Transverse Moraine Ridges Research Articles

Assessment of the Amaruq gold deposit signature in glacial sediments using multivariate geochemical data analysis and indicator minerals

The varying nature and thickness of glacial sediments affect the characteristics of mineralized dispersal trains in the Amaruq gold deposit area in Nunavut, northern Canada. To help evaluate the deposit signature, glacial sediments were collected from frost boils along transects parallel to the main ice-flow direction. A complementary detailed geochemical drift exploration dataset and a new Quaternary map were also used to define and interpret the geometry of the mineralized debris dispersal trains. Principal Component Analysis identifies a gold mineralization signature associating As, Ag, Au, Cu, Pb, Sb, W, S, Fe, and Zn and its mafic-BIF (Banded Iron Formation) host rock. This signature, similar to other lode gold geochemical signatures, follows a general NNW dispersal trend, in agreement with the predominant regional and local ice-flow indicators. In a zone characterized by streamlined landforms composed of thick distally -derived till, the dispersal train shows a higher distance for the first indicator to appear at surface down-ice of the known mineralization (~1 km lag) when compared to other mineralized dispersal trains (~300 m lag). Results from this area also show a lower intensity of deposit signature compared to mineralized dispersal trains located in thin locally-derived till characterized by small transverse moraine ridges. Elevated counts of scheelite and pristine-shaped gold grains are found down-ice of mineralization and their distribution is in general agreement with the dispersal train patterns defined by the till-matrix geochemistry. Our results strengthen the use of PCA and indicator minerals combined with an understanding of ice flow dynamics to map deposit signatures at surface and efficiently guide mineral exploration during glacial sediment surveys at local scales.

Moraine ridges in fjord-type, perialpine Lake Lucerne, central Switzerland

Overdeepened valleys and troughs on the northern and southern margins of the central European Alps have been shaped during the Quaternary glaciations (Preusser et al. 2010). These valleys host a number of fjord-type lakes, remnants of formerly larger water bodies, which show various morphological features that reflect their glacial origin, similar to marine fjords. Among the most prominent of these features are large-scale transverse moraine ridges in Lake Lucerne, a perialpine lake situated in a branched valley system on the northern margin of the Alps (Fig. 1b, c). Fig. 1. Swath-bathymetric data and reflection-seismic profiles from Lake Lucerne, central Switzerland. ( a , d ) Shaded-relief images of the Nase Moraine and Chindli Moraine. Colour represents depth; greyscale for areas outside the lake. Acquisition system GeoAcoustics GeoSwath Plus. Frequency 125 kHz. Grid-cell size 1 m. Greyscale derived from swisstopo swissALTI3D elevation model. Labels: ch, chutes and channels; fa, fan-shaped deposit; cr, secondary crest. ( b ) Location of study area (red box; map from GEBCO_08). ( c ) Overview of Lake Lucerne; areas shown in (a) and (d) are marked by red rectangles. ( e , f ) Reflection-seismic profiles across the moraine ridges. VE×4. Acquisition system RCMG Centipede sparker, SIG single-channel streamer, IXSEA Delph acquisition unit. Vertical scale …

Origin of washboard moraines of the Des Moines Lobe: Spatial analyses with LiDAR data

The Des Moines Lobe (DML)—the largest lobe along the southern margin of the Laurentide ice sheet—deposited low-relief (1–5m) transverse moraine ridges, herein called washboard moraines, that are most prominent in central Iowa. Their origin as either subglacial or ice-marginal features bears on the dynamics of the lobe, geomorphic reconstructions of it, and interpretations of similar ridges elsewhere. Data from airborne laser swath mapping provide the first digital elevation models with sufficient spatial resolution to study in detail the geometric attributes of these topographically subtle features. Spectral analysis of profiles perpendicular to ridge crests indicates that most of them are spaced with statistically significant periodicities, with dominant wavelengths of 70–150m. Normalizing and stacking these profiles indicate that, on average, they display no systematic asymmetry. Locally, washboard moraines are intersected by discontinuous longitudinal ridge segments. Trends of the crests of moraines are scalloped, with cusps that point upglacier and are coincident with outwash trains, which were overridden by the lobe. Our interpretation of these data is that the moraines formed subglacially as crevasse-squeeze ridges. Overridden outwash trains likely supported low basal water pressures and resulted in anomalously slow basal slip, causing upglacier deflection of crevasses that extended to the bed. This crevasse-squeeze interpretation reinforces evidence that the DML surged to its maximum position. Bering Glacier, as a temperate, surge-type glacier that deposited crevasse-squeeze ridges similar to the washboard moraines of the DML, may be a good analog for the lobe.

