Global Sea-level Fluctuations Research Articles

Groundwater salinization under the influence of paleo sea-level fluctuation: a case study in southern Laizhou Bay, China

The groundwater environment in low-lying coastal regions is significantly impacted by global sea-level fluctuation. In Laizhou Bay, three large-scale transgressions have occurred since the late Pleistocene, resulting in the transformation of ancient seawater into brine. This brine has become a major contributor to groundwater salinity in the area. This study establishes a correlation between groundwater occurrence and paleoclimate changes in Laizhou Bay using borehole sediment data. The source and mechanism of groundwater salinity are analyzed based on sediment pore water characteristics and hydrogen and oxygen isotopes. The study reveals that the stratigraphic structures in the area consist of four layers: a Holocene transgressive layer, a continental confining bed from the late Pleistocene, a Cangzhou transgressive layer from the late Pleistocene, and a fluvial aquifer from the middle Pleistocene. All aquifers in the study area have been infiltrated by modern seawater, with the uppermost Holocene aquifer influenced by evaporation and leaching processes, the central late Pleistocene aquifer remaining relatively stable, and the lower middle Pleistocene aquifer affected by subsurface low salinity runoff and exhibiting an increasing trend with depth. Given the presence of numerous hydrogeological environments globally that are similar to the study area, the obtained mechanisms of groundwater salinization in this study will provide theoretical support for groundwater management in similar regions worldwide.

Orbitally-paced climate change during the Carnian Pluvial Episode

Global climate change has profound implications for human survival and prosperity. The Carnian (early Late Triassic, ∼233 Ma) was a time of global environmental perturbations, climatic change, and biotic turnover, commonly known as the Carnian Pluvial Episode (CPE). However, the understanding of possible triggering mechanisms of the CPE is still partially untraveled due to the lack of a high-resolution chronostratigraphic framework. Here we present an astrochronology of episodic negative carbon isotope excursions (NCIEs) observed in the shallow marine sediments of the Bagong Formation in the Qiangtang Basin (Tibetan Plateau, China) to explore the role of orbital forcing during the CPE. This study marks the first identification of five episodic NCIEs in the Carnian strata of the Bagong Formation. These NCIEs correspond with five distinct periods of increased detrital influx. The coupling relationship between each phase of NCIE and related terrigenous input indicates that episodic NCIEs may be influenced by pulses of active continental weathering. Mercury isotope is contemporaneous with the active volcanism that triggered the onset of the NCIEs; however, the impact of volcanism in the Qiangtang Basin was weak and almost non-existent at this time. An anchored floating astronomical timescale (ATS) for the episodic NCIEs is established, revealing evidence for a 405 kyr eccentricity in high-resolution gamma ray data series using time series analysis. A ∼13.16 Myr-long ATS of the Bagong Formation is developed by astronomical tuning of gamma ray logs to the stable 405-kyr long-eccentricity cycles. This floating ATS takes the U-Pb zircon as its anchor point and establishes an anchored floating ATS of the Bagong Formation from 233.16 ± 1.37 Ma to 220.4 ± 1.1 Ma. The innovative astrochronology approach, employing a sedimentary noise model, has successfully reconstructed sea-level changes during the Late Triassic period. These findings align well with the documented global sea-level fluctuations of the same era. The antiphase relationship of the filtered ∼1.2 Myr cycles between the sedimentary noise model sea-level curve and the obliquity modulation cycles demonstrates that the ∼1.2 Myr modulation cycles may be the main driver of sea level changes during the Late Triassic. The ∼1.2 Myr obliquity modulation maxima correlate well with the high sea level, episodic NCIEs, global warming, and marine life crisis, suggesting that obliquity forcing could have played a prominent role during the CPE. Our results reveal that the orbital forcing enhanced the hydrological cycle during the CPE, which provides a broader perspective of the CPE-related to the astronomical forcing.

