Carbonate platforms across Western Europe were superseded at the Middle-Upper Jurassic (Callovian-Oxfordian) boundary either by alternating marl-limestone and widespread marl deposits or by condensed sections containing iron ooids. The characteristics of marine condensed sections in the south-eastern part of the Paris Basin (France) and their distribution pattern are examined here, and a model of iron ooid formation is developed. Iron ooids are found from the shoreface to the offshore zone. They are most abundant in the median-to-distal offshore transition zone, where they originally formed. They also occur commonly, albeit often as reworked grains, in the proximal offshore zone, to which they were transported. The contemporaneous, thick, predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings (distal offshore zone). The iron ooids are composed of goethite. Typically, they have a nucleus made up of a clump of goethite crystals and a laminated cortex. Three distinctive nanostructures are identified in the cortex laminae: (i) a nanograined crystalline structure typical of primary goethite; (ii) a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals; and (iii) a coalesced structure acquired by subsequent diagenetic recrystallization. The iron ooids formed successively (i) by lamina growth when goethite precipitated in the surface layer of the sediment (nanograined structure) and (ii) by interruption of growth when the ooids were remobilized by hydrodynamic agents, as reflected by the flaked nanostructure; (iii) these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried.

Several depositional environments associated with Callovian-Oxfordian condensed series of the southeast of the Paris Basin are defined. As sedimentation rates were very low, variations in palaeodepth, which were synchronous at regional scale, were taken to directly reflect fluctuations in accommodation potential. Within a major trend toward increased accommodation potential, five sharp upturns and one sharp downturn are detected. A biostratigraphic unit preservation index is denned to quantify and discuss the low preservation of sediments in these condensed series. This index is seen to vary with accommodation potential.

The Upper Sinemurian condensed sections of the edge of the Morvan (France) are known to have been part of an outer carbonate platform that was little affected by subsidence. In this paper, the facies distribution is arranged within a time-frame of 14 horizons in order to identify and explain variations in sediment accommodation potential. The condensed sections are valuable inasmuch as they fit into a simplified model in which accommodation space is not modified by the invariably negligible sedimentary input and palaeobathymetric variations directly reflect relative sea level variations. Four facies associations correspond to lower offshore, and upper offshore environments. Facies stacking in each section is analysed and set against biostratigraphic data from three viewpoints. 1 - Facies stacking between two discontinuity surfaces, corresponding either to erosion or to non deposition, allows us to identify preserved sediment volumes, which have been dated (i.e. horizon identified) for 178 of the 189 levels in the 20 sections surveyed. In this narrowly constrained biostratigraphic context where decimetric beds can be correlated over large distances, each maximum biohorizon extension is considered to be a maximum transgression. A Wheeler diagram and a frequency variation curve of horizon occurrence bring out the transgressive-regressive variations. The transgressive maxima are dated to H2, H5, H10 and H13. They coincide with the transgressive maxima at the scale of northern Europe. 2 - Facies stacking between two deepness maxima encompassing a maximum of facies regression or minimum depth allows us to identify regressive-transgressive cycles or generic units. By setting the genetic units against the horizon boundaries, it is possible to date the deepening maxima or to determine whether a biohorizon contains a deepening maximum locally. The percentage of sections where a given horizon contains a deepening maximum allows us to construct a frequency curve of maximum deepening against time. Comparison of the frequency curves of horizon occurrence and maximum deepening leads us to divide the late Sinemurian into two periods. The first (Obtusum and Oxynotum zones) is characterized by synchronism between deepening maxima and transgression maxima and therefore the absence of any local tectonic factor. The second (Raricostatum zone) is characterized by diachronism between the two maxima and attests to the occurrence of local tectonic movements (corresponding to the "Lotharingian crisis" of the literature) and the rejuvenation of differentially subsiding fault-bounded blocks. 3 - Finally, facies stacking of the overall condensed section of each site allows us to distinguish three types of sections, depending on the intensity of condensation and the amplitude of the sedimentary gaps. These correspond to three types of sedimentary preservation area related to reactivated block faulting of thr platform with differential subsidence.

A sedimentological and facies sequence study, coupled with geochemical analyses (Sr, Mg, Fe, Mn and delta(18)O) was made on a core (Ravieres, Yonne; south-east Paris Basin, France) in the Bajocian-Bathonian carbonate-shelf sedimentary succession. By studying the strontium variations, geochemical cycles can be correlated to transgressive-regressive sedimentary cycles. However, the interpretation of the geochemical cycles must refer to a different standard than the studies generally realised in basin environments.

Three types of inherent diagenetic sequences (IDS) of hardgrounds separating subtidal facies have been reported in the Bajocian limestones of the Seuil de Bourgogne. One type, including a meteoric diagenetic phase but no vadose phase before overlapping, is interpreted as the result of marine ablation of exposure surfaces. Evidence is provided by the vertical distribution pattern of phreatic freshwater cements below the affected surfaces.

