The Pleistocene/Holocene transition in Peru and its effects upon human use of the landscape

This paper reviews the state of our knowledge regarding the effects of the Pleistocene/Holocene transition on the kinds and range of human adaptations in what is now Peru. Following a discussion of geological, paleoclimatic, and archaeological data, the paper focuses upon four aspects of environmental change with specific regard to how these would have affected human adaptations: environmental changes on the Pacific littoral, the extinction of Pleistocene faunal and floral species and their replacement with modern faunas, the adaptive radiation of these modern flora and fauna, especially into the Andean highlands, and characteristics of newly available high elevation environments that would have affected the process by which foraging peoples moved into them. Although Pleistocene fauna have been discovered in Peru, none of these finds have been made in the context of indisputable human activity, and therefore, the effect of their extinction on early foraging peoples is unknown. The earliest acceptable archaeological sites in Peru date around 11–12,000 years ago, and are found on the coastal lowlands. The highlands were not occupied until after 11,000 years ago. While high elevation environments were attractive after 11,000 years ago, they were only slowly occupied by humans due to the constraints of the combined effects of hypoxia and cold.     

Evidence of centennial-scale drought from southeastern Massachusetts during the Pleistocene/Holocene transition

A principal method for studying past hydroclimatic change is the reconstruction of paleo-lake levels. Here, we provide high-resolution lake-level records from New Long Pond and Rocky Pond in southeastern Massachusetts, which each contain evidence for multiple, sub-centennial-to-millennial scale low stands during the transition between the Late Pleistocene (15.0 ka) and Middle Holocene (ca 7.0 ka). Data from New Long Pond also demonstrate sedimentary evidence for a drop in water levels in the early to mid AD 20th century, when long-term trends in instrumental data show lower-than-average precipitation in the northeastern United States. Local data show the most precipitous declines in precipitation and groundwater levels are concurrent with the most severe drought in the AD 1960s, which occurred during a period of low sea-surface temperatures in the western North Atlantic. Ground penetrating radar and sediment core data indicate five intervals with numerous paleo-shoreline deposits between ca 15.0 and 7.0 ka, similar to the layer deposited in the AD 1960s. Many of the intervals of low lake levels coincide with proposed meltwater release events or abrupt climate oscillations in the circum North Atlantic. For example, we document at least three low stands during the Younger Dryas (12.9–11.6 ka) and in association with the “9.2” and “8.2” ka events. The combined evidence of (1) concurrent paleo-droughts in southeastern New England with documented North Atlantic abrupt cooling events and (2) recent drought with the modern association of low sea-surface temperatures indicates that freshening and cooling of the western North Atlantic is a viable mechanism for decreasing moisture within the region. Large-scale changes in seasonality and ice sheet extent also may have increased the susceptibility of the northeast to dry conditions triggered by changes in the North Atlantic.     

Lake‐level changes in central Patagonia (Argentina): crossing environmental thresholds for Lateglacial and Holocene human occupation

The role and extent of climate as a cause of the expansion and decline of human cultures is still debatable. It is clear, however, that human–environment interactions are enhanced and interplay more closely in climatically sensitive areas such as around hydrologically closed basins. Lago Cardiel is located at 49° S in the very arid rain shadow east of the Andes, providing an exceptionally receptive system to changes in hydrological balance. Results of a geophysical survey combined with sedimentological and geochemical studies provide a continuous Lateglacial–Holocene record of substantial water‐level changes. These variations, combined with archaeological results from the catchment area, offer a unique possibility to explore the pattern of peopling within this remote area of the globe and its possible relation to climate change. Human occupation in Patagonia is well documented towards the Andes throughout the entire Holocene. Archaeological data from the Lago Cardiel basin, however, show an apparent lack of human activity during the first part of this period, which coincides with well‐constrained high lake levels. Our results show an intriguing coincidence between low lake level and increasing human occupation, suggesting that the Lago Cardiel basin has focused human use during intervals with relatively lower effective moisture such as during the Late Pleistocene, but its evidence may have been submerged. This interpretation is confirmed by archaeological remains from Lago Strobel, another perennial lake with a comparable catchment located in the same climatic region and thus sharing the same climatic history as Lago Cardiel. Copyright © 2009 John Wiley & Sons, Ltd.     

Temporal relationship between Holocene human occupation and vegetation change along the northwestern margin of the Central African rainforest

This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area.     

