ABSTRACT The last-glacial megaflood Kankakee Torrent streamlined hills and the remarkably straight backslope of the Kalamazoo moraine (Lake Michigan lobe of the Laurentide ice sheet) in southwestern Michigan. Flooding ensued as proglacial Lake Dowagiac overflowed across remnants of the Lake Michigan lobe at the position of the inner margin of the Kalamazoo moraine as glacial debris and ablating ice were pinned against Portage Prairie. Proglacial Lake Dowagiac developed in the Dowagiac River valley as the lobe retreated to form the Valparaiso moraine. A minimum age of the Kankakee Torrent (18.7 ± 0.6 k.y. B.P) is indicated by the weighted mean value of six optically stimulated luminescence ages determined from quartz sand in glaciofluvial sediment on the Kalamazoo moraine (Lake Michigan and Saginaw lobes). This value is consistent with tighter age control based on radiocarbon ages of tundra plants within silty sediment forming ice-walled lake plains and in a torrent-scoured lake basin (Oswego channel) in Illinois. Crosscutting relationships of well-dated moraines indicate the Kankakee Torrent occurred sometime between 19.7 and 18.9 calibrated (cal.) k.y. B.P. as it skirted the south margin of the Valparaiso Morainic System.

Abstract Hemlo combines several rare to unique features in the spectrum of Archean greenstone gold deposits. It is an isolated, approximately 800-metric ton (t) gold system in a region of otherwise limited known gold endowment. The geology of Hemlo is dominated by deformed and metamorphosed sedimentary, felsic volcanic, and volcaniclastic units, a premineral coherent felsic porphyry, and a swarm of mainly postmineral, intermediate, feldspar-phyric dikes. Ore is dominantly in the form of gold-bearing lenses of pyritic, feldspathic schist derived from deformation of both the clastic rocks and the felsic porphyry. The deposit and its host rocks were metamorphosed at moderate pressures to assemblages diagnostic of the mid-amphibolite facies, followed by progressive retrogression to those of the greenschist facies. The result is a wide range of silicate mineral species in ambiguous textural relationships. The gold system itself is known for ore and related alteration minerals with significant concentrations of Mo-As-Sb-Hg-Tl-V-Ba-K-Na. The inferences derived from lithologic mapping, structural chronology, U-Pb geochronology, and mineral paragenesis favors an interpretation of Hemlo as a deformed and metamorphosed gold system formed from oxidized hydrothermal fluids in an upper crustal setting. Uncertainty remains as to the exact nature and geometry of that ore-forming hydrothermal system, however, and the role subsequent metamorphism and deformation have played in the local remobilization of ore constituents into their present paragenetically late structural sites.

ABSTRACT The Eagle Lake basin was formed by collapse of the ablating Lake Michigan lobe over a tunnel valley and subsequent reoccupation of the collapse basin by the lobe during local final phase of glaciation. Latest collapse occurred prior to about 16,250 but after 18,600 cal yr B.P. A hydrologically open lake occupied Eagle Lake basin from 16,250 cal yr B.P. to the present. The lake was described in 1834 by the original land survey, but was drained for agriculture by 1939.

ABSTRACT This field guide discusses the dune types and processes, ecology, and geomorphic history of the largest freshwater dune systems on the southeastern shore of Lake Michigan. From north to south, stops include P.J. Hoffmaster State Park, Gilligan Lake/Green Mountain Beach Dune, Saugatuck Harbor Natural Area, and Grand Mere and Warren Dunes State Parks, Michigan. All of the sites are low, perched transgressive dune complexes. Moving from the lake inland, the typical dune complex in this area consists of incipient foredunes, an established foredune ridge, a parabolic dune complex, and a back-dune ridge complex. All stages of ecological succession are typically present in the larger dune complexes. Surface changes in Lake Michigan dunes are driven by spatial gradients in sand flux, which, in turn, are determined by a complex interaction among wind dynamics, vegetation patterns, and preexisting topography. Surface change patterns are modified by seasonal effects, with the majority of sand transport being associated with strong storms in the autumn, winter, and early spring. Sand can be temporarily stored in niveolian deposits during the winter, leading to oversteepened slopes, which collapse during the spring thaw. Current dune complexes largely formed during and after the rise in lake levels to the Nipissing high lake level, ca. 4.5 ka. Broad fields of relatively low dunes developed during the lake-level drop following the Nipissing high. Beginning with the rise to the Algoma high lake level, ca. 3.2 ka, the lakeward edges of these fields were episodically reworked, forming large parabolic dune complexes. A period of widespread dune stability formed the Holland Paleosol, a spodic inceptisol. Dune growth and migration resumed prior to European settlement of the area and continues today. Foredune complexes grow wider and higher during periods of low lake levels, but narrow during periods of high lake level due to scarping at their lakeward edges.