Global Sea-level Changes Research Articles

An Investigation into Sea Level Rise in Sri Lankan Waters with Satellite AltimetryCorrected version of this article has been publshed under the section "Corrigendum" in the same issue on 15th October

Most of the socio-economic activities of Sri Lanka are centred in the coastal regions, which can be described according to its unique geographical and geophysical backgrounds. It is estimated that Sri Lanka has a shore line about 1,700 km in length. Therefore, better knowledge and understanding of the characteristics of sea level is very essential. The sea level has traditionally been measured mainly at tide gauges set up along the coast line. However, the number of tide gauge stations is few and sparse in most countries. But, with the advancements of satellite altimetry technology, it is now accepted as an alternative technique to study regional and global sea level changes. The basic concept in altimetry is the range measurements to the water surface measured from the altimeter antenna. The surface of the sea, or sea level, is continuously changing for many reasons. Here, some changes are fast whereas others occur gradually. Among them, some factors are natural causes, while others occur due to man-made activities such as the greenhouse effect. These changes can be regional or extend at a global scale. The main aim of this research was to examine the trends in sea level rise around the Sri Lankan coastline using two decades of satellite altimetry data from 1993 to 2012. The computed sea level rise trends around Sri Lanka is around 2.5 to 3 mm per year, with a variance of +/- 0.6 mm accuracy. The obtained trend of sea level rise from the altimetry data was validated with tide gauge data in Colombo, and found to be highly correlated, with a correlation coefficient (R2) of 0.93 for annual mean sea level. This study confirms that satellite altimetry can be successfully used to investigate the long term sea level trend studies, particularly in the absence of long term tide data.

Magnetic Properties and Initiation of Biogenic Reefs in Xisha Islands, South China Sea, at the Oligo–Miocene Boundary

Biogenic reefs and carbonate platforms are valuable natural resources, playing an important role in modulating the global climate and in carbon cycles through biological processes. Biogenic reefs in the Xisha (Paracel) Islands began in the late Oligocene and covaried with the deep-sea basin of the South China Sea and with the aeolian deposit in the Chinese Loess Plateau. Core XK-1 was drilled into the Xisha Islands to their granitic base and well dated by magnetostratigraphy, offering an opportunity to reveal the details of how the Xisha reefs initiated. In this report, the lower section of the biogenic reefs (23.0–24.5 Ma) was sampled for studying magnetic properties. The main results are as follows: (1) magnetic minerals in the XK-1 biogenic reefs are dominated by low-coercivity and relatively coarse-grained magnetite; (2) the variabilities of magnetic parameters can be clustered into two sections around 23.6 Ma, and the differences between the two units are evident both in the amplitudes and the means; and (3) changes in the concentration-dependent magnetic parameters can be well correlated with the records of global deep-sea oxygen and carbon isotopes, and the sea level during the Oligo–Miocene boundary. Based on these results, a close link was inferred between biogenic reef evolution in the Xisha Islands and global climate change. This link likely highlights the covariation or the dominant role of the Asian monsoon in biogenic reefs and involves different responses to global temperature, CO2, and sea-level changes on various timescales. Therefore, we proposed that the origin of biogenic reefs in the Xisha Islands was likely paced by orbital obliquity from a long-term perspective.

Climate changes, paleogeography and geological development of the northern part of Bulgarian Black Sea shelf and coast during the Quaternary

The article represents a synthesized reconstruction of the geological development of the northern part of Bulgarian Black Sea shelf and coast during the Quaternary. Marine Quaternary sediments are considered as a component of the marine ecosystem that is strongly affected by the climate changes. As a result, changes in the stratigraphic and sedimentological characteristics of the Pleistocene sediments and in particular the Holocene deposits were recorded. During the Quaternary, which is characterized by short-term, cyclic climatic fluctuations, marine shelf sediments have sealed traces of the alternation of glacial and interglacial phases. Based on detailed lithostratigraphic and biostratigraphic analysis of mollusk fauna and pollen, not only are the complex dynamics of the transgressiveregressive cycles traced, but also their relationship to global and regional changes of climate and sea level is confirmed. As a result of an integrated lithofacies, biostratigraphic, and geomorphological analysis, the stratigraphic sequence of the Quaternary sediments is established as well paleogeographic conclusions are reached. Today, knowledge of natural processes such as coastal abrasion, landslides, storms, tsunami waves, etc., are directly linked to the geological risk forecast and correlate with the geoecology and sustainability of the environment in which we live. In this sense, the reconstruction of the components of the geological environment from the closest geological past – Pleistocene and Holocene, is key to forecast climate change and sea level today.

