Neritic Carbonate Research Articles

Megabeds in Istrian Flysch as markers of synsedimentary tectonics within the Dinaric foredeep (Croatia)

Istrian Flysch was deposited during the Eocene in the Dinaric foredeep and is composed of hemipelagic marls and various gravity flow deposits. The latter are predominantly 5-40 cm thick turbidites, developed mostly as laminated and cross-rippled sandstone beds (Tb-e, Tc-e and Td-e Bouma sequences). In addition to the turbidites, there are deposits characterized by a significant thickness, occasionally more than 10 m, described as complex (bipartite) megabeds. The megabeds are composed of debrites in the lower part (Division I), and high-density turbidites in the upper part (Division II). The distinct clast composition of each megabed indicates that the lithoclasts were derived from tectonically active slopes and fault scarps along which collapses of the different parts of the Cretaceous to Palaeogene neritic carbonate succession, that underlie the Flysch, occurred. The Division II deposits are well cemented, normally graded calcirudite/calcarenites composed mostly of orthophragminids, nummulitids, and red algae, originating from outer ramp environments. Redeposited marl, observed in the matrix of the debrites and as intraclasts in some megabeds, implies that the collapses along the synsedimentary fault scarps and steep slopes also occurred within the foredeep itself, during the rapid tectono-sedimentary evolution of the Dinaric foreland basin.

Tracking a drowning unconformity up to the peritidal zone: Proximal expression of the early Bajocian carbonate crisis in Morocco

The early Bajocian environmental crisis is marked by floral and faunal turnovers, and a positive carbon excursion recognized in both marine and continental archives. In the basinal setting of the Central High Atlas Basin, it is concomitant to a drastic drop of carbonate content, interpreted as a result of a severe carbonate demise event in neritic settings. In order to provide a carbonate platform perspective of this demise event, we have investigated a proximal–distal transect consisting of five sections of the Errachidia Platform, which represents upper neritic settings on the southern margin of the basin. New nannofossils and brachiopod findings, supported by organic matter carbon isotope chemostratigraphy, allow for the establishment of a high-resolution chronostratigraphic framework of the Errachidia Platform and a detailed reconstruction of carbonate factory evolution during the late Aalenian to middle Bajocian interval. The early Bajocian (Propinquans Zone) environmental crisis triggered a severe demise event which restricted carbonate production to supra-to intertidal settings, where microbial and peloidal limestones are the only trace of carbonate production. As a consequence, most of the platform is dominated by extended marl deposits that are usually interpreted as hemipelagic deposits. This observation demonstrates that caution must be exerted when interpreting the depositional environments of marl-dominated successions during time of neritic carbonate factory demise.

Timescale dependent sedimentary record during the past 130 kyr from a tropical mixed siliciclastic–carbonate shelf edge and slope: Ashmore Trough (southern Gulf of Papua)

AbstractIn tropical and sub‐tropical mixed siliciclastic–carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf of Papua), are coupled with global sea‐level curves and anchored to Marine Isotope Stage stratigraphy to constrain models of sediment accumulation at two different timescales for the past 130 kyr: (i) 100 kyr scale for last glacial cycle; and (ii) millennial scale for last deglaciation. During the last glacial cycle, carbonate production and accumulation were primarily controlled by sea‐level fluctuations. Export of neritic carbonate to the slopes was initiated during re‐flooding of previously exposed reefs and continued during Marine Isotope Stage 5e and 1 interglacial sea‐level highs. Siliciclastic fluxes to the slope were controlled by interplay of sea level, shelf physiography and oceanic currents. Heterogeneous accumulation of siliciclastic mud on the slope, took place during Marine Isotope Stage 5d to Marine Isotope Stage 3 sea‐level fall. Siliciclastics reached adjacent depocentres during Marine Isotope Stage 2. Coralgal reef and oolitic–skeletal sand resumed at the shelf edge during the subsequent stepwise sea‐level rise of the last deglaciation. Contemporaneous, abrupt siliciclastic input from increased precipitation and fluvial discharge illustrates that climate controlled deglacial sedimentation. Siliciclastic input persisted until ca 8.5 ka. Carbonate accumulation waned at the shelf edge after ca 14 ka, whereas it increased on the slopes since ca 11.5 ka, when previously exposed reef and bank tops were re‐flooded. When comparing the last sea‐level cycle sedimentation patterns of the southern Gulf of Papua with other coeval mixed systems, sea level and shelf physiography emerge as primary controls on deposition at the 100 kyr scale. At the millennial scale, siliciclastic input was also controlled by climate change during the unstable atmospheric and oceanic conditions of the last deglaciation.

