sub-Andean Region Research Articles

Neogene to modern foreland basin development in the Sub-Andean zone of southern Bolivia and northern Argentina, 21−23°S

The Sub-Andean retroarc region is a unique example of an active continental-scale retroarc foreland basin system. Heavily targeted for hydrocarbon exploration, the region hosts a large volume of subsurface data coupled to surface studies dedicated to refining its evolution in time and space. This paper presents a regional correlation of stratigraphic markers from seismic reflection and well logs across the Sub-Andean foothills at 23−21°S in southern Bolivia and northern Argentina, which reveals the contrasting along-strike history of Mesozoic to Cenozoic tectonics that preceded the foreland basin setting. Supported by published geochronological data and new zircon U-Pb maximum depositional ages, we describe the depositional transition from pre-Andean to Andean stratigraphy and discrete episodes of foreland basin subsidence and shortening. Based on interpreted stratigraphic breaks, we define the extent and stepwise evolution of this foreland basin, which was characterized by the progressive eastward migration of foreland basin depozones. Based on restored thickness profiles, we present flexural models of basin subsidence for the Sub-Andean foothills region. The modeling of discrete episodes of foreland basin subsidence refines the widely accepted bimodal elastic strength in the foreland basin at 21−23°S, which is weaker in the western ranges (∼20 km effective elastic thickness) and stronger eastward (>40 km). Modeling results also reveal minimum values of subsidence rates (up to 1.2 mm/yr) in the sequential foredeep depozones and suggest that the modeled tectonic load migration—as constrained by the record of syntectonic strata—probably increased over time through the incorporation of Sub-Andean rocks into the orogenic wedge.

Soils, Geoenvironments and Ecosystem Services of a Protected Area in Western Brazilian Amazonia.

The Serra do Divisor National Park (SDNP) in the Westernmost Brazilian Amazonia possesses unique Mountain landscapes of sub-andean nature, with high geo-biodiversity and pristine environments, with a potential high contribution in ecosystems services. We studied and mapped the basic geo-environmental units of the main sector of the Park, evaluating soil carbon stocks as a key ecosystem service provided by the Protected Area. For the identification, characterization and mapping of the geoenvironmental units, we integrated pedological, geomorphological and vegetation data obtained by local soil survey and field campaigns, as well as secondary data. Eight geoenvironmental units were identified and mapped, distributed in three main compartments: the Serra do Divisor (SD) the upper Moa River and the medium Moa River. This region presents similar environments to the sub-Andean region, notably the Ceja Forest at the top surface of the SD. Soils at the SD have high organic carbon accumulation, with close association with the nutrient-poor, quartz-rich rocks, and shows organic matter illuviation indicating active podzolization. The SDNP encompasses important ecosystems and services linked with high geo-biodiversity, and high soil carbon stocks, representing a new frontier for scientific research in the only area of transitional sub-andean forested landscape in Brazil.

Morphological description of Pintomyia (Pifanomyia) veintemillasi n. sp., a new sand fly species from the sub-Andean region of Bolivia

BackgroundMost sand fly species are located in the Americas; some act as vectors of leishmaniasis and other human diseases. In Bolivia, about 25% of Neotropical species have been identified, and only a few have been implicated as vectors of cutaneous and visceral leishmaniasis. A new species of anthropophilic sand fly from the sub-Andean region of Alto Beni is described herein.MethodsA large systematic entomological survey was carried out in a subtropical humid forest located in the Marimonos mountain range, at around 900 m altitude, in the municipality of Palos Blancos, Sud Yungas Province, Department of La Paz, Bolivia. Sand flies were captured over a period of 26 months between January 1982 and February 1984, at the ground and canopy level, using both CDC light traps and protected human bait. A total of 24,730 sand flies were collected on the ground, distributed in 16 species, and 3259 in the canopy, with eight species. One of these species was labeled as Pintomia (Pifanomyia) nevesi, although certain morphological features allowed us to doubt that it was that taxon. To define the identity of this sand fly, a re-evaluation (this work) was recently carried out through morphological analyses and measurements of the available specimens mounted on Euparal, previously labeled as Pi. (Pif.) nevesi.ResultsBased on the morphological traits and measurements, the re-evaluated specimens were definitively identified as a new sand fly species, Pintomyia (Pifanomyia) veintemillasi, closely related to Pi. (Pif.) nevesi and Pintomyia (Pifanomyia) maranonensis within the Evansi series. This new sand fly was the third most numerous anthropophilic species at the floor (6.2%) and the second most numerous anthropophilic at the canopy (35.1%).ConclusionsA new anthropophilic sand fly species is described as Pi. (Pif.) veintemillasi n. sp. This sand fly species was caught at about 900 m altitude in the Marimonos mountain range, a highly endemic area for cutaneous and mucosal leishmaniasis due to Leishmania (Viannia) braziliensis. Therefore, this species could be involved in the leishmaniasis transmission in the sub-Andean foothills of Alto Beni, Department of La Paz, Bolivia.Graphical

