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The palynology (150 species of pollen grains, 43 species of spores, eight species of dinoflagellate cysts, five genera of algae, two genera of fungal spores, foraminiferal linings, and copepod eggs) of the Neogene succession in the Marañon Basin, north Peru, was thoroughly investigated for the first time from six industrial wells (Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1). Six palynozones spanning the Early Miocene to the Early Pliocene were defined. The zones in stratigraphically ascending order are as follows: the Mar-A Corsinipollenites oculusnoctis Zone (Aquitanian to early Burdigalian: 23.03–17.71 Ma), delimited by the appearance of Acaciapollenites myriosporites, Retitricolporites wijmstrae and/or Corsinipollenites oculusnoctis and/or the disappearance of Cicatricosisporites dorogensis at the base; the Mar-B Malvacipolloides (Echitricolporites) maristellae Zone (Burdigalian: 17.71–16.1 Ma), from Malvacipolloides maristellae at the base to the disappearance of Retitricolporites wijmstrae at the top; the Mar-C Mauritiidites crassibaculatus Zone (latest Burdigalian to Late Langhian: 16.1–14.2/13.9 Ma), from the appearance of Grimsdalea magnaclavata at the base to the disappearance of Retitriporites dubiosus and/or the appearance of Crassoretitriletes vanraadshooveni and/or Psilastephanoporites tesseroporus; the Mar-D Crassoretitriletes vanraadshooveni Zone (Late Serravallian: 14.2–11.62 Ma), from the appearance of Crassoretitriletes vanraadshooveni and/or Psilastephanoporites tesseroporus to the disappearances of Mauritiidites crassibaculatus, Bombacacidites nacimientoensis, and Cyathidites congoensis; and the Mar-E Psilastephanoporites tesseroporus Zone (Early Tortonian to Late Messinian: 11.62–5.48 Ma) from the disappearance of Corsinipollenites oculusnoctis and/or Cyathidites congoensis to the disappearance of Psilastephanoporites tesseroporus and/or Siltaria santaisabelensis. These zones were corroborated by means of events ordination demonstrated using graphic correlation. The Mar-F Ctenolophonidites suigeneris Zone (latest Messinian to Zanclean) is described only in the Frontera-1 well from the disappearance of Psilastephanoporites tesseroporus to the last record of Ctenolophonidites suigeneris and/or Siltaria hammenii. This study suggests that Pliocene sedimentation is also recorded in the Western Amazonia of Peru, and provides new palynological information compared with the Mio–Pliocene Solimões, Acre, and eastern Amazonas basins. Fil: Parra, Francisco Javier. Universidad Nacional de Colombia; Colombia. Université Paul Sabatier; Francia. Departamento de Bioestratigrafía; Colombia Fil: Navarrete, R.E.. Departamento de Bioestratigrafía; Colombia Fil: Di Pasquo Lartigue, Maria. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina Fil: Roddaz, M.. Université Paul Sabatier; Francia Fil: Calderón, Y.. Departamento de Exploración; Perú Fil: Baby, P.. Université Paul Sabatier; Francia

Late Permian to Early Jurassic strata in northern Peru allow us to carry out a seismostratigraphic, lithotectonic and chemostratigraphic analysis connecting the Andean–Amazonian foreland basins of Huallaga, Ucayali, southern Maranon and the Eastern Cordillera. This analysis and data integration from Ecuador to western Brazil and southern Peru and Bolivia allow us to redefine the timing of the major documented tectonic phases and corresponding palaeogeographies of western Gondwana from the late Permian to the Triassic. Three lithotectonic sequences and four associated deformation stages are recognized: (1) A sequence, tectonic relaxation, during the late Permian; (2) A–B intra-sequence, folding-and-thrusting attributed to a continuation in time of the Gondwanide Orogeny, during the Early to Middle Triassic; (3) B sequence, rifting, attributed to Gondwana breakup during the Middle and late Triassic; (4) C sequence, thermal sag, during the Late Triassic. Evaporites and carbonates (A sequence) dominated a low-subsidence basin with southern restricted marine inflow at the Permian–Triassic boundary. A novel palaeogeographic model for these evaporites suggests that this saline basin extended up to 50 000 km2 in a restricted environment area with a potential bullseye pattern. The last pulse of the Gondwanide Orogeny and associated fold and thrust belt (A–B intra-sequence) exhumed prior to the sequence, generating emerged areas with little to no sedimentation. Red beds (B sequence) characterize the rifting stage, representing the syn-depositional infill of continental grabens, likely extending to the Acre Basin in Brazil. Finally, during the thermal sag, a marine inflow likely from the northwestern part of Peru generated sedimentation of carbonates and evaporites (C Sequence) to the west and east of the Peruvian margin. This sediment differentiation was, in part, controlled by the existence of pre-existing grabens associated with the previous rifting stage. This interpretation, together with other evaporitic occurrences, attributed here to a Late Triassic epoch in south and north Peru and west Brazil, suggest the existence of an evaporitic basin filling an undeformed area of probably c. 170 000 km2. It is therefore suggestive of the existence of a Late Triassic (Norian to Rhaetian; 217 to 204 Ma) salt giant controlled by thermal sag in western Gondwana. Our results are of great relevance for any future interpretation related to mass extinctions, palaeoclimatic analysis and ocean dynamics during the Permian and Triassic as well as natural resource distribution between Ecuador and Bolivia.

