Sea-level Curve Research Articles

Evidence of Middle Holocene landslide-generated tsunamis recorded in lake sediments from Saqqaq, West Greenland

Abstract. The Vaigat strait (Sullorsuaq) in West Greenland is well known for its susceptibility to landslides and historical landslide-generated tsunamis. Recent mapping of the seabed in the Vaigat strait has revealed several prehistoric giga-scale (volumes of 109 m3) tsunamigenic landslides. However, the timing of these giga-scale tsunamis is largely unconstrained, but they are assumed to have occurred after the last deglaciation. Here, we report on lake sediment core records from four coastal lakes located between 19 and 91 m above sea level (a.s.l.) on the Saqqaq foreland at the eastern end of the Vaigat strait. We use a multiproxy approach including X-ray fluorescence (XRF) and magnetic susceptibility core scanning along with a screening for marine diatoms to identify at least two tsunami deposits in two of the four sediment cores. Radiocarbon dating of aquatic macrofossils and bulk samples suggest that the tsunami events occurred at ca. 7.6 and 7.3 ka cal BP. Using a previously published relative sea level curve from Vaskebugt, Arveprinsen Ejland (Alluttoq), located 40 km southeast of Saqqaq, we infer wave runup heights of ca. 41–66 and 45–70 m, respectively, for the two tsunami events. These runup heights from prehistoric tsunamis are 1 to 2 orders of magnitude higher than the historic landslide-tsunami runup heights at Saqqaq which only reached an elevation of ca. 3 m in November 2000. While we found deposits from two tsunami events in the lake sediments, landforms from at least nine giga-scale landslides are present on the seafloor of Vaigat. We infer that these deposits probably represent the two most recent tsunamis identified in the Vaigat strait and that the older tsunamis must have happened between the last deglaciation and the oldest sediment in the lakes, i.e., between ca. 10.0 and 8.5 ka cal BP.

Paleoenvironmental significance of Holocene foraminiferal taphocoenoses in Guayaguayare Bay, Trinidad, West Indies: A coral reef near the Orinoco Delta

A small suite of seafloor sediment samples (water depth less than 20 m) was collected in 2005 from the sheltered, logarithmic-spiral Guayaguayare Bay along the SE coast of Trinidad, West Indies. The easternmost shielded part of the bay was then occupied by a meadow of the seagrass Halodule wrightii, the closest seagrass bed to the Boca Grande, the main distributary of the Orinoco Delta. Four foraminiferal taphofacies were distinguished, ascribable to a relict coral reef system: (1) A shallow-water (approx. 5 m) taphofacies dominated by Pararotalia sarmientoi. (2) A back-reef taphofacies (approx. 5 m) with abundant Discorbis rosea, apparently associated with the H. wrightii. (3) A fore-reef taphofacies (water depth approx. 20 m) co-dominated by Amphistegina gibbosa and Quinqueloculina bicostata. (4) A reef-flat (approx. 5 m) taphofacies dominated by Q. bicostata. A ternary plot of specimen wall types (agglutinated, porcellaneous, calcareous hyaline) clearly distinguished Taphofacies 1 from Taphofacies 4, porcellaneous specimens being rare in the former. A similar plot of staining + test abrasion for A. gibbosa indicated that those on Taphofacies 3, assumed to be in situ, were more heavily stained than those elsewhere and were larger. Tiny but pristine, presumably allochthonous A. gibbosa were recovered from Taphofacies 1. Two formae of Asterigerina carinata, both widely illustrated in the literature, are distinguished for the first time and named A. carinata forma conica and A. carinata forma discoida. The bay is currently filled with turbid water. The coral reef system, postdating the early Holocene transgression, would have required clear water, perhaps when the Orinoco Delta had not prograded sufficiently to impact the bay greatly. The known best depth range for the growth of amphisteginids, which are symbiotic with algae, coupled with known Holocene sea level curves for the SE Caribbean, suggest an age of approx. 4000 YBP. Sedimentation in the protected bay has since the development of the reef been limited.

