Relative Sea-level Oscillations Research Articles

Factors responsible for Witwatersrand gold mineralisation

Abstract The exceptional gold mineralisation in quartz pebble conglomerates of the Witwatersrand Basin is attributed to a combination of factors. These factors are linked to the co-evolution of the atmosphere, hydrosphere, lithosphere and biosphere, at a very specific time in Archaean geological history and the evolution of the Kaapvaal Craton. Following craton stabilisation and its subaerial emergence, intense chemical weathering and erosion of large volumes of granitoid-greenstone basement released detrital and dissolved gold. Shallow-marine reworking in a long-lived and slowly subsiding basin subjected to episodic compressional deformation and relative sea-level oscillations led to sedimentary concentration of detrital gold. The interaction between acidic, anoxic, and sulfurous surface runoff and more oxidizing marine waters in a near-coastal oxygen oasis supported microbially mediated diagenetic pyrite formation and incorporation of dissolved gold in the pyrite crystal lattice. Erosion and reworking of diagenetic pyrite gave rise to detrital pyrite that characterise most reefs. Abundance of detrital uraninite in conglomerates, derived from erosion of Mesoarchaean granites, and episodes of hydrocarbon migration through sedimentary strata during deep burial set the scene for further enhancement of gold grades in the reefs. Granular and seam pyro-bitumen formed by radiation-induced polymerisation of hydrocarbons around detrital uraninite. Gold dissolved in migrating hydrothermal fluids was then reduced and precipitated upon interaction with the reef pyro-bitumen during hydrothermal placer modification.

Historical vertical ground movements in the Campi Flegrei volcano: A new transect across the caldera rim

This research focuses on a geoarchaeological study of the coastal sector extending from Fusaro coastal lake to Punta Pennata Islet, located in the western peripheral area of Campi Flegrei Caldera (Gulf of Pozzuoli, Italy), to reconstruct relative sea-level (RSL) oscillations and related vertical ground movements which have occurred since the Roman period. Campi Flegrei Caldera is characterized by sudden vertical ground movements of volcano-tectonic origin (i.e. bradyseismic crisis) which strongly modified the coastal landscape during the Holocene. Despite this, the area has been densely inhabited since the Greek-Roman times, preserving numerous traces of its ancient splendor. Part of these findings can be interpreted as high- or low- precision sea-level markers, helping in the reconstruction of the RSL change history. By using a multi-technique approach made of both direct and indirect surveys, the latter performed at the key-site of Punta Pennata through the use of an unmanned surface vessel prototype (ARGO), we investigated different archaeological sites with a twofold purpose. We reconstructed the RSL change of the study area during the last 2.1 ka and, by comparing the RSL data with site-specific geophysical models, we demonstrated that during the considered period the area went through five different evolutive phases characterized by an alternation of prevailing uplift, stability, and subsidence of volcano-tectonic origin, bringing the RSL from −4 and +5 m MSL, up to its current elevation. Moreover, by comparing the RSL data with the present-day sea level, we observed a differential overall subsidence of almost 1-m between the inner and outer sectors of the caldera at Miseno Cape. This validated the presence of a fault, crossing the promontory in an NNW-SSE direction, previously mentioned by other authors. Moreover, the integration of our data and historic sources enabled reconstructing the palaeo-environmental scenario of this area during the 1st century BC.

Cenozoic biostratigraphy of larger foraminifera from equatorial carbonate platform of northwestern Brazil

