Whereas deposits of extremely-rapid, 'catastrophic' mass wastings >10 m in volume (for example, the Marocche di Dro rock avalanche in the Southern Alps and the Flims rockslide in the Western Alps) are easily recognized by their sheer mass and blocky surface, the identification of catastrophic mass wastings partly removed by erosion must be based on deposit characteristics. Herein, a 'fossil' (pre-last glacial) rock avalanche, previously interpreted as either a till or debris flow, is described. The deposit, informally called 'Rubble Breccia', is located in the intramontane Campo Imperatore halfgraben that is bounded by a master fault with up to 900 m topographic throw. Based on documentation from field to thin section, and by comparative analysis with post-glacial rock avalanches, tills and debris flows, the Rubble Breccia is reinterpreted as a rock avalanche. The Rubble Breccia consists of an extremely-poorly sorted, disordered mixture of angular clasts from sand to block size. Many clasts show fitted subclast boundaries in crackle, jigsaw and mosaic fabrics, as diagnostic of catastrophic mass wasting deposits. Intercalated layers of angular to well-rounded clasts of coarse sand to fine pebble size, and deformed into open to recumbent folds, may represent shear belts folded during terminal avalanche propagation. The clast spectrum of the Rubble Breccia - mainly shallow-water bioclastic limestones, wackestones and other deep-water limestones and dolostones - is derived from the front range along the northern margin of the basin. Calcite cement found within the Rubble Breccia was dated with the U/Th disequilibrium method to 124.25 ± 2.76 ka bp, providing an age constraint to the rock avalanche event. Because catastrophic mass wasting is a common erosional process, fossil deposits thereof should be more widespread than have been identified to date, although this may be a consequence of misidentification. The criteria outlined here provide a template to identify fossil catastrophic mass wasting deposits of any age.

Remobilization and deformation of surficial subaqueous slope sediments create turbidites and soft sediment deformation structures, which are common features in many depositional records. Palaeoseismic studies have used seismically-induced turbidites and soft sediment deformation structures preserved in sedimentary sequences to reconstruct recurrence patterns and - in some cases - allow quantifying rupture location and magnitude of past earthquakes. However, current understanding of earthquake-triggered remobilization and deformation lacks studies targeting where these processes take place, the subaqueous slope and involving direct comparison of sedimentary fingerprint with well-documented historical earthquakes. This study investigates the sedimentary imprint of six megathrust earthquakes with varying rupture characteristics in 17 slope sediment cores from two Chilean lakes, Riñihue and Calafquén, and evaluates how it links to seismic intensity, peak ground acceleration, bracketed duration and slope angle. Centimetre-scale stratigraphic gaps ranging from 1 to 20 cm - caused by remobilization of surficial slope sediment - were identified using high-resolution multi-proxy core correlation of slope to basin cores, and six types of soft sediment deformation structures ranging from 1 to 25 cm thickness using high-resolution three-dimensional X-ray computed tomography data. Stratigraphic gaps occur on slope angles of ≥2.3°, whereas deformation already occurs from slope angle 0.2°. The thickness of both stratigraphic gaps and soft sediment deformation structures increases with slope angle, suggesting that increased gravitational shear stress promotes both surficial remobilization and deformation. Seismic shaking is the dominant trigger for surficial remobilization and deformation at the studied lakes. Total remobilization depth correlates best with bracketed duration and is highest in both lakes for the strongest earthquakes ( 9.5). In lake Riñihue, soft sediment deformation structure thickness and type correlate best with peak ground acceleration providing the first field-based evidence of progressive soft sediment deformation structure development with increasing peak ground acceleration for soft sediment deformation structures caused by Kelvin-Helmholtz instability. The authors propose that long duration and low frequency content of seismic shaking favours surficial remobilization, whereas ground motion amplitude controls Kelvin-Helmholtz instability-related soft sediment deformation structure development.

