Redeposition Of Sediments Research Articles

Accumulation of an earthquake-induced extremely turbid layer in a terminal basin of the Nankai accretionary prism

Seismic shaking is a major trigger for sediment redistribution in subduction zones, and clouds of dilute suspended sediment have been reported in association with large earthquakes. Dive observations in a basin on the slope of the central Nankai accretionary prism soon after the 2004 off-Kii Peninsula earthquakes documented a layer of suspended sediment with extremely high turbidity. We estimated the thickness of this bottom turbid layer to be more than 2.5 m by comparison of seafloor depths between surveys in 2004 and 2010 and about 2.6 m from instrumental evidence involving the submersion of a heat-flow probe. A high-resolution subbottom profiling survey across the basin revealed acoustically transparent layers thicker than 2 m. Because the slope basin is a terminal basin completely enclosed by topographic highs, we examined the possibility that the uppermost transparent layer was deposited as a consequence of the 2004 earthquakes. Considering the sediment source area and the volume of the basin fills, the mobilization and redeposition of thin surface sediments on the prism slope can account for the volume of the transparent layer. We conclude that the 2004 earthquakes caused widespread disturbance of the prism slope and concentrated surface sediments in this terminal basin. Our results emphasize the utility of a terminal basin in a subduction zone as an earthquake recorder.

Spatial and seasonal distribution of organochlorine pesticides in the sediments of the Yangtze Estuary

The spatial and seasonal distribution of organochlorine pesticides (OCPs) in the sediments of the Yangtze Estuary was investigated. The total concentration of 19 OCPs (∑OCPs), including α-HCH, β-HCH, γ-HCH, δ-HCH, o, p′-DDE, p, p′-DDE, o, p′-DDD, p, p′-DDD, o, p′-DDT, p, p′-DDT, heptachlor, aldrin, heptachlor epoxide (Isomer B, Isomer A), endosulfan I, dieldrin, endrin, endosulfan II and methoxychlor, in the surface sediments ranged from 0.4 to 82.1ngg−1 d.w. The mean values of the ∑OCPs were 8.5±8.3ngg−1 d.w., 26.7±12.1ngg−1 d.w., 40.5±18.2ngg−1 d.w., and 13.0±11.2ngg−1 d.w. for August 2010, November 2010, February 2011 and May 2011, respectively. The highest concentration of OCPs was detected at the river–sea boundary because of the intense resuspension and redeposition of sediments in this area. The OCPs preferred to accumulate in the inner estuary, rather than in the offshore area in the dry season, whereas the opposite occurred in the flood season. This phenomenon was related to the seasonal changes of the Changjiang diluted water (CDW). OCPs in the offshore area were controlled by the ocean currents and the monsoon. There was a southward increase for the OCP deposition in the offshore area in the winter. This increase resulted from the influences of the southward Yellow Sea coastal current and the East China Sea coastal current, as well as the northwest wind in winter. The Three Gorges Dam had an impact on HCH composition by changing the sediment redistribution during the deposition process.

Sedimentation from suspension and sediment accumulation rate in the River Vistula prodelta, Gulf of Gdańsk (Baltic Sea)

The River Vistula is one of the largest suppliers of fresh water and terrigenous matter to the Baltic Sea. The impact of this river on the Baltic coastal system and the fate of the sediment delivered to the Gulf of Gdańsk are not well understood. Spatial transport patterns, as well as the settling, deposition and accumulation of the sediments were studied at the Vistula prodelta in different seasons from January 2012 to January 2013. The concentration of suspended matter in the water column was measured with optical methods, the sedimentation rate was determined with sediment traps, and the sediment accumulation rate was estimated using 210Pb dating. Our data shows that the annual supply of sediment to the sediment-water interface exceeds the annual rate of sediment accumulation in the outer Vistula prodelta by a factor of three. Sediment trapping during rough weather showed that significant sediment redeposition was taking place, even at depths of 55m. The dynamic sedimentary processes occurring in the Vistula prodelta mean that that more than two-thirds of the sediment mass can be remobilized and then redeposited in deeper parts of the Gdańsk Basin.

