The PreColumbian Amazon had a Population of at Least One Million

Parts of the Amazon previously thought to have been almost uninhabited were really home to thriving populations of up to a million people, new research shows.

Archaeologists have uncovered evidence that there were hundreds of villages in the rainforest away from major rivers, and they were home to different communities speaking varied languages who had an impact on the environment around them.

Huge parts of the Amazon are still unexplored by archaeologists, particularly areas away from major rivers. People had assumed ancient communities had preferred to live near these waterways, but the new evidence shows this was not the case.

The discovery fills a major gap in the history of the Amazon, and provides further evidence that the rainforest -- once thought to be untouched by human farming or occupation -- has in fact been heavily influenced by those who lived in it.

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Was Amazonia Really Tamed by PreColumbian Natives?

Comment on Clement et al. 2015 ‘The domestication of Amazonia before European conquest’

Authors:

McMichael et al

Extract:

Clement et al. [1] paint a picture of cultural landscapes blanketing Amazonia prior to European arrival to the Americas in their recent publication entitled ‘The domestication of Amazonia before European conquest’. A colourful narrative indeed, but here we would like to comment on their misinterpretation of previously published literature, use of data that may not be associated with pre-Columbian activities, and the extrapolative nature of their review both in time and across space.

The PaleoPosition of the Amazonian Craton in the Calymmian MesoProterozoic

Reassessment of Aguapeí (Salto do Céu) Paleomagnetic pole of the Amazonian Craton and implications for Proterozoic supercontinents

Authors:

D’Agrella-Filho et al

Abstract:

The Aguapei paleomagnetic pole obtained for mafic sills and dykes from Salto do Céu region at the western margin of the Amazonian Craton constrains its links with Baltica and Laurentia in Rodinian reconstructions. A new U-Pb age on baddeleyites at 1439 ± 4 Ma for the intrusives, constrasts strongly with a previous Ar-Ar age at 981 ± 2 Ma, with important consequences for paleogeographic reconstructions. We report new paleomagnetic and magnetic anisotropy results for sills from the Salto do Céu region and reassess the paleomagnetic data in view of the new geochronological age. A total of 155 samples were collected from thirteen new paleomagnetic sampling sites, five of them corresponding to sedimentary rocks located at the borders of the sills in an attempt to perform baked contact tests. After thermal and alternating field demagnetization, the sills provided a characteristic magnetic component at Dm = 208.2°, Im = 68.5° (N = 8, α95 = 6.4°), with a corresponding paleomagnetic pole at 46.4°S; 277.0°E (A95 = 10.2°). Directions obtained in this study are similar to those reported previously for other mafic sills and dykes in the same region. A pole integrating the new results for the sills with those of the previous Aguapeí pole is situated at 56.0°S; 278.5°E (A95 = 7.9°). This new combined Salto do Céu pole supersedes the previous Aguapeí pole. Magnetic mineralogy studies, optical and electronic microscopy indicates PSD magnetite as the main magnetic carrier in these rocks. The baked contact tests were inconclusive, but the similarity between Salto do Céu pole and other high-quality poles with ages around 1420-1430 Ma suggests they carry a primary thermoremanence of that age. The Salto do Céu and other coeval poles are compatible with a connection between Amazonia and Baltica at the Mesoproterozoic in a paleogeographic configuration slightly different from SAMBA (South America-Baltica). At the same time, the new geochronological and paleomagnetic data imply that all paleogeographic interpretations for the position of Amazonia in Rodinia based on the previously published Aguapeí pole (and now renamed as Salto do Céu pole) must be revised.

Contrary Report: PreColumbian Populations Only Impacted Amazon Rain Forest Within a Day's Walk of the Rivers

New research led by Florida Institute of Technology shows that the impacts of indigenous people prior to European contact impacted riverside forests, but that such impacts were largely limited to an area within a day's walk from a river.

The findings by the international team of archaeobotanists, paleoecologists and ecologists will be published online in the paper "Anthropogenic influence on Amazonian forests in prehistory: An ecological perspective" on Oct. 28 in the Journal of Biogeography.

