Depositional Record最新文献

Establishing along-strike correlations of event deposits in deep-sea environments allows for the reconstruction of spatial and temporal patterns of geological processes, such as seismically triggered turbidites. However, in settings like the ultra-deep Japan Trench, highly variable seafloor topography and limited chronological tie points pose significant challenges for tracing individual deposits between semi-isolated trench basins. Using cores from International Ocean Discovery Program (IODP) Expedition 386 at the central Japan Trench, this study examines how non-destructive X-ray fluorescence core scanning (XRF-CS) combined with multivariate statistics can be used to distinguish and correlate individual event deposits across contrasting depositional settings, based on their geochemical fingerprints. The results of the five-cluster model demonstrate that the XRF-CS properties of event deposits are clearly distinguishable from background sediments, as well as from one another. The chemostratigraphic cluster sequence can be correlated between cores from basin depocentres—where event deposits are thicker but the record is shorter, and cores from topographic highs—where the record extends further back in time but event deposits are thin and difficult to distinguish using previously applied event correlation methods. The high-resolution chemostratigraphy enables a more detailed, geochemically-enhanced stratigraphic interpretation, identifying several previously unrecognised event deposits with unique internal structures that suggest varying depositional processes. Notably, excluding the 2011 event deposit, the three most recent event deposits are allocated to different clusters, implying compositional heterogeneity probably linked to sediment provenance. The results of this study therefore demonstrate a rapid and reproducible technique for using chemostratigraphy to establish high-resolution event correlations in submarine sediment cores, leading to several working hypotheses for Japan Trench palaeoseismology to be tested with future work.

Grand Lake is a large 250 m deep fjord lake located in Labrador, Canada. Previous studies on short and shallow sediment cores identified seasonal hydrological signals and connections with North Atlantic modes of climate variability. This study presents a new 20 m composite sequence from the deepest basin of Grand Lake, providing high-resolution insights into sedimentary processes over the last ca. 3300 years. As a potential key environmental archive for north-eastern Canada, a region where high-resolution palaeoclimate records are scarce, Grand Lake offers a unique opportunity to examine long-term sedimentary and climatic interactions. Previous research did not examine temporal changes in sedimentary processes or the specific mechanisms driving mass sediment deposition, limiting the distinction and interpretation of climate controls on longer time scales. Here, sedimentological and geochemical characteristics are used to reconstruct sedimentation dynamics and erosional processes. Several rapidly deposited layers are characterised over changing depositional environments during the Late Holocene, from a phase when the lake was connected to the sea to a more stable state conducive to varve formation. A combination of end-member modelling analysis, lithofacies descriptions and high-resolution μ-XRF proxies revealed density currents as the dominant sedimentation process. Their origins ranged from proximal sources (gully systems) to distal sources (tributary rivers), with contributions varying over time, reflecting the transition from a marine-influenced system to a post-glacial fjord lake. The results provide a framework for future palaeoclimate studies in the region by contributing to a better understanding of sedimentary dynamics in a deep glacial lake, with implications for regional palaeoclimate reconstructions. Additionally, this study highlights the broader applicability of statistical unmixing for interpreting grain-size variations in both lacustrine and marine environments.

Islands in active carbonate depositional systems can profoundly impact local wave, wind and tidal energy distributions, affecting sediment factories and facies distributions. Island development and facies were investigated for South Joulter Cay, located within the modern Joulters ooid sandbody of Great Bahama Bank, using high-resolution imagery, a digital elevation model, field observations and radiocarbon dating of weakly cemented rock samples. Island ridge morphology exhibits three distinct developmental stages spanning the last 1400 years, with differences in ooid sand distribution, tidal channels, wind, waves and longshore currents driving island development. Radiocarbon dating suggests that the nucleation and development of South Joulter Cay occurred in stages over the last 1400 years. Island development started with linear ridges oriented SE-NW and extending approximately 2 km, and this was followed by a second stage of arcuate ridges influenced by local tidal channels. The third stage consisted of triangular cuspate ridges driven by longshore currents and bidirectional winds and waves. Storm activity and associated shifts in local hydrodynamics appear to have played an important role in forming the initial ridges and those created during transitions between growth stages. Although a single storm event is unlikely to cause lasting changes, prolonged periods of intense storm activity over decades are more probably to drive the island's changes and development. Periods with elevated hurricane activity in the northern Bahamas during the Medieval Climate Anomaly or Little Ice Age may be a possible control on the punctuated development of South Joulter Cay.