Investigating the internal structure of the Antarctic ice sheet: the utility of isochrones for spatiotemporal ice-sheet model calibration

Abstract. Ice-sheet models are a powerful tool to project the evolution of the Greenland and Antarctic ice sheets and thus their future contribution to global sea-level changes. Testing the ability of ice-sheet models to reproduce the ongoing and past evolution of the ice cover in Greenland and Antarctica is a fundamental part of every modelling effort. However, benchmarking ice-sheet model results against real-world observations is a non-trivial process as observational data come with spatiotemporal gaps in coverage. Here, we present a new approach to assess the accuracy of ice-sheet models which makes use of the internal layering of the Antarctic ice sheet. We calculate isochrone elevations from simulated Antarctic geometries and velocities via passive Lagrangian tracers, highlighting that a good fit of the model to two-dimensional datasets such as surface velocity and ice thickness does not guarantee a good match against the 3D architecture of the ice sheet and thus correct evolution over time. We show that palaeoclimate forcing schemes derived from ice-core records and climate models commonly used to drive ice-sheet models work well to constrain the 3D structure of ice flow and age in the interior of the East Antarctic ice sheet and especially along ice divides but fail towards the ice-sheet margin. The comparison to isochronal horizons attempted here reveals that simple heuristics of basal drag can lead to an overestimation of the vertical interior ice-sheet flow especially over subglacial basins. Our model observation intercomparison approach opens a new avenue for the improvement and tuning of current ice-sheet models via a more rigid constraint on model parameterisations and climate forcing, which will benefit model-based estimates of future and past ice-sheet changes.

Sea level dynamics and coastal erosion in the Baltic Sea region

Abstract. There are a large number of geophysical processes affecting sea level dynamics and coastal erosion in the Baltic Sea region. These processes operate on a large range of spatial and temporal scales and are observed in many other coastal regions worldwide. This, along with the outstanding number of long data records, makes the Baltic Sea a unique laboratory for advancing our knowledge on interactions between processes steering sea level and erosion in a climate change context. Processes contributing to sea level dynamics and coastal erosion in the Baltic Sea include the still ongoing viscoelastic response of the Earth to the last deglaciation, contributions from global and North Atlantic mean sea level changes, or contributions from wind waves affecting erosion and sediment transport along the subsiding southern Baltic Sea coast. Other examples are storm surges, seiches, or meteotsunamis which primarily contribute to sea level extremes. Such processes have undergone considerable variation and change in the past. For example, over approximately the past 50 years, the Baltic absolute (geocentric) mean sea level has risen at a rate slightly larger than the global average. In the northern parts of the Baltic Sea, due to vertical land movements, relative mean sea level has decreased. Sea level extremes are strongly linked to variability and changes in large-scale atmospheric circulation. The patterns and mechanisms contributing to erosion and accretion strongly depend on hydrodynamic conditions and their variability. For large parts of the sedimentary shores of the Baltic Sea, the wave climate and the angle at which the waves approach the nearshore region are the dominant factors, and coastline changes are highly sensitive to even small variations in these driving forces. Consequently, processes contributing to Baltic sea level dynamics and coastline change are expected to vary and to change in the future, leaving their imprint on future Baltic sea level and coastline change and variability. Because of the large number of contributing processes, their relevance for understanding global figures, and the outstanding data availability, global sea level research and research on coastline changes may greatly benefit from research undertaken in the Baltic Sea.

