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Shaw, C.E. and Benson, L., 2015. Possible tsunami deposits on the Caribbean coast of the Yucatán peninsula. The western Caribbean Basin is notable for its tectonic stability. It has experienced no historical earthquakes or the tsunami that sometimes accompany them. This paper describes a single, wedge-shaped, boulder-covered, coastal berm on the Yucatán coast of México that stretches unbroken for 50 km across a coastal segment characterized by rocky headlands that alternate with crescent beaches. The remainder of the 350 km of Yucatán coast consists mostly of mangrove that extends 1 to 30 km inland, often behind long, sandy beaches. On the headlands, the surface of the berm is densely paved with boulders-large boulders on its seaward face and smaller boulders and cobbles on its gently sloping inland surface. The top of the berm reaches an elevation >4 m, above the reach of all but the largest modern storm waves. Berm sediments on the headlands consist of two distinct layers of unbedded coarse sand with numerous randomly distributed boulders and cobbles in the lower layer and a crudely textured gravel and sand layer above. At first glance the two layers appear to be separated by 20 cm of white sand above a thin, discontinuous zone of dark, greyish sand that contains isolated balls and smears of black organic material, apparently derived from a soil, or possibly leaf litter. The berm and its associated boulders track the modern coastal morphology in precise detail as it follows the form of modern headlands, bays, and transcoastal channels, indicating that deposition took place after development of the present coast. The berm sediments record two or three large waves, depending on whether the wave that deposited the boulder pavement is regarded as part of the second wave or as a separate wave. Radiocarbon dating indicates that at least one wave struck the coast approximately 1500 years before present. Minimum wave run-up exceeds 4 m above present sea level, and inland inundation reached 400 m along bays and transcoastal channels. The position and elevation of the berm, its lack of well-developed internal bedding, the paving of the berm surface by thousands of boulders, and its 400-m extent inland along channels and bays are features commonly associated with tsunami. However, some recent studies conclude that all of the features listed also can be produced by mega-hurricanes. Placed in the context of our literature search of the recent history of hurricanes and tsunami in the Caribbean Basin, we conclude that the single berm on the Yucatán coast represents an anomalous event for this area and that the berm sediments bear a strong similarity to descriptions of sediments from some historical tsunami and are unlike sedimentary features associated with historical hurricanes. [ABSTRACT FROM AUTHOR]

Rate of global eustatic sea-level rise during the Holocene Epoch has been identified as the principle cause of observed changes or inferred evolution of nontectonic coastal systems in mid- to low-latitude areas. The rate of rise is now three times faster than it was for the past several thousand years and similar to values associated with the middle Holocene marine transgression. This acceleration can be attributed to human-caused global warming. In this investigation, the effects of accelerating sea-level rise on coastal sedimentary environments of the SE Saline Everglades were quantified. The results reveal historic changes to coastal habitat, sedimentation, and stratigraphy that are transgressive. These changes initiated during the early 20th century and are attributed to accelerating sea-level rise. As this acceleration and the resulting geologic record is a suspected consequence of human-induced global warming, the paper concludes with a discussion of the relevance of these observations, in tandem with others, to the current debate over the utility and use of the proposed Anthropocene. [ABSTRACT FROM AUTHOR]

Shaw, C.E., 2016. Late Pleistocene bays and reefs: Ancestors to the modern Caribbean coast, Yucatán Península, México. Low-lying indentations along the modern Caribbean coast of the Yucatán Peninsula host shallow bays with classic crescent-shaped, white-sand beaches. These indentations have previously been explained as products of Holocene dissolution of Pleistocene limestones within a brackish coastal mixing zone. This paper demonstrates that the lows confining the modern bays were formed by sedimentary processes 122,000 ± 2000 YBP, during the late Pleistocene. A 50 km stretch of the Caribbean coast between Tankah and Playa del Carmen, here called the high coast, is characterized by rocky headlands that are underlain by fossilized coral reefs of late Pleistocene age and lows between headlands occupied by modern bays. Study of landforms using aerial photographs together with field examination of late Pleistocene calcarenite exposed in quarries has led to recognition of a series of arcuate Pleistocene beaches with large attached spits that developed during a period of falling sea level that followed the oxygen isotope substage 5e sea-level highstand. Pleistocene beaches and associated triangular spits form a series of cuspate arcs, each precisely aligned with one of the modern bays and each triangular spit aligned with the center of a modern headland. This exact and repeated coincidence of substage 5e bays with modern bays and beaches indicates that low areas occupied by modern bays lie within the lowest portions of late Pleistocene bays that were drained during the Wisconsin glacial and reflooded in their lowest parts during the post-Wisconsin rise of sea level in the Holocene. [ABSTRACT FROM AUTHOR]

