Spit Formation Research Articles

Woodland in the Curonian spit during the 3rd millennium BC based on anthracological evidence from Neolithic sites

In this paper we present the first attempt to apply anthracological analysis in paleoenvironmental research in Lithuania. We present the results of charcoal analysis of three Neolithic archaeological sites in the Lithuanian part of the Curonian Spit. The formation and development of the Curonian Spit was a complex and dynamic process. Constant aeolian processes caused periods of sand deflation, which led to the movement of the dunes and drastic changes in the landscape until the 19th century when a protective dune ridge was built and systemic tree planting began. Curonian woodlands currently consist of mostly planted pine forests. Knowledge of the spit’s vegetation and its dynamics in prehistoric and historic periods is mainly based on palynological data. This study aims to gain a more detailed understanding of the composition and development of the Curonian Spit forests in the 3rd millennium BC. Anthracological analysis of charcoal samples from three sites located in the middle and northern parts of the spit show that broad-leaved tree species such as oak, maple and lime were spreading during the Neolithic and suggest that woodland vegetation in different parts of the spit was not uniform, with broad-leaved species thriving around Nida site and pine forests around Alksnynė. We propose that one of the reasons for the observed difference between the sites is the different phases of the spit formation that these sites underwent during the settlement period, as the middle part of the spit was formed earlier than the northern part and is therefore represented by less developed soils.

Global Distribution and Morphodynamic Patterns of Paired Spits Developed at the Mouths of Interdistributary Bays of Deltas and within Coastal Channels

Previously, paired spits have been described at the mouths of bays, estuaries, and deltas. This study analyzed the worldwide distribution and morphodynamic patterns of paired spits located at the mouths of interdistributary bays of deltas (three systems) and within coastal channels (24 systems). The methodology was based on the detailed analysis of satellite images, nautical charts, and tidal-range databases. The paired spits found were mainly located on microtidal coasts at high or mid latitudes. Waves were the main factor controlling convergent progradation and breaching of the spits, while the hydraulic blockage for the development of these paired spits was mainly due to tide-induced currents, as well as minor fluvial outlets in the interdistributary bays. Three morphodynamic patterns were identified: (i) stable, with low progradation rates, generally without breaching or degradation of any of the spits; (ii) stationary, with high progradation rates, alternating degradation or breaching of any of the spits with the formation of new spits or closure of the breaches; and (iii) instable or ephemeral, which included three subtypes, the severe erosion of one or both spits, the joining of the head of the two spits forming a single barrier, and the merging of each with its channel margin.

River mouth morphodynamics and deflection over the short term: effects on spit growth and mangrove dynamics

The river mouth shows the influence of the dynamics of sediment deposition and the processes organising the deposits. The river mouths of the Guyana coast, as with other coastal systems in the Guianas, are influenced by the deposition of mud banks from the Amazon River and other rivers. This study analysed and probed the influence of the riverine and marine influences on small river mouth morphological developments. In this study, the morphological dynamics of the system were carried out from satellite images through the comparison of the inter-annual morphodynamics of the river mouths, complemented by data from hydrodynamic processes among others. This study demonstrates that the recent advancement and availability of Synthetic Aperture Radar (SAR), remotely sensed data, allow for the classification of migrating river mouth action and processes; effective monitoring of mudflats development and spit formation; and, the exhibition of river mouth transitioning and infilling. Sentinel-1 images of the Mahaica-Mahaicony river mouth in Guyana were processed and analysed using Google Earth Engine (GEE) and ArcGIS to observe the mud dynamics and its effects on deflecting the river mouth, influencing the development of spit and mangrove dynamics. The results of the analyses show that the dynamics of the mud shoal and river mouth are governed by feedback from various estuarine and hydrodynamic processes resulting from the interactions between the river and ocean. The results have not only highlighted the importance of mud infilling and sediment build-up for spit development and river-mouth deflection but the impact of the sediment morphological dynamics on the ecosystem (mangrove) associated with the river mouth.

Transformation of Malacological Fauna of the Sea of Azov in the Holocene and Its Role in the Formation of Coastal Spits

The study and analysis of malacofauna from cores of bottom sediments and cores of the Azov spits showed the nature of the change during the transition from the Ancient Azovian to the New Azovian layers and the uneven distribution of communities in time and space. Shell material from littoral malacocenosis and shallow-water banks is the main component for the formation of spits. Based on a series of cores up to 25 m thick from the Dolgaya Spit, it is shown that its formation began about 2500 years ago, and carbonate material reflects the history of the development of the benthic fauna of the sea.

