Tuesday, July 28, 2009

Trace fossil of the second III: Asteriacites lumbricalis

The Tfots today is Asteriacites lumbricalis von Schlotheim, 1820, a resting trace produced by the (in)activity of ophiuroid echinoderms or brittle stars (Twitchett & Wignall 1996). I took these photographs from material found on the slopes of Costabella mountain in the Dolomites. These slabs are float from an outcrop exposing the Campil Member of the middle Werfen Formation (Lower Triassic, Early Olenekian). These trace are quite widespread in this member and known for more than a hundred years although they were erroneously recognised as body fossils in the first place (e.g. Wittenburg 1908). They come from more or less storm-dominated shoreface deposits composed of micaceous fine-grained sandstones and siltstones.

Thanks to a comment by David, I hoped to see some decent specimens during the recent field session and finally I was really lucky finding these well-preserved traces at the last day of the campaign. I never saw better ones at least in the literature so far.

Fig. 1: Asteriacites lumbricalis preserved as convex hyporelief (positive structure on a lower bedding plane). Black bar represents 5 mm.

Fig. 2: Asteriacites lumbricalis preserved as concave epirelief (negative structure on an upper bedding plane). Black bar represents 5 mm. Note the ripple-marks.


Schlothheim, E.F. von, 1820: Petrefactenkunde auf ihrem jetzigen Standpunktedes Thier- und Pflanzenreichs der Vorwelt. Gotha, Becker, 437 p. durch die Beschreibung seiner Sammlung versteinerter und fossiler überreste.

Twitchett, R.J., Wignall, P.B., 1996: Trace fossils and the aftermath of the Permo-Triassic mass extinction: evidence from northern Italy. Palaeogeography, Palaeoclimatology, Palaeoecology 124, 137–152.

Wittenburg, P. von, 1908: Beiträge zur Kenntnis der Werfener Schichten Südtirols. Geologische und Palaeontologische Abhandlungen 8, 251–289.

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