Defining the Historical Northeastern Forested Boundary of the Great Plains Grasslands in the United States

The Great Plains is the grasslands of the central United States, but precise delineation of this region has evaded agreement due to the transition between Great Plains grasslands and forests of the eastern United States. After comparing Great Plains delineations in readily available geographic information system layers, I established a northeastern boundary using evidence from historical tree surveys during the 1800s. Additionally, I described tree presence within the Great Plains over time and potential drivers of change. The definition documented here diverges from others by including most of Iowa and part of Illinois, and even small sections in Indiana and Wisconsin, but excluding Missouri due to regular tree presence overall at landscape scales of ecological subsections. In this definition, the Great Plains had an extent of 2.29 million km² in fifteen states, including Indiana and Wisconsin, and 2.19 million km² after removal of open forests in Oklahoma and Texas. Tree presence occurs within the Great Plains and tree encroachment is not a new process; however, tree encroachment is increasing in the Great Plains, which causes a decrease in the grasslands region. Nevertheless, clarifying the historical eastern boundary provides a solution to the problem of competing versions of the Great Plains region. Key Words: ecotone, prairie, savanna, tree encroachment.     

Ventures into Viral Cartography: Waffle House,Educational Attainment,and the Social Life of Maps

Viral maps—ones that are shared widely on social media and media outlets—have become an increasingly common part of online conversations about a range of issues. Despite the increasing prevalence of these viral maps, only a few academic researchers have examined the factors leading to their popularity or their social use and effect. In this article, we analyze two case studies of viral maps, a viral tweet about the August 2017 total eclipse and an interactive tool for exploring educational attainment by neighborhood in the United States. By reflecting on our experience as authors of these maps and analyzing the reactions they elicited, we identify several key elements of these maps and their circulation. First, viral maps act as a form of phatic communication, allowing users to restate and react to shared social identities. Second, maps are read from specific times and places, and this spatiotemporal context significantly shapes the reactions of map readers. Finally, viral maps illustrate gaps or improvements in trust between mapmakers and map readers, including questions about map accuracy or the intentions behind the map. We close by considering implications for future research and viral cartography. Key Words: online maps, social networks, viral cartography.     

Mn-oxide: a major source of easily mobilisable Co and Ni under reducing conditions in New Caledonia FerralsolsLes oxydes de Mn : une source majeure de Co et Ni facilement mobilisables en conditions réductrices dans les Ferralsols de Nouvelle-Calédonie

Chemical and bacterial reduction and dissolution of Fe and Mn-oxide and the concomitant solubilisation of Co and Ni were studied in a surface horizon of a New-Caledonia Ferralsol. Chemical extractions showed that Mn and Co were in a large part associated in Mn-oxides. The main part of Ni was associated with goethite, but a very small fraction was also associated with Mn-oxides. Anaerobic reducing bacterial activity was responsible for Fe solubilisation at a smaller extent than for Mn solubilisation and consequently for associated metal release. Submicroscopic investigations revealed the presence of a Mn-oxide containing Co, Ni and Al, close to a lithiophorite–asbolane mixed-layers Mn-oxide, which can be considered as a main source of easily available metals in this soil. To cite this article: C. Quantin et al., C. R. Geoscience 334 (2002) 273–278.     

Deformation and metamorphism in the Fenes Nappe (southern Apuseni Mountains,Romania)Déformation et métamorphisme dans la nappe de Fenes (monts Apuseni méridionaux,Roumanie)

The Fenes Nappe belongs to the stack of tectonic units cropping out in the southern Apuseni Mts (Romania). It is characterised by a structural history consisting of two folding phases that developed during the time spanning from Early Aptian to Late Maastrichtian. The D1 phase produced west-northwest-verging, isoclinal to very tight folds, associated to a slaty cleavage. The main metamorphic imprint of the Fenes Nappe is linked to this deformation phase; illite and chlorite ‘crystallinity’ values indicate metamorphic conditions of the late diagenesis, close to the diagenetic zone/anchizone boundary. The subsequent D2 phase produced north-northwest-verging, parallel folds, not associated with synkinematic recrystallisation. These phases are interpreted as developed during a structural path, which includes burial at a depth of 8–10 km, followed by exhumation at shallower structural levels. To cite this article: A. Ellero et al., C. R. Geoscience 334 (2002) 347–354.     