The new research, conducted using plant fossils, estimates of mammal density, remote sensing and human population modeling, reinforces that Amazonian forests may be very vulnerable to disturbance by logging , mining and other large enterprises. The study refutes an emerging theory from some archaeologists and anthropologists that Amazonian rain forests are the result of ancient managed landscapes - a notion that undermines the ecological view of these forests as fragile ecosystems.

"Nobody doubts the importance of human actions along the major waterways," said Mark Bush, professor of biological sciences at the Florida Institute of Technology and the lead author of the paper. "But whether humans had a greater impact on the ecosystem than any other large mammal has yet to be established in much of western Amazonia."

Dolores Piperno, curator of archaeobotany and South American archaeology at the American Museum of Natural History and co-author of the study, said the recent emphasis on Amazonia as a manufactured and domesticated landscape overstates the facts.

"At nearly the size of the continental United States, Amazonia is a vast landscape with considerable biotic and abiotic heterogeneity. Extrapolations being made from relatively few archaeological sites mainly located along water courses as to the overall effect of prehistoric human occupation must be tempered in the face of available and yet-to-be-accumulated empirical data."

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Determining the Lifestyles of PreColumbian Amazonian Tribes Through Linguistics

In my class on October 5, 2015, we talked about how ancestral languages can be reconstructed on the basis of their present-day descendants and how such linguistic reconstructions (particularly reconstructions of the vocabulary) can be used to reimagine the lives of the speakers of such ancestral languages. While most of our examples in class dealt with Indo-European languages (with a brief foray into the Polynesian world), here I would like to present another example where the same sort of socio-cultural reconstruction can be done on the basis of unwritten languages who offer us a rare glimpse into the lives of the their speakers’ linguistic ancestors. This example concerns three indigenous South American language families: Arawakan, Tukanoan, and Nadahup. These languages are spoken in the Upper Rio Negro region, on the border of Columbia and Brazil (see the map on the left adapted from muturzikin.com). The present-day Arawak languages are shown in pale-green, Tukanoan languages are shown in yellow, and Nadahup languages in brown. (The best-known language in the Nadahup family—at least in linguistic circles—is Nadëb, which exhibits the rarest Object-Subject-Verb order, found only in a handful of languages around the world, 4 in the WALS sample.) Of the three families, only the Nadahup is limited to this region, while Tukanoan languages are also spoken elsewhere through South America and Arawakan languages are found from Brazil to the Caribbean.

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hat tip Randy.

Amazon Rainforest NOT Pristine, BUT Heavily Cultivated & Populated in PreColumbian Times

The domestication of Amazonia before European conquest

Authors:

Clement et al

Abstract:

During the twentieth century, Amazonia was widely regarded as relatively pristine nature, little impacted by human history. This view remains popular despite mounting evidence of substantial human influence over millennial scales across the region. Here, we review the evidence of an anthropogenic Amazonia in response to claims of sparse populations across broad portions of the region. Amazonia was a major centre of crop domestication, with at least 83 native species containing populations domesticated to some degree. Plant domestication occurs in domesticated landscapes, including highly modified Amazonian dark earths (ADEs) associated with large settled populations and that may cover greater than 0.1% of the region. Populations and food production expanded rapidly within land management systems in the mid-Holocene, and complex societies expanded in resource-rich areas creating domesticated landscapes with profound impacts on local and regional ecology. ADE food production projections support estimates of at least eight million people in 1492. By this time, highly diverse regional systems had developed across Amazonia where subsistence resources were created with plant and landscape domestication, including earthworks. This review argues that the Amazonian anthrome was no less socio-culturally diverse or populous than other tropical forested areas of the world prior to European conquest.

The Horror! The Horror! Larval Cthulhu Found in Peruvian Amazon

Deep in the Peruvian Amazon, an odd-looking caterpillar is doing its best to look like just another rain forest twig. But its four long tentacles are coiled, ready to respond to the first sign of danger.

