Present Shoreline Research Articles

Using ground-penetrating radar to investigate deposits from the Storegga slide tsunami and other sand sheets in the Shetland Islands, UK

We use ground-penetrating radar (GPR) to investigate the geometry, inland extent and continuity of sand layers interpreted as tsunami deposits in the Shetland Islands, UK. Four sites where sand layers within peat deposits have been recorded in previous studies are used to provide ground truth. In addition, we describe survey results from one site where deposits are not exposed to test the potential of GPR to identify candidate tsunami deposits in areas that are not well documented. Sand layers can be clearly imaged at all five locations because they are interbedded with peat and the contrast in lithology gives a good reflection on GPR profiles, even very thin sand layers, <1 cm thick, that are beneath the theoretical resolution of the GPR. 2D and 3D surveys show that tsunami deposits appear to drape a buried topography. Most sand layers form continuous reflections, although some gaps are attributed to later erosion, most likely by streams. Sand layers have been traced up to 150 m inland and 10 m above the present shoreline, which is consistent with data from boreholes. If a similar sized event occurred today, it would have a devastating impact on the Shetland Islands.

Geoheritage of the Kaliningrad Region, SE Baltic Coast

The Kaliningrad Region is physiographically a mosaic and travel-attractive part of the SE Baltic coast. The Sambia Peninsula, the geomorphically most interesting, E-W-oriented extension of the mainland, has been shaped by past dynamic processes, starting with the Precambrian tectonics, the Palaeozoic and Mesozoic sea transitions, the Last Ice Age glaciations, the post-glacial riverine network formation, and the present shoreline erosion. The complex geological and palaeogeographical history generated a broad variety of geo-forms and landscapes, relicts of which are seen from the sea coast to the mainland. Rich fossils sealed in ancient, well-stratified formations of specific lithologies, with the famous Palaeogene amber beds, provide witness of past natural settings with flourishing life forms. The great geo-diversity of the peninsula underscores its scientific value as well as national and international tourism significance, adding to the historical architectural sites of this area. Some of these geomorphologically and geologically valuable places are increasingly threatened, besides anthropogenic factors, by storm surges, gravity flows and aeolian activity, causing progressing erosion along undercut cliffs, slumping and degradation of sand dune fields, among other geo-hazards. Survey, mapping and publicity of unique geo-sites are a proviso for their registration in natural heritage programmes with the implementation of appropriate geo-environmental protection strategies in balance with land-use management. This paper outlines the scientific, educational and touristic potential of the national geoheritage in the frame of the Baltic Sea coast geo-conservation initiatives.

Small Muddy Paleochannels and Implications for Submarine Groundwater Discharge near Charleston, South Carolina, USA

The spatial variations in Quaternary sediments on the inner continental shelf are produced by the progression of depositional environments during the latest sea-level rise, and this sedimentary architecture plays a fundamental role in controlling groundwater discharge. However, coincident seismic mapping, sediment cores, and hydrological studies are rare. Here, we combine high-resolution, 0.5–10 kHz, high-frequency seismic profiles with sediment cores to examine the nature of the sediment deposits, including paleochannels, where submarine groundwater discharge has also been studied in a 150 km2 area of the inner shelf north of Charleston, South Carolina. We used high-frequency seismic reflection to interpret seismic facies boundaries, including 16 paleochannel crossings, to 20 km offshore. From 13 vibracores taken at the intersections of the seismic lines, we defined seven lithofacies representative of specific depositional environments. The paleochannels that we cored contain thick layers of structureless mud sometimes interbedded with silt, and mud is common in several of the nearshore cores. Our results indicate that paleochannels are often mud-lined or filled in this area and were most likely former estuarine channels. Neither the paleochannels nor a mud layer were found farther than 11 km off the present shoreline. This offshore distance coincides with the strongest pulses of groundwater discharge, emerging just beyond the paleochannels. This suggests that the muddy paleochannel system acts as a confining layer for submarine groundwater flow.