International audience; Basin modeling is commonly used for the hydrocarbon potential evaluation of underexplored areas, taking into account the full basin history to assess its thermicity and fluid distributions. In the case of forearc basins, however, the influence of the subduction on the internal thermal structure is difficult to predict. The existing subduction thermal models usually focus on the present day lithosphere and do not consider the sediment infill history, while industrial modeling tools handle the thermal evolution of sedimentary basins but not the subduction process. In this paper, we propose a solution model in which the cooling engendered by the subduction is represented by the advective term of the heat conservation energy equation throughout the sedimentation. This study focuses on the Talara-Tumbes-Lancones petroleum province, part of the North Peruvian forearc system. Despite the long term exploration of the Talara Basin, the origin of its massive oil fields still remains questioned. The new subductionsedimentation integrated petroleum system modeling presented here, calibrated by numerous structural and thermometric data, allows to better constrain the thermal structure and source rock maturity history of this forearc system. We show that the exposure of the sedimentary basin to the subducting cold lithosphere, the sedimentation rate and erosion are important factors impacting the maturity of the source rocks. Consequently, even in the same subduction setting, each depocenter of the North Peruvian forearc system presents a different thermal history and maturity timing, and each basin presents an independent petroleum system.

International audience; The forearc of the North-Central Peruvian Andes (FNCPA, 6–10°S) provides an exceptional opportunity to study the long-term processes that affect a convergent plate boundary. First, it shows long-term subsidence, depocenter superimposition and individualization. Second, although being mostly extensional and characterized as a typical erosive margin, the FNCPA shows complex uplifted regions. Older deformation is expressed by basement horst and grabens disposed in a complex geometry which onset may have resulted from strike-slip tectonics. A long-lived episode of regional subsidence affected the forearc and led to the relatively thick and regional deposition of the lower Miocene series coeval with a significant increase of the convergence velocity. This period was followed by an episodic uplift of trench-parallel corridors along the so-called Main Deformation Zone. Uplift ceased through the late Miocene and restarted during Pliocene and Quaternary, generating accommodation space by basin flank uplift for a forearc depocenter characterized by landward tilted strata. Significant along-strike differences in the degree of uplift resulted in either uplifting series producing sharp seaward dipping erosional surfaces or less uplifted areas covered by seawards prograding clinoforms. As a consequence of the shallow-water marine setting, the seismic strata geometry, lateral extent and thickness of the deposits for the Neogene successions in the FNCPA have been also tightly controlled by accommodation changes. Uplift is uneven along-strike independently of fault direction and closely followed the increase of the subsidence of the continental slope produced by subduction-erosion. Therefore, sediment underplating seems the most appropriate mechanism at the origin of uplift; as observed in other parts of the Peruvian and Chilean margins. Although the erosive character of the margin, the effects on basin geometry of the raised zone resemble that of typical outer forearc highs in accretionary margins such as in the Kumano basin in Japan.

