Marly Interval Research Articles

Long-term evolution of a carbonate reservoir submitted to fresh, saline and thermal waters interactions – Jurassic carbonates in the coastal area of the Gulf of Lion margin (southern France)

Securing and managing underground water resources requires a good knowledge of the structure, texture and connections of the reservoir, in order to develop realistic and reliable hydrogeological models. On the coastline of the Gulf of Lion Margin (S. France), the Balaruc-les-Bains deep karst reservoir is subjected to interactions between fresh, marine and deep thermal waters, respectively. Water resource usage for drinking, spa resort, and fish-farming raises important economic and social issues. These were addressed by an integrated research program, involving drilling of an exploratory borehole across the Jurassic carbonate reservoir. This contribution analyses the 750 m cores, in order to (i) characterise the architecture and evolution of the karst reservoir and (ii) investigate the paleo-fluids circulations, witnessed by calcite and dolomite mineralization in the fractures, karst cavities, and as cement of tectonic beccia. The structure of the reservoir is characterised by the superposition of several aquifers separated by marly intervals. At shallow level, the initial grainstone is incompletely dolomitized in metre-thick intervals, while limestone in the 210–340 m interval was completely dolomitized at an early stage. Dolomite has been subjected to penetrative extensional cataclastic deformation, while the preserved limestone is affected by normal faulting, resulting from NNE–SSW extension. Distinct types of karsts have been documented, from the top of the reservoir (paleo-lapiaz filled with Burdigalian marine marls), down to 500 m depth (paleo-endokarst filled with continental silts). The upper reservoir (75–150 m) is intensely karstified, and includes 0.1 to 1 m-wide cavities, where present day water fluxes are documented. Analyses of calcite and dolomite crystallisation under natural light and cathodoluminescence indicate precipitation from distinct fluids: formation water in chemical equilibrium with the host rock, water rich in oxides and hydroxides, ascending hydrothermal fluid and corrosive water of meteoric origin. Alternate dolomitization and calcitization observed in the upper reservoir suggests alternate flows of karstic freshwater and marine salt-water. Vertical, metre-long and centimetre wide open cracks are presently used for large water flows; several generations of syntaxial calcite growth provide evidence for varying chemistry of the circulating fluids. Structural cross cutting relationships allowed us to establish a relative chronology of events, which can be correlated with the regional geodynamic evolution. The study reveals that the present-day reservoir architecture results from the superimposition of structures formed during the Early Cretaceous extension, Maastrichtian-Eocene Pyrenean shortening, and Oligocene rifting of the Gulf of Lion. The reservoir was also shaped by successive karstification episodes and marine transgressions. Although the present-day hydrological system is controlled by, and reactivates structures inherited from a long-term evolution, it is characterised by frequent turn-overs of the water flow, tuned by high-frequency external forcings such as sea-level changes driven by Pleistocene glacio-eustasy, or varying precipitation rates.

The onset of the Early Toarcian flooding of the Pliensbachian carbonate platform of central Tunisia (north–south axis) as inferred from trace fossils and geochemistry

Abstract The flooding of the Lower Jurassic shelf in the North Gondwana Palaeomargin during the early Toarcian occurred on a fragmented and irregular topography affected by differential subsidence – owing to the activity of listric faults along the North–South Axis of Tunisia – that favoured lateral changes in facies and thickness at a kilometric scale. The onset of Toarcian sedimentation (Polymorphum ammonite Zone, NJT5c nannofossil Subzone) in two adjacent sections was characterized by the deposition of limestones under high-energy conditions. The Châabet El Attaris section was located in a depressed sub-basin, and recorded restricted environmental conditions owing to water stagnation and an oxygen-depleted sea bottom. Therefore, dark mudstones developed, with increased total organic carbon contents and enhanced accumulation of redox-sensitive elements. The sedimentation of limestones bearing gutter cast structures is related to gravity flows probably linked to storm activities. These processes favoured the remobilization of sediments at the seafloor, as well as oxygen input to bottom waters, as shown by the record of trace fossils including Zoophycos , Ophiomorpha , and secondarily, Chondrites and Diplocraterion . The thinly interbedded dark mudstones are locally rich in thin-shelled bivalves that re-colonized the sea bottom after the sedimentation of these high-energy deposits, and subsequently underwent mass mortality related to the return of oxygen-depleted conditions. The Kef El Hassine section is located in the upper part of a tilted, less subsident block, as indicated by its reduced thickness compared with the Châabet El Attaris section; the absence of dark mudstones implies oxic conditions. The Polymorphum Zone consists of limestones showing evidence of sedimentation under high-energy conditions, along with hardgrounds. The occurrence of Zoophycos (deep-tiers) in the upper part of some limestone beds of the Polymorphum Zone is linked to minor erosive processes. The top of the high-energy sequence – below the deposits of a marly interval corresponding to the Levisoni Zone – is interpreted as a hardground given the high content of belemnites and Arenicolites , some of them boring on the eroded Zoophycos and Thalassinoides . This study shows that the sedimentary expression of the Jenkyns Event is not uniform across Tunisia, supporting the importance of local conditions in determining the development of anoxic conditions.