Luminescence dating of Holocene sediment cores from a wave-dominated and mountainous river delta in central Vietnam

Sediments of river deltas provide valuable records of past coastal environments. Optically-stimulated luminescence (OSL) dating has become an alternative to radiocarbon dating for constraining the sediment chronology in large deltas that allow for sufficient sunlight bleaching of sediments during the fluvial transport. However, its applicability to smaller deltas with mountainous riverine systems has not been confirmed yet. To check this, we examine multiple signals from two Holocene sediment cores in the wave-dominated Thu Bon River delta in central Vietnam. Two cores were collected, respectively, 3.9 km and 1.2 km inland from the present shoreline and both show a >-25-m thick succession of coarsening-upward mud to sand deposits. Coarse grains (180–250 μm in diameter) of quartz and K-feldspar, and fine grains (4–11 μm in diameter) of quartz and polymineral were extracted from the upper and lower parts of the cores for multi-grain measurements of quartz OSL, and of feldspar infrared-stimulated luminescence (IRSL) at 50 °C (IR50) and post-IR IRSL at 175 °C (pIRIR175) to determine burial ages. In addition, facies analysis and radiocarbon dating were conducted. The landward core consists of transgressive to early regressive estuarine and prodelta facies, which is overlain by a sandy beach-shoreface facies. The seaward core consists of a relatively simple shallowing-upward succession from muddy prodelta facies to sandy beach-shoreface facies. All luminescence ages except for pIRIR175 of fine grains are mostly consistent with the radiocarbon ages. Instead, pIRIR175 ages of fine grains are significantly overestimated with variable offsets. OSL and IR50 of fine grains provide reasonable age estimates, as these grains were likely well bleached during the transport even along a short and steep mountainous river. Consistent age estimates of all signals from sand indicate that sand was well-bleached in the beach and shoreface owing to the frequent sediment reworking by waves and currents. These results support the hypothesis that luminescence dating is applicable to Holocene wave-dominated deltas and reiterate that comparing different luminescence signals is an effective way to check reliability of the age estimates in environments where the sunlight bleaching is not ensured.

Late Holocene development of Bubiyan Island, Kuwait

AbstractBubiyan Island, presently a vast sabkha and salt flat in the westernmost part of the Shatt Al-Arab delta, originated ca. 4000 cal yr BP as prodelta deposits from a paleochannel of the Euphrates River that flowed into a shallow sea. Southeastern Bubiyan Island first surfaced when spits and barrier islands formed on a 1–2 m forebulge caused by heavy sediment load to the northwest; the spits and barriers delineated an incipient shoreline and sheltered a shallow lagoon. Progradation of southeastern Bubiyan Island began when the spits and barriers were gradually stranded as beach ridges during minor sea-level fluctuations and continued marginal uplift. AMS dating of the beach ridges, which are ~1–5 km from the present shoreline, implies that Late Holocene relative sea level fell in three phases: ca. 3700–3400 cal yr BP, ca. 2600–1000 cal yr BP, and ca. 600–500 cal yr BP. Prior to each phase, relative sea level apparently stabilized to near stillstands, allowing spits and barriers to accrete. Torpedo-jar pottery sherds scattered on some of the most prominent beach ridges indicate Sasanian (AD ca. 300–650; 1650–1300 cal yr BP) to early Islamic (AD ca. 650–800; 1300–1150 cal yr BP) periods of human presence, concurrent with the Second phase of beach-ridge formation.

Shifting Baselines May Undermine Shoreline Management Efforts in the United States

Rising sea levels, extreme weather events, and unsustainable coastal zone development pose serious threats to growing coastal communities. Human actions, such as shoreline development and hardening in at-risk areas, can damage nearshore ecosystems and exacerbate existing risks to coastal populations. A comprehensive understanding of shoreline changes in response to development, storm events, and sea-level rise is needed to effectively mitigate coastal hazards and promote adaptive and resilient coastlines. To determine whether human modification of shorelines can be accurately quantified and assessed over time, we evaluated past and present shoreline mapping and classification efforts in the United States. We coupled a review of available US shoreline data with a survey of coastal planners and managers involved with US state shoreline mapping programs. Using these data, we estimated the current extent of shoreline modification along the Atlantic, Pacific, and Gulf US coasts. However, we found that quantifying shoreline modifications over time nationally—or even within a single state—is currently infeasible due to changes in shoreline resolution associated with advances in shoreline mapping methodologies and a lack of regularly updated shoreline maps. State-level analysis from surveys revealed that 20 US coastal states have undertaken shoreline mapping projects, with sixteen tracking shoreline type and/or condition. However, of the 36 shoreline maps and databases identified, only half (18) were updated regularly or had planned updates. Lacking shoreline change data, coastal communities risk accepting increasingly degraded coastal zones and making poor management decisions based on shifted baselines. Thus, we recommend increasing the scale and funding for several ongoing innovative shoreline mapping efforts. These efforts are particularly focused on improving and standardizing shoreline mapping techniques, as well as establishing accurate baselines for shoreline conditions in the United States. Without accurate baselines and regular, consistent updates to shoreline data, managers cannot manage shorelines in a way that effectively mitigates coastal hazards while also promoting socio-ecological resilience in a changing climate.