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Two new Eocene Paleogene South American Platyrrhines Which Verify African Origin for New World Monkeys

Eocene primates of South America and the African origins of New World monkeys

Authors:

Bond et al

Abstract:

The platyrrhine primates, or New World monkeys, are immigrant mammals whose fossil record comes from Tertiary and Quaternary sediments of South America and the Caribbean Greater Antilles. The time and place of platyrrhine origins are some of the most controversial issues in primate palaeontology, although an African Palaeogene ancestry has been presumed by most primatologists. Until now, the oldest fossil records of New World monkeys have come from Salla, Bolivia, and date to approximately 26 million years ago, or the Late Oligocene epoch. Here we report the discovery of new primates from the ?Late Eocene epoch of Amazonian Peru, which extends the fossil record of primates in South America back approximately 10 million years. The new specimens are important for understanding the origin and early evolution of modern platyrrhine primates because they bear little resemblance to any extinct or living South American primate, but they do bear striking resemblances to Eocene African anthropoids, and our phylogenetic analysis suggests a relationship with African taxa. The discovery of these new primates brings the first appearance datum of caviomorph rodents and primates in South America back into close correspondence, but raises new questions about the timing and means of arrival of these two mammalian groups.

Miocene Neogene Peruvian Amazon had Seven Different Crocodile Species

Thirteen million years ago, as many as seven different species of crocodiles hunted in the swampy waters of what is now northeastern Peru, new research shows. This hyperdiverse assemblage, revealed through more than a decade of work in Amazon bone beds, contains the largest number of crocodile species co-existing in one place at any time in Earth's history, likely due to an abundant food source that forms only a small part of modern crocodile diets: mollusks like clams and snails. The work, published today in the journal Proceedings of the Royal Society B, helps fill in gaps in understanding the history of the Amazon's remarkably rich biodiversity.

"The modern Amazon River basin contains the world's richest biota, but the origins of this extraordinary diversity are really poorly understood," said John Flynn, Frick Curator of Fossil Mammals at the American Museum of Natural History and an author on the paper. "Because it's a vast rain forest today, our exposure to rocks--and therefore, also to the fossils those rocks may preserve--is extremely limited. So anytime you get a special window like these fossilized "mega-wetland" deposits, with so many new and peculiar species, it can provide novel insights into ancient ecosystems. And what we've found isn't necessarily what you would expect."

Before the Amazon basin had its river, which formed about 10.5 million years ago, it contained a massive wetland system, filled with lakes, embayments, swamps, and rivers that drained northward toward the Caribbean, instead of today's pattern of eastward river flow to the Atlantic Ocean. Knowing the kind of life that existed at that time is crucial to understanding the history and origins of modern Amazonian biodiversity. But although invertebrates like mollusks and crustaceans are abundant in Amazonian fossil deposits, evidence of vertebrates other than fish have been very rare.

Since 2002, Flynn has been co-leading prospecting and excavating expeditions with colleagues at fossil outcrops of the Pebas Formation in northeastern Peru. These outcrops have preserved life from the Miocene, including the seven species of crocodiles discussed in Proceedings B. Three of the species are entirely new to science, the strangest of which is Gnatusuchus pebasensis, a short-faced caiman with globular teeth that is thought to have used its snout to "shovel" mud bottoms, digging for clams and other mollusks. The new work suggests that the rise of Gnatusuchus and other "durophagous," or shell-crunching, crocodiles is correlated with a peak in mollusk diversity and numbers, which disappeared when the mega-wetlands transformed into the modern Amazon River drainage system.

"When we analyzed Gnatusuchus bones and realized that it was probably a head-burrowing and shoveling caiman preying on mollusks living in muddy river and swamp bottoms, we knew it was a milestone for understanding proto-Amazonian wetland feeding dynamics," said Rodolfo Salas-Gismondi, lead author of the paper and a graduate student at the University of Montpellier, in France, as well as researcher and chief of the paleontology department at the National University of San Marcos' Museum of Natural History in Lima, Peru.

Besides the blunt-snouted crocodiles like Gnatusuchus, the researchers also recovered the first unambiguous fossil representative of the living smooth-fronted caiman Paleosuchus, which has a longer and higher snout shape suitable for catching a variety of prey, like fish and other active swimming vertebrates.

"We uncovered this special moment in time when the ancient mega-wetland ecosystem reached its peak in size and complexity, just before its demise and the start of the modern Amazon River system," Salas-Gismondi said. "At this moment, most known caiman groups co-existed: ancient lineages bearing unusual blunt snouts and globular teeth along with those more generalized feeders representing the beginning of what was to come."

