Sea-level Oscillations Research Articles

Spongy-like porosity in peritidal carbonates: An interaction of cyclic sea-level oscillations, fresh water supply and sediment texture

This paper focuses upon the analysis of a complex paleokarstic system recorded within uppermost Triassic peritidal cycles in northwestern Sicily. Besides documenting spectacular karstification at the Triassic/Jurassic boundary, it provides an example of stratabound ‘spongy’ or ‘swiss-cheese’ dissolution. On the base of field observations, microfacies analysis, transmitted-light and cathodoluminescence petrography and stable-isotope analyses we put forward an original model for the formation of this peculiar stratabound dissolution. It implies a complex interaction of several controlling factors at the interface between the marine and meteoric diagenetic realms during the relative cyclic oscillations of sea-level.The presence of a fresh water supply from an adjacent emerged area is the key for the periodic formation of a mixing water lens during the relative sea level lowstand that brought about the subaerial exposure of the platform. The resulting dissolution pattern in the subtidal unit of a specific cycle is strongly controlled by the textural features of the sediments. In the case of bioturbated wackestones the ‘spongy’ or ‘swiss-cheese’ pattern develops, while in mollusk-rich beds biomoldic porosity occurs. In well-sorted subtidal members, such as algal grainstones, the dissolution originates as randomly distributed vuggy porosity. During periodic flooding of the platform, a new subtidal unit is formed and the dissolution stops as fully marine phreatic conditions are re-established.

Oroclinal bending of the Juan Fernández Ridge suggested by geohistory analysis of the Bahía Inglesa Formation, north-central Chile

The stratigraphy of the Bahía Inglesa Formation in the Caldera Basin west of Copiapó, (north-central Chile) is revised, based on hitherto unpublished stratigraphic sections and 87Sr/86Sr dating. The depositional environment varied from a rocky shoreline to the upper continental slope, with sea-level oscillations and tectonic movements causing numerous local unconformities as well as lateral and vertical facies changes. Geohistory and sedimentological analyses show that the area was close to the concurrent sea level at about 15.3Ma, but at the same time being elevated about 100m above the present sea level. Although the basin then subsided at least 350m until around 6Ma, marine deposition was only recorded after 10.4Ma. This suggests that the sea level initially dropped faster than the rate of subsidence so that subaerial erosion occurred. The period of subaerial exposure before 10.4Ma can be attributed to the presence of a NE-trending branch of the Juan Fernández Ridge below the continental crust at this time, whereas the ensuing subsidence was due to subduction erosion and crustal accommodation in its wake as it migrated south along the South American coastline. The subsequent uplift of at least 250m can be explained by an acceleration in plate expansion and isostatic rebound of the continental crust after being partially submerged in the upper mantle. The uplift–subsidence–uplift pattern mirrors those recorded around the Nazca Ridge in Peru, as well as in similar basins to the south of Caldera. However, a higher southward migration rate of the Juan Fernández Ridge against the edge of the South American Plate and less intense uplift–subsidence–uplift cycles are recorded in the latter basins. This can possibly be attributed to oroclinal bending of the ridge due to friction with the overlying continental plate, which diminished the angle of incidence and the intensity of the stress field, but increased the migration velocity of the ridge relative to the coastline.

Development of coccolithophore-based transfer functions in the western Mediterranean sea: a sea surface salinity reconstruction for the last 15.5 kyr

