Nevertheless, only single phytolith-bearing records are reported from the literature (e.g., Pfeiffer et al., 2018;McRostie et al., 2022), and the knowledge of the regional phytolith taxonomy is restricted to only few plant families (McRostie, 2013). Because of the long-lasting aridity of the Atacama Desert, which may date back as far as the Oligocene (Dunai et al., 2005), paleo-archives from ancient lakes, wetlands or caves are extremely scarce. Paleoclimate information from the Atacama Desert, therefore, still is very sparse and discontinuous. ...
... Within this framework, the 21 Ne concentration most probably represents a minimum cumulated exposure duration, experienced by the quartz grains now embedded in the duricrust, that is between 5.9 ± 0.9 and 13.0 ± 3.0 Myr (9.5 ± 1.7 Myr) whether (a) using a cosmogenic production scaling scheme accounting for temporal geomagnetic variations or not (e.g., Lifton et al., 2015;Stone, 2000), and (b) correcting for nucleogenic 21 Ne content or not (e.g., Siame et al., 2023). This would result amongst the oldest exposure ages determined so far using this cosmogenic nuclide (e.g., Dunai et al., 2005;Schäfer et al., 1999). Altogether, this suggests that the highest geomorphic surface (Chapada do Distrito Federal) is most probably polygenic and might results from an etchplanation episode during the Middle-Late Miocene. ...
Land degradation resulting from increased continental surface erosion is a worldwide and systemic phenomenon due to unsustainable human activities. Already fragile, the intertropical zone is likely to be further affected by climate change like increased aridity, an aggravating factor of soil erosion and land degradation. A major challenge is thus to provide the necessary knowledge to not only deepen our understanding of the Earth's system and its critical thresholds but also to help achieving sustainability. Understanding the factors that control the properties and processes of the critical zone, and especially what will be its responses to ongoing climate and land use changes, requires multidisciplinary efforts to tackle time scales that are compatible with morphogenesis and soil development as well as environmental disturbances of anthropogenic origin. Due to its prominent ecological importance, the Brazilian Cerrado biome is an ideal natural laboratory were to gauge the consequences of recent and intense agricultural activities on continental surface erosion. We focused on the region of Brasília where our approach allows confronting the temporal scales of long‐lived and stable cosmogenic nuclides with that of short‐lived radioactive isotopes, through a comparison of natural and anthropogenically disturbed land surfaces. Our results indicate that long‐term, background denudation rates are lower than 10 mm Kyr⁻¹ whereas recent erosion rates due to human activities may reach rates at least 160 times higher, exceeding by far the sustainability of the soil resource.
... As a result of these changes, the climatic and geological conditions that prevail today in the Peruvian Desert and the Atacama Desert have been established. Significant aridification in these deserts presumably started in the Early Miocene in what is now the hyperarid core of the Atacama Desert (Dunai et al., 2005;Ritter et al., 2018a). Throughout the Miocene to recent times this process has expanded and intensified (Hartley and Chong, 2002;Jordan et al., 2014;Evenstar et al., 2017;Ritter et al., 2018a). ...
... The Atacama Desert in northern Chile is known to be one of the oldest and driest deserts on Earth (e.g., Dunai et al., 2005). The extreme aridity is caused by coupled subtropical atmospheric subsidence, coastal upwelling of cold northward flowing Humboldt current and the temperature inversion created through this interaction (Houston and Hartley, 2003). ...
... In the area here presented it is possible to consider the presence of very old, relict water trapped in old volcanic and intrusive rocks that cooled in presence of seawater millions of years ago, which was later exposed to meteoric waters due to the tectonic uplift of the Cordillera de la Costa in the Pleistocene. The washing out of initial groundwater in these rocks may have been extremely slow, due to low permeability at large scale of the altered volcanic rocks and the small recharge under the hyper-arid conditions prevailing in the Atacama Desert since the late Oligocene to the Present (Dunai et al., 2005;Oerter et al., 2016;Sun et al., 2018). However, the time when hyper-aridity began in the Atacama Desert is still a matter of debate, and range from the late Oligocene to the Pleistocene. ...
... The most widespread approach is one that quantifies the average erosion rate of a catchment 20 from its average CN concentration in a sand sample taken at its outlet (Brown et al., 1995). Since the pioneering work of Repka et al. (1997), other studies have explored the possibility of using the distribution of CN concentrations in distinct grains and possibly grains of different sizes to quantify erosion-deposition processes on hillslopes, in rivers and on alluvial deposits over periods of several thousand to millions of years (Braucher et al., 1998;Dunai et al., 2005;Gayer et al., 2008;Codilean et al., 2008;Carretier et al., 2019). However, it is still difficult to link detrital CN concentration data to specific processes, whether 25 on hillslopes or on a larger scale in river systems (Yanites et al., 2009). ...
The measurement of cosmogenic nuclide (CN) concentrations in riverine sediment has provided breakthroughs in our understanding of landscape evolution. Yet, linking this detrital CN signal and the relief evolution is based on hypotheses that are not easy to verify in the field. A model would help to better understand the statistics of CN concentrations in sediment grains. In this work, we present a coupling between the landscape evolution model Cidre and a model of the CN concentration in distinct grains. These grains are exhumed and detached from the bedrock and then transported in the sediment to the catchment outlet with temporary burials and travel according to the erosion-deposition rates calculated spatially in Cidre. The concentration in the various CN can be tracked in these grains. Because the CN concentrations are calculated in a limited number of grains, they provide an approximation of the whole CN flux. Therefore, this approach is limited by the number of grains that can be handled in a reasonable computing time. Conversely, it becomes possible to record part of the variability in the erosion-deposition processes in the grain-by-grain distribution of the CN concentrations by tracking the CN concentrations in distinct grains using a Lagrangian approach. We illustrate the robustness and limits of this approach by deriving the catchment-mean erosion from the 10Be mean concentration of grains leaving a synthetic catchment uplifting at different rates and by comparing this derived erosion rate to the actual one calculated by Cidre.
... With few year-round freshwater sources, except for the Loa River, the general perception is that of an empty, sterile, inert landscape without a trace of human presence. Geological studies indicate that the rate of erosion here is the lowest recorded, and as such this landscape is considered the oldest on the planet, dated at 25 million years old (Dunai et al. 2005). This high degree of natural conservation has enabled archaeological features such as paths and geoglyphs, for example, to last for thousands of years without major transformation. ...
... Also along an arid-hyperarid coast in the United Arabic Emirates, Abdelfattah (2013) found that (i) Aridisols formed on alluvial fans, dune sands or along the supratidal shore feature elevated CaCO 3 contents mostly exceeding 30% throughout the entire profiles; (ii) pedogenic accumulation of gypsum in the top soils for those pedons developed in coastal dune sand and at the supratidal beach; while (iii) moderate to strong salinity is restricted to the near-shore Aquisalids and Haplosalids. In contrast to those as well as the hyperarid soils in the central Atacama Desert that are formed over much longer timescales than at the coast − on surfaces which date back between the Middle Pleistocene to the Oligocene (e.g., Dunai et al., 2005;Placzek et al., 2010;Baker et al., 2013;Ritter et al., 2018) − leaching of soluble minerals, i.e. CaCO 3 and NaCl, prevails in the south-central coastal Atacama since the last interglacial period ( Fig. 6; Fig. 8b). ...
... The CVZ was selected due to the relatively restricted compositional range that characterizes this volcanic arc (mainly andesitic to dacitic magmas; Stern, 2004;Wörner et al., 2018). The hyper-arid climate conditions since the Miocene (Dunai et al., 2005) caused the formation of unvegetated surfaces and extremely-low erosion rates, so that a remarkable number of stratovolcanoes and lava flows with well-preserved surface structures are present. This study includes 49 andesitic to dacitic lava flows emplaced during the Pleistocene (Table 2, Supplementary material 1) selected from 27 volcanic systems, with compositions ranging from 58.7 to 68.3 wt% SiO 2 . ...
... The Atacama Desert and its surrounding Puna ecoregions are part of the Central Andes, straddle four different countries (Argentina, Bolivia, Chile, and Peru/see Figure 1), and present special features linked to their hyperarid, arid, or semiarid characteristics. Indeed, this widespread aridity has been stable over several million years in recent geological times (Clarke, 2006;Dunai et al., 2005). The presence of marked wind erosion (De Silva et al., 2013;Perkins et al., 2019), intermittent rivers (Houston, 2006), vast areas of evaporites in an endoreic context (Marazuela et al., 2019), complex groundwater recharge (Salas et al., 2016), glacial and periglacial geomorphological landforms (Garc ıa et al., 2017), intense radiation (Matteucci et al., 2012), and the proven presence of extremophiles (Albarrac ın et al., 2015) make this volcanic region (Allmendinger et al., 1997;De Silva, 1989) a possible relevant analog for the conditions that Mars may have experienced during its past geological history, making this particular place of the Earth one of the hypothetical "hot spots" for developing planetary science (De Silva et al., 2002). ...