New insights on landscape and environmental evolution in the Subandean region, Southern Central Andes: Sedimentology and geochronology of Guanaco Formation in the Río Chico (Jujuy, Northwestern Argentina)

During the late Miocene, the development of topography of the eastern margin of the Puna Plateau of the Central Andes, was related to the onset of the eastward migration and foreland fragmentation. The Guanaco and Piquete formations (late Miocene-early Pleistocene, Jujuy Subgroup) represent a thick succession of the adjacent foreland. These units outcrop in the Río Chico (=Xibi Xibi) locality (Jujuy in north-west Argentina), a transition zone between the Eastern Cordillera (EC) and the Subandean Ranges (SR). We combine a detailed stratigraphic section, paleocurrent measurements, provenance and facies analyses, as well as a new absolute age near to the top of the Guanaco Formation (5.7 ± 0.8 Ma), and new data on the Neogene environmental changes in this region to characterize these units in the context of the regional tectono-sedimentary evolution. Our analyses suggest a progradation of an alluvial-fan system over a braided-fluvial system, linked to an increase in relief due to rapid shortening pulses and associated to the regional climatic changes in this part of the Central Andes. In the studied area, the earliest uplift of the eastern margin of the Puna Plateau and other areas of the EC generated higher topographic relief to the north and north-west, which increased the relevance of local sources and caused the deflection of paleo-rivers toward the south. The limit between the Guanaco and Piquete formations was reinterpreted to be located 1000 m higher in the stratigraphic section compared to previous proposals, in agreement with the age of the newly dated tuff. Our analysis improves the temporal and spatial characteristics of tectonic processes in the southern Central Andes and provides a framework for the study of landscape as well as biotic, and environmental changes during the late Miocene within the context of the eastward migration of the orogenic front and coeval foreland evolution in the Central Andes. • Neogene southern Subandean units are analyzed in the context of the Central Andes orogeny evolution. • A novel upper tuff was dated on 5.7 Ma, constraining the span of the Guanaco-Piquete formations limit. • The earliest uplift of the eastern margin of the Puna and other areas of EC generated NW and N highs. • Progradation of alluvial fans over braided fluvial systems was recorded. • Southern deflection of main drainages and restriction of open areas evolved toward latest Miocene.

Silurian and Devonian Heteroconchia Cardiomorphi Bivalves from Bolivia

Heteroconchia Cardiomorphi bivalves from Silurian and Devonian beds of the Central Andean Basin of Western Gondwana are herein presented. This paper is not only a systematic updated revision of three Heteroconchia Cardiomorphi genera, but it also includes the description of new findings and first reports of some taxa in the basin. They were collected in nine scattered outcrops in the Interandean and Subandean regions of Bolivia. A total of 22 specimens, well- to regularly-preserved was studied. The genus Pleurodapis, is reported for the first time from Ludlow–Pridoli successions of Alarache, southern Subandean as Pleurodapis sp. A. The cosmopolitan genus Paracyclas is reported in the Central Andean Basin for the first time, from the Middle Devonian of Subandean as Paracyclas? sp. The species Pleurodapis multicincta and Cardiomorpha oblonga, are described from the central Subandean and the Interandean regions for the first time in the basin. This research is also a contribution to understand the distribution and the richness of Silurian and Devonian bivalves in Central Andean Basin and their relations with the surrounding basins of Gondwana.

Community-based entomological surveillance in three Chagas disease-endemic regions in sub-Andean Bolivia.

