1,721,310 research outputs found
Boulder accumulations related to extreme wave events on the eastern coast of Malta
No full textThe accumulation of large boulders related to waves generated by either tsunamis or extreme storm events have been observed in different areas of the Mediterranean Sea. Along the eastern low-lying rocky coasts of Malta, five sites with large boulder deposits have been investigated, measured and mapped. These boulders have been detached and moved from the nearshore and the lowest parts of the coast by sea wave action. In the Sicily-Malta channel, heavy storms are common and originate from the NE and NW winds. Conversely, few tsunamis have been recorded in historical documents to have reached the Maltese archipelago. We present a multi-disciplinary study, which aims to define the characteristics of these boulder accumulations, in order to assess the coastal geo-hazard implications triggered by the sheer ability of extreme waves to detach and move large rocky blocks inland. The wave heights required to transport 77 coastal boulders were calculated using various hydrodynamic equations. Particular attention was given to the quantification of the input parameters required in the workings of these equations, such as size, density and distance from the coast. In addition, accelerator mass spectrometry (AMS) 14C ages were determined from selected samples of marine organisms encrusted on some of the coastal boulders. The combination of the results obtained both by the hydrodynamic equations, which provided values comparable with those observed and measured during the storms, and radiocarbon dating suggests that the majority of the boulders have been detached and moved by intense storm waves. These boulders testify to the existence of a real hazard for the coasts of Malta, i.e. that of very high storm waves, which, during exceptional storms, are able to detach large blocks of volumes exceeding 10 m3 from the coastal edge and the nearshore bottom, and also to transport them inland. Nevertheless, the occurrence of one or more tsunami events cannot be ruled out, since radiocarbon dating of some marine organisms did reveal ages which may be related to historically known tsunamis in the Mediterranean region, such as the ones in AD963, 1329, 1693 and 1743. © 2016 Author(s)
Eustatic variations and subsidence in Northern Adriatic in the last 130,000 years
No full textThe project wants to gather new data on Upper Pleistocene and Holocene sea level
evolution in the Northern Adriatic Sea. The research investigates: i) the relations between
eustacy and tectonic subsidence in the last 130,000 years; ii) relative and absolute sea level
variations during the post-LGM transgression and, particularly, in the middle and late
Holocene.
The investigation regards the coastal sector between the present Po river mouth and Istria,
comprising the Venetian-Friulian coastal plain, the rocky coast between Monfalcone and
Abbazia (HR) and the sea bottom in Italian territorial waters. The study area covers a
coastline of about 400 km in Italy, Slovenia and Croatia.
A georeferenced database (DB) gathers all the sites with direct or indirect information on
past sea levels: those already known and published as well as the new ones identified and
studied in the project. The DB contains corings, wells, geomorphological sites and
archaeological sites. The elevations of these elements is derived from DTM and digital
cartography; in specific points a survey with a topographic GPS is carried out.
In order to define the long-term subsidence, the coastal-lagoonal sediments of the MIS 5e
highstand (the so-called “Tyrrhenian period” 132-116 ka BP) are considered. Due to postdepositional
deformations, along the Italian Norhern Adriatic coast they are now buried at
depths of 40-120 m. The ratio of the burial depth vs. age provides the mean subsidence rate
(mm/year). These rates, which are largely due to crustal deformation and, with a minor
component, to sediment compaction, represent an average estimate of the so-called
“tectonic subsidence”. Within the project 3 new long cores are scheduled up to a depth of
120 m. Their facies, paleontological and magnetic characterization will support new
important information.
Regarding the post-LGM transgression, geomorphological, stratigraphical and
geoarchaeological indicators are investigated. Geomorphological indicators such as shore
systems now inland in the Venetian-Friulan Plain due to highstand delta progradation,
notches in calcareous rocks and tidal flats in rias are mapped and dated in Karst and Istria
coast. Corings of Holocene lagoonal sediments in the Venetian-Friulian area and in Istrian
rias will be analysed, with hand augers cross sections down to 10 m depth.
