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This paper regards the lower Pleistocene temperate‐water carbonate deposits disconformably overlying an escarpment made up of faulted Cretaceous to Miocene limestones of the Apulia Foreland (southern Italy). Study deposits discontinuously crop out along the present‐day eastern Salento sea cliff, and form isolated fan‐shaped bodies, up to 1 km wide and up to 40 to 50 m thick, each of them covering an area of a few square kilometres. The internal arrangement of beds is represented by up to 25° to 30° lobate, seaward dipping clinobeds thinning and onlapping onto a rocky foreslope in the proximal sector and passing to gently inclined to sub‐horizontal strata in the distal sector. Seven facies were distinguished, mainly composed of coarse‐grained skeletal carbonates made up of a heterozoan association including coralline algae, large and small benthic foraminifera, echinoids, molluscs, bryozoans and serpulids. Since clinobeds were formed thanks to hyperconcentrated density flows (grain flows) bypassing the upper part of the inherited escarpment, these skeletal grains represent ex situ deposits whose shallow‐marine factory was located upward (landward) with respect to the bypassed zone, likely in the almost flat area on top of the Salento Peninsula. Clinobeds are often affected by tens of metres wide and long channel‐like structures interpreted as landslide scars. Inside these gullies, contorted beds (slumps) or matrix‐supported intra‐bioclastic floatstone/rudstone (massive deposits) are present. The occurrence of supercritical‐flow structures (for example, backset‐bedded beds) indicates the development of hydraulic jumps along the steep slope of gullies. Since these clinostratified, fan‐shaped carbonate bodies represent carbonate slopes, and that the latter are known as aprons, normally related to linear sourced sediments, an acceptable oxymoron for studied fan‐shaped carbonate bodies is suggested: 'isolated base‐of‐slope aprons'. [ABSTRACT FROM AUTHOR]

This study presents a detailed facies analysis of an 800 m-thick stratigraphic succession in the basinal turbidites of the Macigno Sandstones Formation (MSF) recording the first foredeep in the northern Apennines (Italy). This stratigraphic succession shows an evident stacking pattern that, besides the basal part (200 m thick) dominated by fine grained and thin beds, is characterized by seven magnificently exposed sandstone lobes (from 90 to 19 m thick) separated by well-developed fine-grained interlobe deposits. Thanks to the detailed facies analysis, not only a well-defined architectural hierarchy has been identified, but a facies scheme has also been proposed, whereby cyclic recurring of three facies associations has in turn been identified. Each facies association records a well-determined evolutionary stage of lobe development, where an early depositional stage of the lobe building phase is followed by a flow impact and bypass stage recording flow decelerations and hydraulic jumps induced by the morphology created by the underlying depositional lobe. The latter phase promotes a switching and channel feeder avulsion that heralds the third phase of abandonment with the deposition of fine-grained interlobes. The facies stacking pattern and the evolutionary model of the MSF - also supported by other similar field and experimental works - are intended as a contribution to the understanding of intrinsic autogenic mechanisms at the basis of sand-rich depositional lobe development. • A detailed facies analysis of the Macigno Sandstone Formation (MSF), i.e. one of the most important foredeeps in the northern Apennines (Italy), has been presented. • A spectacular cyclic stacking pattern, characterized by magnificently exposed sandstone lobes separated by well-developed fine-grained interlobe deposits, has been described • A well-defined architectural hierarchy characterized by three cyclic recurring facies associations has been identified • Each facies association has been interpreted as recording a well-determined evolutionary stage of lobe development. This has allowed an evolutionary model based on autogenic mechanisms to be proposed [ABSTRACT FROM AUTHOR]

