Laminae-scale rhythmicity of inclined heterolithic stratification, Lower Cretaceous McMurray Formation, NE Alberta, Canada

Abstract

Abstract Inclined Heterolithic Stratification, characterized by dipping, interbedded and interlaminated sandstone and mudstone lithosomes comprises a major portion of the Athabasca Oil Sands. Fluvial processes have generally been interpreted to be the major cause of lithological variations and accompanying cyclicity in Inclined Heterolithic Stratification. The objectives of this research are applying quantitative and visual frequency analysis techniques, to determine and interpret the laminae-scale cyclicity of Inclined Heterolithic Stratification lithosomes. The Inclined Heterolithic Stratification in the Pierre River area is subdivided into five lithosomes based on distinct ichnological and sedimentological features. For each lithosome, Continuous Wavelet Transforms, applied to measurements of laminae or bed thicknesses, treated as pseudo time-series, converts these time-series to the frequency domain in order to determine the cyclicity of interlaminated portions of lithosomes. Visual identification of cycle breaks, by splitting series into cycles following troughs and peaks is completed as well. The results from the analysis demonstrate that the interlaminated portions of Inclined Heterolithic Stratification in the Pierre River Area preserve cyclic patterns that are consistent with semidiurnal synodic neap-spring tidal periodicity. Even in bioturbated intervals, interlaminated sandstone and mudstone is indicative of tidal cyclicity. The thicker sandstone or mudstone beds disrupting the tidally interlaminated portions of Inclined Heterolithic Stratification are interpreted to reflect variations in fluvial flux. This study gives a better understanding of the tidal regime during the lower Cretaceous McMurray Formation deposition and of the processes governing Inclined Heterolithic Stratification laminae-scale lithological variability.