In May 2012 the oceanographic cruise NAD2012 was carried out in Northern Adriatic on
board of research vessel Urania. This cruise led to collect about 1200 Mi of CHIRP seismoacoustic
profiles and allowed to accomplish the geological survey of the Slovenian shelf.
Geoarchaeological indicators of sea level since Protohistory, such as piers, docks, fish-ponds
and living floors which interfinger with lagoonal sediments, are considered. The relative
abundance of such elements relative to the Roman times is well known; in the project there
will be an effort for extending these data to Prehistory and the Middle Ages.
The project, sponsored by the University of Padova in 2010, will last in 2013; at the moment
it involves researchers from CNR-ISMAR Bologna, CNR-IGG Padova, ENEA Rome,
University of Trieste, Geological Survey of Slovenia, Harpashea Inc
New archaeological and geomorphological markers along the Istrian coasts (Croatia) and their relations with relative sea level changes
No full textNew data on archeological remains and coastal morphologies have been used to refine published data on the Late- Holocene relative sea-level change along the Northeastern Ardriatic coasts. Data have been compared with predicted curves, in order to detail the tectonic evolution of the studied area
Raised Holocene paleo-shorelines along the Capo Vaticano coast (western Calabria, Italy): Evidence of co-seismic and steady-state deformation
No full textDetailed mapping of geomorphological and biological sea-level markers around the Capo Vaticano promontory (western Calabria, Italy), has documented the occurrence of four Holocene paleo-shorelines raised at different altitudes. The uppermost shoreline (PS1) is represented by a deeply eroded fossiliferous beach deposit, reaching an elevation of ~2.2. m above the present sea-level, and by a notch whose roof is at ~2.3. m. The subjacent shoreline PS2 is found at an elevation of ~1.8. m and is represented by a Dendropoma rim, a barnacle band and by a wave-cut platform. Shoreline PS3 includes remnants of vermetid concretions, a barnacle band, a notch and a marine deposit, and reaches an elevation of ~1.4. m. The lowermost paleo-shoreline (PS4) includes a wave-cut platform and a notch and reaches an elevation of ~0.8. m. Radiocarbon dating of material from individual paleo-shorelines points to an average uplift rate of 1.2-1.4. mm/yr in the last ~6. ka at Capo Vaticano. Our data suggest that Holocene uplift was asymmetric, with a greater magnitude in the south-west sector of the promontory, in a manner similar to the long-term deformation attested by Pleistocene terraces. The larger uplift in the south-western sector is possibly related to the additional contribution, onto a large-wavelength regional signal, of co-seismic deformation events, which are not registered to the north-east. We have recognized four co-seismic uplift events at 5.7-5.4. ka, 3.9-3.5. ka, ~1.9. ka and <1.8. ka ago, superposed on a regional uplift that in the area, is occurring at a rate of ~1. mm/yr. Our findings places new constrains on the recent activity of border faults south of the peninsula and on the location of the seismogenic source the 1905 destructive earthquake
Morphometry and elevation of the last interglacial tidal notches in tectonically stable coasts of the Mediterranean Sea
No full textWe report detailed morphometric observations on several MIS 5.5 and a few older (MIS 11, 21, 25) fossil tidal notches shaped along carbonate coasts at 80 sites in the central Mediterranean Sea and at an additional six sites in the eastern and western Mediterranean. At each site, we performed precise measurements of the fossil tidal notch (FTN) width and depth, and of the elevation of its base relative to the base of the present tidal notch (PTN). The age of the fossil notches is obtained by correlation with biologic material associated with the notches at or very close to the site. This material was previously dated either through radiometric analysis or by its fossiliferous content. The width (i.e. the difference in elevation between base and top) of the notches ranges from 1.20 to 0.38 m, with a mean of 0.74 m. Although the FTN is always a few centimetres wider than the PTN, probably because of the lack of the biological reef coupled with a small erosional enlargement in the FTN, the broadly comparable width suggests that tide amplitude has not changed since MIS 5.5 times. This result can be