Search Results (52)

Recent updates to the reconstructions of Cenozoic environmental changes (global sea level, temperature, and atmospheric carbon dioxide content) have made it intriguing to compare them to paleontological records for original interpretations. Paleogene brachiopods have remained in the shadow of their Paleozoic–Mesozoic predecessors, and the reactions of their diversity to the Earth’s dramatic changes are poorly understood. The present work aims to fill this gap via a comparison of several diversity and paleoenvironmental curves. The generic diversity was established by stages with two essentially different paleontological datasets, and several fresh paleoenvironmental reconstructions were adopted. It was observed that neither Paleogene eustatic fluctuations nor changes in the atmospheric carbon dioxide content correspond well to the generic diversity dynamics of brachiopods. The changes in the total number of genera and the global temperatures demonstrate similarity at the Danian–Ypresian interval, but not later. The fluctuations in the brachiopod diversity are near the same level during the Eocene–Oligocene, despite strong paleoenvironmental changes, implying the intrinsic resistivity of these organisms to external influences. Additionally, the Cretaceous/Paleogene mass extinction, the Paleocene–Eocene thermal maximum, and the Early Eocene optimum could enhance the diversity dynamics together with the long-term temperature changes. In contrast, the influences of the Late Danian warming event and the Oi-1 glaciation were not observed. Full article

Carbonate sedimentation was spread widely on the southern margin of the Neo-Tethys Ocean in the mid-Cretaceous. New information from four exploration wells sheds light on the peculiarities of the Sarvak Formation (late Albian–Cenomanian) at the narrow transition between the Dezful Embayment and Coastal Fars in the southern Zagros. The solution of this task was necessary to understand whether the fragmentation of the Zagros Basin into domains affected the carbonate platform development. The methods included the analyses of carbonate microfacies, paleoecological patterns of foraminifera, and depositional environments. The results of this study show the existence of ten carbonate microfacies. Prevailing wackestones and packstones with a muddy matrix and absent carbonate buildups imply the development of a large carbonate ramp. Paleoecological interpretations based chiefly on foraminifers prove this model. For instance, the presence of oligosteginids signifies shallower parts of the platform, and the cooccurrence of planktonic foraminifera and oligosteginids suggests a deeper environment. The stratigraphical distribution of the established microfacies in the wells indicates three cycles in the evolution of this platform. The third of these cycles marked an abrupt deepening episode because it includes microfacies suggesting the relatively deeper environments. Three maximum flooding surfaces established in the study area are common to the Arabian plate. The discussion of the results suggests that the influence of the Kazerun fault on the carbonate ramp in the Cenomanian is uncertain. Neither eustatic nor tectonic factors of the carbonate platform development can be excluded. Conclusively, it appears that the studied Cenomanian carbonate ramp was integral at the transition between the Dezful Embayment and Coastal Fars. Full article

The Onil and Ibi sections (Prebetic Zone, Betic Cordillera: Alicante, SE Spain) record a late Ypresian (Cuisian) to early Lutetian (~51 to ~43 Myr) carbonate platform succession, dated using larger benthic foraminifera (LBF) and planktonic foraminifera. Seven field lithofacies (L1 to L7) and five thin-section microfacies (Mf1–Mf5) were identified, indicating inner- to mid-ramp environments (from seagrass meadows to Maërl-LBF-dominated) in warm-water and low-latitude conditions. A distinctive feature of these platforms is their dominance by LBF in association with rhodophyceae, contrasting with typical coral reef factories. We propose a novel carbonate production model, “TC-factory”, to describe these warm-temperate systems. Integrated field logging, drone imagery, and microfacies data allowed us to define a sequence stratigraphic framework comprising five lower-frequency sequences (LFS: ~2 Myr average duration), each of them nesting various numbers of high-frequency sequences (HFS: ~0.25 to ~1 Myr). The LFSs belong to a higher-rank sequence bounded by regional unconformities. The five LFSs only broadly match the upper Ypresian and lower Lutetian cycles in global eustatic curves (~51 to ~43 Myr), indicating that other regional or local controls were important. The number of HFSs being fewer than expected also suggests additional controls, such as local tectonics, erosion during lowstands, or carbonate production feedback. Full article

