Wave-dominated Estuary Research Articles

Water renewal and stratification modelling in small estuaries

Water renewal and flushing in small, intermittently open or closed estuaries is receiving increasing attention particularly in light of the climate change induced alterations in run-off, wave and sediment transport conditions along coasts. The challenges of predicting the stratification-circulation state and the balance between tidal or freshwater flushing in response to the mouth dynamics of small, wave-dominated estuaries is the focus of the paper. Such predictions are required for determining estuary freshwater requirements or establishing an estuary's capacity to maintain sound water quality under pollutant discharges. Advances in simulating changes in stratification-circulation over long time scales are limited. Instead attention has focused on generating indices of stratification or water quality state using heuristic methods. In this paper, systems dynamics modelling is applied to simulate the non-linear response of the estuary to changes in river and marine water fluxes. The estuary is modelled as a basin with a specified water volume to water level relationship, connected to the sea by a channel with variable sill height, but fixed width. The direction and magnitude of the flow through the mouth determines whether the sill height erodes or accretes and hence the mouth dynamics (see Slinger, 2017). The tidal flux through the mouth co-determines the volumetric exchange of salt, influencing both the stratification state of the estuary and the degree of tidal or freshwater flushing. This is also influenced by run-off. The resulting dynamic balance is captured in two bulk indices, the Estuarine Richardson number and the bulk densimetric Froude number. Using measured data from the Great Brak Estuary, South Africa, the model is calibrated. Model simulations demonstrate the importance of tidal flushing and concomitant mouth breaching for water renewal as freshwater flushing declines under scenarios of increased water abstraction. Although the estuary remains partially mixed, there is increased average salinity and a more uniform the water column. Water releases and mouth breaching bring about a more natural stratification-circulation state, but these effects are short-lived.

Synthetic seismic forward modeling of a high-frequency depositional sequence: The example of the Tiber depositional sequence (Central Italy)

This research presents the results of a synthetic seismic forward modeling carried out by generating stacked sections of the stratigraphic-depositional architecture in the high-frequency Tiber Depositional Sequence (TDS) (Central Italy). The stacked sections were created using the seismo-acoustic approach provided in the geophysical codes developed by the CREWES consortium and modeled in Matlab. The models reproduce the seismic response of a sedimentary succession showing the upward transition from a wave-dominated estuary to a wave-dominated delta. The synthetic seismic sections reveal the subsurface structure and sedimentary architecture of the TDS, demonstrating the complexity of the sedimentary environments as well as the variation in lithology and petrophysical characteristics across the sections. The results demonstrate the ability of the seismo-acoustic approach to accurately model the seismic response of sedimentary facies in fluvial, coastal, and shelf environments, providing valuable information for exploring potential reservoir systems, with the TDS serving as an analog. In addition, the models identify several seismic facies and reflectors that can be interpreted as boundaries and surfaces of sequence-stratigraphic significance.

Incised-valley filling sedimentation in a small river valley of a wave-dominated, embayed coast in response to Holocene sea level rise, Yeongil Bay, Southeastern Korea

Incised-valley infill deposits are closely related to sea level changes during the post-glacial period of the late Quaternary and are an important topic in sea level history. In Asia, there are many large river basins that receive large amounts of sediment from the land, and the infilling deposits of incised valley systems have been well studied. Yeongil Bay is a semi-enclosed, funnel-shaped topographic feature on the east coast of the Korean Peninsula, located in the southwestern part of the East Sea (Sea of Japan). The Hyeongsan River, a small river flowing into Yeongil Bay, is flows perpendicular to the East sea. During the last glacial maximum (LGM), when the sea level was >120–130 m lower than at present in the Korea Strait, inflowing river processes are thought to have formed incised valleys. In this study, the sediment depositional patterns of incised valley fill since the LGM were examined by analyzing the sedimentary facies, optically stimulated luminescence (OSL) dates, and radiocarbon dates by accelerated mass spectrometry (AMS) of three sediment cores in Yeongil Bay. The infilling sequence consists of sediments from channel lag (>12 ka) and meandering river (12–10 ka), wave-dominated estuary (12–7.8 ka), and wave-dominated delta (7.8–0 ka) systems in ascending order. The barrier appear only in the outer part of Yeongil Bay. The barrier emerged from eroding estuary systems at 8.5 ka. Millennial-scale isochrons based on OSL and radiocarbon dates showed that fluvial and estuary systems were deposited in retrogradation and delta systems were deposited in progradation since LGM. The modern delta of the Asian large rivers were initiated by a decreasing rate of sea level rise during the mid-Holocene, and consideration of this is important for RSL. This study emphasizes the importance of accommodation capacity as much as sediment discharge as a factor in the timing of delta initiation. This study provides important insights into the incised-valley infill deposits and past environmental conditions, and may help to gain a better understanding of how coastal environments have changed with sea level changes.