Palaeoshoreline reconstruction and underwater archaeological potential of Liman Tepe: A long-occupied coastal prehistoric settlement in western Anatolia, Turkey

Rising post-glacial sea levels had a major influence on the prehistoric settlement of the Aegean coastal zone. At Liman Tepe, an important Chalcolithic-Bronze Age coastal settlement on the south coast of the Bay of Izmir, archaeological evidence suggests a Neolithic (ca. 9600-5500 BCE) presence, but no settlement has been discovered on land. Sea levels during the Neolithic period were between 6 and >20 m below present and there is high potential for discovery of submerged prehistoric sites. Marine sediment coring and geophysical investigations (bathymetry, sub-bottom seismic profiling; >600 line-km) were conducted over a 4-km2 inshore area to assess the underwater archaeological potential. Multi-proxy sediment analysis (sedimentary facies, micropalaeontology, micro-XRF geochemistry) was conducted on 20 cores to reconstruct the relative sea level (RSL) history and coastal palaeogeography. Palaeoshoreline positions were estimated by back-stripping of the decompacted sediment thickness from a digital bathymetric model (DBM).The DBM reveals a drowned middle Holocene coastal plain with well-preserved relict river channels, palaeoshorelines and coastal headlands. The inshore stratigraphy consists of shoreface, foreshore and lagoonal deposits overlying terrestrial clay and palaeosols, defining a marine transgressive surface (MTS). The MTS records the inundation of the coastal plain prior to ca. 4000 BCE (transgressive systems tract; TST) and is marked in cores by an increasing abundance of foraminifera and a rise in Ca/Ti. During the Early Neolithic (ca. 6700 BCE), the shoreline was >500 m seaward (RSL ∼ −14 to −16 m) and Karantina Island was a broad coastal headland with a sheltered western embayment. By the Middle Chalcolithic (ca. 4800 BCE), the coastline had transgressed ∼800 m inland of the present shoreline and the Liman Tepe headland was separated from the mainland by a shallow coastal wetland. The maximum transgression (∼1 km inland at ca. 4000 BCE) was followed by a shift to a high-stand systems tract (HST) and rapid coastline progradation by barrier accretion and lagoon development. Palaeogeographic maps identify areas with high underwater archaeological potential: 1) palaeoriver channels and lowland riverine habitats formed during the TST, prior to 4000 BCE, 2) submerged palaeoshorelines and coastal promontories (water depths 10–14 mbsl) with high potential for Neolithic sites, and 3) protected coastal embayments and lagoons representing possible prehistoric anchorage sites.

Holocene sedimentation offshore Southeast Vietnam based on geophysical interpretation and sediment composition analysis

Offshore Southeast (SE) Vietnam is considered a transition zone, with the sedimentary evolution of this area controlled by land-sea interactions, especially by the Holocene sea-level rise. This study presents some new findings regarding Holocene sedimentation and its linkage to the heavy mineral placers within the study area based on high-resolution seismic interpretation and sediment analysis. Our obtained results show that the Holocene sediments directly overlie the Late Pleistocene sedimentary formation, from which they are separated by an erosional/unconformity surface (R­1­ seismic reflector). Sediments deposited in the Early (~11.7-8.2kyr BP), Middle-Late (8.2kyr BP-present-day) Holocene sub-epochs correspond to the Transgressive and Highstand System tracts, which were closely controlled by the three stages of Holocene sea-level rise. The recent sediments distributed on the seafloor are dominated by sand and gravelly sand, demonstrating high-energy conditions, while the heavy minerals are rich in ilmenite and zircon. Most of these are concentrated along the present shoreline zones, but we do not exclude their accumulation in the paleo-shoreline and incised channels. Two ilmenite dispersion halos (1st and 2nd order) and one zircon dispersion halo (1st order) suggest that ilmenite and zircon are the most dominant heavy minerals while gold is only observed locally. The minerals were potentially derived from the weathering products of the Triassic-Cretaceous ilmenite-, zircon-, and gold-bearing granite and granitoid in central Vietnam.

