Carbonate-dominated Sedimentation Research Articles

Lithofacies and cyclicity of sulphate dominated tidal-lagoon deposits of Late Triassic age in Northeast Iberia (western Europe)

Thick gypsum‑carbonate sequences were deposited in different periods and basins of Europe during the westward opening of the Tethys Ocean. Although they seem to represent widespread perimarine sulphate-dominated lagoons in shallow epeiric platforms, the sedimentary characteristics and interpretation of these deposits are still poorly constrained. To advance in the knowledge of these deposits, a detailed study is presented of two distinctive sulphate dominated sequences of Late Triassic age located in NE Iberia (Western Europe), which correspond to the Canelles and Espinagosa units, found in the southern Pyrenees and the Catalan Coastal Ranges respectively. These sequences present a diverse suite of carbonate and sulphate lithofacies, which are stacked in several recurring sedimentary cycles. These cycles consistently present a carbonate base that transitions to a sulphate top, and can be correlated along several tens of kilometres. Each of the observed cycles depicts an initial sudden flooding of a tidal-lagoon system by marine water, which led to carbonate-dominated sedimentation. Progressive evaporation under dominant arid climate conditions triggered the shallowing of the lagoon and salinisation of its water. Then, a transition from carbonate to gypsum/anhydrite precipitation and the early dolomitisation of the underlying carbonate sediments by brine reflux occurred. Gypsum precipitated in the water column as cumulate crystals and deposited at the bottom of the lagoon, forming laminations or being incorporated into microbial mats. Anhydrite precipitated as early diagenetic crystals in the different subaqueous and subaerial environments of the tidal-lagoon system, leading to a variated set of lithofacies until now largely undocumented. It mainly formed as displacive lath-shaped crystals randomly oriented within carbonate muds at the bottom of the lagoon, which were mostly reworked at the lagoon margins by wave and tidal currents resulting in aligned fabrics in cross-lamination structures. Anhydrite also formed as pure massive beds by anhydritisation of subaerially exposed gypsum sediments during the main retraction stages of the lagoon, as well as typical nodular (sabkha) lithofacies. Such sulphate lithofacies are not easy recognisable due to the lack of modern analogues to compare and to their current transformation into secondary gypsum in the outcrops. These are aspects to be taken into account in future sedimentological studies on similar evaporitic materials.

A data-driven hyperspectral method for sampling of diagenetic carbonate fabrics – A case study using an outcrop analogue of Jurassic Arab-D reservoirs, Saudi Arabia

Diagenetic alteration commonly overprints depositional fabrics in carbonate-dominated sediments and impact reservoir quality. Dolomitization is a prevalent diagenetic process observed in subsurface reservoirs that profoundly alters the depositional precursor's pore network, thereby influencing subsurface storage capacity and fluid flow behavior. Typical workflows to characterize the dolomitized sequences, textures, degree and extent of dolomitization rely on mapping, spatial sampling, and time-consuming geochemical, petrographic and petrophysical analysis. In this study, we propose a hyperspectral data-driven workflow for identifying dolomitized horizons and extracting sample sets optimized to characterize textural and chemical variations. Hyperspectral imaging (HSI) data was acquired with 1.5 mm spatial sampling along a 50 m long core drilled behind an outcrop of the Late Jurassic Jubaila-Arab sequence in Wadi Daqlah, Saudi Arabia. Spectral features in the visible (VNIR), shortwave (SWIR), mid-wave (MWIR), and long-wave (LWIR) infrared regions were then used to classify carbonate mineralogy, allowing for the rapid identification of dolomitized zones, and k-means clustering applied exclusively to the dolomitized areas used to identify intra-dolomite variations and suggest representative sample locations. Petrographic and geochemical analyses were carried out on these samples, revealing that clusters identified with the hyperspectral data represent four distinct diagenetic fabrics. These results demonstrate the value of HSI for objective and data-driven sampling, reducing the number of samples required for petrographic, geochemical and geophysical analysis and hence time and costs required to spatially characterize diagenetic alteration.

