Bioturbated Inclined Heterolithic Stratification in the McMurray Formation: Origins and Distributions

Abstract

Inclined Heterolithic Stratification (IHS) is a common element of the McMurray Formation. Within the McMurray Formation, the primary modes of IHS are as laterally accreted point- and channel-bars, and vertically accreted channel fills. This synthesis focuses on the nature and character of IHS in the McMurray Formation, wherein IHS tends to have variable sedimentological expressions. Examples of IHS in the McMurray are presented from several areas. Using a number of techniques, and synthesizing other studies, several observations pertinent to IHS interpretation and occurrence are discussed. 1. Recent research efforts, based on core and statistical analyses show that some IHS of the McMurray Formation displays rhythmicity ascribable to tidal influence. Nevertheless, the dominant mode of sedimentation results from seasonal variations in sediment distribution. 2. As shown in several studies in modern and ancient settings, brackish-water bioturbation in IHS indicates the presence of brackish water and confirms the presence of tidal transport in the scrutinized sedimentary environment. 3. Bioturbation distributions in sand versus mud lithosomes of IHS are good indicators of proximity to fluvial sediment sources. 4. The distribution of IHS in the McMurray is to a degree predictable, as IHS-prone belts appear to start at the tidal limit (based on the presence of brackish-water bioturbation) and extend into the middle-, and in rare cases outer-estuary. However, the nature of tidal and fluvial sediment sources, the volume of the tidal prism and the volume of fluvial flow each strongly influence the distribution of IHS in the McMurray Formation: these parameters were likely variable spatially. The above observations help to formulate interpretations from IHS that contribute to better understanding the sedimentary environment for the McMurray Formation, and may help to predict the distribution of heterolithic belts in strata

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016