The occurrence and the effects of hydraulic jump instabilities on a natural river confluence in a small river basin in Liguria (Italy) is here investigated. Hydraulic jump instability has been extensively studied in controlled and simplified laboratory rectangular flumes. In the present study, a scaled physical model of the Chiaravagna River and Ruscarolo Creek confluence has been used, retaining the realistic geometry of the reaches. This reach has been subject to frequent floods in the last twenty years and the entire area of the confluence has been redesigned to decrease the flood risk. A series of experiments has been performed varying the discharge on the two reaches and the geometrical configurations. Free surface levels and two dimensional horizontal velocities have been measured in several positions along the physical model. The analysis of the water levels and velocities reveals that oscillations characterised by large amplitude and low frequency occur under particular hydraulic conditions. These oscillations have been found to be triggered by the hydraulic jump toe instability of the smallest reach of the confluence. Aiming at reducing the amplitude of the oscillations, which can be of the order of the flow depth, possible constructive solutions have been tested to control or damp the oscillations. Indeed, the insertion of a longitudinal dyke at the confluence has proven to be an effective solution to limit the amplitude of the transversal oscillations. [ABSTRACT FROM AUTHOR]

Bedforms and resulting sedimentary structures of interpreted upper-flow-regime origin are fairly common in various ancient and modern depositional settings, yet outcrop examples of shallow-water strata dominated by sedimentary structures arising from such flow conditions are rarely documented. This outcrop-based study presents the first detailed analysis of mid-Pleistocene beachface-shoreface strata containing sedimentary structures interpreted to have been formed by storm-generated backwash flows during the transition in flow regime from supercritical to subcritical. Here we propose that moving down the steep beachface, backwash flows rapidly accelerated and became thinner, experienced abrupt deceleration and flow thickening passing through an erosional hydraulic jump in the trough at the toe of the beachface, and then waned to thicker and subcritical conditions just downflow of the hydraulic jump. In this frame, landward-dipping backset laminae deposited on the downflow side of the trough evolved into thinner, upper-stage plane-parallel laminae further downstream. The transition from the proximal to the distal upper shoreface records a significant increase of preserved wave ripples and burrowed intervals, in concert with a progressive decrease in thickness and grain-size of individual sets of plane-parallel laminae and increase of gravel-filled gutter casts. • Four facies associations were identified from an outcrop-based study of Pleistocene shallow-water sediments in eastern central Italy. • Depositional settings vary from gravelly beachface to sandy upper and middle shoreface. • Sedimentary structures induced by storm-related supercritical backflows at the beachface-shoreface transition of a gravelly beach has been examined. [ABSTRACT FROM AUTHOR]

Cyclic steps are a type of upper flow-regime bedform consisting of trains of bed undulations with hydraulic jumps in the troughs. They form in free-surface flows and comprise a common, if not the dominant, bedform in subaqueous density flows in oceans, lakes and reservoirs. Cyclic steps originate from alternating Froude-subcritical and Froude-supercritical flow on respectively the stoss side and lee side of individual bedforms. The transition between these flow states is embodied by the hydraulic jump in the trough of the bedform, leading to the permanent or quasi-permanent morphology of cyclic steps. Over the past decade, numerous studies affirmed the dominant role of cyclic steps in generating bed undulations in modern and ancient glacial outwash, deltaic and turbidite environments. Cyclic steps were previously discriminated as net-depositional, transportational and net-erosional in different parts of such systems.These bedforms are here classified as climbing, transportational and falling cyclic steps, respectively. In analogy to the classification of ripples and dunes, the adjectives 'supercritically' and 'subcritically' can be added to indicate the preservation or not of the lee side, respectively. To avoid confusion between the direction of crest-migration (indicated by the terms subcritically and supercritically climbing or falling) and the flow regime (Froude-subcritical and Froude-supercritical flow), it is in most cases preferable to use the following cyclic step descriptors: (1) fully depositional (supercritically climbing), (2) partially depositional (subcritically climbing), (3) partially erosional (subcritically falling) and (4) fully erosional (supercritically falling). The new classification defines distinct depositional signatures for each type of cyclic steps. The most common type of cyclic steps is partially depositional, which is associated with nested scours filled with massive to backset-bedded deposits.The new classification can potentially be used as a predictive tool in the reconstruction of modern and ancient turbidite environments using repeat bathymetry, seismic reflection or outcrop data. To demonstrate this, the classification is applied to the deep-marine West Penghu Channel in the South China Sea, the Howe Sound fjord-delta in British Columbia, Canada and the Pleistocene carbonate slope of Favignana Island, Italy. [ABSTRACT FROM AUTHOR]