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Freakin Awesome Department: Amazonian Bird Chick (Cinereous Mourner) Mimics Poisonous Catepillar

In a study published in the January 2015 issue of The American Naturalist, Gustavo A. Londoño, Duván Garcia, and Manuel Sánchez Martínez report a novel nesting strategy observed in a tropical lowland bird that inhabits an area with very high losses to nest predators.

How can tropical birds cope with the high rates of nest predation that are typical in most tropical habitats? Are there nesting strategies that allow tropical birds to escape predators such as birds, mammals, and snakes that regularly eat eggs and nestlings?

During the fall of 2012, while working on a long-term avian ecological study, the researchers discovered the second nest ever described for the cinereous mourner (Laniocera hypopyrra) at Pantiacolla Lodge in the upper Madre de Dios River in southeastern Peru. They observed that upon hatching, the chicks had downy feathers with long orange barbs with white tips, which was very different from any other nestling they had observed in the area. The peculiar downy feathers attracted their attention, but the nestling behavior provided a more important cue. While researchers were collecting morphological measurements, the nestling started moving its head very slowly from side to side in a way typical of many hairy caterpillars. While working in the area, the investigators found a poisonous caterpillar with similar size and hair coloration as the nestling. Therefore, the researchers suggest that this is an example of Batesian mimicry in which the nestling tricks predators into thinking that it is a toxic, spiny caterpillar rather than a highly edible nestling.

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Middle Miocene Neogene Mammals From Proto-Amazonia

Life in proto-Amazonia: Middle Miocene mammals from the Fitzcarrald Arch (Peruvian Amazonia)

Authors:

Tejada-Lara et al

Abstract:

The Middle Miocene has been identified as a time of great diversification in modern lineages now distributed in tropical South America, and when basic archetypal traits defining Amazonia appear, including climatic humid conditions, basic floral physiognomy and phylogenetic composition of modern rainforests. Nonetheless, Middle Miocene localities in South America are poorly known, especially at low latitudes where only one species-rich locality, La Venta in Colombia, has been extensively studied. The present contribution describes the mammal fauna of Fitzcarrald, a new Middle Miocene local fauna from western Amazonia in Peru. Fitzcarrald is correlated with the Laventan South American Land Mammal Age based on the presence of taxa defining the ‘Miocochilius assemblage zone’ in La Venta. The mammalian fauna of Fitzcarrald comprises 24 taxa among cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes and a possible marsupial. At this time, tropical South America was characterized by the presence of the Pebas megawetland, a huge lacustrine complex that provided unique ecological and environmental conditions most likely isolating northern South America from southern South America. These isolating conditions might have come to an end with its disappearance in the Late Miocene and the establishment of the subsequent Acre system, the predecessor fluvial system of modern Amazonia. Results of faunistic similarity between Fitzcarrald and other Miocene faunas throughout South America support these scenarios. The Fitzcarrald mammal fauna exhibits first appearance datums and last appearance datums of various taxa, showing that tropical South America has played a crucial role in the evolutionary history and biogeography of major clades, and revealing a more complex biological history than previously proposed, based on the record from the southern cone of the continent.

Evidence of Marine Deposits From Miocene Neogene Amazonia

Marine connections of Amazonia: Evidence from foraminifera and dinoflagellate cysts (early to middle Miocene, Colombia/Peru)

Authors:

Boonstra et al

Abstract:

Species composition in the present-day Amazonian heartland has an imprint of past marine influence. The exact nature, timing and extent of this marine influence, however, are largely unresolved. Here we use calcareous tests of foraminifera and marine palynomorphs from Miocene sediments in northwestern Amazonia to extend on current estimates for salinity ranges, paleoenvironments and paleogeography. Our samples mostly contain tests and/or organic linings of euryhaline (tolerant to a wide range of salinity) foraminifera of the genera Ammonia, Trochammina and Elphidium, with Ammonia being by far the dominant genus at all locations. Organic-walled dinoflagellate cysts (dinocysts), such as Spiniferites, Brigantedinium and Tuberculodinium vancampoae, are also common at a number of sites. This association of foraminifera and dinocyst taxa points at varying salinities, with aberrant forms of Ammonia indicating lower limits of 0–10 psu (practical salinity units) whereas dinocyst associations suggest more marine conditions. Such regional heterogeneity is common at the interface of shallow marine to freshwater environments, like estuaries. We conclude that during the early and middle Miocene marginal marine conditions reached at least 2000 km inland from the Caribbean portal. Global high sea level and fast subsidence in the sub-Andean zone are thought to be the controlling mechanisms of the marine incursions. Lowering of global sea level and a change in tectonic regime terminated the incursions in the course of the Plio-Pleistocene.

