Quaternary Science Reviews, Feb 1, Vol.109, p.88(23)
To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.quascirev.2014.09.010 Byline: Jonathan R. Lee, Oliver J.W. Wakefield, Emrys Phillips, Leanne Hughes Abstract: Subglacial drainage systems exert a major control on basal-sliding rates and glacier dynamics. However, comparatively few studies have examined the sedimentary record of subglacial drainage. This is due to the paucity of modern analogues, the limited recognition and preservation of upper flow regime deposits within the geological record, and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments (e.g. glacier outburst flood deposits). Within this study, the sedimentological and structural evolution of a subglacial to subaerial (ice-marginal/proglacial) drainage system is examined. Particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context. Facies are attributed to subglacial meltwater activity and record sedimentation within a confined, but progressively enlargening, subglacial channel system produced under dune to upper flow regime conditions. Bedforms include rare large-scale sinusoidal bedding with syn-depositional deformation produced by current-induced traction and shearing within the channel margins. Subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel-abandonment or a seasonal drainage regime. Retreat of the ice margin, led to the establishment of subaerial drainage with phases of sheet-flow punctuated by channel incision and anastomosing channel development under diurnal, ablation-related, seasonal discharge. The presence of extensive hydrofracture networks demonstrate that proglacial groundwater-levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream. Author Affiliation: (a) British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK (b) British Geological Survey, West Mains Road, Edinburgh, EH9 3LA, UK Article History: Received 30 April 2014; Revised 1 September 2014; Accepted 4 September 2014
Groundwater ; Bedforms ; Sedimentary Structures ; Sediments (Geology)
Cengage Learning, Inc.