Central Cordillera Of Colombia Research Articles

Using remote sensing to map degraded mountain peatlands with high climate mitigation potential in Colombia's Central Cordillera

Peatlands are the most carbon-dense ecosystems on earth. In tropical mountains, peatlands are numerous and susceptible to rapid degradation and carbon loss after human disturbances. Quantifying where peatlands are located and how they are affected by land use is key in creating a baseline of carbon stocks and greenhouse gas fluxes from tropical mountain peatlands. However, mapping peatlands in the páramo of the Northern Andes is difficult because they are in a topographically complex environment with nearly continuous cloud cover and frequent conversion to pastures or cropland. The goal of this effort was to identify the different types of páramo peatlands and their degradation patterns in the Colombian Central Cordillera. Moderate resolution cloud-free composites of optical imagery, temporal variance in ALOS- PALSAR L-band SAR, Sentinel-1 C-band SAR, and topography data were used as inputs in a machine learning classifier to identify was used to map 12 land cover classes including peatlands with natural vegetation and peatlands converted to pasture. Field data from 507 control points collected across the study area, including information on the vegetation and carbon content on the top 20 cm of the soil, were used to train and validate the classifier. Results show that the use of multiple platforms and image dates, including variance of the radar returns, is necessary for a clear separation of disturbed and undisturbed peatland classes. Peatland area varied across the study region, covering 7% and 20% of the landscape in the northern and southern portions of the study area, respectively. Disturbed peatlands with exotic grasses cover nearly 2% of the area. The overall accuracy of the peatland classes was 82.6%. Disturbed peatlands with exotic grasses had less carbon in the top 20 cm than undisturbed peatlands with natural vegetation. These results highlight the prevalence of peatlands in the tropical Andes and a promising approach to detecting peatlands converted to agriculture. Understanding the distribution and extent of these carbon dense ecosystems can facilitate the restoration and protection of peatlands in the northern Andes, with implications for the future trajectories of the national greenhouse gas inventory.

Exceptionally preserved subfossil woods from late Pleistocene volcanic deposits from the Northern Andes of Colombia

The recent geological history of the Northern Andes is characterized by the interaction of dynamic surface processes such as volcanic activity, fluvial erosion, mass movements, etc. that have shaped landscapes for millennia. Despite its great geological and biological importance, the long-term ecological history of middle-elevation tropical habitats (between 1000 and 2500 m.a.s.l.) is unknown, due to the scarcity of suitable paleo archives preserving the paleoecological signal, leading to a critical data gap. This manuscript reports well-preserved subfossil woods of the Pleistocene volcanoclastic deposits from the Central Cordillera of Colombia. Four wood specimens are described and identified as Terminalioxylon gumminae sp.nov., Andesanthus risaraldense sp.nov., Anacardium quindiuense sp.nov., and Chrysochlamys colombiana. This report demonstrates the potential of volcanic deposits in the Northern Andes as paleo archives, and contributes to the fossil record of the tropical Andes, as it contains elements of mid-altitude vegetation preserved in association with the Pleistocene volcanic activity of the Central Cordillera. The environments where these subfossil species lived resemble present environmental conditions. This is a baseline for future paleobotanical exploration and paleoenvironmental analyses.

Geography shapes the microbial community in Heliconius butterflies.

Heliconius butterflies are an ideal organism for studying ecology, behavior, adaptation, and speciation. These butterflies can be found in various locations and habitats in Central and South America, where they encounter and interact with different sources of pollen, nectar, and host plants. However, there is limited knowledge on how geographic and habitat variations affect the microbiota of these insects, and whether microbial associates play a role in their ability to exploit different habitats. To date, research on the microbial communities associated with Heliconius has mainly focused on host phylogenetic signal in microbiomes or microbiome characterization in specific communities of butterflies. In this study, we characterized the microbiomes of several species and populations of Heliconius from distant locations that represent contrasting environments. We found that the microbiota of different Heliconius species is taxonomically similar but vary in abundance. Notably, this variation is associated with a major geographic barrier-the Central Cordillera of Colombia. Additionally, we confirmed that this microbiota is not associated with pollen-feeding. Therefore, it seems likely that geography shapes the abundance of microbiota that the butterfly carries, but not the taxonomic diversity of the microbial community. Based on the current evidence, the bacterial microbiota associated with Heliconius does not appear to play a beneficial role for these butterflies.

