Flood-tidal Delta Research Articles

Morphometry of non-tidal inlet (prorva) channels: Tendra-Dzharylgach barrier system, Black Sea Coast, Ukraine

This study focuses on relatively understudied coastal systems – non-tidal inlets along a barrier coast. We describe the morphological elements of these inlets (prorvas) along the northern coast of the Black Sea using an example of the Tendra-Dzharylgach barrier (TDB) system, Ukraine. Channels vary from 15 m to >700 m in width, with relatively shallow depths of 1.0–1.5 m (rarely >3 m). This is a first comprehensive overview of TDB breaches and their evolution as inlets, with dynamic relationships between the channel and its associated depositional elements (frontal and bay-side deltas). Comparisons are made with the analogs of the latter along tide-influenced coasts: ebb- and flood-tidal deltas, respectively. The region of interest is subject to the effects of both rapid geomorphological change and ongoing military conflict, making this field dataset of great relevance in complementing other remote sensing databases at nearby sites.

Millennial and contemporary dynamics of the barrier estuary entrance at Moruya, SE Australia

ABSTRACT This study presents optically stimulated luminescence (OSL) dates, sediment coring, historical maps and charts and photography and airborne LiDAR to reconstruct the millennial and contemporary history of the Moruya River entrance. OSL dating reveals small estuarine beaches were active between 7000 and 5000 years ago, when the entrance was far more open than at present. At that time, a large flood-tide delta infilling a wide immature estuary is likely to have existed. Continued progradation of the Bengello barrier to the north, and the inception of the Moruya Heads barrier to the south from 4500 years onward, progressively constricted the river entrance. Several more low-energy estuarine beaches developed behind the Moruya Heads barrier and are dated to ~4400 and ~2800 years ago. Concurrently, the open mud basin of the estuary infilled with fluvial sediment. Following the arrival of Europeans in the region, in the early to the mid-1800s, engineering works were undertaken in stages to train the estuary entrance for navigation and have further constrained the system. OSL dating of beaches formed as a result of this activity concur with the historical accounts. These contemporary changes to the entrance have modified the estuary hydrodynamics and shifted the sediment transport and ecological regime of the lower estuary.

Rapid barrier estuary infill in a geologically-constrained setting: Aireys Inlet/Painkalac Creek, Victoria, Australia

The Holocene infill of an intermittently open-closed barrier estuary (Painkalac Creek/Aireys Inlet) was examined on the southern margins of Australia, through aerial LiDAR, coring, sedimentology, radiocarbon dating and pollen analysis. It is found that almost all the accommodation space within the estuary has been occupied, with a thick sequence (>9 m) of sediments being deposited rapidly soon after flooding by the sea. The rate of sedimentation was 4.8 mm/year which closely matches the rate of sea level rise (4.5 mm/year) during the 1200 year period that the estuary infilled, from around 8000–6800 years ago. The evidence of estuarine deposition above the elevation of the modern intertidal zone provides significant further evidence for the presence of the mid-Holocene highstand sea level in this relatively unstudied part of the Australian coast. The pattern of infill departs from the traditional barrier evolution models. The first phase of infill was likely tide dominated with subtidal sand shoals being found landward of a subtidal bedrock sill. Once a beach-barrier sequence formed, the estuary infilled in a more traditional manner, with lateral progradation of a flood tide delta and central mud basin infill. The barrier estuary of Painkalac Creek therefore has undergone a complex evolutionary history, characterised by a change in process dominance from classic tidal to wave-dominated form. Infill occurred in a keep-up (or fast catch-up) mode, with geological control occurring in regard to the presence of an intertidal bedrock sill at the mouth of the estuary.

Lithofacies and Sediment Sequences of a Microtidal, Wave-Dominated Tropical Estuary in Somone Lagoon (Senegal, West Africa)

Estuary sedimentary sequences have been the focus of several papers in the last decades; however, the majority these papers were centered in mesotidal and macrotidal estuaries of the middle latitudes. This present paper studies, from a sedimentological point of view, the infilling of a microtidal, wave-dominated tropical estuary, where wide tidal flats, mangroves and sabkhas are developed. Somone Lagoon is a Senegalese protected environment, very rich from an ecological point of view and with a definitive touristic vocation. For this work, 14 piston cores were studied. Additionally, the grain size, calcium carbonate and organic matter contents of 61 sediment samples vertically distributed in these cores were analyzed. The distribution of facies and the vertical sequences of sediments show the influence of the tropical seasonal fluctuations of fluvial sediment supply and evaporation processes. A high degree of bioturbation and an elevated organic content can be interpreted as the result of a high capacity of retention of the organic material into the estuary influenced by the weak tidal currents typical of a microtidal regime. These processes, acting since the last Holocene invasion of sea level, caused an advanced state of infilling of this estuarine system where both flood tidal deltas and bay head deltas prograde above the fine facies of the central domain of the estuary.

