Holocene Transgression Research Articles

Evolution of a paleolake on Russian Island (Sea of Japan) in middle-late Holocene: record of sea-level oscillations, extreme storms and tsunami

The diatom algae from sediments of a paleolake serve as records of changes to environments over the last 7500 cal yr. The lagoon lake formed when the sea level approximately corresponded to the present-day position. Evolution of the paleolake was controlled by sea-level oscillations and humidity changes. Eight stages have been distinguished. During a dry episode in 7330–7090 cal yr BP the lake size decreased. The salinity reached maximal values at the Holocene transgression peak. Three stages of a higher salinity are recognized (6750–6500, 6080–5830, 5420–5090 cal yr BP). A severe flood occurred in 6080–6000 cal yr BP. The brackish-water lake existed in ∼5090 cal yr BP and the freshwater lake in ∼4090 cal yr BP. A prolonged phase of decreasing humidity, associated with a weakening of summer monsoons, led to a drop in sedimentation rates in ∼3510 cal yr BP. Peat accumulation started at the Little Ice Age. The lake was transformed into a swamp during drop in precipitations in ∼270 cal yr BP. Presence of marine diatoms typical in bay and deep-water forms are evidence of influence of extreme storms and tsunami. The age of the paleotsunami coincides well with the regional data.

Crustal subsidence inferred from reconstruction of the Pleistocene–Holocene palaeogeography in the northern Lake Inba area, central Japan

ABSTRACTTo help characterise the palaeogeographic and lacustrine environmental changes that resulted from the Holocene transgression and residual subsidence in the eastern Kanto Plain of central Japan, we analysed four drill cores and reviewed other core data from the southern part of the Lake Inba area. Fossil diatom assemblages yielded evidence of centennial-scale palaeogeographic and salinity responses to sea-level changes since the late Pleistocene. We determined that the seawater incursion into the Lake Inba area during the Holocene transgression occurred at approximately 9000 yr. We also recognised a late Holocene regression event corresponding to the Yayoi regression, considered to have occurred from ca. 3000 to ca. 2000 yr, and a subsequent transgression. Our data clarify some of the palaeogeographic changes that occurred in the Lake Inba area and document an overall trend toward lower salinity in the lake during the regression. In particular, the environment in Lake Inba changed from brackish to freshwater no later than 1000 yr. From the detailed palaeogeographic and palaeo-sea-level reconstruction, we recognised that residual subsidence occurred during the Holocene in this area. Thus, comparison of sea-level reconstructions based on modelling and fossil diatom assemblages is effective in interpreting Holocene long-term subsidence.

Evolution of the main geomorphological structure of the Holocene Kuban river delta

In the recent epoch the Kuban River delta is characterized by little distributary with low zone of lagoons and flooded areas. This accumulative plain includes different types of mesorelief such as longshore bar, channel bank, liman, plavni and channel distributaries. There are three huge geomorphological types of Kuban delta: old, young deltas and Kuban-Taman region. The main differences between them are diverse geomorphological levels, evolution of marine and fluvial forms and incomplete geomorphological development.
 The relief of the Kuban delta is Holocene. The main factors of its formation were large-scale fluctuations of the Azov-Black Sea basin, the flow of water and sediment of the Kuban River and its distribution in area. In the history of the development of the modern relief of the Kuban delta, there are three stages (epochs). The first is the Bugaz stage of the Holocene transgression (9.57.9 ka), when the relief of the old delta was formed. In the second stage of the Holocene transgression (Vityazevskaya, Kalamitskaya, and Dzhemetyan stages), a transitional type of relief was formed in the area adjacent to the floods of the young delta and the old delta with the formation of large buried bars. In the third stage, the systems of modern estuaries and plavni were formed, separated from the sea by a modern coastal bar.

