Studio dei sedimenti tardo-quaternari del litorale veneziano: contributo alle indagini paleoclimatiche ed ambientali

ABSTRACT The imprints of paleoevolutionary processes that affected the Venice lagoon and its littoral during the Late-Quaternary can be found in the sand and c/ay layers underlying the Venetian basin. Sedimentological characteristics of the Late-Pleistocene and Holocene sand and clay sedimentation during the past 25-30.000 years, before the human impact, in the lagoon of Venice, are reported. The multidisciplinary investigation of clay and sand sediments and the development and application of new analytical techniques and methodologies, allowed the detailed mineralogical, geochemical and textural characterization of the recent sediments. The new data obtained not only may contribute to better understand the paleoevolutionary events that took place in the Venetian basin and the impact of the paleoclimatic variations on the depositional environments, but also they may be used as a sediment natural reference base for a more accurate quantification of the pollution level in the bottom sediments of the lagoon of Venice. RIASSUNTO Gli strati di sabbia e di argilla sottostanti il bacino veneziano conservano le tracce dei processi paleoevolutivi che hanno influenzato la laguna di Venezia ed il suo litorale. Lo studio multidisciplinare dei sedimenti sabbiosi ed argillosi depositatisi durante gli ultimi 25-30.000 anni, prima dell'impatto antropico, e lo sviluppo ed utilizzo di nuove metodologie analitiche, hanno permesso una caratterizzazione mineralogica, geochimica e tessiturale dettagliata dei sedimenti recenti. I nuovi dati ottenuti possono non solo contribuire a meglio comprendere gli eventi paleoevolutivi succedutisi nel bacino veneziano e l'impatto delle variazioni paleoclimatiche sugli ambienti deposizionali, ma possono anche servire come base naturale di riferimento per una più accurata quantificazione dei livelli di inquinamento dei sedimenti di fondo soggetti ad antropizzazione della laguna di Venezia

The Holocene-Pleistocene boundary zone in the Lagoon of Venice (Italy)

The results of a detailed study on the sediments representative of the boundary area from the Late-Pleistocene and the Lower-Holocene sedimentations are reported. Mineralogical, granulometric and geochemical investigations have been carried out to characterize the clay-rich samples taken along the littoral bar and representative of the continental and marine sedimentations. Particular attention was devoted to the study of the overconsolidated clay layer considered to be the last continental deposit before the Holocene (Flandrian) transgression and interpreted as a paleosol

Recent sand sediments grain-size determination by Image Analysis

Presented in this study is the application of the Image Analysis (I.A.) technique as alternative to the traditional mechanical sieving methods for grain size determination (Bonardi & Tosi, 1994a). The application of Image Analysis technique to study the grain size of recent sand sediments has produced analytical data that are comparable to those obtained by conventional methods. Furthermore, the use of the Image Analysis has provided additional morphological parameters such as grain elongation, shape and roundness that can be useful clues to depositional environment reconstruction

Studio sedimentologico di un livello di argilla sovraconsolidata sottostante il litorale veneziano

ABSTRACT The effect of global climatic changes that occurred since the last Würmian glaciation is recognizable in the stratigraphic sequences of the Pleistocene-Holocene boundary zone from several coastal areas in different locations around the world. This study gives the results of mineralogical, chemical, and textural investigations of about fifty samples of the hard clay layers and the clay layers above and below underlying the Venice littoral. This hard clay layer, locally known as caranto, from few centimeters to few meters thick, represents the Holocene/Pleistocene boundary and it carries the marks of climate changes that characterized the last phase of the Pleistocene and the early part of the Holocene. The very dry climate during a period of very limited sedimentation and a long subaerial exposition, desiccated, compacted and oxidized the clay previously deposited, to form the overconsolidated clay level (caranto). RIASSUNTO Gli effetti delle variazioni climatiche succedutesi, su scala globale, a partire dall'ultima glaciazione würmiana sono riconoscibili nelle sequenze stratigrafiche in varie località costiere sparse in tutto il mondo. In questo studio vengono riportati i risultati preliminari di una indagine sulle caratteristiche mineralogiche, geochimiche e tessiturali di circa cinquanta campioni di un livello di argilla sovraconsolidata e degli strati argillosi sopra e sottostanti, lungo il litorale veneziano. Questo strato di argilla sovraconsolidata, noto come "caranto", con spessore variante da pochi centimetri ad alcuni metri, rappresenta il limite Olocene/Pleistocene e conserva gli effetti dei cambiamenti climatici che hanno caratterizzato l'ultima fase del Pleistocene e quella iniziale dell'Olocene. Il clima freddo e molto arido, durante un periodo di sedimentazione molto limitata e la prolungata esposizione subaerea hanno determinato l'essiccamento, la compattazione e l'ossidazione dell'ultima sedimentazione continentale argillosa, sino a formare quel livello sovraconsolidato che e' noto col nome locale di caranto