Modification of climate signals by human activities recorded in varved sediments (AD 1608–1942) of Lake Holzmaar (Germany)

Paleolimnological data from varved sediments in Lake Holzmaar (Eifel, Germany) were combined with documentary data on human activities, long-term data from the Historical Climate Database (HISKLID) for Germany and with recent monitoring data to evaluate changes in deposition that arose from climatic and human influences. The sediment data included seasonal layer thickness in an established varve chronology (1608–1942 AD), subannual chemical element counts, and multiannual organic matter data (TOC, TN, δ13Corg), all combined on an annual scale. Indicators for detritus deposition (lithogenic element counts and detritus layers) determined the first principal component (PC1) of the sediment data. This detritus PC1 was compared to the first PCs of the seasonal precipitation and temperature from HISKLID. While no relation was found to precipitation, the correlation with the temperature PC1 determined by spring to fall temperatures was significant. From 1608 to 1870, a positive correlation of the PCs suggests an increase of detritus deposition in the lake center with increasing non-winter temperatures. These may be linked by lake-internal sediment redeposition that increases when the periods of winter stratification become shorter and that of lake circulation longer. The detritus deposition is modulated by external detritus input depending on the intensity of erosion-conducive land use (wood pasture, wood cutting, and rotational slash-and-burn cultivation). Detritus input diminished when land use slowed down with population decrease as the consequence of plague epidemics, warfare and emigration. After 1870, forest regeneration and improving agricultural practices led to a stabilization of the catchment. Erosion and detritus deposition decreased progressively. The negative correlation of detritus deposition with the gradually increasing temperature presumably mimics a cause-effect relation, although a link with decreasing freeze–thaw action is possible. The modernization of agriculture proceeded with manuring and fertilizing, which caused an increase of lake productivity as indicated by summer blooms of diatoms with enhanced nutrient demand, increased δ13Corg values and sulfur concentrations. Within this well established data base we found combinations of criteria that may be used to deduce natural climatic or anthropogenic influences. The quantitative attribution of these influences remains a challenging task in paleolimnology because their interaction makes the detection of linking mechanisms difficult even at high degree of detail and the processes themselves remain debatable.

Characterisation of the Rota Wewa tank cascade system in the vicinity of Anuradhapura, Sri Lanka

A complex and sustainable watershed management strategy was implemented in Sri Lanka during the ancient Anuradhapura period, from the 5th century BC to the 11th century AD. Like modern watershed management strategies, it focused on flood prevention, soil erosion control, water quality control and water storage for irrigation. Tank cascade systems were the key element of these ancient watershed management installations. The wewas investigated were constructed in valleys characterised by fluvial accumulation. Sedimentological analyses of these tank cascade systems show that a precise age determination and the reconstruction of sediment and water f luxes as triggered by human-environment interactions are difficult. This is caused by the shallow character of the wewas leading to the steady redeposition of the tank sediments by wave motions during the wet season and agricultural use of the desiccated wewas during the dry season. Beyond, the sediments analysed allow to distinguish between the weathered parent bedrock and the overlying sediments. A differentiation between wewa deposits and the underlying fluvial deposits remains challenging.

Middle Eocene Nummulites and their offshore re-deposition: A case study from the Middle Eocene of the Venetian area, northeastern Italy

The Middle Eocene Calcari nummulitici formation from northeastern Italy, Venetian area, represents a shallow-marine carbonate ramp developed on the northern Tethyan margin. In the Monti Berici area, its main components are larger foraminifera and coralline red algal communities that constitute thick carbonate sedimentary successions. Middle ramp and proximal outer ramp environments are recognized using component relationships, biofacies and sedimentary features. The middle-ramp is characterized by larger flattened-lenticular Nummulites on palaeohighs between which rhodoliths formed. Larger Nummulites palaeohighs containing Nummulites millecaput, Nummulites crassus, Nummulites discorbinus and Nummulites cf. gizehensis developed more basin-wards. The following relatively quiet environments of basin-wards of the palaeohighs represent areas of maximum carbonate production. The transition between the distal middle- and the proximal outer-ramp settings is marked in the study area by a large erosional surface which is interpreted to have been formed as a result of an erosive channel body filled in by deposits re-sedimented from shallower depths. These off-shore re-sedimented channelized deposits, ascribed to the Shallow Benthic Zone SBZ 15, lying on hemipelagic marls (planktonic foraminiferal zone E9 (P11)) allow for a biostratigraphic correlation to the Late Lutetian.The studied deposits, represented by packstone to rudstones, were displaced whilst still unlithified. The Lutetian–Bartonian regression along with the local tectonic activity promoted the production of a high amount of biogenic shallow-water carbonates mainly produced in the Mossano middle-ramp settings. These prograded towards the basinal areas with high-sedimentation rate of carbonate deposits characterized by the larger Nummulites rudstones. Such high amounts of sediment led to sediment instability which potentially could be mobilized either by return currents due to occasional major storms or by earthquakes induced by tectonic activity. These will have led to the offshore re-deposition of the Nummulites sediments into deeper water setting via the observed channels. Since potential migration pathways are short, such distal re-sedimented channel-filled material surrounded by hemipelagic marls is optimally placed for the formation of potential subsurface oil reservoirs.