A Paleomagnetic Inspection of the Paleocene-Eocene Thermal Maximum (PETM) in the Southern Pyrenees

Rock magnetic properties can be useful determining paleonvironmental changes. A dramatic climate change as occurred in the PETM modified the environment and hence the magnetic properties recorded in the sediments. New paleomagnetic data from the marine record of the PETM in the Southern Pyrenean Zone shows the variation on the magnetic parameters in four different sections. The magnetic signal reveals a positive excursion of magnetic values starting before the onset of the marly interval of La Faja de las Flores Mb (beginning of the PETM record, Ilerdian) in the Carriata section with a maximum value in the marly interval. A similar magnetic signal is observed in Bujaruelo section (~10 km south of Carriata at PETM times) directly related to the marly interval of Faja de las Flores Mb. However more to the south, the PETM interval does not appear in the sedimentary record, therefore in the southern Gallisue section no magnetic excursion occurs, and in the southernmost studied Entremon section a magnetic positive excursion occurs in a thin marly interval unrelated to the PETM, and in two lower intervals of the column. All sections were subjected to later deformation during the pyrenean orogeny and the three northernmost are in the regional cleavage front where pressure-solution and remagnetizations have been described. A postfolding remagnetization component is found in the three northern sections.

The Lower Toarcian Serrone Marls (Northern Apennines, Italy): A 3.5 Myr record of marl deposition in the aftermath of the T-OAE

The early Toarcian sedimentary record is frequently characterized by the occurrence of marls, shales, and organic rich facies comprising the Toarcian oceanic anoxic event (T-OAE), which are broadly synchronous to the emplacement of the Karoo-Ferrar large igneous province (LIP) with a main pulse at ~181.7 Ma. Here we describe the chronology and rock magnetic properties of the early Toarcian Marne del Serrone Formation (Serrone Marls) from the Monte Serrone section in the Northern Apennines of Italy, and interpret them as reflecting the local environmental response to the transient CO2 rise and accelerated hydrological cycle most likely induced by the emplacement of the Karoo-Ferrar LIP. The studied 62 m-thick section is characterized by a succession of micritic limestones and marls, interrupted by a few slumps, and contains a record of the T-OAE represented by posidonia beds and a ~40 cm-thick black shale interval. The age of the section has been constrained using magnetostratigraphy and ammonite biostratigraphy to the Spinatum to Variabilis zones. Rock-magnetic properties have been used to characterize fluctuations in the magnetite and hematite input throughout the section. Spectral analysis of continuous IRM2.5T and IRM0.1T/IRM2.5T records indicates a duration of the studied marly interval of ca. 3.5 Myr, regarded as a first-order estimate of the duration of the response of the environmental system (hydrological cycle) to the transient climate perturbation triggered by the emplacement of the Karoo-Ferrar LIP, and a duration of the Bifrons zone of ca. 3.4 Myr.