Late Quaternary geological history of the Sydney estuary, Australia

The present study provides valuable new information on the evolution of Sydney estuary by tracing the development of the complete marine–estuarine–fluvial system through a full glacial cycle (Last Interglacial, LIG, to the present Interglacial). Extensive seismic (361.3-line km) and sedimentological studies provided a sound foundation for production of a detailed litho- and seismic-stratigraphic record for the estuary. In the absence of reliable age data, a relative chronology was constructed based on Quaternary flooding surface elevations constrained by a recent local relative sea-level record supported by other global studies. A thick, ubiquitous estuarine unit deposited during the LIG period (MIS 5.5; 130–115 ka BP) was an important chronological marker horizon and played a critical role in controlling seismic interpretation and correlation throughout the estuary. Deposition during the MIS 5.1/5.3 interstadial period (100–80 ka BP) resulted in deposition of fine-grained, estuarine sediments in the lower estuary and time-equivalent, fluvial-sourced estuarine and channel sediments, and marsh sediments in the upper and central estuary, respectively. The MIS 3 interstadial event did not play a significant role in sedimentation in Sydney estuary. An eolian dune field formed adjacent to the southern shores of the estuary during the last glacial (31–24 ka BP) when most of the sediment in the lower estuary had been removed by fluvial erosion. Transgressive marine sand, which deposited in the lower paleovalley after the ocean re-entered the estuary, experienced repeated erosion and infilling by laterally migrating paleoriver channels. A marine flood-tide delta now occupies the estuary mouth, and the lower and upper/central estuary are mantled in a veneer (mean 7 m) of Holocene sand and mud, respectively. KEY POINTS A relative chronology was based on Quaternary flooding surface elevations constrained by relative sea-level. First geological history of the Sydney estuary with a complete marine–estuarine–fluvial system. A late Quaternary estuary evolution through a full glacial cycle. Geological history includes an interstadial (MIS 5.3/5.1) estuarine sequence.

Paleocene (65–63 and 58.5 ma) marine flooding and 62–60 ma sediment bypass in southern Wyoming, U.S.A.: Implications for Laramide sediment flux to the Gulf of Mexico

ABSTRACTSedimentary structures unique to tidally influenced environments and unambiguously salinity-stressed marine ichnofossil assemblages in the lower Paleocene Ferris and upper Paleocene Hanna formations of Wyoming's Hanna Basin (HB) necessitate major revision of local and regional reconstructions of the Paleocene Western Interior Seaway (WIS). Preserved in sandy estuarine bars, sandy tidal flats, heterolithic distributary channels, bayhead delta, and flood-tide-delta deposits similar those in the modern Trinity River, its bayhead delta, and the San Luis Pass flood-tidal delta on the Texas coast, these these assemblages include Arenicolites, Bergaueria, Fuersichnus, Gyrochorte, Ophiomorpha, Palaeophycus, Planolites, Psilonichnus, Rhizocorallium, Rosselia, Siphonichnus, Skolithos, Spongeliomorpha, Taenidium, Thalassinoides, and tetrapod tracks. Mapping an ∼ 325-m-thick succession of lower Paleocene strata (65 to 63 Ma) around the western HB reveals a series of marine flooding events, each followed by coal accumulation. A similar, 170-m-thick succession of interfingering coastal-plain and restricted-marine strata occurs in the upper Paleocene (58.5 Ma) Hanna Formation, following accumulation of lacustrine and floodplain deposits and an episode of major gravel and cobble progradation from 62 to 60 Ma. These younger ichnofossils record the final major transgression of the WIS and have major implications for the depositional environment of the time-equivalent Waltman Shale in the Wind River Basin to the north and for sediment routing to the Gulf Coast Wilcox sands. Ichnofossils are an underutilized source of physicochemical proxy data that are lifting the veil from the cryptic Paleocene transgressions of the WIS that have for so long remained undetected because of the absence of open-marine body fossils.