Abstract. A new data set of 88 marine surface sediment samples and related oceanic environmental variables (temperature, salinity, chlorophyll a, oxygen, etc.) was studied to quantify the relationship between assemblages of coccolithophore species and modern environmental conditions in the western Mediterranean Sea and the Atlantic Ocean, west of the Strait of Gibraltar. Multivariate statistical analyses revealed that coccolithophore species were primarily related to sea surface salinity (SSS), explaining an independent and significant proportion of variance in the coccolithophore data. A quantitative coccolithophore-based transfer function to estimate SSS was developed using the modern analog technique (MAT) and weighted-averaging partial least square regression (WA-PLS). The bootstrapped regression coefficient (R2boot) was 0.85MAT and 0.80WA-PLS, with a root-mean-square error of prediction (RMSEP) of 0.29MAT and 0.30WA-PLS (psu). The resulting transfer function was applied to fossil coccolithophore assemblages in the highly resolved (~ 65 years) sediment core CEUTA10PC08 from the Alboran Sea (western Mediterranean) in order to reconstruct SSS for the last 25 kyr. The reliability of the reconstruction was evaluated by assessing the degree of similarity between fossil and modern coccolithophore assemblages and by a comparison of reconstructions with fossil ordination scores. Analogs were poor for the stadials associated with Heinrich events 2 and 1 and part of the Last Glacial Maximum. Good analogs indicate a more reliable reconstruction of the SSS for the last 15.5 kyr. During this period, several millennial and centennial SSS changes were observed and associated with sea-level oscillations and variations in the Atlantic Water entering the Alboran.

PDO and ENSO modulations intensified decadal sea level variability in the tropical Pacific

AbstractAccording to long‐term sea level reconstruction and steric sea level data, regional sea levels in the tropical Pacific have oscillated between east and west on a decadal time scale over the past 60 years, but the oscillation has been intensified significantly in the last three decades. Using conditional composite analysis, we show that the recent intensification in sea level variability is caused by modulation between the Pacific Decadal Oscillation (PDO) and El Niño‐Southern Oscillation (ENSO), i.e., an El Niño in a positive PDO or a La Niña in a negative PDO phase. Our analysis of meteorological fields indicates that atmospheric circulation associated with the changes in ENSO‐PDO phase relationship plays a positive role in enhancing the decadal sea level oscillation. The intensified sea level oscillation, when superimposed on the global trend of sea level rise, will have profound implications for coastal communities, therefore, the combined effect of PDO and ENSO should be taken into account in the decadal sea level prediction in the tropical Pacific.

Baltic sea level low-frequency variability

The low-frequency sea level spectrum in the Baltic Sea has been analysed based on long-term time series of sea level data (15–124 yr) from three tide gauge stations in the Baltic Sea and two stations in the North Sea. The principal periodicities detected in the spectrum are seasonal and tidal oscillations including the pole tide with a period of about 14 months. Cross-spectral analysis has been applied to estimate the frequency response of sea level oscillations in the Baltic Sea relative to the North Sea. It is demonstrated that the basic factor in the formation of the low-frequency sea level spectrum in the Baltic Sea is the barotropic water exchange through the Danish straits. The limited throughput of these straits plays the role of a natural low-pass filter for the sea level variations: high-frequency sea level variations from the North Sea are effectively damped, while the low-frequency signal can pass through into the Baltic Sea almost undisturbed. A simple model of the barotropic water exchange used in the study allows us to estimate the parameters of the filter. It is shown that the cutoff frequency is about 0.014 cpd (74 d period): the energy of sea level oscillations at this frequency is reduced by one half after their penetration into the Baltic Sea. This study contributes to quantifying extreme sea level events in the Baltic Sea in height and time to improve their predictability.

Spatio-temporal evolution of sediment waves developed on the Gulf of Valencia margin (NW Mediterranean) during the Plio-Quaternary