Aptian major changes in accommodation. New sedimentary evidence from the Maestrat Basin (E Iberia)

Global sea-level fluctuations with amplitudes of tens of metres and durations between 0.5 and 3 Myr are well-known oceanographic events of the Cretaceous Period. During recent years, major Cretaceous changes in accommodation recorded in different basins have been mainly interpreted as eustatically driven. Two episodes of major relative sea-level fall and rise of late early and early late Aptian age were investigated in the Maestrat Basin (E Iberian Peninsula). Previously documented in eight outcrops, these Aptian records of major changes in accommodation have now been identified in five additional localities within the basin, suggesting at least a basin-wide significance of these relative sea-level fluctuations. The records of relative sea-level fall analysed are associated with the local development of incised valleys and forced regressive wedges. Two upper lower Aptian incised valleys, which are downcutting highstand platform carbonates dominated by rudists and corals, were studied and show depths of approximately 10 and 80 m. The incision depths measured indicate amplitudes of relative sea-level variations in the order of tens of metres. During subsequent base-level rise, the lower part of these incised valleys was respectively infilled with orbitolinid limestones and high-energy carbonate deposits influenced by tides. Further evidence of major relative sea-level drop and rise during the late early Aptian includes a detached backstepping carbonate platform of reduced extension, underlain and overlain by basinal marly deposits, which flourished basinwards of a highstand platform margin. Although incised valleys or smaller-scale incisions are local features, evidence for relative declines in sea level can be identified from other evidence. For example, by the development of palaeokarst or by the presence of sharp or slightly erosive stratigraphic surfaces covered by deposits of higher energy influenced by tides, as observed in the late Aptian examples investigated herein. Comparable Aptian sedimentary features of subaerial exposure and subsequent transgressive genetic types of deposits have been observed in other basins across different tectonic plates, indicating that eustasy likely played a role in controlling accommodation changes during this stage. The discovery of new evidence for major relative Aptian sea-level fluctuations in various outcrops within the Maestrat Basin calls for further investigation in other underexplored Aptian platform carbonate successions in this basin. These investigations would contribute to a more accurate understanding of oceanographic dynamics during the Aptian Stage along the western margin of the Alpine Tethys.

Paleoenvironmental Evaluation Using an Integrated Microfacies Evidence and Triangle Model Diagram: A Case Study from Khurmala Formation, Northeastern Iraq

The sequence of the Khurmala Formation located in northeastern Iraq was measured and sampled to evaluate its paleoenvironmental features, including sedimentological and microfacies analyses. The studied formation was analyzed under an optical microscope and was dominated by three main types of microfacies: coralligenous–algal wackestone, foraminiferal–peloidal packstone, and foraminiferal–peloidal grainstone. These hosted microfacies in the Khurmala Formation rarely contain a non-geniculate algae that insufficient for complete reef-building as a crest, but among the common algae, there are calcareous geniculate and green algae associated with benthic foraminifera and a minor component of planktonic foraminifera in the basin due to high-energetic open shallow-water environmental conditions during the deposition of the Khurmala Formation. The relative percentages of foraminifera, including both benthic and planktonic, plotted on triangular diagrams revealed a graphic indicator of paleoenvironment analyses. Detailed examination and analyses for microfacies, new findings of calcareous green algae (Acicularia and Clypeina), and microfacies analyses based on the triangle method and standard facies zones, denote that the upper part of the Khurmala Formation was richer in fined grain and Acicularia green algae, reflecting lower energy conditions than during deposition in the lower part of the formation, which was represented by algal wackestone microfacies and dominated by Clypeina green algae. In summary, these fluctuations in facies/microfacies changes, the appearance of new green algae, and different percentages of foraminiferal content are linked to the global sea level fluctuation that occurred during the Paleocene–Eocene interval.

Astronomical Forcing of Sea‐Level Changes and the History of the Solar System 1,640 Million Years Ago

AbstractThe Paleoproterozoic was an important stage in the evolution of life and the environment during Earth's history. Understanding astronomical rhythms and solar system behavior in the Paleoproterozoic is often challenging. In this study, ∼190 m high‐resolution magnetic susceptibility (MS) and ∼30 m high‐resolution Ba/Al data are used to conduct cyclostratigraphic analyses of the Chuanlinggou Formation in the Yanliao Rift, North China Craton. Spectral analysis indicates significant peaks at wavelengths of 12.1–7.7, 2.8–1.6, 0.58–0.33, and 0.29–0.22 m, which matches well with the astronomical cycles predicted by Waltham for ∼1,640 Ma. A 9.9‐Myr astronomical time scale is constructed by tuning the MS series to the 405‐kyr‐long eccentricity cycle. The geological records show ∼1.56‐Myr very long eccentricity period and ∼1.0‐Myr very long obliquity period (close to 3(s4 − s3) − 2(g4 − g3) = 0) in the Paleoproterozoic. The sea‐level change curve predicted by dynamic noise models reveals a significant ∼1.0‐Myr period, indicating that sea level fluctuation may have been driven by the very long obliquity period. Bayesian inversion is used to further estimate the evolution of the ancient Earth‐Moon orbital parameters, constraining a precession rate of 87.14 ± 0.25 arcsec/year and an Earth‐Moon distance of 341,530 ± 390 km for the Paleoproterozoic Changcheng System. These results indicate that astronomical orbital forcing may have played an important role in climate and sea‐level changes in the Precambrian, increasing the understanding of the fundamentals of global sea level fluctuations, orbitally driven mechanisms and the chaotic behavior of the Precambrian solar system.

