Suspended Mud Research Articles

Floc size and settling velocity within a Spartina anglica canopy

There is increasing interest in tidal wetlands as mechanisms for sustainable and long-term coastal defence. The complexities of the interaction between the deposition of suspended particulate matter (SPM) and submerged vegetation, however, is to a large extent poorly understood. Consequently, accurate parameterisation of cohesive sediment settling fluxes in these environments is a crucial requirement for the development of high-resolution numerical models of wetland morphodynamics. A novel laboratory experiment is described in which the turbulent flow structure within a canopy of the halophytic macrophyte Spartina anglica is examined, and floc characteristics quantified using a unique floc camera configuration able to measure directly the full spectral floc size ( D) and settling velocity ( W s ). We provide the first quantitative observations of floc characteristics from shallow ( h<0.5 m), vegetated flows and investigate the potential influence that variations in vegetative density may have on flocculation, and thus depositional fluxes, in comparison to unvegetated flows. Turbid mud suspensions with concentrations of 100, 250 and 500 mg L −1 were sheared at current speeds of 0.1, 0.2 and 0.3 m s −1 through mono-culture arrays of S. anglica in an annular flume. Experimental stem densities were set at 200, 400 and 800 stems m −2. Mean absolute velocity exhibits an inverse, approximately exponential relationship with vegetative density. The threshold for maximum current attenuation (an 89–90% reduction of free stream velocity) is 400 stems m −2. D and W s range over 3 orders of magnitude from 20 to 1265 μm and from 3.96×10 −3 to 3.37 mm s −1, respectively. Maximum D is larger by a factor of 18 than that observed during the closest comparable in situ study. Our observations exhibit a pronounced positive skew due to incorporation of large, low-density, fast settling aggregates with maximum W s 33% greater than that used in current exploratory numerical models of saltmarsh surface deposition, and 236% greater than that observed during previous in situ studies. The inability to include the largest macroflocs (>160 μm)—the top 4% of our data set (ranked according to D) comprising 223 individuals between 250.46 and 1265.19 μm with settling speeds of 0.23–3.37 mm s −1)—may lead to serious under prediction of total mass settling flux (MSF). Parameterisation and incorporation of these observed distributions for use in numerical models of cohesive sediment deposition on saltmarsh surfaces is a high priority.

Observations and modeling of wave-supported sediment gravity flows on the Po prodelta and comparison to prior observations from the Eel shelf

A mooring and tripod array was deployed from the fall of 2002 through the spring of 2003 on the Po prodelta to measure sediment transport processes associated with sediment delivered from the Po River. Observations on the prodelta revealed wave-supported gravity flows of high concentration mud suspensions that are dynamically and kinematically similar to those observed on the Eel shelf [Traykovski, P., Geyer, W.R., Irish, J.D., Lynch, J.F., 2000. The role of wave-induced density-driven fluid mud flows for cross-shelf transport on the Eel River continental shelf. Continental Shelf Research 20, 2113–2140]. Due to the dynamic similarity between the two sites, a simple one-dimensional (1D) across-shelf model with the appropriate bottom boundary condition was used to examine fluxes associated with this transport mechanism at both locations. To calculate the sediment concentrations associated with the wave-dominated and wave-current resuspension, a bottom boundary condition using a reference concentration was combined with an “active layer” formulation to limit the amount of sediment in suspension. Whereas the wave-supported gravity flow mechanism dominated the transport on the Eel shelf, on the Po prodelta flux due to this mechanism is equal in magnitude to transport due to wave resuspension and wind-forced mean currents in the cross-shore direction. Southward transport due to wave resuspension and wind forced mean currents move an order of magnitude more sediment along-shore than the down-slope flux associated wave-supported gravity flows.

Effect of ionic surfactants on bauxite residues suspensions viscosity

Measurement of the rheological property of bauxite residue sample received from an Australian alumina refinery, treated with a number of cationic and anionic surfactant in laboratory has been carried out using a Brookfield viscometer for the assessment of the effect of surfactants on the residue viscosity. Sodium laurate, prepared with an excess of sodium hydroxide, was found to be effective while direct addition of anionic surfactants (lauric acid and sodium laureth sulphate) and cationic (cetyl trimethyl ammonium bromide) produce only moderate effect on the red mud suspension apparent viscosity at 65 °C. The experimental data appear to confirm the crucial role of the cation sodium in the process of adsorption of anionic surfactants on the flocculated red mud particles.