Measuring sheet erosion using synthetic color-contrast aggregates

The bulk of eroded soils measured at the outlets of plots, slopes and watersheds are suspended sediments, splash-induced sheet erosion. It is depending on rainfall intensity and antecedent soil moisture contents and contributes to a significant proportion of soil loss that usually is ignored in soil erosion and sediment studies. A digital image processing method for tracing and measuring non-suspended soil particles detached/transported by splash/runoff was therefore used in the present study. Accordingly, fine mineral pumice grains aggregated with white cement and coloured with yellow pigment powder, with the same size, shape and specific gravity as those of natural soil aggregates, called synthetic color-contrast aggregates, were used as tracers for detecting soil particle movement. Subsequently, the amount of non-suspended soil particles detached and moved downward the slope was inferred with the help of digital image processing techniques using MATLAB R2010B software (Mathworks, Natick, Massachusetts, USA). The present study was conducted under laboratory conditions with four simulated rainfall intensities between 30–90 mm h-1, five antecedent soil moisture contents between 12–44 % v v-1 and a slope of 30%, using sandy loam soils taken from a summer rangeland in the Alborz Mountains, Northern Iran. A range of total transported soil between 90.34 and 1360.93 g m-2 and net splash erosion between 36.82 and 295.78 g m-2were observed. The results also showed the sediment redeposition ratio ranging from 87.27% [sediment delivery ratio (SDR) = 12.73%] to 96.39% (SDR = 3.61%) in various antecedent soil moisture contents of rainfall intensity of 30 mm h-1 and from 80.55% (SDR = 19.45%) to 89.42% (SDR = 10.58%) in rainfall intensity of 90 mm h-1. Copyright © 2013 John Wiley & Sons, Ltd.

The Leptodictyo Riparii-Hygroamblystegietum Varii Ass. Nov., A Dead Wood-Dwelling Association of Near-Natural Alluvial Forests in the Rhône Valley (France)

HUGONNOT, V. & CELLE, J. 2013. The Leptodictyo riparii-Hygroamblystegietum varii ass. nov., a dead wood-dwelling association of near-natural alluvial forests in the Rhône valley (France). - Herzogia 26: 187–195.The description of the Leptodictyo riparii-Hygroamblystegietum varii ass. nov. is given. It is characterized by two species, Leptodictyum riparium and Hygroamblystegium varium. This eutrophic and sciaphilic association thrives on dead wood that is alternately subject to flooding and limited periodic desiccation. It is recognized in the Rhône valley (France) but is most probably more widely distributed in western and central Europe. It is most characteristic of naturally functioning river valleys with a constant erosion of banks and redeposition of alluvial sediments in strongly dynamic soft-wooded forests.

Depositional processes of the mixed carbonate–siliciclastic rhodolith beds of the Miocene Saint-Florent Basin, northern Corsica

Many sedimentary processes can lead to the formation of mixed carbonate–siliciclastic sediments in shallow shelf environments. The Miocene Saint-Florent Basin (Corsica), and in particular the Monte S. Angelo Formation, offers the possibility to analyze coarse mixed sediments produced by erosion of a rocky coast, ephemeral stream input, and shallow-water carbonate production dominated by red algae. The Monte S. Angelo Formation was deposited during the Burdigalian to Langhian interval. During this interval, the island of Corsica experienced increased subsidence related to the development of the Ligurian-Provencal Basin and associated Sardinia-Corsica block rotation. Four main rhodolith-rich subfacies have been recognized: conglomerate with rhodoliths, massive rhodolith rudstone, well-bedded rhodolith rudstone, and rhodolith floatstone. The four facies have been interpreted as having been deposited in different environments of a gravel-dominated, nearshore to offshore prograding wedge. Deep-water melobesioids dominate the red algal assemblage from shoreface to offshore. Shallow-water subfamilies of lithophylloids and mastophoroids occur in only accessory amounts. Poor illumination is believed to be due to terrigenous input by ephemeral streams and wave- and current-resuspension. Resuspension processes are favored by the limited occurrence of seagrasses. Two types of siliciclastic–carbonate mixing processes characterize the investigated rhodolith-rich deposits: (1) punctuated mixing, produced by the re-deposition of terrigenous sediments by debris-flow processes during flooding events onto carbonate sediments together with rhodoliths of the shoreface environments, and (2) in situ mixing, produced by growth of coralline algae on siliciclastic pebbles to form the rhodoliths.