Relación entre vulcanismo dacítico monogenético y poligenético. Caso de estudio del domo Tapias (<95 ka) y volcán Cerro Machín (<50 ka), Colombia

The Tapias lava dome is located ~5 km SE of the explosive, Cerro Machín polygenetic volcano, both located on the Colombian Central Cordillera. The edifices have been interpreted as generated by the same magmatic system; however, the genetic and temporal relations between both edifices have not been established. In this work, the Tapias dome is studied using petrographic characterizations, mineral-, whole-rock- and isotopic chemistry, geothermobarometric calculations, and a K/Ar radiogenic age, and subsequently it is explored the relationship with the Cerro Machín. The rocks from Tapias dome are porphyritic with phenocrysts of plagioclase (An28-48), amphibole (tschermakite and magnesiohastingsite), biotite, quartz, and Fe-Ti oxides, embedded in a glassy groundmass. Petrographically, two types of amphibole crystals were recognized: type I, which is homogeneous, and type II, which displays different rims. The composition of Tapias is dacitic (SiO2: 66.59 wt.%) with calc-alkaline affinity. Our geothermobarometric calculations indicate that type I amphibole crystallized at 871-874°C, between 10.2 and 10.4 km depth. The core of the type II amphibole crystallized at 852-920°C, between 8.5 and 12.3 km depth, while its rim did it at higher temperatures (880-973°C), but at similar depths (9.1-11.8 km). The K/Ar radiogenic age obtained for the groundmass shows an emplacement age not older than 95 ± 0.05 ka. When comparing the results to the Cerro Machín, it is noted that the mineral and compositional characteristics are nearly identical. These results suggest that indeed both volcanoes share the same magmatic system and are fed by magma hosted between ~9 and ~12 km depth. Moreover, it is proposed that the vent location of both edifices, as well as the time gap between the eruption at Tapias and the beginning of the activity at the Cerro Machín (~50 ka), are the result of crustal deformation caused by the interaction between the Otú-Pericos and Ibagué faults.

Selaginella rachipterygia (Selaginellaceae–Lycopodiophyta), a Notable New Species from Colombia and Ecuador, and New Distribution Records for S. simplex

We describe and illustrate Selaginella rachipterygia Valdespino, Cornejo & C. López as a new species found on the inter-Andean eastern slopes of the Central Cordillera of Colombia and on the slopes on both sides of the Andes of Ecuador and compare it to S. flagellata Spring. Selaginella rachipterygia is notable for its often flagelliform branch, stem, and strobilus tips, which are often gemmiferous, and by its lateral leaves perpendicular to the main stems below the first branches, which give the stems the appearance of having wings. In addition, we document the expanded distribution range of S. simplex Baker to include Panama and Ecuador. Finally, we contrast S. simplex with the similarly small-sized species S. correae Valdespino and S. minima Spring, which overlap either in part of or throughout their distribution ranges.

Modeling of the large Miocene epithermal and porphyry gold deposits of Colombia using Monte Carlo simulations

The Cauca metallogenic belt is an inter-Andean area located along the Cauca-Romeral fault zone, which is made up of a group of twelve Miocene magmatic-hydrothermal Au-Ag-Cu mineral deposits positioned between the Western and Central Cordillera of Colombia. In addition to being a widely developed region in exploration and exploitation with known Au endowments of over 1,700 tons, this area represents an exceptional metallogenetic laboratory for modeling a typical Andean-type mineralization from a calc-alkaline source with high Sr/Y ratios. Efficiency processes such as ion and halogen transport, oxygen fugacity and sulfur content have been extensively studied with a geochemical approach; however, the quantification and modeling of these efficiency processes currently debated. Through multiple iterations using Monte Carlo simulations (N > 2 million), the modeled reservoirs corresponding to the upper crust, using a high flux of dacitic magma of 0.007 km3/year and efficiencies of 1 – 2 %, showed that gold endowments bear heavily with magmatic and hydrothermal Au deposits in the Cauca Metallogenic Belt. Outcomes including Au endowments up to 1,000 tons can be obtained for reservoirs below 400 km3 of hydrous melt in brief mineralization intervals between 40 to 120 ka and for volumes of 400 to 800 km3 in a 120 to 200 ka window. In contrast, the hypothetical reservoirs for the lower and middle crust, through a basaltic calc-alkaline magma flux between 0.0007 and 0.0011 km3/year, an efficiency of ~0.7%, and pressures below 5 kbar, showed sufficient available content of exsolvable H2O and gold to feed the reservoirs in the upper crust or to generate gold deposits from them, but in longer time intervals (>1 Ma).