Eco-morphological evolution of the Bolivar Peninsula (Texas, U.S.A.) during the last 2,000 years: A multi-proxy record of coastal environmental changes

In the face of rapidly changing climate and increasing natural and anthropogenic disturbances, the long-term dynamics of coastal ecosystems in relation to hurricanes and human activities has become a focus of research for ecologists and geomorphologists across the Gulf of Mexico. This study integrates diatom, remote sensing, geochemical, and hydrodynamic analyses to document the ecological and morphological development of the barrier-island and estuary-wetland complex bordering Galveston Bay, Texas, from the late Holocene to the Anthropocene. The multi-proxy dataset revealed two major ecological shifts between 1320 and 840 cal yr BP and between 230 cal yr BP and 2008 AD in Galveston Bay. The first shift was driven by the landfall of a backdoor hurricane at ∼1000 cal yr BP in combination with the aperiodic and intense long-shore current that caused the barrier complex to retreat over fluvial deposits while the Bolivar Peninsula was growing toward the west. These morphological changes resulted in a narrower inlet, hence, restricting the marine influence from entering the bay and converting Galveston Bay to a wave-dominated estuary that was shallower and fresher. The second shift was caused by increasing modification to the waterway and infrastructures since 1800 AD. As a result, rapid sediment accretion was induced near the North Jetty, forming the current Bolivar Flats and setting the stage for mangrove colonization. The warming climate and hurricanes in recent decades acted as catalysts that accelerated mangrove expansion on the Bolivar Peninsula. Our results imply that the proposed coastal barrier system will likely increase the sediment deficit, alter the biogeochemical environment, and impact the primary productivity in the bay. However, on a regional scale, more and more mangrove stands are expected to appear around estuaries and lagoons, and along man-made jetties and barriers along the Gulf.

Late Pleistocene to Holocene facies architecture and sedimentary evolution of the Zhejiang coast, East China Sea

The Holocene mud wedge that extends from the Yangtze River mouth to the Taiwan Strait along the Zhejiang–Fujian coast, East China Sea, has attracted considerable research attention; however, the pre-Holocene sedimentary evolution of the same area has been less well documented owing to limited data. We conducted an integrated analysis of 7000 km of high-resolution shallow seismic profiles and two ∼60–80-m-long borehole cores from the Zhejiang coast of eastern China to improve our understanding of the formation of the mud wedge in the context of the post-Late Pleistocene sedimentary evolution of the coastal area. Five major seismic units (numbered SU 1 to SU 5 in descending order) and various subunits that have formed since Marine Oxygen Isotope Stage (MIS) 5 were identified in the study area. SU 5 is recognizable only in the southeastern part of the study area and is interpreted to comprise subtidal to inner-shelf deposits (SU 5b) that were formed during MIS 5 and littoral to tidal-flat deposits (SU 5a) that were formed during the overall sea-level fall of MIS 4 and early MIS 3 (∼60–40 ka). These two subunits are divided by an intervening erosional surface that was likely generated by subaerial exposure of the study area during the sea-level lowstand of MIS 4. During the period from late MIS 3 to MIS 2, the study area was gradually exposed subaerially owing to further sea-level fall, with numerous small rivers incising the underlying strata to form a subaerial unconformity surface (T4). During the early postglacial transgression between ∼15.0 and ∼ 14.0 ka, the study area was progressively flooded, and the river channels were transformed into small estuaries (tidal rivers) that then coalesced into a large-scale, wave-dominated estuary during sea-level rise from ∼14.0 to ∼10.0 ka. The sandy fluvial and/or tidal-river deposits above T4 constitute SU 4. The wave-dominated estuary included a central estuarine bay on the landward side and an estuary-mouth complex on the seaward side, corresponding to fine-grained (muddy) deposits (SU 3a) and coarse-grained (sandy) deposits (SU 3b), respectively. The estuarine deposition concluded with the formation of a transgressive ravinement surface by erosional shoreface retreat during the rising sea level in the early MIS 1 from ∼13.5 ka in the southeasternmost part of the study area to ∼10.0 ka in the area closer to the shore. During the following transgressive phase, the study area was under coastal to shelf sedimentary environments during deposition of SU 2a. Tidal sand ridges (SU 2b) in the eastern part of the study area were formed at ∼11.5 ka and have been active since then. The maximum flooding surface was formed at ∼7.6 ka, and a mud wedge (SU 1) in the study area (except in the eastern part) has been developing since that time and is interpreted to have resulted from the deposition of sediments derived predominantly from the Yangtze River under the modern current system established since the maximum flooding in the Middle Holocene. The study provides new insights into the paleoenvironmental and paleogeographic evolution and facies architecture of the Zhejiang coast since MIS 5, which were controlled by preexisting geomorphological conditions and changes in sea level, hydrodynamics, and sediment supply.

