Bioturbation, heavy mineral concentration, and high gamma-ray activity in the Lower Cretaceous McMurray Formation, Canada

In the Lower Cretaceous McMurray Formation (Alberta, Canada), many intervals of intensely bioturbated (Bioturbation Index = 5–6) fine-grained sediments are characterized by high gamma-ray (GR) readings. Several methods, including sedimentary facies analysis, thin-section petrography, handheld spectral gamma-ray, portable X-ray fluorescence, diffraction, inductively coupled plasma-mass spectrometry, microprobe K-feldspar, energy dispersive spectroscopy, and detrital zircon geochronology laser ablation-inductively were used to investigate interval interest in core samples. The mineralogical analysis shows that these enriched heavy mineral grains, particularly zircons. content radioactive elements is variable. Thorium commonly elevated up three times, uranium nil two potassium usually remains normal. studied consist interbedded, bitumen-saturated cross-bedded and/or ripple cross-laminated sandstone (high-energy deposits) light-gray mudstone (low-energy deposits), addressed as inclined heterolithic strata (IHS). IHS represent tidally influenced, brackish-water, upper point-bar deposits. grains become concentrated while hydraulic processes interact with bioturbation: burrowing animals cause significant sediment mixing allows lightest particles go back into suspension. Additionally, bioturbation increases surface roughness along sediment-water interface and, causes more turbulent flow, allowing for quartz other light be removed traction saltation, dispersed heavier trapped open burrows. So far, this study first demonstrate importance enrichment IHS. interaction explains apparently counter-intuitive minerals a low-energy depositional setting. This scenario likely applies numerous similar GR zirconium spikes across Formation. Furthermore, it can expected basins stratigraphic units, studies will proposed mechanism universal.