International audience; New 3D seismic data collected over 4870 km2 in the 3°45'–12°30'S Peruvian segment of the East Pacific subduction system image seafloor erosional surfaces that can be mapped across the forearc basins. Forearc basins experience various stresses, from their base where basal tectonic erosion acts to the seafloor which is influenced by aerial, shallow and deep water currents driven by waves or thermohaline oceanic currents. Previously there has been little interest in stresses on the upper layer and there is a lack of documentation of unconformities and the erosive processes in certain bathymetric domains in forearc basins. We address this with the study of examples sourced from 3D seismic reflection surveys of the seafloor offshore Peru. Unconformities occur in two distinctive bathymetric domains associated with the continental shelf and the upper slope of the margin. Identification and characterization of unconformity surfaces yield estimates of the amount of erosion at the modern seafloor that range from 18 to 100%. Regional physical oceanography allows us to calibrate potential candidates for these two distinctive domains. The first control on erosion is the dynamics of deep to intermediate oceanic currents related to the Humboldt-Peru Chile water masses, while the second is wave action in the shallower erosional surfaces. This study illustrates the unseen landscape of the forearc basins of South America and helps to highlight the importance of erosive surficial processes in subduction landscapes.

International audience; Identification of a previously undocumented hydrate system in the Tumbes Basin, localized off the north Peruvian margin at latitude of 3°20′—4°10′S, allows us to better understand gas hydrates of convergent margins, and complement the 36 hydrate sites already identified around the Pacific Ocean. Using a combined 2D–3D seismic dataset, we present a detailed analysis of seismic amplitude anomalies related to the presence of gas hydrates and/or free gas in sediments. Our observations identify the occurrence of a widespread bottom simulating reflector (BSR), under which we observed, at several sites, the succession of one or two BSR-type reflections of variable amplitude, and vertical acoustic discontinuities associated with fluid flow and gas chimneys. We conclude that the uppermost BSR marks the current base of the hydrate stability field, for a gas composition comprised between 96% methane and 4% of ethane, propane and pure methane. Three hypotheses are developed to explain the nature of the multiple BSRs. They may refer to the base of hydrates of different gas composition, a remnant of an older BSR in the process of dispersion/dissociation or a diagenetically induced permeability barrier formed when the active BSR existed stably at that level for an extended period. The multiple BSRs have been interpreted as three events of steady state in the pressure and temperature conditions. They might be produced by climatic episodes since the last glaciation associated with tectonic activity, essentially tectonic subsidence, one of the main parameters that control the evolution of the Tumbes Basin.

This study of the seismic geomorphology of riverine deposits describes and discusses the spatial resolution at which we can detect fluvial features and how the subsequently collected data can help with our understanding of ancient fluvial reservoirs. For this assessment we use three dimensional seismic reflection data, borehole data from ancient deposits in the Maranon foredeep basin of Peru, as well as digital elevation and satellite imagery data from the present day fluvial systems of the Amazonian Basin in the same area of Peru. Based on seismic stratigraphic principles on amplitude display we test parameters to highlight the details of the internal structure of horizons interpreted on continuous wavelets. Seismic attributes such as amplitude, phase, sweetness and spectral decomposition techniques have been successfully applied to make a framework of seismic stratigraphic surfaces that highlight the internal architecture and morphologic details of the studied intervals. This work confirms the presence of a Cenozoic fluvial system in Peru with straight, meandering and anastomosing channels. The observed fluvial features are associated with narrow to medium sized channels (10–∼700 m). Evolution of parameters such as sinuosity allows the variation of load in the identified channel features to be constrained. Cenozoic Maranon Basin rivers/streams size and shape are comparable to those observed in the present-day fluvial Amazon Basin. The fluvial dynamics in the study area are identified to be at least present since the deposition of the Pozo-Chambira Formation (Eocene-Oligocene) in the Maranon Basin.

International audience; The Huallaga Basin is a deformed foreland basin located in North Peru. The basin comprises several syntectonic depocenters. The most significant is the Biabo Syncline located at the back of the Chazuta Thrust, a long, flat-floored thrust detaching on an evaporitic décollement, which has accommodated more than 40 km of horizontal displacement. The hangingwall of the Chazuta Thrust has remained remarkably intact with little or no internal deformation and has incorporated a large volume of evaporites at its base.In order to unravel the formation and evolution of this thrust, we conducted a series of physical experiments that tested the role of various parameters. The goal is to investigate a system in which most of the deformation is accommodated in the frontal part of the chain (Chazuta Thrust), whereas deformation of the thrust sheet itself remains minor.Results from our experimental investigations suggest that the three key parameters that have allowed for such a long-lived, large-slip frontal thrust to operate are (1) the wedge-shaped syn-kinematic sedimentation, (2) the presence of the Biabo Syncline, which acted as a bulldozer pushing the evaporites forward, forcing their distal inflation and (3) the erosion at the front that favored farther advance of the frontal thrust, dragging passively large volumes of evaporites along with it.