The off-shore Cenozoic succession of the Pará-Maranhão Basin of the Brazilian equatorial margin is studied to investigate skeletal and foraminiferal assemblages during the Oligocene-Miocene interval, one of the fundamental moments in the environmental evolution of our planet. The material from core 1-MAS-16-MA is analyzed using a combination of conventional paleontological analyses, and innovative approaches like micro-CT scan and U/Pb dating on carbonates. The results allowed to clearly constrain the Oligocene – Miocene interval and divide it into four foraminiferal assemblages and seven biofacies useful for both paleoenvironmental reconstructions and stratigraphic correlations. The paleoenvironmental analysis indicates a common pattern of relative sea-level oscillations with the nearby Foz do Amazonas Basin, highlighting a common behavior of this part of the equatorial passive margin during the Oligocene – Miocene interval. The comparison between the succession of skeletal and foraminiferal assemblages of the investigated core and other successions of the Southern and Central American area indicated the presence of stratigraphically relevant foraminiferal assemblages that could be useful for improving the correlation between the various Cenozoic successions of the area (assemblages dominated by nummulitids and lepidocyclinids in the Rupelian; assemblages dominated by Heterostegina (Vlerkina) antillea, lepidocyclinids, and primitive miogypsinids in the Chattian; assemblages dominated by Heterostegina (Vlerkina) antillea, lepidocyclinids, and miogypsinids other than Miogypsinoides and Miogypsinella, in the Aquitanian; assemblages dominated by advanced miogypsinids in the Burdigalian; post Early Miocene assemblages characterized by the lack of abundant lepidocyclinids and miogypsinids). Finally, the overall resilience of most of the large benthic foraminifera taxa to the Oligocene – Miocene transition testifies once more to the adaptability of this group of carbonate producers.

On the influence of vertical ground movements on Late-Quaternary sea-level records. A comprehensive assessment along the mid-Tyrrhenian coast of Italy (Mediterranean Sea)

The mid-Tyrrhenian coast is the most complex volcano-tectonic sector in the Mediterranean basin. Here the vertical ground movements (VGMs) due to the interaction between extensive tectonic processes and volcano-tectonic activities have a significant impact on both past and future sea-level evolution. This area represents the youngest basin of the western Mediterranean and it hosts one of the most active volcanic districts, formed by the Campi Flegrei and Vesuvius volcanoes, which are worldwide known for the vertical ground movements accompanying their volcanic activity since the Late Pleistocene. The short-lived alternation of subsidence and uplift has induced great changes in inland areas and abrupt coastal landscape transformations since that time. This study aimed to spatially constrain the magnitude of the vertical displacements which significantly affected this coastal sector during the last millennia. We then reconstructed the multiple relative sea-level oscillations that occurred during the Late-Quaternary by developing a comprehensive WebGIS of sea-level index and limiting points (https://dist.altervista.org/seaproxy/). This includes newly produced sea-level data from recent marine surveys, which were coupled to previously available data standardized according to the recent international guidelines for RSL studies. This allowed producing a multiproxy dataset composed of depositional, erosional, biological, and archaeological sea-level markers, in this very complex Mediterranean area. The collected sea-level data were further compared with a number of geophysical predictions in order to disentangle the different components which influenced the sea-level evolution. Moreover, the tectonic rates derived from the available MIS 5e sea-level data were used to shift the LIG elevations vertically and backwards in time in order to constrain the Last Interglacial RSLs to certain levels depending on the areas. Finally, we used GIS techniques to spatially constrain the coastal sectors more vulnerable to the coupled effects of future sea-level rise and VGMs in the next decades.

Relative sea-level curve during the Holocene in Rio de Janeiro, Southeastern Brazil: A review of the indicators - RSL, altimetric and geochronological data

A review of relative sea-level (RSL) oscillations during the Holocene in Rio de Janeiro, southeastern Brazil, is presented based on new data. This new data encompasses analytical techniques, altimetric corrections and age recalibrations, using the marine local radiocarbon reservoir correction of 96 ± 48 yrs. The effectiveness of geological and biological RSL indicators was tested, aiming to provide consistent information for future researches on the east coast of South America. Results confirm that RSL during Late Pleistocene - Holocene transition (11,970–11,122 cal yrs BP) was 4.5 m below Mean Sea-level (MSL). After that transition, a relatively rapid rise began. At approximately 7948–7598 cal yrs BP, the MSL was 0.5 m below the current marine level. Present-day, “zero”, was reached for the first time in the Holocene, at approximately 7686–7269 cal yrs BP. The maximum level of the Holocene marine transgression occurred around 4787 - 4104 cal yrs BP with a height of 3.0 m above MSL. At the point of maximum transgression, the sea-level began a general behavior of lowering. However, between 3981 and 3345 to 1852 - 1413 cal yrs BP, evidence from vermetids suggests several alternating periods of slow and rapid sea-level, identified by four oscillations. New records, between 1220 - 780 and 1055 - 665 cal yrs BP, have indicated a continue lowering trend of RSL.

