Ichnofossils, cracks or crystals? A test for biogenicity of stick-like structures from vera rubin ridge, mars

New images from Mars rover Curiosity display millimetric, elongate stick- like structures in the fluvio-lacustrine deposits of Vera Rubin Ridge, the depositional environment of which has been previously acknowledged as habitable. Morphology, size and topology of the structures are yet incompletely known and their biogenicity remains untested. Here we provide the first quantitative description of the Vera Rubin Ridge structures, showing that ichnofossils, i.e., the product of life-substrate interactions, are among their closest morphological analogues. Crystal growth and sedimentary cracking are plausible non-biological genetic processes for the structures, although crystals, desiccation and syneresis cracks do not typically present all the morphological and topological features of the Vera Rubin Ridge structures. Morphological analogy does not necessarily imply biogenicity but, given that none of the available observations falsifies the ichnofossil hypothesis, Vera Rubin Ridge and its sedimentary features are here recognized as a privileged target for astrobiological research

Prehistoric stone disks from entrances and cemeteries of north-eastern Adriatic hillforts|Prazgodovinski kamniti diski z vhodov in grobi[; na gradi[;ih na severovzhodnem Jadranu

The paper presents a group of four, approximately 0.5m large, stone disks from entrances or cemeteries of two protohistoric hillforts of north-eastern Adriatic. The disks, having a sparse chronology with the exception of one dated to the Middle Bronze Age, show flat and plain surfaces or covered with sub-circular depressions. One disk shows two larger cup-marks at the centre of both faces. They are interpreted as ritual artefacts based on the association with sacred settlement locations and comparisons with similar coeval stones found mainly close to citadel entrances, burials and thresholds in the Aegean area and Anatolia

Padrão geográfico de diversidade genética em populações naturais de Pau-rosa (Aniba rosaeodora), na Amazônia Central

Rosewood (Aniba rosaeodora Ducke, Lauraceae) is an Amazonian evergreen tree and a source of the purest linalool, the main component of its essential oil, which is very valuable in the international perfumery market. After decades of over-exploitation it is currently considered as threatened. We evaluated the genetic diversity and its distribution in four populations in Central Amazonia. Thirty-five reliable RAPD markers were generated, of which 32 were polymorphic (91.4%). Variation was higher within the populations (76.5%; p < 0.0001) and geographic distribution contributed to population differentiation (23.4%; p < 0.0001). The Amazon River had a small influence on gene flow (3.3%; p < 0.0001), but we identified evidence of gene flow across the river. There were significant differences in marker frequencies (p < 0.05), in agreement with the low gene flow (Nm = 2.02). The correlation between genetic distance and gene flow was - 0.95 (p = 0.06) and between geographic distance and gene flow was -0.78 (p = 0.12). There was a geographic cline of variability across an East-West axis, influenced as well by the Amazon River, suggesting the river could be a barrier to gene flow. Although threatened, these Rosewood populations retain high diversity, with the highest levels in the Manaus population, which has been protected for over 42 years in a Reserve.O Pau-rosa (Aniba rosaeodora Ducke, Lauraceae) é uma árvore amazônica fonte do mais puro linalol, o qual é o principal componente do seu óleo essencial e muito valioso no mercado internacional de perfumaria. Após várias décadas de intensa exploração, a espécie foi levada à categoria de ameaçada de extinção. Quatro populações naturais distribuídas na bacia Amazônia Central foram avaliadas quanto ao nível e a distribuição da diversidade genética. Trinta e cinco marcadores RAPD reprodutíveis foram gerados, dos quais 32 foram polimórficos (91,4%). A diversidade foi maior dentro das populações (76,5%; p < 0,0001) e a distribuição geográfica contribuiu para a diferenciação entre as populações (23,4%; p < 0,0001). A AMOVA indicou que pode haver uma influência parcial do Rio Amazonas no fluxo gênico (3,3%; p < 0,0001), mas foram identificadas evidências de fluxo gênico atravessando o rio. Houve diferenças significativas nas freqüências dos marcadores (p < 0,05) e o fluxo gênico estimado foi relativamente baixo (Nm = 2,02). A correlação entre a distância genética e o fluxo gênico foi de - 0,95 (p = 0,06) e para a distância geográfica e o fluxo gênico foi de - 0,78 (p = 0,12). Houve um padrão geográfico de variabilidade ao longo do eixo Leste - Oeste, influenciado também pelo Rio Amazonas, o que sugere que o rio poderia funcionar como uma barreira para o fluxo gênico. Apesar de ameaçadas, estas populações de Pau-rosa possuem alta diversidade, com o maior valor na população de Manaus, que vem sendo protegida por 42 anos em uma reserva

