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The International Symposium on Andean Geodynamics (ISAG) is an international conference that was held, on average, every 3–4 years in different European cities between 1990 (Grenoble) and 2008 (Nice). These symposia usually offer an opportunity for researchers from Latin American countries and Europe as well as other countries to review the state of knowledge in geosciences on the Andes. After a long period without an edition, the 8th ISAG was organized for the first time in a Latin American country, Ecuador, from 24th to 26th September 2019. The organizing committee led by Pablo Samaniego relied heavily on the Instituto Geofísico of the Escuela Politécnica Nacional (IG-EPN) and the Institut de Recherche pour le Développement (IRD), in particular through its office in Quito, and through the Laboratoire Mixte International in France and Ecuador: "Seismes et Volcans dans les Andes du Nord" (LMI-SVAN); and the French Embassy in Ecuador. Field trips in tectonics, seismotectonics and volcanology at emblematic sites in Ecuador were organized by researchers from the IRD (Isterre and LMV), the Institut de Radio Protection Nucléaire (IRSN), IG-EPN and the University of Geneva. Four invited speakers gave presentations: Peter Molnar (University of Boulder) on the mechanisms of the Andes uplift, Suzanne Kay (Cornell University) on its magmatism, Victor Ramos (University of Buenos Aires) on the scientific approaches developed through time for the Andean orogeny and Eric Calais (Ecole Normale Supérieure de Paris) on the difficulty of dialog between seismic risk specialists and the authorities in Haiti. The symposium also provided an opportunity for more than 250 participants to meet, with more than 80 oral presentations and over 150 posters. As a result of this conference, the Editor of the Journal of South American Earth Sciences proposed to the organizing committee to publish a special issue on the contours of these presentations. Following the peer review process, 19 papers are published in this special issue. These manuscripts reflect the various disciplinary fields, geophysics and deep imaging, tectonics, volcanism, geomorphology and seismic hazard, from the local scale to the Andes as a whole. Not surprisingly, a higher density of works is found in Ecuador and the northern Andes (Figure 1). As this collection of articles reflects the outlines of a symposium and not a specific scientific question, our aim here is not to develop a synthesis of current knowledge on the Andes. We therefore present these articles in sequence, by discipline, although this categorization may appear subjective since some articles are multidisciplinary. [ABSTRACT FROM AUTHOR]

This paper presents the geomorphological features of four areas of subtropical, southernmost Brazil displaying striking landforms developed upon Precambrian Camaquã Basin conglomerates in the southern Brazilian shield areas. The distinctive and unique features of the Serra do Segredo cuesta, the Rincão do Inferno canyon, the Casa de Pedra inselberg, and the Pedra da Cruz cap-shaped hills are important examples of such conglomerate geomorphology in South America and in Brazil, where few occurrences were available so far. They are the first documented conglomerate landforms in southernmost Brazil, widening the distribution of such terrains in South America and in the subtropical, southern hemisphere areas, considering recent global reviews. Besides the high scientific relevance for geomorphology as a whole, such features are important also for (1) evidencing the decisive role of lithology, structure, and water flows in the formation of such landforms; as well as (2) ecology and tourism, being distributed within and in the vicinity of the Caçapava UNESCO Global Geopark of southernmost Brazil. • Novel description of conglomerate geomorphology developed upon Ediacaran alluvial/fluvial deposits of the Camaquã Basin in subtropical, southernmost Brazil. • Different landforms developed according to bed tilting and arrangement, as well as to tectonic structures "pre-design". • Decisive role of lithology and water in shaping ranges and hills. • Contribution to a global distribution of conglomerate landforms, especially in humid, subtropical areas. • Geological heritage potential, features within and in the surroundings of the Caçapava UNESCO Global Geopark. [ABSTRACT FROM AUTHOR]