Deposition of Mo, Re and U under contrasting redox conditions; assessment of the [Re/Mo]sw redox proxy

We have analyzed concentrations of Mo, Re and U in the suspended particles, water column, underlying carbonate-dominated sediments and pore waters of two contrasting marine lakes situated on the Adriatic Coast of Croatia. Our data are the first for Re in these lakes. Rogoznica Lake is mainly euxinic, but subject to occasional oxygenation events, whereas Mljet Island’s Malo Jezero is currently oxic year around but historically was seasonally euxinic. These characteristics make the lakes useful testing grounds for redox proxies. We devote particular attention to Re/Mo ratios, which have great promise as redox proxies. In marine sediments, the range of log[Reauth/Moauth] exceeds 2, and typical analytical uncertainty is ±0.05, providing resolving power similar to δ98Mo. Authigenic [Res/Mos] ratios in sediments depend on varying supplies of three components: FeMo,Re)S4 coprecipitates, Fe(III) oxyhydroxides (plus Mn(III,IV) oxyhydroxides in some cases) and a still-uncharacterized Re-rich, Mo-poor component possibly of biological origin. Removal of the latter component explains a 50% depletion of Reaq without Moaq from Rogoznica’s oxic waters. Water column concentrations of Moaq and Reaq, as well as [Res/Mos] ratios in Rogoznica’s suspended particles are predicted successfully by a model that attributes these elements’ removal from sulfidic seawater solely to coprecipitation in Fe(Mo,Re)S4, assuming a partition coefficient of 0.6. However, to predict sediment compositions, additional authigenic Mo supplied by mainly Fe(III) oxyhydroxides during sporadic oxygenation events must be considered. In Malo Jezero, sulfide concentrations are too low even in pore waters for precipitation of Fe(Mo,Re)S4. Consistent with earlier work, Uaq profiles are best explained by eddy diffusive transport to the sediment rather than capture by a precipitate in the water column. In Rogoznica pore waters, Moaq extracted through 0.45 μm pore size filters exceeds by 50-fold concentrations predicted by the model and measured previously with 0.15 μm filters. This observation implies presence of ferrothiomolybdate colloids, which could be important, overlooked participants in the sedimentary geochemistry of Mo.

More gaps than record! A new look at the Pliensbachian/Toarcian boundary event guided by coupled chemo-sequence stratigraphy

The Pliensbachian/Toarcian boundary (Pl/To) event precedes by ca. 1 Myr the onset of the Toarcian Oceanic Anoxic Event. It corresponds to a second order mass extinction associated with an outstanding collapse of shallow marine ecosystems at global scale. Yet, our knowledge about its exact driver(s) and unfolding is relatively ambiguous due to the numerous hiatuses present in the sedimentary record during this critical time interval. In this study, an integrated carbon isotope chemostratigraphy and sequence stratigraphy approach is applied to two case studies (the upper Pliensbachian in South-East France and the Pliensbachian–Toarcian transition in Morocco) to demonstrate how the major changes in sea-level and sedimentation supply accompanying the Pl/To event led to the formation of ubiquitous, often cryptic hiatal surfaces in the sedimentary record. Hence, as a consequence of strongly progradational stacking pattern during the latest Pliensbachian related to a global sea-level lowstand associated with cold greenhouse climate, proximal settings were characterized by bypass and/or erosion, inducing an incomplete record of the Spinatum chronozone in localities situated in the outer part of sedimentary basins. In the earliest Toarcian, the collapse of the neritic carbonate factory led to a halt of carbonate mud export into the basin, resulting in sediment starvation in most basins characterized by a carbonate-dominated sedimentation regime before the environmental perturbation. Only localities where vigorous siliciclastic sediment supply took over are likely to have a more complete sedimentary record of the immediate aftermath of the carbonate production collapse. This combination of causes explains the ubiquitous incompleteness of the record of the Pliensbachian/Toarcian transition in numerous European localities where the bulk of our current understanding about the Pl/To event derives from. A comparison between the two known most expanded and complete records of the Pliensbachian–Toarcian transition of the Llanbedr (Mochras Farm) core in Wales and Bou Oumardoul n'Imazighn section in Morocco shows that the onset of the environmental perturbations is associated with a positive carbon isotope excursion spanning the Pliensbachian/Toarcian boundary. This is followed by a negative carbon isotope excursion during the earliest Toarcian that coincides with the global collapse of neritic carbonate factory and an ample sea-level fall.

