Barrier-lagoon Systems Research Articles

Sedimentary facies and environments of the Upper Jurassic (Kimmeridgian-Tithonian) Nakanosawa Formation of the Somanakamura Group in Fukushima Prefecture, Japan: transition from siliciclastic wave-dominated shallow-marine to carbonate barrier-lagoon systems

相馬中村層群中ノ沢層（上部ジュラ系）の館ノ沢砂岩部層は，砂質河川成の栃窪層に波浪ラビンメント面を介して重なる海進残留相から始まり，外洋浅海から内湾-ラグーンに至る上方浅海化を示す，海退性の砂質堆積物であり，数回の小規模な振動を伴う相対海水準の緩やかな上昇期に，珪質砕屑性堆積システムが前進することによってできた．小池石灰岩部層は，珪質砕屑物供給が停止することで成立した炭酸塩バリア-ラグーンシステムとして，東西数 km南北10 km超の炭酸塩プラットフォームを構成していた．分布全域に追跡される5層の上方細粒化堆積相累重（層厚数－10数m）は，バリア浅瀬→浅瀬後背→ラグーンへの変化をもたらした，5回の小規模な相対海水準変動による海退-海進の繰り返しで形成された．中ノ沢層はキンメリッジアンからチトニアン前期の第2オーダー高海水準期に，第3オーダー海水準変動周期に対応して形成された可能性が指摘される．

Genesis of a coastal aquifer in the coastal plain of the Pelotas Basin, southern Brazil: Implications for stratigraphic evolution

In the coastal plain of the Pelotas Basin, southernmost Brazil, a granular aquifer close to 70 m deep, formed by coarse and angular sediments, caught the attention of drillers, who gave it the suggestive nickname of “Coarse Salt” (“Sal Grosso”). Despite being almost unknown in geological and stratigraphic terms, the aquifer has been increasingly used to supply the growing coastal population. Considering that stratigraphic knowledge is essential for the management of groundwater resources, we sought to understand the configuration of this aquifer and investigate its genesis based on drilling samples from 29 groundwater wells and through 19 vertical electrical soundings. The sedimentary record investigated has an approximate thickness of 100 m, and is formed by three units, interpreted as: alluvial (where the aquifer is located), marine and coastal barriers. The analysis of the sediments that make up the Coarse Salt (Sal Grosso) aquifer led to the interpretation that the investigated region represents the distal (fluvial) portion of an alluvial system. Spatially, the aquifer constitutes an elongated feature in the NW-SE direction, perpendicular to the current coastline. The geometry and sedimentology led to the interpretation of a paleochannel, responsible for the transport of sediments from the granitoid rocks of the Sul-Riograndense Shield, associated with the paleodrainage system of the Jacuí River. A greater stratigraphic variability present in wells closer to the continent, with intercalation of continental and marine deposits, indicated the position of a coastline, prior to the formation of the coastal barrier unit, which is the predominant depositional system in the actual coastal plain. The stratigraphic analysis resulted in the paleogeographic model corresponding to a complete depositional sequence, indicating that the Coarse Salt (Sal Grosso) aquifer was formed during a lowstand. Later, a marine transgression allowed the deposition of a thick bundle of muddy sediments, which constitutes an important protection to the aquifer. Afterwards, the coastline started to prograde, with the development of the barrier-lagoon systems in a highstand/falling stage systems tracts context. The understanding of stratigraphy generates framework for decision-making that enable better management of this groundwater resource.