Vegetation Reconstructed From Pleistocene/Holocene Quaternary Marajo Island From Amazonia

Relation between carbon isotopes of plants and soils on Marajó Island, a large tropical island: Implications for interpretation of modern and past vegetation dynamics in the Amazon region

Authors:

Francisquini et al

Abstract:

We assess the relation between the contrasting vegetation types of rainforest, open savanna and wooded savanna coexisting in close contact on Marajó Island at the mouth of the Amazon River. Floristic and carbon isotopic characterizations of modern plants were combined with organic matter carbon isotope and grain size records of soil to characterize vegetation evolution at six locations on southeastern and northeastern Marajó Island and its relations to climate changes since the late Pleistocene. C3 plants contribute 100% of the biomass in the rainforest on post-Barreiras sediments (site 1). No significant vegetation changes are evident in these places since at least ~ 7860 cal yr B.P. Rainforests on paleochannels (sites 4 and 6) are protected from flooding by slightly elevated sandy levee and have flora very similar to site 1. These forests were formed since the early-mid Holocene after channel abandonment. C3 grasses are predominant in open savanna areas (sites 4, 5 and 6), with less representation in wooded savannas (sites 2 and 3). However, C4 grasses, despite having fewer species, constitute significant biomass in the wooded (~ 60%) and open savanna vegetation areas, especially during the dry season. The reconstructions of past vegetation together with the distributions of modern vegetation allow prediction that climate changes to drier conditions can significantly influence the future Marajó Island landscape, likely enabling expansion of C4 plants in the flooding zone and of trees in the rainforests.

Hints of Human Presence in the Late Holocene in the Amazon From Charcoal in Lake Deposits

Palaeofires in Amazon: Interplay between land use change and palaeoclimatic events

Authors:

Campello Cordeiro et al

Abstract:

Interpreting the geological record of Amazon biomass combustion requires comparing charcoal accumulation rates in various biomes at different time scales. Charcoal accumulation rates, a proxy for palaeofire records, were obtained in sediment cores from Amazon lakes surrounded by several vegetation types and from a reservoirs in an intense land use change region. The records presented in this study were obtained in the following areas i) a reservoirs in Alta Floresta region (northern Mato Grosso State); ii) Lago do Saci (southern Pará State), a lake close to Alta Floresta and located at the southern border of Pará State; iii) a bog in an ecotone area in the Humaitá region (southern Amazonas State); iv) lakes in lateritic iron crust of the Carajás Hills (southeastern Pará State); v) Lago Comprido, a floodplain lake close to the Amazon River and surrounded by tropical rain forest (Monte Alegre, Pará State; vi) Lagoa da Pata in the Morro dos Seis Lagos alkaline complex (São Gabriel da Cachoeira, Amazonas State) and vii) Lago Caracaranã, a secluded lake in the northern Amazon cerrado (Roraima State). The highest charcoal accumulation rates were observed for modern records related to an intense change in land use at Alta Floresta, which had no precedent during the Holocene history of the Amazon. High charcoal accumulation rates that were observed in the Carajás region during low lake level phases in the Amazon in the mid-Holocene were comparable to those at the onset of the human settlement in Alta Floresta region. An increase in charcoal accumulation rate was observed in the late Holocene when the lake level was high, suggesting an interaction between climates and human presence. Low charcoal accumulation rates are typical of modern high rainfall environments, as observed in Lagoa da Pata where the environment is not susceptible to occurrences of wildfires even during relatively drier climatic phases. Low charcoal accumulation rates also exist in the relatively dry cerrado (savanna type) biome even during relatively dry phases in the Caracaranã region where the savanna-type vegetation biomass is lower and thus generates less charcoal particles than forest ecosystems.

Evidence of an Amazon Megaflood in ~ 700 BC?

