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, X-ray diffraction, inductively coupled plasma-mass spectrometry, microprobe of K-feldspar, energy dispersive spectroscopy, and detrital zircon geochronology by laser ablation-inductively coupled plasma-mass spectrometry, were used to investigate the interval of interest in core samples. The mineralogical analysis shows that these intervals are enriched in heavy mineral grains, and particularly in zircons. The content of radioactive elements is variable. Thorium is commonly elevated up to three times, uranium nil to two times, and potassium content usually remains normal. The studied intervals consist of interbedded, bitumen-saturated cross-bedded and/or ripple cross-laminated sandstone (high-energy deposits) and light-gray bioturbated mudstone (low-energy deposits), commonly addressed as inclined heterolithic strata (IHS). IHS represent tidally influenced, brackish-water, upper point-bar deposits. The zircon grains become concentrated while hydraulic processes interact with bioturbation: the burrowing animals cause significant sediment mixing that allows the lightest sediment particles to go back into the suspension. Additionally, bioturbation increases the surface roughness along the sediment-water interface and, causes more turbulent flow, allowing for quartz and other light grains to be removed by traction and/or saltation, while dispersed heavier zircon grains become trapped and concentrated in open burrows.

So far, this study is the first to demonstrate the importance of bioturbation in the enrichment of zircon grains in IHS. The interaction of bioturbation and hydraulic processes explains the apparently counter-intuitive enrichment of heavy minerals in a low-energy depositional setting. This scenario likely applies to numerous intervals characterized by similar GR and/or zirconium spikes across the McMurray Formation. Furthermore, it can be expected that in other sedimentary basins and stratigraphic units, similar studies will demonstrate that the proposed mechanism is universal.

在下白垩统麦克默里组（加拿大艾伯塔省），许多间隔强烈生物扰动（生物扰动指数= 5-6）的细颗粒沉积物具有较高的伽马射线（GR）读数。几种方法，包括沉积相分析，薄层岩石学，手持式谱伽马射线，便携式X射线荧光，X射线衍射，电感耦合等离子体质谱法，钾长石微探针，能量色散光谱法和碎屑锆石激光烧蚀-电感耦合等离子体质谱法进行地质年代学研究，以研究岩心样品中的关注区间。矿物学分析表明，这些层段富含重矿物颗粒，尤其是锆石。放射性元素的含量是可变的。通常会升高三倍，铀为零，而钾含量通常保持正常。研究的层段包括互层，沥青饱和的层状和/或波纹状的交叉层状砂岩（高能矿床）和浅灰色生物扰动泥岩（低能矿床），通常称为倾斜异质地层（IHS）。IHS代表受潮汐影响的微咸水上点矿床。当水力过程与生物扰动相互作用时，锆石颗粒变得集中：挖洞的动物引起大量的沉积物混合，使最轻的沉积物颗粒返回悬浮液。此外，生物扰动会增加沿沉积物-水界面的表面粗糙度，并引起更多的湍流，从而允许通过牵引和/或盐化去除石英和其他轻质颗粒，

到目前为止，这项研究首次证明了生物扰动在IHS中富集锆石的重要性。生物扰动和水力过程的相互作用解释了在低能量沉积环境中重矿物的明显违反直觉的富集。这种情况可能适用于以麦克默里地层中相似的GR和/或锆尖峰为特征的许多层段。此外，可以预期，在其他沉积盆地和地层单元中，类似的研究将证明所提出的机制是通用的。