DECODING ALBERTA'S BURIED VALLEYS: GENESIS, GEOLOGIC HISTORY AND THE IMPORTANCE OF FORMATION-RANK STRATIGRAPHIC DEFINITIONS

Sand and gravel deposits overlying the bedrock floors of buried valleys across the Canadian Interior Plains (basal gravel) are included in the Empress Group. The group is time-transgressive, comprising units deposited before Laurentide glaciation of the plains and between subsequent glacial events. However, these deposits are rarely defined at the formation rank. This lack of stratigraphic resolution limits our understanding of the relationships between Empress Group sediments and chronologically intervening tills.

In this study, we examine Empress Group sediments at both provincial and regional scales to better understand their genesis and geologic history. At the provincial scale, we map basal gravel in three dimensions using a novel machine-learning approach. At the regional scale, we formally define basal gravel formations at either end of Alberta's largest buried valley system.

Our results confirm that Alberta's buried valley network has a palimpsest genesis, with Empress Group sediments deposited across progressively younger, fluvial erosion surfaces, across which they are chronostratigraphically intercalated with tills. To advance Neogene-Quaternary stratigraphic studies in the Canadian Interior Plains, we strongly advocate for formation-rank stratigraphic definition of Empress Group sediments. Particular focus should be placed on identifying and delineating bounding unconformities including fluvial erosion surfaces and the bases of tills.