Studio granulometrico mediante Image Analysis (I.A.) delle sabbie tardo quaternarie del cordone litoraneo della laguna di Venezia

Vengono riportate le analisi granulometnche, ottenute mediante l'analizzatore d'immagini (I.A.) , di 140 campioni di sabbia, prelevati da 18 sondaggi a carotaggio continuo terebrati lungo il cordone litorale veneziano. Queste analisi sono state eseguite per contribuire allo studio sedimentologico dei terreni incoerenti con lo scopo, unitamente ad altre indagini multidisciplinari, di ricostruire le varie fasi evolutive tardo pleistoceniche ed oloceniche dell 'area litorale veneziana. L'utilizzo dell 'I.A. e' nato dall 'esigenza di determinare le variazioni della granulometria di campioni rappresentati da livelli sabbiosi a volte molto sottili e spesso con quantita' minime di materiale a disposizione, sui quali successivamente o contemporaneamente dovevano essere eseguite altre indagini mineralogiche e geochimiche. L'I.A., oltre ad offrirei queste possibilita', ha anche permesso la determinazione di altri paramentri morfologici quali il grado di allungamento e di arrotondamento di ogni grano di sabbia, non ottenibile con il metodo di setacciatura tradizionale. L'analisi granulometrica delle sabbie eseguito con l 'LA. non solo ci fornisce dati paragonabili a quelli ottenibili con i metodi tradizionali, ma presenta anche il vantaggio di poter essere eseguito congiuntamente allo studio mineralogico e chimico effettuato mediante un microscopio elettronico a scansione (SEM) o una microsonda elettronica (EMP)

Investigation of Late-Quaternary sediments from the South Yellow Sea and the Yangtze River Delta (China)

The results of a study to determine the geochemical, mineralogical, magnetic and textural characteristics done on Late-Quaternary sediments from drill cores from the South Yellow Sea (core H106) and the Yangtze River Delta (core LA) (China) are reported. The Late-Pleistocene continental sedimentation is represented by clayey silt and hard clay layers, while the marine Holocene sediments consist mainly of clay (H106) and sand and clay layers (LA)

Urban Geology for the Enhancement of the Hypogean Geosites: the Perugia Underground (Central Italy)

AbstractUrban geology analyses natural risks and promotes geoheritage in urban areas. In the cities, characterized by a high cultural value, the hypogean artificial cavities, often present in the downtown, offer a unique opportunity to show the geological substratum. Moreover, these places could be a point of interest in urban trekking with the abiotic component of the landscape as a topic (geotourism). To investigate these areas, rigorous bibliographic research and a geomorphological assessment are the first steps, but, besides, non-invasive methods are new techniques increasingly in demand. In this paper, we present a multidisciplinary study on the Etruscan Well (third century B.C.), one of the most important Etruscan artefacts in Perugia (Umbria region, Central Italy). The characteristics of the sedimentary deposits outcropping along the perimeter walls have been collected. Moreover, to show the underground geoheritage, we provide a 3D model of the well and the surrounding area integrating a georeferenced laser scanner survey with ground-penetrating radar prospecting. We aim to obtain a tridimensional mapping of accessible internal rooms to depict the geological characteristics of the Etruscan Well, also revealing a surrounding network of buried galleries. The results are not only a meaningful advancement in the archaeological, geological and historical knowledge of the downtown of Perugia but are a hint for the geoheritage promotion and dissemination, providing images and 3D reconstruction of underground areas

Investigations on ancient beads from the Sultanate of Oman (Ra's al-Hadd - Southern Oman)