Chagas disease is endemic throughout most of Bolivia, with prevalence rates of 25% observed in some geographic areas located mainly in the sub-Andean region. Community-based entomological surveillance was carried out in the sub-Andean departments of Cochabamba (municipalities of Cochabamba, Punata and Sacaba), Tarija (municipality of Tarija) and Chuquisaca (municipality of Sucre). The surveillance parameters evaluated were: (i) the proportion of cards with the presence of triatomines; (ii) the distribution of positive cards by area; and (iii) the proportion of cards with the presence of infected triatomines. Of the cards returned, in 852 (3.1%) there was a mention of the presence of triatomines. The species Triatoma infestans, Triatoma sordida and Triatoma guasayana were identified in 812 (95.3%), 39 (4.6%) and 1 (0.1%), respectively. The median monthly positivity rate of the cards during 2011-2018 was higher in Punata (9.1%; IQR=3.2-15.4%). The median monthly rate was highest in 2012 (2.7%; IQR=0-5.6%). Fifty positive cards (5.8%) presented insects that were positive for trypanosomatids, mainly in Cochabamba and Punata. The report of triatomines foci by inhabitants represents an effective surveillance system coordinated by a network of specialized and multidisciplinary health centers. These strategies, which should be included in the health policies of endemic countries, enable extending and deepening the dialogue among technicians, communities and their local authorities.

The first Peruvian record of Enchodus (Actinopterygii, Aulopiformes, Enchodontidae) in the Upper Cretaceous Vivian Formation

We describe isolated teleostean teeth found in no association with the jaw bone. The specimens have been recovered in Late Cretaceous marine deposits of the Vivian Formation in the Peruvian Sub-Andean Region. The deposition sequence from where the teeth come is interpreted as a shallowing-upward sequence of low salinity. The fish material is identified as Enchodus aff. E. gladiolus based on the presence of a small but well-developed post-apical barb, an anterior cutting edge, the crown is symmetrical in cross-section, have a sigmoidal profile, and bears strong ridges (=striations). The Peruvian material differs from the typical E. gladiolus teeth in having a faintly serrated anterior cutting edge which is absent in most specimens referred to E. gladiolus. We also highlight that taxonomic assignments made based on isolated teeth must be taken with care. Despite scarce, the material recovered denotes that the marine units of Peru can give valuable information about the Pacific fish fauna during the Late Cretaceous.

A new mammalian assemblage for Guanaco Formation (northwestern Argentina), and the description of a new genus of New World porcupine

The Guanaco Formation (Orán Group) is one of the Neogene units outcropping in the Subandean region of northwestern Argentina. The fossil assemblage from the middle section was studied in a few contributions. Here we present new remains for the middle section (~6.3 Ma) and the first records for the upper section (<5.7 Ma) of this unit, collected in the Río Chico locality of Jujuy Province. The remains from the middle section include very well-preserved cranium, cephalic armor, and part of the carapace of a small glyptodontid assigned to Cranithlastus xibiensis, representing the second specimen known for the species. The remains from upper section represent the youngest mammalian association known for the Guanaco Formation, and include fragmentary remains of five caviomorph rodent taxa, including Lagostomus sp., Caviinae indet., Caviodon sp., Octodontoidea indet., the latter three representing new taxa for the unit. The fifth taxon of the upper section corresponds to a new genus and species of porcupine (Erethizontidae), represented by a fragment of left maxilla with DP4-M1. This and other recent paleontological studies, together with sedimentological and geochronological data of Guanaco Formation, are contributing to the knowledge of the past diversity of the area, and the faunistic and environmental evolution of the Central Andes ecoregions in northwestern Argentina. The preliminary characterization of the youngest faunistic association reveals the presence of forest-dweller taxa with conservative occlusal and postcranial morphologies, concurs with the context of local and regional progressive break-up of basins, increasing of moisture supply, and development of powerful streams related to a stepper slopes landscape. The evidence supports forested foothill environments, including subtropical components, for the upper levels of the Guanaco Formation, giving clues regarding to the tempo and mode in which Chacoan-like communities were replaced by subtropical mountain rain forests communities of Yungas.

