La Distribution de la matiere organique dans la formation de Noto, roche-mere du bassin de Ragusa (Sicile)

Depositional environments and iron ooid formation in condensed sections (Callovian Oxfordian, South-eastern part of the Paris basin, France)

Carbonate platforms across Western Europe were superseded at the Middle–Upper Jurassic (Callovian–Oxfordian) boundary either by alternating marl–limestone and widespread marl deposits or by condensed sections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 t…

Caractérisation et interprétation de cycles géochimiques sur la plate-forme bourguignonne (France) au Bajocien-Bathonien

Resume Un forage (Ravieres, Yonne; Sud-Est du Bassin de Paris, France), dans les sediments de plate-forme carbonatee du Bajocien-Bathonien, permet une analyse sedimentologique et sequentielle couplee a des analyses geochimiques (Sr, Mg, Fe, Mn et δ18O). Grâce au signal du strontium, des cycles geochimiques correlables aux cycles sedimentaires de transgression-regression de facies sont mis en evidence. Cependant, l'interpretation des cycles geochimiques necessite un changement de referentiel par rapport aux travaux jusqu'ici realises en domaine de bassin.

Séries condensées et indice de préservation d'unité biostratigraphique: exemple de l'ennoiement de la plate-forme nord-bourguignonne (France) au Callovo-Oxfordien

Abstract 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.

Signification du signal isotopique (δ18O, δ13C) des carbonates néritiques : composante diagénétique et composante originelle (Jurassique supérieur de l'Est du bassin de Paris, France)

Resume Le long d'une coupe de reference traversant les formations carbonatees du Jurassique superieur de Lorraine (forage HTM102, Nord-Est de la France), des analyses isotopiques ( δ 18 O, δ 13 C) sont realisees sur la phase carbonatee de la roche totale ( bulk analysis ). Le dechiffrage de ces signaux isotopiques dans les carbonates neritiques etudies est effectue par confrontation des donnees isotopiques obtenues sur roche totale avec differents ensembles de parametres (sedimentologiques, donnees isotopiques sur produits separes, donnees petrophysiques). Il apparait que l'utilisation du δ 18 O en tant que descripteur chimiostratigraphique est impossible, car les valeurs obtenues sont le r…

Geodynamic control on carbonate diagenesis: Petrographic and isotopic investigation of the Upper Jurassic formations of the Paris Basin (France).

23 pages; International audience; The Oxfordian and Kimmeridgian carbonates of the eastern edge of the Paris Basin display poor reservoir properties (Φb15% and Kb0.1 md). The petrographic investigation and the resultant paragenetic sequence show that this is due to extensive precipitation of 2 types of almost synchronous blocky LMC (Low Magnesian Calcite) cements during mesogenesis (burial). Stable isotope investigation of these non-recrystallized cements, through both microdrilling sampling and in-situ SIMS (Secondary IonMass Spectrometry) analysis, shows that they originated from slightly buffered meteoric fluids (−3‰SMOW to −8‰SMOW) flowing through the Malm carbonate aquifers of the east…

Some sedimentological and geochemical characters of the late Triassic Noto formation, source rock in the Ragusa basin (Sicily)

URA 724 du CNRS a intégré UMR 6113 - ISTO CNRS Université d'Orléans; 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 relate…

Burial dissolution of micrite in Middle East carbonate reservoirs (Jurassic–Cretaceous): keys for recognition and timing.

14 pages; International audience; This paper discusses burial diagenesis and especially a burial dissolution phase and its effects on micrite microtexture in reservoirs in the Middle East. Three microporous reservoirs were selected: the Cenomanian Mishrif Formation in Iraq; the Kimmeridgian–Tithonian Arab D and the Barremian Kharaib Formations, both in Abu Dhabi. Staining, cathodoluminescence and scanning electron microscopy were used for petrographic observations. In the selected reservoirs, three typical micrite microtextures are distinguished: micro-rhombic, compact anhedral, and rounded. The chronology of diagenesis, based on petrographic observations, shows that mineralogical stabilisa…

Emersion generalisee intra-maastrichtienne de la plate-forme de Gavrovo-Tripolitza (Grece); effets sur les populations de foraminiferes Rhapydionininae

Abstract The reliability of biostratigraphic correlations in neritic carbonate platforms is often questioned because the benthic fauna on which biozonation is based are particularly sensitive to environmental change. It is crucial to know whether a population change corresponds strictly to a facies change. Conversely, there arise the questions of determining how populations are renewed over time and how new species appear even if facies associations remain unchanged. This is the case with the Gavrovo-Tripolitza zone of Greece, an isolated shallow carbonate platform surrounded by two oceanic domains (Pindos-Olonos Zone and Ionian Zone). The absence or scarcity of faunas generally used in Upp…