Quaternary climate,environment, and the human occupation of the south-central Andes

This paper reviews the paleoenvironmental context for Paleoindian and Early Archaic settlement of the south-central Andes. I attempt to reconcile proposals for late-glacial and early Holocene environmental changes that have originated in several Quaternary sciences. Most useful are the records of changing lake levels, geomorphological indicators of glacial advance and retreat, changes in vegetation as seen through pollen stratigraphy, the record of large mammal extinctions, and the archaeological settlement pattern itself. High lake stands in the central and south-central Andes, c. 12,500 to 11,000 B.P., seem to correspond to glacial retreat. Palynological studies also suggest higher temperatures, coincident with greater summer precipitation from 11,500 B.P. to perhaps 10,000 B.P., followed by some reduction in temperatures and then widespread aridity from about 8500 to 5000 B.P. Environmental change at the Pleistocene/Holocene boundary was at least a major contributing factor to the extinction of horse and sloth around 10,000 B.P. Archaeology of the salt puna and Punta Negra region conforms well with the environmental record, showing human entry by the Early Archaic (11,000-8000 B.P.), subsequent depopulation and perhaps abandonment, then readaptation to more localized resources in the Late Archaic (5500-4000 B.P.).     

The last occurrence of Pleistocene megafauna in the Ecuadorian Andes

The latest Pleistocene—Holocene megafauna extinction is a global event, particularly dramatic in the Americas. In a previous paper the authors hypothesised a scenario for this extinction event in South America, where mastodonts first suffered from the changing climate environment, followed by the mylodonts and equids. These different latest Pleistocene—Holocene megafauna extinction “waves” in Ecuadorian Andes have been dated using ¹⁴C methods on material from selected sites in north and central Ecuadorian Interandean Depression. An outline of the physiographic evolution of the Interandean Depression in Ecuador is offered and the stratigraphic setting of the fossiliferous sites is discussed. The present results confirm the author's hypothesis on the megafauna extinction pattern, previously published in terms of relative age. The importance of climatic changes during Last Glacial Maximum at low latitudes is discussed.     

The Pleistocene/Holocene boundary in marine deposits from the Oslofjord area

Feyling-Hanssen, R. W.: The Pleistocene/Holocene boundary in marine deposits from the Oslofjord area. Boreas, Vol. 1, pp. 241–246. Oslo 1st September, 1972.
In marine deposits from the southern Oslofjord area in Norway the boundary between Holocene and Pleistocene is found within a formation characterized by Arctic species, the so-called Yoldia Clay or zone A in the foraminiferal stratigraphy. The fossil assemblage on the Holocene side of the boundary is even poorer than that on the Pleistocene side, which is explained by the rapid Preboreal ice recession. The boundary is not conspicuously reflected in the faunas but still discernible and applicable.     

The paradigm of paraglacial megafans of the San Juan river basin,Central Andes,Argentina

The spatial distribution and several morphometric characteristics of the Quaternary alluvial fans of the San Juan River, in the province of San Juan, at the Central and Western part of Argentina, have been studied to classify them as paraglacial megafans, as well to ratify its depositional environmental conditions. The high sedimentary load exported by San Juan river from the Central Andes to the foreland depressions is estimated about 3,682,200 hm³. The large alluvial fans of Ullum-Zonda and Tulum valleys were deposited into deep tectonic depressions, during the Upper Pleistocene deglaciation stages. The outcome of collecting remotely sensed data, map and DEM data, geophysical data and much fieldwork gave access to morphometric, morphographic and morphogenetic data of these alluvial fans. The main drainage network was mapped on processed images using QGis (vers.2.0.1). Several fan morphometric parameters were measured, such as the size, the shape, the thickness, the surface areas and the sedimentary volume of exported load. The analyzed fans were accumulated in deep tectonic depressions, where the alluvium fill reaches 700 to 1200 m thick. Such fans do not reach the large size that other world megafans have, and this is due to tectonic obstacles, although the sedimentary fill average volume surpasses 514,000 hm³. The author proposes to consider Ullum-Zonda and Tulum alluvial fans as paraglacial megafans. According to the stratigraphic relationships of the tropical South American Rivers, the author considers that the San Juan paraglacial megafans would have occurred in the period before 24 ka BP, possibly corresponding to Middle Pleniglacial (ca 65–24ka BP). They record colder and more humid conditions compared with the present arid and dry conditions.     

