Evolution and architecture of a West Mediterranean Upper Pleistocene to Holocene coastal apron‐fan system

Abstract

The Quaternary deposits of tectonically stable areas are a powerful tool to investigate high-frequency climate variations (<10 ka) and to distinguish allogenic and autogenic factors controlling deposition. Therefore, an Upper Pleistocene-Holocene coastal apron-fan system in north-western Sardinia (Porto Palmas, Italy) was studied to investigate the relations between climate changes, sea-level fluctuations and sediment source-supply that controlled its development. The sedimentary sequence records the strong influence of local (wet/dry) and worldwide (sea-level) environmental variations in the sedimentation and preservation of the deposits. A multi-disciplinary approach allowed subdivision of the succession into four major, unconformity-bounded stratigraphic units: U1 U2, U3 and U4. Unit U1, tentatively dated to the warm and humid Marine Isotopic Stage (MIS) 5, consists of sandy, gravelly coastal/beach deposits developed during high sea-level in low-lying areas. Unit U2 consists of debris-flow dominated fan-deposits (ca 74 ka; MIS 4), preserved as partial fills of small valleys and coves. Unit U2 is mainly composed of reddish silty conglomerate to pebbly siltstones sourced from the Palaeozoic metamorphic inland hills (bedrock), superficially disintegrated during the preceding warm, vegetation-rich MIS 5. The cold and semi-arid climate strongly reduced vegetation cover along the valley flanks. Therefore, sediment gravity-flow processes, possibly activated by rainstorms, led to deposition of debris-flow dominated fans. Unit U3 consists of water-flow dominated alluvial-fan deposits (ca 47 to 23 ka; MIS 3), developed on a slightly inclined coastal plain. Unit U3 is composed of sandstone and sandy conglomerate fed from two main sediment sources: metamorphic inland bedrock and Quaternary bioclastic-rich shelf-derived sands. During this cold phase, sea-level dropped sufficiently to expose bioclastic sands accumulated on the shelf. Frequent climate fluctuations favoured inland aeolian transport of sand during dry phases, followed by reworking of the aeolian bodies by flash floods during wet phases. Bedrock-derived fragments mixed with water-reworked, wind-blown sands led to the development of water-flow dominated fans. The Dansgaard-Oeschger events possibly associated with sand landward deflation and main fan formations are MIS 1), preserved on a coastal slope, were developed during the Holocene transgression (ca 10 to 5 ka; MIS 1). The studied sequence shows strong similarities with those of other Mediterranean sites; it is, however, one of the few where the main MIS 4 and MIS 3 climatic fluctuations are registered in the sedimentary record.

Pedogenic and palaeoclimatic evidence from an Eemian calcrete in north‐western Sardinia (Italy)

“…Overall, unit U3 is interpreted as a coastal strand plain with a dune‐field system migrating inland. This unit developed during a sea‐level rise culminating with a short period of high sea level (1.5 ± 1 m higher than at the present), tentatively referred to as the MIS 5c (about 100 ka) interstadial (Andreucci et al , ).…”

“…The OSL dating method has been applied to terrigenous siliciclastic deposits of various aeolian, fluvial and shallow marine environments (Andreucci et al, 2012;Pascucci et al, 2014). This dating method is conventionally applied to quartz grains (Murray & Wintle, 2003); however, in recent years a method based on K-feldspar grains has been developed and applied successfully to coastal and alluvial deposits (Buylaert et al, 2012;Andreucci et al, 2014).…”

Depositional environment and age of some key Late Pliocene to Early Quaternary deposits on the underfilled Cedrino paleovalley (Orosei): Insight into the Neogene geodynamic evolution of Sardinia

“…Widespread coastal dune systems also developed during the Pleistocene on the northwest coast of Sardinia under cold and relatively dry conditions. They are interlayered by colluvial and paleosols, the oldest wind dominated system being dated from MIS 8 (Andreucci et al, 2010(Andreucci et al, , 2013Pascucci et al, 2014). It is suggested that this uppermost Orosei succession of aeolian origin was emplaced under the first cooling conditions of the Late Pliocene or the Early Pleistocene around 2.6 Ma (Ruddiman et al, 1989).…”

Archean to Recent aeolian sand systems and their sedimentary record: Current understanding and future prospects

“…Particularly well‐developed carbonate aeolian systems occur in the Western Mediterranean region (Clemmensen et al ., ; Fornós et al ., ; Andreucci et al ., ). Quaternary successions with carbonate‐rich aeolian sand units crop out quasi‐continuously along the north‐west coast of Sardinia near the town of Alghero (Andreucci et al ., ,b, ). The aeolian units, which are lithified, occur along a cliffed coast and can be subdivided into cliff‐front dune accumulations and valley‐head sand ramps (Andreucci et al ., ; Fig.…”