Abstract #4308 Genetic variation of IL-6 expression modulates age-related memory decline

An integrated approach combining swath bathymetry, high-resolution seismic reflection and seabed sediment sampling was performed to characterize a field of sand ridges on the Murcia continental shelf in the western Mediterranean Sea. The aim of this work was to improve knowledge about the formation, evolution and present-day dynamics of these bedforms on a narrow, tideless continental shelf receiving little sediment input. Sand ridges are observed on the middle shelf at water depths ranging between 58 and 78 m. The sand ridges are 1.5 to 3 m high and show a predominant E-W orientation oblique to the present-day shoreline. Smaller-scale subaqueous dunes (0.3–1.3 m high) appear superimposed on the sand ridges and beyond the ridge field. The subaqueous dunes show a NW-SE orientation and asymmetric profiles, with the lee side facing southwest. The comparison of two bathymetric surveys 10 years apart revealed that the subaqueous dunes are migrating towards the southwest at very low rates (~ 3 m yr− 1). Internally, both sand ridges and dunes display southwestward dipping oblique reflections, indicating long-term migration in that direction.The morphology, architecture and distribution of the Murcia sand ridges suggest that they were formed in a shallow-water environment during the Holocene transgression and were later detached from the coast due to the subsequent sea level rise. The shallow architecture of the sand ridges reveals the presence of small, mound-like features within the sand ridges, most probably associated with coastal deposits, which could have served as a precursor for the development of the sand ridges. The preservation of these deposits within the sand ridges evidences limited offshore ridge migration. At present, active subaqueous dunes superimposed on the sand ridges suggest that they may play a significant role in the ridge evolution. At a regional scale, the comparison of the Murcia sand ridges with those described in the western Mediterranean allows us to propose a gradation from partially evolved to fully evolved sand ridges with increasing water depth.

How a river submerges into the sea: a geological record of changing a fluvial to a marine paleoenvironment during early Holocene sea level rise

ABSTRACTCoastal seas, and in particular estuarine systems, were significantly affected by Quaternary sea level changes. Furthermore, the dynamics of shelf and coastal evolution have had a strong impact on coastal landscapes inhabited by humans. The postglacial evolution of the vast North Sea shelf with its huge drainage systems, e.g. the Elbe Paleovalley and its tributary system, is an excellent research target to understand how coastal shelf environments change in response to sea level rise. In this study, we investigate infill sediments of the Paleo‐Ems valley – a drowned extension of the modern Ems River and part of the Elbe Paleovalley drainage system. Radiocarbon‐dated transgression sequences provide several new observations regarding the mode and rate of the river system submerging due to the Holocene transgression. Thus, the Paleo‐Ems valley submerged within a short time span of~200 years since the river was not able to adjust its gradient to the rapid rising sea level. The fate of the Paleo‐Ems is exemplary for the rapid change of a former fluvial landscape into a coastal landscape and finally into a submarine seascape. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

Buried late Quaternary channel systems in the Danish North Sea – Genesis and geological evolution

The Danish North Sea has been subject to extensive seismic surveying (both 2D and 3D) during the past four decades. The 3D seismic data from the area has mainly been used for hydrocarbon exploration, but in the last decade, it has also been utilized for investigating the Quaternary sediments and especially buried incised valleys. The erosional and depositional processes involved in forming such valleys are important in paleolandscape reconstruction, but are often difficult to determine, since sediment deposited by flowing water, displays ambiguous geometric structures. In this study, we combine the analysis of infill geometries, from high-resolution 2D seismic data, with plan-view morphology analysis, from 3D seismic data, and lithological data from borehole reports, in order to constrain the origin of buried channels in the Danish North Sea. This data integration makes differentiations of a subaerial vs. subglacial origin more robust. The study focusses on analyzing a proglacial to fluvial channel system, which was initiated as a subglacial tunnel valley system during the Last Glacial Maximum, and subsequently evolved as a fluvial system after deglaciation. The channel system was active in a marsh environment during a period of subaerial exposure in the late Weichselian to early Holocene. During the Holocene transgression, the system was gradually flooded leaving estuarine tidal deposits in the underfilled channels. Once the area was completely flooded, the channel system was buried under marine sands.

