Bedding and bedding surfaces in carbonate and mixed siliciclastic–carbonate successions can be diagenetic, not depositional, in origin and require interrogation to determine their true origins. This study reviews the different models and implications associated with diagenetic bedding and diagenetic bedding surfaces in such successions. Weathering, especially where strong lithological and mechanical differences occur, can make distinguishing primary and diagenetic bedding more difficult, and criteria are reviewed. Early, shallow diagenetic processes linked to mineral instability of aragonite, mediated by biochemical processes, are capable of producing bedding and bedding surfaces. Zones of early cementation within sediments can produce discrete beds and surfaces exemplified in the formation of limestone–marl alternations (LMAs). Variations in the degree of early cementation (‘stratified cementation’) in shallow buried argillaceous carbonate sediments affected by later compaction can produce layering, with beds showing little compaction separated by highly compacted, argillaceous fissile interbeds which develop bedding surfaces within those fissile units (‘couplets’). Where such diagenetic limestone beds form intrastratally, as in LMAs, they do not obey the principle of superposition and, by virtue of never having been deposited laterally adjacent to their associated deposits, do not comply with Walther's Law of Facies. Bedding surfaces associated with LMAs only become true surfaces when exhumed to produce some types of firmgrounds and hardgrounds.

Temporary exposures recording the Upper Triassic-Lower Jurassic transition near Bridgend, South Wales provided a rare opportunity to assess how this major stratigraphical interval is manifested in terrestrial deposits in close proximity to the intensively studied marine and marginal marine successions in SW Britain. Following the progradation and exposure of a shoreline sandbody, up to 8 m of coastal plain deposits formed during a subsequent punctuated transgression. These deposits host a series of palaeosols with unusual carbonate textures, complex mottling styles and marked lateral variability, with evidence of several changes in hydrological conditions. Initially calcrete-bearing soils capped the shoreline sandstones but were overprinted by ferroan-carbonate-bearing gleys likely marking the influence of marine waters. Subsequently, a transition to well-drained soils with calcrete horizons occurred. Continued mud grade deposition was marked by the development of pseudo-gley conditions culminating in gleyed soils, overlain by marine sediments. This provides an example of the often complex polyphase and polygenetic nature of palaeosols encountered in aggrading sedimentary systems. (c) 2025 The Geologists' Association. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Soils and, hence, palaeosols develop at geomorphic surfaces comprising landscapes. As most develop they reorganize the substrate to create texturally and chemically defined units (horizons) parallel to the land surfaces and some of these horizons become lithified resembling beds. Palaeosols, in many cases do not represent hiatuses but developed during deposition and represent condensation not lost time. The degree of pedogenic reorganization can be used to estimate the temporal significance of the length of soil formation but soils are commonly polygenetic and have not followed a simple, time-related developmental pathway. The complexity of soil development is illustrated with reference to the late Silurian–early Devonian polyphase alluvial palaeosols from South Wales which provide an example of how dynamic changes in sedimentation and erosion have occurred without changes in soil processes. The significance of these polyphase palaeosol profiles is reviewed in the broader context of mid Paleozoic landscape changes.

Continental red beds are coloured by secondary Fe(III)-oxy-hydroxides (mainly hematite) which makes them excellent archives of ancient near-surface redox conditions. However, colour is often treated as a subjective physical property, and opinions differ widely as to the environment and timing of colouration of the red beds. This study utilizes diffuse spectral reflectance to address the degree of reddening (hematitization) of the Siluro-Devonian Old Red Sandstone representing a dryland fluvial system with abundant palaeo-Vertisols, coinciding with the period of land colonization by vascular plants. The hematitization was studied along with the stratigraphy, facies, pedogenic features, petrology, element and Molybdenum isotope geochemistry. The mudstones and palaeosols are typically red while sandstones are often grey. The red colouration corresponds to approximately 30 to 36% of red band (625 to 700 nm) reflectance and high hematite to goethite ratios. The red sediments contain hematitized biotite, submicronic hematite in mudstone and sandstone matrix, and hematite cement in calcretes. The hematitization was synchronous with formation of pedogenic mudcracks, Vertic slickensides, calcretes, reduction spots, sometimes hydrodynamic reworking, and accompanied by local (grain-scale) depletion in Fe(II), enrichment in Fe(III), and mobilization of U, V, As, Cu, Zn and Mo. It is estimated that the hematite growth was rapid (several hundred to thousand years) but the average sedimentation rates were low (approximately 3 to 10 cm/kyr). Erosion led to development of reactivation surfaces separating layers with contrasting hematite content and geochemistry. It is suggested that high rates of pedogenesis and low sedimentation rates favour the reddening and may represent an important control on the formation of continental red beds. Limited levels of soil waterlogging, and the published delta 13C values (-9 to -12 parts per thousand Vienna Pee Dee Belemnite) of the pedogenic carbonate, might reflect the changes in the nature of the soil biomantle during the early Devonian land colonization by vascular plants.