Limited foraging overlap between introduced Apis mellifera and native Melipona eburnea in a Colombian moist forest as revealed through pollen analysis

Honey farming is a young industry in Colombia, where it is gaining relevance as a source of jobs and food security, especially in post-conflict low-income communities that place bee colonies in native forests. Previous studies on the palynological composition of this honey are insufficient and the role of native plants for the production of honey is therefore unknown. Here we present a palynological analysis of honey produced by two bee species, the introduced Apis mellifera and the native Melipona eburnea, both commonly used by low-income communities in the eastern region of the Department of Antioquia, in the Central Cordillera of Colombia. We analyzed species richness and diversity of pollen, characterized some life history traits of those species preferred by bees, and estimated the interaction web between the bee and selected plant species. The overlap between the two species was very small. We found that the source of nectar for A. mellifera were plants with different growth habits, both native and introduced. Instead, M. eburnea used mostly native tree and shrub species, at a constant height level. Our results suggest that setting bee colonies of A. mellifera close to those of M. eburnea may not result in competition between them. However, it is key to evaluate whether this pattern is the same using other sources of food, such as pollen, or in other geographic regions.

Coffee plantation soil characterization using a multi-method approach near the Volcano Nevado del Ruiz, Colombian Central Cordillera

The presence of iron oxides may provide a sensitive indicator of the effects of cropping practices on coffee plantations. Authors characterized the mineral phases present in soil A horizons at three different farms located in the Department of Tolima within the regions of Líbano and Villahermosa. Our analysis includes X-ray diffraction, Mössbauer spectroscopy, and remote sensing to discriminate the distribution of the different magnetic mineral phases. X-ray diffraction was used to identify the mineralogical properties of iron oxide such as hematite, goethite, and ferrihydrite (Fh), as well as tectosilicate minerals such as albite and sanidine. Mössbauer spectroscopy results for samples taken at room temperature indicate the presence of Fe2+ and Fe3+ mineral phases, which possibly correspond to ilmenite or magnetite. Finally, Sentinel-2A multi-spectral imager (MSI) data was used to map the distribution of iron oxides and study the influence of their distribution throughout the study area. A high correlation between Mössbauer spectroscopy and Sentinel-2A MSI data exists throughout the study area. The results suggest that farms close to the main Nevado del Ruíz Volcano have a more significant mineralogical variability. In contrast, more distant farms are characterized by soils with more iron oxides, the product of weathering, erosion, and human activities.

Effect of climate seasonality and vegetation cover on floral resource selection by two stingless bee species

The response of two stingless bees (Tetragonisca angustula and Melipona eburnea) to changes in vegetation cover was evaluated on seasonal and spatial scales. Seasonal variation was analysed for 15 months, with monthly melitopalinological assessments of hives located in three different vegetation covers: forests, fallows, and grasslands, in the Colombian Central Cordillera. Fallows, with an intermediate disturbance degree, presented the highest pollen taxa richness for both bee species (33 and 40 taxa for M. eburnea and T. angustula, respectively). Both bee species presented a high preference for plant families Melastomataceae, Sapindaceae, and Peraceae. Miconia minutiflora and Mi. prasina (Melastomataceae) were the most selected species, with an alternation in their use between dry and wet seasons. Clethra spp., Pera arborea, and Ilex laureola were also highly selected by both bee species. M. eburnea showed higher pollen richness values during the dry season, when the largest number of plant species flowered. Despite both bee species being polylectic, T. angustula presented higher pollen richness values during wet periods, which was reflected in a greater amplitude of trophic niche compared to M. eburnea. Both bee species showed a higher preference for typical plants in forest environments, enhancing meliponiculture as an economically sustainable practice that can promote forest conservation and the maintenance of stingless forest interactions.