Carboniferous Manning Canyon Formation, northern Utah, USA: A carbonate-mud-dominated cyclothem motif recording the main onset of the late Paleozoic Ice Age

A poorly understood Mississippian to basal Pennsylvanian succession is preserved in parts of northern Utah, western USA. The mudrock- and carbonate-dominated Manning Canyon Formation and lateral equivalents have been referred to as “cyclothems” and might therefore be expected to preserve a record of repeated, late Paleozoic sea-level excursions similar to cyclothemic successions elsewhere in the paleotropics. In this paper, we document the sedimentology and stratigraphy of the Serpukhovian to earliest Bashkirian Manning Canyon Formation, focusing on surface exposures in the Oquirrh and Uinta Mountains and a cored subsurface intersection from central Utah. Four facies associations were identified in the Manning Canyon Formation: Mid-Shelf, Muddy Inner Shelf, Deltaic, and Coastal Plain, which are herein interpreted in the context of a muddy, semi-enclosed, epicontinental carbonate shelf fringed by a low-relief coastal plain. These facies associations are broadly comparable to recent and extant environments from a range of equatorial, clay-rich, deltaic, coastal plain, and offshore carbonate-producing environments in the Caribbean Sea, northern Australia, and SE Asia, which can be used as first-order analogues for the Manning Canyon Formation. These modern analogues suggest that several relative sea-level excursions of <40 m are recorded in the unit. The stratigraphically oldest records of substantial relative sea-level oscillations are in the lowermost Manning Canyon Formation. These preceded a more sustained pattern recorded by at least nine 4th-order, high-frequency and high-magnitude (≥40 m) sea-level cycles that characterize the upper two-thirds of the formation. Sea-level highstands are recorded by open marine shelf facies, whereas lowstands are recorded by incised channel and valley fills, and (presumed) laterally equivalent paleosols and thin coals. No record of high frequency/high magnitude relative sea-level oscillations comparable in character to those preserved in the Manning Canyon Formation was documented in the underlying stratigraphy. It is concluded that the Manning Canyon Formation may record the main onset of the eustatic signal associated with the main phase of the late Paleozoic Ice Age at ~330 Ma.

Late Holocene relative sea‐level fluctuations and crustal mobility at Bataneh (Najirum) archaeological site, Persian Gulf, Iran

AbstractThe impacts of relative sea‐level (RSL) variations and crust mobility on the development of ancient harbours in the northern Persian Gulf are poorly understood. Many unanswered questions remain with regard to the main reasons for a shift in the location of the most important ancient harbours in the northern part of the Persian Gulf coastal since 50 BC. Furthermore, some important early Islamic harbours, such as Siraf, have ancient city quarters that are today below the present sea level. The aim of this study is to evaluate the relationship between halokinesis and RSL changes using geophysical models and multidisciplinary geoarchaeological methods at the ancient Sassanid–Islamic site of Bataneh (presently known as Najirum) located at the foothill of an active Darang salt diapir. The results reveal that after the mid‐Holocene highstand, RSL regression was not continuous. The studied facies have recorded three RSL oscillations. The oscillations are correlated with the eustatic sea‐level position. During the first lowstand, important Sassanid harbours shifted from Rishar to Apologus. The second lowstand is consistent with the transition of maritime trade from Apologus to Siraf, during the Abbasid dynasty. Uplift of the Bataneh coastal zone exposed the city to risks from flooding and fluvial debris flows. With a modification of the local watershed, runoff water originating from the salt anticlinal was controlled and used for the extraction of gypsum in evaporation ponds. The economic expansion of Siraf led to Bataneh being abandoned with a shift in trade to Kish Island.

