Relative Sea-level Highstand Research Articles

Middle Ordovician paleoenvironmental evolution of the western Laurentian carbonate platform: Evidence for persistent oxygenation of the shallow ocean and implications for biodiversification

The Great Ordovician Biodiversification Event (GOBE) encompasses a series of rapid and sustained diversification pulses unparalleled in Earth history. Despite the uniqueness and magnitude of the GOBE, a singular driving force for this critical interval has not been identified. Multiple hypotheses have been presented, some pairing the GOBE as cause and effect with extrinsic factors such as changing global temperatures, ocean chemistry, or paleogeography, while others have pointed to factors intrinsic to biology itself, such as the proliferation of skeletonization, predator-prey escalation, or the development of complex tiered seafloor communities. Sufficient data are not available at present to ascertain what combination of these factors was the key to generating the GOBE.Here, we present new paired carbon and sulfur isotope data (δ13Ccarb, δ13Corg, and δ34SCAS), along with iodine concentration data from a Darriwilian carbonate sequence exposed at Meiklejohn Peak in southwestern Nevada, USA. Within a detailed lithologic and biostratigraphic framework, these new data provide a robust correlation to chemostratigraphic zonation established in Baltica and eastern Laurentia along with insights into the evolution of Middle Ordovician biogeochemical cycling. Carbon isotope data indicate a slight (2 ‰) increase in the fractionation between carbonate carbon and organic matter (Δ13C) during the onset of the middle Darriwilian carbon isotope excursion (MDICE), and new carbonate-associated sulfate (CAS) sulfur isotope data are consistent with a decrease in global pyrite burial during this time. Both of these observations support previous work arguing for a synchronous increase in the [O2] of the global oceans. New iodine concentration data from Meiklejohn Peak also suggest a progressive and sustained increase in the [O2] of regional waters throughout the Darriwilian during a period of relative sea-level highstand. This expansion of stable and well‑oxygenated ecospace could have laid the foundation for rapid diversification during one of the largest pulses of the GOBE.

Last interglacial and MIS 9e relative sea-level highstands in the Central Mediterranean: a reappraisal from coastal cave deposits in the Cilento area, Southern Italy

A revaluation of the relative sea-level (RSL) indicators in the Baia di Infreschi (Cilento, Southern Italy) supported by new 30 U/Th dating on speleothems indicates that the upper level of Lithophaga burrows identified by Bini et al. (2020) at ∼9 m a.s.l. and correlated to the Last Interglacial (LIG) highstand should be referred to the highstand of the MIS 9e, whereas the local RSL for the highstand of the LIG is now reassessed at 5.3 ± 0.18 m a.s.l. The upper level of the Lithophaga marker can be followed for ∼12 km along the coast, suggesting a substantial absence of important relative tectonic movements. In the Baia di Infreschi an additional marine indicator, a notch sealed by a flowstone dated ∼110 ka, indicates several phases of RSL stationing below the maximum highstand of the LIG. The presence of flowstones as low as 2 m a.s.l. dated to the MIS 7 shows that the highstand of MIS 7 was probably below the present sea level. All these evidences allow us to reassess the stratigraphy of some archaeological caves in the area, indicating that the sedimentary successions preserved there are older than what was previously believed.

Constraining the end of the Last Interglacial (MIS 5e) relative sea-level highstand in central Mediterranean: New data from Grotta delle Capre, central Italy

The current rapid change of the Earth's climate has resulted in an increasing interest for the past warm periods as potential long-term scenarios of the effects of the present global warming. The last such a period occurred 129–116 ka, known as the Last Interglacial (LIG), when the continental ice volume was significantly smaller than present, leading to a global sea-level (GSL) higher than present one. Detailed morpho-stratigraphic data, supported by a robust U/Th chronology, from Grotta delle Capre, central Italy, provided new chronological insights on the relative sea-level (RSL) dynamic during the LIG in the Mediterranean region. Our results indicate that, on Tyrrhenian Sea coasts of the central Italy, after having stationed at ∼9 m a.s.l., the LIG RSL fell at an elevation <3 m a.s.l. as early as before 123 ka, and then no longer rose above this elevation either during the later stages of the LIG or afterwards. The results match previous studies based on U/Th dating of terrestrial limiting points from Grotta Infreschi, ∼200 km SE from Grotta delle Capre along the same Tyrrhenian Sea coasts, and are in agreement with the Red Sea RLS and GSL records and the probabilistic LIG sea level assessments based on globally distributed records. On the other hand, our reconstruction is not supported by implications of U/Th dating of corals and phreatic overgrowth on speleothems from the Balearic Island of Mallorca. Such an inconsistency in the overall knowledge around the LIG RSL reconstruction results in a high uncertainty in modelling the ice and sea-level dynamic during this warm period, which needs to be reduced through more and more high-resolution, stratigraphic and chronological investigations of the morphological and sedimentary sea-level records.