Comment on “Emplazamiento del magmatismo Paleoceno-Eoceno bajo un régimen transtensional y su evolución a un equilibrio dinámico en el borde occidental de Colombia” by Grajales et al., Rev. Mex. Cienc. Geol. (2020), 37(3), 250-268

Grajales et al. (2020) reviewed geochronological and geochemical data from Paleogene volcanic and plutonic rocks outcropping in the Panama-Choco Block (north western Cordillera) and southern Western Cordillera, as well as the Central Cordillera of Colombia. These data were used to support a model of continuous Paleogene arc magmatism along the Colombian continental margin, and to propose a paleogeographic model for the arc. The authors did not discuss previously published paleomagnetic, geochemical, geochronological, thermochronological and provenance constraints from Cretaceous to Miocene rocks of western and northern Colombia, Panama, and Ecuador that support a more plausible model of a double subduction system controlled by the convergence of the Caribbean and Farallon plates beneath the north Andean block during Paleogene. In this comment, we discuss shortcomings in the data and model proposed by Grajales et al. (2020) and present an alternative interpretation for contemporaneous arc-like magmatism during the Paleogene in the Northern Andes. We conclude that the double subduction system is the more plausible explanation for the contemporaneous arc-like magmatism during the Paleogene, currently exposed in the northern and southern portions of the Northern Andes.

Phenology of the endangered palm Ceroxylon quindiuense (Arecaceae) along an altitudinal gradient in Colombia

Introduction: Understanding the phenology of plant populations is vital for their conservation and management. We studied the vegetative and reproductive phenology of the endangered palm Ceroxylon quindiuense along an altitudinal gradient in the Central Cordillera of Colombia. Objective: We describe the leaf production rate, and flowering and fruiting cycles, and calculate food offer for the fauna, as a tool for the proper management of the palm. Methods: At each sampling site (2 400, 2 600, 2 800, 3 000 m.a.s.l.), we marked 40 adult individuals (20 pistillate, 20 staminate), which we followed bimonthly for 24 months. We studied leaf production by counting fallen leaves. We followed flower and fruit production through observations with binoculars and photographs. Results: Each adult individual produced, on average, one leaf every 61 days. Although isolated individuals flowered throughout the year, most palms flowered synchronously at each elevation in October 2016-August 2017 and in August 2018-February 2019 and had ripe fruits 7-13 months later. Flowering started at 2 600 m, followed by 2 800 and 3 000 m. Palms at 2 400 m, the lower limit of the palm stands in the area, showed a singular behavior, with scarce flower and fruit production, some individuals that changed sex, and a higher proportion of pistillate palms. Each palm produced 1-11 (x̄ = 5.3, SD = 2.2) inflorescences and 1-10 (x̄ = 5.3, SD = 2.2) infructescences. The average number of fruits per infructescence was 4 465 (SD = 1 488). With an estimated population of adult palms between 256 000 and 600 000 and an overall ratio of pistillate: staminate individuals 1:1 or 1:2, total fruit production in the area during each fruiting period is estimated as 2.0-7.1 billion fruits. Conclusions: The huge number of flowers and fruits and their gradual availability along the altitudinal gradient have a major impact on the spatial and temporal distribution of food offer for fauna associated with the palm.

Petrology and geochemistry of high-Al chromitites from the MedellÍn Metaharzburgitic Unit (MMU), Colombia

The Medellin Metaharzburgitic Unit (MMU), emplaced onto the western continental margin of Pangea during Triassic time, is located in the Central Cordillera of Colombia and consists of metaharzburgites, minor metadunites and chromitite bodies (Patio Bonito and San Pedro ore deposits). The ultramafic rocks contain relicts of mantle-derived olivine, chromian spinel and minor orthopyroxene, and a later metamorphic mineral assemblage composed by tremolite, chlorite, talc, fine-grained recrystallized olivine, serpentine-group minerals, magnetite, and secondary chromian spinel, formed during the thermal evolution of the unit. The Cr# [Cr/(Cr+Al) atomic ratio] of the accessory primary chromian spinel in the metaperidotites ranges from 0.58 to 0.62 and overlaps those of supra-subduction peridotites from ophiolites. According to textural and compositional variations, the accessory chromian spinel in the metaperidotites can be classified into three groups: i) partially altered chromian spinel with an Al-rich core, ii) porous, Cr-Fe2+-enriched and Al-Mg-depleted chromian spinel, and iii) homogeneous Fe3+-rich chromian spinel. These variations can be related to superimposed medium-T metamorphism that reached amphibolite facies (ca. 600 ºC). Chromitite bodies associated with the metaperidotites have massive and semi-massive textures, and mainly consist of chromian spinel crystals, which show large unaltered cores surrounded by thin alteration rims of ferrian chromian spinel and chlorite. Chromitites are Al-rich (#Cr <0.6) and strongly depleted in platinum group elements (ΣPGE <41 ppb). The primary petrological and geochemical characteristics preserved in the metaperidotites and chromitites indicate that the MMU formed at shallow levels of a suboceanic lithospheric mantle related to a supra-subduction zone (back-arc basin/incipient arc scenario), and that the chromitites crystallized from a tholeiitic magma (back-arc basin basalt type).