This work presents a 1:10,000 geomorphological mapping of an area in southeastern Brazil, based on morphometric analysis of Digital Elevation Models (DEMs), while classical methods focus on photo interpretation. Data derived from the DEM include elevation, slope gradient, slope aspect, vertical and horizontal curvatures, amplitude, elongation and wavelength of landforms. These parameters were used along with slope shape and drainage patterns to classify the landforms according to the Land Systems method, in which portions of the landscape that presents similar terrains attributes are grouped from regional (low detail) to local (high detail) scales, respectively, Land Systems, Land Units and Land Elements. The São Paulo State geomorphological map at 1:1,000,000 scale is considered the best reference source, and was compared with the results obtained in this project. Two Land Systems, four Land Units and twelve Land Elements were identified in the study area. In this area, karst terrains are common and easily identified due their characteristics drainage patterns, amplitude and slope gradient. Karst terrain boundaries defined in this study do overlap with those defined in the state map, however the morphometric analysis allowed a better description of the terrain attributes used to define them. The terrain attributes derived automatically from the DEM enabled an accurate geomorphological classification of the study area. The methodology presented in this paper is considered effective for mapping landforms at a detailed scale and can be employed in regional scale mapping using coarser resolution DEMs. Image 1 • A geomorphological map was created based on DEM-extracted terrain attributes. • Attributes were grouped from low to high detail in Land Systems, Units and Elements. • The same Land Systems and Units of a map based on traditional methods were identified. • Land Elements were defined by attributes unavailable from aerial imagery. • Automatic identification of karst areas produced fair results to existing maps. [ABSTRACT FROM AUTHOR]

The Araucaria Plateau is a geomorphological unit that occupies approximately three-quarters of the terrain in the southern region of Brazil. The plateau displays different altitudinal levels (600 to <1400 m a.s.l.) that are locally recognized as remnants of planed surfaces (S8-S1). These surfaces are maintained by basic (S3-S8) and acidic (S1 and S2) volcanic flows from the Neocretaceous period of the Paraná Basin. The largest extent of this plateau is located in a humid subtropical climate zone. Colluvial, colluvial-alluvial, alluvial sediments and paleosols (Ab diagnostic horizons) occur predominantly in S2. The paleosols are located in low-hierarchical-order fossil valleys (first- to fourth-order in Strahler's stream classification) and valley heads, which are referred to as paleovalleys in this paper. We employed these paleosols as stratigraphic level markers of the pedogenesis of the regional Upper Quaternary and propose their importance as records of the paleoenvironmental conditions of the Araucaria Plateau in areas above 1200 m a.s.l. These paleosols were dated by 14C and show ages between 23.8 ± 0.05 kyr BP (28.06-29.08 kyr cal. BP) and 41.16 ± 0.48 kyr BP (44.13-45.58 kyr cal. BP). The calibrated ages are related to Marine Isotope Stage 3 (MIS 3), in which the last period of global warming occurred (approximately 60-25 kyr cal. BP). We integrated the morphological, pedogeochemical, clay fraction mineralogy, micromorphological and δC-13 analyses of five paleosols from S2 to verify the paleoenvironmental conditions of the Araucaria Plateau and its correspondence with the paleoclimatic phenomena that were identified on a global scale during MIS 3 in the Southern Hemisphere. We obtained the following conclusions: a) the properties of paleosols reflect pedological processes that are adjusted to the paleoenvironmental conditions at the end of MIS 3 and the transition to MIS 2 (Last Glacial Maximum); b) aplasmogenic partial acidolysis was the predominant pedogeochemical process during MIS 3; c) during this period, the water regime was sufficiently humid to develop hydromorphic horizons in the valley bottoms of the entire drainage network to the valley heads; d) regional change toward a drier hydric regime occurred in MIS 2, when erosion of the paleosols predominated; and e) in MIS 1 (current Holocene interglacial), burial of the paleosols and relief inversion occurred, which resulted in fossilization of the valleys. [ABSTRACT FROM AUTHOR]

