Stratigraphy
The Oak Ridges Moraine consists of numerous layers of sedimentary material, for some of which the origin is unknown. The base of the moraine touches bedrock; "it is not clear if the bedrock valley itself was sculpted by a subglacial meltwater event, or was of a preglacial fluvial origin, or was possibly a combination of both." (Davies and Holysh, 2004, pg 27-5) Above the bedrock are the Lower Sediments (as styled by the Geological Survey of Canada), consisting of diamict and fine-grained glaciolacustrine sediments at its base, and an upper sandy aquifer layer. (Davies and Holysh, 2004, pg 27-5). Overlaying this is a thick sequence of Newmarket Till, a sandy loam sedimentary layer common in the area.
Each wedge exhibits different characteristics and sedimentary patterns, thus displaying many incongruities and depositional unconformities. The Rice Lake wedge, for instance, achieves a peak of 180 m above sea level, with a 20 m layer of shallow surface Oak Ridges Moraine sediments, underlain by the Newmarket Till. The other wedges, which peak at up to 335 m, have thicker and more varied surficial deposits, and the Newmarket Till lies deeper below the surface. Moreover, the sedimentary deposits are underlain by Halton Till on these wedges, which is not present in the Rice Lake wedge.
Thus, from top to bottom, the stratigraphy of the moraine is:
- Oak Ridges Moraine sediments
- Halton Till (not present at Rice Lake)
- Channel sediments
- Newmarket Till
- Lower sediments (sandy aquifer above, diamict and glaciolacustrine units below)
- Bedrock
Read more about this topic: Origin Of The Oak Ridges Moraine