Sequence stratigraphy and reservoir quality of the Gulf of Suez syn-rift deposits of the Nukhul formation: Implications of rift initiation and the impact of eustacy and tectonic on deposition

The Nukhul Formation represents the sediments deposited during the earliest phase of the syn-rift period in the Gulf of Suez rift. It is the primary hydrocarbon reservoir for fifteen fields in the region. However, the timing of rifting needs to be better constrained, and the influence of local tectonics and global eustatic sea-level fluctuations on reservoir quality and deposition is still being determined. This research aims to establish a stratigraphic sequence framework, determine the age of the Suez Rift commencement, use changes in paleobathymetry, and assess reservoir quality. The methods employed involve the analysis of four boreholes in the Abu Rudeis-Sidri field, incorporating biostratigraphy, well-logs, and 3D seismic data. The integrated paleo-structure and biostratigraphic analyses indicate that the beginning of rifting in the Gulf of Suez occurred at 23.53 Ma at the first common occurrence (FCO) of Trilobatus primordius. The paleobathymetric analysis of the Nukhul Formation reveals deeper paleo-water depths during certain intervals, indicating deposition during a phase of high subsidence and rift-climax. The Nukhul stratigraphic sequence reflects sea-level changes leading to shifts in accommodation, and facies changes, erosion, and sequence formation during the late Chattian and early Burdigalian stages. However, the reservoir characterization of the Nukhul Formation is significantly affected by various factors, including cementation, pore system properties, sediment sorting, rift system geometry, and relative sea-level fluctuations. These factors must be carefully considered in any regional exploration or development efforts. The study also reveals that tectonic activity played a role in forming fault-bounded basins, and eustatic sea-level changes influenced the rate and timing of sediment accumulation. These findings can aid in predicting the distribution of the Nukhul sedimentary deposits and improve the ability to explore and develop their resources.

The Shanxi Formation responses to astronomically forced climate changes during the Upper Paleozoic in the Eastern Ordos Basin, NW China

A clearly defined geochronology and stratigraphic interpretation will enhance our understanding of the evolution of paleo water depth and transitional facies, contributing to hydrocarbon exploration. Transitional deposition is extensively observed in the upper Paleozoic of the Ordos Basin. Nevertheless, the correlation between the variations of paleo water depth and global sea-level changes remains uncertain. In this study, we employed gamma-ray logging (GR) data to analyze the cyclostratigraphy of the upper Paleozoic Shanxi Formation in the Ordos Basin. We characterized the elemental geochemistry of the Shanxi Formation using X-ray fluorescence. We reconstructed changes in Paleo Water Depth in the Ordos Basin during the upper Paleozoic by employing sedimentary noise modeling of the tuned GR logging data. Time series analysis showed evidence of the existence of 405 kyr long eccentricity, 125 kyr short eccentricity, and 35.5 kyr obliquity in sedimentary records, which was supported by a sediment accumulation rate model. Using the tuned GR data, we constructed a ∼3.07 Myr astronomical time scale in the Shanxi Formation of the sampling well. Moreover, we used the volcanic ash age (298.18 ± 0.32) Ma at the boundary of the Shanxi Formation and Taiyuan Formation as the anchor point to provide an absolute astronomical time scale from 295.11 Ma to 298.18 Ma for the study area. The variation of Paleo Water Depth in the upper Paleozoic transitional facies was confirmed by both the sedimentary noise model and the X-ray fluorescence (XRF) data, thus supporting each other. Additionally, we discovered a long-period obliquity of approximately 1.2 million years in this model, which is consistent with the global sea-level fluctuations observed during the same period. These results reveal a novel approach for evaluating the Paleo Water Depth variations in transitional facies. Furthermore, our study offers a detailed explanation of the relationship between the evolution of the sedimentary environment and the climate change resulting from astronomical orbit during the glacial period.