Morphological and sedimentary patterns of a semi-arid shelf, Northeast Brazil

The semi-arid shelf of Northeastern Brazil, adjacent to the State of Ceara, was analyzed using high-resolution seismic imaging, side-scan sonar imaging, sedimentary patterns, remotely operated vehicle (ROV), scuba dive surveys, and satellite images. Three geomorphic sectors were found according to physiographic, sedimentological, and morphological aspects: Coreau, Mundau, and Jaguaribe. The Ceara shelf is characterized by a mixed sedimentological pattern including a significant modern carbonate supply, relict siliciclastic grains, and a mixing of carbonates and siliciclastics. The modern siliciclastic supply is concentrated near the coast (shoreface/shoaling zone) and solid discharge from rivers is low due to a semi-arid climate. The subaqueous features (dunes, ripples, reefs, beachrocks, and incised valleys), both relict and modern, formed both as a result of sea-level changes (Wisconsin Glacial and Holocene transgression) and modern processes (longshore and wind-driven currents, waves, and tides).

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.

The Study of Hydrogeochemical Environments and Microbial Communities along a Groundwater Salinity Gradient in the Pearl River Delta, China

The salinization of groundwater is an issue in coastal areas because it causes the deterioration of freshwater resources, significantly impacting human livelihoods and ecosystems. This study integrated isotopic geochemical measurements with high-throughput sequencing of 16S rRNA gene amplicons to evaluate the source of groundwater salinity and the influence of hydrogeochemical variations on microbial communities under different salinity gradients in the Pearl River Delta of China. Results showed that the groundwater salinity in this area varied from fresh water in the inland area to brackish water, and then to saline water close to the southeast shoreline. The major ions (Na+, K+, Ca2+, Mg2+, Cl−, NO3−, SO42−, and HCO3−) and isotope analyses (2H, 3H, 18O, and 14C) indicated that the groundwater in the confined aquifer was recharged by local precipitation and seawater. A further 14C analysis showed that the salinity of the groundwater was likely attributed to the Holocene transgression. Analysis of the microbial community showed that γ-proteobacteria were frequently observed in all the groundwater samples, while the other main microbial community at class level varied greatly, from β-proteobacteria in the freshwater wells to ε-proteobacteria in the brackish wells and to Bacilli in the saline wells. Exiguobacterium and Acinetobacter were dominant in saline water and the brackish water sample of Q144, while Sulfuricurvum dominated in the brackish water sample of Q143. Aeromonas, no rank Gallionellaceae, no rank Methylophilaceae, Acidovorax, and Comamonas unevenly thrived in the freshwater samples collected from different locations. Therefore, the distribution of microbial communities reflected the salinity and hydrogeochemical characteristics of a groundwater aquifer, and can be regarded as a potential environmental indicator in the groundwater.

Algal reefs (Coralligenous) from glacial stages: Origin and nature of a submerged tabular relief (Hyblean Plateau, Italy)