Facies analysis and depositional model for the Oxfordian Hanifa Formation, Central Saudi Arabia

The Jurassic was a time for major global changes in climate, tectonics, and oceanography, reflected in the southern Neo-Tethys Ocean by a distinct transition from carbonate-poor to carbonate-dominated sedimentation. To better constrain the effect of this turning point in the Late Jurassic, key outcrops of Oxfordian deposits of the Arabian Plate were investigated through detailed sedimentologic analysis. High-resolution (centimeter-scale) description and analysis of eight outcropping sections with a cumulative thickness of 461 m through the Oxfordian Hanifa Formation along a N–S 535 km-long transect in central Saudi Arabia are used to develop a comprehensive conceptual depositional evolution through time. Nine sedimentary lithofacies are interpreted and grouped into four facies associations. These associations include: I) outer-ramp association (FA1), II) mid-ramp association (FA2), III) inner-ramp grainy-facies association (FA3), and VI) inner-ramp reefal association (FA4). The lithofacies succession distinguishes two depositional phases, a middle Oxfordian homoclinal ramp (Phase 1) that corresponds to the Hawtah Member, and a late Oxfordian reef-bearing carbonate ramp (Phase 2) that corresponds to the Ulayyah Member. After being restricted to the high latitudes in the northern Neo-Tethys during early and middle Oxfordian ages, the carbonate ramp evolution within the Hanifa Formation reflects the expansion of scleractinian coral reefs over the southern Neo-Tethys passive margin in the late Oxfordian. However, the distribution of the corals in the Arabian Plate is mainly controlled by water salinity and siliciclastic input; they are absent northward due to hypersalinity and southward due to siliciclastic input. Furthermore, the differential subsidence and the resulting uneven topography, in addition to the eustatic sea level variation during the Oxfordian age, controls the distribution of different depositional styles over the Arabian Plate (homoclinal ramp, distally-steepened ramp, rimed shelf, and intrashelf basin).

Geochemical characterization of surface sediments from the Ridracoli reservoir area and surroundings, Italy. Details on bulk composition and grain size

Sediment characterization of Ridracoli reservoir, an artificial lake for water supply, and surroundings of the Fiumi Uniti catchment in the northern Apennines, Emilia-Romagna, Italy, is carried out to evaluate the overall status of the drainage basin encompassing the reservoir. The study area combines the reservoir catchment that is part of the Foreste Casentinesi-Monte Falterona-Campigna National Park, formed by the construction of a dam operating since 1982 for drinking water storage and electricity production, and the upstream side of Fiumi Uniti catchment that flows into the Adriatic Sea, including also nearby sub-catchments of Ridracoli reservoir, named Corniolo and Pietrapazza.We collected surface sediments within the area of the reservoir and riverbed sediments of surroundings catchments, analyzed grain size distribution and the chemical composition, including carbon and nitrogen. This work investigates the chemistry and distribution of elements within the study area, evaluates the dam's effect upstream and downstream, and studies the processes that happen in rivers and the reservoir. The bulk composition is mainly represented by SiO2, Al2O3, CaO, with high Corg content reflecting the Marnoso Arenacea Formation geology of the area. Statistical data analysis on the available parameters suggests the presence of two main types of sediment, namely clayey and carbonate-dominated sediments. On the reservoir area, the relationship between elements and clay matrix and organic matter, besides iron, points to a potential grain size influence, degradation of organic matter, and mineralization processes. The grain size analysis shows that silty and clayey sediments are in the bottom of the reservoir, and sand, is apparent in sediment samples from the tributaries, due to sorting effects and likely directly explained by metals concentrations. This reasoned investigation included further samples from the literature to consider the entire surrounding area and was supported by Principal Component Analysis and Cluster Analysis.

On the kinematics and timing of Rodinia breakup: a possible rift–transform junction of Cryogenian age at the southwest cape of Congo Craton (northwest Namibia)

AbstractAfter tilt correction for Ediacaran thick-skinned folding, a pair of Cryogenian half grabens at the autochthonous southwest cape of Congo Craton (CC) in northwest Namibia restore to different orientations. Toekoms sub-basin trended east-northeast, parallel to Northern Zone (NZ) of Damara belt, and was bounded by a normal-sense growth fault (2 290 m throw) dipping 57° toward CC. Soutput sub-basin trended northwest, oblique to NZ and to north-northwest-trending Kaoko Belt. It was bounded by a growth fault (750 m down-dip throw) dipping steeply (~75°) toward CC. Soutput growth fault could be an oblique (splay) fault connecting a Cryogenian rift zone in NZ with a sinistral transform zone in Kaoko Belt. A transform origin for the Kaoko margin accords with its magma-poor abrupt shelf-to-basin change implying mechanical strength, unlike the magma-rich southern margin where a gradual shelf-to-basin change implies a mechanically weak extended margin. A rift−transform junction is kinematically compatible with observed north-northwest−south-southeast Cryogenian crustal stretching within CC. Post-rift subsidence of the CC carbonate platform varies strongly across the south-facing but not the west-facing shelf. A sheared western CC margin differs from existing Kaoko Belt models that posit orthogonal opening with hyper-extended continental crust. Carbonate-dominated sedimentation over southwest CC implies palaeolatitudes ≤35° between 770 and 600 Ma.