High-resolution acoustic data revealing periplatform sedimentary characteristics in the Xisha Archipelago, South China Sea

Newly collected high-resolution acoustic data are used to describe the morphologies and sedimentary characteristics along the slopes of isolated carbonate platforms in the Xisha (Paracel) Archipelago. Based on multibeam bathymetric and seismic data, we have identified seven types of morphological and depositional features around the platforms, including erosive grooves, mass transport deposits, gullies, confined channels, canyons, mounded sediments, and marginal contourite depressions. The occurrence of erosive channelized features around the platforms indicates that gravity flow is a major sediment-export mechanism for the transportation of excess neritic carbonates towards the slope. Marginal contourite depressions and mounded sediments are interpreted as bottom-current reworking products, suggesting an important role of bottom current and deepwater circulation of the South China Sea in shaping the slope morphology of the carbonate platforms. Furthermore, the bottom-current products tend to develop along the slopes of the carbonate platforms at the Xisha Uplift margin; in particular, erosional features formed by bottom current frequently occur in the southern side of the carbonate platforms. By comprehensive analysis of morphological and depositional features, we establish a facies model around the carbonate platforms to interpret different sedimentary transport processes, such as off-platform and along-slope sediment transport processes. These findings highlight a notable and complex relay-style channelized transport system consisting of grooves/gullies-channels-canyons, which has implications for linking neritic carbonate platforms into deep-sea basins.

Constraining the Passive to Active Margin Tectonics of the Internal Central Apennines: Insights from Biostratigraphy, Structural, and Seismic Analysis

The polyphase structural evolution of a sector of the internal Central Apennines, where the significance of pelagic deposits atop neritic carbonate platform and active margin sediments has been long debated, is here documented. The results of a new geological survey in the Volsci Range, supported by new stratigraphic constraints from the syn-orogenic deposits, are integrated with the analysis of 2D seismic reflection lines and available wells in the adjacent Latin Valley. Late Cretaceous syn-sedimentary faults are documented and interpreted as steps linking a carbonate platform to the adjacent pelagic basin, located to the west. During Tortonian time, the pelagic deposits were squeezed off and juxtaposed as mélange units on top of the carbonate platform. Subsurface data highlighted stacked thrust sheets that were first involved into an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We distinguish up to four groups of thrust faults that occurred during in-sequence shortening (thrusts 1–3; about 55–60 km) and backthrusting (thrust 4). During Pliocene to recent times, the area has been uplifted and subsequently extended by normal faults cross-cutting the accretionary wedge. Beside regional interest, our findings bear implications on the kinematic evolution of an orogenic wedge affected by far-traveled units.

Microfossil and strontium isotope chronology used to identify the controls of Miocene reefs and related facies in NW Cyprus