Neapolitan volcanic area Tide Gauge Network (Southern Italy): Ground Displacements and Sea-Level Oscillations

Abstract. In this study, we investigate the oscillations of relative sea level through the analysis of tide gauge records about 10-year long collected in the Gulfs of Pozzuoli and Napoli (Southern Italy). The main goal of this study is to provide a suitable resolution model of the sea tides including low frequency (seiches), tidal bands and non-linear tides. The spectral analyses of the tide gauge records lead us to identify a number of seiche periods some of them already known from the literature and some other unknown. Furthermore, we target a non-conventional purpose of the tidal analysis, namely extracting from the tide gauge records the volcano-tectonic signal (vertical ground displacement) in the resurgent Campi Flegrei caldera. We suggest a method to filter out the volcano-tectonic signal (bradyseism) from the tide gauge records by deconvolving it from two records, one collected in the active volcanic area (Pozzuoli) and the other one collected in a tectonically stable station (Napoli), located beyond the caldera rim. Finally, we retrieve the relative mean sea level change in the Gulf of Naples and compare it with the trend found in five tide gauges spread along the Italian coast.

Chronology of Middle Pleistocene Coastal Karst Evolution and Relative Sea-Level Changes in Mallorca

Lucia, G.; Polyak, V.J.; Gines, J.; Fornos, J.J.; Gines, A.; Asmerom, Y., and Onac, B.P., 2021. Chronology of middle Pleistocene coastal karst evolution and relative sea-level changes in Mallorca. Journal of Coastal Research, 37(2), 408–420. Coconut Creek (Florida), ISSN 0749-0208.Sea-level change affects the geomorphic evolution of littoral regions in multiple ways. In carbonate coastal regions, sea-level oscillations control the type and occurrence of karst processes such as mixing corrosion, speleothem deposition, and collapse. A variety of cave deposits exist above, below, and at sea level. Among these, the vadose speleothems can provide indirect constraints on maximum sea-level boundaries, record changes from vadose to phreatic phases as littoral groundwaters flood the caves due to sea-level rise, and document different coastal speleogenetic stages. Here, new U-series ages for speleothems from three sites along the eastern coast of Mallorca (Cala Falco, Dimoni, and Sa Ferradura) are presented and used to discuss the effects of relative sea-level oscillations upon coastal karst evolution between ∼1500 and ∼440 kyr before present. The paleo-speleothem record provides new timeframes for periods of vadose conditions allowing to place some relative sea-level constraints in the western Mediterranean, particularly for the Marine Isotope Stages 16 to 12. Periodic sea-level oscillations following glacial/interglacial cycles caused morphological changes within the paleo-caves. The sequences of collapsed karst features and vadose speleothems, coupled with geomorphological evidence and previous published sea-level records, support an interpretation for the occurrence of breakdown events during cold intervals following MIS 11, 9, and 7 sea-level high stands. Further collapses and dismantling of caves happened after MIS 5 high sea stands and throughout the Holocene.

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.

A 32-million year cycle detected in sea-level fluctuations over the last 545 Myr

Spectral analyses of past relative sea-level oscillations as represented by the ages of 57 Phanerozoic (the last 545 Myr) stratigraphic sequence boundaries from the Canadian Arctic show a strong spectral peak at 32 Myr (>99.9% confidence). These findings concur with previous reports of significant cycles with periods of around 30 Myr in various records of fluctuations of sea level, and in potentially related episodes of tectonism, volcanism, climate, and biotic extinctions. Sequence boundaries commonly coincide with stage boundaries based on biostratigraphy, and are correlated with episodes of extinction and times of flood-basalt volcanism. The connection between tectonics and sea-level variations may come from changes in rates of ocean-floor spreading and subduction, intraplate stresses from plate-reorganizations, and pulsations of hotspot volcanism. These coordinated periodic fluctuations in tectonics, sea level and climate may be modulated by cyclical activity in the Earth’s mantle, although some pacing by astronomical cycles is suspected.

