Parallel tunnel channels of the Huron-Erie Lobe of the Laurentide Ice Sheet: A variation of tunnel channels with implications on lobe history and subglacial meltwater dynamics

Abstract

Newly available high resolution elevation data across North America and Europe have revealed previously unknown glacial landforms. This study focuses on the morphology and stratigraphy of a variation of tunnel channels with unique morphology that we have named parallel tunnel channels (PTCs). They are found in northeastern Indiana, northwestern Ohio, and southeastern Michigan, which were previously glaciated by the Huron-Erie Lobe (HEL) of the Laurentide Ice Sheet (LIS). PTCs are discontinuous, quasi-parallel pairs of depressions separated by a continuous central ridge that can extend upwards of 50 km, cross-cut multiple recessional moraines, and transition into standard tunnel channels. The PTCs range in width from 200 to 900 m, and the depressions range in width from 100 to 200 m and in depth from 3 to 10 m. Using water well logs and multiple electrical resistivity surveys, we determined that the stratigraphy beneath and surrounding the PTCs consists of a lower layer of sand and gravel (confined aquifer) and an upper layer of New Holland till, both of the Lagro Formation. A vibracore and multiple resistivity surveys reveal that depressions are filled with ~4 m of lacustrine sediment and occasionally are floored with gravel channel deposits. The depressions are erosional in origin, rather than a product of ice block melt-out and are cut into the upper surface of the New Holland till. We interpret the PTCs as subglacial, erosional landforms, similar to tunnel channels, which represent distinct pathways transporting subglacial meltwater from the interior to the ice margin. Identification of these landforms has several important implications for understanding the deglaciation of the HEL: 1) the major recessional moraines may not record the final deglaciation of the HEL (i.e., are palimpsest features); 2) a large portion of the HEL must have stagnated to preserve the subglacial landscape including the PTCs; and 3) the combined network of PTCs, tunnel channels, and proglacial spillways may represent a partially complete subglacial drainage network with distinct morphological changes as meltwater was transported from the interior to the margin of the HEL. An initial formational model is proposed for the formation of the PTCs by way of a supra- and/or subglacial lake draining through an ice-walled subglacial tunnel, but additional work is required to understand the distinct pattern of depressions observed.