Beach Ridge System Research Articles

Late-Holocene sea-level markers preserved in a beach ridge system on Phra Thong Island, Thailand

Instrumental sea-level records are insufficient to understand the response of sea-level changes to global temperature on centennial timescales. Sea-level histories spanning at least the Common Era have not been widely studied in Southeast Asia. This period is crucial for providing a pre-industrial context to understand sea-level change with climate. Linking sea-level change to climate change is proxy dependant, with most proxies only providing decadal to centennial scale resolution of both sea level and climate. This study examines the efficiency of beach ridge stratigraphy as a proxy for reconstructing regional sea-level histories in the tropics. We present topographically corrected Ground Penetrating Radar (GPR) profiles from a prograded coast in Phra Thong Island, Thailand, where we identify downlap point marking the boundary between the foreshore and shoreface subzones and use this as a past low-tide marker. The low-tide markers were corrected (considering the tidal range) and then connected to approximate the past sea level. Optically Stimulated Luminescence (OSL) samples collected at locations slightly offset from the shore-normal GPR profile line were incorporated to create a relative sea-level record. Overall, the shore-normal GPR record shows a ∼ 1.06 m fall in sea level between ∼2660 and ∼ 370 years ago. The study also highlighted stepwise fluctuations in sea level that were not identified in previous studies. Between ∼2600 and ∼ 2200 years ago, the record indicates a steep fall in sea level, followed by a phase of relatively stable to slightly falling sea level between ∼2200 and ∼ 550 years ago. Finally, for the seaward side, between ∼550 and ∼ 350 years ago, the record indicates an accelerating sea-level fall. This study confirms that the investigation of tropical beach ridge systems using GPR and OSL techniques can be a highly efficient and effective means for reconstructing regional sea-level trends throughout the Common Era and beyond.

Nature and Distribution of Beach Ridges on the Islands of the Greater Caribbean

Beach ridges originate from various depositional processes and occur in a variety of settings. This paper assesses their nature and distribution on the islands of the Greater Caribbean based on a literature review and the identification of sites using Google Earth© 7.3 imagery. The morphological and orientation parameters were measured for each site, and a measure of storm density was developed. These were statistically analysed to develop a classification of beach ridge types. The results show a diversity of beach ridge systems, in terms of setting, morphology, composition and preservation. The presence or absence of an adjacent coral reef is a major differentiating element at the regional level. A regional beach ridge plain classification is proposed, including two main classes, marine beach ridges and river-associated beach ridges, with further sub-divisions based on exposure to hurricanes or hurricanes plus swell waves.

Late holocene progradation in a mixed siliciclastic-carbonate beach ridges system, Northeast Brazil

A morpho-sedimentary analysis based on grain size, texture, composition, luminescence ages, and morphologic pattern was performed in a beach ridge system located on the Brazilian semiarid coast to understand the siliciclastic and bioclastic mixtures during a progradation of strandplain. Moreover, the rhodolith beds were adopted as a new sea-level proxy to analyze the coastline displacement trajectory of the mixed siliciclastic-carbonate sedimentary environment. The beach ridges system shows a succession of ridges and swales interrupted in the central part by a lagoon plain, the western sector exhibits the crest relief related to the ancient foredune on top and underlying foreshore deposits, and the eastern sector shows a great presence of transgressive dunes overlying beach ridges. Foredune/aeolian facies and the foreshore facies (with rhodolith beds associated) show siliciclastic and bioclastic mixture related to the late Holocene coastal progradation with a progressive increase in carbonate influence, mainly calcareous algae, foraminifera, and molluscs. Moreover, comparing the modern counterpart of the older beach ridges, finer and better-sorted sediments were found in the ancient deposits than in the modern ones. Thus, the progradation was marked by an eminently dissipative beach system. This coeval sedimentation is controlled by key local settings, such as the semi-arid climate, the absence of local fluvial input, the shallow shelf, and the carbonate factory for bioclastic supply. The presence of rhodolith beds in the foreshore facies with an elevation lowering trend towards the modern coastline reinforces the hypothesis that the mixed progradational pattern was accompanied by a small fall in sea level, which corroborates with late Holocene regional curves and provides pioneering preliminary contributions for the studied area.