Zanclean/Piacenzian transition on Cyprus (SE Mediterranean): calcareous nannofossil evidence of sapropel formation

Quantitative analyses of calcareous nannofossils in the sediments of Pissouri South section on the island of Cyprus have produced a paleoceanographic record reflecting the paleoclimatic conditions during the Zanclean/Piacenzian transition. Pissouri South cyclical lithological alternations between organic-rich laminated layers and grey marls reflect the Earth’s orbital precession. According to the calcareous nannofossil biostratigraphy which has been performed, the studied section is correlated with MNN14/15 and MNN16 calcareous nannofossil biozones and is astronomically dated between 4.065 and 3.217 Ma. Intervals of increased organic carbon content, along with the positive values of Florisphaera profunda, Helicosphaera sellii, Discoaster spp. and the subsequent increase of stratification S-index, correspond to the sapropel deposition during periods of wetter climate and intense continental runoff, especially from the river Nile. These layers alternate with grey marly intervals, featured by the increased values of small placoliths of Reticulofenestra and Gephyrocapsa species, which are indicative of eutrophic conditions during intense surface-water mixing. Our data support the prevalence of a generally warm phase characterized by the absence of high-frequency climate variations in the southeastern Mediterranean during the Zanclean/Piacenzian (Early/Late Pliocene) transition.

The Early Toarcian Oceanic Anoxic Event in the External Subbetic (Southiberian Palaeomargin, Westernmost Tethys): Geochemistry, nannofossils and ichnology

The analysis of macroinvertebrates, trace fossils, calcareous nannofossils and geochemistry from Pliensbachian to Lower Toarcian deposits of the Subbetic (Southern Spain) allows us to interpret the incidence of the Toarcian Oceanic Anoxic Event (T-OAE) in the boundary between the Tethys and the Hispanic Corridor. Trace fossils from the marl-limestone rhythmite (Upper Pliensbachian to Lower Toarcian) indicate an oxygenated bottom. A dark marly interval occurs above a fossil-rich condensed surface with a negative excursion of δ18O, interpreted as evidence of the Early Toarcian transgression and a climate warming. The carbon cycle perturbation is recorded by decreasing CaCO3 content and the negative excursion of δ13C at the base of the Serpentinum Zone, NJT 6 nannofossil Zone. The barren interval for nektonic and benthic organisms at the beginning of the Serpentinum Zone confirms the oxygen restricted conditions in the sea-floor. Environmental conditions were unfavourable for the development of calcareous nannoplankton, as attested by the drop in absolute abundances. The deep photic zone seemed to be particularly hostile to phytoplankton, as shown by the decrease in relative abundance of the deep-dweller Mitrolithus jansae, related to shoaling of the oxygen minimum zone in the water column. Increasing values of redox sensitive elements and total organic carbon, as well as the record of pyrite framboids <5μm size, confirm the anoxic conditions (probably euxinic conditions in any moment) at the base of the dark marly interval (NJT 6). The return to oxic or dysoxic conditions is confirmed by the record of fossil-poor marls with scarce macroinvertebrates and microfossils, as well as the recovery of trace fossils mainly (low-oxygen tolerant Chondrites tracemakers). Increasing abundance of calcareous nannofossils and deep-dweller M. jansae indicate ameliorated environmental conditions in the water column. Geochemistry supports the recovery of carbonate production (increasing CaCO3) and oxygen availability (decrease of TOC and redox sensitive elements).

Cyclically-arranged, storm-controlled, prograding lithosomes in Messinian terrigenous shelves (Bajo Segura Basin, western Mediterranean)

This work focuses on a Messinian shallow-marine terrigenous unit, termed the La Virgen Formation, which forms part of the sedimentary infill of the Bajo Segura Basin (Betic margin of the western Mediterranean). This formation was deposited during a high sea level phase prior to the onset of the Messinian Salinity Crisis. Stratigraphically, it comprises a prograding stack of sandstone lithosomes alternating with marly intervals (1st-order cyclicity). These lithosomes are characterized by a homoclinal geometry that tapers distally, and interfinger with pelagic sediments rich in planktonic and benthic microfauna (Torremendo Formation). An analysis of sedimentary facies of each lithosome reveals a repetitive succession of sandy storm beds (tempestites), which are separated by thin marly layers (2nd-order cyclicity). Each storm bed contains internal erosional surfaces (3rd-order cyclicity) that delimit sets of laminae. Two categories of storm beds have been differentiated. The first one includes layers formed below storm wave base (SWB), characterized by traction structures associated to unidirectional flows. The second category consists of layers deposited above the SWB, which display typical high regime oscillatory flow structures. The 1st-order cyclicity recorded in the La Virgen Formation corresponds to sapropel/homogeneous marl precessional cycles formed in a pelagic basin context (Torremendo Formation).

