Penecontemporaneous partial disaggregationand/or resedimentation during the formation and deposition of subglacial till

Abstract

Glacier ice has been always considered to be the geologic agent that forms and deposits till. However, the reality is more complex: meltwater and gravity participate to various degrees at the formation, deposition and penecontemporaneous redeposition of till, even though the glacier is the principal agent and thedeposition of till takes place in contact or near-contact with glacier ice. Boulton's (1980) and Lawson's (1981) cntena for the differentiation of "tills" from "nontills" are tested here, by using mainly their own data on glacial sedimentation and  penecontemporaneous resedimentation at Breidamerkurjokull, Iceland, and Matanuska Glacier, Alaska, but re-interpreting some of their conclusions or pointing out some discrepancies in their own conclusions. A strict adherence to some of Boulton's (1980) and Lawson's (1981) critetia would not permit calling most of Matanuska Glacier's melt-out tills, and the Breidamerkurjokull, lodgement till, particularly its dilated top portion, a true till. However, they may be considered tills, if the broad definition of: "Till is a sediment that has been transported and subsequently deposited by or from glacier ice, with little or no sorting by water" is applied instead.