NETWORK THEORY IN ICHNOLOGY: FROM BEHAVIOURAL TOPOLOGY TO THE DEPOSITIONAL ENVIRONMENT

This study aims to (1) develop quantitative approaches for the study of ichnological systems; (2) model, for the first time, ichnosites as networks; (3) analyze the response of ichnological systems to global dynamics, with particular regard to Late Paleozoic fluvial-influenced settings. In this regard, the modern peritidal environments of the Grado lagoon (Italy, Adriatic Sea), the Nurra ichnosite (Permian-Triassic; Italy) and the Pramollo ichnolagerst\ue4tte (Carboniferous-Permian; Italy) have been selected for developing, applying and testing network analysis for the study of ichnological systems. Results show that network theory is able to depict the traces-environment relationships both for modern and fossil ichnological systems. It is therefore suggested that network theory may have great potential for understanding Phanerozoic bioturbation patterns

The IchnoGIS method : Network science and geostatistics in ichnology. Theory and application (Grado lagoon, Italy)

A new method is proposed for capturing, managing, analyzing, and displaying geographically referenced ichnological data: IchnoGIS. This approach is based on the integration of spatial, geostatistical techniques with network theory, aiming to characterize the environmental significance of recent traces. The efficiency of the IchnoGIS method is tested against a case-study: the Grado lagoon (Italy). The studied site, located within the epeiric Northern Adriatic Sea, consists of a complex mosaic of peritidal environments in a barrier-island context. Here, a diverse ichnofauna includes the following incipient ichnotaxa: Arenicolites, Helminthoidichnites, Lockeia, Macanopsis, Monocraterion, Parmaichnus, Polykladichnus, Skolithos, Thalassinoides and 'squat burrows'. Ichnofaunal distribution is described by the spatial and geostatistical tools proper of the IchnoGIS approach. Additionally, the application of network theory documents the emergence of organized structures (ichnoassociations) from interactions driven by environmental factors. Our results elucidate the role that environmental processes play in producing the complex ichnological patterns of the Grado site. In particular, emersion time, hydrodynamics, substrate firmness and microbial binding are the major control factors determining the structure and distribution of trace associations. These structuring factors are used to define a predictive model of ichnoassociation composition, providing an immediate tool for future palaeoenvironmental reconstitutions

Neoichnology of a barrier-island system: The Mula di Muggia (Grado lagoon, Italy)

Barrier-islands are common landforms and biodiverse habitats, yet they received scarce neoichnological attention. This gap is tackled by studying the Mula di Muggia barrier-island system (Grado lagoon, Italy), focusing on morphology, ecology and ethology of individual traces. The following incipient ichnotaxa are identified: Archaeonassa, Arenicolites, Bergaueria, 'diverging shafts', Helminthoidichnites, Lockeia, Macanopsis, Monocraterion, Nereites, Parmaichnus, Polykladichnus, Skolithos, Thalassinoides and 'squat burrows'. Vertebrate (Avipeda-/Ardeipeda-like, Canipeda) and invertebrate tracks ('parallel furrows') are also described.For each ichnotaxon, tracemaker and behavior are discussed, together with their position with respect to sediment barriers. Results suggest that sediment barriers impose a sharp contrast in terms of ichnological composition. Back-barrier is dominated by branched burrows (i.e. Thalassinoides, Parmaichnus), while the fore-barrier presents vertical and U-shaped burrows (Arenicolites, Skolithos). The environmental conditions of the back-barrier show that low-oxygen substrates favor intense bioturbation, provided that the water column is sufficiently oxygenated

Geographic information systems for ichnofabric analysis: modelling a modern lagoon (Grado, Italy) with the IchnoGIS method

