Asterosoma

    An excellent Asterosoma occurrence is found in fine-grained sandstone within an ancient delta front of a river-influenced delta lobe (Wall Creek Member, Frontier Formation, Powder River Basin, Wyoming).  Note the characteristic sand-filled inner core, the surrounding mud ball and the diagnostic target-like appearance of concentric rings.  Asterosoma is a horizontal Rosselia; although,this example may be a re-deposited broken off top of a Rosselia trace fossil.

    In this image, several Asterosoma occurrences are identified in bioturbated delta front sandstones.  Asterosoma is readily recognized in split cores—the characteristic concentric bands surrounding a central shaft can be seen in this image.  Single Asterosoma occurrences can actually be re-deposited Rosselia bulbs which have been torn from the original burrow.  The Asterosoma occurrences above are in situ and have not been transported and re-deposited.

    Another Asterosoma example from the Panther Tongue sandstone Utah.  The trace fossil is found within deltaic shoreface sandstones that contain abundant Scolicia occurrences.  Scolicia occurrences and Asterosoma do appear similar at first glance.  Scolicia is produced by irregular echinoderms (sea urchins) and lacks a central sand-filled shaft.  However, after careful examination, one can see a central burrow surrounded by concentric rings which indicates this is an Asterosoma and not a Scolicia occurrence.

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