Caractérisation des variations lithologiques saisonnières des sédiments de la baie de Seine orientale ; impact des crues de la Seine (France)Characterisation of seasonal lithological variations of the superficial sediment in the eastern part of the Bay of Seine: impact of floods Seine River (France)

This paper presents the first results obtained during cruises since 1995 in the southeastern part of the Bay of Seine. New sedimentological data concerning sediment samples, box cores and water column measurements have been obtained recently in the framework of the Research Programme PNEC (French National Coastal Environment Programme). Fine sediments are deposited on form of temporary veneers of fluid-to-soft mud formed during high floods episodes. In the subtidal area (<10 m water depth), mobility of fine sediments is important and temporary mud deposited during high discharge period composes part of the distal estuarine system of the Seine River. To cite this article: S. Garnaud et al., C. R. Geoscience 334 (2002) 323–330.     

Homogénéisation et validation des corrections de terrain gravimétriques jusqu'à la distance de 167 km sur l'ensemble de la FranceUpdating and validating the French gravity terrain corrections out to a distance of 167 km

For regional and national study purposes, there is a high need for updating the terrain corrections (TC) in the French gravity database. We have recomputed the TC for all the French gravity stations from 50 m out to a distance of 167 km. We compute the TC with a flat-top-prism algorithm and three DEM with grid spacing of 50, 250 and 1000 m, used in the zones 53 m/3 km, 3 km/10 km et 10 km/167 km, respectively. Analysing the DEM/station Δz and comparing our results to the ones previously obtained in the Alps area, we estimate the accuracy of our TC to be better than 1 mGal. To cite this article: G. Martelet et al., C. R. Geoscience 334 (2002) 449–454.     

Peut-on évaluer le rôle de la sédimentation sur l'effet de serre à l'échelle de temps des cycles orbitaux ?Can the role of sedimentation in the greenhouse effect at the time scale of orbital cycles be evaluated?

The evolution of the atmospheric CO₂ content is partly a response to the lack of balance between oceanic sedimentation and continental weathering, because the oceanic C reservoir tends to balance net inputs or losses from slow processes by rapid exchanges with the atmospheric reservoir. This response strongly depends on both amplitudes and time scales of the related processes. At Milankovitch or lower time scales, global models generally do neglect organic matter fossilisation, but such an assumption is only valid for oligotrophic systems. In eutrophic or mesotrophic systems, organic matter is not negligible and should be considered relatively to the carbonate sedimentation in order to know whether the impact of the sedimentation was a source or a sink for atmospheric CO₂. To cite this article: P. Bertrand, C. R. Geoscience 334 (2002) 521–528.     

High-pressure,low-temperature metamorphism in Alpujarride Units of southeastern Betics (Spain)Métamorphisme de haute pression et basse température dans les unités Alpujarrides du Sud-Est de la cordillère Bétique (Espagne)

We present the first occurrences of high-pressure, low-temperature ferro-magnesiocarpholite-bearing mineral assemblages associated to quartz segregations in the Alpujarride units of southeastern Betics (Sierra de Almagro, Sierra de los Pinos and Sierra Cabrera). Thermobarometric results show that the carpholite-bearing rocks underwent the same P–T conditions in the three outcrops, i.e. 8–10 kbar, 350–400 °C. Metamorphic and structural data allow us to conclude that these rocks belong to the same Alpujarride unit. In the Sierra de Almagro, tectonic units with carpholite-bearing rocks overlie low-pressure, low-temperature Alpujarride units, then forming a stack with an inverted tectono-metamorphic sequence, as observed in the central and western part of the Alpujarride complex. The preservation of carpholite-bearing assemblages in these rocks implies that no significant temperature increase occurred during the exhumation history. To cite this article: G. Booth-Rea et al., C. R. Geoscience 334 (2002) 857–865.     

Natural minerals and divided solids: methodology for understanding surface phenomena related to industrial uses and environmental problems

This introductory paper aims at presenting the series of articles in this special issue of Comptes Rendus Geoscience devoted to the study and use of natural minerals. The research methodology that can be applied to the investigation of surface phenomena related to adsorption, exchange and retention onto the surface of natural minerals and divided solids is presented. A special focus is given to the retention of surfactant molecules, in view of their considerable importance in numerous industrial fields, such as, for instance, mineral flotation and enhanced oil recovery. Throughout this introductory paper, the relevance of this research approach to the field of geosciences is stressed by listing various applications where it can provide conclusive answers, especially for environmentally related issues. To cite this article: J.-M. Cases, C. R. Geoscience 334 (2002) 585–596.