Anthropogenic sediments and soils: Geoarchaeology

Archaeology has gradually but consistently increased its interest in the study of soils and sediments over the last decades. As a result of this emphasis, the discipline has not only sought to characterize the terrigenous matrix within which the great majority of archaeological materials are found but, increasingly, to also understand soils and sediments in their double dimension: as archives of archaeological and environmental data and as sui generis artifacts (Butzer 1982; Waters 1992; French 2003; Holliday 2004; Goldberg & Macphail 2006; Walkington 2010). This salience notwithstanding, a tendency to conflate the meaning of sediments and soils continues to exist within the discipline. In some cases, this owes much to the nature of archaeological findings and their context; artifacts are found in sediment deposits that have stratigraphy and which, generally speaking, are sufficiently close to the surface to be affected by soil-forming processes. Be that as it may, it is useful to draw a contrast between “anthropogenic sediments” and “anthropogenic soils” (and indeed between sediments and soils) because the distinction highlights different earthly processes that can affect the formation of this type of archaeological evidence. Put another way, both anthropogenic sediments and anthropogenic soils imply terrigenous material with distinctive characteristics resulting from the strong and enduring influence of past human activity. However, each concept emphasizes a different aspect of the life history of the landscape, that demands the separate attention of archaeological research, especially the subdiscipline of geoarchaeology

Amazonian Dark Earths: Geoarchaeology

Amazonian Dark Earths (hereinafter ADEs) are expanses of anthropogenic soils that formed on generally nutrient-poor upland soils of the Amazon basin during pre-Columbian times. Expanses of ADEs range from <1–80 ha, and overall agricultural aptitude is higher than the vast majority of soils in the region. These soils are much sought after by local farmers who use them to grow specific crops. Most of the documented expanses of ADEs are found on Tertiary-age sediments located in riparian and interfluvial positions of the Amazon basin. However, instances are also reported on Quaternary alluvial sediments and on human-made earthworks, highlighting that the formation of these soils was an outcome of specific forms of pre-Columbian settlement. The discovery of ADEs alongside the main waterways of the region has been a crucial Rubicon for Amazonian archaeology: these soils record the effects of pre-Columbian indigenous societies’ creative manipulation of environmental affordances. Thus, they highlight that human inhabitation of the Amazon basin was, and is, much more than efficient adaptation to environmental limitations. Their ubiquity provides strong evidence for the existence of more sedentary and demographically denser indigenous societies in the Amazon basin before European colonization. Moreover, examined from a strictly archaeological perspective, ADEs are one of the best archaeological signatures of sedentary occupations in a region with limited archaeological preservation potential. ADEs are sui generis archaeological artifacts of extraordinary relevance for present-day concerns: soil scientists are currently studying the properties and formation of ADEs in order to develop techniques of soil amelioration that permit recuperation and amendment of degraded and infertile soils

Widespread population decline in South America correlates with mid-Holocene climate change

Quantifying the impacts of climate change on prehistoric demography is crucial for understanding the adaptive pathways taken by human populations. Archaeologists across South America have pointed to patterns of regional abandonment during the Middle Holocene (8200 to 4200 cal BP) as evidence of sensitivity to shifts in hydroclimate over this period. We develop a unified approach to investigate demography and climate in South America and aim to clarify the extent to which evidence of local anthropic responses can be generalised to large-scale trends. We achieve this by integrating archaeological radiocarbon data and palaeoclimatic time series to show that population decline occurred coeval with the transition to the initial mid-Holocene across South America. Through the analysis of radiocarbon dates with Monte Carlo methods, we find multiple, sustained phases of downturn associated to periods of high climatic variability. A likely driver of the duration and severity of demographic turnover is the frequency of exceptional climatic events, rather than the absolute magnitude of change. Unpredictable levels of tropical precipitation had sustained negative impacts on pre-Columbian populations lasting until at least 6000 cal BP, after which recovery is evident. Our results support the inference that a demographic regime shift in the second half of the Middle Holocene were coeval with cultural practices surrounding Neotropical plant management and early cultivation, possibly acting as buffers when the wild resource base was in flux

Human niche construction and population growth in pre-Columbian Amazonia

The use of Niche Construction Theory in archaeological research demands that we establish empirically how human-constructed niches acted as legacies that shaped the selection pressures affecting past human populations. One potential approach is to examine whether human demography changed as a result of the continued use of landscapes enduringly transformed by past societies. This paper presents proxies for Amazonian population growth during the late Holocene and discusses their significance within the broader context of landscape legacies resulting from cumulative anthropic environmental alteration during pre-Columbian times

Did pre-Columbian populations of the Amazonian biome reach carrying capacity during the Late Holocene?