Aragonitic muds from the upper Trias occur in laminites between two laminae rich in clays and/or organic matter. Two types of aragonite are identified. The first shows rod or needle morphology, with Sr content (9,300 ppm), delta(18)0 (-1.1 to -1.7) and delta(13)C (+2.1 to +2.8) mostly similar to aragonite of Recent sediments. It is not biodetrital in origin but results from direct precipitation at 22-30 degrees C in sea water with a Sr-m(2+)/Ca-m(2+) ratio very near to Recent values. The second aragonite showing greater prismatic crystals with inclusions of relics of rods and needles, a high content in strontium (15,800 ppm) and a negative delta(13)C (-13.0 a -14.4), is diagenetic.

Along a NW-SE transect in Savoy, stratigraphy of "Delphino-helvetic Zone", "Breches de Tarentaise Zone" and "Subbrianconnais Zone", is revised by using sequential analysis and all available biostratigraphic data. From the early Rhetian to the late Aalenian, four to six unconformities were identified from one structural and paleogeographical unit to the other. They are boundaries of 2nd order cycles of a duration between 3 and 16 Ma. The Rhetian cycle is common to the different domains and shows the predominant eustatic control on its origin. However, the boundary at the top is weekly marked because of the beginning of regional subsidence. A Hettangian-Sinemurian cycle is specifically evidenced in the "Dauphinois Basin" in Savoy (Mont-Joly Nappe) and on the "Subbrianconnais" slope (Perron des Encombres Unit). The unconformity at the top of this cycle (Turneri-Obtusum boundary) is not observed in the other Zones but is recorded in all the West European basins. It is considered as a tectonically enhanced unconformity where eustatic and tectonic effects were added. In the other Zones, Hettangian-early Carixian versus Hettangian-early Domerian 2nd order cycles are different on both sides of the Penninic Thrust. The transgressive half cycle ended earlier in the West (Angulata zone) than in the East (Semicostatum zone) and earlier in the northern (Savoy) part of the "Dauphinois Basin" than in the South (Digne Basin). On the "Valaisan" platform and "Subbrianconnais" slope, the unconformity at the cycle boundary corresponds to a significant distensive and block tilting episode throughout the Carixian (Jamesoni-Ibex zone boundary or intra Ibex zone). On the Mont-Blanc and Rocheray shoals (horsts), significant distensive events with block tilting were post-Carixian (post Davoei, probably Margaritatus zone). An additional cycle is differentiated through the Pliensbachian at the East of the Penninic Thrust. The unconformity surface in the early part of Margaritatus zone seems to be common to all the Units of the studied area and is known in all West European basins showing that it was influenced by eustatic effects and was tectonically enhanced. The "Valaisan" platform was drowned during and after Domerian. Most of the Toarcian seems to be characterized by an overall starvation hiatus.

A new graphic visualization, the diagenetic log, has been conceived to represent unconformity cement stratigraphy. This has allowed some diagenetic phases to be dated in relation to the different sedimentary episodes and to be distinguished from the burial phases. This visualization permits display of the different unconformity signatures which are used to reconstruct the changes occurring in the environment during the gaps in sedimention. Within a middle Bajocian biodetrital reef complex in the Paris Basin (France), two freshwater dissolutions, separated by a marine cement, show that a double fluctuation in the relative sea-level must have occurred during the sedimentary gap. As paleokarst traces are found at the base of paleoreliefs, relative sea level variations greater than 30 m should be envisaged.

In the Ragusa basin (southeastern Sicily), the late Triassic Noto formation is considered as the main oil source rock. We provide a detailed description of the sedimentary facies determined from core samples, and discuss geochemical results, obtained for both kerogens and chloroform extractable hydrocarbons from samples where sedimentary organic matter is immature.Two main sedimentary sequences were encountered: (i) layers of limestones and of marls (or shales) alternating at a metric scale, and (ii) laminites having various types and carbonate contents. The high petroleum potentials (S2 up to 100 kg HC/t rock) are related to sedimentary lithologies that contain a minimum of clay.Two types of algal organic matter are probably mixed in the sediments studied. These two types can be distinguished by the oxygen content. They also do not have the same kinetic behavior in thermal evolution.Special attention has been paid to the possible use of bitumens and of pyrolysates obtained from kerogens for understanding "organic facies". Bulk properties together with several biomarker distributions were examined through different facies. But most of the parameters measured or computed are more clearly related to the maturity of the sequences analyzed rather than to the intrinsic nature of the in situ organic matter.A modeling approach is proposed, taking into account geological and geochemical data. Different situations of the Noto source rock lead to different timings of oil formation. The importance of source rock heterogeneities at different scales in basin evaluation is underlined.