In the framework of the Italian multidisciplinary research project “Mud volcanoes Ecosystem study - Sicily Channel”, cores MV02_GC01 and MV03_GC02 were recovered from a tabular relief at 140 m water depth, to investigate the nature of such uncommon shallow seep-related morphology trough micro- and macro-paleontological, mineralogical, sedimentological and geochronological analyses.Both cores record muddy surficial sedimentation, hosting a strictly circalittoral molluskan death assemblage typical of mobile substrate, coherent with the present-day seafloor depth and environment. The core bottom recovered a biogenic framework, in which the molluskan fossil assemblage is characteristic of shallow-water, possibly infralittoral, representing a past sea level low stand. The biogenic framework shows structure and composition that are similar to present day algal reefs indicated as coralligenous build-ups. Both cores recorded the Holocene transgression. Core MV02_GC01 is longer and its basal section records cobbles and pebbles of both terrigenous and biogenic origin partially covered by a dark patina, and finely preserved Halimeda sp. fragments. The dark patina reveals a fibrous nature, often containing framboid pyrite crystals, ankerite, but no organic matter. We interpret the dark patina level as the last lowstand, possible forming in a lagoon-like paleoenvironment. Below such level, another coralligenous build-up occurs, U/Th dated to MIS 6, in agreement with the available seismic interpretation. The tabular relief lays up to 10 m above the surrounding seafloor and reveals a complex inner architecture, in which at least two generations of coralligenous build-ups shaped its geomorphological development, and the local tectonic activity contributed to its uplift.

Origin of the Mushroom Stone Forest at the southeastern foot of the Little Sangpu Mountain in eastern Guangdong, China: A palaeo-sea-level indicator or not?

The Mushroom Stone Forest, which consists of granite boulders looking like mushrooms with flared sidewalls, is located in eastern Guangdong, China, and is a famous scenic spot that draws many tourists each year. The Mushroom Stone Forest has been traditionally recognized as a collection of wave erosion landforms and used for the reconstruction of palaeo-sea-level changes along the coastal areas of eastern Guangdong in previous coastal researches. By combining in situ measurements of the aspect, vertical profile and height of boulder sidewalls, palaeo-coastal wave direction estimation, rock density determination, major elemental analysis, and petrographic thin section analysis, this paper presents an alternative origin for the Mushroom Stone Forest. Our results suggest that wave or wind erosion cannot offer a satisfactory explanation for the formation of the Mushroom Stone Forest; The boulders that make up the Mushroom Stone Forest originated from the corestones in the granite weathering crusts of the Little Sangpu Mountain; When the debris of the weathering crust was removed, the corestones are perched on rocky outcrops or half-buried by weathering debris beneath the natural land surface; The flared sidewall (concave vertical profile) of the boulders is a particular form developed in the foot zone of a half-buried boulder through increased chemical weathering beneath the land surface. A recent exposed half-buried boulder found in the study area provides convincing evidence to support this argument. Sea water reached the foot of the Sangpu Mountain during the Holocene transgression, but it merely provided a mechanism to erode the weathering debris from the bottom of the mushroom rocks and enhanced salt weathering that created tafoni on the boulders. These findings demonstrate that the boulders of the Mushroom Stone Forest are not sea stacks and cannot be served as a palaeo-sealevel indicator.

From a river valley to a ria: Evolution of an incised valley (Ría de Ferrol, north‐west Spain) since the Last Glacial Maximum

AbstractThe evolution of incised valleys is an important area of research due to the invaluable data it provides on sea‐level variations and depositional environments. In this article the sedimentary evolution of the Ría de Ferrol (north‐west Spain) from the Last Glacial Maximum to the present is reconstructed using a multidisciplinary approach, combining seismic and sedimentary facies, and supported by radiocarbon data and geochemical proxies to distinguish the elements of sedimentary architecture within the ria infill. The main objectives are: (i) to analyse the ria environment as a type of incised valley to evaluate the response of the system to the different drivers; (ii) to investigate the major controlling factors; and (iii) to explore the differentiation between rias and estuaries. As a consequence of the sea‐level rise subsequent to the Last Glacial Maximum (ca 20 kyr bp), an extensive basin, drained by a braided palaeoriver, evolved into a tide‐dominated estuary and finally into a ria environment. Late Pleistocene and Holocene high‐frequency sea‐level variations were major factors that modulated the type of depositional environments and their evolution. Another major modulating factor was the antecedent morphology of the ria, with a rock‐incised narrow channel in the middle of the basin (the Ferrol Strait), which influenced the evolution of the ria as it became flooded during Holocene transgression. The strait acted as a rock‐bounded ‘tidal inlet’ enhancing the tidal erosion and deposition at both ends, i.e. with an ebb‐tidal delta in the outer sector and tidal sandbanks in the inner sector. The final step in the evolution of the incised valley into the modern‐defined ria system was driven by the last relative sea‐level rise (after 4 kyr bp) when the river mouths retreated landward and a single palaeoriver was converted into minor rivers and streams with scattered mouths in an extensive coastal area.

