Event Deposits

In seismically active areas, long term records of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes. In the western Corinth Rift, one of the most active areas in Europe in terms of seismicity, data about ancient earthquakes are still insufficient, despite historical records covering the last two millenia and several studies in onshore paleoseimology. In this paper, we test the use of offshore sediments from the Gulf of Corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes. Two shelves (40-100 m deep), one sub-basin (180 m) and the basin floor (330 m) have been sampled by short gravity cores. The cores were analyzed in order to identify and characterize event deposits. The age control has been provided by 137 Cs and 210 Pb activity measurements showing that the cores represent 2 to 4 centuries of sedimentation. In each site, sandy event deposits are interbeded in the muddy, hemipelagic sedimentation. The age of event deposits has been compared to the record of historical earthquakes using new and published macroseismic data. This comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity ≥ VII in the area, e.g. in 1861 CE, 1888 CE and 1909 CE. In nearshore, shallow-water settings, the record of event deposits does not exactly fit with the historical record of large earthquakes because too few event deposits are present. This may be due to the absence of sediment failures or to a lower preservation of the deposits in such settings. In the deepest site, in the basin floor, the correspondence is better: a sandy turbidite probably corresponds to each large earthquake since 1850 CE, except one aseismic sediment density flow that occurred at the end of the 20th century. Surprisingly, the Ms = 6.2, June 15, 1995 Aigion earthquake is only possibly recorded in one nearshore site on the Aigion Shelf, in the form of a tsunami back-wash flow deposit. This study showed that moderate earthquakes (M 5.8-6.5) can significantly impact marine sediments. Regarding the evaluation of seismic hazard in the area, the basin floor is proposed as a promising site for long term paleoseismology in the Gulf of Corinth, while shallower settings need to be considered more carefully.

Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210 Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representing different hydrodynamic conditions (probably during run-up and backwash phase). These sedimentological observations were supported by geochemical and physical data and were confirmed using 210 Pb dating. A sediment core taken from a depth of 57 m at a distance of 25 km offshore did not reveal clear event deposits. Comparisons with available data from offshore tsunami deposits showed that there is no single set of signatures that could be applied to identify this kind of deposits.

The continental shelf southeast and northwest of the Amazon River mouth is overlain by a sediment layer of about a meter in thickness, characterized by "'Pb profiles consisting of one or more segments with nearly-uniform excess activity. Uniform 'rOPb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments; however, biological activity is minimal in this area. Hence, this surficial layer (SL) is a result either of physical reworking of the sediments, or of rapid (possibly episodic) deposition of sediment. Factors controlling the formation of the SL were examined during the AmasSe& project between August 1989 and October 1991. Primarily using ""Pb (tljz = 22.3 yr) activity profiles and X-radiography, the thickness and character of the SL were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions (e.g., discharge stage, wind stress); one of these stations was reoccupied during semidiurnal and fortnightly periods. Additionally, replicate sediment cores were obtained at stations in order to assess small-scale spatial variability of geochemical and sedimentological characteristics in the seabed. The SL thicknesses in replicate sediment cores obtained at each site were found to vary within f 5 cm. Normalized thickness of the SL decreased by an average of 17 cm between August 1989 and February 1990, a period of increasing wind stress during falling-to-rising river discharge. The SL thickness subsequently increased slightly (8 cm) from February to May 1990, and increased again (27 cm) between May 1990 and October 1991. The maximum SL thicknesses were observed in October, a period of low wind stress and minimal river input, suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge. Variations in SL thickness are reflected by changes in suspended sediment (mostly as fluid muds), as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when SL thickness is at a minimum. Although a significant SL was present during all of the sampling periods, changes in the character of "'Pb profiles at two of the stations suggest that substantial, perhaps complete, removal and redeposition of the SL occurred some time between February and May. Preserved strata (i.e., below the SL) is characterized by greater evidence of bioturbation and increased sand content, but otherwise is similar to that of the SL. Long-term preservation of strata is thought to occur through episodic suspension and redeposition of the SL, with net accumulation of decimeter-thick, hiatus-bounded layers.

Delivery and dispersal of fluvial sediment in Hanalei Bay, Kaua'i, Hawai'i, have important implications for the health of local coral reefs. The reef community in Hanalei Bay represents a relatively healthy ecosystem. However, the reefs are periodically stressed by storm waves, and increases in sediment and dissolved substances from the Hanalei River have the potential to cause additional stress. Increased turbidity and sedimentation on corals during Hanalei River floods that occur in seasons of low wave energy, when sediment would not be readily remobilized and advected out of the bay, could affect the health and sustainability of coral reefs and the many associated species. Measurements of short-lived isotopes 7 Be and 137 Cs in sediment cores have been used to trace the thickness and distribution of terrestrial sediment in Hanalei Bay, in order to assess spatial and temporal patterns of sediment deposition and remobilization relative to coral-reef locations. A third isotope, 210 Pb, derived primarily from seawater, provides additional information about recent sedimentary history. Isotope profiles and observations of sedimentary facies from cores collected at multiple locations in June 2005, and again in August 2005, indicate the presence of recent fluvial sediment and organic debris in the east part of the bay near the mouth of the Hanalei River. Away from the immediate vicinity of the river mouth, sediment in the uppermost 1 m below the sea floor had not retained a significant quantity of fluvial sediment within the eight months prior to either sampling effort. During the study interval in summer 2005 the Hanalei River had no major floods and there was relatively little sediment input to the bay. Sediment away from the river mouth was dominated by carbonate sand, although some terrestrial sediment was present in sub-sea-floor horizons. Sedimentary facies and isotope inventories throughout the bay showed substantial spatial heterogeneity. Sediment cores will be collected again at the same sites discussed here during early and late summer 2006. If possible, additional sites will be sampled in the Black Hole depocenter near the river mouth. Major floods in winter and spring 2006 are expected to leave a significant new sediment signal in the bay that should be detected in summer 2006.

Sediment samples were collected from continental slopes and marginal basins in the Gulf of Papua and analyzed for excess 210 Pb to elucidate transport processes of finegrained particles to this region. Estimated excess 210 Pb fluxes of 1.0-12.8 dpm cm À2 a À1 were derived from measured seabed inventories. Highest sediment accumulation rates (0.28-0.35 cm a À1) were measured along the northeastern shelf edge, and they decrease in seaward directions and along isobaths to the southwest. The excess 210 Pb flux could result from either focused deposition of high-210 Pb activity sediments from the continental shelf and upper slope or scavenging of 210 Pb brought landward from deep-sea waters. This sediment flux is concentrated in the northeastern Gulf of Papua, where the shelf is narrow and calcium carbonate contents are lowest. Analysis of sedimentary fabric and 210 Pb distributions in cores suggests sediment delivery to the slope occurs on a 100-year timescale as both diffuse hemipelagic deposition as well as turbidity flows. The flux of sediment in turbidity flows is not well constrained but may be producing additional deepsea accumulation in the Moresby Trough, as well as export from the study area.