Silurian and Devonian Modiomorphidae Bivalves from Bolivia

Modiomorphid bivalves from the Silurian and Devonian beds of the Central Andean Basin of Western Gondwana are herein presented. This paper is not only a systematic updated revision of certain species of modiomorphids but also includes the description of newly found ones in Bolivia. They were collected from 17 scattered outcrops along Eastern Cordillera, Eastern Altiplano, Interandean, and Subandean regions of Bolivia. A total of 55 specimens, well- to regularly-preserved, were studied. The Sphenotomorpha orientalis new species from the Interandean of Mataral is described. The genus Sphenotomorpha is reported for the first time from Ludlowian layers of the Central Andean Basin with Sphenotomorpha sp. A. Other species described and systematically discussed are Modiomorpha concentrica, Modiomorpha cf. pimentana, Sphenotomorpha ulrichi and Sphenotomorpha cf. bodenbenderi? Forms classified as Modiomorphidae indet. A, B, and C are studied and some discussions about their previous and current taxonomic designations are herein presented. The biostratigraphic distribution of the two cosmopolitan genera, Sphenotomorpha, 1916, and Modiomorpha, 1869, is proposed. From the Eifelian to the Frasnian, endobyssal forms, such as Modiomorpha concentrica, coexisted with foot forms like Modiomorphidae indet. C and Sphenotomorpha sp. B, which would have developed a discreet byssus. This research contributes to the still inaccurately known Silurian and Devonian palaeogeography of the Central Andean Basin.

A singular Hegetotheriinae (Notoungulata, Typotheria) from the late Oligocene-Early Miocene of the Subandean Region of Bolivia

Abstract Geological studies in the northern sector of the Chaco foreland Basin, Bolivia, yielded new fossils coming from late Oligocene-late Miocene of the Petaca Formation. Few fossil mammals were known from the Subandean Region of Bolivia. We report a partially complete mandible of a hegetotheriid Hegetotheriinae (Notoungulata, Typotheria) from Abapo (Rio Grande River). The specimen (YPFB-LIT-PAL-005) is very close in size and dental morphology to the late Oligocene (Deseadan South American Land Mammal Age, SALMA) — Santacrucian (early Miocene) Prohegetotherium schiaffinoi (Kraglievich 1932) from Fray Bentos (Uruguay and Argentina), Salla (Bolivia), Divisadero Largo-Potrerillos and Quebrada Fiera (Argentina). However, mandibular characteristics, as the shape with a marked change in height along its length, increasing towards the back, a prominent masseteric crest, a deep mandibular groove, and a remarkable thickening of the ventral rim of the mandible, indicate differences between this specimen and Prohegetotherium schiaffinoi and the other Hegetotheriinae. The affinity of YPFB-LIT-PAL-005 with P. schiaffinoi suggests a late Oligocene to early Miocene for the upper bearing horizon of the Petaca Formation (in Abapo), an older age than previously assigned to the top of this unit (late Miocene), and confirms the taxon distribution between ∼ 36 ° to ∼ 17 ° south latitude.

Have the Amazonian lowlands evidenced late Pleistocene-Holocene compression?

Neotectonic reactivation has been increasingly documented in many areas of the Amazonian lowlands, but the evidence has been only for extensional structures. This work investigates a large-scale sinusoidal-shaped morphology (Ssm) in a relief dominated by Late Quaternary deposits in the north of the Solimões Basin. The digital elevation model (DEM) of the shuttle radar topography mission (SRTM) was used as a basis to characterize this structure and improve the knowledge of its geological context. The Ssm is a Z-shaped sinusoid with a wavelength of approximately 135 km, formed by two merged asymmetrical curves. The north curve has an amplitude of 70 km and a core topographically lower and geologically younger than the limbs, while the south curve has an amplitude of 90 km and a core with older geological units and higher relief than the limbs. A main NE-trending morphostructural lineament has horizontally displaced the rocks near the axial plane in the north curve. Several NW-trending lineaments that laterally displaced the modern and ancient valley segments are also described. Our morphological data led to hypothesize that the Ssm north and south curves record a plunged syncline and an anticline, respectively, and that the laterally displaced lineaments are strike-slip faults. Although this type of fault has already been described in the region, the propagation of folds in the Pleistocene-Holocene deposits is a new finding. Assuming this model, the SW- to WSW-plunging folds would suggest a main NW- to WNW-oriented maximum horizontal compression, activated contemporaneously or shortly after the Pleistocene-Holocene deposition. This proposed orientation for the stress field is interesting because it would reveal a rotation, in this region, of the main E-W stress field recorded for South America. On the other hand, the suggested NW- to WNW-oriented compression is compatible with the models based on earthquake focal mechanisms comparing data from Brazil and the sub-Andean region. As such, the present work can bring new insights to discuss the impact of the late stage displacement of the South American plate in an intraplate region away from the passive margin, although the contribution of local stresses must be also considered.