In 2019, while launching a multidisciplinary research project aimed at developing the Puna de Atacama region as a natural laboratory, investigators at the University of Atacama (Chile) conducted a bibliographic search identifying previously studied geographic points of the region and of potential interest for planetary science and astrobiology research. This preliminary work highlighted a significant absence of local institutional involvement in international publications. In light of this, a follow‐up study was conducted to confirm or refute these first impressions, by comparing the search in two bibliographic databases: Web of Science and Scopus. The results show that almost 60% of the publications based directly on data from the Puna, the Altiplano, or the Atacama Desert with objectives related to planetary science or astrobiology do not include any local institutional partner (Argentina, Bolivia, Chile, and Peru). Indeed, and beyond the ethical questioning of international collaborations, Latin‐American planetary science deserves a strategic structuring, networking, as well as a road map at national and continental scales, not only to enhance research, development, and innovation, but also to protect an exceptional natural heritage sampling extreme environmental niches on Earth. Examples of successful international collaborations such as the field of meteorites, terrestrial analogs, and space exploration in Chile or astrobiology in Mexico are given as illustrations and possible directions to follow to develop planetary science in South America. To promote appropriate scientific practices involving local researchers, possible responses at academic and institutional levels will eventually be discussed.
... The hyperaridity of the Atacama Desert, where average annual precipitation in Chile's northern coastal stretch does not exceed 10 mm/yr (Dirección Meteorológica de Chile, 2020), and the transient nature of erosion in this part of the Andes provide unique conditions that lead to very low erosion rates (Carretier et al., 2018 and references therein). In fact, average subaerial erosion rates of <1 cm/kyr are generally measured in Northern Chile using terrestrial cosmogenic nuclide (e.g., Dunai et al., 2005;Nishiizumi et al., 2005;Kober et al., 2007;Placzek et al., 2014;Carretier et al., 2018), and data show that some marine terraces have been eroded <1 mm/kyr even south of the driest sectors of the Atacama Desert (Saillard et al., 2009;Martinod et al., 2016). ...
Coastal cliff evolution is modulated by several factors, such as uplift, marine erosion, previous topographical conditions, and changes in global sea level. In this study, a numerical model is used to understand the influence of these processes on the evolution of coastal cliffs. This model is based on erosional and tectonic conditions of the Great Coastal Cliff in the Atacama Desert, the tallest and most uninterrupted coastal cliff on Earth. The results show that a faster uplift rate (> 0.3 mm/yr) or an older onset of uplift (3 Myrs) favors the formation of inactive cliffs, whereas active cliffs preferentially form under conditions of a slow uplift (0.2 mm/yr) or a younger uplift onset (1 Myr). Low erosion rates (< 1 m^2⁄yr) also favor the preservation of sequences of staircase marine terraces, separating the seashore from an inactive coastal cliff. In contrast, high erosion rates (> 1 m^2⁄yr) inhibit marine terrace formation, keeping the cliff active. The effect of erosion on cliff activity is enhanced or reduced by the slope of the initial topography. Steep coasts (> 5-10°) may hamper cliffs from reaching an inactive state. Thus, this model gives insights on the relative importance of these variables on the development of active and inactive cliffs, especially in an environment such as the Atacama Desert in northern Chile.
... 33.9-23 Ma), thus making it also one of the oldest deserts (e.g. Dunai et al., 2005;Evenstar et al., 2017). Paleoclimate records and geomorphic studies from various sites of the Atacama Desert, however, indicate variations in the overall aridity over time, which was repeatedly punctuated by more humid phases on millennial and orbital timescales (Ritter et al., 2019;Diederich et al., 2020). ...
Geomorphic and sedimentologic data indicate that the climate of today's hyper-arid Atacama Desert (northern Chile) was more humid during the mid-Pliocene to Late Pliocene. The processes, however, leading to increased rainfall in this period are largely unknown. To uncover these processes we use both global and regional kilometre-scale model experiments for the mid-Pliocene (3.2 Ma). We found that the PMIP4–CMIP6 (Paleoclimate Modelling Intercomparison Project–Coupled Model Intercomparison Project) model CESM2 (Community Earth System Model 2) and the regional model WRF (Weather Research and Forecasting) used in our study simulate more rainfall in the Atacama Desert for the mid-Pliocene in accordance with proxy data, mainly due to stronger extreme rainfall events in winter. Case studies reveal that these extreme winter rainfall events during the mid-Pliocene are associated with strong moisture conveyor belts (MCBs) originating in the tropical eastern Pacific. For present-day conditions, in contrast, our simulations suggest that the moisture fluxes rather arise from the subtropical Pacific region and are much weaker. A clustering approach reveals systematic differences between the moisture fluxes in the present-day and mid-Pliocene climates, both in strength and origins. The two mid-Pliocene clusters representing tropical MCBs and occurring less than 1 d annually on average produce more rainfall in the hyper-arid core of the Atacama Desert south of 20∘ S than what is simulated for the entire present-day period. We thus conclude that MCBs are mainly responsible for enhanced rainfall during the mid-Pliocene. There is also a strong sea-surface temperature (SST) increase in the tropical eastern Pacific and along the Atacama coast for the mid-Pliocene. It suggests that a warmer ocean in combination with stronger mid-tropospheric troughs is beneficial for the development of MCBs leading to more extreme rainfall in a +3 ∘C warmer world like in the mid-Pliocene.
... e. fastest) uplift occurred in the mid-Miocene (12 Ma) and early Pliocene (5 Ma) (Ramos and Ghiglione, 2008;Jordan et al., 2014) that created an even larger rain shadow to the west (Rech et al., 2006;Hoorn et al., 2010) and the formation of the Arid Diagonal of South America (Luebert, 2021), a narrow region with little precipitation (less than 300 mm/year) located between 32 • and 52 • S. Throughout the late Cenozoic, Andean orogeny is known to have created new habitats, acting as an east-west dispersal barrier and playing an essential role in generating the high diversity of South American montane environments (Hoorn et al., 2010). The hyper-arid core of the Atacama Desert (20 • -25 • S) is estimated to have originated between the late Miocene (Dunai et al., 2005;Houston, 2006;Rech et al., 2006) and the early Pliocene (Placzek et al., 2009). Some authors suggest that this hyperaridity may have decreased due to periodic Pleistocene pluvial episodes caused by either enhanced summer easterlies, such as the Central Andean Pluvial Events (Placzek et al., 2009;Gayo et al., 2012) or the increased influence of extra-tropical winter storms (Maldonado et al., 2005). ...
We performed a systematic review of the scientific literature on the coastal lomas, and discuss their origin, fog dependence, biodiversity patterns, and conservation. Coastal lomas are isolated vegetation oases, found from northern Peru (7 • S) to central Chile (30 • S), that depend entirely on marine fog, occurring in the Peruvian and Chilean Desert. To identify key topics in the scientific literature we fit structural topic models and identified shortfalls in knowledge using alluvial graphs. Our results show that there is no consensus on when coastal lomas originated. The spatial and temporal dynamics of the marine fog that maintains the vegetation are also not well understood. Yet, there is evidence that variation in the influx of marine fog is associated with the El Niño Southern Oscillation (ENSO), which increases moisture supply. While the taxonomic diversity of plants and fog variability have been extensively studied at local spatial scales, larger scale diversity patterns, as well as those of other facets of biodiversity, have yet to be assessed. Conservation of coastal lomas has been limited to establishing conservation areas, but their efficacy has not been examined. Major research gaps in our current understanding of coastal lomas include: macroecological patterns of assemblages, the relative importance of biotic and abiotic filters in shaping communities, and the impacts of climate change on coastal lomas and the ecosystem services that they provide. Research in these areas should be prioritized to improve conservation efforts that enhance ecosystem resilience of coastal lomas and our ability to forecast and monitor the impacts of climate change and desertification.
... Ma (Dunai et al., 2005), otros, como Hartley y Chong (2002) quienes proponen una edad Pliocena (3 -4 Ma) para el comienzo de la hiperaridez. ...
La configuración actual antearco del norte de Chile es el resultado de la combinación de procesos magmáticos, tectónicos y climáticos que han ocurrido desde el comienzo del Ciclo Andino en el Jurásico temprano. Esta evolución ha producido cuatro grandes elementos fisiográficos, de Oeste a Este: La Cordillera de la Costa, Depresión Central, Precordillera y el Salar de Atacama en Antofagasta. Con la ayuda del programa Cidre, investigue los factores dominantes involucrados en la formación del relieve actual en el antearco del norte de Chile. Para esto, modelé la evolución del antearco durante los últimos 26 Ma. utilizando como condiciones de borde los estudios sobre la historia de alzamiento y los controles de primer orden relacionados a la construcción del relieve actual.
