23,903 research outputs found

    Spatial adaptive settlement systems in archaeology. Modelling long-term settlement formation from spatial micro interactions

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    Despite research history spanning more than a century, settlement patterns still hold a promise to contribute to the theories of large-scale processes in human history. Mostly they have been presented as passive imprints of past human activities and spatial interactions they shape have not been studied as the driving force of historical processes. While archaeological knowledge has been used to construct geographical theories of evolution of settlement there still exist gaps in this knowledge. Currently no theoretical framework has been adopted to explore them as spatial systems emerging from micro-choices of small population units. The goal of this thesis is to propose a conceptual model of adaptive settlement systems based on complex adaptive systems framework. The model frames settlement system formation processes as an adaptive system containing spatial features, information flows, decision making population units (agents) and forming cross scale feedback loops between location choices of individuals and space modified by their aggregated choices. The goal of the model is to find new ways of interpretation of archaeological locational data as well as closer theoretical integration of micro-level choices and meso-level settlement structures. The thesis is divided into five chapters, the first chapter is dedicated to conceptualisation of the general model based on existing literature and shows that settlement systems are inherently complex adaptive systems and therefore require tools of complexity science for causal explanations. The following chapters explore both empirical and theoretical simulated settlement patterns based dedicated to studying selected information flows and feedbacks in the context of the whole system. Second and third chapters explore the case study of the Stone Age settlement in Estonia comparing residential location choice principles of different periods. In chapter 2 the relation between environmental conditions and residential choice is explored statistically. The results confirm that the relation is significant but varies between different archaeological phenomena. In the third chapter hunter-fisher-gatherer and early agrarian Corded Ware settlement systems were compared spatially using inductive models. The results indicated a large difference in their perception of landscape regarding suitability for habitation. It led to conclusions that early agrarian land use significantly extended land use potential and provided a competitive spatial benefit. In addition to spatial differences, model performance was compared and the difference was discussed in the context of proposed adaptive settlement system model. Last two chapters present theoretical agent-based simulation experiments intended to study effects discussed in relation to environmental model performance and environmental determinism in general. In the fourth chapter the central place foragingmodel was embedded in the proposed model and resource depletion, as an environmental modification mechanism, was explored. The study excluded the possibility that mobility itself would lead to modelling effects discussed in the previous chapter. The purpose of the last chapter is the disentanglement of the complex relations between social versus human-environment interactions. The study exposed non-linear spatial effects expected population density can have on the system and the general robustness of environmental inductive models in archaeology to randomness and social effect. The model indicates that social interactions between individuals lead to formation of a group agency which is determined by the environment even if individual cognitions consider the environment insignificant. It also indicates that spatial configuration of the environment has a certain influence towards population clustering therefore providing a potential pathway to population aggregation. Those empirical and theoretical results showed the new insights provided by the complex adaptive systems framework. Some of the results, including the explanation of empirical results, required the conceptual model to provide a framework of interpretation

    Bivalve-barnacle pseudoplanktonic colonisation of wood from the Toarcian, Lower Jurassic, Strawberry Bank Lagerstätte, Somerset UK

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    Pseudoplankton are organisms that are adapted for a mode of life attached to floating objects. In modern oceans common examples are lepadid barnacles, which attach themselves to man-made and natural objects, especially wood logs. In the fossil record, pseudoplankton examples are commonly found in black shales, such as the lower Toarcian Posidonia Shale Formation of Germany. Here there are occasional large logs of fossil wood covered in specimens of the inoceramid bivalve Pseudomytiloides dubius, with or without specimens of the pentacrinitid crinoid Seirocrinus subangularis. Some Posidonia Shale logs show evidence of for intra-species succession with younger S. subangularis specimens attached onto the stems of older ones. Another example of pseudoplankton from the Posidonia Shale is the occurrence of the numerous disarticulated specimens of the phosphatic-shelled eolepadid barnacle Toarcolepas mutans associated with a piece of fossil wood, which constitutes the oldest example of pseudoplanktonic barnacles in the fossil record. Here we report a limestone concretion from the lower Toarcian Strawberry Bank Lagerstätte (Ilminster, Somerset, UK) that preserves a piece of fossil wood with a pseudoplanktonic colony comprising at least a hundred specimens of T. mutans that attached onto a layer of P. dubius bivalves, that had already attached onto the wood. This is one of very few examples of temporal succession for pseudoplankton in the Toarcian and is also unusual in being preserved in a mixed carbonate-siliciclastic facies, rather than a black shale. The occurrence of T. mutans in the Strawberry Bank Lagerstätte concretion represents the second record of the species and also the equal oldest example of pseudoplanktonic barnacles in the fossil record

    A blueprint for integrating scientific approaches and international communities to assess basin-wide ocean ecosystem status

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    Ocean ecosystems are at the forefront of the climate and biodiversity crises, yet we lack a unified approach to assess their state and inform sustainable policies. This blueprint is designed around research capabilities and cross-sectoral partnerships. We highlight priorities including integrating basin-scale observation, modelling and genomic approaches to understand Atlantic oceanography and ecosystem connectivity; improving ecosystem mapping; identifying potential tipping points in deep and open ocean ecosystems; understanding compound impacts of multiple stressors including warming, acidification and deoxygenation; enhancing spatial and temporal management and protection. We argue that these goals are best achieved through partnerships with policy-makers and community stakeholders, and promoting research groups from the South Atlantic through investment and engagement. Given the high costs of such research (€800k to €1.7M per expedition and €30–40M for a basin-scale programme), international cooperation and funding are integral to supporting science-led policies to conserve ocean ecosystems that transcend jurisdictional borders