Quaternary Coastal Landscape Evolution and Sea-Level Rise: An Example from South-East Sicily

Coastal depositional environments are the site of complex interactions between continental and marine processes. Barrier islands are highly dynamic coastal systems, typical of these transitional environments, and are affected by sea level changes and the accumulation of transgressive deposits with the landwards migration of the coast. The offshore of Marzamemi (Syracuse Province, Sicily), in the south-eastern portion of the Hyblean foreland, represents an excellent site for the study of transgressive deposits and their connection with the sea-level changes. The available dataset consisted of new high-resolution bathymetry (Multibeam), whose description and interpretation through a Digital Elevation Model (DEM) was integrated with a grid of eighteen seismic profiles (SPARKER). In the investigated bathymetric range, from about −5 m to −60 m, a sensibly different morphological setting between the northern and southern sectors was evident. Within the whole study area, three bathymetric contours (−45 m, −35 m and −20 m) were identified and assumed as the markers of the main locations of the paleo-coastlines during the recent changes in the sea level. Along the northern sector, three submerged barrier-lagoon systems developed on a calcarenite substratum, marking important steps of the Late Quaternary sea-level rise. They coexisted with numerous karst forms (poljes and dolines). In the southern sector the transgressive environmental evolution was significantly different and submerged lagoons did not form. Here the outcropping calcarenite substratum was affected by the development of paleo-rivers and karsts structures, a tract in common along with many Mediterranean carbonate coastal areas.

The Santa Vitória Alloformation: an update on a Pleistocene fossil-rich unit in Southern Brazil

The Santa Vitória Formation is a lithostratigraphic unit known for its fossil assemblage of Pleistocene mammals, established in 1973 from sediments exposed along the banks of Chuí Creek, in the southern coastal plain of the state of Rio Grande do Sul (CPRS), Brazil. The original description was presented in a Masters’ dissertation and never formally described in a peer-reviewed publication. Moreover, surveys and fossil collecting efforts developed in the last decade have led to a better understanding of its origin and nature. An updated description of this unit is presented here, which outcrops in areas occupied by barrier-lagoon depositional systems originated by eustatic oscillations. The formation encompasses Middle-Upper Pleistocene fluvial and eolian depositional systems and paleosols formed chiefly of fine to medium quartz sand, with subordinate clay, concentrations of iron and manganese oxides, and caliche nodules of pedogenic origin. It conformably overlies upper shoreface-foreshore marine deposits, and is overlain by loess deposited during the last glacial period. Here is proposed to re-define it as Santa Vitória Alloformation, considering that the use of an allostratigraphic framework to characterize this unit has the practical purpose of grouping depositional systems genetically unrelated to the barrier-lagoon systems.

Rauk - A Forgotten Witness of Holocene Sea-level Change and Development of Baltic Rocky Coasts: A Pilot Geomorphological Study in Lergrav Raukar Field

Strzelecki, M.C.; Duszyński, F.; Tyszkowski, S.; Zbucki, Ł., and Kasprzak, M., 2020. Rauk - Forgotten witness of Holocene sea-level change and development of Baltic rocky coastal zone: A pilot geomorphological study in Lergrav raukar field. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 659–663. Coconut Creek (Florida), ISSN 0749-0208.The Holocene history of Baltic Sea evolution is definitely one of the most interesting and intriguing stories of environmental change in Europe. To date, the key information on changes in sea-level and shifts in the environment associated with climate fluctuations were found in coastal lakes, marshes and wide stripe of barrier-lagoon systems of southern Baltic. Only limited research was conducted along rocky coasts, so characteristic features for Baltic islands from Bornholm, through Oland, Gotland, Fårö, Hiiumaa, Saarema to thousands of isles of Åland Archipelago. Among the most thrilling natural wonders found along Baltic coasts are rauks or raukars, unique limestone stacks—often with humanlike features—that tower above rocky shore platforms in northern Gotland and on Fårö, Gotland's sister island. Raukar coasts are one of the greatest touristic attractions in Sweden and the mythical coastal landscape of northern Gotland and Fårö had inspired many artists, including Ingmar Bergman. Surprisingly, what attracts tourists and artists, have been neglected by geomorphologists and those fascinating landforms still wait for detailed explanation of their origin and preservation. This paper provides insight into pilot geomorphological study of raukar coast in Lergrav, NE Gotland. Schmidt hammer rock tests were applied to characterize the degree of weathering of rock surface of well-preserved notches. The results of notch rock surface resistance and elevation above present sea-level are discussed with recent relative sea-level curves developed in the region.