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.

The tsunami deposits left by the 26 December 2004 tsunami in the coastal zone of Thailand were studied within two months of the event and before any significant postdepositional changes could occur. The sediment structure and texture (grain size), as well as its thickness and spatial distribution, were documented for the tsunami deposits in 12 shore-perpendicular transects from areas of various tsunami runup and wave heights. The tsunami deposits were as thick as 0.4 m and were located as far as 1.5 km inland. They were composed mostly of poorly sorted sand and often consisted of one to four normally graded, massive or laminated layers. The deposits generally became finer in the landward direction; however, landward thinning trend of the deposits is not clear, and the maximum accumulation often is not located close to the shoreline but rather is further inland. In comparable coastal environments with similar available sediment sources the tsunami size (represented as the tsunami runup height) is reflected in the resulting deposits. Larger tsunamis are associated with deposits that are thicker, have a maximum accumulation located farther inland, include a finer sediment fraction (likely from deeper offshore areas) and frequently are composed of normally graded layers.

ABSTRACT The offshore region of Nha Trang, southern Vietnam, was investigated to determine conditions, rates and processes of modern sedimentation. Seismic surveys, X-ray radiography, granulometry, magnetic susceptibility, coarse fraction analysis and mineralogic composition, carbon and heavy metal contents and 210Pb dating of gravity- and box-core material were carried out. The inner shelf is up to 40 m deep and is characterised by reworking and bypassing of sediment. The middle shelf is dominated by an up to 40 m thick clastic sediment wedge down to a water depth of about 100 m. The outer shelf shows several small basins below 100 m water depth. Modern sediments are generally fine-grained. The sand fraction (less than a few percent) consists almost entirely of carbonate skeleton particles of shells, foraminifers etc., and lithoclasts, mostly mica and quartz. The sediments are homogeneous and strongly bioturbated with some relicts of primary stratification, which suggest non-steady sedimentation. The organic carbon content is about 1% and increases shorewards. Pb, Cr, and Cu contents are highest in the nearshore surface sediments. The sedimentation rate estimated on 210Pb dating reveals values between 0.33 – 0.37 cm/yr at 92 m and 103 m water depth. Most of the material is delivered from the short mountainous rivers reaching Nha Trang Bay. In the inner shelf area intensive reworking is caused by high-energetic action of waves and tidal currents. In the deeper parts the influence of biogenic activity is increasing in form of bioturbation and production of carbonates.

The continental shelf off southern Vietnam is relatively well studied regarding the dominant transport paths of bulk and fine-grained sediments discharged by the Mekong River. Thus, this region is particularly suitable for testing the applicability of heavy mineral analysis in determining the extent and origin of the sandy fraction of continental shelf deposits supplied mainly by a large river and their distribution over the adjacent extensive shelf. The fine sand fraction of 105 sediment samples from the Mekong River Delta and neighbouring continental shelf is investigated, applying two approaches: i) considering only the transparent non-micaceous mineral assemblage and ii) considering all the identified heavy minerals. The geological complexity of the source areas and local dominance of micaceous and non-transparent heavy minerals require the inclusion of all heavy mineral components when interpreting sediment provenance and dominant transport paths. The most diagnostic heavy minerals, amphibole, chlorite, epidote, limonite, opaques, tourmaline and zircon, are used for this purpose. The investigated continental shelf can be divided into two main regions characterised by various heavy mineral assemblages, namely, SW and NE off the Mekong River Delta. The southwestern region is dominated by chlorite and limonite, indicating prevailing southward sediment transport from the Mekong River, whereas the northeastern region is characterised by amphibole, epidote, opaques, tourmaline and zircon, indicating various sources from SE Vietnam and relict sediments partly covering the continental shelf. Between the two main regions, a large mixing zone is found where sediments from all sources are present, including Mekong River sediments transported eastward.

Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210 Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representing different hydrodynamic conditions (probably during run-up and backwash phase). These sedimentological observations were supported by geochemical and physical data and were confirmed using 210 Pb dating. A sediment core taken from a depth of 57 m at a distance of 25 km offshore did not reveal clear event deposits. Comparisons with available data from offshore tsunami deposits showed that there is no single set of signatures that could be applied to identify this kind of deposits.

Flood frequency, magnitude and duration all contribute to the control on river channel morphology and sedimentary architecture. In rivers with very variable discharge, illustrated herein by the Burdekin River Australia, most sediment movement is restricted to a few days each year and at other times little sediment moves. However the maximum discharge magnitude does not directly correlate with the amount of morphological change and some big events do not produce large deposit volumes. The event duration controls the work that the event can do and thus the volume of the event deposit, so that large magnitude events with short duration may cause less channel change than moderate events with longer duration. The Burdekin channel features and facies consist of five main depositional elements: a) unit bars, b) vegetation-generated bars, c) gravel sheets and lags, d) Page 1 of 51 Sedimentology antidune trains, and e) sand sheets. The proportions of each preserved in the deposits depend on the history of successive individual large discharge events, the duration of the events and the rate at which they wane. Floods with similar peak magnitude but different rate of decline preserve event deposits and architectures that are different. The high intra-and inter-annual discharge variability and rapid rate of stage change, make it likely that small and moderate scale bed morphology will usually be out of equilibrium. Consequently, dune and unit bar size and cross-bed set thickness are not good indicators of channel size. Antidunes may be more useful as indicators of flow depth than high-angle cross-bed sets formed by dunes or unit bars. Rivers with very high coefficient of variance of maximum discharge such as the Burdekin form distinctive channel sediment bodies, but with component parts that if examined in isolation may lead to misleading interpretation of the nature of the depositional environment if conventional interpretations are used.

In seismically active areas, long term records of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes. In the western Corinth Rift, one of the most active areas in Europe in terms of seismicity, data about ancient earthquakes are still insufficient, despite historical records covering the last two millenia and several studies in onshore paleoseimology. In this paper, we test the use of offshore sediments from the Gulf of Corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes. Two shelves (40-100 m deep), one sub-basin (180 m) and the basin floor (330 m) have been sampled by short gravity cores. The cores were analyzed in order to identify and characterize event deposits. The age control has been provided by 137 Cs and 210 Pb activity measurements showing that the cores represent 2 to 4 centuries of sedimentation. In each site, sandy event deposits are interbeded in the muddy, hemipelagic sedimentation. The age of event deposits has been compared to the record of historical earthquakes using new and published macroseismic data. This comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity ≥ VII in the area, e.g. in 1861 CE, 1888 CE and 1909 CE. In nearshore, shallow-water settings, the record of event deposits does not exactly fit with the historical record of large earthquakes because too few event deposits are present. This may be due to the absence of sediment failures or to a lower preservation of the deposits in such settings. In the deepest site, in the basin floor, the correspondence is better: a sandy turbidite probably corresponds to each large earthquake since 1850 CE, except one aseismic sediment density flow that occurred at the end of the 20th century. Surprisingly, the Ms = 6.2, June 15, 1995 Aigion earthquake is only possibly recorded in one nearshore site on the Aigion Shelf, in the form of a tsunami back-wash flow deposit. This study showed that moderate earthquakes (M 5.8-6.5) can significantly impact marine sediments. Regarding the evaluation of seismic hazard in the area, the basin floor is proposed as a promising site for long term paleoseismology in the Gulf of Corinth, while shallower settings need to be considered more carefully.

