Climate change and human settlement around the late-glacial laguna De Punta Negra,northern Chile: The preliminary results

Major bodies of fresh water are extremely scarce in the dry Atacama region. Unlike the Salar de Atacama, which has no outlet, the Salar de Punta Negra (24$ 35′ S, 3000 m elevation) used to spill north into the Atacama drainage. Archaeological survey of the beaches and spillway above today's salar indicates late-glacial human use of the 800 km² lake and environs under a contrasting climate regime. The histories and water budgets of the Pleistocene lakes of the south-central Andes are not well understood, but archaeological data can be interpreted to support (1) hypotheses that would bring westerly storm tracks and winter rain further north 14,000 to 10,000 B.P., especially if accompanied by increasing warmth for part of the period, and/or (2) theories of orbital variation, increased summer insolation, and strengthened monsoons that would provide generally increased rainfall at the Tropics 10,000 to 9000 B.P. Archaeological, paleoclimatological, and geomorphological studies come together to show how this large lake could be a focus of human activity from the time of first settlement of the Atacama region.     

Late Mesozoic to Paleogene stratigraphy of the Salar de Atacama Basin, Antofagasta, Northern Chile: Implications for the tectonic evolution of the Central Andes

The Salar de Atacama basin, the largest “pre-Andean” basin in Northern Chile, was formed in the early Late Cretaceous as a consequence of the tectonic closure and inversion of the Jurassic–Early Cretaceous Tarapacá back arc basin. Inversion led to uplift of the Cordillera de Domeyko (CD), a thick-skinned basement range bounded by a system of reverse faults and blind thrusts with alternating vergence along strike. The almost 6000-m-thick, upper Cretaceous to lower Paleocene sequences (Purilactis Group) infilling the Salar de Atacama basin reflects rapid local subsidence to the east of the CD. Its oldest outcropping unit (Tonel Formation) comprises more than 1000 m of continental red sandstones and evaporites, which began to accumulate as syntectonic growth strata during the initial stages of CD uplift. Tonel strata are capped by almost 3000 m of sandstones and conglomerates of western provenance, representing the sedimentary response to renewed pulses of tectonic shortening, which were deposited in alluvial fan, fluvial and eolian settings together with minor lacustrine mudstone (Purilactis Formation). These are covered by 500 m of coarse, proximal alluvial fan conglomerates (Barros Arana Formation). The top of the Purilactis Group consists of Maastrichtian-Danian alkaline lava and minor welded tuffs and red beds (Cerro Totola Formation: 70–64 Ma K/Ar) deposited during an interval of tectonic quiescence when the El Molino–Yacoraite Late Cretaceous sea covered large tracts of the nearby Altiplano-Puna domain. Limestones interbedded with the Totola volcanics indicate that this marine incursion advanced westwards to reach the eastern CD slope. CD shortening in the Late Cretaceous was accompanied by volcanism and continental sedimentation in fault bounded basins associated to strike slip along the north Chilean magmatic arc to the west of the CD domain, indicating that oblique plate convergence prevailed during the Late Cretaceous. Oblique convergence seems to have been resolved into a highly partitioned strain system where margin-parallel displacements along the thermally weakened arc coexisted with margin-orthogonal shortening associated with syntectonic sedimentation in the Salar de Atacama basin. A regionally important Early Paleocene compressional event is echoed, in the Salar de Atacama basin by a, distinctive, angular unconformity which separates Paleocene continental sediments from Purilactis Group strata. The basin also records the Eocene–Early Oligocene Incaic transpressional episode, which produced, renewed uplift in the Cordillera de Domeyko and triggered the accumulation of a thick blanket of syntectonic gravels (Loma Amarilla Formation).     