Tectonostratigraphic revision and a crustal balanced cross-section of the northern Peruvian margin show that the Western Andean Escarpment and the Calipuy Plateau-Basin topographic features are related to a major west-verging basement thrust: the Western Andean Escarpment Thrust (WAET). Thermochronological data through the Coastal Batholith display a regional exhumation since at least 29 Ma and a step-change pattern in the cooling ages that we partly attribute to the WAET activation. Thermal modeling shows higher exhumation rates (~ 170–270 m/Myr) between 12 and 8 Ma, due to the onset of the Nazca Ridge subduction. This regional offshore-onshore study allows as well to unravel the Paleogene-Neogene complex tectonic evolution of the northern Peruvian Andes: (1) a middle Eocene regional erosion (~ 41 Ma) erasing the Incaic orogen nowadays partially preserved in the Western Cordillera and in the offshore Trujillo-Salaverry basins; (2) a late Eocene to early Oligocene postorogenic relaxation and extension (Yaquina and Trujillo basins); (3) the westward WAET propagation and a ~ 150 km eastward jump of the double verging Andean orogen since the late Oligocene.

Weprovide a synopsis of ~60million years of life history in Neotropical lowlands, based on a comprehensive survey of the Cenozoic deposits along the Quebrada Cachiyacu near Contamana in PeruvianAmazonia. The 34 fossilbearing localities identified have yielded a diversity of fossil remains, including vertebrates,mollusks, arthropods, plant fossils, and microorganisms, ranging from the early Paleocene to the lateMiocene–?Pliocene (N20 successive levels). This Cenozoic series includes the base of the Huchpayacu Formation (Fm.; early Paleocene; lacustrine/ fluvial environments; charophyte-dominated assemblage), the Pozo Fm. (middle + ?late Eocene; marine then freshwater environments; most diversified biomes), and complete sections for the Chambira Fm. (late Oligocene–late early Miocene; freshwater environments; vertebrate-dominated faunas), the Pebas Fm. (late early to early late Miocene; freshwater environments with an increasing marine influence; excellent fossil record), and Ipururo Fm. (late Miocene–?Pliocene; fully fluvial environments; virtually no fossils preserved). At least 485 fossil species are recognized in the Contamana area (~250 ‘plants’, ~212 animals, and 23 foraminifera). Based on taxonomic lists from each stratigraphic interval, high-level taxonomic diversity remained fairly constant throughout themiddle Eocene–Miocene interval (8-12 classes), ordinal diversity fluctuated to a greater degree, and family/species diversity generally declined, with a drastic drop in the early Miocene. The Paleocene–?Pliocene fossil assemblages from Contamana attest at least to four biogeographic histories inherited from (i) Mesozoic Gondwanan times, (ii) the Panamerican realm prior to (iii) the time of South America’s Cenozoic “splendid isolation”, and (iv) Neotropical ecosystems in the Americas. No direct evidence of any North American terrestrial immigrant has yet been recognized in the Miocene record at Contamana., Facultad de Ciencias Naturales y Museo

Biostratigraphic, sedimentological and provenance analyses suggest that a proto-Andean Cordillera already existed in southern Peru by late Maastrichtian–late Palaeocene times. A 270-m-thick stratigraphic section shows changes in depositional environments from shallow marine (early Maastrichtian) to non-marine (late Maastrichtian) then back to estuarine (late Palaeocene) conditions. An erosional surface separates lower Maastrichtian from upper Maastrichtian deposits. Above this surface, the late Maastrichtian unit exhibits moderately developed palaeosols and syn-sedimentary normal faults. The sedimentary evolution is accompanied by a decrease in sedimentation rate and by changes in provenance. Shallow marine lower Maastrichtian deposits have a cratonic provenance as shown by their low eNd(0) values (-15 to -16) and the presence of Precambrian inherited zircon grains. The upper Maastrichtian deposits have a mixed Andean and cratonic origin with eNd(0) values of ~12.6 and yield the first Cretaceous and Permo-Triassic zircon grains. Estuarine to shallow marine upper Palaeocene deposits have an Andean dominant source as attested by higher eNd(0) values (-6 to -10) and by the presence of Palaeozoic and Late Cretaceous zircon grains. The changes in depositional environments and sedimentation rates, as well as the shift in detrital provenance, are consistent with a late Maastrichtian–late Palaeocene period of Andean mountain building. In agreement with recently published studies, our data suggest that an Andean retro-arc foreland basin was active by late Maastrichtian–late Palaeocene times. This article is protected by copyright. All rights reserved.