Glacial geomorphology of terrestrial-terminating fast flow lobes/ice stream margins in the southwest Laurentide Ice Sheet

Glacial geomorphological mapping of southern Alberta, Canada, reveals landform assemblages that are diagnostic of terrestrial-terminating ice streams/fast flowing outlet glaciers with lobate snouts. Spatial variability in features that comprise the landform assemblages reflects changes in (a) palaeo-ice stream activity (switch on/off); and (b) snout basal thermal regimes associated with climate sensitive, steady state flow. Palaeo-ice stream tracks reveal distinct inset sequences of fan-shaped flowsets indicative of receding lobate ice stream margins. Former ice lobe margins are demarcated by (a) major, often glacially overridden transverse moraine ridges, commonly comprising glacitectonically thrust bedrock; and (b) minor, closely spaced recessional push moraines and hummocky moraine arcs. Details of these landform types are well exhibited around the former southern margins of the Central Alberta Ice Stream, where larger scale, more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges (MTR types 1–3), hummocky terrain (HT types 1–3), flutings, and meltwater channels/spillways. The MTR type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined. The MTR type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts. The MTR type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain. The close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin, where the HT type 3 hummocks represent former ice-walled lake plains. The ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern Alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream/fast flow lobes of the southern Laurentide Ice Sheet, where alternate cold, polythermal, and temperate marginal conditions associated with climate sensitive, steady state flow sequentially gave way to more dynamic streaming and surging activity.

Rogen moraine: an example of glacial reshaping of pre-existing landforms

Rogen moraine is widely distributed in the core areas of the former Scandinavian and Laurentide ice sheets. It is generally agreed upon that these gently arched, ice-flow transverse ridges can be used in reconstructions of paleo-ice-flow patterns and that they indicate a melted-bed or poly-thermal basal ice regime. However, the processes of ridge generation have been contentious. This study proposes a two-stage formation of Rogen moraine, based on detailed sedimentological and structural investigations in excavated trenches in a Rogen moraine landscape in the province of Dalarna, central Sweden. Field data suggest that Rogen moraine ridges are the reshaped remains of pre-existing transverse moraine ridges, originally deposited from ice-cored moraines in an ice-marginal zone. Due to back- and down-wasting of ice-cores, inter-ridge troughs were filled with debris flow and fluvial deposits, which after landscape inversion were transformed to areas of transverse and hummocky moraines. It is proposed that this primary landscape formation occurred during an Early Weichselian deglaciation. This relict landscape was later preserved beneath cold-based Mid- to Late-Weichselian ice sheet(s), which turned wet-based during the Preboreal deglaciation phase and re-moulded the precursor landforms into Rogen moraine.

Ribbed moraine formation

Ribbed (Rogen) moraines are conspicuous landforms found in interior parts of formerly glaciated areas. Two major theories for ribbed moraine formation have been suggested in recent years: (i) the shear and stack theory, which explains ribbed moraine formation by shearing and stacking of till slabs or englacially entrained material during compressive flow, followed by basal melt-out of transverse moraine ridges, and (ii) the fracturing theory, according to which ribbed moraines form by fracturing of frozen pre-existing till sheets, at the transition from cold- to warm-based conditions under deglaciating ice sheets. In this paper, we present new data on the distribution of ribbed moraines and their close association with areas of frozen-bed conditions under ice sheets. In addition, we show examples of ribbed moraine ridges that fit together like a jig-saw puzzle. These observations indicate that fracturing and extension of a pre-existing till sheet may be a predominant process in ribbed moraine formation. In summary, we conclude that all described characteristics of ribbed moraines are compatible with the fracturing theory, while the shear and stack theory is hampered by an inability to explain many conspicuous features in the distribution pattern and detailed morphology of ribbed moraines. One implication of the fracturing theory is that the distribution of ribbed moraines can be used to reconstruct the extent of areas that underwent a change from frozen-bed to thawed-bed conditions under former ice sheets.

Origin, chronology and climatological significance of annual-moraine ridges at Myrdalsjökull, Iceland

Minor, transverse moraine ridges have formed annually at the retreating north margin of Myrdalsjökull, 550-600 m a.s.l., in south Iceland during the period 1928-1981. They are composed of slabs of clast-paved lodgement till and their formation at the glacier edge results from subglacial freezing-on of sediment slabs during winter and the annual cycle of ice-front activity. This type of annual-moraine ridge is likely to be characteristic of retreating temperate glaciers where the glacier toe is thin and winters are cold. The speed of glacier retreat is finely balanced with changes in mean summer temperature suggesting that the short-term ice-front fluctuations are climatically induced and not a result of surge activity.

The genesis and significance of ‘hummocky moraine’: Evidence from the Isle of Skye, Scotland

The range of genetic and climatic interpretations of Scottish ‘hummocky moraine’ is reviewed, and new data are presented from the Isle of Skye, western Scotland, which are used as the basis of a genetic classification. ‘Hummocky moraine’ on Skye is shown to consist of three principal sediment-landform associations: (1) recessional moraines; (2) chaotic ice-stagnation moraines; and (3) drumlins and fluted moraines. The recessional moraines consist of transverse moraine ridges and chains of mounds, and were formed by a combination of glaciotectonics and debris accumulation at active ice margins. Second, chaotic moraines consist of randomly-distributed hummocks, mounds and rim-ridges and record deposition in contact with inactive ice. Finally, drumlins and fluted moraines are longitudinally-oriented subglacial bedforms formed by a combination of lodgement and sediment deformation. Individual occurrences of ‘hummocky moraine’ may comprise one, two or all of these associations. The detailed study and differentiation of Scottish ‘hummocky moraine’ provides a valuable source of information on former glacier dynamics and landscape change.