Integrated stratigraphy of the Lower and Middle Cenomanian in a Tethyan section (Blieux, southeast France) and correlations with Boreal basins

A detailed stratigraphic analysis was carried out on the Lower–Middle Cenomanian hemipelagic deposits of the Blieux section (Alpes-de-Haute-Provence; southeast France) in order to identify the Middle Cenomanian event I (MCE I) in the Vocontian Basin. These deposits are represented by five bundles composed of limestone–marl alternations that are separated by thick marly intervals. The Blieux section, which is well exposed, very thick, continuous and relatively rich in macrofauna, provides an ideal succession for an integrated approach. Biostratigraphy by ammonoids and sequence stratigraphy have been established for the whole succession whereas calcareous nannofossil and geochemical analyses have been carried out on a restricted interval across the Lower/Middle Cenomanian boundary. The uppermost part of the Mantelliceras mantelli Zone, the Mantelliceras dixoni Zone and the lower part of the Acanthoceras rhotomagense Zone have been recognized. The appearance of the genus Cunningtoniceras (C. inerme or C. cunningtoni) is used to place the base of the A. rhotomagense Zone and the Lower/Middle Cenomanian boundary. This boundary is also well characterized by the presence of nannofossil Subzone UC2C. Two orders of hierarchically stacked depositional sequences have been identified. Medium- and large-scale sequences correspond to 400 ky eccentricity cycles and to third-order cycles, respectively. The duration of the interval studied (from the uppermost part of the M. mantelli to the lower part of the A. rhotomagense zones) is estimated to be 2.8 my. Carbon-isotope values determined from bulk carbonate sediments show a first positive excursion (+0.6‰) corresponding to the MCE Ia, in the lower part of the A. rhotomagense Zone. A subsequent increase (+1.1‰) is recorded and could correspond to MCE Ib, but a sharp return to baseline values as expected in an excursion is not observed. The duration of the MCE I is estimated to be less than 400 ky. The Blieux section is correlated with some classical sections of the Anglo-Paris (Southerham, Folkestone, Cap Blanc-Nez) and Lower Saxony (Baddeckenstedt and Wunstorf) basins using ammonoid biostratigraphy, sequence stratigraphy, and chemostratigraphy. It is proposed as a candidate for the Middle Cenomanian GSSP (Global Boundary Stratotype Section and Point).

Relative sea-level change, climate, and sequence boundaries: insights from the Kimmeridgian to Berriasian platform carbonates of Mount Salève (E France)

The present study analyses the stratal architecture of the Late Jurassic (Kimmeridgian) to Early Cretaceous (Berriasian) sedimentary succession of Mount Saleve (E France), and four Berriasian stratigraphic intervals containing four sequence-boundary zones reflecting lowering trends of the relative sea-level evolution. Massive Kimmeridgian limestones characterized by the presence of colonial corals appear to be stacked in an aggrading pattern. These non-bedded thick deposits, which are interpreted to have formed in balance between relative sea-level rise and carbonate accumulation, suggest a keep-up transgressive system. Above, well-bedded Tithonian-to-Berriasian peritidal carbonates reflect a general loss of accommodation. These strata are interpreted as a highstand normal-regressive unit. During the early phase of this major normal regression, the vertical repetition of upper intertidal/lower supratidal lithofacies indicates an aggrading depositional system. This is in agreement with an early stage of a highstand phase of relative sea level. The Berriasian sequence-boundary zones investigated (up to 4 m thick) developed under different climatic conditions and correspond to higher-frequency, forced- and normal-regressive stages of relative sea-level changes. According to the classical sequence-stratigraphic principles, these sequence-boundary zones comprise more than one candidate surface for a sequence boundary. Three sequence-boundary zones studied in Early Berriasian rocks lack coarse siliciclastic grains, contain a calcrete crust, as well as marly levels with higher abundances of illite with respect to kaolinite, and exhibit fossilized algal-microbial laminites with desiccation polygons. These sedimentary features are consistent with more arid conditions. A sequence-boundary zone interpreted for the Late Berriasian corresponds to a coal horizon. The strata above and below this coal contain abundant quartz and marly intervals with a higher kaolinite content when compared to the illite content. Accordingly, this Late Berriasian sequence-boundary zone was formed under a more humid climate. The major transgressive–regressive cycle of relative sea level identified and the climate change from more arid to more humid conditions recognized during the Late Berriasian have been reported also from other European basins. Therefore, the Kimmeridgian to Berriasian carbonate succession of Mount Saleve reflects major oceanographic and climatic changes affecting the northern margin of the Alpine Tethys ocean and thus constitutes a reliable comparative example for the analysis of other coeval sedimentary records. In addition, the stratigraphic intervals including sequence-boundary zones characterized in this study constitute potential outcrop analogues for sequence-boundary reflectors mapped on seismic profiles of subsurface peritidal carbonate successions. The detailed sedimentological analyses provided here highlight that on occasions the classical principles of sequence stratigraphy developed on seismic data are difficult to apply in outcrop. A sequence-boundary reflector when seen in outcrop may present successive subaerial exposure surfaces, which formed due to high-frequency sea-level changes that were superimposed on the longer-term trend of relative sea-level fall.

