Depositional Record最新文献

The interplay between microbial activity and mineral precipitation in extreme environments plays a critical role in shaping sedimentary textures and influencing biosignature preservation. This study explores coupled Mg silicate and carbonate precipitation in the marginal lakes of the Salar de Atacama, Northern Chile, expanding previous findings from the Salar de Llamara. Using field samples from the Aguas de Quelana and Soncor sectors, sedimentary deposits classified as sediments, unlithified microbial mats and lithified microbial buildups are each characterised by distinct microbial architectures and mineralisation processes. Detailed analyses conducted via scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-ray diffraction identified minerals and mineral associations and revealed pathways of coupled Mg silicate–carbonate precipitation. Results indicate that organic matter production is followed by precipitation of amorphous to nanocrystalline Mg silicate. Aragonite then templates on and replaces Mg silicate and infills voids. Dense microbial colonies within high-viscosity extracellular polymeric substances (EPS) promote precipitation of welded Mg silicate (W-MS), conferring structural stability, while loosely organised EPS networks result in porous deposits of granular sediments. W-MS serves as a scaffolding that enhances preservation of morphological biosignatures. Overall, sedimentary product diversity reflects variations in microbial density and EPS organisation, suggesting that variations in initial microbial colony distribution and EPS determine the eventual sedimentary product. Our results also highlight the role of Mg silicate–carbonate precipitation in the formation of grainy sediments, expanding prior work on Mg silicate–carbonate coupling forming microbialites and unlithified microbial mats in the Atacama Desert. The data set presented here provides a robust analogue for interpreting ancient sedimentary systems and emphasises the significance of microbe–mineral interactions forming Mg silicate–carbonate deposits in extreme environments.

We examine the depositional dynamics and paleoclimatic significance of the evaporite–dolomite association in Laguna Fuente de Piedra (LFP), a modern saline, endorheic playa lake system in southern Spain. This study presents results from a multidisciplinary approach, examining the two longest continuous sediment cores retrieved from the basin. One core was drilled in the Salina area, located in the eastern part of the basin, which represents the zone that dries last and is referred to as the Salina core (14.4 m). The second core, Las Latas (46.2 m), was retrieved from the southwestern part of the basin, which is the zone that dries first. This study characterises carbonate minerals and their precipitation mechanism in the sediments from these two cores over the past ~50,000 years. Six major lithofacies were identified based on variations in mineralogy (carbonates, sulphates and siliciclastic minerals) and sedimentary patterns. Observed shifts in the depositional environment are hypothesised to result from changes in the hydrological balance, which in turn is controlled by paleoclimatic evolution. During dry and cold periods, the basin experienced higher evaporation rates, leading to the deposition of evaporites along with dolomite in a continental sabkha environment with ephemeral floods. These arid conditions favoured large production of endogenic sulphates and carbonates (dolomite) and reduced clastic input. In contrast, wetter periods were characterised by increased clastic influx and the precipitation of calcite–aragonite facies, in a shallow ephemeral to permanent lake, mostly during the Pleistocene–Holocene transition, continuing into the Holocene. These findings show the high sensitivity of shallow continental sedimentary systems to climate variations and provide information on significant short-lived climatic events, tentatively correlated with Heinrich events, in the western Mediterranean region.

This study investigates the formation mechanisms of anthropogenic tufa deposits resulting from the chemical breakdown of legacy paper mill sludge (PMS) at the former Dalmore Paper Mill site in Auchendinny, Scotland. Tufa, a form of calcium carbonate (CaCO₃), typically forms in natural freshwater environments; however, this research explores its precipitation through interactions between alkaline industrial waste (PMS) and atmospheric CO₂. Field and laboratory analyses were carried out to assess the geochemical characteristics of the stream water, as well as the mineralogical and isotopic composition of the associated tufa deposits. X-ray diffraction (XRD) analysis revealed that PMS is composed predominantly of calcite, while tufa samples also contain minor amounts of quartz and kaolinite. Stream water measurements indicated alkaline conditions (pH 8.27–8.98) and elevated calcium concentrations, with calcite saturation indices suggesting conditions favourable for carbonate precipitation. Stable isotope analysis of tufa deposits (δ¹³C −24.62‰ to −13.74‰; δ¹⁸O −17.50‰ to −7.66‰) revealed a dominant contribution from atmospheric CO₂, confirming a precipitation mechanism driven by CO₂ ingassing and hydroxylation reactions. The results support a model where rainwater infiltrates PMS heaps, leaching calcium into stream waters. As these calcium-rich waters mix with atmospheric CO₂, supersaturation occurs, leading to rapid calcite precipitation. The resulting tufa deposits exhibit laminated structures and high porosity, indicating episodic deposition under variable geochemical conditions. This study provides the first detailed evidence of tufa formation from PMS and suggests that such industrial waste materials can act as carbon sinks, capturing and mineralising atmospheric CO₂. These findings expand the understanding of anthropogenic carbonate systems and highlight the potential of PMS as a low-cost material for environmental remediation and carbon sequestration, supporting sustainable waste management strategies and contributing to climate mitigation goals.