Several fields of large-scale sediment waves have been observed along the Gulf of Valencia continental margin (NW Mediterranean). The largest sediment waves develop on the continental slope, extending from 250 to 850m water depth, with wavelengths ranging between 500m and 1000m and wave heights from ~2m to ~50m. On the lower part of the slope, sediment waves are quasi-stationary “vertically accreting”, becoming up-slope migrating towards the mid- and upper part of the slope. A second group of sediment waves have developed over the outer continental shelf, with wavelengths of 400 to 800m and heights of 2 to 4m, also displaying an up-slope migrating pattern. Multi-channel seismic lines crossing the continental margin show that the sediment waves over the continental slope region have been continuously developed on the foreset region of the prograding margin clinoform. Several units of sediment waves have been identified in the sedimentary record, evolving in accordance with the margin progradation. Detailed analysis of single-channel (sparker) seismic profiles revealed the presence of several sediment depositional subunits over the outer continental shelf, some of them with successive development of sediment waves being truncated by erosive surfaces, likely related to Quaternary eustatic sea-level oscillations. These erosional surfaces can be followed downslope into paraconformable strata of the sediment waves on the continental slope, where constant bedform growth is observed, without being affected by sea level changes. Based on geophysical data, the thickness of the sediment waves mapped units show that the largest sediment waves (in wave ratio, length and height) develop where sediment deposition rates are the highest, coinciding with the upper part of the continental slope (foreset clinoforms), confined by the presence of structural highs. The development of these sediment waves has been previously explained by the interaction of internal waves over the continental slope. Because sediment waves are preserved in the sedimentary record since the Lower/Pliocene, internal waves activity could have been present in this part of the margin shortly after the Zanclean reflooding of the Mediterranean Basin, following the Messinian desiccation event ~5.6 My ago. Deep water hydrodynamic conditions were re-established at that time, modulating sediment transport and deposition over the continental slope and outer continental shelf.

Subaerial exposure and drowning processes in a carbonate platform during the Mesozoic Tethyan rifting: The case of the Jurassic succession of Western Sicily (central Mediterranean)

The Liassic carbonate platform succession outcropping at Monte Maranfusa (central Western Sicily) consists of a shallowing-upward sequence of peritidal carbonates, with Jurassic to Paleogene pelagic limestone and siliciclastic Tertiary covers above. The cyclic sequences of subtidal wackestones/packstones, intertidal microcrystalline carbonates with bird's-eye pores, and supratidal bioclastic grainstones are interbedded with dark layers of the following composition: 1) dark-gray, compact, and well-cemented limestone with blackish clasts, interpreted as calcretes (a type of carbonate soil) and 2) reddish calcite laminae, deformed by elongated cavities, filled with vadose silt, interpreted as paleokarst. This succession is crossed by almost vertical faults, of the Late Liassic to Miocene, which often coincides with neptunian dykes, filled by several generations of Toarcian–Early Miocene pelagic sediments. Another system of dykes, known as neptunian sills, filled by injected Upper Lias–Dogger pelagic sediments, lies parallel to the stratification. The parallel dykes were caused by the flexure of the platform during the Jurassic and presumably by a planar slip in the carbonate rocks, whereas neptunian dykes are caused by faulting episodes. Here, we present evidence that the dark layers in the Liassic succession of Monte Maranfusa, previously described by many authors only as parallel dykes, can actually be interpreted as a) neptunian sills, b) pedogenic calcretes, and c) paleospeleothems. Therefore, we found evidence of exposure/flooding intervals in the evolution of the carbonate platform during the Liassic, linked to different pulses in both the subsidence/tectonic activity and the sea-level oscillations. At the top, Fe–Mn crusts (hardgrounds) seal the carbonate platform succession, which is in turn overlain by condensed pelagic deposits, confirming its drowning during rifting processes.

Wavelet analysis of coastal-trapped waves along the China coast generated by winter storms in 2008

This study applies the wavelet analysis to the tidal gauge records, alongshore winds, atmospheric temperature and pressure along the China coast in winter 2008. The analysis results show three events of sea level oscillations (SLOs) on the shelf induced by winter storms. The first event occurred from January 9 to 21. The SLO periods were double-peaked at 1.6–5.3 and 7.0–16.0 d with the power densities of 0.04–0.05 and 0.10–0.15 m2·d, respectively. The second event occurred from February 5 to 18. The SLO period was single-peaked at 2.3–3.5 d with power density of 0.03–0.04 m2·d. The third event occurred from February 20 to March 8. The SLO periods were doublepeaked at 1.5–4.3 and 6.1–8.2 d with the power densities of 0.08–0.11 and 0.02–0.08 m2·d, respectively. The SLOs propagated along the coast from Zhejiang in north to Guangdong in south. The phase speeds ranged about 9–29 m/s from Kanmen to Pingtan, 5–11 m/s from Xiamen to Huizhou and 11–22 m/s from Huizhou to Shuidong. The dispersion relation of the SLOs shows their nature of coastal-trapped wave.

