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Stratigraphy and age of Quaternary sediment in the Middle Swedish End Moraine zone

Journal article
Authors Mark D. Johnson
Published in , Bulletin of the Geological Society of Finland
Issue Special Issue 1
Publication year 2006
Published at Department of Earth Sciences
Language en
Keywords middle swedish end moraine quaternary younger dryas OSL
Subject categories Quaternary geology

Abstract

Recent drilling and geophysical studies in the moraine ridges of the Middle Swedish End Moraine Zone (MSEMZ) show them to be made primarily of clay, but also to contain coarser sediment (sand and some till) particularly on their proximal slopes. Resistivity measurements reveal structures in the clay that are interpreted as thrusts. The moraines are interpreted to be thrust moraines, formed subaqueously at the margin of the Scandinavian Ice Sheet. In addition to the thrust ridges, numerous sites along the former ice-margin positions reveal proximal meltwater sediment deposited in ice-contact deltas that were fed by subglacial meltwater channels. Recent drilling in the intermorainic flats reveal 20 to 30 m of stratified fine sediment (gray to brown silt and clay) overlying till or bedrock. The fine sediment is capped by sand and gravel that contains abundant shale and sandstone clasts eroded from Mt. Billingen. The fine sediment is similar in color, grain size, and sedimentary structure to the clay in the moraine ridges; however their stratigraphical relationship is unclear. That is, it is not clear if the clay in the intermorainic positions is a younger, an older, or the same stratigraphic unit as the clay in the thrust ridges. Two OSL dates on sand grains from the clay in the thrust-moraine ridges yield preliminary dates of 45±5 ka and 67±8 ka, similar to previously reported luminescence ages on the same clay. These dates suggest the clay in the ridges to have been deposited before the Late Weichselian.

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