Geological and taphonomic significance of electron spin resonance (ESR) ages of Middle-Late Pleistocene marine shells from barrier-lagoon systems of Southern Brazil

The Coastal Plain of Rio Grande do Sul state (CPRS), southern Brazil, encompasses Quaternary barrier-lagoon depositional systems developed in response to successive marine transgressions driven by glacial-interglacial cycles. As an attempt to refine he chronostratigraphy of the Pleistocene depositional systems, electron spin resonance (ESR) ages were obtained in 42 disarticulated shells of the marine bivalve Amiantis purpurata preserved in deposits in the southern CPRS, consisting of 35 specimens from five boreholes made during the construction of wind farms, plus another 7 shells from an irrigation channel. The shells were obtained from depths between 5.5 and 14 m, in two chronostratigraphically distinct depositional units (Barrier-Lagoon Systems II and III). Although the ages in each group of samples vary widely, the youngest age from the Barrier II (~247 ka) is consistent with the timing of the transgression of the marine isotope stage (MIS) 7 inferred from other luminescence and ESR ages of sediments and shells. The ages obtained in shells from the Lagoon III deposits located landward of the Barrier III indicate deposition by the sea-level highstand of the substage MIS 5e, despite being older than the estimated age of ~120 ka of the latter. The younger shells from the seaward side of the Barrier III dated as of ~100 ka indicate deposits formed by the low-amplitude MIS 5c highstand, in agreement with luminescence ages of ~109, 104 and 101 ka obtained in outcrops on the shoreline. One shell dated as ~87 ka could indicate another highstand during MIS 5a. The presence of shells much older than the depositional systems indicate that marine deposits older than MIS 7 existed in the CPRS but were totally eroded by subsequent transgressions, and that shells can be preserved for periods of about 100–200 kyrs under certain conditions. Moreover, the ages younger than the highstand of MIS 5e on the seaward side of the Barrier III indicate that one (and possibly two) smaller amplitude highstands previously unrecognized in the CPRS left geological and fossil records in the study area.

What is the topset of a shelf‐margin prism?

AbstractThe siliciclastic topset of a continental margin, or a shelf‐margin prism in subsiding nonplate‐margin deepwater basins, is the flat‐lying upper part of the margin succession; it is coeval basinwards with deepwater slope clinoforms. Topsets develop by the aggradation of repeated, cross‐shelf, shoreline regressions and transgressions, thereby hosting the shelf portion of stacked, fourth‐order stratigraphic sequences. Sediment spreading downdip and along strike during the cross‐shelf transit of the sediment delivery system, as well as process regime changes of deltas and shorefaces (regressive) and of estuaries, barrier–lagoon systems and shelf ridges (transgressive) are highly variable over short distances, so that correlation within a single stratigraphic sequence is far more difficult than correlation of the cross‐shelf maximum flooding surface boundaries. Thickness of individual regressive–transgressive, fourth‐order sequences is given by shelf accommodation, typically <10 m in embayment or on the inner shelf and up to 200 m on outer shelf. Tectonic subsidence and compaction will enhance this thickness only if rates are very high compared to shelf‐transit time. In very high subsidence rate settings, the transgressive tracts are well preserved and often thickly developed. Topset sequences in an Icehouse climate setting tend to have a high proportion and greater landward development of marine vs nonmarine deposits, compared to Greenhouse sequences, because of the importance of eustatic rise of sea level in the former. Previous numerical experiments show that even for very wide shelves and irrespective of Icehouse or Greenhouse conditions, deltas rarely take more than 10 s of ky to reach their shelf edge, suggesting that it is fourth‐order (or higher) sequences that are the fundamental ones in sequence stratigraphy.