Permian marine sedimentation in northern Chile: new paleontological evidence from the Juan de Morales Formation,and regional paleogeographic implications

Permian marine sedimentary rocks that crop out in northern Chile are closely related to the development of a Late Paleozoic magmatic arc. A study of Upper Paleozoic units east of Iquique (20°S) identified three members within the Juan de Morales Formation, each of which were deposited in a different sedimentary environment. A coarse-grained terrigenous basal member represents alluvial sedimentation from a local volcanic source. A mixed carbonate-terrigenous middle member represents coastal and proximal shallow marine sedimentation during a relative sea-level rise related with a global transgression. Preliminary foraminifer biostratigraphy of this middle member identified a late Early Permian (late Artinskian–Kungurian) highly impoverished nodosarid–geinitzinid assemblage lacking fusulines and algae, which is characteristic of temperate cold waters and/or disphotic zone. The upper fine-grained terrigenous member represents shallow marine siliciclastic sedimentation under storm influence. The Juan de Morales Formation consists of continental, coastal and shallow marine sediments deposited at the active western margin of Gondwana at mid to low latitudes. A revised late Early Permian age and similar paleogeography and sedimentary environments are also proposed for the Huentelauquén Formation and related units of northern and central Chile, Arizaro Formation of northwestern Argentina, and equivalent units of southernmost Peru.     

Age of Cu(-Fe)-Au mineralization and thermal evolution of the Punta del Cobre district, Chile

The Punta del Cobre belt is located 15?km south of Copiapó, northern Chile. It comprises several Cu(-Fe)-Au deposits in the Punta del Cobre and Ladrillos districts, east of the Copiapó river, and the Ojancos Nuevo district, with the new Candelaria mine, and Las Pintadas district, west of the river. The mineralization in the Punta del Cobre belt is characterized by a simple hypogene mineral assemblage of chalcopyrite, pyrite, magnetite, and hematite. Average ore grades are 1.1 to 2% Cu, 0.2 to 0.6?g/t Au, and 2 to 8?g/t Ag. Massive magnetite occurs as veins and irregularly shaped bodies. The ore is spatially associated with alkali metasomatism and in particular with potassic alteration. The Cu(-Fe)-Au deposits are hosted mainly in volcanic rocks of the Punta del Cobre Formation (pre-upper Valanginian) that underlie Neocomian limestones of the Chañarcillo Group. This region experienced backarc basin formation in the Neocomian, uplift and granitoid intrusions in the middle Cretaceous, and eastward migration of the magmatic front of about 30?km between middle Cretaceous and Paleocene. To determine the timing of ore deposition and to reconstruct parts of the thermal history of the Punta del Cobre district, in the eastern part of the belt, we have obtained ⁴⁰Ar/³⁹Ar incremental-heating and Rb-Sr analyses of mineral and whole-rock samples. An ⁴⁰Ar/³⁹Ar incremental-heating experiment on hydrothermal biotite, formed synchronous with the Cu(-Fe)-Au mineralization, yielded an inverse isochron age of 114.9?±?1.0 Ma (all errors reported at ±2σ), consistent with a Rb-Sr isochron of 116.8?±?2.7 Ma calculated from 7 whole-rock samples. These data are interpreted to represent the age of potassic alteration that accompanies mineralization. Ore formation temperatures of 400?°C to 500?°C were previously estimated based on paragenetic relationships. Shearing at the Candelaria deposit occurred after ore deposition and before the main stage of batholith emplacement. Published K-Ar ages for the middle Cretaceous batholith near the Punta del Cobre belt range from 119 to 97?Ma. Our data suggest that the mineralization is related to the earlier stages of batholith emplacement. The biotite age spectrum indicates that the Punta del Cobre district was not affected by temperatures above ～300?°C–350?°C, the closure temperature for argon in biotite, during the contact metamorphic overprint produced by later emplaced batholithic intrusions. Whole-rock ⁴⁰Ar/³⁹Ar ages are considerably younger; incremental-heating experiments yielded an inverse isochron age of 90.7?±?1.2?Ma and weighted mean plateau ages of 89.8?±?0.6?Ma and 89.5?±?0.6?Ma. These samples are dominantly K-feldspar, for which we assume an argon closure temperature of ～150?°C, thus they give the age of cooling below ～150?°C–200?°C.     

Isotopic composition and origin of the precipitation in Northern Chile

A 3 a data set of isotopes in precipitation from northern Chile show a very distinct pattern, with δ¹⁸O values ranging between −18 and −15‰ at high altitude stations, compared to δ¹⁸O values between −10 and −6‰ at the lower altitude areas. The ¹⁸O-depleted values observed in the high altitude area, the Altiplano, are related to processes that affect the air masses that originated over the Atlantic, cross the Amazon Basin (continental effect), ascend the Andes (altitude effect) and precipitated (convective effect) in the Altiplano. It is postulated that a second source of moisture, associated with air masses from the Pacific, may contribute to the ¹⁸O-enriched values observed in the lower altitude areas. Similar isotopic patterns are documented in springs and groundwater indicating that the data presented in this paper are an accurate representation of the long term behavior isotopic composition of rain in northern Chile.     

