Marcello Gugliotta

Within the context of increasing plastic pollution, rivers act as the main source of these materials into the seas and oceans. A better understanding of their role as drivers of plastic dispersal is still necessary. A selected part of the northeastern coast of Sicily (southern Italy) is used as a case study to fill this gap. Uncrewed aerial system surveys combined with machine learning-based analysis are used to detect and quantify plastic accumulated on beaches following flash flood events and to assess the associated depositional mechanisms. Polystyrene foam was the dominant beached plastic across all datasets, accounting for the highest number and largest total accumulated size. Polyurethane foam and polyethylene terephthalate bottles were the next most frequently recorded plastics. Spatial analysis revealed that plastic concentration was highest immediately adjacent to the river mouth and decreased with distance, consistent with the river acting as the main source of plastics during flash floods, although simultaneous wave action disrupted this pattern at some sites, redistributing plastic along the shoreline. No relationship was observed between plastic size and distance from the river mouth, though polystyrene foam size varied across rivers and years, reflecting differences in fragmentation associated with fluvial energy, wave action, and dry period duration. Drainage basin size and population density also influence the amount of accumulated plastic. This study shows that flash flood-driven plastic accumulation displays significant spatial and temporal variability across rivers and events. A deeper understanding of these processes can lead to more precise predictions and solutions for plastic pollution.

Deltaic systems are dynamic environments that can experience repeated spatial and temporal reorganisation; however, the stratigraphic expression of transitional states and their preservation in the rock record, specifically how fluvial‐dominated deltaic systems change through transgressive events, remains poorly understood. To address this gap this study focuses on a ~100 m thick interval of the Pilmatué Member (Lower Cretaceous, Neuquén Basin, Argentina), spanning a transgressive surface between two depositional sequences of this unit. Analysis of 228 m of cores from three wells revealed seventeen facies grouped into eight associations, namely: distributary channels (FA1), interdistributary plain (FA2), terminal distributary channels (FA3), proximal mouth bars (FA4), distal mouth bars (FA5), prodelta (FA6) and proximal and distal ‘estuary’ (FA7 to FA8). FA1 to 5 comprise predominantly sandstone to mixed sandstone–mudstone deposits with abundant carbonaceous material, soft‐sediment deformation and limited bioturbation, reflecting fluvial‐dominated deltaic conditions that grade laterally into the mudstone‐dominated prodelta deposits of FA6. FA7 to FA8 record heterolithic sandstone–mudstone intercalations with abundant bioclasts, carbonate cement, marine trace fossils and dewatering structures within a distinct fining‐upward trend. This evidences a shift towards more marine‐dominated settings, in contrast to the coarsening‐upward trend of the underlying progradational facies (FA1 to FA6). The stacking patterns allowed the recognition of five units (U1 to U5). Basal U1 to U3 comprise regressive deltaic deposits (FA1 to FA6), whereas U4 records a short‐lived transgressive episode with atypical facies resembling ‘estuarine’ deposits (FA7 to FA8), interpreted as a drowned‐delta stage. Overlying, U5 marks the return to progradational deltaic deposition (FA3 to FA6), with prodelta sediments grading into mouth‐bar deposits. This succession thus illustrates a temporary reorganisation of a fluvial‐dominated delta during a disequilibrium stage driven by relative sea‐level rise and/or reduced sediment supply, followed by a recovery of its progradational nature. The studied interval of the Pilmatué Member serves as an ancient analogue of delta response to environmental perturbations. This rarely recorded reorganisation highlights the significance of out‐of‐equilibrium conditions while contributing to more integrated models of dynamic fluvio‐marine systems.

Investigating fluvio‐marine depositional environments from early geological times is of great importance, as they provide key insights into the palaeoenvironmental conditions of the early Earth. The present study aims to reconstruct the deposition and evolution of these systems from the Palaeoarchean Moodies Group in the Stolzburg Syncline of the Barberton Greenstone Belt, South Africa. It is based on a detailed investigation of the new, ~490 m‐long research drillcore BASE‐5B, using sedimentological logging, facies analysis and palaeocurrent measurements. Thirteen sedimentary facies were recognised and grouped into five facies associations. The stratigraphically lower section of the core, from ~490to ~294 m drilled depth, with an overall coarsening‐upward trend, is mainly characterised by unidirectionally cross‐stratified sandstones with occasional conglomerates and silicified sulphate concretions; this section was interpreted as a regressive, river‐dominated fluvio‐deltaic environment. The stratigraphically upper section, from ~294 to ~17 m, with an overall fining‐upward trend, is characterised by cross‐stratified sandstones with mudstone drapes and bidirectional palaeocurrents; this section was interpreted as a transgressive, fluvio‐estuarine environment dominated by combined tidal and riverine processes and with a well‐defined turbidity maximum. The vertical stacking pattern implies an evolution from a fluvio‐deltaic to a fluvio‐estuarine system with an overall regressive to transgressive trend due to an increase in basin subsidence and/or decrease in sediment supply. Two orders of transgressive–regressive cycles are superimposed on this general trend, reflecting relative sea‐level fluctuations, most probably driven by changes in sediment supply. These results help in understanding the sedimentary dynamics of Archean fluvial‐marine systems and their response to external forcings.