Robust upfront reservoir characterization is vitally important when problems arise later in the management of a field. In this case, thin high-permeability zones were mapped, even though no water injection was planned. This proved critical when, 10 years later, gas souring problems could be rapidly addressed. The Late Cretaceous R1 Inférieur reservoir comprises an upward-shallowing succession ( c. 60 m thick) of offshore to shoreface and foreshore carbonates, which passes conformably up-section into an anhydrite-bearing lagoonal–peritidal succession ( c. 13 m thick), the R1 Supérieur. H 2 S well monitoring confirmed the migration of H 2 S from the terrace sour gas area to the core sweet gas area of the field. High H 2 S concentrations are a safety hazard, and there are limitations on the concentration of H 2 S that the Miskar pipeline can handle. Understanding the distribution of high-permeability layers in the R1 reservoir is critical to identify preferential pathways for gas migration and resulting gas souring. Gas souring is controlled by a high-permeability layer formed by bioclastic rudstones deposited at the shoreface–foreshore interface. Identifying this thin interval in uncored wells and predicting its lateral continuity are essential to minimize the impact of gas souring on field development.

Abstract Basin hydrology and subcrop are key controls on carbonate sedimentation in continental basins. Hydrologically sensitive carbonates can record groundwater fluctuations within an aquifer in deep time. Late Jurassic extension, footwall uplift, erosion and karstification of marine Jurassic carbonates in the western Cameros Basin (Spain) saw deposition of ?Upper Kimmeridgian‐Tithonian syntectonic alluvial fan deposits (Señora de Brezales Formation). Biogenic laminar calcretes and phreatophytic rhizocretions record roots exploiting capillary fringe groundwater. Progressive infill of rift topography and footwall erosion lowered sedimentary gradients and clastic supply during deposition of the ?Tithonian–Berriasian Rupelo Formation. Distal alluvial marls (Las Viñas Member) contain charophytes, with 2 m thick carbonate lenses at the top reflecting intermittent rise of groundwater in ponds on the basin floor. Stacked palustrine limestones with rare charophytes and laminar calcretes (Ladera Member) record overstep of seasonal carbonate wetlands onto basin margins and footwall highs with intense pedogenetic modification during lengthy seasonal exposure. Overlying Berriasian charophyte‐ostracod wackestones, displaying microkarst cavities and interbedded intraclastic conglomerates, with vivianite sauropod bones, footprints and polygonal desiccation cracks at the top (Mambrillas de Lara Member) record open lacustrine conditions with limited subaerial exposure and high water tables. Desiccation‐cracked limestones and marls with correlatable evaporite horizons (Rio Cabrera Member) contain marginal marine foraminifera and dasycladaceae at the top. Lagoonal conditions reflected transgression to seaward and intermittent marine connection via the Basco‐Cantabrian Basin. The distribution and thicknesses of hydrologically sensitive carbonates reflected onlap onto a faulted and karstified marine Jurassic carbonate pediment and the subtle influence on hydroperiod of fault (and potentially localised Triassic salt) controlled differential subsidence and transgressive groundwater rise. Hydrological facies evolution reflects progressive basin infilling and eustasy beyond. Transitions in this continental succession from clastic to carbonate facies and from closed to open hydrology record hydrological change over time rather than contemporaneous deposition under Walther's Law.