A Quantitative Evaluation of Hyperpycnal Flow Occurrence in a Temperate Coastal Zone: The Example of the Salerno Gulf (Southern Italy)

The inner continental shelf is regarded as a repository of hyperpycnal flow (HF) deposits the analysis of which may contribute to hydrogeological risk assessment in coastal areas. In line with the source to sink paradigm, we examined the dynamics of the coastal watersheds facing the Salerno Gulf (Southern Tyrrhenian Sea) in generating hyperpycnal flows and investigated the shallow marine sediment record to verify their possible occurrence in the recent past. Thus, the morphometric properties (hypsometric integral, hypsometric skewness, hypsometric kurtosis, density skewness and density kurtosis) of the watersheds together with the potential rivers’ discharge and sediment concentration, calculated by applying altitude- and extent -based experimental relations, allowed to detect the rivers that were prone to producing HFs. In the shallow marine environment record of the last 2 kyr, anomalous sedimentation, possibly linked to HF events, was identified by comparing the sand-mud ratio (S/M) down-core —at three sites off the main river mouths — to the expected S/M calculated by applying the relation governing the present-day distribution of sand at the seabed in the Salerno Gulf. A return period of major HF events ≤ 0.1 kyr can be inferred for rivers which fall into the category “dirty rivers”. In these cases, the watersheds have a hypsometric index ranging between 0.2 and 0.3, coastal plains not exceeding 30% of the entire catchment area and a maximum topographic height ≥1000 m. A return period of about 0.3 kyr has been inferred for the “moderately dirty rivers”. In these other cases, about 50% of the watersheds develop into a low gradient coastal plain and have a hypsometric index ranging between 0.09 and 0.2. The observations on land and offshore have been complemented to reach a more comprehensive vision of the coastal area dynamics. The method here proposed corroborates the effectiveness of the source to sink approach and is applicable to analogous sediment records in temperate continental shelves which encompass the last 3 kyr, a time interval in which the oscillations of relative sea level can be overlooked.

Onset of the Late Paleozoic Glacioeustatic Signal: A Stratigraphic Record from the Paleotropical, Oil-Shale-Bearing Big Snowy Trough of Central Montana, U.S.A.

AbstractIn the Big Snowy Mountains of central Montana, USA, late Visean to Bashkirian strata preserve a nearly complete, but poorly documented, paleotropical stratigraphic succession that straddles the range of current estimates of the onset of the Late Paleozoic Ice Age (LPIA). Sedimentologic and stratigraphic investigation of the Otter (late Visean to Serpukhovian) and Heath (Serpukhovian) formations, with secondary focus on the overlying Tyler (late Serpukhovian to Bashkirian) and Alaska Bench (Bashkirian) formations, facilitated an appraisal of paleotropical environmental change preserved in this succession. Three facies associations reminiscent of environments currently forming in Shark Bay, Australia, were identified in the Otter Formation: shallow semi-restricted littoral platform, intertidal platform, and supratidal plain. Five facies associations broadly comparable to modern environments present in the Sunda Shelf and southern coast of the Persian Gulf were identified in the Heath Formation: offshore outer ramp, mid- to outer ramp, inner ramp, coastal plain, and sabkha. Facies associations preserved in the Heath Formation are here explained in the context of a protected, homoclinal carbonate ramp situated in a partially silled epicontinental embayment. A shift from low-magnitude relative sea-level oscillations preserved in the Otter Formation to a cyclothemic stratigraphic pattern entailing ≥ 6 fourth-order, high-frequency and high-magnitude relative sea-level fluctuations in the Heath Formation is here interpreted to record the main eustatic signal of the LPIA in central Montana. Current published biostratigraphic constraints for the observed stratigraphy estimate the main eustatic signal of the LPIA to have occurred approximately between 331 (base Serpukhovian) and 327 Ma in central Montana. A distinct upward transition from coal and paleosol-bearing depositional sequences in the lower Heath to evaporite and limestone-bearing depositional sequences in the upper Heath preserves a broad humid to arid paleoclimate shift during deposition of this unit, which influenced hydrographic circulation patterns and the resultant distribution of anoxic environments in the Big Snowy Trough during this time interval. Improved depositional and sequence stratigraphic models of the Heath Formation proposed in this study permit new insight into the theoretical distribution of, and water depth necessary to preserve, black, organic-rich claystone and shale in partially silled intracratonic basins, in addition to new temporal constraints on LPIA onset in paleotropical western Laurentia.