Late Holocene evolution of São Tomé cape (Rio de Janeiro, Brazil): Insights from geomorphological, geophysical and geochronological data

At wave-dominated coasts it is common to find coastal barriers that might be in a progradational pattern and can compose sedimentary capes. Those prograding coastal barriers can be characterized by beach ridges or barrier spits, or even by a more complex pattern depending on the processes controlling their formation. In this study geomorphological mapping, topographic surveys, ground-penetrating radar profiles and optically stimulated luminescence (OSL) dating were performed on the coastal barrier systems of São Tomé cape (north of Rio de Janeiro state, Brazil). The aim was to reconstruct its spatial and temporal evolution and, by this, better understand the interplay between sedimentary cape formation and its driving mechanisms as well as their function as potential archives for long-term environmental dynamics. The study site is characterized by lagoonal and fluvio-lagoonal depressions, and a lagoon surrounded by beach ridges that are interleaved with barrier spits and erosional truncations. Both types of coastal barriers reach up to 6 m above sea-level. Shallow geophysical analysis identified seven radar facies that characterize the stratigraphy of the targeted morphologies. Beach ridges are mainly composed by planar, seaward dipping, subparallel, continuous reflectors which represents their progradation, while barrier spits have planar to convex up, parallel, landward migrating reflectors. Geochronological results demonstrate that the coastal barriers were formed during the Late Holocene. Beach ridge formation until ~2700 years ago was interrupted by the formation of a barrier spit system between ~2300 and ~2000 years ago. This barrier spit system was responsible for the formation of an enclosed lagoon, the Salgada lagoon, and was truncated by a set of beach ridges formed since ~2000 years ago and continuing to the present shoreline. The different types of coastal barriers indicate a change in hydrodynamic processes during the Late Holocene, with an alternation between the predominance of wave-induced cross-shore transport, responsible for the formation of beach ridges, and the predominance of longshore transport, responsible for the formation of barrier spits. Besides that, erosional truncations and unconformities indicate the interruption of shoreline progradation and the impact of erosion due to the storms. This illustrates the complex and highly dynamic development of São Tomé Cape with wave climate and storms as its most important drivers. More generally, this study shows that sedimentary capes may be regarded as geoarchives with potential for the reconstruction of coastal processes over Holocene timescales.

A drowned Mesolithic shell midden complex at Hjarnø Vesterhoved, Denmark and its wider significance

Anthropogenic shell accumulations (shell middens), often of great size, occur in their tens of thousands around the world’s coastlines. They mostly date from the Mid-Holocene onwards and are frequently taken as symptomatic of a Postglacial ‘revolution’ involving world-wide population growth and intensification in exploitation of marine resources. However, the comparative rarity of earlier deposits may have as much to do with Postglacial sea-level rise and the loss of evidence from earlier palaeoshorelines as with genuine socio-economic trends. Here we investigate the underwater Mesolithic (Ertebølle) shell midden of Hjarnø Vesterhoved in Denmark, one of the first underwater shell middens to be systematically verified as an anthropogenic shell deposit in a region world-famous for its many hundreds of Ertebølle shell mounds on the present shoreline. We show how a combination of geophysical survey, coring, excavation, stratigraphic interpretation and macroscopic analysis of midden contents can be used to identify underwater deposits, to unravel their taphonomic and post-depositional history in relation to surrounding sediments, and to distinguish between cultural and natural agencies of shell accumulation and deformation. We demonstrate the presence of an intact underwater shell-midden deposit dated at 5400–5100 cal BC, one of the earliest in Denmark. We demonstrate the usefulness of such material in giving new information about early coastal subsistence economies and greater precision to the measurement of palaeo-sea levels. We discuss the implications of our results for an improved understanding of the Mesolithic record in Denmark and of biases in the archaeological record of Late Pleistocene and Early-to-Mid Holocene coastal contexts. We emphasise the importance of researching more fully the geomorphological and taphonomic processes that affect the accumulation, destruction, burial, preservation and visibility of underwater archaeological deposits, the need to extend underwater investigations more widely and to more deeply submerged palaeoshorelines, and the combination of methods required to advance such investigations.

