Multiple flow and support mechanisms and the development of inverse grading in a subaquatic glacigenic debris flow

Subaquatic glacigenic debris flows of Late Wisconsinan age occur as lobes within an ice-marginal glaciomarine lithofacies at Victoria, British Columbia. Flow was initiated by release of supraglacial debris during an interval of glacial ablation prior to advance and deposition of lodgement till. Many of the lobes developed a common morphology during deposition, consisting of an outer layer surrounding an inner core of rafted material. In the largest lobe reworking of the sediment during flow produced improved sorting, a coarsening of mean grain size, and a shift in skewness toward the negative. This occurred simultaneously within the core and outer layer as a result of different transformations in mechanisms of flow and support. Normal grading, produced in the outer layer, was conveyed around the nose and buried in an inverse position along the base of the flow. These data enable us to present a model that may be applicable to similar flows elsewhere. The flow studied demonstrates that transformations between flow types and sediment support mechanisms can occur simultaneously and serially in subaquatic debris flows.     

A TEST OF THREE FITTING CRITERIA FOR MULTIRESPONSE NON-LINEAR MODELING

This work evaluates objective functions for multiresponse non-linear modeling using computersimulations.Tests are performed under a variety of signal-to-noise ratios and noise variance-covariancestructures.The standard error of prediction for the model parameters,computed from 50 trials,is usedfor performance comparisons.The full rank and rank-deficient problems are considered.For the fullrank problem one model was investigated,a first-order two-step consecutive reaction model,and twoobjective functions were considered,the total sum of squares and the determinant criterion.Nodistinction could be made between the two objective functions for this model.For the rank-deficient case two models were investigated,a first-order two-step consecutive reactionas in the full rank case,and a pH titration model described by the Henderson-Hasselbalch equation.Three objective functions were investigated for the rank-deficient case,the total sum of squares,aweighted total sum of squares and the determinant criterion.The total sum of squares was found toperform poorly under all conditions tested compared to the weighted total sum of squares and thedeterminant criterion.The determinant criterion was found to perform much better than the other twocriteria when the data have a combination of a low signal-to-noise ratio and high variance-covariancenoise structure.     

On Convective Style and Vigor in Sheet-like Magma Chambers

The well known absence of magrnatic superheat is held here tobe a direct reflection of the ease and efficiency of large Rayleighnumber (Ra) convection in evacuating all convectable heat fromthe magma. Magmatic temperature is thus continually bufferedat or below the convective liquidus where the temperature differencedriving convection is vanishingly small and the governing Rais also always small regardless of body size. It is furtherheld here that for bodies where side wall cooling is of lesserimportance, the more common perception of magma chambers isof cooling from above and below where both the initial, isothermal(i.e. isodensity), and final (solid) states are dynamicallystable and that convection is necessarily a transient processconnecting these states. Extensive theoretical and experimentalstudies of cooling from above show that regardless of boundaryconditions transient, small Ra convection is independent oflayer thickness. Instead, convection is driven by formationof a thin, cool, and dense sublayer along the top boundary,and the characteristic length scale of the governing Rayleighnumber, which is time-dependent, is the sublayer thickness (d<<L).All dynamic features of the flow, including heat transfer relyon this length scale and not body thickness; virtually any sheet-likemagmatic body appears infinitely thick to such convection. BecauseRa is small, this transient stage persists for most, if notall, of the period of solidification to mush, whence the bodyis dynamically dead. Under conditions of strongly variable viscosity, only the leadingpart of d (i.e. d'), forward of a critical rheological front,is unstable. Convection itself is restricted to a region whereviscosity changes by no more than a factor of about 3 to 10.Most of the cool, dense sublayer is rigid, immobile crust, unableto participate in convection and cool the body. Rapid advanceof this crust due to cooling inhibits convection by consuminginstabilities before maturation to finite amplitude. Inclusionof solidification in the stability analysis changes the lengthscale in the governing Rayleigh number (Ra_v) to K/V (thermaldiffusivity/advance velocity). Ra is subcritical for large V₀(early times) and only with time becomes supcrcritical. Thisis in striking contrast to the usual Ra_L, which is initiallythe largest it will ever be. Because of continual collapse ofthe unstable sublayer, convection may remain near the criticalRa_v. Convection is thus initially weak and, because the heatflux from the system monotonically decreases with time due tothe thickening conductive crust and cooling, it is preventedfrom becoming indefinitely strong and instead slowly diminisheswith time. Conduction through the advancing crust is balanced by latentheat of crystallization at the crystallization front and convectionoccurs in response to this cooling. Because convection is confinedto the nearly isoviscous, nonsuperheated magma, crust growthis unaffected by convection, even when it is artificially forcedat unnatural rates. The crusts of Hawaiian lava lakes reflectthis in growing at the same rate regardless of lake thicknessand, in numerical convective modeling, imposed Rayleigh number.Overall cooling is well approximated by that of a stagnant,purely conducting layer whose central temperature is constantuntil arrival of the slowly moving cooling front In fact, therate of change of a body's central temperature is a direct measureof the total rate of heat transfer (i.e. Nusselt number, Nu)from that region. This is shown to be very nearly zero for Hawaiianlava lakes, precluding all but the weakest of convective heattransfer within the magma itself. The maximum heat transfer in terms of Nusselt number of anyunheated body within a conductive medium and always kept perfectlywell mixed thermally, relative to the same stagnant body, isshown to be Nu=2 regardless of shape and size. This thermalevolution is closely followed by previous calculations thatassume a large Rayleigh number based on layer thickness. Thermal convection in unheated, sheetlike magma chambers isa transient, sluggish process governed by solidification andsmall scale, small Rayleigh number instabilities; thermallydriven convective turbulence, in the usual sense, is out ofthe question.     