Magnesian Limestone zoned dolomite (red and non-luminescent zones) now partly dedolomitized), calcite (yellow luminescence), blue luminescent albite has non-luminescent overgrowths) Mansfield Quarry, Nottinghamshire. Photo credit: J.A.D. Dickson.

The current understanding of the origins of modern carbonate muds and their early stages of transformations are reviewed. The fine-grained nature of such sediments makes them susceptible to intensive structural and chemical alteration at relatively shallow burial depths driven especially by mineral instability under microbially mediated reactions within the sediment associated with the decay of organic matter. Whereas the transformation of high Mg calcite (HMC) to low magnesian calcite (LMC) generally takes place incongruently and in situ, that of aragonite is predominantly via congruent dissolution. The loss of aragonite produces a huge potential flux of carbonate which is translocated within the sediment. Parallel to studies on Quaternary sediments, investigations in the stratigraphic record have shown that in low-energy settings the transformation of the aragonite component leads to the formation of diagenetic bedding (such as limestone-marl-alternations or LMAs), and related bipartite lithologies, some types of hardgrounds, secondary carbonate mudrocks, and to the significant modification of the original skeletal biota. There are uncertainties such as the exact sources for the precursor aragonite, where the released carbonates reprecipitate in the shallow sediment column, how much carbonate (and hence carbon) is back-fluxed to the water column, how this affects palaeoenvironmental proxies, and the environmental distributions of these processes. The evidence from the stratigraphic record, from settings where organic matter was able to accumulate promoting these transformations, is that these changes in carbonate-rich sediments took place very early, at shallow (decametre or less) burial depths, affecting what we now see from the micron to the outcrop scale. The complexity and inter-relationships of these fundamental processes has received more attention in recent years, though their implications still seem remarkably undervalued.

The dynamic inter-relationships between marine and freshwater carbonate depositional environments are illustrated in the Sian Ka'an Wetlands, a 5 280 km(2) complex of groundwater-fed freshwater marshes, lakes and brackish coastal lagoons in the South-East Yucatan Peninsula (Mexico). The Yucatan Platform was subaerially emergent and extensively karstified during the last glacial maximum at 18, 000 yr bp. The Late Holocene transgression has caused progressive reflooding of the continental margin, backstepping of the MesoAmerican Reef and encroachment of coastal environments into the platform interior as rising groundwaters flood an interconnected cave and sinkhole system and feed seasonal marshes above. The Sian Ka'an Wetlands form a vast palustrine carbonate factory which is directly juxtaposed and dynamically linked with the marine carbonate factory to seaward. Continuing sea-level rise has caused synchronous landward migration of marginal marine and freshwater environments as beach barriers were breached and palustrine sloughs flooded to form marginal marine seagrass lagoons. The Rio Hondo Fault conditions fluid inflow while the sub-environments of the Sian Ka'an Wetlands reflect tectonic controls on microtopography and hydroperiod. Modern analogues for the Sian Ka'an Wetlands include the Florida Everglades, formed during transgression of the Florida Platform, and relict marsh environments preserved on leeward shores of Andros, Abaco and other Bahama islands. A wide range of ancient examples deposited in coastal and continental interior settings similarly reflect seasonal aquifer rise in response to marine transgression and/or onlap of late-stage basin fill onto a karstified pediment. Freshwater palustrine carbonate factories on carbonate platforms are transient deposystems, controlled by subtle water depth, climate, vegetation and hydrological factors while being critically sensitive to sea-level changes and tectonics. The preservation potential of palustrine carbonates may be relatively low in coastal settings due to erosion or shallow marine overprinting, while greater further inland where marine flooding is rarer and in tectonically subsident continental interior basins where accommodation space is continuously created.

