HOW IMPORTANT IS THE ROLE OF TIME IN GLACIAL SEQUENCES?

Glacial sequences of different times are more similar than not. The primary controls on the nature of a glacial sequence are bedrock source, topography, and climate. Since the first two do not vary much over time and the third factor displays a strong cyclic nature, the hypothesis advanced here is that glacial processes will reproduce the similar sequences time and again.

An implication (assumption?) of this hypothesis is that a triangular facies model with just debris load, relief, and water abundance can represent the range of glacial sequences. Bedrock erosion controls the grain size of the drift, topographic elements exert a primary control on the distribution and accumulation of gravity flow deposits; and volume of runoff (meltwater and rain induced) dictate the ratio of non-stratified and stratified material. For a given geographical location only the production of water varies over time.

A second point is that erosion, both glacial and non-glacial, are the primary means to alter and hence mask the repetitive nature of this sequence. At glacial margin positions the sequences are complete whereas at interior positions erosive processes truncate any sequence. Slope processes during non-glacial intervals shave all the drift. This removal of an ideal sequence may be the primary reason sequences differ.

The pattern observed is: 1) organic silts (from accumulating alluvium/ colluvium processes) giving way abruptly to 2) local lacustrine sediments or debris flows which merge into 3) lodgement till with upper portions of local meltout tills and 4) finally a thick sequence of intermixed debris flows and stratified deposits.