ABSTRACT Koster, K.; Cohen, K.M.; Stafleu, J., and Stouthamer, E., 2018. Using 14C-dated peat beds for reconstructing subsidence by compression in the Holland coastal plain of the Netherlands. Subsidence in the Holland coastal plain of the Netherlands was reconstructed from the vertical displacement of Holocene peat layers below their reference groundwater levels at the time of peat formation. This quantifies the part of subsidence that is due to compression processes and allows specification of the current state of peat compression in a map. 14C-dating of peat layers found intercalated in the Holocene sequence were used in the reconstruction. This dataset was combined with results from a recent coastal-deltaic plain wide three-dimensional (3D) interpolation of reference palaeo-groundwater levels, at which the intercalated peats are thought to have formed before they were buried, compressed, and vertically displaced. Empiric relations between reconstructed displacement and the thickness of overburden were determined and deployed in a national 3D geological subsurface model to establish a subsidence map with continuous cover of the coastal plain. The resulting maps show compressed peat layers under urbanized areas with 1 to 8 m of natural and anthropogenic overburden have subsided 1 to 5 m below the original level of formation. In the agricultural area of the coastal plain, where overburden is merely decimetres thick, consisting of fluvial flood- and sea-ingression deposits, peat generally experienced less than 1 m subsidence. The reference-level reconstruction method is deployable over large coastal plain areas to reconstruct subsidence caused by postdepositional vertical displacement of intercalated peat layers. It could therefore serve as an alternative approach for methods based on soil mechanics, which require input often not available for coastal plains on regional scales. [ABSTRACT FROM AUTHOR]

ABSTRACT Tõnisson, H.; Suursaar, Ü.; 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 (uplift rates around 3 mm/yr) and well-exposed western and northern coasts, where they were located on the heights of up to 18 m. The average temporal periodicity (30–40 years) in such ridge systems is in good agreement with 25–40 year cyclicity, which is detectable in Estonian tide-gauge records, wave hindcasts, regional storminess and the NAO indices. However, typical average ridge spacing was 2–3 times longer in the study areas with lower (0.5–2 mm/yr) uplift rates. It suggests that the cyclicity in ridges depends on uplift rate and is additionally enhanced or modified by decadal-scale variations in forcing conditions that is locally available. [ABSTRACT FROM AUTHOR]

Erdmann, W.; Kelletat, D., and Kuckuck, M., 2017. Boulder ridges and washover features in Galway Bay, Western Ireland. Boulder deposits of the Aran Islands in the Galway region (western Ireland) have been under investigation for more than 10 years, whereas marine and littoral deposits inside Galway Bay have only been mentioned cursorily. The aim of this study is to investigate all coastal deposits along the most exposed bay coasts from the opening of South Sound to Black Head 25 km inside Galway Bay. Long ridges with imbricated large boulders exist near the surf belt, whereas boulder deposits in clifftop positions are mostly chaotic. The size of individual boulders is similar to those on the exposed island sites of the Aran archipelago. Landward of boulder ridges, stratified fine sediments occur that point to quiet sedimentary conditions. Two more forms and deposits are mapped that are rarely mentioned for western Europe: boulder ridges with crossway secondary ridges and tonguelike washover deposits of medium boulders, both from extraordinary flow events. Dating of all units resulted in ages back to the first half of the Holocene and mid-Holocene times. During the older periods, sea level in the area was several meters lower than today and the coastline was farther west. Dislocation of very large boulders some thousands of years ago was higher and farther inland than by the strongest storms of recent times. This requires interpretation with respect to formation processes and their results in exposed and more sheltered littoral environments. [ABSTRACT FROM AUTHOR]

Strachan, K.L.; Hill, T.R.; Finch, J.M.; Barnett, R.L., and Frenzel, P., 2017. Distribution of salt-marsh foraminifera in two South African estuaries and the application as sea-level indicators. The global mean sea level is rising as a result of climate change and is likely to affect millions of people. It is essential to understand and quantify regional relative sea-level variability to be able to predict future changes. Proxy evidence is necessary for extending our understanding of past sea-level changes beyond the industrial era, and salt-marsh foraminifera have become an important tool for reconstructing late Holocene sea-level changes. In South Africa, little is known regarding the distribution of salt-marsh foraminifera and their use as sea-level indicators, thereby limiting their application in sea-level research. This study therefore describes the distribution of living and dead surface foraminifera from two study sites along the SE South African coastline. The full surface dataset has been compiled from 139 samples that are used to describe the contemporary distribution of salt-marsh foraminifera. Cluster analysis is used to define four biozones; high marsh, middle marsh, low marsh, and mudflats. In the high marsh, where environmental conditions reach the survival threshold, a greater abundance of agglutinated foraminifera occurs. In the low-marsh zone, where subaerial exposure is restricted and environmental conditions are usually stable, a greater diversity of calcareous species occurs. The tidal mudflats have the highest diversity of calcareous assemblages with some agglutinated taxa present. Distributions of living foraminiferal populations are similar to the population distributions of dead foraminifera at both sites in the low-marsh and mudflat zones. In the high-marsh zones, however, the living-to-dead ratio and distributions are different, which could be a result of different influences of environmental variables along with seasonal variations. This study provides insights into foraminiferal distributions along the SE coastline of South Africa, which will be useful for interpreting late Holocene sea-level changes. [ABSTRACT FROM AUTHOR]