Flexural isostatic response of continental-scale deltas to climatically driven sea level changes

Abstract. The interplay between climate-forced sea level change, erosional and depositional processes, and flexural isostasy in deep time on passive margin deltas remains poorly understood. We performed a series of conceptual simulations to investigate flexural isostatic responses to high-frequency fluctuations in water and sediment load associated with climatically driven sea level changes. We model a large drainage basin that discharges to a continental margin and produces a large deltaic depocenter, then prescribe synthetic and climatic-driven sea level curves of different frequencies to assess flexural response. Results show that flexural isostatic responses are bidirectional over 100–1000 kyr timescales and are in sync with the magnitude, frequency, and direction of sea level fluctuations and that isostatic adjustments play an important role in driving along-strike and cross-shelf river mouth migration and sediment accumulation. Our findings demonstrate that climate-forced sea level changes produce a feedback mechanism that results in self-sustaining creation of accommodation into which sediment is deposited and plays a major role in delta morphology and stratigraphic architecture.

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.

Depositional environment and sequence stratigraphy of the Qom Formation (Miocene) from the Ghalibaf section, Central Iran

The Miocene strata of the Qom Formation from the Ghalibaf section, Central Iran (NW Semnan) documented a high diversity of shallow-marine microfacies. These deposits in the Ghalibaf section, with a total thickness of 445 m, are characterized by twenty-one microfacies. The carbonate microfacies are deposited into five facies belts, including a lagoon, upper slope, lower slope, platform-margin sand shoals and margin facies. The presence of barrier reefs, intraclasts, oncoids, and grainstone aggregates, along with the absence of vast tidal flat areas, are distinguished. According to the aforementioned evidences, these sediments were deposited on a rimmed carbonate platform. In addition, the heterolithic calciturbidite deposits also show that the carbonate sequences were sedimented on a rimmed carbonate platform. Based on the available data of sequence stratigraphy analysis, seven third-order depositional sequences are bounded by type-1 and type-2 sequence boundaries. The relative sea-level changes between the upper and lower sequence boundaries in accord with the global sea-level curves reveal a reasonable correlation. However, some differences in other sequence boundaries might be due to local tectonic activities in the Qom Formation sedimentary basin, thereby leading to local sea-level changes. Moreover, biostratigraphic data based on the larger foraminifera index markers, including Praebullalveolina curdica, Borelis melo, Dendritina rangi, Meandropsina iranica, Elphidium sp. 14, Neorotalia viennoti, and Miogypsina sp. suggests the Miocene Shallow Benthic Zones, SBZ24-SBZ25 equivalent to the late Aquitanian-Burdigalian timespan.

A city against the current: A reconstruction of Holocene sea-level changes and the evolution of coastal landscapes in ancient Abdera (Thrace, Gr.)

This paper presents an integrated Geoarchaeological approach to Holocene landscape change and socio-environmental interaction around ancient Abdera, a Greek colony in Aegean Thrace. A combination of remote sensing, geomorphological mapping, sedimentary coring, and radiocarbon dating was used to build the first detailed Holocene sea-level curve in the Northern Aegean, and to reconstruct the palaeogeographic evolution around Abdera from the Neolithic onwards. The discussion of these results, alongside the available archaeo-historical data, sheds new light on the role of historical and environmental factors in the rise and eventual decline of Abdera, thereby challenging previous narratives. This study is the first to detect evidence of the Neolithic landscapes in this coastal area being submerged by marine transgression c. 5000 cal. BC. A lagoonal landscape developed from the Neolithic until Greek colonists settled in the area c. 654 BC. The results presented here suggest that the relocation of the city in the 4th century BC was not caused by the silting up of the bay but was due to historical events. The coastal progradation only became significant after 300 cal. BC and accelerated in the following centuries. Based on the data acquired, it is hypothesized that this was due to anthropogenic forcing of the sedimentary systems both at local and regional levels, caused by the development of the productive activities of the colony. The evidence presented here demonstrates that while Abdera retained good access to the sea, its decline in the 4th c. AD was certainly due to the gradual shift of the economic axis inland. By 400 cal. AD the coastline was very close to its current position. The results of this study also add to the catalogue of known tsunamis in the Northern Aegean, by providing new evidence of a tsunami on this section of the Thracian coast in 544 AD.