Ordovician chitinozoans and review on basin stratigraphy, biostratigraphy and paleobiogeography of northern Argentina along the Proto-Andean margin

Ordovician strata exposed across the Cordillera Oriental and the Sierras Subandinas in northwestern Argentina were part of a large retroarc foreland basin developed along the Proto-Andean margin within the Central Andes in South America. A revised chitinozoan biostratigraphy along and across-strike for the Tremadocian, Floian, Dapingian, Katian and Hirnantian stages, calibrated with other fossil groups in the basin, allow pinpointing the most characteristic events that affected the basin fill testing global versus local controls in accommodation, and suggesting comparisons with other peri-Gondwanan records. According to the chitinozoan data, the glacially-related Ordovician deposits in northwestern Argentina are restricted to the Hirnantian, and unconformably overlie late Katian deposits. In the Caspalá area (Cordillera Oriental), an interval with synsedimentary deformation and reworked chitinozoans correlate with glacially-related deposits in other sites of the eastern part of the basin (Río Capillas and Mecoyita areas). A glacial waning stage is determined by a thin interval of organic‐rich black shales with sparse dropstones at the top of the Zapla Formation, containing Spinachitina oulebsiri associated with Desmochitina gr. minor, which together are typical latest Hirnantian components in other regions of Gondwana. Our study strengthens the foreland systems tract for the Ordovician Central Andean Basin with a volcanically fed interarc and foredeep depozone to the west (Puna region); a lower-accommodation forebulge depozone in the central area (mostly the Cordillera Oriental region); and a backbulge depozone (Sierras Subandinas and Sierras de Santa Bárbara) extending as far as the eastern Paraná Basin (reaching Paraguay and Brazil). Contemporaneous unconformities driven by global sea-level fluctuations were amplified or reduced due to deepening-narrowing or widening-shallowing, allowing contrasted accommodation, respectively associated to loading and relaxation. Ordovician chitinozoans from the Central Andean Basin indicate Northern, Western and peri-Gondwanan affinities, although locally some more cosmopolitan species described in Baltica, Avalonia and South China, are also recorded.

Litho- and biostratigraphy of the early Eocenelarger benthic foraminifera-dominated carbonates of the central Tethys domain, Zagros Foreland Basin, SW Iran

The Early Paleogene Tethyan domain saw the development of large platform carbonates rich in large benthic foraminifera (LBF), of which the Taleh Zang Formation in Lurestan Basin, SW Iran, represents an excellent example. The LBF assemblage is dominated by alveolinids, together with a variety of foraminiferal genera such as Nummulites, Rotalia, Sackesaria, Assilina, Operculina, and Glomalveolina. Smaller benthic foraminifera, calcareous algae, gastropods, echinoids, and bivalves constitute minor components of the carbonate. Biostratigraphy analysis of the LBF is conducted on two distinct sections of the Taleh Zang Fm. The sections referred to as TZ-1 and TZ-2 have respective thicknesses of 87 m and 132 m. This analysis has constrained the formation age to the early Ypresian within Shallow Benthic Zones (SBZs) 5–7. Facies analysis supports the major accumulation of these successions in a shallow water environment within the euphotic zone. We recognize 9 distinct facies and microfacies representing four main depositional environments including tidal flat, lagoon, bioclastic shoal, and shallow open marine. These environments are distributed along a low-angle homoclinal ramp and form the foundation of a stratigraphic interpretation characterized by intervals displaying shallowing and deepening trends. Three shallowing-upward intervals have been identified within the Taleh Zang succession. The determined intervals cannot be solely attributed to global sea level fluctuations and support a significant impact of the regional structural context resulting from collision-induced uplift and variable subsidence rates. The identified intervals exhibit local and regional correlation and compatibility on the Arabian Plate, providing robust confirmation of the significant roles played by both tectonics and eustasy at a regional scale.