Zhou, C.Y.; Zheng, J.H.; Dong, P.; Zhang, J.S.; Zhu, Y.L., and Zhang, Z.H., 2016. Tidal evolution in the Yellow and East China Sea during Holocene. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 785-789. Coconut Creek (Florida), ISSN 0749-0208. The impact of the sea level (SL) change on the propagation of tides in the Bohai Sea, Yellow Sea and East China Sea (BYECS) during Holocene was investigated by a 3D numerical model with SL of −60, −30, −15, 0 and +2 m, respectively. Same amplitude and phase of tidal constituents M2, S2, K1 and O1 were applied along the open boundaries in all the cases. The results showed that the number of amphidromic points of M2 increased from 2 to 4 while that of K1 increased from 1 to 2 as the SL rising. Both M2 and K1 co-phase lines rotated anti-clockwise as sea-level rising. S2 shared similar evolution pattern with M2 while O1 evolved similarly with K1. The +2 m SL can have significant influence on the tide pattern. Mainly because the new basin area enlarged, especially the vast area around the Subei and Changjiang estuary, also very near the amphidromes in the south Yellow Sea, which dissipated large amount of tide energy. The new coastline and bathymetry changed the propagation pattern of M2, the tide energy decreased significantly at the north Yellow Sea and Bohai Sea while increased along the Yangtze estuary and Korea west coast. The strong tidal current area corresponded well with the sand ridges during Holocene while weaker tidal current area corresponded with finer muddy deposit, indicating tide force is the dominate factor controlling the bedform generation and sediment distribution in BYECS. [ABSTRACT FROM AUTHOR]

Peterson, C.D.; Stock, E.; Meyer, J.; Kaijankoski, P., and Price, D.M., 2015. Origins of Quaternary coastal dune sheets in San Francisco and Monterey Bay, central California coast, U.S.A.: Reflecting contrasts in shelf depocenters and coastal neotectonics. The San Francisco and Monterey Bay coastal dune sheets derive from similar origins in the central California coast but differ substantially in size (respectively, ~400 and ~900 km2) and age (respectively, <0.1 and >1.0 Ma). The San Francisco dune sheet is restricted to a short alongshore interval (<20 km) within a relatively straight coastline (150 km in length) that borders a broad shelf (~40 km in width). The Monterey Bay dune sheet is restricted to the Monterey Bay embayment (41 km alongshore length). The embayment includes a very narrow shelf (3-15 km in width), which is dissected by the Monterey Submarine Canyon. Generally low onshore topographic relief (<150 m elevation) likely enhanced inland transgression of Late Pleistocene dune fields in both the San Francisco and Monterey Bay areas. The locations of the dune sheets are directly related to sand accumulations in marine low-stand depocenters that supplied sand to the adjacent dune fields by eolian transport across the emerged inner shelves. The San Francisco shelf depocenter is apparently localized at a midshelf bight (−50 to −100 m elevation) that extends 25 km (east-west) offshore of a paleoriver mouth of a major river system, the Sacramento-San Joaquin River. The Monterey Bay shelf depocenter is bounded alongshore by major headlands and converging paleoshorelines (−30 to −90 m elevation) that effectively trapped littoral sand from small coastal drainages, primarily the Salinas River. High vertical rates of neotectonic deformation in the San Francisco dune sheet (0.4-1.0 mm y−1) limited dune sheet longevity and deposit thickness (5-35 m). Low uplift rates (~0.1 mm y−1) in the central Monterey Bay dune sheet permitted deposit accumulations of up to 250 m thickness. The differences in dune sheet extent, thickness, and age resulted from key differences in localized shelf accommodation space and coastal neotectonic vertical movements. [ABSTRACT FROM AUTHOR]