The Pleistocene/Holocene boundary: a proposed boundary-stratotype in Gothenburg, Sweden

The boundary between the last two geological epochs, the Pleistocene and the Holocene, is placed at 'the date 10,000 B.P., measured in radiocarbon years'. In the European chronostratigraphy, this corresponds to the Younger Dryas/Preboreal boundary, the pollen zone III/IV boundary and the Late Glacial/Postglacial boundary. The stratal sequence in the Botanical Garden of Gothenburg is proposed as a suitable boundary-stratotype of the Pleistocene/Holocene that fulfils the stratigraphical rules of marine environment and accessibility. A core, labelled B 873, has been analyzed for multiple parameters by various authors. The suggested Pleistocene/Holocene boundary in Core B 873 is indicated by a lithologic boundary, a palynological change tentatively correlated with the pollen zone III/IV boundary, and a distinct palaeomagnetic intensity maximum, the 'Gålön Magnetic Intensity Maximum', identified in numerous other cores at the Younger Dryas/Preboreal boundary and at the drainage of the Baltic Ice Lake in varved clay sequences (with the peak dated at the drainage ±4 varves). This boundary is closely radiocarbon dated at 10,000 B.P. (10,000–9950 B.P.) in terrestrial-lacustrine sequences within the proposed type area in Gothenburg and in Southern Sweden, the established type region for the Pleistocene/Holocene boundary. The corresponding varve date is 9965 varves B.P. (De Geer's varve –1073). The various parameters directly and indirectly connected with the study of Core B 873 make global correlations possible. Because every region has its own local characteristics, however, it will be necessary to establish regional type sections, hypostratotypes.     

Editor's column: Core B 873 and the Pleistocene/Holocene boundary-stratotype

The various problems in defining and dating a Pleistocene/Holocene boundary in Core B 873, proposed as the world boundary-stratotype by N.-A. Mörner, are pointed out. It is suggested that a terrestrial-lacustrine section might be a better alternative.     

Effect of aridity and rainfall seasonality on vegetation in the southern tropics of East Africa during the Pleistocene/Holocene transition

Fossil pollen analyses from northern Lake Malawi, southeast Africa, provide a high-resolution record of vegetation change during the Pleistocene/Holocene transition (~ 18–9 ka). Recent studies of local vegetation from lowland sites have reported contrasting rainfall signals during the Younger Dryas (YD). The Lake Malawi record tracks regional vegetation changes and allows comparison with other tropical African records identifying vegetation opening and local forest maintenance during the YD. Our record shows a gradual decline of afromontane vegetation at 18 ka. Around 14.5 ka, tropical seasonal forest and Zambezian miombo woodland became established. At ~ 13 ka, drier, more open formations gradually became prevalent. Although tropical seasonal forest taxa were still present in the watershed during the YD, this drought-intolerant forest type was likely restricted to areas of favorable edaphic conditions along permanent waterways. The establishment of drought-tolerant vegetation followed the reinforcement of southeasterly tradewinds resulting in a more pronounced dry winter season after ~ 11.8 ka. The onset of the driest, most open vegetation type was coincident with a lake low stand at the beginning of the Holocene. This study demonstrates the importance of global climate forcing and local geomorphological conditions in controlling vegetation distribution.     

Porphyry to epithermal transition in the Agua Rica polymetallic deposit, Catamarca, Argentina: An integrated petrologic analysis of ore and alteration parageneses