A través de tres análisis de sensibilidad, modelé la zona de Arica y la zona de Antofagasta, esta última dos veces, de acuerdo a dos hipótesis diferentes sobre la historia de alzamiento de la Depresión Central. Para esto testeé cinco parámetros que, a priori, son importantes en la formación de relieve: (1) largo de transporte, (2) fracción de tiempo de la precipitación, (3) intensidad de la actividad tectónica, (4)
coeficiente de erodabilidad e (5) intensidad de la precipitación. Asumiendo topografías iniciales simplificadas, basadas los antecedentes disponibles, se concluye que el largo de transporte es uno de los parámetros más importantes, dada su sensibilidad y su influencia en los tiempos que tardan en desarrollarse las redes de drenaje, lo que a su vez, influye en la cobertura sedimentaria depositada en la Depresión Central. La fracción de tiempo de la precipitación, también es un
parámetro importante, dado que al disminuirlo, aumenta el largo de transporte efectivo, lo que promueve la conservación de los depósitos sedimentarios, inhibiendo el desarrollo de extensas redes de drenajes, así como también conserva rasgos estructurales tales como el Escarpe El Bordo. La influencia de la
intensidad de la actividad tectónica es disímil en las áreas de estudio. Por una parte, el relieve del antearco de Arica está controlado por la intensa actividad tectónica registrada en la Precordillera, mientras que el antearco de Antofagasta no muestra variaciones al aumentar la intensidad de la actividad tectónica. El coeficiente de erodabilidad es un factor fundamental en la formación del relieve del norte de Chile, dado que con pequeñas variaciones, se generan modelos diametralmente opuestos. La intensidad de la precipitación, al igual que la intensidad de la actividad tectónica, tiene influencias disimiles entre ambas áreas de estudio. El relieve del antearco de Antofagasta no muestra grandes variaciones al aumentar la intensidad de la precipitación, no así Arica, donde este factor tiene especial relevancia en la mantención de los espesores de las cuenca de la Depresión Central y la del Altiplano.
... A specificity of the Central Western Andes is its hyperarid climate prevailing since at least the Miocene (Rech et al., 2019) and making the Atacama Desert one of the driest and oldest desert on Earth (Hartley et al., 2005) which enable exceptionally long landscape preservation due to slow, long-term erosion (Dunai et al., 2005). ...
The western flank of the Central Andes offers a unique geomorphological record of large paleolandslides that are well preserved on long time‐scales (i.e. ≥ Pleistocene) due to the long‐lasting aridity of this region. However, the lack of chronological constraints on those landslides limits our understanding of the respective role of tectonics and climate on their triggering. Here, we report new 10Be surface exposure dating obtained on one of those giant slope‐failures: the Limaxina landslide (northern Chile, 19°S). Five tightly grouped exposure‐ages (one outlier discarded) point to a single landslide failure at 80 ± 4 ka. This timing being consistent with others local records of a wet episode in the Atacama Desert, it suggests a primary role of climate‐forcing on landslide activity in this region, calling to further slope failures dating in the arid Central western Andes to explore landscapes responses to Quaternary climate oscillations and extreme events.
... Due to the hyperaridity, the geomorphic processes are taking place in remarkable slowness, which is evident by the age of surfaces and landforms (Clarke, 2006;Dunai et al., 2005;Matmon et al., 2015). Nevertheless, there are several records, especially from the last decade, that indicate that flash floods can even reach hyper-arid parts of the Atacama, e.g. ...
Recent research indicates an inverse relation between Synthetic Aperture Radar (SAR) signal and near-surface soil moisture (SM) over very dry sediments, arid to hyper-arid soils resp., caused by subsurface scattering effects. This phenomenon can lead to large errors when it comes to modelling and remote sensing-based estimation of SM. While the effect of subsurface scattering and its influence on SM estimates is well described and modelled in literature, its actual presence in recorded SAR data is largely unknown. Here we investigate the relation between C-Band SAR backscatter and SM in the hyper-arid environment of the Atacama Desert (Chile). Time series (2018–2020) of Sentinel-1 VV/VH intensities are compared to in situ SM, measured at 17 stations located across the Atacama Desert. Linear and non-linear regression modelling is applied to uncover the relationship between the SAR intensities and in situ SM, while, in addition, SM variations triggered by seasonal varying humidity (i.e., not by precipitation) are investigated. Results indicate (i) a very weak linear relationship between SM variations and SAR intensities (VV/VH) for most meteorological stations in the Atacama (R² < 0.5). In particular, noticeable and significant exceptions are found for stations located in the northern uplands of the Coastal Cordillera and on sediments, which are characterized by thick atmospheric dust deposits on top of subsurface cemented crusts; (ii) over these sites a strong inverse linear relationship is present (R² up to 0.84) and the observable seasonal variations in SAR intensity are linked to the seasonal variations in SM; (iii) remarkably low changes in SM (ranging from approx. 1 to 3%) lead to comparable high changes in SAR intensity (up to 5.5 dB in VH and up to 4.0 dB in VV); (iv) employing a non-linear regression modelling to the SAR time series allowed identifying the occurrence and the strength of seasonal variations over the central desert. This study contributes to a better understanding of SAR scattering over arid to hyper-arid soils, indicates a moisture-regulated complex interplay of surface and subsurface scattering, and proves the presence of subsurface scattering effects in Sentinel-1C-Band data to occur over large parts of the Atacama Desert.
... For this reason, even though the erosion rates seem to be very low in the Atacama, it is important to assess their maximum value. The gently sloping surfaces in the Atacama lead to very low erosion rates (e.g., Dunai et al., 2005;Hall et al., 2005;Carretier et al., 2018). The cosmogenic nuclides concentrations from the earth's surface indicate a maximum for the local erosion rate, even though the samples were collected first to calculate the surface ages. ...
We explore coastal morphology along a 500 km long uplifted coastal segment in the central
Andes, between the cities of Chala (Peru) and Arica (Chile). We use accurate DEM and
field studies to extract uplifted shoreline sequences along the study area. In addition, we
consider continental pediment surfaces that constrain both the geographic and vertical
extent of marine landforms. We establish a chronology based on published dates for marine
landforms and pediment surfaces. We extend this corpus with new 10Be data on uplifted
shoreline platforms. We find that the last 12 Ma is marked by three periods of coastal
stability or subsidence dated at ~12-11 Ma, ~8-7 Ma, and ~5-2.5 Ma. Uplift that
accumulated between these periods of stability has been ~1000 m since 11 Ma; its rate is
up to 0.25 mm/a (m/ka). For the last period of uplift only, during the last 800 ka, the forearc
uplift has been accurately recorded by the cutting of numerous coastal sequences. Within
these sequences, we correlated marine terraces with high sea levels (interglacial stages
and substages) up to MIS 19 (790 ka), i.e., with a resolution of ~100 ka. The uplift rate for
this latter uplift period increases westward from 0.18 mm/a at the Peru-Chile border to
~0.25 mm/a in the center of the study area. It further increases northwestward to 0.45 mm/a
due to the influence of the Nazca Ridge. In this study, we document unusual cyclic forearc
uplift with cycles of ~4 Ma in duration. This periodicity is consistent with predictions made by
Menant et al. (2020) based on numerical models, and may be related to episodic tectonic
uplift (subduction slab detachment) beneath the coastal forearc zone.
... Cosmogenic radionuclide dating has emerged as one of the most promising methods for studying Quaternary geological events (Ivy-Ochs and Kober, 2008). It is used to date sedimentary units such as moraines (Bohra, 2016) on a centennial to millennial-scale (Dunai et al., 2005). The principle behind cosmogenic radionuclide dating is that any stable exposed geological surface can be dated by measuring the amount of accumulated cosmogenic nuclides (Dunai, 2010). ...
Quantitative glacial chronologies of past glaciations are sparse in the Himalaya, and mostly absent in the Kashmir Himalaya. We used cosmogenic 10Be exposure dating, and geomorphological mapping to reconstruct glacial advances of the Thajwas Glacier (TG) in the Great Himalayan Range of the Kashmir Himalaya. From 10Be exposure dating of ten moraine boulders, four glacial stages with ages ~20.77 ± 2.28 Ka, ~11.46 ±1.69 Ka, ~9.12 ±1.39 Ka and ~4.19 ±0.78 Ka, were identified. The reconstructed cosmogenic radionuclide ages confirmed the global Last Glacial Maximum (gLGM), Younger Dryas, Early Holocene, and Neoglaciation episodes. As per area and volume change analyses, the TG has lost 51.1 km2 of its area and a volume of 2.64 km3 during the last 20.77± 2.28 Ka. Overall, the results suggested that the TG has lost 64% of area and 73% of volume from the Last glacial maximum to Neoglaciation and about 85.74% and 87.67% of s area and volume, respectively, from Neoglaciation to the present day. The equilibrium line altitude of the TG fluctuated from 4238 m a.s.l present to 3365 m a.s.l during the gLGM (20.77± 2.28 Ka). The significant cooling induced by a drop in mean ambient temperature resulted in a positive mass balance of the TG during the gLGM. Subsequently the melting accelerated due to the continuing rise of the global ambient temperature. Paleo-glacial history reconstruction of the Kashmir Himalaya, with its specific geomorphic and climatic environment, would help close the knowledge gap about the chronology of past regional glacial episodes.