Sedimentation dynamics and metal loading in Lake Pyhäjärvi, Finland

Post-isolation (9,600 year BP) sedimentology in Lake Pyhajarvi, Finland, was studied using sub-bottom echo-sounding and sediment coring. The sediment sequence appeared in the echo-sounding profiles as two sections: (1) a lower section of homogenous, light grey gyttja clays, and (2) an upper section with dark layers of mainly clay gyttjas and gyttjas, here referred to as C_gyttja. We investigated the thickness and volume of sediments as well as their morphology and areas of accumulation. Approximately 77 % of the lake represents areas of accumulation, containing 34 and 1.3 million tons of dry matter and carbon, respectively. Spatial variability in sedimentological properties indicates that accumulation in the Kirkkoselka sub-basin was focused into the deepest areas since lake isolation. In the Isoselka sub-basin, however, accumulation was focused partially onto the flanks of the depression, whereas the deepest parts (23–27 m) of the sub-basin represent erosional areas. There appears to have also been sediment re-suspension and re-deposition, as indicated by erosion surfaces. This, combined with dune-like bottom morphology in the accumulation areas, provides evidence for the role of wind-driven bottom currents on sedimentation dynamics in the Isoselka sub-basin. Increases in Cu and Zn concentrations, driven by Pyhasalmi mining activities, were used as a geochemical marker for recent sedimentation (RS) between 1966 and 2008. As a consequence of wind-driven bottom currents, 60 % of the metals accumulated in the Kirkkoselka sub-basin and 40 % accumulated in the Isoselka sub-basin. There is a spatial correlation between amounts of C_gyttja and RS. In the middle of dune-like C_gyttja formations in the Isoselka sub-basin, the RS grain size is smaller than in other areas. Variations in RS are greatest along the borders of the accumulation area, likely a consequence of bottom currents in those areas.

Multibeam Bathymetry and Slope Stability of Isvika Bay, Murchisonfjorden, Nordaustlandet

A research expedition to the polar region of Murchisonfjorden (Nordaustlandet, Svalbard) on the research vessel Horyzont II took place in August 2009. This paper presents results from an extensive bathymetric measurement campaign of the Isvika Bay, southern part of Murchisonfjorden. The aim of this campaign was to select optimal sites for sediment sampling. A detailed analysis of the bathymetric features is performed with a special emphasis on the slope stability conditions. A simple method for identifying areas of sediment redeposition is proposed. The results confirm that the Isvika Bay has two distinct basins separated by a ridge. Both basins display flat central regions surrounded by steep slopes with gullies. In addition, results of analysed Quaternary geological data have indicated that the area was affected by ice repeated glacial activity in the past and that there is no morphological form typical for glacier erosion and sedimentation.

Bajocian to Tithonian age of radiolarian cherts in the Tolmin basin (NW Slovenia)

Abstract The Tolmin basin is a typical example of a deep-water Mesozoic basin that developed on the rifted south Tethyan continental margin. Remnants of this basin are preserved at the intersection of the Dinarides and the southern Alps in northwestern Slovenia. The Jurassic successions consist of carbonate gravity-flow deposits, radiolarian cherts and shales, and are overlain by pelagic Biancone limestone. A distinctive chert-dominated interval (the upper member of the Tolmin Formation) was dated with radiolarians. The base of this interval was assigned to the late Bajocian in the distal part of the basin and to the middle Callovian-early Oxfordian in the more proximal part of the basin. The topmost radiolarian cherts are early Tithonian in age. The mid-Tithonian transition from chert to the Biancone limestone was also determined with nannoplankton. The beginning of highly siliceous sedimentation in the Bajocian correlates well over the entire western Tethys and was linked to two factors: an increase in water depth due to regional subsidence and an increase in plankton productivity. The pronounced silica enrichment coincided with the opening of the Alpine Tethys and with the intraoceanic subduction that occurred in the Meliata-Maliac-Vardar Ocean. Reorganization of the plate boundaries may have induced substantial changes in the circulation of water masses that, in turn, had a long-term effect on surface productivity. On the basin scale, radiolarian dating revealed considerable lateral and vertical variations in the thickness of chert successions. This distributional pattern implies that, in narrow continental-margin basins, sedimentation rates were primarily determined by the redeposition of pelagic sediments. Important stratigraphic gaps occur even in the distal basinal setting.

