ICHNOLOGICAL DISTRIBUTIONS ON A BRACKISH-WATER POINTBAR

This study focuses on the application of ichnology within a single seismically resolved point bar from the Cretaceous McMurray Formation, Alberta, Canada, to refine previous paleodepositional interpretations.

The dataset comprises bioturbation intensity, bioturbation index, ichnofossil size, and ichnofossil diversity, which were measured and recorded on a bed-by-bed scale for each core that penetrates the point bar. Using a series of time-slice maps through point bar, including the distribution of sedimentary facies, bioturbation index, and size diversity index, several interpretations are arrived at: (1) brackish water was present throughout the entire depth of the channel; (2) the point bar was persistently under the influence of brackish water throughout its history; (3) the point bar is capped by an intertidal flat deposit; and (4) the distribution of sedimentary facies and ichnofacies are consistent with proposed tidal-current orientation. Taken as a whole, the laterally accreted body bears all of the facies characteristics expected of estuary-associated point bars, but “geomorphological” characteristics of a fluvial bar, a combination of characters for which no modern analogue is known.