extended to the MIS 11 features because of a comparable notch width, but not to the MIS 21 and 25 epochs. Although observational control of these older notches is limited, we regard this result as suggesting that changes in tide amplitude broadly occurred at the Early-Middle Pleistocene transition. The investigated MIS 5.5 notches are located in tectonically stable coasts, compared to other sectors of the central Mediterranean Sea where they are uplifted or subsided to ~100 m and over. In these stable areas, the elevation of the base of the MIS 5.5 notch ranges from 2.09 to 12.48 m, with a mean of 5.7 m. Such variability, although limited, indicates that small land movements, deriving from slow crustal processes, may have occurred in stable areas. We defined a number of sectors characterized by different geologic histories, where a careful evaluation of local vertical land motion allowed the selection of the best representative elevation of the MIS 5.5 peak highstand for each sector. This elevation has been compared against glacial isostatic adjustment (GIA) predictions drawn from a suite of ice-sheet models (ICE-G5, ICE-G6 and ANICE-SELEN) that are used in combination with the same solid Earth model and mantle viscosity parameters. Results indicate that the GIA signal is not the main cause of the observed highstand variability and that other mechanisms are needed. The GIA simulations show that, even within the Mediterranean Basin, the maximum highstand is reached at different times according to the geographical location. Our work shows that, besides GIA, even in areas considered tectonically stable, additional vertical tectonic movements may occur with a magnitude that is significantly larger than the GIA. © 2018 Elsevier B.V
Timing of the emergence of the Europe-Sicily bridge (40-17 cal ka BP) and its implications for the spread of modern humans
No full textThe submerged sill in the Strait of Messina, which is located today at a minimum depth of 81 m below sea level (bsl), represents the only land connection between Sicily and mainland Italy (and thus Europe) during the last lowstand when the sea level locally stood at about 126 m bsl. Today, the sea crossing to Sicily, although it is less than 4 km at the narrowest point, faces hazardous sea conditions, made famous by the myth of Scylla and Charybdis. Through a multidisciplinary research project, we document the timing and mode of emergence of this land connection during the last 40 kyr. The integrated analysis takes into consideration morphobathymetric and lithological data, and relative sea-level change (both isostatic and tectonic), resulting in the hypothesis that a continental land bridge lasted for at least 500 years between 21.5 and 20 cal ka BP. The emergence may have occurred over an even longer time span if one allows for seafloor erosion by marine currents that have lowered the seabed since the Last Glacial Maximum (LGM). Modelling of palaeotidal velocities shows that sea crossings when sea level was lower than present would have faced even stronger and more hazardous sea currents than today, supporting the hypothesis that earliest human entry into Sicily most probably took place on foot during the period when the sill emerged as dry land. This hypothesis is compared with an analysis of Pleistocene vertebrate faunas in Sicily and mainland Italy, including a new radiocarbon date on bone collagen of an Equus hydruntinus specimen from Grotta di San Teodoro (23-21 cal ka BP), the dispersal abilities of the various animal species involved, particularly their swimming abilities, and the Palaeolithic archaeological record, all of which support the hypothesis of a relatively late land-based colonization of Sicily by Homo sapiens. © The Geological Society of London 2016
A potential GSSP for the Upper Pleistocene
No full textHere we present the results of an integrated stratigraphic study performed in the Taranto area for the definition of the Tarentian stage for the Upper Pleistocene
A potential global boundary stratotype section and point (GSSP) for the Tarentian Stage, Upper Pleistocene, from the Taranto area (Italy): Results and future perspectives