The existing chronostratigraphic framework in NW Cyprus of two-phase, Early and Late Miocene reef and associated facies development is tested and improved using a combination of calcareous nannofossil, benthic and planktonic foraminiferal, and also Sr isotope dating. Following localized Late Oligocene neritic carbonate deposition (e.g. benthic foraminiferal shoals), reefs and related facies (Terra Member) began to develop c. 24 Ma (Aquitanian) and terminated c. 16 Ma (end-Burdigalian). Early Miocene reef and marginal facies were then extensively redeposited as multiple debris-flow deposits until c. 13.7 Ma, influenced by a combination of global sea-level fall (related to growth of the East Antarctic Ice Sheet) and local- to regional-scale tectonics. Reef growth and related deposition resumed (Koronia Member) c. 9.1 Ma (Tortonian), then terminated by c. 6.1 Ma (Middle Messinian), followed by the Messinian salinity crisis. Neritic accumulation in NW Cyprus began earlier (Late Oligocene), than in southern Cyprus (Early Miocene). The Early Miocene reefs developed on a roughly north–south-trending structural high in the west (Akamas Peninsula area) whereas the Late Miocene reefs developed on both flanks of the neotectonic Polis graben. The two-phase reef development is mirrored in SE Cyprus and in some other Mediterranean areas (e.g. southern Turkey, Israel, Italy, southern Spain). Supplementary material: Global positioning system locations of dated samples, the Sr isotope method and the samples examined for planktonic foraminifera biostratigraphy are available at https://doi.org/10.6084/m9.figshare.c.5205315

Sedimentology and Stratigraphic Evolution of the Early Eocene Nammal Formation, Salt Range, Pakistan

The Early Eocene succession of the Salt Range from base to top comprises the Nammal Formation, Sakesar Limestone and Chor Gali Formation. The Nammal Formation of Ypresian age is well exposed throughout the Salt Range. Detailed sedimentological and palaeontological analyses of the Nammal Formation were carried out, based on six stratigraphically important measured sections in the Salt Range. Lithologically, the formation is predominantly composed of interbedded nodular limestone, marl and shale. Wackestone, packstone, wackestone to packstone, dolomitic limestone and grainstone facies dominate the Nammal Formation in a fine-grained bioclastic matrix with abundant grains of larger benthic foraminifera. The diagnostic larger benthic foraminifera are recorded, which includes Nummulites mamillatus, Assilina spinosa, Assilina subspinosa, Assilina granulosa, Assilina laminosa, Discocyclina dispansa, Alveolina dolioliformis, Alveolina pasticillata, Alveolina globula, Lockhartia tipperi, and Lockhartia conditi. Stable carbon and oxygen isotopic signatures of the Nammal Formation designate shallow marine depositional environment. During Eocene a carbonate sequence developed in the Salt Range, lower boundary of which is marked as SB-II at the base of the Nammal Formation overlying the Palaeocene Patala Formation. The Nammal Formation presents the retrogradational facies suggesting the transgressive system tracts. The Sakesar Limestone shows agradational to progradational pattern of facies, which developed in highstand system tracts. The Chor Gali Formation possesses shallowing-upward trend by forming progradational shift of facies, and represents the falling stage system tracts. Early Eocene carbonate sequence is terminated by a regional sub-aerial unconformity SB-I marked between marine carbonate sequence of the Chor Gali Formation and the overlying non-marine clastic Miocene Kamlial Formation. Overall, the Nammal Formation presents shallow water neritic carbonate deposits containing larger benthic foraminifers.

Reconstructing Depositional Rates and Their Effect on Paleoenvironmental Proxies: The Case of the Lau Carbon Isotope Excursion in Gotland, Sweden

AbstractVariations in depositional rates affect the temporal depositional resolutions of proxies used for paleoenvironmental reconstructions; for example, condensation can make reconstructed environmental changes appear very abrupt. This is commonly addressed by transforming proxy data using age models, but this approach is limited to situations where numerical ages are available or can be reliably inferred by correlation. Here we propose a new solution, in which relative age models are constructed based on proxies for depositional rates. As a case study, we use the onset of the late Silurian Lau Carbon Isotope Excursion (LCIE) in Gotland, Sweden. The studied succession is a gradual record of shallowing upward in a tropical, neritic carbonate platform. As proxies for depositional rates we tested thorium concentration, carbonate content, and the concentration of pelagic palynomorphs. These three proxies were used to create relative age models using the previously published DAIME model. We applied these models to transform the δ13Ccarb values as well as concentrations of selected redox‐sensitive elements. The three relative age models yielded qualitatively similar results. In our case study, variations in depositional rates resulted in peaks of redox proxies appearing up to 76% higher when taken at face value, compared to when accounting for these rates. In the most extreme cases, our corrections resulted in a reversal in the stratigraphic trend of elemental concentrations. This approach can be applied and developed across depositional setting and types of paleoenvironmental proxies. It provides a flexible tool for developing quantitative models to improve our understanding of the stratigraphic record.

