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A porção sul da Bacia sedimentar intracratônica do Paraná carece de estudos que considerem a possível influência de atividade tectônica na evolução do relevo após o Cretáceo. Este trabalho visa hierarquizar morfoestruturas na porção sul da Bacia do Paraná, abrangendo as Formações Tupanciretã e Serra Geral, com base em topologia de redes de drenagem e lineamentos morfoestruturais. O estudo é desenvolvido com o uso de dados de sensoriamento remoto, incluindo: modelo digital de elevação (MDE) World 3D30 (AW3D30), adquiridos a bordo do Advanced Land Observing Satellite (ALOS); imagens do Satélite Sentinel-2, sensor MSI (MultiSpectral Instrument); e imagens do veículo aéreo remotamente pilotado (VARP) Phantom 4 PRO. As informações obtidas desses produtos foram integradas com dados morfológicos coletados em campo, bem como com a base cartográfica oficial do Estado do Rio Grande do Sul em escala de 1:25.000. O resultado da análise morfoestrutural revelou relevo com indícios de deformação tectônica, registrada por inúmeras anomalias, com destaque para: padrões de drenagem anômalos, como o treliça e subtipos; inflexões abruptas de canais formando ângulos de 90º; e lineamentos morfoestruturais. Duas fases deformacionais principais foram hierarquizadas: a primeira de direção NE-SW, compatível com estruturas tectônicas do Cenozoico Inferior da Bacia do Paraná; e a segunda de direção E-W, concordante com estruturas transcorrentes do Cenozoico Superior, formadas durante a abertura do Oceano Atlântico Sul. Além disso, ocorrem lineamentos morfoestruturais de direção N-S, que foram relacionados com compressão decorrente da colisão das placas de Nazca e Sulamericana.

The post-rift tectono-sedimentary history of passive margins has been an issue of increased interest after the perception of their unsteady nature during the Neogene and Quaternary. The evolution of the eastern South America margin might be benefited from investigations of the sedimentary record in a number of marginal basins. The Paraiba Basin is of particular interest to discuss the post-rift evolution of the South American passive margin, because it represents the last bridge with the African plate. This work aims to analyze the post-rift sedimentary record of the onshore Paraiba Basin as a contribution to discuss the neotectonic history of the South American passive margin. Surface and subsurface data were integrated from outcrops, deep stratigraphic profiles, airborne geophysical maps and remote sensing products. The depositional and denudational processes in this basin were a result of tectonic subsidence and uplifting. Tectonics after the main rifting phase are indicated by abundant structures, including normal, reverse, and strike–slip faults, as well as folds that affected the Neogene and Late Pleistocene sedimentary deposits. The ductile and brittle deformation resulted mainly from multiple reactivations of E–W, NE–SW and NW–SE trending basement shear zones. The deformation mechanism included distension and compression under a strike–slip regime. Tectonic reactivations even during the late Pleistocene support an unsteady South Atlantic passive continental margin throughout the post–rifting stage.

Relative sea-level (RSL) rise associated with decreased fluvial sediment discharge and increased hurricane activity have contributed to the high rate of shoreline retreat and threatened coastal ecosystems in Port Fourchon, Louisiana, USA. This study, based on QuickBird/drone images (2004–2019) and LIDAR data (1998–2013), analyzed the impacts of shoreline dynamics on mangroves (Avicennia germinans) and marshes before and after the initiation of a beach nourishment project in 2013. The coastal barrier and dune crest migrated landward between 1998 and 2013. Meanwhile, the dune crest height increased between 1998 and 2001, then decreased in 2013, probably due to hurricane impacts. The total sediment volume along this sandy coastal barrier presented an overall trend of decline in the 1998–2013 period, resulting in a wetlands loss of ~15.6 ha along 4 km of coastline. This has led to a landward sand migration onto muddy tidal flats occupied by Avicennia germinans (1.08 ha) and Spartina (14.52 ha). However, the beach nourishment project resulted in the advancement of the beach barrier from Nov/2012 to Jan/2015, followed by a relatively stable period between Jan/2015 and Mar/2019. Additionally, both the dune crest height and sediment volume increased between 2013 and 2019. This set of factors favored the establishment and expansion of mangroves (3.2 ha) and saltmarshes (25.4 ha) along the backbarrier environments after 2013, allowing the tidal flats to keep pace with the RSL rise. However, waves and currents caused shoreline erosion following the beach nourishment project between Oct/2017 and Nov/2019, threatening wetlands by resuming the long-term process of shoreline retreat.