No full textWe present new data collected at the Fronte composite section near Taranto, where the Upper Pleistocene marine sedimentary succession is continuously exposed. Above a fossiliferous calcarenite yielding the "Senegalese" fauna, and abundant Cladocora, the 230Th/U age of which is consistent with Marine Isotope Stage (MIS) 5, a 6.25 m thick pelitic unit is characterized by lithologically homogeneous marine sediments in which stable oxygen isotope, micropaleontological and palynological analyses suggest a long and undisturbed sedimentary interval across the Marine Isotope Stage (MIS) 5.5 peak (plateau). High sedimentation rates and a successful paleomagnetic pilot study indicate the probability of locating brief chronostratigraphic events useful for correlation with both continental and marine successions elsewhere. These results show the composite section to be a very promising candidate in the search for the Upper Pleistocene global boundary stratotype section and point (GSSP). © 2014 Elsevier Ltd and INQUA
Holocene sea level change in Malta
No full textA multidisciplinary approach has been applied to study sea level changes along the coast of Malta using data collected from underwater archaeological remains. The elevation of archaeological markers have been compared with predicted sea level curves providing new bodies of evidence that outline the vertical tectonic behaviour of this region, allowing estimation of the relative sea level changes that occurred in this area of the Mediterranean since the Bronze Age. During the Roman Age, sea level was at -1.36 ± 0.1 m, while in the Midde Age it was at -0.56 ± 0.2 m, in agreement with previous estimations for the Mediterranean region. Data indicate that Malta was tectonically stable during the studied period. The occurrence of the present-day notch along the coasts of the island indicates recent vertical stability of the area. The lack of MIS 5.5 deposits all over the island could simply be due to high rates of erosion, as its coasts are highly exposed to storm waves, rather than tectonic movements. However, even very slight vertical movements could completely remove field evidence. The relative stability of the Maltese Islands allowed a first attempt to provide a palaeoenvironmental reconstruction of its coasts at different time windows since the Last Glacial Maximum. The results have been used to infer time and mode of mammal dispersal to the island during the Pleistocene. © 2012 Elsevier Ltd and INQUA
Submerged geomorphological evidence for isotope stage 3 paleo-sea level at about -20 m b.s.l. along the Italian coasts [Evidenze geomorfologiche sommerse nelle aree costiere italiane di uno stazionamento del livello del mare ubicato circa -20m e attribuito allo stadio 3]
No full textUnderwater investigations along the Italian coasts have shown a recurrent paleo-sea level at -18÷-22 m below the present sea level. Geochronoiogical age determinations on submerged speleothems used as sea-level markers and sampled at around -20 m, suggest that the paleo-sea level corresponds to the highest stand reached by the sea during the isotope stage 3, between 48 and 27 ka. Geomorphological evidence of this paieo-sea level are remains of a subhorizontal abrasion surface, which is visible on cliffs bordering carbonate promontories. Analogous surfaces (terraces) are mainly observed in the Tyrrhenian Sea from Tuscany to Sicily and in Sardinia at similar depths (-16÷-22 m); examples are also visible along the Apulia's coast in the Adriatic Sea. Recurrent geomorphological features of these terraces are: a) discontinuous but frequent occurrence; b) width lower than 10 m; c) location at the base of ancient cliffs; d) notch and pot-holes at the inner margin; e) in many cases terraces are laterally connected with the wave-enlarged mouth and levelled bottom of submerged caves, and with the flat top of ancient buttes. The general tectonic stability since Eutyrrhenian times (stage 5e of the oxygen isotope curve) in the regions where the observed forms occur, confines the relative age to well definite times. The absolute age of the paleo-sea level is yielded by speleothems sampled at about -20 m b.s.l. in Tuscany. These display marine biogenic episodes interlayered with continental ones. The 14C radiometric ages of the different layers keep such alternating episodes within the time span ranging from 27 to 42 ka (Alessio et al. 1992; 1994), namely during the highstand related to the isotope stage 3 (Aharon & Chappel, 1986). It is concluded that abrasion terraces and related morphological features found within the same depth interval formed during the stage 3 oscillating highstand
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