Holocene filling of a narrow estuary in a regressive coast: The Paleo-Kinu Bay region, central Japan

Estuaries are typical depositional systems of transgressive coasts; however, depositional systems with similar geometry also occur on regressive coasts. Such “regressive estuaries” are found in areas of Asia, South America, and Australia that have experienced relative sea-level lowering since the middle Holocene. Regressive estuaries form in incised valleys that were drowned by the last deglacial sea-level rise and receive relatively little riverine sediment discharge. The largest estuary in Japan, with a length of 120 km and a width of 10 km, is in the Paleo-Kinu Bay region. A partly unfilled wave-dominated estuary developed in this region prior to the artificial diversion of the Tone River during the 17th century. In this study, we document the Holocene filling of the Paleo-Kinu Bay on the basis of 14 sediment cores and 171 radiocarbon dates. Unfilled wave-dominated estuary at 7–4 ka has more pronounced wave-built morphologic elements than at 4–0 ka. As a result of sea-level lowering and weakening of tidal currents at 4–0 ka, the bay mouth became narrowed by lateral accretion of sandy tidal river sediments and the central basin was filled by progradation of muddy bayhead delta sediments. The acceleration of the bay mouth narrowing and central basin infilling similar to what happened during 4–0 ka in the Paleo-Kinu Bay region have not been identified in transgressive estuaries, but are common features of regressive estuaries.

The role of antecedent morphology and changing sediment sources in the postglacial palaeogeographical evolution of an incised valley: The sedimentary record of the Ría de Arousa (NW Iberia)

Incised valleys represent dynamic coastal and shelf systems in continuous change in response to different temporal and spatial scales. Their sedimentary record offers valuable data to unveil the effect of different drivers, such as relative sea-level rise, on the evolution of coastal systems and provide invaluable records of palaeoenvironmental changes. In this work, the palaeogeographical evolution of the Ría de Arousa (NW Spain) from the Last Glacial Maximum to the present is reconstructed by identifying the main elements of sedimentary architecture. These elements are characterised using a multidisciplinary approach combining seismic, sedimentary, geochemical and palynological data. The general succession of the sedimentary infilling of the incised valley records an overall transgression in response to postglacial sea-level rise. A large fluvial valley evolves into a tide-dominated estuary and later to a wave-dominated estuary as it is progressively flooded. The complex interaction between variable rates of relative sea-level rise and the antecedent morphology exerts a strong control on hydrodynamics within the valley controlling the sediment dynamics and facies distribution, displaying some similarities with conceptual facies models for tide- and wave-dominated estuaries. The analysis of sediment sources also denotes significant changes in response to varying hydrodynamic regimes and climate, shifting from a predominant fluvial source in the earliest phases of the transgression to an increase in local sources (cliffs and local coastal deposits), including a likely reworking of older deposits (sediment recycling) during the Early Holocene. These changing sediment sources may have a clear impact on the palynological signal recorded within the incised valley, hypothetically masking and overprinting the climatic signal during phases of intense reworking of older deposits. Sediment recycling seems extensive within the incised valley and represents a key process that needs to be evaluated to understand the source-to-sink sediment flux to the deeper ocean. Its impact on the sedimentary records may have major implications for palaeoenvironmental studies in coastal settings, stressing the importance of applying multi-proxy approaches. • Palaeogeographical evolution of an incised valley from Last Glacial Maximum to present. • Multidisciplinary analysis of elements of sedimentary architecture • Antecedent morphology exerts a strong control on hydrodynamics and facies distribution. • Shift from a fluvial source to local sources, including reworking of older deposits. • Changes in sediment sources may have an impact on the palynological signal recorded.

Long-term morphodynamic evolution in the Modaomen Estuary of the Pearl River Delta, South China

Anthropogenic activities and natural disturbances will cause large-scale changes in the morphology of estuarine systems. Studies of estuarine morphology tended to focus on a single driving factor, however, the intertwined effects (e.g., land reclamation, sand excavation, tides, waves, runoff) are rarely mentioned in the literature. This work characterizes and conceptualizes the morphodynamics of the Modaomen Estuary (ME), the largest estuary in the Pearl River Delta (PRD), China, based on Landsat satellite imagery, high-resolution bathymetry survey data, and in situ hydrographic measurements. The morphodynamic evolution of the ME since the 1970s–2010s is analyzed with respect to planform configuration and bathymetry. Quantification of estuarine hydrodynamic and sediment parameters for the most recent years indicates that the ME has transformed from a traditional fluvial- and tide-dominated estuary into a fluvial- and wave-dominated estuary. Ocean currents intrude along the eastern channel and draw down along the western channel, in which estuarine flow deflection is induced by the combined effect of upstream runoff, coastal waves, and littoral currents. Furthermore, a life-cycle model of the morphological migration of the ME is presented by synthesizing hydrodynamics and sediment dynamics. This conceptual model of three geomorphological states clearly shows that the main channel experiences a life cycle covering several decades, from the origin of the main channel to its bifurcation into two distributaries, and finally a recovery and westward deflection of the main channel. The cognition of the appearance and disappearance with one sandbar and two channels will be helpful in numerical modeling of estuary evolution, and it also has important implications for the regulation of estuarine regions, hazard prevention and channel navigability.