International audience; The link between plate tectonics and the evolution of active margins is still an ongoing task to challenge since the acceptance of plate tectonic paradigm. This paper aims at deciphering the structural architecture and uplift history of the North Peruvian forearc system to better understand the evolution and the mechanics that govern the Late Cretaceous-Cenozoic building of this active margin. In this study, we report surface structural geology data, interpretation of seismic reflection profiles, apatite fission-track data, and the construction of two offshore-onshore crustal-scale balanced cross sections. The structure of the North Peruvian forearc system is dominated by an accretionary style with northwestward propagation of thrust-related structural highs involving continental/oceanic basement rocks, and off-scrapped sediments. The thrust systems bound thick thrust-top forearc depocenters mainly deformed by crustal normal to strike-slip faults and thin-skinned gravitational instabilities. The sequential restoration of the margin calibrated with apatite fission-track data suggests a correlation between uplift, shortening and plate convergence velocity during Late Cretaceous and Miocene. Pliocene-Quaternary shortening and uplift of the coastal zone is rather related to the subduction of asperities during convergence rate decrease. The development of crustal normal to strike-slip faulting and subsidence zones might be the consequence of slab flexure, local basal erosion along subduction fault, and/or oblique subduction associated with sediment loading control. We conclude that the evolution of the North Peruvian forearc system was controlled by subduction dynamics, strong sediment accumulation and recent ridge subduction, and it recorded the orogenic loading evolution of the Andes over the Cenozoic.

In the Peruvian sub-Andean foreland basin system, the construction of serial balanced cross-sections from a good set of structural data and an extensive knowledge of the stratigraphy and geodynamic evolution allow a more refined definition of the unexplored plays, as subthrusts, duplexes, or pre-Andean structures. Sequential restorations are proposed by coupling thermochronologic analyses with growth strata studies. The results show significant north–south variations in geometry, timing and rates of deformation, and foreland sedimentation. These latitudinal variations are not only related to the pre-Andean basins’ inheritance but also to the interactions between thrusts propagation, erosion, and sedimentation. Thermochronologic ages correspond to the most recent thrust-related uplifts and are supplemented by the study of stratigraphic foreland basin records that can bring to light oldest tectonic events. North of the Peruvian sub-Andean zone, thrusts propagation is controlled by thick-skinned and thin-skinned salt tectonics. Northern thick-skinned tectonics has westward vergence and is inherited from a Middle Permian fold-and-thrust belt. To the south, thrusts deformation is largely controlled by the geometry of the preserved Paleozoic sedimentary wedge and becomes progressively thin skinned. Total sub-Andean shortening varies between 70 km (43 mi) in the north and 47 km (29 mi) in the south. Sub-Andean deformation started in the Late Cretaceous. After a period of quiescence during the middle Eocene, it reactivated and is still active. Three stages of sub-Andean deformation are clearly identified and help to define the preservation time in the suggested petroleum plays.

We investigate the mass balance of the Cenozoic Andes-Amazon source to sink system using rock uplift proxies and solid sedimentation of the Marañón Basin in Peru. The evolution of sedimentation rates is calibrated with regional structural restored cross-section. The quantification of eroded sediments from reliefs to sedimentary basin is achieved with ×10 Myr resolution and compared to present day proxies from the HYBAM (HYdrologie et Biogéochimie du Bassin Amazonien) Critical Zone Observatory. Erosion of the early Andean landforms started during the Upper Mesozoic period, but sediment rates significantly increase during the Neogene. This is in agreement with the calibrated increase of rock uplift in the Andean orogenic belt.