The syn-rift stratigraphic record across a fossil hyper-extended rifted margin: the example of the northwestern Adriatic margin exposed in the Central Alps

To understand the overall spatial and temporal evolution and resulting sedimentary stacking patterns within an evolving hyper-extended rift system, we investigated the Austroalpine and Upper Penninic nappes in the Central Alps. These nappes preserve pristine remnants of the northwestern Adriatic rifted margin showing the transition from stretched and hyper-extended continental crust to exhumed mantle of a sediment-starved, magma-poor rifted margin. Our paper reviews sedimentological and structural data that enable us to determine a general chrono-tectono-stratigraphic framework for the syn-rift succession of the margin. The detailed study of the facies distribution within the different rift domains, including proximal, necking, hyper-extended, and exhumed mantle domains, allow us to identify syn- and post-tectonic sedimentary packages. The correlation of these sedimentary packages between the rift domains is based on the identification of basin-wide correlative stratigraphic intervals linked to global or basin-wide Jurassic events: (1) the Early Toarcian Oceanic Anoxic Event; (2) an Early Bajocian bio-siliceous event; and (3) the onset of Tithonian carbonate-dominated sedimentation. Using these timelines, we could recognize the oceanward propagation of the syn-tectonic package from the proximal to the exhumed mantle domains as a function of time. A key observation is that syn-tectonic packages can be compartmentalized into four tectonic system tracts across the margin. Each system tract and their associated bounding surfaces record the stratigraphic evolution and change in deformation mode related to distinct and successive syn-rift phases that correspond to the stretching (~ 10My), necking (~ 6My), hyper-extension (~ 15My), and mantle exhumation (~ 18My) phases.

Evaluating the effects of diagenesis on the δ13C and δ18O compositions of carbonates in a mud-rich depositional environment: A case study from the Midland Basin, USA

Marine carbonate δ13C and δ18O values are commonly utilized as indicators of past climate and are thought to record primary seawater conditions. However, these minerals can be altered following deposition and burial, overprinting the primary signal to reflect subsurface conditions. Whereas the influence of post-depositional alteration is widely understood in carbonate-dominated sediments (Swart, 2015), the influence has not been as widely studied in mud-rich settings. This study analyzed the carbonate δ13C and δ18O values from carbonate intervals in the Late Pennsylvanian Wolfcamp D shale unit in the Midland Basin to evaluate the impact of post-depositional alteration on the interpretation of stable isotope compositions of carbonates in a mud-rich depositional environment. Here we show the importance of using multiple indicators to fully evaluate the impact of post-depositional alteration on the interpretation of the marine carbonate δ13C and δ18O values in mud-rich environments. The extent of diagenesis in the Wolfcamp D was primarily controlled by fluctuations in benthic redox chemistry, which controlled sulfate reduction and the preservation of organic matter. These processes influenced the extent of carbonate cementation in the bacterial sulfate reduction zone and during deep-burial, making the carbonates unreliable for intra-basinal correlations. The results of this study were incorporated into a conceptual model that can likely be applied as a framework for other studies in mud-rich depositional environments.

Age and Paleobathymetry of Salodik Group in PohPagimana section, East Arm of Sulawesi Based on Foraminiferal Assemblages

Planktonic and benthic foraminiferal assemblages were used for age and paleobathymetry analysis of outcropping carbonate succession of the Salodik Group in Poh–Pagimana section, East Arm of Sulawesi. Twenty spot samples of carbonate rocks were collected from cut slope along the road between Poh and Pagimana. Age analysis conducted for each sample by its planktonic foraminifera assemblages and group into their age interval. The age range from Early Eocene to Pliocene. Benthic foraminiferal assemblages indicate paleobathymetry ranging from middle shelf to upper bathyal settings. Age analysis of the studied section show an older sediments (Early–Middle Eocene) overlie younger sediment (Early Miocene). This is interpreted as the evidence of thrust fault in the Poh–Pagimana section as part of thrust sheets of Batui thrust complex which imbricated on deformation zone. The youngest sediment which have suffered deformations shown by disordered age sequence is Pliocene in age (N20-21). The Eocene to Pliocene carbonate succession in the studied section was deposited relatively in the more basinward position compared to the carbonate-dominated sediments in the Tomori area which was deposited in the more landward position.