Modelling study on the sediment dynamics and the formation of the flood-tide delta near Cullendulla Beach in the Batemans Bay, Australia

The first 3-D current-wave-sediment coupled model of the semi-exposed estuary Batemans Bay, New South Wales, Australia, was developed in our study based on the Finite Volume Coastal Ocean Model (FVCOM). Our study explored the hydrodynamics, sediment dynamics and morphology change inside the Batemans Bay under large wave events. The modeled monthly-averaged residual flow, sediment flux and suspended sediment concentration with a combined tidal and wave forcing in the inner bay were significantly different to those only with tidal forcing, this is because the storm wave events can generate wave-induced currents and large bottom stresses, influencing the sediment transport. In addition, the morphology change of the flood-tide delta (FTD) inside the Batemans Bay under wave effects was also investigated in this study. According to previous studies, the FTD is a sediment deposit located on the landward side of tidal inlets, formed by the incoming tidal currents and ocean waves, which is an important morphology coastal feature influencing the sediment exchange with adjacent beach systems. Yet, the dynamic processes of FTDs have not been fully understood and explored quantitatively in sheltered estuaries. Based on our model results, the FTD near Cullendulla Beach is controlled by wave effects and was in an equilibrium status: when the FTD was eroded deeper to a critical value (about 2 m) by waves, sedimentation occurred. The rocky headland adjacent to the FTD contributed to the formation of the FTD due to sheltering effects, and the FTD actually developed at the ‘wave shadow areas’ behind the headland in Batemans Bay, which were dominantly controlled by sheltering effects. Despite being termed a ‘Flood-Tide Delta’, ‘Tide’ here is misleading, and a new name of ‘Wave Shadow Shoal’ should be given to describe such wave-dominated coastal features. In conclusion, this study demonstrated that waves played the dominant role in the hydrodynamic processes, sediment transport and morphology change in Batemans Bay.

Estimation of bedload sedimentation rate in a paleo-drowned river-valley

Extensive, high-resolution seismic data were correlated with borehole, land use, and geological data to calculate the mass of genetically different sediment deposits in the Middle Harbour estuary in Sydney, Australia. Middle Harbour is a drowned-river valley located adjacent to the larger Sydney estuary. The estuary follows a well-defined sedimentation model featuring small fluvial bedload delta deposits in the upper reaches of the embayments, a deep, central extensive mud basin overlying transgressive basal accumulations and a large flood-tide delta at the entrance. Deposits of an estimated 5094 t of bedload, 21,143 t of suspended sediment and 5947 t of transgressive basal material located in the estuary provided average sediment accumulation rates of 0.68 t year−1, 1.29 t year−1, and 2.86 t year−1, respectively. These rates, determined from measured accumulations, were surprisingly low and substantially smaller than modelled rates. However, low sediment accumulation rates for suspended material may be due to fine sediment escaping over the top of the marine tidal delta, which effectively traps all bedload material from exiting the Harbour. Results of this study indicate that Holocene bedload sedimentation in Middle Harbour was slow and regular until a rapid increase after urbanisation commenced in the catchment. Most pre-Holocene material was eroded from Middle Harbour during the Last Glacial period with sediment currently present in the estuary having been deposited since sea-level recovery.

Haulover sandbar dredging controversy

Bakers Haulover Inlet in Miami-Dade County, Florida, is an important waterway for recreational boaters connecting Biscayne Bay to the Atlantic Ocean. The dredging of the Haulover sandbar (properly termed the flood tidal delta) by the U.S. Army Corps of Engineers is very controversial because it has become a major attraction for boaters. This narrow inlet was artificially created for non-commercial watercraft in 1925 to provide access to the Atlantic Ocean, but it also helps promote flushing of Biscayne Bay, which is presently having pollutant problems. Maintenance dredging has occurred every three to five years since the 1960s, with the last project completed in 2017. The Corps of Engineers is providing 100% funding of the forthcoming dredging project in order to provide maintenance of the Atlantic Intracoastal Waterway and beach nourishment for the downdrift beach of Bal Harbour. Haulover sandbar parties are advertised by Trip Advisor among others as a Miami hot spot for outdoor recreation, drawing hundreds of boats and thousands of people during low tide, especially during the weekend.