... The rate of erosion in this catchment is significantly high. Moreover, most of the hillslopes are of sedimentary rock, susceptible to erosion from surface runoff [2,3]. The UKM practices regular trimming of grass on the slope at ground level, especially in the roadside bottom slopes. ...
Malaysia like many Southeast Asian countries is experiencing a large-scale soil erosion problem. The catchment area along with the Universiti Kebangsaan Malaysia (UKM) located in the Langat River basin in Peninsular Malaysia releases a substantial amount of sediment. Hill slopes are of sedimentary rock, susceptible to erosion from surface runoff. Establishing permanent vegetation cover is known to be an effective measure to control severe erosion. The objective of this study is to estimate the performance of hydro-mulching as a rapid control measure for soil erosion. Rainfall was measured using the digitized HBO data logger. We measured TSS concentration and discharge rates of the barren and three natural vegetation covered plots from the water samples collected during rainfall events. TSS concentration and discharge rates were measured in hydro-mulched plots. All plots were demarcated by natural fragmentation and hand prepared thin drains on top, right, and left of the slopes, wherever was necessary. The plots were digitized using ArcGIS 9.3 which measured their area slope and elevation. Validation was done through extensive field visits and reviewing existing studies. Our study shows that the performance of experimental vegetation-Resam, Vetiver, and Elephant creeper has effectiveness in controlling erosion. It may suggest that hydro-mulching is an effective measure of controlling the rapid soil erosion on the steep slope.
... This region of the Andean Cordillera has no historical record of site-specific weather or climate due to its remoteness, lack of permanent settlements, and poor accessibility [41]. However, observed physiographic conditions and climate data from lower elevations in the Atacama Desert [35,37,38,[42][43][44] to the west of the Cordillera can be used to infer it. Some data are available for the Chilean Altiplano, including evaporation rates (up to 1500 mm/yr) [43] and the world's highest solar radiation flux (ca. ...
Mineral precipitation can be observed in natural environments, such as lagoons, rivers, springs, and soils. The primary precipitation process has long been believed to be abiotic due to evaporation, leading to phase supersaturation. However, biotic interactions of microbial metabolism, organic compounds, and dissolved ions leading to mineral precipitation has been shown in laboratory studies using single-organism culture. The increase in pH inducing calcium carbonate precipitation due to oxygenic photosynthesis by Cyanobacteria and the release of ions due to organic matter decomposition by Firmicutes-inducing magnesium carbonate precipitation are recognized examples. As microbes do not live as pure cultures in natural environments but form complex communities, such pure culture lab studies do not reflect natural conditions. In this study, we grew natural complex microbial communities in microcosm conditions using filtered brine as water column and two types of natural gypsum substrates, and we replenished incubations to avoid evaporation. We monitored microbial communities through optical microscopy and analyzed mineral paragenesis in association with and without microbes, using different analytical techniques, such X-ray diffraction, and optical and field emission scanning electron microscopies. To detect changes throughout the experiment, small amounts of water column brine were extracted for physicochemial determinations. We were able to detect mineral paragenesis, avoiding evaporation, including major phases of chemical sedimentary rocks, such as gypsum, calcium carbonate, and some silicates in association to microbes. In addition, we evidenced that the use of natural substrates positively impacts growth of microbial communities, promoting the development of more biomass. This study can be seen as the first attempt and proof of concept of differentiating biotic and abiotic participation in evaporitic deposits, as they can form mineral paragenesis without evaporation. Future studies with microcosm experiments using microbial mats will be needed to establish mineral precipitation induced by micro-organisms and their extracellular polymeric substances (EPS), specifically to replicate mineral paragenesis sedimented from natural brines.
The Atacama Desert in Chile is known to be one of the driest deserts on Earth, with dominating hyperaridity at least since the Miocene. During recent times, however, especially the southern part of the Atacama repeatedly experienced exceptional precipitation events, like in 2015 and 2017. Locally, these events with high rainfall rates caused catastrophic floods with significant destruction and human fatalities. Although the meteorological drivers of these heavy rains are widely understood, only little is known about the frequency and amplitude of similar events on geological timescales. Here we present the results of a study on an endorheic clay pan at the southern edge of the hyperarid core of the Atacama, an area with a mean precipitation of approx. 5 mm per year. A modern ground-truthing approach combining sediment data, remote-sensing and meteorological data as well as climate-modelling was applied. Our observations indicate that the clay pan reacted very sensitively to local precipitation during the past 30 years, with four events >20 mm total rain causing sufficient surface run-off in the catchment to partially flood the basin. Comparative analyses of the four events illustrate that the amount of run-off is dependent on the maximum rain rate during the events rather than the total rain sum. A 1.88-m long sediment core recovered from the centre of the clay pan records the local hydrological and -environmental history since the Late Pleistocene. Sedimentological, mineralogical, geochemical, and biological core analyses imply strong variations in the amplitude of the recorded rainfall, with a clear shift from enhanced alluvial activity caused by higher-amplitude rain events during the Late Pleistocene to lower-amplitude Holocene events. The Holocene background sedimentation is superimposed by seven severe “Millennial-scale rain events”, which imply precipitation maxima on sub-orbital timescales that are potentially driven by changes in the El Niño Southern Oscillation (ENSO). The results of the study shed new light on the glacial-interglacial but also the sub-orbital precipitation variability in the Coastal Cordillera of the Atacama Desert and its potential driving mechanisms, and provide perspectives of the future precipitation development in the region under progressive global warming.
Soils in hyper‐arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0–10 cm) from each of 54 subsites, including sites in direct adjacency (<10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite‐based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10–23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl‐extractable inorganic P (d18O_HCl-Pi). Total P (P t ) concentration exponentially increased from 336 mg kg ⁻¹ to a maximum of 1021 mg kg ⁻¹ in inland areas ≥10 km. With increasing distance from the coast, soil d18O_HCl-Pi values declined exponentially from 16.6‰ to a constant 9.9‰ for locations ≥10 km inland. Biological cycling of HCl-Pi near the coast reached a maximum of 76%–100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (<5 mm) as single water source, only 24 ± 14% of HCl‐P i was biologically cycled. We conclude that biological P cycling in the hyper‐arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment.
The Atacama Desert is a biodiversity hotspot of neo-endemic radiation, where long-term aridity and complex physiographic processes create a unique environmental setting. Current species assemblages are mainly concentrated in highly patchy loma formations, and plant populations occurring in these are often geographically isolated from each other. Despite a general consensus on long-term aridity in the Atacama, climatological and geological evidence points to repeated climate change, making the Atacama Desert an ideal system for studying population genetic processes in highly unstable habitats. We are analyzing the genetic structure within and between populations of Huidobria fruticosa, a paleo-endemic lineage of the Atacama Desert, to shed new light on its biogeographic history and broaden our understanding of the evolution of life in extreme aridity, as well as plant evolution in response to a changing environment. To do this, we analyzed SNP data from genotyping-by-sequencing of 354 individuals from 21 populations. Our results suggest that, despite being an ancient lineage, the current population structure of Huidobria fruticosa only reflects changing abiotic conditions over the last 2 million years. We therefore conclude that the present distribution, together with the evolutionary processes documented here, is the result of climatic fluctuations and prolonged periods of hyperaridity during the Pleistocene. Building on this understanding, our findings contribute to a global narrative that highlights the complex interplay between climate change and evolutionary dynamics, and emphasize the importance of deserts as living laboratories for deciphering how species have historically adapted to some of the most extreme habitats on Earth.
The measurement of cosmogenic nuclide (CN) concentrations in riverine sediment has provided breakthroughs in our understanding of landscape evolution. Yet, linking this detrital CN signal and relief evolution is based on hypotheses that are not easy to verify in the field. Models can be used to explore the statistics of CN concentrations in sediment grains. In this work, we present a coupling between the landscape evolution model Cidre and a model of the CN concentration in distinct grains. These grains are exhumed and detached from the bedrock and then transported in the sediment to the catchment outlet with temporary burials and travel according to the erosion–deposition rates calculated spatially in Cidre. The concentrations of various CNs can be tracked in these grains. Because the CN concentrations are calculated in a limited number of grains, they provide an approximation of the whole CN flux. Therefore, this approach is limited by the number of grains that can be handled in a reasonable computing time. Conversely, it becomes possible to record part of the variability in the erosion–deposition processes by tracking the CN concentrations in distinct grains using a Lagrangian approach. We illustrate the robustness and limitations of this approach by deriving the catchment-average erosion rates from the mean 10Be concentration of grains leaving a synthetic catchment and comparing them with the erosion rates calculated from sediment flux, for different uplift scenarios. We show that the catchment-average erosion rates are approximated to within 5 % uncertainty in most of the cases with a limited number of grains.