Three-dimensional glacial isostatic adjustment modeling reconciles conflicting geographic trends in North American marine isotope stage 5a relative sea level observations

Abstract Glacial isostatic adjustment (GIA) simulations using earth models that vary viscoelastic structure with depth alone cannot simultaneously fit geographic trends in the elevation of marine isotope stage (MIS) 5a relative sea level (RSL) indicators across continental North America and the Caribbean and yield conflicting estimates of global mean sea level (GMSL). We present simulations with a GIA model that incorporates three-dimensional (3-D) variation in North American viscoelastic earth structure constructed by combining high-resolution seismic tomographic imaging with a new method for mapping this imaging into lateral variations in lithospheric thickness and mantle viscosity. We pair this earth model with a global ice history based on updated constraints on ice volume and geometry. The GIA prediction provides the first simultaneous reconciliation of MIS 5a North American and Caribbean RSL highstands and strengthens arguments that MIS 5a peak GMSL reached values close to that of the Last Interglacial. This result highlights the necessity of incorporating realistic 3-D earth structure into GIA predictions with continent-scale RSL data sets.

Leveraging Sequence Stratigraphy to Accelerate Site Remediation: Pliocene Citronelle Formation, Eglin Air Force Base, Florida, USA

AbstractAt Eglin Air Force Base (AFB) in the Florida Panhandle, a groundwater extraction and treatment system was installed to contain and remediate a chlorinated solvent plume. After 2 years of operation, the system was not removing the contaminant mass at the rate predicted or required to meet performance‐based contract terms. As a result, a sequence‐stratigraphic analysis was initiated to develop a strategy to improve performance. Sequence Stratigraphy methods were employed to identify a marine flooding surface (mfs) formed during a relative sea level highstand. The analysis also found that the mfs was locally eroded away, indicating that incised valleys were eroded into the formation during a relative lowstand of sea level. These valleys were backfilled with coarse‐grained fluvial and estuarine strata. The analysis concluded that the groundwater extraction system lacked an extraction well screened within the coarse‐grained valley fill. An additional extraction well was installed, which targeted the incised valley fill and resulted in a significant increase in contaminant mass removal rate without increasing system capacity or operational costs. This case study suggests that efficiency improvements are tenable at many sites where groundwater remediation is occurring within the Surficial Aquifer System of the Gulf Coast (Citronelle Formation) as well as sites in similar geologic settings worldwide.

Holocene relative sea-level changes in northwest Ireland: An empirical test for glacial isostatic adjustment models

The late-Quaternary relative sea-level (RSL) history of Ireland is complex, positioned at the margins of the former British-Irish Ice Sheet, and subject to the influence of ice unloading and forebulge collapse. Geophysical models of post-glacial isostatic adjustment (GIA) provide estimates of the pattern of RSL change since deglaciation which may be tested and validated with empirical data from proxy records. For the region of northwest Ireland, there is a paucity of high-quality RSL data and, therefore, equivocal evidence to support the GIA models that predict a mid to Late-Holocene RSL highstand of between +0.5 and +2 m above present. This study aims to investigate this model-data discrepancy by reconstructing RSL change from a near continuous salt-marsh sequence at Bracky Bridge, Donegal, spanning the last ca. 2500 years. We develop a transfer function model to reconstruct the vertical position of sea level using a regional diatom training set to quantify the indicative meaning and predict the palaeomarsh elevation of the core samples. A chronology is provided by a combination of 14C and 210Pb data, with sample specific ages derived from an age-depth model using a Bayesian framework. Our reconstruction shows ca. 2 m of relative sea-level rise in the past 2500 years. This is not compatible with some previously published sea-level index points from the region, which we re-interpret as freshwater/terrestrial limiting data. These results do not provide any evidence to support a Mid-Holocene RSL highstand above present sea level. Whilst none of the available GIA models replicate the timing and magnitude of the Late-Holocene RSL rise in our reconstruction, those which incorporate a thick and extensive British-Irish Sea Ice Sheet provide the best fit.