Life history aspects of the buthid scorpion Tityus forcipula (Gervais, 1843) with remarks on its thermal limits

Observations on the entire life history of scorpion species are uncommon, and these studies primarily focus on postembryonic development. So far, little is known on how changes in temperature or humidity could affect communities of scorpions. Here, we present data on the embryonic and postembryonic development of Tityus forcipula (Gervais, 1843), a scorpion living in the Colombian Central Cordillera that was subjected to different climate regimes. For a comparative approach, one group was raised under lower conditions (23–24°C) and another group was raised under higher temperatures (25–27°C, meaning a 2–3°C increase). Our results clearly demonstrate that T. forcipule reared under laboratory conditions is not able to thrive under constant higher temperatures. A minority of the latter group (< 10%) reached adulthood, but never reproduced. Of the 43 specimens kept under lower temperatures (with a mild diapause), 21 females and 19 males reached maturity in the 5th instar; only one female and two males required an extra molt to mature. Tityus forcipula specimens reached maturity after 463 days of postembryonic development. The average for embryonic development was 208 days, with an average of 12 neonates per litter. Twenty-four different morphometric measurements were taken from all specimens for each exuvium of the juveniles and the adult stage. The results indicated a relationship, albeit partly poorly developed, between the sexes, in several measured structures and the instars.

El Escondido tuff cone (38 ka): a hidden history of monogenetic eruptions in the northernmost volcanic chain in the Colombian Andes

El Escondido is a dacitic monogenetic volcano situated in the Samana monogenetic volcanic field, within the Central Cordillera of Colombia. The tuff cone was emplaced in a deeply incised and rainy mountainous zone, ca. 38 ky ago by an explosive eruption that affected not only the metamorphic and igneous basement but also the remnants of the ~ 154 ka Pela Huevos volcano. The El Escondido volcaniclastic deposits are composed of juvenile pumice and lithic fragments including dense volcanic rocks from the Pela Huevos volcano, as well as metamorphic and igneous rocks from the basement. The pumice shows tubes and spongy textures. The volcanic lithics are dominantly angular and fresh, and exhibit different mineralogy and whole-rock geochemistry in comparison to the pumice. Plagioclase and amphibole are ubiquitous; however, biotite and quartz crystals occur only in the pumice fragments (~ 70 wt% SiO2 volatile-free), whereas olivine and pyroxene crystals are only found in the volcanic lithics (~ 65 wt% SiO2 volatile-free). The El Escondido tuff cone is strongly eroded and Pela Huevos is a dome-like remnant in the SE sector. Because of this, along with the highly vegetated tropical zone where the volcanoes are emplaced as well as difficult political issues in the region, the edifices were not recognized until recently; this is why the younger cone was named “El Escondido” (which means “The Hidden”). These eruptions evidence that recent volcanism has occurred in a zone of the Central Cordillera that has been considered as non-volcanogenic in recent studies.

Origin of pre-mesozoic xenocrystic zircons in cretaceous sub-volcanic rocks of the northern Andes (Colombia): paleogeographic implications for the region

This paper reports the presence of xenocrystic zircons in sub-volcanic rocks (Guarco Andesite and Porphyritic Intrusives units) exposed in the northeast of the Western Cordillera of Colombia (WCC) and provides a new contribution to the understanding of the tectono-magmatic evolution of the area during the Upper Cretaceous associated with the geological history of the Caribbean Large Igneous Province (CLIP). The study area is located in an accretionary terrane constituted by a basement of oceanic affinity (Barroso Formation and San José de Urama Diabases unit), amalgamated against the northwestern South American margin and associated with the development of CLIP. The elemental and isotopic geochemical data (with an initial ratio of 87Sr/86Sr between 0.70334 and 0.70543 and εΝd between +6.25 and + 7.42) indicate an island arc environment for the formation of sub-volcanic rocks and a mantle wedge source area (and/or the arc itself), which presents subordinate levels of crustal material. U-Pb zircon ages by SHRIMP IIe and LA-ICP-MS show ages from the Mesoarchean to the Upper Cretaceous, with representative peaks of approximately 2700, 2100, 600 and 90 Ma. The younger age population is interpreted as the crystallization age of the studied rocks and indicates a spatial and temporal relationship with the basement rocks associated with the CLIP. The older zircons are interpreted as xenocrysts coming from terrigenous sediments that were dragged down into the subduction channel (reflecting crustal recycling processes through the mantle in subduction zones). Alternatively, the xenocrystic zircons could have come from the assimilation of crustal sediments that were previously deposited over the primitive arc. We suggest that the source areas of zircon xenocrysts probably are located close to the Arequipa Massif and the Marañon Complex inliers, and close to the ensialic Basement of the Central Cordillera of Colombia (CCCB). Using these source areas and paleogeographic/paleomagnetic models published by other authors, we propose two possible paleogeographic scenarios differentiated by the polarity of the subduction zone.