Placing constraints on the nature of short‐term eustatic curves

AbstractThe isolation of the eustatic signal from the sedimentary record is a challenging task, and accordingly, there is no consensus on the magnitude and pace (rate) of eustatic events in the geological record. Here we critically assess various published short‐term Cretaceous eustatic curves using insights from forward stratigraphic modelling. We generate a range of simulations with varying eustatic rates and sediment supply against a background of constant subsidence. From these, we generate statistics on the accommodation change associated with the various systems tracts for different sediment supply. We quantify the minimum rate needed to generate transgressive systems tracts (TST). Using this threshold and average subsidence rates for passive margins and intracratonic basins, we document some key challenges with a range of Cretaceous eustatic curves. While it is possible to complexify, this approach through the inclusion of other parameters, our results provide a framework for evaluating eustatic (or relative sea level) curves in terms of the implied rate of change of accommodation. Given these caveats, we also show that many estimates of the magnitude of short‐term transgressions are of insufficient rate to generate observable TST. Further, our work places an upper limit on the time frame over which aquifer and thermo‐eustasy can have observable impacts on the rock record, providing support for the action of glacio‐eustasy during the Cretaceous.

Early–mid Holocene relative sea-level rise in the Yangtze River Delta, China

Regional-scale Holocene sea-level reconstruction is the key to understanding natural climatic variability. The tidal flat, salt marsh, and tidal floodplain in the Yangtze River Delta were very sensitive to morphological changes and sea-level variation during the early Holocene. In this study, the lithology, radiocarbon ages, sediment grain size, benthic foraminifera, and ostracods of three new cores were analyzed. Twenty-four sea-level index points were extracted from incised-valley fills beneath the westernmost part of the Yangtze River Delta and used to construct a detailed relative sea-level curve for 11.03–7.25 ka. The relative sea level were − 38.90 ± 3.48 and 1.59 ± 3.28 m at 11.03 and 7.25 ka, respectively, and the average rate of sea-level rise was 10.71 mm/yr. The relative sea level gradually increased at 11.03–10.10 and 9.29–8.33 ka from 4.80 to 13.30 and 3.19 to 19.59 mm/yr, respectively. The rate of relative sea-level rise gradually decreased from 19.59 mm/yr at 8.33 ka to 13.40 mm/yr at 7.82 ka and further decreased to 5.53 mm/yr at 7.25 ka. The Yangtze River Delta recorded accelerations in the rate of sea-level rise from 8.72 to 8.18 ka of 14.2–19.59 mm/yr, corresponding to the pre-8.2 ka event. A comparison of the sea-level histories of the Yangtze River Delta and other regions indicates tectonics, glacial isostatic adjustment, and coastal levering effects caused by the marine inundation of the continental shelves. These new sea-level data contribute to the understanding of the difference in the sea-level rise rate during the early–mid Holocene.

Paleocene–Eocene boundary in the Gabal El-Gir, east Qena, Egypt: Paleoenvironment and sequence stratigraphy interpretations

Comprehensive field, litho-, biostratigraphy, and paleoenvironmental studies of the upper Paleocene–lower Eocene (P–E) boundary interval in the Gabal El-Gir area were conducted. Two selected sections El-Gir-1 and El-Gir-2 were investigated. The prevailed paleoenvironmental conditions were discussed in the frame of the nannofossils, planktonic, and benthic foraminiferal assemblages. Benthic foraminifera assemblages indicate a remarkable turnover across the PETM. The extinction of Angulogavelinella avnimelechi at the base of the PETM represents a significant marker for the base of the benthic foraminifera extinction event at this site and other neritic sites in the Tethyan region. The dominance of calcareous planktonic excursion taxa at the base of the PETM indicates adaptation to extremely warm sea surface temperatures and low nutrient levels. Also, our data suggests that the biotic responses to environmental change in the early Eocene resembled those observed in the early Eocene hyperthermals at the nearbay Dababiya and El-Ballas sections. This could indicate that similar processes characterized the Egyptian sedimentary basin during the early Eocene. Stratigraphically, despite the limited distance between the studied sections, the Dababiya Quarry Member (DQM) in El-Gir-1 resemble those of the Global Stratotype Section and Point (GSSP) but reduced in thickness. While in El-Gir-2, the lower part of the DQM was missing. These findings could indicate that the DQM was deposited in a submarine channel. Three third-order depositional sequences were recognized covering the P–E interval. The reconstructed sea level curve shows the presence of eustatic similarities with the global sea level.