A 2500-YEAR SEA LEVEL RECORD FROM PHRA THONG ISLAND, THAILAND

Temporally changing coastline configurations and local sea-level changes pose a considerable threat to coastal communities and infrastructure. However, regional sea-level (RSL) histories spanning the last 3000 years have not been widely studied in Southeast Asia, even though the region shows significantly different RSL records from place to place (Horton et al., 2005). This period is crucial for understanding sea-level changes from pre-industrial time. Here, we investigate the record of past sea-level(s) preserved within the stratigraphy of the beach ridge system of Phra Thong Island (PTI), Thailand.

Post-glacial RSL changes and the demise of a local remnant Laurentide Ice-Sheet ice cap: A view from Anticosti island beach-ridges (Gulf of St Lawrence, Canada)

Widely spread worldwide, beach-ridge systems are established along prograding coastlines, either fostered by a falling Relative Sea-Level (RSL), by substantial sediment stocks being provided to the coastline, or by the combination of both agents. As such, they can form valuable archives of either large scale RSL and isostatic dynamics and/or of more local coastal processes, e.g. related to variations in riverine sediment supply. In this study, we analyze three raised beach-ridge complexes located on the island of Anticosti (Gulf of St.-Lawrence, Québec, Canada). Using both field and LiDAR DEM data, we produce new RSL histories for the north-eastern and north-western sectors of Anticosti Island region over the ca. 14.400 to 8.300 yrs cal. B.P. period. These new sea-level data allow to considerably refine the postglacial RSL history of the region, hence carrying large implications for the comprehension of the isostatic dynamics of the St-Lawrence region. Considerable misfits between our observations and outputs of the GIA models notably allow to propose refinements on the LIS architecture and melting history as well as on the rheological characteristics of the St-Lawrence valley. Locally, chronologies of progradation of the beach-ridges were mostly forced by RSL changes, yet also apparently recorded the demise of the local Anticosti remnant ice-cap throughout the changes in sediment supply the melting of the latter produced locally. Finally, some results of paleo-oceanographic significance could also be derived from the study of the beach-ridges, pertaining for instance to changes in sea-ice cover.

A 4000-year paleoenvironmental reconstruction and extreme event record from Laguna Nuxco, Guerrero, Mexico

Reconstructing paleoenvironments on Mexico's Pacific coast is crucial to determine past climate conditions and natural hazard periodicities, vital for predicting future activities. Two sediment cores extracted from Laguna Nuxco, a coastal lagoon in Guerrero, were analyzed to provide a 4000-year paleoenvironmental record. Sediments dominated by shelly clay with low water and organic content, high carbonate content, low Ti/Ca ratio and the presence of Anomalocardia subrugosa suggest that a sheltered bay existed from ~4000–~1300 cal yr BP. During this stage, intermittent beach ridge gaps facilitated the deposition of storm-induced shell deposits, likely from tropical cyclones. Frequent thick shell hash deposition toward the top of the lithologic unit indicates heightened storminess likely from an increase in ENSO activity. An intense tropical cyclone, or perhaps multiple storms during an active period deposited a thick shell hash layer at ~1500 cal yr BP, which helped strengthen the beach ridge system and lead to the modern lagoon phase (~1300 cal yr BP to present), as suggested by the presence of Mytella sp. A more isolated lagoon with significant terrestrial sediment input was reflected by the predominance of lagoonal clay with decreased shell and carbonate contents, increased water and organic contents, and increased Ti/Ca ratio. A quiet period with lower tropical cyclone activity occurred from 1300 to 800 cal yr BP and from 300 cal yr BP to the present, as inferred from no or relatively few shell hash deposits, respectively. A period of hyperactivity occurred from 800 to 300 cal yr BP, as evidenced by seven shell hash layers. During the modern lagoon phase, shell hash deposition was not caused by marine inundation processes, but rather ‘blowout’ events driven by intense precipitation during heightened ENSO activity. Findings shed additional light on Late Holocene environmental changes in a dynamic coastal zone related to regional controlling factors such as tropical cyclone activity, ENSO, and beach ridge development. • A 4000-yr reconstruction at Laguna Nuxco uncovers a transition from bay to lagoon. • Thick shell hash units indicate marine deposition via tropical cyclones. • Thin shell hash layers indicate lagoon “blowouts” from heavy precipitation events. • Activity regimes are largely tied to periods of heightened ENSO. • Notable activity periods occurred from 1500 to 1300 and 800–300 cal yr BP.