Use of Remote-Sensing to Quantify the Distribution of Progradation/erosion Along a Forced-Regressive Modern Coastline: Driving Factors and Impact on the Stratigraphic Record

The long-term development of ancient and modern coastal distributive fluvial systems (DFSs) during periods of relative sea-level highstand or fall usually drives net-progradation of shorelines. Such systems often develop in periods of relative sea-level highstand or fall and typically record annual to millennial-scale deviations in coastal trajectories. A new continental dataset (Digital Earth Australia Coastlines: DEA Coastlines) provides an opportunity to examine such variations in coastal behaviour over annual to decadal scales (1988-2019) at local to continental spatial scales. This dataset is herein applied to the 655 km coastline fronting Australia’s largest amalgamated coastal distributive fluvial systems, which is situated in the epicontinental seaway of the Gulf of Carpentaria in the north of the continent. Despite the overall forced regressive conditions (i.e. progradation during relative sea-level fall), only 54% of this coastlines length net-prograded, whereas 47% was eroded. Though temporal cyclicity in progradation and erosion is evident along segments of this coast, these patterns could not be correlated with either the Southern Oscillation Index (R2 = -0.20) or rainfall (R2 = 0.24). Instead, short-term coastline dynamics appear to be the result of complex interactions between fluvial, wave, longshore current, and tidal processes. The high-resolution DEA Coastlines dataset highlights the diachronous, heterochronous, composite, and amalgamated nature of net-progradational stratigraphic strata that can develop in shallow-marine environments where hinge-points between prograding and retrograding coastal segments are dynamic features that migrate with time. Our conclusions show that shorelines display granular temporal and spatial deviations in coastal trajectory, with contemporaneous progradation and erosion occurring over 1-100 km length scales. This is significantly more heterogeneity than previously envisaged, thereby suggesting the need for updating models of coastal systems.

Stratigraphic variability of Upper Holocene marginal marine sediments along the Al Qahmah Coast of Red Sea, Saudi Arabia

The stratigraphic architecture of Upper Holocene sediments along the coast of Al Qahmah in southern Red Sea, Saudi Arabia, provides a high-resolution analog of marginal marine carbonate and siliciclastic sedimentation under variable climatic, tectonic, and sea-level conditions. The sediments include a basal shallow marine limestone and overlying beach, deltaic, fluvial, eolian, and sabkha siliciclastic deposits, comprising four stratigraphic units ranging from 10s to 100 s cm thick. A lithostratigraphy is established using subsurface stratigraphic and petrographic data from 64 trenches and three shallow refraction seismic sections. A chronostratigraphy is established using four age points and sedimentation rates. The entire interval has been deposited in the last ~4000 years. Significant stratigraphic variability is reflected by vertical and lateral changes in the thickness, type, and stratal geometry of the four units. Five major geological events are interpreted: Initial shallow marine carbonate deposition during a relative sea-level highstand was terminated by seaward progradation of deltaic-beach sediments during a slow shoreline regression. This is followed by a major stream channel incision during the maximum regression and a relative sea-level fall. The ensuing fluvial channel filling, transgressive ravinement, and deposition of beach sediments signify a relative sea-level rise. Finally, eolian, sabkha, and beach sediments have been deposited in a stabilized and diversified environmental setting under an arid climate. The lacuna associated with stream erosion and transgressive ravinement is up to ~400 years long, resulting in a stratigraphic completeness of ~88%. The sedimentation rate of the siliciclastic sediments is ~0.1 cm/year estimated at a scale of 1000s of years. Episodic syn-depositional faulting in the source area and depositional site, relative seal-level change, autogenic environmental shift, and/or climatic changes between humid and arid conditions have collectively played variable roles in the formation of the stratigraphic variability. The interpreted tectonic, relative sea-level, and climatic trends offer an important data point for future studies in the Red Sea region and beyond for the Late Holocene.

Sedimentological and palynological assessment of three wells in eastern Dahomey Embayment, southwestern Nigeria, West Africa