The interplay of environmental constraints and bioturbation on matground development along the marine depositional profile during the Ordovician Radiation.

This study documents the distribution of matgrounds in a wide variety of environments recorded in the Ordovician Lashkerak and Ghelli Formations in the Alborz Mountains of northern Iran in order to evaluate controls on their distribution along the marine depositional profile. Detailed facies analysis allowed differentiating three groups of facies associations in the Lower to Upper Ordovician deposits of the Lashkerak formation: (i) estuarine system; (ii) wave-dominated shoreface-offshore complex; and (iii) mixed river- and wave-influenced deltaic system. The Middle to Upper Ordovician deposits of the Ghelli formation are divided into two groups of facies associations: (i) tide-influenced deltaic succession and (ii) deep-water fan system. Microbially induced sedimentary structures (MISS) are present in deposits formed in the central estuarine basin (Lashkerak formation) and in proximal lobes and lobe fringes of deep-water turbidite fans (Ghelli formation). On the contrary, MISS are absent in deposits from the wave-dominated shoreface-offshore complex, river- and tide-dominated deltas, and various subenvironments of the incised wave-dominated estuary (i.e., bayhead delta and estuary mouth) and the deep-marine turbidite fan system (i.e., turbidite channel, slope, and outer lobe). The lack of evidence of mat-building microorganisms in the deltaic systems may have resulted from two factors: (1) high physico-chemical stressors caused by river-induced processes, and (2) increase in degree of sediment disturbance, biodiffusion, and bioirrigation by burrowing organisms. Formation of microbial mats in the wave-dominated shoreface-offshore complex was inhibited by the activity of an abundant and diverse infauna capable of reworking the sediment. Our analysis shows that the spatial distribution of microbial mats was controlled by an interplay of environmental factors and innovations in animal-substrate interactions, mostly expressed by secular changes in bioturbation. This study supports the notion that the agronomic revolution was diachronic, with marginal-marine and deep-sea ecosystems lagging behind shallow-marine settings.

The qualitative and quantitative classification of modern clastic marginal-marine depositional systems, Trinidad

ABSTRACT Trinidad's modern coastal depositional systems are for the first time documented by (traditional) descriptive and (modern) semiquantitative and quantitative classification methods. The processes controlling the morphology and distribution of these systems are also investigated. Google Earth™ satellite images, together with published basinal processes data (e.g., significant wave height, surface littoral currents, and tidal cyclicity) are used to describe system morphology, map depositional elements, and to determine the processes responsible for system distribution, respectively. Coastal depositional systems along Trinidad's east, south, and west coasts comprise deltas, estuaries, tidal-inlet complexes, strandplains, and tidal flats. Their distribution is controlled by the wave regime, although they are also influenced by tidal and fluvial processes. The wave regime changes from wave-dominated along the open east coast, to mixed-energy wave-dominated along the semi-sheltered south coast, and to mixed-energy tide-dominated along the sheltered west coast. Distribution of depositional systems related to this regime are such that the wave-dominated east coast sees the development of wave-dominated estuaries. The south coast has a series of wave-dominated, tide- and river-influenced deltas. The sheltered west coast is the most morphologically diverse with river- and wave-dominated deltas, strandplains, and tidal flats. The application of semiquantitative and quantitative classification methods on modern systems has showed their competence in classifying mixed-influence systems from their morphology and sedimentary record. Quantitative classification using depositional elements lends an appreciation to the morphological signatures of mixed-influence systems. Quantitative classification for sedimentary sections gives an appreciation of the preservation of mixed-influence physical processes. The combination of both allows the correlation of the impact of physical properties on morphology and sedimentary record (i.e., possible disparities between morphology and processes). The combination of semiquantitative and quantitative methods may also hold the key to unlocking the mixed-processes classification of depositional elements.