Savanna patches are features of the Amazonian landscape that have been long under intense debate, but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix. In particular, their geological substrates were poorly documented. The aim of this work is to reconstruct the tectono-sedimentary history of four savanna patches in the middle Madeira River, southwest Amazonia, and discuss its potential control over the development of the savanna communities. The approach consisted in the integration of geomorphological, sedimentological, chronological and floristic data. The results revealed that the savanna substrates are sandy deposits aged between 118.9 and 35.6 ky, overlain by late Pleistocene to Holocene muddier successions

Neotectonic activity was increasingly recorded over the Amazonian lowlands, even during historical times of a few tens of centuries. However, detailed analyses linking structures and styles of deformation are still few considering the large dimension of the region. Such events in a relatively recent time are expected to have caused conspicuous impacts on Amazonian ecosystems and forest disturbance. Changes in topography and hydrology by fracturing, faulting and folding during either subsidence or uplifting are direct effects on landscape that leave marks on the structure of the current forest, such as tree mortality and community succession. Two rectangular elbow-like shaped wetlands from the left margin of the middle Negro River valley in northwestern Amazonia were attributed to neotectonics. Remote sensing imagery was applied to test this hypothesis and also provide a tectonic model that can explain deformation dynamics in this area. The studied wetlands and adjacent river systems display various morphostructural anomalies compatible with a tectonic control, as well as lineaments paralleling main NW and NE-trending regional structures. The geomorphic analysis led to suggest that the wetlands are depressions formed by NW and NE-trending master boundary faults of horizontal displacements intercepted by various subsidiary faults. Transtensional strike slip regime is recorded by both left and right-lateral faults, with the wetlands corresponding to subsiding areas owned to conjugate strike slip faults. Habitat fragmentation and other ecological processes promoted by tectonic deformation would have impacted the overlying forest canopy by changing its structure due to tree mortality. The complex compartmentalization imposed by active tectonics would have exposed the ground to contrasting hydrological conditions, which controlled the rate of tree mortality within the wetlands. We pose that the tectonic disturbance and associated tree mortality documented in the middle Negro River evidence contemporary seismicity within the intracratonic Brazilian Amazonia.

The relief evolution of several areas of northeastern Brazil has been increasingly related to tectonic events. This is the case for the Paraiba Basin, where an abundance of faults and folds were recorded in Neogene and even Late Pleistocene-Holocene deposits. We tested whether dome-like morphologies in the northern sector of this basin, where geological exposures are scarce, were also formed by tectonic deformation. The work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc-second digital elevation model provided by the Shuttle Radar Topography Mission. The geomorphic indices of basin asymmetry factor (AF), swath topographic profiles, enhanced transverse hypsometry index (THi*) and normalized river long-profiles were used for validating a neotectonic origin for the dome-like morphologies. This interpretation was also supported by other morphological evidence of the dome relief, including: recurving channels featured in radial to recurved trellis patterns; tectonically-controlled drainage sub-basins; high relative relief values related to increased fluvial incision; and anomalous river long-profiles indicative of ungraded rivers. The domic structures were attributed to fault- and fold-related strike-slip deformation during the late Quaternary. This record supports the proposal that the South American passive margin remained under tectonic stress long after the main rifting in the late Jurassic-early Cretaceous.

Documenting neotectonic instabilities and determining the style and time of deformation in the vast and difficult to access central Amazonia region is challenging. We focus on these issues by investigating a large area of the Negro River drainage basin, applying morphostructural analysis based on synthetic aperture radar data. The digital elevation models of the C-band Shuttle Radar Topography Mission and the L-band Protection System of Amazonia were used as the database. We also used subsurface magnetic information from the Earth Magnetic Anomaly Grid global model to validate the morphostructures. The results revealed NW-oriented morphostructural lineaments bounding multiple depositional valley fills. These were extensively fragmented to form regularly distributed en échelon rectangular blocks commonly offset horizontally by several kilometers. Strike-slip faults and oblique, either normal or reverse, faults are present. These structures were reactivated along the main NE- and SW-oriented regional structural trends due to N-S-oriented horizontal compression and E-W-oriented horizontal extension in the late Pleistocene and Holocene. The extensive neotectonic faulting results from the interplay of plate motion and Andean uplifting since the late Pleistocene, combined with local stresses.