A sed i ment bud get for the cen tral Viet nam shelf off Nha Trang over the last deglacial Ho lo cene highstand pe riod has been inves ti gated on the ba sis of shal low seis mic and sed i ment core data and em pir i cal equa tions. The an nual sus pended sed i ment dis charge to the Nha Trang shelf ranges from: 4.3 to 5.4 Mt/year. Es ti mates based on pub lished em pir i cal equa tions sug gest that the sed i ment dis charge by three main lo cal moun tain ous rivers (the Cai, Dinh and Van Phong rivers) that en ter the Nha Trang shelf ranges be tween 1.7 and 4 Mt/year, which im plies that the lo cal rivers dis charge ap prox i mately 75% of the to tal an nual sed i ment in put to the shelf. The an nual sed i ment sup ply of the Cai River is ap prox i mately 2 and 6 times higher than that of the Dinh and Van Phong rivers, re spec tively. The highstand sed i ment depocentre of the Nha Trang shelf is mostly attached to the lo cal river out flows, in di cat ing their im por tance as the prin ci pal sed i ment sup ply sources to the shelf. Ad di tional sources of sed i ment sup ply to the Nha Trang shelf can prob a bly be re lated to along-shore trans port from the nearby shelves. Cal cu la tions based on seis mic and sed i ment core data in di cate that the net sed i ment vol ume stor age on the Nha Trang shelf is ap prox i mately 2.15 Mt/year. Ap prox i mately 50% of the to tal sed i ment yield sup plied to the shelf is prob a bly trans ported along-shore to the south. The sed i ment bud get model for highstand de pos its on the Nha Trang shelf is typ i cal for a small moun tain ous river ba sin, which is sig nif i cantly dif fer ent from that of the large river delta sys tems in Viet nam such as the Mekong and Red rivers where 90% of the river sed i ments are cap tured on the delta plain/sub aque ous part and only 10% of the river sed i ments are trans ported to the nearby shelf. In con trast, most of the sed i ments sup plied by small moun tain ous rivers off Nha Trang are trans ported to the mid-shelf, form ing a shore-par al lel mud depocentre. Key words: sed i ment bud get, Nha Trang shelf, cen tral Viet nam, Ho lo cene highstand, se quence stra tig ra phy.

Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210 Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representing different hydrodynamic conditions (probably during run-up and backwash phase). These sedimentological observations were supported by geochemical and physical data and were confirmed using 210 Pb dating. A sediment core taken from a depth of 57 m at a distance of 25 km offshore did not reveal clear event deposits. Comparisons with available data from offshore tsunami deposits showed that there is no single set of signatures that could be applied to identify this kind of deposits.

A sed i ment bud get for the cen tral Viet nam shelf off Nha Trang over the last deglacial Ho lo cene highstand pe riod has been inves ti gated on the ba sis of shal low seis mic and sed i ment core data and em pir i cal equa tions. The an nual sus pended sed i ment dis charge to the Nha Trang shelf ranges from: 4.3 to 5.4 Mt/year. Es ti mates based on pub lished em pir i cal equa tions sug gest that the sed i ment dis charge by three main lo cal moun tain ous rivers (the Cai, Dinh and Van Phong rivers) that en ter the Nha Trang shelf ranges be tween 1.7 and 4 Mt/year, which im plies that the lo cal rivers dis charge ap prox i mately 75% of the to tal an nual sed i ment in put to the shelf. The an nual sed i ment sup ply of the Cai River is ap prox i mately 2 and 6 times higher than that of the Dinh and Van Phong rivers, re spec tively. The highstand sed i ment depocentre of the Nha Trang shelf is mostly attached to the lo cal river out flows, in di cat ing their im por tance as the prin ci pal sed i ment sup ply sources to the shelf. Ad di tional sources of sed i ment sup ply to the Nha Trang shelf can prob a bly be re lated to along-shore trans port from the nearby shelves. Cal cu la tions based on seis mic and sed i ment core data in di cate that the net sed i ment vol ume stor age on the Nha Trang shelf is ap prox i mately 2.15 Mt/year. Ap prox i mately 50% of the to tal sed i ment yield sup plied to the shelf is prob a bly trans ported along-shore to the south. The sed i ment bud get model for highstand de pos its on the Nha Trang shelf is typ i cal for a small moun tain ous river ba sin, which is sig nif i cantly dif fer ent from that of the large river delta sys tems in Viet nam such as the Mekong and Red rivers where 90% of the river sed i ments are cap tured on the delta plain/sub aque ous part and only 10% of the river sed i ments are trans ported to the nearby shelf. In con trast, most of the sed i ments sup plied by small moun tain ous rivers off Nha Trang are trans ported to the mid-shelf, form ing a shore-par al lel mud depocentre. Key words: sed i ment bud get, Nha Trang shelf, cen tral Viet nam, Ho lo cene highstand, se quence stra tig ra phy.

Coarse-grained sediments like cobbles, stones and boulders commonly occur in the southwestern Baltic Sea, mainly on submarine abrasion platforms in front of retreating soft-rock cliff coasts. These residual sediments seem to be an important source for the development of coarse-grained beach ridges, which play an essential role as shore protection element of the adjacent coastal lowlands. A new small-scaled, high frequency side-scan sonar (SSS) is used, to analyse largescaled distribution pattern and characteristics of residual sediments in near-shore zones of the southwestern Baltic Sea. Ground-truthing is done by scientific scuba divers. For the first time, detailed mapping of sediment distribution from the water line down to 8 m water depth were done in 2009, reflecting a broad spatial distribution of different residual sediments and sand bar systems.

Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210 Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representing different hydrodynamic conditions (probably during run-up and backwash phase). These sedimentological observations were supported by geochemical and physical data and were confirmed using 210 Pb dating. A sediment core taken from a depth of 57 m at a distance of 25 km offshore did not reveal clear event deposits. Comparisons with available data from offshore tsunami deposits showed that there is no single set of signatures that could be applied to identify this kind of deposits.