Abstract Side‐scan sonar and Compressed High Intensity Radar Pulse mapping of Great Salt Lake, Utah, linked to reprocessing of acoustic data from bathymetric surveys, has enabled the distribution of microbial bioherms to be assessed. Bioherms occupy an estimated area >700 km2 in the south arm and >300 km2 in the north arm. Distributions vary from statistically dispersed to clustered, and in this latter case, are predominantly located on metre‐scale, fault‐controlled topographic highs, with sediment infilling intervening lows between adjacent offsets. Individual bioherms are circular to oblate and range from centimetres to over 2 m in diameter. In some areas, bioherm heights were measured at more than 1.5 m above adjacent substrate. Sublittoral bioherms are made of aragonite, calcite and minor dolomite precipitated due to physico‐chemical, biologically induced and influenced carbonate mineralization processes in association with microbial mats. Bioherm fabrics vary at the millimetre to centimetre‐scale and consist of leiolitic and clotted peloidal micrite‐grade carbonate, sinuous threads of spherulitic fibrous aragonite crystals, laminated micrite boundstone and internal carbonate mud sediment with peloids and ooids. The identification of factors that influence microbial bioherm occurrence and spatial distribution in Great Salt Lake is limited to a set of collinear physical, chemical and biological variables that are confined to a localised closed system, such as salinity, water depth, wave energy, stable substrate and sediment accumulation. Anthropogenic modifications to Great Salt Lake resulting in increased salinity have exceeded the salinity range in which bioherm‐mediating microbial communities can survive, effectively defining an upper limit of salinity for bioherm microbial community viability. The better understanding of the distribution of microbial bioherms has significant implications for managing and protecting the lake ecosystem and may provide insights into the physical and chemical controls that existed during the formation of fossil microbialites in deep time.

During the Aptian (Cretaceous), in what is now the South Atlantic, the largest chemogenic (abiotic) carbonate factory so far identified in the Phanerozoic geological record developed as a vast hyper‐alkaline lake system. This covered at least 330 000 km2, producing carbonates, locally over 500 m thick, in what are now the offshore Santos and Campos basins (Brazil), and Kwanza Basin (Angola). Current evidence supports the view that almost all of this carbonate was chemogenic in origin, precipitated from hyper‐alkaline, shallow lake waters, probably by evaporation. This unit, best documented from offshore Brazil and known as the Barra Velha Formation (Santos Basin) and the Macabu Formation (Campos Basin), consists of just two basic carbonate components, millimetre to centimetre sized crystal shrubs and spherulites. These are commonly in situ but can also be reworked into a range of detrital facies. Demonstrable microbialites are generally rare. These carbonates are associated with Mg silicates (as clays) which had a profound influence not only on the textural development of the in situ carbonates, but also on their diagenesis. The dissolution of the clays produced much of the porosity in these limestones, which are the hosts for multi‐billion barrel oil fields. The source of the carbonate was most likely from metasomatic alteration of mafic rocks, such as continental flood basalts related to Atlantic opening, with some contribution from much older continental basement. Clear evidence that serpentinization of possible exhumed mantle is lacking but mantle CO2 is likely to have been a critical factor in determining the composition of the fluids from which the carbonates formed and the high alkalinities of the lake waters.

A revised age provided by conodonts from the Gilwern Oolite of the Clydach area of South Wales allows a clearer understanding of the palaeohydrology, palaeoclimatic history and diagenesis of previously correlated oolitic units. Earlier uncertainty over the apparent sub-regional differences in climate during the early Visean (Chadian—Arundian) lowstand is resolved. Previously a humid interval evidenced by prominent palaeo-epikarst capping the Gilwern Oolite along the northern outcrops of the South Wales synclinorium, was not recognized in what were regarded as correlative outcrops in the Chadian Gully Oolite in the southern part of the synclinorium. Conodont dating now shows that the Gilwern Oolite is much older (Courceyan) than the Chadian Gully Oolite, and during the prolonged exposure of the former there was an interval of weathering under a humid climate. This also explains the contrast between the diagenesis seen between the Gilwern and Gully oolites, which are no longer seen as correlatives.

The Urbasa-Andia plateau, in the western Pyrenees (North Spain), provides the opportunity to asses in detail the facies types and architecture of a Danian (lower Paleocene) greenhouse ramp to rimmed shelf system, from the slope to the coralgal reefal margin, through to highly restricted evaporitic inner shelf areas, all integrated with a range of porosity forming diagenetic phases associated with highstand and lowstand of sea-level. The detailed nature of the stratal architecture of this greenhouse platform provides an understanding of potential reservoir layering, lateral facies changes and early dolomitization. Significantly, the Danian platform system also allows a whole macroporosity system related to a third order lowstand to be accessed in relative continuity, illustrating how eogenetic karstic porosity can change drastically across a carbonate platform, from the near-massive margin to a layered shelf interior. The outcrops to visit serve as potential analogues for fields in North Africa.

