Guiana Shield Research Articles

Upper-lithospheric structure of northeastern Venezuela from joint inversion of surface-wave dispersion and receiver functions

Abstract. We use 1.5 years of continuous recordings from an amphibious seismic network deployment in the region of northeastern South America and the southeastern Caribbean to study the crustal and uppermost mantle structure through a joint inversion of surface-wave dispersion curves determined from ambient seismic noise and receiver functions. The availability of both ocean bottom seismometers (OBSs) and land stations makes this experiment ideal to determine the best processing methods to extract reliable empirical Green's functions (EGFs) and construct a 3D shear velocity model. Results show EGFs with high signal-to-noise ratio for land–land, land–OBS and OBS–OBS paths from a variety of stacking methods. Using the EGF estimates, we measure phase and group velocity dispersion curves for Rayleigh and Love waves. We complement these observations with receiver functions, which allow us to perform an H-k analysis to obtain Moho depth estimates across the study area. The measured dispersion curves and receiver functions are used in a Bayesian joint inversion to retrieve a series of 1D shear-wave velocity models, which are then interpolated to build a 3D model of the region. Our results display clear contrasts in the oceanic region across the border of the San Sebastian–El Pilar strike-slip fault system as well as a high-velocity region that corresponds well with the continental craton of southeastern Venezuela. We resolve known geological features in our new model, including the Espino Graben and the Guiana Shield provinces, and provide new information about their crustal structures. Furthermore, we image the difference in the crust beneath the Maturín and Guárico sub-basins.

Monograph of tribe Sipaneeae (Rubiaceae, Ixoroideae). A Neotropical group with its center of diversity on the Guiana Shield

The tribe Sipaneeae (subfamily Ixoroideae) includes the genera Chalepophyllum (3 spp.), Dendrosipanea (3 spp.), Limnosipanea (3 spp.), Maguireothamnus (3 spp.), Neblinathamnus (2 spp.), Neobertiera (5 spp.), Pteridocalyx (1 sp.), Sipanea (17 spp.), Sipaneopsis (8 spp.), and Steyermarkia (1 sp.), for a total of 44 species. This tribe has its center of diversity on the Guiana Shield (northern South America), where 9 of the 10 genera occur. Only Sipanea and Limnosipanea are also present on the Brazilian Shield and the Orinoquía Region with a total of 4 species, while Steyermarkia, Sipanea and Limnosipanea are present in Central America with one species each. The genera Sipaneopsis, Chalepophyllum, and Dendrosipanea are endemic to white sand areas of the Amazon Basin. The habit in the tribe Sipaneeae ranges from herbs (terrestrial, amphibian or rarely aquatic), subshrubs, shrubs to treelets. Within the tribe, Chalepophyllum, Dendrosipanea, Neobertiera, Pteridocalyx and Sipanea are heterostylous, while the other genera are homostylous. Several recent articles have been dedicated to the description of new species in this tribe, and only Limnosipanea spruceana var. macrantha is newly described here. In the present work 21 names are newly typified; a list of these names is present at the end of the taxonomic treatment. For all the taxa of this tribe, full synonymy, typification, description, ecological observations, geographic distribution, illustrations, IUCN conservation assessment, and cited specimens are provided.

Historical biogeography highlights the role of Miocene landscape changes on the diversification of a clade of Amazonian tree frogs

