Clastic sedimentary rocks of the Michipicoten Volcanic-sedimentary belt, Wawa, Ontario

The Wawa area, part of the Michipicoten greenstone belt, contains rock assemblages representative of volcanic sedimentary accumulations elsewhere on the shield. Three mafic to felsic metavolcanic sequences and cogenetic granitic rocks range in age from 2749 + or - 2Ma to 2696 + or - 2Ma. Metasedimentary rocks occur between the metavolcanic sequences. The total thickness of the supracrustal rocks may be 10,000 m. Most rocks have been metamorphosed under greenschist conditions. The belt has been studied earlier and is currently being remapped by Sage. The sedimentrologic work has been briefly summarized; two mainfacies associations of clastic sedimentary rocks are present - a Resedimented (Turbidite) Facies Association and a Nonmarine (Alluvial Fan Fluvial) Facies Association

Interplay between spatially explicit sediment sourcing, hierarchical river-network structure, and in-channel bed material sediment transport and storage dynamics

Understanding how sediment moves along source to sink pathways through watersheds„from hillslopes to channels and in and out of floodplains„is a fundamental problem in geomorphology. We contribute to advancing this understanding by modeling the transport and in-channel storage dynamics of bed material sediment on a river network over a 600æyear time period. Specifically, we present spatiotemporal changes in bed sediment thickness along an entire river network to elucidate how river networks organize and process sediment supply. We apply our model to sand transport in the agricultural Greater Blue Earth River Basin in Minnesota. By casting the arrival of sediment to links of the network as a Poisson process, we derive analytically (under supply-limited conditions) the time-averaged probability distribution function of bed sediment thickness for each link of the river network for any spatial distribution of inputs. Under transport-limited conditions, the analytical assumptions of the Poisson arrival process are violated (due to in-channel storage dynamics) where we find large fluctuations and periodicity in the time series of bed sediment thickness. The time series of bed sediment thickness is the result of dynamics on a network in propagating, altering, and amalgamating sediment inputs in sometimes unexpected ways. One key insight gleaned from the model is that there can be a small fraction of reaches with relatively low-transport capacity within a nonequilibrium river network acting as ñbottlenecksî that control sediment to downstream reaches, whereby fluctuations in bed elevation can dissociate from signals in sediment supply. ©2017. American Geophysical Union. All Rights Reserved

Controls on Subglacial Rock Friction: Experiments With Debris in Temperate Ice

Glacier sliding has major environmental consequences, but friction caused by debris in the basal ice of glaciers is seldom considered in sliding models. To include such friction, divergent hypotheses for clast‐bed contact forces require testing. In experiments we rotate an ice ring (outside diameter = 0.9 m), with and without isolated till clasts, over a smooth rock bed. Ice is kept at its pressure‐melting temperature, and meltwater drains along a film at the bed to atmospheric pressure at its edges. The ice pressure or bed‐normal component of ice velocity is controlled, while bed shear stress is measured. Results with debris‐free ice indicate friction coefficients \u3c 0.01. Shear stresses caused by clasts in ice are independent of ice pressure. This independence indicates that with increases in ice pressure the water pressure in cavities observed beneath clasts increases commensurately to allow drainage of cavities into the melt film, leaving clast‐bed contact forces unaffected. Shear stresses, instead, are proportional to bed‐normal ice velocity. Cavities and the absence of regelation ice indicate that, unlike model formulations, regelation past clasts does not control contact forces. Alternatively, heat from the bed melts ice above clasts, creating pressure gradients in adjacent meltwater films that cause contact forces to depend on bed‐normal ice velocity. This model can account for observations if rock friction predicated on Hertzian clast‐bed contacts is assumed. Including debris‐bed friction in glacier sliding models will require coupling the ice velocity field near the bed to contact forces rather than imposing a pressure‐based friction rule

Sedimentology of quartz-pebble conglomerates and quartzites of the Archean Bababudan Group, Dharwar Craton, South India: evidence for early crustal stability

The 3200 to 3000 Ma Bababudan Group, locally as thick as 1800 m, consists of a variety of rocks indicating deposition on a stable platform. U- and Au-bearing pyritiferous quartz-pebble conglomerate a few meters thick overlies a regolith at the basal unconformity with a gneissic basement. The bulk of the column consists of mafic volcanics, including subaerial flows, lahars, and sills. Ultramafic and felsic rocks, iron-formation, and pelites are minor lithologies in most of the sequence, but iron-formation forms a major unit at the top of the group. Quartzite units, intercalated with the volcanics, are generally less than 40 m thick and make up 25 to 50% of the column. They are mineralogically mature and texturally submature. Recrystallization generally obscures original textures, but units that were originally clayey quartz arenites have survived total recrystallization. Rounded zircons dominate the nonopaque detrital heavy mineral suite, verifying a history of extensive abrasion. Paleocurrent patterns based on 197 cross-beds and 145 trough axes show general current directions to the S, SE, and E. Variance calculations from outcrops and combinations of outcrops range from 1815 to 8696; the average is 4451. The suggested depositional environment is a dominant braided fluvial plain on a peneplaned granitic craton, perhaps passing into shallow marine. The source rocks appear to have been gneissic and/or granitic rocks, probably portions of the Peninsular Gneiss complex situated to the west, northwest, and north of the outcrop belts. The source terrane was probably a low-lying, deeply weathered surface upon which wind abrasion of the quartz sand was an important process. The stable platform upon which the sediment was accumulating was repeatedly rifted, as indicated by the dominantly mafic lavas; a rifted continental margin or an intracratonic basin are possible tectonic settings. This Archean sequence of continental flows and quartz arenites is one of the oldest extensive examples of rocks deposited on a stable cratonal platform

Sustainable Wellbeing Society—A Challenge for a Public Sector Institution

The purpose of this article is to analyse some key value-loaded structural factors that influence the operational culture of basic education. These factors have to be recognised when aiming to develop school work and promote sustainable wellbeing society. The study of school history in the USA and Finland has long recognized certain permanent dilemmas affecting the development work of basic education. Visions of educational policy, new curriculum targets or technological applications relating to education cannot remove the tensions existing inside education, and people working on this kind of development are not always aware of the part it plays in the development work. This article deals with the tensions between different values that are produced by the educational institutions and the surrounding society, and that can be found in the educational rhetoric, in the curriculum and the instruction models and pedagogic practices of basic education.Peer reviewe