The sedimentology, petrography and mineralogy of the seemingly monotonous Late Triassic Mercia Mudstone Group across the Severn Basin and Bristol Channel region reveals a bipartite division of mudrock facies above and below the Arden Sandstone Formation. Frequently cryptic sedimentary and pedogenic features reveal diverse alluvial, aeolian, playa-lacustrine and pedogenic processes operating at different times, locations and scales probably in response to climate change. The current study found no evidence of significant marine influence in either of the two mudrock facies associations that are described here. Blocky claystones dominate the lower Mercia Mudstone Group (Sidmouth Mudstone Formation), with pedogenic features such as slickensides, mottling, tubules and carbonate/sulphate nodules common and widespread. The claystones are of alluvial/lacustrine origin with subordinate sheet sandstones, themselves overprinted by pedogenic features, reflecting occasional high intensity rainfall events. These facies reflect a seasonal (wet/dry) semi-arid climate favouring development of transformed/neoformed (smectite-rich) clay minerals of intrabasinal origin. Massive to weakly stratified silty mudstones dominate the upper Mercia Mudstone Group (Branscombe Mudstone Formation). Commonly conchoidally weathered, locally gypsiferous, but with distinct sedimentary structures scarce, they alternate with subordinate blue-grey laminated silty mudstones. Together they reflect fluctuating hydrological conditions within extensive saline mudflats and ephemeral playa lakes, with laminated facies deposited under subaqueous conditions during more humid phases whereas massive mudstones reflect modification through interstitial growth/dissolution of sulphates and deflation of surface sediments during drier episodes. These facies reflect increased aridity during deposition of the upper Mercia Mudstone Group compared with the lower Mercia Mudstone Group, favouring development of detrital/transformed (illite-chlorite) clay minerals of extrabasinal origin. The described facies associations and the sedimentary fabrics and structures that characterize them, occur widely in the Mercia Mudstone Group across the United Kingdom and comparable facies associations may be anticipated in other fine-grained red bed successions. Recognition of these facies may aid palaeoenvironmental interpretation of such sequences on Earth and, potentially, on Mars also.

A previously undocumented, diverse assemblage of very shallow-water larger benthic foraminifera (LBF) is described from the Panna-Mukta fields, offshore India. This location lies at the margin of the late Eocene to early Miocene Arabian Peninsula marine biodiversity hotspot. The assemblage has similar characteristics to those from the Middle East, Oman and Turkey, but shares little in common with onshore western Indian assemblages. In addition, the material contains several unusual and possibly new taxa, and extends the geographic ranges of several existing LBF. The succession spans the Eocene and Oligocene, with an unconformity between the middle and upper Eocene. As such it offers insight into the response of shallow-water taxa to the Eocene-Oligocene Transition extinction event from an unusual setting in a little studied region. Our data show that LBF taxonomic richness in the Panna Mukta fields is comparable with highly diverse assemblages found in Oman, indicating it may be an eastward extension of this high diversity region. Moreover, significant decreases in diversity are seen between the middle and upper Eocene and the upper Eocene and Oligocene. Major extinctions are known to occur in global LBF records at both of these levels, and the Panna Mukta succession therefore further confirms these are global events, extending across the platform and having a dramatic (at least short-term) effect on high biodiversity regions.