Topography and morphodynamic study of intertidal mudflats along the eastern coast of the Gulf of Khambhat, India using remote sensing techniques

The intertidal mudflats that are exposed subaerially between the high and low tides have a complex morphology comprising ebb and flood tidal deltas, spits, shoals, and tidal sandbanks intervened with a network of meandering and branching tidal channels and inlets. The intertidal zones are highly transient and understanding their morphodynamics is critical to the ecology and economy of the region. Monitoring intertidal mudflat dynamics is imperative for sustainable development activities along coastal regions. The topography of intertidal mudflat is estimated for the eastern coast of the Gulf of Khambhat (north-western coast of India) using the waterline detection method from a series of satellite images. We have used Modified Normalized Difference Water Index and image threshold techniques to delineate waterlines from satellite images of high to low tidal conditions at different tidal heights. The waterlines are considered as elevation contours corresponding to tidal height during satellite observation, and a series of elevation contours delineated from satellite images of various tidal heights are then used to calculate the mudflat topography. The estimated topography is validated with the Differential Global Positioning System (DGPS), the Sound and navigation ranging (Sonar), and ICESat-2 ATL03 dataset observations, which results in R2 values of 0.97, 0.89, and 0.9, respectively, as well as RMSE values of 0.39 m, 0.33 m, and 0.49 m, respectively. The mudflat dynamics are studied by comparing the topographical changes estimated between the satellite images of 1998-99 and 2019. The major morphological changes are the landward shift of the low waterline, lateral migration of tidal bars, narrowing of the river mouth, as well as anthropogenic influences such as mudflat reclamation and impedance of long-shore sediment transport. The region with deposition of sediment above Mean Sea Level (MSL) has flattened the slope, making the mudflat stable and promoting mangroves expansion, while erosion has steepened the mudflats with loss of mangrove cover. These mudflats exhibit highly complex morphological changes mainly induced by sediment transport, two-way tidal currents, and fluvial fluxes. The estimated topography shall find its application in modeling coastal processes, identifying vulnerable coastal stretches, and site suitability for mangrove plantations.

Leveraging the Interdependencies Between Barrier Islands and Backbarrier Saltmarshes to Enhance Resilience to Sea-Level Rise

Barrier islands and their backbarrier saltmarshes have a reciprocal relationship: aeolian and storm processes transport sediment from the beaches and dunes to create and build marshes along the landward fringe of the island. In turn, these marshes exert a stabilizing influence on the barrier by widening the barrier system and forming a platform onto which the island migrates, consequently slowing landward barrier migration and inhibiting storm breaching. Here, we present a novel framework for applying these natural interdependencies to managing coastal systems and enhancing barrier-island resilience. Further, we detail application of these principles through a case study of the design of a marsh creation project that showcases the interdisciplinary engagement of scientists, engineers, stakeholders, and policymakers. Specifically, we describe: (1) the ecologic, sedimentologic, stratigraphic, and morphologic data obtained from the southern 4 km of Cedar Island (Virginia, United States) and nearby backbarrier tidal channels, tidal flats, and flood-tidal deltas, and (2) the use of those data to develop an engineering and design plan for the construction of a high (46 ha) and low (42 ha) fringing marsh platform located behind the island, proximal to a former ephemeral inlet. Additionally, we chronicle the process used to narrow five initial alternative designs to the optimal final plan. This process involved balancing best-available existing science and models, considering design and financial constraints, identifying stakeholder preferences, and maximizing restoration benefits of habitat provision and shoreline protection. Construction of this marsh would: (1) provide additional habitat and ecosystem benefits, (2) slow the rapid migration (up to 15 m/yr at present) of the barrier island, and (3) hinder island breaching. Ultimately, this project – presently at the final design and permitting stage – may enhance the storm and sea-level rise resilience of the island, backbarrier marshes and lagoons, and the mainland town community; and provide an example of a novel science-based approach to coastal resilience that could be applied to other global barrier settings.