Centennial- to millennial-scale change of Holocene shallow marine environments recorded in ostracode fauna, northeast Japan

Using the record of shallow-marine ostracode fauna and sediment grain size data from an 865-cm-long piston core obtained from Mutsu Bay, northeast Japan, paleoceanographic changes of the bay were determined at high resolution for the early to middle Holocene. Changes in the relative frequencies of several species showed periodicities of 1300–1800 years similar to Bond cycles. At around 10,300calyr BP and again, at 9500–9300calyr BP, cold water strongly influenced the bay owing to cooling events. Since at least 10,200calyr BP the Tsugaru Warm Current influenced the surface waters, and, since ca. 7400calyr BP, also the bottom waters of the bay. Since ca. 8400calyr BP the water depth rapidly increased and peaked at 7000–5900calyr BP due to global sea-level rise. Subsequently, a drop of water temperature and sea level in the bay at 5900 and around 4000calyr BP influenced the composition of the ostracode assemblages. These millennial-scale oscillations in relative sea level and bay temperature during the Holocene can be correlated to paleoclimate records elsewhere.

Wings, mushrooms, and Christmas trees: The carbonate seismic geomorphology of Central Luconia, Miocene–present, offshore Sarawak, northwest Borneo

Central Luconia is a geological province of the Sarawak Basin, offshore northwest Borneo, characterized by extensive development of Miocene to Holocene carbonate buildups. The buildups are up to 2-km (1-mi) thick and reveal complex seismic geomorphologies including out-building, in-building, carbonate-siliciclastic intercalations, and coalescence of neighboring carbonate bodies. Intermittent carbonate and siliciclastic deposition is interpreted to have been governed by frequently oscillating sea level and variable siliciclastic input. Location of the buildups with respect to deltaic facies and the seismic expressions of marginal carbonate strata, locally known as wings, are used here to classify carbonate seismic geomorphologies. Buildups encompassed by deltaic topsets are said to reside onshelf and are flanked by marginal carbonate deposits conformable with the onlapping siliciclastics and interpreted as thin carbonate platforms deposited in situ over prominent erosional unconformities and flooding surfaces. Such marginal facies are described on the basis of their appearance as open wings. In contrast, buildups downlapped by prodelta foresets or bottomsets, or those draped by pelagic sediments, are said to reside offshelf and are characterized by high relief, steeply dipping marginal carbonate strata discordant with respect to the relatively flat-lying platform carbonates as well as the onlapping siliciclastics. These marginal strata have an appearance of closed wings and are interpreted as slope aprons composed of carbonate material derived from the productive platform tops and deposited off-platform in deeper water. Carbonate geometries range from contracting-upward pinnacles to expanding-upward platforms in onshelf settings, whereas buildups located offshelf have mostly contracting-upward or aggrading morphologies. Buildups deposited onshelf have generally maintained a similar height of depositional slopes as they evolved, reflecting rates of background siliciclastic deposition approximating those of carbonate growth. In contrast, depositional slopes of offshelf buildups have become progressively higher, owing to limited siliciclastic input. Observations presented here on carbonate geomorphology and adjacent siliciclastic stratigraphy provide important clues for the understanding of the geology of the province. Because carbonates and siliciclastics intercalate frequently, siliciclastic biostratigraphy can be used to precisely date and correlate geographically remote carbonate-reservoir intervals and intrareservoir depositional and diagenetic events such as marine transgressive or exposure surfaces or karst networks. Conversely, basin paleobathymetry can be measured by the size of carbonate clinoforms and the thickness of buildups established over flooded siliciclastic surfaces. Deposition of low-relief carbonate platforms over siliciclastic substrates indicates shallow-marine conditions, as opposed to the prevalent notion of kilometer-scale paleobathymetry. These interpretations have important implications for understanding of the sedimentology and lithology of the ambient basinal siliciclastics, with fundamental applications to hydrocarbon exploration.

