Investigating submerged morphologies by means of the low-budget “GeoDive” method (high resolution for detailed 3D reconstruction and related measurements)

Geophysical methods allow to collect geological data on lake and sea bottoms and characterize large areas, even at high depths, but with high costs. Moreover, the most widespread acquisition methods for morpho-bathymetric survey and the related instruments used are almost always ship-, ROV- or AUV-based and consequently they require high budgets. It is known that shallow waters can represent a limit for certain vessels and techniques, preventing the acquisition in the shoreface zone. To overcome the limits, i.e. to survey with high accuracy nearshore shallow waters with a low budget, we tested and tuned the “GeoDive” method that allowed us to survey two test sites, featured by the presence of “block fields” (i.e., accumulations of huge blocks and boulders of gravitational origin) under shallow waters. The “GeoDive” method allowed us to map the submerged morphologies and to acquire high-resolution optical images for further photogrammetric processing. The latter was fundamental to obtain 3D high-resolution models, also with conditions of low visibility. An Action Sport Cam with high definition resolution has been used for video acquisition, in addition to the equipment used during scientific diving. By coupling the processing of underwater-acquired data with the direct surveys performed by underwater SCUBA operators, it was possible to perform some morphological and sedimentological measurements and observations on the experimental targets, with the help of suitable markers

Sedimentary facies and foraminiferal assemblages from Posidonia oceanica meadows of western Mediterranean Sea

Sedimentary facies and foraminiferal assemblages of sediments sampled into seven Posidonia oceanica meadows from Western Mediterranean Sea were investigated. Six sampling sites are localised in Italy (Maratea, Ponza Island, Santa Marinella, Giglio Island, Osalla and Alghero), and one in France (Argentella, Crovani Bay, Corsica). The role of P. oceanica meadows in the sedimentary processes was investigated in different contexts: sampled meadows are set up both on soft and hard substrates, often forming “mattes”, in geographical areas subject to different wind and sea conditions (waves and longshore currents) and characterised by various coastal landforms and terrigenous inputs derived from costal erosional processes and/or fluvial contributions. A sedimentological, compositional, micropaleontological and geochemical characterisation of 111 bottom sediment samples, collected by SCUBA diving between 0 and 35 mwd, was carried out and finally tested with a Q-mode cluster analysis. Five sedimentary facies have been recognised, from terrigenous to mixed siliciclastic-carbonate and carbonate. Facies (and subfacies) are distinguishable by sorting, gravel content, abundance and maturity of clastic sediments, and weighted average of carbonate content. In all facies, foraminifers and red algae dominate the bioclastic fraction, whereas other bioclastic components are very subordinate and show a variable distribution. In all the investigated sites, benthic foraminiferal assemblages are generally dominated by typical epiphytic species, such as Asterigerinata mamilla, Lobatula lobatula, Peneroplis pertusus, Planorbulina mediterranensis, Rosalina spp. and miliolids. Nevertheless, these assemblages show some differences in the different sites according to the presence or absence of terrigenous contributions and, consequently, to the water turbidity. This parameter influences symbiont-bearing foraminifer as P. pertusus. Moreover, the samples from Argentella (Crovany Bay) are characterised by a peculiar assemblage, in which Miniacina miniacea dominates with very high frequencies.</jats:p

Evaluating the role of seagrass in Cenozoic CO2 variations

Marine seagrass angiosperms play an important role in carbon sequestration, removing carbon dioxide from the atmosphere and binding it as organic matter. Carbon is stored in the plants themselves, but also in the sediments both in inorganic and organic forms. The inorganic component is represented by carbonates produced by calcareous organisms living as epiphytes on seagrass leaves and rhizomes. In this paper, we find that the rate of seagrass epiphyte production (leaves and rhizomes) averages 400 g m−2 yr−1 , as result of seagrass sampling at seven localities along the Mediterranean coasts, and related laboratory analysis. Seagrasses have appeared in the Late Cretaceous becoming a place of remarkable carbonate production and C sequestration during the whole Cenozoic era. Here, we explore the potential contribution of seagrass as C sink on the atmospheric CO2 decrease by measuring changes in seagrass extent, which is directly associated with variations in the global coastal length associated with plate tectonics. We claim that global seagrass distribution significantly affected the atmospheric composition, particularly at the Eocene-Oligocene boundary, when the CO2 concentration fell to 400 ppm, i.e., the approximate value of current atmospheric CO2

Fibrous mineral detection in natural soil and risk mitigation (1(st) paper)