Rifting and related normal stress regime in the equatorial continental margin of Brazil ceased during the Late Cretaceous, when the stress regimes in eastern South America and West Africa changed to induce strike-slip or reverse motion. In this study, we explore the postrift tectonic, geomorphic, magmatic, and sedimentary responses to stress changes using the Potiguar Basin, the easternmost basin in the equatorial margin of Brazil, as a case study. We use field and topographic data, 2D seismic reflection lines, vertical electric soundings, and geochronological and borehole data to constrain the stress evolution of the Potiguar Basin from the Late Cretaceous to the Quaternary, discussing the role of basin inversion on sedimentation and landforms. Our results indicate the presence of two strike-slip stress regimes after rifting. The first stress field (SF1) occurred from Late Cretaceous to the middle Miocene and consisted of a N-S-oriented maximum subhorizontal compression and an E-W-oriented extension. The second stress field (SF2) took place from the middle Miocene to the present day and included subhorizontal E-W to NW-SE compression combined with N-S and NE-SW subhorizontal extension. Emplacement of volcanic rocks occurred along transtensional faults, with a principal peak during SF1 at 20–30 Ma and a subordinate peak during SF2 at 5–10 Ma. In response to shortening during SF2, a 70-km-long and 50-km-wide dome formed, where marine Miocene strata were uplifted to ~250 m asl. This uplift induced the displacement of alluvial channels away from the dome. Anticlines formed by transpression along the main NE-SW-striking faults during both SF1 and ST2 acted as traps in the petroleum system. Similar shifts and stress field inversions documented in other areas of the Brazilian continental margin are consistent with the Neogene rise of the Andes and may have implications for reconstructing the tectonic history of the Equatorial Atlantic margin of South America.

Pollen data recovered from the sedimentary record of western Amazonia is still inadequate to fully address climate changes over the Last Glaciation in this region. The present work focuses vegetation dynamics from an area of southwestern Amazonia during the past 42,000 cal yr B.P. based on the integration of previous and new pollen data. Sediment cores were sampled from two sites covered by tropical rainforest in fluvial terraces of the Madeira River, a major southern Amazonian tributary. The results indicated a significant proportion of cold-adapted Andean tree species, represented by Alnus (0–20%), Hedyosmum (1–15%), Podocarpus (0–5%), Illex (1–11%) and Weinmannia (0–1%) at least between > 43,163–42,018 cal yr B.P. and 10,394–10,240 cal yr B.P. During the Holocene, only pollen representative of herbs and modern Amazonian vegetation persisted. The new pollen record confirmed previous documented results that vegetation communities presently restricted to Andean areas at altitudes higher than 2000–3000 m, occupied this region of the Amazonian lowlands close to the onset and probably also during the Last Glacial Maximum.

Global warming has led to a tropicalization of ecosystems, especially in the northern hemisphere, where freeze-sensitive plants, such as Avicennia germinans, are expanding northward, exposing tropical species to greater annual climate extremes. The effects of this driver on the boreal limits of mangroves need to be investigated for projecting the fate of mangroves in the face of global warming. Based on QuickBird, aerial/drone images, and historic air/seawater temperatures, this work analyzed the 2017–2018 winter freeze impacts on mangroves of Bay Champagne, Louisiana, USA. This winter freeze, marked by 14 days of subfreezing daily minimum temperatures, degraded ~90% (111 ha) of the studied mangroves. This macroclimatic setting caused defoliation and dry branches on Avicennia trees. Such degradation occurred mainly in mangroves established after 2004, where trees of low heights (1–1.5 m) and density between 1000 and 10,000 trees/ha were present mainly on topographically lower tidal flats (13–26 cm above mean sea-level). By contrast, healthy Avicennia trees were typically taller (1.5–2.2 m), growing at intermediate-density (4000–8000 trees/ha) stands, and occupying higher grounds (20–46 cm) in the inner part of mangrove areas. Canopy height and tree density modulated the winter freeze damages on Avicennia trees, as these factors attenuated the wind impacts along a microclimatic gradient. The microtopography of tidal flats may have also influenced the Avicennia degradation. The recovery of mangroves was rapid (~1 year) and regulated by a microclimatic and microtopographic gradient. Winter freeze impacts on mangroves will probably be attenuated as the increase in the stature and density of mangrove trees. These processes could contribute to the continued northward expansion of mangroves. However, recurring winter freezes affect mangrove productivity that is a critical factor for mangroves to keep pace with relative sea-level rise (SLR).