Coralline algal and foraminiferal records of the Pliocene paleoclimatic conditions and water-depth changes in the northern South China Sea

Detailed paleontological and sedimentological data from the Pliocene interval of core XK-1 allow for a detailed documentation of the carbonate system in the northern South China Sea (SCS). Six facies are identified. Based on a comprehensive analysis of facies changes, the paleoclimatic conditions and paleowater depths during the Pliocene in the Xisha area in the northern SCS are reconstructed. The changes in the abundance of the algal genus Sporolithon and the planktonic foraminifera species Orbulina universa, Globigerinoides quadrilobatus, Globorotalia menardii, and Globigerinoides obliquus indicate that the climate in the SCS gradually became warmer from 5.3 to 4.3 Ma and then cooled from 4.3 to 2.6 Ma, which was attributed to the changes in atmospheric pCO2. The high abundance of encrusting acervulinids and coralline algae and the low coral abundance suggest periods of elevated nutrient level, possibly linked to increases in nutrient input from the higher latitudes. Distinct changes in coralline algal and foraminiferal facies help the reconstruction of paleowater depths during the Pliocene in the Xisha area. The water depth was generally rising from 5.3 to 4.3 Ma and declining afterward, which was similar to that in the Yinggehai–Qiongdongnan Basin (located on the northern part of the Xisha area). This similarity indicates that there was a common factor controlling the long-term variation in water depth in the northern SCS. The comparison between paleowater depth changes and global eustatic sea-level fluctuations indicates that the regional tectonic subsidence was important from 5.3 to 4.7 Ma. Such subsidence was probably related to thermal subsidence after the magmatism intrusion activity beneath the basement at the initial stage of the Pliocene. This study indicates that the comprehensive analysis of algal and foraminiferal facies has great potential to reconstruct the climatic conditions and water depths in the ancient times.

Reconstruction of Lake-Level Changes by Sedimentary Noise Modeling (Dongying Depression, Late Eocene, East China)

The late Eocene succession of the Dongying Depression forms a highly productive hydrocarbon source. However, due to lack of an unambiguous fine chronostratigraphic framework for the late Eocene stratigraphy, it is challenging to understand the paleolake’s evolution and the driven mechanism of lake-level variation, a limitation which hinders hydrocarbon exploration. In this work, high-resolution gamma-ray logging data were analyzed to carry out the cyclostratigraphic analysis of the third member (Es3) of the Shahejie Formation in the Dongying Depression. Significant 405-kyr eccentricity cycles were recognized based on time series analysis and statistical modeling of estimated sedimentation rates. We abstracted ~57 m cycles of the GR data in the Es3 member, which were comparable with the long eccentricity cycles (~405-kyr) of the La2004 astronomical solution, yielding a 6.43 Myr long astronomical time scale (ATS) for the whole Es3 member. The calibrated astronomical age of the third/fourth member of the Shahejie Formation boundary (41.21 Ma) was adopted as an anchor point for tuning our astrochronology, which provided an absolute ATS ranging from 34.78 ± 0.42 Ma to 41.21 ± 0.42 Ma in Es3. According to the ATS, sedimentary noise modeling for the reconstruction of lake-level changes was performed through the late Eocene Es3. The lake-level changes obtained based on sedimentary noise modeling and spectrum analysis reveal significant ~1.2 Myr cycles consistent with global sea level variations which were related to astronomical forcing. Potential driven mechanisms of marine incursion and/or groundwater table modulation were linked to explain the co-variation of global sea level changes and regional lake level changes. Our results suggest global sea level fluctuations may have played an important role in driving the hydroclimate and paleolake evolution of the late Eocene Dongying Depression.

Facies variations in response to tectonic evolution, climate and sea-level changes since the Late Cretaceous in Wuhu region, Eastern China

Eastern China has a complex environmental dynamics system in the western Pacific tectonic domain, and the study of its sedimentary records controlled by tectonic movements is distinctly significant for exploring sea-land interactions, global climate change and sea level fluctuations. A reliable OSL (Optically Stimulated Luminescence) chronostratigraphic framework was established based on a systematic investigation of the stratigraphic lithology of the boreholes in Wuhu area, Eastern China, and the depositional environment since the Late Cretaceous was reconstructed by multiple environmental proxies. Significant regional changes in sedimentary activity since the Mesozoic indicate that the Yanshan movement and the Neotectonic movement controlled the evolution of sedimentary basins and fracture tectonics in the study area and influenced the paleo-geographic environment and sedimentary patterns in a regional geotectonic context. Since the Middle Pleistocene, the temperature and sea level trends were split into six stages, four of which (MIS 6, 4, 3 and 2) can be categorized as periods of decline, with MIS 1 being a period of significant increase. The other phase (MIS 5) was characterized by violent fluctuations in climate and sea level, with periods of increase in MIS 5a, 5c and 5e and decrease in MIS 5b and 5d. Sedimentary process in eastern China are mainly controlled by regional geotectonic activity, and the specific evolution of the depositional environment is also influenced by the combined effects of regional climate and sea level.

