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TitleConverging ice streams: an unreasonable hypothesis for deposition of the Oak Ridges Moraine, southern Ontario
AuthorSharpe, D R; Russell, H A J; Pugin, A
SourceCanadian Journal of Earth Sciences .
Alt SeriesNatural Resources Canada, Contribution Series 20180421
ProgramGroundwater Geoscience, Aquifer Assessment & support to mapping
The hypothesis that the Oak Ridges Moraine (ORM) formed between two converging (roughly NS) ice streams is tested based on critical, available field data. These data (e.g., DEMs, geological mapping, high-resolution reflection seismic profiles, continuous core, and, analysis of sediment type, architecture, and paleoflow data) refute the converging ice stream hypothesis for deposition of the ORM. Streamlined landforms, used to re-construct ice stream flow paths, go beneath ORM as shown by surface mapping, seismic profiles and cored boreholes; hence, the streamlining event is older than ORM and has no direct bearing on its formation. Meltwater channels that truncate the streamlined landforms are part of the ORM ice stream hypothesis, and they are inferred to represent (sub-aerial) spillways that end at the north side of ORM. These NS meltwater channels are also shown to extend beneath ORM; they have eskers on their floors, and thus, are subglacial not sub-aerial channels. Halton Till, the inferred southern, ice-stream bed, is not present in the predicted ice stream areas. Halton Till overlies ORM sediment; thus, Halton can not represent an ice-stream event that formed ORM. Halton sediment, in addition, occurs in transition from ORM glaciofluvial sediment, and, comprises interbedded diamicton and glaciolacustrine sediment, not the predicted ice-stream, deforming-bed sediment facies. ORM glaciofluvial to glaciolacustrine sequences have a clear east to west paleoflow, in conflict with the expected ~NS sediment flux from the converging-ice-stream hypothesis. The failure of the ice stream hypothesis to explain field data in the area and formation of ORM as predicted, casts doubt on applying this process model in the ORM area, and, in adjacent areas of southern Ontario.
Summary(Plain Language Summary, not published)
This presentation makes the case that the ORM was not formed by fast flowing ice streams because the hypothesis does not conform with published field data on sediment type, geometry, composition and former flow directions. ORM formed from discharge of stored glacial meltwater at the end of the last glacial episode. Its sand and gravel composition makes it one of the most important groundwater resources in the Toronto region and in southern Ontario.