Tsunami waves leave sedimentary signatures both onshore and offshore, although the latter are hardly known. The objective of the present study is to provide new evidence for the 2004 Indian Ocean tsunami deposits left on the inner continental shelf of the Andaman Sea (Thailand) and to identify diagnostic sedimentological and geochemical properties of these deposits. Based on extensive seafloor mapping, three sediment cores were selected for study and were analysed for their sedimentary structures, grain size composition, chemical elemental composition, physical properties and 210Pb activity. Sediment cores retrieved from shallow water (9-15 m) within 7.5 km off the shore revealed distinct event layers, which were interpreted as being tsunami deposits. These 20-25 cm thick deposits were already covered with post-tsunami marine sediments. They were composed of several units, marine sand layers alternating with poorly sorted mud with terrigenous and anthropogenic components, representi...

The project 'Biodiversity of the Andaman Sea Shelf (BIOSHELF)' attempted to cover the west coast of Thailand, from the Burmese border in the north to the Malaysian border in the south. The objective of the project, during 1996-2000, was to expand our general knowledge of the diversity of benthos at depths down to 1000 m within the Thai Economic Exclusive Zone (EEZ). Ninety-eight stations from twelve transects were sampled at depths of 40-900 m, with an extra sixteen stations in the Thai EEZ and three near-shore stations, ten stations from Phang-nga Bay, three stations near Racha Yai Island, and three stations near Racha Noi Island. Materials were collected using the following equipment-Olsen box corer, Smith-McIntyre grab, Ockelmann detritus sledge, Pearcy-Rothlisberg epibenthic sledge, triangular dredge, heavy rectangular dredge, beam trawl, 2 m Agassiz trawl, otter trawl, and baited traps. Samples of polychaetes, crustaceans, molluscs, and fishes are currently being worked up. Some recent BIOSHELF material will be distributed to various specialists. The remaining material will be studied in greater detail in the future. This interim report gives an itinerary of the cruises and addresses progress, problems, comments and future plans for activities conducted under the BIOSHELF Project.

High energy marine sediments are described from Livadia and Stavros, Astypalaea Island, Greece, which are tentatively interpreted to be associated with the southern Aegean tsunami of 9th July AD 1956. At Livadia, the marine provenance of Ž. imbricated pebble deposits referred to here as the Imbricated Clast Unit, or ICU are inferred from two observations. Firstly, the similarity between the clasts comprising the ICU and contemporary beach sediments, and secondly the inclusion of foraminiferal tests within the sediment matrix. Derivation from the AD 1956 tsunami, rather than from a storm surge, is inferred from the uniqueness of the deposits within the sedimentary record, their distinct imbrication, and 137 Cs and 210 Pb Ž. dating of overlying and underlying sediments. The top of the ICU occurs at q2.00 metres above sea level m a.s.l. indicating a minimum flood level at this location. At Stavros, a gravel with rounded clasts incorporating marine mollusca is found on exposed cliff surfaces up to an elevation of q10.00 m a.s.l. These gravels are also interpreted as having been deposited by the AD 1956 tsunami. The elevation of the deposits and topographic observations indicate that previously reported run-up elevations were overestimated. The results shown here represent the first systematic investigation into sedimentary deposits possibly associated with a modern tsunami within the Aegean Sea region of Greece.

This study documents seafloor morphology and sediments based on multibeam, side-scan sonar and boomer surveys, as well as sediment samples taken on the inner to mid shelf of the Andaman Sea after the 2004 Indian Ocean tsunami. Preservation of submarine relief in former underwater mining areas points to limited impact of the tsunami, while channel structures parallel to the observed tsunami backwash indicate a possible higher impact. Therefore, the tsunami impact seems to be focused on some areas. The impact was probably most effective during the backwash, when stiff mud deposits containing grass, wood fragments and shells were transported by high density backwash flows. Moreover, several boulders, which might have been deposited during the tsunami backwash flow, were found in the channels in front of Pakarang Cape.

The narrow shelf along the coast of central Vietnam is seasonally supplied by large amounts of sediment from the adjacent mountainous hinterland following monsoonal precipitation. This study examines the fate of these sediments, and their accumulation rates along two transects across the shelf, based on analyses of radionuclides (210 Pb, 137 Cs), sediment texture and structure, as well as carbonate content. The inner shelf is covered by sands, and probably serves as bypass zone for fine sediments transported offshore. Sediment characteristics suggest that the transport to the mid and outer shelf is related to flood events. Averaged over the last century, the 210 Pb-based mud mass accumulation rates on the mid and outer shelf vary between 0.25 g cm −2 and 0.56 g cm −2 year −1 (corresponding to linear sediment accumulation rates of 0.20-0.47 cm year −1). Along with high excess 210 Pb inventories, these high accumulation rates suggest a significant sediment depocentre on the mid shelf. The 210 Pb-derived sediment accumulation rates were found to be several times higher than 14 C-derived rates previously reported for the Holocene, at the same location on the outer shelf. This is probably due to the incompleteness of the Holocene record, and an overestimation of the modern rate. Another explanation would be increased erosion within the rivers' drainage basins, due to 20th century deforestation. This hypothesis is supported by the difference between recent (less sand, more lithic grains in the sand fraction) and older sediments. In terms of modern sedimentation processes and rates, the central Vietnam shelf, although being a part of a narrow passive continental margin, is similar to active flood-dominated continental margins.

Coarse-grained sediments like cobbles, stones and boulders commonly occur in the southwestern Baltic Sea, mainly on submarine abrasion platforms in front of retreating soft-rock cliff coasts. These residual sediments seem to be an important source for the development of coarse-grained beach ridges, which play an essential role as shore protection element of the adjacent coastal lowlands. A new small-scaled, high frequency side-scan sonar (SSS) is used, to analyse largescaled distribution pattern and characteristics of residual sediments in near-shore zones of the southwestern Baltic Sea. Ground-truthing is done by scientific scuba divers. For the first time, detailed mapping of sediment distribution from the water line down to 8 m water depth were done in 2009, reflecting a broad spatial distribution of different residual sediments and sand bar systems.

The occurrence of numerous, recent, large tsunami suggests that they are a common natural event, yet tsunami deposits in the geological record are rare. This apparent anomaly may be due to a real infrequency of events and/or poor preservation potential but alternatively may be due to misidentification. Robust criteria for the discrimination of tsunami deposits from other sources such as storms is still lacking, establishing these criteria is essential if we are to improve our understanding of tsunami frequency over geological timescales. By this means we will improve the identification of tsunami hazard and improve risk assessment. This special issue focuses on tsunami deposits, identifying their characteristics and their discriminating features from other sources such as storms. Although perhaps not as common as other 'event' sediments, it is considered likely that a reappraisal of the geological record is required to place them in their representative context.