Geochemistry and organic petrography of Cretaceous sediments of the Calabar Flank, southeastern, Nigeria

Detailed bulk geochemistry and organo-petrography of outcrop Cretaceous sediments (with no significant effects of weathering) from the Calabar Flank, southeast Nigeria were performed to understand the organic carbon source, accumulation and degradation, and paleo-climatic, paleoceanographic and paleoenvironmental conditions in West Africa during Early Cretaceous (Aptian) to Maastrichtian times. This study was based on microscopic, elemental analyses (organic carbon, nitrogen, iron and sulphur), Rock-eval pyrolysis and carbon-isotope analyses. In general, the Calabar Flank shales are characterised by highly variable total organic carbon (TOC) contents, which range between 0.1% in Aptian–Albian Mfamosing Limestone and 9.9% in the Awi Formation sediments. The organic matter (OM) is a mixture of immature to early-mature marine and terrigenous OM of types III and IV. This is indicated by low hydrogen indices (HI value (10–190 mg HC/g TOC), Tmax (417–460 °C), vitrinite reflectance %Ro (0.39–0.62 %Ro), low to high C/N ratios (3.4–1158.0) and high amounts of terrigenous macerals (vitrinite + inertinite). Based on carbon isotope, C/N ratios and sulphate reduction index (SRI), OM degradation (up to 70%, SRI > 2.5) is most pronounced for shales deposited in a marine environment. The geochemical and petrographic data indicate that local factors such as low bioproductivity, down slope transport and redeposition of sediments from a fluvial–deltaic basin to nearshore facies, shallower, oxic and mildly oxygen-deficient environments, humid–arid paleogeographic conditions, specifically controlled the amount and quality of the OM during Aptian–Mastrichtian stages where marine sediments have been assumed to be deposited during the global anoxic events. Therefore, the order of the main factors controlling OM content in sediments are: input of terrigenous material transported from the land > low OM productivity by marine photoautotrophs > low preservation.

U–Pb geochronology of zircons from fossiliferous sediments of the Hajnáčka I maar (Slovakia) – type locality of the MN 16a biostratigraphic subzone

AbstractLacustrine sediments of the Hajnáčka I maar of southern Slovakia contain teeth and skeletal remains of a mammal fauna, including index Early Villanyian arvicoline rodents. U–Pb dating of magmatic zircons extracted from the redeposited fossiliferous maar sediments revealed a total of six volcanic events. The oldest age of 3.43 Ma was interpreted as that corresponding to the initial phreato-magmatic eruption that created the maar. Most zircons grouped around 3.06 ± 0.03 Ma, the age attributed to the catastrophic eruption that killed the mammal assemblage thriving within and around the maar studied. This age coincides with the 3.1 Ma boundary between the MN 16a and 16b subzones of the European Mammal Neogene chronostratigraphic scale estimated from the succession of Early Villanyian palaeontological localities according to the hypsometry of rodent teeth. Younger zircon ages overlapped those of the neighbouring basaltic lava flows, necks and dykes, thus recording superimposed effusions. The youngest 1.58 Ma old zircon defines the age limit for the final redeposition of the fossiliferous sediments in the maar drainage lake regime.

