181 Quaternary Geology/Geomorphology IV

Thursday, 8 November 2001
1:30 PM - 5:30 PM

LATE WISCONSINIAN GLACIOLACUSTRINE SEDIMENTS DEPOSITED IN FRONT OF A SUBMERGED GLACIER FRONT, LAKE ERIE BLUFFS, CANADA

Paper number: 181-2
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

A detailed study was conducted to understand late Wisconsinian glaciolacustrine sediments deposited in front of a submerged end moraine. The Jacksonburg delta developed with its sediments exposed along the north shore of Lake Erie. Regionally a coarsening upward succession of four facies associations characterizes the delta. Clay rhythmites overly a till substrate, followed successively by silt rhythmites, sand rhythmites, and upper trough and low-angle cross-bedded and plane bedded sand.

Within 400 m of the submerged end moraine, the delta lacks clay and silt rhythmites. Sandy units deposited laterally in juxtaposed diachronous sequences infill shallow wide valley cuts. Two lower sequences exist: (1) ripple cross-laminated sand near the moraine is locally interrupted by apparently massive to cross-laminated sandy silt deposited by hyperpycnal flows. Sands near the moraine contain lenses of subaqueously slumped diamicton. These deposits represent glaciolacustrine delta facies. (2) Approximately 500 m from the moraine edge, a more distal sequence is characterized by plane bedded sand with heavy mineral concentrations along laminae alternating with thin (<1 cm) massive beds and minor ripple cross-laminations. These beach-like deposits constitute the transgressive filling of a wide (~450 m) shallow (<15 m) valley cut into the more proximal lower sequence 1.

Both lower sequences are overlain by a coarser sand sequence characterized primarily by shallow dipping cross-beds alternating with plane beds and locally by ripple cross-laminated units. This upper sequence represents a complex frontal distributary bar of a braided delta. Periodical subaerial exposure allowed development of local beach deposits and some aeolian sands. A well-developed soil unit formed after the last lake level drop and was later buried under a field of sand dunes.