Sedimentary environmental change induced from late Quaternary sea-level change in the Bonaparte Gulf, northwestern Australia

Low-latitude continental shelves, mixed siliciclastic–carbonate sedimentary systems, provide an understanding of sedimentary environments driven by paleoclimatological processes. The Bonaparte Gulf, northwestern Australian continental shelf, is among the widest in the world, ranging to 500 km, with shallow carbonate terraces and platforms that were exposed during periods of lower sea level. The dominant sediments type switches between carbonate and siliciclastic over a sea-level cycle. However, the mechanism of sedimentary environmental change in the Bonaparte Gulf is not clearly understood. Here, we present a record of sedimentary environmental change from ca. 24 to 35 ka that is related to sea-level variability and exposure of carbonate terraces and platforms. Multi-proxy data from a marine sediment core show a sea-level change induced switch in sedimentary environment from siliciclastic to carbonate-dominated sedimentation during the last glaciation. Radiocarbon ages constrain the timing of this switch to ca. 26 ka, associated with a local sea-level fall of −90 m.

A new model evaluating Holocene sediment dynamics: Insights from a mixed carbonate–siliciclastic lagoon (Bora Bora, Society Islands, French Polynesia, South Pacific)

Mixed carbonate–siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition. Sediment sources include lagoonal carbonate production, the marginal reef and the volcanic hinterland. Mixed carbonate–siliciclastic continent-attached coastal lagoons have been intensively studied, however, their isolated oceanic counterparts have been widely disregarded. Here, we present a new model of Holocene sediment dynamics in the barrier–reef lagoon of Bora Bora based on sedimentological, paleontological, geochronological and geochemical data. The lagoonal succession started with a Pleistocene soil representing the Lowstand Systems Tract. As the rising Holocene sea inundated the carbonate platform, peat accumulated locally ~10,650–9400yearsBP. Mixed carbonate–siliciclastic sedimentation started ca. 8700–5500yearsBP and represents the Transgressive Systems Tract. During that time, sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon. Siliciclastic content decreases throughout the Holocene. After the rising sea had reached its modern level, sand aprons formed between reef crest and lagoon creating transport pathways for reef-derived material leading to carbonate-dominated sedimentation ca. 6000–3000years BP during the Highstand Systems Tract. However, mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron. From ca. 4500–500yearsBP, significant variations in grain-size, total organic carbon as indicator for primary productivity, Ca and Cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen. Such patterns could indicate event (re-)deposition and correlate with contemporaneous event deposits found in the lagoon of nearby Tahaa, which are supposed to be induced by elevated cyclone activity. Correspondingly, enhanced erosion and run-off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall. Increased amounts of coarse-grained sediment from marginal reef areas would be transported into the lagoon. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid-Holocene. Also, benthic foraminiferal faunas do not validate reef-to-lagoon transport of sediment. Alternatively, the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher-than-present sea level, which are supposed for the mid-late Holocene in the south Pacific. Sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity. We propose the shift towards coarser-grained sedimentation patterns during the mid-late Holocene to reflect sediment-load shedding of sand aprons due to oversteepening of slopes at sand apron/lagoon edges during times of stronger trades and higher-than-present sea level of the Highstand Systems Tract, which led to redeposition of sediment even within the lagoon center. Modern conditions including a sea-level fall to modern level were reached ca. 1000yearsBP, and lagoonal infill has been determined to a large part by fine-grained carbonate-dominated sediments produced within the lagoon and derived from the marignal reef. Infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons. Contrary to the commonly supposed assumption that coarse-grained sediment layers within fine-grained lagoonal successions represent overwash events induced by storms or periods of higher storm activity, we postulate a new model of long-term lagoonal sediment dynamics including sea level, climatic change and geomorphological variation of the barrier reef lagoon.

