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The Middle Swedish End-Moraine Zone lies in central Sweden and represents ice-margin build-ups formed during the Younger Dryas cold event. Immediately west of Mt. Billingen between Skara and Götene, Sweden, lie seven prominent ice-margin positions indicated by moraine ridges. It has long been know that these ridges are composed primarily of clay. Recent drilling and investigation of new highway exposures reveal that the ridges are push moraines composed primarily of deformed glaciomarine varved clay. Sediment exposed in the moraines ridges include folded and faulted varved clay, highly deformed clay, and clay-rich diamicton, with minor amount of sandy, gravelly diamicton, and rippled sand with clay clasts. Orientation of thrust faults, folds, and conjugate fractures indicate stress from the north, perpendicular to the moraine trend. Rippled sand in the Ledsjö ridge is undisturbed to highly deformed, and in places occurs in boudin-like structures.
The study area lay below the marine limit during ice retreat, and only a few of the moraine crests would have stood above sea level. Dating of nearby undisturbed marine varves shows them to be of Younger Dryas Chronozone age. Based on dating, stratigraphic relationships, and structural features, we present the following model: As ice retreated from the southern-most Skara ice-margin limit, marine varves accumulated on the sea floor (in most places, directly on newly exposed bedrock). A small readvance of the ice margin created each push moraine. The Gullhammar ridge is small and consists of folded varves and deformed clay with till on the proximal side. The larger Ledsjö ridge shows more complex deformation and penecontemporaneous sedimentation of sand. Reasonable values of sedimentation rates and retreat and advance rates indicate that deposition of the thick clay in the region and formation of these seven push moraines could easily have occurred during the constraints of available dates.
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