A striking characteristic of modern environments is their variability: you cannot swim over the sea floor without seeing small patches. If modern environments are so variable, then the sedimentary record of past environments, facies, should look like a pile of dirty laundry: random stacks of facies patches creating a facies mosaic. Instead, the sedimentary record often consists of neatly stacked sheet-like layers (beds) of rock only centimeters thick that can be traced for tens of kilometers in what is often described as layer-cake. The apparent disconnect between modern environments and the sedimentary record has long been a concern.
The 450 million-year-old fossil-rich sediments of the Cincinnati region have been described both as a layer cake and a facies mosaic. Recent study on the origin of beds in these rocks shows, paradoxically, that both descriptions are correct.