Vocontian Basin Research Articles

Strontium-isotope stratigraphy of the Early Cretaceous (Valanginian–Barremian): Implications for Boreal–Tethys correlation and paleoclimate

The interpretation of past oceanographic events on a supra-regional scale requires precisely dated and well correlated biostratigraphic schemes. Only synchronous events can be interpreted in a global context. Events of local or regional character have therefore to be accurately correlated with time-equivalent shifts in other areas in order to be interpreted in a wider context. One of the problems of inter-basin correlation based on biostratigraphy lies in floral and faunal provincialism of the relevant index fossils. In order to overcome such limitations, chemostratigraphy can be used as a stratigraphic tool independent of biostratigraphy.This study presents 87Sr/86Sr-isotope data for the Lower Cretaceous (Valanginian to Barremian) based on previously published findings from Speeton (northeast England) and the Vocontian Basin (southeast France). These belemnite-based 87Sr/86Sr-isotope data allow a correlation of the Lower Cretaceous sequences of the Boreal Realm and the Tethys independent of biostratigraphy. This chemostratigraphic approach may help to overcome the biostratigraphic problems which have been discussed for more than 40 years.The two different 87Sr/86Sr-isotope curves modeled for the Boreal Realm and the Tethys show two offsets, asking for the following adjustments of the current correlation scheme. In the Boreal Realm, the base of the lower Hauterivian, currently defined by the first occurrence of the ammonite Endemoceras amblygonium, should be shifted into the Endemoceras amblygonium zone. The base of the upper Barremian, in the Boreal Realm defined by the first occurrence of the ammonite Paracrioceras elegans, correlates with the uppermost part of the Tethyan Kotetishvilla compressissima zone in the lower Barremian. To adjust for this mismatch a shift of the lower/upper Barremian boundary is necessary either in the Boreal Realm or in the Tethys.The combined 87Sr/86Sr and δ18OBel isotope datasets suggest a synchronous negative δ18OBel shift for the middle Barremian. This shift, seen both in the Boreal and in the Tethys, indicates a major European wide phase of high humidity and increased run-off.

Radiolarian biostratigraphy across the Lower to Upper Cretaceous boundary in the Vocontian Basin, SE France

Radiolarian biostratigraphy across the Lower to Upper Cretaceous boundary in the Vocontian Basin, SE France

High-resolution analysis of the mid-Cretaceous Oceanic Anoxic Event 1b in the Vocontian Basin, Southeast France

High-resolution analysis of the mid-Cretaceous Oceanic Anoxic Event 1b in the Vocontian Basin, Southeast France

Cretaceous standard chronostratigraphic framework based on integrated stratigraphy of planktic foraminifer and carbon isotope and U-Pb age of the Yezo Group and the Vocontian Basin sequence

Cretaceous standard chronostratigraphic framework based on integrated stratigraphy of planktic foraminifer and carbon isotope and U-Pb age of the Yezo Group and the Vocontian Basin sequence

Radiolarian and planktic foraminifera biostratigraphy of the Early Albian organic rich beds of Fahdene Formation, Northern Tunisia

The lower part of Fahdene Formation outcropping in northeastern Tunisia is represented by pelagic sequences and characterized by an important siliciclastic fraction that includes radiolarian and organic-rich beds of Allam Member. Litho-biostratigraphic analysis based on planktic foraminifera and radiolaria shows that deposition of organic-rich beds of Allam Member is confined to the Microhedbergella rischi Zone through the lower part of Ticinella primula Zone. Age diagnostic radiolaria recovered from these beds has been identified to constrain a direct age of black shale deposition. The assemblages can be correlated with the radiolarian biochronozone U.A.10–11 indicating an Early Albian to early Middle Albian in age. Radiolarian assemblages composed of species characteristic of U.A.10 biochronozone (A. montisserei, D. gracilis) are associated with radiolarian taxa belonging to Costata Zone (U.A.9 Pseudoeucyrtis hanni and Thanarla pseudodecora), which can be correlated with Dercourt Member in the Ionian Zone and Paquier level of the Vocontian Basin (southeast of France). Biostratigraphic and abundance curves analysis has demonstrated significant diversification of cryptocephalic Nassellaria and Archaeodictyomitrae, probably adapted to eutrophic conditions that characterized the Aptian-Albian transition. Ecological conditions may have governed the stratigraphic range of many cosmopolitan taxa (i.e., Pseudodictyomitrae lodogaensis) compared with stratigraphic distributions schemes reported from other domains. The timing of black shales deposition was diachronic due to local geodynamic conditions and upwelling currents distribution. The Allam black shales are correlative with the oceanic anoxic event OAE1b which is characterized by the widespread of supraregionnally organic-rich beds in the Mediterranean Tethys basins across the Aptian-Albian transition.