Misfit rivers under ENSO regimes: The deactivation of the Colorado River system of Argentina

The Colorado River has significantly diminished its drainage area and annual discharge. Today it flows across several provinces of Argentina (Neuquén, Mendoza, La Pampa, Río Negro and Buenos Aires) although during the Upper Pleistocene this watershed area was more extended. Its discharge also diminished significantly during documented times although floods occurred episodically during anomalous ENSO years. The delta plain is composed of several lobes of different ages. Four distributary arms were operating during the Mid-Holocene highstand. At the northernmost distributary arm, Tagelus plebeius remains of 350 ± 50 14C years BP were collected living in position on the supratidal flat. Close to this modern channel several foredune ridges were recognised. A blocking of the river occurred in 1906, and originated a conic lobe located 36 km from the present shoreline. Due to a flood caused by a sudden scabland of the Cari Lauquen Lake in 1914, the blockage opened. Another blockage was achieved between 1924 and 1925, but another flood in 1931 originated a new arm: the Colorado Nuevo. The ENSO-triggered flood of 1983 signified the last connection of the Desaguadero-Curacó River system. Man-made alterations are responsible for the increase in salinity along the lower floodplain and increasing the risk of onion crops. These particular processes of desertification with floods should be monitored in relation to climate-change previsions.

Stratigraphic analysis and geomorphological reconstruction of Grumari coastal plain, Rio de Janeiro, Brazil

Between Marambaia spit and Jacarepagua barrier island system, two major coastal plains in Rio de Janeiro State, Grumari's type of evolution remains unknown, since it was anthropologically modified from the 1960s, where all superficial sedimentary deposits were devastated, intensively changing its natural landscape, and hiding how it has been formed through the Holocene. Aiming to fill these blanks in Grumari's geological history and complementing Rio de Janeiro's coastal studies, the Ground Penetrating Radar method (GPR) was applied to enable the 2D subsurface imaging. The reflection patterns recognition and their correlation with geological features allow a radarfacies interpretation, in a radar stratigraphy context. For coastal plain studies, geological interpretation takes into consideration the sedimentary processes involved in their formation, driven by the balance between sedimentary supply and sea level variations. In the adjacent areas' researches, geological and geophysical data show, from bottom to top, continental deposits formed during the last regional marine regression, in the Late Pleistocene, covered by sand deposits and marine fossils deposited during the last marine trangression, already in the Holocene, followed by sand barriers and lagoons formed and exposed during the last sea falling until the present shoreline. For Grumari coastal plain, this work presents geophysical data interpretation of five GPR sections, collected in about 15 m thick sedimentary deposit, with a sequence of three main units, separated by regional stratigraphic surfaces: a transgressive unit followed by a regressive one, being this one covered by the most recent deposits composing a third unit. The Unit 1 is related to the Holocene sea level rise, from about 7,000 yr BP, and is characterized by truncation relationships between seawards downlapping reflectors and flat-parallel ones, showing a constant change in deposition direction, as the accommodation space was still small at the beginning of this process. At the Unit 1 top, as the accommodation space rate increased, the deposition became more regular, seen by a flat-parallel reflection pattern. While mean sea level reached its maximum range, from about 5,500 yr BP, its rising rate decreased, while the sedimentary supply rate raised due to the continental shelf and the mountain system erosion. This variation in radarfacies sequence is registered by a regional surface, marking the regressive Unit 2 beginning. The change in the rates led to the continental progradation through sand ridges formation, represented by seawards sigmoidal radarfacies. The mean sea level continued to drop gradually to the current level, exposing the sand ridges to erosion, and newer aeolian, fluvial, lagoonal and storm deposits could be formed above them, composing the Unit 3, limited at the bottom by a second regional high amplitude surface. Storm deposits from 4,450 ± 180 yr BP and 3,780 ± 200 yr BP, as washover fans, have been already identified in Jacaperagua plain, therefore, there were episodical events in the region, in the last 4,450 years, seen also in Grumari's data. This primary radar stratigraphic analysis and geomorphological reconstruction of Grumari most recent deposits show that the most recent evolution occurred through the prograding sand ridges formation, mostly attached to each other, with some inter-ridge areas development, and then is likely to be considered as a strandplain.

