Comparisons between the Urgonian platform carbonates from eastern Serbia (Carpatho-Balkanides) and northeast Iran (Kopet-Dagh Basin): Depositional facies,microfacies, biostratigraphy,palaeoenvironments and palaeoecology

In the Getic of the Carpatho-Balcanides (eastern Serbia) and the Tirgan Formation of the Kopet-Dagh Basin (northeast Iran), platform carbonates were deposited during the Barremian/Early Aptian in environments in the domain of the northern Alpine Tethys and deformed during the Alpine orogeny. In this study, Urgonian carbonate platform deposits are discussed in detail with regard to depositional facies, microfacies, biostratigraphy, palaeoenvironments and palaeoecology. Detailed sedimentological and palaeontological investigations have been carried out on five sections in eastern Serbia and three sections in northeast Iran supported by an analysis of 392 thin-sections. Petrographic analysis of thin-sections led to the recognition of eight microfacies types grouped into four facies zones. A supratidal–intertidal (restricted)–intertidal (open-lagoon)–platform-margin sand-shoal transition was recorded in both areas. Supratidal facies are characterized by bioclastic mudstones and fenestral and peloidal wackestones and packstones; intertidal (restricted) facies are represented by bioclastic wackestones, whereas intertidal (open-lagoon) facies are indicated by bioclastic packstones/grainstones and oncoid grainstones. High-energy sand-shoal facies are dominated by ooid grainstones/rudstones followed by orbitolinid packstones. Benthic foraminifera are especially abundant and along with calcareous algae are the most important fossils used for age determination of shallow-marine carbonate deposits. Thirty-two benthic foraminiferal genera were identified from eastern Serbia with an additional 38 genera from northeast Iran dominated by agglutinated forms. Identified calcareous algae provide significant data for depositional environments and palaeoecology. The microfossil associations in the two regions are very similar and share a number of common characteristics, but also some differences and show a strong affinity to those of the northern margins of Tethys. In both study areas shallow-marine environments of the Barremian/Early Aptian were replaced by deep-marine conditions during the Late Cretaceous.     

Ulster White Limestone Formation (Upper Cretaceous) of Northern Ireland: effects of basalt loading on chalk diagenesis

The Ulster White Limestone Formation is an unusual chalk because it underwent a period of post-depositional emergence and erosion, followed by burial under 1·5–2·0 km of Tertiary basalts. A high degree of pressure solution and cementation produced a well-lithified limestone with low porosities (2·3–10·4%). The Ulster White Limestone shows no evidence of thermally induced textural alteration, except for thin (<0·5 m) pseudospar contact recrystallization zones adjoining basalt dykes. Whole-rock δ¹⁸O values of samples not associated with basalt dykes range from - 3·26%o to - 6·50%o (PDB). The δ¹⁸O values of macropore cements range from - 4·96%o to - 11·52%o (mean=-8·27%o). Modelling of the diagenesis of the Ulster White Limestone using trace element concentrations and carbon, oxygen and strontium isotopic ratios of whole rock and cement samples suggests a low water-rock ratio and either marine or mixed marine-meteoric pore water environment during the main episode of recrystallization. The maximum possible burial temperature was modelled to be ? 105°C. The diagenetic history of the Ulster White Limestone is similar to that of North Sea chalks that are at comparable burial depths as the Ulster White Limestone after basalt deposition. The geochemical data show no indication of hydrothermal alteration associated with the overlying basalts. The degree of alteration of fine-grained limestones composed predominantly of low-magnesium calcite, such as the Cretaceous/Tertiary chalks, appears to be controlled largely by the burial (effective stress) history of the limestone.     

Structural and petrophysical characterization of mixed conduit/seal fault zones in carbonates: Example from the Castellas fault (SE France)

The Castellas fault in SE France affects carbonate rocks with a plurimeter scale offset along 1.5 km of outcrop. In order to decipher the structural control on fault petrophysical and hydraulic character, we performed high resolution field structural mapping, laboratory porosity-Vp measurements, and thin sections analysis of deformations and diagenesis. Field mapping shows that the fault zone architecture displays strong lateral variations at the hectometer scale characterized by core thicknesses of 0–5 m, one or several slip planes, and varying fracture patterns within the damage zone. The fault zone heterogeneity may be related to the magnitude of the throw, the position along the fault and the affected rock facies. Laboratory measurements revealed a strong porosity reduction correlated to a Vp increase, related to the cementation of pore volumes within a decameter area around the fault plane. This fault-sealing occurred mainly through a chemical diagenesis related to fluid circulation within fault-zone heterogeneities. A 3D conceptual model of a mixed conduit/seal fault zone is proposed, characterized by sealed impermeable fault tips and more or less permeable units within which flow can occur either perpendicular or parallel to the fault strike.     