As located in one of the oldest and driest deserts on Earth, soils in the Atacama Desert are greatly affected by atmospheric dust deposited on soil surface and the related fate of water-dispersible colloids (WDCs, <300 nm). We hypothesize that formation and content of these WDCs change with topography and age of natural soils. To highlight the processes involved, we investigated a mid-sized and gently (∼5°) sloping alluvial fan system of multi-phase evolution at 1480 m a.s.l. in the Paposo region of the hyper-arid Atacama Desert, which is considered typical for this part of the Coastal Cordillera. Sampling was done along a topographic transect in 11 pits, and assessed the distribution and composition of WDCs by means of asymmetric flow field-flow fractionation (AF4). The younger fan section (optically stimulated luminescence (OSL)-age of ∼13.6 ka) exhibited a pronounced surface roughness and steep slopes. Here, WDCs from the top soils (0–1 cm) free of plants contained nearly 54 ± 7% of medium-sized colloids (MCs, 210–300 nm) with a dominance of Si and Al. The elevated concentrations of fine colloids (FC, 24–210 nm) and particularly nanocolloids (NCs, 0.6–24 nm) was shown in levelled surface soils near shrubs with predominance of organic carbon (OC) and Ca. With higher collodial OC and Ca content in soils near shrubs, more WDC-P was formed concomitantly through increased OC-Ca-P associations. Larger variations in total WDC content were detected in the surface soils of the older fan section, which was dated to ∼56.4 ka. Here, the peaking NC had almost disappeared and thus MC dominated, probably reflecting re-aggregation and wind erosion over longer periods of time across a relatively smooth land surface. The WDCs and WDC-P peaked at 5–10 cm depth in the older fan section, as here a solid mineral/salt layer was present, while in the younger fan section the WDCs were more likely to be translocated from ‘permeable’ surface into deeper layers, likely reflecting leaching with occasional heavy rainfall. Overall, forms and distribution of WDCs depended on both topographic position and sediment age, thus making colloids as unique tracers of soil development processes during myriad or more years.
The search for life on other planets is one of the most important scientific challenges of this century, centered mainly on Mars. The Atacama Desert is one of the places on the planet with an environment similar to the red planet, with a hyper-arid core that constitutes an extreme environment and scarce life, due to environmental factors. At the moment it has not been possible to confirm the existence of life in this planet, but it is planned to take the life to this planet by means of potato crop. Also has been research the application of microorganisms for the recovery of desert soils, with high salinity or low fertility, through the interaction of microorganisms and plants. The present review describes the similarities between the La Joya desert in Atacama and Mars, showing its importance for the search for life on that planet. Show the recent advances in the investigation of potato crops for its development on Mars or in similar conditions, in addition to the importance of the application of microorganisms that facilitate the growth and adaptability of this crop to inhospitable conditions.
Sourcing of high-quality toolstone is considered a paramount task in the study of lithic procurement among hunter-gatherers due to the key role that it played in their technological and social organization. Provenance research of artifacts made of high-quality cryptocristalline silicates (e.g. chert, chalcedony, flint, and jasper) faces the challenges of large spatial scale and the physical and chemical variation inherent between and within siliceous rocks deposits. This imposes the need for thorough geological sampling strategies to achieve representative results. Focusing on a case study of the southern Atacama Desert (northern Chile), we present and test the results of a strategy for the characterization of chert primary and/or secondary deposits through systematic field sampling and VNIR and FTIR reflectance spectroscopy. Canonical discriminant analysis of the samples spectra showed 100% accuracy of the base model in assigning the samples to their respective source area. This result shows: 1) the effectiveness of the sampling strategy to cover the cumulative variability of chert deposits belonging to different geological formations and also from the same parent geological formation; and 2) the ability of VNIR and FTIR reflectance spectroscopy as an analytical technique to differentiate between types of siliceous rocks with high geological and geographical resolution.
Background
Tenebrionidae (Insecta: Coleoptera) are a conspicuous component of desert fauna worldwide. In these ecosystems, they are significantly responsible for nutrient cycling and show remarkable morphological and physiological adaptations. Nevertheless, Tenebrionidae colonizing individual deserts have repeatedly emerged from different lineages. The goal of our study was to gain insights into the phylogenetic relationships of the tenebrionid genera from the Atacama Desert and how these taxa are related to the globally distributed Tenebrionidae.
Methods
We used newly generated transcriptome data (47 tribes, 7 of 11 subfamilies) that allowed for a comprehensive phylogenomic analysis of the tenebrionid fauna of this hyperarid desert and fills a gap in our knowledge of the highly diversified Tenebrionidae. We examined two independent data sets known to be suitable for phylogenomic reconstructions. One is based on 35 neuropeptide precursors, the other on 1,742 orthologous genes shared among Coleoptera.
Results
The majority of Atacama genera are placed into three groups, two of which belong to typical South American lineages within the Pimeliinae. While the data support the monophyly of the Physogasterini, Nycteliini and Scotobiini, this does not hold for the Atacama genera of Edrotini, Epitragini, Evaniosomini, Praociini, Stenosini, Thinobatini, and Trilobocarini. A suggested very close relationship of Psammetichus with the Mediterranean Leptoderis also could not be confirmed. We also provide hints regarding the phylogenetic relationships of the Caenocrypticini, which occur both in South America and southern Africa. Apart from the focus on the Tenebrionidae from the Atacama Desert, we found a striking synapomorphy grouping Alleculinae, Blaptinae, Diaperinae, Stenochinae, and several taxa of Tenebrioninae, but not Tenebrio and Tribolium . This character, an insertion in the myosuppressin gene, defines a higher-level monophyletic group within the Tenebrionidae.
Conclusion
Transcriptome data allow a comprehensive phylogenomic analysis of the tenebrionid fauna of the Atacama Desert, which represents one of the seven major endemic tribal areas in the world for Tenebrionidae. Most Atacama genera could be placed in three lineages typical of South America; monophyly is not supported for several tribes based on molecular data, suggesting that a detailed systematic revision of several groups is necessary.
Miocene is an important period for the development of global stromatolites. The petrological and geochemical characteristics of stromatolite (dense and porous) laminae record the changes in paleo-environment, from a drilling hole, ZK-1 at Wudaoliang in the Hoh Xil Basin, Northern Tibetan Plateau. Based on the drilling core observations, these lacustrine stromatolites are hummocky, stratiform, or domelike in shape. The stromatolites consist of dense laminae (microspar-rich) and porous laminae (microcrystalline). The oxygen isotopes suggest that these stromatolites in the Wudaoliang Formation formed in a relatively warm environment which was suitable for stromatolite growth. The isotopic variation of lacustrine stromatolites indicates the periodic hydrological closure and opening of the Miocene Hoh Xil Basin. Most of the trace elements (Ba, Pb, Th, U, Hf, Y, V, Cr, Cu, Co, Ni, and Zn) are relatively depleted in the upper continental crust. And, the rare earth elements (REE) show a slight negative Eu anomaly. The Sr/Ba and B/Ga ratios are used as paleo-salinity proxy as well, together with the results of X-ray diffraction (XRD), showing that the stromatolites tended to exist in the condition of decreased salinity. Meanwhile, the arid-dominated climate of the Miocene is more suitable for stromatolite development during the Cenozoic.
The growth of vertically laminated calcium-sulphate wedges in the Atacama Desert is assumed to be driven by the interaction of moisture supply and salt dynamics in the subsurface. Geochronological data of these wedge laminations is yet sparse but indispensable to resolve wedge-growth phases and episodes of moisture supply and to use these deposits as a palaeoclimate archive in the hyperarid environment. Our pilot study presents a first approach of dating a calcium-sulphate wedge from the Atacama Desert using coarse-grain feldspar luminescence dating. Our results show a widespread and clustered equivalent-dose distribution of two wedge samples from ∼20 Gy up to saturation. Optically stimulated luminescence (OSL) of quartz revealed unsuitable properties for dating wedge deposits. Consequently, we applied post-infrared infrared stimulated luminescence (post-IR IRSL) to coarse-grained feldspars. Since feldspar single-grain measurements yielded a low number of luminescent grains, we used 1 mm aliquots as reliable single-grain proxies for genuine single-grain measurements. Data from energy-dispersive x-ray spectroscopy (EDX) showed that the feldspar single grains have large differences in their internal K content, resulting in an averaged internal K content of 3.9 ± 1.0% for all luminescent grains. This result was subsequently used for dose rate and age calculations. Our results of equivalent-dose distributions and palaeodoses derived from the minimum age model reveal most recent wedge-growth activities at 10.6 ± 2.2 ka and 7.9 ± 1.8 ka for the two wedge samples.
In this paper, we review ideas on the geomorphological history of the southwest African passive margin, focusing on the central Namib sector and presenting new evidence on the late Neogene landscape evolution of this region. The hyperarid central Namib Desert occupies the 100–150-km-wide pediment at the foot of the Great Escarpment and forms part of the southwest African passive margin, which formed after breakup in the South Atlantic at around 118 Ma. Previous apatite fission track (AFT) and cosmogenic isotope studies and numerical models of coupled tectonic-surface processes in the same area suggest that long-term denudation rates of this passive margin (after a period of significant post-rift denudation) have been very low, ∼5 m/my.
