Depositional Record最新文献

The lacustrine Gördes Supradetachment Basin developed along the Simav Detachment Fault during the Early–Middle Miocene postorogenic extension in the north of the Menderes Massif in western Anatolia. The basin-fill consists of alluvial fan, Gilbert-type delta, shoal-water delta, foreshore, shoreface, offshore-transition and peat-forming mire deposits. The alluvial fans and fan deltas deposited along all the margins serve as sensitive recorders of tectonic, climatic, and base-level variations. Process-based facies analyses of the alluvial fan and fan-delta deposits provide an excellent opportunity to reconstruct the palaeogeographical evolution. The alluvial fans consist of braided channel-fill, hyperconcentrated flow and debris flow facies, indicating high-energy sediment transport mechanisms. Progradational wedges of Gilbert-type fan deltas formed atop the alluvial fans reflect a rapid rise in lake level. This rise resulted from asymmetrical subsidence of the basin floor, which shifted the water mass laterally, causing rapid regression on one coast and coeval transgression on the other. Changes in basin floor configuration in the Gördes Basin were driven by movement of the Simav Detachment Fault on the southern margin, while the hanging wall was segmented by an antithetic normal fault on the northwestern margin. Consequently, faulting on both sides increased the depth of the accommodation through a sudden lake level rise. Climate controlled both the lake water budget and the catchment sediment yield. The subsidence rate subsequently decelerated, sediment yield decreased and shallow lake conditions prevailed on the NW margin, as evidenced by the shoal-water deltas. This occurred due to tectonic activity insufficient to produce the large-scale deepening required for Gilbert-type delta development. Finally, the clastic components of the offshore transition facies diminished as the carbonate content increased towards the basin's interior and in the upper parts of the succession during the maximum lake expansion.

The last interglacial (LIG) is the last time global climate was about as warm as today, with global sea-levels several metres higher. The LIG probably had a reduced latitudinal temperature gradient, with warmer poles and cooler tropics than today. Well-constrained records from low latitudes can test this overall model. We used bivalve shells sampled from six localities thought to expose the LIG age Cockburn Town Member of the Grotto Beach Formation on both San Salvador and Great Inagua Islands, The Bahamas. Previous work described two LIG depositional intervals: older ‘Reef I’ and younger ‘Reef II’, separated by a disconformity. New amino acid racemisation (AAR) data were used to date each locality in this context and clumped isotope palaeothermometry was used to reconstruct LIG temperatures and the isotopic composition of sea water. AAR data are described from six sites: four with similar AAR values to the well-dated Reef II Cockburn Town site, one Reef I age site on Great Inagua and one distinctly younger outcrop on San Salvador previously thought to be LIG age that may be MIS 5a. All LIG shells record cooler than modern conditions. The Δ₄₇ thermometry shows that the Reef I-age shell population preserves the warmest mean temperature (25 ± 2°C) and most positive water δ¹⁸O values (+0.7 ± 0.4‰) across all sites. This contrasts with cool mean temperatures (~21–23°C) and fresher water δ¹⁸O values (−0.5 to +0.6‰) found from Reef II populations. Regional glacial isostatic adjustment through the LIG would have resulted in peak sea levels that post-dated peak LIG temperatures. It is suggested that apparent cooler temperatures of Reef II do not reflect peak LIG temperatures but instead document the beginning of cooling into MIS 5d. Comparison with Δ₄₇ data from Bermuda supports a reduced latitudinal gradient throughout the LIG.

The Eocene Epoch is characterised by multiple hyperthermals, which promoted extensive carbonate sediment deposition and dolomitisation, particularly across the Arabian Plate. The Dammam Formation, a key Eocene aquifer and hydrocarbon-bearing unit in the Arabian platform, is extensively dolomitised. Several models have been proposed to explain its dolomitisation, many of which invoke sea water or its derivatives as the dolomitising fluid. However, the specific sea water-driven mechanisms remain poorly understood. More broadly, the effectiveness of commonly used diagenetic proxies (e.g. stable isotopes, stoichiometry and trace elements) in distinguishing between closely related sea water-driven dolomitisation processes has not been systematically assessed. This study addresses these issues by integrating petrographic, mineralogical, chemical and stable isotopic (δ¹³C and δ¹⁸O) analyses of a shallow subsurface core from the Dammam Formation. Two distinct dolomite types were identified: Type I (TI), predominantly subhedral and Type II (TII), exhibiting euhedral and subhedral textures. Both types are pervasive, fabric non-selective and non-mimetic. The dolomite pre-dates all other diagenetic processes, such as the formation of palygorskite, calcite, pyrite and stylolite, indicating early, shallow emplacement. Mineralogical data reveal that TI dolomite is near-stoichiometric (51.4 mol%CaCO₃), and well-ordered, while TII is non-stoichiometric (56.3 mol%CaCO₃) and poorly ordered. Trace element concentrations (Fe, Mn, Sr) align with some previously reported sea water dolomites. The δ¹⁸O values (−2.59‰ to 0.95‰) and temperatures (24–40°C) suggest formation within Eocene marine conditions, with potential evidence of warmer fluids or recrystallisation. The δ¹³C values (0.89–1.83‰) indicate buffering during dolomitisation, consistent with Eocene sea water. Contrary to previous interpretations suggesting sabkha mixing or evaporated sea water, this study proposes that the Saudi Dammam dolomite formed primarily through normal-to-mesohaline sea water dolomitisation, driven most probably by reflux of mesohaline fluids. This study adds to the understanding of sea water-driven dolomitisation, emphasising that recrystallisation can make distinction between mesohaline reflux and syn-depositional sea water-driven mechanism, in shallow marine dolomitised carbonates, challenging.

Marine whitings are enigmatic phenomena characterised by milky water plumes rich in suspended aragonite needles, believed to contribute significantly to mud deposition in ancient carbonate systems. Their formation remains debated, with mechanisms including chemical precipitation due to oversaturation, sediment resuspension or carbonate sand abrasion. This study presents the first report of whitings in the Red Sea, specifically in the southern outer lagoon of Al Wajh Lagoon. Using PlanetScope satellite imagery, in situ loggers (temperature, pH, currents), sea water chemistry, CTD profiles, sediment and SEM analyses, we identified 21 whiting events between June 2021 and November 2022. The largest whiting, in December 2021, covered 51 km². All whitings were preceded by westerly winds (>5.4 m s⁻¹), sudden deep-lagoon temperature anomalies (up to 1.7°C) and strong inflow currents (up to 0.6 m s⁻¹). During a September 2022 event, pH remained constant (~8.35) for several days, disrupting typical diurnal cycles. Surface waters showed aragonite oversaturation. Sediment analyses revealed in the lagoon a 16 km² mud hotspot, enriched in aragonite needles (>80% in weight content). The prolonged duration of whitings of up to 12 days without sustained wind or wave action suggests they are not caused by sediment resuspension. Instead, anomalous pH behaviour supports a chemical precipitation origin. We propose that strong, short-lived westerly winds drive dense offshore or shallow rim sill waters into the stratified lagoon, with whitings occurring twice as often in fall/winter as in spring/summer. In fall/winter, cooling creates high-density waters in the shallows; in spring/summer, high density is created by high salinity due to strong evaporation. The cascading dense waters disrupt stratification, bringing nutrient-rich deep waters to the surface and triggering phytoplankton blooms. Resulting CO₂ drawdown raises alkalinity, which is balanced by CaCO₃ precipitation in surface waters. This study offers new insights into whiting formation and carbonate mud production in restricted tropical platforms.

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.