The Miocene Hanjiang Formation (HJF) is a remarkable exploration target in the Pearl River Mouth Basin (PRMB). However, challenges such as bias in current sequence stratigraphic schemes, limitations in high-resolution stratigraphic schemes, and incomplete understanding of genetic mechanisms may present obstacles for refining hydrocarbon exploration strategies. This study integrates gamma ray (GR) logging data, lithological variations, sequence stratigraphy, and cyclostratigraphy to delineate connections between sequence stratigraphy and astronomical forcing. The analysis utilizes gamma-ray logging data from boreholes LFA (1250–1960 m) and LFB (1070–1955 m) in the HJF. We constructed an absolute astronomical time scale anchored at the HJF’s top boundary (10.221 ± 0.4 Ma), identifying 6 third-order sequences through detailed analysis. Notably, 18 long-eccentricity cycles (405 kyr) and distinctive 1.2-Myr obliquity modulation signals were detected in the stratigraphic record. Our study demonstrates distinct connection between third-order sequence boundaries and the 1.2-Myr obliquity cycles, congruent with both global eustatic sea-level fluctuations and regional sea-level changes in the PRMB. The integration of cyclostratigraphic methods with sequence stratigraphic analysis proves particularly valuable for objective stratigraphic subdivision and understanding third-order sequence evolution in the divergent continental margin settings of the South China Sea. This approach enhances temporal resolution on a regional scale while revealing astronomical forcing mechanisms governing sedimentary cyclicity. Full article

Many organic-rich marine mudstones, which are key hydrocarbon sources, were deposited on continent margins in mid-water oxygen-minimum zones (OMZs) that expanded and intensified during oceanic anoxic events (OAEs). Other marine hydrocarbon sources include platform and forearc black shales that record trans-continental, long-erm anoxic/dysoxic environments with no modern analog. Their explanation as recording deep-water, Black Sea-type basins or low-oxygen upwelling is not satisfactory for occurrences on shelves that lack significant epeirogenic activity, while modern studies show that upwellings do not cross the shelf break. The alternative is the Bakken model, which concludes that regionally extensive shelves and forearc organic-rich mudstones are shallow-water facies. These Bakken facies reflect hyper-warming conditions with high sea-levels, high water temperatures with increased insolation and low oxygen solubility, turbid water due to algal blooms and mud eroded from orogenic highlands, and possible LIP activity. Early Paleozoic black shales indicate that increased nutrients presumed to accompany the Devonian appearance of forests with deep roots that enhanced weathering simply cannot explain older Cambrian–Ordovician shelf anoxia/dysoxia. Shallow-marine deposition by the Bakken model is mandated by black shales deposited on subaerial unconformities that show high-energy facies (wave cross beds, HCS) and common bioturbation. The Bakken model explains shallow anoxia/dysoxia with high Paleozoic sea levels and tropical distribution of large continents. It is based on the Upper Devonian–lower Mississippian Bakken Formation (western U.S. and adjacent Canada). Rising temperatures, diminished oxygen solubility, and eustatic rise with deglaciation accompany modern climate change and mean that near-future platform seas will feature the reappearance of low-oxygen Bakken facies and environments. Full article

Quaternary climate has been characterized by pronounced glacial–interglacial cycles, with eustatic sea-level fluctuations directly controlling coastal sedimentary environments. The Yellow River Delta, situated on the southwestern coast of Bohai Bay, bears a distinct stratigraphic imprint of marine–terrestrial environmental transitions. However, critical knowledge gaps persist in reconstructing an integrated continental–marine stratigraphic framework. This study focuses on the nearshore core CB2302, integrating sediment lithology, grain size, foraminiferal assemblages, and geochemical proxies to establish a regional stratigraphic chronology since MIS5. Three depositional units (DU1–DU3) and 12 sedimentary subunits (C1–C12) were identified based on grain-size distributions, geochemical signatures, hydrodynamic, and microfossil assemblages. Integration of AMS ¹⁴C dating and sequence stratigraphic analysis establishes a post-MIS 5 stratigraphic framework for the northern Yellow River Delta, revealing sedimentary responses to three transgressive–regressive cycles (MIS 5e, 5c, and 5a) and confirming widespread terrestrial deposition during MIS 4–2, with no detectable marine influence in MIS 3 strata. Furthermore, correlation with representative cores across the Yellow–Bohai Sea coastal system elucidates a unified model of shoreline migration patterns driven by post-MIS5 sea-level oscillations. These findings advance the understanding of Quaternary sediment–landscape interactions in deltaic systems and provide critical stratigraphic benchmarks for petroleum exploration and coastal engineering in active depositional basins. Full article

