Rogen moraine: an example of glacial reshaping of pre-existing landformsIntroductionMethodsGeneral geology and geomorphology of the study areaGlacial geomorphology of the Indån and Våmån river valleysThe Eggling sectionSediment descriptionGenetic interpretation of sediments and depositional processesThe Kipholstjärnen sectionSediment descriptionReddish diamictonOlive-green diamictonDark grey diamictonStructural geologySediment and process interpretationsA model of Rogen moraine formationSediment build-up and precursor ridge formationDeformation of the ridgesSummary of the Rogen moraine formation model and its palaeoenvironmental and chronological implicationsDiscussionComparison to other models of Rogen moraine formationThe ’fracturing model’mdasha critical discussionThe soil mechanics counter-evidenceThe geomorphological counter-evidenceFinal conclusions and remarksAcknowledgementsReferencesQuaternary Science Reviews 25 (2006) 362–389Rogen moraine: an example of glacial reshapingof pre-existing landformsPer Mo¨llerGeoBiosphere Science Centre/Quaternary Sciences, Lund University, So¨lvegatan 12, SE-22362 Lund, SwedenReceived 23 May 2004; accepted 19 January 2005AbstractRogen moraine is widely distributed in the core areas of the former Scandinavian and Laurentide ice sheets. It is generally agreedupon that these gently arched, ice-flow transverse ridges can be used in reconstructions of paleo-ice-flow patterns and that theyindicate a melted-bed or poly-thermal basal ice regime. However, the processes of ridge generation have been contentious. Thisstudy proposes a two-stage formation of Rogen moraine, based on detailed sedimentological and structural investigations inexcavated trenches in a Rogen moraine landscape in the province of Dalarna, central Sweden. Field data suggest that Rogenmoraine ridges are the reshaped remains of pre-existing transverse moraine ridges, originally deposited from ice-cored moraines inan ice-marginal zone. Due to back- and down-wasting of ice-cores, inter-ridge troughs were filled with debris flow and fluvialdeposits, which after landscape inversion were transformed to areas of transverse and hummocky moraines. It is proposed that thisprimary landscape formation occurred during an Early Weichselian deglaciation. This relict landscape was later preserved beneathcold-based Mid- to Late-Weichselian ice sheet(s), which turned wet-based during the Preboreal deglaciation phase and re-mouldedthe precursor landforms into Rogen moraine.r 2005 Elsevier Ltd. All rights reserved.1. IntroductionRogen moraine forms one of the most conspicuousexamples of glacially sculptured landscapes. Theselandforms, named after Lake Rogen in Ha¨rjedalen,Sweden, where they were first described (Hoppe, 1959;Lundqvist, 1969), are typical of the core areas of formerice sheets. They cover considerable areas in central andnorthern parts of Sweden (Lundqvist, 1981) and theformer core-areas of Laurentide ice sheets in NorthAmerica, where they are often called ‘ribbed moraines’(e.g. Hughes, 1964; Cowan, 1968; Aylsworth and Shilts,1989). Rogen moraine areas, in the classical sense, arecharacterized by anastomosing to curved ridges andintervening troughs, all lying trans verse to former ice-flow direction. A characteristic feature, at least in someareas, is the gradual up- and down-ice flow-directiontransition to drumlins (Lundqvist, 1969, 1989), some-times with streamlined moraine hummocks in betweenthe end-member landforms. Equally characteristic is anon-transitional lateral shift to streamlined terrain(cf. Aylsworth and Shilts, 1989).Few glacial landforms have been subjected to suchchange in their genetic interpretation as Rogen moraine.At first they were regarded as end moraines (Fro¨din,1925), but were later suggested to be supraglacial,stagnant ice features deposited in open crevasses(Lundqvist, 1943, 1958). Contrary to this, Granlund(1943) suggested that deposition took place in basalcrevasses, into which till was squeezed due to iceoverburden pressure. Formation by active-ice processeswas suggested by Cowan (1968), Lundqvist (1969) andSugden and John (1976, p. 245), further advanced byShaw (1979), Bouchard (1989) and Aylsworth and Shilts(1989). The latter authors suggested a two-phaseformation of Rogen moraine, with an active phaseduring which there was a near-base folding (Shaw, 1979)ARTICLE IN PRESS0277-3791/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.quascirev.2005.01.011Tel.: +46 46 2229888; fax: +46 46 2224419.E-mail address: [email protected] stacking (Bouchard, 1989; Aylsworth and Shilts,1989) of debris-rich ice, followed by stagnation andpassive, mainly subglacial, melt-out of the differentiallydistributed debris-rich ice into Rogen ridges. The studiesby Shaw (1979) and Bouchard (1989) are so far the onlyones based on more comprehensive sedimentologicaland structural investigations. For a more comprehensivereview of previous studies on Rogen moraine, seeLundqvist (1989) and Ha¨ttestrand and Kleman (1999).This wide array of theories on Rogen moraineformation and the large differences observed in the typeof internal sediments—including tills, inter preted to belodgement till, melt-out till and flow till, and glacio-fluvial sediments—led Lundqvist (1989), after a thor-ough review of Rogen moraine properties, to propose atwo-step formation of Rogen moraine. He discussed theconcept of both steps taking place within the sameglacial cycle as well as the possibility that the sedimentswere deposited during an older glacial event and thenlater re-shaped into Rogen moraine during a laterglacier advance. Lundqvist (1989) favoured the latterpossibility, which indicates that Rogen moraine wasformed by the remoulding of pre-existing sediments/landforms. More recently, Lundqvist (1997) furtherstressed the two-step model but offered no newsedimentological or structural data supporting this view.A new model of ribbed-moraine formation (intowhich Rogen moraines sensu Lundqvist (1989) areincorporated) has been proposed by Ha¨ttestrand(1997a, b), Ha¨ttestrand and Kleman (1999) and Klemanand Ha¨ttestrand (1999). This model advocates subgla-cial fracturi ng and horizontal extension of frozen, pre-existing subglacial sediments. During deglaciation, theupper portion of the subglacial sediment remains frozenbut overlies thawed sediment. The horizontal boundarybetween these is called the Phase Change Surface (PCS)and