The role of particle aggregation/disaggregation in muddy sediment dynamics and seasonal sediment turnover in a back-barrier tidal basin, East Frisian Wadden Sea, southern North Sea

In order to better understand the processes controlling the deposition of mud in the East Frisian Wadden Sea, the seasonal response of the nearshore muddy sand facies was investigated along four shore-normal transects. For this purpose, the textural characteristics and internal sedimentary structures of the surface sediments were analysed at two-monthly intervals over two years. In addition, current velocities, in-situ particle size distributions, and the concentration of suspended sediment were measured near the dike using a high-resolution acoustic Doppler current profiler (PC-ADP) and an in-situ laser particle sizer (LISST-ST). A clear seasonal cycle emerges from the time-series data. The mud content of the surface sediment increases in summer and decreases in winter. This seasonal pattern is also reflected in the internal sedimentary structures of the upper sediment layer. In summer the surface sediment comprises a mud drape which disappears in winter when it is replaced by sand associated with wave-generated sedimentary structures. Grain-size analyses of dispersed mud samples reveal a pronounced deficiency of particles around 7 phi (8 μm). This is interpreted to reflect the transition between cohesive flocs/aggregates and non-cohesive coarser silt particles. A comparison of the particle size distributions of dispersed pump samples with those of the in-situ laser particle sizer confirms that the bulk of suspended mud consists of flocs and aggregates composed of particles finer than 8 μm. The destruction of such flocs during sample processing for size analysis in the laboratory produces strongly distorted size–frequency distributions and, as consequence, prevents a meaningful hydraulic interpretation of such data. Under calm weather conditions typical of the summer months, mean floc sizes (MFS) increase up to a critical current velocity of about 10 cm s − 1 during both the flood and ebb phase of the tidal cycle. This coincides with lower suspended sediment concentrations (SSC). Since the tidal cycle is ebb dominated under calm weather conditions, and current velocities during the flood phase do not exceed the critical value, most of the tidal cycle under typical summer conditions is dominated by large flocs and low sediment concentrations. Besides physico-chemical flocculation effects, the formation of particle aggregates is further promoted by microbial processes in summer. Such aggregates have considerably higher settling velocities than their constituent particles, especially in summer when water temperatures and, hence, kinematic viscosities are high. This explains the observed mud drape covering the intertidal area in summer. Under high-energy conditions, by contrast, the situation is reversed, the system being flood dominated, MFSs being smaller, and SSCs higher. Due to more frequent high-energy events in winter, higher current shear and turbulence cause floc break-up and resuspension of deposited muds. The sediment distribution pattern is thus clearly controlled by particle aggregation and disaggregation in response to seasonal changes in energy flux, water temperature and microbial activity.

An experimental investigation of sand–mud suspension settling behaviour: implications for bimodal mud contents of submarine flow deposits

AbstractThe settling behaviour of particulate suspensions and their deposits has been documented using a series of settling tube experiments. Suspensions comprised saline solution and noncohesive glass‐ballotini sand of particle size 35·5 μm &lt; d &lt; 250 μm and volume fractions, φs, up to 0·6 and cohesive kaolinite clay of particle size d &lt; 35·5 μm and volume fractions, φm, up to 0·15. Five texturally distinct deposits were found, associated with different settling regimes: (I) clean, graded sand beds produced by incremental deposition under unhindered or hindered settling conditions; (II) partially graded, clean sand beds with an ungraded base and a graded top, produced by incremental deposition under hindered settling conditions; (III) graded muddy sands produced by compaction with significant particle sorting by elutriation; (IV) ungraded clean sand produced by compaction and (V) ungraded muddy sand produced by compaction. A transition from particle size segregation (regime I) to suppressed size segregation (regime II or III) to virtually no size segregation (IV or V) occurred as sediment concentration was increased. In noncohesive particulate suspensions, segregation was initially suppressed at φs ∼ 0·2 and entirely inhibited at φs ≥ 0·6. In noncohesive and cohesive mixtures with low sand concentrations (φs &lt; 0·2), particle segregation was initially suppressed at φm ∼ 0·07 and entirely suppressed at φm ≥ 0·13. The experimental results have a number of implications for the depositional dynamics of submarine sediment gravity flows and other particulate flows that carry sand and mud; because the influence of moving flow is ignored in these experiments, the results will only be applicable to flows in which settling processes, in the depositional boundary, dominate over shear‐flow processes, as might be the case for rapidly decelerating currents with high suspended load fallout rates. The ‘abrupt’ change in settling regimes between regime I and V, over a relatively small change in mud concentration (&lt;5% by volume), favours the development of either mud‐poor, graded sandy deposits or mud‐rich, ungraded sandy deposits. This may explain the bimodality in sediment texture (clean ‘turbidite’ or muddy ‘debrite’ sand or sandstone) found in some turbidite systems. Furthermore, it supports the notion that distal ‘linked’ debrites could form because of a relatively small increase in the mud concentration of turbidity currents, perhaps associated with erosion of a muddy sea floor. Ungraded, clean sand deposits were formed by noncohesive suspensions with concentrations 0·2 ≤ φs ≤ 0·4. Hydrodynamic sorting is interpreted as being suppressed in this case by relatively high bed aggradation rates which could also occur in association with sustained, stratified turbidity currents or noncohesive debris flows with relatively high near‐bed sediment concentrations.