Deposition and sea-level evolution models for Upper Pleistocene/ Holocene in the São Sebastião Channel (SE Brazilian coast) inferred from 5th order seismic stratigraphy

In this paper, we used seismic stratigraphy for the study of deposition and sea-level evolution on the São Sebastião Channel (SSC), southern Brazilian coast. About 60 km of high-resolution single-channel seismic lines were acquired to establish a 5th order seismic stratigraphy model for the area. After graphical processing for noise attenuation and enhancing of deep-reflections, we could interpret six seismic horizons and the acoustic basement which together defined six seismic units. Studying those units in a late Quaternary relative sea-level oscillations context, we propose a 4-phase deposition evolution model that took place since the Marine Isotopic Stage (MIS) 5e in the SSC area. The first phase comprises the deposition of seismic units U1 and U2 prior to MIS 4 with the deposition of one lowstand systems tract (LST) and one highstand systems tract (HST). Before the second phase, the sea-level dropped eroding the top layers of the previous units. During the second phase, after the Last Glacial Maximum (LGM), another LST (unit U3) was formed in one of the three stabilization periods of Upper Pleistocene/early Holocene sea-level rise on the Brazilian coast. Following an increase in sea-level rise velocity, we interpreted a transgressive system tract (unit U4) and another HST (unit U5) developed until the maximum sea-level of the Mid-Holocene, at 6 ky B.P during the third phase of our model. During the fourth phase, sea-level fall evolved to the present level, giving conditions to the deposition of the last HST (unit U6) interpreted in the region.

Cenomanian–Turonian depositional history of a post–Gondwana rift succession in the West Beni Suef Basin, Egypt

The structural and stratigraphic evolution of rift basins has been documented globally from modern systems, outcrop and subsurface datasets. Extensive fragmentation and break-up of Gondwana during the Cretaceous created a complex suite of rift basins in the Northern Africa. The Beni Suef rift basin straddles the River Nile and is infilled by a thick Mesozoic–Tertiary succession. Cenomanian–Turonian deposition commenced with the sandstone-dominated Bahariya Formation. Depositional environments transitioned stratigraphically from fluvial-marine to shallow marine and finally to mixed clastic and non-clastic shelfal deposits of the Abu Roash Formation. Sedimentation styles were tectonically controlled showing transgressive-to-regressive depositional cycles developed over the Gondwana rift systems. Cycles were controlled by short-lived, small-scale tectonic oscillations of the platform, resulting in four depositional sequences. Deposition environments in the Cenomanian transitioned from shallow marine to deeper marine shelfal deposits and finally to a coastal environment. During Late Cenomanian–Early Turonian, rapid platform submergence resulted in a transgressive facies succession, topped by deltaic deposits. In the Middle–Upper Turonian, two sequences formed with an intervening short-lived period of lower relative sea level. Relative sea-level oscillations were partly in phase with the global sea-level changes, controlled by local tectonics induced by the fragmentation of Gondwana during the Late Cretaceous.