Understanding the factors that controlled the development of large rivers lacks information from modern and ancient analogues. The Amazonian basin contains several of the largest rivers on Earth, with many having tectonic control. The study of these rivers can contribute to test the claim that large rivers have a tectonic forcing. Addressing the evolution of the Jurua River is relevant, since this is the longest Amazonian river that parallels the Solimoes Megashear Zone, a major NE-striking structure with a long history of reactivation of faults and folds even in the Cenozoic. This work discusses the geological evolution of the Jurua River along the Pleistocene-Holocene based on digital elevation models, integrated with subsurface data (well log and seismic reflection). The goal was to characterize some ancient large river valleys in forested areas of Amazonia and to analyze whether they might be related to previous paths of the Jurua River. A physical connection was found between this river and three elongated belts (i.e., PV1, PV2, and PV3) with low topographic and dissection values and surfaces marked by sinuous to meandering strings or curved lines. These characteristics led to relate the belts to ancient Jurua River valleys, an interpretation also suggested by the correspondence between paleovalley morphologies and subsurface Pleistocene-Holocene deposits with concave-up erosional bases. A tectonic hypothesis could explain the development of these paleovalleys around drainage basins with an annular pattern associated with a large convex-up relief, which we relate to rock upwarping by folding. Reconstructing the geological evolution of the Jurua River can introduce new data in discussions focused on the origin of large tropical rivers and on the neotectonic history of the South American intraplate.

The factors that control the heterogeneous canopy of the Amazonian rainforest have long been a topic of interest for research. Among all hypotheses, changes in landscape due to geological processes have been increasingly defended. Large areas of open vegetation in the northern Amazonian lowlands are confined to paleolandforms created by the abandoning of megafan depositional systems. Previous investigations related the megafan sedimentation in this region to Late Pleistocene-Holocene tectonic reactivations. However, the influence of neotectonics on both the Amazonian megafans and associated vegetation cover remains to be further investigated. We studied a depression preliminarily noticed in the south-central sector of one Amazonian megafan (i.e., Virua megafan) aiming to determine if its genesis was due to recent tectonic subsidence after the megafan abandoning. The investigation combined morphostructural, hydrological and remote sensing reflectance analyses, as well as characterization of floristic communities in the modern and ancient environments based respectively on field inventories and palynological data. The results indicated a nearly 10-km long and rectangular-shaped area having straight margins paralleling NNE/SSW-trending regional structural lineaments. Hydrological analysis suggests that this area experiences the largest floods during wet seasons, a condition compatible with the topographic data that revealed a smoother gradient of ~ 3 m comparing this area with others from the megafan plain. In the studied depression, numerous forest patches are arranged as sets of parallel straight lines trending consistently in the NE/SW direction. The patches have spectral values that differ significantly from other forest patches over the megafan surface, being compared to those of seazonally-flooded forests, such as igapos and varzeas, that surround the megafan paleolandform. In addition, a forest patch within the depression revealed trees physiologically adapted to tolerate submersion 6 to 7 months per year, which is also a characteristic of the inundated forests external to the megafan. These data altogether led us to conclude that the studied depression consists of a shallow subsiding basin formed by tectonic reactivations in the mid/late Holocene. Tectonic instability at around 2 cal kyr BP further disturbed this system by creating NE/SW-trending lakes and leading to the replacement of seazonally-flooded forests by grasslands. Thus, tectonic activity in a relatively recent geological time must be accounted when analyzing plant distribution in the Amazonian wetlands.

A number of publications have documented the effect of the Miocene transgression on several coasts of the world. However, this event is incompletely documented along the Brazilian margin, despite the existence of an impressive record of Miocene deposits exposed mostly as several coastal cliffs along more than 5000 km of distance. The transgressive nature of Miocene deposits, so far recognized only in a few localities of northeastern Brazil, needs to be amplified in order to better characterize the impact of the Miocene transgression in eastern South America. In this work, we provide facies analysis of early/middle Miocene strata exposed in the Paraiba Basin, northeastern Brazil, aiming reconstruct the depositional paleoenvironments and analyze their evolution within the context of relative sea-level fluctuations data. The results revealed deposits characterized by several features that were related to the action of tidal currents, such as alternating thicker/thinner forest packages, abundant reactivation surfaces, mud drapes and oppositely-dipping (herringbone) cross sets. These sedimentary structures were associated with an ichnological assemblage indicative of marine-influenced and brackish water, best represented by Ophiomorpha, Planolites-Palaeophycus-Thalassinoides and Thallassinoides-Planolites-Palaeophycus ichnofabrics. Sedimentation occurred in environments consisting of estuarine channel, estuarine central basin, tidal inlet/tidal channel, tidal delta/washover, tidal flat/shoal and foreshore, which were related to an estuarine setting, at least in part of a wave-dominated type. Analysis of facies stratal patterns led to suggest that the estuarine deposits of the Paraiba Basin reflect a rise in relative sea level probably during the transgressive and/or highstand stage of a depositional sequence formed directly overlying Cretaceous rocks. This rise can be correlated with the worldwide early/mid Miocene marine transgression. However, while the eustatic sea level remained rising through the middle Miocene, the estuarine sedimentation in the study area was cut off, being replaced by a regional unconformity marked by lateritic paleosols. Thus, a relative sea-level fall is recorded in the Paraiba Basin while the eustatic sea level remained rising through the middle Miocene, before its fall in the Tortonian. It follows that other factors, such as tectonics, is proposed to explain the mid-Miocene fall in sea level along the Paraiba coast, while the eustatic sea level was rising.