Ongoing shortening in the Dinarides fold-and-thrust belt: A new structural model of the 1979 (Mw 7.1) Montenegro earthquake epicentral region

This study focuses on structure and kinematics of the 1979 Mw 7.1 Montenegro earthquake. Although this event represents the strongest instrumentally recorded event in the entire Dinarides-Hellenides fold-and-thrust belt, no tectonic model relating this event to any particular fault existed so far. We combined onshore geological information with well logs, seismic lines, bathymetric data, seismotectonic and seismological data as well as cross-section balancing techniques into a new structural model for the area. Our results suggest that main shock and strongest aftershock (Mw 6.2) occurred on the NE-dipping basal thrust of a largely Palaeogene-age nappe system involving Cretaceous neritic carbonates. Ongoing propagation of this thrust system is documented by the existence of elongated ridges located 15 km offshore. Reflection seismic and bathymetry data reveal that the ridges form crests of actively growing fault-related anticlines. Slip distribution models of the strongest events imply that the basal thrust below the ridges accommodated up to 2.7 m of coseismic displacement. Ongoing shortening along the basal thrust also induced surface uplift of structurally higher thrust imbricates, evidenced by dry valleys incising onshore anticline crests. Combining all evidence, we speculate that the observed structural and geomorphic features resulted from repeated seismogenic faulting events as in 1979.

Morphotype differentiation in the Great Barrier Reef Halimeda bioherm carbonate factory: Internal architecture and surface geomorphometrics

AbstractThe calcareous Halimeda bioherms of the northern Great Barrier Reef, Australia are the largest actively accumulating Halimeda deposits worldwide. They contribute a substantial component of the Great Barrier Reef neritic carbonate factory, as well as the geomorphological development of Australia's northeast continental shelf. Halimeda bioherm geomorphology is complex, expressing three distinct variations in morphotype patterns: annulate, reticulate and undulate. Similar regular and irregular geomorphological patterning often results from scale‐dependent biophysical feedback mechanisms. Therefore, a better understanding of morphotype differentiation can inform the biotic and abiotic drivers of spatial heterogeneity in the bioherm ecosystem. Here, 3D LiDAR bathymetry is integrated with 2D sub‐bottom profile datasets to investigate surface topography and internal sedimentary architecture of Halimeda bioherms through space and time. Using the ESRI ArcGIS 3D Analyst and Benthic Terrain Modeller extensions, the bioherm surface and subsurface geomorphometric characteristics were quantified for the annulate, reticulate and undulate morphotypes. Significant variation was found between the three bioherm morphotypes in their surface topography, internal structure, volume, slope gradients and terrain complexity. Therefore, their geomorphology is probably influenced by differing processes and biophysical feedback mechanisms. The complex surface topography does not appear to be inherited from the antecedent substrate, and preferred aspect orientations resulting from hydrodynamic forcing appear to be limited. It is suggested here that autogenic dynamics or biotic self‐organization similar to patterns and processes in other marine organo‐sedimentary systems modulates Halimeda bioherm geomorphology, and some hypotheses are offered towards future studies. Morphotype differentiation has implications for the development of the Halimeda bioherm carbonate factory, rates of sediment aggradation and progradation, and variable capacity to fill accommodation space. Self‐organization dynamics and morphology differentiation in Modern bioherm systems could potentially inform palaeo‐environmental interpretations of fossil bioherms and phylloid algal mounds on geological timescales.