Some Mechanisms of Controlled Moraine Development, Antarctica

AbstractContemporary processes of moraine development at the margins of polar glaciers encompass a wide range of subtly different mechanisms. Two types of “controlled” moraine evolution, applicable to hummocks and transverse moraine ridges, are identified from Wright Lower Glacier and Webb Glacier, southern Victoria Land, Antarctica. Type 1 moraine complexes involve a relatively abundant supply of supraglacial debris, the development of transverse thrust blocks in the ablation-zone ice and the subsequent re-arrangement of ablation debris in ablation cusps and on inactive thrust blocks. Relict landform suites, apparently formed in this manner, reveal large coarse-grained hummocks inset behind moraine ridge remnants.Type 2 moraines may develop where the supply of supraglacial debris is meagre but the growth of ablation cusps concentrates primarily englacial debris into small irregular hummocks. The gravel component of this debris is usually of finer texture than for type 1 deposits, reflecting abrasion/attrition effects of prior englacial transportation. Transverse moraine ridges may or may not be associated with type 2 hummocks, depending on local variations of ice motion, ice decay, and debris supply.

Some Mechanisms of Controlled Moraine Development, Antarctica

AbstractContemporary processes of moraine development at the margins of polar glaciers encompass a wide range of subtly different mechanisms. Two types of “controlled” moraine evolution, applicable to hummocks and transverse moraine ridges, are identified from Wright Lower Glacier and Webb Glacier, southern Victoria Land, Antarctica. Type 1 moraine complexes involve a relatively abundant supply of supraglacial debris, the development of transverse thrust blocks in the ablation-zone ice and the subsequent re-arrangement of ablation debris in ablation cusps and on inactive thrust blocks. Relict landform suites, apparently formed in this manner, reveal large coarse-grained hummocks inset behind moraine ridge remnants.Type 2 moraines may develop where the supply of supraglacial debris is meagre but the growth of ablation cusps concentrates primarily englacial debris into small irregular hummocks. The gravel component of this debris is usually of finer texture than for type 1 deposits, reflecting abrasion/attrition effects of prior englacial transportation. Transverse moraine ridges may or may not be associated with type 2 hummocks, depending on local variations of ice motion, ice decay, and debris supply.

Genesis of the Sveg tills and Rogen moraines of central Sweden: a model of basal melt out

Shaw, John 1979 1201: Genesis of the Sveg tills and Rogen moraines of central Sweden: a model of basal melt out. Boreas, Vol. 8, pp. 409–426. Oslo. ISSN 0300–9483.Climatic amelioration in permafrozen regions causes basal melting of Polar glaciers. Supraglacial debris concentrated at the ice surface by ablation at first inhibits the ablation process. When the surface debris is equal in thickness to the active layer no further surface melting occurs. Till deposition processes in permafrozen areas are consequently dominated by melt out from a basal isothermal zone at melting point. The basal melt‐out process is influenced by englacial structures and forms which are also largely responsible for the resultant landforms and deposits. Such basal melt out may also occur in areas with less severe climate. A model for deposition largely by basal melt out is documented by field observations in central Sweden. Melt‐out tills in areas of former extending or uniform glacier flow show an upward facies change corresponding to poorly attenuated and highly attenuated englacial facies. The till facies are recognised in terms of stratigraphic position, surface form, internal structure, and clast lithology, size, shape, and long‐axis orientation and dip. Areas of former compressive flow are characterised by basal melt out of folded and dislocated englacial debris zones in which the stacking of debris produced transverse moraine ridges. The internal structure of the ridges includes folded till bodies dislocated by thrust planes, horizontal, stratified layers cross‐cutting the tectonic structures, and characteristic distributions of clast long‐axis orientation and dip. The morphology of the ridges at both the macro and micro scales is in accord with the proposed model of formation. The morphological and sedimentological associations produced largely by basal melt out are summarized. An additional implication of the proposed model is that gradual lowering of the supraglacial sediment surface by bottom melting of regionally stagnant ice may be the cause of widespread marine or lacustrine transgression.

Transverse moraine ridges of basal origin in Härjedalen

Abstract A series of transverse moraine ridges in the area immediately east of Storsjön, Härjedalen, have been investigated, The ridges are 80–120 m long and 6–8 m high. The distances between the crests of the ridges are 80–100 m. The ridges are composed of a silty till, within which there are beds of shattered bedrock. These beds can be both folded and overthrust. They are overlain by a foliated till. Movement of material was in part directly upward: ore boulders occur directly above the sub-glacial outcrop of the parent mineralization. It is suggested that the ridges were formed as a result of the folding of frozen till and pure ice in a strongly compressive environment. The folding progressed into a continuous upward movement of rock material as a result of the power and duration of the compressive flow.