Shales play a crucial role in the global carbon cycle through organic matter accumulation and hydrocarbon generation. However, the influence of organoclay interaction on organic matter enrichment and hydrocarbon generation remains unclear. To address this, PY-GC/MS, along with a series of experiments, was employed to investigate the Ed₃-Es₁ Formation in the Nanpu Sag. Organic matter in the shales occurs in two forms: mineral-bound organic matter and free organic matter. Mineral-bound organic matter, chemically bound to clay minerals, is primarily derived from aquatic organic matter. Free organic matter, physically associated with minerals, mainly originates from terrestrial plants. The organic matter in the source rocks from the Nanpu Sag varies in occurrence between units. In Es₁, it is primarily composed of mineral-bound organic matter, whereas in Ed₃, it consists of both mineral-bound organic matter and free organic matter. The diversity was the result of the combined influences of sedimentary environment, mineral input, and organic matter source. The deep palaeo-lake during Es₁ deposition, characterised by moderately high salinity and low-energy hydrodynamic conditions, promoted the development of aquatic organic matter and the input of fine-grained minerals, thereby facilitating the formation of mineral-bound organic matter. The shallow palaeo-lake during Ed₃ deposition, characterised by relatively low salinity and strong hydrodynamic conditions, experienced a substantial input of terrestrial detrital minerals and plant fragments, resulting in the abundant presence of free organic matter in the shales. Furthermore, the hydrocarbons produced from the different units exhibit significant variation in yield and composition. Above all, source rock assessment should take organoclay interactions into account. This research can also enhance the understanding of the influence of lacustrine sediment on the global carbon cycle.

Tepee structures are upward-buckling fracture rims that form a reticulated network of polygonal boundaries when viewed from an aerial perspective. These structures are thought to result from crystallisation forces of cement, causing lateral expansion of consolidating sedimentary materials. Tepee structures are indicative of subaerial exposure and can serve as stratigraphic markers in ancient carbonate sequences. While tepee structures are common in ancient carbonate sequences, in modern settings, they have only been described in the Arabian Gulf. The discovery of fields of polygonal structures, on satellite images of the Red Sea Island of Sheybarah, Saudi Arabia, motivated the authors to assess their genesis and distribution in Arabia. The objectives are to describe in detail tepees and their arrangement in polygonal patterns, investigate the timing of their formation and constrain the relative timing of tepee generation. Furthermore, this study investigates, based on a detailed satellite image survey, whether similar polygonal features can be identified around the Arabian Peninsula. The polygonal crusts on Sheybarah Island are found in intertidal to supratidal settings overlying a well-lithified ravinement surface. They are composed of locally derived poorly sorted sand-to-pebble-sized coral, mollusc and foraminifera debris of predominantly aragonite and high Mg-calcite mineralogy with minor admixtures of siliciclastics. Based on petrographic analysis, microbial-induced cement precipitation is the major lithification agent. Lithification occurs in the upper intertidal zone based on the ubiquitous presence of keystone vugs. Radiocarbon (¹⁴C) dates reveal elevation-aligned ages between approximately 1.5 and 3.0 ka BP, allowing the reconstruction of late Holocene minor sea-level changes aligned with major global climate variations. Hence, polygonal tepee structures may serve as proxies for sea-level changes. Of 126 occurrences of polygonal fields identified from satellite images, 89 in the Red Sea are probably composed of polygonal reefs. The authors hypothesise that polygonal coral reefs originated on tepee crust.