The paper describes a fibrous mineral detection methodology, which is based on the use of alternating rotary motion sieving equipment. The equipment was redesigned to meet additional requirements with respect to initial ones. Under this methodology, the fine fraction passing through the sieves was recovered and analysed to determine the sedimentology, mineralogy and morphology of the potentially particulating fraction. Reliance was made on the following analytical techniques: laser granulometry, scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) and polarised and phase contrast light microscopy (PLM, PCLM) for fibrous mineral identification and Walton-Beckett / whole field fibre counting. The samples for the analyses came from known areas with fibrous minerals, e.g. Lauria (Basilicata), and less known areas, e.g. the Natural Reserve of Mt. Rufeno (Latium) and Biancavilla (Sicily). With this methodology, fibres may be directly detected in both farmed and unfarmed soil with fibrous minerals and the process may be repeated in the various stages of farming or during works for creation of fire barriers or lanes, hydrogeological restoration etc. The goal is to identify risks arising from the natural occurrence of asbestos upon atypical activities, such as farming and forestry. With regard to exposure, consideration was given to fibrous minerals not currently classified in the relevant legislation, thus going beyond the search for asbestiform minerals in quarry sites located in ophiolite outcrop areas

High resolution with small budget. The “GeoDive” method for detailed 3D reconstruction of submerged morphologies and related measurements

The most widespread acquisition methods for lakes and sea bottom geological data are ship-, ROV- or AUV-based; geophysical methods and the related instruments for morpho-bathymetric survey allow to characterize large areas, even at high depths, but with high costs. It is known that shallow waters can represent a limit for certain vessels and techniques, preventing the acquisition in the nearshore zone. To overcome the limits, i.e. to survey with high accuracy nearshore shallow waters with a low budget, we tested and tuned the “GeoDive” method that allowed us to survey two test sites, featured by the presence of “block fields” (i.e., accumulations of huge blocks and boulders of gravitational origin) under shallow waters. The “GeoDive” allowed us to map the submerged morphologies and to acquire high-resolution optical images for further photogrammetric processing. The latter was fundamental to obtain 3D high-resolution models, also with conditions of low visibility. An Action Sport Cam (ASC) HD has been used for video acquisition, in addition to the equipment used during scientific diving. By coupling the processed underwater-acquired data with the direct surveys performed by underwater SCUBA operators, it was possible to perform some morphological and sedimentological measurements and observations on the experimental targets, with the help of suitable markers

The sedimentary facies of Posidonia oceanica seagrass meadows from the central Mediterranean Sea

Sedimentary facies of seven Posidonia oceanica meadows of western Mediterranean Sea were investigated. Five meadows are located in the Tyrrhenian coast, two are placed in the western coast of Sardinia and Corsica. These meadows develop on soft and hard substrates, often forming ``mattes'', in areas characterized by different oceanography, morphology, and terrigenous inputs produced by coastal erosion and fluvial runoff. A total of five sedimentary facies have been recognized ranging from pure terrigenous to bioclastic: terrigenous sand to gravelly sand, bioclastic sands, skeletal gravelly sands, mixed siliciclastic--carbonate sands, well to moderately sorted skeletal siliciclastic sands. All of the sedimentary facies associated with P. oceanica are in the sand grain size. The gravelly fraction is generally subordinated and variable, whereas the muddy fraction is generally low. The very low frequencies of the muddy fraction can be attributed to re-suspension processes and to the lack of carbonate mud production. The rate of epiphytic carbonate production obtained by two of the investigated meadows averages 400 g m−2 year−1. This value is in the range of temperate Mediterranean as well as of tropical and subtropical seagrasses. The epiphytic carbonate production plus the calcareous biota living on seagrass substrate contributes to form mixed siliciclastic--carbonate sediments of the nearshore environment of the Mediterranean. Lastly, the carbonate production associated with seagrass was derived by biota belonging to the heterozoan assemblage, where aphotic organisms are dominant, together with oligophotic biota such as coralline algae and symbiont-bearing foraminifera. Consequently, in the well-illuminated seagrass settings, the prevalent skeletal assemblages is represented by the heterozoan association while the components of the photozoan assemblages are absent or subordinate. This a key point for the paleoenvironmental reconstruction of the photic zone in the fossil record. Because the skeletal components of many seagrass dwellers greatly contribute to the carbonate sediment production of photic shallow-water environments, the seagrass meadows became substantial places of carbonate production and C (organic and inorganic) sequestration during the Cenozoic