The Late Holocene archaeological record of the South American tropical lowlands (the Amazon basin, the Orinoco basin, and the Guianas) provides evidence of major biome-scale cultural and technological transitions. Accompanying changes in population size and density however, are often estimated on the basis of unreliable assumptions and guesswork. Drawing on recent developments in the aggregate analysis of large radiocarbon databases, here we present and examine multiple proxies for relative population change between 1000 BC and AD 1500. With a robust model-testing approach, we investigate both biome-wide and local palaeodemographic parameters of interest. Our analysis a) documents overall adhesion to a logistical model of demographic growth over the 1,700 years prior to European colonisation, b) detects a possible demographic ceiling in pre-Columbian times and, c) observe considerable variability when this signal is projected geographically. Our results, therefore, provide important demographic insights to reframe current understandings of Late Holocene demic expansion, language diversification, and subsistence intensification in the Amazon biome. Our simulation-based palaeodemographic approach, employing the most complete database of 14C data, stands to scaffold future enquiry into links between demographic and palaeoclimatic patterns in South America

La arqueología del río Napo: noticias recientes y desafíos futuros

The archeology of the Napo River: recent news and future challenges. The archaeology of the Napo River initially became known through the pioneering work of Clifford Evans and Betty Meggers in Ecuador. These investigations led to the formulation of a ceramic sequence that continues to be the backbone of archaeological understandings in the region. During the last decades, however, new archaeological data have refined our understanding of the precolonial process of human occupation in the region. These data comprise, observations derived from collecting activity of missionaries, new information produced through contract archaeology in Ecuador, and recent archaeological survey data from the Peruvian territory of the basin, among others. In this article we summarize these archaeological observations, discuss techno-stylistic aspects of the archaeological ceramics of the region, present new archaeological evidence suggesting Napo phase occupations existed along the entire lowland Napo river, and assess the current state of our knowledge on precolonial occupations of the Napo River basin

The deep human prehistory of global tropical forests and its relevance for modern conservation

Significant human impacts on tropical forests have been considered the preserve of recent societies, linked to large-scale deforestation, resource mining, livestock grazing, and plantation industries. Cumulative archaeological evidence now demonstrates, however, that Homo sapiens has actively manipulated tropical forest ecologies for at least 45,000 years. It is clear that these millennia of impacts need to be taken into account when studying and conserving tropical forest ecosystems today. Nevertheless, archaeology has so far provided minimal practical insight into contemporary human-tropical forest interactions. Here, we review significant archaeological evidence for impacts of prehistoric hunter-gatherers, agriculturalists, and urban settlements on global tropical forests. We compare the challenges faced, as well as the solutions adopted, by these groups with those confronting present-day societies, which rely on tropical forests for ecosystem services, ranging from the maintenance of global carbon sinks to bioprospection for medicinal plants. We emphasise archaeology’s importance in not only promoting natural and cultural heritage in tropical forests, but also taking an active role in informing modern conservation and policy-making

Micropedologia de um Argissolo amarelo com horizontes antrópicos (Terra Preta de Índio) na Amazônia Central.

Estudos micropedológicos foram carreados em Terra Preta de Índio (TPI) com o objetivo de elucidar os processos envolvidos em sua gênese, bem como suas formas de utilização pré-colombiana. Blocos indeformados de solo foram coletados por horizonte e em suas respectivas transições em um perfil de Argissolo Amarelo A Antrópico (TPI) localizado no município de Iranduba, AM. As lâminas delgadas confeccionadas a partir dos blocos foram descritas por meio de microscopia óptica. Os resultados mostraram que os processos envolvidos na gênese desse solo envolveram: i) condições pedoambientais diferentes das atuais (pedorrelíquias - nódulos ferruginosos); ii) argiluviação, indicada por revestimentos de ferri-argilãs orientados na parede de poros entre agregados e canais; iii) migração de ferro impregnando o fundo matricial (cutãs de difusão); iv) bioturbação, atestada por preenchimento de poros por pelotas fecais e microagregação zoogenética e v) antropismo, que contribuiu com a queima de resíduos (partículas de carvões) e descarte de artefatos cerâmicos. A análise dos fragmentos cerâmicos corroborou a utilização de cauixi (Tubella reticulata e Parnula betesil) e cariapé (Bignoniacea) como antiplástico para o seu fabrico