TRANSFORMATION OF THE MALACOLOGICAL FAUNA OF THE SEA OF AZOV IN THE HOLOCENE AND ITS ROLE IN THE FORMATION OF COASTAL SPITS

The study and analysis of malacofauna from cores of bottom sediments and cores from the Azov spits showed the nature of the change during the transition from the Ancient Azovian to the New Azovian layers, the uneven distribution of communities in time and space. The shell material from littoral malacocenosis and shallow-water banks is the main component for the formation of spits. Based on a series of cores up to 25 m thick from the Dolgaya Spit, it is shown that its formation began about 2500 years ago, and carbonate material reflects the history of the development of the benthic fauna of the sea.

Opak and Bogowonto Coastal Inlet Sand Spit Morphodynamics using Landsat and Sentinel Satellite Images

Sand spits are elongated sand deposits on the beach that often form at the inlet or the headland’s tip. The hydrodynamics of the river flow, waves, storm surge, and tide affect the sand spit formation, which was created by the longshore transport along the coast. Bogowonto and Opak inlets are located in southern coastal Java facing directly to the Indian ocean where micro-tidal, waves, and river flow affecting both inlets, are chosen for this case study. Morphodynamics analysis of sand spit using Landsat 7 and 8, Sentinel 2 image from 2000 to 2020, coastline identification using Modified Normalized Different Water Index (mNDWI). In November 2007 and October 2013, Opak Inlet migratory routes were detected, and closures related to the east season occurred at both of them. Inlet tend to close occur on east season during July until November.

Identification of littoral cell and its impact on shoreline dynamics along the Purba Medinipur–Balasore coastal stretch, Bay of Bengal, India: A numerical modelling and geospatial study

The northern boundary of Bay of Bengal, between Subarnarekha and Rasulpur River is divided into five coastal sectors by the four inlets, namely, Talsari, Ramnagar, Jaldha, and Pichaboni. Each sector being characterized by severe coastal erosion, beach lowering and narrow beach segments. To bring such coastal areas under proper coastal management, delineation of littoral cell and sub-cell boundaries and assessment of sediment budget is required. This study attempts to identify these hydrodynamic characteristics, by investigating the wave-induced radiation stress of dominant wave, derived from offshore wave in order to simulate longshore current and associated sediment transport using the two-dimensional deterministic MIKE 21/3 Coupled Model that is based on two dimensional shallow water, Reynolds averaged Navier–Stokes equations and fully spectral wave action conservation equation. The shoreline dynamics in terms of shoreline retreat or spit formation, is quantified by Digital shoreline analysis system (DSAS)The result of the simulation shows the dominant westerly and comparatively weaker easterly longshore flow and the resultant bed level changes. By analysing the diverging and converging flow pattern of littoral current, rate of bed level change and magnitude of shoreline oscillation, six and five littoral sub-cell (LSC) have been identified for westerly and easterly circulation respectively. The coastal inlets indirectly influence the flow direction through the development of different depositional features at mouth. Because of that inlet mouths often function as littoral cell boundaries.Periodic observation reveals that the introduction of shore-normal engineering structures has positive impact on beach nourishment and inlet stability.

Numerical Prediction of Siltation Patterns at a Tidal Inlet in Karaikal, India

Tidal inlets are an ecologically sensitive and significant constituent of the coastal environment, where an opening along the shoreline permits the free exchange of fresh and seawater. Predominant longshore currents along the shore result in the formation of sandbars, spits and shoals. Frequent occurrence of such sediment depositions acts as barriers, preventing the ingress of tidal flow. Conventionally training walls are constructed at the inlet to prevent sandbar and spit formations. The volume of water exchanged at the inlet mouth and ebb tidal currents primarily govern the inlet dimensions and the rate of littoral transport, respectively. The case study of a trained micro-tidal inlet at Karaikal (10[Formula: see text]52[Formula: see text]N; 79[Formula: see text]E), India is discussed in this paper. A numerical model using the finite volume method is applied to estimate the siltation rate and distribution within the study domain, driven by tide-induced currents and riverine discharge. A revetment structure is proposed to combat siltation within the inlet to facilitate smooth navigation. The study highlights the notable changes in the presence and absence of the proposed revetment.