Late Barremian–Early Aptian palaeoenvironmental change: The Cassis-La Bédoule section, southeast France

The well-dated section of Cassis-La Bédoule in the South Provencal Basin (southern France) allows for a detailed reconstruction of palaeoenvironmental change during the latest Barremian and Early Aptian. For this study, phosphorus (P) and clay-mineral contents, stable-isotope ratios on carbonate (δ13Ccarb) and organic matter (δ13Corg), and redox-sensitive trace elements (RSTE: V, U, As, Co, and Mo) have been measured in this historical stratotype. The base of the section consists of rudist limestone, which is attributed to the Urgonian platform. The presence of low P and RSTE content, and content of up to 30% kaolinite indicate deposition under oligotrophic and oxic conditions, and the presence of warm, humid climatic conditions on the adjacent continent. The top of the Urgonian succession is marked by a hardground with encrusted brachiopods and bivalves, which is interpreted as a drowning surface. The section continues with a succession of limestone and marl containing the first occurrence of planktonic foraminifera. This interval includes several laminated, organic-rich layers recording RSTE enrichments and high Corg:Ptot ratios. The deposition of these organic-rich layers was associated with oxygen-depleted conditions and a large positive excursion in δ13Corg. During this interval, a negative peak in the δ13Ccarb record is observed, which dates as latest Barremian. This excursion is coeval with negative excursions elsewhere in Tethyan platform and basin settings and is explained by the increased input of light dissolved inorganic carbon by rivers and/or volcanic activity. In this interval, an increase in P content, owing to reworking of nearshore sediments during the transgression, is coupled with a decrease in kaolinite content, which tends to be deposited in more proximal areas. The overlying hemipelagic sediments of the Early Aptian Deshayesites oglanlensis and D. weissi zones indicate rather stable palaeoenvironmental conditions with low P content and stable δ13C records. A change towards marl-dominated beds occurs close to the end of the D. weissi zone. These beds display a long decrease in their δ13Ccarb and δ13Corg records, which lasted until the end of the Deshayesites deshayesi subzone (corresponding to C3 in Menegatti et al., 1998). This is followed by a positive shift during the Roloboceras hambrovi and Deshayesites grandis subzones, which corresponds in time to oceanic anoxic event (OAE) 1a interval. This positive shift is coeval with two increases in the P content. The marly interval equivalent to OAE 1a lacks organic-rich deposits and RSTE enrichments indicating that oxic conditions prevailed in this particular part of the Tethys ocean. The clay mineralogy is dominated by smectite, which is interpreted to reflect trapping of kaolinite on the surrounding platforms rather than indicating a drier climate.

Taphonomic analysis and sequence stratigraphy of the Albarracinites beds (lower Bajocian, Iberian range, Spain). An example of shallow condensed section