Integrated studies were carried out on one hundred and eleven (111) ditch samples retrieved from three wells drilled in Lagos area within the Dahomey Embayment, coastal southwestern Nigeria. The purpose of this study is to determine the provenance, heavy mineral assemblage(s), establish the lowstand - highstand episodes, Quaternary palaeoenvironment and date the encountered lithofacies which constitute sandstones, siltstones with thin beds of lignite. The textural parameters show that the sandstones are medium to fine grained with the lignite consisting of plant fragment remains. Petrographic analyses showed abundant detrital minerals with average modal composition of quartz (Q = 90%), feldspar (F = 2%) and rock fragments (RF = 4%). The QFR ternary plots revealed that the sandstones are quartz arenites of continental block provenance origin deposited under humid climatic setting. This lithofacies has undergone medium distance range of transportation and have been subjected to mechanical and chemical weathering prior deposition. The heavy mineral assemblages and the ratios of Zircon-Tourmaline (ZTR index) in the wells suggest matured sediments. The Apatite: Tourmaline (ATi) ratios showed variations within the studied wells indicating differences in rate of weathering. It is evident that the periods of residence on the floodplain despite similar provenances and fluctuations in ratios, suggest sea level changes. The fluctuations in apatite: tourmaline ratios with respect to weathering are attributed to rapid changes in climatic conditions during the floodplain residence. The high ATi values in sandstone were deposited during relative sea level highstand (transgression), while sandstones with low ATi were deposited during lowstand (regression) in Nigeria and along the West African region. The abundance species of Rhizophora sp., Avicennia africana, Acrostichu mauruem, Laevigatosporite sp., Combretaceae sp., Mitrogynaciliata, Sapotaceae sp., Disopyros sp., Elaeis guineensis and Alchronea spp. indicated depositional transition from mangrove to fresh water swamp due to the episodic highstand and lowstand regimes. The abundance of Podocarpus milianjanus and Retitricolporites hians and the absence of Miocene diagnostic forms suggest late Pleistocene (Tarantian = 0.012–0.126 Ma) deposition.

Disentangling natural vs. anthropogenic induced environmental variability during the Holocene: Marambaia Cove, SW sector of the Sepetiba Bay (SE Brazil).

Multiproxy approach based on textural, mineralogical, geochemical, and microfaunal analyses on a 176-cm-long core (SP8) has been applied to reconstruct the Holocene paleoenvironmental changes and disentangling natural vs. anthropogenic variability in Marambaia Cove of the Sepetiba Bay (SE Brazil). Sepetiba Bay became a lagoonal system due to the evolution and development of the Marambaia barrier island during the Holocene and the presence of an extensive river basin. Elemental concentrations from pre-anthropogenic layers from the nearby SP7 core have been used to estimate the baseline elemental concentrations for this region and to determine metals enrichment factors (EF), pollution load index (PLI), and sediment pollution index (SPI). Record of the core SP8 provides compelling evidence of the lagoon evolution differentiating the effects of potentially toxic elements (PTEs) under natural vs. anthropic forcing in the last ~ 9.5 ka BP. The study area was probably part of coastal sand ridges between ≈ 9.5 and 7.8 ka BP (radiocarbon date). Events of wash over deposited allochthonous material and organic matter between ≈ 8.6 and 7.8 ka. Climatic event 8.2 ka BP, in which the South American Summer Monsoon was intensified in Brazil causing higher rainfall and moisture was scored by an anoxic event. Accumulation of organic matter resulted in oxygen depletion and even anoxia in the sediment activating biogeochemical processes that resulted in the retention of potentially toxic elements (PTEs). After ≈ 7.8 ka BP at the onset of the Holocene sea-level rise, a marine incursion flooded the Marambaia Cove area (previously exposed to subaerial conditions). Environmental conditions became favorable for the colonization of benthic foraminifera. The Foram Stress Index (FSI) and Exp(H'bc) indicate that the environmental conditions turned from bad to more favorable since ≈ 7.8 ka BP, with maximum health reached at ≈ 5 ka BP, during the mid-Holocene relative sea-level highstand. Since then, the sedimentological and ecological proxies suggest that the system evolved to an increasing degree of confinement. Since ≈ 1975 AD, a sharp increase of silting, Cd, Zn, and organic matter also induced by anthropic activities caused major changes in foraminiferal assemblages with a significant increase of Ammonia/Elphidium Index (AEI), EF, and SPI values and decreasing of FSI and Exp(H'bc) (ecological indicators) demonstrating an evolution from "moderately polluted" to "heavily polluted" environment (bad ecological conditions), under variable suboxic conditions. Thus, core SP8 illustrates the most remarkable event of anthropogenic forcing on the geochemistry of the sediments and associated pollution loads and its negative effect on benthic organisms.