A fossil diatom-based reconstruction of sea-level changes for the Late Pleistocene and Holocene period in the NW South China Sea

Marine transgressions-regressions have profoundly shaped marginal seas following global sea-level fluctuations driven by climate change. This study on a sedimentary core profile SO219/31-4 from the Beibu Gulf, northwestern South China Sea (SCS), reveals information about paleoenvironment, paleoceanography and paleoclimate changes through fossil diatom assemblages and grain size distributions during the last ca. 12900 cal. yr. BP. Eight local diatom assemblage zones were distinguished and assigned to paleoenvironmental fluctuations recording sea-level and depositional environment changes in eight stages, ca. 12900–11700 (stage 1), ca. 11700–9500 (stage 2), ca. 9500–7200 (stage 3), ca. 7200–5800 (stage 4), ca. 5800–3800 (stage 5), ca. 3800–2400 (stage 6), ca. 2400–800 (stage 7) and ca. 800–0 (stage 8), cal. yr. BP. After the low sea level of stage 1 within the last deglaciation, rapid increases in sea level in stages 2 and 3 were recorded as meltwater events pulse-1B and pulse-1C resulting in marine transgression rates of ca. 16 m/kyr and 8 m/kyr, respectively. The high sea level, above the present level, in stages 4 and 5, in the Middle Holocene Climatic Optimum period, was clearly documented by more significant open sea/tropical diatom species and coastal planktonic species percentages, respectively. The late Holocene regression of sea levels was marked by a pronounced reversion of diatom taphocoenosis, responding to neoglacial climate. Fossil diatom assemblages outlined responded to paleoclimate of global warming in the deglacial and early Holocene. This study provides additional insights into the late Pleistocene and Post-glacial history of a tropical-subtropical shallow water gulf, in the NW-SCS.

OSL dating of coastal sand dunes in southeastern China provides new insights into the relationship between aeolian activity and eustatic sea-level fluctuations

The southeastern coastal region of China has coastal sand dunes, which are usually called paleo-sand dunes or “Old Red Sandstone”. The ages and geological implications of these coastal dunes have been studied for tens of years but are still controversial. In this paper, we used optically stimulated luminescence (OSL) dating to establish the chronology of the paleo-aeolian reddish sand dunes from two representative sites in the coastal region of SE China. Our results indicate that the sand dunes were mainly accumulated in three periods, including 9–6 ka (broadly corresponding to marine isotope stage (MIS) 1), 50–26 ka (MIS 3), and 110–74 ka (MIS 5). Based on the comparison between the regional aeolian dune records and the global sea-level fluctuations, we concluded that the reddish sand dunes were associated with the aeolian processes during interglacials and interstadials when sea-level were relatively higher compared with glacial maxima. We proposed a conceptual model to interpret the formation of the coastal sand dunes. We suggest that coastal dunes that formed during the glacial maxima could not be preserved in highstands above the present sea-level due to the lower altitude of sand dunes and the erosion by water waves during the subsequent marine transgression. Therefore, only aeolian sand dunes accumulated in higher altitudes during sea-level rise were preserved as in the coastal region of SE China.

Tracing glacial-interglacial water mass changes in the Gulf of Corinth (IODP Expedition 381) using iron-sulphur geochemistry and magnetic susceptibility

The Gulf of Corinth is a rapidly rifting basin that has been alternately connected to/isolated from the Mediterranean due to Quaternary global sea levels fluctuations. A recently retrieved sediment record from the Gulf of Corinth (IODP Expedition 381) shows variations in magnetic susceptibility, with relatively higher and more variable values in isolated/glacial sediments and lower, more stable values in connected/interglacial sediments. Using geochemical methods, we find that not the primary input of magnetic minerals, but diagenetic processes generated the magnetic susceptibility pattern. Easily reducible sulphides (most likely greigite) increase in high magnetic susceptibility (isolated/glacial) sediments, whilst magnetite shows no systematic relationship to magnetic susceptibility. After discounting several possible causes for the formation and preservation of greigite (bottom water redox conditions, high sedimentation rates, reactive Fe and organic matter availability), a decrease in sulphate concentrations in the Gulf of Corinth during isolated/glacial periods is the most likely explanation, supporting parallel microfossil evidence for a freshening of the water column. This sulphate limitation appears to stall sedimentary pyrite formation at the stage of ferrimagnetic monosulphides like greigite. Greigite formation as an indicator of paleosalinity variations has been observed in other depositional settings (e.g., Chesapeake Bay, the Baltic Sea, the Miocene Paratethys and the Black Sea), supporting our interpretation. Specific to the Gulf of Corinth, linking a proxy for basin connectivity to a high resolution (at least 40, and up to 7 year temporal resolution) magnetic susceptibility record over 750,000 years offers an opportunity to investigate, in detail, the tectonic evolution of this rift basin and its link to global sea level fluctuations.