Integration of borehole depth imaging and seismic reflection results in reservoir delineation: An example from The Alam El Bueib 3C field, Northern Western Desert, Egypt

The Alam El Bueib 3C Field is located in the eastern part of the Dahab-Mireir sedimentary basin in the north Western Desert of Egypt. The Lower Cretaceous Alam El Bueib Sandstone reservoir is a potentially producing reservoir in the field. Lithostratigraphic correlation and ditch cutting description have helped in stratigraphically locating the potential sandstone reservoirs within the basal part of Alam El Bueib 3A Bed and locally dividing it into three potential separate reservoirs. Qualitative analysis of borehole depth imaging logs helped in revealing the stratigraphic trap style of Basal Alam El Bueib sandstone reservoirs and detection of deposition paleoenvironment as a shallow marine environment of wave-dominated estuary channelized system. Structural seismic interpretation for available Pre-Stack-Depth-Migrated 3D seismic data has revealed that AEB 3C Field structure is a four-way dip anticlinal closure that trends north east-south west. A better understanding of the geological nature of the Alam El Bueib 3A sandstone reservoirs combined with the structural-stratigraphic trap style has led to a lower risk exploratory/development plan for Alam El Bueib potential sandstone reservoirs in the Alam El Bueib 3C field. Borehole depth imaging analysis results, integrated with seismic structural interpretation maps and information from conventional electrical well logs, represented a high-quality workflow that showed remarkable efficiency in a better understanding of reservoir distribution in the case of present heterogeneous Alam El Bueib sandstone reservoirs and providing the optimum solution for similar geological conditions in other areas.

Multi-stage Holocene evolution of the River Murray Estuary, South Australia

The River Murray Estuary, South Australia exhibits a morphology typical of a wave-dominated estuary and comprises two large, shallow central basin lakes – Lakes Alexandrina and Albert. Contested interpretations of the estuary’s limnological history and uncertainty surrounding the sustainability of current basin water usage practice warrant a robust investigation into how the system has evolved. Here we combine lithostratigraphic, geochemical and sedimentological evidence from a transect of sediment cores to reconstruct the sediment infill history of the system. We uncover multiple stages of sediment infill over the history of the system, associated with (1) the low gradient morphology of the estuary and lower river channel, (2) the mid- to late-Holocene sea-level regression and (3) anthropogenic modifications to the fluvio-estuarine system. We show that while estuarine conditions in the system were fully established during the mid-Holocene highstand (~6.4 kyr BP), central basin facies sedimentation was focussed further inland before prograding with the lowering of base level and shifting of tidal influence as sea-level fell. Central basin facies sedimentation within northern Lake Albert occurred from 5.4 to 4.0 cal kyr BP at ~0.25 cm yr-1. The uppermost accumulation of this unit was eroded by continued reduction in base level until sea-level regression concluded at 3.5 cal kyr BP. Barrage and weir installation (1940 CE) re-initiated and expanded central basin facies sedimentation in the estuary (~0.32 cm yr-1). Recently deposited sediments exhibit geochemical markers of increased trophy and more frequent acid sulfate soil acidification, exposing human impacts on the estuary.

Evolution from estuary to delta: Alluvial plain morphology and sedimentary characteristics of the Shoalhaven River mouth, southeastern Australia

The Shoalhaven River in southern New South Wales (NSW) drains a catchment of ~7000 km2, forming a barrier estuary at its mouth with a prograded strandplain to its north. Previous coring and dating across the floodplain and adjacent strandplain indicate progressive infill of the estuarine basin over the past 7000 years. Over this time the system transitioned from a wave-dominated estuary to a wave-dominated delta. The Shoalhaven River appears to have initially discharged to the sea at Crookhaven Heads, until it adopted a more direct route through an intermittently open mouth at Shoalhaven Heads; construction of Berrys Canal in 1822 now permanently links the Shoalhaven River to the adjacent smaller Crookhaven River. Airborne LiDAR reveals details of topography of prominent levees and meander scroll bars that flank the lower reaches of the river and beach/foredune ridges to the north. Sedimentological and mineralogical characteristics of modern sediment samples collected from the river channel, the beach, and the barrier reveal that the Shoalhaven River is dominated by quartz sand along its predominantly straight course through the infilled estuarine plains. This is in contrast to the tripartite classification of sedimentary depositional environments, comprising sandy fluvial delta, central mud basin, and sandy marine barrier, that characterised the initial wave-dominated estuary 7000 years ago, and is typical of most barrier estuaries in NSW. Grain size decreases downstream and sands have a higher feldspar content, and angularity, than is typical of marine sand that has been reworked in the nearshore. This fluvially-derived component is delivered to the coast intermittently by floods that re-open Shoalhaven Heads, as shown by retrospective analysis of aerial photography and satellite imagery. Grain size decreases with distance alongshore from the river mouth indicating that these sands are transported north by longshore drift to augment a gradual onshore delivery of sand within this coastal compartment. Scanning electron microscopy of selected grains implies that this fluvial sand has been contributing to incremental formation of beach ridges for much of the past 3000 years since the estuarine basin has been largely infilled, with a slight detectable acceleration in the rate of progradation.

