Recent Carbonate Sediments Research Articles

Evolution of shallow post-bog soils developed on Holocene carbonate sediments in NW Poland

Evolution of shallow post-bog soils developed on Holocene carbonate sediments in NW Poland

Cadmium isotope systematics in sedimentary carbonate: Extending the utility of the cadmium isotope palaeo-productivity proxy

The cadmium (Cd) isotope compositions of seven Holocene (<11.7 ka) carbonate sediments, including the bulk carbonate, as well as the > 140 μm (zooplankton), <63 μm and < 20 μm (phytoplankton) fractions, and individual species of foraminifera isolated from the bulk carbonate were obtained for sub-samples processed using the Cd-cleaning and Mg/Ca cleaning methods. The respective Cd isotope systematics of each carbonate archive were then compared with the Cd isotope signature within the ocean using modern seawater data. We show that a constant Cd isotope fractionation factor of −0.25 ± 0.03 ‰ (2SE, n = 4) describes the partitioning of Cd from seawater into the carbonate phase (Δ114CdCdCO3-seawater), allowing for accurate reconstructions of the past seawater nutrient regime. The Cd isotope signature of the < 63 µm and < 20 µm (phytoplankton) fractions can display comparable values to those recorded in the modern surface ocean, and can be used to model the magnitude of Cd uptake and utilisation in the past ocean. Individual species of planktic and benthic foraminifera, which inhabit different depths of the water column, can provide a full surface to deep water column reconstruction of the Cd nutrient regime, while infaunal benthic foraminifera can be used to interrogate the Cd isotope systematics of sediment porewaters. Bulk sediment and the > 140 µm (zooplankton) fraction also retain important information relating to the overlying water column Cd isotope systematics and can serve as essential archives for palaeo-productivity reconstructions where the separation of individual components from the bulk sediment is not possible. This new Cd isotope palaeo-productivity toolkit can considerably aid reconstruction efforts and vastly improves the ability to quantify the role of phytoplankton in modulating carbon sequestration through transitions in Earth’s climate evolution.

Evolution of Shallow Post-Bog Soils Developed on Holocene Carbonate Sediments in Nw Poland

Evolution of Shallow Post-Bog Soils Developed on Holocene Carbonate Sediments in Nw Poland

Environmental controls on the Late Holocene carbonate sedimentation of a karstic lake in the Middle‐Atlas Mountains (Lake Afourgagh, Morocco)

AbstractThe Lake Afourgagh sediment record and facies successions provide an outstanding example of environmentally controlled carbonate sedimentation. Afourgagh is a small, shallow permanent lake located in the Middle‐Atlas Mountains in Morocco in a karstic context. It is fed by ground waters that are relatively enriched in Mg resulting from the leaching of the Jurassic dolomitic bedrock of the catchment. This eutrophic lake is episodically restricted and characterized by alkaline waters with a fluctuating high Mg/Ca ratio. The maximum extension of the Holocene shoreline coincides with evidence of a lake stabilization level corresponding to the outflow of the lake through a wadi. Lakeshore terrace sediments deposited on an alluvial fan siltstone during the past ca 2500 cal yr bp comprise four main facies: a littoral crust, palaeosols, palustrine silts and charophyte tufas, which reflect different environments from the shoreline toward the deeper water. In the more distal parts, the charophyte tufas display a well‐expressed lamination punctuated by the development of microstromatolites on algae thalli. The mineralogical composition of the carbonates is linked to the facies. While the charophyte tufas are characterized by a relatively high content in aragonite, in addition to low‐Mg calcite, the littoral crust is mainly composed of magnesite. This pattern is related to the evolving chemistry of water due to the influence of charophyte proliferation during dry summers. Calcium‐carbonate precipitation on algae thalli (both bioinduced and microbially mediated) progressively induces an increase in the Mg/Ca ratio of the lake water, while the capillary evaporation of shallow ground waters causes precipitation of a magnesite precursor on the shoreline, producing magnesite during early diagenesis. This effect is characteristic of two episodes: part of the Roman Warm Period and the beginning of the Dark Age Cold Period. The carbonate mineralogy of the different depositional sequences at Afourgagh indicates lake‐level and water‐chemistry fluctuations under a climatic influence. Therefore, among other regional records, the Lake Afourgagh sedimentary record provides useful evidence for reconstructing these environmental changes.