Agua Rica (27°26′S–66°16′O) is a world class Cu–Au–Mo deposit located in Catamarca, Argentina. In the E–W 6969400 section examined, the Seca Norte and the Trampeadero porphyries that have intruded the metasedimentary rock are cut by interfingered igneous and hydrothermal heterolithic and monolithic breccias, and sandy dikes. Relic biotite and K-feldspar of the early potassic alteration (370° to > 550 °C) with Cu (Mo–Au) mineralization are locally preserved and encapsulated in a widespread, white mica + quartz + rutile or anatase halo (phyllic alteration) with pyrite + covellite that suggests fluids with temperatures ≤ 360 °C and high f(S₂). The Trampeadero porphyry and the surrounding metasedimentary rock with phyllic alteration have molybdenite in stringers and B-type quartz veinlets and the highest Mo grades (> 1000 ppm).Multistage advanced argillic alteration overprinted the earlier stages. Early andalusite ± pyrite ± quartz is preserved in the roots of the argillic halo rimmed by an alumina–silica material and white micas. This alteration assemblage is considered to have been formed at temperatures ≥ 375 °C from condensed magmatic vapor. At higher levels, pyrophyllite replaces muscovite and illite in clasts of hydrothermal breccias in the center and east sector of the study section, suggesting temperatures of 280 to 360 °C. Clasts of vuggy silica in the uppermost levels of the central breccia, indicates that at lower temperatures (< 250 °C), fluids reached very low pH (pH < 2). In this early stage of the advanced argillic alteration, hydrothermal fluids seem to have not precipitated sulfides or sulfosalts.Hydrothermal brecciation was concurrent with fluid exsolution (↑? V), which precipitated intermediate-temperature advanced argillic alunite (svanbergite + woodhouseite) ± diaspore ± zunyite as breccia cement along with abundant covellite + pyrite + enargite ± native sulfur ± kuramite at intermediate depths and in lateral transitional zones to unbrecciated rocks. This mineral assemblage indicates temperatures near 300 °C, oxidized and silica-undersaturated hydrothermal fluids with high sulfur fugacity to prevent gold precipitation. Multiple generations of pyrite, emplectite, colusite, Pb- and Bi-bearing sulfosalts, and native sulfur with Au and Ag, accompanied by alunite introduction in the upper level breccias, probably occurred at lower temperatures, but still high sulfur and oxygen activity. An independent Zn and Pb (as galena) mineralization stage locally coincides with Au–Ag and sulfosalts, and advanced at depth, controlled by fractures and overprinting much of the previous mineralization. A later paragenesis of veinlets of alunite + woodhouseite + svanvergite + pyrite ± enargite that cut the phyllic halo suggests temperatures ~ 250 °C and without woodhouseite + svanvergite, temperatures ~ 200 °C. Kaolinite occurs in the phyllic halo as a late mineral in clots and in veinlets thus, in this zone, the fluid had cooled enough for its formation.     

Geoarchaeological context of late Pleistocene and early Holocene occupation at the Cooper's Ferry site,western Idaho,USA

Archaeological excavations at the Cooper's Ferry site (10IH73), located in the lower Salmon River canyon of western Idaho, revealed a stratified sequence of cultural occupations that included a pit feature containing stemmed points. However, radiocarbon ages determined on charcoal and bone in the pit feature range between ca. 12,000 yr B.P. and 7300 yr B.P. By considering the effects of postdepositional processes on dated samples, and by comparing the lithostratigraphy, pedostratigraphy, and stable isotope geochemistry of pedogenic carbonates from Cooper's Ferry with other well‐dated stratigraphic sections in the canyon, site geochronology is clarified. Based on the presence of key radiocarbon ages and distinctive stratigraphic criteria, we argue that the initial occupation and interment of lithic artifacts in a pit feature at Cooper's Ferry occurred during the late Pleistocene, between ca. 11,410 and 11,370 yr B.P., and not during the early Holocene. Records of geomorphic change and paleoenvironmental proxy data from the site reveal that early occupation in the lower Salmon River canyon corresponds with evolving riparian ecosystems, which must be considered as a contextual aspect of local prehistoric cultural ecology. © 2004 Wiley Periodicals, Inc.     

The structure of the eastern border of the Andes in north-western Argentina

In the eastern border area of the Andes of north-western Argentina two structural units are represented: the Cordillera Oriental and the Sierras Subandinas.The Cordillera Oriental represents a structural unit of faulted blocks strongly uplifted in relation to the Sierras Subandinas. In the Cordillera Oriental, the metamorphic basement has been partially folded together with the sedimentary cover. In some cases the cover has been detached away from its substratum and folded independently of it.It was generally accepted that the Sierras Subandinas coincide with big asymmetrical anticlines produced in the cover rocks by tilting of rigid basement blocks. The detailed geological mapping of the region situated between the parallels 24° 45 and 26° latitude south and the meridians 64° 30 and 66° west has provided data that permit to modify considerably this scheme.The existence of important strike-slip faults running highly oblique to the main regional structural pattern and controlling the shape of the Sierras Subandinas folds has been verified. These highly oblique faults with strike-slip movements, that affect the whole region, are probably ancient lineaments reactivated during Andean diastrophism in Upper Pliocene to Early Pleistocene time.