Re-evaluating mid-Holocene reef “turn-off” on the inshore Southern Great Barrier Reef

In the face of changing global climate the future of corals reefs is uncertain. High latitude reefs may offer potential refugia for corals under projected increasing sea surface temperatures (SSTs). To understand the reef growth potential of modern high latitude reefs it is first necessary to understand past reef growth and response to climatic and environmental changes. The history of the Great Barrier Reef (GBR) has been shown to be punctuated by a multi-millennial Mid-Holocene reef “turn-off” or initiation hiatus in the Northern and Southern GBR (∼5500–2500 years before present [yr. BP]). Here we present the results of chronologically constrained reef matrix cores from five continental island fringing reefs and coral communities in the Keppel Islands to revaluate the timing, extent and possible drivers of the Mid-Holocene hiatus in the Southern GBR. Earliest initiation occurred at Wedge and Halfway Islands at 7773 ± 19 yr. BP and 7455 ± 20 yr. BP, respectively. Following initiation, vertical reef accretion at Halfway was comparable to previously reported rates for the GBR of ∼3.4 mm yr−1, increasing to ∼8.0 mm yr−1 between 6100 and 5500 yr. BP. Conversely, the coral community at Wedge Island, located closer to mainland terrestrial influence, accreted <1.0 mm yr−1 to 5500 yr. BP after which a 3000-year stratigraphic hiatus is observed. A negative relative sea level oscillation at 5500 yr. BP coincides with the transition of Halfway reef from vertical accretion to lateral progradation and the “turn-off” of the Wedge Island coral community. The reef at Middle Island appears to have initiated in the midst of the Mid-Holocene hiatus period at ∼3500 yr. BP, with vertical accretion at both Middle and Halfway Islands being the highest for the region’s history at 12.5 ± 3.3 mm yr−1 and 15.0 ± 6.0 mm yr−1, respectively, between 3500 and 3000 yr. BP. A proposed late-Holocene relative sea level highstand of ∼1 m at ∼2000 yr. BP coincides with the first dates identified at near-shore Divided Island, and the re-initiation of coral growth at Wedge Island, although both showed limited net vertical accretion. These near-shore sites “turned-off” again between 1300 and 900 yr. BP, likely associated with a rapid relative sea level fall. Reef progradation also slowed at Halfway Island and Middle Island after 1200 yr. BP until a recent increase in reef growth at Middle Island since the late 1970’s associated with modern increases in average SSTs. Our data suggests that although reef-scale “turn-off” events occurred, there is no evidence for a regional scale hiatus in coral growth or initiation comparable to that found further north on the GBR. A comparison with other Southern and south-Central GBR reef cores suggests that relative sea level oscillations in conjunction with changes to climate, appear to have driven varying, but synchronous, modifications to reefs at 5500, 4600, 2800 and 1200 yr. BP.

Influence of the Holocene relative sea level on the coastal plain of Sepetiba Bay (Southeast Brazil)

This work analyzes the results of the SP2 core (50.30 m length) collected in the coastal plain of Sepetiba Bay (SB; SE Brazil), 2 km away from the Guandu River mouth (latitude 22° 55′S, longitude 43° 46′W). It aims to study the influence of the Holocene relative sea level (RSL) on the coastal plain of SB. After description, the SP2 core was sampled at every 5 cm for grain size, geochemical, mineralogical and foraminiferal analyses. Four radiocarbon dates obtained in the first 18 m were modulated with Bayesian statistics. The SP2 core is composed of basement rocks, gneisses (50.30–43.80 m); river sediments (43.80–21.00 m) up to about ≈ 5.0 kyr BP; a sediment package marked by sudden textural and compositional changes, accumulated between ≈ 5.0 and 4.7 kyr BP; muddy sediments deposited between 4.7 and 0.8 kyr BP (18.80–3.35 m) with intercalations of sandy levels; an upper part of disturbed embankment sediments used for the implantation of Santa Cruz Thermoelectric Power Plant. The fluvial sands accumulated before ≈ 5.0 kyr BP were deposited before the maximum Mid-Holocene relative sea level. They were probably eroded and transported by the drainage network of the N region of SB, namely by the Guandu River. Between ≈ 4.5 and 3.5 kyr BP, the foraminiferal abundance and assemblage composition indicate that the study site was a shallow marine environment, due to the Mid-Holocene relative sea-level highstands (MHSLH). Between ≈ 3.5 and 3.0 kyr BP, the sediment accumulation rate (SAR) was the lowest of the last ≈ 5 kyr BP and the study site was exposed to subaerial weathering processes, in a scenario of the relative sea-level drop. A new phase of marine influence was recorded between ≈ 3.0 and 1.9 kyr BP, associated with the highest SAR of this record, up to ≈ 27.4 m/kyr BP. Between ≈ 1.9 and 1.8 kyr BP, the study site was under subaerial weathering processes. Since then the SAR reduced significantly to a mean value of ≈ 4.5 m/kyr and, between ≈ 1.8 and 0.8 kyr BP, the study site was again under the marine influence. Foraminifera were not found, after ≈ 0.8 kyr BP, in the SP2 core. However, the occurrence of a shallow marine environment was identified in another core, between ≈ 1.4 and 0.35 kyr BP, in the Guaratiba Mangrove, NE of SB. The results of the SP2 core suggest that MHSLH left a striking record in the study area, although some of the identified environmental changes are probably related to adjustments of the lower course of Guandu River and tidal channels and variations in the configuration of sandy littoral strands. The growth of a barrier–island system, the Marambaia barrier island, since the last ≈ 8–7.5 kyr BP may also have induced changes in the study area.