The Effect of Climate on the Chemical Composition of the Coral Reefs around Kubbar Island—Kuwait

Thick recent carbonate sediments cover all the intertidal and subtidal zones consist of mainly different shell and coral reef debris. The chemical investigations of the coral fragments were done on controlled bases, which depend on the coral size and seasons, in order to elucidate the effect of weather parameters on the coral reefs. Geochemical investigation indicated that corals gathered from high-tide mark are mainly contaminated by copper, cobalt, and chromium and the corals gathered from low-tide mark are contaminated by lead and zinc. All the analyzed coral samples are contaminated by copper. The major contamination sights by heavy metals are related to the weather pattern around the islands. Calcium concentration in all the corals indicates a low-Magnesium calcite or aragonite composition, except for some coral samples which were gathered during October from the high-tide mark. Trace element concentration levels show high concentrations at sights of low-wave action around the island during the various seasons. Chemical analysis on the coral derbies indicates compositional variations regarding calcium and magnesium mole% between the seasons and at different locations and it is dependant on wind direction and water salinity. Some localities are iron rich others are aluminum and potassium rich. Generally, aluminum, iron, and potassium occur in lower quantities than the other elements. Therefore, all the chemical data regarding trace elements indicate relationship to weather and environmental parameters.

Reconstruction of the Holocene climate based on a carbonate sedimentary record from shallow saline Lake Verkhnee Beloe (western Transbaikalia)

We present results of mineralogical and crystallochemical studies of the Holocene carbonate sediments of a small saline lake localized in the Borgoi dry-steppe region, western Transbaikalia. Mg-calcites with a varying Mg content are predominant in the assemblage of endogenic carbonate minerals from bottom sediments. Mathematical modeling of the XRD spectra of carbonates permitted us to identify excess-Ca dolomites, which are an indicator of a shallow (playa) lake. The studies showed that the lacustrine Mg-calcites do not form a continuous series from low- to high-Mg varieties. We discuss the cause of this phenomenon and also consider the existing viewpoints of the structure of low-temperature Mg-calcites and excess-Ca dolomites and their formation conditions in lacustrine sediments. Juxtaposing the carbonate record with the data of lithological analysis, determined stable isotopes (δ18O and δ13C), and distribution of some geochemical indicators of climatic changes, we reconstructed the intricate evolution of Lake Verkhnee Beloe, which was controlled by the regional climate since the postglacial period till the present day.

Fish as major carbonate mud producers and missing components of the tropical carbonate factory

Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts ("low" and "high" Mg-calcite and aragonite), but that very fine-grained (mostly < 2 μm) high Mg-calcite crystallites (i.e., > 4 mole % MgCO(3)) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce ∼6.1 × 10(6) kg CaCO(3)/year across the Bahamian archipelago, all as mud-grade (the < 63 μm fraction) carbonate and thus as a potential sediment constituent. Estimated contributions from fish to total carbonate mud production average ∼14% overall, and exceed 70% in specific habitats. Critically, we also document the widespread presence of these distinctive fish-derived carbonates in the finest sediment fractions from all habitat types in the Bahamas, demonstrating that these carbonates have direct relevance to contemporary carbonate sediment budgets. Fish thus represent a hitherto unrecognized but significant source of fine-grained carbonate sediment, the discovery of which has direct application to the conceptual ideas of how marine carbonate factories function both today and in the past.

Contribution of black carbon in recent sediments of the Gulf of Cadiz: Applicability of different quantification methodologies

In the Southwestern Iberian Peninsula, vegetation fires are rather common, and produce a considerable amount of charred material that, due to erosion, is fluvially transported to the continental margins. The present study constitutes the first comparative assessment of the contribution of this charred material (generally black carbon, BC) to marine sediments of the inner continental shelf of the Gulf of Cádiz (GoC). Given the ambiguity of BC definition and the heterogeneity of quantification techniques, four of the most common and well established methodologies were applied to obtain a representative range of the BC content on four surface sediments: chemical-thermal oxidation (GBC), molecular markers (benzenopolycarboxylic acids, BPCA), thermogravimetry coupled to mass spectrometry (TG-DSC-QMS), and chemical oxidation with sodium chlorite. The BC results obtained for the GoC sediments are compared, and the applicability of each technique on marine sediments is discussed. The mean BC values of the four methods (4.4–14.4% total organic carbon) were within ranges previously reported for marine sediments from diverse origins. However, a large variability was observed within individual samples when comparing the BC results obtained with the four methods (relative standard deviation from 31% to 75%). The BPCA approach produced the highest BC values, whereas the GBC method the lowest. This reflects the analytical variability derived from the different windows composing the BC continuum. The results derived from the TG-DSC-QMS application generated certain uncertainties, despite the correction factor introduced to reduce the BC overestimation previously reported for this method. Considerable differences in the BC content of spatially close samples evidenced the complexity of coastal currents and sediment fluxes in the area, suggesting the existence of other factors affecting the BC distribution. The lack of correlation between the BC and TOC, as well as between the BC and lignin contents in all samples, ruled out the occurrence of charring artifacts. Preferential degradation and/or erosion of BC could explain the BC distribution in the area. The use of ancillary terrigenous biomarkers (lignin and inorganic silica) pointed to a preferential fluvial transport of the terrestrial organic matter and indicated that the longer distance from the source, the greater degradation of the OM. In addition, the northern dominant winds in the region may have favored the additional introduction of airborne transported BC in the marine system.