Regional and oyster microenvironmental scale heterogeneity in the Pacific oyster bacterial community.

Different organs of a host represent distinct microenvironments resulting in the establishment of multiple discrete bacterial communities within a host. These discrete bacterial communities can also vary according to geographical location. For the Pacific oyster, Crassostrea gigas, the factors governing bacterial diversity and abundance of different oyster microenvironments are poorly understood. In this study, the factors shaping bacterial abundance, diversity and composition associated with the C. gigas mantle, gill, adductor muscle and digestive gland were characterised using 16S (V3-V4) rRNA amplicon sequencing across six discrete estuaries. Both location and tissue-type, with tissue-type being the stronger determinant, were factors driving bacterial community composition. Bacterial communities from wave-dominated estuaries had similar compositions and higher bacterial abundance despite being geographically distant from one another, possibly indicating that functional estuarine morphology characteristics are a factor shaping the oyster bacterial community. Despite the bacterial community heterogeneity, examinations of the core bacterial community identified Spirochaetaceae bacteria as conserved across all sites and samples. Whereas members of the Vulcaniibacterium, Spirochaetaceae and Margulisbacteria, and Polynucleobacter were regionally conserved members of the digestive gland, gill and mantle bacterial communities, respectively. This indicates that baseline bacterial community profiles for specific locations are necessary when investigating bacterial communities in oyster health.

Evolução estratigráfica dos depósitos cretáceos da porção norte da Bacia de São Luís-Grajaú (NE do Brasil)

Os depósitos cretáceos da Bacia de São Luís-Grajaú são recorrentemente organizados, nos trabalhos prévios, em três sequências deposicionais, consolidadas desde o Neoaptiano até uma idade incerta no Neocretáceo, abrangendo as formações Grajaú e Codó, como também o Grupo Itapecuru. Este trabalho objetivou aplicar a estratigrafia de sequências, com base na correlação de perfis litológicos e de raios gama, na análise dos depósitos cretáceos localizados na parte norte da bacia. Para esse propósito, esta pesquisa utilizou dados de cinco poços, interpretados em uma etapa 1D, que posteriormente serviram de base para a construção de uma seção estratigráfica, interpretada em uma fase 2D. Além disso, trabalhos prévios acerca dos sistemas deposicionais envolvidos na sedimentação desses depósitos cretáceos foram cotejados para propor um modelo evolutivo para o intervalo estudado. A partir da integração dessas interpretações, individualizou-se o intervalo em duas sequências deposicionais (A e B), sendo cada uma delas composta por três tratos de sistemas: de nível baixo (TSNB), transgressivo (TST) e de nível alto (TSNA). A Sequência A foi, primariamente, dominada por processos flúvio-deltaicos correspondentes ao TSNB. Posteriormente, representando o TST, houve a ampliação das fácies lacustres, paralelamente à retração do sistema flúvio-deltaico desenvolvido durante a fase anterior. Finalmente, caracterizando o TSNA, ocorreu uma continuação dos processos suspensivos vistos no TST, porém com a influência de fluxos hiperpicnais. No tocante à Sequência B, inicialmente instalou-se um sistema deltaico representativo do TSNB. Subsequentemente, no TST, esse delta deu lugar a um estuário dominado por ondas. Por fim, em um estágio atribuído ao TSNA, um sistema deltaico novamente se estabeleceu, encerrando assim a história evolutiva do intervalo analisado.

Integrated sedimentological and palynological analysis from Early Cretaceous estuarine deposits in the southern-central Neuquén Basin, Argentina

The Mulichinco Formation represents one of the main gas producer unit in the Neuquén Basin and particularly, an improvement in its reservoir qualities are mostly indicated in subsurface for its upper section. Because the economic importance of this interval, sedimentological and palynological analysis were made on deposits from outcrops of the upper section of the unit, located at the southern-central Neuquén Basin. The studied section includes four main facies association which represent accumulations in a wave-dominated estuary, non-previously described for the Mulichinco Formation in the study area. In addition, sixty-six new palynomorphs species were identified which were new for the unit, including fifty-six spore species, twenty-five pollen grain taxa, and two algae. Ferns and conifers species were identified as dominant taxa. Moreover, mega and palynofloristic assemblages provide information about drainage conditions of the inhabited environment, suggesting spatial variations when comparing upland subaerial well-drained plains with lowland subaqueous poorly-drained areas and, at the same time, climatic variations are considered, inferring temperate to warm and wet palaeoclimatic conditions. The integration of sedimentological and palynological interpretations provides a more complete picture of the Valanginian estuarine system and ecosystem that developed towards the southern-central area of the Neuquén Basin. Furthermore, the studied palynological assemblages are consistent with a Late Valanginian age, and can be referred to the Zone 2 and to the Cyclusphaera psilata-Classopollis Association suggested for the Neuquén Basin.