Distribution and cementation characteristics of beachrocks along southern, southwestern and western coast of Sri Lanka

Beachrocks are sedimentary structures where gravelly or sandy beaches have been transformed into rock outcrops formed through precipitation of connective cements amid their interstices. They are well-noted coastal features along the coastal belt of Sri Lanka due to the prevalent tropical climate. This study was aimed at gathering data on surface nature and cementation characteristics of beachrock occurrences along a part of Sri Lankan shoreline through field observations and a series of analyses including X-ray diffraction, X-ray fluorescence, scanning electron microscopy (SEM) techniques and petrographic thin-section analysis. The combined research findings from different techniques are also employed as a preliminary step to determine the formation mechanism of the studied beachrocks. The seaward-inclined low-angle beds running parallel to present shoreline are composed mostly of sandstone with occasional conglomerate. Almost all the beachrocks are made of quartz grains amalgamated by cement. One remarkable feature of Sri Lankan beachrocks is the presence of heavy minerals generally in thin lamina form. The cementing agents are predominantly composed of metastable carbonate phases, high magnesium calcite (HMC) and aragonite (Ar) with varying microfabrics and textures. From SEM examinations and thin-section images, main morphologies identified are acicular Ar, scalenohedral magnesium calcites along with bridge cements and micritic coatings which are typical of a marine-phreatic precipitation with the exception of occasional meniscus cements. Further, the presence of evidences of living organisms may be an indication of influence from the biological aspects which can be confirmed by more detailed analyses.

The Paleobeach Ridges of Digha Coastal Tract, West Bengal, India: Observation and Implication for Sea Regression from 500 YBP to 200 YBP

Abstract Paleobeach ridges in and around the Digha coast, West Bengal, India give significant information about the sea regression in eastern Indian coast during Holocene. Beach ridges paralleling the Bay of Bengal coast in West Bengal and a few remnants beach ridges further landward in Kanthi (West Bengal) and Jaleswarpur (Odisha), give a tentative boundary of the north eastern most palaeo-shoreline. From optically stimulated luminescence (OSL) dates of the Paleobeach ridges, it is suggested that around 500 YBP, the sea was near Kanthi and around 378 YBP the sea was near Jaleswarpur (35 km inland). After that, the sea sequentially regressed in phases towards south and attained the present position at Digha. The Photogeology & Remote Sensing (PGRS) Study of different satellite imageries (2006 onwards) along with the Survey of India Toposheets (1930, 1972) of Digha area indicates that the coast line to be steadily regressed in the east of Digha, whereas, it shows fluctuation in the west of it. This fluctuation of strand line position may be due to the differential sediment influx through the Subarnarekha river mouth with time. Regional neotectonic activities also play a role in shaping the coast. The concave orientation of the beach ridge plains to the present shoreline reflects the supply of sediments in the direction of palaeolongshore currents. The shape of the inner beaches shows that the deposition prograded north-west wards. Major type of cross-beddings present in the Paleobeach ridges represented by low angle laminated sand, indicates the wide seaward dipping part of longshore bars. The grain size analysis of the sediment samples of the beach ridges indicate positively skewed and mesokurtic. The mean size of resultant sediments is finer, indicating that the energy level or turbulence of the eroding processes was incapable of transporting sediments coarser than the mean size of the source sediments.

Tidal strait to embayment: Seismic stratigraphy and evolution of a rock-bounded embayment in the context of Holocene sea level change

Elongate, rock-framed Santa Catarina Island partly encloses a low-energy marine embayment that communicates with the ocean via narrow, rock-bounded inlets with ebb and flood-tide deltas. The bay shoreline consists of low-energy sandy beaches, strandplains, mangroves and bayhead deltas while the exposed Atlantic shoreline comprises a series of headland-embayment littoral cells in a linked, north-directed longshore drift system.New and previously published seismic stratigraphic investigations enable assessment of the palaeogeographic/geomorphic evolution of the area since the early Holocene. At a sea level of ca. −50 m a sandy mainland-attached shoreline complex (dune and beach) developed on a coastal plain setting some 6–7 km offshore of the present shoreline. North of the island, a barrier island and tombolo were formed in a coastal re-entrant adjacent to the northern entrance to Florianopolis Bay. The open coast beach/dune system was overstepped by rapid sea-level rise during MWP-1B whereas the barrier island and tombolo continued to accrete until MWP-1C when they too were overstepped.The back-island embayment contains up to 40 m of sediment overlying an irregular bedrock surface. It was initially flooded during MWP-1C and the early muddy sedimentation suggests a distal, sheltered marine embayment. The subsequent development of many large bioherms on bedrock and mud suggests a change to more fully marine conditions as sea-level continued to rise. In the North Bay, these were subsequently enveloped by tidal dunes migrating north from the mid-bay. The vertical stacking of 3-D and 2-D sandy bedforms suggests that a tidal strait had developed with strong tidal currents radiating from a constriction in the vicinity of modern Florianopolis City. The strong tidal currents may be linked to the Holocene sea-level high that is well documented for this region.A fall in sea level from this highstand, coupled with accumulation of tidal strait sediments, reduced the tidal prism and strength of tidal currents in the bay. At the same time, regressive beachridge plains developed in open coast and bay environments. This coincided with development of the contemporary tidal inlet complexes at the north and south outlets of the bay. As a consequence, the upper surface of the tidal strait sand deposits experienced tidal ravinement and the bay switched to a sheltered back-barrier environment dominated by deposition of mud and silt which blanket the contemporary bay floor. The tidal inlets sequestered sand from the littoral drift system in ebb and flood-tide deltas, which created breaks in the longshore drift system, causing littoral sediment to accumulate at the north of the island in a series of spits, and promoting strandplain development south of the island.