Influence of continental fraction in recent biogenic carbonate sedimentation in the oriental shelf of Northeastern Brazil

Influence of continental fraction in recent biogenic carbonate sedimentation in the oriental shelf of Northeastern Brazil

Influence of continental fraction in recent biogenic carbonate sedimentation in the oriental shelf of Northeastern Brazil

The influence of continental sediments on formation of recent marine sediments, has been mineralogically and geochemically studied using shelf-floor whole sediments (WS). The studied area corresponds to the oriental shelf of Northeastern Brazil between the 10 to 80m isobaths, adjacent to a continental area dominated by semi-arid to humid tropical climate. 47 representative samples from the dominating facies in this shelf have been analyzed by X-ray diffraction (XRD) and chemical analisis and results allowed identification of two types of floor sediments of: (a) quartz-terrigenous dominance and (b) carbonate dominance, whose fraction present distinct mineralogical and geochemical characteristics. In the terrigenous facies, that occur from 10 to 25-55m depths, quartz, potassic feldspar and high Mg-calcite predominate, with Sr generally 2,600 ppm. In both cases, low-Mg calcite is absent. Even when the terrigenous fraction is found in accessory amounts (< 3% WS), geochemical signatures, marked by strong intercorrelations SiO2 - Al2O3 - K2O - Rb, exhibit correlation coefficients with r ≥ 0.9, reflecting a continental felsic source. The statistical analyses (co-variation between Mg/Ca and SiO2), chemistry and mineralogy of the sediments indicate that textural and mineralogical nature of the substratum is the main factor controlling the biota (dominantly benthonic in this shelf) and that, in these conditions, quartzous terrigenous facies favor species that are preserved in high Mg-calcite instead of those preserved in aragonite. This tendency showed to be independent of depth of sampling between 10 and 55 m.

The Miocene palaeoenvironmental and palaeoceanographic evolution of the Gippsland Basin, Southeast Australia: a record of Southern Ocean change

The Gippsland Basin in southeastern Australia preserves up to 2.5 km thick Tertiary to Recent marine carbonate sediments included in the Seaspray Group. During the Neogene, the Seaspray Group carbonates of the Mackerel and Flounder petroleum fields lay at the shelfal to bathyal palaeoenvironmental transition, an ideal palaeoceanographic setting to study the Neogene history of events in the evolving Southern Ocean. Seismic, foraminiferal and facies analyses of the Miocene Seaspray Group sediments at the Mackerel-1 and Flounder-1 wells have revealed the following palaeoenvironmental history of the area. Relatively cool to temperate upwelling conditions prevailed in the area during the earliest Miocene. During this time, low energy, upper slope Globigerina ooze (calcareous mudstone) was deposited in the oxygen minimum zone. During the Early to lower Middle Miocene, upper slope marl was deposited in oligotrophic conditions. The presence of neritic subtropical foraminifera and abundant shallow and deep dwelling warm to cool-temperate plankton in the upper slope suggests that warm poorly stratified oceanic conditions prevailed in the region. This upper Early Miocene warm phase and Mid Miocene Climatic Optimum in Gippsland corresponds to a time when global ocean conditions were much warmer and less vertically and latitudinally stratified than at present. These oceanic conditions were associated with a reduced East Antarctic Ice Sheet (a higher sea level), a relatively weak Antarctic Circumpolar Current, and weak atmospheric and wind driven circulation. During the upper Middle Miocene to Late Miocene cool phase (after c. 14.5 Ma) strong upwelling and cooler oceanic conditions prevailed in the outer shelf to upper slope canyon facies in Gippsland. The occurrence of common deep dwelling plankton taxa in this interval suggests that regional oceanic conditions became more vertically stratified during this time. From 14.5 and 5 million years ago, the Middle to Late Miocene palaeoenvironmental change recorded in Seaspray Group sediments corresponds to global cooling and major Antarctic Ice Sheet expansion, when the world's oceans became more vertically and latitudinally stratified. From around 14.5 million years the transition from a warm ‘Miocene Optimum’ to cooler oceanic conditions was associated with a strengthened Antarctic Circumpolar Current and more intense wind driven atmospheric circulation in the Southern Ocean.