High Diversity in Cretaceous Ichthyosaurs from Europe Prior to Their Extinction

BackgroundIchthyosaurs are reptiles that inhabited the marine realm during most of the Mesozoic. Their Cretaceous representatives have traditionally been considered as the last survivors of a group declining since the Jurassic. Recently, however, an unexpected diversity has been described in Upper Jurassic–Lower Cretaceous deposits, but is widely spread across time and space, giving small clues on the adaptive potential and ecosystem control of the last ichthyosaurs. The famous but little studied English Gault Formation and ‘greensands’ deposits (the Upper Greensand Formation and the Cambridge Greensand Member of the Lower Chalk Formation) offer an unprecedented opportunity to investigate this topic, containing thousands of ichthyosaur remains spanning the Early–Late Cretaceous boundary.Methodology/Principal FindingsTo assess the diversity of the ichthyosaur assemblage from these sedimentary bodies, we recognized morphotypes within each type of bones. We grouped these morphotypes together, when possible, by using articulated specimens from the same formations and from new localities in the Vocontian Basin (France); a revised taxonomic scheme is proposed. We recognize the following taxa in the ‘greensands’: the platypterygiines ‘Platypterygius’ sp. and Sisteronia seeleyi gen. et sp. nov., indeterminate ophthalmosaurines and the rare incertae sedis Cetarthrosaurus walkeri. The taxonomic diversity of late Albian ichthyosaurs now matches that of older, well-known intervals such as the Toarcian or the Tithonian. Contrasting tooth shapes and wear patterns suggest that these ichthyosaurs colonized three distinct feeding guilds, despite the presence of numerous plesiosaur taxa.Conclusion/SignificanceWestern Europe was a diversity hot-spot for ichthyosaurs a few million years prior to their final extinction. By contrast, the low diversity in Australia and U.S.A. suggests strong geographical disparities in the diversity pattern of Albian–early Cenomanian ichthyosaurs. This provides a whole new context to investigate the extinction of these successful marine reptiles, at the end of the Cenomanian.

The neglected history of Oceanic Anoxic Event 1b: insights and new data from the Poggio le Guaine section (Umbria–Marche Basin)

The upper Aptian to lower Albian interval (~114–109 Ma) represents a crucial period during Earth’s history, with a major evolution in the nature of mid–Cretaceous tectonics, sea level, climate, and marine plankton communities. Interestingly, it also includes multiple prominent black shale horizons that are the sedimentary expression of oceanic anoxic event (OAE) 1b. However, due to a set of geological, stratigraphic, and taxonomic challenges, difficulties constraining this OAE may sometimes result in inaccurate correlation. At Poggio le Guaine (central Italy), a continuous and undisturbed section of central western Tethyan pelagic sediments deposited during the latest Aptian and earliest Albian, complete with black shale horizons that record the OAE1b carbon cycle perturbations, has provided a unique opportunity to address the shortcomings referred to above. High–resolution geochemical proxies (CaCO3, TOC, and δ13C), along with planktonic foraminifera and calcareous nannofossils, were used to establish an integrated and robust global stratigraphic framework in order to: (1) precisely correlate the prominent black shale horizons of OAE1b in different marine environments (the Vocontian Basin in southeast France, Deep Sea Drilling Project Site 545 and Ocean Drilling Program Hole 1049C in the eastern and western North Atlantic, respectively); and (2) provide an effective tool to reconstruct, in high resolution, the paleobiological, paleoceanographic and paleoclimatic changes across the upper Aptian to lower Albian interval. The Poggio le Guaine section stands out as a valuable reference section for OAE1b, its constituent subevents, and the δ13C record for the uppermost Aptian to lower Albian interval. The exceptional chemo- and biochronostratigraphic control allow direct comparison to the proposed candidate for the GSSP for the base of the Albian Stage at the Col de Pré-Guittard section in France.