Shallow-water deltas are not only a hot spot for sedimentological research but also a key target for oil and gas exploration. In this paper, taking the third member (E₁f₃) of the Funing Formation in the Upper Jurassic as an example, based on observations made from core samples, well logging, cathode luminescence characteristics, and analytical assays, the development conditions, sedimentary characteristics, and sedimentary models of shallow-water deltas are summarized. These shallow-water deltas were deposited in conditions with the following characteristics: a gentle terrain platform, a subtropical climate with ample rainfall, an abundant source supply, strong hydrodynamic forces, shallow water bodies, and a frequently eustatic lake level. Shallow-water deltas are characterized by sediment deposition from traction currents, numerous underwater distributary channel scour structures, overlapping scouring structures, sand body distribution with planar features, underwater distributary channels as skeletal sand bodies, and undeveloped mouth bars. Based on these, it is believed that during the deposition period of E₁f₃, the Gaoyou Sag in the Subei Basin had favorable geological conditions for the development of shallow-water delta deposition. The shallow-water delta deposition that occurred during the sedimentary periods of the five major sand units in the Funing Formation is characterized by front subfacies, with underwater distributary channels as the framework for sand bodies, and multiple intermittent positive rhythms overlapping vertically with the Jianhu Uplift as the source of material supply. In this paper, a depositional model for shallow-water delta deposition during the E₁f₃ deposition period in the Gaoyou Sag is established, expanding the scope of oil reservoir exploration in the north slope region of the Gaoyou Sag and providing important geological evidence for the selection of favorable subtle zones. Full article

Late Pennsylvanian cyclothems are documented from the carbonate platform margin in Guizhou, South China, providing a unique opportunity to study glacio-eustatic fluctuations and their impact on reef development. This paper focuses on a shallow-water, reef-bearing succession and a deep-water succession in the Houchang area of Guizhou. Fourteen microfacies, grouped into seven associations, represent distinct depositional environments. These microfacies associations exhibit vertical cyclicity, interpreted as cyclothems, similar to those observed globally, which are attributed to the waxing and waning of the Gondwana ice sheet. The cyclothems are primarily composed of sediments below the wave base within a shallow-water platform margin and deep-water settings. Those cyclothems show strong correlations with those observed in South China, Ukraine, and the North American Midcontinent, suggesting a potential connection to global glacio-eustatic processes. A brief and rapid sea-level rise during the late Kasimovian may correspond to a recently recognized global warming event. A microfacies analysis indicates that these cyclothems reflect glacial-type sea-level fluctuations ranging from 15 to 35 m. Notably, the reef-bearing cyclothems correspond to intermediate, major cyclothems identified in South China and the Midcontinent from the late Moscovian to early Kasimovian stages. The global cyclothem correlations and reef development patterns in South China suggest that intermediate, major cycles were the primary controls on reef growth and demise, while minor cycles influenced biostromes and community succession within the reefs. These findings underscore the pivotal role of the Late Paleozoic Ice Age (LPIA) in shaping reef development in far-field regions during the Late Pennsylvanian. Full article

Farmers have a pivotal responsibility in soil conservation: they can either preserve or deplete it through their choices. The responsibility of agriculture increases when practised in delicate ecosystems, such as lagoonal ones. The Venetian Lagoon islands, which are increasingly subjected to natural and anthropic subsidence, occasional flooding events (acqua alta), and eustatic sea level rise, are constantly exposed to erosive processes that challenge farmers to play with their adaptive capability. This research was carried out on the islands of Sant’Erasmo and Vignole, the most representative of island agriculture in the Venetian Lagoon: they almost exclusively rely on agriculture, which is almost nil in the other islands. This empirical research aimed to explore farmers’ agricultural practices, perceptions of soil changes, and how they adapt to them. It was fundamental for this study that the field research involved direct human contact with farmers (through semi-structured interviews) for data collection and using qualitative methods for data analysis, integrating scientific and non-scientific forms of knowledge and actors. The final purpose was to demonstrate the sustainability (valued on the potential depletion or regeneration capability) of agricultural practices and adaptation strategies on a theoretical basis. Despite their polycultural landscape (maintained by low-input farming systems), escaped from the predominant landscape oversimplification, Sant’Erasmo and Vignole are also subjected to unsustainable agricultural practices, including heavy mechanisation and synthetic inputs. Coupled with natural soil salinity that is exacerbated by increasing drought periods, these practices can contribute to soil degradation and increased salinity. The reported adaptation strategies, such as zeroed, reduced, or more conscious use of machines, were guided by the need to reduce the negative impact of soil changes on productivity. Our research revealed some of them as sustainable and others as unsustainable (such as increasing irrigation to contrast soil salinity). Participatory action research is needed to support farmers in designing effective sustainable agricultural practices and adaptation strategies. Full article