Outer shelf sedimentary records are promising for determining the recurrence intervals of tsunamis. However, compared to onshore deposits, offshore deposits are more difficult to access, and so far, studies of outer shelf tsunami deposits are scarce. Here, an example of studying these deposits is presented to infer implications for tsunami-related signatures in similar environments and potentially contribute to pre-historic tsunami event detections. A multidisciplinary approach was performed to detect the sedimentary imprints left by the 1755 CE tsunami in two cores, located in the southern Portuguese continental shelf at water depths of 58 and 91 m. Age models based on 14C and 210Pbxs allowed a probable correspondence with the 1755 CE tsunami event. A multi-proxy approach, including sand composition, grain-size, inorganic geochemistry, magnetic susceptibility, and microtextural features on quartz grain surfaces, yielded evidence for a tsunami depositional signature, although only a...

Following recent tsunamis, most studies have focused on the onshore deposits, while the offshore backwash deposits, crucial for a better understanding of the hydrodynamic processes during such events and offering an opportunity for sedimentary archives of past tsunamis, have mostly been omitted. Here, we present a unique sedimentary record of the backwash from two historical tsunamis sampled in a sheltered bay in American Samoa, namely the 2009 South Pacific Tsunami and the 1960 Great Chilean Earthquake Tsunami. Although not always concomitant with a marked grain size change, backwash deposits are identified by terrestrial geochemical and mineralogical signatures, associated with basal soft sediment micro-deformations. These micro-deformations, including asymmetric flame structures, are described for the first time in historic shallow marine backwash deposits and lead us to propose an improved depositional mechanism for tsunami backflow based on hyperpycnal currents. Moreover, this study brings a potential new criterion to the proxy toolkit for identifying tsunami backwash deposits, namely the basal soft sediment micro-deformations. We suggest that further studies focus on these micro-deformations in order to test the representability of this criterion for tsunami backwash deposits. Sheltered shallow marine environments in areas repeatedly impacted by tsunamis have a higher potential for the reconstruction of paleo-tsunami catalogs and should be preferentially investigated for coastal risk assessment. Over the last two decades, interest in tsunami-related research has increased significantly, with peaks in the number of published articles following the 2004 Indian Ocean Tsunami (IOT), the 2009 South Pacific Tsunami (SPT) and the 2011 Tohoku-Oki Tsunami (TOT) 1. However, most studies have focused on onshore deposits, with only a few tackling the issue of backwash depositional processes 2-16. Unlike onshore deposits, offshore deposits are not subject to subaerial erosion and less to anthropic reworking, but can be altered by waves, currents, mixing and bioturbation 1,16. Most of the studies of historic tsunami backwash were carried out in open beach environments following the 2004 IOT and 2011 TOT 5,13,14,16-18. However, such environments have a poor preservation potential due to their exposure to waves. In contrast, sheltered bays may provide a higher preservation potential due to less reworking by waves. Thus, the choice of the study zone is key when looking for marine backwash deposits. We suggest that in shallow marine sheltered environments characterized by a low hydrodynamic setting, a complete and uninterrupted record is more likely to be preserved. Most studies of backwash deposits are based on grain size, geochemical data and microfossils 1. Shallow marine tsunami deposits are usually characterized by an increase of the mean grain size within usually fine marine mud, due to the inclusion of coarse terrestrial sediment originating from the onshore-inundated or beach areas 5,6,12,15,16 , often accompanied by a higher Ti/Ca ratio reflecting the terrestrial input 8,15,16. Deep offshore foraminifera species,

The continental shelf southeast and northwest of the Amazon River mouth is overlain by a sediment layer of about a meter in thickness, characterized by "'Pb profiles consisting of one or more segments with nearly-uniform excess activity. Uniform 'rOPb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments; however, biological activity is minimal in this area. Hence, this surficial layer (SL) is a result either of physical reworking of the sediments, or of rapid (possibly episodic) deposition of sediment. Factors controlling the formation of the SL were examined during the AmasSe& project between August 1989 and October 1991. Primarily using ""Pb (tljz = 22.3 yr) activity profiles and X-radiography, the thickness and character of the SL were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions (e.g., discharge stage, wind stress); one of these stations was reoccupied during semidiurnal and fortnightly periods. Additionally, replicate sediment cores were obtained at stations in order to assess small-scale spatial variability of geochemical and sedimentological characteristics in the seabed. The SL thicknesses in replicate sediment cores obtained at each site were found to vary within f 5 cm. Normalized thickness of the SL decreased by an average of 17 cm between August 1989 and February 1990, a period of increasing wind stress during falling-to-rising river discharge. The SL thickness subsequently increased slightly (8 cm) from February to May 1990, and increased again (27 cm) between May 1990 and October 1991. The maximum SL thicknesses were observed in October, a period of low wind stress and minimal river input, suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge. Variations in SL thickness are reflected by changes in suspended sediment (mostly as fluid muds), as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when SL thickness is at a minimum. Although a significant SL was present during all of the sampling periods, changes in the character of "'Pb profiles at two of the stations suggest that substantial, perhaps complete, removal and redeposition of the SL occurred some time between February and May. Preserved strata (i.e., below the SL) is characterized by greater evidence of bioturbation and increased sand content, but otherwise is similar to that of the SL. Long-term preservation of strata is thought to occur through episodic suspension and redeposition of the SL, with net accumulation of decimeter-thick, hiatus-bounded layers.

One of the most famous blue sapphire deposits in Thailand and SE Asia is from the Bo Phloi District, Kanchanaburi Province, Western Thailand. This paper presents the results of our gemstone investigation as well as establishing the Bo Phloi depositional sequence as one of the Quaternary Type Sections in the region. Relationships among the sedimentology, depositional sequences and geomorphology were investigated in order to understand the gemstone depositional features. Sedimentary structures and textures of the sequences show that the deposition of gemstones is related genetically to¯uvial processes. Gemstones are recognized in¯oodplain and low terrace deposits where gemstone paystreaks concentrate mostly inside layers of gravel beds and foreset-bedded gravels lithofacies. C-14 dating of wood and peat within gemstone-bearing layers indicated that the deposit formed during the middle to late Pleistocene. The gemstone-bearing gravel bed de®nes a north±south trend along the incised palaeo-channel of an ancient braided river system in the middle part of the basin.