Mapping the rise and demise of Urgonian platforms (Late Hauterivian - Early Aptian) in southeastern France and the Swiss Jura

Lower Cretaceous carbonate deposits historically called “Urgonian limestones” are widely exposed around the margins of the Vocontian basin in southeastern France and in the adjacent Swiss Jura. This paper presents the history of their rise, growth and sudden demise. Eleven maps were constructed for deposits ranging in age from the Late Hauterivian pro parte to the Early Aptian (Bedoulian) pro parte. Based on sequential interpretations, they illustrate the present geographical distribution of the inner platform facies (Urgonian limestones stricto sensu, with rudists), the outer platform facies (essentially bioclastic deposits) and the basinal facies (slope, hemipelagic, pelagic deposits). These maps depict only the final terms of each successive sequence (the late highstand intervals). Chronostratigraphy is constrained by ammonites found mainly in basinal deposits, by echinoids, by rudists and to a lesser extent by dinoflagellates and calcareous nannoplancton. Inner platform, outer platform and slope (talus) deposits are dated by rich assemblages of orbitolinids and dasycladalean algae. Currently 39 species of orbitolinids have been recognized and their ranges collated with those of the ammonites in the area.In the Jura and in Provence the oldest Urgonian deposits are dated early Late Hauterivian, thus showing the synchroneity of the onset of platform carbonates development on both the southern and northern margins of the basin. Thereafter, growth of the platforms led a clearly regressive shallowing-upward trend, resulting from a stepwise progradation toward the center of the Vocontian area, coordinated with cyclical exposures in the inner platform areas. The maximum reduction of the platform deposits occurred early in Late Barremian times, coeval with a noticeable turnover in the orbitolinids assemblages.Thereafter, carbonate platform deposition shifted toward the margins of the Vocontian basin. In Early Aptian time, a well-dated discontinuity of regional extent marks the sudden, almost synchronous disappearance of the Urgonian deposits.     

Barite concretions as evidence of pauses in sedimentation in the Marnes Bleues Formation of the Vocontian Basin (SE France)

Several intervals rich in barite nodules occur in the mid-Cretaceous marls of the Vocontian Trough (SE France). These concretions, which grew on heterogeneities in the sediment, are arranged as horizons parallel to the bedding, and are often associated with carbonate and phosphate nodules. Detailed sedimentological and stratigraphical observations suggest that they represent the consequence of short-term pauses in sedimentation during early diagenesis, but the most important occurrences of barite are below prominent discontinuities. This may be explained by the frequency of pauses in sedimentation caused by a progressive starvation, or an increase in the energy of bottom-water currents. The high number of barite occurrences on the basin margins is directly linked to the recurrence of sedimentary breaks. The geochemical data show that the host sediment corresponds to a pelagic setting, far from hydrothermal influences, but generally in a restricted, dysoxic to suboxic, depositional environment. The sulphur isotopic composition of the barite sulphate (+16 to +76‰ rel. CDT) supports the hypothesis of an early diagenetic origin of the barite nodules. Their genesis may be explained by the fixation of a diagenetic front corresponding to the penetration of a sulphate reduction zone from the seawater–sediment interface down in the sediment which is in contact with barium-rich porewaters expelled upwards as a consequence of compaction. The barium of biogenic origin, initially stored in the underlying black shale, was mobilized under strongly reducing conditions. Such fixation is normally induced by a pause or a stop in sedimentation due to starvation or renewed bottom-water circulation. Together with other concretions, the barite nodules mark condensed stratigraphic intervals and often represent major breaks. As such they shed light on variations in sedimentary activity and their importance in the sedimentology and stratigraphy of pelagic marly sequences cannot be ignored.     

