Glacier fluctuations in the western Alps during the Neoglacial,as indicated by the Miage morainic amphitheatre (Mont Blanc massif,Italy)

Holocene glacier variations pre‐dating the Little Ice Age are poorly known in the western Alps. Studied for two centuries, the Miage morainic amphitheatre (MMA) is composed of three subconcentric sets of c. 25 moraines. Because of its location and of a dominant mode of morainic accretion, the MMA is a well‐preserved marker of the glacier dynamics during the Neoglacial. Radiocarbon dates were obtained by digging and coring in inter‐ morainic depressions of the MMA and through a deep core drilling in a dammed‐lake infill (Combal); complementary data for the inner MMA were obtained by lichenometry and dendrochronology. Radiocarbon chronology shows that (i) the MMA not only pre‐dates the Little Ice Age (LIA), but was built at least since 5029–4648 cal. yr BP (beginning of the Neoglacial); (ii) outer sets of moraines pre‐date 2748–2362 cal. yr BP; (iii) the MMA dammed the Lake Combal from 4.8 to 1.5 cal. kyr BP, while lakes/ponds formed inside the moraines (e.g. from 2147–1928 to 1506–1295 cal. yr BP). The ‘Neoglacial model’ proposed here considers that the MMA formed during the whole Neoglacial by a succession of glacier advances at 4.8–4.6 cal. ky BP (early Neoglacial), around 2.5 cal. ky BP (end of Göschener I), at AD 600–900 (end of Göschener II) and during the LIA, separated by raising phases of the right‐lateral moraine by active dumping because of the Miage debris cover.     

Morphology and facies architecture of a falling sea level strandplain, Umiujaq, Hudson Bay, Canada

Coastal strandplain deposits near Umiujaq, eastern Hudson Bay, Canada, were formed under falling relative sea level conditions resulting from postglacial isostatic uplift. Ground-probing radar profiles across the strandplain reveal a lower progradational unit (LPU) discordantly overlain by an upper progradational unit (UPU), which were correlated with stratigraphic sections exposed in incised valley walls. The discordance is a wave erosion surface (WES) that separates fine shoreface sands of the LPU from coarse-sand and gravel of the UPU. Major basal downlap surfaces can be traced updip into marine terraces and define downstepping wedges. The downstepping is interpreted as representing ‘autocyclic’ morphological reconfiguration rather than a response to changes in the rate of sea level fall. The internal architecture is strongly dependent on the accommodation and thus on antecedent topography. A conceptual model for strandplain deposition under falling sea level incorporates a bipartite shallowing-upward sandy succession when sufficient accommodation is available. Where accommodation space is limited, a sharp-based bar-and-beach sandbody directly overlies muddy deeper water deposits and the WES resembles a regressive surface of erosion.     

Shallow-burial dolomite cement: a major component of many ancient sucrosic dolomites

Dolomite cement is a significant and widespread component of Phanerozoic sucrosic dolomites. Cements in dolomites that were never deeply buried are limpid, have planar faces (non‐saddle forms), often distinct zonation in cathodoluminescence and form syntaxial overgrowths on crystals facing pores. Five samples of sucrosic dolomites, interpreted as having had mostly lime‐mudstone or wackestone precursors in four carbonate aquifers, provide insights into the abundance of planar cements in sucrosic dolomites. Such cement comprises 11% to 45% (32% mean) of peritidal to sub‐tidal dolomites on an outcrop in the Edwards aquifer (Early Cretaceous) of central Texas; 19% to 33% (25% mean) of ramp dolomites in the Hawthorn Group (Oligo‐Miocene) and 50% to 70% in shelf dolomites of the Avon Park Formation (Eocene) in the Upper Floridan aquifer of sub‐surface peninsular Florida; 18% to 45% (32+% mean) of sub‐tidal shelf dolomites in quarry sections of the Burlington‐Keokuk Formation (Early Mississippian) in south‐eastern Iowa; and 18% to 76% (50% mean) in shallow cores and outcrops of outer‐shelf dolomites from the Gambier Limestone (Oligo‐Miocene) of South Australia. Backstripping the cement phases revealed by cathodoluminescence colour photomicrographs documents the effects of cements on textural coarsening, pore‐space reduction, induration and general ‘maturation’ of these dolomites. Most pre‐Holocene dolomites are multiphase crystalline rocks composed of: (i) seed crystals or ‘cores’; (ii) crystal cortices that concentrically enlarged the cores; and (iii) free‐space, syntaxial precipitates of limpid cement around the crystals. Remaining CaCO₃ grains and micrite can be replaced by dolomite, but typically they are dissolved between stages (ii) and (iii), creating systems of intercrystal and mouldic pores typical of sucrosic dolomites. Networks of cement overgrowths, aided by water‐filled pore systems under hydrostatic to lithostatic pressure, are judged to slow or prevent compaction in sucrosic dolomites. It can be argued that cortex growth involves both replacement of CaCO₃ particles and microcementation of their interparticle pores. This interpretation, and the abundance of cements in so many dolomites, would obviate the controversy over the volumetrics of ‘replacement dolomitization’. Limpid, planar and syntaxial dolomite cements of early diagenetic origin are interpreted to have precipitated from clear pore waters, at low temperatures (<30 to 35 °C) and shallow burial depths (<100 m), in water‐saturated networks of dolomite ‘silt’ and ‘sand’. Cements in many dolomites in island and continental–aquifer systems appear to result from event‐driven processes related to sea‐level highstands. Cementation events can follow ‘replacement dolomitization’ events by time intervals ranging from geologically ‘instantaneous’ to tens of million years.     