Microfacies Analysis of Mixed Siliciclastic-Carbonate Deposits in the Early-Middle Ordovician Meitan Formation in the Upper Yangtze Platform in SW China: Implications for Sea-Level Changes during the GOBE

During the Early-Middle Ordovician, the Upper Yangtze Platform experienced extensive development of a distinctive set of mixed siliciclastic-carbonate deposits known as the Meitan Formation. To conduct a comprehensive study of the relationship between mixed sedimentation and sea-level changes, the Hailong section, situated at the southwest margin of the Upper Yangtze Platform in SW China, was selected as the study area due to its typical mixed sedimentary sequence. This section was effectively compared with sections in other regions. Clustering analysis of the point-count groups from the Honghuayuan and Meitan Formations revealed nine microfacies that developed during this period. Such a diverse range of microfacies provides the evidence of frequent sea-level changes in the Yangtze Platform throughout this period. Specifically, two sea-level rises were identified during the early TS.2b and early TS.3b, with the early TS.2b event occurring globally. Furthermore, four sea-level falls were observed in the late TS.2b, TS.2c, TS.3a, and late TS.3b periods. The late TS.2b sea-level fall was globally significant. From TS.2c onwards, distinct variations in sea-level changes among the Yangtze Platform, North China, Baltoscandia, Australia, and North America emerged due to alterations in the paleogeographic pattern. By comparing the sea-level curves in the Upper Yangtze Platform with the diversity curves of chitinozoans, acritarchs, and brachiopods, it became evident that environmental changes played a crucial role in the Great Ordovician Biodiversification Event (GOBE), especially during the Floian. The rising sea level and increased detrital materials fostered the development of diverse habitats, prompting organisms to adapt to varying environments. In general, rising sea levels favored increased brachiopod diversity, while falling sea levels favored enhanced planktonic diversity among chitinous and acritarch species. By shedding new light on the relationship between Ordovician sea-level changes and biodiversification in the Yangtze region, this study offers a fresh perspective on the subject from the microfacies analysis.

Where ice gave way to fire: deglacial volcanic activity at the edge of the Coast Mountains in Milbanke Sound, BC

Kitasu Hill and MacGregor Cone formed along the Principe Laredo Fault on British Columbia’s central coast as the Wisconsinan ice sheet withdrew from the Coast Mountains. These small-volume Milbanke Sound Volcanoes (MSV) provide remarkable evidence for the intimate relationship between volcanic and glacial facies. The lavas are within-plate, differentiated (low MgO < 7%) Ocean Island Basalts, hawaiites, and mugearites that formed from ∼1% decompression melting of asthenosphere with residual garnet. Kitasu Hill, on glaciated bedrock, formed between 18 and 15 cal ka BP. Dipping, poorly stratified, admixed hyaloclastite, and glacial diamicton with large plutonic clasts and pillow breccia comprise its basal tuya platform (0–43 masl). Subaerial nested cinder cones, with smaller capping lava flows, sit atop the tuya. New marine samples show McGregor Cone formed subaerially but now sits submerged at 43–200 mbsl on an eroded moraine at the mouth of Finlayson Channel. Seismic data and cores reveal glaciomarine sediments draping the cone’s lower slopes and show beach terraces. Cores contain glaciomarine diamictons, ice-rafted debris, delicate glassy air fall tephra, and shallow, sublittoral, and deeper benthic foraminifera. Dates of 14.1–11.2 cal ka BP show volcanism spanned ∼2000 years during floating ice shelf conditions. The MSV have similar proximal positions to the retreating ice sheet, display mixed volcano-glacial facies, and experienced similar unloading stresses during deglaciation. The MSV may represent deglacially triggered volcanism. The dates, geomorphic and geological evidence, constrain a local relative sea level curve for Milbanke Sound and show how ice gave way to fire.