Anatomy of a transgressive tidal inlet reconstructed through high-resolution seismic profiling

Although the morphology and morphodynamics of modern tidal inlets have been analysed in a wealth of studies, these systems can be considered representative only for highstand conditions, while little is known about the characteristics and evolution of their transgressive counterparts. Through the analysis of high-resolution seismo-acoustic profiles, this work investigates a rare example of a preserved filled tidal inlet formed during the early Holocene on the continental shelf of the northern Adriatic Sea. The quantity and quality of the available data allowed a detailed reconstruction of the morphology and internal architecture of this feature. This 1.2 km-long, 17 m-thick channelized scour formed in a microtidal environment between 9.0 and 9.5 kyr cal BP. The tidal prism is estimated to have been ca. 4.4 × 107 m3. The internal geometry of the filling material shows no evidence of migration of the inlet, which lasted only for a few centuries and was soon after drowned by the sea transgression. This rapid evolution is in contrast with the millennial-scale lifespan of most of the modern highstand lagoon systems. This work provides a new outlook on the evolution of tidal inlets during phases of marine transgression and in relation to variable rates of sea-level rise. In many cases, paleo tidal inlets are the only witnesses of the presence of transgressive barrier-lagoon systems which had been completely eroded by the wave action after their submersion. These features represent therefore an important proxy to infer the position of the related coastline and to constrain the past relative sea level.

The Use of Heavy Minerals in the Investigation of Barrier-Lagoon Coasts Development in Dapeng Peninsula, China

Typical barrier-lagoon systems are developed at Dongchong and Xichong on the southern coast of the Dapeng Peninsula of Guangdong, China. This paper studies the evolution of the barrier coasts of the peninsula, using the examples of the Dongchong and Xichong Bays. The Holocene stratigraphic records from borehole drilling on the coast of Dongchong and Xichong show that lagoon sediments are overlaid with beach deposits, indicating that the barriers migrated landward and climbed over the lagoon sediments when the shoreface retreated during the Holocene transgression, reaching the present positions after 7–8 ka BP. Heavy mineral analysis in this paper shows that: (1) the ancient beach sediments of the two bays have the same heavy mineral assemblages, which are different from those of modern beaches; (2) the present beaches of the two bays have different heavy mineral assemblages, even they are located less than 3000 m from each other on the same coast. This supports the hypothesis that the barriers originally came from the inner shelves during the Holocene transgression, but draws a new conclusion that the source of the beach sediments changed to inland rivers over the last thousand years because of a lack of sediment source from the sea floor.

Identification of the agonist of trace amine-associated receptor 5 (TAAR5) and its action on brain physiology and neurochemistry

New geological analysis of the Ravenna coastal plain has allowed a major update of the geological coastal model, with anthropogenic overprints removed from an area heavily affected by human actions in the last four centuries, a period in which the Little Ice Age (LIA) has had a large influence on the coastal dynamics. The geological build-up of the coastal plain is a natural occurrence that is important for understanding the present-day coastal buildup. However, coastal zone anthropization has defined the actual coastal morphology, canceling out most of surface expression needed to create an accurate coastal evolution model, as the beach ridges morphology in the study area. As the lack of surface expression due to the anthropogenic actions has changed the coastal zone under study, it is not possible to only use geomorphological analysis to construct a local coastal evolution model. Because of this, building a new model and understanding how coastal evolution would proceed without human influence would allow us to understand the interaction between natural forces and anthropogenic influence, which has acted to shape the actual morphology of the study area from the LIA period to the present days. We therefore propose an integration of data using the following: actual data from the surface, such as the high-resolution digital surface model (DSM) and the digital terrain model (DTM); the actual database from the Emilia-Romagna Region Geological Survey, including the shapefile with the regional soil chart and the geological elements present in the study area; knowledge from previous work carried out in the area; and the subsurface data from Ground Penetrating Radar (GPR), which would make the study the first to use a GPR survey of the coastal plain of the northwest Adriatic. In addition, the work will follows a successful case study done in the southern Brazilian coastal plain that integrated previous works done in the coastal plain with new methods such as GPR data acquisition. The GPR data allows for corroboration of the interpretation of the coastal model constructed using the surface data. Finally, the surface geological model proposed in this work may aid by providing the following: i) a new means for local coastal geology research; ii) a methodology to apply to other barrier-lagoon systems around the world in order to update our knowledge about these systems; and iii) powerful information to support coastal managers and decision makers in constructing a long-term master plan for effective Integrated Coastal Zone Management.