The shape and size of sedimentary bedforms play a key role in the reconstruction of sedimentary processes in modern and ancient environments. Recent laboratory experiments have shown that bedforms in mixed sand-clay develop at a slower rate and often have smaller heights and wavelengths than equivalent bedforms in pure sand. This effect is generally attributed to cohesive forces that can be of physical origin, caused by electrostatic forces of attraction between clay minerals, and of biological origin, caused by 'sticky' extracellular polymeric substances (EPS) produced by micro-organisms, such as microalgae (microphytobenthos) and bacteria. The present study demonstrates, for the first time, that these laboratory experiments are a suitable analogue for current ripples formed by tidal currents on a natural mixed sand-mud-EPS intertidal flat in a macrotidal estuary. Integrated hydrodynamic and bed morphological measurements, collected during a spring tide under weak wave conditions near Hilbre Island (Dee Estuary, north-west England, UK), reveal a statistically significant decrease in current ripple wavelength for progressively higher bed mud and EPS contents, and a concurrent change from three-dimensional linguoid to two-dimensional straight-crested ripple planform morphology. These results agree well with observations in laboratory flumes, but the rate of decrease of ripple wavelength as mud content increased was found to be substantially greater for the field than the laboratory. Since the formation of ripples under natural conditions is inherently more complex than in the laboratory, four additional factors that might affect current ripple development in estuaries, but which were not accounted for in laboratory experiments, were explored. These were current forcing, clay type, pore water salinity and bed EPS content. These data illustrate that clay type alone cannot explain the difference in the rate of decrease in ripple wavelength, because the bed clay contents were too low for clay type to have had a measurable effect on bedform development. Accounting for the difference in current forcing between the field and experiments, and therefore the relative stage of development with respect to equilibrium ripples, increases the difference between the ripple wavelengths. The presence of strongly cohesive EPS in the current ripples on the natural intertidal flat might explain the majority of the difference in the rate of decrease in ripple wavelength between the field and the laboratory. The effect of pore water salinity on the rate of bedform development cannot be quantified at present, but salinity is postulated herein to have had a smaller influence on the ripple wavelength than bed EPS content. The common presence of clay and EPS in many aqueous sedimentary environments implies that a re-assessment of the role of current ripples and their primary current lamination in predicting and reconstructing flow regimes is necessary, and that models that are valid for pure sand are an inappropriate descriptor for more complex mixed sediment. This study proposes that this re-assessment is necessary at all bed clay contents above 3%.

Carbonate sediments in non-vegetated habitats on the north-east Adriatic shelf are dominated by shells of molluscs. However, the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because: (i) monitoring of ecosystems prior to the 20th century was scarce; and (ii) ecosystem history inferred from cores is masked by condensation and mixing. Here, based on geochronological dating of four bivalve species, carbonate production during the Holocene is assessed in the Gulf of Trieste, where algal and seagrass habitats underwent a major decline during the 20th century. Assemblages of sand-dwelling and opportunistic are time-averaged to >1000 years and shells are older by >2000 years than shells of co-occurring . This age difference is driven by temporally disjunct production of two species coupled with decimetre-scale mixing. Stratigraphic unmixing shows that declined in abundance during the highstand phase and increased again during the 20th century. In contrast, one of the major contributors to carbonate sands - - increased in abundance during the highstand phase, but declined to almost zero abundance over the past two centuries. and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top-core increments but are rarely alive. Although is not limited to vegetated habitats, it is abundant in such habitats elsewhere in the Mediterranean Sea. This live-dead mismatch reflects the difference between highstand baseline communities (with soft-bottom vegetated zones and hard-bottom beds) and present-day oligophotic communities with organic-loving species. Therefore, the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century. More than 50% of the shells on the sea floor in the Gulf of Trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats.

Upper Proterozoic carbonate successions from central East Greenland (the Limestone-Dolomite 'Series' of the Eleonore Bay Group) and Svalbard (the Backlundtoppen Formation of the Akademikerbreen) Group, Spitsbergen, and the Upper Russo Formation of the Raoldtoppen Group, Nordaustlandet) contain thick sequences dominated by pisolites. These rocks were generated in shallow marine environments, and the pisoids are essentially oversized ooids. A marine environment is supported by the thickness and lateral extent of the carbonates; by a sedimentary association of pisolites with stromatolites, flake-conglomerates, calcarenites, calcilutites, microphytolites, and ooids similar to that found in numerous other Proterozoic carbonate successions; by sedimentary structures, including cross-beds and megaripples that characterize the pisolitic beds; and by microorganisms that inhabit modern marine ooids of the Bahama Banks. Petrographic features and strontium abundances suggest that the pisoids were originally aragonitic, but neomorphism, silicification, calcitization, and dolomitization have extensively modified original mineralogies and fabrics. The East Greenland and Svalbard pisolitic carbonates reflect similar depositional environments and diagenetic histories, reinforcing previous bio-, litho-, and chemostratigraphic interpretations that the two sequences accumulated contiguously in a coastal zone of pisoid genesis which extended for at least 600, and probably 1000 or more, kilometres.

Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.