Effect of surfactants on bauxite residues suspensions viscosity

Measurement of the rheological property of bauxite residue samples received from an Australian alumina refinery (red mud and neutralised mud suspension) has been carried out using a Brookfield viscometer. The plant samples were treated with two anionic surfactants (sodium polyphosphate and sodium laurate) in the laboratory and the effect of the surfactants on the residues viscosity was determined. It was found that the addition of sodium laurate, prepared with an excess of sodium hydroxide causes reduction of the viscosity of both red mud and neutralised mud while sodium polyphosphate shows very little effect on either samples. The suspensions exhibit non-Newtonian behaviour and obey the power law model over a range of solid concentrations at 75 °C.

Municipal wastewater treatment with anodizing solid waste

In this study we have investigated the feasibility of the use of aluminium anodizing waste as coagulant for the treatment of municipal wastewaters instead of conventional inorganic materials. We have selected three different anodizing aluminium facilities for this study. The fresh mud was collected in the industrial facilities and prepared for tests. The anodizing muds were tested in two different forms: as powder and as mud suspension. For the powder form the fresh muds were submitted to a stabilisation process, homogenised and grinded. For the mud suspension form, water was added to the fresh mud in a way that the content of solids was known. A series of coagulation/flocculation tests were made, being controlled important parameters as pH, coagulant dose, and impeller type, stirring conditions (time and speed) and settling time for the different sludges. The effective coagulant capacity of the anodizing sludges was verified based on the final turbidity and on the pollutant removal (COD) of the supernatant samples as a function of the coagulant dose and pH.

海底堆積物を用いた有明海１００年変遷史の環境評価

Submarine sediments in Ariake Bay, Kyushu Japan, were examined to assess geoenvironmental changes in the area. 6 core samples from representative stations (Stas. 1-6) were analyzed for 16 minor elements (S, Cl, Ba, Rb, Th, Nb, Zr, Y, Ga, V, Zn, Cu, Ni, Co, Cr, and Pb) using XRF. Based on measurements of 210Pb radioactivity, sedimentation rates at 2 stations, one off the Chikugo River (Sta. 2) and the other at the mouth of Isahaya Bay (Sta. 4), were calculated, respectively, at 0.24 cm/year and a maximum of 0.15 cm/year.The concentrations of heavy metals, such as Cr, Ni, Zn, and Pb, in the marine sediments are about one-third of those of the highly polluted marine sediments recorded in Tokyo Bay around 1970. The vertical profile of a minor element can be divided into an upper section and a lower section. The upper section indicates various gradual changes, but the lower section is almost constant. The boundaries between the sections roughly correspond to the beginning of the 20th century, based on the sedimentation rate.Zn and Pb in the submarine sediments can be useful indicators to trace suspended mud derived from the Chikugo River. The complementary relationship of the vertical profiles in the spatial distribution suggests that the continuous migration of the sedimentary province may be governed by the geometrical arrangement of the estuaries of major rivers and by the tidal circulation pattern in Ariake Bay. Probably, large dams built on the major rivers have hampered the sedimentation process dominated by traction flow and have decreased the maximum drainage speed. As a result, such processes have promoted the expansion of the muddy area in Ariake Bay.Planktonic dinoflagellata (Sta. 2) and diatom (Sta. 4) fossils were also analyzed. Assuming such sedimentation rates at the stations, marine phytoplanktons (Brigantedinium spp., Rhizosorenia spp. and Skeletonema costatum), which indicate eutrophication of the sea water, have increased in relative abundance during the past 10 years.