Tachigali inca (Caesalpinioideae – Leguminosae), a new species of giant tree from Amazonian forests

The new species Tachigali inca is described and illustrated. It grows in lowland ‘terra firme’ forest of Amazonian Brazil, in the sub-Andean Amazon region of Peru, and in northeastern Bolivia. The species differs markedly from its most closely related species (T. amarumayu, T. prancei and T. setifera, all belonging to the “setifera group”), by the large cylindrical domatia on the leaf rachis, and by the brown-orange pulverulent indumentum on the abaxial surface of the leaflets and the young twigs; on older branches the indumentum becomes darker, degrades and then breaks off. It also differs by its linear petals with the upper half densely tomentose, the hairs forming small tufts.

New bird records for the Serran&amp;iacute;a de Las Quinchas, Colombia: inventory update and comments on distributions in an altitudinal gradient

The diversity of birds in the Las Quinchas mountain range amounted to 374 taxa in 2007, most of them distributed in the tropical region of the massif. We made five sampling trips between March and October 2019 to different locations in the Tropical and Sub-Andean regions of Las Quinchas, we added 11 species increasing in 3% the avian richness of the mountains. The 383 species are distributed in 55 families and 22 orders. One species is categorized as Critically Endangered and four are the Vulnerable. There was greater species richness in the upper part of the mountains and low turnover between altitude ranges.

Kinematic deformation model of the south-central subandean zone, Bolivia

The Bolivian Subandean region is characterized as a thin-skinned fold-thrust belt with structures persisting for 50–100 km along strike in a broadly North-South direction. The evolution of the Subandean structures is related to shortening and mass transfer. The stratigraphy comprises ~12 km of Ordovician to Recent sediments, which are dominated by the Paleozoic section including Devonian source and reservoir horizons capped by the Middle Devonian Los Monos regional seal. Detachments occur at top of basement, dipping 2° to the west, within the Silurian and two Devonian levels, including the Los Monos shale.The fold-belt contains the Mega Gas Fields of Bolivia. This study focused on an exploration target in the Igüembe structure, located nearby the Margarita and Incahuasi Gas Fields. In addition to the standard methodology of integrating seismic lines, surface geology and well data, this study also utilized magnetotelluric (MT) analysis to create regional structural sections that were balanced and restored, recording ~40% shortening between 12Ma and the present. The compression was propagated from west to east along a basal detachment along top basement at ~12 km depth, creating four different and superimposed structural units. The Ordovician to Middle Devonian section deformed as antiformal stacks at ~15 km spacing, with the highly ductile Los Monos horizon overlying it and acting as a major detachment and seal. The Upper Devonian to Cretaceous section was buttressed by over 5 km of overlying Neogene sequence; in such a way, that it was forced to propagate to the surface directly above the antiformal imbricates in a sequence of triangle zones above and along the Los Monos detachment. The 5+ km thick Neogene section is preserved as parallel bedded open synclines between the triangle zone culminations. The Middle Devonian source and reservoir may have been buried 6–8 km prior to deformation, which has reduced porosity, but also generated hydrocarbons. It is plausible that during the Siluro-Devonian Cordilleran compressional phase, gentle regional anticlines or inversion structures might have been formed, perhaps with ~15 km spacing. These may have trapped the early-formed hydrocarbons and preserved porosity. These anticlines would be the nuclei for subsequent contractional deformation in the Neogene, with hydrocarbons re-migration and some hydrocarbons remnants trapped in the original structures.