Morphostratigraphy of an active mixed sand–gravel barrier spit (Baie de Somme, northern France)

ABSTRACTThis study focuses on the architectural characterization of a mixed sand‐and‐gravel spit in relation to its multi‐decadal evolution. The spit, located in the Somme estuary in northern France, is a 5 km long sedimentary body made of several amalgamated ridges with a hooked terminus. Flint pebbles originating from the erosion of Cretaceous chalk cliffs and sands reworked from the tidal flat constitute the spit. Aerial photographs demonstrate that the spit formation started in the 1940s and document its growth through time. The architecture of the spit has been characterized by ground‐penetrating radar (GPR) investigation using 400 MHz and 900 MHz antennas. The GPR data are used to distinguish progradational, aggradational and transgressive geometries that are related to cross‐shore and longshore construction, respectively. Three main morpho‐stratigraphic domains characterize the spit from the root to the terminus: (i) a beach‐ridge domain mainly made of progradational structures; (ii) an intermediate domain formed by beach‐drift structures topped by deposits with cross‐shore geometries; and (iii) a spit‐terminus domain mainly composed of beach drift structures which incorporate sand deposits. At the scale of an individual ridge, high‐frequency GPR data indicates five types of sedimentary architectures associated with the evolution from a hook stage to the subsequent elongation stage. The overall development of the barrier spit is the result of complex interactions between wave and storm dynamics, potentially modulated by the variability of submersion time related to the 18.6 year tidal cycle, and anthropogenic activities including groyne construction and gravel reloading.

Modelling the contribution of wind waves to Cap Ferret's updrift erosion

Wind waves breaking at an angle with the shoreline force the drifting of littoral sediments, which is known for contributing to the formation and growth of barrier spits. Intriguingly, increased rates of longshore wave power have also been associated with the erosion of some barrier spits on the updrift margin of tidal inlets. Therefore, a numerical experiment was designed and is presented here, which investigates the possible links between the longshore wave power and the shortening of these elongated coastal barriers. Based on a process-based model, the experiment provides new insights into the forces at play in the redistribution of sediments between a sandspit and its adjacent inlet, respectively the Cap Ferret and the Bay of Arcachon's tidal inlet, in SW France. More particularly, model scenarios were defined that show how combined waves and tide create gradients of residual sediment transport responsible for a sediment deficit at the spit – inlet boundary. The deficit was also found to deepen with increasing longshore wave energy, as if the transfer of sediment from the spit to inlet shoals was accelerated. This physically explains the previously observed retreat of the spit's distal end during periods dominated by the positive phase of North Atlantic Oscillation (NAO) in winter. Indeed, according to model results, higher and/or more oblique waves associated with the positive phase of the NAO are expected to increase the transfer and storage of the drifting sediments to and by the inlet shoals, and this at the expense of the spit. While these conclusions remain valid, we noticed that the sensitivity of model results to the bottom friction enhanced the importance of accurately representing the spatio-temporal distribution of bed roughness when investigating the morphodynamic interactions between real-world tidal inlets and their margins.

Tidal inlet morphodynamics through numerical prediction and measurements

The formation of sandbars, spits and shoals are common at the inlet mouth particularly along coasts dominated by longshore sediment transport. These formations act as barriers, thus preventing the ingress of tidal flow. Sandbar and spit formation can be preferably averted by the construction of a pair of training walls, after which monitoring the behaviour of the stability of the tidal inlet is of prime importance. In cases where the tidal inlet meets a riverine estuary, the inlet dimensions and rate of littoral transport are primarily governed by the volume of water exchanged at the inlet mouth and the ebbing tidal currents, respectively. This paper discusses the case study of a micro-tidal inlet at Karaikal (10°54′52″N; 79°51′09″E), situated along the southeast coast of the Indian peninsula. This inlet coincides with the mouth of the Arasalar estuary, a tributary of the Cauvery river. A numerical model using the finite volume method is applied to estimate morphodynamic changes in the inlet channel driven by tide-induced currents and riverine discharge during the North-East monsoon season and the same has been validated through field measured data. The ultimate aim is to arrive at mitigation measures to combat siltation within the inlet.