The modern Amazonian ecosystem outcomes from the complex interplay of different factors performed over the geological history, with tectonics being long speculated as perhaps a fundamental one. Nevertheless, areas where tectonic activity can be fully characterized are still scarce in view of the large dimension of this region. In this work, we investigate the signature of neotectonics in one megafan paleolandform that typifies a large sector of the Negro-Branco basin in northern Amazonia. The approach joined regional morphostructural descriptions of the Virua megafan surface and the acquisition of topographic, sedimentological, and chronological data focusing on the central sector of the megafan. The results revealed an abundance of rivers that form dendritic, subdendritic, and trellis patterns. These rivers also have numerous straight segments, orthogonal junctions, and orthogonal shifts in courses. Structural lineaments, defined by straight channels and also straight lake margins, are aligned along the NW-SE and NE-SW directions that are coincidental with the main regional structural pattern in Amazonia. This study also led to recognize two large areas of lower topography in the south-central part of the megafan that consist of rectangular depressions parallel to the morphostructural lineaments. A sedimentological survey indicated that cores extracted external to the largest depression have only distributary channel and overbank sand sheet megafan deposits. Optically stimulated luminescence (OSL) ages ranged from 17.5 ± 2.0 to 46.9 ± 3.4 ky and radiocarbon ages ranged from 5.9–5.7 to 20.1–19.6 cal ky BP. In contrast, cores extracted within the depression consisted of fluvial deposits younger than 2.1–1.9 cal ky BP that increased in thickness toward the central part of the depression. We propose that the studied megafan was affected by tectonic reactivation until at least a couple thousand years ago. Tectonics would have produced subsiding areas more prone to flooding than adjacent terrains, which constituted sites for renewed deposition of fluvial sediments reworked from the megafan surface following its abandonment. A comparison of our data with those from other Amazonian areas with similar records of late Holocene tectonics suggests a landscape imprinted by faulting, probably of strike-slip motion. This finding increases the record of neotectonic activity in the Amazonian wetlands and may be useful in studies aiming at discussing the origin and extension of late Holocene deformation in the South American intraplate. In addition, we present a megafan with an unusual development in a cratonic region under the combined effect of climate and tectonics.

In order to contribute to the discussion of Holocene climate changes, four sediment cores were collected from the northern Brazilian Amazonia lowland. These cores were studied through pollen analysis and sedimentary features, and the results were discussed within a chronological framework provided by radiocarbon dating. The cores were sampled from fluvial terraces representative of channel, floodplain/lake and crevasse splay deposits formed since the mid-Holocene. The pollen samples derive from floodplain/lake deposits and the pollen grains are mainly composed by families Moraceae, Euphorbiaceae, Caesalpiniaceae, Fabaceae, Rubiaceae, Melastomataceae, Combretaceae, Sapindaceae, Poaceae, Cyperaceae, Aizoaceae, Apiaceae and genusSebastiana. The pollen data suggest no significant vegetation changes in the study area for the past 4808–4886 cal yr BP. This led to proposing stable climatic conditions since at least the middle Holocene. Such a finding is contrary to the occurrence of a dry period during the middle Holocene. The stabilization of the relative sea level about 6000 cal yr BP along the northern Brazilian littoral may have influenced the water table, and favored the establishment and maintenance of Amazonian lowland forest during the mid- and late Holocene. In addition, this process may have attenuated the impact of that dry period in areas under most fluvial influence.