The geological record of the Western Andean Escarpment (WARP) reveals episodes of uplift, erosion, volcanism and sedimentation. The lithological sequence at 18°S comprises a thick pile of Azapa Conglomerates (25–19 Ma), an overlying series of widespread rhyodacitic Oxaya Ignimbrites (up to 900 m thick, ca. 19 Ma), which are in turn covered by a series of mafic andesite shield volcanoes. Between 19 and 12 Ma, the surface of the Oxaya Ignimbrites evolved into a large monocline on the western slope of the Andes. A giant antithetically rotated block (Oxaya Block, 80 km×20 km) formed on this slope at about 10–12 Ma and resulted in an easterly dip and a reversed drainage on the block's surface. Morphology, topography and stratigraphic observations argue for a gravitational cause of this rotation. A “secondary” gravitational collapse (50 km3), extending 25 km to the west occurred on the steep western front of the Oxaya Block. Alluvial and fluvial sediments (11–2.7 Ma) accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall, indicating further shortening between 8 and 6 Ma. Flatlying Upper Miocene sediments (<5.5 Ma) and the 2.7 Ma Lauca–Peréz Ignimbrite have not been significantly shortened since 6 Ma, suggesting that recent uplift is at least partly caused by regional tilting of the Western Andean slope.
Geochronology and paleotopographic reconstruction of the porphyry-copper deposit at La Escondida, Chile, are used to calculate long-term erosion rates and to deduce the timing of Tertiary climatic change for a portion of the Atacama Desert region. Hypogene hydrothermal alteration and protore mineralization at La Escondida took place between 33.7 ± 1.4 and 31.0 ± 1.4 Ma based on K-Ar dating of hydrothermal biotite and sericite. Supergene weathering and copper-sulfide en-richment processes were active from 18.0 ± 0.7 to 14.7 ± 0.6 Ma based on K-Ar dating of supergene alunite, distinguished from hypogene alunite by grain size, color, and sulfur isotopic composition. Reworked lenses of volcanic ash in the vicinity of La Escondida provide useful time-stratigraphic markers at 8.7 ± 0.4, 6.5 ± 0.2, and 4.2 ± 0.2 Ma within present soil profiles. Long-term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at La Escondida using mass-balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid-inclusion geobarometry at similar deposits. The observed trend of decreasing long-term average erosion rates with time is consistent with arid to semiarid conditions in the early Miocene changing to hyperarid conditions during the middle Miocene. This climatic desiccation caused termination of significant supergene copper-suffide enrichment at La Escondida and elsewhere in the Atacama region and preservation of surficial features, including the ash horizons and the leached capping. Middle Miocene climatic desiccation in northern Chile and southern Peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral Humboldt Current and an increase in upwelling intensity as the Antarctic ice cap became established at approximately 15 to 13 Ma. The Central Andes Cordillera, which now provides a rain shadow protecting the Atacama region from precipitation from the east, must have attained at least half its present elevation prior to about 15 Ma to have played a similar role in the middle Miocene.
Landforms on the Pacific slope of the Cordillera Occidental (Western Cordillera) in S Peru reflect the episodic epeirogenic uplift of the Central Andes since the earliest Miocene. In the geomorphic history, 3 major stages are distinguished and are described in detail.-after Authors
The Atacama Desert forms one of the major hyperarid deserts of the world. Previous studies suggest that desertification commenced at 14 Ma during global climate desiccation. Sedimentologic data from middle Miocene to upper Pliocene successions in the modern Atacama Desert indicate that a semiarid climate persisted from 8 to 3 Ma, punctuated by a phase of increased aridity at ca. 6 Ma. As such, hyperaridity did not commence until the late Pliocene. Implications are (1) that the rain shadow generated by the Andean Cordillera has had a minor influence on climate change, and (2) that the upwelling, north- flowing, cold Humboldt Current, although important in establishing the generally arid climate of western South America, did not control the shift to hyperaridity. The formation of the hyperarid Atacama Desert in the late Pliocene accompanied the development of the current phase of aridification in the Sahara and Namib Deserts and is attributed to a phase of global climate cooling.
The Atacama along the Pacific Coast of Chile and Peru is one of the driest and possibly oldest deserts in the world. It represents an extreme habitat for life on Earth and is an analog for life in dry conditions on Mars. We report on four years (September 1994-October 1998) of climate and moisture data from the extreme arid region of the Atacama. Our data are focused on understanding moisture sources and their role in creating suitable environments for photosynthetic microorganisms in the desert surface. The average air temperature was 16.5 degrees C and 16.6 degrees C in 1995 and 1996, respectively. The maximum air temperature recorded was 37.9 degrees C, and the minimum was -5.7 degrees C. Annual average sunlight was 336 and 335 W m(-2) in 1995 and 1996, respectively. Winds averaged a few meters per second, with strong föhn winds coming from the west exceeding 12 m s(-1). During our 4 years of observation there was only one significant rain event of 2.3 mm, which occurred near midnight local time. We suggest that this event was a rainout of a heavy fog. It is of interest that the strong El Niño of 1997-1998 brought heavy rainfall to the deserts of Peru, but did not bring significant rain to the central Atacama in Chile. Dew occurred at our station frequently following high nighttime relative humidity, but is not a significant source of moisture in the soil or under stones. Groundwater also does not contribute to surface moisture. Only the one rain event of 2.3 mm resulted in liquid water in the soil and beneath stones for a total of only 65-85 h over 4 years. The paucity of liquid water under stones is consistent with the apparent absence of hypolithic (under-stone) cyanobacteria, the only known primary producers in such extreme deserts.
The west slope of the central Andes exhibits a pronounced rainshadow effect. Precipitation between 15° and 27 °S is dominated by summer convective activity from Amazonia, and data analysis shows that the increase in precipitation with elevation due to the rainshadow effect best fits an exponential correlation. Coupling with limited data from high elevations suggests that the correlation is accurate to 4500 m above sea level (m a.s.l.) and perhaps to 5500 m a.s.l., suggesting that increased precipitation goes unrecorded over the peaks of the western Cordillera. South of 27 °S the precipitation is dominated by winter frontal sources and shows no well-defined relationship with elevation. The core zone of hyper-aridity in the Atacama Desert extends from 15 to 30 °S at elevations from sea level to 3500 m a.s.l. Although the Atacama Desert has existed since at least 90 Ma, it is considered that the initial onset of hyper-aridity was most likely to have developed progressively with the uplift of the Andes as they reached elevations between 1000 to 2000 m a.s.l. coupled with the intensification of a cold, upwelling Peruvian Current between 15 and 10 Ma. Also apparent in the palaeogeographic record are subsequent fluctuations between (semi-) arid to hyper-arid conditions that were probably largely controlled by changes in orbital and oceanic forcing. Copyright © 2003 Royal Meteorological Society
Separate regions within the Transantarctic Mountains, the uplifted flank of the West Antarctic rift system, appear to have distinct Neogene histories of glaciation and valley downcutting. Incision of deep glacial outlet valleys occurred at different times throughout central and northern Victoria Land. This is corroborated by measurements of cosmogenic nuclides 21Ne, 10Be and 26Al of glacial erosion surfaces and high-elevated moraines. 21Ne ages of two summit plateaus, at elevations of 1650 m in central Victoria Land and ∼2800 m in northern Victoria Land, range from 3.84 to 11.2 Ma, respectively. The latter date indicates that these glacial erosion surfaces are the oldest known exposure dated surfaces on Earth. Glacial erosion terraces, remnants of early phases of valley downcutting, have 21Ne ages of 1.27 and 6.45 Ma for central and northern Victoria Land, respectively. Therefore, deglaciation of summit plateaus, valley downcutting and topographic uplift occurred during the Mid-Miocene in northern Victoria Land and not earlier than the Mid-Pliocene in central Victoria Land. In northern Victoria Land, ice flow directions changed markedly from the time a regional ice sheet occupied the level of the highest summits to the present condition with summits rising up to 800 above the valley glaciers. In central Victoria Land, the oldest documented ice flow direction occupying the summit erosion surface prior to incision was SW–NE, draining the East Antarctic Ice Sheet along an outlet glacier at least 10 times as wide as the present E–W-flowing David Glacier.
Spectral analyses of an uninterrupted 5.5-million-year (My)-long chronology of late Oligocene-early Miocene climate and ocean carbon chemistry from two deep-sea cores recovered in the western equatorial Atlantic reveal variance concentrated at all Milankovitch frequencies. Exceptional spectral power in climate is recorded at the 406-thousand-year (ky) period eccentricity band over a 3.4-million-year period [20 to 23.4 My ago (Ma)] as well as in the 125- and 95-ky bands over a 1.3-million-year period (21.7 to 23.0 Ma) of suspected low greenhouse gas levels. Moreover, a major transient glaciation at the epoch boundary ( approximately 23 Ma), Mi-1, corresponds with a rare orbital congruence involving obliquity and eccentricity. The anomaly, which consists of low-amplitude variance in obliquity (a node) and a minimum in eccentricity, results in an extended period ( approximately 200 ky) of low seasonality orbits favorable to ice-sheet expansion on Antarctica.
Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which
are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming
and cooling driven by tectonic processes on time scales of 105to 107 years, rhythmic or periodic cycles driven by orbital processes with 104- to 106-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 103 to 105 years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily
on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation
of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen
mechanisms for altering climate.
Causal links between the rise of a large mountain range and climate have often been considered to work in one direction, with significant uplift provoking climate change. Here we propose a mechanism by which Cenozoic climate change could have caused the rise of the Andes. Based on considerations of the force balance in the South American lithosphere, we suggest that the height of, and tectonics in, the Andes are strongly controlled both by shear stresses along the plate interface in the subduction zone and by buoyancy stress contrasts between the trench and highlands, and shear stresses in the subduction zone depend on the amount of subducted sediments. We propose that the dynamics of subduction and mountain-building in this region are controlled by the processes of erosion and sediment deposition, and ultimately climate. In central South America, climate-controlled sediment starvation would then cause high shear stress, focusing the plate boundary stresses that support the high Andes.
In the Central Andes, the frictional coupling between South America and the subducting Nazca Plate occurs beneath the Coastal Cordillera of northern Chile. One of the most distinctive characteristics of the Coastal Cordillera is a suite of EW topographic scarps located between 19° and 21.6°S latitude. These scarps are associated with predominantly south dipping reverse faults that have almost pure dip slip and produce shortening parallel to the plate boundary. Limited geochronology as well as more regional studies indicate that the scarps formed during the late Miocene and early Pliocene, though some show activity extending into the Quaternary. In several areas, the scarps dammed local drainages, producing internally drained basins that accumulated evaporites. This relationship indicates that the Coastal Cordillera was probably moister during the Late Mocene and Pliocene than it is today and also indicates that the Coastal Cordillera has been significantly uplifted or that the Coastal Escarpment of northern Chile has advanced significantly eastward since the Pliocene. The limited latitudinal extent of the EW scarps and their location symmetrically about the axis of topographic and Wadati-Benioff zone symmetry suggest that they owe their origin to the concave seaward shape of the continental margin due to prior formation of the Bolivian orocline.
New radiometric ages of about 25 m.y. on volcanic materials in a marine intercalation within clastic continental strata of the Upper Moquegua Formation near Caraveli, southern Peru, together with an age of 25.3 +/- 0.4 m.y obtained by Tosdal et al. from a locality about 300 km to the ESE, show that the formation contains strata of late Oligocene as well as Miocene age, and demonstrate that the coastal region was at a low elevation during latest Oligocene time. Because the unconformities between the Upper Moquegua Formation and the underlying Lower Moquegua Formation, and between the Lower Moquegua Formation and underlying Paleocene rocks cannot both represent the same tectonic event, two discrete Paleogene events must be present in the Andes of Peru. Although the exact timing of these events is uncertain, the unconformities are likely to be of Paleocene and middle Eocene age or possibly of middle Eocene and Oligocene age.
Radiometric ages for lava flows of northern Chile indicate that a regional Oligocene erosion surface was faulted when the Cordillera de la Costa was uplifted at the end of the Paleogene. Uplift of the coastal mountains caused the longitudinal depression to infil with sediment until aggradation virtually ceased in the Middle Miocene.
Ignimbrites of the Rhyolite Formation were deposited in the Pampa del Tamarugal and across the Cordillera de la Costa in the earliest Miocene, whereas volcanoes of the “Andesite” Formation were locally active at least as early as the Middle Miocene.
The 51.8 Ma Cerro Colorado porphyry Cu(-Mo) deposit is situated at 20degrees 2' 41" S; 69degrees 15, 351, W at an altitude of 2,600 in a.s.l. on the Pacific slope of the central Andean Cordillera Occidental. Supergene processes at Cerro Colorado generated a complex weathering profile that attains a present depth of 450 in and incorporates the Cu orebody of ca. 228 Mt at 1.0 percent. The extant supergene profile comprises four facies: (1) Leached cap, underlying the Choja pediplain, a regionally extensive mid-Tertiary erosion surface; (2) Upper Supergene ore; (3) Lower Leached zone; and (4) Lower Supergene ore. Both the Leached cap and Lower Leached zone are mainly hematitic, implying chalcocite-rich precursors. The Upper Supergene ore is dominated by brochantite and atacamite with relics of chalcocite, but it includes a superimposed zone of abundant chrysocolla veins. Chalcocite, usually accompanied by supergene kaolinite and smectite, is the main ore mineral of the Lower Supergene ore, which overlies the 0.4- to 0.5-percent-Cu hypogene protore. Dating of supergene alunite-group mineral separates from various ore facies and elevations by laser Ar-40/Ar-39 incremental heating reveals a supergene history extending over at least 20 m.y. Fifteen multistep age spectra for alunite, natroalunite, and jarosite yielded acceptable plateau dates, ranging from the earliest Oligocene, 35.26 +/- 0.68 Ma, to the middle Miocene, 14.59 +/- 2.46 Ma; five samples of alunite-natroalunite mixtures, however, produced staircase spectra with no direct age significance. Following hypogene mineralization in the middle Eocene, the deposit was probably unroofed at ca. 42 Ma, at the initiation of the Incaic orogeny in northern Chile. An age of 35.26 +/- 0.68 (2sigma) Ma for alunite associated with hematite in a clast in gravel overlying the Leached cap demonstrates that both formation and oxidation of a stage I chalcocite blanket had occurred by earliest Oligocene. During stage II (>35.26 +/- 0.68 Ma to <22.42 +/- 1.6 Ma), continued uplift and pedimentation caused leaching and thickening of the blanket, forming the surviving hematitic Leached cap and chal-cocite-dominated Upper Supergene ore. Stage III (>21.49 +/- 0.49 Ma to 19.25 +/- 0.43 Ma) was initiated by the major Pehuenchean (Aymara) tectonic event, when rapid regional uplift and a drastic fall in the water table renewed intense leaching to form the Lower Leached zone. At this time the chalcocite blanket was thickened below the Lower Leached zone, generating the Lower Supergene ore, and oxidized above it to form the Cu oxide-dominated Upper Supergene ore. At 19.25 +/- 0.43 Ma, an ignimbrite flow, up to 95 in thick, covered much of the deposit, temporarily interrupting supergene activity but imposing lateral ground-water flow through the lower 20 m. Oxidation was then reactivated, generating chrysocolla veins along northwest-trending fractures, which are inferred to be genetically linked to exotic mineralization in gravels below the ignimbrite 1.5 km north of the deposit. Further uplift and climatic desiccation in the middle Miocene, during stage V (<14.59 +/- 2.46 Ma), terminated significant supergene processes and preserved the existing supergene orebody from lateral dispersion of metal. Evidence from Cerro Colorado and elsewhere in northern Chile (e.g., Spence and Angelina) confirms that Paleocene to middle Eocene porphyry and allied Cu deposits experienced intense enrichment both in the late Eocene to early Oligocene and the late Oligocene to early Miocene. We argue that the establishment of a "proto-Humboldt Current" and the onset of the Incaic orogeny in the late Eocene provided a climatic and physiographic environment favorable for supergene enrichment of Cu deposits undergoing exhumation in the rain shadow of an uplifting terrain. Some of the earliest, upper Eocene, deposits emplaced along the Domeyko fault system (e.g., El Salvador) may similarly have been upgraded during the Incaic orogeny, but the main enrichment in the upper Eocene to lower Oligocene Cu deposits occurred during the late Oligocene to early Miocene, coinciding with formation of the Lower Leached zone at Cerro Colorado. The pyrite-rich hypogene assemblages of the giant deposits of the younger belt, e.g., Chuquicamata and Escondida, resulted in stronger and more rapid enrichment than in the relatively pyrite-poor older deposits, such as Cerro Colorado, despite the more protracted supergene histories experienced by the latter. The low enrichment rate of the Paleocene to middle Eocene deposits may also be attributed to the lateral copper loss during Oligocene pedimentation. Because the Upper Supergene ore at Cerro Colorado formed during the Oligocene tectonic quiescence following the Incaic orogeny, we propose a single Cenozoic supergene metallogenic epoch in northern Chile, ca. 20 or even 30 m.y. in duration, which attained its greatest efficacy in the early Miocene.