High‐resolution facies analysis of a coastal sabkha in the eastern Gulf of Salwa (Qatar): A spatio‐temporal reconstruction

AbstractSabkhas are key landforms along the southern coast of the Arabian Gulf and represent modern analogues for depositional and diagenetic processes controlling properties and quality of ancient hydrocarbon‐bearing carbonates. While previous investigations of coastal sabkhas in Qatar have mainly focused on dolomitization processes, presented here is one of the first studies reconstructing facies changes and coastal formation in great detail. In the sabkha of Al‐Kharayej (Gulf of Salwa), fifteen different facies types were distinguished based on twelve sediment cores, two trenches, as well as grain‐size distribution, X‐ray powder diffraction, thin section and microfossil analyses. Age estimates were based on seventy‐eight 14C‐AMS and optically stimulated luminescence data. The sabkha parasequence comprises pre‐transgressive dune sands, a thin, transgressive layer of reworked dune material, a mid‐energy open‐coast to open‐lagoon facies, a low‐energy lagoon facies, saline lake facies (salina: swallow‐tail gypsum and gypsum mush) and the supratidal sabkha characterized by diagenetic overprinting (buckled gypsum crusts and halite crust). Transgressive marine flooding created open‐coast to open‐lagoon sedimentation after ca 7000 cal yr bp, followed by initial spit formation at the northern sabkha end at the beginning of the relative sea‐level highstand (6000 cal yr bp). This main outer spit prograded southward and a more narrow, low‐energy spit, diverted landward, closing a small lagoon in the northern sabkha 4500 to 4000 cal yr bp. The falling relative sea‐level and longshore drift intensified the southward extension and widening of the main spit, and the main lagoon became more shallow. At 2000 to 1500 cal yr bp, the outer spit had almost closed the main lagoon, leading to salina and, finally, sabkha conditions. It is shown how specific local conditions (coastline orientation; wind, wave, tidal energy, longshore drift; depositional relief; sediment sources) created a spit‐controlled sabkha that is genetically distinct from the classical model of shore‐perpendicular accumulation of coarser sediment during high tides or storms.

The formation and morphodynamics of complex multi‐hooked spits and the contribution of swash bars

AbstractNumerous studies have been devoted to recurved and hooked spits in micro‐ and meso‐tidal environments, but none have really focused on the peculiar right‐angle plan shape exhibited by some spit hooks. The morphodynamics of a complex multi‐hooked spit in a macrotidal inlet in Normandy, France, have been investigated using aerial photographs and 12 topographic LiDAR surveys from 2000 to 2017, complemented by hydrodynamic data. Merville Spit is a 2.5 km‐long hooked spit, composed of four ‘nested’ ridges each with a right‐angle hook at its tip, that has developed in the vicinity of the sand‐rich outlet of the Orne River. Monitoring of the two last ridges shows that ridge formation starts with the attachment of the tip of a swash bar to the fulcrum point of the previous ridge, and ends following its westward elongation and counter‐clockwise rotation when its hook impinges on the Orne outlet. The main factor controlling ridge plan‐view shape is swash bar dynamics in the vicinity of the spit. The offshore wave direction has no significant impact on ridge and hook behaviour due to the large number of swash bars on the ebb‐tidal delta. Over the study period, between 5 and 10 swash bars massively assured sand supply to the upper foreshore, favouring the growth of existing ridges, but also enabling the building of a new ridge. The bars contribute to imparting hook right angles at the tips of the ridges by creating local wave refraction or by providing a sheltering effect. Strong tidal currents in the Orne channel act as a hydrodynamic barrier that stops hook elongation at the edge of the river's outlet. The similar behaviour of the two studied ridges has been synthesized into a new and original conceptual model of complex multi‐hooked spit formation and evolution under the influence of swash bars.