Stratigraphic modeling of a transgressive barrier-lagoon in the Permian of Paraná Basin, southern Brazil

Barrier-lagoon systems occur in most coastal regions worldwide. The sedimentary record of these environments is of scientific and economic relevance because important coal deposits are associated with them. We show the evolution of an ancient coal-bearing barrier-lagoon system in the subsurface on the southern Paraná Basin, Brazil, from a stratigraphic modeling approach. The main objective is to simulate and understand the origin and evolution of this system controlled by relative sea level changes and sediment supply. Database comprises 75 logged boreholes that provided data about the main coal bed deposited in the back-barrier, as well as 19 cored and logged boreholes distributed along two stratigraphic sections, one parallel (NE-SW) and another perpendicular (NW-SE) to the paleocoastline. The dataset was uploaded in the Diffusive Oriented Normal and Inverse Simulation of Sedimentation (DIONISOS) software to establish basic parameters and simulate different scenarios. Described facies are interpreted as swamp, lagoon, sandy barrier and tide-influenced deposits, developed during a relative sea level rise of 16 m. The coal bearing succession was deposited during the transgressive system tract of fourth-order depositional sequence and included peat deposition in a swamp in the back-barrier, barrier breakup and landward migration. Results are of high relevance for understanding this paleoenvironment evolution and similar systems in intracratonic basins. This environment occurs both in ancient and recent coasts, and the present model supports the understanding of several barrier-lagoon systems with coal formation in the world.

Socio-ecological adaptation to Early-Holocene sea-level rise in the western Mediterranean

Consecutively to the global sea-level rise, coastal landscapes significantly changed during the Early Holocene. We explored how coastal mutations have affected ancient human systems in the western Mediterranean. The Pego-Oliva basin (Spain) provides a thick sediment sequence located in proximity to two well-studied Mesolithic and Neolithic archaeological sites. Based on 16 sediment cores, sedimentological analyses, 14C dates, and integration of previous works, we reconstructed the architecture of the sedimentary facies and the chronology of deposition for the last 9500 years. From 9500 to 8200 cal. BP, the stepwise inland migration of the coastline is characterised by the deposition of peat layers at distinct depths indicating four phases of barrier-lagoon systems development. The marine transgression caused the disappearance of the lagoon at 8200 cal. BP, and reached a maximum inland position at 7300 cal. BP. Since 5800 cal. BP, sea-level stabilisation induced coastal progradation and barrier-lagoon system construction. Five marine flooding phases dated at 9500, 9100–9000, 8750–8650, 8450–8200, and 8100–7300 cal. BP match Atlantic meltwater pulses. Comparison to archaeology shows that the long-lasting Mesolithic occupation corresponds to the presence of coastal offering easily exploitable local intertidal resources. In contrast, during the Late Mesolithic, we observe a lagoon contraction and the reduction of lagoon bivalves size arguing for a decrease in resource productivity. This changes in the lagoon ecosystems negatively impacted to Late Mesolithic populations leading to a less intense occupation of this area. Therefore, the 700 years' temporal hiatus between the last hunter-gatherers and the first farmers occupying this area is explained by the disappearance of the formerly exploited biotopes because of sea-level rise, a situation that may have been aggravated by coincidence of the 8200 cal. BP climate event. The maximal sea transgression corresponded to a shift from intertidal to infralittoral species between the Impressa/Precardial and the Postcardial Neolithic, indicating a good adaptation to changing environments at that time. However, comparison between Late Mesolithic to Early Neolithic suggests that communities with different cultural baggage have had a different perception of the same environment. By the past perspective, it emphasises that perception of the ecosystem value as a benefit or constraint, and of the risks associated with sea-level rise, relies first on the local and regional scales adaptive capacity of society to global changes.