Detection of sedimentary cycles is difficult in fine-grained or homogenous sediments but is a prerequisite for the interpretation of depositional environments. Here we use a new autocorrelation analysis to detect cycles in a homogenous sediment core, E602, from the northern shelf of the South China Sea. Autocorrelation coefficients were calculated for different mean grain sizes at various depths. The results show that sediments derived from rapid depositional events have a better autocorrelation. Analysis of two other cores confirms this result. Cores composed of sediments deposited quickly under stable and/or gradually changing hydrodynamic conditions, have higher autocorrelation coefficients, whereas, those composed of sediments deposited during calm periods have relatively low autocorrelation coefficients. It shows that abrupt changes in autocorrelation coefficients usually indicate the existence of a boundary between adjacent sedimentary cycles, with each cycle beginning with a high positive autocorrelation coefficient of grain size and ending with a low negative one.

The sediment transport around the Mekong delta was clarified by using geochemical data and modeling indicating the southwestward transport of re-suspended sediments under the influence of NE monsoon. However, the detail pattern of grain-size distribution of the surface sediments in the subaqueous Mekong River delta has not been well understood. This paper presents characteristics of grain-size parameters of the surface sediments in order to interpret the sediment-transport pattern and the linkage to coastal erosion and deposition off the Mekong River delta. Surface sediments collected in the coastal water of Mekong River delta (as far south as Ca Mau Peninsula) were analyzed to determine the grain-size distribution and sediment transports in subaqueous Mekong delta. Results indicated that the net sediment transport was southwestward to the Ca Mau peninsula and the sediments were finer from the delta topset downward the delta foreset. In contrast, the sediment particles on the adjacent inner shelf were coarser and are more poorly sorted due to the increase in carbonate shell fragments and the Early Holocene sediments. The sediment grain-size parameters were variable in different sedimentary sub-environments of the subaqueous Mekong delta and controlled by the distance of sediment transport, the hydrodynamic regime of each region and coastal erosion of the delta coast.

Tsunami field evidence is a critical resource for determining coastal risk. However, in many cases there is low potential for long term preservation of such deposits on land. A growing body of evidence suggests that tsunami deposits can be present in the shallow offshore realm and may present a largely untapped, but important worldwide sedimentological reference set for investigating past tsunami events. Here, different proxies for tsunami sediment identification and differentiation (granulometry, XRD, XRF, FT-IR) were used to determine the presence or absence of such deposits in a core collected offshore at Jisr al-Zarka, midway between Tel Aviv and Haifa. The study aimed to recognize anomalous deposits and test different analytical methods to define their origins. Five anomalous sedimentological horizons were identified, four of which were interpreted as tsuna-migenic by comparison to previously identified poorly sorted, shell-rich tsunamites found nearby in Caesarea and contrast to the fine-sand, Nile-derived background sediments. The remaining anomaly was distinctive, but not determined to be tsunamigenic due to a lack of coarse shell in the matrix. The oldest tsunamigenic layer, coinciding with the Chalcholithic cultural period (5.7 ka), is the oldest such deposit identified offshore Israel to date and the non-tsunamigenic anomalous horizon may correspond with a transitional climatic phase (~ 5.5 ka). This research reinforces the importance of offshore investigations as a means of improving tsunami catalogues and identifying environment-altering events.

Abstraet--Preliminary analysis of data collected during the course of a cooperative Spanish-United States investigation of the Valencia Shelf (western Mediterranean) reveals a storm-dominated, mud-accumulating sedimentary regime. Calcareous mud is accumulating seaward of a narrow band of shoreface sand and gravel. On the outer shelf the mud is enriched by a pelagic calcareous component. Preliminary 21°pb data from vertical profiles of box cores yield nominal accumulation rates from 2.6 mm y-' near the Ebro Delta to 1.3 mm y-t on the southern portion of the Valencia Shelf. Storm-current winnowing has resulted in the development of a biogenic lag sand over the mid-shelf mud in the northern part of the study area.

Studies of recent environmental perturbations often rely on data derived from marine sedimentary records. These records are known to imperfectly inscribe the true sequence of events, yet there is large uncertainty regarding the corrections that should be employed to accurately describe the sedimentary history. Here we show in recent records from the Gulf of Aqaba, Red Sea, how events of the abrupt disappearance of the planktonic foraminifer Globigerinoides sacculifer, and episodic depo-sition of the artificial radionuclide 137 Cs, are significantly altered in the sedimentary record compared to their known past timing. Instead of the abrupt disappearance of the foraminifera, we observe a prolonged decline beginning at core depth equivalent to $30 y prior to its actual disappearance and continuing for decades past the event. We further observe asymmet-ric smoothing of the radionuclide peak. Utilization of advection–diffusion–reaction models to reconstruct the original fluxes based on the known absolute timing of the events reveal that it is imperative to use a continuous function to describe biotur-bation. Discretization of bioturbation into mixed and unmixed layers significantly shifts the location of the modeled event. When bioturbation is described as a continuously decreasing function of depth, the peak of a very short term event smears asymmetrically but remains in the right depth. When sudden events repeat while the first spike is still mixed with the upper sediment layer, bioturbation unifies adjacent peaks. The united peak appears at an intermediate depth that does not necessarily correlate with the timing of the individual events. In a third case, a long lasting sedimentary event affected by biotur-bation, the resulting peak is rather weak compared to the actual event and appears deeper in the sediment column than expected based on the termination of the event. The model clearly shows that abrupt changes can only endure in the record if a thick sediment layer settled on the sediment–water interface at once or if bioturbation rates decreased to very low values for a prolonged period of time. In any other case smearing by bioturbation makes an abrupt event appear to have started shortly before the real timing and end long after its true termination.

Analysis of the CARLA-11 core drilled along the lower Loukkos valley near Larache in northern Morocco shows a thin level of shelly sand at 465 to 482 cm depth, whose sedimentological features are those of a high-energy, certainly a tsunami deposit. The level can be subdivided into 3 subunits: Subunit 1 (6 cm) shows a sharp erosive base and comprises basal medium to coarse sands containing numerous marine shell fragments of bivalves, plant fragments and rip-up clasts of organic matter. Subunit 2 (7 cm) is a flame structure consisting of coarse sand containing a layer of organic matter and another one of greyish clay. Subunit 3 (4 cm) is similar to subunit 1 and consists of coarse sands containing numerous complete or broken shells of bivalves, plant fragments and dark organic matter. The deposit is mostly composed of subangular to subrounded quartz grains derived from nearby Miocene sandstones. Benthic and planctonic foraminifera are common within the samples. Magnetic susceptibility measurements show two major lows at ~350 cm, and especially at 477 cm within the high-energy deposit. Subunit 1 can be interpreted as the result of the first wave uprush of a tsunami,

We discuss the contribution "Sedimentary features of tsunami backwash deposits in a shallow marine Miocene setting, Mejillones Peninsula, northern Chile" [Sedimentary Geology, 178 (2005) 259-273] by Cantalamessa and Di Celma in which coarse clastic deposits of Miocene age near Antofagasta, northern Chile, were interpreted as tsunami backwash deposits. Here we present sedimentological and structural evidence that the sediments in question are debris flow deposits connected to the formation of a small Neogene graben. They represent physically continuous distal subaqueous equivalents of graben flank debris flow alluvial fan breccias, and not tsunami deposits of any kind.