In the Ragusa Basin (Southeastern Sicily), the Noto (Late Triassic) and Streppenosa (Early Liassic) formations, considered as the main source-rock of oil, are composed of millimetric to metric recurrences of clays, marls and carbonates. Together with a sedimentological and mineralogical description, a characterization of the organic matter is performed, at the same scale of investigation. Organic matter is analyzed in immature samples, using Rock-Eval technique and isolated kerogens. Generally, in terms of Total Organic Carbon, the richest sediments (TOC > 3%) are the most clayey. But very often, in all the encountered lithotypes, the Hydrogen Index reaches very high values (HI up to 900), and the H/C atomic ratio of kerogens ranges between 1.2 and 1.6. On the other hand, the kerogens present a rather large distribution of O/C atomic ratios, and it is possible to define two poles of composition. The kinetic parameters of cracking of representative organic samples of each pole are calculated by the OPTIM method. The variations of organic matter quantity and quality are discussed with respect to a typification of the sediments, especially the laminites, based upon observations performed with optical microscope and SEM. A tentative paleoenvironmental approach is proposed, and the most favourable conditions for organic enrichment are outlined. The general context is a local collapse of the Triassic carbonate platform. The highest petroleum potentials are neither associated to the algal-sedimentary laminites of the Noto formation nor to the basinal silty facies of the Streppenosa formation, but to the black-shales intercalated within these facies and to the laminites rich in clay.

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During ODP Leg 103, serpentinized peridotite (clinopyroxene-spinel harzburgite) was cored within the basement approximatively at the boundary between the North Atlantic oceanic curst to the west, and the thinned continental crust of the Galicia passive margin (Spain) to the east. The exposure of mantle derived peridotite on the seafloor occurred at the end of the period of rifting, roughly 110 Ma ago. Ductile shear zones observed in the cored peridotite are consistent with movements along a deep low-angle, normal fault rooted within the upper mantle and dipping eastward, beneath the Galicia margin. To explain the tectonic denudation of the mantle at the ocean-continent boundary, we use a non-uniform stretching model for the lithosphere, set up from the Wernicke's model (1985).

During ODP Leg 103 (April-June 1985) and the Galinaute cruise (June-July 1986), serpentinized peridotite (clinopyroxene-spinel harzburgite) was recovered within the basement approximately at the boundary between the North Atlantic ocean crust to the west and the thinned continental crust of the Galicia passive margin (Spain) to the east. The exposure of mantle-derived peridotite on the sea floor occurred at the end of the period of rifting, roughly 110 Ma. Ductile shear zones observed in the peridotite are consistent with movements along a deep, low-angle normal fault rooted within the upper mantle and dipping eastward beneath the Galicia margin. To explain the tectonic denudation of the mantle at the ocean-continent boundary, they use a nonuniform stretching model for the lithosphere, set up from Wernicke's model.

In 1986 the french submersible Nautile dived to 3.500 m-5.500 m at Galicia Margin in the area drilled by the JOIDES Resolution O-V (CDP, Leg 103). Three different kinds of seafloor were investigated: a) the Galicia passive margin (basement and sediments); b) a basa/tic seafloor (probably a piece of Cretaceous oceanic crust of the Biscay Bay; c) a 100 km long belt of serpentinized peridotites (ultramafic seafloor) extended between the oceanic and the thinned continental crust

La campaña oceanográfica 103 del Ocean Drilling Program (ODP) ha estado dedicada a dilucidar la evolución tectónica y sedimentación del Margen Atlántico-Ibérico. Se realizaron un total de 14 sondeos., en cinco puntos de posicionamiento, sobre el extremo más profundo del margen; al S del Banco de Galicia. Los resultados obtenidos revelan que previamente al inicio de la expansión oceánica entre Terranova e Iberia ocurrió una historia compleja de distensión cortical, fracturación y subsidencia asociadas. Los resultados fundamentales son los siguientes: 1) Carbonatos de plataforma marina somera, de edad Jurásico superior-Cretáceo basal constituyen los primeros depósitos mesozóicos en ese ámbito del margen y dan lugar a un reflector sísmico considerado interiormente como basamento, 2) El hundimiento de la plataforma, fallamiento y basculamiento de los bloques ocurre desde 25 m.a. antes de iniciarse la acreción oceánica. 3) En el límite entre corteza oceánica-corteza continental se ubica una cresta constituida por peridotitas serpetinizadas. 4) El reflector sísmico «S», generalmente considerado como el límite dúctil-frágil en la corteza continental, corresponde realmente a la base de los depósitos sinrift.

In 1986, the French submersible Nautile was used to investigate at depths of 3500 to 5500 m in the area west of Galicia (Spain) where the JOIDES Resolution had drilled 12 holes in 1985 during ODP Leg 103.Three different kinds of seafloor were investigated with the Nautile: (1) the Galicia passive margin, where crystalline continental basement and Paleozoic(?)-Mesozoic sediments outcrop; (2) a basaltic seafloor, interpreted as a piece of Cretaceous oceanic crust that is presently incorporated into the northern slope of Galicia Bank as a result of Eocene tectonics; and (3) an ultramafic seafloor, composed of serpentinized peridotite locally cut by dolerite dikes.The ultramafic rocks form a 100-km-long belt between North Atlantic oceanic crust to the west and thinned continental crust of the Galicia margin to the east.New data from the Nautile dives complement and confirm some of the ODP Leg 103 results; they also force reassessment of some of the preliminary interpretations proposed by the Leg 103 shipboard scientific party.