Controls on effective settling velocities of mud flocs in the Changjiang Estuary, China

AbstractTheoretical and experimental studies were undertaken to gain insight into physical parameters controlling the flocculation and settling properties of mud flocs in the Changjiang Estuary, China. The Rouse equation is applied to vertical profiles of suspended sediment concentration to determine the bulk mean settling velocity (ws) of sediment suspended in the Changjiang Estuary. Both in situ point‐sampled and acoustically measured profiles of suspended mud concentrations were fit selectively. The calculated settling velocities ws mainly ranged from 0·4 to 4·1 mm s−1 for the point‐sampled data set, and from 1·0 to 3·0 mm s−1 for the acoustically measured data set. Furthermore, the settling velocities of mud flocs increased with mean concentration (C̄) of mud flocs in suspension and were proportional to increasing bottom shear stress (τb) of tidal flow. The best equation for the field settling velocity of mud flocs in the Changjiang Estuary can be expressed by the power law: ws = mC̄n (m, 1·14–2·37; n, 0·84–1·03). It is suggested that C̄ and τb were the dominant physical parameters controlling the flocculation and ws of mud flocs in suspension. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Gravity-driven sediment transport on the continental shelf: implications for equilibrium profiles near river mouths

An analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward, convex upward portion of subaqueous deltas and clinoforms. The model builds on recent field results demonstrating that gravity-driven flux of suspended mud is important on shelves provided that wave-induced suspension of sediment supports the requisite turbid hyperpycnal layer. Because the maximum sediment load is determined by the critical Richardson number, the results are independent of the properties of the suspended mud or the bed. The model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave-supported turbid near-bed layers. Progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity. The model is consistent with shelf profiles off the mouths of the Eel (California), Ganges-Brahmaputra (Bangladesh), Waiapu (New Zealand), Po (Italy), and Rhone (France) Rivers. The equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only, with deeper and broader profiles associated with decreasing sediment supply, increasing wave height and/or increasing wave period.

Mudflats and mud suspension observed from satellite data in French Guiana

The littoral of French Guiana is characterized by the north-westward migration of large mud banks along shore and by high suspended particulate matter concentrations (SPMC) coming from the Amazon River. A correspondence function is established between in situ optical data and SPMC measurements obtained from three coastal surveys on the Kaw River, the Mahury estuary, and the adjacent continental shelf, respectively. This function is applied to SPOT satellite images to estimate SPMC distributions near the sea surface on five dates between 1998 and 2001. Two typical situations have been observed: the mud suspensions are generally confined near the coast by a strong north-westward coastal current, while in one case (SPOT scene of 2 July 2001) the turbid plumes, probably resulted from the wave action on the mud banks, are directed seaward. SPMC varies from more than 300 mg l −1 adjacent to the intertidal zone to a few mg l −1 offshore. Turbid plumes are observed downstream, with regard to the Guyana Current, of small islands along the coast. Mud undulations are observed on the emergent surface of the mudflats, parallel to the crest waves and characterized by a wavelength of 200–1000 m. These structures are interpreted to form by wave action on the soft mudflat surface. Mangrove colonization of the mudflat follows these primary topographic structures.

Sediment exchange between Amazon mudbanks and shore-fringing mangroves in French Guiana

Time-series remote sensing data, sediment cores, and water column profiles of fluid properties and suspended sediment concentration were utilized to examine the mechanisms and volumes of sediment exchange between the mangrove fringe and the coastal zone in French Guiana. Remote sensing estimates of sediment yield from mangrove shoreline erosion by wave attack during the ∼30-year periods when offshore Amazon mudbanks are not adjacent to a 30–40 km long section of the shoreline are 6–23 million tons year −1. 7Be, 137Cs, and 210Pb inventories in sediment cores from inner (<5 m water depth) mudbank areas suggest the mangrove erosion occurs primarily during the January–April period of high wave energy, and is responsible for the bulk of sediment deposition on the leading edge of the mudbank. Remote sensing estimates of shoreline accretion associated with onshore flux of sediment from a mudbank are also large (8–26 million tons year −1). Radiotracer-generated strata age relationships indicate that the lower intertidal zone of the leading (depositional) edge of the mudbank is a relict surface, suggesting the offshore mudbank is decoupled from the shoreline. Water column profiles and radiochemical signatures point to fluid mud suspensions (10–400 g l −1) as the primary mechanism for delivering sediment across the relict intertidal zone to create the accretion at the shoreline. If the estimates of sediment volume involved in shoreline accretion and erosion in the studied area are extrapolated along the entire 1400-km-long Guianas coastline possessing offshore mudbanks, the annual exchange of sediment to and from the mangrove fringe is at least equivalent to the average input of new sediment from the Amazon.