Holocene coastal evolution, past tsunamis, and extreme wave event reconstructions using sediment cores obtained from the central coast of Hidaka, Hokkaido, Japan

Investigating coastal areas far from tsunami sources can improve the understanding of the magnitude and origin of giant tsunamis. However, distinguishing tsunami deposits from extreme storm deposits is more challenging since the layers are less prominent compared to the those in the locations near a tsunami source. This study reconstructed the Holocene coastal environments on the central coast of Hidaka, Hokkaido, ~250 km from the Kuril Trench. Sand layers induced by extreme waves were identified by examining the sea-level index points in the late to mid-Holocene by diatom-assemblage analysis through the combination of chemical analyses with the investigation of sediment cores. Detailed facies analyses on sediment cores obtained from several transects showed that sediment preservation differs according to the location of the cores relative to the ambient coastline. In the zone behind the beach ridge, the paleoenvironments changed from a saltmarsh formed by transgression to a swamp closed by a beach ridge formed by sea regression in the mid-Holocene. Conversely, the seaward zone indicated various environmental changes due to meandering rivers and the development of the beach ridge system due to sea regression. We found four volcanic ash layers and seven sand layers with clear basal contact with peat or organic mud. According to their sedimentological features, these sand layers were formed by tsunamis or storm surges; at least four of the sand layers are likely to be tsunami deposits, considering the ages of tsunami deposits in the surrounding region. Dramatic changes in the depositional environment associated with relative sea-level changes resulted in a short period of preservation of the sand layers. In addition, their distributions were limited, ranging from a few tens of meters to hundreds of meters from the beach ridge. Thus, in an area far from tsunami sources, the traces of extreme waves may be overlooked if the coastal evolutional process is not considered.

Rainfalls And Salinity Effects On Fecal Coliform Most Probable Number (MPN) Index Distribution In A Beach Ridge-Shore Ridge System In Mengabang Telipot, Terengganu, Malaysia

A Holocene beach ridge and present day shore ridge system located in a rural area north east of Kuala Terengganu was studied. The relation between fecal coliform (FC) MPN Index (Most Probable Number) distribution with rainfalls and saline intrusions into the unconfined aquifer of the beach ridge–shore ridge system was examined. The probable primary source of the pollutants was also investigated in order to highlight the susceptibility of such aquifers to pollution. Six sampling sessions were made from September 2009 to January 2010. Three represent drier conditions and the other 3, heavier rainfalls corresponding to the northeast monsoon season. This sampling period represent a condition when this area was still not subjected to major coastal erosions and subsequent rock revetment work. Altogether, water samples were taken from 13 wells and 3 river stations. Physical-chemical measurements were made in-situ, while FC was tested at UMT laboratory. Essentially, the results indicated that the groundwater in the unconfined aquifer layer of the beach ridge was moderately to highly polluted with FC (up to 1600 MPN). In contrast, the shore ridge was only slightly polluted, whereas river stations had mixed conditions but generally worse than the beach ridge and shore ridge. These phenomena could be associated with salinity spatial-temporal variations. Samples from heavy rainfall conditions indicated lower pollution levels compared to drier conditions. This phenomenon could be associated with the availability of more infiltrated atmospheric water to dilute pollutants in a high hydraulic conductivity environment as the ridges are made of fine to coarse sands. The results underscore the sensitivity of such environment to pollution transport and distribution and hence implied special attention with regards to water resource management.