Pleistocene terrace formation, Quaternary rock uplift rates and geodynamics of the Hellenic Subduction Zone revealed from dating of paleoshorelines on Crete, Greece

Quaternary paleoshorelines are common landforms on the island of Crete, a forearc high above the Hellenic Subduction Zone. These geomorphic markers are useful on Crete and elsewhere in determining coastal uplift rates, the identification of active geologic structures, and to constrain geodynamic models and seismic hazards. Controversy exists in the literature regarding the formation mechanisms and age of late Pleistocene paleoshorelines on Crete that has led to competing models of the uplift history, tectonic evolution, and seismic hazards of the Hellenic forearc. We present new mapping and results from luminescence and radiocarbon geochronology of paleoshoreline deposits that constrain the spatial and temporal pattern of rock uplift around the Cretan coastline. Existing and new radiocarbon data are variable and show no obvious age-elevation trends within individual terrace sequences. By contrast, nearly all luminescence ages, some from shorelines dated with radiocarbon, show positive age-elevation trends and range from 60–220 ka suggesting that all dated paleoshorelines are beyond the limits of radiocarbon. We propose that the inconsistencies between the different geochronological methods are the result of secondary contamination of young carbonate, possibly from meteoric waters, that bias radiocarbon in Cretan Pleistocene marine fossils. Most luminescence ages closely correlate with the timing of mid-to-late Pleistocene relative sea level highstands, consistent with stratigraphic observations. Calculated coastal uplift rates using a Monte-Carlo error analysis range from ∼0–1.2 mm/yr; the lowest uplift rates are found along the northern and eastern coasts of the island, while the most rapid are focused along the southern and western coasts where active normal faults are observed offsetting paleoshoreline sequences. Based on this new data, we favor a tectonic model where slip along upper crustal normal faults acts to locally augment a steady regional signal of uplift along the south and west coast, interpreted to result from the deep underplating of rock at the base of the subduction wedge beneath Crete. Arcward of the contact between the upper plate Moho and the top of the subducting slab, crustal thinning will occur in the orogenic wedge resulting in subsidence along the north coast of Crete.

Fluvial shoal water deltas: pre‐vegetation sedimentation through the fluvial–marine transition, Lower Cambrian, English Channel region

AbstractLower Palaeozoic fluvial systems tend to be more sand‐prone than those of later eras and the nature of coastal environments less certain. Field studies are presented that characterize the fluvial to marine transition over a distance of 80 km, in the Lower Cambrian of the Cotentin Peninsula, northern France. The sedimentary rocks are divided into six facies associations which represent deposition in proximal fluvial, distal fluvial, delta plain, delta front, pro‐delta and offshore carbonate bank environments. The basin fill is sandstone‐dominated and subdivided into three stratigraphic intervals. A 200 to 300 m thick basal interval contains very coarse‐grained fluvial sandstones deposited during a relative sea level lowstand. An overlying interval, 250 to 1500 m thick, is a facies mosaic. Fluvial strata in the north‐west pass laterally south‐east into deltaic and shallow marine pro‐delta sediments. The delta front deposits show repetitively stacked, upward‐coarsening parasequences, 8 to 10 m thick, which reflect the repeated progradation of lobate, fluvially‐dominated deltas onto a shallow marine shelf. The deltas formed following marine transgression and accumulated during a period of gradually rising relative sea level. An upper unit, 130 m thick, containing offshore stromatolitic and oolitic limestones, caps the study interval and represents deposition during a relative sea level highstand. The fluvial and delta distributary channel sandstones of the middle unit contain &lt;1% mudstone. The cohesionless substrate determined that deltaic distributaries were predominantly braided in character and subject to common bifurcations which resulted in an ordered diminution of channel size and competence in a seaward direction. Terminal distributary channels show evidence of migratory levées and mouth‐bars and consistently delivered fine to medium‐grained sand to the delta front. The study highlights an example of pre‐vegetation deltaic sedimentation that was hydraulically organized and predictable, despite being fed by braided fluvial systems with high levels of peak discharge.