The Upper Serpukhovian (Mississippian) interval of the Karachaganak reservoir comprises stratified platform interior carbonates, which are characterised by relatively high porosity and matrix permeability (maximum 23.8% and 2198 mD, respectively), and comprise high frequency (fourth-order) glacio-eustatic cycles. Based on static (geological) and dynamic (well test and production) data, this cyclicity exerts a strong control on gas migration pathways, and reservoir quality is predictable within a third- and fourth-order sequence stratigraphic framework that defines two discrete flow units. The contribution to flow made by fourth-order cycles within flow units is dependent on their position within third-order transgressive or highstand systems tracts. An upper flow unit comprises thick (up to 40 m) fourth-order cycles within a third-order transgressive systems tract. These fourth-order cycles contain large scale, clinoformal bedforms, can be correlated for up to 6 km, and are the main pathways of injected gas through the Upper Serpukhovian reservoir. A lower flow unit comprises fourth-order cycles (within a third-order highstand systems tract) that are thinner, and less laterally continuous, than those in the upper flow unit, and contribute far less to horizontal gas flow. Pressure data indicate that vertical permeability baffles are developed at the third-order sequence boundary that separates the two flow units (linked to diagenetic alteration during prolonged subaerial exposure), and also within the low porosity, mud-rich, transgressive bases of thick fourth-order cycles of the upper flow unit, that formed during periods of increased accommodation space across the platform top during third-order transgression. The scale at which this data set is observed is critical to understanding the dynamic behaviour of the reservoir. Relatively small differences in the composition of microfacies of cycles within both flow units do not explain the variations in dynamic data. This variation is better explained within the broader context of the sequence stratigraphic framework as defined from analysis of cycle stacking patterns. Thicker high frequency cycles deposited in increased accommodation space on the platform top during third-order transgressive intervals are key to developing thick intervals of net pay.

The Aptian lacustrine carbonates of the Barra Velha Formation, offshore Brazil, have undergone a highly unusual paragenetic and diagenetic history and present significant terminological problems if current textural classifications are applied. Existing limestone classifications invoke the concept of textural maturity, whereby the ratio of matrix to grain is a critical property and can be used to infer energy levels and the degree of transport prior to deposition. In the Barra Velha Formation, some critical carbonate grains grew in a matrix which later dissolved, congruently, producing what appears to be primary intergranular porosity. In addition, apparent boundstone textures occur, not due to organic trapping or binding, but ones which can be shown to be diagenetic, and were also related in part to the former presence of labile matrices. Thus, applying some terms in existing classifications can lead to false interpretations, and to avoid misinterpretations criteria for identifying ghost (former) matrices are provided.

Research Article| April 18, 2019 Memes, False News, and the Death of Empiricism V. Paul Wright V. Paul Wright Natural Sciences, National Museum of Wales, Cardiff, U.K. and PW Carbonate Geoscience, Cardiff, U.K. Search for other works by this author on: GSW Google Scholar Author and Article Information V. Paul Wright Natural Sciences, National Museum of Wales, Cardiff, U.K. and PW Carbonate Geoscience, Cardiff, U.K. Publisher: SEPM Society for Sedimentary Geology First Online: 18 Apr 2019 Online Issn: 1938-3681 Print Issn: 1527-1404 Copyright © 2019, SEPM Society for Sedimentary Geology Journal of Sedimentary Research (2019) 89 (4): 310–311. https://doi.org/10.2110/jsr.2019.21 Article history First Online: 18 Apr 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation V. Paul Wright; Memes, False News, and the Death of Empiricism. Journal of Sedimentary Research 2019;; 89 (4): 310–311. doi: https://doi.org/10.2110/jsr.2019.21 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Sedimentary Research Search Advanced Search When the editors of the Journal asked me to provide an article for this new section I was reminded of the risks such an invitation can carry. Being a veteran member of SEPM (joining as a student member in 1974), writing like this simply invites an expectation that this will be a polemic about how things used to be better. I will not do that. However, when I talk to other veteran sedimentologists at some point the conversation focusses on how many really flawed papers we have seen of late. So, I would like to discuss the types of flaws... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Latest Precambrian to Early Palaeozoic biosphere evolution triggered changes in early diagenesis and carbonate precipitation which fed back to biodiversity through colonisation of hard substrates. Progressive increase in the depth and intensity of bioturbation and bio-irrigation lowered the zone of early carbonate cementation in the uppermost sediment column. This firstly led to a decline in the abundance of the flat pebble conglomerates which had been a common feature of Cambrian to Early Ordovician successions, replaced by the peak and subsequent decline in the Palaeozoic abundance of submarine hardgrounds. The availability of very widespread lithified sea floors in shallow subtidal settings during the Ordovician promoted a rapid expansion in sclerobiont diversity and contributed to the Great Ordovician Biodiversification Event (GOBE).