The Mekong River is one of the major suppliers of sediments to the ocean, resulting in the formation of one of the largest river deltas. A major portion of the supplied sediments is accumulated in the subaqueous delta front, which progrades directly off the river mouths and also forms at a distance of more than 200 km westward, next to the Camau Peninsula. This study presents evidence of the existence of a Mekong-fed prodelta further offshore and provides a first quantitative assessment of the modern fluvial-derived sediment dispersal pattern to the subaqueous prodelta, the outer continental shelf and the deep region of the South China Sea. The study is based on 96 surface shelf sediment samples and five short sediment cores, which were analyzed for grain-size composition, carbonate and total organic carbon contents, sedimentary structures (X-ray radiographs), clay mineralogy and bulk geochemistry as well as 210 Pb and 137 Cs-based sediment accumulation rates. The major sediment types in water depths of 18 m to 112 m include muddy sand, sand, gravelly muddy sand, sandy mud, gravelly sand and mud. The mud is composed mostly of silt fraction, while gravel is primarily composed of shell hash. The sedimentary structures include lamination, cross-stratification, truncation surfaces and burrows of various types. The carbonate content in the sediments varies from 3% close to the Mekong River mouths to 81% further on the shelf. Total organic carbon is from 0.02% in sand to 0.94% in mud. The highest average elemental concentrations are of Si, Ca, Al, Fe, Mg and K. The spatial variability is similar for Al, K and Ti, as well as for Ca and Sr, suggesting the common presence in phyllosilicates and calcium carbonate minerals, respectively. The most common clay mineral is illite followed by smectite, kaolinite and chlorite. The spatial distribution of clay minerals suggests that they are primarily derived from the Mekong River, except in the northeastern region. The sediment accumulation rates in the mud-rich portion of the study area are in the range of 0.1 to 1.5 cm yr −1. According to these results, the shelf environment is divided into three zones. Westward and southward from the Camau Peninsula, the subaqueous prodelta (water depth b 32 m) appears as a mud-dominated, organic-rich, high-accumulation (up to 1.5 cm yr −1) zone. South of the river mouths, a wide zone is dominated by terrigenous sands, which most likely represent the sink for river-supplied bedload sediments. The third and most offshore located zone of moderate-accumulation (0.3–0.4 cm yr −1) is dominated by muddy sands that are rich in biogenic carbonate. Evidence of redeposition, event deposition and changing sedimentary conditions is found in each of these zones reflecting the combined effects of tides, the changing monsoonal current and wind regimes and episodic tropical storms. The sediment budget calculation reveals that the subaqueous delta front stores approximately 50% of the fine-grained sediments supplied by the Mekong River. Roughly one-fourth of the sediments are retained in the subaerial region of the delta (including the Tonle Sap Lake), and approximately 25% accumulates on the shelf around the Camau Peninsula, primarily in the form of prodelta deposits. These results do not suggest a significant export of fine-grained sediments into the deep region of the South China Sea.

Keywords: marine sediments sediment accumulation rate sediment geochemistry clay minerals Mekong South China Sea

Although the Gulf of Aqaba-Eilat is located in the tectonically active northern Red Sea, it has been described as low-risk with regard to tsunami activity because there are no modern records of damaging tsunami events and only one tsunami (1068 AD) referred to in historical records. However, this assessment may be poorly informed given that the area was formed by and is located along the seismically active Dead Sea Fault, its population is known to fluctuate in size and literacy in part due to its harsh hyper-arid climate, and there is a dearth of field studies addressing the presence or absence of tsunamigenic deposits. Here we show evidence from two offshore cores for a major paleotsunami that occurred ~2300 years ago with a sedimentological footprint that far exceeds the scarce markers of the historically mentioned 1068 AD event. The interpretation is based on the presence of a laterally continuous and synchronous, anomalous sedimentological deposit that includes allochtonous inclusions and unique structural characteristics. Based on sedimentological parameters, these deposits could not be accounted for by other transport events, or other known background sedimentological processes.

In this study we question the former interpretation of a shallow marine backwash tsunami origin of a conspicuous Pliocene coarse clastic unit at Hornitos, northern Chile, and instead argue for a debris flow origin for this unit. We exclude a relation to a tsunami in general and to the Eltanin impact in particular. The observed deposit at Hornitos was not generated either directly (impact-triggered tsunami) or indirectly (submarine mass flow caused by seismic shaking) by an impact. Re-calculation of the alleged impact tsunami including consideration of the Van Dorn effect shows that an impact in the Southern Ocean did not cause a significant tsunami at Hornitos. Impact-related seismic shaking was not able to trigger slides several thousands of kilometers away because the Eltanin event was a deep sea-impact that did not create a crater. Additionally, the biostratigraphic age of 5.1-2.8 Ma of the associated La Portada Formation is not concurrent with the newly established age of 2.511 ± 0.07 Ma for the Eltanin impact. Instead, we argue for an origin of the conspicuous unit at Hornitos as a debris flow deposit caused by an earthquake in the Andean subduction zone in northern Chile. Our re-interpretation considers the local synsedimentary tectonic background, a comparison to recent submarine tsunami sediments, and recent examples of mass wasting deposits along the Chilean margin. The increased uplift during the Pliocene caused oversteepening of the coastal scarp and entailed a contemporaneous higher frequency of seismic events that triggered slope failures and cliff collapses. The coarse clastic unit at Hornitos represents an extraordinary, potentially tsunami-generating mass wasting event that is intercalated with mass wasting deposits on a smaller scale.

We discuss the contribution "Sedimentary features of tsunami backwash deposits in a shallow marine Miocene setting, Mejillones Peninsula, northern Chile" [Sedimentary Geology, 178 (2005) 259-273] by Cantalamessa and Di Celma in which coarse clastic deposits of Miocene age near Antofagasta, northern Chile, were interpreted as tsunami backwash deposits. Here we present sedimentological and structural evidence that the sediments in question are debris flow deposits connected to the formation of a small Neogene graben. They represent physically continuous distal subaqueous equivalents of graben flank debris flow alluvial fan breccias, and not tsunami deposits of any kind.