Brill, D.; Pint, A.; Jankaew, K.; Frenzel, P.; Schwarzer, K.; Vött, A., and Brückner, H., 2014. Sediment transport and hydrodynamic parameters of tsunami waves recorded in onshore geoarchives. In regions with a short historical tsunami record, the assessment of long-term tsunami risk strongly depends on geological evidence of prehistoric events. Whereas dating tsunami deposits is already well established, magnitude assessment based on remaining sedimentary structures is still a major challenge. In this study, two approaches were applied to deduce transport processes and hydrodynamic parameters of tsunami events from onshore deposits found in the coastal plain of Ban Bang Sak, SW Thailand: (1) The maximum offshore sediment source was determined using granulometry, geochemistry, mineralogy and foraminifera of the tsunamites, and reference samples from various marine and terrestrial environments, and (2) the onshore flow velocities and flow depths of associated tsunami waves were estimated by means of sedimentation modelling. In the case of the Indian Ocean tsunami (IOT) of 2004, modelled flow velocities of 3.7 to 4.9 m/s, modelled onshore flow depths of up to 5.5 m, and a sediment source from offshore areas shallower than a 45-m water depth-including littoral sediments transported as bedload and suspended load from the shallow subtidal zone-are in agreement with quotations based on survivor videos and posttsunami surveys. For a 500- to 700-year-old predecessor, comparable flow velocities and flow depths of 4.1 to 5.9 m/s and 4.0 to 7.5 m, respectively, were modelled, indicating a similar magnitude as the IOT 2004. Comparable values of maximum transport distance and depth of wave erosion were also found. In the case of three older tsunami candidates, dated to 1180 to 2000 cal BP, the deposits indicate partly similar source areas with water depths of less than 45 m and partly shallower source areas restricted solely to the beach. Whereas the former tsunamis are interpreted as events similar to 2004, the latter are more likely storms or tsunamis of a lower magnitude. [ABSTRACT FROM AUTHOR]

Barboza, E.G., Rosa, M.L.C.C., Dillenburg, S.R and Tomazelli, L.J., 2013. Preservation potential of foredunes in the stratigraphic record. In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.) Foredunes occur worldwide on shorelines, especially those which are wave-dominated and with moderate to high sediment supply. Pelotas Basin, located in southern Brazil, has a significant record of foredunes which are present on modern beaches as well as in the geological record. Many locations along the Holocene coastal plain of Pelotas Basin were investigated with a Ground Penetrating Radar (GPR). Foredunes are present in almost all the investigated areas. However some peculiarities were found along these areas. At some places it is still possible to see foredune morphology in the field. At these places GPR profiles show a convex ridge morphology preserved and its separation by concave, sometimes filled swales. At other sites foredunes are covered by transgressive dunes, the morphology is not preserved and erosive surfaces are found on the top of the unit. Along the progradational sectors, dip profiles show that even where foredunes have their morphology preserved, some erosive scarps are found at the seaward face. These patterns indicate that high frequency events lead to the erosion of foredunes. The combination of sedimentary budget with climatic events sets foredune preservation and its pattern. Where sedimentary budget is high, progradation occurs faster and foredunes are preserved. However, where the sedimentary budget is not very expressive, the progradation is slower and part of the foredune is destroyed forming transgressive dunes or sand sheets. [ABSTRACT FROM AUTHOR]

The Florida Middle Ground is a complex of north to northwest trending ridges that lie approximately 180 km northwest of Tampa Bay, Florida. The irregular ridges appear on the otherwise gently sloping West Florida shelf and exhibit between 10-15 m of relief. Modern studies interpret the ridges as remnants of a Holocene coral-reef buildup that today provide a hard substrate for growth of a variety of benthic organisms including hydrocorals, scleractinians, alcyonarians, and algae. Recent rotary coring reveals that the core of the eastern ridge of the Florida Middle Ground complex consists of unconsolidated marine calcareous muddy sand that is capped by a boundstone composed primarily of the sessile vermetid gastropod Petaloconchus sp., and overlays a weathered, fossiliferous limestone. Accelerator Mass Spectrometry radiocarbon ages (uncalibrated) on the 3.6-m thick vermetid worm rock indicate that it developed during a sea-level stillstand in the early Holocene (8,225 ± 30-8,910 ± 25 yr B.P.). Our observations suggest that the Florida Middle Ground is a remnant of a series of shore parallel bars that formed in the early Holocene and were capped by a 3.6-m thick unit of vermetid gastropods. During a rapid sea-level rise that began ~8,000 yr B.P. the vermetids growth ceased and the worm rock preserved the ridges structure. Diver observations document that the edges of the ridges are currently being eroded and undermined by biological activity and current action, leading to calving of large capstone blocks. [ABSTRACT FROM AUTHOR]