Despite important progress on Amazonian floodplain research, the flooded forest of the Negro River “igapó” has been little investigated. In particular, no study has previously focused the linkage between fluvial geomorphology and the floristic variation across the course of the river. In this paper we describe and interpret relations between igapó forest, fluvial geomorphology and the spatial evolution of the igapó forest through the Holocene. Therefore, we investigate the effect of geomorphological units of the floodplain and channel patterns on tree diversity, composition and structural parameters of the late-successional igapó forest. Our results show that sites sharing almost identical flooding regime, exhibit variable tree assemblages, species richness and structural parameters such as basal area, tree density and tree heights, indicating a trend in which the geomorphologic styles seem to partially control the organization of igapó's tree communities. This can be also explained by the high variability of well-developed geomorphologic units in short distances and concentrated in small areas. In this dynamic the inputs from the species pool of tributary rivers play a crucial role, but also the depositional and erosional processes associated with the evolution of the floodplain during the Holocene may control floristic and structural components of the igapó forests. These results suggest that a comprehensive approach integrating floristic and geomorphologic methods is needed to understand the distribution of the complex vegetation patterns in complex floodplains such as the igapó of the Negro River. This combination of approaches may introduce a better comprehension of the temporal and spatial evolutionary analysis and a logic rationale to understand the vegetation distribution and variability in function of major landforms, soil distributions and hydrology. Thus, by integrating the past into macroecological analyses will sharpen our understanding of the underlying forces for contemporary floristic patterns along the inundation forests of the Negro River. [ABSTRACT FROM AUTHOR]

Abstract: The Parana River is one of the most important fluvial systems of South America and its floodplain includes the most diverse subtropical ecosystem on the continent. However, the relationship between basic aspects, such as the vegetation and geomorphology of the river floodplain, has scarcely been investigated. In this paper, the annual dynamics of vegetation in relation to the geomorphologic and hydrological characteristics of a river floodplain around 31° 30′ S, are analyzed. The annual dynamics of vegetation was investigated using values of the Normalized Difference Vegetation Index (NDVI) obtained from satellite images at two scales of spatial analysis: the first, at the geomorphologic unit level, through several transects crossing the total width of each unit and, the second, through some transects selected from each unit. Our analysis considered variables of different temporal stability (such as geomorphology, hydrology, vegetation, precipitation, and ground temperature), using scenes corresponding to two hydrological cycles of the system (2009 and 2010), which represented relatively “dry” and “humid” years. Five main geomorphologic units were identified in the floodplain of this anabranching system, which were named considering the predominant landforms and the most important (or typical) water course of each area: Bars and Islands of the Main Channel of the Parana River (BI-MCH), Scroll Bars of the Colastine Branch (SB-C), Scroll Bars of the San Javier River Channel (SB-SJ), Crevasse Splays and Levees of the Malo–Mendieta minor channels (CSL-MM), and Crevasse Splays and Levees of the Santa Fe–Coronda river channels (CSL-SFC). These major units are assembled at different general levels and with variable slopes, which partially control the permanence and other characteristics of the flood flow. The crevasse splays and river levees units were predominantly characterized by herbaceous–bushy marshy vegetation, with low mean NDVI values, while SB-C and BI-MCH units showed two types of forests. The latter showed the highest NDVI values. Unit SB-SJ showed mixed characteristics between the two above-mentioned groups. Mean NDVI values were different among the varying geomorphologic units and during the studied years, showing extreme values of 0.25 and 0.80 after both hydrological cycles. According to our results, the main variations in the seasonal dynamics of vegetation show a higher dependence on the dynamics of the hydrological cycle than on surface temperature or precipitation. The hydrological dynamics of the Parana River floodplain are in turn regulated by its geomorphological architecture, so the annual dynamics of vegetation activity in this system are finally influenced by the geomorphologic unit's level, rather than by the short duration modeling processes (i.e., hydrological cycles or drought–flood pulses). [Copyright &y& Elsevier]