The Dolomite Problem Revisited1

A reassessment of the abundance of dolomite in carbonate sediments has confirmed that carbonates deposited during the past 150 Ma contain, on average, less dolomite than Proterozoic and Paleozoic carbonates. The lower dolomite content of the more recent carbonate sediments results from the increase in the deposition of CaCO3 in deep-sea sediments, and to the difficulty of dolomitizing deep-sea CaCO3 by reaction with cold, unevaporated seawater. The decrease in the rate of dolomite formation during the past 150 Ma has led to an increase in the output of oceanic Mg+2 by the reaction of seawater with clay minerals and with ocean-floor basalts. The increase in the output of marine Mg+2 into these reservoirs has been brought about by an increase in the Mg+2 concentration of seawater. During the past 40 Ma, the concentration of Mg+2 in seawater has probably increased by ∼18 mmol/kg, and probably has been accompanied by an equimolar increase in the concentration of SO4−2.

Environmental Controls on Groundwater Chemistry in an Offshore Island Aquifer: Fiesta Key, Florida

A field study was undertaken on the Florida Bay side of Fiesta Key, Florida, to identify the chemical characteristics of a previously unexplored offshore groundwater system and to define the critical parameters affecting groundwater movement and interaction with sediment pore fluids and bedrock. Emphasis was placed on the upper 2 meters of bedrock, where groundwater recharge and discharge potentials are maximized, along a 100 meter transect extending from the island margin. Bedrock cores were used to describe Pleistocene depositional textures, and were sampled at discrete depths to determine the extent of water-rock interaction. Piezometers installed into each core hole were used to monitor surface and ground water tide levels, and for the systematic collection of water samples for a large suite of chemical determinations. Aqueous chemical data indicate that these groundwaters are marine in origin, anoxic, and moderately hypersaline (S = 36–40). Exchange of bedrock pore fluids with overlying Bay waters is restricted by a layer of Holocene sediment and a discontinuous soilstone crust formed at the modern bedrock surface. Groundwater chemistry near the sediment/bedrock interface is marked by elevated concentrations of total alkalinity and Ca2+, and by significant Mg2+ depletion. These waters likely acquired their unusual chemistry by mixing between deeper groundwaters and overlying, early diagenetically altered, sediment porewaters. High alkalinity and calcium concentrations presumably result from the combination of the effects of aerobic metabolism, carbonate dissolution, and sulfate reduction. Mg-depletion most likely resulted from the precipitation of Mg-calcite. These unusual chemistries disappear by 2 m depth in the groundwater system, where Ca2+ and Mg2+ concentrations are similar to those expected for seawater under slightly hypersaline conditions. The Pleistocene bedrock contains low Mg, Sr, F, and P concentrations relative to the overlying unconsolidated Holocene carbonate sediments. This is consistent with the diagenetic recrystallization processes that the bedrock has undergone. Hydraulic conditions favor the net recharge of Florida Bay seawater to the groundwater system, but there are insufficient tide data to identify cyclical water exchange rates or groundwater flow patterns.