The Toarcian stage of the Early Jurassic witnessed warm global temperatures, oceanic anoxia (Toarcian Oceanic Anoxic Events) and extensive deposition of organic-rich black shales. While black shale deposition in the Southwest German Basin on the Northwest Tethyan shelf has been well-studied, the palaeodepositional conditions in the Northwest German Basin remain poorly constrained. The present study aims to bridge that gap by examining a completely cored well covering Upper Pliensbachian to Upper Toarcian sediments in the Hils Syncline. Inorganic and organic geochemical, as well as biostratigraphic information, carbon isotope and organic petrological results are interpreted to reconstruct depositional conditions and organic matter accumulation in a shallow Jurassic Sea. The study results demonstrate a Late Pliensbachian regression leading to the deposition of claystone in shallow water under humid conditions with a high terrigenous and freshwater influx, and well-oxygenated bottom water environments. A transgression in the Early Toarcian initiated the deposition of laminated and organic matter-rich calcareous black shale, the so-called Posidonia Shale. This climatic shift caused deepening of the water column, resulting in salinity stratification and bottom water anoxia that favoured organic matter preservation. Black shale deposition was probably triggered by low oxygen solubility in warm waters and intensified monsoonal rainfall. The lowermost part of the Posidonia Shale (basal Unit I) represents the time of most intense carbonate deposition and strictly anoxic bottom water. The middle part (Unit II) is characterised by periodical, short-term oxygenation of the sea floor, while the thick upper part (Unit III) represents a time of re-establishment of anoxic conditions. In the Late Toarcian and Aalenian, bottom water reoxygenation marked the deposition of claystones with moderate contents of marine organic matter, above a decimetre-thick breccia. The Hunzen section thus offers detailed insights into late Early to Middle Jurassic palaeodepositional changes in central Europe.

Integrating sedimentological and ichnological data from the uppermost unit of the Mobarak Formation (early Viséan, Northern Iran), deposited in a distally steepened ramp, provides insights into deep-water muddy gravity flows in mud-rich slope settings. The succession is characterised by mudstones formed from hemipelagic suspension settling and diluted, muddy calciturbidite currents, hosting four ichnocoenoses: Chondrites-Trichichnus (Cho-Tr), Phycosiphon-Planolites (Ph-Pl), large Nereites-Zoophycos (Ne-Zo) and Thalassinoides-Zoophycos (Th-Zo). Basin-floor mudstones exhibit low bioturbation intensity, small trace fossils and patchy distributions, with abundant opportunistic chemosymbionts (Chondrites and Trichichnus), alongside pyritised burrows. Slope mudstones show higher bioturbation intensity, larger burrows and greater ichnodiversity due to diluted calciturbidite currents, increased oxygen levels and nutrient input. Critically, hemipelagic processes remain ecologically decisive on slopes (40%–60% hemipelagic facies), evidenced by: (1) Cho-Tr traces in hemipelagic interbeds confirming sustained suspension settling; (2) vertically accreting mudstones homogenising substrates and suppressing Nereites and graphoglyptids; and (3) background redox conditions shaping tiering patterns, with turbidites causing only temporary perturbations. This explains the ubiquity of the Zoophycos ichnofacies and absence of Nereites ichnofacies across all settings. Slope deposits display a higher ratio of shallow-tier deposit-feeding traces (Phycosiphon, Nereites) to deep-tier traces (Zoophycos, Thalassinoides), reflecting better oxygenation and nutrient availability. The absence of graphoglyptids and other Nereites ichnofacies indicators stems directly from persistent hemipelagic sedimentation and high sediment homogeneity disrupting oligotrophic conditions required for farming strategies. The study demonstrates that integrated ichnological-sedimentological criteria effectively distinguish between basin-floor and slope mudstones. Variations in trace fossil assemblages and ichnocoenoses reflect changes in environmental factors such as hydrodynamic regime, oxygen levels, organic content and sedimentation rates, providing a robust framework for interpreting deep-water muddy gravity flows in mud-rich slope-basin settings.