Transient and secular changes in global carbon cycling during the early Bajocian event: Evidence for Jurassic cool climate episodes

Abstract The early Bajocian event was characterized by a protracted, ca. 4 Myr-long positive carbon isotope excursion that has been recognized in both marine and continental records. It is concomitant with a marine eutrophication event that led to regional demises of the neritic carbonate factory, as well as floral and faunal turnovers. The ultimate cause and modality of this event remains uncertain. In this study, we present a high-resolution, biostratigraphically calibrated, bulk organic matter carbon isotope dataset derived from the marine sedimentary record of the Central High Atlas Basin in Morocco and spanning the upper Aalenian–lower upper Bajocian. Within the context of the overall lower Bajocian positive carbon isotope excursion, this curve displays a complex trend of subordinated positive and negative shifts, which can be correlated to the high-resolution bulk carbonate carbon isotope record of southeastern France and southern Spain. The presence of a similar complex shape in these carbon isotope records over a large paleogeographic area highlights that the carbon cycle perturbation associated with the early Bajocian event was more intricate than previously depicted. Using the difference in carbon isotope fractionation between the carbonate and organic matter records as a first-order tracer of atmospheric pCO2 variations implies that the late early Bajocian was characterized by two interludes (late Propinquans and late Humphriesianum chronozones) of low greenhouse gas concentrations. This inference is supported by high-resolution paleotemperature and global sea-level records, suggesting the transient development of polar ice caps during the Middle Jurassic.

Seagrass-related carbonate ramp development at the front of a fan delta (Burdigalian, New Caledonia): Insights into mixed carbonate-siliciclastic environments

Past shallow-water carbonate environments of the main island of New Caledonia (NC) have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate-siliciclastic systems under a tropical climate. More particularly, we focused on Burdigalian carbonate sedimentary records cropping out on the western coast of NC, in the Népoui area. Based on a comprehensive sedimentological study of cores and outcrops, we established a new depositional model of an alluvial fan to carbonate ramp transition. Shallow-water (euphotic) carbonate production was dominated by seagrass-related biota and corals derived from small-sized bioconstructions. Extensional tectonics and associated normal faulting, driven by post-obduction isostatic rebound, favored carbonate ramp aggradation and preservation. The carbonate ramp was incised by conglomerate-filled terminal distributary channels, which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories. Phytal substrates induced by seagrass and/or macro-algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal-coralline algal sediments. Seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter-feeding biota in such a high terrigenous influx setting.

Akkise-Yalıhüyük (Konya) Arasının Stratigrafisi

In the vicinity of Akkise-Yalıhüyük (south of Konya) region, the Mesozoic sequence of the autochthonous Geyikdağı and the allochthonous Bozkır units is overlain by Neogene-Quaternary Neo- autochthonous cover units with an angular unconformity. Geyikdağı Unit is represented by Late Cretaceous Saytepe formation cosisting of abundant rudist neritic carbonates at the bottom and Campanian-Maastrihtian Alan formation made up of cherty, clayey pelagic limestone and marls at the top. These autochthonous units are overlain by Maastrihtian Hatip ophiolitic melange forming the lower tectonic zone of the allochthonous Bozkır unit. The second allochthonous tectonic unit in the region is represented by Boyalıtepe formation including Late Cretaceous pelagic deposits such as cherty limestone, clayey limestone-marl and radiolarite. The upper allochthonous package of the study area is also represented by the Middle Triassic-Jurassic Gencek formation consisting of medium-thick bedded, abundantly jointed neritic carbonate. The boundaries of autochthonous and allochthonous and Neo-autochthonous rocks in the region are generally faulted. Therefore, the semi-peneplene-peneplene areas of the region are in the form of a depression area. As a result of lacustrine transgression in the Miocene-Early Pliocene period, lacustrine deposition environments were formed in these depression areas. Therefore, today, some lacustrine sediments such as gravelly-sandy-muddy detritics (Sille formation), muddy-clayey carbonates (Ulumuhsine formation) and volcano-sedimentary units (Küçükmuhsine formation) and also dacitic-andesitic volcanics (Erenlerdağı volcanics) are seen in these depression areas. The newest deposits of the study area are the foothill-alluvial fan deposits (Topraklı formation) which were deposited in Late Pliocene-Pleistocene and alluvials in Holocene age.