Arid environments are dynamic systems due, in part, to the action of hydrological processes. However, studies on the relationship between the abiotic factors and the properties of arid vegetation communities of Argentina are scarce. In this paper, the connection between these two parameters is researched using DEM analysis and exhaustive field work in order to model vegetation changes and landform evolution. The aim of this paper is to determine whether geomorphological properties influence vegetation patterns along the Cerro Zonda Mt. This mountain range is located in an arid central sector of Monte Desert, a phytogeographic region of Argentina. The classification of geomorphological units was made by combining interpretation of images provided by Google Earth and the analysis of Alos Palsar DEM using SAGA GIS. The geomorphic units were sorted into categories based on slope, elevation, hillslope aspect, terrain roughness and topographic wetness. In addition, surface characteristics of units were evaluated considering the properties of coverage of rock fragments, fine sediment and mulch. Afterwards, community patterns were explored using PCA analysis and linear correlations. Our results showed five geomorphological units: a) Pediment of mountain upland; b) Active landforms; c) Inactive landforms; d) Inactive landforms raised by neotectonics and e) Lacustrine landforms. The vascular flora is represented by 35 species distributed in 15 families. The landforms' surface property of rock fragments is correlated both directly with species richness and inversely with vegetation coverage. Furthermore, roughness explains the higher vegetation diversity while slope promotes an increase in the vegetation cover, but this does not suggest more species richness. In addition, our results indicate that topographic wetness, as well as hillslope aspect and elevation, are not determining variables of vegetation patterns across the landforms. The vegetation patterns of Cerro Zonda Mt. are associated with topographic properties as slope and roughness. In turn, rock fragment surface coverage also affects these vegetation patterns. The landforms' properties not only expose spatial changes in the development of the plant communities but also show the direct implications of geomorphological changes over such communities. In particular, there is a need to integrate a geomorphological view for the analysis of vegetation in arid zones. • The geotechnical characteristics of landforms are a key element in the classification process. • The vegetation of all five landform types was represented graphically along a toposequence. • Slope values and roughness determine the vegetation coverage at a regional scale. • The high coverage of rock fragments contributes to the formation of new areas due to the retainment of fine sediments. [ABSTRACT FROM AUTHOR]

In the last decade, detailed geomorphological analyses of northeast Brazil led the authors to publish a model of landscape development in which long-term landform evolution was driven by regional swell-like uplift post-dating Early Cretaceous intracontinental rifting and the formation of the Atlantic passive margin in Aptian times. The post-Cenomanian uplift caused an inversion of Cretaceous basins and generated a landscape in which the most elevated landforms correspond either to resistant post-rift sedimentary cover, or to residuals of Cretaceous rift shoulders, above a low erosion surface. Since no evidence of a former post-Cenomanian sedimentary cover of significant thickness was found outside the coastal fringe, we could evaluate the uplift to 600 m at most and the mean erosion rates to 10 m/Ma or less. However, according to models based upon the results of thermochronological analyses (apatite fission tracks analysis-AFTA), two slices of 1000 m to 2500 m would have been deposited over the present pile in the south part of the study area, respectively in Campanian and Oligocene-Miocene times, before being totally removed. We examine here the diverging scenarios of geomorphic evolution respectively based upon morphostratigraphy (our model) and upon low temperature thermochronology, submitting them to available evidence provided by an updated and geographically extended review of geomorphological and sedimentological data, and trying to decipher some of the reasons that might lead to disputable geomorphic interpretations. We stress the fundamental importance of taking into account all the available results of geomorphological and geological approaches in any interpretation of thermochronological and other analytic methods used for reconstructing long-term landscape evolutions. This is one of the conditions for reinforcing the trust one can have in their results, which may bring complementary or unique information, peculiarly in places where sedimentary or volcanic markers are missing. • A model of landscape evolution in NE Brazil is proposed based on morphostratigraphy. • Thermochronological studies suggest another scenario of regional landform evolution. • This review paper aims to explain the discrepancies between both types of scenarios. • Recent geological data confirm the general overestimation of denudation by AFTA. • Morphostratigraphic constraints are fundamental to interpret AFT primary results. [ABSTRACT FROM AUTHOR]

