ABSTRACTMAPPING AND CHARACTERIZING A RELICT LACUSTRINE DELTA IN CENTRAL LOWER MICHIGANByChristopher B. ConnallonThis research focuses on, mapping and characterizing the Chippewa River delta - a sandy, relict delta of Glacial Lake Saginaw in central Lower Michigan. The delta was first identified in a GIS, using digital soil data, as the sandy soils of the delta stand in contrast to the loamier soils of the lake plain. I determined the textural properties of the delta sediment from 142 parent material samples at ≈1.5 m depth. The data were analyzed in a GIS to identify textural trends across the delta. Data from 3276 water well logs across the delta, and from 185 sites within two-storied soils on the delta margin, were used to estimate the thickness of delta sands and to refine the delta's boundary. The delta heads near Mount Pleasant, expanding east, onto the Lake Saginaw plain. It is ≈18 km wide and ≈38 km long and comprised almost entirely of sandy sediment. As expected, delta sands generally thin away from the head, where sediments are ≈4-7m thick. In the eastern, lower portion of the delta, sediments are considerably thinner (≈<1-2m). The texturally coarsest parts of the delta are generally coincident with former shorezones. The thick, upper delta portion is generally coincident with the relict shorelines of Lakes Saginaw and Arkona (≈17.1k to ≈ 16k years BP), whereas most of the thin, distal, lower delta is generally associated with Lake Warren (≈15k years BP). Delta sediments from neighboring drainages merge with lower Chippewa Delta sediments, obscuring landform boundaries. Together, these data suggest that the Chippewa Delta formed and prograded as lake levels episodically fell, producing a two-tiered delta complex and an overall, thin, sandy landform.
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