Late Holocene environmental changes and anthropogenic impact in Dee Why Lagoon, New South Wales

Late Holocene environmental changes were examined in Dee Why Lagoon, New South Wales, based on the sedimentological, geochemical and geochronological analysis of six cores collected from the fluvial delta and lagoon basin. The lagoon formed about 7300–7200 cal yr BP, following the post-glacial marine transgression and establishment of a sand barrier. Infilling of the lagoon occurred at a rate of 0.09–0.15 mm/yr until about 3300–3200 cal yr BP, when the barrier closed, resulting in mostly freshwater conditions, as evidenced by a change from pyrite-rich units to sediment containing little sulfur and a lack of foraminifera. Sedimentation rates increased to 0.23 then 0.43 mm/yr until about 100 years ago. Post-European land clearance led to an increase in sedimentation rates to 1.0–1.3 mm/yr on the fluvial delta, which are lower than those from other wave-dominated estuaries in New South Wales as well as those estimated by previous studies in Dee Why Lagoon. Our study shows that the fluvial delta started forming much earlier than originally thought, based on results of radiometric dating, and confirmed using sedimentological and geochemical data, as well as a critical examination of historic aerial photographs. Human impact has resulted in an increase in heavy metal (Cu, Pb, Zn) and metalloid (As) concentrations in the recent sediment, most likely attributed to stormwater discharge. Pb and As concentrations are above the ANZECC high sediment quality guideline values at the site closest to the stormwater outlet, with As-based pesticides one of the possible sources. Using the mean enrichment quotient, which is based on normalised Cu, Pb and Zn concentrations over their normalised background concentrations, we show that the surface sediments in Dee Why Lagoon are severely enriched, reflecting the recent anthropogenic impact that has also led to an increase in sedimentation rates.

Interconnected Accommodation Space Controls Between Sand-Charged Shallow Tidal Channels and Wind-Wave Truncated Tidal Flats During Latest-Holocene Sea Level Rise (~3.0 m) in a Large Mesotidal Wave-Dominated Estuary, Grays Harbor, Washington, USA

The late-Holocene (5–0 ka) record of accommodation space controls of tidal channel and tidal flat deposition in the shallow mesotidal wave-dominated Grays Harbor estuary (236 km2 surface area) was investigated in previously reported drill cores (n=15) and new vibracores (n=20), reaching 3–10 m depth subsurface. Continuous vibracore facies sequences (3–4 m depth subsurface) discriminate between tidal channel and tidal flat deposition and demonstrate responses of both depositional settings to interseismic uplift and coseismic subsidence (1±0.5 m vertical) from cyclic neotectonic forcing (200–800 yr recurrence intervals) in the Cascadia subduction zone. Vibracore channel samples, at 0.5 m or 1.0 m depth intervals, were analyzed for sediment grain size (sample n=124) and sand source mineralogy (sample n=67). The mean and standard deviation of sand size in the sand fraction is 175±x34 1σ µm. Sediment 14C dates (n=29) range from 376 to 6,579 median calyrBP and establish long-term sedimentation rates in subtidal channel accretionary banks (average 4.2 m ka-1), intertidal channel accretionary banks (average 3.7 m ka-1), and tidal flats (average 1.1 m ka-1). Tidal channel accretionary bank deposition largely reflects reworking of pre-existing estuary deposits. Long-term total basin sediment accumulation rates (232x106 m3 ka-1) are tied to rates of net sea level rise (1.0 m ka-1) or increasing basin accommodation space. In latest Holocene time (3–0 ka) littoral sand import (117x106 m3 ka-1) was about twice as large as the retention of river sand and mud in the estuary. The selective export of winnowed mud from the estuary provided the necessary accommodation space for the import of littoral sand in latest-Holocene time. Shallow intertidal settings in Grays Harbor (60% by surface area) are maintained by self-regulating conditions of channelized sediment import, wind-wave erosion of tidal flats, and tidal prism forcing of tidal channel discharge. Hind-casted wind-wave bottom orbital velocities (>20 cm sec-1) are sufficient to truncate tidal flat elevations to lower-intertidal levels, which maintain substantial tidal prism volumes (modern MLLW-MHHW ~6.1 x 108 m3) and associated tidal channel discharge in the shallow estuary. Net sediment deposition in the estuary is controlled by the interaction of limiting accommodation space controls in the tidal flats and tidal channels. The balance between sediment supply, energy of sediment transport/resuspension, and sediment export has survived small changes in relative sea level (1±0.5 m) from cyclic neotectonic forcing. However, the prehistoric (natural) balance could be altered by future anthropogenic impacts from sustained global sea level rise (> 1.5 m during the next century) or diminished wind-wave fetch distances, which could result from tidal flat diking/filling or uncontrolled spread of non-native invasive stabilizing sea grass (Spartina). In this regard, the susceptibilities of prehistorically-balanced sediment dynamics in Grays Harbor serve as warning for other similar mesotidal wave-dominated estuaries that could be impacted by future global sea level rise, changing sediment inputs, and/or tidal flat diking/filling, which could reduce intertidal habitat and associated ecosystem functions.