Definitive criteria for identifying the triggers of soft-sediment deformation structures (SSDSs) from sedimentary deposits are still under construction. In this work, we aimed to contribute to advancing this issue describing the sedimentological characteristics of an interval of SSDSs formed in a region of the Amazonian lowlands having numerous morphostructural evidences of neotectonic reactivation. The deformed interval is 1.5 m thick and consists of load and flame structures interbedded with massive beds sandwiched between well-stratified deposits of a fluvial sandy channel succession with a radiocarbon age of 1301–1382 cal yr BP. The SSDSs are intercepted by numerous small-scale, normal graded-faults. The most interesting is that these faults display segmented, NW-SE trending planes that propagate upward after horizontal displacements of a few millimeters. Processes intrinsic to channel dynamics could not justify this fault morphology, which is related to recurrent short-lived seismic perturbations with intervening sedimentation following a main tremor. A relation to fault reactivation is proposed with basis on the fault trend compatible with the regional structural pattern and the numerous morphostructural anomalies verified in the study area, including: trellis and sub-trellis drainage; rectangular and, to a less extent, annular channels; anomalously enlarged channels; orthogonal channels and valleys; channel captures; sudden changes in channel morphology; moderate to high basin asymmetry factor (AF between 10 and 27); moderate to high transverse topography symmetry factor ( T = 0.3–0.5); and anomalous longitudinal river profiles, with concavity values (11 to 30%) indicative of rivers in process of adjustments. The morphology of the fault-graded beds described herein might constitute a feature of relevance for identifying seismites in other fluvial deposits.

Generally, palaeoenvironmental interpretations consider only allogenic processes, when autogenic factors may have a strong influence on proxies of stratigraphic sequences. For instance, the Holocene history of the vegetation along the southern littoral of the State of Bahia in north-eastern Brazil is characterized by mangrove dynamics controlled by allogenic processes. However, over smaller timescales (~700 years), autogenic processes may have controlled vegetation dynamics and hence observed pollen distribution. This work proposes tidal channel dynamics as one of the main cause for changes in pollen assemblage along the studied stratigraphic profiles during the last centuries, based on sedimentology, pollen and elemental analysis (δ13C, δ15N and C/N) and radiocarbon dating of sedimentary organic matter from two cores sampled from an abandoned meander and a tidal flat at the mouth of the Jucurucu River. One core was sampled from a mangrove formed during the past ~550 cal yr bp. Another core recorded sediments in a varzea forest (swamp seasonally and permanently inundated by freshwater) located ~2.7 km from the current shoreline, which displayed a maximum age of ~680 cal yr bp. Two facies associations were identified: tidal channel (A) and tidal flat/oxbow lake (B). This work proposes allogenic processes as the main driving forces controlling the wetlands dynamics at the studied site during the Holocene. However, our data also reveal that part of the changes in vegetation over the last ~700 years reflect tidal channels and tidal flats development, which represent autogenic processes. The change in timescale analysis from the Holocene to recent centuries may have weakened the influence of allogenic factors. However, this needs interpretation with reference to the spatial scale of the depositional environment as the larger the depositional system analyzed, the stronger the influence of autogenic processes on stratigraphic sequences over longer timescales. Copyright © 2017 John Wiley & Sons, Ltd.

A preliminary analysis of a segment of the Paraíba littoral in northeastern Brazil revealed a prograding shoreline in a coast currently characterized by estuarine transgressive depositional systems. Detailed study of coastal geomorphology is of relevance to reconstruct the sea-level history in this shoreline. Such investigation can help improve the record of past sea-level curves of northeastern Brazil, an issue still open to debates. In this work, we explored remote sensing imagery for the geomorphological characterization of this prograding shoreline and combined this information with geological field data aiming to establish the various phases of shoreline progradation. In addition, we also analyzed the potential forcing factors responsible for the morphological changes in the eastern section of the littoral of Paraíba during the late Holocene, comparing changes with other prograding shorelines along the east coast of Brazil. Geomorphological interpretation was based on the analysis of Phased Array type L-band Synthetic Aperture Radar (PALSAR) images acquired aboard the Advanced Land Observing Satellite 1 (ALOS-1). Geological data comprised dating of sand samples by the optically stimulated luminescence (OSL) technique for the establishment of the chronological context. The coastal deposits are represented by a cuspate morphology and numerous internal beach ridges that prograded seaward from a roughly north–south trending palaeocliff. The chronological data indicate shoreline progradation during the past 2.1 ± 0.1 ka, after the mid-Holocene sea-level fall. Several prograding episodes occurred during this time, some not matching with proposed sea-level rises punctuated upon the overall fall. Together with the regional geological context of the study area, we propose that eustatic sea-level was not the only factor triggering coastal progradation in this region.