A new species of glyptodontine (Mammalia, Xenarthra, Glyptodontidae) from the Quaternary of the Eastern Cordillera, Bolivia: phylogeny and palaeobiogeography

Xenarthrans constitute a relict clade of endemic South American placental mammals with a long evolutionary history starting, at least, in the early Eocene. Within Xenarthra, Glyptodontidae (late Eocene–earliest Holocene) was a conspicuous group of large-sized armoured herbivores. During the Pleistocene (ca. 2.6–0.001 Ma) several genera (e.g. Panochthus and Glyptodon) achieved a remarkable latitudinal distribution in South America, as members of one of the xenarthran groups that participated in the Great American Biotic Interchange. Knowledge of the evolutionary history of this clade in some areas remains poorly known, especially in the high elevation Andean and sub-Andean regions of South America. Here we describe a new species, Glyptodon jatunkhirkhi sp. nov., from several localities of the Eastern Cordillera in Bolivia (ca. 2500–4100 m above sea level). From a phylogenetic viewpoint this new taxon appears as the sister group of the two lowland species recorded in southern South America (Glyptodon munizi + G. reticulatus), and this is congruent with the morphological differences observed between both clades, mainly with respect to the general morphology of the dorsal carapace and the skull. This new species expands the complex biogeographical scenario for Pleistocene glyptodonts and highlights the importance of Andean areas as key in understanding the evolutionary history of this clade. According to this revision, the diversity of Glyptodon is limited to G. munizi and G. reticulatus (two chronologically successive lowland species) plus this new species. The genera Panochthus (P. hipsilis) and Glyptodon seem to be the only Pleistocene glyptodonts to have been adapted to high elevation environments.http://zoobank.org/urn:lsid:zoobank.org:pub:7B5EFC11-626A-4BB5-8A00-DF657741698C

Efficacy of factory-treated and dip-it-yourself long lasting insecticide-treated bednets against cutaneous leishmaniasis vectors in the sub-Andean region of Colombia: results after two years of use.

BACKGROUND Long lasting insecticide-treated nets (LLINs) may be effective for vector control of cutaneous leishmaniasis (CL). Their efficacy, however, has not been sufficiently evaluated.OBJECTIVE To evaluate the large-scale efficacy of LLINs on Lutzomyia longiflocosa entomological parameters up to two years post-intervention in the sub-Andean region of Colombia.METHODS A matched-triplet cluster-randomised study of 21 rural settlements, matched by pre-intervention L. longiflocosa indoor density was used to compare three interventions: dip it yourself (DIY) lambda-cyhalothrin LLIN, deltamethrin LLIN, and untreated nets (control). Sand fly indoor density, feeding success, and parity were recorded using CDC light trap collections at 1, 6, 12, and 24 months post-intervention.FINDINGS Both LLINs reduced significantly (74-76%) the indoor density and the proportion of fully engorged sand flies up to two years post-intervention without differences between them. Residual lethal effects of both LLINs and the use of all nets remained high throughout the two-year evaluation period.CONCLUSIONS Both LLINs demonstrated high efficacy against L. longiflocosa indoors. Therefore, the deployment of these LLINs could have a significant impact on the reduction of CL transmission in the sub-Andean region. The DIY lambda-cyhalothrin kit may be used to convert untreated nets to LLINs increasing coverage.

Four highland species of Galianthe (Rubiaceae: Spermacoceae) with restricted distribution in South America: conservation assessment and complete descriptions

Full descriptions of four Galianthe species, complemented by new data on fruits and seed characters are presented. These species occur at 500–3000 m elevations: G. gertii and G. reitzii in southeastern Brazil; G. guaranitica in eastern Paraguay and central-western Brazil; and G. boliviana in the sub-Andean region of northern Bolivia and southern Peru. Conservation status, with comments on distribution, is provided for three of them and is reassessed for one. The lectotypification of G. guaranitica is discussed.