Vertical Land Motion as a Driver of Coastline Changes on a Deltaic System in the Colombian Caribbean

To face and properly mitigate coastal changes at a local level, it is necessary to recognize and characterize the specific processes affecting a coastline. Some of these processes are local (e.g., sediment starvation), while others are regional (e.g., relative sea-level change) or global (e.g., eustatic sea-level rise). Long tide gauge records help establish sea-level trends for a region that accounts for global (eustatic, steric) and regional (isostatic) sea-level changes. Local sea-level changes are also the product of vertical land motion (VLM), varying depending on tectonic, sedimentological, and anthropogenic factors. We investigate the role of coastal land subsidence in the present-day dynamics of an abandoned delta in the Colombian Caribbean. Satellite images and synthetic aperture radar acquisitions are used to assess decadal-scale coastline changes and subsidence rates for the period 2007–2021. We found that subsidence rates are highly variable alongshore. Local subsidence rates of up to −1.0 cm/yr correspond with an area of erosion rates of up to −15 m/yr, but coastal erosion also occurs in sectors where subsidence was not detected. The results highlight that local coastline changes are influenced by multiple, interacting drivers, including sand supply, coastline orientation and engineering structures, and that subsidence alone does not explain the high rates of coastal erosion along the study area. By the end of the century, ongoing coastal erosion rates of up to −25 m/yr, annual rates of subsidence of about −1 cm/yr, and current trends of global sea-level rise are expected to increase flooding levels and jeopardize the existence of the deltaic barrier island.

The Miocene stratigraphy of the Laberinto area (Río Ica Valley) and its bearing on the geological history of the East Pisco Basin (south-central Peru)

Global sea-level changes and substantial vertical displacement along the Monte Grande Fault (MGF) in the lower Río Ica Valley of south-central Peru influenced the accumulation of bioclast-bearing and diatom-bearing Miocene siliciclastic sediments in an area of the East Pisco forearc basin (EPB) colloquially known as Laberinto. Two depositional hiatuses in the Laberinto area (~17–14 Ma, ~12.5–10 Ma) manifest as sediment-filled erosional depressions a few kilometers in breadth. Erosion of the older depression was preceded by an ~18-Ma massive debris flow, possibly triggered by motion on the MGF causing lower Miocene lithoclastic olistoliths of up to two hundred meters length to spill off the footwall block. Sediment shed from the same footwall block may have formed previously recognized early Miocene deltas. From 14 to 13 Ma, the older depression filled with sediments herein assigned to the provisionally named Laberinto, Pampa, and Naranja members of the Pisco Formation, the latter member being characterized by marine delta foreset beds. The three members are at least partly correlative with the Pisco-0 sequence of the Pisco Formation. The younger depression was overrun at 10 Ma by debris flows of lithoclastic and granitic cobbles and boulders, then filled with diatomaceous silty sand with 5-m-sized lithoclastic olistoliths. The two lithologies constitute the provisionally named Mature Formation. Radiometric and newly revised biochronological data from throughout the EPB coupled with new diatom data from the Laberinto area have provided new insights into the correlation of sequences within the Chilcatay and Pisco formations and the interaction of local and basin-wide tectonism and global eustatic sea-level events across the basin.

The AntSMB dataset: a comprehensive compilation of surface mass balance field observations over the Antarctic Ice Sheet

Abstract. A comprehensive compilation of observed records is needed for accurate quantification of surface mass balance (SMB) over Antarctica, which is a key challenge for calculation of Antarctic contribution to global sea level change. Here, we present the AntSMB dataset: a new quality-controlled dataset of a variety of published field measurements of the Antarctic Ice Sheet SMB by means of stakes, snow pits, ice cores, ultrasonic sounders, and ground-penetrating radar (GPR). The dataset collects 3579 individual multi-year-averaged observations, 687 annually resolved time series from 675 sites extending back over the past 1000 years, and daily resolved records covering 245 years from 32 sites across the whole ice sheet. These records are derived from ice cores, snow pits, stakes/stake farms, and ultrasonic sounders. Furthermore, GPR multi-year-averaged measurements are included in the dataset, covering an area of 22 025 km2. This is the first ice-sheet-scale compilation of SMB records at different temporal (daily, annual, and multi-year) resolutions from multiple types of measurement and is available at https://doi.org/10.11888/Glacio.tpdc.271148 (Wang et al., 2021). The database has potentially wide applications such as the investigation of temporal and spatial variability in SMB, model validation, assessment of remote sensing retrievals, and data assimilation. As a case of model estimation, records of the AntSMB dataset are used to assess the performance of ERA5 for temporal and spatial variability in SMB over Antarctica.

