3-D STRATIGRAPHIC AND FACIES MODELS OF THE GLACIAL AQUIFER SYSTEM OF BERRIEN COUNTY, SOUTHWESTERN MICHIGAN

The 3-D models of the glacial aquifer system of Berrien County, Michigan, consist of a series of overlapping map-unit files, organized from oldest to youngest, showing the extent of surface (exposed) and subsurface (buried) parts of each unit, coupled with files of surface and subsurface topographic contours for all the parts. Other files define the coincident extent and altitudes of single or multiple sedimentary facies within each unit, such that each model defines 100 percent of the system volume.

The glacial aquifer system of Berrien County, Late Wisconsinan in age, comprises stratified-moraine and till-ridge moraine segments, and incised fluvial segments along the major rivers. Deposits of the higher, inland stratified moraine segment are correlated with local glacial lakes in the Kalamazoo/Valparaiso morainic systems. Twenty-four overlapping allostratigraphic map units portray 48 ice-marginal glacial deltas, having characteristic morphology, exposed delta topset and upper foreset facies, and upward-coarsening grain-size trends. The deltas are shingled from south to north (older to younger), shown by contacts of distal bottomset facies onlapping onto collapsed coarse facies of older deltas to the south. Mappable surface sediment facies are: 1) delta topset coarse fluvial gravel, 2) delta topset fluvial sand and gravel, 3) upper delta foreset sand and gravel, and 4) upper delta sandy foreset facies. Subsurface facies include: 1) lower foreset sand and gravel, and 2) lower foreset sand, which includes distal delta bottomset sand. Glacial lake-bottom deposits, 1) sand, 2) sandy silt, and 3) silt-clay, overlap deltaic deposits and are extensive aquitards.

Deposits of the lower, coastal till-ridge moraine segment in the Lake Border morainic system contain interbedded till-sheet aquitards and poorly producing aquifers composed of lake-bottom deposits. Till units are modeled as discrete sheet deposits, <20m thick, that rise from the bottom of the basin to culminate eastward in moraine ridges. Interbedded lake deposits, 15-80m thick, are modeled as fill deposits in deep basin troughs. Incised meltwater terrace segments are juxtaposed with river alluvium, which is graded to local bedrock knickpoints inland and at the coast, providing a thick permeable conduit for ground-water discharge to Lake Michigan.