Material exchange between the continental shelf and mangrove-fringed coasts with special reference to the Amazon–Guianas coast

Mangrove-fringed coasts are a major coastal environment in the tropics that exchange enormous quantities of inorganic and organic materials and dissolved ions with the adjacent ocean in unique ways. The 1,600 km long Guiana coast, from the Amazon River mouth to the Orinoco, the world's most extensive example, is exposed to significant oceanic wave and tidal energy but is almost exclusively composed of mud deposits. The huge alluvial discharge of the Amazon advected along the inner continental shelf is reworked into 20–25 shore-attached and mobile mud-banks 10–40 km in length. Frequent and deep resuspension created by the energetic conditions results in fluid mud suspensions (10–400 g 1 −1) that dewater upon re-deposition, resulting in extreme shoreline progradation rates (up to hundreds of metres per year) that are equally rapidly mobilized by wave attack. Biological assemblages (mangroves, foraminifera, diatoms, etc.) and biogeochemical conditions are strongly controlled by the intense recycling of sediments on the shoreface. Differences in sedimentary, ecological and biogeochemical processes are striking when this coast is compared with mangrove-fringed deltaic and estuarine coasts elsewhere, including those of west Africa and southeast Asia.

Passivity of iron in red mud?s water solutions

Red mud suspensions are studied as passivating agents for iron in alkaline chloride media. Red mud particles in alkaline media are negatively charged, and can absorb considerable amounts of protons without significant changes in pH. These particles adhere easily to an iron surface forming aggregates of heterogeneous shape, smaller than 10μm×10 μm. These adhered particles recrystallise on potential cycling, and hinder metal dissolution and magnetite formation. Carbon steel samples passivated in red mud suspensions become resistant to corrosion in alkaline chloride media. Corrosion potential versus time records and impedance spectroscopy measurements allow formulating some hypotheses about the inhibiting mechanism.

Passivity of iron in red mud’s water solutions

Red mud suspensions are studied as passivating agents for iron in alkaline chloride media. Red mud particles in alkaline media are negatively charged, and can absorb considerable amounts of protons without significant changes in pH. These particles adhere easily to an iron surface forming aggregates of heterogeneous shape, smaller than 10 μm×10 μm. These adhered particles recrystallise on potential cycling, and hinder metal dissolution and magnetite formation. Carbon steel samples passivated in red mud suspensions become resistant to corrosion in alkaline chloride media. Corrosion potential versus time records and impedance spectroscopy measurements allow formulating some hypotheses about the inhibiting mechanism.

Does subterranean flow initiate mud banks off the southwest coast of India?

Coastal waters off the southwest coast of India draw special attention because of the occurrence of mud banks at certain locations during southwest monsoon period. The present study puts forward a hypothesis of a subterranean flow, which could be a plausible mechanism to initiate the mud banks. The subterranean flow is believed to be coupled with activated trending faults and originate from the adjacent watershed (Vembanad Lake) separated from the sea by a narrow strip of land where submerged porous lime shell beds are present. When the lake water injection occurs through the fault, the mud/clay gets excited by its thixotrophic properties (as the overlying water looses its electrolyte) and transforms into a flowing fluid. The lowering of salinity due to the introduction of fresh water keeps the mud suspension in the water column for longer duration, leading to the formation of mud banks. The idea of subterranean flow through lime shell beds initiating formation of mud banks may apply globally to any coastal regions hugged by wetlands and of similar geological conditions.

EROSIONAL THRESHOLDS OF FLUID MUD IN LAKE KASUMIGAURA CAUSED BY PLANE JET

Critical conditions of bottom sediment erosion were examined in a large test flume for practical estimations of mud suspension in Lake Kasumigaura. The experiments were directed to investigate how planar jet, which brings mean shear flow and turbulent fluctuations, erodes the fluid mud in the lake.The results of the experiments were analyzed for relationships between critical water content of the mud and a combined index of mean velocity and velocity fluctuation. A relational expression was derived using least square method. The expression simulated the experimental results of critical water content distributions quite well.