Abstract: Low resolution of the continental sedimentary record is a common source of skepticism about the application of geomorphology and sedimentology to Quaternary studies. In spite of this, when supported by independent proxy data, geomorphology and sedimentology may favor palaeo-hydrologic interpretation. This paper associates geomorphologic, stratigraphic, sedimentologic, isotopic, palynologic and geochronologic data. The research was conducted in valley head sites in southern Brazilian highlands, under mild subtropical climate. The results point to environmental changes, the ages of which coincide to Marine Isotopic Stages (MIS) 5b, 3, 2 and 1. Although late-Pleistocene temperatures and precipitation were lower than those of today, the study valley heads seem to have sustained locally wetter environments, which fed shallow soil–water saturated zones. These saturated zones are believed to have expanded during transitions between stadial and interstadial states, contributing to hillslope erosion and sedimentation regardless of the sign of the climatic change. The interior organization of holocenic slope-wash deposits suggests that the mid-Holocene climate was drier than today’s and was under the influence of seasonally contrasting precipitation regimes. The predominance of overland flow-related sedimentary records suggests that an excess of precipitation over evaporation influenced local palaeo-hydrology. This palaeo-hydrologic condition seems to have been recurrent and also explains the alternating periods of pedogenesis and sedimentation. [Copyright &y& Elsevier]

Mirim Lake is located in the southern Brazilian/northeastern Urugayan coastal plain. Fossils of mollusks have been discovered on its shores since the XIX century, and in recent years, several new remains of invertebrates and vertebrates have been found in the Brazilian area of the lake that provide insights on the geological evolution and environmental changes that affected this lake during the late Quaternary. In this first of two papers describing these new findings we focus on vertebrates, consisting of aquatic and terrestrial taxa. The former include the first associated fossil remains of one adult and one juvenile balaenid whale known in Brazil, probably a female and calf of the southern right whale (baleia-franca) Eubalaena australis , besides bull sharks (Carcharhinus leucas) also recorded for the first time in southern Brazil, rays (Dasyatidae and Myliobatidae) and teleost fishes. The fossils of terrestrial vertebrates include several extinct mammals, found on the margins and retrieved from the lake bottom by fishermen at depths of up to 4 m. One molar tooth of Toxodon discovered in situ in one irrigation channel yielded an electron spin resonance (ESR) age of 68 ± 13 ka, in agreement with an age of 32.8 ± 5.1 ka obtained in quartz grains extracted from a caliche nodule collected above that fossil and dated by optically-stimulated luminescence (OSL). Other quartz grains in the same nodule that yielded ages of 16.9 ± 2.5 ka indicate partial dissolution of the caliche by increased rainfall at the beginning of the last glacial-interglacial transition (Termination I). The lake was invaded by marine waters and organisms during the Holocene sea-level highstand of +3 m around 5–6 ka b2k through paleo-connections with the Atlantic Ocean, becoming a paleo-lagoon. At that time coastal waters were warmer than today, as indicated by the presence of the tropical shark C. leucas. The ESR and OSL ages indicate chronocorrelation with the Pleistocene fossil-bearing Santa Vitória Formation that outcrops to the east. The fossil and sedimentary records indicate that the geological evolution and environmental conditions of the lake were controlled by climate and sea-level oscillations related to glacial-interglacial cycles. • Fossil assemblages of terrestrial and marine vertebrates were found in Mirim Lake. • Terrestrial mammals were transported to or died on the lake shore during lowstands. • During sea-level highstands the lake became a lagoon with fully marine conditions. • Marine fauna, including whales, occupied the lake during sea-level highstands. • The first record of tropical sharks Carcharhinus leucas in southern Brazil. [ABSTRACT FROM AUTHOR]