The diversification processes underlying why Amazonia hosts the most species-rich vertebrate fauna on earth remain poorly understood. We studied the spatio-temporal diversification of a tree frog clade distributed throughout Amazonia (Anura: Hylidae: Osteocephalus, Tepuihyla, and Dryaderces) and tested the hypothesis that Miocene mega wetlands located in western and central Amazonia impacted connectivity among major biogeographic areas during extensive periods. We assessed the group’s diversity through DNA-based (16S rRNA) species delimitation to identify Operational Taxonomic Units (OTUs) from 557 individuals. We then selected one terminal for each OTU (n = 50) and assembled a mitogenomic matrix (~14,100 bp; complete for 17 terminals) to reconstruct a Bayesian, time-calibrated phylogeny encompassing nearly all described species. Ancestral area reconstruction indicates that each genus was restricted to one of the major Amazonian biogeographic areas (western Amazonia, Guiana Shield and Brazilian Shield, respectively) between ~10 and 20 Mya, suggesting that they diverged and diversified in isolation during this period around the Pebas mega wetland. After 10 Mya and the transition to the modern configuration of the Amazon River watershed, most speciation within each genus continued to occur within each area. In Osteocephalus, only three species expanded widely across Amazonia (< 6 Mya), and all were pond-breeders. Species with other breeding modes remained mostly restricted to narrow ranges. The spectacular radiation of Osteocephalus was probably driven by climatic stability, habitat diversity and the acquisition of new reproductive modes along the Andean foothills and western Amazonia. Our findings add evidence to the importance of major hydrological changes during the Miocene on biotic diversification in Amazonia.

The recovery of logged forests proves that a viable management is possible in the Venezuelan Guayana Shield

Aim of study: To compare the diversity and biomass of logged forests, with different ages after harvesting and the risk of their degradation to liana forests.&#x0D; Area of study: We studied 18 plots at the central zone of the Imataca Forest Reserve (Guayana shield), Venezuela.&#x0D; Material and methods: We used 1-ha plots, to measure individuals with dbh &gt; 10 cm in control plots (0 years) and in logged plots with 3, 9, 12, 15 and 18 years after logging. The main variables evaluated were enlarge importance index (EII), richness (R), Shannon-Weaner index (H´), Alpha Fischer (α), basal area for commercial species (BA_comm), above-ground carbon (C) and lianas abundance at the understory (Lianas_%Au).&#x0D; Main results: Diversity variables (R: 62-77 spp ha-1, p: 0.117-0.838; H´: 2.8-3.4, p: 0.181-0.677; α: 18.6-25.4, p: 0.293-0.922) and biomass (89.6-180.2 MgC ha-1, p: 0.171-0.895) did not have significant differences between control and most of the logged plots. Only the 18 years-old forests had statistically higher values of diversity (R: 81-94 spp ha-1, p: 0.000; H´: 3.8-3.9, p: 0.000; α: 26.8-31.7, p: 0.000), perhaps due to a high impact skidding operation. Commercial species were not recovering after logging.&#x0D; Research highlights: Forest management can be viable in this area, but it requires reduced impact logging techniques and better silvicultural systems to guarantee future harvest of high value commercial timber.

A new species of rain frog (Anura: Strabomantidae: Pristimantis) from the Guiana Shield and amended diagnosis of P. ockendeni (Boulenger, 1912)

Pristimantis is already the most speciose genus among vertebrates, yet the current number of species remains largely underestimated. A member of the P. unistrigatus species group from the Guiana Shield has been historically misidentified as P. ockendeni, a species described from southern Peru. We combined mitochondrial (16S and COI) and nuclear (RAG1) loci, external morphology, skull osteology (μ-CT scan), vocalization (advertisement and courtship calls), geographic distribution and natural history data to differentiate the Guiana Shield populations from P. ockendeni, and describe them as a new species. The new species is crepuscular and nocturnal and inhabits the understory of unflooded (terra firme) forests in Brazil, Guyana and Suriname. It is phylogenetically related to P. arda­lonychus, P. martiae and undescribed species from Brazilian Amazonia. The new species notably differs from P. ockendeni and its congeners in the P. unistrigatus species group occurring in the Guiana Shield by the combination of the following characters: absence of dentigerous processes of vomers, presence of vocal slits in males, body size (SVL 16.2–20.7 mm in males and 21.4–25.7 mm in females), advertisement call (call with 4–6 notes, call duration of 158–371 ms and dominant frequency of 3,466–4,521 Hz) and translucent groin coloration in life. To facilitate the recognition and description of cryptic species previously hidden under the name P. ockendeni, we provide an amended diagnosis of this taxon based on external morphology and advertisement call of specimens recently collected nearby the type locality and additional localities in southwestern Amazonia.