Short communication: Driftwood provides reliable chronological markers in Arctic coastal deposits

Abstract. Originating from the boreal forest and often transported over large distances, driftwood characterizes many Arctic coastlines. Here we present a combined assessment of radiocarbon (14C) and dendrochronological (ring width) age estimates of driftwood samples to constrain the progradation of two Holocene beach-ridge systems near the Lena Delta in the Siberian Arctic (Laptev Sea). Our data show that the 14C ages obtained on syndepositional driftwood from beach deposits yield surprisingly coherent chronologies for the coastal evolution of the field sites. The dendrochronological analysis of wood from modern drift lines revealed the origin and recent delivery of the wood from the Lena River catchment. This finding suggests that the duration of transport lies within the uncertainty of state-of-the-art 14C dating and thus substantiates the validity of age indication obtained from driftwood. This observation will help us better understand the response of similar coastal systems to past climate and sea-level changes.

Optical dating of cobble surfaces determines the chronology of Holocene beach ridges in Greenland

We constrain the age of a cobble beach ridge system in Greenland using Optically Stimulated Luminescence (OSL) dating of buried cobble surfaces. Luminescence signals from six cobbles are measured using infrared (IR) stimulation at 50 °C (IR50) and 180 °C (pIRIR180); these cobbles represent four progressively younger beach ridges lying between ~35 and ~6 m above present sea level. Luminescence–depth profiles show that the IR50 signals in all the samples and pIRIR180 signals in four out of six samples are well bleached to depths >1.2 mm into the cobble surfaces. Equivalent doses in well‐bleached cobble surface slices (i.e. <1.2 mm) are measured and divided by the effective environmental dose rate to the cobble surfaces in order to derive burial ages. Both IR signals are corrected for anomalous fading using the sample‐specific ratio of the field to the laboratory saturation levels. Our results are consistent with a depositional model predicting that the investigated portion of the beach ridge system built out continuously during relative sea level fall between ~5.3 and ~1.9 ka ago. The optical ages suggest that the rate of construction varied considerably, with the highest rates ~3.4 ka ago. Additionally, the lowest‐elevation beach ridge investigated here provides the first evidence for a higher‐than‐present relative sea level, between 1.5 and 2 ka ago, in the Disko coastal region.

Indication of Holocene sea-level stability in the southern Laptev Sea recorded by beach ridges in north-east Siberia, Russia

The rapid warming of the Arctic may affect the stability of coastal geomorphological systems. Prograded sequences of wave-built deposits, so-called beach-ridge systems, preserve a proxy record of the long-term variability in the drivers of coastal evolution. Information on relative sea level (RSL), climate forcing and sediment supply can be reconstructed from these archives. Buor Khaya Bay is one of the few places along the Siberian Arctic coast where wide beach-ridge systems exist. A previously undescribed field site was surveyed in order to obtain information on the geomorphological processes along the modern shoreline under the current environmental conditions, and the characteristics of the Holocene beach-ridge deposits (e.g., elevation, sediment and age). Our data show that the system formed under storm wave/surge conditions. The beach ridges prograded ca. 1100 m between 6200 and 2600 cal yr BP, with only minor variations in surface elevation. This suggests a continuous and high sediment supply and similar storm wave run-up heights during that time. This relationship is interpreted as indicating RSL stability at a similar-to-present elevation during the period of beach-ridge formation. The hiatus in coastal progradation is concurrent with a deteriorating climate (cooling) in the Laptev Sea area and our data hence suggest increased rates of coastal change during periods of warmer climate conditions. Our study illustrates the potential of coastal sedimentary archives to provide a more complete view of the forcing, resilience and long-term evolution of unconsolidated Arctic coasts in a changing environment.