Seven tephra layers in the submerged fill of the Lower Columbia River Valley (LCRV) are radiocarbon dated (0.5-13 ka in age). They are correlated to reported eruption sources in the adjacent Cascade Range volcanic arc. The tephras provide a stratigraphie framework for the transgressive depositional filling of the tidal Columbia River system (~200 km in length). The thickest and most continuous tephra marker beds in the LCRV are from the Mount Mazama set-0 eruption at 7.7 ka. The eruption source for this tephra (1-10 m thick) is confirmed by glass geochemistry and radiocarbon dating of borehole samples from depths of -13 to -38 m (North American Vertical Datum of 1988 [NAVD88]). The Mazama set-0 tephra conveniently divides the depositional sequences of the Early Holocene from the Late Holocene in the deep valley fill (50-120 m axial valley depth). A much deeper tephra, at -84 m, is attributed to Mount St. Helens set-S/J eruptions at ~13 ka, which confirms the end of the Glacial Lake Missoula Flooding in the LCRV. Late Holocene tephra marker beds in the LCRV include the Mount St. Helens set-J/P eruptions (2.5-4.0 ka),set-W/T eruptions (~AD 1480), and an intermediate-depth tephra, attributed to a Mount St. Helens or Mount Adams eruption (~1.3 ka).The Late Holocene tephras date the ages of tidal flats and extensive floodplains throughout the length of the LCRV. The Late Holocene marker beds provide the first widespread constraints on wetland sedimentation rates and preservation potentials for archaeology sites in the LCRV. [ABSTRACT FROM AUTHOR]

The Ensenada de la Colonia embayment, NE Tierra del Fuego, presents an extensive and wide Holocene beach ridge plain composed of gravel and coarse sand. These deposits have revealed a regressive behavior since 6000 years BP. A Pleistocene gravel beach ridge plain was recognized in the area. Several erosive scarps are present at the embayment, indicating strong and episodic erosive events. Seaward and immediately behind the present storm berm, a high and unique overtopping fan develops. Tierra del Fuego is a seismic area, and the subduction zone of the South Sandwich Islands constitutes a potential source of tsunamis. The abrasion platform of embayment shows a glacifluvial carved paleomorphology. This feature conditions the wave refraction pattern, concentrating the orthogonal rays in its central section. In this setting, a tsunami backwash could generate megavortexes in the nearshore zone of the bay linked to the depressed areas of the abrasion platform. The combined action of large seepage, tsunami backwash currents, and tangential currents of the vortex applied on saturated gravel beaches would cause carving of the lower section of the beach and instability of the entire profile. Then collapses of relevant volumes of gravel and sand would lead to the formation of semicircular erosive scarps. The overtopping fan architecture displays a sequence of three to five landward onlapping radar facies of overwashing and overtopping events. The semicircular erosive scarps and the overtopping fan were created by tsunamis that reached the Atlantic coast of Tierra del Fuego. At least three pulses of a unique tsunami episode constructed the overtopping fan. [ABSTRACT FROM AUTHOR]

Barrier islands in sheltered settings are rare coastal geomorphic features. Here we present a case study of controls on the evolution of Tapora Island, North Island, New Zealand. Tapora Island is an active barrier island located opposite the entrance to the Kaipara Harbour on a high-energy coast. Subsurface facies form an aggradational barrier island succession from subtidal to subaerial elevations. This facies succession, combined with surface samples and geomorphic and geologic relationships, indicates that Tapora Island is the most recent barrier island at this location in the estuary and forms part of a prograded coast opposite the entrance. Wave data indicate that ocean swell waves penetrate the inlet for approximately 2 hours either side of high tide and are capable of transporting sand onto the island. The combined effects of swell waves, abundant sediment supply, and exposed aspect are the critical factors that have formed the barrier island. Despite the ''sheltered' estuarine setting, Tapora Island has formed under conditions that are more akin to open ocean coasts. The origin and development of Tapora Island broadly conforms to the accumulating barrier island model. [ABSTRACT FROM AUTHOR]

Coastal dune systems are very sensitive geoindicators that reflect rapid geological change and its environmental consequences. Detailed analysis of the long-term trends in the dynamics of the shifting Holocene dunes using satellite images and ground survey data revealed that during the 20th century, erosion, flattening, and sylvanization of the dunes along the entire 33-km length of the still-active Great Curonian dune ridge was taking place at a very rapid rate and scale. Flattening of the shifting dune ridge because of exhaustion of sand supplies, plant succession, and human activity is the main dune management problem, important both for the maintenance of landscape diversity and for the conservation of the traditional heritage features of the Curonian Spit as a World Heritage site. A radical shift in dune-handling paradigm-from forestation to the removal of pine plantations—and the enhancement of dune dynamism is critically needed for the protection of the Great Curonian shifting dune ridge. [ABSTRACT FROM AUTHOR]

The Loxahatchee River, a 500 km2 watershed on the southeast Florida coast, is a barrier-impounded drowned river valley experiencing rapid urbanization during the past 50 years. The estuary is currently composed of a sandy central basin with bifurcating forks accumulating organic-rich muddy sands. The Northwest Fork drains natural forest, residential, and agricultural catchments and has a much larger bayhead delta than the channelized Southwest Fork, which is only 50 years old and diverts much of the flow from the Northwest Fork. Sediment accumulation rates within muddy sand deposits are about 2-3 mm a-1, commensurate within error of the current rate of local sea-level rise. Previously established Holocene accumulation rates are close to relative sea-level rise, implying that sediment accumulation is in equilibrium with the creation of accommodation space. The main anthropogenic influences have been changes in surface sediment texture corresponding to dredging-induced modification of tidal currents and a localized>threefold increase in sediment accumulation rate supplied by sources local to the estuary. Late Holocene sedimentation has been episodic, and lithofacies vary from bioturbated transgressive sands at depth to peat and laminated fine-grained sediments then back to mottled muddy sands in the uppermost strata. This facies transition is attributed to a change of water column stratification conditions caused by decreased tidal flushing in the estuary possibly brought about by variation in sea level or episodic inlet closure by littoral sand transport. The magnitude of the anthropogenic changes in sedimentation is roughly equal with natural changes in lithofacies formation. [ABSTRACT FROM AUTHOR]