Abstract Several ammonite fossil assemblages from Sierra de Albarracín (Teruel, Castilian Branch) contain abundant specimens of the Ovale and Laeviuscula zones (lower Bajocian, Middle Jurassic), including microconchs and macroconchs of the characteristic genus Albarracinites. Over 1500 ammonites from the type horizon of the species A. albarraciniensis, in the outcrop of Masada Toyuela, have been studied. Ammonites are commonly preserved as phosphatized, calcareous, concretionary internal moulds (mean size = 50.5 mm) of unflattened shells, partially or completely filled with relatively heterogeneous mudstone to wackestone sediment. Incomplete, fragmented phragmocones with calcitic septa are the dominant remains, generally bearing traces of rounding, incrustation and bioerosion. Taphonomic data, such as the predominant taphonomic populations of type 3, composed of reelaborated, relatively heterogeneous concretionary internal moulds, isolated concretionary body chambers and hollow ammonites, bearing traces of abrasion, bioerosion and encrusting organisms, are indicative of low rate of sedimentation and occasional high rate of sediment accumulation, due to sedimentary winnowing and bypassing interrupted by storm depositional events, in shallow-water marine environments. The exceptional occurrence of taphonic populations of type 2 belonging to Albarracinites and Hebetoxyites, with dominant shells of pre-adults and absence of juveniles, suggests autochthonous biogenic production of shells by indigenous populations of Sub-Mediterranean taxa at the Iberian platform system. In the outcrop of Masada Toyuela, the Albarracinites beds correspond to a condensed section, developed in shallow-water, open-marine, carbonate environments of the External Castilian platform. The sharp, irregular base of beds and the normal grading of reworked elements suggest these carbonate deposits were affected by tractive currents, scouring and redeposition. Limestone beds represent storm-related sedimentary events, whereas the local marly intervals represent background-sedimentation time-intervals of winnowing and bypassing on the seafloor. This condensed section is composed of at least four, decimetric or centimetric, expanded-deposit intervals, stacked and showing an overall thinning upward, which constitute a deepening sequence developed during two biochrons. Taphonomic results also corroborate the development of an incipient-deepening phase, which represents the first episode of a deepening half-cycle of third order, in the Albarracín area within the Castilian platform, during the Ovale and Laeviuscula biochrons (early Bajocian).

Major palaeoenvironmental perturbation in an Early Aptian carbonate platform: Prelude of the Oceanic Anoxic Event 1a?

The Early Aptian Oceanic Anoxic Event (OAE 1a) was characterized by intensified greenhouse climate conditions, widespread accumulation of organic deposits in open-marine settings, major perturbations in the C cycle and a generalized increase in terrestrial runoff. Sedimentological, diagenetic and chemostratigraphic analyses of Lower Aptian platform carbonates from the North Cantabrian basin (N Spain) illustrate the regional impact and effects of those global conditions on shallow marine environments. The studied interval outlines four stages of platform evolution. Stage 1 (earliest Bedoulian) is defined by an initial rapid marine transgression that led to deposition of shallow water oligotrophic photozoan skeletal assemblages, and by a later interval of subaerial exposure. Stage 2 (early Bedoulian) starts with a rapid transgression followed by deposition of grainstones that yield heterozoan assemblages, more typical of mesotrophic conditions, along with ferruginized oolites. Stage 3 (early Bedoulian) is defined by the drowning of the carbonate platform and subsequent deposition of open-marine marls, which are thought to represent the local expression of the OAE 1a. Finally, stage 4 shows the return of shallow water photozoan carbonate sedimentation. The carbonate O and C stable isotope records have revealed prominent negative excursions during deposition of the marly interval of the stage 3, which may be associated with the important global changes that occurred at the onset of the OAE 1a. The change in skeletal assemblages that preceded the isotopic excursions and the platform drowning documents conditions of environmental stress caused by a combination of local and global factors. The global change, coupled with increased basin subsidence, triggered the drowning of the platform by progressive reduction of the growth potential of the carbonate factory.

A new facies model for the Upper Gypsum of Sicily (Italy): chronological and palaeoenvironmental constraints for the Messinian salinity crisis in the Mediterranean