Euendolithic microorganisms, capable of bioerosion in carbonate substrates, play an important role in modern marine ecosystems and have a fossil record extending into deep time. Understanding the factors driving microboring behaviour is essential for interpreting their ecological impact and reconstructing ancient environmental conditions. In this study, we conducted field incubation experiments across multiple sites at Little Ambergris Cay in the Turks and Caicos Islands, examining microboring density in abiotic optical calcite and aragonite under varying conditions of light, subaerial exposure, current energy, substrate mineralogy and trace metal content. We observed sinuous tunnels within 1 week of incubation in transparent calcite, with longer deployment times (2.5–5 months) resulting in meaningful increases in boring density. We also documented boring activity in dark conditions, suggesting potential for enhanced mineral dissolution at night when geochemical conditions are more optimal. Trace metal analysis of our experimental substrates revealed Fe/Ca and Mn/Ca ratios exceeding western Atlantic sea water estimates by 1–3 orders, with calcites more enriched in Mn than aragonites, offering preliminary support for the novel hypothesis that dissolution of CaCO₃ minerals might be a useful source of trace metals for euendoliths. Sea water chemistry varied across sites, particularly between restricted interior and open platform sites. A comparison of boring densities suggests that trace metal abundance, mineralogy, local sea water CaCO₃ mineral saturation state (Ω) and subaerial exposure (e.g. intertidal vs. shallow subtidal) may all influence microboring. These findings offer new perspectives on the euendolithic lifestyle, showing how substrate selection and temporal partitioning of dissolution activity balance metabolic costs with environmental constraints. They also enhance our ability to interpret the fossil record and bioerosion dynamics under changing conditions.

A 300 m thick section at Nini Hill in the proximal foredeep of the Western Canada Foreland Basin is dominated by shallow-marine mudstone that spans the Cenomanian–Turonian boundary (CTB). The section preserves a 185 m thick record of OAE2, characterised by an ornate positive excursion in the organic carbon-isotope profile. Osmium-isotopes show the characteristic shift to unradiogenic ratios 21 m below the onset of OAE2. Carbon-isotope events (CIE) at Nini Hill are correlated with both the Chalk reference section at Eastbourne, UK and the well-dated SH#1 core in Utah, the latter permitting correlation to other sections in the southern USA. However, only the ~450 m thick, deep-water CTB section in the Saku Formation, Japan, appears to match the CIE detail at Nini Hill. High-resolution correlation utilising CIEs allows, for the first time, sea-level changes, mapped in the poorly fossiliferous strata of Western Canada, to be correlated with coeval events in the USA and Europe. The globally-recognised sub-plenus unconformity that underlies OAE2 in many passive-margin sections spanning the North Atlantic region is correlative with up to six high-frequency sequences preserved in the highly expanded foredeep. Various studies have inferred sea-level change of 10–40 m for this event, suggesting that thermo- and aquifer-eustasy may have been supplemented by glacio-eustasy. Other sea-level changes of ~10–30 m recognised in Canada correlate with coeval events in the USA and Europe. Lower-amplitude sea-level cycles of ~5–10 m, form a persistent signal throughout the Canadian CTB interval. Strata thin dramatically from foredeep to forebulge due to condensation and lap out, hiatuses being represented by cryptic mud-on-mud disconformities. Without knowledge of physical stratigraphy, interpretation of carbon- and osmium-isotope profiles in attenuated successions is prone to misinterpretation. Osmium data show that the influence of a large igneous province diminished markedly northward within the Western Interior Seaway.