1. Introduction The Grado-Marano lagoon is one of the major transitional systems of the Adriatic Sea, consisting of a barrier island system extended for over 30 km (Baucon, 2008a; Turri, 1999). Characterized by significant biodiversity and heterogeneous environments, this area provide optimal conditions to assess the ichnologic and sedimentary features of siliciclastic, marginal-marine settings. The complex relationships that exist among ichnological, physical, and environmental proprieties require advanced, integrated analysis techniques to visualize spatial patterns and determine the factors controlling trace distribution. For these reasons, a new method for quantitative ichnosedimentological analysis (IchnoGIS) has been developed. The goal of this work is to discuss a quantitative ichnological model of the external margin of the Grado lagoon and test the application of the IchnoGIS method for ichnofabric analysis. 2. Geographical and geological setting The study area (Fig.1) is located on the external margin of the Grado basin, between Grado town and the locality Pineta. Tides, which are the main driving forces of the lagoon hydrodynamics, created a composite mosaic of marginal marine environments, among which vast siliciclastic intertidal flats. A very peculiar environment is represented by microbial-related settings: large sections of the tidal flat are colonized by microbial mats, which are presenting a diverse ichnofauna, preliminary described by Baucon (2008a) and discussed in this study. Fig. 1 \u2013 Study area. Modified from Baucon, 2008a. 3. Method and approach Similarly to a geographic information system, the proposed approach integrates hardware, software, and data for capturing, managing, analyzing, and displaying geographically referenced ichnological data. For this reason, the method has been named \u2018IchnoGIS\u2019. Its development derived from previous work on the application of GPS and GIS techniques to neoichnology (Baucon, 2008b; 2008a). IchnoGIS is an orderly procedure consisting of 6 steps: a. Survey design: The starting point is defining the objects of interest and the sampling size. b. Sampling: If we want to know how traces are distributed in a particular habitat, it is usually impossible to count each and every one present. For this reason, the second step of IchnoGIS is based on quadrat sampling, a method widely used in the interpretation of large ecological data sets with environmental gradients (McIntyre & Eleftheriou, 2005). It consists of characterizing ichnological, sedimentological, environmental attributes (i.e. number of Arenicolites, grain size, salinity) contained in a square frame (in this study: 0.25 m2; Fig.2). c. Significance test: In the simplest case, the result of the sampling process is a spreadsheet including X Y coordinates, facies type and abundance of each structure (Fig. 3). For this reason, nearest neighbour analysis (Borradaile, 2003) is an efficient method to assess the sampling quality. d. Descriptive statistics. One of the primary goals is to describe the influence of the sedimentological features on the numbers and types of traces. This aim can be achieved by cross-tabulating frequency counts of ichnotaxa respect to facies. Another possibility is to provide a measure of central tendency (i.e. Fig.5A) and/or distribution. e. Ichnoassemblage analysis. Ichnoassemblages are verified by cross tabulating the abundance of a trace in relation to that of another trace. f. Spatial analysis. Spatial analysis is performed through (a) classed post maps (b) geostatistical interpolation techniques (i.e. Fig.4B, 5B). Classed post maps are simpler to implement, but interpolation can estimate the value of a variable (facies type, number of traces) in unsampled positions, delivering accurate ichnosedimentary maps. It appears manifest that IchnoGIS emphasizes the recognizement of distinct structures on the sediment surface. This is apparently in contrast with the ichnofabric approach, whose application is usually related to vertical rock slabs/core samples. However, the approach of this study aims to integrate these philosophies by complementing ichnofabric analysis with the quantitative study of discrete ichnofabric-forming ichnotaxa. Fig. 2 \u2013 Quadrat sampling in IchnoGIS. Frame area: 0.25m2. A \u2013 Overview of the tidal flat with the sampling frame (quadrat). B \u2013 Spatial, sedimentological and ichnological attributes are collected for each sampling site and stored in a spreadsheet. 4. Ichnofabrics The studied area comprises six ichnofabrics, which are named for their most representative ichnotaxa. Some structures presents doubtful affinities with existing ichnogenera, therefore the corresponding ichnofabrics are named for their producer. \u2022 Arenicolites (large type) ichnofabric: This ichnofabric mainly occurs within medium- to fine-grained sands with abundant ripple marks (facies B in Figs.4,5). The ichnofabric is characterized by large U-shaped burrows (Arenicolites) penetrating for 20-40 cm into the substrate. Thalassinoides and Siphonichnus can be present, although in rare clusters. Intensity of bioturbation is variable, usually low (BI 1-2). \u2022 Thalassinoides-Arenicolites (small type) ichnofabric: This ichnofabric is commonly associated to sandy muds (facies C in Figs.4,5). The predominant component of this ichnofabric is Thalassinoides, at times associated to small Arenicolites (penetration depth: 5-8 cm; Fig. 3A). The degree of bioturbation is moderate to high (BI 3-6). \u2022 Thalassinoides ichnofabric: This ichnofabric consists of monotypic Thalassinoides-dominated firmgrounds (facies F, Figs.4, 5). The degree of bioturbation