Redating the earliest evidence of the mid-Holocene relative sea-level highstand in Australia and implications for global sea-level rise.

Reconstructing past sea levels can help constrain uncertainties surrounding the rate of change, magnitude, and impacts of the projected increase through the 21st century. Of significance is the mid-Holocene relative sea-level highstand in tectonically stable and remote (far-field) locations from major ice sheets. The east coast of Australia provides an excellent arena in which to investigate changes in relative sea level during the Holocene. Considerable debate surrounds both the peak level and timing of the east coast highstand. The southeast Australian site of Bulli Beach provides the earliest evidence for the establishment of a highstand in the Southern Hemisphere, although questions have been raised about the pretreatment and type of material that was radiocarbon dated for the development of the regional sea-level curve. Here we undertake a detailed morpho- and chronostratigraphic study at Bulli Beach to better constrain the timing of the Holocene highstand in eastern Australia. In contrast to wood and charcoal samples that may provide anomalously old ages, probably due to inbuilt age, we find that short-lived terrestrial plant macrofossils provide a robust chronological framework. Bayesian modelling of the ages provide improved dating of the earliest evidence for a highstand at 6,880±50 cal BP, approximately a millennium later than previously reported. Our results from Bulli now closely align with other sea-level reconstructions along the east coast of Australia, and provide evidence for a synchronous relative sea-level highstand that extends from the Gulf of Carpentaria to Tasmania. Our refined age appears to be coincident with major ice mass loss from Northern Hemisphere and Antarctic ice sheets, supporting previous studies that suggest these may have played a role in the relative sea-level highstand. Further work is now needed to investigate the environmental impacts of regional sea levels, and refine the timing of the subsequent sea-level fall in the Holocene and its influence on coastal evolution.

Testing the mid-Holocene relative sea-level highstand hypothesis in North Wales, UK

Accurate Holocene relative sea-level curves are vital for modelling future sea-level changes, particularly in regions where relative sea-level changes are dominated by isostatically induced vertical land movements. In North Wales, various glacial isostatic adjustment (GIA) models predict a mid-Holocene relative sea-level highstand between 4 and 6 ka, which is unsubstantiated by any geological sea-level data but affects the ability of geophysical models to model accurately past and future sea levels. Here, we use a newly developed foraminifera-based sea-level transfer function to produce a 3300-year-long late-Holocene relative sea-level reconstruction from a salt marsh in the Malltraeth estuary on the south Anglesey coast in North Wales. This is the longest continuous late-Holocene relative sea-level reconstruction in Northwest Europe. We combine this record with two new late-Holocene sea-level index points (SLIPs) obtained from a freshwater marsh at Rhoscolyn, Anglesey, and with previously published regional SLIPs, to produce a relative sea-level record for North Wales that spans from ca. 13,000 BP to the present. This record leaves no room for a mid-Holocene relative sea-level highstand in the region. We conclude that GIA models that include a mid-Holocene sea-level highstand for North Wales need revision before they are used in the modelling of past and future relative sea-level changes around the British Isles.

Holocene sea-level change and evolution of a mixed coral reef and mangrove system at Iriomote Island, southwest Japan

Exposed fossil microatolls and core samples from a coral reef and a mangrove forest at the Yutsun River mouth, Iriomote Island, southwest Japan, reveal the internal structure and temporal changes in the sedimentary processes of a mixed reef–mangrove system. Evidence from the core samples and fossil microatolls suggests sea level reached its present position before 5100 cal yr B.P., and a relative sea-level highstand of 1.1–1.2 m above the present sea level occurred from 5100 to 3600 cal yr B.P. This was followed by a gradual fall in relative sea level. The tectonically corrected sea-level curve indicates a stable sea level after 5100 cal yr BP., with a sea-level highstand of up to 0.4 m between 5100 and 3600 cal yr B.P.A nearshore reef dominated by massive Porites and arborescent Acropora initially developed at 6500–3900 cal yr B.P. Reef development was potentially terminated by relative sea-level fall and sediment discharge from the Yutsun River that affected the backreef environment. An offshore coral reef reached present-day sea level by 1000 cal yr B.P., forming a wave break that enabled the foundation of mangrove forest on the fringing reef after ∼1000 cal yr B.P. The reef development was significantly delayed compared with other coral reefs in the region with similar medium-to high-energy conditions, but it provided a calm environment in the backreef area that allowed the development of mangroves. These features demonstrate the chronology and causal relationship between coral reef and mangrove development under the influence of Holocene sea-level change and river discharge.