Climate changes and human impact on the Mistras coastal barrier system (W Sardinia, Italy)

Integrated archaeological and geological studies conducted on Mistras coastal barrier system of central Sardinia showed that it developed as transgressive systems during the final stages of the Holocene sea level rise (final stage of the Holocene Climate Optimum, about 6300–6000caly BP), and become regressive (prograding) from about 2500caly BP, when sea level reached the present elevation.The regression of the coast was, however, not continuous, but characterized by distinct Transgressive-Regressive phases (T-R), associated to precise climatic fluctuations, tied with global eustatic and climatic phases.The first regression occurred between 2500 and 1900caly BP. This time interval, known as Roman Warm, coincides with the Phoenician, Punic and Roman attendance of the west Sardinia coast. At that time, areas close to the coastal cities had to host landings and perhaps ports probably located at short distance from the shoreline. Archaeological excavations and findings have documented that in the Mistras area Punic constructed a long boulder structure (probably dated from the 4th century BCE) to better protect an incipient lagoon used as the harbour of the city of Tharros. This had the effect to modify the normal behaviour of the beach system that transformed from spit to barrier lagoon.During the second regressive phase, the well-established beach lagoon system developed quasi continuously for >1200y (650 and 1850CE). This progradation started during a new warm period (Medieval) and continued favoured by gentle sea level fall occurred during the cold Little Ice Age time. During this time, after the abandonment of the city of Tharros and of the Sinis Peninsula, the Mistras area was poorly populated. As consequence, there was no more an active harbour and large sandy dunes developed and nourished the shore allowing a no man-influence progradation of the coast.The third stage is the current one and begun about 165y ago (post 1850CE) after the relative sea level rise occurred after the end of the Little Ice Age.Geological and archaeological data of western Sardinia barrier lagoon systems revealed that the Mistras barrier lagoon evolution was human influenced since the Punic time. The study pointed that little human activities on the coast could influence its natural behaviour and landscape, and that little climatic changes both positive and negative can induce progradation or erosion of the system as well.

Large accumulative forms of relief on the southeastern coast of the Baltic Sea

The paper describes the conditions of formation of large accumulative forms on the southeastern coast of the Baltic Sea and presents the results of a comparative analysis of these structures. It has been established that Baltic barrier–lagoon systems have a complex geological and geomorphologic structure. Sandy barriers, which are, in general, marine accumulative formations, often comprise various fragments of different genesis (moraine remnants, glaciolacustrine and deltaic plains, etc.). The formation and development of large accumulative forms in the southeastern Baltic occurred against the background of sea level fluctuations in the Littorina time following a unified scenario for the entire coast.

High-Frequency Sequences in the Quaternary of Pelotas Basin (coastal plain): a record of degradational stacking as a function of longer-term base-level fall

ABSTRACT: The aim of this work was to analyze the sedimentary record of the coastal plain of Pelotas Basin, placing it in the context of temporal and spatial scales, and proposing a stratigraphic hierarchical framework. The coastal plain, located in southern Brazil and in northern Uruguay, is mainly formed by four Quaternary barrier-lagoon systems. Three of these systems were studied through the integration of surface and subsurface data (geomorphological and topographical mapping, outcrops description, geoprocessing, dating and Ground Penetrating Radar - GPR - records) and interpreted as the preserved, onshore portion of depositional sequences mainly controlled by glacioeustatic cycles of about 100 kyr. The stacking pattern comprising these sequences is progradational with seaward downsteping (highest sea-levels measured: 9.5, 8 and 3 m, respectively), comprehending a degradational sequence set, or the regressive/falling stage systems tract of a higher order depositional sequence identified in seismic sections, with about 0.5 Ma. The youngest sequence has diachronous systems tracts - while some sectors have already transitioned from the transgressive to the highstand/falling stage systems tract, others are still under a transgressive context. It indicates that, in this time and scale, the sea level is not the main control of coastal evolution, and autogenic factors are fundamental in the run of geological record.