A New Species of Sternopygus (Gymnotiformes: Sternopygidae) from the Atlantic Coast of the Guiana Shield

Sternopygus sabaji, new species, is described from the Atlantic drainages of the Guiana Shield region of South America using traditional methods of morphometrics and meristics and microcomputed tomography (µCT) scans for osteological analysis. The new species is diagnosed from all other species of Sternopygus by the lack of dentition on the anteroventral surface of the endopterygoid and by the possession of a wider mouth. It further differs from its congeners by the following combination of characters: reduced humeral spot with low-contrast and poorly defined margins, possession of a light-colored mid-lateral stripe along posterior portion of lateral line, possession of 1–3 dark saddle-like markings along dorsum of smaller individuals, and a relatively low precaudal vertebrae count. This work provides the first description of a species of Sternopygus that is endemic to the Guiana Shield, joining S. astrabes and S. macrurus in elevating the species richness of the clade in that region to three species and the total number of valid Sternopygus to ten species.

A new Chiasmocleis (Anura: Microhylidae) from the eastern Guiana Shield with an amended definition of C. haddadi Peloso, Sturaro, Forlani, Gaucher, Motta, &amp;amp; Wheeler, 2014

The existence of an unnamed (candidate) species from French Guiana and the state of Amapá (Brazil) closely related to Chiasmocleis haddadi has been hypothesized in previous DNA-based studies. With an integrative use of genetic, morphological and acoustic data we confirm that these populations are indeed distinct from C. haddadi and all other known congeners. We herein describe and name this new species, and amend the definition of C. haddadi since the type-series and its original diagnosis included specimens of the new species. Geographically, the new species occurs eastward of its sister species C. haddadi from which it can be distinguished by having a larger body, a proportionally smaller eye and a distinct dorsal colouration. We suspect that the new species breeds in the leaf litter and that tadpoles undergo endotrophic development whereas co-occurring C. haddadi and C. hudsoni lay clutches in the leaf litter nearby standing water of temporary ponds where exotrophic tadpoles complete their development. This new species is a new addition to the already long list of animals being endemic to the easternmost part of the Guiana Shield, a region identified as a singular bioregion within Amazonia by previous research.

Diversification of the Pristimantis conspicillatus group (Anura: Craugastoridae) within distinct neotropical areas throughout the Neogene

Determining the relative importance of dispersal and vicariance events across neotropical regions is a major goal in biogeography. These events are thought to be related to important landscape changes, notably the transition of Amazonia toward its modern hydrological configuration ca. 10 million years ago. We investigated the spatio-temporal context of the diversification of one of the major lineages of Pristimantis, a widespread and large genus of direct-developing Neotropical frogs. We gathered a spatially and taxonomically extensive sampling of mitochondrial DNA sequences from 754 Pristimantis gr. conspicillatus specimens, which led to delimiting 75 Operational Taxonomic Units (OTUs). Complete mitogenomes of 35 of these OTUs were assembled and collated with two nuDNA loci to reconstruct a time-calibrated phylogeny. We identified five major clades that diverged around the Oligocene-Miocene transition and that are largely restricted to distinct Neotropical regions i.e. Western Amazonia (P. conspicillatus clade), the Brazilian Shield (P. fenestratus clade), the Atlantic Forest (P. ramagii clade), the Guiana Shield (P. vilarsi clade) and the northern Andes (P. nicefori clade). The majority of the diversification events within these clades occurred in-situ from the early Miocene onward. Yet, a few ancient dispersal/vicariance events are inferred to have occurred among trans-Andean forests, the Atlantic Forest, the Brazilian and the Guiana Shields, but almost none in the last 10 Ma. The radical landscape transformations during the Miocene caused by the Andean orogeny and hydrological barriers such as the Pebas System and the subsequent transcontinental configuration of the Amazon drainage is a likely explanation for the isolation of the different clades within the P. gr. conspicillatus.