Eocene to Oligocene high paleolatitude neritic record of Oi-1 glaciation in the Otway Basin southeast Australia

Multiple stable isotope investigations from upper Eocene to lower Oligocene deep-water marine sequences record the transition from global greenhouse to the icehouse conditions (Oi-1 glacial). While Southern Ocean high latitude deep sea records of this transition are well known, their shallow marine equivalents are rare and have the potential to record the eustatic and oceanic consequences of Paleogene glacial variability. The well-known high paleolatitude (~55°S) neritic carbonate sequence at Browns Creek and Castle Cove in the Otway Basin in southeast Australia spans the Eocene-Oligocene boundary. During this time the area lay on the northeastern margin of the Australo-Antarctic Gulf facing the evolving Southern Ocean. The importance of this record has been hampered by a lack of a consistent stratigraphy and contradictory microfossil interpretations. To reconcile these issues we combine new bio-, chemo- and lithostratigraphic analyses of the outcrops and a new core (Colac-2) with pre-existing data to revise the stratigraphy. This confirms the middle/upper Eocene boundary is near the base of the section. The overlying upper Eocene siliciclastic strata are truncated by an unconformity (of ~0.8 Ma in duration) and overlain by glauconitic sand (the Notrostrea greensand) deposited after ~35.9 Ma. Subsequently deepening to middle to outer neritic depths deposited cyclic carbonates. Shallowing after ~35 Ma deposited laterally variable calcareous siliciclastic facies. These strata were tilted and eroded prior to 34 Ma leading to shallow water facies that may have been subaerially exposed during uplift. Brachiopod strontium isotope dates and an 0.5‰ carbon isotope excursion above this unconformity suggests the top of the Browns Creek and the base of the Castle Cove section correlate to Eocene-Oligocene transition (EOT-1) at ~34 Ma. The subsequent persistence of positive C/O isotope values above this level records the transition to the Oi-1 glaciation at ~33.7 Ma. Strong cyclicity in the inner shelf Castle Cove limestone is interpreted to record the commencement of obliquity dominated glacio-eustacy during the Oi-1 glacial phase. The shallowing from outer to inner shelf palaeodepths from the late Eocene to the early Oligocene is likely related to the onset of cryosphere expansion, however, palaeodepth estimates are complicated by the onset of regional compressional tectonism at the Eocene/Oligocene boundary that caused localized tilting and an unconformity with possible antisiphoning effects in this near-field site.

Carbonate platform production during the Cretaceous

AbstractPlatform carbonates are among the most voluminous of Cretaceous deposits. The production of carbonate platforms fluctuated through time. Yet, the reasons for these fluctuations are not well understood, and the underlying mechanisms remain largely unconstrained. Here we document the long-term trend in Cretaceous carbonate platform preservation based on a new data compilation and use a climate-carbon cycle model to explore the drivers of carbonate platform production during the Cretaceous. We show that neritic carbonate preservation rates followed a unimodal pattern during the Cretaceous and reached maximum values during the mid-Cretaceous (Albian, 110 Ma). Coupled climate-carbon cycle modeling reveals that this maximum in carbonate deposition results from a unique combination of high volcanic degassing rates and widespread shallow-marine environments that served as a substrate for neritic carbonate deposition. Our experiments demonstrate that the unimodal pattern in neritic carbonate accumulation agrees well with most of the volcanic degassing scenarios for the Cretaceous. Our results suggest that the first-order temporal evolution of neritic carbonate production during the Cretaceous reflects changes in continental configuration and volcanic degassing. Geodynamics, by modulating accommodation space, and turnovers in the dominant biota probably played a role as well, but it is not necessary to account for the latter processes to explain the first-order trend in Cretaceous neritic carbonate accumulation in our simulations.

