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SUBMARINE PUSH MORAINES OF THE MIDDLE SWEDISH END MORAINE ZONE

Conference paper
Authors Mark D. Johnson
Ívar Örn BENEDIKTSSON
Lennart Björklund
Published in Geological Society of America abstracts with programs Minneapolis 2011
Publication year 2011
Published at Department of Earth Sciences
Language en
Keywords moraine push younger dryas
Subject categories Earth and Related Environmental Sciences, Quaternary geology, Physical Geography

Abstract

During the Younger Dryas cold event (YD), the Scandinavian Ice Sheet formed the Middle Swedish end-moraine zone (MSEMZ) in south-central Sweden. The area around Skara was below sea level during the YD, and thick marine, varved clay was deposited proglacially on scoured bedrock in the ocean prior to, during, and after the YD. Recent highway exposures in four of the seven ridges in the MSEMZ reveal that, during overall retreat, the ice margin oscillated and, during each oscillation, deformed the marine clay into moraine ridges. The push moraines have little to no till, and then only on the proximal sides. A range of deformation structures are present including folded-and-thrusted to remobilized varved clay. At Ledsjö, a double oscillation is apparent with a grounding-line fan of sand formed between the two oscillations, which was then deformed. The grounding-line-fan sands are faulted and boudinized within 100 m of the former ice margin. Sand in boudins in places retains primary sedimentary structures, but elsewhere show fluidized flow. Farther up-ice, the clay and sands are complexly sheared along down-glacier-dipping reverse faults of several scales (cm to 10´s of m) indicating a subglacial tensional environment. At Ledsjö and Gullhammar, an upper, structureless clay likely represents proglacial, submarine, mudflow sediment deposited on the distal slope of the moraine. These exposures provide models for recent submarine push moraines imaged in fjords in Norway and Svalbard.

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