Psychogeography Reimagined

A majority of the scholarship on psychogeography focuses on the impact of architecture, urban environments, and the physical construction of space and place on the psyche, emotions, behaviour, and health of individuals and society. Some use this approach as a way to delve into the soul of a city. Theoretical work on historical ecology, spiritual ecology, and spiritual geography offer new perspectives on the human-landscape dynamic, yet they lack psychological depth. This article explores the psychogeographical dimension of non-urban, Indigenous and novel landscapes, with an emphasis on early childhood development and spatial justice. Case studies—on the Akawaio in the Guiana Highlands of South America; and Indigital Schools, an educational technology startup in Australia—demonstrate the applicability of psychogeography for diverse contexts. Ultimately, this reimagining blazes a trail deeper into the soul(s) of the land.

Chromosomal Diversification in Pseudacanthicus Species (Loricariidae, Hypostominae) Revealed by Comparative Mapping of Repetitive Sequences.

Simple SummaryThe fishes of the Loricariidae family have a huge genetic diversity, mainly involving variations in the number and shape of chromosomes. The recognition of the species genus Pseudacanthicus is complex due to the large diversity of forms and limited knowledge of their genetic diversity. In this study, the karyotypes of three Pseudacanthicus species were comparatively analyzed using classical and molecular methods. They presented the same diploid number, but with different compositions of repetitive DNA sequences. Such information can be useful for the recognition of distinct species, in addition to providing important insights into the real biodiversity of this important group of Neotropical fish.Pseudacanthicus is a genus of Neotropical fish with eight valid species, in addition to numerous lineages not formally identified. It occurs along the Amazon and Tocantins River basins, in Suriname and in the Guiana shield. There are no karyotypic data in the literature for species of this genus. Here, the karyotypes of three Pseudacanthicus species (P. spinosus, P. leopardus and Pseudacanthicus sp.) were comparatively analyzed by classical cytogenetics and fluorescence in situ hybridization using 18S and 5S rDNA probes, U2 snDNA and telomeric sequences. The analyzed species presented 52 chromosomes and KF = 18 m + 34 sm. Constitutive heterochromatin occurred in blocks on a few chromosomes. The 18S rDNA occurred in a single pair; interestingly, P. leopardus presented only one locus of this sequence in its diploid genome. The 5S rDNA sequence occurred in only one pair in P. leopardus, and in multiple sites in Pseudacanthicus sp. and P. spinosus. The snDNA U2 occurred in only one pair in all analyzed species. Telomeric sequences did not show interstitial sites. Although Pseudacanthicus species share the same 2n and KF, repetitive sequence analysis revealed karyotypic diversity among these species. The occurrence of DNA double-strand breaks related to fragile sites, unequal crossing over and transpositions is proposed as the mechanism of karyotypic diversification, suggesting that the conservation of the karyotypic macrostructure is only apparent in this group of fish.

A new genus in the diverse Andean Pedaliodes complex uncovered using target enrichment (Lepidoptera, Nymphalidae)

AbstractA new genus of Neotropical Satyrinae butterflies, Viloriodes Pyrcz &amp; Espeland gen. n. is described in the Pedaliodes Butler complex comprising 11–13 genera and more than 400 species. Support for the new genus is provided by a phylogenetic analysis based on target enrichment (TE) data including 618 nuclear loci with a total of 248,940 nucleotides, and the mitochondrial gene cytochrome oxidase subunit 1 (COI). Five species, whose DNA sequences were obtained by TE during this study, form a strongly supported clade sister to the large clade comprising Pedaliodes and four other genera. Complementary COI analysis confirms the monophyly of Viloriodes gen. n., with the above five plus eight other species clustering in highly supported clades in both Bayesian Inference and Maximum Likelihood analyses, and a TE + COI concatenated tree. Based on molecular and morphological data, 30 species are assigned to Viloriodes gen. n. The new genus can be recognized by a set of subtle morphological characteristics of colour patterns and male and female genitalia. An analysis of divergence times indicates that Viloriodes gen. n. and Steromapedaliodes Forster separated around 5.9 Mya. Viloriodes gen. n. has a wider geographic distribution than any other genus of the Pedaliodes complex, being found from central Mexico to northern Argentina and to the Guyana Shield, typically occurring at lower elevations than Pedaliodes.