Holocene relative sea-level changes on the southern east coast of the Yellow Sea

Projections indicate increasing coastal hazards in the Yellow Sea region owing to relative sea-level rise. Accordingly, regional studies of such change over the Holocene timescale could be helpful in mitigating these threats. Here, we describe the Holocene record of relative sea-level change in the Gochang-Yeonggwang area of South Korea. We compared this record with that of other sites around the coast of the Yellow Sea, including Bohai Bay (China), the Tando Estuary and Gunsan Bay (South Korea), and sites on the east coast of the South Sea and Toyo-oka Basin, Japan. The findings are based on a multi-proxy study, including lithostratigraphy combined with radiocarbon dating and analyses of grain size distribution, magnetic susceptibility, and geochemistry, which facilitated the generation of 89 paleo-sea-level points reconstructed from 28 borehole cores. The early Holocene transgression was found to start later at Gochang-Yeonggwang than at Gunsan Bay, although the distance between them is only 150 km. This result was inferred from substantial differences in sediment delivery owing to Holocene differences in river basin size, topography, and tectonic context. Before ∼7 ka, the slope and highstands from the predicted mean sea-level models at Bohai Bay, Tando Estuary, and Gochang-Yeonggwang were steeper and lower, respectively, from north to south in the Yellow Sea, approaching the slope of the glacio-eustatic sea-level curve. Therefore, the levering effect of transgression in the early Holocene decreased southward in the Yellow Sea. The slight fluctuation in mean sea-level points of the late Holocene resulted from the formation of storm deposit layers in the coastal area, erosion and redeposition in the channel, and geomorphic effects. A partial difference occurred between the relative sea levels at Gochang-Yeonggwang and Toyo-oka. Future relative sea-level research at the southernmost part of the east coast of the Yellow Sea would further improve understanding of the coastal evolution of the region.

Cretaceous–Paleogene (K–Pg) boundary in south Sinai, Egypt: Paleoenvironment and sequence stratigraphy implications

High-resolution quantitative analysis of the benthonic foraminifera throughout the K–Pg boundary interval on four sections (Wadi Nukhul, Abu Qada, Thamad, and Sudr Al Hitan) in south Sinai, Egypt was conducted. Planktonic foraminiferal biostratigraphy indicates a complete K–Pg boundary interval in W. Nukhul section, while minor hiatuses characterized the other sections. Benthonic foraminifera reflect outer neritic-upper bathyal setting for the studied interval, while outer neritic setting marks the latest Maastrichtian. The upper Maastrichtian assemblage indicates mesotrophic to slightly eutrophic marine conditions. At the K–Pg boundary in W. Nukhul, benthonic foraminifera display a significant turnover. A major change in the benthonic foraminifera assemblage which is marked by a decrease in the infaunal taxa and buliminids indicates a shortage in the food supply to the sea floor at the K–Pg boundary. This pattern was associated with increased abundance of the epifaunal taxa indicating oligotrophic conditions that linked to the food web collapse due to extinction of the marine primary producers. A partial recovery of the benthonic foraminifera was observed in the early Danian (Pα and lower part of P1a zones). A comparison between the data of the present study and other K–Pg boundary sites in the Tethyan realm indicates a similar shortage in the food supply with no oxygen deficiency. Two third-order sequences were identified in the studied interval based on the biotic attributes of the fauna. The obtained sea level curve was compared to the global sea level curve.

A new deglacial climate and sea-level record from 20 to 8 ka from IODP381 site M0080, Alkyonides Gulf, eastern Mediterranean

Records of relative sea-level rise for the last deglaciation are mostly limited to coral reef records and geophysical model estimates, but observational data from regions with temperate climates is sparse. We present a new relative climatic and regional sea-level rise record for glacial Termination 1 (Marine Isotope Stages [MIS] 2–1) based on ostracode paleoecology from the upper 8 m of the International Ocean Discovery Program (IODP) Site M0080 collected on Expedition 381, in the Gulf of Alkyonides, eastern Corinth basin of the Mediterranean Sea. Results show a series of major faunal transitions from lacustrine (Ponto-Caspian, Lake Corinth) glacial-age assemblages to fully marine (Mediterranean) interglacial assemblages between 20 and 8 ka. During glacial and early deglacial intervals, the Gulf of Alkyonides was characterized by non-marine lacustrine conditions with episodic sediment input from coastal, saline lake environments. Relatively stable lake shoreline conditions marked by the distinctive Tuberoloxoconcha sp. Existed from ∼17.5 to 15 ka. During the peak deglacial interval, the BØlling-AllerØd (B-A, ∼15–13.5 ka), rapid sea-level rise is indicated by a fully marine ostracode fauna colonization, which persisted from 13.5 to 7.5 ka (Late Pleistocene-Early to Middle Holocene).The transition from lacustrine to marine environments confirms that during the last glacial maximum (LGM) low sea level (130 - 125 m below present day), the Corinth-Alkyonides depocentres were lacustrine. Marine water breached the shallow Rion and Acheloos-Cape Pappas sills, which today are ∼50–60 m deep, separating the Mediterranean and Corinth-Alkyonides system beginning about 15 ka. Based on Alkyonides sedimentation rates, mean rates of sea-level rise during the B-A flooding of the Corinth-Alkyonides system are comparable to those obtained from coral reef sea level (SL) records, at least 10–20 mm yr−1. Changes in sedimentation and sill depths in this tectonically active region may have played a role in reconnection of the Mediterranean and Corinth/Alkyonides system over a prolonged period. However, the ages and scale of the faunal changes and their clear correspondence with previously published global sea-level curves and the regional sea-level curve based on deglacial land elevation changes predicted by the ICE-7G model suggests the M0080A deglacial is dominated by the glacio-eustatic sea-level rise and records details of global climate changes during Termination 1.