Surface and subsurface data integration and geological modelling from the Little Ice Age to the present, in the Ravenna coastal plain, northwest Adriatic Sea (Emilia-Romagna, Italy)

New geological analysis of the Ravenna coastal plain has allowed a major update of the geological coastal model, with anthropogenic overprints removed from an area heavily affected by human actions in the last four centuries, a period in which the Little Ice Age (LIA) has had a large influence on the coastal dynamics. The geological build-up of the coastal plain is a natural occurrence that is important for understanding the present-day coastal buildup. However, coastal zone anthropization has defined the actual coastal morphology, canceling out most of surface expression needed to create an accurate coastal evolution model, as the beach ridges morphology in the study area. As the lack of surface expression due to the anthropogenic actions has changed the coastal zone under study, it is not possible to only use geomorphological analysis to construct a local coastal evolution model. Because of this, building a new model and understanding how coastal evolution would proceed without human influence would allow us to understand the interaction between natural forces and anthropogenic influence, which has acted to shape the actual morphology of the study area from the LIA period to the present days. We therefore propose an integration of data using the following: actual data from the surface, such as the high-resolution digital surface model (DSM) and the digital terrain model (DTM); the actual database from the Emilia-Romagna Region Geological Survey, including the shapefile with the regional soil chart and the geological elements present in the study area; knowledge from previous work carried out in the area; and the subsurface data from Ground Penetrating Radar (GPR), which would make the study the first to use a GPR survey of the coastal plain of the northwest Adriatic. In addition, the work will follows a successful case study done in the southern Brazilian coastal plain that integrated previous works done in the coastal plain with new methods such as GPR data acquisition. The GPR data allows for corroboration of the interpretation of the coastal model constructed using the surface data. Finally, the surface geological model proposed in this work may aid by providing the following: i) a new means for local coastal geology research; ii) a methodology to apply to other barrier-lagoon systems around the world in order to update our knowledge about these systems; and iii) powerful information to support coastal managers and decision makers in constructing a long-term master plan for effective Integrated Coastal Zone Management.

Sandy barrier overstepping and preservation linked to rapid sea level rise and geological setting

In an era of global rising sea level, quantifying future shoreline behaviour is a key societal concern. The potential for dramatic shoreline change via overstepping or barrier disintegration on barrier-lagoon coasts as a result of future rapid sea level rise has been considered by various authors, but documented examples of barrier overstepping generally involve either coarse grain sizes or early diagenesis as beachrock. Where overstepping has been inferred, the overstepped barrier is seldom preserved. Using high resolution seismic data we describe the mid-Holocene overstepping of a sandy coastal barrier system and subsequent geomorphological changes that ultimately transformed it into a strandplain fronted by a muddy shoreface. This complete change in character is interpreted in the context of rapid sea level rise (tentatively linked to the 8.2ka event) during which the former sandy shoreface-barrier was overstepped and decoupled from the contemporary shoreline, leaving the latter sand-starved. Upon overstepping, the wave-influenced shoreline was displaced rapidly to the landward margin of the former lagoon. Preservation of the overstepped uncohesive sandy barrier is attributed to the relatively wave-sheltered location, rapid sea level rise and rapid burial by shoreface sediments. This situation provides an insight into the conditions under which overstepping occurs, and thereby, the future response of barrier-lagoon systems to predicted rapid rates of future sea level rise.

Rapid evolution of coastal lagoons in response to human interference under rapid sea level change: A south Caspian Sea case study