Formation of magnesium‐smectite during lacustrine carbonates early diagenesis: Study case of the volcanic crater lake Dziani Dzaha (Mayotte – Indian Ocean)

The volcanic crater lake of Dziani Dzaha in Mayotte is studied to constrain the geochemical settings and the diagenetic processes at the origin of Mg‐phyllosilicates associated with carbonate rocks. The Dziani Dzaha is characterized by intense primary productivity, volcanic gases bubbling in three locations and a volcanic catchment of phonolitic/alkaline composition. The lake water has an alkalinity of ca 0·2 mol l^?1 and pH values of ca 9·3. Cores of the lake sediments reaching up to one metre in length were collected and studied by means of carbon–hydrogen–nitrogen elemental analyzer, X‐ray fluorescence spectrometry and X‐ray powder diffraction. In surface sediments, the content of total organic carbon reaches up to 20 weight %. The mineral content consists of aragonite and hydromagnesite with minor amounts of alkaline feldspar and clinopyroxene from the volcanic catchment. Below 30 cm depth, X‐ray diffraction analyses of the <2 μm clay fraction indicate the presence of a saponite‐like mineral, a Mg‐rich smectite. The saponite‐like mineral accumulates at depth to reach up to ca 30 weight %, concurrent with a decrease of the contents of hydromagnesite and organic matter. Thermodynamic considerations and mineral assemblages suggest that the evolution of the sediment composition resulted from early diagenetic reactions. The formation of the saponite‐like mineral instead of Al‐free Mg‐silicates resulted from high aluminum availability, which is favoured in restricted lacustrine environments hosted in alkaline volcanic terrains commonly emplaced during early stages of continental rifting. Supersaturation of the lake water relative to saponite is especially due to high pH values, themselves derived from high primary productivity. This suggests that a genetic link may exist between saponite and the development of organic‐rich carbonate rocks, which may be fuelled by the input of CO₂‐rich volcanic gases. This provides novel insights into the composition and formation of saponite‐rich deposits under a specific geodynamic context such as the Cretaceous South Atlantic carbonate reservoirs.     

Cretaceous rudist-bearing platform carbonates from the Lycian Nappes (SW Turkey): Rudist associations and depositional setting

Lycian Nappes (in SW Turkey) lie between the Menderes Massif and Bey Dağları carbonates and comprise thrust sheets (nappes piles) of Paleozoic-Cenozoic rocks, ophiolitic and tectonic mélanges and serpentinized peridodites. This study focuses on identification of rudists and their palaeoenvironmental features observed within the Cretaceous low grade metamorphic successions (dominated by recrystallized limestones) from the Tavas and Bodrum nappes. The study is based on fifteen stratigraphic sections measured from Tavas, Fethiye, Köyceğiz, Bodrum, Ören and Bozburun areas. The Lower Cretaceous successions with rudists are very sparse in the Lycian Nappes and a unique locality including a Berriasian epidiceratid-requieniid assemblage is reported so far. A new requieniid-radiolitid assemblage was found within the pre-Turonian (?Albian-?Cenomanian) limestones. Four different Late Cretaceous rudist assemblages were firstly identified as well: 1) Caprinid-Ichthyosarcolitid assemblage (middle-late Cenomanian); 2) Distefanellid assemblage (late Turonian); 3) Hippuritid-Radiolitid assemblage (late Coniacian-Santonian-Campanian); 4) Radiolitid-Hippuritid assemblage (‘middle’-late Maastrichtian). Microfacies data and field observations indicate that the rudists lived in the inner and outer shelves of the Cretaceous carbonate platform(s) in this critical part of the Neotethys Ocean. Rudists formed isolated patchy aggregations in very shallow palaeoenvironments and deposited as shell fragments particularly on the outer shelf environment, which is characterized by higher energy and platform slope characteristics.     

Isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates (Miocene, Great Bahama Bank)

The stable isotope geochemistry of Miocene sediments from the leeward margin of the Great Bahama Bank was examined to investigate burial diagenetic processes in periplatform carbonates. Data indicate that, in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope, rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined. The present study focuses on Ocean Drilling Program Sites 1006 and 1007, the most distal of five sites drilled from marginal to deep basin environments during Leg 166. These Miocene sections are characterized by their cyclic appearance, manifest as decimetre‐ to metre‐scale alternations between light‐coloured ooze/chalk/limestone and dark‐coloured marl/marlstone. The section at Site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of ～675 m. Fluctuations in δ¹⁸O and δ¹³C values at this site are independent of lithological variation and reflect primary conditions. At Site 1007, located at the toe‐of‐slope and composed of a mixture of bank‐derived and pelagic carbonate, limestones are densely cemented, show little evidence of compaction and have δ¹⁸O values up to 2‰ higher than coeval sediments at Site 1006. Marlstones at Site 1007 are poorly cemented, exhibit an increase in compaction‐related features with depth and have lower and more variable δ¹⁸O values that are similar to those of coeval sediments at Site 1006. Isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first ～100 m of burial. Higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones; in spite of significant compaction and pressure solution during burial, original isotopic compositions appear to be best preserved in these intervals at Site 1007. The documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of considering such factors when interpreting geochemical data from ancient shelf and slope limestones.     

