Thursday, February 13, 2014

Diamicton: keeping it close to the source

We are logging diamicton, one of my favorites considering its esthetic quality! These sediments were generated by glacial erosion, and probably originate from the Scandinavian Ice Sheet abrading ancient rock surfaces to the north. Baltica, which carried the Scandinavian craton used to be a separate continent before it collided with first Eurasia and then North America (Laurentia) some 400 million years ago. It is composed of the three rock groups: igneous, metamorphic, and sedimentary rocks. Igneous rocks, such as granite were formed through consolidation of magma, metamorphic rocks through a rise in pressure and temperature during  mountain building, and the sedimentary rocks accumulated in ancient basins. Much later, during the last Ice Age, when people were populating Europe, ice sheets plucked rock fragments out of the Baltic Shield and dumped them into the Baltic Sea Basin to form these diamictons. The diamictons are competely barren of macro and microfossils and are only composed of detrital components, meaning rock fragments derived from erosion of pre-existing rock. The rock fragments in the diamicton range from invisible to several centimeters across and are angular and not chemically weathered: we call this an immature sediment. The composition of the diamicton can tell us about the mode of deposition and source regions of the ice, a topic to be studied later in the lab at Montclair State University. For these post-expedition studies, samples are taken. The diamictons are very hard and consolidated and require the sampling team to use hammers as you can see in this picture.

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