Evolution of a Shelly Beach Ridge System over the Last Decades in a Hypertidal Open-coast Embayment (Western Mont-Saint-Michel Bay, NW France)

Tessier, B.; Poirier, C.; Weill, P.; Dezileau, L.; Rieux, A.; Mouaze, D.; Fournier, J., and Bonnot-Courtois, C., 2019. Evolution of a shelly beach ridge system over the last decades in a hypertidal open-coast embayment (western Mont-Saint-Michel Bay, NW France). In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 77–88. Coconut Creek (Florida), ISSN 0749-0208.The behavior of the shelly beach ridge system forming a more or less continuous barrier lying along the southern coast of the hypertidal Mont-Saint-Michel bay (NW France) is examined using a set of various data including aerial photographs since 1947, sediment cores collected in back-barrier salt marshes, ground penetrating radar profiles, and differential digital elevation models (DEMs). The latter shows that since the middle of the 20th century, the tidal flats extending in front of the ridge system experience erosion and accretion that alternate spatially according to cross-shore corridors. The shelly ridges are better developed on line with the erosional bands. The reasons for this erosion/accretion compartment pattern are not totally elucidated. It probably results from the combined influence of shellfish farms, tidal channels and reef present on the tidal flats on wave and current dynamics. At the decadal to pluri-decadal scale, the shelly beach ridge system behavior as well as its internal organization can partly be related to the fluctuations of hydrodynamic conditions controlled by the 18.6 years nodal tidal cycle. Periods of intense landward migration alternate with periods of relative stability during the peak and the trough of the cycle respectively. This general scheme is complicated due to variations in storm wave dynamics. The most morphogenic events happen potentially during coinciding nodal cycle peaks and enhanced storminess. Such conditions actually occurred around 1995-2000, resulting in the most prominent washover fan deposit preserved within the back-barrier infilling successions. These sediment successions evidence as well that no beach ridge system older than the 19th century is preserved in front of the Medieval dike built during the 11th century on a relict beach ridge, and on which the present-day system is backed. We suggest that the enhanced storminess conditions of the Little Ice Age provoked the reworking of beach ridges formed between the 11th and 19th centuries. Changes in quantity and type of mollusk shells, related to the shellfish farming development during the 20th century are also thought to have had positive consequences on the barrier building and stability.

Holocene coastal environmental changes and human occupation of the lower Hérault River, southern France

Sea-level rise, human impacts and climate change have deeply affected coastal environments during the Holocene. These forcing factors are studied using the Lower Hérault valley, which constitutes a very representative Mediterranean case study because of (i) its very early, intense and continuous land use since Neolithic times, and (ii) its sensitivity to sea-level rise and Mediterranean climate changes over a relatively small watershed. 34 cores and 61 AMS radiocarbon dates, associated with biological and geochemical analyses, have allowed us to precisely reconstruct the Holocene evolution of the lower valley. Until 6500 cal yr BP, a wave-dominated morphology and retrogradational dynamics were reconstructed. During this phase, ephemeral channels and successive river mouths formed and were rapidly submerged by sea-level rise. The progradational phase began after 6500 cal yr BP, and the alluvial plain gradually built seawards with the formation of a beachridge system outside the valley. Growth of the fertile alluvial plain was coeval with the development of Neolithic agriculture. This alluvial progradation gradually filled the estuary with advances of the mouths, several shallow lagoons and sandbar. The high density of information collected allows us to recognize, for the first time, a pronounced fluvial-dominated deltaic morphology, especially 3000 years ago, during the Bronze Age. Lagoonal and coastal shores were continually inhabited. Human land use continually adapted to geomorphological and environmental changes. Around 300 years ago, the delta shifted to a wave-dominated system.