This paper examines the interdependence of different factors in the evolution of a coastal lagoon system of the Sefidrud Delta (SW Caspian Sea) based on multi-proxy sedimentary and palaeoecological analyses and remotely sensed data. According to historical aerial photographs and multiple strands of chronology, these coastal lagoons formed between 1955 and 1964, when the sea-level was relatively stable. However, formation of barrier-lagoon systems due to sea level rise is quite typical in different areas of the world, but in this case study high sediment input and longshore currents were the main driving mechanisms that permitted the establishment of a sand spit complex. After 1964, the evolution of these coastal lagoons has been mainly controlled by changing sediment input due to dam construction and rapid sea-level fluctuation. Dam flushing operations and rapid sea-level rise (∼3 m between 1977 and 1995) have accelerated the infilling of the coastal lagoon system. This rapid infilling (3.1 cm y−1) makes the whole system more prone to sediment encroachment in the short term. Because the lagoons are short-lived and have a dynamic evolution, rapid natural changes interact with anthropogenic modifications of the Caspian Sea environments. The short-lived nature of these lagoonal systems (total duration of 115 years for Zibakenar Lagoon) can be used as a model for lagoonal development and evolution, in other places in the world. The Caspian coast and the lagoons along it may provide a natural laboratory for what might happen in other lagoons along other coasts in the world, in response to global sea level fluctuation.

Taxonomic and taphonomic signatures of mollusk shell concentrations from coastal lagoon environments in Belize, Central America

Faunal composition and distribution patterns of mollusk assemblages from 20 shell concentrations in cores collected in coastal lagoons, a mangrove-fringed tidal inlet, and the marginal marine area (shallow subtidal) along the central coast of Belize show considerable variation due to environmental heterogeneity and the interplay of several environmental factors in the course of the mid-late Holocene (ca. 6000 cal BP to modern). The investigated fauna ≥2 mm comprises 2246 bivalve, 789 gastropod, and 11 scaphopod specimens. Fifty-three mollusk species, belonging to 42 families, were identified. The bivalve Anomalocardia cuneimeris and cerithid gastropods are the dominant species and account for 78 % of the total fauna. Diversity indices are low in concentrations from lagoons and relatively high in the marginal marine and tidal inlet areas. Based on cluster analysis and nonmetric multidimensional scaling, seven lagoonal assemblages and three marginal marine/tidal inlet assemblages were defined. A separation between lagoonal and marginal marine/tidal inlet assemblages seen in ordination indicates a lagoon-onshore gradient. The statistical separation among lagoonal assemblages demonstrates environmental changes during the Holocene evolution of the coastal lagoons, which is probably related to the formation of barriers and spits. The controlling factors of species distribution patterns are difficult to rule out, probably due to the heterogeneity of the barrier–lagoon systems and the interaction of paleoecological and paleoenvironmental factors. In addition to the taxonomic analysis, a taphonomic analysis of 1827 valves of A. cuneimeris from coastal lagoons was carried out. There is no relationship between depth and age of shells and their taphonomic condition. Size-frequency distributions and right-left valve ratios of A. cuneimeris suggest that valves were not transported over long distances but were deposited parautochthonously in their original habitat. Shells from tidal inlet and marginal marine environments were also predominantly deposited in their original habitats.

Genetic diversity of the swamp rat in South America: Population expansion after transgressive-regressive marine events in the Late Quaternary

We examined the phylogeography of the South American swamp rat Scapteromys tumidus using complete mitochondrial DNA cytochrome b sequences. This species is endemic to the Pampas biome and lives near the coastal plain but also in inland continental areas. The coastal domain of such region experienced a highly dynamic geological history. The inland fraction is part of Precambrian and Mesozoic spills and sedimentary basins, while most of the coastal plain was shaped by transgressive-regressive marine events in the Late Quaternary. As fluctuations in the sea level during this period produced large lateral displacements of the shoreline, originating four barrier–lagoon systems that shaped the present coastline, continental area significantly increased from this time. We hypothesized that the S. tumidus have expanded its range from that period, ramped by its adaptive ability to humid areas. Thus, we examined whether historical Pleistocene events had affected genetic variation of this species along its distributional range. Bayesian phylogenetic analysis and the haplotype network inferred two major genetic clusters along the distribution of S. tumidus. Neutrality tests suggest that populations experienced demographic changes and Bayesian skyline plot evidenced a marked recent demographic expansion pattern, intensified from 350 to 300kya. Such date coincides with the formation of the lagunar barrier II (dated to ca. 325kya) and the concurrent initial formation of the coastal plain and increase in continental area.