    The Early Cretaceous coastal lake Konservat-Lagerstätte of La Pedrera de Meià (Southern Pyrenees)

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    A state of the art of the Barremian Konservat-Lagerstätte of la Pedrera de Meià site (Southern Pyrenees) is compiled here including the acquisition of new geological data. The relevance of this site, together with the nearby la Cabroa site, is due to its paleobiotic richness and the fact that 113 holotypes and paratypes of flora and fauna have already been defined. Since its discovery at the end of the 19th century and its exploitation as a lithographic limestone quarry, the site has been the object of paleontological interest by national and foreign research teams that are summarized here (including the catalogue of 223 publications). A survey of the existing type specimens in collections all over Europe is also provided, being France and Germany, the countries where more fossils are hosted other than Spain. The geological frame of this site is also reviewed, by revisiting unpublished geological mappings (mainly that of Krusat, 1966) and integrating it in a comprehensive map that includes 4 revisited outcrops of lithographic limestone which could be potential paleontological sites. The available stratigraphic sections did allow the precise location of paleontological data and findings and environmental proxies. The stratigraphic sections obtained have a thickness of about 50m and contain a minimum of 40.000 limestone layers, being an approximation of the years represented in the la Pedrera de Meià site, and the time expanded of the lake during the Barremian

    Searching for the Ordovician–Silurian boundary in Estonia, Latvia and Lithuania

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    The present study focuses on determining the position of the lower boundary of the Silurian System in the eastern Baltic region. To achieve this, we conducted a comprehensive analysis of stable isotopic curves, combined with previously published data on the graptolite record. Our isotopic correlations are primarily based on the δ13Corg curve of the Dobâs Linn section, the GSSP of the Silurian System, and the δ13Ccarb curve of the Monitor Range section in Nevada. Our results provide robust evidence for correlating the basal Varbola Formation, the lower part of the Ãhne Formation and the StaÄiÅ«nai Formation, and suggest their latest Ordovician age. The integration of stable isotopic data and graptolite records allows for a more accurate characterisation of the OrdovicianâSilurian boundary in this region

    A new species of the problematic organism Webbyites from the Early Ordovician Fezouata Biota of Morocco

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    The problematic colonial organism Webbyites has previously been considered to be a hydroid (phylum Cnidaria). In this paper, we describe a new species, Webbyites felix sp. nov., from the Early Ordovician Fezouata Konservat-Lagerstätte of Morocco. One specimen preserves some soft-tissue zooid remains. The presence of a stolon system in the new species and the type species indicates that Webbyites is a benthic graptolite. Webbyites lacks bithecae; thus, it is not a dendroid graptolite

    An evo-devo perspective on no Ordovician land plants

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    Molecular phylogenetic studies of land plant (embryophyte) origins have begun to tease apart those evolutionary contributions derived from prior algal genes and those de novo genes that evolved during a charophyteâembryophyte transition. Applying the concept of genomic assembly in plant evolution to the fossil record leads to a paradigm shift in the interpretation of the Ordovician record of land plants. Traditional phylogenetic thinking requires fossil species taxa to occupy nodes on a phylogeny. An evo-devo approach can view character evolution separately from species taxa, freeing up fossil spores and tissue fragments to become clues to underlying developmental pathways or gene regulatory networks. This results in a re-assessment of what is meant by the presence of land plants in the Ordovician landscape. The new model helps to reconcile discrepancies between molecular time-trees and the âmissingâ record of fossil plants during the Ordovician Period

    "Excess Ar" by laboratory alteration of biotite

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    Many biotite phenocrysts from marine tephra layers have substoichiometric potassium concentrations and alkali occupation << 2.0 atoms per formula unit. Diagenetic alteration is an expected effect of exposure of fresh magmatic minerals to interstitial water and brine intrusions after the deposition and burial of sediments. To test the effect of diagenetic alteration on potassium-argon ages, we irradiated and step heated untreated Fish Canyon biotite (t = 28.2 Ma) and several aliquots leached to various extents in strong and weak acids. Laboratory alteration caused loss of K, age spectrum discordance, high step ages and total gas ages, Ar release at lower furnace temperature, higher Cl/K and Ca/K, and a slight decrease in 36Ar concentration. Potassium loss was always higher than 40Ar* loss. Electron microprobe element maps document that acids preferentially penetrate in phyllosilicate interlayers, removing K (and Na). Because Ar* is removed to a lesser extent than K, we propose that natural 40K decay partly implants radiogenic Ar* into the tetrahedral-octahedral-tetrahedral (T-O-T) phyllosilicate layer, where Ar is shielded from interlayer leaching. The recoiled 39Ar, which was produced by irradiation after the leaching, also partitioned between T-O-T and the interlayer; age spectrum discordance was probably enhanced by the heterogeneous partition of 39Ar and 40Ar* in leached samples
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