We investigate the role of reactivation of Precambrian basement fabric in the tectono-sedimentary and geomorphological evolution of the Paraiba Basin, continental margin of northeastern Brazil, during the Cretaceous, Neogene, and Quaternary. This basin represents part of the last bridge between South America and Africa before the last breakup stage of the South Atlantic rifting in the early Cretaceous. The Paraiba Basin infill is composed of siliciclastic and carbonate Cretaceous units, as well as aeolian, fluvial and marine Quaternary units. We used shuttle radar imagery, aeromagnetic, wellbore and field data. The reduced-to-the-pole magnetic map (RTP) indicates the continuity of the steeply dipping Precambrian basement shear zones beneath the Paraiba Basin. The combined analysis of surface and subsurface data shows that NE–SW and E–W-striking shear zones were subjected to brittle reactivation in the Aptian–Middle Albian during the basin opening and again in the Neogene–Quaternary, forming a system of horsts and grabens along the basin; some of these structures such as the E–W-oriented Pernambuco shear zone present modern-day seismicity. N–S- and mainly NW–SE-striking transfer faults cut across Aptian–Middle Albian to Neogene–Quaternary strata. These four main fault directions control main river channels and alluvial valleys up to 2 km wide. Topographic breaks up to 50 m were created by late reactivation of rift faults, which mark the boundary between horsts and grabens along the basin. In addition, structural data evidence syn-tectonic faulting with vertical offsets up to 80 m in the Cretaceous and up to 70 m in the Neogene–Quaternary. We conclude that shear zones across the study area are long-lived structures that have behaved as weakness zones. Their neotectonic brittle reactivation has controlled sediment deposition and landform development, which continued through the Neogene–Quaternary.

The Late Quaternary climate in Amazonia is an issue still open to debate, with hypotheses varying from alternate dry and wet episodes to stable climate with undisturbed rainforest. We approach this question using δ13C, C/N, and, to a lesser extent, δ15N from deposits derived from four cores, with the results combined with published pollen data from two of these cores. These data were analyzed within the context of radiocarbon dating, which revealed ages ranging from 42.8–41.8 to 2.3–2.2 cal ka BP. Fluvial channel and floodplain deposits with freshwater phytoplankton recorded a trend of wet climate with dry episodes before ~40 cal ka BP, followed by humid and cold climate until the Last Glacial Maximum, with intensified aridity towards the end of the Late Pleistocene. Peaks of increased contributions in C4land plants in the mid- to late Holocene were not synchronous and have no correspondence with Amazonian Holocene dry episodes, being due to sedimentary processes related to fluvial dynamics during the establishment of herbaceous fields on abandoned depositional sites. Thus, the climate remained wet in the Holocene, which would have favored the expansion of the Amazonian rainforest as we see today.

Winter temperature and sea-level position are critical factors affecting the global distribution of mangroves and saltmarshes. The replacement of saltmarshes by mangroves is expected due to global warming, reflecting the long-term natural trends in the Holocene and anthropogenic impacts since the 20th century. We documented the Holocene history of wetlands dynamics in the boreal limits of the American mangroves, located at Bay Champagne, Louisiana (USA), by integrating sedimentological, palynological, geochemical (δ13C and C\N), X-ray fluorescence (XRF) data, and radiocarbon chronology from two sediment cores. The results indicated a freshwater lake environment with herbs and wetland ferns, as well as C3 terrestrial plants, between ~8100 and ~6500 cal yr BP. This environment shifted into a lagoon and saltmarshes having sedimentary organic matter sourced from marine algae between ~6500 and ~1500 cal yr BP. In the final stage, washover sediments were deposited in the lagoon during the last ~1500 cal yr BP. Despite the increased marine influence over the last ~6500 cal yr BP, mangrove pollen were not recorded between ~8100 and ~1500 cal yr BP, suggesting that mangroves were absent in the study area during that time interval. Historical evidence and a comparative analysis of our multi-proxy data with other mangrove studies from the Gulf of Mexico, Caribbean, and eastern South America revealed a gradual mangrove expansion from tropical to subtropical coasts of South and North America during the mid-late Holocene. The mangrove colonies at their current boreal (29° 09′ N) and austral (28° 29′ S) limits were established in the early and mid-20th century, respectively. This mangrove dynamics on a continental scale suggests that the poleward mangrove migration was likely caused by the warming climate during the Holocene. More importantly, the industrial-era warming has likely accelerated the mangrove expansion, but it was not the primary force that drove the mangrove migration into temperate zones.

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 Solimoes 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.

