Late Quaternary transgressive large dunes on the sediment-starved Adriatic shelf

Abstract

The Adriatic epicontinental basin is a low-gradient shelf where the late-Quaternary transgressive systems tract (TST) is composed of thin parasequences of backbarrier, shoreface and offshore deposits. The facies and internal architecture of the late-Quaternary TST in the Adriatic epicontinental basin changed consistently from early transgression to late transgression reflecting: (1) fluctuations in the balance between sediment supply and accommodation increase, and (2) a progressive intensification of the oceanographic regime, driven by the transgressive widening of the basin to as much as seven times its lowstand extent. One of the consequences of this trend is that high-energy marine bedforms such as sand ridges and sand waves characterize only areas that were flooded close to the end of the late-Quaternary sea-level rise, when the wind fetch was maximum and bigger waves and stronger storm currents could form.We studied the morphology, sediment composition and sequence-stratigraphical setting of a field of asymmetric bedforms (typically 3 m high and 600 m in wavelength) in 20-24 m water depth offshore the Venice Lagoon in the sediment-starved North Adriatic shelf. The sand that forms these large dunes derived from a drowned transgressive coastal deposit reworked by marine processes. Early cementation took place over most of the dune crests limiting their activity and preventing their destruction. Both the formation and deactivation of this field of sand dunes occurred over a short time interval close to the turn-around point that separates the late-Quaternary sea-level rise and the following highstand and reflect rapid changes in the oceanographic regime of the basin.

Imaging continental shelf shallow stratigraphy by using different high-resolution seismic sources: an example from the Calabro-Tyrrhenian margin (Mediterranean Sea)

“…The comparison of the stratigraphic reconstruction achieved with those from other high-resolution studies (e.g. CHIOCCI et al, 1989;CORREGGIARI et al, 1996;HERNANDEZ-MOLINA et al, 2000) suggests that the Postglacial depositional sequence is mainly characterized by: 1) thin seismic units (from a few meters to a few tens of meters); 2) the shift of depocentres across the shelf due to variation in accommodation space (e.g., during transgression); 3) the occurrence of units composed of unconsolidated sediments deposited in different environments (e.g., shelf mud overlying relict sands). Within this framework, the degree of resolution, penetration and seismic facies depiction capability may be considered crucial factors in the interpretation, as they systematically control the main steps of stratigraphic interpretation of seismic profiles.…”

“…The transgressive systems tract is composed of well defined parasequences arranged in a retrogradational stacking pattern, and bounded by marine flooding surfaces; the greatest number of parasequences (up to three) is to be observed corresponding to the maximum thickness of the systems tract. If compared with other Mediterranean shelves, the transgressive systems tract is seen to be particularly well developed (thickness of up to 33 m); in fact, these deposits are usually nearly absent or confined to narrow areas on other shelves (e. g., the Adriatic shelf - Correggiari et al, 1996-and the central Tyrrhenian shelf -Chiocci, 2000. The overlying high-stand systems tract, bounded at the base by the maximum flooding surface, shows quite uniform characteristics throughout the area.…”

Bathymetry of the Adriatic Sea: The legacy of the last eustatic cycle and the impact of modern sediment dispersal

“…The morphological map of Giorgetti and Mosetti (1969) was drawn with the purpose of representing a pictorial view of seafloor structures, without labels and with bathymetric contours at 20 m intervals accompanied by hatched patterns to highlight local relief. It is remarkable how the main features of the basin were correctly outlined and reported in their map; examples of features confirmed by more recent surveys include: the field of sand dunes offshore Venice (Correggiari, Field et al, 1996); the drowned coastal sand ridges found offshore Ravenna (Correggiari, Roveri et al, 1996); and the slide scars and seamounts on the South Adriatic slope (Minisini, Trincardi, & Asioli, 2006;Verdicchio & Trincardi, 2006).…”

“…The main morphological features detected on the bathymetry of the Adriatic reflect this oceanographic circulation that is responsible for banking fine sediments along its western side, at current sea levels (Cattaneo, Trincardi, Asioli, & Correggiari, 2007). Away from the near-shore area, the seafloor morphology of the Adriatic reflects, instead, processes that were active when global sea level was 120 m lower than today and the area occupied by the modern continental shelf was a broad alluvial plain (Correggiari, Field, & Trincardi, 1996;Correggiari, Roveri, & Trincardi, 1996;Trincardi, Correggiari, & Roveri, 1994).…”

Living and Quaternary Ostracoda from the Eastern Adriatic Sea: Biocoenoses, thanatocoenoses or palaeothanatocoenoses?

“…The sediments in the units C and D are interpreted as lag deposits, typical of the sediment-starved North Adriatic shelf (Corregiari et al, 1996). The Highstand Systems Tract (HST) in the last 5 ka BP especially yields more phases of non-deposition than deposition and these latter are concentrated in the western part of the Adriatic Sea (Po delta and adjacent lobes Corregiari et al, 2005).…”