Stratigraphy and sedimentary evolution of a modern macro‐tidal incised valley: An analogue for reservoir facies and architecture

AbstractIncised valley fills are complex as they correspond to multiple sea‐level cycles which makes interpretation and correlation of stratigraphic surfaces fraught with uncertainty. Despite numerous studies of the stratigraphy of incised valley fills, few have focused on extensive core coverage linked to high fidelity dating in a macro‐tidal, tide‐dominated setting. For this study nineteen sediment cores were drilled through the Holocene succession of the macro‐tidal Ravenglass Estuary in north‐west England, UK. A facies and stratigraphic model of the Ravenglass incised valley complex was constructed, to understand the lateral and vertical stacking patterns relative to the sea‐level changes. The Ravenglass Estuary formed in five main stages. First, incision by rivers (ca 11 500 to ca 10 500 yrs bp) cutting through the shelf during lowstand, which was a period of fluvial dominance. Secondly, a rapid transgression and landward migration of the shoreline (10 500 to 6000 yrs bp). Wave action was dominant, promoting spit formation. The third stage was a highstand at ca 6000 to ca 5000 yrs bp, creating maximum accommodation and the majority of backfilling. The spits narrowed the inlet and dampened wave action. The fourth stage was caused by a minor fall of sea level (ca 5000 to ca 226 yrs bp), which forced the system to shift basinward. The fifth and final stage (226 yrs bp to present) involved the backfilling of the River Irt, southward migration of the northerly (Drigg) spit and merging of the River Irt with the Rivers Esk and Mite. The final stage was synchronous with the development of the central basin. As an analogue for ancient and deeply buried sandstones, most of the estuarine sedimentation occurred after transgression, of which the coarsest and cleanest sands are found in the tidal inlet, on the foreshore and within in‐channel tidal bars. The best‐connected (up to 1 km) reservoir‐equivalent sands belong to the more stable channels.

Hydrodynamic stability of tidal inlet system: A case study of Pichaboni inlet, Purba Medinipur, West Bengal, India

The hydraulic geometry of tidal inlets, like, cross-sectional area, wetted perimeter and hydraulic gradient is controlled by the dynamics of tides and wave-induced littoral drift along coastlines, pushing materials into the inlet during the flood tide and flushing them out during the ebb tide. An inlet which maintains its hydraulic stability has its velocity so adjusted that it can flush out all the materials pushed into the inlet. The Pichaboni inlet situated along the Bay of Bengal coast, is a linear channel and the tidal inflow is restricted by a sluice gate. This paper investigates the impact of hydraulic geometry, morphological changes and tidal behaviour on the hydrodynamic stability of the Pichaboni inlet. The longitudinal profile shows a reverse gradient from sea to inland. The smallest cross-sectional area (throat cross-section, AC) is located 672 m inland, which is slightly smaller than the cross-sectional area required to maintain the equilibrium flow velocity. Hence, the actual flow velocity through the throat cross-section is greater than that required for the equilibrium state, and the enlargement of the cross-section area may be caused by sediment scouring which decreases the flow velocity and leads to shoaling at the mouth. The dominant west to east longshore transportation brings a huge amount of sediment influx responsible for continuous sedimentation and the associated formation of spit at the inlet mouth. Any constriction at throat due to spit formation leads to accelerated flow velocity associated with scouring at the throat area and breaching of the spit. This results in the gradual shifting of the inlet mouth by the mechanism of bar by-passing. The economic importance of the main inlet channel and its adjacent intertidal basin necessitates evaluation of the long-term stability of the tidal inlet through analysis of hydraulic and sedimentary characteristics of the inlet.

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

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

Microbially Induced Sedimentary Structures (MISS) and their Involvement in Sediment Stabilization and Formation of Gravelly Coastal Landforms (Berms, Spits and Bars) in Salman Hypersaline Lagoon, Red Sea Coast of Saudi Arabia

his study documents the occurrence of several MISS such as laminated microbial mats, biostabilized ripples, gas domes, mat folds, erosional pockets and remnants, microbial cracks, and gypsified mat chips in Salman hypersaline lagoon, north Jeddah city, Saudi Arabia. This study indicates that both microbial and physical processes are reponsible for sediments biostablization and formation of spits,

Efficient Modeling of Complex Sandy Coastal Evolution at Monthly to Century Time Scales