Taxonomic note: Watznaueria okadai, a newspecies of calcareous nannofossil from the Vocontian Basin, southeastern France.

Taxonomic note: <i>Watznaueria okadai,</i> a newspecies of calcareous nannofossil from the Vocontian Basin, southeastern France.

The Mid-Cenomanian Event in southeastern France: Evidence from palaeontological and clay mineralogical data

Reconstruction of main palaeoenvironmental conditions across the Mid-Cenomanian Event (MCE I) in the hemipelagic Tethyan section of Blieux (Southeast France, Vocontian Basin) is proposed. Quantitative analyses of calcareous nannofossil, ammonoid and clay mineral assemblages have been made and compared with respect to sea level changes and the carbon cycle perturbations. The nannofossil primary productivity, as recorded by nannofossil fluxes and relative abundances of meso-eutrophic taxa, is low just below and during the MCE Ia, then slightly increases in the interval including the MCE Ib. The clay assemblages mainly consist of illite/smectite mixed-layers with a smaller proportion of kaolinite. The percentage of kaolinite strongly decreases in the interval including the MCE Ia and slightly increases in the interval including the MCE Ib. The clay assemblages are mainly detrital in origin and reflect environmental changes including differential settling processes, climate, intensity of runoff and detrital sources. The ammonoid assemblages are characterised by a significant change during the MCE I: planispirals (mainly Schloenbachia) are dominant until the MCE Ia, whereas heteromorphs (mainly Sciponoceras) become dominant from the MCE Ib onwards. Strongly oligotrophic levels in sea surfaces are recorded during the MCE Ia and are related both to arid climatic conditions and major sea level fall (both 3rd order and medium scale lowstand deposits). A decrease in bathymetry could partly explain the decrease in the relative abundance of Schloenbachia. The first occurrence of Sciponoceras took place during the MCE Ib; this second positive increase in δ13C is not associated with enhanced nannofossil primary productivity. No clear relations can be established between the occurrence of Sciponoceras and trophic resources.

Paleoenvironmental changes during the Valanginian: New insights from variations in phosphorus contents and bulk- and clay mineralogies in the western Tethys

Paleoenvironmental and paleoclimatic changes during the Valanginian carbon isotopic excursion (CIE) have been investigated in the western Tethys. For this purpose, bulk-rock and clay mineralogies, as well as phosphorus (P) contents were evaluated in a selection of five sections located in the Vocontian Basin (Angles, SE France; Alvier, E Switzerland; Malleval, E France), and the Lombardian Basin (Capriolo, N Italy; Breggia, S Switzerland).Within the CIE interval, bulk-rock and clay mineralogies are inferred to reflect mostly climate change. The onset of the CIE (Busnardoites campylotoxus ammonite Zone) is characterized by higher detrital index (DI: sum of the detrital minerals divided by calcite contents) values and the presence of kaolinite in their clay-mineral assemblages. In the late Valanginian (from the Saynoceras verrucosum Zone up to the end of the Valanginian), the samples show relatively variable DI and lower values or the absence of kaolinite. The variation in the mineralogical composition is interpreted as reflecting a change from a climate characterized by optimal weathering conditions associated with an increase in terrigenous input on the southern European margin during the CIE towards an overall unstable climate associated with drier conditions in the late Valanginian. This is contrasted by a dissymmetry (proximal vs distal) along the studied transect, the northern Tethyan margin being more sensitive to changes in continental input compared to the distal environments.P accumulation rates (PAR) present similar features. In the Vocontian basin, P content variations are associated with changes in terrigenous influx, whereas in the Lombardian basin (i.e. Capriolo and Breggia), PAR values are less well correlated. This is mainly because the deeper part of the Tethys was less sensitive to changes in continental inputs. The onset of the CIE (top of the B. campylotoxus Zone) records a general increase in PAR suggesting an increase in marine nutrient levels. This is linked to higher continental weathering rates and the enhanced influx of nutrients into the ocean. In the period corresponding to the shift itself, P contents show a dissymmetry between the Vocontian and Lombardian basins (proximal vs distal). For the sections of Malleval, Alvier and Angles, a decrease in P concentrations associated to a decrease in detrital input is observed. In Capriolo and Breggia, PAR show maximum values during the plateau, indicating a more complex interaction between different P sources. The time interval including the top of S. verrucosum Zone up to the end of the Valanginian is characterized by variable PAR values, suggesting variable nutrient influxes. These changes are in agreement with an evolution towards seasonally contrasted conditions in the late Valanginian.

