TEXTURAL AND LITHOLOGICAL ANALYSIS OF BERM SEDIMENT ALONG THE SOUTHERN SHORES OF LAKE MICHIGAN

This study presents textural and lithological analysis of seventeen samples of berm sediment collected from the beaches of Lake Michigan in Indiana. Granule size (2-4mm) sediment fraction was examined with optical microscope and compared with lithology of modern beach gravel (>8mm), which was examined in previous study (Kilibarda et al., 2013). Subangular to subrounded particles predominate in all samples and suggest relatively immature sediment. Most of the berm sediment, from Gary to Michigan border (Northeastern, Eastern, and Central sectors of Indiana’s shoreline), is similar in composition, with most abundant clastic (~40-50%) and crystalline particles (~25-30%). Even though clastic granules are most abundant grain lithology, their relative abundance never reaches as high content (>90%) as in gravel size (>8 mm) fraction. Carbonate granules relative abundance diminishes westward (from Michigan border to Gary), from ~20% to ~7%, while chert granules relative abundance increases westward from ~6% to ~17%. Carbonate granules never reach as high content (> 70%) as they do in gravel size fraction. Relative abundance of anthropogenic particles (7-12%) is larger than in gravel size fraction (0.5-3%). From Gary to Illinois border (Western sector of Indiana’s shoreline), chert (26%) and clastic (26%) are slightly more abundant than crystalline (19%) granules, while anthropogenic and carbonate granules comprise the rest and are more abundant than in other sectors of the coast. This study indicates that there is a less impact of beach nourishment, lake fill, and release of industrial waste in changing lithology of granule size beach sediment than in changing lithology of gravel size sediment along southern beaches of Lake Michigan. Most of carbonate particles introduced through beach nourishment, and most of chert grains brought in as a lake fill, were of gravel size or larger diameter and likely did not yet break down into smaller particles. More constant presence and relatively larger amount of anthropogenic particles in granule than in gravel size fractions likely reflect relatively more rapid weathering of glass, brick, concrete, and slag, released by industrial and urban areas along the shoreline.