Twenty-five samples of supergene alunite collected from deeply developed supergene profiles in porphyry copper deposits and prospects between latitudes 20° and 27° S in northern Chile yield K/Ar ages ranging from about 34 to 14 Ma. Therefore supergene oxidation and enrichment processes were active from the early Oligocene to the middle Miocene, a minimum of 20 m.y. Supergene activity at individual deposits lasted for at least 0.4 to 6.2 m.y. The early Oligocene supergene activity affected deposits in the Paleocene porphyry copper belt, whereas early and middle Miocene supergene processes are documented in the Early Cretaceous, Paleocene, and late Eocene to early Oligocene porphyry copper belts. Middle Miocene oxidation also affected the oldest epithermal gold-silver deposits in the Maricunga belt farther east. Supergene activity commenced no less than 11 m.y. after generation of each porphyry copper deposit because of the time required to unroof the copper-bearing parts of the system. Supergene activity throughout northern Chile ceased at -14 Ma. The geologic features of deposits and prospects and their morphotectonic positions, present latitudes, and present elevations display no obvious correlations with the supergene chronology. Exploration for major cumulative enrichment blankets should not be carried out either beneath thick sequences of piedmont gravels (± ignimbrites) of Oligocene through middle Miocene age unless their accumulation is demonstrably late in the documented history of supergene activity, or in porphyry copper provinces, such as those of central Chile and northwestern Argentina, which formed after ∼ 14 Ma. The uplift responsible for efficient cumulative copper enrichment is difficult to correlate convincingly with the brief pulses of compressive tectonism postulated for northern Chile and contiguous areas unless their effects were much more prolonged. Intensifying aridity is confirmed as the likely reason for the cessation of supergene activity in northern Chile, and tectonic uplift was its most probable cause. However, more fundamental global controls producing a period of chemical weathering followed by worldwide dessication also may have played a role.
Potassium-bearing manganese oxides, cryptomelane, K1–2(Mn³⁺Mn⁴⁺)8 O16 · xH2Oand hollandite, (K,Ba)1–2 (Mn³⁺,Mn⁴⁺)8 O16· xH2O, are often authigenically precipitated in weathering profiles. The presence of structural potassium in manganese oxides makes these minerals datable by the K-Ar and methods. Dating of these phases allows us to time the progression of oxidation fronts during weathering and pedogenic processes. Detailed age resolution of the weathering history allows us to use deep weathering profiles as land-based stratigraphic records of past climatic and geomorphic events, complementing evidence from the marine sedimentary and paleontological record.
Absolute dating of river terraces can yield long-term incision rates, clarify the role of climate in setting times of aggradation and incision, and establish the rates of pedogenic processes. While surface exposure dating using cosmogenic 10Be and 26Al would seem to be an ideal dating method, the surfaces are composed of individual clasts, each with its own complex history of exposure and burial. The stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport, and during post-depositional stirring, results in great variability in clast nuclide concentrations. We present a method for dealing with the problem of pre-depositional inheritance of cosmogenic nuclides. We generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories. Depth profiles of such amalgamated samples allow us to constrain the mean inheritance, to test for the possible importance of stirring, and to estimate the age of the surface. Working with samples from terraces of the Fremont River, we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration. Depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth-dependent post-depositional nuclide production. That the depth-dependent parts of the profiles are exponential argues against significant post-depositional displacement of clasts within the deposit. Our technique yields 10Be age estimates of 60±9, 102±16 and 151±24 ka for the three highest terraces, corresponding to isotope stages 4, 5d and 6, respectively. The mean inheritance is similar from terrace to terrace and would correspond to an error of ∼30–40 ka if not taken into account. The inheritance likely reflects primarily the mean exhumation rates in the headwaters, of order 30 m/Ma.
Extraordinarily high surface exposure ages have been determined for Sirius Group tillites of Mt. Fleming and Mt. Feather as well as at localities in the Inner Dry Valleys using cosmogenic helium and neon. Ages of 10 Ma at Mt. Fleming, 5.3 Ma at Mt. Feather and 6.5 Ma at Insel Mountain are among the highest nominal exposure ages published so far. These values are minimal ages as they are based on the assumption of zero erosion and uplift. The Mt. Feather sample independently confirms the pre-Pliocene age of the Sirius Group sediments in the Dry Valleys as previously determined at Mt. Fleming. The Insel Mountain samples provide evidence for a landscape formation of the Inner Dry Valleys not later than Late Miocene time. Assuming conservatively low values of 2.5 cm Ma−1 for erosion rate and 50 m Ma−1 for uplift rate we infer that the Sirius Group tillites at Mt. Fleming were deposited earlier than 20 Ma ago. This indicates that the overriding of the Dry Valleys block of the Transantarctic Mountains by the East Antarctic Ice Sheet occurred not later than the Early Miocene. Maximum long-term erosion rates in the Inner Dry Valleys must be <15 cm Ma−1 down to altitudes <1000 m. Since such low erosion rates require permanently cold and hyperarid conditions, the response of Antarctica to the Pliocene warm climatic episode must have been small. Cosmogenic nuclide data from both the Inner Dry Valleys and the Sirius Group sediment localities support the hypothesis of a stable East Antarctic Ice Sheet since at least Late Miocene time, implying that the climate of Antarctica was decoupled from that of lower southern latitudes. We present also new elemental 21Ne production rates of P21(Mg) = 196 atoms g−1 yr−1 and P21(Al) = 55 atoms g−1 yr−1 at sea level and high geomagnetic latitude. These figures are consistent with a 3He production rate of P3 = 110 atoms g−1 yr−1, similar to previously published values. This consistency provides evidence that pyroxene is retentive for both helium and neon over at least 10 Ma. Cosmogenic Ne in quartz and pyroxene has a (22Ne/21Ne)cos ratio of 1.266 ± 0.040 and 1.159 ± 0.040, respectively.
Cosmogenic noble gas studies in the oldest landscape on Earth: Surface exposure ages of the Dry Valleys, Antarctica: Earth and Planetary Science Letters
- J M Schäfer
- S Ivy-Ochs
- R Wieler
- I Leya
- H Baur
- G H Denton
- C Schlüchter
Schäfer, J.M., Ivy-Ochs, S., Wieler, R., Leya, I., Baur,
H., Denton, G.H., and Schlüchter, C., 1999, Cosmogenic noble gas studies in the oldest landscape
on Earth: Surface exposure ages of the Dry Valleys, Antarctica: Earth and Planetary Science Letters, v. 167, p. 215-226, doi: 10.1016/S0012-821X(99)00029-1.
Late Neogene passive margin denudation history: Cosmogenic isotope measurements from the Central Namib Desert: Global and Planetary Change, v. 30
- F M Van Der Wateren
- T J Dunai
Van der Wateren, F.M., and Dunai, T.J., 2001, Late Neogene passive margin denudation history: Cosmogenic isotope measurements from the Central
Namib Desert: Global and Planetary Change,
v. 30, p. 271-307, doi: 10.1016/S0921-8181(01)00104-7.
Middle Miocene climatic change in the Atacama Desert, northern Chile: Evidence from supergene mineralization at La Escondia: Geological Society of America Bulletin, v. 100
- C N Alpers
- G H Brimhall
Alpers, C.N., and Brimhall, G.H., 1988, Middle Miocene
climatic change in the Atacama Desert, northern
Chile: Evidence from supergene mineralization at
La Escondia: Geological Society of America Bulletin, v. 100, p. 1640-1656, doi: 10.1130/0016-7606(1988)1002.3.CO;2.
Late Pliocene age for the Atacama Desert: Implications for the desertification of western South America: Geology, v. 30
- A J Hartley
Hartley, A.J., and Chong, G., 2002, Late Pliocene age
for the Atacama Desert: Implications for the desertification of western South America: Geology,
v. 30, p. 43-46, doi: 10.1130/0091-7613(2002)
0302.0.CO;2.
Cosmogenic dating of fluvial terraces
- J L Repka
- R S Anderson
- R C Finkel
Repka, J.L., Anderson, R.S., and Finkel, R.C., 1997,
Cosmogenic dating of fluvial terraces, Fremont
River, Utah: Earth and Planetary Science Letters,
v. 152,
p. 59-73,
doi:
10.1016/S0012-821X(97)00149-0.
Cenozoic polyphase landscape and tectonic evolution of the Cordillera Occidental
- R M Tosdal
- A H Clark
- E Ferrar
Tosdal, R.M., Clark, A.H., and Ferrar, E., 1984, Cenozoic polyphase landscape and tectonic evolution
of the Cordillera Occidental, southernmost Peru:
Geological Society of America Bulletin, v. 95,
p. 1318-1332.
Evolution of the West Andean Escarpment at 18ЊS (N. Chile) during the last 25 Ma: Uplift, erosion and collapse through time: Tectonophysics
- G Wörner
- D Uhlig
- I Kohler
- H Seyfried
Wörner, G., Uhlig, D., Kohler, I., and Seyfried, H.,
2002, Evolution of the West Andean Escarpment
at 18ЊS (N. Chile) during the last 25 Ma: Uplift,
erosion and collapse through time: Tectonophysics, v. 345, p. 183-198, doi: 10.1016/S0040-1951(01)00212-8.
- Bouzari