Giant deer (Megaloceros giganteus) diet from Mid‐Weichselian deposits under the present North Sea inferred from molar‐embedded botanical remains

ABSTRACTThe molar of a giant deer, Megaloceros giganteus (Blumenbach, 1799), was discovered in sandy deposits of the North Sea, about 10 km west of the present shoreline of the Netherlands. Compacted masticated plant remains were preserved in the molar's deep folds. A palaeoecological analysis of these plant remains shows the complete dominance of pollen from Artemisia (sage) and other Asteraceae Tubuliflorae (Compositae), indicating that the animal foraged in a steppe environment, and may have preferred to eat Artemisia, which contain a high level of nutrients such as calcium and phosphorous components, which are important for antler building. Radiocarbon dating indicates that the plant remains are of mid‐Weichselian age [38 570 (+300, −290) 14C a BP, Greenland Interstadial‐11]. This is the first study of the food choice of M. giganteus based on palaeoecological evidence. We hypothesize about links between the extirpation of M. giganteus at the onset of the Holocene in North‐West Europe and the transition from a landscape with highly dynamic geomorphological processes and consequently prevalence of immature and nutrient‐rich soils, to a less dynamic landscape with stable, leached and acidifying soils, and the decline of Artemisia and other calciphilous plants.

Medieval fan aggradation in the wetland fringe of Lake Shkodra, Albania

The analysis of sediment cores and auger holes from the wetland fringe of Lake Shkodra were used to interpret Late Holocene shoreline fluctuations in northwestern Albania. Dry bulk density, organic carbon, magnetic susceptibility, particle size determination, sediment composition, X-ray diffraction, and AMS 14C dating provide the basis for interpretation. The Kir River may have sourced the 50 km2 Late Pleistocene-Holocene Shtoj alluvial fan at the terminus of the 372 km2 Kir River drainage basin on the western slopes of the Bjeshkët e Namuna Mountains. However, the Kir River has not transected the fan since at least the first century BC. The vertical succession of facies in sediment cores from peat to lacustrine clay and then to over 1.1 m of alluvial silt and sand documents an expansion, then contraction of the lake to its current size after 1390 cal yr BP. Sand influx off the fan is attributed to sheetflow, rill, or gullying related to increased anthropogenic activity across the fan during Medieval time. Archaeological surveys support abandonment of hill fort dwellings for the plain around 500 CE. Since 1390 cal yr BP, the Lake Shkodra shoreline has fluctuated at least 1.5 km to the east of the present shoreline.

The evolution of Chabahar beach ridge system in SE Iran in response to Holocene relative sea level changes