Post mortem modifications (pseudopaleopathologies) in middle-late Pleistocene mammal fossils from southern Brazil

Here are described post mortem modifications (pseudopaleopathologies) in 762 specimens of extinct mammals from three middle to late Pleistocene assemblages (Campanha, Chui Creek and continental shelf) of the state of Rio Grande do Sul, southern Brazil. These assemblages include mostly large-sized herbivores preserved in fluvial facies, although the assemblage from the shelf consist of remains that were reworked several times by sea-level oscillations. Although some patterns of modification are similar between the assemblages (e.g. post-fossilization plain fractures), others such as the grade of abrasion or weathering varies according to the depositional setting. The scarcity of modifications that could be attributed to predators or scavengers indicate that carnivory was not a major process driving the formation of the assemblages. Most of the fossils from the Campanha are complete, but a relatively high proportion of them exhibits advanced stage of weathering, whereas those from Chui Creek and the continental shelf are mostly unweathered. Most of the remains from the Campanha and Chui Creek are unabraded, whereas all fossils from the shelf were subject to abrasion. Few fossils exhibit signs of modification by organisms such as plants and insects. Fossils from the continental shelf have crusts of beach rock, and some specimens from the Campanha and Chui Creek have crusts of calcium carbonate or iron oxide. Besides the abrasion, the main difference between fossils from the continental and marine assemblages is the dark color and higher mechanical resistance of the latter. This difference is related to post depositional geochemical processes in the marine environment. The chemical composition of fossils from Chui Creek and continental shelf was qualitatively analyzed using energy dispersive X-ray spectrometry (EDX) and compared with recent bones. The results show the presence in the fossils of several elements not found in recent bones, incorporated through diagenetic processes controlled by specific conditions of each depositional environment.

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.

Sea-Level Forcing by Synchronization of 56- and 74-Year Oscillations with the Moon's Nodal Tide on the Northwest European Shelf (Eastern North Sea to Central Baltic Sea)

ABSTRACT Hansen, J.M.; Aagaard, T., and Kuijpers, A., 2015. Sea-level forcing by synchronization of 56- and 74-year oscillations with the Moon's nodal tide on the northwest European Shelf (eastern North Sea to central Baltic Sea). The North Sea and Baltic Sea long-term records reveal a strong correlation (0.997) between sea-level changes and the sum of identified harmonic oscillations, corresponding to the lunar nodal period and four multiples of it. We developed a transparent method for iterative least residual sine regression that is capable of identifying harmonic sea-level oscillations, e.g., gravitational sea-level effects of the lunar nodal oscillation. Three relatively large harmonic sea-level oscillations with period lengths of 18.6 (18.6), 60.5 (55.8), and 76.1 (74.4) years correspond well to factors 1, 3, and 4 of the 18.6-year lunar nodal period (multiple periods in parentheses). The sum of these oscillations leaves small residuals that can be resolved into two further, statistically less signi...

Near-field sea-level variability in northwest Europe and ice sheet stability during the last interglacial

Global sea level during the Last Interglacial (LIG, Marine Isotope Sub-stage 5e) peaked between c. 5.5 and 9 m above present, implying significant melt from Greenland and Antarctica. Relative sea level (RSL) observations from several far- and intermediate-field sites suggest abrupt fluctuations or jumps in RSL during the LIG highstand that require one or more episodes of ice-sheet collapse and regrowth. Such events should be manifest as unique sea-level fingerprints, recorded in far-, intermediate- and near-field sites depending on the source(s) of ice-mass change involved. To date, though, no coherent evidence of such fluctuations has been reported from near-field RSL studies in northwest Europe. This is an important problem because RSL fluctuations during the LIG are portrayed as warning signs for how polar ice sheets may behave in a future, warmer than present, world. Here we review the evidence for RSL change during the LIG using stratigraphic data from the best resolved highstand records that exist in the near-field of northwest Europe, from a range of settings that include lagoonal, shallow marine, tidal flat, salt marsh and brackish-water fluviatile environments. Consideration of previously published stratigraphic records from two sites in the Eemian coastal-marine embayment that existed in the central Netherlands, yields no clear indications for abrupt RSL change during the attainment of the near-field highstand. Nor do we find any such indications common to other records from countries bordering the North Sea, the Baltic Sea and the White Sea. Two modelling experiments that explore the global signal of hypothetical sea-level oscillations caused by partial collapse and regrowth of either the Greenland or Antarctic LIG ice-sheet, show that the North Sea region is relatively insensitive to mass changes sourced from Greenland but should clearly register events with an Antarctic origin, especially those that occur late in the LIG. The lack of evidence for abrupt sea-level fluctuations at this time in northwest Europe concurs with a lack of clear near-field evidence for ice sheet collapse.

