GLACIODELTAIC ORIGIN OF THE VALPARAISO MORAINE IN BERRIEN COUNTY, MICHIGAN

The Valparaiso morainic system in eastern Berrien County, southwestern Michigan, is a 10-18 km-wide continuous belt of collapsed glacial landforms. Previously, this moraine belt was inferred to be composed of unsorted materials, including coarse- to fine-textured tills, and some stratified deposits. Recent mapping using well records, geophysics, and test drilling revealed the moraine to be composed of glacial meltwater deposits, commonly 100 ft thick. The deposits include >50 glaciodeltaic morphosequences, mostly ice-marginal deltas, graded to proglacial Lakes Madron and Dowagiac. Both Lake Madron and younger Lake Dowagiac were dammed to the south by the Kalamazoo moraine and to the west by the retreating edge of the Michigan glacial lobe. Each delta grades from ice-contact landforms underlain by coarse-grained facies at its head to non-collapsed landforms underlain distally by fine-grained facies. Proximal deltaic deposits are coarse grained, locally containing boulders and lenses of poorly sorted flowtill with zones of collapsed bedding along ice-contact slopes. A composite section of a delta, derived from a gravel pit exposure extended by a drillhole showed, from top to bottom: 20 ft glaciofluvial sand and gravel; 15 ft deltaic foreset sand, silt, and gravel, dipping SSE, 10 degrees; 30 ft pebbly sand; 35 ft coarse to medium sand; 26 ft medium to very fine sand and silt at the base; overlying 5.5 ft of gray silty (Saugatuck?) till. Lake Madron deltaic glaciofluvial plains grade from 840 ft altitude to distal distributary plains at 790 ft, controlled by the lake level and spillway at 785 ft. Lake Dowagiac deltas have fluvial plains as high as 820 ft graded to distal plain altitudes of 740 ft. The Lake Dowagiac spillway crossed older deposits south of Niles, MI. Both lakes discharged through the St. Joseph River valley south across the regional drainage divide. Wide heads of deltas trending ENE within the Valparaiso moraine belt document nine ice-margin retreat positions, similar to older ice margins within the outer Kalamazoo Moraine.