Although admired and examined since antiquity, carbonate sediment and rock research really began with Charles Darwin who, during a discovery phase, studied, documented and interpreted their nature in the mid-19th century. The modern discipline, however, really began after World War II and evolved in two distinct phases. Breakthroughs during an advancement phase came about via the numerous studies by many researchers globally on both modern and ancient carbonates that were eventually merged into carbonate sedimentology as a whole in the 1970s. Formulation of the factory concept and integration of recurring facies into facies models solidified the discipline and allowed integration to move ahead. Stromatolites were discovered growing in modern environments and it was realised that the spectrum of diverse fossil structures called reefs also existed in the modern world. Internal reef structure was largely interpreted as ecological. At the same time, development of radiogenic and stable isotopes allowed Pleistocene carbonate stratigraphy and processes to be accurately dated, and precipitates related specific formation waters. Cementation, long postulated as mostly meteoric, was also realised to be a common synsedimentary phenomenon. Breakthroughs during the more recent refinement phase were likewise synthesised into books, but incrementally as the science progressed. Research on the genesis of critical components such as ooids, stromatolites and carbonate muds was at last convincing. The whole new realm of cool-water carbonates was revealed with resulting different interpretations of rock record facies and the critical role of aragonite in diagenesis. Reconciling the relationship between sea water nutrient levels, factory type and taphonomy was a major advancement to interpreting the stratigraphic record. Sequence stratigraphy, coupled with shallow drilling and isotopes, led to progressively more dynamic interpretations, especially of reefs. Use of stable isotopes became more sophisticated, and development of clumped isotopes held out possibilities of even more precise interpretations. Finally, although prediction of a future phase is futile, much more needs to be done on mixed carbonate-siliciclastic systems, and the implications of mixed carbonate ironstone and chert in Precambrian accumulations, especially using new geochemical techniques. Perhaps, philosophically, it is time to use attributes of the exquisite carbonate rock record to tell us about the future of our rapidly changing world.

Gypsum and marls from the 15 cycles of the Messinian Yesares Member in the Sorbas Basin, SE Spain, were analysed using a multi-isotope approach to reconstruct palaeo-hydrological conditions of the basin and the wider Mediterranean region during the deposition of the Primary Lower Gypsum (PLG) of the Messinian Salinity Crisis (MSC) (~5.97–5.60 Ma). By analysing structurally-bound water in sedimentary gypsum (CaSO₄·2H₂O), the past oxygen and hydrogen isotopic composition of waters during evaporite formation is determined. These measurements are combined with water salinity inferred from gypsum fluid inclusions and isotopic analysis of strontium (⁸⁷Sr/⁸⁶Sr), calcium (δ⁴⁴/⁴⁰Ca), sulphur (δ³⁴S) and oxygen of sulphate ($��{\delta }^{18}�O_{{\mathrm{SO}}_4}�$) in the same samples, as well as isotopic analysis (δ⁴⁴/⁴⁰Ca, ⁸⁷Sr/⁸⁶Sr, δ¹⁸O_carb, δ¹³C) of the interbedded carbonate marls. The PLG in the Sorbas Basin did not form solely from the evaporation of seawater but rather precipitated from a hybrid brine consisting of seawater and a significant input of freshwater. The seawater/freshwater ratio changed through time and was influenced by (1) tectonic uplift and basin restriction, (2) obliquity-driven glacial–interglacial sea level changes and (3) precession-driven freshwater influx. A progressive freshwater increase up-section reflects tectonic restriction of the basin, supported by ⁸⁷Sr/⁸⁶Sr trends, which start at seawater values in Cycle 2 and deviate upward. Two minor reversals in ⁸⁷Sr/⁸⁶Sr at ~5.84 and ~5.72 Ma reflect the role of obliquity-controlled sea level and eccentricity-modulated precession. Maximum divergence of ⁸⁷Sr/⁸⁶Sr from the seawater curve, as well as precipitation of authigenic dolomite with high δ¹⁸O_carb, represent a temporary regime change to a freshwater-dominated system coincident with the strongest glacial stages (Marine Isotope Stage TG20) and an eccentricity minimum at ~5.75 Ma. A gradual tectonic restriction of the Atlantic connection, superimposed on orbitally controlled glacio-eustatic (obliquity-dominated) and freshwater input (precession-dominated) changes, led to gypsum-marl deposition in Mediterranean marginal basins during the early MSC.