Sedimentary noise modeling of lake-level change in the Late Triassic Newark Basin of North America

Two different hypotheses, glacioeustasy and groundwater aquifer eustasy, have been proposed to explain short-term, high-amplitude sea-level oscillations during past greenhouse-dominated intervals. However, the veracity of aquifer eustasy on long-term, high amplitude sea level has never been rigorously tested. We evaluate these competing hypotheses using the objective approach of sedimentary noise modeling for lake-level reconstruction. Statistical tuning and astronomical calibration of paleoclimate and paleoenvironment proxies (depth rank, rock color, gamma ray, and sonic velocity) from the lacustrine Newark Basin enable the construction of a 31.55-Myr long astronomical time scale (ATS) for the Late Triassic that is comparable to the classic Newark ATS previously presented. Using this timescale, sedimentary noise modeling in the lacustrine Newark Basin is carried out through the Late Triassic. Lake level fluctuations reconstructed by sedimentary noise modeling and principal component analysis reveal that million-year scale lake-level variations were linked to astronomical forcing with periods of ~3.3 Myr, ~1.8 Myr, and ~1.2 Myr. Our results demonstrate that astronomical forcing, as a driver of groundwater dynamics, may have had an impact on global sea-level changes during the Late Triassic. This study thus emphasizes the importance of high-resolution, objective reconstruction of sea- and lake-levels for further testing the hypotheses of glacioeustasy and aquifer eustasy under warm conditions. • We reconstruct high-resolution lake-level changes in the Late Triassic. • Long-period astronomical forcing drove lake-level and sea-level variations. • Continental groundwater could have an impact on global sea-level fluctuations. • High-resolution, objective reconstruction of lake- and sea-levels is key to test aquifer eustasy versus glacioeustasy.

Volcanism-induced late Boda warming in the Late Ordovician: Evidence from the Upper Yangtze Platform, South China

Late Boda warming was the last warm episode in the Late Ordovician, and little is known about its cause. Volcanism was a hypothetical candidate that triggered this warming event owing to its potential to enhance the atmospheric CO2 level. Here, we conducted a high-resolution petrographic and geochemical study on the bentonite beds-bearing intervals from the Upper Ordovician Wufeng Formation in South China. This investigation enables us to find the detailed process of paleoenvironmental repercussions induced by volcanism from both short-term and long-term perspectives. The short-term effect was revealed by a 25-cm-long drill core bracketing three cycles of volcanic activity. Three nearly identical cycles have been identified, and each cycle is comprised of a bentonite bed, a siliceous clay-rich mudstone interval, a radiolarian bed, and a siliceous mudstone interval with intercalations of thin pyrite layer. During the eruption stage, a series of environmental and biogeochemical disruptions were brought to the local system, including ocean fertilization, the elevation of paleoproductivity, the onset of euxinia/intensified ocean anoxia, a warmer climate, and enhanced weathering. With the waning of volcanic activities, the volcanic impacts weakened, and a relatively stable water-column chemistry, microbial populations, diversity, and community structure were established until the onset of the subsequent volcanic event that broke equilibrium. The long-term effect was illustrated by the correlation between the distribution of bentonite beds and coeval global sea-level fluctuations. Our results show that intense and frequent volcanic activities in South China, probably contributed by coeval volcanic activities from other regions worldwide, exerted a cumulative heating effect on the global system, contributing to late Boda warming.