AbstractThe Upper Gypsum unit of the Caltanissetta Basin (Sicily) records the last phase of the Messinian salinity crisis comprising the so‐called ‘Lago Mare’ event. A new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies, and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization. A basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies. A marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost (seventh) gypsum body. The terrigenous Arenazzolo Formation, in turn followed by the lower Pliocene Trubi Formation, is considered here to form the uppermost part of the Upper Gypsum unit. The rhythmic alternation in the sandy marls and gypsum/sandstone bodies records the response of sediments from shelfal to deltaic systems to precession‐driven arid‐wet climate fluctuations causing cyclical changes of both base‐level and water concentration. During wet climate phases (at insolation maxima) marl and sandstone were deposited in a hypohaline environment as suggested by: (i) the typical Lago Mare faunal assemblage and (ii) the negative δ18O values. During arid phases (at insolation minima) the reduced meteoric supply, recorded by higher δ18O values in the carbonate, caused the development of a negative hydrological budget leading to evaporite precipitation. At a basinal scale the Upper Gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia (the so‐called ‘Calcare di Base’) and/or clastic gypsum. Towards the basin centres, where the basal contact becomes conformable, a primary gypsum cumulate horizon is present. This layer is interpreted as a possible lateral equivalent of the Halite unit present only in the deepest depocentres. Based on astronomical calibration of the depositional cycles, the Upper Gypsum unit, including the Arenazzolo Formation, spans the interval between 5·33 and 5·53 Ma. This new age calibration allows the deposition of the Halite unit to be dated between 5·6 Ma (top of the Lower Evaporites) and 5·55 Ma (base of the Upper Evaporites) corresponding to isotopic stages TG12 and/or TG14.

Foraminiferal stratigraphy and palaeoecological implications in turbidite-like deposits from the Early Tortonian (Late Miocene) of Greece

Abstract. The Lower Tortonian Ag. Giannis section, in Gavdos Island, Greece, consists of an outer neritic to upper bathyal, marly hemipelagic sequence which is interrupted by thick turbidite-like sandy deposits. During deposition of the marly intervals, reworking was considerably reduced.This paper contributes to knowledge concerning benthic foraminiferal response to dynamic sedimentary environments. Important palaeoecological information for benthic foraminiferal assemblages was gathered and analyzed in order to create a regionally consistent picture of the palaeoenvironment. Samples were analyzed statistically in order to identify the different palaeoenvironmental settings during turbiditic sedimentation. Undisturbed basal marls of the section are characterized by the predominance of a diversified Uvigerina striatissima assemblage typified by a broad variety of morphotypes with different inferred habitat preferences and feeding strategies, indicating rather well-oxygenated bottom waters. This environmental stability was subsequently disrupted by recurrent deposition of turbidite-like sands. A low-diversity Valvulineria complanata-Globobulimina sp. assemblage is dominant in this part of the succession, as these specialized endobenthic species could keep pace with high-energy sedimentary settings. Just above the turbidites, a “recolonization” fauna (Bolivina alata assemblage), composed entirely of infaunal elements is observed, indicating a nutrient-rich substrate. This oligotypic fauna is later replaced by a more diversified microfauna capable of occupying a wider range of ecological niches.

Dropstones, pseudoplanktonic forms and deep-water decapod crustaceans within a Lutetian condensed succession of central Istria (Croatia): relation to palaeoenvironmental evolution and palaeogeography

In central Istria (western Croatia) a middle Eocene unit, some tens of metres thick, marks the transition from shallow-water carbonate to deeper-water clastic sedimentation. This unit consists of a basal interval, rich in macrofossils, made of clayey fossiliferous wackestones and packstones (known as Marls with crabs) and of an overlying marly interval (Globigerina Marls). Integrated paleontological, sedimentological, and petrographical analyses of three key sections, supplemented with data from several other sites, reveal the history of the depositional environment and the changes that occurred up-section in the carbonate deposition and the faunal assemblages. Palaeobathymetric reconstruction, based on the benthic and planktonic foraminiferal assemblages, shows a rapid deepening-upward from the base (palaeodepth is about 200 m) to the top (about 1000 m) of the unit. The base of the unit represents a condensed section that contains abundant macrofossils consisting of autochthonous (mainly decapod crustaceans and deep-water mollusks) and allochthonous (macroforaminifers and shallow-water mollusks) benthic, as well as pelagic (nautiloids and nektonic remains) and pseudoplanktonic (teredinids and ostreids) forms. The abundance of decapod crustaceans, probably represented by only one species that lived in deep-water, can be correlated with the substantial arrival of plant organic detritus at the bottom. The further deepening of the environment caused the disappearance of most of the benthic autochthonous forms. Dropstones, wood-boring bivalves and other pseudoplanktonic forms, and vegetation remains are mainly found within and just above the basal fossiliferous horizon. The abundance of vegetation remains and teredinids reflects the input of wood into deep-marine environments and condensation associated with sediment starvation, both related to a phase of sea-level rise. Dropstones were transported by vegetation rafting and, probably, at a lesser rate, by kelp rafting. Petrologic studies of the dropstones provide information on the source areas (deltaic areas of the Collio region, NE Italy) and on the little known palaeogeography of the Southern Alps and Outer Dinarides during the Lutetian tectonic phase of regional relevance.