Decadal shoreline erosion and recovery of beaches in modified and natural estuaries

Sandy beaches in estuaries and bays (BEBs) are common landforms on the coasts of many major cities. They exist under a wide range of settings and their morphology is controlled by their distance from the estuary/bay entrance, exposure to different types of waves (e.g., ocean swells vs locally generated wind waves), proximity to flood-tide delta/shoals, and anthropogenic interventions (e.g., dredging, groynes). Both swell waves propagating into estuaries/bays and locally generated wind waves can erode BEBs. However, more understanding of BEB storm erosion and recovery over decadal timescales is needed, as they typically respond slower than open coast beaches. Here we present decadal shoreline behaviours of nine BEBs from two estuarine systems in SE Australia are presented in this study, using 76 years of aerial imagery (1941–2017). We quantify and compare decadal behaviour between beaches, developing a new typology of BEBs based on shoreline evolution. We identify four decadal behaviours: prograding, quasi-stable, retreating and storm relict – and assess the influence of flood-tide deltas, river mouths, distance from the ocean entrance, and anthropogenic interventions. Swell-exposed BEBs near the entrance are quasi-stable and recover after storms at rates comparable with open coast beaches (<3 years). In contrast, BEBs further from the entrance and those with less swell exposure, have slower recovery timescales (3–15 years) and will only be quasi-stable if storms are sufficiently infrequent. Thus, long-term behaviour is controlled by storm return timescales. Prograding BEBs are typically far from the entrance, where fluvial and tidal processes dominate and erosion events due to wind waves are less pronounced. Whether BEBs recover (quasi-stable), partially recover between storms (retreating) or never recover (storm relict) relates to storm frequency, recovery rates and proximity to sediment sources and sinks (e.g., dredge sites, flood-tide deltas, tidal channels) and anthropogenic interventions. Findings will help to better understand and manage BEB shorelines in major cities.

The effect of coastal landform development on decadal-to millennial-scale longshore sediment fluxes: Evidence from the Holocene evolution of the central mid-Atlantic coast, USA

The behavior of siliciclastic coastal systems is largely controlled by the interplay between accommodation creation and infilling. Factors responsible for altering sediment fluxes to and along open-ocean coasts include cross-shore mobilization of sediment primarily from tidal currents and storms as well as changes in alongshore transport rates moderated by changing wave conditions, river sediment inputs, artificial shoreline hardening and modification, and natural sediment trapping in updrift coastal landforms. This paper focuses on the latter relationships. To address understudied interactions between updrift coastal landforms and downdrift coastal behavior, we quantify the volume and fluxes of sediment trapped in the Assateague-Chincoteague-Wallops barrier-island complex along the Virginia, USA coast and relate these volumes to downdrift coastal-system behavior. During the last ca. 2250 years, these barriers trapped 216 million m3 of sand through the growth of complex beach- and foredune-ridge systems. A period (ca. 400 to 190 years ago) of reduced/no progradation on Chincoteague and Assateague islands corresponds with sediment sequestration in updrift flood-tidal deltas. This finding emphasizes the important control of tidal inlets on alongshore sediment fluxes on barrier-island coasts. Rapid historical spit elongation during the last 190 years has trapped an average of 681,000 m3 yr−1 of sand; this occurred coincident with downdrift barrier-island erosion/migration at long-term rates of >3 m yr−1. Historical sand fluxes to the elongating spit on southern Assateague Island and progradational beach ridges on northernmost Wallops Islands are equivalent to at least 60% of estimated regional longshore transport rates. We therefore propose that sediment trapping and associated wave refraction are the primary drivers of downdrift barrier erosion, while storminess and sea-level rise are secondary forcings of change affecting equally the entire barrier-island chain. Global context is provided by a compilation of sediment trapping through growth of similar longshore sand sinks, which indicates the volume of sediment incorporated into the elongating spit end of Assateague Island is similar to sandy beach- and foredune-ridge plains (108 m3), but average annual trapping at the spit is at least six times greater than those at most mainland-attached, progradational systems. However, Chincoteague and Wallops, two progradational barrier islands, incorporate sand at rates broadly similar to large strandplains. Our findings emphasize the need to account for natural longshore sediment trapping in multi-decadal coastal management efforts on sandy, siliciclastic coasts.