Wave-generated structures in the Devonian lacustrine sediments of south-east Shetland and ancient wave conditions

The most common wave-generated structures in the nearshore lacustrine sediments of the south-east Shetland basin are cosets of undulatory and unidirectional ripple cross-lamination. The undulatory lamination was produced at relatively high oscillatory flow strengths by accretion of rolling grain (post-vortex) ripples, and the unidirectional cross-sets were formed by the migration of vortex (orbital) ripples at lower strengths. Unidirectional solitary lenses were generated under moderate but discontinuous wave activity on a partly sand-starved substrate. Some lenses were reworked during periods of more prolonged wave activity. The Inman-Komar plot of near-bottom orbital diameter versus ripple spacing (λ= 0.80d₀ for small d₀, or λ= 0.65d₀ as modified by Miller & Komar) may only be used in estimating ancient wave conditions for vortex ripples with low Vertical Form Indices and small wavelengths. This laboratory based relationship (minimum d₀ conditions) is utilized in this study since wave periods in lakes are small. The estimation of ancient wave conditions suggests that the ripples were produced in water depths of up to 10 m and in most cases less than 5 m. The formative waves possessed periods of up to 3.4 sec and suggest that the lake was relatively small, perhaps of the order of 20 km wide.     

GRAPHICS FOR LINEARITY AND SELECTIVITY AND PREDICTION DIAGNOSTICS FOR MULTICOMPONENT SPECTRA

Modern scanning infrared reflectance/absorption spectroscopes measure absorptions or reflectance at asequence of around 1000 wavelengths. Training data may consist of 10-100 carefully designed samplemixtures whose true compositions are either known by formulation or accurately determined by wetchemistry. In future, one wishes to predict the true composition of a newly presented sample from itsspectrum. Varying compositions of a mixture of three sugars in water are used for illustration of severaldifferent graphical techniques; the spectral measurements here are near-infrared (NIR) absorbances, butthere is nothing exclusively infrared about the methodology. Graphs display the adequacy of a linearexplanation of absorbance variability at each wavelength by wavelength linearity plots. These highlightregions of the spectrum where non-linearities and interaction effects are substantial. By selecting out thesesubstantially non-linear regions, one can concentrate on linear formulae for prediction with resultantrobust linear modelling. Such selections are further aided by plots which identify the component sugarfor which each wavelength is most selective. Such plots offer rather natural pre-screening as an alternativeor supplement to the wavelength selection method of Brown. We also display prediction diagnostics (R, Rx) which on a sample-by-sample basis may diagnose aparticularly unusual presented spectrum. These diagnostics are shown to have predictive import for avalidation data set.     

Quantitative estimation of sediment erosion and accretion processes in a micro-tidal coast

Spatio-temporal cross-shore profiles and textural characteristics are the key parameters for understanding dynamics of the inter-tidal sedimentary environment.This study describes short-term dynamics of the inter-tidal sedimentary environment at beaches along the micro-tidal coast.Further a correlation is estimated in cross-shore morphodynamics and textural characteristics of surface sediments.The sedimentary environment is examined for a complete annual cycle using monthly collected cross-shore profiles and sediment samples.The Devbag beach（northern side） and Ravindranath Tagore beach（southern side） at the Kali river mouth,Karwar,west coast of India are characterized from extremely gentle to average slope,and broadly composed of unimodal sands.The sedimentary environment is significantly composed of textures having fine to medium sand,well to moderately sorted,fine to coarse skewed,and platykurtic to leptokurtic in nature.During the annual cycle a reversal pattern is observed between the two adjacent beaches,where a slower rate of sediment accretion is observed at Devbag beach while Ravindranath Tagore beach exhibited erosion.The beach dynamics along with the propagation of south-west（SW） and south-west-west（SWW） waves towards the coast significantly exhibit a dominance of northward sediment transport with the existence of a northerly alongshore current.In addition,the study reveals that an eroded beach may not be significantly identified composed of coarse grains.The poor correlation in morpho-sedimentary characteristics reveals the prediction of grain characteristics based on beach profile and vice-versa is unrealistic.