The Chabahar Strandplain (CHS) stretches along the Chabahar bay at a width of more than 5 km along the northern coast of the Gulf of Oman and SE Iran; an area that has been subjected to tectonic uplift as a part of the Makran accretionary prism. The CHS comprises of beach ridges, inter-ridge swales, sand dunes, tidal channels and fluvial deposits. We present the first documentation of the spatial distribution and the internal architecture of the CHS based on topographic surveys, sediment percussive coring, trenching and ground penetrating radar (GPR) transects. Radiocarbon dating on marine shells from foreshore deposits of 8 representative beach ridges yielded ages between 4800 and 270 cal. years BP at respective distances of 4800 to 670 m from the present shoreline. We interpret the boundary between the foreshore (beach) and the foredune deposits as indicator of past sea levels by analogy to present shore processes. This boundary is readily recognizable in sediment profiles from cores and trenches as well as GPR reflectors. Based on the age model and depositional features, we estimate relative sea level fall of up to 15 m over the past 4800 years. Considering that the eustatic sea level changes for this period are negligible for the Makran coast, this relative sea level fall is related to tectonic uplift across the coastal Makran. The elevation of palaeo-shorelines with similar ages decrease from east to west of the CHS, which suggest that alongshore variations in uplift rates are likely related to different movements of coastal fault blocks.

Beach ridge sets reflect the late Holocene evolution of the St Lucia estuarine lake system, South Africa

Sets of sandy beach ridges and intervening swales define shoreline sections of the shallow St Lucia wetland system within the iSimangaliso Wetland Park, World Heritage Site in northern KwaZulu-Natal province, South Africa. The sets comprise 3–10 beach ridges, the most prominent being 80–150 m wide and rising 0.5–2 m above the adjacent swales. The highest beach ridge crests elevated 3.2–4.6 m above mean sea level are furthest from the present shoreline and the lowest ridges, rising about 0.5 m above the swales, occur closest to the present mean lake level shoreline. This investigation assesses the genesis of the sandy beach ridges on five strand plain remnants within the estuarine lake. The ridges were topographically surveyed and their ages estimated using optically stimulated luminescence (OSL) dating. OSL dating reveals that the oldest beach ridge formed around 6240 years ago, with a sequence of beach ridges having accumulated during the period ~4000 to 1500 years ago reflecting coeval accretion around the lake. The present mean lake level shoreline was only reached within the past ~600 years. Sedimentation changed from marine-dominated to lacustrine deposition in the estuary during the period of beach ridge accretion. The dated beach ridges, supported by new radiocarbon dates of fixed biological indicators from Holocene intertidal zone settings on the coast, are used with published sea-level curves to set the context of periodic beach ridge accretion in the marine-linked estuarine lake. The dated ridges suggest that episodic regression of the estuarine lake shoreline occurred after a mid-Holocene sea-level highstand. The record of sea-level change is also reflected by the long-term natural shrinking and shallowing of the proto-St Lucia lagoon/estuarine lake in the context of reduced marine influences due to closure of former marine channels by progressive barrier dune accretion. The sequence of coeval beach ridges reflects a pulsed lowering of relative sea-level in the shallowing estuarine lake. Height differences between the coeval ridges at sites around the lake reflect local environmental controls including the range of wind fetch distances across shallow lake compartments, wave height and wind-induced seiche effects.

Historical Tsunami Records on Russian Island, the Sea of Japan

In this article, we provide data evidencing tsunamis on Russian Island over the last 700 years. Reconstructions are developed based on the analyses of peat bog sections on the coast of Spokoynaya Bay, including layers of tsunami sands. Ancient beach sands under peat were deposited during the final phase of transgression of the Medieval Warm Period. We used data on diatoms and benthic foraminifers to identify the marine origin of the sands. The grain size compositions of the tsunami deposits were used to determine the sources of material carried by the tsunamis. The chronology of historical tsunamis was determined based on the radiocarbon dating of the underlying organic deposits. There was a stated difference between the deposition environments during tsunamis and large storms during the Goni (2015) and Lionrock (2016) typhoons. Tsunami deposits from 1983 and 1993 were found in the upper part of the sections. The inundation of the 1993 tsunami did not exceed 20 m or a height of 0.5 m a.m.s.l. (0.3 above high tide). The more intensive tsunami of 1983 had a run-up of 0.65 m a.m.s.l. and penetrated inland from the shoreline up to 40 m. Sand layer of tsunami 1940 extend in land up to ~ 50 m from the present shoreline. Evidence of six tsunamis was elicited from the peat bog sections, the deposits of which are located 60 m from the modern coastal line. The deposits of strong historic tsunamis in the Japan Sea region in 1833, 1741, 1614 (or 1644), 1448, the XIV–XV century and 1341 were also identified on Russian Island. Their run-ups and inundation distances were also determined. The strong historic tsunamis appeared to be more intensive than those of the XX century, and considering the sea level drop during the Little Ice Age, the inundation distances were as large as 250 m.