The Rudgea hostmanniana complex (Rubiaceae) in the Guiana Shield region

A taxonomic revision of the Rudgea hostmanniana complex in the Guiana shield region is presented. This group includes species with sheathing stipules bearing dorsal appendages, thick glabrous leaves lacking domatia, inflorescences thyrsoid to glomerulate but not regularly dichotomous, a calyx tube absent or very short, a corolla tube 2–7(–13) mm long, and fruits usually brownish when immature and turning red or orange at maturity. Eight species are recognized, among which Rudgea billietiae, endemic to Kaw Mountain in French Guiana, is newly described and illustrated; it is assessed as Endangered according to IUCN criteria. The other species are R. bolivarensis, R. cornigera, R. coussareoides, R. hostmanniana, R. maypurensis, R. pungens, and R. tanaosepala. A key to the species is presented, as well as a table summarising their diagnostic characters.

Revision of Carapichea (Rubiaceae-Psychotrieae) in the Guianas, with two new combinations and transfer of three species to Notopleura

Background and aims – The genus Carapichea (Rubiaceae), recently resurrected and separated from Psychotria, currently includes 24 Neotropical species and is morphologically heterogeneous. A revision of the genus in the Guianas is presented here, as part of the authors’ work on the Rubiaceae treatment in the Flora of the Guianas series. Material and methods – This paper is based on a study of herbarium specimens from BBS, BM, BR, BRB, CAY, INPA, K, P, P-JJR, and U; type specimens from other herbaria were consulted online. Some of the species were also studied in the field by the authors. Normal practices of herbarium taxonomy have been applied. Results – Three species previously included in Carapichea (C. altsonii, C. nivea, and C. sandwithiana) show aberrant characters for the genus and are transferred to Notopleura; new combinations are published for the former two (N. altsonii and N. nivea). Eight species of Carapichea, one of them still imperfectly known, are recorded from the Guianas; a ninth species, C. araguariensis, is included in this revision as it is expected to occur in the region. New combinations are published for two species: Carapichea galbaoensis and C. squamelligera, based on Psychotria galbaoensis and P. squamelligera, respectively; the former species was previously included in synonymy of C. guianensis, which is here redefined in a narrower sense. The delimitation of C. ligularis is expanded to include C. pacimonica as a synonym. The first records of C. adinantha in French Guiana – and the Guiana Shield – are documented. The taxonomy of the two remaining species, C. tillettii and C. urniformis, is left unchanged. For every species a complete description is presented, as well as data on distribution, ecology, phenology, local names (when known), and a list of collections studied.

Mercury background values in soils and saprolites in the gold-rich greenstone belt of Suriname, Guiana Shield: The role of parent rock and residual enrichment

In order to develop criteria to distinguish polluted from unpolluted materials in areas subjected to artisanal small-scale gold mining, background mercury values were established in 62 natural soil and saprolite profiles on 16 different parent rock types in the greenstone belt of Suriname. Hg values in pristine topsoils often amount to up to 200 μg/kg, about 100 times higher than Hg in common parent rocks. Additional analyses of 40 major and trace elements in two pilot profiles show that Hg values are strongly correlated to Fe, Cr and V values, which suggests that just as those elements Hg is residually enriched in topsoils by laterisation processes. In the deeper pallid zones of the profiles, Hg has often been leached almost completely together with iron by reducing groundwater action. In this way the range of Hg values within a single profile can be greater than between profiles. Maximum and average Hg values of 196 samples from the 16 different parent rock types fall apart into two main groups. Felsic parent rocks with predominance of quartz and feldspar have maximum Hg values around 100 μg/kg and averages around 50 μg/kg, mafic ones with less silica and higher Fe, Mg and Ca have maximum values around 250–300 μg/kg and averages around 150 μg/kg. In general the natural soil and saprolite Hg values are in the same order of magnitude as many published mine tailings and stream sediments, and therefore cannot be used to separate polluted from unpolluted materials.