Assimilation of Crustal Material by Basaltic Magma: Strontium Isotopic and Trace Element Data from the Edgecumbe Volcanic Field, SE Alaska

The Edgecumbe volcanics, which range from basalt through rhyodacite,have Sr contents between 125 and 370 p.p.m., Rb contents of1 to 70 p.p.m., Ba ranging from 50–550 p.p.m. and initial⁸⁷Sr/⁸⁶Sr ratios between 0.70291 and 0.70404. No simple correlationexists between these components and silica. The highest ⁸⁷Sr/⁸⁶Srvalues occur in a group of intermediate lavas (55–60 wt.per cent SiO₂) while the rhyodacites have initial ratios between0.7035 and 0.7038. With increasing silica, Sr increases to amaximum in the andesites and then steadily decreases; Ba andRb increase over the same compositional range. The highest ⁸⁷Sr/⁸⁶Srlavas have major and trace element concentrations which departfrom trends defined by most of the lavas. The variation in strontiumisotopic compositions suggests interaction between parentalbasaltic magma and crustal material. Attempts to model the assimilationprocess using fixed end-member assimilation and assimilation-fractionalcrystallization models have failed to produce the observed chemicaltrends. Because the parental basaltic liquid underwent littlefractionation, the variability in hybrid lavas is attributedto variation in contaminant composition. Initial melts werelow in CaO, A1₂O₃, MgO and Sr and enriched in SiO₂. K₂O, Na₂O,Rb and Ba. As melting progressed, melts became enriched in themore refractory components. Because hybrid strontium isotopiccomposition is a function of Sr concentration as well as isotopiccompositions, the Sr content of the assimilant strongly influencesresultant isotopic systematics. The development of the assimilantssuggests plagioclase was a residual phase during early melting.This model of crustal assimilation represents one end-memberin the spectrum of processes responsible for the generationof continental volcanic suites.     

Sedimentology of cherts in the Early Proterozoic Wishart Formation, Quebec-Newfoundland, Canada

The siliciclastic Wishart Formation of the Early Proterozoic Labrador trough is a high-energy shelf deposit. Wishart sandstones contain both interstitial chert with textures of void-filling cement and thin chert intercalations contaminated with siliciclastic mud. Although volumetrically minor, these cherts occur in several thin, areally extensive stratigraphic intervals. The Wishart contains intraclasts of both the chert-cemented sandstone and the impure chert layers (as well as several other types of chert sand and gravel). This suggests the cherts formed penecontemporaneously, which is consistent with the absence of any signs of replacement in all but one of the chert types and the clear-cut distinctions between chert types, even where they are side by side in a single thin section. The origin which appears to be most compatible with available evidence is that the cherts represent silica precipitated from thermal waters that rose through the sediments of the Wishart shelf and discharged into suprajacent seawater. A biogenic origin is unlikely in view of the lack of appropriate organisms during the Early Proterozoic and the rapidity with which the cements formed. A volcanogenic origin is unlikely because volcaniclastic textures are plentiful in associated formations but absent from the Wishart. Precipitation induced by evaporative concentration is unlikely in view of the widespread evidence of tidal currents and the lack of evidence of desiccation in the Wishart. Finally, the cherts are not restricted to the lowest-energy facies, and therefore they presumably did not accumulate as a background sediment. Deposition of silica above the sediment/water interface was probably made possible by ambient concentrations of silica that were significantly higher than those of Phanerozoic seawater. Cherts with similar textures occur in other Early Proterozoic sediments, most notably arenitic or granular iron-formations.     

TENSORIAL RESOLUTION:A DIRECT TRILINEAR DECOMPOSITION

Modern instrumentation in chemistry routinely generates two-dimensional(second-order)arrays of data.Considering that most analyses need to compare several samples,the analyst ends up with a three-dimensional(third-order)array which is difficult to visualize or interpret with the conventional statisticaltools.Some of these data arrays follow the so-called trilinear model,(?)These trilinear arrays of data are known to have unique factor analysis decompositions which correspondto the true physical factors that form the data,i.e.given the array (?),a unique solution can be found inmany cases for each order X,Y and Z.This is in contrast to the well-known second-order bilinear datafactor analysis,where the abstract solutions obtained are not unique and at best cannot be easilycompared with the underlying physical factors owing to a rotational ambiguity.Trilinear decompositions have had the disadvantage,however,that a non-linear optimization withmany parameters is necessary to reach a least-squares solution.This paper will introduce a method forreducing the problem to a rectangular generalized eigenvalue-eigenvector equation where the eigenbectorsare the contravariant form(pseudo-inverse)of the actual factors.It is shown that the method works wellwhen the factors are linearly independent in at least two orders(e.g.X_(jr),and Y_(jr) are full rank matrices).Finally,it is shown how trilinear decompositions relate to multicomponent calibration,curve resolutionand chemical analysis.     

Inquisitiones Post Mortem,GIS, and the creation of a land-use map of medieval England

Although GIS are used extensively in modern socio-economic studies, their application to historical analysis, especially of relatively early periods, is in its infancy. Yet, as this paper demonstrates, GIS has particular utility both for combining information from disparate and unstandardized historical sources and for reconstructing broad distribution patterns from spatially discontinuous data. When combined with cluster analysis, it also provides a powerful tool for analysing and classifying data sets and representing the results thereby obtained. This paper describes the stages whereby data extracted from almost 10 000 original Inquisitiones Post Mortem, dating from 1300 to 1349, are ultimately transformed into a national land-use classification map for the critical period immediately prior to the Black Death of 1348.