Holocene carbonate sedimentation on the west Eucla Shelf, Great Australian Bight: a shaved shelf

The southern continental margin of Australia is a cool-water carbonate sedimentary province located in a high-energy, swell-dominated oceanographic setting. A vibrocore transect of 14C-dated sediments across the centre of the Eucla Shelf is the first record of Holocene shelf deposition in the Great Australian Bight. Much of the seafloor shallower than 70 m water depth, the base of wave abrasion, is bare Cenozoic limestone, in some places encrusted by (?) Late Pleistocene, coral-rich, limestone that is cemented by high-magnesium calcite (12 mole% MgCO 3). The areally extensive, 100 km-wide, hard, bored substrate supports an epibiota of coralline algae, minor bryozoans and soft algae or is covered by patches of Holocene sediment up to 1.5 m thick; generally a basal bivalve lag (< 3 ka) overlain by quartzose-bioclastic palimpsest sand. This pattern of active carbonate production but little accretion on the wave-swept mid- to inner-shelf is similar to that on other parts of the southern Australian continental margin. The term shaved shelf is proposed for this style of carbonate platform, formed by alternating periods of sediment accretion, cementation and erosion. The palimpsest sand is typically rich in bivalves, coralline algae and locally, detrital dolomite. Outer shelf Holocene sediment, below the base of wave abrasion but inboard of the shelf edge, is a metre-thick unit of fine, microbioclastic muddy sand with minor delicate bryozoans overlying a 9–13 ka rhodolith gravel. Some of this outer shelf sediment appears to have been resedimented. The shelf edge is a sandy and rocky seafloor with active bryozoan growth and sediment production. The Holocene sediments are enriched in coralline algal particles and conspicuous large foraminifers (cf. Marginopora) and depleted in bryozoans, as compared to coeval deposits on the Lacepede and Otway shelves off southeastern Australia. These differences are interpreted to reflect warmer waters of the Leeuwin Current and prevalent downwelling in this area as opposed to the general upwelling and colder waters in the east.

Ground‐Water Flow Dynamics and Development Strategies at the Atoll Scale

AbstractOne of the most difficult tasks in hydrogeology is to develop sustainable supplies of potable ground water from small atoll islands. Fresh ground‐water systems within atolls, if they exist at all, are extremely fragile and sensitive to development stresses. In this study, the mathematical model SUTRA was used to examine development alternatives for a two‐phase miscible ground‐water system in a cross section through the Laura area of Majuro Atoll, Marshall Islands. The geological framework modeled for Laura is a multilayered aquifer system in which the primary members are a sequence of moderately permeable Holocene carbonate sediments overlying highly permeable Pleistocene sediments and reef materials. Ground water in this system consists of a thin layer of fresh water separated from underlying sea water by a relatively thick, transitional layer of mixed saline and fresh water. Sensitivity analysis indicates that the modeled depth to the 50% salinity contour is most sensitive to permeability, and the transition‐zone thickness is most sensitive to transverse dispersivity. Results from the development analysis verify that shallow, linear skimming wells, or galleries, are the most efficient means of extracting fresh ground water.

Diagenetic processes in Holocene carbonate sediments: Florida Bay mudbanks and islands

ABSTRACTThe sedimentology, mineralogy and pore fluid chemistry of seven cores from the Holocene sediments of Florida Bay were studied to determine the physical processes and diagenetic reactions affecting the sediments. The cores were taken in a transect from a shallow mudbank onto a small adjacent island, Jimmy Key. Steady state models of pore fluid chemistry are used to estimate the rates of various reactions.In the mudbank sediments, little carbonate mineral diagenesis is taking place. No change in sediment mineralogy is detectable and pore water profiles of Ca2+, Mg2+ and Sr2+ show only minor variation. Chloride concentrations indicate substantial biological mixing of seawater from the bay into the sediments in one of the cores. Pore water analyses of sulphate and alkalinity show only a low degree of sulphate depletion and a decreasing extent of sulphate reduction downcore. Models of sulphate reduction in the mudbank show that there is substantial chemical exchange between the sediment pore fluids and water from the bay probably as a result of bio‐irrigation. The sulphate and alkalinity data also suggest that the underlying Pleistocene rocks contain water of near normal seawater composition.Stratigraphic analysis and δ13C analyses of the organic carbon in the sediments of the island cores show that the sediments were primarily deposited in a subtidal mudbank setting; only the upper 20–30 cm is supratidal in origin. Nevertheless, island formation had a significant effect on pore fluid chemistry and the types of diagenetic reactions throughout the sediment column. Chloride in the sediment pore fluids is more than twice the normal seawater concentrations over most of the depth of the cores. The constant, elevated chloride concentrations indicate that hypersaline fluids which formed in ponds on the island are advected downward through the sediments. Models of the chloride profiles yield an estimate of 2·5 cm yr−1 as a minimum advective velocity. Changes in pore water chemistry with depth are interpreted as indicating the following sequence of reactions: (1) minor high‐Mg calcite dissolution and low‐Mg calcite precipitation, from 0 to 35 cm; (2) Ca‐ or Mg‐sulphate dissolution and low‐Mg calcite precipitation, from 5 to 35 cm; (3) dolomite or magnesite precipitation together with sulphate reduction, from 35 to 55 cm; and (4) little reaction below 55 cm. In addition, one or more as yet unidentified reactions must be taking place from 5 to 55 cm depth as an imbalance in possible sources and sinks of alkalinity is observed. The imbalance could be explained if chloride is not completely conservative. Despite the pore fluid chemical evidence for diagenetic reactions involving carbonate minerals, no changes in sediment mineralogy were detected in X‐ray diffraction analyses, probably because of the comparatively young age of the island.