US polyethylene supplies gradually ease as run rates increase

The behavior of siliciclastic coastal systems is largely controlled by the interplay between accommodation creation and infilling. Factors responsible for altering sediment fluxes to and along open-ocean coasts include cross-shore mobilization of sediment primarily from tidal currents and storms as well as changes in alongshore transport rates moderated by changing wave conditions, river sediment inputs, artificial shoreline hardening and modification, and natural sediment trapping in updrift coastal landforms. This paper focuses on the latter relationships. To address understudied interactions between updrift coastal landforms and downdrift coastal behavior, we quantify the volume and fluxes of sediment trapped in the Assateague-Chincoteague-Wallops barrier-island complex along the Virginia, USA coast and relate these volumes to downdrift coastal-system behavior. During the last ca. 2250 years, these barriers trapped 216 million m3 of sand through the growth of complex beach- and foredune-ridge systems. A period (ca. 400 to 190 years ago) of reduced/no progradation on Chincoteague and Assateague islands corresponds with sediment sequestration in updrift flood-tidal deltas. This finding emphasizes the important control of tidal inlets on alongshore sediment fluxes on barrier-island coasts. Rapid historical spit elongation during the last 190 years has trapped an average of 681,000 m3 yr−1 of sand; this occurred coincident with downdrift barrier-island erosion/migration at long-term rates of >3 m yr−1. Historical sand fluxes to the elongating spit on southern Assateague Island and progradational beach ridges on northernmost Wallops Islands are equivalent to at least 60% of estimated regional longshore transport rates. We therefore propose that sediment trapping and associated wave refraction are the primary drivers of downdrift barrier erosion, while storminess and sea-level rise are secondary forcings of change affecting equally the entire barrier-island chain. Global context is provided by a compilation of sediment trapping through growth of similar longshore sand sinks, which indicates the volume of sediment incorporated into the elongating spit end of Assateague Island is similar to sandy beach- and foredune-ridge plains (108 m3), but average annual trapping at the spit is at least six times greater than those at most mainland-attached, progradational systems. However, Chincoteague and Wallops, two progradational barrier islands, incorporate sand at rates broadly similar to large strandplains. Our findings emphasize the need to account for natural longshore sediment trapping in multi-decadal coastal management efforts on sandy, siliciclastic coasts.

Sedimentary facies and Holocene depositional evolution of the Maricá Lagoon, Rio de Janeiro, Brazil

This study aims to improve the knowledge on the geological evolution of the Maricá Lagoon (Rio de Janeiro) during the Holocene. One hundred and three samples from four boreholes and GPR data were acquired. Laboratory analyses included grain size and morphology, color, organic matter contents, fossils, mineral composition, and 14C dating. The results indicate that the 12.5 m thick sedimentary section studied here represents the last 8111 years of lagoonal deposition. Five sedimentary facies were identified: (1) subrounded sand facies (containing a gravel subfacies) which occur along the southern margin; (2) silty sand facies occurring at the transition from the margin to the lagoon center; (3) sandy silt facies and (4) silt/clayey silt facies which cover the calmer, central areas of the lagoon; and (5) angular sand facies which occur only at the surface of the northern margin. The organic matter content in the mud varied from 18% to 81%. Sedimentation rates up to 4277 cal years BP in the western margin were 0.27 cm/y and 0.15 cm/y in the deeper, central lagoon areas, and 0.20 cm/y since then. The sedimentary facies and organisms (molluscs and sponges) indicated that the Maricá Lagoon has changed little during the Holocene. At about 8111 cal years BP, the lagoon was an important freshwater basin with occasional saltwater influence. At about 5600–5000 years ago, during the maximum Holocene transgression, the lagoon attained its maximum dimensions and prevailing marine influences. Overwash processes and inlets enabled the formation of washover fans and flood-tidal delta deposits that have been recognized since the early formation stages of the Pleistocene barrier. From 4645 cal years BP to the present day, the connection between the lagoon and the sea has occurred sporadically at the southeast extreme of the lagoon (Barra Lagoon). Today's sedimentary dynamics are influenced by fluvial input (which is building up a lagoonal delta) and by winds, which transport sands from the barrier into the lagoon, in addition to generating waves capable of remobilizing the marginal and bottom lagoon sediments.