Black shales and other sediments with high organic matter contents in Phanerozoic climatic cycles: Communication 1. Black shales at the Gondwanan stage of biosphere evolution

The terminal Neoproterozoic was marked by the formation of a supercontinent, which was located during a long period at high latitudes of the Southern Hemisphere. The supercontinent named Gondwana united present-day Africa, Australia, Antarctica, South America, Arabia, Hindustan, and several other small continental blocks. It was separated from other, smaller continental blocks by ocean basins with the thinned continental and oceanic crust with the Panthalassa Ocean being largest among them. The Gondwanan stage, which comprised the Vendian and significant part of the Paleozoic, was one of the longest stages defined in the Neoproterozoic and Phanerozoic geological history lasting over 300–330 Ma. During this stage, the continental sector of the Earth’s crust included the Laurentia, Baltica, Siberia, Kazakhstan, and North China (Tarim) blocks, in addition to Gondwana, which were largely located at low latitudes of the Northern Hemisphere. In the Early Paleozoic, main tectonic events were related to the breakup in peripheral parts of Gondwana with the separation of small continental massifs, which moved in the northerly direction. Their collision with other continents was accompanied by the folding and formation of mountainous structures with corresponding foredeeps. For example, the Taconian phase of fold—thrust deformations resulted from the convergence of Laurentia with the Avalon block, which was separated from the northern margin of Gondwana in the Late Cambrian or Early Ordovician. The movement of Gondwana toward the equator and its amalgamation with other continents and smaller continental blocks in the terminal Cambrian resulted in the formation of the Pangea supercontinent, whose location near the equator for more than 150 Ma up to its disintegration at the terminal Jurassic—initial Cretaceous transition was responsible for significant global changes in the floral and faunal communities. Paleozoic epochs of the relatively stable warm climate alternated with shorter periods, which were characterized by global cooling due to expansion of the ice sheet in Gondwana. These periods are reflected in frequent migrations of climatic belts and rapid sea level oscillations, which were accompanied by changes in boundaries of facies zones and extinctions of biotic communities. Distribution patterns of black shales and other organic-rich sediments in sections imply cyclic climatic variations during the entire Paleozoic. Duration of individual cycles, which included a long phase of the dominant warm or even hot climate and shorter cooling phase crowning the cycle, was as long as 47 Ma. Two such cycles terminated with glaciations; others, with a less significant growth of the Gondwanan ice sheet.

Microfacies and carbon isotope records of Mississippian carbonates from the isolated Bama Platform of Youjiang Basin, South China: Possible responses to climate-driven upwelling

Changes in Mississippian global paleogeography derived from the reconfiguration of the continents have been suggested to result in a change in oceanic circulation, carbon cycling, as well as in global cooling. Here, integrated δ13Ccarb chemostratigraphy and foraminiferal biostratigraphy across the Mississippian (late Tournaisian, Visean, early Serpukhovian; MFZ6–MFZ16 foraminiferal biozones) of the Gongchuan section located in the isolated Bama Platform in the Youjiang Basin, South China, are presented. The δ13Ccarb trend shows an abrupt decline during late Visean (Asbian-early Brigantian; MFZ13–14). This decline is also observed in subequatorial western Euramerica, whereas coeval sections in subequatorial eastern Euramerica show consistently elevated δ13C values across the entire Visean. The δ13C decline in western Euramerica and the South China Block (eastern Paleo-Tethys) coincides with a global regression with a suggested glacioeustatic origin, the onset of high-frequency climate and sea-level oscillations, and the closure of the Rheic seaway between Euramerica and Gondwana. We propose a model explaining the divergence of δ13C records resulting from the closure of the Rheic seaway and development of upwelling zones in the western margin of Euramerica and the eastern Paleo-Tethys realm. Quantitative microfacies analysis across the Mississippian succession in the Gongchuan section shows facies-independent disappearance of corals and increased proportion of cortoids and filter-feeding organisms at the onset of the Asbian δ13C decline, which may support an increase in nutrient level that can be expected as a result of upwelling.