Mixed arenites are widespread in the Quaternary record of the peri-Mediterranean region where they accumulated in a variety of marginal-marine depositional environments. In this study, Early Pleistocene mixed arenites and their associated conglomerates and sandstones were studied in detail near the town of Cataforio, in Calabria, southern Italy. Sedimentological logging, facies and palaeocurrent analyses and characterisation of trace and body fossils were combined with the interpretation of drone-derived panoramic photographs and orthomosaics. Three major units, with the upper two separated by a major erosional surface, and a total of seven sedimentary facies were recognised. The basal Unit 0 is found near the fault bounding the basin to the east and consists of at least several decametres of conglomerates and sandstones (Facies S1). Unit 1 is up to 45-m thick and consists of fossiliferous mixed arenites (Facies M1–4), whereas Unit 2 is at least 30-m thick and mainly consists of conglomerates and sandstones (Facies S2–3). The mixed arenites of Unit 1 show single cross-beds up to several metres thick and with a predominant dip direction to the west; these are intercalated with plane-parallel-bedded facies. The cross-bedded deposits also show complex architectures up to 6-m thick and hundreds of metres long interpreted as compound dunes. They are inferred to have formed in a strait environment, although this probably had more complex geometries and dynamics than previously suggested by other authors and other alternative hypotheses were also considered in this study. The siliciclastic-dominated deposits of Unit 0 and Unit 2 were interpreted to have formed at the base of scarps and in submarine canyons, respectively. This study suggests that the inferred palaeo-strait was not necessarily a wider and similarly oriented expression of the modern Strait of Messina. We advocate that straits and similar systems show a high level of spatio-temporal complexity that should be investigated in detail.

Chile's west coast is frequently struck by megathrust earthquakes and tsunamis, as illustrated by the CE 2010 Maule (M_w 8.8) and CE 1960 Valdivia (M_w 9.5) events. Despite numerous palaeoseismic and palaeotsunami studies, uncertainties remain regarding the rupture extent and tsunamigenic potential of M_w 8–9 earthquakes. This study examines the sedimentary record of Laguna Gemela West, a coastal lake at 5–6 m a.s.l. and of 17.5 m depth. It is separated from the Pacific by a 400 m long channel bordered by northward-propagating dunes and controlled by Pleistocene sandstones forming a knickpoint in the channel profile. Multiple sedimentary proxies (e.g. grain-size, X-CT, XRF scanning) identified five distinct sand-enriched layers, interpreted as tsunami deposits. Age-depth modelling (based on 137Cs and 14C) allowed linking these deposits to the CE 2010, 1960, 1837, 1737 and 1575 megathrust earthquakes. While historical records confirm significant tsunamis in CE 2010, 1960, 1837 and 1575, no reports exist for a CE 1737 tsunami. However, a potential tsunami deposit and evidence for subsidence were found at the nearby Chaihuín site, albeit with large dating uncertainty (CE 1600–1820). The more precise age for a sand layer at Laguna Gemela West (CE 1672–1746) supports the occurrence of a local tsunami in CE 1737. Additionally, deposits linked to the CE 1837 and 2010 events suggest tsunamis can impact sites >100 km adjacent to megathrust ruptures. A second pulse in the uppermost sand layer may reflect the CE 2011 Japan tsunami, which reached a similar height (~1.6 m a.s.l.) in the nearest tide gauge as the CE 2010 tsunami. Unlike coastal plain sites, which often require coseismic subsidence for deposit preservation, coastal lakes can capture a more complete tsunami history. This study highlights their complementary role in palaeotsunami research, providing insights in local, regional and transoceanic tsunami events.