Detachments and normal faulting in the Marche fold-and-thrust belt (central Apennines, Italy): inferences on fluid migration paths

In the outermost domains of the central Apennines fold-and-thrust belt, the structural architecture of the late Miocene–early Pliocene contractional edifice was controlled by competence contrasts in the Calcareous–Marly sequences of Mesozoic–Tertiary age, and by a different state of lithification of the rock units at the onset of deformation. Field data on relative chronology of outcrop-scale structures (cleavage, veins, faults, folds) are presented for the three largest thrust-ramp anticlines of the Marche fold-and-thrust belt: Monte Gorzano, Acquasanta and Montagna dei Fiori-Montagnone. The data show that the timing and geometry of deformation structures differ for: (1) the lower Calcareous interval of late Triassic–early Cretaceous age (LCI) bounded on top by the intermediate detachment (ID) of the Fucoidi Marls; (2) the upper Calcareous–Marly interval (UCMI) of late Cretaceous–Oligocene age; (3) the uppermost detachment zone (UDZ) of lower–middle Miocene age; (4) the topmost Messinian Flysch sequence (FS). In the UDZ early episodes of deformation are manifested by compaction of a poorly lithified sequence followed by pervasive development of layer-parallel pressure-solution cleavage. Reverse faults ramp obliquely across the stratigraphic sequence, and are coated by multiple overgrowths of calcite fibers. These structures are deformed by large, eastward-verging asymmetric folds with N–S axial trends, and are cut by late generations of reverse faults. Normal faults started to develop in the fold backlimbs during the final stages of shortening, in middle–late Pliocene times. These early normal faults were reactivated during episodes of late Pliocene–Pleistocene extensional downfaulting, and are now superposed on the compressional edifice. The UDZ is interpreted to have temporarily sealed the upward escape of fluids during the initial episodes of shortening. Pervasive interlayer flow in the poorly lithified sequence was responsible for development of broken beds and scaly fabrics, similar to those observed in accretionary prisms. Only in the latest stages of deformation did propagation of discrete faults provide an interconnected pathway for fluid migration, until the final offset of the UDZ. The structural relationships suggest that fluids trapped within the fold cores and sealed by the UDZ were finally driven upwards due to progressive disruption of the thrust belt by late normal faults of late Pliocene to Pleistocene and Holocene age. Large-scale fluid migration along structurally-controlled pathways was enhanced by the strong components of uplift consequent to the final stages of deformation in the Marche fold-and-thrust belt, and was eventually associated with episodes of normal seismic faulting.

A correlation of subsurface andsurface data of the Middle-Upper Jurassic between the Ebro Basin and the central Iberian chain (Eastern Spain)

Evidence coming from subsurface studies of Middle and Upper Jurassic in the Ebro Basin (easten Iberia) shows ageneral homogeneity and a good correlation with Iberian Chain on what concerns the distribution of facies and the main litho-stratigraphic units: (1) the thick, carbonate Chelva Formation (Middle Jurassic); (2) the sponge limestone, Yátova Formation (middle-upper Oxfordian), (3) The Sot de Chera formation (upper Oxfordian — lower Kimmeridginan) formed by a uniform marly interval; (4) the Loriguilla Formation (Kimmeridgian), formed by a homogeneous interbedding of shaley marls and limestones. The uppermost Jurassic unit, the oncolitic limestone Higueruelas Formation (Tithonian to Berriasian) has not been evidenced so far in the Ebro Basin due, most probably, to erosion. Correlation appears much less evident with other adjacent areas, such as the Catalan Coastal Range, farther East, or the Pyrenees, at the North, where lithological successions are distinct and facies are predominantly dolimitic. On the other hand, the Middle-Upper Jurassic successions appear much more complete at the southern part of the Ebro Basin than in the north, where they are progressively affected by pre-Cretaceous and pre-Tertiary erosion.