High-frequency sea level oscillations in the Mediterranean and their connection to synoptic patterns

This paper contains a basin-wide assessment of high-frequency sea level oscillations in the Mediterranean Sea for the period from 2010 to 2014. Sea level series with temporal resolutions of 1min were taken from 29 tide gauges that had been operational for at least 4years with high-quality time series. The contribution of high-frequency sea level variance (2min–6h) to the total and residual sea level variance was estimated to vary between 0.4% and 9.5% and between 0.6% and 12.1%, respectively, but to become dominant at some stations during extreme high-frequency events. A total of 36 high-frequency sea level events were extracted from the series, with some occurring locally in one of the four selected regions of Spain, Sardinia, Sicily and the Greece–Ionian Sea (6 events), some occurring over two or three regions (19 events), and some occurring in all of the selected regions within a period of 1–3days (11 events). The basin-wide events normally propagate from the western to the eastern parts of the basin, with an average velocity of approximately 30km/h. Synoptic patterns associated with high-frequency events were analysed, and a high resemblance to patterns associated with meteotsunamis was observed: (i) a cyclone with a centre W-NW from the affected area, (ii) a strong thermal front in the lower troposphere, and (iii) a forefront of an unstable strong mid-tropospheric jet placed over the affected area. The strong coherence between high-frequency sea level events and synoptic patterns introduces the possibility of a timely forecast of these events.

Formation of the Baltic Sea level spectrum

The Baltic Sea is an internal shelf basin of theAtlantic Ocean. Almost complete closure of the basin,which is connected with the open ocean only throughshallow narrow Danish straits, leads to the formationof sea level variation absolutely not typical for the openocean [1]. The fluctuation of the sea level is the oceanbreathing [2] formed under the influence of differentfactors: tidal and meteorological forcing, componentsof the water balance, and variations in the water density. These factors cover a wide range of periods; therelative role of different processes varies in differentbasins.In order to understand the water dynamics of theBaltic Sea, one has to have an idea about the formationof the entire spectrum of the sea level fluctuations withperiods from hours to tens of years. According to [3],one can distinguish the following five variability rangesin the classification of the sea level fluctuations withperiods smaller than 10 years: mesoscale (from 2 hoursto 2 days), synoptic (from 2 days to one month), intraannual (from 1 month to 1 year), seasonal (annualperiod and divisible harmonics), and interannual(from 1 year to 10 years). The tides make the greatestenergetic contribution to the dispersion of the sea levelfluctuations in the open ocean (approximately 85%).Due to the narrowness of the Danish straits, the tidesalmost do not propagate to the Baltic Sea and themesoscale variability of the sea level is determinedmainly by internal oscillations, which are generatedwithin the sea [4]. However, the longrange fluctuations of the sea level penetrate from the North Seaalmost without distortions.The research object of this work is the North Sea–Baltic Sea system. Such an approach allows us to studyin detail the mechanisms of the formation of the BalticSea level spectrum in various frequency ranges and todistinguish its main peculiarities.It is convenient to consider the sea level fluctuations as a probability process. One can use the spectralanalysis methods of random processes to estimate thefrequency distribution of the energy of sea level fluctuations. The fluctuations of the sea level are not strictlya stochastic process because tides have a strong influence on them. The tide is a regular deterministic process, which is manifested in the sea level spectra assharp deltashaped peaks (discrete spectrum). Theseasonal fluctuations also have a discrete spectrum, inwhich the annual and semiannual harmonics dominate, although these fluctuations are not strictly deterministic [5]. The pole tide is a special type of sea leveloscillations, which is anomalous in the Baltic andNorth seas [6]: this process also has a harmonic character (with a period of approximately 14 monthscaused by the Chandler wobble of the Earth’s axis ofrotation); however, its dominant period has specifictime variations. The other components of the sea levelfluctuations are characterized by random noise andform a continuous energy distribution by frequency(continuum).In this work, we apply spectral analysis to describethe spectrum of the sea level variations and estimatethe energy contribution of different frequency bandsto the total dispersion of fluctuations. With this inmind, we considered longterm time series of hourlyand monthly observations of the sea level at fourcoastal tide gauge stations: Cuxhaven (Germany) inthe North Sea, Stockholm, Furuogrund, and Kronstadt in the Baltic Sea (Table 1, Fig. 1) Joint application of longterm monthly mean time series togetherwith the hourly data of high quality (the percentage ofgaps at all stations did not exceed 1%) gave us the possibility to estimate the energy of sea level fluctuationsin a wide range of periods with the maximum highspectral resolution.The Danish straits separating the Baltic Sea fromthe North Sea serve as a lowfrequency filter that letthe longperiod sea level fluctuations propagate to theBaltic Sea (longterm and seasonal) and suppress thesynoptic and mesoscale sea level fluctuations [7]. Thisis the reason why synoptic and mesoscale sea levelvariations are formed within the Baltic Sea and arecharacterized as eigen (internal) oscillations [8]. Thestructure of internal oscillations of the Baltic Sea level

