A trace fossil assemblage from the Silurian (Llandovery) black shales of the Genna Muxerru Formation is re- ported for the first time. The ichnofossil record is abundant, well-preserved and comprises Alcyonidiopsis, Cochlichnus, Phymatoderma, Planolites (large morphotype), Planolites (rough morphotype) and a ‘Small chon- dritid’. Sedimentological and ichnological evidence indicates that the bioturbated black shales were deposited in outer shelf (or deeper) settings with severe depletion in oxygen. The seafloor provided a high food supply for the infauna. The palaeoenvironment of the Genna Muxerru Formation is an ancient analogue of modern oxygen- minimum zones. Burrow fills are apparently massive in macroscopic view, whereas observations under the petrographic and stereoscopic microscope show that a lifestyle dominated, i.e. that of pellet-filling sediment- feeders. As such, the Genna Muxerru Formation provides not only a new ethologic reference for low-oxygen settings but also a methodological benchmark for ichnological analysis of black shales. Bioturbation in black shales may be commoner than expected but its recognition requires microscopic observation.

Life in near-anoxic conditions: A case study of the ichnology and infaunal ecology of Silurian graptolitic black shales from Sardinia, Italy

Baucon, Andrea;Briguglio, Antonino;Cabella, Roberto;Campomenosi, Nicola;Piazza, Michele;
2020

Abstract

A trace fossil assemblage from the Silurian (Llandovery) black shales of the Genna Muxerru Formation is re- ported for the first time. The ichnofossil record is abundant, well-preserved and comprises Alcyonidiopsis, Cochlichnus, Phymatoderma, Planolites (large morphotype), Planolites (rough morphotype) and a ‘Small chon- dritid’. Sedimentological and ichnological evidence indicates that the bioturbated black shales were deposited in outer shelf (or deeper) settings with severe depletion in oxygen. The seafloor provided a high food supply for the infauna. The palaeoenvironment of the Genna Muxerru Formation is an ancient analogue of modern oxygen- minimum zones. Burrow fills are apparently massive in macroscopic view, whereas observations under the petrographic and stereoscopic microscope show that a lifestyle dominated, i.e. that of pellet-filling sediment- feeders. As such, the Genna Muxerru Formation provides not only a new ethologic reference for low-oxygen settings but also a methodological benchmark for ichnological analysis of black shales. Bioturbation in black shales may be commoner than expected but its recognition requires microscopic observation.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11567/1018632
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