Sediment provenance and tidal current-driven recycling of Yellow River detritus in the Bohai Sea, China

A detailed sediment-provenance study is presented on the modern Bohai Sea, China, the innermost gulf of the Yellow Sea, using framework petrography, heavy-mineral and grain-size analyses. A series of subaqueous river deltas, characteristic of multisource, is distinguished along the coastal zone. First-cycle fluviodeltaic sediments are attributed principally to three large source areas: the Loess Plateau, the Yanshan highlands, and the Horqin sandland. Coastal sands along eastern Liaodong Bay are produced by weathering and physical erosion of near-source Mesozoic granitoid rocks during Quaternary lowstands. Apart from subaqueous deltas and coastal sands, sediment provenance is only attributed to two end-member mixing with various proportions between recycled Holocene Yellow River sediments and ancient fluvial sediments of the Liaohe river system, even though detrital sources are multiple along the coast. Relative contributions are quantified on a ternary diagram of heavy-mineral compositions, using the proportion of relative distances between a given mixed area and the two end-member deltas. The eastern Bohai flood-tidal delta, characterized by abundant garnet and ilmenite, is regarded as a large repository of ancient Liaohe sediments, which had been intermittently accumulated during Quaternary lowstands and reworked during multiple transgressions. As a secondary sediment source detached from the present-day Liaohe River delta, it is remobilized and involved in the modern sedimentation. A complete tidal current-dominated depositional pattern is proposed throughout the Bohai Sea to explain sediment accumulation and recycling. We suggest that dominant ebb tidal currents, prevailing in the southern Bohai Strait, are a primary driver carrying fine-grained Yellow River sediments eastward to the Yellow Sea. In contrast, the recycling of Yellow River sediments is driven by flood tidal currents, prevailing in the northern Bohai Strait. The internal recycling process in the Bohai Sea builds the sand sheet and its terminal lobe, i.e., the eastern Bohai mud belt, whereas the external recycling process that involves the depocenters of Yellow River sediments in the outside North Yellow Sea builds the sand ridges and its terminal lobe, i.e., the quartz-rich area. This study improves our understanding on the Yellow River dispersal system. It also provides a typical example that demonstrates how ancient alluvial sediments accumulated during eustatic lowstands are reactivated and join the modern sedimentation processes.

Holocene infill of the Anglesea Estuary, Victoria: a keep-up estuary in a geologically constrained environment

Holocene coastal infill was examined in Anglesea Estuary, an intermittently open barrier-type estuary in Victoria. Based on coring and radiocarbon dating, it was found that accommodation space in the estuary was almost entirely occupied in the early–mid Holocene corresponding to periods of higher sea-level. The pattern of infill is in stark contrast to established models of estuarine sedimentation developed on the east Australian coast. The contemporary estuary is composed of two distinct sedimentary basins. The upper basin is infilled by autochthonous peaty-marsh sediments, whereas the lower basin is infilled by saltmarsh material. The traditional tripartite flood-tide delta–central mud basin–fluvial delta sequence is absent. The contemporary estuary appears to have evolved as two distinct basins, which are connected through hydrodynamic rather than sedimentological processes. This pattern of connected basins occurs from the top of the catchment to the wave base, with the contemporary estuary infilling the two basins coincident with modern sea-level. Low sediment supply from both terrestrial and marine sources and bedrock-limited accommodation space means that Anglesea can be considered to be geologically constrained barrier estuary. KEY POINTS Geological-control limits mud basin development. Low allochthonous sediment supply significantly affected estuarine facies in Anglesea. Anglesea Estuary infilled to higher mean sea-level elevations in the mid Holocene. Anglesea Estuary is composed of two distinct sedimentary basins.

Sediment transport and deposition in flood-tidal deltas: Insight from the Texas Coast

While tidal environments are ubiquitous around the planet, limited work on these systems, particularly those that are in microtidal settings, hinders our understanding of tidal paleo-environments. In this study, we analyze the modern sediment dynamics of the San Luis Pass area, a microtidal system located on the Texas Gulf Coast. The focus of this work is to characterize sediment distribution and establish a quantitative relationship between sedimentary structure geometry, water depth, sediment grain size, and current velocities. A total of 160 seafloor sediment samples were collected in the modern San Luis Pass tidal delta between July 2017 and August 2018; this time span coincided with the landfall of Hurricane Harvey in the area in August 2017. Ripple geometry was measured in 46 locations along the flood-tidal delta. There is a rapid transition in grain size, from proximal (fine sand) to distal (silt and very fine sand) sediments at about 4.3 km from the mouth of the tidal inlet. This change is likely due to a decrease in current velocities away from the inlet entrance, resulting in a change in sediment transport from a combined bedload/suspension to suspension. Post Hurricane Harvey sediments are finer grained compared to those collected before the hurricane landfall, most likely due to high runoff during the storm event. In addition, increased water depths were measured after the hurricane landfall, indicating a significant erosion in the San Luis Pass area. Current ripples were only present in the proximal (sandier) area. We found a positive correlation between ripple height/ripple wavelength and water depth. However, the correlation is much stronger for ripple wavelength, even when compared to other published ripple measurements. We, therefore, propose to use ripple wavelength as a more reliable means to estimate paleo-water depths instead of ripple height. Nevertheless, more measurements from modern environments are necessary to establish a more robust geometric relation from ripples in a variety of paleoenvironments.