Geological characteristics of the Serra do Navio Formation, Guiana Shield, Brazil, and its manganiferous ores: queluzite as a source rock of oxide and carbonate manganese ores

Geological characteristics of the Serra do Navio Formation, Guiana Shield, Brazil, and its manganiferous ores: queluzite as a source rock of oxide and carbonate manganese ores

Ongoing landscape transience in the eastern Amazon Craton consistent with lithologic control of base level

AbstractGeomorphic features such as drainage captures, knickpoints, paleochannels, and wind‐gaps have long been observed in the Amazon region and typically thought to result from climate change and intraplate tectonics. The influence of rock type as a trigger of these landscape transients is largely overlooked. In the eastern Guiana Shield of the Amazon Craton, shield rivers flow over to the sedimentary rocks of the Amazon Basin across a sharp lithologic transition before their confluence with the Amazon River. This transition is marked by an expressive main escarpment (ME) formed over resistant sandstones of the basal units of the Amazon Sedimentary Basin. Here, systematic patterns of divide migration and river captures provide a natural laboratory to study the influence of rock type in landscape transience in a cratonic setting. Through quantitative geomorphologic analysis of the topography, drainage divides, and rivers, we investigate if this sharp lithologic transition contributed to the observed patterns of drainage rearrangement. The results revealed that rivers of larger drainage areas flowing across shorter lengths over the resistant rocks of the ME systematically capture neighbouring basins. We argue that, as tributaries draining the shield respond to downcutting and/or base‐level fall of the Amazon River, bedrock incision and knickpoint propagation are differentially slowed down by the resistant rocks according to their incision capacity, generating a series of transients such as drainage capture and divide migration. The widespread and systematic geomorphic features suggest this mechanism could be an important autogenic control of drainage network rearrangement in the Amazon region and other post‐orogenic landscapes as well. The protracted exhumation of resistant rocks in cratons and intraplate settings may keep landscapes in perpetual disequilibrium depending on their lithological complexity and offer an exceptional natural laboratory to study landscape dynamics associated with rock type.

Species diversity and systematics of the Leptodactylus melanonotus group (Anura, Leptodactylidae): review of diagnostic traits and a new species from the Eastern Guiana Shield

The Leptodactylus melanonotus species group is an anuran clade widely distributed in the Neotropics. This clade harbours many species that are difficult to identify because of incomplete taxonomic knowledge, ambiguous species boundaries and distribution. Here we expand the understanding of species diversity of this Leptodactylus clade by analysing mtDNA sequences for over 600 individuals, delimiting Operational Taxonomic Units (OTUs), and updating species identifications and distributions by linking sequences to morphotypes and calls. Also, we review the morphological and acoustic traits traditionally used as diagnostic characters of species within this group. The DNA-based species delimitation analyses yielded 57 OTUs. Given that only 19 taxa are currently recognized as valid species, our results suggest the existence of many unnamed species within the L. melanonotus group. After reassessing morphological traits in the group, we concluded that the combined use of dorsolateral fold, upper lip stripe, and belly colouration is sufficiently informative for species identification in most cases, especially when associated with data on geographic distribution and habitat use. Regarding advertisement calls, the patterns of amplitude and frequency modulation, calling rate, and dominant frequency were also informative for species discrimination. Furthermore, we designate a neotype for L. wagneri, for which we also describe the advertisement call, and make comparisons with congeners of the L. melanonotus group, especially with the partially sympatric L. leptodactyloides. Lastly, we name and describe a new species endemic to the Eastern Guiana Shield. Patterns of distribution and habitat use in the L. melanonotus group revealed that sympatric occurrences are more commonly found among distantly related species, whereas allopatric occurrences correspond to closely related ones. Speciation between closely related species of the group seems to be related to ecological divergence (open vs. forest habitats) in parallel with clear morphological and acoustic differentiation. http://www.zoobank.org/urn:lsid:zoobank.org:pub:867A8EA9-A8F2-4FA4-8746-A0D9BB2E4286

