In Sardinia, Quaternary deposits are mostly represented by beach deposits and cross-bedded aeolian sands attributed to the middle Pleistocene. These are followed by conglomerate beach deposits corresponding to the MIS 5.5 sea level high stand, and by cross-bedded aeolian sands which bear reddish paleosols. Tracks and trackways, belonging to the ichnogenus Bifidipes Demathieu, Ginsburg, Guerin & Truc, 1984, produced by “Praemegaceros” cazioti (Depéret, 1897) have been recently discovered in Pleistocene deposits cropping out along the northern and western coast of Sardinia (Fanelli et al, 2007). The “Praemegaceros” cazioti is an endemic middle size deer of Sardinia which lived in the island from the middle Pleistocene until the early Holocene (Palombo, 2005). This work focuses on Porto Paglia coastal area (south-west Sardinia), where Quaternary deposits are exposed along a high cliff for several kilometres, and where several thousand of tracks are well preserved. The Porto Paglia deposits are composed of different dune generation deposited during middle to early Pleistocene (Orru & Ulzega, 1986). The aim of our study was to identify the environment most conducive to the preservation of tracks and show the significance of “Praemegaceros” cazioti footprints for paleoenviromental reconstruction. The paleoenviromental reconstruction was achieved through sedimentological study: faces analysis, depositional geometry and petrographic observations. The results of this study allow us to describe two broad systems one retrogradational and one progradational. The deposits are separated by erosion/abrasive surfaces with which periods of retrogradation and progradation are expressed. By using these surfaces we can identify three sedimentary cycles corresponding to transgressive-regressive phases during the Pleistocene. The retrogradation deposits, which formed during the transgressive periods, are represented by a system of beach-sand bar-lagoon and associated foredune deposits. Intense slope erosion during sea level fall led to a system of sandy delta-fans and conglomerate fans deposits. The most suitable environment for track preservation is the lagoon. These, were subject to water level oscillations and desiccation. Abundant tracks are also present in the distal portions of sandy bars, where moist, coherent sediments are present in the backshore and relatively poorly in dune deposits. In contrast, footprints are not preserved in the coarse grained progradational deposits.

Suitable facies for ichnofossil preservation: example from the Pleistocene coastal deposits of Sardinia (Italy)

FANELLI, FABIO;IBBA, ANGELO
2009-01-01

Abstract

In Sardinia, Quaternary deposits are mostly represented by beach deposits and cross-bedded aeolian sands attributed to the middle Pleistocene. These are followed by conglomerate beach deposits corresponding to the MIS 5.5 sea level high stand, and by cross-bedded aeolian sands which bear reddish paleosols. Tracks and trackways, belonging to the ichnogenus Bifidipes Demathieu, Ginsburg, Guerin & Truc, 1984, produced by “Praemegaceros” cazioti (Depéret, 1897) have been recently discovered in Pleistocene deposits cropping out along the northern and western coast of Sardinia (Fanelli et al, 2007). The “Praemegaceros” cazioti is an endemic middle size deer of Sardinia which lived in the island from the middle Pleistocene until the early Holocene (Palombo, 2005). This work focuses on Porto Paglia coastal area (south-west Sardinia), where Quaternary deposits are exposed along a high cliff for several kilometres, and where several thousand of tracks are well preserved. The Porto Paglia deposits are composed of different dune generation deposited during middle to early Pleistocene (Orru & Ulzega, 1986). The aim of our study was to identify the environment most conducive to the preservation of tracks and show the significance of “Praemegaceros” cazioti footprints for paleoenviromental reconstruction. The paleoenviromental reconstruction was achieved through sedimentological study: faces analysis, depositional geometry and petrographic observations. The results of this study allow us to describe two broad systems one retrogradational and one progradational. The deposits are separated by erosion/abrasive surfaces with which periods of retrogradation and progradation are expressed. By using these surfaces we can identify three sedimentary cycles corresponding to transgressive-regressive phases during the Pleistocene. The retrogradation deposits, which formed during the transgressive periods, are represented by a system of beach-sand bar-lagoon and associated foredune deposits. Intense slope erosion during sea level fall led to a system of sandy delta-fans and conglomerate fans deposits. The most suitable environment for track preservation is the lagoon. These, were subject to water level oscillations and desiccation. Abundant tracks are also present in the distal portions of sandy bars, where moist, coherent sediments are present in the backshore and relatively poorly in dune deposits. In contrast, footprints are not preserved in the coarse grained progradational deposits.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11584/102814
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