Forearc basins are areas underexplored by academic or industrial research. They are not considered as potential areas by the industry because only three giant oil fields have been formed in this type of basin. One of them is located in the northern Peruvian forearc system: the Talara Basin (1.7 billion bbl to date). The aim of this work is to provide insights for the oil industry about the tectonic style and the tectonic-sedimentation relationships within this basin to decipher its petroleum potential, using surface and subsurface data (seismic lines, well-logs). From a tectonic point of view, we demonstrate that the basin is not a pull-apart basin, but an accretionary prism built by deep-seated north-verging thrusts reworked by shallow gravitational normal faults. A tectonic model is developed, which involves the north-westward propagation of thrust culminations accompanied by the development of southeast-facing normal faults since Eocene times. This tectonic model renews our perception about the entire Peruvian forearc and suggests that anticline traps, which have never been explored, should become a new target for a future hydrocarbon exploration.

In northern Peru, a 500 km long regional balanced section has been constructed across the eastern Andean wedge, using fieldwork, industrial seismic sections, and wells. The structure is characterized by a thin-skinned thrust system involving the Eastern Cordillera (EC), the sub-Andean zone (SAZ), and the Maranon foredeep. In the SAZ and the easternmost foredeep the development of the thrust system has been driven by the combination of two structural events. Permian thrust faults had been reactivated to form a basement duplex underlying the SAZ and the foredeep. At the same time a Triassic-Jurassic extensional basin has been transported as a crustal ramp anticline on to the duplex roof fault, giving rise to the EC. The impingement of the EC was responsible for the deformation of the SAZ and the propagation of the thrust wedge. The minimum shortening calculated is 142 km, representing a shortening strain of ~ −28%. A sequential restoration calibrated by (U-Th)/He and Fission Track dating on apatites and vitrinite reflectance values shows that shortening rates vary from 7.1 mm yr−1 between 17 and 8 Ma to 3.6 mm yr−1 between 8 Ma and today and suggests that the thrust wedge commenced propagation between 30 and 24 Ma. When compared with other Andean thrust wedges, we suggest that the timing of the thrust wedge propagation is not a simple function of the distance to the hinge of the Bolivian orocline and the propagation is not controlled by the precipitation regime. We rather suggest that reactivated basement faults favored thrust wedge propagation.

Quantifying interactions between uplift, climate, deformation and exhumation processes remains difficult, mainly due to a paucity of data relevant to all processes. Central Andes are a prime example to study the respective role of climate forcing and tectonic activity on mountain building. In this study we propose new data (thermochronology, biostratigraphy, field observations and seismic interpretations) focused on the Eastern Cordillera (EC) and the Sub-Andean Zone (SAZ) of southern Peru between 12oS and 14oS, in order to i) constrain the timing of deformation, and to ii) demonstrate that contrary to recent studies, our new data outline that the Plio-Peistocene uplift and erosion of the Andes are more likely related to thrust induced exhumation than to a climate forcing. Low temperature thermochronological results obtained for the EC and the SAZ, as well as the growth strata documented in seismic and on the field allow to determine two main deformation periods: i) from the Oligocene to Middle Miocene (~25-14 Ma), and ii) from the Late Miocene to Pleistocene (~10-2.8 Ma). The Plio-Pleiostocene cooling induced by the erosion of the EC in southern Peru is not controlled by climatic change, but better by the development of duplex in the Andean front.

In the Peruvian Subandean fold and thrust belt, the construction of 4 serial balanced cross-sections from a good set of structural data and an extensive knowledge of the stratigraphy and geodynamic evolution allow a more refined definition of the unexplored plays, as sub-thrusts, duplexes or pre-Cretaceous structures. Sequential restorations are proposed by coupling thermochronologic analyses with growth strata studies. The results show significant north-south variations in the geometry, the timing and the rate of the deformation. This latitudinal variation is related to the pre-Andean basins inheritance, but also to the Andean slab geometry. Thermochronologic ages correspond to the most recent tectonic uplifts and cannot be disassociated from the study of growth strata that might have recorded oldest events. North of the Peruvian Subandean zone, the thrusts propagation seems continuous since the Late Cretaceous. In the south, two stages of Cenozoic deformation are clearly indentified.