A siliciclastic braid delta within a lower Paleogene carbonate platform (Ordesa-Monte Perdido National Park, southern Pyrenees, Spain): Record of the Paleocene–Eocene Thermal Maximum perturbation

The La Pardina Formation is a siliciclastic-dominated unit up to 26m thick intercalated within a 300m thick Danian–lower Ilerdian succession of shallow marine carbonates in the southern Pyrenees. The unit is composed of four interdigitated facies, three of them of a coarse-grained siliciclastic character (Sf1, Sf2, Sf3), and the fourth one composed of bioclastic packstones with argillaceous matrix (calcareous facies, Cf). The siliciclastic facies make up the bulk of the La Pardina Formation in the Ordesa-Monte Perdido National Park, while the Cf is subordinate in the Park but widespread throughout the southern Pyrenees. Biostratigraphic and isotopic data suggest that the Cf pertains to the Paleocene–Eocene Thermal Maximum (PETM). No isotopic or biostratigraphic information could be obtained from the siliciclastic facies, but they are also assigned to the PETM because of their interfingering with the Cf. The siliciclastic facies were accumulated in a braid delta system fed by either a major river or by several minor rivers draining the Ebro Massif. The Sf3, Sf2 and Sf1 respectively represent the top-set, foreset and bottomset parts of the braid delta, whereas the Cf correspond to the prodelta. In proximal parts of the braid delta the Sf3 overlies a subaerial surface carved into upper Thanetian marine carbonates, a proof of a pre-PETM sea-level fall. In the remainder of the braid delta, the La Pardina Formation exhibits an overall thickening-coarsening-up trend that attests to rapid progradation. The development of the braid delta implies a dramatic increase in the influx of both coarse- and fine-grained siliciclastics, which temporarily halted a long-lasting period of carbonate-dominated sedimentation. This abrupt change demonstrates that the environmental impact caused by the intensification of the hydrological cycle during the PETM was particularly severe at middle latitudes.

Fluvial discharge and sea-level changes controlling black shale deposition during the Paleocene–Eocene Thermal Maximum in the Dababiya Quarry section, Egypt

The formation of black shales along the Tethyan margins at the Paleocene–Eocene Thermal Maximum (“PETM”; ~ 55 Ma) may have been an important feedback mechanism to reduce the warming by excess carbon burial. However, the detailed evolution of sediment redox conditions during this event is still poorly constrained. We address this issue by a high-resolution mineralogical and geochemical investigation of the outer neritic Dababiya Quarry PETM section in Central Egypt, which serves as the Global boundary Stratotype Section and Point for the base of the Eocene. There, the base of the PETM beds corresponds to the onset of sediment lamination indicative of oxygen-deficiency at the seafloor. The absence of calcium carbonate and a major increase in phyllosilicate abundance and change in detritus-sensitive trace elements is indicative of severe carbonate dissolution in addition to enhanced fluvial input, erosion of coastal low lands, and deposition during low or slightly rising sea level. Subsequently, fully anoxic conditions were established for a short period during the peak phase of the PETM as recorded by the strong relative enrichment of redox-sensitive trace elements and organic carbon compared to background sediments. The decoupling of the Fe and Mo contents from the detrital fraction may even indicate that euxinic conditions existed with free hydrogen sulfide in the water column. Concurrent to the onset of anoxia, high carbonate and quartz contents as well as high elemental ratios of Si/Al suggest a major drop of siliciclastic sediment supply (sediment starvation), most likely caused by a rapid sea level rise. The final recovery phase of the PETM is associated with a progressive restoration of the pre-PETM siliciclastic sedimentation, temporary (seasonal) anoxic to dysoxic conditions, and high phosphorus enrichment, followed by carbonate-dominated sedimentation and the return to well-oxygenated conditions. We conclude that after a period of strong fluvial discharge, several parameters inherent to the PETM (e.g., warming, water-column stratification, and enhanced fluvial discharge) may have contributed to the development of anoxia and increased the burial efficiency of organic carbon by reducing water column oxygenation. The temporal coincidence of sediment starvation and onset of black shale deposition during the PETM suggests that a rapid sea-level rise was an additional important triggering factor. Therefore, our results support not only current views that Tethyan continental shelf areas may have acted as large carbon sinks during the PETM, but also indicate that transgressions may have provided an important feedback mechanism for organic carbon drawdown during hyperthermal events.