The Roraima Alkaline Province: A cretaceous alkaline province in the Amazonian Craton

The rift-related magmatism that generated the Roraima Alkaline Province (RAP) took place along main faults and shear zones that stretch out for circa 200 km in the central Guyana Shield, northern Amazonian Craton. As such, RAP is the first alkaline province proposed to the Guyana Shield. It encompasses felsic and mafic rock types – the former constituting foid-syenites and phonolites, while the latter including lamprophyre, tephrite and tephriphonolite dikes. In this paper, we examine whether these rocks are cogenetic and construct a genetic model for RAP with coupled petrography, geochemistry, and U-Pb zircon geochronology. Our data show that the RAP rocks are nepheline-normative, metaluminous to peralkaline, and miaskitic to agpaitic. The geochemical signatures indicate that fractional crystallization was the primary mechanism that produced the compositional variability between mafic and felsic magmas. Increasing peralkalinity is attributed to extensive alkali feldspar fractionation. Elemental, isotopic, geochronological and petrographic features show that crustal assimilation also played a role in magma genesis. Both ages obtained in this study and compiled from previous works range from 100 to 116 Ma, indicating that the Cretaceous alkaline magmatism in the Guyana Shield was short-lived. The Sr-Nd isotopic signatures of the least-contaminated samples require mixing of depleted and enriched mantles. Depleted-mantle model ages obtained from the least-contaminated samples fall in relatively short intervals, between 548 and 657 Ma, which coincide with the model ages of the Central Atlantic Magmatic Province (CAMP) tholeiites, suggesting that the same metasomatic event affected both Mesozoic alkaline and tholeiite magmatic occurrences of the Guyana Shield. It is concluded that the lithospheric mantle metasomatism took place shortly before magmatism, triggered by an extensional tectonic event involving the Tacutu rifting and the opening of the Atlantic.

The discovery of Scaphyglottis punctulata (Orchidaceae: Laeliinae) in the highlands of Brazilian Amazonia with a key to the species of the region

The genus Scaphyglottis Poepp. &amp; Endl. presents 78 species and occurs from Mexico to Brazil. Scaphyglottis punctulata (Rchb.f.) C.Schweinf. is known from various high elevation locations from Panama to Bolivia. Here, we report new records in two regions of the Brazil portion of the Guiana Shield. We provide a detailed description, photographic plates, updated distribution map, ecological and taxonomic comments for S. punctulata, and an identification key for Scaphyglottis species from the Brazilian portion of the Guiana Shield.

Influence of Local Climate and ENSO on the Growth of Cedrela odorata L. in Suriname

In this study, we used retrospective dendroclimatological analyses to explore whether El Niño Southern Oscillation (ENSO) and local precipitation patterns have an influence on tree growth in Suriname, a country located on the Guiana Shield, as annual precipitation patterns on the Guiana Shield are related to ENSO. Discs were taken from 20 trees of Cedrela odorata, whose stem forms very distinct annual growth rings, for tree ring analyses. The trees grew in unmanaged tropical wet forests of Suriname. The tree-ring series of individual trees started between 1836 and 1931 and extended over a period of 84–180 years. The 20 dated series were utilized for constructing a tree-ring chronology. Unlike many other studies that used local anomalies such as flood pulse, precipitation, and drought events to describe the influence of El Niño on tree growth, we used monthly precipitation and ENSO indices as predictors of tree growth to calculate response and correlation functions. The study observed that tree ring growth of Cedrela odorata is influenced by precipitation in August and June of the current year and in August of the previous year, as well as by the ENSO indices SSTA, TSA, TNA, and NAO. Systematic increases in the strength of the El Niño southern oscillation (ENSO) teleconnection due to climate change could affect the growth of trees on the Guiana Shield.