A Drowned Lagunar Channel in the Southern Brazilian Coast in Response to the 8.2-ka Event: Diatom and Seismic Stratigraphy

Drowning of the coast was initiated by a marine inundation after the Last Glacial Maximum (marine isotope stage (MIS) 2) and has continued during the mid-Holocene and highstand (MIS 1). Detailed analyses of two previously examined core stratigraphy and seismic profiles combined with new grain-size and detailed diatom analyses are used to study the history of the Barra Falsa paleochannel over the last 11,000 years BP and to document the peculiar deposition within the channel fill. A rapid sea-level rise was responsible for flooding the coast in 11,180–10,780, 8420–7930, 8150–7870, and 7640–7430 cal years BP, infilling a low topographic back-barrier region. High deposition rates suggest a rapid filling of the channel, which coincides with an accelerated period of sea-level rise, closely linked to the global 8.2-ka event. The morphology of the channel is recognized by facies units in the underlying strata related to one episode of cut and fill during a single cycle of base-level fall and rise. An overall transgressive sequence above the regional surface is related to marine and marine-brackish sediments, which corresponds to a seaward/central basil fill of a wave-dominated estuary.

Tidal Flat Depositional Response to Neotectonic Cyclic Uplift and Subsidence (1–2 m) as Superimposed on Latest-Holocene Net Sea Level Rise (1.0 m/ka) in a Large Shallow Mesotidal Wave-Dominated Estuary, Willapa Bay, Washington, USA

The late-Holocene record of tidal flat deposition in the large shallow Willapa Bay estuary (43 km in length), located in the Columbia River Littoral Cell (CRLC) system (160 km length), was investigated with new vibracores (n=30) and gouge cores (n=8), reaching 2–5 m depth subsurface. Reversing up-core trends of muddy sand to peaty mud deposits in marginal tidal flat settings demonstrate episodic submergence events resulting from cyclic tectonic uplift and subsidence (1–2 m) in the Cascadia subduction zone. These short-term reversals are superimposed on longer-term trends of overall sediment coarsening-up, which represent the transgression of higher-energy sandy tidal flats over pre-existing lower-energy tidal flat mud and peaty mud deposits in late-Holocene time. Fining-up trends associated with channel lateral migration and accretionary bank deposition occurred only infrequently in the broad intertidal flats of Willapa Bay. Vibracores and gouge cores were dated by 14C (n=16) and paleo-subsidence event contacts (n=17). Vibracore median probability 14C ages ranged from 0 to 6,992 yr BP and averaged 2,174 yr BP. Dated sample ages and corresponding depths of tidal flat deposits yield net sedimentation rates of 0.9–1.2 m ka-1, depending on the averaging methods used. Net sedimentation rates in the intertidal flat settings (~1.0 m ka-1) are comparable to the rate of net sea level rise (~1.0 m ka-1), as based on dated paleo-tidal marsh deposits in Willapa Bay. Reported modern inputs of river sand (total=1.77x104 m3 yr-1), from the three small rivers that flow into Willapa Bay, fall well short of the estimated increasing accommodation space (1.9x105 m3 yr-1) in the intertidal (MLLW-MHHW) setting (1.9x108 m2 surface area) during the last 3 ka, or 3.0 m of sea level rise. The under-supply of tributary sand permitted the influx of littoral sand (1.1x105 m3 yr-1) into Willapa Bay, as based on the net sedimentation rate (~1.0 m ka-1) and textural composition (average 60 % littoral sand) in analyzed core sections (n=179). The long-term littoral sand sink in Willapa Bay’s intertidal setting (55 % of total estuary area) is estimated to be about 5 % of the Columbia River supply of sand to the CRLC system, and about 30% relative to the littoral sand accumulated in barrier spits and beach plains during late-Holocene time. A 2.0 m rise in future sea level could yield a littoral sand sink of 2.2x108 m3 in the Willapa Bay intertidal setting, resulting in an equivalent shoreline retreat of 600 m along a 50 km distance of the barrier spit and beach plains that are located adjacent to the Willapa Bay tidal inlet. Willapa Bay serves as proxy for potential littoral sand sinks in other shallow mesotidal estuary-barrier-beach systems around the world following future global sea level rise.