Which types of sedimentary rocks formed in low-oxygen Devonian seas?

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Devonian paleogeography — Devonian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the early Devonian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

In the Devonian Period, the formation of locally extensive black shale deposits is considered a distinctive indicator of low-oxygen (hypoxic or anoxic) conditions in marine environments.12

These black shales, such as the Upper Devonian Antrim, New Albany, and Chattanooga shales in North America, or the Hunsrückschiefer and Wissenbacherschiefer in Europe, are frequently characterized by a lack of benthic fossils, which serves as evidence that seafloor oxygen levels were extremely low at the time of their deposition. These sedimentary events are often associated with periods of significant environmental stress and marine extinction, as the lack of oxygen in bottom waters hindered the survival of many marine species.12