Coastal landscape evolution on the western margin of the Bahía Blanca Estuary (Argentina) mirrors a non-uniform sea-level fall after the mid-Holocene highstand

Sedimentary descriptions and radiocarbon ages from two cores obtained from coastal plains along the western margin of the Bahia Blanca Estuary (Argentina) were integrated with previous information on landscape patterns and plant associations to infer landscape evolution during the mid-to-late Holocene. The study area comprises at least two marine terraces of different elevations. The old marine plain (OMP), at an average elevation of 5 m above mean tidal level (MTL), is a nearly continuous flat surface. The Recent marine plain (RMP), 2 to 3 m above MTL, is a mosaic of topographic highs and elongated depressions that may correspond to former tidal channels. Mollusks at the base of the OMP core (site elevation 5.09 m above MTL), with ages between 5,660 ± 30 and 5,470 ± 30 years BP, indicate a subtidal setting near the inland limits of the marine ingression. The sandy bottom of the core is interpreted as the last stage of the transgressive phase, followed by a tight sequence of dark laminated muds topped by a thick layer of massive gray muds. The RMP core (site elevation 1.80 m above MTL) has a similar sedimentary sequence, but unconformities appear at lower elevations and the massive mud deposits are less developed. The thickness of the grayish mud layer is a major difference between the OMP and RMP cores, but deeper layers have similar ages, suggesting a common origin at the end of the transgressive phase. The overlying massive muds would correspond to rapid sedimentation during a high sea-level stillstand or slow regression. It is proposed that, after a rapid sea-level drop to about 3 m above MTL, a flat and continuous surface corresponding to the OMP emerged, and more recent coastal dynamics shaped the dissected landscape of the RMP. For the Bahia Blanca Estuary, smooth regressive trends have been proposed after the mid-Holocene highstand, but also stepped curves. A stillstand or slowly dropping sea level was described around 3,850 ± 100 years BP, as well as negative relative sea-level oscillations. In this study, the differentiation between the OMP and the RMP supports the occurrence of a stepped regressive trend that, at least locally, presented two different stages.

Sea Level Rise and Land Subsidence Contributions to the Signals from the Tide Gauges of China

AbstractThe tide gauges measure the local oscillations of the sea level vs. the tide gauge instrument. The tide gauge instrument is generally subjected to the general subsidence or uplift of the nearby inland, plus some additional subsidence for land compaction and other localised phenomena. The paper proposes a non-linear model of the relative sea level oscillations including a long term trend for the absolute sea level rise, another term for the subsidence of the instrument, and finally a sinusoidal approximation for the cyclic oscillations of periodicities up to decades. This non-linear model is applied to the tide gauges of China. The paper shows that the limited information available for China does not permit to infer any proper trend for the relative rates of rise, as the tide gauge records are all short or incomplete and the vertical movement of the tide gauge instruments is unassessed. The only tide gauge record of sufficient length that may be assembled for China is obtained by combining the North Point and Quarry Bay tide gauges in Hong Kong (NPQB). This NQPB composite tide gauge record is shown to have similarities with the tide gauge records of Sydney, equally in the West pacific, and San Diego, in the east Pacific, oscillating about the longer term trend mostly determined by the local subsidence. As it is very well known that China generally suffers of land subsidence, and the tide gauge installations may suffer of additional subsidence vs. the inland, it may be concluded from the analysis of the other worldwide tide gauges that the sea levels of China are very likely rising about the same amount of the subsidence of the tide gauges, with the sea level acceleration component still negligible.

Microstratigraphy and interpretation of the karst sedimentary fillings associated to the Aptian–Albian unconformity in Jebel Semmama (central Tunisia)