The stratigraphic and geochemical imprints of Late Ordovician glaciation on far-field neritic carbonates, Anticosti Island, eastern Canada

The storm-dominated, open marine neritic carbonate facies, continuously exposed in coastal cliffs and wide rocky tidal flat exposures at the western end of Anticosti Island, form a 315-m-thick, expanded section spanning the Ordovician-Silurian boundary. These carbonate facies display deepening-shallowing trends of different orders, resulting in a hierarchical stacking of sedimentary cycles. The carbonate facies within these multi-order cycles represent sediments that were deposited from shoreline to deeper outer carbonate ramp (>80 m in water depth) and exhibit sea-level changes of several tens of metres in magnitude. Field, petrographic and geochemical evidence support a well-preserved primary δ18O signal in close equilibrium with the original paleoenvironmental conditions. The δ18O intracycle variations, up to 1.0‰ in magnitude, reveal repeated decreasing and increasing values during the transgressive and regressive portions of decametre TR cycles respectively. Although temperature, salinity, and ice volume influenced the recorded primary δ18O signal, orbital scale glacioeustasy ultimately controlled facies and cycle development and δ18O signal during the Katian immediately before the latest Ordovician (Hirnantian) glaciation. The ~3.5 myr-long δ18O signal recorded by our entire succession supports a protracted period of cooling leading into the main phase of latest Ordovician (Hirnantian) glaciation. Spectral analysis of the δ18O record also reveals decametre variations, which are associated with decametre scale transgressive-regressive (TR) cycles; possibly reflecting eccentricity orbital signals. Our study shows the importance of a thick expanded stratigraphic succession sampled at the highest resolution possible to decipher potential linkages between facies changes, multi-order stratigraphic cycles, δ18O signal and the Earth's orbital parameters.

An epeiric glass ramp: Permian low-latitude neritic siliceous sponge colonization and its novel preservation (Phosphoria Rock Complex)

Glass ramps are shallow-marine depositional settings in which siliceous sponge meadows dominate coastal environments. They are increasingly recognized throughout the Phanerozoic and represent a biosiliceous counterpart to neritic carbonate factories. Detailed reexamination of the Permian Tosi Chert in the Bighorn Basin indicates that it records a glass ramp that extended over at least 75,000 km2. Outcrops, cores, and wireline logs are used to discriminate previously unidentified shallow subtidal to peritidal facies in its landward extent. These facies indicate that sponge meadows ranged from variably oxygenated offshore settings through low-energy, well-oxygenated, and saline shallow subtidal settings, with spicules transported into supratidal environments affected by enterolithic evaporite growth. This range of subenvironments is largely unique among glass ramps. This is the result of the Tosi's accumulation in an epicontinental sea where waves impinged offshore but frictional attenuation caused low-energy nearshore environments. As a result, the Tosi shares similarity with epeiric sea carbonate deposition and is referred to herein as an epeiric glass ramp. The low palaeolatitude of the Tosi and hot and arid desert it bordered also contributed to its uniqueness as shallow waters were warmer and more saline than higher-latitude counterparts. As a result, a minor sea-level fall at the termination of biosiliceous deposition was associated with increased lagoonal circulation and refluxing brines that caused evaporite and dolomite precipitation within the upper Tosi. Preservational attributes of the Tosi also add to the range of unique traits that can be used to reconstruct neritic biosiliceous environments. These include three disparate colours of chert (black, grey, and purple) related to the host strata and diagenetic redox conditions, early chertification that preserved sedimentary structures within nodules, and nodule shape related to bioturbation intensity. The Tosi glass ramp thus expands the known extent and context of Permian glass-ramp deposition along the western Laurentian margin and illustrates key properties that will aid future glass ramp identification.