Phase relationships between fine sediment suspensions and tidal currents in coastal seas

In shelf and coastal waters, point measurements of fine suspended sediment concentrations commonly display phase and frequency differences with respect to local current forcing. Phase shifts are often attributed to tidal advection and slow‐settling velocities of cohesive sediments. The phase relationship between tidal current speeds and near‐bed mud concentrations obtained at a site off the east coast of England is investigated. A simple depth‐averaged advection‐diffusion model is introduced and used to explore the influence of relative changes in settling, advection, and local erosion on the temporal evolution of suspension events. The model includes two source terms: local resuspension in phase with current speed and advection of a horizontal gradient in phase with tidal displacement. Incorporating a settling (or sink) term introduces a negative or positive phase shift in the advection or resuspension term, respectively. The settling term accounts for the vertical structure of suspension and becomes important at slack water when the near‐bed concentration, and thus deposition, rapidly increases. Model results are compared with suspended mud concentration data to help explain the observed phase relationships between concentration and current speed.

Turbidite depositional architecture across three interconnected deep‐water basins on the north‐west African margin

ABSTRACT The Moroccan Turbidite System (MTS) on the north‐west African margin extends 1500 km from the head of the Agadir Canyon to the Madeira Abyssal Plain, making it one of the longest turbidite systems in the world. The MTS consists of three interconnected deep‐water basins, the Seine Abyssal Plain (SAP), the Agadir Basin and the Madeira Abyssal Plain (MAP), connected by a network of distributary channels. Excellent core control has enabled individual turbidites to be correlated between all three basins, giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology. Large‐volume (&gt; 100 km3) turbidites, sourced from the Morocco Shelf, show a relatively simple architecture in the Madeira and Seine Abyssal Plains. Sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin‐wide muds. However, in the Agadir Basin, the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume. A single, very large turbidity current (200–300 km3 of sediment) deposited most of its sandy load within the Agadir Basin, but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the MAP. Large turbidity currents (100–150 km3 of sediment) deposit most of their sand and mud fraction within the Agadir Basin, but also transport some of their load westwards to the MAP. Small turbidity currents (&lt; 35 km3 of sediment) are wholly confined within the Agadir Basin, and their deposits pinch out on the basin floor. Turbidity currents flowing beyond the Agadir Basin pass through a large distributary channel system. Individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction, whereas the geochemistry and micropalaeontology of the mud fraction remain very similar. This is interpreted as evidence for separation of the flow, with a sand‐rich, erosive, basal layer confined within the channel system, overlain by an unconfined layer of suspended mud. Large‐volume turbidites within the MTS were deposited at oxygen isotope stage boundaries, during periods of rapid sea‐level change and do not appear to be specifically connected to sea‐level lowstands or highstands. This contrasts with the classic fan model, which suggests that most turbidites are deposited during lowstands of sea level. In addition, the three largest turbidites on the MAP were deposited during the largest fluctuations in sea level, suggesting a link between the volume of sediment input and the magnitude of sea‐level change.

The mineralised springs of the Adriatic region, central Italy

In the Adriatic region of central Italy, there are many mineralised (salt and sulphureous) springs, often used for therapeutic purposes. The hydrogeological characteristics of the springs and their tectonic set-up are examined in this paper. The salt springs generally emerge from the Plio-Pleistocene and Messinian deposits. The waters emerging from the Messinian deposits originate from marine waters subjected to evaporation. This leads to the precipitation of gypsum and formation of brines isolated by clayey deposits. Even the salt waters emerging from the Plio-Pleistocene deposits originate from marine waters trapped in the arenaceous Pliocene deposits. The waters are subjected to an ultra-filtration process through the clayey membrane with the formation of brines.&#x0D; The study reveals that the springs are located in the main thrust fronts, and the springs with higher salinity emerge in the thrusts that squeezed out the brine waters from the post-orogenic Plio-Pleistocene sequence.&#x0D; The sulphureous springs emerge from the Messinian and Plio-Pleistocene deposits and from the Apennine Meso-Cenozoic limestone ridges. The sulphureous springs emerging from the terrigenous sequence are connected with the Messinian evaporites, while the sulphureous springs emerging from the limestone ridges are related to the Messinian and Triassic evaporite deposits of the Umbrian-Marchean sequence.&#x0D; In the emergence zones of the salt waters, typical mud volcanoes or puddles are present due to suspended mud in the waters. Generally, the sulphureous springs emerge along streams whose waters are whitish and emit the typical smell because of sulphur precipitation.