With large-scale human interventions and climate change unfolding as they are now, coastal changes at decadal timescales are not limited to incremental modifications of systems that are fixed in their general geometry, but often show significant changes in layout that may be catastrophic for populations living in previously safe areas. This poses severe challenges that are difficult to meet for existing models. A new free-form coastline model, ShorelineS, is presented that is able to describe large coastal transformations based on relatively simple principles of (1) alongshore transport gradient driven changes as a result of coastline curvature and (2) spit formation at high-angle wave incidence. An arbitrary number of coast sections is supported, which can be open or closed and can interact with each other through relatively straightforward merging and splitting mechanisms. Rocky parts or structures may block wave energy and/or longshore sediment transport. These features allow for a rich behavior including shoreline undulations and formation of spits, migrating islands, merging of coastal shapes, salients and tombolos. The main formulations of the (open-source) model are presented. Test cases show the capabilities of the flexible, vector-based model approach, while field validation cases for a large-scale sand nourishment (the Sand Engine; 21 million m3) and an accreting groyne scheme at Al-Gamil (Egypt) show the model’s capability of computing realistic rates of coastline change as well as a good representation of the shoreline shape for real situations.

Coastal Erosion Threat on the Kızkumu Spit Geotourism Site (SW Turkey): Natural and Anthropogenic Factors

The uniqueness of the spits comes from their special coastal geomorphology. Spit’s evolution is controlled by the fragile environmental conditions, the sediment input, long shore currents, wave, wind and river processes. The Kizkumu Spit, one of the attractive examples (400 m long; 18–48 m wide) is located in an environmentally protected area in southwestern Turkey (Datca-Marmaris). Extending 50 cm below the sea as a red carpet, the spit with its distinctive appearance and mysterious history enhance the site’s attractiveness which brings on the possible anthropogenic effects as overpopulation during summer tourism and the lower sediment influx from improper marine structure. This study characterizes the spit formation via recent and the past satellite images, geological and topographical maps to better figure out the protection pathways. Six locations were defined and twelve beach sediments in total were sampled. The particle size distribution by sieving together with micro-imaging the sediments are combined with the statistical analyses. Mode values from sieve analysis and the red-coloured sediments along the coast which are also visible on satellite images point out that the Kizkumu Spit is fed from north (via Kocapinar Stream Delta and its coast) and east (via Bozegri Brook). An uncontrolled sand-drawing from the coast, establishing the breakwaters to prevent the longshore currents and waves onto the coastal structures and experiencing walking along the spit, all cause the dispersion of the sediments and very intense erosion on the spit. The results of this study suggest that immediate protection measures (including spit-monitoring, prevention of sand drawing, limitation of daily tourist activities) should be taken for future sustainability of the Kizkumu spit.

The sedimentology and development of a modern sandspit (Miankaleh Peninsula) and a lacustrine lagoon (Gorgan Bay), Caspian Sea, Iran

Gorgan Bay is a ~240 km2 lacustrine lagoon on the southeastern margin of the Caspian Sea, from which it is separated by the 48 km long barrier beach/sandspit of the Miankaleh Peninsula to the north. The northern, windward side of the sandspit displays an eroded berm. The bulk of the sandspit is characterized by the presence of beach ridges and transverse, nebkha and parabolic dunes. The southern, leeward side of the sandspit faces the muddy low-energy lagoon of Gorgan Bay. The shore sediments are well sorted, negatively skewed, very fine to fine sands. The sand dunes are composed of well sorted, positively skewed fine sand. Grain types of the shore and dune sediments are very similar, with quartz grains and small superficial ooids being the major constituents. These similarities suggest the dune deposits represent windblown shore sediments. In contrast, the Gorgan Bay sediments are poorly sorted, positively skewed very fine to coarse sands with abundant bivalves, gastropods, ostracods, and charophyte oogonia. Clay minerals include chamosite, illite and chlorite, all of volcanic origin. The presence of pyroxenes and amphiboles may suggest a provenance from the Gorgan Metamorphic Complex. The study shows that the growth of the Miankaleh Peninsula sandspit is a result of predominantly eastward longshore transport of littoral fine sands, which has been thrown by storm waves above the mean spring tide waterline in the form of slightly curved beach ridges. This has allowed the development of dry beach conditions (backshore) and the growth of vegetation. The beach ridges have been successively accreted in an eastern direction (younging to the east). The formation of superficial ooids is mainly linked to low-energy conditions. However, occasional high-energy events existed, and long, hot summers may also have played also a role in ooid formation. The sand was reworked by the prevailing northwesterly winds (dune formation). Spit formation facilitated the infilling of the sheltered lagoon by the trapping of sediment derived from the Gorgan Metamorphic Complex to the south.