Cultural heritage assets face significant threats from climate change and land subsidence, leading to extensive social, economic, and environmental losses, and damage to artistic and monumental heritage in Italian coastal cities. In particular, addressing these challenges in the Venetian context necessitates the development of an adaptation plan for the lagoon area and the identification of targeted intervention strategies to preserve cultural and territorial heritage. To address these objectives, a systematic study was conducted to investigate the deterioration patterns exhibited by the most representative lithologies used in Venetian buildings. Thirty samples of five carbonate stone varieties subjected to natural aging were monitored in six different areas of Venice’s historic center and on Torcello Island, selected based on altimetry relative to tidal zero and exposure to environmental forces. An integrated multi-analytical approach was employed to identify and map macro- and micro-morphologies of stone surfaces related to chemical weathering and physical decay. Stones underwent evaluation during nine monitoring periods using various tests (ultrasound P-wave velocity and colorimetric measures) and analyses (µX-Ray Fluorescence, X-ray powder diffraction, stereomicroscope observations, and recognition of biological patinas). Data processing aimed to elucidate how microclimate and intrinsic stone features influence the occurrence and progression of deterioration phenomena. From the experimental findings, a Stone Deterioration Index and Intervention Procedures (SDIi) were proposed to estimate deterioration rates and assess the need for targeted intervention through conservative actions. Full article

To reveal the characteristics and environmental indications for the combination of the grain size and magnetic susceptibility of coastal sediments, we provided a necessary basis for further study on their genetic mechanisms. Based on the data of grain size and magnetic susceptibility of the 36.10 m long core 07SR01 sediments in the Xiyang tidal channel of western South Yellow Sea, we analyzed their variations and correlations and further revealed their environmental indications and corresponding regional sedimentary evolution via the combination of the aforementioned analysis results, the reinterpretation results of the sedimentary sequence and the age of core 07SR01 and shallow seismic profiles, and the findings of climate and glacial–eustatic cycles during Late Quaternary. The three stages of the sedimentary evolution of the Xiyang tidal channel between marine isotope stage (MIS) 7 and MIS 5 were summarized as follows: First is the stage of marginal bank and riverbed developments in the tidal estuary under a relatively high sea level and strong hydrodynamic conditions during MIS 7 (core section: 36.10–26.65 m). The sediments deposited in this stage were mainly affected by the paleo-Changjiang River and characterized by a coarse grain size (mean: 4.02 Φ) and relatively high magnetic susceptibilities (mean: 27.06 × 10⁻⁸ m³·kg⁻¹), with small fluctuations which were strongly and positively correlated with the sand component. Second is the stage dominated by fluviolacustrine and littoral environments with the weak hydrodynamics during MIS 6–5, in which the climate changed from cold and dry to warm and humid as the sea level rose after a drop (core section: 26.65–15.77 m). The sediments deposited in this stage were characterized by a fine grain size (mean: 5.27 Φ) and low magnetic susceptibilities with minor variations (mean: 10.83 × 10⁻⁸ m³·kg⁻¹) which were weakly and positively correlated with the coarse silt component. Third is the stage of delta front in the tidal estuary with a relatively high sea level and strong hydrodynamics during MIS 5 (core section: 15.77–0 m). The sediments deposited in this stage were strongly influenced by the paleo-Yellow River and characterized by a relatively coarse grain size (mean: 4.86 Φ), and high magnetic susceptibilities (mean: 37.15 × 10⁻⁸ m³·kg⁻¹) with large fluctuations which were weakly and positively correlated with the sand and coarse silt components. Full article

A recent research has identified an inverse amplitude link between obliquity damping and short eccentricity amplification during the Mid-Late Pleistocene based on LR04 δ¹⁸O and equatorial Pacific Site 846 sea surface temperature records that is associated with the Earth’s long-term cooling. In the present study, new evidence of this anticorrelation is presented from Antarctic δD-CO₂-CH₄ records, global benthic–planktic δ¹⁸O, and regional (Atlantic, Pacific, Mediterranean, and Indian) climate-related proxies. Based on a critical review of theoretical constraints (Earth’s oblateness changes and ice-volume phase lag in the obliquity band <5.0 kyr), this widespread and symmetric (bipolar) obliquity response damping has been interpreted as an effect of the obliquity–oblateness feedback, which could be the latent physical mechanism at the origin of the Mid-Pleistocene Transition (MPT). Indeed, results and considerations of the present work suggest that fast and positive/negative net variation in the Earth’s oblateness in the obliquity band was controlled by a dominant glacio-eustatic water mass component and, assuming a rapid response of the ice volume to surface temperature changes, the mean obliquity lag response is estimated to be <5.0 kyr over the past 800 kyr. These elements may explain the interglacial/glacial damping observed in the obliquity response. The consolidation of the Earth’s long-term icy state in the subtrend IV, culminating with the post-MPT obliquity damping, might have contributed to the strengthening of the short eccentricity response by mitigating the obliquity ‘ice killing’ during obliquity maxima (interglacials), favouring the obliquity-cycle skipping and a feedback-amplified ice growth in the short eccentricity band (obliquity damping hypothesis). This suggests a different impact of the climate friction than what is generally believed, which is presumably the latent physical mechanism that triggers the transient ‘competitive’ interaction between obliquity and short eccentricity started early during the Piacenzian. Full article