Palaeontology, taxonomic revision and variability of some species of the genus Gassendiceras Bert et al., 2006 (Ammonitina, Upper Barremian) from southeastern Franc

Abstract Bed-by-bed sampling of twelve Barremian sections in southeastern France from pelagic basin (Vocontian Basin) to neritic platforms (Arc of Castellane, Arc of Nice and Provencal Domain) has enabled the collection of isochronous samples of the ammonite genus Gassendiceras. Three poorly known species of the Toxancyloceras vandenheckei Zone (Upper Barremian) are revised: G. alpinum, G. multicostatum and G. hoheneggeri; two new species are described (G. rebouleti nov. sp. and G. bosellii nov. sp.). The intraspecific variability of particular species was recognised. This variability is between slender peramorphic and robust paedomorphic extreme morphologies, with the presence of all intermediates.

Porosity gain and loss in unconventional reservoirs: Example of rock typing in Lower Cretaceous hemipelagic limestones, SE France (Provence)

We characterize porosity evolution in hemipelagic limestones of the Lower Cretaceous Vocontian Basin (Northern Provence, SE France), which are surface analogs for deep unconventional reservoirs. Firstly, a structural and sedimentologic analysis was conducted on outcrops and on borehole cores of Berriasian to Lower Valanginian rocks. Secondly, 330 plugs were analyzed for facies, pore typing, porosity and acoustic Vp velocity measurements. This petrophysical dataset was compared to the burial-uplift history of the host rock.Hemipelagic carbonates include four sedimentary formations comprising nine facies splitted into mud- and grain-dominated formations which display 0–8% porosity range depending on the initial grain to mud ratio of the sediments and on basin stress regime evolution during burial-uplift history. Initial porosity was better preserved in grain dominated formations where early micritic cements built bridges between grains, generating a solid skeleton that prevented/inhibited the burial compaction effects. In mud dominated facies, micrite was initially diffuse within the rock matrix but was progressively rearranged under burial stress, while the generation of an extensive amount of stylolites occurred. The differential response of compacted grain and mud dominated facies to a late regional 1 km uplift resulted in large porosity generation (should range from 15 to 35%) localized in the mud dominated facies through the dilatancy of stylolite and pressure-solution seams.This study highlights how important is the combination of classical approaches including facies, pore type and diagenesis characterization with the structural analyses. One key result applicable to several types of unconventional reservoirs is the effective porosity generated by reactivation of compaction structures.

Evaluating Mg/Ca in belemnite calcite as a palaeo-proxy

The Mg/Ca, Sr/Ca, δ18O and δ13C compositions are given for well-preserved specimens of ten belemnite species/genera from three stratigraphic intervals. The data help assess the use of these proxies for palaeo-oceanography. Samples are from Dorset, UK (Pliensbachian; 5 species); Cambridgeshire, UK (Callovian; 1 species); and the Vocontian Basin, SE France (Valanginian; 4 genera). In none of these belemnite populations (at species or genera level) does Mg/Ca correlate with δ18O. Neither do values of δ18O correlate with Mg/Ca along a microsampled radial profile across a single specimen of Cylindroteuthis puzosiana (Callovian). The use of Mg/Ca is therefore considered to be unreliable as a palaeo-temperature indicator for these belemnite species and genera.