is low to moderate (BI 1-3). \u2022 \u2018Insect burrows\u2019 ichnofabric: This ichnofabric is present within microbial-bound deposits, consisting of laminated sands with an upper, organic-rich layer and a lower mineral-rich one (facies E, Figs.4, 5). The ichnoassemblage is dominated by vertical clavate burrows (Fig.3B) and horizontal unbranched burrows, respectively produced by coleopterans and larvae of Diptera. Small Arenicolites can be present. Intensity of bioturbation is generally low (BI 1-2). \u2022 Macanopsis-Arenicolites (small type) ichnofabric: This ichnofabric occurs in sandy muds colonized by filamentous algal turf (facies D). The ichnoassemblage is dominated by crab traces, consisting of gently bending unbranched burrows with a circular-to-oval cross (Macanopsis). Crab burrows are often accompanied by small Arenicolites. Intensity of bioturbation is generally high (BI 3-6). \u2022 Unbioturbated deposits: Sands with indisturbed lamination are common in the study area (i.e. facies A, Figs.4, 5). Intensity of bioturbation is low (BI 0). Fig. 3 \u2013 Ichnofabrics from the Grado lagoon. A \u2013 Thalassinoides-Arenicolites ichnofabric. B \u2013 \u2018Insect burrows\u2019 ichnofabric. 5. Data analysis This section presents the results of the IchnoGIS method. \u2022 Callianassid mounds and openings. Callianassid shrimps are responsible for producing Thalassinoides burrow systems, whose surface expression is represented by sediment mounds and characteristic funnel-linke openings. When abundant, they are responsible for the Thalassinoides\u2013Arenicolites and Thalassinoides ichnofabrics. IchnoGIS revealed two peculiar trends in their distribution: a. Distance from the coastline. These structures are absent in the upper (landward) foreshore. This phenomenon is probably linked to prolonged subaerial exposure during low tide, which is a stressful condition for the Thalassinoides producers (Fig. 4B). b. Facies-dependent distribution. Such structures are restricted in sedimentological range, being more abundant in protected conditions with disposability of organic material. However, they can be also associated to firmgrounds (Fig. 5A). Fig. 4 \u2013 Spatial analysis. A \u2013 Facies map, derived from the information gathered during quadrat sampling. Coordinates in metres (Datum: WGS84). B \u2013 Exposure time controls the abundance of Thalassinoides. Area corresponds to the rectangle in A. \u2022 Large Arenicolites. High numbers of Arenicolites are mainly related to sandy sediments (Fig.5B) with moderate to low exposure times. Such conditions correspond to the Arenicolites ichnofabric. \u2022 Macanopsis. From the ichnologic characterization of sedimentary facies (Fig. 5A), it emerges a clear facies-related distribution of crab traces (Macanopsis). Crab burrows are present specifically within the algal turf zone. Fig. 5 \u2013 Traces and facies. A \u2013 Ichnologic characterization of sedimentary facies. Facies codes refer to Fig.4. B \u2013 Interpolated distribution of Arenicolites (large) and Thalassinoides (openings) stacked on facies map. The dashed areas correspond to Arenicolites 651 per sampling unit; the same is valid for Thalassinoides. 6. Discussion and Conclusions Ichnofabric analysis, integrated with the IchnoGIS approach, revealed four main environmental controls: exposure time, hydrodynamism, sediment binding (algal or microbial) and firmness. Environmental significance of each ichnofabric is shown in Fig.6. It should be noted that the application of quadrat sampling alone would not cover all the ichnofabric-forming ichnogenera (i.e. insect traces). Hence the necessity of complementing the quadrat sampling approach with observations of vertical sections or, more accurately, with quantitative measurements in section. One possible technique could be quantifying burrow type and abundance within sections of a given area. As Gingras et al. (2011) argued, the models we have for animal-sediment relations are largely based on neoichnological studies of the 1950s, 1960s and 1970s. For higher-resolution models, new studies on modern environments are required. The IchnoGIS method could contribute to solve these issues by producing realistic models of trace distribution in modern environments, that are immediately comparable with examples from the fossil record. Fig. 6 \u2013 Environmental significance of the studied ichnofabrics. Firmness measured with the modified Brinnell test (Gingras & Pemberton, 2000); main processes derived from field observations and examination of the main geomorphic features (island, shoreline) in Fig.4A. References Baucon, A. (2008a). Neoichnology of a microbial mat in a temperate, siliciclastic environment: Studi Trent. Sci. Nat. Acta Geol., 83, 183-203. Baucon, A. (2008b). GPS and GIS techniques applied to neoichnology: a case study from a temperate, lagoonal microbial-mat (Adriatic Sea, Italy). Proceedings of Ichnia 2008, 2nd International Congress on Ichnology, Kracow. Borradaile, G. J. (2003). Statistics of earth science data. Springer, Amsterdam, 351 pp. Gingras, M. K., & Pemberton, S. G. (2000). A field method for determining the firmness of colonized sediment substrates. Journal of Sedimentary Research, 70(6), 1341-1344. Gingras, M. K., MacEachern, J. a, & Dashtgard, S. E. (2011). Process ichnology and the elucidation of physico-chemical stress. Sedimentary Geology. In press, doi: 10.1016/j.sedgeo.2011.02.006. McIntyre, A. D., & Eleftheriou, A. (2005). Methods for the study of marine benthos. Wiley-Blackwell, London, 418 pp. Turri, E. (1999). Lagune d\u2019Italia: visita alle zone umide lungo le coste dei nostri mari. Touring Editore, Torino, 144 pp.