Fades of subglacial channel sedimentation in late-Pleistocene drumlins, Northern Ireland

The sedimentology of three sand-cored drumlins in central Ulster. Northern Ireland is described. The sand-cores of the drumlins consist of complex sequences of cohesive sediment gravity forms, grain-flow deposits, turbiditic sands and deltaic sands and gravels, showing complex fades relationships. The bulk of the sediments formed in water-filled cavities associated with a major subglacial meltwater escape route excavated in bedrock. The sand-cores are overlain by a streamlined carapace of basal melt-out till. A model is presented to account for spatial variations in faeies arrangement within the sand-cores. Three specific meltwater depositional subenvironments were recognised: (1) main channel axis, (2) main channel flank, and (3) minor tributary channel. The sand-cores formed prior to the main phase of basal melt-out till deposition and before drumlin streamlining.     

Lascar Volcano, Northern Chile; Evidence for Steady-State Disequilibrium

Lascar Volcano, located in the Central Volcanic Zone of NorthernChile, is a medium-to high-K calc-alkaline stratovolcano. Threestages are recognized in the construction of the edifice, withactivity ranging from andesitic fissure eruptions to a large-volumedacitic pumice flow, the Soncor Flow. The eruption productsare predominantly two-pyroxene andesites and dacites, with somehornblende dacites occurring in the Soncor Flow. Disequilibriumtextures resulting from mixing between mafic and acid end-membersare recognized in all the eruption products, and geochemicalmodelling has been carried out to quantify the effects of magmamixing and fractional crystallization. A model is developedwhich explains the observed textures by the existence of a continuouslyfractionating magma chamber which receives periodic influxesof basaltic andesite. Primary anhydrite has been found in theSoncor pyroclastic flow. Anhydrite formation and sulphur dioxidedegassing are explained in terms of oxidation and quenchingof sulphide-rich mafic magma during mixing with the residentmore evolved magmas.     

Growing folds and sedimentation of the Gosau Group, Muttekopf, Northern Calcareous Alps, Austria

Analysis of the three-dimensional geometry of Upper Cretaceous clastics in the Muttekopf area (Northern Calcareous Alps, Austria) indicate fold and fault structures active during deposition. Coniacian continental to neritic sedimentation (Lower Gosau Subgroup) was contemporaneous with displacements on NW-trending faults and minor folding along NE-trending axes. From the Santonian onwards (sedimentation of the deep-marine Upper Gosau Subgroup) the NW-trending faults were sealed and large folds with WSW-trending axes developed. The direction of contraction changed to N-S after the end of Gosau deposition in the Danian (Paleocene). Synorogenic sedimentation patterns indicate continuous contraction from the Coniacian to the Late Maastrichtian/?Danian. Therefore, large-scale extension as observed in the central part of the Eastern Alps cannot be documented in the western parts of the Northern Calcareous Alps. A combination of subduction tectonic erosion for the frontal parts and gravitational adjustment of an unstable orogen after nappe stacking for the internal parts possibly accounts for the different development of Gosau basins in the frontal and trailing regions of the Austroalpine wedge.     

The hot spring and geyser sinters of El Tatio, Northern Chile

The siliceous sinter deposits of El Tatio geothermal field in northern Chile have been examined petrographically and mineralogically. These sinters consist of amorphous silica (opal-A) deposited around hot springs and geysers from nearly neutral, silica-saturated, sodium chloride waters. Water cooling and evaporation to dryness are the main processes that control the opal-A deposition in both subaqueous and subaerial settings, in close spatial relation to microbial communities. All fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse (cyanobacteria, green bacteria, and diatoms). The most important ecological parameter is the temperature gradient, which is closely related to the observed depositional settings: 1) Geyser setting: water temperature = 70–86 °C (boiling point at El Tatio: 4200 m a.s.l.); coarse laminated sinter macrostructure with rapid local variations; biota comprises non-photosynthetic hyperthermophilic bacteria. 2) Splash areas around geysers: water temperature = 60–75 °C; laminated spicule and column macrostructure, locally forming cupolas (< 30 cm); predominant Synechococcus-like cyanobacteria. 3) Hot spring setting: water temperature = 40–60 °C; laminated spicules and columns and subspherical oncoids characterize the sinter macrostructure; filamentous cyanobacteria Phormidium and diatoms (e.g., Synedra sp.) are the most characteristic microbes. 4) Discharge environments: water temperature = 20–40 °C; sinter composed of laminated spicules and oncoids of varied shape; cyanobacterial mats of Phormidium and Calothrix and diatoms (e.g., Synedra sp.) are abundant. El Tatio is a natural laboratory of great interest because the sedimentary macrostructures and microtextures reflect the geological and biological processes involved in the primary deposition and early diagenesis of siliceous sinters.     