Remains of past sea levels such as tidal notches may provide valuable information for the investigation of relative sea-level changes (RSL) of eustatic/tectonic origin. In this review, we focus on case studies of coastal changes from the Corinth Gulf, where impacts of past earthquakes can be traced through various indicators. The southern coast has undergone a tectonic uplift during the Holocene, whereas the northern coast has undergone subsidence. The magnitude of RSL fall in the south Corinth Gulf is larger than RSL rise in the north. Exploiting previous measurements and datings, we created a geodatabase regarding the relative sea-level changes of the whole gulf, including geodetic data based on permanent GNSS observations. The combination of geomorphological (long-term) and geodetic (short-term) data is a key advance for this area, which is characterized by fast rates of N-S crustal extension and strong earthquakes. The joint dataset fits the tectonic model of an active half-graben where the hanging wall (northern coast) subsides and the footwall (southern coast) is uplifted. The highest uplift rates (3.5 mm/year) are near Aigion, which indicates an asymmetric localization of deformation inside this active rift. Full article

In this paper, the physiography, geomorphological features, and sedimentary bedforms of the offshore Egadi Islands (Italy) have been illustrated and mapped through an integrated analysis of high-resolution bathymetric, seismo-acoustic, and sedimentological data. The study area is characterized by a wide, up to 25 km, continental shelf which is separated by a NNW-trending linear incision, the Marettimo Channel, along which several erosional and depositional features have been detected and mapped. Sedimentary prograding wedges were detected at water depths between 100–125 m along the shelf margin, which accumulated during the sea-level fall and lowstand stages of the last glacio-eustatic cycle (post- MIS 5.5). This study detected several slope breaks defining scarps across the continental shelf, which were interpreted as coastal cliffs that originated during the post-LGM eustatic sea-level rise. Several fields of different types of sedimentary bedforms, including 2-D and 3-D hydraulic dunes and sorted bedforms, were found across the continental shelf, providing evidence of a high hydrodynamic regime affecting the seafloor. Further on, this study recognized erosive and depositional features related to bottom currents (contourites) in the Marettimo Channel. These findings provide a better understanding of the morpho-sedimentary evolution of the Egadi Islands offshore in the latest Quaternary. Moreover, they offer essential scientific support for effectively managing the most valuable priority habitats for conservation, such as the Posidonia oceanica meadow and coralline algae bioconstructions (Coralligenous habitat). Full article

The sedimentary facies, architecture, and depositional mechanism of deltaic systems have been one of the global research hotspots in recent decades; however, the detailed distribution, sedimentary evolution, source rock potential, and major control factors of the coal-bearing shallow-water delta are still unclear. A typical shallow-water braided delta with coal-bearing source rocks developed in the Middle–Late Triassic Mungaroo Formation of the North Carnarvon Basin, which can be a good study area for an analysis of coal-bearing source rocks. In this study, the sedimentary facies, distribution and evolution, and coal-bearing source rock features of the Triassic strata were analyzed based on the integrated study of wireline logs, drilled cores, thin sections, seismic facies and attributes, and geochemical data. A range of shallow-water delta sedimentary facies was identified, including the proximal delta plain channel/interdistributary bay, distal delta plain channel/interdistributary bay, and the delta front. The coal-bearing shallow-water delta system of the Middle–Late Triassic Mungaroo Formation was characterized by the largest scale delta system with relatively broad proximal and distal delta plains and relatively narrow delta front subfacies. The scale of the delta system showed a trend of increasing from the Early Triassic Locker Shale to the Middle–Late Triassic Mungaroo Formation and then decreasing to the Late Triassic Brigadier Formation. The distal delta plain subfacies of the Mungaroo Formation should have the highest potential coal-bearing source rock, and the proximal delta plain also can be a favorable target for source rock evaluation. The major control factors of the coal-bearing source rocks of the Mungaroo shallow-water delta mainly included the Triassic megamonsoon climate, the topographic features, eustatic changes, and provenance supply. The proximal and distal delta plains of the shallow-water delta system with thin coal seams, carbonaceous mudstone, and dark mudstone lithologies’ association could be a favorable source rock exploration facies for the next stage of natural gas field exploration. Full article