Paleobiogeographic distribution of rudist bivalves (Hippuritida) in the Oxfordian–early Aptian (Late Jurassic–Early Cretaceous)

In the Late Jurassic and Cretaceous the warm shallow water seas were characterized, within benthic marine organisms, by rudist bivalves, a peculiar group of mollusks that originated in the Late Jurassic and became extinct at the end of the Cretaceous. In this paper their global distribution in neritic carbonates is considered since their first appearance in the middle Oxfordian up to the first main extinction event at the end of the early Aptian. The information and data regarding global rudist occurrences throughout neo-Tethys and paleo-Pacific oceans are critically reprised from literature and organized in an Oxfordian-early Aptian Rudist database (OXAP_RDB) that encompasses 235 rudist-bearing localities all across the world, with 845 total rudist occurrences, 34 valid genera and 148 species. Actual rudist geographic distribution is investigated in order to contribute to the identification of the paleobiogeographic pattern of these benthic organisms in the paleoclimatic and paleogeographic setting of neo-Tethys and paleo-Pacific oceans, allowing to reconstruct dispersal patterns and to define four broad paleobiogeographic Provinces in the Barremian–early Aptian.

Marine carbonate factories: a global model of carbonate platform distribution

Platform carbonates are a major component of the Earth system, but their spatial distribution through geological times is difficult to reconstruct, due to the incompleteness of geological records, sampling heterogeneity, and their intrinsic complexity. Beyond this complexity, carbonates are not randomly distributed in the world oceans, neither in the modern nor in the past, and thus, global trends exist. In the present review, we focus on the understanding of the spatial distribution of carbonate production at a global scale. We use a deterministic approach, which focuses on discriminating components, stratigraphic architectures, and environmental features to relate shallow-water carbonate production to oceanographic parameters. The work is based on extensive literature reviews on carbonate platforms. Ecological niche modelling coupled with deep-time general circulation models is used to calibrate a predictive tool of carbonate factory distribution. A carbonate factory function is set up that is based on sea-surface oceanographic parameters (temperature, salinity, and primary productivity). The model was tested using remote-sensing and in situ oceanographic data of Modern times, while outputs of paleoceanographic models are utilized for Lower Aptian (Cretaceous) modelling. The approach allows determining four neritic carbonate factories that are called the marine biochemical, photozoan, photo-C-, and heterozoan factories. The model finely simulates the global distribution of Lower Aptian and Modern carbonate platforms. Carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation. This conceptual scheme appears to be able to provide a simple, universal model of paleoclimatic zones of shallow-water marine carbonates.

Chemostratigraphy of Late Sinemurian – Early Pliensbachian shallow-to deep-water deposits of the Central High Atlas Basin: Paleoenvironmental implications

Shallow water carbonate rocks are especially prone to diagenetic alteration. As such they are sometimes problematic archives of past carbon cycle perturbations, casting doubt on the reliability of shallow-water carbonates carbon isotopes analyses for chemostratigraphic purposes. In this paper, bulk organic carbon isotopes (δ13Corg) is used as a robust replacement of the more sensitive carbonate carbon isotope systems for the establishment of a refined chronostatigraphic framework for the evolution of Sinemurian-Pliensbachian neritic carbonate systems in the Central High Atlas Basin of Morocco. These data show very similar patterns and characteristics in the organic carbon isotope curves of basinal and platform sections and thus illustrate the reliability of these archives. Simultaneously, we explore the expression of the global carbon isotope excursion at the Sinemurian-Pliensbachian boundary (SP event) in the study area in Morocco. This event has been previously described as a negative carbon isotope excursion of ∼2‰ associated with a large transgression in numerous basins. In Morocco and other neritic carbonate records, the SP event is better described as a return to previous values after a positive carbon isotope excursion coinciding with a major latest Sinemurian regression recognised on a global scale. Similar patterns are also found in other sections, although sometimes poorly expressed. However, it shows, that the SP event has ambiguous characteristics and questions the conventional hypothesis of it being linked to the massive injection of 13C-depleted carbon into the atmosphere-ocean system.