New Evidence of Ancient Mitochondrial DNA of the Southern Andes (Calchaquí Valleys, Northwest Argentina, 3,600–1,900 Years before Present)

Genetic studies on pre-Hispanic populations of the Southern Andes have been increasing steadily in the last decade. Nevertheless, ancient DNA characterization of Formative Period archaeological human remains is particularly scant, especially for Northwest Argentina. To expand current information on genetic characterization of the first agricultural communities of the southern Calchaquí Valleys, we present and discuss the first mitochondrial ancient DNA information obtained on samples dated to ca. 3,600-1,900 years before present from the Cajón Valley, Catamarca Province. Reproducible mtDNA hypervariable region 1 (HVR-1) sequences were obtained in seven individuals. Mitochondrial HVR-1 haplotypes were assigned to three of the four founding haplogroups, D1 (57.1%), C1 (28.5%), and B2 (14.2%), with absence of A2. Our results show that the Cajón Valley sample, with predominance of D1 and C1, differs from that commonly observed in ancient and modern Andean populations, which usually show a high prevalence of haplogroup B2. The fact that the Cajón Valley and Pampa Grande (Salta Province, Argentina) share a prevalence of haplogroup D1 could provide additional evidence to support possible genetic affinities between the valleys and the eastern sub-Andean region during the Formative Period in Northwest Argentina, expanding the archaeological evidence of contact between both populations. Future complete mitogenomic analysis will provide substantial information to formulate new hypotheses about the origins and phylogenetic relationships between the individuals of the Cajón Valley and other groups from the Andes, Gran Chaco, and the Amazon.

New age constraints on the palaeoenvironmental evolution of the late Paleozoic back-arc basin along the western Gondwana margin of southern Peru

The tectonic evolution of the western Gondwana margin during Pangaea amalgation is recorded in variations in the Permo-Carboniferous back-arc basin sedimentation of Peru. This study provides the first radiometric age constraints on the volcanic and sedimentary sequences of south-central eastern Peru up to the western-most tip of Bolivia, and now permits the correlation of lateral facies variations to the late Paleozoic pre-Andean orogenic cycle. The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in two major changes in this sedimentary environment.Our detrital U-Pb zircon ages demonstrate that the timing of Ambo Formation deposition corroborates the Late Mississipian age estimates. The transition from the Ambo to the Tarma Formation around the Middle Pennsylvanian Early Gondwanide Orogeny (c. 315 Ma) represents a relative deepening of the basin. Throughout the shallow marine deposits of the Tarma Formation evidence for contemporaneous volcanism becomes gradually more pronounced and culminates around 312 - 309 Ma. Continuous basin subsidence resulted in a buildup of platform carbonates of the Copacabana Formation. Our data highlights the presence of a previously unrecognized phase of deposition of mainly fluvial sandstones and localized volcanism (281–270 Ma), which we named ´Oqoruro Formation'. This sedimentary succession was previously miss-assigned to the so-called Mitu Group, which has recently been dated to start deposition in the Middle Triassic (∼245–240 Ma). The emersion of this marine basin coincides with the onset of a major plutonic pulse related to the Late Gondwanide Orogeny (c. 260). Exhumation lead to the consequent retreat of the epeiric sea to the present-day sub-Andean region, and the coeval accumulation of the fluvial Oqoruro Formation in south eastern Peru. These late Paleozoic palaeoenvironmental changes in the back-arc basins along the western Gondwana margin of southern reflect changes in tectonic plate reorganization in a long-lived Paleozoic accretionary orogeny.

Fire, rituals and domesticity. Forest resource management in the sub-Andean region of Jujuy, Argentina (2000 BP): First anthracological evidence

In this article, we present the results of anthracological analysis from an archaeological site located in the foothills of the Argentinian northwest, which is assigned to the lower Formative period (2000yearBP). We analyzed thirty-four charcoals from different depositional events over an excavated area of 94m2. Most of them were assigned to Mimosoideae-Fabaceae. In general, the most represented taxonomic groups correspond to species with excellent fuel properties. Others species, represented at the carpological level and belonging to plants valuable for food and dyes, have not been identified at an anthracological level. Some wood fuel species were selected for specific functions, like human cremations, and were part of complex funerary rituals, while others were selected for high heat power in pyretic structures (earth oven). The diversity of identified taxa in the different samples indicates both the provisioning of available species and a knowledge of the different properties needed for different ends (e.g. Fabacea and Anacardiaceae). The presence of Salix in earth ovens and Allophylus clustered in small groups of charcoals on the floors evidence an environment with humid seasons, and a population that lived near a possibly permanent body of water.