The integration of drainage analysis and topographic metrics provides excellent tools to assess the Quaternary tectonic activity modeling landscape evolution in evolving orogens. Furthermore, detecting active structures through the geomorphological analysis of landscapes helps to identify potentially seismogenic structures that could impact the socio-economic conditions in developing countries. Therefore, this paper presents a tectonic geomorphology study conducted on the Santander Massif (SM, Colombian Eastern Cordillera) and surrounding areas. The SM has structures with reported Quaternary activity such as the Bucaramanga, Morro Negro-Las Mercedes, and Chitagá faults, which summed to a poorly-constrained paleosismological history with significant shallow events is the prime incentive of this work. Our study is based on the acquisition of topographic data through swath profiles, local relief, slope variability, filtered topography, minimum bulk erosion, which along with geomorphic indices like the normalized concavity steepness (k sn), the hypsometric integral (HI), the ratio valley floor width to valley height (Vf) and normalized river profiles provided new insights on the recent landscape evolution in this part of the Northern Andes. We compared published apatite fission tracks (AFT) data for the study area with the uplift pattern deciphered from the geomorphic indices to detect the consistency in exhumation and denudation processes both in the long and short-term. Consequently, the central SM, as well as the faulted block between the Bucaramanga and Guamalito faults, evidence a highly-incised landscape with local relief values exceeding the 1500 m, then, responding with a sharp incision to recent surface uplift. Interestingly, this uplift pattern in central SM matches with published AFT data and is related to Neogene exhumation events controlled by secondary structures like the Suratá Fault. We attribute this exhumation event, and accelerated denudation rates within the SM, to the influence exerted by the "collision" between the SM and the Pamplona Indenter, leading to the unroofing of basement rocks at the deformation front (e.g., the Vetas High) and the topographic building of the range. For the upthrown block (hanging wall) of the Bucaramanga Fault, the occurrence of poorly-graded river profiles with an average concavity factor of 12.01, as well as irregular hypsometric curves with convex lower reaches, reinforce the hypothesis that late Cenozoic topographic rejuvenation in the SM was also forced by the tectonic activity of the Bucaramanga Fault. We expect empirical uplift rates >0.08 mm/yr (very high to high tectonic activity) for the mountain front encompassed between La Esperanza and Bucaramanga localities. We state this assumption since the mountain front delimited by the structure mentioned above is quite straight, it preserves remarkable morphostructural features and displays V-shaped valleys with an average Vf index of 0.38. This uplift rate is in good agreement with recent thermochronological exhumation rates (0.1 to > 0.3 mm/yr) published by Siravo et al. (2019). Higher uplift rates associated with the Bucaramanga Fault were also constrained with the erosion proxy index, i.e., the k sn index. High k sn values (above 128) were observed following a linear pattern, which in turn seems controlled by the main trace of the Bucaramanga Fault. For instance, the river system draining the western piedmont of the SM, near Aguachica, records slope-break knickpoints that we interpret as evidence of an incisional wave migrating upstream and adjusting a late Neogene uplift event associated with the Bucaramanga Fault. Conversely, the northern SM presents variable tectonic activity with the inner part, east of the Guamalito Fault, presenting low tectonic activity with little surface uplift and dominant strike-slip kinematics. We recognize the Ocaña-Ábrego zone as a relict landscape with well-preserved non-consolidated deposits that may record the initial exhumation and denudational pulses of the SM during the Andean Orogeny. • A DEM-based comprehensive landscape analysis of the Santander Massif and surrounding areas is presented. • Geomorphic indexes reflect along-strike variations in topography and recent surface uplift in the Santander Massif. • The Bucaramanga Fault constitutes an active structure with higher uplift rates at central Santander Massif. • The relative westward motion of the Mérida Andes into the central Santander Massif controlled recent landscape evolution. • Northern Santander Massif records a Neogene relict landscape at the Ocaña-Ábrego zone with little vertical deformation. [ABSTRACT FROM AUTHOR]