Effect of the supercontinent cycle on the longest-term sea-level change from a simple conceptual and theoretical model

The longest-term (first-order) sea-level change is considered to be within ∼ 200–300 million years, which is roughly half or less of the period of the supercontinent cycle of ∼ 500–700 Myr. It is recognized that the assembly of supercontinents involves either the closure of the “interior ocean” that resulted from the breakup of the supercontinent or the closure of the “exterior ocean” that surrounded the supercontinent. The former process is termed “extroversion,” while the latter is termed “introversion,” both of which are an end-member scenario of the supercontinent cycle. A “combination” process is also proposed to explain the complex behavior of continental drift on the actual Earth. Despite recent advances in a time-dependent mantle convection model, some difficulties still remain in self-consistently recovering plate tectonics and continental drift of the past Earth. Therefore, it is worth addressing the fundamental physics of the effects of the history of plate motion and the associated continental drift on the longest-term sea-level change from the perspevtive of the supercontinent cycle in a timescale of the order of 100 million years. In this study, a simple conceptual model of mantle convection with various supercontinent cycle processes was constructed, and the effects of the supercontinent cycle on the longest-term sea-level change were addressed. The sea-level change is estimated from bathymetry over the oceanic plates under different free parameters that control the fluctuation of the sea-level change. The present analytical results suggest that the asymptotic bathymetry due to the plate flattening effect of oceanic plates in the exterior and interior oceans is essential to recover the realistic magnitude of sea-level fluctuations that is comparable to the sea-level curve of the past Earth. In addition, the absolute volume change in the seawater due to its recycling into the mantle may be important to fit the observed sea-level curves from stratigraphic studies since 200 million years ago.

Holocene Sea Level Recorded by Beach Rocks at Ionian Coasts of Apulia (Italy)

Beach rocks are located along many coasts of the Mediterranean basin. The early diagenesis environment and the mean sea level along the shoreline make these landforms useful in the reconstruction of relative sea-level changes and, in particular, as SLIPs (sea-level index points). The beach rocks surveyed along the Ionian coast of Apulia were found to be well preserved at three specific depth ranges: 6–9 m, 3–4 m, and from the foreshore to about 1.20 m. Morpho-bathymetric and dive surveys were performed to assess both the geometries and the extension of the submerged beach rocks. Samples were collected at these different depths in the localities of Lido Torretta, Campomarino di Maruggio, San Pietro in Bevagna, and Porto Cesareo. Bivalve shells were identified and isolated from the beach rock samples collected at a depth of 7 m; AMS dating provided a calibrated age of about 7.8 ka BP. Their morphology and petrological features, along with the time constraints, enabled us to (i) reconstruct the local sea-level curve during the Holocene, (ii) corroborate acquired knowledge of the relative sea-level history, and (iii) identify possible local vertical land movement (VLM).

Age Assignment, Palaeoecology and Sequence Stratigraphic Framework of the Nukhul Formation at Wadi Baba, West-Central Sinai (Egypt)

The Nukhul Formation has been a point of controversy until now due to a lack of index fossils, varied facies modifications, and different time gaps. As a result, the calcareous nannofossils of the exposed Miocene rocks at Wadi Baba, west-central Sinai have been studied quantitatively for the first time. An important sequence of calcareous nannofossil bioevents has been recorded in the Nukhul Formation, including the FOs of Discoaster druggii, Sphenolithus dissimilis, Helicosphaera ampilaperta, and Sphenolithus disbelemnos, which correspond to the Aquitanian age of upper NN1 and NN2 zones. The Nukhul Formation contains four intervals that reflect eutrophic conditions in the nearshore habitats with substantial nutrient input from the terrigenous influx, as shown by the dominance of cool-water taxa, Coccoliths pelagicus and Reticulofenestra minuta. The lithofacies, microfacies types, abundance, dominance, and diversity of nannofossil assemblages classified the studied interval into two depositional sequences with four system tracts. These tracts refer to fluctuations in relative sea level changes in response to the eustatic sea-level curve.