Reconstructing human–landscape interactions in the context of ancient iron smelting on Elba Island, Italy, using sedimentological evidence

AbstractWe reconstruct human–landscape interactions in the context of ancient bloomery smelting on Elba Island, Tyrrhenian Sea, based on sedimentological evidence. Elba was, together with Populonia, the center of iron production in antiquity (mid‐6th century B.C.E. to 1st century C.E.). The sediment sequences obtained by vibracoring in the Campo plain reveal that the Holocene transgression triggered aggradation during the Early–Middle Holocene (>5.4 ka cal BP). Nevertheless, wetland conditions prevailed in low‐lying areas during Roman times. Correspondingly, ancient smelting sites are found only on elevated areas along the edge of the plain. The palaeolandscape thus plays a key role in understanding location factors for smelting sites in antiquity. Our sediment sequences indicate that during Etrusco–Roman times (2.4–2.0 ka cal BP) morphodynamics on the island increased, as is evident from the alteration of slope deposits and slack water deposits in upstream positions, and the change from lacustrine to alluvial deposition in downstream areas. The charcoal record shows that fire dynamics increased simultaneously. The sediments that are synsedimentary to the ancient smelting period show significantly increased arsenic contents and high sediment magnetic susceptibility, whereas overall concentrations of heavy metals remain in the range of the geogenic background signal.

Podzol development on different aged coastal bars of Lake Ladoga

This paper presents the result of the studies of soil formation on different aged coastal bars in the transgression zone of Lake Ladoga in the Nizhnesvirsky Nature Reserve (Leningrad region, North-West of the Russian Federation). The investigation presents the data on soil chronoseries, located on four Ladoga coastal bars of different ages from 70±25 to 1590±25 years BP. We estimated the trends of accumulation and transformation of organic matter, elemental composition of humic acids (HAs), development of plant communities and the influence of soil formation factors on the formation rate of soil horizons. We assessed the degree of soil organic matter stabilization using modern instrumental methods (spectroscopy of nuclear magnetic resonance CP/MAS 13C-NMR). An integral indicator of the hydrophobicity of HAs, which represents the total fraction of unoxidized carbon atoms, is proposed. The Ladoga Holocene transgression is one of the most informative and applicable models for pedogenesis; successional processes occurring in young and mature areas can be traced here. We identified local processes of soil formation such as podzolization, gleyfication, peat formation and humus accumulation. Physical, physical-chemical and biological soil properties with a detailed description of the morphology of soil of different aged coastal bars are presented.

Coastal evolution and sediment succession of Sri Lanka: a review on quaternary sea levels, climates and sedimentation processes