Two new species of Lejeuneaceae tribe Lejeuneeae (Marchantiophyta) from Colombia

Abstract We describe the new liverwort species Lejeunea ryszardii from montane rainforest in the Central Cordillera of Colombia (Dept. Quindío) and Rectolejeunea halinae from submontane rainforest in the Western Cordillera (Dept. Risaralda). Both species stand out by copious vegetative reproduction via caducous leaves. Lejeunea ryszardii resembles the Caribbean L. paucidentata in the leaf lobes with toothed margins and a narrow base but strikingly differs from the latter species in: 1) leaf margins with mamillose cells, which are sometimes crowned by a small papilla, and with scattered rhizoids with or without a tooth-like base; 2) lobules with narrowly elongate, curved, sharp tooth; 3) stem epidermis brownish and somewhat thick-walled; 4) copious production of caducous leaf lobes. Moreover, L. ryszardii is dark green to brown in color and probably dioicous while L. paucidentata is light green and autoicous. Rectolejeunea halinae resembles the neotropical R. flagelliformis in having ciliate caducous leaves but clearly differs from the latter in the pointed leaf tips, the presence of ocelli in underleaves, and the flagelliform shoots with flat, entire-margined underleaves. The discovery of these new species adds two further endemic taxa to the rich bryophyte flora of the Colombian Andes.

Erosion and regional exhumation of an Early Cretaceous subduction/accretion complex in the Northern Andes

ABSTRACTA multi-technique provenance analysis, together with whole-rock geochemistry from arc related volcano-sedimentary rocks of the Albian-Aptian Quebradagrande Complex (Central Colombian Andes, Northern Andes), were conducted to reconstruct the tectono-stratigraphic relations with the adjacent Early Cretaceous subduction/accretion Arquía Complex, in order to understand the tectonic modification of the Andean margin before the onset of the Andean orogeny.The presence of olivine, spinel, serpentine, high-pressure garnets and glaucophane in the sandstones of the Quebradagrande Complex suggests that the subduction/accretion Arquía Complex was a major source area during basin filling. Carboniferous and older detrital zircons suggest that the pre-Cretaceous continental basement of the Colombian Central Cordillera, which limits the Quebradagrande Complex to the east, was also a major basin source. Whole-rock geochemistry from associated volcanic rocks, showing suprasubduction to NMORB signature, is characteristic of a magmatic arc formed in thinned continental crust.Integration of the results with the Early Cretaceous record of the Central Cordillera indicates that the continental margin experiences a major slab-roll back event that promotes extensional tectonics, affecting the arc and facilitating the exhumation of a subduction/accretion complex. During the Late Cretaceous, both complexes were deformed and a new magmatic arc was formed. The extensional tectonics reflects the complex plate kinematic readjustments that affected western South America during the Cretaceous.

Diversity, structure and natural history of amphibians in the upper Claro River basin, a buffer zone of the National Natural Park Los Nevados, Central Cordillera of Colombia

We present an assessment on composition, diversity and structure of amphibians in three zones along an elevation gradient (2,400–3,000 m) in the Central Cordillera of Colombia.  For this purpose, we carried out two field trips in November 2014 and February 2015, covering rainy and dry seasons, respectively.  Diurnal (08:00–12:00 h) and nocturnal (18:00–22:00 h) visual encounter surveys were made without spatial restrictions.  The diversity for each zone (alpha) and for the entire landscape (gamma) was evaluated by the effective number of species, and the structure of the communities was analyzed by range-abundance curves.  The inequality factor for each of the sampling zones was also calculated.  A total of 15 species belonging to seven genera and three families were recorded, all of the order Anura.  Craugastoridae with 11 species (73.3% of richness) and Pristimantis (eight species) were the most diverse family and genus, respectively.  The average alpha diversity per zone was 6.6 effective species, with zone A being the most diverse with eight species.  In terms of beta diversity we found 2.5 effective communities at the landscape level, and differences between zones are given by the rare species, while the most abundant ones (e.g., Pristimantis uranobates) are shared between them.  It is presumed that the greater diversity of zone A is due to the lower elevation and better state of conservation if compared to the other two zones.  Of the total species recorded, three are threatened with extinction: Endangered (Hypodactylus latens, Osornophryne percrassa), and Critically Endangered (Niceforonia adenobrachia).  The finding of three yet undescribed species is highlighted.