The recorded evidence of AD 1755 Atlantic tsunami on the Gibraltar coast

Evidence of the AD 1755 tsunami consisting of the same type of accretions produced by the re-deposition of earlier sediments, has been recorded at three different height along the coast of Gibraltar: Along a shallow sandy shore, the tsunami wave reached a run-up of 2–3 m, whereas along steep, cliff–lined shores (Rosia Bay) it surpassed 5 m. An overwash deposit was also identified at the bottom of a lagoon (The Inundation), at 0.5 m b.s.l., on the isthmus that joins the Rock with the mainland. Southern submerged platforms (Vladi’s Reef) were also affected by the erosional backwash to a depth of 22 m. The tsunamigenic sediments exhibit a bimodal granulometry, mainly composed of sands with a coarser fraction composed of marine faunal shells remains, together with larger clasts derived from the rocky substrate. All remobilized sediments were dated by historical methods and radiocarbon dating.

The post-depositional changes of the onshore 2004 tsunami deposits on the Andaman Sea coast of Thailand

The Indian Ocean tsunami flooded the coastal zone of the Andaman Sea and left tsunami deposits with a thickness of a few millimetres to tens of centimetres over a roughly one-kilometre-wide tsunami inundation zone. The preservation potential and the post-depositional changes of the onshore tsunami deposits in the coastal plain setting, under conditions of a tropical climate with high seasonal rainfall, were assessed by reinvestigating trenches located along 13 shore-perpendicular transects; the trenches were documented shortly after the tsunami and after 1, 2, 3 and 4 years. The tsunami deposits were found preserved after 4 years at only half of the studied sites. In about 30% of the sites, the tsunami deposits were not preserved due to human activity; in a further 20% of the sites, the thin tsunami deposits were eroded or not recognised due to new soil formation. The most significant changes took place during the first rainy season when the relief of the tsunami deposits was levelled; moderate sediment redeposition took place, and fine surface sediments were washed away, which frequently left a residual layer of coarse sand and gravel. The fast recovery of new plant cover stabilised the tsunami deposits and protected them against further remobilisation during the subsequent years. After five rainy seasons, tsunami deposits with a thickness of at least a few centimetres were relatively well preserved; however, their internal structures were often significantly blurred by roots and animal bioturbation. Moreover, soil formation within the deposits caused alterations, and in the case of thin layers, it was not possible to recognise them anymore. Tsunami boulders were only slightly weathered but not moved. Among the various factors influencing the preservation potential, the thickness of the original tsunami deposits is the most important. A comparison between the first post-tsunami survey and the preserved record suggests that tsunamis with a run-up smaller than three metres are not likely to be preserved; for larger tsunamis, only about 50% of their inundation area is likely to be presented by the preserved extent of the tsunami deposits. Any modelling of paleotsunamis from their deposits must take into account post-depositional changes.

Persistent organic pollutants associated to water fluxes and sedimentary processes in the Colorado River delta, Baja California, México

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were studied in sediment cores from two distinctive modern channels of the Colorado River (CR) delta. Their abundance and temporal changes are associated with flood-flows from the CR across the USA–Mexico border. The CR channel is directly exposed to river flood-flows while the Hardy River (HR) is a local channel derived mainly from agricultural runoff, geothermal effluents, and treated urban wastewater. Different headwater compositions and degrees of exposure to flood-flows appear to be the factors controlling the composition of persistent organic pollutants (POPs). Enrichment of OCPs (46 ng g −1 dwt in HR and 4.37 ng g −1 dwt in CR) occurred during or a few years after flooding. PCB-138 (4.2 ng g −1 dwt) is enriched in HR suggesting its origin in dielectric oils from the geothermal power plant. PCB-28 (2.1 ng g −1 dwt) in CR may be related with atmospheric input and/or re-deposition of upstream sediments. In surficial sediments (0–3 cm), only HR exceeds international sediment quality guidelines (4,4′-DDE = 8.16 ng g −1 dwt and ΣDDT = 8.34 ng g −1 dwt).

The paleogeodynamic conditions of redeposition of conodont elements in the late devonian-early carboniferous sediments of the Southern Urals

The peculiarities of conodont fauna redeposition of the Upper Devonian-Lower Carboniferous sediments from different structural-facial zones of the Southern Urals (the Zilair megasynclinorium on the western slope of the Southern Urals (paleocontinental sector) and the Magnitogorsk-Bogdanovsk graben in the central part of the Magnitogorsk megasynclinorium on the eastern slope (paleooceanic sector)) have been studied. The regularities of conodont fauna redeposition in the flysch foredeep and riftogenous depression (of graben) formed in the back of the volcanic arc after volcanism termination have been described.