A 2700 cal yr BP extreme flood event revealed by sediment accumulation in Amazon floodplains

Authors:

Moreira-Turcq et al

Abstract:

Climatic conditions are one of the most important factors affecting hydrological processes in fluvial systems. Higher discharges are responsible for higher erosion, greater transport, and also higher deposition. Consequently, sediment accumulation in Amazonia floodplain river-connected lakes can be directly related to hydrological patterns of the Amazon River mainstream. In this context, we analyzed five sediment cores taken in two floodplain systems situated in the lower Amazon River, to investigate sediment accumulation patterns during the Holocene. Our records show abrupt fluctuations in sedimentation rates in lakes that can reach more than 2 cm/yr during some periods. We find that in all cores, sediment stratigraphy is characterized by packages of sediments of uniform age, which are typically 10–80 cm thick and present a variegated color. The 14C age of the upper package is about 2700 cal yr BP. During this abrupt event, sediment accumulation rates in floodplain lakes can be at least 200 times higher than those of “normal” periods. This sedimentation event is interpreted as being the consequence of one or several successive extreme floods. The 2700 cal yr BP event has been also observed in other sites in South America and other regions in the world, although different impacts can be observed in each system. This event probably corresponds to a conjunction of favorable conditions for extreme Amazon discharge associated with the Middle to Late Holocene increase of austral summer insolation and shifts of the Intertropical Convergence Zone (ITCZ) from northern to southern positions. In this context, a marked negative peak in solar irradiance at 2700 cal yrs BP seems to have provoked cooling on the continents and a southward shift of the ITCZ associated with a probable reduction in the Atlantic Meridian Overturning Circulation.

Evidences for a Paleocene Paleogene Marine Incursion in Southern Amazonia

Evidences for a Paleocene marine incursion in southern Amazonia (Madre de Dios Sub-Andean Zone, Peru)

Authors:

Louterbach et al

Abstract:

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

The Civilizations of PreColumbian Amazonia Reconsidered

Integrated palaeoecology and archaeology – a powerful approach for understanding pre-Columbian Amazonia

Authors:

Mayle et al

Abstract:

The old paradigm that Amazonia's tropical ecosystems prevented cultural development beyond small-scale shifting agricultural economies, that had little environmental impact, no longer holds true for much of Amazonia. A diversity of archaeological evidence, including terra preta soils, raised fields, causeways, large habitation mounds, geometric earthworks, and megalithic monuments, all point to considerable cultural complexity and environmental impacts. However, uncertainty remains over the chronology of these cultures, their diet and economy, and the scale of environmental impact and land use associated with them. Here, we argue that a cross-disciplinary approach, closely coupling palaeoecology and archaeology, can potentially resolve these uncertainties. We show how, with careful site selection (pairing small and large lakes, close proximity to archaeological sites, transects of soil pits) and choice of techniques (e.g., pollen, phytoliths, starch grains, charcoal, stable isotopes), these two disciplines can be successfully integrated to provide a powerful tool for investigating the relationship between pre-Columbian cultures and their environment.

West African Sedimentation From the Orosirian PaleoProterozoic From an Enigmatic Source

New insights on Proterozoic tectonics and sedimentation along the peri-Gondwanan West African margin based on zircon U-Pb SHRIMP geochronology

Authors:

De Waele et al

Abstract:

New mapping and age data from rocks of the West African Craton and its western margin, as well as a review of published age data for the region indicate that the southwestern margin of the craton is composed of an Archaean basement of TTG gneisses and granitoid rocks that formed over a long period of time between 3.54 and 2.64 Ga. The age data refute the previously held notion of two craton-forming events, the ∼3.0 Ga Leonian and ∼2.7 Ga Liberian cycles, but instead indicate a pulse at ∼3.4 Ga, followed by near-continuous crustal growth between ∼3.05 and 2.64 Ga. Age data for the Kenema Assemblage, a strip of Archaean rocks separated from the main Archaean exposure further east by Neoproterozoic cover, suggest that this represents a tectonic window.