Timing of early to mid-cretaceous tectonic phases along North Africa: New insights from the Jeffara escarpment (Libya–Tunisia)

The Jeffara escarpment spans 400 km from southeastern Tunisia to sorthwestern Libya, and marks the northern edge of the Berkine–Ghadames Basin. Its horseshoe shape provides a good 3D control of regional-scale depositional architecture. Historically, the political border between Tunisia and Libya hindered the integration of studies over its entirety, which led to the establishment of separate litho-biostratigraphic frameworks. Field-work undertaken on both sides of the border has allowed the unification of lithostratigraphic schemes developed in both countries. Published stratigraphic ages of the different formations and members are compared and integrated in order to propose a unified bio-lithostratigraphic framework. The correlation of serial sections along the Jeffara escarpment shows that two major tectonic unconformities divide the Early Cretaceous sedimentary pattern. The first one is dated as Late Aptian and is commonly associated with the European “Austrian” tectonic phase. The second, which has previously not been recognized as a regional significant surface in Libya, occurs during the Middle Albian and marks moreover the transition from a siliciclastic to a carbonate-dominated sedimentation regime. These two important regional unconformities form the lower and upper boundaries of the Kiklah–Aïn el Guettar Formations, and can be associated with intra-plate deformation linked with the opening of the central segment of the South Atlantic and the Equatorial Atlantic oceans.

Last interglacial coastal environments in the Mediterranean–Saharan transition zone

The coast of Tunisia stretches from the western Mediterranean climate belt in the north to the Saharan desert climate belt in the south. The sediments of this coastal strip provide a record of sea level change if an accurate chronology of the coastal deposits is available. We have here surveyed and analysed coastal sites and established a chronology based on optical dating techniques. The optical ages range from 156 ka to 62 ka (2σ level) and cluster around the last interglacial period (~ 125–75 ka). Our study shows that sea level rose after Termination II for about 25 ka leading to a transgressive deposit at ~ 120 ka. A disconformity shown by some deposits suggests a brief drop of sea level during this transgressional phase. Subsequently, for around 40 ka the coastal area became covered by soils, colluvia and aeolian sediments indicating a slowly falling sea level. While the composition of sediments at the north coast did not change, the deposits at the central and south coast experienced a drastic change from a quartz- to a carbonate-dominated sedimentation sometime during the last interglacial. Littoral sedimentation ceased at ~ 70 ka when the coast became sediment starved in the course of the falling sea level.

Sedimentology and tectonic setting of the Pindos Flysch of the Peloponnese, Greece

Abstract The Palaeogene Pindos Flysch of the Peloponnese shows important differences from the flysch of northern Greece. Stratigraphic sections and palaeocurrent indicators were measured in the Pindos Flysch Formation and the underlying Kataraktis Passage Member throughout the Peloponnese. The Kataraktis Passage Member records carbonate-dominated sedimentation from the Apulian continental margin to the west, with intercalated terrigenous sediment also derived from the west. Variations in thickness and turbidite facies show that the overlying Pindos Flysch Formation was deposited in channels with levees and in channel-termination lobes in the western Peloponnese and in a distal basin plain, locally ponded, in the east. At least in the central Peloponnese, facies variation, palaeocurrents and detrital petrology show that the Pindos Flysch was derived from the Apulian margin. The Pindos Flysch of northern Greece, of late Paleocene to Oligocene age, was deposited in a foreland basin and derived from the rising Pelagonian nappes to the east. A younger microcontinental collision south of the Gulf of Corinth line resulted in the Pindos Flysch of the Peloponnese being incorporated in the accretionary prism by Mid-Eocene time.

New stratigraphical results and significance of reworking based on nannofossil, foraminiferal and sedimentological records in the Lower Tertiary sequence from the northern Isparta Angle, Eastern Mediterranean