Electrical resistivity tomography (ERT) of a coastal carbonate aquifer (Port-Miou, SE France)

As part of a larger regional research program “KarstEAU”, the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry.     

Mineralogical and isotopic record of biotic and abiotic diagenesis of the Callovian-Oxfordian clayey formation of Bure (France)

The Callovian-Oxfordian (COx) clayey unit is being studied in the Eastern part of the Paris Basin at depths between 400 and 500 m depth to assess of its suitability for nuclear waste disposal. The present study combines new mineralogical and isotopic data to describe the sedimentary history of the COx unit. Petrologic study provided evidence of the following diagenetic mineral sequence: (1) framboidal pyrite and micritic calcite, (2) iron-rich euhedral carbonates (ankerite, sideroplesite) and glauconite (3) limpid calcite and dolomite and celestite infilling residual porosity in bioclasts and cracks, (4) chalcedony, (5) quartz/calcite. Pyrite in bioturbations shows a wide range of δ³⁴S (−38‰ to +34.5‰), providing evidence of bacterial sulphate reduction processes in changing sedimentation conditions. The most negative values (−38‰ to −22‰), measured in the lower part of the COx unit indicate precipitation of pyrite in a marine environment with a continuous sulphate supply. The most positive pyrite δ³⁴S values (−14‰ up to +34.5‰) in the upper part of the COx unit indicate pyrite precipitation in a closed system. Celestite δ³⁴S values reflect the last evolutionary stage of the system when bacterial activity ended; however its deposition cannot be possible without sulphate supply due to carbonate bioclast dissolution. The ⁸⁷Sr/⁸⁶Sr ratio of celestite (0.706872-0.707040) is consistent with deposition from Jurassic marine-derived waters. Carbon and oxygen isotopic compositions of bulk calcite and dolomite are consistent with marine carbonates. Siderite, only present in the maximum clay zone, has chemical composition and δ¹⁸O consistent with a marine environment. Its δ¹³C is however lower than those of marine carbonates, suggesting a contribution of ¹³C-depleted carbon from degradation of organic matter. δ¹⁸O values of diagenetic chalcedony range between +27‰ and +31‰, suggesting precipitation from marine-derived pore waters. Late calcite crosscutting a vein filled with chalcedony and celestite, and late euhedral quartz in a limestone from the top of the formation have lower δ¹⁸O values (∼+19‰), suggesting that they precipitated from meteoric fluids, isotopically close to present-day pore waters of the formation. Finally, the study illustrates the transition from very active, biotic diagenesis to abiotic diagenesis. This transition appears to be driven by compaction of the sediment, which inhibited movement of bacterial cells by reduction of porosity and pore sizes, rather than a lack of inorganic carbon or sulphates.     

High-resolution analysis of submarine lobes deposits: Seismic-scale outcrops of the Lauzanier area (SE Alps, France)

The Lauzanier area represents the northernmost extension of the Annot Sandstone series and contains deposits between 650 and 900 m-thick. This basin was active from upper Bartonian or lower Priabonian to early Rupelian. It is composed of two superposed units separated by a major unconformity. The sediment supply is due to channelled flows coming from the south. Flow processes include mass flow to turbidity currents. The size of the particles and the absence of fine-grained sediment suggest a transport over a short distance. The Lower Unit is made of coarse-grained tabular beds interpreted as non-channelled lobe deposits. The Upper Unit is made of massive conglomerates interpreted as the channelled part of lobes. These lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale. The abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area. This uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts.This field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse-grained turbidite system. The outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non-channelled lobe system. These results of high-resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep-sea turbidite system that are either restricted to cores, or with a lesser resolution (seismic).     