Tertiary insects and arachnids have been virtually unknown from the vast western Amazonian basin. We report here the discovery of amber from this region containing a diverse fossil arthropod fauna (13 hexapod families and 3 arachnid species) and abundant microfossil inclusions (pollen, spores, algae, and cyanophyceae). This unique fossil assemblage, recovered from middle Miocene deposits of northeastern Peru, greatly increases the known diversity of Cenozoic tropical–equatorial arthropods and microorganisms and provides insights into the biogeography and evolutionary history of modern Neotropical biota. It also strengthens evidence for the presence of more modern, high-diversity tropical rainforest ecosystems during the middle Miocene in western Amazonia.

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd-Sr isotopic provenance from five outcrops of southern Amazonia (MD-85, MD-177 MD-184, MD-255 and MD-256) to document for the first time the presence of a shallow marine ingression in the Paleocene of southern Amazonia basin. The co-occurrence of a selachian assemblage encompassing Potobatis sp., Ouledia sp., and Pristidae indet with the ostracod Protobuntonia sp. and the charophytes Peckichara cf. varians meridionalis, Platychara perlata, and Feistiella cf. gildemeisteri suggests a Paleocene age for the studied deposits (most likely Thanetian but potentially Danian). Fifteen fades have been recognized and have been grouped into three facies assemblages. Facies association A corresponds to the sedimentary filling of a tide-influenced meandering channel formed in the fluvial-tidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarsh deposits. Facies association C corresponds to a stressed shallow marine environment such as a bay or a lagoon. The delta C-13(TOC) value (- 23.4%) of MD-184 is enriched in C-13 compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The delta C-13(TOC) values of samples from other outcrops ( - 27.3 to - 29.8%) indicate a mixed organic matter origin, from terrestrial to brackish environments. The analyzed sediments have similar Nd-Sr isotopic compositions as those of the Cenozoic sediments of the Altiplano (epsilon Nd(0) values from - 6.2 to - 10.7 and Sr-87/Sr-86 compositions from 0.712024 to 0.719026) indicating a similar volcanic source. This multidisciplinary dataset documents the presence of a tide-dominated estuary sourced by the proto-Westem Cordillera debouching into a shallow marine bay during Paleocene times. This transgression might be explained by subsidence created in response to the proto-Western Cordillera loading. Similar to Miocene marine incursions affecting the Pebas megawetland, Paleogene marine incursions in the Amazonian foreland basin associated with Andean uplift may have played a role in the Neotropical biodiversity dynamics in favoring biogeographical isolation and promoting allopatric speciation for terrestrial organisms.

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd–Sr isotopic provenance from five outcrops of southern Amazonia (MD-85, MD-177 MD-184, MD-255 and MD-256) to document for the first time the presence of a shallow marine ingression in the Paleocene of southern Amazonia basin. The co-occurrence of a selachian assemblage encompassing Potobatis sp., Ouledia sp., and Pristidae indet. with the ostracod Protobuntonia sp. and the charophytes Peckichara cf. varians meridionalis, Platychara perlata, and Feistiella cf. gildemeisteri suggests a Paleocene age for the studied deposits (most likely Thanetian but potentially Danian). Fifteen facies have been recognized and have been grouped into three facies assemblages. Facies association A corresponds to the sedimentary filling of a tide-influenced meandering channel formed in the fluvial–tidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarsh deposits. Facies association C corresponds to a stressed shallow marine environment such as a bay or a lagoon. The δ13CTOC value (− 23.4‰) of MD-184 is enriched in 13C compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The δ13CTOC values of samples from other outcrops (− 27.3 to − 29.8‰) indicate a mixed organic matter origin, from terrestrial to brackish environments. The analyzed sediments have similar Nd–Sr isotopic compositions as those of the Cenozoic sediments of the Altiplano (eNd(0) values from − 6.2 to − 10.7 and 87Sr/86Sr compositions from 0.712024 to 0.719026) indicating a similar volcanic source. This multidisciplinary dataset documents the presence of a tide-dominated estuary sourced by the proto-Western Cordillera debouching into a shallow marine bay during Paleocene times. This transgression might be explained by subsidence created in response to the proto-Western Cordillera loading. Similar to Miocene marine incursions affecting the Pebas megawetland, Paleogene marine incursions in the Amazonian foreland basin associated with Andean uplift may have played a role in the Neotropical biodiversity dynamics in favoring biogeographical isolation and promoting allopatric speciation for terrestrial organisms.