Keywords: 1755 Lisbon tsunami tsunami deposits grain size distribution X-ray fluorescence X-ray tomography anisotropy of magnetic susceptibility A multi-proxy approach using trench sediment analysis on the southwestern coast of Spain (Los Lances Bay, Andalusia) provides a high-resolution record of the 1755 Lisbon tsunami and offers new means to interpret tsunami deposits. A combination of sedimentological (grain size, sorting, AMS), micromorphological (X-ray tomography and radiography, thin sections) and geochemical analyses (X-ray microfluorescence, ICP-AES) combines to provide a comprehensive reconstruction of the different phases of tsunami deposition and flow dynamics. Vertical variations in sediment texture, fabric and composition of the 1755 tsunami deposits in Los Lances are then discussed with reference to existing literature on diagnostic criteria commonly used for identifying and interpreting tsunami deposits. Finally possible leads for future investigation are proposed.

Analysis of the CARLA-11 core drilled along the lower Loukkos valley near Larache in northern Morocco shows a thin level of shelly sand at 465 to 482 cm depth, whose sedimentological features are those of a high-energy, certainly a tsunami deposit. The level can be subdivided into 3 subunits: Subunit 1 (6 cm) shows a sharp erosive base and comprises basal medium to coarse sands containing numerous marine shell fragments of bivalves, plant fragments and rip-up clasts of organic matter. Subunit 2 (7 cm) is a flame structure consisting of coarse sand containing a layer of organic matter and another one of greyish clay. Subunit 3 (4 cm) is similar to subunit 1 and consists of coarse sands containing numerous complete or broken shells of bivalves, plant fragments and dark organic matter. The deposit is mostly composed of subangular to subrounded quartz grains derived from nearby Miocene sandstones. Benthic and planctonic foraminifera are common within the samples. Magnetic susceptibility measurements show two major lows at ~350 cm, and especially at 477 cm within the high-energy deposit. Subunit 1 can be interpreted as the result of the first wave uprush of a tsunami,

Although the Gulf of Aqaba-Eilat is located in the tectonically active northern Red Sea, it has been described as low-risk with regard to tsunami activity because there are no modern records of damaging tsunami events and only one tsunami (1068 AD) referred to in historical records. However, this assessment may be poorly informed given that the area was formed by and is located along the seismically active Dead Sea Fault, its population is known to fluctuate in size and literacy in part due to its harsh hyper-arid climate, and there is a dearth of field studies addressing the presence or absence of tsunamigenic deposits. Here we show evidence from two offshore cores for a major paleotsunami that occurred ~2300 years ago with a sedimentological footprint that far exceeds the scarce markers of the historically mentioned 1068 AD event. The interpretation is based on the presence of a laterally continuous and synchronous, anomalous sedimentological deposit that includes allochtonous inclusions and unique structural characteristics. Based on sedimentological parameters, these deposits could not be accounted for by other transport events, or other known background sedimentological processes.

Due to their destructive potential and their unpredictability tsunamis represent an important risk source for coastal zones and their inhabitants. The tsunami of Dec. 26, 2004 revealed a gap in scientific knowledge beginning from offshore triggering of tsunamis to the various impacts to natural environments like the shelf, coastal areas, onshore environments and to economic and social system consequences. The interdisciplinary research project TRIAS was launched to get a clear picture about destructive forces and processes of tsunamis and to elaborate measures how to avoid and/or mitigate future tsunami impacts and destructions. Project structure and first results are presented.

Coarse-grained sediments like cobbles, stones and boulders commonly occur in the south-western Baltic Sea, mainly on submarine abrasion platforms in front of retreating soft-rock cliff coasts. These residual sediments seem to be an important source for the development of coarse-grained beach ridges, which play an essential role as shore protection element of the adjacent coastal lowlands. A new small-scaled, high frequency side-scan sonar (SSS) is used, to analyse largescaled distribution pattern and characteristics of residual sediments in near-shore zones of the south-western Baltic Sea. Ground-truthing is done by scientific scuba divers. For the first time, detailed mapping of sediment distribution from the water line down to 8 m water depth were done in 2009, reflecting a broad spatial distribution of different residual sediments and sand bar systems.

The Strickland River is the primary sediment source for the Fly River system, a large tropical river that ranks in the global top 20 for both water and sediment discharge. Over the past decade the Strickland sediment discharge has been gauged at many locations. Comprehensive studies are now underway to study the delivery, transport, and storage of sediment throughout this

Sugai, S.F., Alperin, M.J. and Reeburgh, W.S., 1994. Episodic deposition and 137Cs immobility in Skan Bay sediments: A ten-year 2X°pb and 13~Cs time series. In: M.I. Scranton (Editor), Variability in Anoxic Systems. Mar. Geol., A geochronology time series provides a powerful tool for elucidating sedimentary processes such as episodic deposition and diffusive mobility of particle-reactive constituents. Depth distributions of 21°Pb and 137Cs from Skan Bay, Alaska were determined for sediment cores collected in 1980, 1984, 1987, and 1990. Sediment X-radiographs reveal distinct layers indicating that sediments were not continuously mixed by bioturbation. However, the geochronology time series is inconsistent with an undisturbed, steady-state sediment column. Profiles from 1980Profiles from , 1984Profiles from , and 1990 reveal subsurface regions in which 21°pb activity is relatively constant. In addition, the depth of the primary 137Cs maximum (reflecting the 1963 peak in atmospheric bomb testing) does not increase in a regular fashion between 1980 and 1990. The 21°pb and 137Cs geochronologies can be reconciled by removing the effects of an instantaneous depositional event. The average 2X°pb sedimentation rate (corrected for episodic deposition) in cores that were collected over a ten year period (0.241 +0.006 g cm -2 yr-1) is in excellent agreement with the average 137Cs sedimentation rate (0.258 _+ 0.008 gcm-2 yr-1) calculated from three stratigraphic markers [peak fallout (1963), first appearance in the sediment record (1952), and the Chernobyl accident (1986)]. The mobility of bomb-derived 13VCs under in situ conditions was evaluated by a time-dependent numerical model applied to the 137Cs time series. The model indicates that bomb-derived cesium is immobile in Skan Bay sediments with a solid-liquid distribution coefficient (Kd) of/> 105 (ml g-1).

On March 11 th , 2011 the Mw 9.0 2011 Tōhoku-Oki earthquake resulted in a tsunami which caused major devastation in coastal areas. Along the Japanese NE coast, tsunami waves reached maximum run-ups of 40 m, and travelled kilometers inland. Whereas devastation was clearly visible on land, underwater impact is much more difficult to assess. Here, we report unexpected results obtained during a research cruise targeting the seafloor off Shimokita (NE Japan), shortly (five months) after the disaster. The geography of the studied area is characterized by smooth coastline and a gradually descending shelf slope. Although high-energy tsunami waves caused major sediment reworking in shallow-water environments, investigated shelf ecosystems were characterized by surprisingly high benthic diversity and showed no evidence of mass mortality. Conversely, just beyond the shelf break, the benthic ecosystem was dominated by a low-diversity, opportunistic fauna indicating ongoing colonization of massive sand-bed deposits.