In spite of the small size, the coastal environments of the four cardinal quadrants of Sri Lanka indicate different morphologies and evolutionary characteristics. Therefore, a review of the coastal evolution and sediment succession of Sri Lanka is presented with formal published data and multi-proxy data using modern techniques. The Sri Lankan coasts have provided insightful evidence of paleo-sea level oscillations during the last glacial period and Late-Holocene epoch. The prevailing climate since the last glacial maximum has provided excessive sediment to coastal lowlands and produced Pleistocene sedimentary signatures driven with aeolian and fluvial processes. Major coastal sediment barriers developed during late Holocene transgressions and were modified afterwards. Both northwestern (NW) and southeastern (SE) coastal zones experienced the monsoon rain-shadow effect. In the NW quadrant, the shielding effect of the Indian sub-continent preserved much of the evidence for paleo-sea level oscillations and paleo-climate, although the basement rock is Miocene limestone. In contrast, the rocky crystalline SE coast has less preservation due to its considerable exposure to the wind driven forces. The energy of the of eastward moving currents is higher due to the combined effect of westerly wind bursts (WWB) and SW monsoons, and hence, southwestern (SW) and southern coastal areas show regressive coasts due to current generated coastal processes. However, the eastern zone of the SE quadrant is progressive due to its position in the conjunction zone of the eastward moving sea currents and westward moving lowsalinity water flows of the Bay of Bengal. The pattern of sea currents and monsoon strength controlled the wind driven morphologies of the NE and SW quadrants. Though the geology is similar in the NE and SW quadrants, the general geological strike of the SW coast is parallel to the turning SW monsoon currents and most likely the rock types has supported erosion. Sediment loads generated from NE monsoon and east India coastal currents (EICC) are upwelled with the strong circulations within the Bay of Bengal and deposit on the NE coasts indicating heavy mineral beds that were sorted by swash and backwash activities. This review notes how tropical monsoon induced sea currents and other currents around the Bay of Bengal region are factors in the differences in the geology and structure of coastal morphologies in four quadrants of Sri Lanka. These factors traced/erased the global melting events on a tropical small island during the Quaternary.

Examining the chronology of transgressions since the late Pleistocene in the Fujian coast, southeastern China

The chronological framework of late Pleistocene and Holocene transgressional strata along the Fujian coasts in southeastern China were examined using new 14C dates, OSL ages, and diatom data from cores drilled in Longhai. This location was chosen because previous studies in the region have interpreted the occurrence of MIS3, MIS2, and Holocene transgressions. Our study, and a critical review of previous studies, show that 14C dates of bulk samples from coastal areas tend to be erroneously older than the depositional age due to enhanced input of old carbon via erosion of Mesozoic basement rocks from mountainous inlands. Also, OSL dates of deltaic and fluvial sediments either vary widely due to unsuitable luminescence properties of quartz grains or tend to be older than true depositional ages due to partial bleaching. As such, the previously considered late Pleistocene transgression may have occurred in the Holocene. Overall, the early Holocene transgression is well documented along Fujian coast revealing largely consistent early Holocene sea level histories from northern and southern sectors of Fujian coast. However, late Pleistocene transgressions are not well preserved along Fujian coasts, likely due to pervasive erosion. Our examination of the chronology of transgression in Fujian coast suggests cautions for 14C dating of bulk samples and for OSL dating of sediments in fluvial-deltaic settings, and emphasizes the importance of establishing a reliable chronological framework for understanding relative sea level history in this region and in similar settings elsewhere.

Diversity and predictive metabolic pathways of the prokaryotic microbial community along a groundwater salinity gradient of the Pearl River Delta, China

Almost half of the groundwater in the Pearl River Delta (PRD) contains salt water originally derived from paleo-seawater due to the Holocene transgression, which then generates intense physicochemical gradients in the mixing zone between freshwater and saltwater. Although some studies have been conducted on the hydrological and geochemical characteristics of groundwater in the PRD to monitor the intrusion of seawater, little attention has been paid to the microbial community of this particular region. In this study, we implemented a high-throughput sequencing analysis to characterize the microbial communities along a salinity gradient in the PRD aquifer, China. Our results indicated that the microbial community composition varied significantly depending on the salinity of the aquifer. The presence of abundant anaerobic microorganisms of the genera Desulfovibrio and Methanococcus in certain saltwater samples may be responsible for the gas generation of H2S and CH4 in the stratum. In saline water samples (TDS > 10 g/L), the linear discriminant analysis effect size (LEfSe) analysis found two biomarkers that usually live in marine environments, and the aquifers of the PRD still contained large quantity of saltwater, indicating that the impact of the paleo-seawater has lasted to this day. The predictive metagenomic analysis revealed that the metabolic pathways present in the groundwater samples studied, included the degradation of pesticides and refractory organics (dichlorodiphenyltrichloroethane (DDT), atrazine and polycyclic aromatic hydrocarbons), matter cycling (methane, nitrogen and sulfur), and inorganic ion and mineral metabolites. This study can help enhance our understanding of the composition of the microbial assemblages and its implications as an environmental indicator in an aquifer affected by saltwater intrusion.