Geochemical and sedimentary facies study – Implication for driving mechanisms of organic matter enrichment in the lower Silurian fine-grained mudstones in the Baltic Basin (W Lithuania)

More than 100 m-long core sections from Western Lithuania (Baltic Basin), presenting an almost continuous lower Silurian fine-grained siliciclastic organic matter-rich sedimentary record from Aeronian to Homerian, were investigated to evaluate the main forces governing the organic matter enrichment. The methods applied include organic and inorganic geochemistry, organic petrology, sedimentological and petrographic studies along with framboidal pyrite analysis, as well as analysis of stable nitrogen and organic carbon isotopes. The petrographic observations showed distinct mudstone diversity reflecting a variety of paleoenvironmental depositional conditions evolving against a backdrop of post-Ordovician climate, thus, sea level variations, and progressing development of foreland basin throughout the early Silurian. Reflectance measurements on vitrinite-like particles, supported by molecular organic geochemical and Rock-Eval data prove that kerogen from the studied section reached the oil window maturity stage. Rock-Eval pyrolysis, organic geochemical and petrographical as well as δ13Corg data clearly confirm the marine origin of the organic matter. Various geochemical proxies and sedimentary features indicate that in Aeronian a period of more humid climate favored enhanced nutrient input, which in turn intensified organic matter productivity resulting in large amounts of organic matter accumulation. Redox proxies (TOC/TS ratio, trace elements enrichment, molecular organic geochemical indices, framboidal pyrite analysis, TOC/P ratio) demonstrate a rather broad spectrum of bottom water oxygenation levels in the lower Silurian sediments accumulated under oxic - dysoxic – anoxic conditions interrupted by several episodes of euxinia. A highly condensed section of Aeronian black-grey mudstones manifests a very good organic matter preservation under sediment-starved and oxygen-depleted settings. Here, the oxygen-depleted water bottom conditions are well evidenced by low values of δ15N and δ13Corg pointing to the presence of diazotrophic N-fixing and chemoautotrophic organisms. The Sheinwoodian-Homerian section of monotonous grey calcareous mudstones evenly and moderately enriched in organic matter reflects the most steady environmental settings developed under more arid climate in comparison to Llandovery. Throughout the early Silurian sedimentation rates were overall low, although probably enhanced in Wenlock, and played a role in organic matter preservation. It was a critical factor during sedimentation of grey-greenish mudstone of the Telychian characterized by comparatively the lowest organic matter preservation efficiency. Variations in the intensity of the pycnocline, thus organic matter preservation, were probably controlled by climate-triggered sea level changes, although tectonically-driven paleoenvironmantal effects, bathymetry, and, at some point, intensified paleoproductivity inducing oxygen-restricted conditions, were likely contributing. Although MoEF/UEF ratios mainly indicate fully open marine settings during the entire early Silurian, Mo–TOC covariation clearly displays strict basinal restriction in the Aeronian. The profile of δ13Corg demonstrates six carbon isotope excursions along the lower Silurian section. The identified Late Aeronian and Early Sheinwoodian Carbon Isotope Excursions are linked to global sea-level changes, thus, changes in oceanic water circulation pattern. A high percentage of tiny pyrite framboids within the interval of Early Sheinwoodian CIE could reflect an increased pyrite burial under highly reducing conditions and might be associated with an Oceanic Anoxic Event. The three positive δ13Corg excursions within the Telychian seem to be related to an early diagenetic partial oxidation of organic matter.