Revealing the hidden Milankovitch record from Pennsylvanian cyclothem successions and implications regarding late Paleozoic chronology and terrestrial-carbon (coal) storage

The widely held view that Pennsylvanian cyclothems formed in response to Milankovitch-controlled, glacio-eustatic, sea-level oscillations lacks unambiguous quantitative support and is challenged by models that are based on climate-controlled precipitation-driven changes in depositional style. This study shows that cyclothem successions do in fact contain a clear record of Milankovitch-controlled oscillating sea level, but that it is prerequisite that besides cyclothem thickness, cyclothem composition is taken into account. A simple subdivision of cyclothems into subaqueous and subaerial facies is sufficient to reveal the signal, provided that sufficiently long and complete successions are studied. Two Duckmantian–Bolsovian (Westphalian B–C) successions were studied—one from a high-accommodation setting in the Netherlands and another from a medium-accommodation setting in Kentucky in the United States. The Dutch record comprises an exceptional, 1728-m-long, continuously cored interval, and it shows a distinct twofold cyclicity in the subaerial-facies ratio of subsequent cyclothems at wavelengths of ∼256 m and ∼59 m, which is confirmed by power-spectral analysis. The signal is not present in the Kentucky succession due to subsidence-controlled low preservation of only one out of three to four cyclothems, and that explains why many cyclothem studies have yielded inconclusive results. Recent U/Pb ages indicate that the 256 m cycle represents ∼395 k.y., which matches with long eccentricity (413 k.y.). This then gives a 95 k.y. duration for the 59 m cycle (short eccentricity). Individual cyclothems in the high-accommodation Dutch succession are mostly between 5 and 35 m thick, which points to a sub-eccentricity duration (mean 21 k.y.). The highly variable thickness may be due to interference of precession-, obliquity-, and eccentricity-driven sea-level fluctuations or alternatively to autocyclic or climate-controlled variations in sediment supply. Integration of the results with U/Pb calibrated radiometric ages for “tonstein” ash layers from North America and Europe allowed refinements of the chronology of the main Westphalian (Moskovian–Bashkirian) coal interval; these refinements are consistent across Euramerica. An analysis of cumulative coal-bed thickness further indicates that terrestrial-carbon (coal) storage patterns are comparable in the two remote areas: in the Netherlands ∼5 m coal per m.y. during the Langsettian (Westphalian A) and increasing abruptly to ∼20 m/m.y. at the start of the Duckmantian substage (Westphalian B). In Kentucky, storage rates were lower, but when standardized to Dutch subsidence, the pattern is identical. This suggests that burial of terrestrial carbon during the Late Paleozoic Ice Age was globally controlled and possibly very predictable.

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.