Amazonian white-sand vegetation has unique tree communities tolerant to nutrient-poor soils of interest for interpreting processes of adaptation in neotropical forests. Part of this phytophysionomy is confined to Late Quaternary megafan palaeo-landforms, thus we posit that sedimentary disturbance is the main ecological factor controlling tree distribution and structuring in this environment. In this study, we characterize the topographic trend of one megafan palaeo-landform using a digital elevation model and verify its relationship to the forest by modelling the canopy height with remote sensing data. We also compare the composition and structure (i.e. canopy height and diameter at breast height) of tree groups from the outer and inner megafan environments based on the integration of remote sensing and floristic data. The latter consist of field inventories of trees ≥ 10 cm dbh using six (500 × 20 m) plots in várzea, terra firme and igapó from the outer megafan and 20 (50 × 20 m) plots in woodlands and forests from the inner megafan. The unweighted pair group method with arithmetic mean (UPGMA) and the non-metric multidimensional scaling (NMDS) were applied for clustering and dissimilarity analyses, respectively. The megafan is a sand-dominated triangular wetland with a topographic gradient of < 15 cm km−1, being more elevated along its axis. The outer megafan has a higher number of tree species (367), taller canopy height (mean of 14.1 m) and higher diameter at breast height (mean of 18.2 cm) than the white-sand forest. The latter records 89 tree species, mean canopy height of 8.4 cm and mean diameter at breast height of 15.3 cm. Trees increase in frequency closer to channels and toward the megafan's axis. The flooded and nutrient-poor sandy megafan substrate favoured the establishment of white-sand vegetation according to the overall megafan topography and morphological heterogeneities inherent to megafan sub-environments.

The geomorphometric characterization of central Amazonia reliefs is specially challenging because of its large dimension and rather uniform low topography of sedimentary units. In such conditions, usual techniques applied for general geomorphometry are ineffective and thus disabling direct bottom-up approaches for delimitations. Specific geomorphometry is a more promising approach for terrain analysis in this area, since procedures can be adapted to analyze the particular features of each geomorphological context. Therefore, delimitation of subdomains is a requirement for specific geomorphometry, to address proper approaches in the different strata. This paper presents a first level delimitation of major subdomains of Central Amazonia, carried out through combined techniques of geoprocessing guided by visual assessment. The three targeted subdomains, floodplains, plateau and highland, were mapped at the 1:2,000,000 scale using SRTM and derivative data as inputs. The relief of highland, as influenced by Precambrian to Cretaceous basement rocks, was firstly delimited using mostly height and relative relief combinations. The partition of the remaining lowland area into plateaus (Neogene) and floodplains (Quaternary sediments) was based on residual relief (subtraction of regional relief from full detail elevation data), with a regional relief modeled as the 9th order trend surface of elevations. Thresholds of negative residues were determined to create extents of visually assessed boundaries between plateau and floodplain areas. The continuous visual supervision of procedures and concerning interventions were based on interpretation of output displays of DEM and derived data prepared with image processing techniques. Delineation of subdomains was implemented through steps of supervised classifications and map algebra to operationally enable the task over the full area extension and corresponding data volume. Observation of data combined with knowledge and conceptual inputs were decisive to provide useful and unambiguous criteria to choose specific variables and analyses along this development.

There has been a considerable number of studies focusing on the analysis of river long profiles based on stream power incision models aiming to detect areas affected by neotectonics. Most of these studies have successfully uncovered active tectonics in mountainous landscapes, with some examples in areas of low reliefs around the globe. However, this kind of investigation has rarely been used in large tropical lowlands, such as the Amazonian lowlands, where the application of river long profiles is still challenging. The main aim of the present work was to test the functionality of methods based on river profiles to detect neotectonic reliefs in lowland landscapes. The Negro River basin was selected for this investigation, assuming the several indications of tectonic activity during the late Pleistocene and Holocene. We tested the normalized channel steepness index (ksn), with the identification of knickpoints and interpretation of swath profiles, computed from the 30 m digital elevation model provided by the Shuttle Radar Topography Mission. The results showed streams with profiles bounded by a set of knickpoints represented by very low ksn values in the right (average ksn = 8) and left (average ksn = 10) margins of the Negro River. These values contrast with the high range of ksn values generally found for rivers of tectonically active mountainous landscapes. Even with low values, we verified that a slight increase in ksn values was enough to detect transient rivers related with strike slip faults in Amazonia lowlands. The swath profiles also showed sectors on relief compatible with changes in the base level of the tributaries, with the record of knickpoints and an increase in ksn values. The experimental results obtained in this work motivate further quantitative investigation in Amazonian lowlands by testing geological data with new robust techniques from river profiles.