Palaeozoic flysch series in the Coastal Cordillera of Northern Chile

A discontinuous outcrop of Palaeozoic rhythmic clastites appears in the North Chilean Coastal Cordillera. The Formación El Toco (21°15–22°15S) whose scarce flora points to a presumably Upper Devonian age forms the northernmost part of the outcrop. It is discordantly overlain by Lower Jurassic volcanics (Fm. La Negra), its base, however, is not exposed. Hercynian heteromorphous deformation led to predominantly NW trending folds strongly inclined mostly to the SW. Chevron-like folds of 0.1 to 30 m occur locally and seem to display properties transitional between synsedimentary-gravitational and early tectonic deformation.The series which is at least 2300 m thick consists of proximal, in parts pebbly turbidites with non-turbiditic finegrained intercalations. Incomplete BOUMA-sequences frequently begin with A-beds of grey to green immature, badly sorted coarse sandstones of up to 6 m thickness containing isolated quartz- and pelite-clasts.Measurements of flute casts and f oresets show palaeocurrents which came from NW and NNE. Along with petrographic observations they indicate southward directed transport of detritus from low metamorphic sedimentary and magmatic source areas into an Upper Devonian nonvolcanic basin.

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Zusammenfassung Die Formación El Toco ist der nördlichste Aufschluß einer Kette von Vorkommen paläozoischer rhythmischer Klastite in der nordchilenischen Küstenkordillere. Diese Formation (21°15–22°15S), deren spärliche Flora vorbehaltlich dem Oberdevon zuzuordnen ist, wird diskordant von unterjurassischen Vulkaniten (Fm. La Negra) überlagert —das Liegende ist nicht aufgeschlossen. Variszische heteromorphe Deformation führte zu vorherrschend NW-streichender Faltung, die meist starke SW-Vergenz zeigt. Lokal tritt eine scharfe Verfaltung im 0,1 bis 30 m-Bereich hinzu, die sowohl synsedimentär-gravitative als auch frühtektonische Deformationsmerkmale zeigt.Die mindestens 2300 m mächtige Serie ist ein proximaler Flysch mit z. T. kiesführenden Turbiditen, in die nichtturbiditische feinkörnige Partien eingeschaltet sind. Die unvollständigen BOUMA-Sequenzen beginnen häufig mit einer aus grauen bis grünen unreifen und schlechtsortierten Grobsandsteinen bestehenden A-Division von bis zu 6 m Mächtigkeit, die isolierte Quarz- und Pelitklasten enthalten kann.Flute cast- und Foreset-Messungen weisen auf Paläoströmungsrichtungen aus NW und NNO hin. Zusammen mit petrographischen Analysen läßt sich daraus ein südwärts gerichteter Transport von schwachmetamorphsedimentärem und magmatischem Detritus in ein oberdevonisches nicht-vulkanisches Becken ableiten.