Geochemical investigation of the taphonomy, stratigraphy, and palaeoecology of the mammals from the Ouled Abdoun Basin (Paleocene-Eocene of Morocco)

We performed different geochemical analyses of Paleogene terrestrial mammal remains to establish their taphonomy, stratigraphic provenance, and palaeoenvironmental conditions. Rare earth element (REE) results indicate a similar diagenetic history to that of previously investigated marine taxa from these beds. Therefore, the mammal remains were initially deposited in a marine setting, and probably not long after the death of the animals their bodies were washed into the sea. The Ce/Ce* and Pr/Pr* ratios for the mammal fossils were compared with the background dataset from the phosphate mines, which varies with time. This allowed us to characterize the stratigraphic levels bearing the fossils. The provenances of fossils with known origins were confirmed, while remains with unknown origins could be assigned to certain stratigraphic horizons that are compatible with previously proposed phylogenic relationships.Marine diagenesis affected the various skeletal tissues differently, with the largest alteration in the bone and the least or none in the enamel. This is mostly demonstrated by the high F concentration, high Ca/P, and seawater related 87Sr/86Sr in the bone/dentine samples. Enamel shows the opposite, and retained the most pristine terrestrial values. The δ18OPO4 and δ13C results from mammal enamel revealed warm (>20 °C mean annual temperature-MAT) and dry (<500 mm mean annual precipitation) conditions for Paleocene-Eocene period in the region. From the early to mid-Ypresian about +5 °C ΔMAT is recorded that might be linked to the Early Eocene Climatic Optimum.Furthermore, the 87Sr/86Sr ratios derived from shark tooth enameloid fit the global open ocean Sr-isotope record during the latest Paleocene and early Eocene providing further evidence for the age of these phosphate beds in the Ouled Abdoun Basin. However, older marine fossils yielded higher ratios than the global Sr-isotope curve, reflecting an alteration and/or somewhat restricted conditions in the Moroccan coastal basins, possibly triggered by global sea-level changes.

Stratigraphic Development and Sedimentary Environment Evolution in the Bohai Sea Since the Late Pleistocene

In recent years, there have been controversies in the evolution of sedimentary environment and stratigraphic division in the Bohai Sea since the Late Pleistocene. Based on the data (lithology, sedimentary structure, micro‐paleontology, and dating data) of 5 boreholes (core of BT113, BT114, BQ1, YRD-1101, and Lz908) in the Bohai Sea, the stratigraphic development and sedimentary environment evolution were revealed in the area since the Late Pleistocene: a marine bed of each borehole in study area was developed during MIS 5 (the MIS 5 bed of core BQ1 is not exposed); during MIS 4, there were fluvial deposits in the cores of BT113, BT114 and BQ1of the study area, but showed be a transitional sedimentary face in cores of YRD-1101 and Lz908,which may be due to the fact that the sea water has not completely withdrawn from the Bohai Sea with short time and temperature decline less than that of the Last Glacial Age. In the early MIS 3, a transgression has been occurred in cores of Lz908, YRD-1101, and BQ1 of the study area, but a fluvial deposit in cores of BT113 and BT114; from the middle and late MIS 3 to the Last Glacial Maximum, the study area was showed a regression during this period; there was have a marine bed due to wide transgression during the Holocene. According to the stratigraphic records of each borehole in the study area, we find that the evolution of the sedimentary environment is consistent with the trend of global sea level changes, indicating that stratigraphic development and the evolution of the sedimentary environment are mainly controlled by global sea level changes in the study area since the Late Pleistocene. In addition, we need further study to find out other factors.

Projected sea level rise on the continental shelves of the China Seas and the dominance of mass contribution

We analyze the projected sea level rise (SLR) for the 21st century for the China Seas (the Bohai Sea, Yellow Sea, East China Sea, and South China Sea) using the Coupled Model Intercomparison Project Phase 5 dataset. We find that the projected SLR over the shallow continental shelves of the China Seas is nearly the same as the global mean sea level change in all future emission scenarios, with a magnitude of 43.6 cm (20.8–67.7 cm, 90% confidence interval) in RCP2.6 and 74.5 cm (41.7–112.8 cm, 90% confidence interval) in RCP8.5 by the year 2100 relative to 1986–2005. We further analyze the causes of SLR and find that more than 90% of the total projected SLR over the continental shelves of the China Seas will result from mass contributions and only a minor contribution will result from local steric height adjustments. This increase in water mass over the continental shelves is not only caused by the loss of land ice, but also from the change in sterodynamic, which tends to push water mass onto the continental shelves from the open oceans.