The Hydrogeochemistry of Early Meteoric Diagenesis in a Holocene deposit of Biogenic Carbonates

ABSTRACT This study presents the results of a quantitative hydrogeochemical investigation of early meteoric diagenesis in a deposit of biogenic, mixed-mineralic Holocene carbonate sediments at Ocean Bight in the southeastern Bahamas. Ground-water samples were collected from a network of 27 wells arranged into 4 transects across the 1.5 km2 strand-plain deposit. Four wells provided multi-depth samples at 0.5 m intervals, thus allowing for the construction of vertical chemical profiles. Analyses of the water consisted of temperature, pH, alkalinity, CI- , Ca2+, Mg2+, SR2+, SO42-, and 13C. Data derived from these analyses were used in a series of equilibri m and mass-balance equations to calculate mineral saturation levels and magnitudes and rates of mineral transformation reactions. Interpretation of measured and calculated parameters provided a detailed picture of patterns and processes of meteoric diagenesis at Ocean Bight. Four features of meteoric diagenetic processes operating at Ocean Bight are distinct from processes documented at previously studied non-biogenic and aragonite dominated Holocene systems: 1) lighter cementation with respect to magnitudes of calcite precipitation, 2) diminished magnitudes of aragonite dissolution, 3) elevated rates of mineral stabilization, and 4) lower efficiencies of transformation reactions. Another distinction of this study, which is not thought to be attributed solely to the presence of mixed biogenic carbonates, is the isolation of transformation reactions to the vadose and upper phreatic zone. This result contradicts the popularly held belief that metastable carbonate deposits undergo rapid equilibration throughout the freshwater phreatic zone. This distribution of diagenetic reactions, along with the analytical results, characterizes a chemical environment dominated by carbonate mineral transformation reactions linked mainly to the oxidation of organic matter and not only to the relative solubility of the different carbonate minerals. This finding may prove important in attempts to explain the preservation of metastable minerals in ancient geologic sequences despite repeated exposure to freshwater phreatic zones. This finding also questions the assumption that the extent of paleo-phreatic lenses is equal to the observed extent of freshwater phreatic alteration.

Environmental gradients in carbonate sediments and rocks detected by correspondence analysis: examples from the Recent of Norway and the Dinantian of southwest England

ABSTRACTContinuous sedimentary gradients are only crudely expressed by standard facies and microfacies methods which are more appropriate to situations where changes occur in relatively discrete steps. In carbonate sediments and rocks, continuous gradients are often represented by the arrangement of component grain types in a relay, that is, a systematic shifting of the relative importance of the components. Subdivision of such relays into (micro)facies can only be arbitrary.Correspondence analysis is shown to be useful for detecting, isolating and describing relays. Particular use is made of the arch effect in which samples and components from data sets with a strong unidimensional structure (a relay) plot in the form of an arch in the plane of the first two factor axes. A relay index, indicating the position of samples in the relay, can be extracted from the analysis and plotted on maps and stratigraphic logs to reveal details of the sedimentary gradient in areal and/or stratigraphic context.Examples are given from: (i) Recent shallow‐marine carbonate sediments from northern Norway, illustrating a relatively simple depositional setting where surface sediments are viewed in plan; and (ii) Lower Carboniferous carbonates of southwest England, representing a more complex regional study of a particular stratigraphic interval viewed in cross‐section. In both examples the relays can be related to identifiable environmental gradients.

Dissolution of Recent platform carbonate sediments in marine pore fluids

Dissolution of Recent platform carbonate sediments in marine pore fluids

Recent carbonate sedimentation and brine evolution in the saline lake basins of the Cariboo Plateau, British Columbia, Canada

Recent carbonate sedimentation and brine evolution in the saline lake basins of the Cariboo Plateau, British Columbia, Canada