This report is a summary of geological investigations in the Fort McMurray region to update the bedrock topography, delineate buried valleys and channels that have incised the bedrock surface, and characterize Quaternary sediments. Completion of these tasks included examination of 55 cores that intersect the sediment-bedrock contact and comparing the core descriptions with the associated geophysical logs to develop criteria for identifying the bedrock top. These criteria were applied to the interpretation of geophysical logs from wells without core in the area, which led to the stratigraphic delineation of 2900 new bedrock top picks
During core analysis, complexities were identified such as the nature of the sediment-bedrock contact and how the contact varies with different sediment and bedrock types. Examination of cores revealed three types of sediment-bedrock contact including 1) sharp till-bedrock interface; 2) glaciogenic deformation of the bedrock interface; and 3) water-laid sediments at the sediment-bedrock interface. This report includes representative geophysical logs and cores that illustrate each contact type as well as the specific difficulties related to picking the bedrock top based on the underlying bedrock formation (i.e., Clearwater, Grand Rapids, or McMurray formation).
New work from this study along with compiled information from previous work was used to generate an updated bedrock topography map. From this map, areas of thick sediments (up to 200 m) are evident, particularly on the northern side of Muskeg Mountain and the Firebag Hills. To better characterize the sedimentary succession resting on bedrock, two representative cores were selected for detailed analysis and description. From these data, five till units were discerned and tentatively correlated with previously identified tills and ice-flow events.
Six geographic domains with different Quaternary stratigraphic sequences were delineated in this study. The Muskeg Mountain domain, in the central part of the study area, is typified by a thick sequence of multiple fine-grained tills capped by sandy till. To the north, the Firebag Hills domain is also composed of thick till sequences with sandy till overlying fine-grained till. In the area near the confluence of the Firebag River with the Athabasca River (Firebag River domain), glaciofluvially reworked McMurray Formation oil sand rests on pink clay-rich sediments thought to relate to deposition in a proglacial lake impounded by the Fort Hills ice flow. Although not well defined due to a paucity of data, the Steepbank Plain domain, south of Muskeg Mountain, is characterized by an extensive buried sand deposit, which is overlain by till containing rafts of bedrock. The bedrock surface in the MacKay Plain domain in the southwestern part of the study area has been incised by channels that may have both a subaerial and subglacial origin. Here, channel-fill stratified sediments are overlain by a thin cover of till. Similarly, the lowland flanking both sides of the Athabasca River (Dover and Kearl Lake plains domain) has also been incised by subglacial channels, and overlying sediments include channel-fill stratified sediments and rafts of bedrock. These six domains might be used as a basis for hydrogeological or other subsurface studies in the area.
Utting, D.J. and Andriashek, L.D. (2020): Revised bedrock topography and characterization of Quaternary sediments in the Fort McMurray region, northeastern Alberta; Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Report 101, 171 p.