Rapid changes in the redox conditions of the western Tethys Ocean during the early Aptian oceanic anoxic event

The early Aptian (125 to 121Ma) records an episode of severe environmental change including a major perturbation of the carbon cycle, an oceanic anoxic event (OAE 1a, 122.5Ma), a platform drowning episode and a biocalcification crisis. We propose to trace changes in the oxygenation state of the ocean during the early Aptian anoxic event using the redox-sensitive trace-element (RSTE) distribution, phosphorus accumulation rates (PARs) and organic-matter characterization in three different basins of the western Tethys. The following sections have been investigated: Gorgo a Cerbara (central Italy) in the Umbria Marche basin, Glaise (SE France) in the Vocontian basin and Cassis/La Bédoule (SE France) located in the Provencal basin.In the Gorgo a Cerbara section, RSTE distributions show a low background level along the main part of the section, contrasted by different maxima in concentrations within the Selli level. In the Glaise section, the Goguel level displays a weak increase in RSTE contents coeval with moderate TOC values. At Cassis/La Bédoule, no significant RSTE enrichments have been observed in sediments equivalent to the Selli level. These differences in the records of the geochemical proxies of the Selli level or its equivalent indicate the deposition under different redox conditions, probably related to the paleogeography. Our data indicate the development of anoxic–euxinic conditions in the deeper part of the Tethys during OAE 1a, whereas in the shallower environments, conditions were less reducing. Moreover, at Gorgo a Cerbara, the Selli level is characterized by rapid changes in the intensity of reducing conditions in the water column. Ocean eutrophication seems to be a major factor in the development and the persistence of anoxia as suggested by the PAR evolution. Higher PAR values at the onset of OAE 1a suggest an increase in nutrient input, whereas the return to lower values through the first part of the OAE 1a interval may be related to the weakened capacity to retain P in the sedimentary reservoir due to bottom-water oxygen depletion. This general pattern is contrasted by the data of Gorgo a Cerbara, where the sediments deposited during the OAE 1a interval show P-enrichments (mainly authigenic P). This is associated with maxima in TOC values and Corg:Ptot ratios, suggesting that a part of the remobilized P was trapped in the sediments and as such prevented from returning to the water column.

Secular change in northwestern Tethyan water-mass oxygenation during the late Hauterivian–early Aptian

The Mesozoic is punctuated by several extreme episodes of oxygen drawdown in the ocean, known as Oceanic Anoxic Events (OAE). Beside these discrete events, little is however known about longer-term oxygen level fluctuations and their controls. A high-resolution dataset of Rare Earth Elements (REE) content in carbonate deposited in the Vocontian Basin (SE France) has allowed to survey the evolution of the Cerium anomaly (Ce/Ce*) during part of the Early Cretaceous (latest Hauterivian–early Aptian). This ratio is used as a proxy for the degree of oceanic oxygenation. The Cerium anomaly is compared to the coeval evolution of relative sea level, organic-rich occurrences, and nutrient level proxies, in order to infer a cause-and-consequence relationship between these parameters and the evolution in sea-water oxygenation. The long-term evolution of the Cerium anomaly shows that northwestern Tethyan water masses have evolved from less oxygenated during the latest Hauterivian–early Barremian interval to more oxygenated during the late Barremian–earliest Aptian time, before being strongly oxygen-depleted during the early Aptian OAE 1a time interval. This trend is correlated with both the long-term trend in nutrient levels, as well as with the frequency of organic-rich layers within the rock record. On a medium-term scale (sub-stage level), there is a good correlation between the Cerium anomaly and tectono-eustatism (as deduced by the Mn content of the basinal carbonate and sequence stratigraphic observation on surrounding shallow-water areas). This suggests that sea-level changes, by altering ocean stratification and currents, as well as modulating the amount of nutrient delivered from the continent, exert control on oceanic oxygenation via changes in primary productivity.