Holocene overbank deposition in the drainage basin of Lake Khanka

Overbank deposits in the Komissarovka River valley consist of alternating silt, clay silt, sand, and soils produced by lacustrine, alluvial, and aeolian deposition and by soil formation. Silt and sand layers in the lower part of the section correlate with the events of Early Holocene transgression and Middle Holocene regression of Lake Khanka. Deposition in the lowermost reaches of the Komissarovka River provides a faithful record of local Holocene landscapes controlled by level changes in Lake Khanka.

Molluscan benthic communities at Brijuni Islands (northern Adriatic Sea) shaped by Holocene sea-level rise and recent human eutrophication and pollution.

The effects of and the interplay between natural and anthropogenic influences on the composition of benthic communities over long time spans are poorly understood. Based on a 160-cm-long sediment core collected at 44 m water depth in the NE Adriatic Sea (Brijuni Islands, Croatia), we document changes in molluscan communities since the Holocene transgression ~11,000 years ago and assess how they were shaped by environmental changes. We find that (1) a transgressive lag deposit with a mixture of terrestrial and marine species contains abundant seagrass-associated gastropods and epifaunal suspension-feeding bivalves, (2) the maximum-flooding phase captures the establishment of epifaunal bivalve-dominated biostromes in the photic zone, and (3) the highstand phase is characterized by increasing infaunal suspension feeders and declining seagrass-dwellers in bryozoan-molluscan muddy sands. Changes in the community composition between the transgressive and the highstand phase can be explained by rising sea level, reduced light penetration, and increase in turbidity, as documented by the gradual up-core shift from coarse molluscan skeletal gravel with seagrass-associated molluscs to bryozoan sandy muds. In the uppermost 20 cm (median age <200 years), however, epifaunal and grazing species decline and deposit-feeding and chemosymbiotic species increase in abundance. These changes concur with rising concentrations of nitrogen and organic pollutants due to the impact of eutrophication, pollution, and trawling in the 20th century. The late highstand benthic assemblages with abundant bryozoans, high molluscan diversity, and abundance of soft-bottom epi- and infaunal filter feeders and herbivores represent the circalittoral baseline community largely unaffected by anthropogenic impacts.

Late Quaternary infilling of the Assu River embayment and related sea level changes in NE Brazil

A detailed geomorphological survey using Light Detection and Ranging (LiDAR) was carried out along the western part of the Assu River valley, NE, Brazil. The study was complemented by the investigation of sedimentological, mineralogical, and sediment benthic foraminifera indicators within the 14C geochronological framework. The integration of data sets permitted the reconstruction of the main phases in the evolution of this area during the Holocene. The shallow embayment, which is now completely infilled, acquired its present form within the limits of antecedent morphology developed since the last interglacial period. The main forcing factors responsible for repositioning the shoreline, which ran along the strike-slip Afonso Bezerra fault at an angle of approximately 35° to the present coast in the Early/Mid Holocene, were as follows: (1) tectonic activity along the strike-slip Afonso Bezerra fault, (2) fast inundation of the shallow paleo-valley embayment during the last pulse of Holocene transgression ca. 8000 cal yr BP, (3) advance of the Assu river mouth through accretion of fluvial bay head delta and costal drift sediments and (4) sheltering of embayment by barrier islands which permitted a widespread development of mangrove forest during the last 3 millennia. The estimated rate of progradation of the Assu estuary that led to the present stage of terminal infilling is in the order of 3–4 m/yr.