Mathematical model of the Late Pleistocene and Holocene transgressions of the Black Sea

Although the Late Pleistocene–Holocene fluctuations in the Black Sea have been studied over many years, no overall picture of this difficult natural phenomenon has as yet been developed and described. Moreover, in the literature, many researchers have provided mutually exclusive opinions about many of the processes occurring within this time interval. The variation in conceptualizations about the filling of the Black Sea basin is explained by the following reasons. (1) Fluctuations of sea level in the basin were never properly studied as physical processes under conditions of increased freshwater runoff, change in Bosporus strait depth, increase in World Ocean level, etc. Therefore, some conclusions about sea-level changes were not verified by appropriate calculations and have not been physically substantiated. (2) The study of sea-level fluctuations are conducted according to modern sea depth markers and sediment age, but as the sediment was formed under varying depth conditions, and could have moved relative to modern markers by the agency of various geological processes, it is possible that that every core may give a different level curve. (3) Processes of sedimentation, erosion and redeposition of sediment occurring in the sea have been studied insufficiently. For this reason the same geological material has been interpreted differently by various researchers. Therefore, mathematical modeling of sea-level fluctuations based on various physical laws seems to be of great importance. In this paper, the value and sign for the Black Sea freshwater balance during the Upper Pleistocene–Holocene are discussed. The hypothesis suggests that during the specified period of time, the freshwater balance of the sea was always positive, the sea was filled with water up to the sill mark in the Bosporus strait, and a river flowed into the Sea of Marmara along the strait bottom. In the present paper, geologic evidence of the river flow in the strait during the glacial age and later is presented. Other points of view about the sea's freshwater balance change are considered. A mathematical model of the Black Sea basin filling with freshwater in the Upper Pleistocene–Holocene is suggested. It considers that change in water volume inflowing to the Black Sea to be a result of ablation, neotectonic processes in the strait, bottom erosion, and sediment accumulation. Black Sea level change calculations have shown the following. As a result of repeated increases in river runoff during glacial melting, the level of the Black Sea started to rise from −80 m, probably to −20/−30 m, making, in the process, numerous secondary fluctuations. The reason for this phenomenon was the circumstance that the water volume brought by the rivers could not flow to the Sea of Marmara through the narrow canyon of the Bosporus strait at the time. Therefore, water collected in the sea, raising its level. At approximately 12 ka BP, the World Ocean level rose to the river surface and began to increase its depth. As a result of the increase in strait depth, the accumulated water in the Black Sea flowed out, thereby lowering its level to a mark close to the Ocean level. According to calculations, this occurred ca. 11 ka BP. Thereafter, the Black Sea level rose together with the Ocean level. Water within the Sea of Marmara has flowed to the Black Sea since approximately 9 ka BP in the form of a bottom counterflow. With a small time delay, theoretical change in the Black Sea level practically corresponds to data obtained from geological investigations. The theory offered here of fluctuations in Black Sea level is self-sufficient; it explains all processes from the melting of the glaciers, by physical laws and does not demand the application of any additional hypotheses. In the conclusion of this paper, the debatable questions about the Black Sea's possible lowering and the subsequent flooding of the basin are considered.

Deposition and taphonomy of the Hound Island Late Triassic vertebrate fauna: Fossil preservation within subaqueous gravity flows

Late Triassic marine vertebrates occur in the Hound Island Volcanics exposed on the eastern shore of Hound Island, southeastern Alaska. This fossil assemblage derived from slope deposits within an intra-arc basin of a volcanic island arc complex. It is associated with the allochthonous Alexander Terrane prior to its northern translation from tropical latitudes to its current latitude. Fossils occur within a 13-m-thick succession of interbedded calcareous shale and volcaniclastic-rich bioclastic limestone. The limestone layers are skeletal (vertebrate and invertebrate) packstones to wackestones and are interpreted as episodic thin-bedded turbidite and debris flow deposits that resulted from redeposition of slope sediments. Forty-seven vertebrate fossils were collected that consist of complete and fragmented cranial and postcranial elements belonging to Eosauropterygia, Thalattosauria, and Ichthyosauria, including the genus Shonisaurus. Bones are frequently disassociated and show predepositional abrasion and breakage. Another less common taphonomic mode is observed, characterized by several large associated elements, representing a single individual, found parallel to bedding and draped by shale. Rare Osteichthyes and Chondrichthyes teeth are also present. Bivalve and conodont fossils indicate a middle Norian age for the assemblage.