Optically stimulated luminescence (OSL) dating of quartz grains extracted from beachrock on the southeast coast of India was attempted. Preliminary OSL ages of beachrock indicate that during the Late Holocene (3.6-2.1 ka) sea level along this coast was higher than at present. This observation is broadly consistent with the existing data based on radiocarbon dating of bioclasts in the beachrock, which suggests a higher sea stand during 4.3-2.3 ka. This study demonstrates the potential of optical luminescence dating of beachrock for refining sea-level chronology and shoreline evolution on the southeastern coast of India. [ABSTRACT FROM AUTHOR]

Sediment cores (up to 6 m in length) from the bottom of the Blue Hole, a 125 m deep Pleistocene sinkhole located in the lagoon of Lighthouse Reef Atoll, Belize, consist of undisturbed, annually layered biogenic carbonate muds and silts with intercalated coarser grained storm beds. The sedimentation rate of the layered sections is 2.5 mm/y on average, and the long cores span the past 1500 years. Oxygen isotopes of laminated sediment provide a late Holocene climate proxy: A high-resolution δ18O time series traces the final Migration Period Pessimum, the Medieval Warm Period, the Little Ice Age, and the subsequent temperature rise. Carbon isotopes (δ13C) decrease up core and show the impacts of the decline of the Mayan culture and the Suess effect. Time series analyses of δ18O and δ13C content reveal 88-, 60-, 52-, and 32-year cyclicities, and suggest solar forcing. Storm event beds are most common during AD 650-850, around AD 1000, during AD 1200-1300, and AD 1450-1550. Major storm beds are rare during the past 500 years BP. [ABSTRACT FROM AUTHOR]

During the Holocene, the western part of the present-day Thessaloniki coastal plain (north-central Greece) was flooded by the rising sea level and formed a bay as a consequence of the last postglacial transgression. The rate of the sea-level rise subsequently decelerated, and this bay began to fill with sediments delivered by the Aliakmon and Axios, as well as by other smaller rivers. The palaeogeographic and palaeoenvironmental reconstruction of the Thessaloniki Plain was the focus of several studies published during the past century. Most of these studies are based on the interpretation of historical sources and support the assumption of a fast filling of the bay between the fifth century BC and the fifth century AD. In this work, we first present the results of the analysis of data collected from six boreholes recently drilled in the western part of the plain, up to the western bank of the Axios River. Our study was mainly based on sedimentological and palaeontological analyses and accelerator mass spectrometry and conventional radiocarbon dating of shells and peat. Second, we evaluate the results of this study, as well as of other geological studies, which permit the description of the large-scale stratigraphic pattern of the plain. Data were evaluated on the basis of a geographic information system, used for the first time in such type of work, and were supplemented and assessed with analysis of Landsat imagery. Based on this evidence, we propose a new, detailed palaeogeographic reconstruction for the evolution of the Thessaloniki Plain during the Late Holocene. This plain corresponded to a wide marine bay during the Neolithic times (6000 BP), and later it was characterised by a fast displacement of the shoreline, mainly during Late Bronze Age, Iron Age, and Classical-Archaic periods (2650-2300 BP). A slowing down of the progradation of the alluvial plain occurred during Roman times (2100-1600 BP), and the plain obtained its present-day topography during the second part of the 20th century. [ABSTRACT FROM AUTHOR]

