Sedimentation models for glacial deltaic successions in the Thunder Bay area / by Susan Patricia Craig
Craig, Susan Patricia
SubjectGeology Ontario Thunder Bay Region
Deltas Ontario Thunder Bay Region
Sedimentation and deposition Ontario Thunder Bay Region
MetadataShow full item record
The comparison of three mapped successions in northern Ontario to glacial deltas reviewed in the literature results in the definition of four end-member depositional environments for glacial deltaic sedimentation. Similar processes of sedimentation occur within two main glacial delta types, distal-fed, and ice-contact. Distal-fed deltas divide into nonglacial and ice-influenced. The other two end member types defined are subglacial and supraglacial ice-contact deltas. Fine-grained laminated beds sedimented by interflows and overflows, as well as diamict and subaqueous outwash deposits underlie the glacial deltaic sequences. The prodelta region consists of multiple reverse-graded beds, massive units, and laminated sediments deposited from interflows and overflows, and minor rippled units indicating intermittent underflows. Within the delta front underflows deposited rippled and graded units, and occasionally planar cross-stratified units were sedimented by grainflows. The delta plain contains trough cross-stratified sands and gravels which infill multiple distributary channels. Dropstone deposition was restricted to the prodelta and delta front regions of ice-influenced distal-fed deltas, and ice-contact deltas. Distributary mouth bars, large scale cyclic sedimentation, subaqueous outwash systems overlain by a glacial deltaic sequence, multiple processes of sedimentation within the delta front, and reworking of glaciogenic deposits have not previously been documented in glacial deltaic systems. These deposits and processes, as well as the inability to define the strandline position indicate glacial deltaic systems are complex.