To the west of the Archaean craton, the Rokel-Kasila Belt occurs, which incorporates two tectonic terranes: the Palaeoproterozoic Kasila terrane, accreted to the Archaean craton and comprised of granulite-facies paragneiss units of the Kasila Group, and the Meso- to Neoproterozoic Marampa terrane, thrust on top of the Archaean basement, and comprised of greenschist-facies schists and metabasites of the Marampa Group. A metavolcanic unit in the Kasila Group provides an age of 1941 ± 4 Ma interpreted to date the emplacement of the Kasila succession. Xenocrystic zircon in the sample suggest the presence of cryptic older crust with components of 2.7-2.6 Ga and 2.2 Ga, and the Kasila Terrane is interpreted to represent a Ganderian-type peri-Gondwanan terrane left attached to the West African Craton. Detrital age data on two schist units of the Marampa Group suggest a maximum age of deposition of between 1076-1030 Ma. The detrital age peaks indicate source terranes in part consistent with a West African affinity, but also comprising significant sources of between 2.0 and 1.0 Ga for which no suitable source terranes are known in West Africa. We suggest that at the time the Marampa Group was deposited along the West African margin at ∼1.05 Ga, a source terrane with significant matching components of Palaeoproterozoic and Mesoproterozoic source rocks, was present to provide the sedimentary input, possibly the Amazonian Craton.

The Amazon Basin Drained Through Mexico in the Norian Triassic

Early Mesozoic Southern Mexico-Amazonian connection based on U-Pb ages from detrital zircons: The La Mora Paleo-River in the Mixteca Terrane and its paleogeographic and tectonic implications

Authors:

Silva-Romo et al

Abstract:

The La Mora Formation is the oldest Mesozoic floodplain succession in the Mixteca Terrane of Southern Mexico. The presence of Amazonian detrital zircons in the La Mora Formation and in the overlying volcanic Diquiyú Unit indicates a major fluvial system that drained the Mixteca Terrane. The La Mora Paleo-River crossed the Oaxaquia microcontinent and the Mixteca Terrane prior to the breakup of Pangea, during Late Triassic-Early Jurassic time, when the Acatlán-Oaxaquia block was part of the northwestern portion of the Amazonian craton. Detrital zircons in the La Mora Formation have ages between 3307 ± 31 and 210 ± 12 Ma, which suggest that they originated in Amazonia and Southern Mexico: 33.2% of the detrital zircons have ages that are found only in Amazonian sources; whereas 66.7% of the zircons may be associated with either the Amazonian craton, the Andean basement, or Southern Mexico. We propose that the La Mora fluvial system drained the Amazon basin in a westward direction, with its mouth in central Pangea, and that it most likely fed the Tolimán submarine fan. The inferred location of the Acatlán-Oaxaquia tectonic block at the time of the La Mora fluvial system implies that the basement of Southern Mexico experienced right lateral displacement of at least 2300 km with respect to South America during the Mesozoic.

Evidence of Amazonia With Baltica During the Assembly of Supercontinent Rodinia

Mesoproterozoic crust in the San Lucas Range (Colombia): an insight into the crustal evolution of the northern Andes

Authors:

Cuadros et al

Abstract:

The San Lucas Range (SLR) is located at the northernmost end of the Central Cordillera of Colombia and is considered part of the Chibcha Terrane, which is characterized by medium- to high-grade rocks with Late Mesoproterozoic-Early Neoproterozoic metamorphic ages. Granite-gneiss and metamafic rocks, including metamonzogabbro, amphibolite and granulite, crop out in the northern portion of the SLR, with a Lower Jurassic granodioritic batholith intruding all the above mentioned units. The geochemical features, in terms of major and trace element contents and U-Pb zircon geochronology, suggest protolith crystallization of both felsic and mafic rocks in a post-collisional setting between 1.54 and 1.50 Ga. In addition, positive ɛNd values and initial 87Sr/86Sr ratios less than 0.7045 indicate a mantle origin for this bimodal association, with TDM values between 1.7 and 1.5 Ga, suggesting a juvenile character. A correlation between the studied granitic rocks and the A-type Rio Uaupés Granitic Suite in the Rio Negro Province of the Amazonian Craton can be established, thus constraining a provenance from southern latitudes for the Chibcha Terrane, as suggested by earlier models. Metamorphic rims of zircons from both felsic and mafic rocks yielded ages between 1180 and 930 Ma, which are consistent with the ages of related metamorphic terranes in Ecuador, Venezuela, Perú, México and Central America. The latter terranes are regarded as having been part of the northwestern border of Amazonia during its collision with Baltica in the context of the Grenvillian/Sveconorwegian orogeny, which was related to the final assembly of Rodinia