Geoheritage significance of three Pleistocene formations recording a succession of climates and sea levels on the Yalgorup Plain in southwestern Australia

The Yalgorup Plain of southwestern Australia is underlain by two limestone formations and a linear quartz-sand formation containing limestone lenses. These limestones record carbonate deposition in seagrass banks during the Pleistocene; they are capped either by a prograding beach-ridge system of small cuspate forelands or a quartz-rich shore-parallel coastal barrier. The cuspate forelands formed behind protective offshore limestone reefs within a given Pleistocene wind-and-wave field, while the quartz-rich coastal dune barrier formed under enhanced swell conditions. These formations record three different Pleistocene interglacial depositional events, separated by unconformities, each linked to a distinct climate and mean sea level. Foraminiferal assemblages within the two limestones and within the limestone lenses of the quartz-sand formation faithfully record changes in minimum seawater temperature, reflecting these changes in climate. They indicate a cycle of warm–cool–warm water accumulation of carbonates. Such a record of both climate and sea level history for southwestern Australia is unique, contributing greatly to the Pleistocene coastal sedimentary history of limestones within southwestern Australia. These formations occur within the globally unique setting of Western Australia and are conserved within a National Park and represent an outstanding record of Quaternary coastal geomorphic development in terms of both carbonate and siliciclastic sedimentation linked to both climate and sea level changes. Given their array of lithofacies, environmental setting, sea level and climate changes, as well as their biostratigraphy reflecting these changes, these formations form a sedimentary ‘package’ that is of global geoheritage significance, with many of its inherent geological features also of global to national geoheritage significance.

Human settlement and Mid-Late Holocene coastal environmental change at Cape Krusenstern, Northwest Alaska

Archaeologists hypothesize that mid-late Holocene environmental variability played a role in several significant western Arctic cultural developments including population fluctuations, the evolution of Arctic maritime adaptations, and Arctic-wide migrations. Further evaluation of these hypotheses requires higher resolution archaeological and paleoecological datasets than are currently available. In response, we undertook an interdisciplinary study at Cape Krusenstern, a large coastal site complex in northwest Alaska, which was occupied over the last ca. 5000–6000 years. Our goals were to refine local cultural and paleoenvironmental chronologies and to explore the question of how local environmental change may have influenced local settlement history. The resulting revised chronology and depositional units confirm and refine prior interpretation of the local archaeological settlement history. New geomorphological data on coastal environmental change and post-depositional modification of the Cape Krusenstern beach ridge system also provide information about patterns of archaeological site preservation, indicating periods of potentially poorer site preservation around 3990 cal BP; this informs interpretation of forager settlement data. Furthermore, our findings suggest that climate-driven changes in the coastal environment at Cape Krusenstern may not be as determinative in terms of landscape evolution as previously thought. Future work should focus on further investigating the relationship between beach ridge development and regional climatic patterns on a regional scale, as this has implications for use of beach ridges as a mid-late Holocene climate proxy. Continued efforts to build paleoenvironmental reconstructions of higher temporal and spatial resolution for the region will help address remaining questions about the relationship between local coastal environmental changes and regional patterns, and the impacts of these environmental shifts on local residents.

Sedimentary records of extreme wave events in the southwestern Caribbean

High-energy events in the Caribbean Sea include hurricanes, tropical storms, cold fronts and tsunamis. El Rosario Archipelago, located on the Colombian Caribbean shelf (SW Caribbean) consists of a set of ancient and successive coralline formations, uplifted by tectonic and diapiric activity. We undertook an integrated analysis of instrumental climate records and sediment records from a beach ridge system, a reef lagoon and a mangrove lagoon in the Archipelago, to determine whether historical extreme weather events influenced the coastal geomorphology and reef sedimentation. Statistical analysis of historical extreme winds and waves was accomplished using ERA-Interim reanalysis data. Extreme sea-level events were identified with calibrated data from the nearest tide gauge. Sediments from the reef and mangrove lagoon were dated using 210Pb and 14C. Beach ridges were dated indirectly thorough their relationship with the closure of the mangrove lagoon. The eroding capacity of the historical extreme waves (i.e. maximum grain size that could be entrained by the orbital velocity of the waves) was compared with the grain sizes present in the deposits, and foraminifera species helped to determine the provenance of those deposits. Storms typically occur during the dry season associated with cold fronts. Foraminifera and coral fragments indicated that beach ridges were supplied with sediment that eroded from ancient terraces. In the reef lagoon, a 56-cm-thick unit of coarse coral and shell debris, grading to a finer sediment, represents a major high-energy event that occurred after ca. 1655 CE. This event was also recorded by the beach ridges. The probable explanation for this high energy unit is that a strong event carried coarse sediments into the lagoon, with subsequent reworking by minor events, such as those reported in the historical record. Two tsunamis occurred in the Caribbean after 1655, but the associated waves reaching the area were not strong enough to deposit the coarser clasts of the unit. Thus, coarser material was probably delivered to the lagoon as a consequence of sudden diapiric and/or tectonic activity. Our data show that major storms and other high-wind, extreme-wave events shape the beach ridges on Rosario Island, every 70 years. The findings suggest that if global climate change increases the frequency and/or magnitude of major storms and other high-wind, extreme wave events that impact the Caribbean coast of Colombia, then El Rosario Archipelago will be susceptible to future, significant landscape transformations.