Sedimentary facies and model of shallow water carbonates platform of the Lower Cambrian Longwangmiao Formation in Sichuan Basin

Building the sedimentary model accurately and delineating the spatial-temporal distribution of grain bank are the keys to increase the rate of success in natural gas exploration. Thus,the types and characteristics of sedimentary facies of the Longwangmiao Formation in the Sichuan Basin were studied based on field outcrops,drilling,logging and seismic data. Taking a fourth-order sequence systems tract as a unit,the spatial-temporal distribution characteristics of sedimentary facies within the chronostratigraphic framework were precisely described,and the depositional model of the Longwangmiao Formation was established to reveal the development mechanisms of grain bank and point out the future natural gas exploration. The results showed that: (1)The typical shallow carbonate platform depositional system was developed in the Longwangmiao Formation of the Sichuan Basin and its surrounding areas. Mixed tidal flat,restricted platform(microfacies types including grain bank,dolomitic tidal flat,lagoon,and gypsum lagoon),open platform(microfacies types including grain bank,lime tidal flat),platform margin,and slope-basin were developed from the edge to the interior of the basin;(2)A sedimentary model was established,which was characterized by “one depression,two uplifts,and two grain banks in the form of belts”. The development of grain banks was mainly controlled by palaeo-topography and relative sea-level fluctuation. It was mainly developed in the highstand systems tract of a fourth-order sequence vertically,and distributed as a belt along the platform margin and around the lagoon area horizontally. Our paper pointed out the grain shoal deposits are the material basis for the development of high-quality reservoirs,the results thus provide a sedimentary geological basis for future natural gas exploration of the Cambrian Longwangmiao Formation in the Sichuan Basin.     

四川盆地下寒武统龙王庙组浅水碳酸盐岩台地沉积相特征及模式*

准确建立四川盆地龙王庙组沉积模式和精细刻画颗粒滩时空分布规律,是提高天然气勘探成功率的关键。依据野外露头、钻井、测井和地震等资料,综合分析四川盆地及周缘下寒武统龙王庙组沉积相类型及特征;以四级层序为单元,精细刻画等时地层格架内沉积相时空展布特征,建立沉积模式,揭示颗粒滩发育规律,指出下一步天然气勘探方向。结果表明: (1)四川盆地及周缘龙王庙组发育典型浅水碳酸盐岩镶边台地沉积体系,自盆地西缘向东依次发育混积潮坪、局限台地(颗粒滩、云坪和咸化潟湖等微相类型)、开阔台地(颗粒滩、灰坪等微相类型)、台地边缘和斜坡—盆地等沉积相类型;(2)建立了“一凹两隆,双滩成带”的沉积模式,颗粒滩的发育主要受控于古地貌和相对海平面升降,具体表现为垂向上主要发育于四级层序海退时期,平面上沿台地边缘带和围绕咸化潟湖的相对隆起区呈带状分布。由于颗粒滩是优质储集层发育的有利相带,因此该结果可为四川盆地寒武系龙王庙组下一步天然气勘探提供沉积地质基础。     

Cold seep deposits of Beauvoisin (Oxfordian; southeastern France) and Marmorito (Miocene; northern Italy): microbially induced authigenic carbonates

The relation of two well-known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study. Archaea are found to be associated with the formation of Oxfordian seep carbonates from Beauvoisin and with a Miocene limestone from Marmorito ("tube-worm limestone"). Carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative δ¹³C_carbonate values, respectively. Highly positive values (+15‰) reflect the use of ¹³C-enriched CO₂ produced by methanogenesis. Low δ¹³C values of the Marmorito carbonates (–30‰) indicate the oxidation of seepage-derived hydrocarbons. Likewise, the δ¹³C content of specific tail-to-tail linked isoprenoids, biomarkers for archaea, was found to be strikingly depleted in these samples (as low as –115‰). The isotopic signatures corroborate that archaea were involved in the cycling of seepage-derived organic carbon at the ancient localities. Another Miocene limestone ("Marmorito limestone") shows a strong imprint of methanotrophic bacteria as indicated by δ¹³C values of carbonate as low as –40‰ and biomarker evidence. Epifluorescence microscopy and field-emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation. In addition to lucinid bivalves previously reported from both localities, we infer that sponges from Beauvoisin and tube worms from Marmorito depended on chemosynthesis as well. Low δ¹³C values of nodules related to sponge taphonomy (–27‰) indicate that sponges might have been linked to an enhanced hydrocarbon oxidation. Tube worm fossils from Marmorito closely resemble chemosynthetic pogonophoran tube worms from Recent cold seeps and are embedded in isotopically light carbonate (δ¹³C –30‰). Received: 13 October 1998 / Accepted: 5 February 1999     