Bioturbation beyond Earth: potential, methods and models of Astroichnology

Traces \u2013 burrows, borings, footprints \u2013 are major evidences of biological behaviour on Earth, yet they received little attention in the field of astrobiology. This study aims to discuss the application of ichnology (i.e. the study of life activity traces) to the search for past and modern life beyond Earth (i.e. herein called Astroichnology). Why to look for traces is a central question, given that organisms (and their body fossils) apparently represent a more direct evidence of life in present and past times. The reason is fourfold. First, the Earth\u2019s ichnological record shows that traces record accurately the activity of soft-bodied organisms \u2013 from annelids to bacteria \u2013 that are comparatively underrepresented in the fossil record but that constitute the most part of the benthic biomass. Second, trace fossils are commonly preserved in sediments that are otherwise unfossiliferous. Third, bioturbation and bioerosion change permanently the physico-chemical properties of the substrate and leave geochemical, petrographic and geotechnical signals that enable to relate with the presence of life. In addition, the bioturbating activity of organisms commonly results in structures that are far more abundant and more visible than their tracemakers (e.g. several arthropod taxa produce km-scale mounded topographies in aquatic and continental environments; ectomycorrhizal fungi are responsible for soil microbioturbation; cm-sized organisms shaped the geochemistry of the Earth\u2019s benthic ecosystem during the Cambrian Agronomic revolution). With increasing availability of high-resolution imagery, the search for past and modern traces is possible for several terrestrial bodies, among which the Moon, Mars, Venus, Titan and Mercury. Nevertheless, finding ichnological evidences beyond Earth is still a significant challenge because of (a) resolution issues, (b) relative paucity of bedding-plane imagery, (c) lack of core data, (d) lack of method-specific instrumentation. For these reasons, there is a great potential for developing tools that incorporate ichnology into an astrobiological framework. Specifically, tools for the analysis of sediment and/or rock cores are needed for observing biogenically-produced sedimentary fabrics (ichnofabrics) beyond Earth. Applied ichnology provides a vast set of practical tools (i.e. CT-scanning, borehole imagery) for studying ichnofabrics. Finally, a question might arise: What to expect? Models of bioturbation beyond Earth are extremely complex and variable due to the variety of geodynamical conditions existing on exoplanets. Nevertheless, burrowing and boring behaviours are expected to be a general pattern for life because they allow to face harsh surficial physico-chemical conditions (e.g. cosmic rays) and/or evolutionary pressures, both for mineralized or soft-bodied organisms. Identifying more precisely the forms and variation of Earth\u2019s traces in extreme environments and their evolutionary paths is likely to provide a more robust predictive model for bioturbation beyond Earth