A study has been carried out on the mineralogical composition of stone beads found in the course of archaeological excavations carried out at the site of Ra's al-Hadd in Southern Oman. The data provide information about the raw material and technology used for beads production. Several beads and micro-beads made of white paste of different shapes and sizes have been analysed. They range, in size, from two to four millimetres in diameter, two to fifteen millimetres in height, and the diameter of the hole is approximately one millimetre. The shape is tubular for the biggest bead, cylindrical for slender beads and ring-shaped for micro-beads. The beads were analysed using X-ray diffraction (XRD); the method was optimised to minimise the amount of the sample necessary for analysis (15 milligrams were necessary using special sample holders while in traditional holders 300 milligrams are needed). XRD analysis revealed that the beads arc made of “synthetic enstatite”, a magnesium silicate belonging to pyroxene group (orthopy-roxene Mg2Si2O6). The relative intensity of the main peaks confirms that the material is “synthetic enstatite”. Natural enstatite is a hard mineral (its hardness is five or six on the Mohs scale), therefore we propose that a softer magnesium-bearing mineral was used: steatite (Mg5Si4O10 (OH)2 commonly known as massive talc - hardness one on the Mohs scale). The beads might have been worked from soft steatite bulk material and then hardened by transformation of the steatite to synthetic enstatite during firing at about 1000 °C so that the formerly soft beads became hard and durable. Some preliminary heating experiments on talc bulk fired at about 1000 °C was carried out to compare powder diffractograms of the beads and the fired massive talc; a good overall resemblance of the two patterns is evident. The raw material of the examined beads might have came from the ultramafic rocks of Oman and it is very likely that these beads were produced from locally available raw materials.Nous avons étudié la composition minéralogique des petites perles trouvées lors des fouilles archéologiques effectuées sur le site de Ra's al-Hadd situé au sud de l'Oman. Nous avons analysé beaucoup de petites perles et micro-perles fabriquées avec un matériel blanc et de différentes formes et dimensions. Les résultats de l'analyse ont livré des informations sur le matériel et la technologie utilisés pour la production des petites perles. Les dimensions sont de deux à quatre millimètres de diamètre et de deux à quinze millimètres de haut, le diamètre du trou perforé est approximativement de un millimètre. La forme est tubulaire pour la perle la plus grande et cylindrique pour les plus petites perles, de forme circulaire pour les micro-perles. Les petites perles ont été analysées par diffraction de rayons X. Nous avons optimisé la méthode pour minimiser la quantité de matériel utilisé pour l'analyse (15 mg de poudre sont nécessaires avec un porte échantillon spécial contre 500 mg de poudre nécessaires avec un porte échantillon traditionnel). L'analyse par diffraction de rayons X indique que les petites perles sont en enstatite synthétique, un silicate de magnésium appartenant au groupe des pyroxènes (ortopyroxène Mg2Si2O6). L'intensité relative des pics principaux confirme que le matériel utilisé est l'enstatite synthétique. L'enstatite naturelle est un minéral très dur (il a une dureté de cinq à six sur l'échelle Mohs) et c'est pourquoi nous proposons que la stéatite (Mg2Si4O10(OH)2 normalement connue comme talc massif de dureté un sur l'échelle de Mohs) est le matériel utilisé pour la réalisation des petites perles. Les petites perles pourraient avoir été réalisées avec de la stéatite et être ensuite transformées en enstatite synthétique par cuisson au four à une température d'environ 1000 degrés centigrades. Cette méthode permettrait la production de petites perles très dures, réalisées à partir d'un matériel tendre. Nous avons fait des expériences avec du talc italien chauffé à 1000 degrés centigrades pour comparer les diagrammes de diffraction des petites perles avec les diagrammes de diffraction du talc chauffé

MORPHODYNAMICS PROCESSES IN THE LAGOON OF VENICE: THE SCANELLO SALT MARSH AREA

Geomorpholgical variations have been naturally occurring in the Lagoon of Venice since its formation. In recent times, however, complex morphodynamic changes, caused by natural processes and by the direct or indirect impact of man activities have been recognised. Moreover, there remains a lack of knowledge concerning sediment erosion, re-suspension, transport and sedimentation, sea-lagoon balance and the role played by the hydrodynamics. A detailed study of the Scanello salt marsh area, in the Northern part of the Venice Lagoon, was carried out, in order to better understand the erosion-transport-sedimentation processes and the hydrodynamics interaction. Understanding the role that the hydrodynamics plays in the erosion, transportation and deposition of sediments in this test area, is essential to the understanding the morphological variations, that are presently occurring in the Venice Lagoon and morphological and environmental restorations required. A 2D hydrodynamic finite element model was used to provide the circulation field of the entire Venice basin. Results obtained by different simulations allowed the investigation of the main hydrodynamic features of the Scanello area