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Zusammenfassung Im östlichen Grenzgebiet der Anden im nordwestlichen Argentinien liegen zwei strukturell unterschiedliche Einheiten vor, die Cordillera Oriental und die subandinen Sierren (Sierras Subandinas).Die Cordillera Oriental besteht aus Leistenschollen eines leicht metamorphisierten Sockels. Sie ist als Ganzes im Verhältnis zu den subandinen Sierren stark herausgehoben worden. In der Cordillera Oriental wurde dieser Sockel zum Teil zusammen mit seinen sedimentären Deckschichten verfaltet, zum Teil wurden sie aber auch von ihrem Unterlager abgeschert und unabhängig von ihm gefaltet.Bisher wurde allgemein angenommen, daß die subandinen Sierren aus großen assymmetrischen Falten aufgebaut werden, die in den Deckschichten durch Kippung starrer Blöcke im tieferen Untergrund hervorgerufen wurden. Die genaue geokartographische Aufnahme eines Gebietes zwischen den Breitenkreisen 24° 45 und 26° südl. Breite und den Längenkreisen 64° 30 und 66° westl. Länge erbrachte Daten, die es erlauben, diese Vorstellung erheblich zu modifizieren.Weit durchhaltende Seitenverschiebungen, die die übergeordneten Strukturen des gesamten Gebietes schräg durchziehen und die Gestalt der Falten in den Sierren erheblich beeinflussen, wurden nachgewiesen. Sie stellen wahrscheinlich alte, präandine Lineamente dar, die während der Anden-Orogenese im Jungtertiär bis Altpleistozän reaktiviert Wurden.

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Resumen En el borde oriental de los Andes del Noroeste Argentino están representadas dos unidades estructurales: la Cordillera Oriental y las Sierras Subandinas.La Cordillera Oriental es una unidad constituida por bloques fallados y, en conjunto, elevada con respecto a las Sierras Subandinas. En la Cordillera Oriental el basamento metamórfico ha sido parcialmente plegado junto con la cobertura sedimentaria. En algunos casos lo cobertura ha sido despegada de su substrato y plegada independientemente.En general se aceptaba que las Sierras Subandinas coincidian con grandes anticlinales asimétricos producidos en la cobertura sedimentaria por el basculamiento de bloques rígidos de basamento situados en el subsuelo. La cartografía geológica-estructural detallada de la región comprendida por los paralelos 24° 45 y 26° S y los meridianos 64° 30 y 66° W ha proporcionado datos que permiten modificar considerablemente este esquema.Se ha comprobado la existencia de importantes fallas transcurrentes, fuertemente oblicuas con respecto a la estructura regional, que han tenido profunda influencia sobre la forma de los pliegues subandinos. Estas fallas oblicuas son probablemente lineamientos antiguos en los que el diastrofismo Andico (Plioceno-Pleistoceno) ha producido considerables desplazamientos paralelos al rumbo de los mismos.

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Résumé Dans la bordure orientale des Andes du Nord-ouest de l'Argentine, deux unités structurales différentes sont présentes: les Sierras subandines et la Cordillère orientale.La Cordillère orientale est composée d'un socle faiblement métamorphique faillé en blocs fortement surélevés par rapport aux Sierras subandines. Dans la Cordillère orientale, ce socle métamorphique a été en partie plissé avec sa couverture sédimentaire; mais parfois celle-ci a été décolée de son substratum et plissé indépendentement.Jusqu'à présent, on admettait que les Sierras subandines sont constituées de grands anticlinaux assymétriques produits dans la couverture par l'ascension de blocs faillés du socle. La cartographie géologico-structurale detaillée de la région comprise entre les parallèles 24° 45 et 26° de latitude sud et les méridiens 64° 30 et 60° ouest conduit à modifier considérablement ce schéma.D'importants décrochements très obliques par rapport à la direction de la structure régionale et qui ont fortement influencé la forme des plis subandins sont probablement des accidents anciens rajeunis pendant le diastrophisme andin au cours du Pliocène supérieur et du Pléistocène inférieur.

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Climatic effect of ENSO associated with landslide occurrence in the Central Andes, Mendoza Province, Argentina

Temporal distribution of landslides can be verified by means of climatic anomalies linked to the ENSO phenomenon. An increasing number of landslides triggered by rainfall have been recorded during warm episodes (El Niño) in the Cordillera Frontal, and a decreasing number during cold episodes (La Niña), concluding that this geological province is mainly influenced by the Pacific Anticyclone. However, slope instability in the Precordillera, located east of the Cordillera Frontal, seems to be mainly influenced by the Atlantic Anticyclone. Analysis of variance shows that there is no significant difference between landslide records and cold-warm episodes, and a higher number of landslides were recorded in years linked to wet periods than during dry periods. Furthermore, the precipitation threshold value associated with landslide occurrence and antecedent precipitation are analysed.     