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.

Chronology and late-Holocene evolution of Caleta de los Loros, NE Patagonia, Argentina

Geomorphological and sedimentary records of Holocene coastal deposits may serve as archives for the local reconstruction of trends in coastal evolution and of the key forcing parameters controlling long-term change. We here present new observations on the sedimentology, chronology, and surface properties of a coupled beach ridge and coastal lagoon system located on the northern shore of San Matías Gulf, NE Patagonia, Argentina. The study is based on remotely sensed data, sediment cores, and a large number of samples dated using optically stimulated luminescence (OSL). The field site is located in a topographical depression within a cliffed shoreline composed of friable sand and gravel stones. The oldest preserved lagoonal deposits formed in the protected inner part of the system c. 2300 years ago. An up to 4-km-wide strandplain prograded rapidly between c. 1000 and 500 years in the more exposed western part of the system. Lagoonal deposition occurred primarily during the last 500 years. The chronology and spatial arrangement of landforms appear to result from a switch-over in sediment delivery probably caused by local implications of major shifts in climate regime. Even though we were not able to identify or benchmark the precise triggers of geomorphological change at Caleta de los Loros, our study presents an example of the potential importance of environmental changes on the rapid and non-linear development of coastal sedimentary systems.

Rhythmic Patterns of Coastal Formations as Signs of Past Climate Fluctuations on Uplifting Coasts of Estonia, the Baltic Sea

ABSTRACT Tonisson, H.; Suursaar, U.; Kont, A.; Muru, M.; Rivis, R.; Rosentau, A.; Tamura, T., and Vilumaa, K., 2018. Rhythmic patterns of coastal formations as signs of past climate fluctuations on uplifting coasts of Estonia, the Baltic Sea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 611–615. Coconut Creek (Florida), ISSN 0749-0208. On uplifting and tideless Baltic Sea Coasts in Estonia, a number of elevated mid to late Holocene beach ridge systems with rhythmic patterns are identified. Such uplifted coastal formations serve as archives of past variations in sea level and climate, as well as extreme events. Luminescence dating and interpretation of airborne LiDAR elevation data were used to identify the main formation mechanisms of such beach ridge systems. More extensive (up to 100–150 ridges) and clearer ridge patterns were found on faster emerging (up...

Two-dimensional chronostratigraphic modelling of OSL ages from recent beach-ridge deposits, SE Australia

Abstract Optically-stimulated luminesecne (OSL) dating, in concert with two-dimensional ground-penetrating radar (GPR) profiling, has contributed to significant advances in our understanding of beach-ridge systems and other sedimentary landforms in various settings. For recent beach-ridges, the good OSL properties of coastal quartz permit a high sample throughput thanks to shorter measurement times and simpler sample preparation prompting the collection of more samples at higher sampling resolution. However, sampling at high resolution increases the chance of age inversions because random errors between samples may be larger than the difference in sample ages. Age inversions can be avoided, however, if the stratigraphic constraints are included in the age estimation process. Here, we create a custom Bayesian chronological model for a recent (