Reconstructing Valanginian (Early Cretaceous) mid-latitude vegetation and climate dynamics based on spore–pollen assemblages

Changes in terrestrial vegetation patterns during the Valanginian (Early Cretaceous) and their link to major climatic and environmental alterations are poorly studied. In this study, the spatial and temporal changes in plant community structure are reconstructed based on spore–pollen records from two mid-latitude sites located in the Mid-Polish Trough (MPT, central Poland), and the Vocontian Basin (VB, southeast France). Stratigraphic control is provided by δ13Ccarb chemostratigraphy and calcareous nannofossil biostratigraphy. Reconstruction of hinterland vegetation is based on palynological investigations of 83 samples from hemipelagic (VB) and marginal marine (MPT) sediments rich in terrestrial palynomorphs. A total of 45 palynomorph taxa were identified at generic level (30 spores, 15 pollen). Vegetation around the MPT was dominated by araucarian/cupressacean conifers while that surrounding the VB was dominated by drought-resistant cheirolepidiacean conifers. At both sites the understorey and/or vegetation of open areas was dominated by pteridophytes. An early Valanginian gradual trend towards humid conditions at the MPT, well expressed by a distinct increase in the spore–pollen ratio, culminates in a short-lived spore-maximum stratigraphically located at the lower/upper Valanginian boundary. It is characterized by low conifer abundances and high abundances of the fern spore taxa Cyathidites, Leiotriletes and Gleicheniidites accompanied by enhanced abundances of the pteridosperm pollen Vitreisporites pallidus, whose parent plants are assumed to be indicative of swamp habitats. The spore-maximum is coeval to a similar peak observed in the VB, characterized by essentially the same taxa. Here, the spore-maximum is preceded by a protracted phase of arid conditions, characterized by low spore abundances and exceptionally high numbers of the cheirolepidiacean conifer pollen Classopollis. Changes in moisture, identified as the key climatic factor determining trends and turnovers in vegetation, were probably controlled by a monsoonal circulation. The supra-regional humid phase expressed by the coeval spore maxima was probably induced by an intensified monsoonal climate. The temporal influence of a northern hemisphere arid belt at the VB, under the influence of the subtropical high-pressure belt, may have caused the temporal drying not affecting the MPT site, located further north.

Erratum to Abrupt planktic foraminiferal turnover across the Niveau Kilian at Col de Pré-Guittard (Vocontian Basin, southeast France): new criteria for defining the Aptian/Albian boundary

Erratum to Abrupt planktic foraminiferal turnover across the Niveau Kilian at Col de Pré-Guittard (Vocontian Basin, southeast France): new criteria for defining the Aptian/Albian boundary

Astrochronology of the Valanginian Stage from reference sections (Vocontian Basin, France) and palaeoenvironmental implications for the Weissert Event

High-resolution gamma-ray measurements performed on five biostratigraphically well-dated reference sections from the Vocontian Basin (south-eastern France) are used to develop a new astrochronology of the Valanginian Stage and its subdivisions (i.e. ammonite and calcareous nannofossil zones and subzones). Spectral analyses show a pervasive dominance of 405-kyr eccentricity cycles with the expression of 100-kyr eccentricity, obliquity and precession. Previous rough estimates of Valanginian Stage duration ranged from 3.9 to 6.5myr but were generally based on less reliable or indirect methods. This study provides a precise duration of 5.08myr, tuning the series to the 405-kyr eccentricity cycle, thus further enhancing the accuracy of the Geologic Time Scale. New durations of magnetochrons are proposed based on intercalibration between ammonite and calcareous nannofossil biozones, cyclostratigraphy and carbon-isotope stratigraphy. After integrating orbitally calibrated durations and available radio-isotopic ages for the Berriasian–Hauterivian interval, a link between the Weissert Event and the emplacement of the Paraná–Etendeka Traps now appears unlikely.Strontium, carbon and oxygen isotope stratigraphy, sedimentological and palaeontological features, clay mineralogy, and the orbital record during the Upper Valanginian all suggest that a transient cool, arid climate occurred after the carbon isotope event, possibly associated with limited polar ice.