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Résumén Ritmitas clásticas de edad paleozoica forman afloramientos discontinuos en la Cordillera de la Costa del Norte de Chile. La Formación El Toco (21°15–22°15S), que contiene una flora escasa de probable edad Devónico Superior, constituye la parte más septentrional de estos afloramientos. La base no se conoce, mientras que el techo infrayace discordantemente a volcanitas jurásicas inferiores (Fm. La Negra). Deformaciones hercínicas heteromórficas llevan a la formación de pliegues orientados predominantemente al NW inclinados fuertemente al SW. Localmente aparecen pliegues en forma de chevron de un tamano de 0.1 a 30 m que muestran caracteristicas de deformación transicional entre sinsedimentana-gravitativa y tectónica temprana.La serie que tiene una potencia de por lo menos 2300 m consiste en turbiditas proximales parcialmente con gravas e intercalaciones finas no-turbidíticas. Secuencias incompletas de BOUMA empiezan frecuentemente con capas de la division A (espesor maximo 6 m) los cuales se componen con frecuencia de areniscas gruesas gris-verdes, composicionalmente inmaduras y mal seleccionadas, con clastos aislados de cuarzo y pelita.Medidas de flute casts y foresets muestran paleocorrientes provenientes de NW y NNE. Junto con observaciones petrográficas, las paleocorrientes indican un transporte de material detrítico, originado de áreas con rocas sedimentarias, metamórficas de bajo grado e ígneas, dirigido al sur hacia una cuenca no volcánica de edad Devónico Superior.

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西南天山琼恰特北一带物化探异常特征及找矿效果

研究区位于西南天山科克布克三山晚古生代铅锌铜金铁钒钛五级成矿带,成矿地质条件优越。20世纪90年代以来,发现一些找矿线索,但在研究区未能取得找矿突破。为解决该区的找矿问题,通过系统地开展1∶50000水系沉积物测量工作,圈定了一批化探综合异常,优选Hs46 乙_2综合异常为铅锌找矿靶区,采用激电中梯测量、激电测深工作确定了隐伏的矿化体分布和埋深,最终通过钻探验证发现了琼恰特北铅锌矿床,取得良好的找矿效果。     

Estimating suspended sediment yield, sedimentation controls and impacts in the Mellah Catchment of Northern Algeria

This paper is an assessment of the suspended sediment yield in the Mellah Catchment of northern Algeria. We use discharge–sediment load relationships to explore the variability of water discharge and sediment load, and to investigate the impact of geomorphic factors disturbance on erosion and sedimentation. Suspended sediment load was analyzed in the Mellah Catchment (550 km²) which was controlled by a gauging station to measure discharge and sediment transport. The relations between daily mean sediment concentration and daily mean water discharge were analyzed to develop sediment rating curves. For storms with no water samples, a sediment rating curve was developed. The technique involves stratification of data into discharge-based classes, the mean of which are used to fit a rating curve according to single flow data and season to provide various rating relationships. The mean annual sediment yield during the 24 years of the study period was 562 T km^?2 in the Mellah Catchment. This drainage basin had high rainfall and runoff, the erosion was high. The high sediment yield in the Mellah basin could be explained by a high percentage of sparse grassland and cultivation developed on shallow marly silty-clayey soils with steep slopes often exceeding 12%. Almost all suspended sediment loads are transported during storm events that mainly occur in the winter and spring heavy and medium downpours. The scarceness of these events leads to a very large interseasonal variability of the wadi sediment fluxes. The negative impacts of this enhanced sediment mobility are directly felt in the western part of the basin which shows many mass movements, bank and gully erosion because cultivated areas are often bared during autumnal brief flash floods and furrowed downslope during the winter season.     

Late Jurassic tectonics and sedimentation: breccias in the Unken syncline,central Northern Calcareous Alps

This study analyses and discusses well preserved examples of Late Jurassic structures in the Northern Calcareous Alps, located at the Loferer Alm, about 35 km southwest of Salzburg. A detailed sedimentary and structural study of the area was carried out for a better understanding of the local Late Jurassic evolution. The Grubhörndl and Schwarzenbergklamm breccias are chaotic, coarse-grained and locally sourced breccias with mountain-sized and hotel-sized clasts, respectively. Both breccias belong to one single body of breccias, the Grubhörndl breccia representing its more proximal and the Schwarzenbergklamm breccia its more distal part, respectively. Breccia deposition occurred during the time of deposition of the Ruhpolding Radiolarite since the Schwarzenbergklamm breccia is underlain and overlain by these radiolarites. Formation of the breccias was related to a major, presumably north-south trending normal fault scarp. It was accompanied and post-dated by west-directed gravitational sliding of the Upper Triassic limestone (“Oberrhätkalk”), which was extended by about 6% on top of a glide plane in underlying marls. The breccia and slide-related structures are sealed and blanketed by Upper Jurassic and Lower Cretaceous sediments. The normal fault scarp, along which the breccia formed, was probably part of a pull-apart basin associated with strike slip movements. On a regional scale, however, we consider this Late Jurassic strike-slip activity in the western part of the Northern Calcareous Alps to be synchronous with gravitational emplacement of “exotic” slides and breccias (Hallstatt mélange), triggered by Late Jurassic shortening in the eastern part of the Northern Calcareous Alps. Hence, two competing processes affected one and the same continental margin.     

