What is "ribbed moraine"?

Category Environmetal Geology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Mِller, Per; Lindén, M.
Holding Date 07 October 2008

Ribbed moraine, originally described as Rogen moraine, covers considerable areas of formerly glaciated terrain. Recently, Dunlop & Clark (2006) presented a classification scheme of ribbed moraine comprising 12 different form types. While subglacial formation of ribbed moraine is widely recognized, their exact genesis is less clear and heavily debated: monogenetic or polygenetic in origin? The former perception is that ribbed moraine has a single common origin regardless of morphology or composition, e.g. as stated by Dunlop & Clark (2006): "the most successful hypothesis will be the one that provides the most complete explanation of ribbed moraine characteristics". However, a few regional examples of various expressions according to the terminology of Dunlop & Clark (2006) illustrate that a polygenetic origin must be considered. "Åsnen-type ribbed moraine" in southern Sweden fit in planform, size and spatial distribution with "anastomosing ribbed moraine ridges" of Dunlop & Clark (2006). Based on sedimentological and structural studies it was concluded that they formed due to areal stagnation of debris-rich ice, followed by in situ sub- and supraglacial passive meltout (Möller 1987). "Downstream curving ribbed moraine ridges" in central Sweden (classic Rogen moraine) were studied by Möller (2006), who concluded that internal sedimentary facies and architecture in mid-ridge and horn positions suggest that these are the reshaped remains of precursor ridges.
It was further argued that these were built up as stacked sequences of debris-flow sediments during an Early Weichselian deglaciation and preserved due to cold-based conditions in the interior part of the Scandinavian ice sheet during the last glacial, transformed into classic Rogen shape at a late stage of the last deglaciation. "Niemisel-type ribbed moraine" in northern Sweden fit in planform, size and distribution to the "broad arcuate ribbed moraine ridges" of Dunlop & Clark (2006). Sedimentology and architecture indicate the combined influence of subglacial folding, thrust stacking and leeside cavity infilling (Linden et al. 2008).
Considering the above-standing cases, I oppose to the use of "ribbed moraine" as a genetic term for iceflow-transverse moraine and argue that "ribbed moraine" should only be used as a descriptive, morphological term that enclose a polygenetic group of glacial landforms.
References: Dunlop, P. & Clark, C. D., 2006. The morphological characteristics of ribbed moraine. Quaternary Science Reviews 25, 1668-1691. Lindén, M., Möller, P. & Adrielsson, L., 2008. Ribbed moraine formed by subglacial folding, thrust stacking and lee-side cavity infill. Boreas 37, 102-131. Möller, P., 1987. Moraine morphology, till genesis and deglaciation pattern in the Åsnen area, South central Småland, Sweden. LUNDQUA Thesis 20, 146 pp. Möller, P., 2006. Rogen moraine: An example of glacial reshaping of pre-existing landforms. Quaternary Science Reviews 25, 362-389.