The late Wisconsin and Holocene development of the St. Joseph River drainage basin, southwest Michigan and northern Indiana.

摘要

The St. Joseph River and its tributaries drain approximately 11,137 km2 in southwestern Michigan and northcentral Indiana. It originates from Baw Beese Lake near Hillsdale, Michigan through a total length of 316 kilometers with a head of 158.8 meters above base level in Lake Michigan at Benton Harbor, Michigan.;Evidence for the events that shaped the St. Joseph River drainage basin is seen in the longitudinal profile of the river which can be used as a proxy for events that occurred in the drainage basin given a proper understanding of how disequilibrium in the drainage basin changes the slope of the profile. The longitudinal profile of the St. Joseph River has four nickpoints that divide the profile into 5 distinct sections: a base-level affected section at the mouth, a stream-capture section, a central section where proglacial lakes overflowed to the south, a convex-upward section immediately downstream of flow loss due to stream capture, and a final section that was a former tributary that became the main stem due to the aforementioned stream capture.;The longitudinal profile shows evidence that the St. Joseph River drainage basin was sequentially constructed from the distal areas to the proximal areas. Glacial retreat added sections to the basin in step-wise fashion as the glacier margin moved basinward. The accepted pattern of regional slope and stream- network development corresponding to a pre-existing structural or stratigraphic pattern in combination with continuous extension via headward erosion does not apply. The drainage basin was constructed in discrete parts during glacial retreat. Each discrete part has a distinct depositional history separate from each subsequently added segment. The relative positions of the ice margins also imparted controls on the volume of meltwater into the distal part of each basin. In addition, the ancestral St. Joseph River contains underlying deglacial terrain originating within the Lake Michigan, Huron/Erie, and Saginaw lobes that all contributed to the final drainage-basin geomorphology.;Early deglacial drainage was initially south toward the Wabash River and later west to the Kankakee River before attaining its final configuration draining to Lake Michigan. Glaciers acted as dams and ponded water in proglacial lakes that overflowed to the south. Post-glacial drainage basin development was controlled by Holocene lake-level fluctuations, stream capture, and the inherited hydraulic gradients of glacial flow regimes. Two major terraces document the final meltwater pulses through the drainage basin both originated from the Huron/Erie lobe. The St. Joseph River did not drain into the Lake Michigan basin until the Calumet phase of glacial Lake Chicago, 1500 years after previously thought.