Subglacial sediment deformation in the Ross Sea, Antarctica

The Ross Sea embayment is the outlet for one-third of all Antarctic ice flow, receiving input from both East and West Antarctica. Marine-based ice streams, whose stability is susceptible to global sea-level changes, expand and contract across the Ross Sea continental shelf, eroding and deforming the substrate and transporting sediment subglacially. Deposits from the Last Glacial Maximum in the western Ross Sea provide an opportunity to investigate paleo-ice stream processes using sediment cores associated with glacial landforms. This study combines micro-to macro-sedimentological analyses to characterize lithofacies that represent a glacial-interglacial succession. We observe subtle variations in sediment properties within the subglacial unit that suggest till heterogeneity. Physical characteristics that vary both laterally and vertically indicates different sediment response to glacial stress, resulting in non-pervasive deformation within the till. These observations are consistent with the interpretation that a dynamic ice sheet with variable flow regimes existed across the Ross Sea during the Last Glacial Maximum. Further microscopic evidence of dynamic subglacial conditions includes sediment aggregates preserved as discrete grains in the form of soft sediment clasts or till pellets. Till pellet-rich sediment is commonly associated with the transition from a subglacial to proximal glaciomarine environment, although here we demonstrate they are widespread in both facies. Their widespread occurrence downcore and distribution across the continental shelf provides sedimentological evidence of a deformable bed beneath an ice stream during the Last Glacial Maximum. Ultimately, better tools for discriminating between glacial deposits will allow for more detailed reconstructions of ice-sheet history, and thus determine the forcing mechanisms to which the ice is responding.

Measuring Global-Mean Sea-Level Rise With Surface Drifting Buoys

AbstractWe propose to establish a new ocean observing system for monitoring global and regional mean sea-level changes. This system will consist of a global array of thousands of water-following drifting buoys tracked by a global navigation satellite system—such as the Global Positioning System (GPS)—which will continuously provide the geographical positions and the height of the sea surface along the buoys' trajectories. The sea-level height data collected in this way, averaged over regional basins and the global ocean, will provide daily measures of regional and global mean sea levels. An essential climate variable, mean sea level is an intrinsic measure of climate change, integrating the thermal expansion of the ocean's waters and additions to the ocean's mass from melting terrestrial ice. The realization of this new system requires that standardized vertical position measurements with controlled accuracy be acquired and regularly transmitted from relatively small and expendable drifting buoys, which constitutes a technological challenge, yet one with a clear path for being met. The development and implementation of this ocean shot concept will ultimately provide an independent, resilient, sustainable, and economical observational system to quantify natural and anthropogenic sea-level changes, augmenting the existing satellites and tide gauge observing systems.

Long‐Term (1979‐Present) Total Water Storage Anomalies Over the Global Land Derived by Reconstructing GRACE Data

AbstractThe Gravity Recovery and Climate Experiment (GRACE) mission has monitored global total water storage anomalies (TWSA) with an unprecedented accuracy since 2002. Yet, many applications require a longer record, that is, extending prior to the GRACE period. Here, we present a new global reconstruction of long‐term (1979–2020) TWSA fields by combining machine learning with time series decomposition and statistical decomposition techniques. We find that the long‐term TWSA reconstructed from GRACE fits well with the GRACE‐FO observation over most grids (0.5° resolution) of the global land and successfully reproduces the strong El Niño signal. Comparisons to Satellite Laser Ranging solutions and to observed global mean sea level change suggest our reconstruction (doi: https://doi.org/10.5061/dryad.z612jm6bt) is more reliable than previously published products. This study provides a viable approach for both reconstructing past TWSA and filling the GRACE data gap at the global scale.