Tides are a key component in the Earth system as they help regulate climate and sustain life. Mars very likely had a surface ocean around 4–3 billion years ago. The NASA Curiosity Rover and the CNSA Zhurong Rover were sent to Gale Crater and the Vastitas Borealis Formation (VBF) on Mars to explore the surface and search for evidence of the past presence of water. Both rovers have since documented sedimentary rocks with features interpreted as deposited by tides. These include oppositely dipping cross‐laminations and cross‐stratifications, as well as bundled cross‐stratifications with systematic patterns, reactivation surfaces and mudstone drapes. To determine if tides on Mars had the capacity to transport sediment and form these structures, Martian tides were simulated using a numerical tidal model. Because the Martian moons are too small to generate a tide, the focus was on the solar tide. The resulting tidal current speeds were used in a Shields curve, modified to take into effect the lower gravity on Mars, to evaluate the sediment transport capacity of the tidal currents. The maximum current speeds at both rover locations are less than 0.01 m s ⁻¹ , below the calculated threshold for the movement of silt, and thus dispute the interpretation that the sedimentary features seen by the Zhurong Rover are tidal in origin and agree with previous interpretations that the Gale Crater was a paleo‐lake. However, there are other areas of the planet where tides may have had the energy necessary to form tidal deposits.

This study examines the distributions and dynamics of litter accumulation in a part of the northeastern coast of Sicily, southern Italy, using a multidisciplinary approach with manned and unmanned aerial systems imagery, a machine-learning algorithm and analysis of meteorological data. Aerial imagery shows that litter accumulations are present on beaches near the river mouths and potentially after flash floods. At least five distinct flash flood events depositing litter have been inferred since March 2015 to January 2024 in the study area. Meteorological data show that high precipitation, resulting in flash floods, and prevailing wind direction from the sea are the primary contributors to litter accumulation in this area. The algorithm applied on drone imagery on one of the accumulations detected a composition of polystyrene (42.6%), wood (35.6%), polyurethane (6.1%) and polyethylene terephthalate (5.4%). The general composition of the litter accumulation and its distribution near river mouths suggests that its source is associated with the input from nearby towns through mismanagement on the riverbeds, followed by flash floods. This study highlights the importance of considering river floods when investigating litter dynamics in coastal environments, as well as the potential of using aerial imagery and machine learning to help assess this problem. This article is part of the Theo Murphy meeting issue ‘Sedimentology of plastics: state of the art and future directions’.

Mixed arenites are widespread in the Quaternary record of the peri‐Mediterranean region where they accumulated in a variety of marginal‐marine depositional environments. In this study, Early Pleistocene mixed arenites and their associated conglomerates and sandstones were studied in detail near the town of Cataforio, in Calabria, southern Italy. Sedimentological logging, facies and palaeocurrent analyses and characterisation of trace and body fossils were combined with the interpretation of drone‐derived panoramic photographs and orthomosaics. Three major units, with the upper two separated by a major erosional surface, and a total of seven sedimentary facies were recognised. The basal Unit 0 is found near the fault bounding the basin to the east and consists of at least several decametres of conglomerates and sandstones (Facies S1). Unit 1 is up to 45‐m thick and consists of fossiliferous mixed arenites (Facies M1–4), whereas Unit 2 is at least 30‐m thick and mainly consists of conglomerates and sandstones (Facies S2–3). The mixed arenites of Unit 1 show single cross‐beds up to several metres thick and with a predominant dip direction to the west; these are intercalated with plane‐parallel‐bedded facies. The cross‐bedded deposits also show complex architectures up to 6‐m thick and hundreds of metres long interpreted as compound dunes. They are inferred to have formed in a strait environment, although this probably had more complex geometries and dynamics than previously suggested by other authors and other alternative hypotheses were also considered in this study. The siliciclastic‐dominated deposits of Unit 0 and Unit 2 were interpreted to have formed at the base of scarps and in submarine canyons, respectively. This study suggests that the inferred palaeo‐strait was not necessarily a wider and similarly oriented expression of the modern Strait of Messina. We advocate that straits and similar systems show a high level of spatio‐temporal complexity that should be investigated in detail.