Coastal morphodynamics and Holocene environmental changes in the Pearl River Delta, southern China: New evidence from palynological records

Coastal morphodynamics and environmental changes have been obviously altered by global warming, sea-level fluctuations, and human activities. Palynological analysis is one of the most important tools for providing information on vegetation, climate, and environmental change, which can be relatively sensitive indicators of human activity during the Holocene. However, Holocene coastal morphodynamics and palynological evidence from the Pearl River Delta and coastal areas has not been sufficiently studied. In this paper, we carry out analyses using detailed grain-size and palynological records of pollen, spores, freshwater algae, and marine dinoflagellate cysts from Borehole QZK13 in the Pearl River Estuary (PRE), southern China. The results show information relating coastal morphodynamics, vegetation evolution, climate changes, and anthropogenic activities during the Holocene based on radiocarbon chronology. In general, the PRE experienced marine transgressive processes; sea-level and the coastline tended to migrate landward between 10,700 and 4250 cal yr BP. Meanwhile, abundant arboreal pollen (mainly Castanopsis, Quercus-evergreen, Oleaceae, and Castanea) and small amounts of non-arboreal pollen (mainly Poaceae, Cyperaceae, and Artemisia) were observed in Borehole QZK13, which suggests that subtropical evergreen broadleaved forests were distributed throughout the PRE and adjacent areas, and relatively warm and moist climatic conditions were present during the early-middle Holocene. After that, there were relatively cool and wet climatic conditions, and marine regressive processes occurred in the PRE during the Late Holocene (ca. 4250–960 cal yr BP) indicated by an abrupt increase in aquatic herbs and Dicranopteris. Moreover, we hypothesize that the Neolithic “cultural fault” in the PRE is likely related to frequent storm surges induced by extreme typhoon events that occurred ca. 3000–2700 yr BP.

Environmental conditions during the late Oligocene transgression in the North Alpine Foreland Basin (Eferding Formation, Egerian) – A multidisciplinary approach

The North Alpine Foreland Basin (NAFB) comprises one of the most complete sedimentary records of the Oligocene and Miocene, driven by global sea-level fluctuations, vast sedimentary influx and tectonic movement. The locality of Unterrudling near Eferding (Upper Austria) exposes the largest succession of sedimentary deposits from the late Oligocene in the eastern NAFB. Additionally, this section shows the facies transition from the shallow-water Linz-Melk Formation to the deep-water Eferding Formation. In this work, the fossil fauna and flora of the Eferding Formation as well as its lithology are re-evaluated using a multidisciplinary approach to gain new insights into the palaeoenvironment, palaeoclimate, and palaeoecology. A transgressive sequence is documented using sedimentological and ichnological data. Furthermore, a correlation to the late Chattian transgressive Ch-3 sequence is suggested. The impact of rising sea-level on marine biota is shown in detail by analysing various groups (Bivalvia, Echinodermata, Anthozoa, Foraminifera, Chondrichthyes and Osteichthyes), with several newly reported species for the Eferding Formation. Moreover, washed in plant material was analysed for the interpretation of the terrestrial climate indicating mainly humid subtropical conditions. Finally, the presence of phosphatic nodules indicates eutrophication on the shelf environment and the possibility of upwelling currents.

Revised chrono and lithostratigraphy for the Oligocene-Miocene Patagoniense marine deposits in Patagonia: Implications for stratigraphic cycles, paleogeography, and major drivers

Richly fossiliferous upper Oligocene to lower Miocene Patagoniense marine deposits constitute a conspicuous feature of the sedimentary record of most basins in Patagonia. Patagoniense meaning and subdivisions have been confusing, and correlation and elucidation of factors controlling sedimentation in a region as extensive as Patagonia are still highly debated. Our revision of the distribution, correlation, stratigraphic arrangement, and timing of deposition, allows redefining the Patagoniense as a succession of widely distributed marine sediments accumulated in Patagonia from ~25 to 15 Ma, showing different timing of accumulation for each basin. It can also be conceived as a higher rank stratigraphic cycle of relative sea-level fluctuation, which comprises two medium rank stratigraphic cycles spanning 2–4 Myr each, in turn enclosing several lower rank cycles of less than 1 Myr. The late Oligocene (~25-23 Ma) medium rank cycle shows deposits restricted mostly to the coastal area of Tierra del Fuego and Santa Cruz provinces in the Austral-Magallanes Basin, which respond to a combination of global sea-level fluctuations and flexural subsidence. The overlying early Miocene (~22-15 Ma) medium rank cycle comprises sediments deposited over extensive areas of Patagonia with a maximum flooding at 20-19 Ma suggesting, in addition to tectonic subsidence in the Austral-Magallanes Basin, regional long-wavelength subsidence and a global sea level component for this episode. The timing and thickness of the regressive part of this cycle show differences for each basin, suggesting the action of local sedimentary controls such as differential rates of sediment supply. Further geochronological and stratigraphic studies are necessary, especially for the northern exposures, which will allow improving time-constrained paleogeographic reconstructions.