The interplay between deformation and deposition in a Pleistocene push moraine: New insight from structural interpretation and area-depth-strain analysis of the growth strata

Abstract

There are many examples suggesting that push moraine formation requires building up of the proglacial wedge and then post-depositional folding and/or faulting. Only a few studies have been carried out on syntectonic deposition and erosion within proglacial sediment wedges; however, the resulting growth strata were determined based on the high variability in thickness and occurrence of erosional unconformities across the deformed sequence. This study shows how structural interpretation and the area-depth-strain (ADS) balancing method of the growth strata can be applied to better understand the interplay between deformation and deposition within an evolving push moraine primarily composed of a folded sequence of a glaciofluvial fan. This approach, together with analysis of the onlap/overlap relationships, allowed us to determine the relative rate between deposition and deformation. Moreover it provides an insight into the topography of the push moraine that may be inherited not only from the geometry of deformation structures but also from depositional processes controlling the spatial distribution and thickness variation of the growth strata. This study also gives an opportunity to reconstruct the ranges of probable parameters to quantitatively describe the heavily eroded push moraine in terms of the primary topography, height and relative time frame within which it formed. In addition, the probable thermo-hydro-mechanical properties of the deformed strata are interpreted in terms of drained/undrained conditions of volume strain evidenced by structural data and possibilities of lateral flow from beneath synclines into anticlines indicated by ADS-based balancing.