A 3.5-m gravity core (DJ6-93SF-6) from San Francisco Bay reveals a complex paleoclimatic history of the region over the last 3870 cal YBP. A polynomial equation based on 11 AMS 14C ages provides an excellent age model for the core, and environmental proxies for water temperature and salinity are derived from various foraminiferal abundances, stable carbon and oxygen isotopes, and Mg/Ca ratios. Two foraminiferal associations were identified by Q-mode cluster analysis: a colder-water Elphidium excavatum association and the warmer-water Ammonia beccarii-Elphidium gunteri association. The E. excavatum association dominates the core for all but about 600 years out of the last four millennia. At 3870 cal YBP, water temperatures were warm (13.9°C) and freshwater inflow was reduced compared with today. From 3590 to 2860 cal YBP, temperatures dropped 0.5°C and the climate remained dry. This was followed by a period of pronounced lower δ13C values, indicating that conditions became considerably wetter from 2860 to 2170 cal YBP. During this interval, the temperature oscillated frequently, peaking at 13.9°C at 2710 cal YBP, then dropping shortly thereafter to 12.8°C at 2420 cal YBP. Freshwater inflow gradually decreased between 2170 and 1950 cal YBP with a minimal rise in temperature, then changed quickly to colder and wetter conditions at 1900 cal YBP. Drier conditions then prevailed until 1480 cal YBP with water temperatures fluctuating between 13.1°C and 13.8°C, followed by wetter climate from 1480 to 1320 cal YBP. A significant faunal shift from the E. excavatum association to the A. beccarii-E. gunteri association occurred from 1250 to 650 cal YBP, possibly due to regional warming, decreased oxygen availability, and/or a change in the phytoplankton community. Associated with this change in faunal composition were warm and dry conditions, representative of the Medieval Warm Period (Medieval Climatic Anomaly). A climatic shift coincident with the onset of the Little Ice Age (LIA I and LIA II) is evident from 650 to 280 cal YBP, with the return of the E. excavatum association and an extreme drop in δ18O values, all indicating increased precipitation and fresh water inflow. This was followed by generally drier conditions to the present, except for a brief wet period around 100 cal YBP, and fairly consistent water temperatures in the middle 13°C, except for a drop to 12.8°C at 200 cal YBP. Two significant faunal changes occur near the top of the core. First, there is the reappearance of the A. beccarii-E. gunteri association, suggesting that, once again, regional warming has taken place, oxygen availability has declined, and/or environmental conditions changed such that diatoms have become a scarce food source. Second, there is the first appearance of the invasive Japanese foraminifera Trochammina hadai Uchio, a species that commonly lives in highly polluted areas and is an indicator of eutrophication in its native estuaries. At the same time, freshwater inflow decreased, which may be explained by global warming during the last 100 years, or more likely due to modern water diversion for agriculture in the central valley of California. [ABSTRACT FROM AUTHOR]

The northwestern coastal zone of Portugal between Mondego cape and Minho River preserves a series of fluvio-aeolian, lagoonal, and dune formations that are archives of evolution during the late Pleistocene and Holocene. The existing chronology of these formations is based mainly on radiocarbon dating of in situ organic materials. In this study, we present the results of optically stimulated luminescence (OSL) dating of these formations and discuss their implications for the existing chronostratigraphy, climate, and neotectonic changes in this area since the late Pleistocene. Three major periods of aeolian activity have been identified based on the OSL ages and are bracketed to 25-14 ka, 9.9-3.4 ka, and 1.4-0.1 ka. These OSL ages suggest intense sand deposition during oxygen isotope stage 2, the mid- Holocene, and the Little Ice Age. The dune ages in the last 500 years provide temporal constraints on the initiation of coastal erosion in the area. Further, the chronostratigraphic correlations suggest tectonic uplift in the coastal sections, between ca. 17 ka and 14 ka, and erosion due to eustatic sea-level rise. [ABSTRACT FROM AUTHOR]

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Clay mineral analysis was conducted on the fine-grained sediments of a 20-meter core of Late Quaternary deposit in the south-central portion of the modern Chanjiang delta plain to understand and characterize paleoenvironmental depositional conditions. Four clay mineral suites (Zones I to W) were recognized in the core. The lowest level (Zone I, Late Pleistocene) of kaolinite (48%) and illite (45%) is representative of a pedogenic formation of alluvial environment. The next upper suite (Zone II, Early Holocene) of kaolinite (44%) and chlorite (22%) is related to an erosional coastal environment associated with an encroaching sea level. The suite (Zone III, Early to mid-Holocene) overlying Zone II incorporates the addition of smectite (6%), the abundance of which is closely linked to the topographic change and the relative sea level fluctuation in the study area. The uppermost suite (Zone IV, Late Holocene) of illite (53%) and smectite (7%) accumulated during the period of major deltaic progradation and presents a change of sediment source from the more local western highlands to the regional Changjiang River basin. Significant variations in the clay mineral signatures support concepts of morphologic change from a subaerially exposed area to the present depression-centered southern Changjiang delta plain during the Holocene as the delta margin was affected by sea level rise and sediment supply and source. [ABSTRACT FROM AUTHOR]

The distinctive blue hole terrains of the Houtman Abrolhos reef complex have been previously interpreted as the result of karst processes controlling Holocene reef growth and morphology. The apparent intensity of karst modification, indicated by the abundance and density of blue holes, steered the general perception of the reef complex as one that was stressed and marginal for Holocene coral growth. This view is commensurate with the high-latitude location (28°–29° S) of the reefs. Through an investigation of the reef morphology, lithe and seismic stratigraphy, and the growth chronology of these reef complexes, we demonstrate that the blue hole terrains of the Houtman Abrolhos are not karst features but are growth forms that are characteristic of these reefs. [ABSTRACT FROM AUTHOR]

