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Image analysis study of the size, shape and surface-texture distributions of genetically different glacial deposits
Stratigraphic relationships in glacial deposits are often difficult to establish. This is because the sediments often appear to be similar and they often are difficult to date. Image analysis can provide detailed information concerning the size distribution of all three axes as well as the shape distribution of all the particles in a sample. Image analysis is sensitive to small variations that are not detectable with sieve analysis. Thus it should be possible to reveal differences in sediment that appear to be similar but are in fact of different genesis.
This project can incorporate several master’s student projects. Each project will focus on one geographical area where previous researchers have documented the glacial history and where there seems to be some difficulty in establishing criteria for stratigraphic relationships. Some examples are:
· Hillefors presents the occurrence of large, more than 2 meters deep, ice wedges in the middle of a sequence of coarse aggregate sediment. There is no obvious difference in the sediment in which the ice wedge is situated and the 2 meters of sediment overlying the ice wedge. Without the occurrence of the ice wedge there would be seemingly no evidence of a hiatus and the cold climate associated with it. Since the aggregates are proven to be of different genesis one would expect there to be differences in the size and shape distributions.
· Fernlund presents the occurrence of coarse aggregate sediment at Hunnestad, an ice marginal delta. The upper layer appears to be a “top set bed” deposited in association with the delta. However the clast composition suggests that there is a hiatus between the uppermost bed and the underlying sediment. The uppermost bed contains clasts of flint while the underlying beds lack flint. With out this difference no obvious difference exists between the sediments. Since the aggregates are of different genesis, besides the difference in clast composition, there may also be differences in the size and shape distribution
· Svensson presents the occurrence of wind polished boulders at Våxtorp, an ice marginal delta deposit. These are overlain by sand. A TL date, by Fernlund not yet published, of the sand suggests that it is pre late Weichselian in age. The sediment otherwise appears to be typical for a topset bed of an ice marginal delta. Since the date suggests that the Våxtorp delta is much older than the other ice marginal deltas in southern Halland there might also be a difference in the size and shape distributions.
· Robison interprets a late glacial transgression based on the sediment relationships at several ice marginal deposits in southern Halland. It is interpreted that the topset bed in overlain by a wave reworked sediment. This interpretation is based upon the observed angular character of the uppermost sediment. They are interpreted to be the result of frost fracturing of clasts in a cold land environment followed by a transgression of the sea that reworked these angular fractions. The difference between the two is particle shape.
· In northern Sweden there are several references to “old blue till” that is assumed to be stratigraphically older than the “normal” till. With image analysis we should be able to establish that these tills do differ with respect to size, shape and surface-texture distributions.
These are just a few of numerous examples of coarse clastic sediments w
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