Bioturbated black shales
Black shales are dark, fine-grained rocks that conjure up with images of lifeless seafloors. In fact, they usually originate as muds deposited in low-oxygen seafloors. As such, they are expected to be devoid of life… but there is a burrow in this 440-million-years-old black shale from the Genna Muxerru Formation (Sardinia, Italy)!
There is more than one burrow in the Genna Muxerru Formation. Do you want to know more? I just published a co-authored paper on the black shale ichnofauna of the Genna Muxerru Formation. Thanks to the publisher, anyone clicking on this link before September 05 will be taken directly to the final version of the paper!