Cenomanian–Turonian oceanic anoxic event (OAE2) imprint on the northwestern part of the Adriatic Carbonate Platform and a coeval intra-platform basin (Istria and Premuda Island, Croatia)

The Cenomanian–Turonian boundary (CTB) on the intra-Tethyan Adriatic Carbonate Platform (AdCP) is generally characterised by a transition between microbially laminated and/or bioclastic limestones to calcisphere-rich massive limestone with bioturbated intervals, organic-rich interbeds, firmgrounds, as well as neptunian dikes, carbonate turbidites, tempestites and slumped structures. Compilation of the results from two study sites in the northwestern part of the AdCP and from previous research (on Istria Peninsula and islands in the Adriatic Sea in Croatia) provides a more complete overview of geological events and paleoenvironmental conditions that transformed the formerly contiguous shallow-marine environments during this time period. For the first time, a comparison between protected inner-platform area (Barban section) and a coeval intra-platform basin (Premuda Island section) during the CTB was made. This study utilized a combination of litho-, bio-, and microfacies studies with SEM, EDS, TOC, δ13C and δ18O stable isotope analyses. The stratigraphic successions start with shallow-marine carbonate deposits of the Milna Formation that is conformably overlain by the drowned-platform deposits of the Sveti Duh Formation on the platform and by the Veli Rat Formation in the contemporaneously developed intraplatform basin. These deposits are in turn overlain by the Gornji Humac Formation, which represents re-establishment of shallow-marine depositional systems on the AdCP, whereas the deeper water environment persisted in the intra-platform basin until the Santonian.Despite diagenetic modifications of shallow-marine carbonate deposits, the results of TOC and stable isotope analyses indicate the influence of global Oceanic Anoxic Event 2 (OAE2). Combination of local and regional synsedimentary tectonics and global Late Cretaceous sea-level changes accompanied by anoxic and hypoxic conditions, extinction of numerous benthic foraminifera, diversification and expansion of planktonic foraminifera and calcareous dinoflagellates, provide new insights into the character of the CTB interval in this part of the Tethyan realm.

Tectono-eustatic controls on depositional setting and spatial facies distribution of Coniacian–Santonian sequences of the Zagros Basin in Fars area, S. Iran

New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santonian homoclinal carbonate ramp (Ilam Fm.) developed on the subaerially exposed mid-Turonian surface at the top of Sarvak Fm. in Fars zone of the Zagros Basin (northeastern margin of the Arabian Plate). Spatial facies distribution, sequence stratigraphy, and lateral variation in the thickness of Ilam Fm., as well as extend of erosion of the underlying Sarvak Fm. suggest that a combination of regional tectonic activities and global sea-level changes controlled the development of this succession. A major tectonic configuration in the Zagros belt including several basement faults subdivide the belt into different blocks with distinctive sedimentary records. Reactivation of these preexisting basement faults during Late Cretaceous provided a horst and graben geometry due to the closure of Neo-Tethys. Three of our studied sections are located on an upthrown block, bounded between Kazerun and Karebas basement faults, include inner and mid-ramp deposits. These sections represent an eastward deepening trend which correspond to eastward tilting of this fault block. The easternmost section is located in the eastern neighboring downthrown block , bounded between Karebas and Bastak faults, and includes outer ramp and basin deposits confirming a significant paleo-bathymetrical contrast between the two blocks. Furthermore, eastward thickening of the Ilam Fm. independently confirms the increase of accommodation space, as a result of deeper depositional condition, toward center of the Fars zone. Absence of subaerial exposure features at top of the Sarvak Fm. in the downthrown block shows that the global sea-level fall and regional tectonic regime also controlled the extend of unconformity underlying the Coniacian-Santonian platform deposits (Ilam Fm.).

Characteristics of late Miocene Lithofacies - Paleogeography in the Southeast Region of Hanoi Depression

The characteristics of late Miocene lithofacies in the southeast region of Hanoi depression have been revealed on the basis of sedimentary evolution in relation to sea level change and tectonic movement. During late Miocene, global sea level change has created one depositional sequence and three sedimentary systems tract. The lowstand systems tract (LST) is characterized by 5 rhythms of alluvial lithofacies. These rhythms are represented by rough, humoc seismic wave fields. This environment is not favorable condition for coal formation. The transgressive systems tract (TST) is characterized by 6 transitional lithofacies rhythms. Each lithofacies rhythm consists of 4 facies: the tidal flats sand facies of the bay, the mud facies of the river mouth lagoon, the coastal marshy mud facies creating coal and the bay greenish-gray clay facies. The pacing process involves changes in the local sea level caused by tectonic lift. Each tectonic subsidence phase takes place at a very slow velocity, so it is compensated for fine-grained sediment creating marshy mud facies to develop mangroves on a large scale. It is a prerequisite to create thick coal seams distributed near the end of each rhythm. A part of highstand systems tract (HST) are eroded due to the improved folding process, creating an angular unconformity boundary with Pliocene-Quaternary sediments. However, after reconstracting of deformated section, it was clear that this systems tract had only one rhythm including 2 facies: prodelta mud facies and alluvial fan sandstone facies.&#x0D; Keywords: Lithofacies-paleogeography, sedimentary systems tract, sedimentary rhythm