An archaeological perspective of the Pleistocene/Holocene boundary in northern South America

In this paper, I examine Late Pleistocene/Early Holocene adaptations of hunter-gatherers to different ecosystems in northern South America. The role played by the climatic events associated with the Pleistocene/Holocene boundary in the evolution of culture in that part of the Americas is assessed in the light of those adaptations. The conclusion is that the Pleistocene/Holocene boundary is not very useful in understanding the human process of early colonization and adaptation to the various ecosystems of northern South America, because a mechanism of cultural change cannot be linked to that boundary.     

The British Pleistocene fluvial archive: East Midlands drainage evolution and human occupation in the context of the British and NW European record

This paper reviews the Pleistocene evolution and human occupation of the River Trent, the major fluvial artery draining Midland Britain, and places it within a modern Quaternary context. In contrast to the sedimentary records of the River Thames and the erstwhile Bytham system, which extend back to the early Pleistocene, present knowledge of the terrace sequence of the Trent, its tributary systems and associated ancestral courses extends back only to the Anglian glaciation (Marine Isotope Stage (MIS) 12), although the regional pre-Anglian drainage configuration is demonstrably complex. The post-Anglian sequence is well developed, with major terrace sand and gravel aggradations associated with each subsequent cold stage. Temperate-climate sediments correlating with MIS 7 and 5e have been recorded, although deposits relating to earlier interglacials during MIS 11 and 9 have yet to be identified. Evidence for human occupation in the form of Lower and Middle Palaeolithic artefacts has been recorded from terrace sediments correlated with MIS 8 and MIS 4, but the majority of this material is heavily rolled and abraded, suggesting significant reworking from older deposits. This review demonstrates that there is a rich palaeo-environmental record from the Trent but the lack of a high-resolution chronostratgraphic framework raises issues about correlation with other systems.     

Holocene settlement in the rio de la plata littoral (argentina): A methodological approach

Cultural and faunal remains from archaeological sites of the Rio de La Plata littoral, Argentina, have been studied, attempting to verify their primary associations and occupations during the Holocene. the sites were localized within shell beach ridges more or less parallel to the present shore and are composed of bivalves, gastropods, scarce barnacles, and sandy sediments. the thanatocoenosis found could be equivalent to a transitional area between fluviomarine (mixohaline) and oceanic (polyeuhaline) gradients, i.e., an environment with greater salinity conditions than that of the adjacent coast in the present estuary. These deposits correspond to the Las Escobas Formation (Holocene). Archaeological remains were found from the base of the shell ridge up into the overlying sediments. the hypothesis proposed here is that the human occupation is not contemporaneous with the formation of the shell ridge. the cultural sequence in this kind of site can be altered by disturbances of the stratigraphy as a consequence of environmental and geological events.     

Curved structures and interference fold patterns associated with lateral ramps in the Eastern Cordillera, Central Andes of Argentina

The conspicuous curved structures located at the eastern front of the Eastern Cordillera between 25° and 26° south latitude is coincident with the salient recognized as the El Crestón arc. Major oblique strike-slip faults associated with these strongly curved structures were interpreted as lateral ramps of an eastward displaced thrust sheet. The displacement along these oblique lateral ramps generated the local N–S stress components responsible for the complex hanging wall deformation. Accompanying each lateral ramp, there are two belts of strong oblique fault and folding: the upper Juramento River valley area and El Brete area.On both margins of the Juramento River upper valley, there is extensive map-scale evidence of complex deformation above an oblique ramp. The N–S striking folds originated during Pliocene Andean orogeny were subsequently or simultaneously folded by E–W oriented folds. The lateral ramps delimiting the thrust sheet coincident with the El Crestón arc salient are strike-slip faults emplaced in the abrupt transitions between thick strata forming the salient and thin strata outside of it. El Crestón arc is a salient related to the pre-deformational Cretaceous rift geometry, which developed over a portion of this basin (Metán depocenter) that was initially thicker. The displacement along the northern lateral ramp is sinistral, whereas it is dextral in the southern ramp. The southern end of the Eastern Cordillera of Argentina shows a particular structure reflecting a pronounced along strike variations related to the pre-deformational sedimentary thickness of the Cretaceous basin.