Recent tectonic and volcanic influence on the fluvial dynamics of the Anaime River (Cajamarca, Central Cordillera of Colombia)

El valle del río Anaime, localizado en la parte central de la Cordillera Central, se encuentra en una zona con influencia tectónica importante por estructuras regionales que hacen parte de los Sistemas de Fallas de Palestina e Ibagué. Además de lo anterior, esta zona ha estado bajo influencia de eventos volcánicos regionales como producto de la actividad reciente durante los últimos 5000 años del Volcán Cerro Machín. En este trabajo se presenta un análisis geomorfológico cuantitativo a partir del uso de diferentes índices geomorfológicos tales como la curva e integral hipsométrica, el índice de forma de la cuenca, el factor de asimetría, la relación ancho-altura del valle, perfiles longitudinales normalizados y el índice de extensión pendiente-relativa con el objetivo de analizar la influencia de la tectónica y la actividad volcánica en la evolución reciente del paisaje en el río Anaime. Los análisis geomorfológicos muestran que la evolución reciente del paisaje a lo largo de la parte alta del valle del río Anaime ha estado controlada por caídas locales en el nivel base inducidas por actividad tectónica reciente de la Falla de Palestina y con menor influencia por la Falla de Ibagué. La presencia de múltiples knickpoints móviles a lo largo de algunos tributarios del río Anaime y su correlación positiva con las estructuras asociadas a la Falla de Palestina permiten suponer que esta estructura ha estado activa. Por otro lado, la actividad Holocena del Volcán Cerro Machín ha inducido ajustes en el paisaje y la red de drenaje con el objetivo de compensar el gran volumen de material piroclástico depositado sobre el valle del río Anaime, anomalías que han perdurado en escalas de tiempo de entre 102 a 103 años y que pueden ser analizadas con la curva hipsométrica y los perfiles longitudinales normalizados de algunas quebradas tributarias al río Anaime.

The Paleogene arcs of the northern Andes of Colombia and Panama: Insights on plate kinematic implications from new and existing geochemical, geochronological and isotopic data

The northern Andes of Colombia comprise two non-cogenetic Paleogene arcs formed in contrasting geodynamic settings including continental and oceanic domains. New whole-rock geochemistry and isotopic constraints, together with a review of 332 geochemical, 76 isotopic and 204 geochronological data from Paleocene to Eocene volcanic and plutonic rocks exposed in central and western Colombia and Panama, are used to evaluate cause-effect relations between regional plate kinematics and the spatio-temporal distribution of the circum-Caribbean magmatic arcs. Short-lived, ~60–45 Ma arc-like magmatism in the Central Cordillera of Colombia was emplaced in a thickened continental crust due to the oblique subduction of the Caribbean oceanic plate underneath South America, as suggested by the high Sr/Y ratios. Conversely, the Panama Arc, and its poorly explored extension in the northwestern segment of the Western Cordillera of Colombia document a major phase of tholeiitic to calc-alkaline arc magmatism between ~71 Ma and ~34 Ma, mostly derived from a hydrated mantle wedge, and emplaced in an oceanic plateau crust. This arc record a major phase of magmatic activity between 40 Ma and 50 Ma that can be associated to changes in the convergence direction and subduction rates of the Farallon plate.Farther to the south, in the Pacific region of Colombia, Eocene arc-related rocks from the Timbiqui Complex show a geochemical signature that suggests a magmatic origin from melting of both a subduction-modified mantle and lower tectonically thickened crust. A possible interpretation for the Pacific and Western Colombia-Panama Arc systems, and its analogous in Ecuador, recall an Aleutian-type convergent margin in which the continental arc laterally switches to a purely oceanic system along the trailing edge of the Caribbean plate as consequence of eastward subduction of the Farallon plate.