Geochemical characteristics of marine shale in the Wufeng Formation–Longmaxi Formation in the northern Sichuan Basin, South China and its implications for depositional controls on organic matter

Marine black shales of Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in the Sichuan Basin are considered as excellent source rocks in South China. According to the geochemical characteristics of source rocks, the formation and preservation conditions of organic matter in source rocks are showed. In order to study the aggregation mechanism of organic matter, geochemical proxies were proposed, including redox proxies (V, V/Al, U, U/Al, Mo, and Mo/Al), paleoproductivity proxies (P, P/Ti, Ba, Ba/Al, and SiXS), paleoclimate proxies (CIA), and terrigenous flux proxies (Al, Zr, and Zr/Al). At present, the average content of TOC in Wufeng Formation is 3.63 wt%, which is in the range of 2.59–4.22 wt%. The average content of TOC in Longmaxi Formation is 1.02 wt%, and ranges from 0.45 to 2.07 wt%. The redox proxies show that the Wufeng shale is mainly accumulated under anoxic conditions. Longmaxi shale is mainly accumulated under suboxic-oxic conditions. The P/Ti and excess silicon (SiXS) values indicated that the whole sedimentary sequence had high paleoproductivity, but it was reduced to some extent in the Longmaxi Formation. The reduced Corg/Ptot ratios implies that the decrease of productivity may be caused by the increase of P (phosphorus) burial. The restricted degree of watermass shows that Wufeng shale deposits under strongly restricted watermass, while Longmaxi shale deposits under weakly restricted watermass. During the sedimentary period of the Wufeng Formation, the strongly restricted of the ocean circulation of the northern Sichuan Basin and the effective stratification of water column is beneficial to the preservation of organic matter. During the Longmaxi shale sedimentary period, tectonic movement and global sea level changes controlled the production and preservation of organic matter, affecting terrestrial clastic material flux, redox conditions and nutrient cycling.

Facies character and geochemical signature in the late Quaternary meteoric diagenetic carbonate succession at the Xisha Islands, South China Sea

The late Quaternary shallow-water carbonates have been altered by a variety of diagenetic processes, and further influenced by high-amplitude global and regional sea level changes. This study utilizes a new borehole drilled on the Yongxing Island, Xisha Islands to investigate meteoric diagenetic alteration in the late Quaternary shallow-water carbonates. Petrographic, mineralogical, stable isotopic and elemental data provide new insights into the meteoric diagenetic processes of the reef limestone. The results show the variation in the distribution of aragonite, high-Mg calcite (HMC) and low-Mg calcite (LMC) divides the shallow-water carbonates in Core SSZK1 into three intervals, which are Unit I (31.20–55.92 m, LMC), Unit II (18.39–31.20 m, aragonite and LMC) and Unit III (upper 18.39 m of core, aragonite, LMC and HMC). Various degrees of meteoric diagenesis exist in the identified three units. The lowermost Unit I has suffered almost complete freshwater diagenesis, whereas the overlying Units II and III have undergone incompletely meteoric diagenesis. The amount of time that limestone has been in the freshwater diagenetic environment has the largest impact on the degree of meteoric diagenesis. Approximately four intact facies/water depth cycles are recognized. The cumulative depletion of elements such as strontium (Sr), sodium (Na) and sulphur (S) caused by duplicated meteoric diagenesis in the older reef sequences are distinguished from the younger reef sequences. This study provides a new record of meteoric diagenesis, which is well reflected by whole-rock mineralogy and geochemistry.