Terrazas marinas levantadas por deformación tectónica costera activa a lo largo del este de Argel: implicaciones para la convergencia de las placas africana y europea y las curvas del nivel del mar

Marine terraces are geological features composed of elevated, flat surfaces and steep slopes. The evolution of these terraces is largely influenced by active coastal tectonic deformation. This study investigates the uplift of marine terraces along the east coast of Algiers and its implications for the African and European plate convergence and sea-level curves. The objective of studying marine terraces in the Zemmouri area is to gain a deeper understanding of the evolution of the Earth's coastlines and how they have been shaped over time by natural processes such as sea level changes, tectonic activity, geomorphic parameters, and erosion. Marine terraces provide valuable information about the history of sea level changes and the rate of tectonic uplift or subsidence of the coastal areas. Secondary data sources, including qualitative information and high-resolution satellite imagery (SRTM 30 m and ALOS 12.5 m), were used to analyze the impact of sea level on marine terraces. Fieldwork using GPS and altimeter measurements at the site of the Mw=6.8 Zemmouri earthquake that occurred on May 21, 2003, revealed the presence of two well-preserved marine terraces, which serve as important markers for measuring the long-term fault slip rate. The analysis highlights the significance of active coastal tectonic deformation in shaping the coastlines. This research offers new insights into the ongoing processes of plate convergence and sea level change along the east coast of Algiers, contributing to our overall comprehension of coastal evolution and the potential for seismic hazards in the region.

ClinoformNet-1.0: stratigraphic forward modeling and deep learning for seismic clinoform delineation

Abstract. Deep learning has been widely used for various kinds of data-mining tasks but not much for seismic stratigraphic interpretation due to the lack of labeled training datasets. We present a workflow to automatically generate numerous synthetic training datasets and take the seismic clinoform delineation as an example to demonstrate the effectiveness of using the synthetic datasets for training. In this workflow, we first perform stochastic stratigraphic forward modeling to generate numerous stratigraphic models of clinoform layers and corresponding porosity properties by randomly but properly choosing initial topographies, sea level curves, and thermal subsidence curves. We then convert the simulated stratigraphic models into impedance models by using the velocity–porosity relationship. We further simulate synthetic seismic data by convolving reflectivity models (converted from impedance models) with Ricker wavelets (with various peak frequencies) and adding real noise extracted from field seismic data. In this way, we automatically generate a total of 3000 diverse synthetic seismic datasets and the corresponding stratigraphic labels such as relative geologic time models and facies of clinoforms, which are all made publicly available. We use these synthetic datasets to train a modified encoder–decoder deep neural network for clinoform delineation in seismic data. Within the network, we apply a preconditioning process of structure-oriented smoothing to the feature maps of the decoder neural layers, which is helpful to avoid generating holes or outliers in the final output of clinoform delineation. Multiple 2D and 3D synthetic and field examples demonstrate that the network, trained with only synthetic datasets, works well to delineate clinoforms in seismic data with high accuracy and efficiency. Our workflow can be easily extended for other seismic stratigraphic interpretation tasks such as sequence boundary identification, synchronous horizon extraction, and shoreline trajectory identification.

The variable nature of the coastal 14C marine reservoir effect: A temporal perspective for Rio de Janeiro

The radiocarbon (14C) marine reservoir effect (MRE) is very sensitive to physical and chemical processes affecting the local carbon (C) cycle. In coastal zones, these tend to be numerous and complex, hindering the derivation of local marine reservoir offsets (ΔR) for the establishment of archaeological chronologies. Although discussions of how the magnitude of the MRE responds to factors such as the presence of coastal upwelling are common in the literature, little has been done to assess how the effect is influenced by a changing relative sea level. Here, we address the MRE temporal variation on the coast of Rio de Janeiro in the light of updated 14C calibration curves and considering the Holocene relative sea-level curve for the region. To achieve this, we employ Bayesian modelling to analyze published and new 14C ages from Brazilian archaeological sites and pre-bomb samples. In this study, we show evidence for a Late Holocene increase in the MRE, varying from −577 ± 56 14C yr at ca. 5500 cal BP to −29 ± 25 14C yr at present, associated with a decreased relative sea-level.