Berriasian and early Valanginian environmental change along a transect from the Jura Platform to the Vocontian Basin

AbstractValanginian sedimentary archives display a positive anomaly in the carbon‐isotope record which is associated with a crisis in neritic and pelagic carbonate production. This study aims to reconstruct the evolution of palaeoenvironments in the Jura area and the Vocontian Basin during late Berriasian and early Valanginian times, in order to better understand the controlling factors leading to the Valanginian episode of major environmental change. Three sections along a transect through the Jura platform (Switzerland and France) and the Vocontian Basin (France) have been studied. Stratigraphic correlations have been established by combining biostratigraphy (benthic foraminifera, ammonites and calpionellids), with geochemistry (δ13C trends) and sequence stratigraphy. A change from a rimmed ramp to a swell‐dominated ramp morphology is observed through the Berriasian–Valanginian boundary. The disappearance of the barrier appears to have been controlled by large sea‐level variations in combination with the arrival of significantly more humid climate conditions. This barrier played a major role in the distribution of geochemical, mineralogical and palynological fluxes towards the basin: during the Berriasian, continental fluxes (detrital particles, nutrients, pollen and spores) were buffered by the platform morphology, whereas in the early Valanginian they were more readily transported towards the basin. The initiation of a major transgression onto lateritic soils, leading to their intense reworking, instigated a fertilization of ocean waters during the earliest Valanginian and with that a change towards heterozoan carbonate production, and subsequently to the demise of the already weakened carbonate platform.

Shallow water carbonate platforms (Late Aptian–Early Albian, Southern Apennines) in the context of supraregional to global changes: re-appraisal of palaeoecological events as reflectors of carbonate factory response

Abstract. This paper discusses the palaeoenvironmental significance of the "Orbitolina Level", the microbial carbonates and the Salpingoporella dinarica-rich deposits encased in the Aptian/Albian shallow water carbonate platform strata of Monte Tobenna and Monte Faito (Southern Italy). These facies show a peculiar field appearance due to their color and/or fossil content. In the shallow water carbonate strata, the Late Aptian "Orbitolina Level" was formed during a period of decreasing accommodation space. Microbial carbonates occur in different levels in the composite section. They reach their maximum thickness around the sequence boundaries just above the "Orbitolina Level" and close to the Aptian–Albian transition, and were not deposited during maximum flooding. S. dinarica-rich deposits occur in the lower part of the Monte Tobenna-Monte Faito composite section, in both restricted and more open lagoonal sediments. S. dinarica has its maximum abundance below the "Orbitolina Level" and disappears 11 m above this layer. On the basis of δ13C and δ18O values recorded at Tobenna-Faito, the succession has been correlated to global sea-level changes and to the main volcanic and climatic events during the Aptian. Deterioration of the inner lagoon environmental conditions was related to high trophic levels triggered by volcano-tectonic activity. Microbial carbonates were deposited especially in periods of third-order sea level lowering. In such a scenario, periods of increased precipitation during the Gargasian induced the mobilization of clay during flooding of the exposed platform due to high-frequency sea-level changes, with consequent terrigenous input to the lagoon. This and the high nutrient levels made the conditions unsuitable for the principle carbonate producers, and an opportunistic biota rich in orbitolinids (Mesorbitolina texana and M. parva) populated the platform. In the more open marine domain, the increased nutrient input enhanced the production of organic matter and locally led to the formation of black shales (e.g. the Niveau Fallot in the Vocontian Basin). It is argued that the concomitant low Mg/Ca molar ratio and high concentration of calcium in seawater could have favoured the development of the low-Mg calcite skeleton of the S. dinarica green algae. During third-order sea-level rise, no or minor microbial carbonates formed in the shallowlagoonal settings and S. dinarica disappeared. Carbonate neritic ecosystems were not influenced by the environmental changes inferred to have been induced by the mid-Cretaceous volcanism. The "Orbitolina Level", the microbial carbonates and the Salpingoporella dinarica-rich deposits in the studied Aptian/Albian shallow water carbonate strata are interpreted to be the response to environmental and oceanographic changes in shallow-water and deeper-marine ecosystems.