Groundwater resources associated with sediments filling the Marion and Mahomet Valley Sections of the Lafayette Bedrock Valley System vary from miniscule to substantial, reflecting the wide range of glacigenic aquifer facies contained in the fill. These aquifer facies include braid-stream deposits that range from thin units within till sequences to immense, valley-filling masses. Also included is a variety of proximal to distal, subaerial to subaqueous, fan and fan-delta deposits; these range from thick masses of ice-proximal, cobbly rubble interspersed with thin diamicts and clays, to thin, discontinuous lentils of sand confined within lacustrine clays. Valley-fill aquifers are confined by capping till units, except where exhumed at the crossings of the Maumee-Wabash Trough (modern Wabash River Valley). A variety of aquifers typically are available within the valley-capping sediments; for this reason, much of the deep valley-fill has not been extensively explored or developed. Some valley-fill aquifers are so thin and/or deeply buried that their exploitation is unlikely, but others are so thick and areally extensive that exploitation easily can support sustainable yields of tens of millions of gallons per day.

ABSTRACT About 17,000 yr ago, Glacial Lake Maumee breached the Fort Wayne Moraine, sending an unimaginably large torrent of meltwater down the upper Wabash River Valley (UWRV). The Maumee Megaflood (MM) may have lasted only a few weeks, but it scoured out a deep trough along the main stem of the river, radically lowering regional base level in what amounts to a geological instant and imposing a strong disequilibrium on a landscape that continues to experience major geomorphic, environmental, and ecological adjustments. In Huntington and Wabash Counties, the central part of the trough is engorged in resistant, Late Silurian reef-associated and inter-reef rocks, producing the largest natural bedrock exposure in heavily glaciated northern Indiana. Unlike the immature, deranged drainage pattern that characterizes most of the glaciated region, streams adjacent to the UWRV form well-integrated drainage networks that exhibit features and processes more typical of high-relief bedrock areas, such as steep fall zones with prominent, lithologically controlled knickpoints, canyons, large terraces, falls and cascades, and a variety of bluff and hillside morphologies and associated groundwater phenomena. The exceptional exposures and diverse landscape of this region have attracted well over a century of interest from geomorphologists and glacial geologists, sedimentologists, stratigraphers, and paleontologists, as well as hydrogeologists, anthropologists, ecologists, and geoscience educators. Among other firsts, the organic origin of fossil reefs in the southern Great Lakes was definitively established in the UWRV, as was the occurrence of convulsive meltwater outbursts during deglaciation of the Laurentide Ice Sheet; likewise, the first direct Mississippi River–Great Lakes connection was also established here by early voyageurs. Today, the region is a popular destination for both nature tourism and history buffs, due in no small part to the burgeoning number of geologically inspired natural areas and historical sites. This field trip traces the MM from its outlet at Fort Wayne, through the bedrock gorge of the upper Wabash River, to the confluence with the late Tertiary Teays Bedrock Valley, with major emphasis on how the depositional framework and diagenetic history of the Late Silurian reef archipelago continue to reverberate in the modern geomorphic response of the valley to Pleistocene events. The first three stops focus on the Wabash-Erie Channel, which acted as the principal outlet of Glacial Lake Maumee and whose underlying geologic characteristics controlled the overall incision history of the MM. Several stops in the Wabash bedrock gorge and Salamonie Narrows will examine the handiwork of this flood, which created the spectacular klintar, or pinnacle-like reefs, of the UWRV, within a landscape that early geomorphologists likened to the scablands of eastern Washington. There, we will see world-class exposures of the fossilized Late Silurian reefs and how their organic framework and diagenesis are controlling the ongoing adjustment of the UWRV landscape and its streams to the convulsive changes imposed by the MM. Stop 9 will showcase the elusive Teays Bedrock Valley and its complex pre-Wisconsin fill, where it converges with the modern river and has been partially exhumed by a major tributary, and offers a study in contrasts between the bedrock-controlled landscapes of earlier stops and an equally steep one excavated entirely into unconsolidated deposits. After a brief stop at the iconic Seven Pillars landmark, the trip concludes at the spectacular Pipe Creek Jr. Quarry, which features several km of tall exposures through the Late Silurian carbonate complex, a late Neogene sinkhole deposit, and the overlying Pleistocene section.

Two floods of extreme magnitude occurred in the Wabash Valley during late Wisconsinan time. The First flood occurred when meltwater that was stored in disintegrating ice to the north was rapidly released into the valley at a point near Delphi Indiana. During the period of gradually increasing flow, a coarsening- and thickening-upward sequence was deposited, and at peak flow, crossbedded cobble gravels accumulated in sets as much as 5 m thick. Trough crossbeds were deposited along narrow reaches of the valley where flow depths and velocities were greatest. Along wider reaches, however, where velocities and depths were less, tabular and convex upward crossbeds were deposited, and in the widest parts of the valley, where the flow was too shallow to maintain equilibrium bedforms, planar-bedded gravels accumulated. The second flood occurred when a morainal dam was breached and glacial Lake Maumee drained out of the Lake Erie basin and into the valley at Fort Wayne. During initial stages the flood eroded a deep trench in older outwash in the valley, sculpted bedrock outcrops in the valley floor, and carved flutes in uplands where the flow topped valley margins. Deposition occurred during the waning stage, when disorganized cobble gravels in lee-eddy, pendant, and expansion bars were deposited, a train of megaripples was established, and sediments accumulated in the lee of large-scale obstructions on the channel floor. During both floods, flow strength declined quickly. Waning stage of the first flood is marked only in the uppermost parts of the sequence, where increased sand content, channel-Fills of sand and Fine gravel, and diminished bed-set thickness occur. In the upper parts of the bars deposited during the second flood, sediments fine upward markedly and are organized into well-defined planar beds.