In this paper, the aim was proposing a new microstratigraphy and interpretation of the karst sedimentary fillings associated to the Aptian–Albian unconformity in Jebel Semmama, central Tunisia. In all the previous studies, this unconformity was interpreted as the result of a major sea-level fall followed by a continuous emersion of the Aptian platform that lasted broadly the Lower and Middle Albian. In the present work, the field examination of the exposure surface in Jebel Semmama area in central Tunisia shows several centimetric epikarsts filled with different marine and non-marine deposits. According to the sedimentologic and microstratigraphic analyses, the karstic fillings may be linked with several sea-level oscillation cycles. Accordingly, the presence of such fillings suggests that the Aptian platform was not continually emerged during the lower and middle Albian as already assumed in previous works. Rather, it was episodically inundated by marine incursions. At least eighteen different sedimentary fillings have been recognized and sampled from the epikarsts. As these fillings are never totally regrouped in the same epikarst, the reconstruction of their microstratigraphy was based on (i) identification of their facies (ii) comparison and correlation of the different fillings between epikarsts (iii) analysis of the stratigraphic relation between the different fillings. A composite microstratigraphic column was established, it shows a regular alternation of shallow marine and non-marine deposits which are arranged into nine karstic sedimentary cycles. The latter may understandably be the result of nine relative sea-level oscillation cycles that broadly happened during the Lower and Middle Albian. For lack of biostratigraphic markers, the previous karstic cycles remain neither dated nor correlated with any eustatic chart. Moreover, the previous cycles have been controlled by significant local salt tectonics.

Early–middle Holocene relative sea-level oscillation events recorded in a submerged speleothem from the Yucatán Peninsula, Mexico

Geomorphological and biological archives of relative sea-level change in the western North Atlantic-Caribbean region following the Last Glacial Maximum have traditionally supported the hypothesis of a punctuated rise towards the present sea level. Such records, however, are often at insufficient resolution to discern centennial-scale changes. In caves where the water table is closely controlled by sea level, active periods of speleothem growth constraining maximum sea level, used in combination with marine overgrowths constraining minimum sea level, are a promising alternative archive recording sea-level variability at higher resolution. Here, we present a U-Th-dated early–middle Holocene speleothem record from a submerged cave on the tectonically stable Yucatán Peninsula, Mexico. Our record shows that polychaetes (Annelida, Polychaeta) colonised a sub-aerially deposited stalagmite during four individual submergence events. Submergence events occurred at approximately 8.9, 8.6, 8.4 and 6.0 ka, which we attribute to previously unrecognised minor sea-level oscillation events (OE1–OE4) above and below −6.12 ± 0.1 m relative to present sea level (r.s.l.). Combining these results with mangrove-derived relative sea-level constraints from another submerged cave on the Yucatán Peninsula, we are able to suggest that OE1 and OE2 did not reach as high as −5.26 m r.s.l., but that OE3 and OE4 exceeded −5.22 m r.s.l. We conclude that subsidence of the North American ice-load bulge was the main cause of relative sea-level rise. Superimposed on the glacio-isostatic adjustment were periods of widespread northern hemisphere cooling and ice margin re-advance, resulting in a relative sea-level fall on four occasions during the early–middle Holocene.

Holocene coastal response to monsoons and relative sea-level changes in northeast peninsular Malaysia

Sedimentological, geomorphic, and ground penetrating radar (GPR) data are combined with optically stimulated luminescence data to define the Holocene evolution of a coastal system in peninsular Malaysia. The Setiu coastal region of northeast Malaysia comprises five geological and geomorphic units representing distinct evolutionary phases of this coastline. Estimated marine limiting point elevations indicate deposition of an early aggradational shoreline associated with a sea-level elevation of −0.1 to +1.7m (MSLPMVGD datum) between ∼6.8ka and 5.7ka, in agreement with previous sea-level studies from the Malay–Thai peninsula. A hiatus occurs in the record between ∼5.7ka and 3.0ka, possibly due to a relative sea-level oscillation and shoreline erosion. Long-term relative sea-level fall and possible still-stands created strandplains that are interrupted by aggradational to transgressive paleo-barrier and estuary formation corresponding with brief episodes of RSL rise. Analyses of GPR facies and OSL ages suggest annual clinoform deposition, with geometries dictated by variations in ENSO. These data demonstrate the utility of high resolution studies of coastal facies as useful proxy indicators for paleoclimate studies at subdecadal to millennial time-scales.