Relative sea-level highstands in Thailand since the Mid-Holocene based on 14C rock oyster chronology

The relative sea-level highstands in Thailand from the Mid-Holocene to the present day have been studied in horizontal tidal erosion notches and inside a sea cave in limestone and marble coastal cliffs through 14C dating of rock oysters. Rock oyster ages progressively increase with elevation up from a ~1 m wide living oyster band at the present day sea level and up into the roof of the notch. The oldest age obtained is 6513–6390 cal yr B·P. (Mid-Holocene) for a shell at an elevation of 2.5 ± 0.1 m above present day MSL. However, comparison of the results from different sites shows that oysters of the same age occur at different elevations due to different environmental conditions: ~6000 cal yr B.P. old oysters can be found from between 3.8 ± 0.1 m to 2.5 ± 0.1 m above present day mean sea level. A conservative view of these results from Thailand is that relative sea levels were 2.5 ± 0.5 m above the present sea level during the temperature maximum of the Holocene Climactic Optimum between 7000 and 6000 cal yr B.P. Since then, relative sea levels fell until the onset of the Industrial Revolution.

Migration of Barchan Dunes in Qatar–Controls of the Shamal, Teleconnections, Sea-Level Changes and Human Impact

Barchan dune fields are a dominant landscape feature in SE Qatar and a key element of the peninsula’s geodiversity. The migration of barchan dunes is mainly controlled by dune size, wind patterns, vegetation cover and human impact. We investigate the variability of dune migration in Qatar over a time period of 50 years using high-resolution satellite and aerial imagery. We then explore its relation to the regional Shamal wind system, teleconnection patterns, and limitations in sand supply associated with the transgression of the Arabian Gulf. Strong size-dependent differences in migration rates of individual dunes as well as significant decadal variability on a dune-field scale are detected, which are found to correlate with the intensity of the North Atlantic Oscillation (NAO) and the Indian Summer Monsoon (ISM), in particular during years of relatively strong (weak) summer Shamals. High uncertainties associated with the extrapolation of migration rates back into the Holocene, however, do not permit further examination of the timing of the loss of sand supply and the onset of the mid-Holocene relative sea-level (RSL) highstand. For the youngest phase considered in this study (2006–2015), human impact has likely accelerated dune migration under a weakening Shamal regime through sand mining and excessive vehicle traffic upwind of the core study area.

Storm-related sedimentation influenced by coastal configuration in the stratigraphic record of a tectonically active shelf (Upper Pleistocene Le Castella terrace, Italy)

Analysis of patterns of coastal circulation and sediment dispersal is an essential step for the study of controlling factors influencing the long-term dynamics of coastal systems. Modern settings offer the possibility to monitor relevant parameters over relatively short time spans. However, geological examples complement this perspective by providing a time-averaged record where longer trends and stratigraphically significant processes can be evaluated. This study investigates the shallow marine deposits of Le Castella terrace (Upper Pleistocene, southern Italy) to document how patterns of circulation influenced by coastline configuration can affect the preserved millennial-scale depositional record of a progradational shoreline system. The regressive portion of the Le Castella terrace deposits, developed during a relative sea-level highstand and falling stage, consists of a progradational wedge mainly composed of redistributed skeletal particles of a coeval shallow water carbonate factory. Preservation of the morphology of the paleocoastline and abundant current-related sedimentary structures allow reconstruction of the predominant sediment dispersal dynamics responsible for the formation of this sedimentary wedge. Facies and paleocurrent analysis indicate offshore and alongshore sediment transport modes, consistent with coastal circulation driven by storms normally incident to the shoreline and a sharp change in coastline orientation. This coastal inflection influenced circulation patterns causing flow separation and eddy formation in the lee of the curved coastline. Syndepositional tectonic deformation also affected the architecture of the preserved deposits, controlling the nucleation and development of a clinostratified body and determining localized lateral stratigraphic variability. This study illustrates how transient but recurrent circulation patterns associated with changes in coastal orientation and related to high-energy storm events can leave a predominant signature in the stratigraphic record of microtidal shallow-marine successions.