Microspar development during early marine burial diagenesis: a comparison of Pliocene carbonates from the Bahamas with Silurian limestones from Gotland (Sweden)

Comparison of ultrastructures in Pliocene periplatform carbonates from the Bahamas with Silurian limestones from Gotland (Sweden) reveals that despite the differences in primary sediment composition and age, they reflect a similar mechanism of lithification. In both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis. Neither significant compression nor meteoric influence are necessary for the formation of calcite microspar. A model is proposed for the process of microsparitic cementation of fine-grained aragonite needle muds comprising four stages: (1) unconsolidated, aragonite-dominated carbonate mud; (2) precipitation of microspar that engulfs aragonite needles; (3) dissolution of aragonite, resulting in pitted surfaces of the microspar crystals; and (4) slight recrystallization. Our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite.     

Correlation of Barremian-Aptian (mid-Cretaceous) dinoflagellate cyst assemblages between the Tethyan and Austral realms

Quantified organic-walled dinoflagellate cyst (dinocyst) assemblages are presented for two sedimentary successions deposited in neritic environments of the Tethys Ocean during the Barremian and Aptian in an attempt to reconcile established dinocyst biostratigraphic schemes for Tethyan and Austral regions. One section is at Angles, southeast France (the Barremian stratotype section); the other is at Deep Sea Drilling Project Site 263, off northwest Australia. We also construct a carbon isotope record for Site 263 using bulk organic carbon.Both sections contain abundant, well-preserved dinocyst assemblages. These are diverse, with 89 taxa identified at Angles and 103 taxa identified at Site 263. Of these, more than 93% are cosmopolitan. When combined with other work at Angles and Site 263, we found that nine dinocysts have their first occurrence (FO) or last occurrence (LO) at both locations. These dinocyst events are, in alphabetical order: LO of Cassiculosphaeridia magna, FO of Criboperidinium? tenuiceras, LO of Kleithriasphaeridium fasciatum, LO of Muderongia staurota, FO of Odontochitina operculata, LO of Phoberocysta neocomica, FO of Prolixosphaeridium parvispinum, FO of Pseudoceratium retusum var. securigerum, and FO of Tehamadinium sousense. Although these events support a Barremian–Aptian age for both sections, their stratigraphic order is not the same in the sections. The δ¹³C_org record at Site 263 displays a characteristic series of changes that have also been recorded in other carbon isotope curves spanning the Late Barremian–Early Aptian. Such independent dating (along with ammonite zones at Angles) suggests that three of the nine dinocyst events are approximately isochronous at Angles and Site 263: the LO of K. fasciatum in the mid Barremian, the FO of P. retusum var. securigerum and the FO of C.? tenuiceras in the earliest Aptian; the other six dinocyst events are diachronous. Dinocyst assemblages at Site 263 can be loosely placed within existing Australian zonation schemes, providing much-needed calibration. Our data suggest that the Muderongia testudinaria Zone ends in sediments of mid Barremian age, the succeeding Muderongia australis Zone extends into the Early Aptian, and the younger Odontochitina operculata Zone begins in Early Aptian deposits. The boundary between the M. australis and O. operculata zones, and the Ovoidinium cinctum (as Ascodinium) Subzone, positioned at the top of the M. australis Zone when present, could not be recognized incontrovertibly. Interestingly, however, this horizon broadly correlates with the onset and extent of the Selli Event, a time of major biogeochemical change.     

Sedimentology and palaeoenvironment of the southeast Sicilian Tertiary platform carbonates

A thick succession of shelf and shelf-slope carbonates is developed in southeastern Sicily. Sedimentological aspects of the Oligocene to Tortonian sequence, including distribution and palaeoenvironmental factors, are considered. A new formation and four new members are proposed in the upper part of the succession.The region comprises a western half, typically exhibiting the principal deeper-water planktonic facies including marls, and an eastern area displaying typically inner-shelf carbonates and an attenuated succession. Coralline algal limestones and calcarenites are more typical of this latter region but there are also some volcanic intercalations. An attempt is made to relate the Hyblean succession to that of the Maltese Islands which lie at the southern end of this Tertiary carbonate platform.