Özyurt, M. (2025) Trace elements, rare earth elements and isotopes of poorly preserved fossils from lower Cretaceous carbonates (Eastern Black Sea): Implications for early diagenetic alteration. The Depositional Record, 11, 1107–1131. Available from: 10.1002/dep2.70026

In the Methodology section, the electron microprobe analyses were performed at LMU Munich, not at the University of Hamburg. The electron beam current was 2 nA, not 20 nA, and the electron beam size was 5 μm, not 10 μm.

In the Acknowledgements section, the correct institutional affiliation for Dr. Dirk Müller, who provided help with the electron microprobe analyses, is LMU Munich, not the University of Hamburg.

The author apologises for these errors.

The fate of sediment-laden density flows is strongly controlled by the density contrast between the flow and the basin fluid, which fundamentally influences the character of the sedimentary deposit. However, differentiating the deposits of hyperpycnal and hypopycnal flows, in addition to slope-failure-related turbidity currents, remains a source of debate. In part, this can be attributed to the difficulty in determining the density of the fluid in an ancient depositional basin. In this study of a nearly modern succession of fine-grained (silt-clay) glaciogenic deposits, basin fluid conditions are well-constrained and the sedimentological make-up of these sediments was determined using X-ray computed tomography and microscopy. Deposits of bottom-hugging hyperpycnal flows consist of a distinctive alternating pattern of silt-rich and clay-rich laminae attributed to the rhythmic alternation of shear thinning and shear thickening processes in the mm- to sub-mm-thick, non-Newtonian very-near-bed region. A similar pattern is observed in fine-grained turbidites, suggesting similarity in depositional mechanism. This similarity suggests that differentiating the deposits of fine-grained hyperpycnal flows from turbidity currents based solely on physical stratal attributes is challenging. Alternatively, hypopycnal flows form buoyant plumes from which sediment settles, spawning bottom-hugging secondary turbidity currents. In these flows, insufficient sediment concentration and shear stress prevent shear thinning and shear thickening processes from operating, and instead, entropic Brownian fluid motion results in an unstratified deposit with a disorganised fabric. Additionally, these strata contain irregularly spaced, well-sorted silt lenses that range from a single silt grain to a few silt grains thick and record outer flow disturbances that reworked the previously deposited silt and clay. Whereas differentiating fine-grained hypopycnal flow deposits from hyperpycnal flows or turbidity currents may be straightforward, differentiating them from pure suspension fallout would appear to rely on the recognition of the thin, well-sorted silt lenses indicating advection rather than pure particle settling.

Worldwide, reefs are under significant pressure, and hence, understanding the consequences of natural and anthropogenically driven sediment influx to reef systems is crucial to planning future protection strategies. Most reef systems are associated with clear water settings, but reefs also evolved in turbid water environments stressed by high rates of sediment influx. Mixed carbonate–clastic environments have been considered unfavourable to reef-building organisms. Currently, we lack generally applicable models for (i) reef growth under the stress of siliciclastic sediment influx and (ii) tools that diagnose ancient reefs that developed in sediment-stressed environments. Case studies of sediment-stressed reefs from the Devonian to the recent reviewed here demonstrate that reef organisms show the ability to survive, and even thrive, under clastic sediment influx. These case studies were selected based on (i) the presence of a mixed carbonate-clastic matrix and (ii) the existence of a coral framework. For each example, the system was characterised in terms of sediment input, organism growth forms and the overall reef architecture. The host sediment from Cenozoic reefs is typically better described than that within Palaeozoic and Mesozoic communities. This may be due to the closer affinity between Cenozoic communities and recent species compared to more ancient systems. The same reasoning accounts for the paucity of data describing the internal structure of many fossil reefs, a feature also related to outcrop quality. Moreover, the juxtaposition of siliciclastic interbeds and ancient reefal bodies should not be taken as conclusive evidence that clastic influx was contemporaneous with the active growth stages of the framework organisms. Based on the data reviewed here, no relationship was identified between the nature of the reef builders, the character of the siliciclastic component and the reef structure. We suggest that this lack of understanding of mixed carbonate-clastic reef systems significantly compromises potential forecasts of future reef development.