Mounds and depressions containing dense fossil accumulations occur in a bed of Middle Ordovician age in the Upper Ottawa Valley (Canada). The appearance of these relict seabed features is similar to modern features containing dense accumulations of live species in the North Sea. It is suggested that the Middle Ordovician fossil accumulations relied on a similar local upward flux of minerals and nourishment as North Sea communities which live in areas where sediments contain light hydrocarbon gases. If further petrological and sedimentological studies on the Middle Ordovician deposits could confirm such a relationship, then it would be the first time relict or "fossil" pockmarks were found in the sedimentary column.

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