Internal architecture of a till sheet, Tiskilwa Formation, north‐central Illinois, USA: Application of architectural element analysis

Abstract

Thick till sheets deposited during the Quaternary form significant aquitards in many areas of North America. However, the detailed sedimentary heterogeneity and architecture and depositional history of till units are not well understood. This study utilizes architectural element analysis to delineate the internal sedimentary architecture of the Tiskilwa Formation exposed at two outcrop sections in north-central Illinois, USA. Architectural element analysis facilitates systematic delineation of sedimentary architecture based on the nature of facies contacts and change in facies associations, delineation of unit geometries and understanding of depositional processes at different scales of resolution; making architectural element analysis suitable for the sedimentological analysis and palaeoenvironmental reconstruction of subglacial deposits. Eleven facies types are identified in this study, including sand, gravel and diamict facies that record a suite of subglacial depositional processes. Detailed analysis of facies contacts (bounding surface hierarchy) and change in facies associations allows the delineation of five architectural elements, including coarse-grained lens, coarse-grained sheet, mixed zone, diamict lens and diamict sheet elements. The spatial arrangement and genetic interpretation of elements, and their spatial relationship with fifth-order bounding surfaces, allows the delineation of five larger scale architectural units ('element associations'), which can be mapped in the local study area and record at least three stacked successions of meltwater accumulation and till deposition. The results of this study can be utilized for architectural analysis of till sheets and provide insight to groundwater flow pathways through till in the study area and elsewhere.

The pre-Late Wisconsin stratigraphy of southern Simcoe County, Ontario: implications for ice sheet buildup, decay, and Great Lakes drainage evolution

“…Evidence of both lodgement and deformation within each of the tills may indicate transient changes in subglacial dynamics and (or) hydrology over varying spatial and temporal scales (Slomka et al 2015). The presence of intervening glaciolacustrine deposits between the two compositionally distinct till facies suggests a period of ice withdrawal following the deposition of the lower till unit.…”

“…The predominantly massive matrix likely reflects high cumulative strain (Boulton 1987) and complete homogenization of transported debris. Stratified horizons may record changes in subglacial dynamics (ice flow velocity, thermal regime, bed coupling and decoupling, production of basal meltwater (Brown et al 1987;Meriano and Eyles 2009;Slomka et al 2015)), variations in the composition and stone content of debris bands at the base of the glacier, or changes in the substrate fronting the advancing ice margin (Roberts and Hart 2005).…”

Three‐dimensional architecture and hydrostratigraphy of cross‐cutting buried valleys using airborne electromagnetics, glaciated Central Lowlands, Nebraska, USA

“…Janszen et al ., ), outcrops (e.g. Slomka et al ., ), a combination of boreholes and outcrops (e.g. Boyce & Eyles, ) or, in some cases, ground‐based, two‐dimensional geophysical profiles supplemented by boreholes (e.g.…”