This study presents new stratigraphical data on the sediments of the Lower Tertiary sequence outcropping in the northern Isparta Angle, Southwest Anatolia. These data, which are based on field observations, foraminifera and nannofossil studies, and sedimentological findings, contribute to the paleoenvironmental and structural interpretations. Reworking of fossils that was neglected in previous work is an important factor for understanding and clarifying the Early Tertiary geological evolution of the region. This investigation particularly focuses on the significance of reworking in the stratigraphic record. The Early Tertiary unconformity-bounded unit consist of two transitional lithofacies, varying from marine clastics to carbonates. The first lithofacies mainly composed of clastics, whereas the second contains carbonate-dominated sediments. The Lower Tertiary sequence unconformably overlies an irregular surface composed of ophiolitic rocks, deep marine bedded cherts and carbonates of early Mesozoic age, Mesozoic carbonates and marine clastics and carbonates of Late Cretaceous age. The unit is unconformably overlain by Lower Miocene marine clastics. Both the unconformity and tectonic relationships between the Eocene and Lower Miocene sequences are seen in the northern study area. These exposures are proof of pre-Miocene erosion and post-Miocene deformation. In this study, two nannofossil interval zones, NP12 and NP13, were identified from fine-grained clastics and carbonates. According to benthic foraminifera and nannofossil contents, the formation is Early Eocene (Ypresian) in age. The percentages of reworked (older) fossils range from 75% in the lower levels to 15% in the higher levels of the Lower Tertiary sequence. This study demonstrates that detailed analyses of fossil reworking are needed in order to obtain more reliable results. The evidence of strong reworking, plant traces, biostratigraphical and sedimentological data indicate that a single cycle of Early Eocene sedimentation occurred in a shallow to open-marine depositional environment, becoming shallower as time progressed. The obtained data indicate a marine transgression from north to south in the northern part of the Isparta Angle during Eocene time.

Hydrological changes related to the variability of tropical South American climate from the Cabo Frio lagoonal system (Brazil) during the last 5000 years

From west to east, the Fluminense coastline, composed of two series of lagoons, presents an aridity gradient induced by a local upwelling that is controlled by trade winds coming from the south Atlantic. The physico-chemical conditions of the lagoons are controlled by the duration of the dry season. They are characterized by hypersaline conditions with organic-carbonate sedimentation in the upwelling-influenced area, and by hyposaline conditions with organic-detrital sedimentation out of the upwelling-influenced area. On a core collected in the Brejo do Espinho hypersaline lagoon, diatom analysis supported by sedimentological data revealed a varying high water level from 4500 to 2200 14C yr BP induced by successive freshwater inputs in to the lagoon. Two major dry events occurred during this period, probably related to relative sea-level fluctuations. At 2200 14C yr BP, a drastic change occurred, as indicated by a carbonate nodule, carbonate-dominated sediments and polyto hypersaline diatoms, all suggesting arid conditions. The Brejo do Espinho record suggests that before 2200 14C yr BP, the central part of the Brazilian coast was mostly subjected to south to southeasterly winds and weaker trade winds, whereas after 2200 14C yr BP, trade winds dominated, implying drier conditions at the easternmost part of the Fluminense coastline. These results would also suggest a late Holocene increase in El Ninlo activity (after 2200 14C yr BP), consistent with several El Nifio records from western South America.

Neoproterozoic allochthonous salt tectonics during the Lufilian orogeny in the Katangan Copperbelt, central Africa

The Neoproterozoic Katangan rocks in the Copperbelt of Shaba (Democratic Republic of the Congo) and Zambia contain the world's largest concentration of stratiform copper-cobalt ores. We propose that during the Lufilian orogeny, the Katangan basin was radically transformed first by extrusion of allochthonous evaporites, then by orogenic shortening. Salt tectonics plausibly explains spectacular breccias underlying 25,000 km2 and containing gigaclasts up to 10 km long. The brecciated Shaban Roan Supergroup—the lowermost Katangan unit—forms regional detachments and diapirs. The former existence of Roan evaporites is indicated by sabkha facies, crystals, and pseudomorphs of gypsum and anhydrite, stratigraphic gaps underlain by collapse breccias, chloride inclusions in ores, hydrothermally propylitized ore hosts, and saline springs. Salt tectonics began during deposition of the Roan Supergroup between 1050 and 950 Ma. In mid-Roan time, small walls and extrusions of evaporite-gigabreccia began to be emplaced. In early Kundelungu time (940–850 Ma), evaporitic diapirs enlarged. Lufilian deformation began between 850 and 650 Ma by laterally squeezing diapirs to form salt welds. Then, a large sheet of commingled Roan evaporite and carbonate-dominated sediments and ores was extruded northward by ∼65 km. Extrusion was fast enough to blanket a uniform preorogenic footwall unit without overriding any synorogenic deposits. Continued shortening then emplaced large thrust sheets, lubricated by the preexisting salt-sediment extrusive sheet. Restoration suggests that the Lufilian foreland in this area shortened from 193 km to 85 km. The depositional northern edge of the evaporite basin controlled the shape of the Outer Lufilian Arc. We infer three original salt provinces. The large-scale salt tectonics inferred here has implications for ore genesis and may yet be recognized in other Precambrian basins.