An extended period of marine-dominated back-barrier sedimentation, truncated by the deposition of two large-volume, laterally extensive sand sheets that extend up to 3 km inland from the modern coastline, is present at Minnamurra in southeastern Australia, The sand sheets are anomalous as they drape the entire back-harrier succession and infill the estuary. The lower sand sheet contains mud clasts and significant amounts of organic matter including coastal dune grasses indicating that significant overwash and erosion incorporated material from both the barrier and estuary into the lower sand sheet deposit. The first sand sheet is overlain by a poorly developed soil that records a time break before the now infilled system was inundated once more. The second sand sheet covers the poorly developed soil and incorporates a number of erosional features, such as ripped-up soil clasts, cobbles, and organic-rich sand. Along this part of the coast, large laterally extensive sand sheets are spatially and sedimentologically unique, occurring only in embayments that face southeast. This, along with a lack of evidence of wave action or beach structures, suggests that the deposits are not evidence for higher Holocene sea level hut are the result of overwash sedimentation from the southeast. The sand sheets share many of the characteristics of those emplaced by tsunami waves, although the possibility of exceptionally large storm events cannot he entirely discarded. However, such a storm would have to be several orders of magnitude higher than those in recorded history. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Coastal Research is the property of KnowledgeWorks Global, Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper illustrates an integrated physical-biological approach toinvestigate the effects on the coastal environment of the construction of a large embankment along the shore of Monterosso Bay, NW Italy.The embankment protrudes from the natural shoreline for more than 100 meters and has deflected the longshore current toward the offshore,as indicated by grain-size and mineralogical areal distributions of bottom sediments, and by the orientation of bedforms. Consequently, the downcurrent portion of the beach relative to the embankment has become sediment-starved and the site of finer-grained sedimentation, and severe shoreline retreat has occurred, as indicated by sequential analysis of topographic maps and by the comparison of non-parametric photographs. This trend is recorded by the areal distribution of two seagrasses (marine phanerogams) along the bay: Posidonia oceanica-whose slow growth requires stable environmental conditions and a preference for coarse-grained sandy substratum-is present as dense and healthy meadows in the upcurrent portion of the bay whereas Cymodocea nodosa-an opportunistic, pioneer species capable of surviving in stressfulenvironments-is present only along the downcurrent (eastern) portionof the bay where it is replacing a progressively retreating Posidonia meadow. This is substantiated by (i) direct underwater observation of the remnants of a dead P. oceanica meadow along the eastern portion of the bay and (ii) interviews with the local population pointing to a more extensive Posidonia meadow along the eastern portion of the bay prior to the construction of the embankment. Thus, biological parameters such as the density and health of marine phanerogams match physical parameters (grain-size distribution patterns) more traditionally employed in coastal studies and can provide significant clues on both natural and anthropogenic medium-term coastal dynamics. [ABSTRACT FROM AUTHOR]

Freitas, M. C., Andrade, C., Ferreira, T., Cruces, A. and Araújo, M. F. 2007. Wet dune slacks, sea-level and coastal evolution in the south-western Portuguese façade. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 231 – 236. Gold Coast, Australia, ISSN 0749.0208 Dune slacks are peculiar features of the Portuguese coast with evident scenic, ecological and geological value and yet the existing knowledge on their origin, evolution and dynamics is poor. A number of wet dune slacks in the South-western Iberian coast (Poços do Barbaroxa and Lagoa da Sancha) have been studied using sedimentological and geochemical proxies which, coupled with radiocarbon dating, were allowed to establish major steps of coastal evolution, environmental changes and relations with sea-level throughout the Holocene. The Barbaroxas basins are blind freshwater lakes while Lagoa da Sancha is, at present, connected with a small rivulet. The size and shape of interdune depressions reflect a palaeotopography inherited from a ridge and swale complex that accreted seaward in the Pleistocene. The interdune infill consists essentially of peat resting upon dune sand; accumulation of organic material initiated diachronically in the different slacks, between circa 7700 and 4160 cal BP, in dependence of piezometric level. At Barbaroxas this organic facies persisted until present, whereas at Lagoa da Sancha it was replaced circa 670 cal BP by minerogenic sedimentation. At the present state of knowledge it is unclear if this change represents a capture of the tributary stream, either natural or man-induced, or a massive release of top soil due to contrasting land-use in the watershed. At present, the peat surface in Barbaroxas stands 1 to 2 m above mean sea level and is fairly horizontal. Assuming similar relation in the past, then sea level should have been positioned at -3/-4 m and -0.5/-1.5 m by 7400 and 4100 cal BP, respectively. These figures are consistent with the most recent sea-level data published for the Portuguese coast. [ABSTRACT FROM AUTHOR]