Spatiotemporal Distribution Characteristics of Nutrients in the Drowned Tidal Inlet under the Influence of Tides: A Case Study of Zhanjiang Bay, China.

The tidal dynamics and the characteristics of pollutant migration in the drowned-valley tidal inlet, a typical unit of coastal tidal inlets, are strongly influenced by geomorphological features. Along with the development of society and the economy, the hydrodynamic and water quality environment of the tidal inlet is also becoming more disturbed by human activities, such as reclamation of the sea and the construction of large bridges. In this study, a typical drowned-valley tidal inlet, Zhanjiang Bay (ZJB), was selected for the establishment of a model via coupling of a tidal hydrodynamic model and water quality numerical model. This model can be used to simulate the migration and diffusion of pollutants in ZJB. The spatial and temporal variation processes of water quality factors of the bay under the influence of special geomorphic units was simulated at the tidal-inlet entrance, the flood/ebb tidal delta, and the tidal basin. The results show that ZJB has strong tidal currents that are significantly affected by the terrain. Under the influence of the terrain and tidal currents, the phosphorus and nitrogen concentration at the flood-tide and ebb-tide moments showed obvious temporal and spatial differences in the ebb-tide delta, tidal-inlet entrance, flood-tide delta, and tidal basin. In this study, we analyzed the response mechanism of the water quality environment to the drowned-valley tidal inlet, and this can provide theoretical guidance and a basis for decision-making toward protecting the ecology and water security of ZJB.

Sedimentological analysis and reservoir quality of the early Cenomanian transgressive sandstones, northern Western desert, Egypt

Depicting depositional models of transgressive sandstone reservoirs is challenging due to their internal complexity and limited case studies. This study presents an example for transgressive sandstone reservoirs from the Bahariya Formation at Hayat-Yasser oil field, Shushan Basin (northern Western Desert, Egypt). The upper part of the Bahariya Formation accumulated in an estuarine setting as a consequence of a successive sea level rise. Detailed reservoir characterization, employing sequence stratigraphic and sedimentological approaches, revealed that the studied reservoir consists of a mixed siliciclastic-carbonate transgressive estuarine-shelf succession. Four conventional core samples of this succession at Khalda ridge (Shushan Basin), permit the analysis of their sedimentology and internal architecture (mesoscopic heterogeneities) along correlation lines parallel or slightly oblique to depositional dip. The succession consists of six backstepping parasequence sets that record the overall shift from tidal-dominated to wave-dominated estuaries/bays. The transgressive component of the parasequences sets includes bay mudstones, flood-tidal deltas, and shoreface/barrier deposits; while the regressive component includes estuarine point bars, bay head deltas, and tidal deltas. The reservoir properties show significant variation according to the facies assemblages. The tidally-dominated estuarine channels show low net-to-gross, as it is characterized by lenticular sandstone bodies with several lateral and vertical baffles and barriers. On the other hand, the shoreface/barrier and tidal delta sandstones show high net-to-gross and consist of amalgamated sandstone bodies with little mud barriers or baffles. Petrographically, the upper Bahariya reservoir includes intergranular and secondary porosities. The microscopic heterogeneities are mainly due to the fine grain nature, poor sorting, presence of matrix, and continuous mud barriers or baffles. Destruction of porosity, affecting the reservoir quality, occurred by silica overgrowths, ferroan calcite, grain coating chlorite, and kaolinite cementation, as well as compaction. Feldspar dissolution is the main diagenetic process responsible for the formation of secondary porosity, enhancing the reservoir quality.