Link of ocean deep water thermohaline anomalies with atmospheric state anomalies in the Northern Atlantic

Anomalies of thermohaline characteristics of the ocean deep waters formed in the subpolar North Atlantic are shown to be controlled by the natural oscillations of the atmospheric state in the region, i.e., the North Atlantic Oscillation (NAO). A general mechanism behind the NAO effect on the deep water temperature and salinity on a decadal time scale is proposed. The main factors determining the close link of the deep water thermohaline anomalies and the NAO are the zonal extension of the subpolar gyre and the wintertime deep convection intensity in the Labrador Sea.     

Impact of the 1960 major subduction earthquake in Northern Patagonia (Chile,Argentina)

The recent sedimentation processes in four contrasting lacustrine and marine basins of Northern Patagonia are documented by high-resolution seismic reflection profiling and short cores at selected sites in deep lacustrine basins. The regional correlation of the cores is provided by the combination of ¹³⁷Cs dating in lakes Puyehue (Chile) and Frías (Argentina), and by the identification of Cordon Caulle 1921–22 and 1960 tephras in lakes Puyehue and Nahuel Huapi (Argentina) and in their catchment areas. This event stratigraphy allows correlation of the formation of striking sedimentary events in these basins with the consequences of the May–June 1960 earthquakes and the induced Cordon Caulle eruption along the Liquiñe-Ofqui Fault Zone (LOFZ) in the Andes. While this catastrophe induced a major hyperpycnal flood deposit of ca. 3×10⁶ m³ in the proximal basin of Lago Puyehue, it only triggered an unusual organic rich layer in the proximal basin of Lago Frías, as well as destructive waves and a large sub-aqueous slide in the distal basin of Lago Nahuel Huapi. A very recent mega-turbidite in the two distal basins of Reloncavi fjord located close to the LOFZ suggests that 1960 co-seismic movements in this area may have triggered the remobilization of ca. 187×10⁶ m³ of marine sediments.     

Overheated, Cu-bearing magmas in the Zaldívar porphyry-Cu deposit, Northern Chile. Geodynamic consequences

The Zaldívar porphyry copper deposit, Northern Chile, consists of two major intrusions, the 290 Ma Zaldívar, and the more recent Miocene (38.7 Ma) Llamo porphyry. Five types of inclusions have been identified in quartz phenocrysts from Llamo porphyry, including melt inclusions (M), and four types of fluid inclusions, called MS (multi solids), B (brines), G (vapor-rich) and W (aqueous), respectively.Melt remnants, well preserved as M-inclusions, homogenize around 1000 °C. They show a rhyolitic composition, comparable to the most evolved acidic rhyolitic end member found elsewhere in the regional magmatism and to worldwide volcanic rhyolitic glass. High silica content in some inclusions can, however, be due to partial remelting of the quartz host during the heating run. Copper content in the same inclusions ranges between 0.03 and 0.57 wt.%, with an average concentration of 0.10 wt.%, suggesting a major magmatic source for the copper (orthomagmatic model).MS inclusions, which contain a number of solids at room temperature, mostly H₂O-bearing phases (system NaCl–KCl–((Fe, Mg, Cu)Cl)–H₂O, average salinity 70 wt.% NaCl equiv.), homogenize at magmatic temperatures (around 1000 °C). They represent the first fluids to have exsolved from the magma at depth, at a pressure of about 2 kbar. Their high homogenization temperature, comparable to values measured for melt inclusions (1000 to 1050 °C), may indicate trapping of MS and M inclusions in host phenocrysts from an immiscible mixture of silicate melt and highly saline fluids expelled from the magma during the early stage of quartz crystallization.The data indicate a magmatic origin for copper, as well as extremely high melt temperatures. These features are interpreted by magmatic differentiation of mantle-derived primitive melts, corresponding to major changes in the tectonic regime of the Andean margin, which occurred in Miocene times.