G. Deroo

Bio: G. Deroo is an academic researcher from Institut Français. The author has contributed to research in topics: Cretaceous & Cenomanian. The author has an hindex of 9, co-authored 10 publications receiving 2054 citations.

La pyrolyse Rock-Eval et ses applications. Première partie.

Abstract: Concue pour repondre aux besoins de l'exploration petroliere, la methode de pyrolyse Rock-Eval est maintenant largement utilisee. Elle fournit, en effet, et d'une facon rapide, differentes informations sur le contenu organique des roches, telles que le potentiel petrolier des series rencontrees, la nature des kerogenes, leur etat de maturation. En ce qui concerne le materiel, deux nouvelles versions ont ete mises au point a l'Institut Francais du Petrole (IFP) depuis l'apparition en 1977 des premiers appareils Rock-Eval : un Rock-Eval II completement automatise grâce a un microprocesseur et dote, en option, d'un module de dosage du carbone organique; un Rock-Eval III (Oil Show Analyzer) qui se distingue du precedent par le fait qu'il analyse separement le gaz et l'huile et qu'il effectue le dosage du carbone organique a la place du pic S3. En ce qui concerne l'interpretation de la methode, l'experience acquise tant par les applications aux bassins sedimentaires que par les etudes experimentales menees en laboratoire a permis de mieux connaitre les parametres utilises (pics S1, S2, S3, temperature de pyrolyse Tmax) a travers leurs variations et, de la, de mieux discerner les limites d'application de la methode. En ce qui concerne l'application de la methode, la representation verticale des resultats sous forme de logs geochimiques conduit a une interpretation a la fois efficace et pratique. Des abaques et des diagrammes de reference permettent de caracteriser les roches meres (potentiels petroliers, types de matiere organique, degre d'evolution, alterations. . . ) ainsi que les phenomenes de migration. L'etablissement de cartes geochimiques a l'echelle du bassin devient alors possible. Enfin la methode est sortie du domaine de l'exploration petroliere proprement dite pour trouver des applications a l'etude des charbons, des roches bitumineuses, des sediments recents et meme aux techniques du raffinage et de la recuperation secondaire des bruts.

La pyrolyse Rock-Eval et ses applications. III

Abstract: Presentation, sur 3 series geologiques, de la signification geochimique pouvant etre attribuee aux parametres obtenues par la pyrolyse Rock-Eval effectuee sur des matieres organiques pures ou sur des roches riches en matiere organique

Ocean-wide stagnation episode in the late Cretaceous

Abstract: In this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid-Cretaceous, here called the Cenomanian–Turonian Black Shale Horizon (CTBSH). The occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments. The stratigraphic record above and below the CTBSH in environments as different as the deep North Atlantic Ocean and marginal and epicontinental seas over enormous areas in North America, North Africa and northwestern Europe is characterized by a stratigraphic gap, a disconformity or a continuous but strongly condensed stratigraphic section. The anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2. No simple model has yet been found to explain the occurrence of the CTBSH in such a wide range of depth and palaeoenvironmental conditions.

Organic-rich sediments and palaeoenvironmental reconstructions of the Cretaceous North Atlantic

Abstract: Summary A survey of DSDP black shales from the North Atlantic has been carried out in order to study the evolution of Cretaceous palaeoenvironments in the region. The study involved a reappraisal of the biostratigraphy of the Cretaceous formations and considered accumulation rate, mineralogical and organic geochemical data. Special attention was paid to distinguishing between redeposited and autochthonous sediments. Three main phases of deposition are recognized which are separated by two unconformities: The Blake-Bahama phase (Valanginian-early Aptian (Bedoulian)) corresponds to relatively uniform depositional conditions over the whole of the North Atlantic with periods of anoxia. The clay mineral assemblages reflect different sedimentary influxes from the continents into the eastern and western parts of the basin which were separated by the mid-ocean ridge. The transition to the Hatteras phase (Event E1) is marked by a drastic fall in sediment accumulation rate and by a rapid rise in the CCD but not by any appreciable change in clay mineral fluxes. The Hatteras phase (late Aptian-late Cenomanian) is characterized by distinctly diverse depositional conditions. In the southeastern part of the basin anoxic conditions were persistent, while in the northeast along the European margin there is no, or only very rare, evidence of anoxia. In the west, periods of oxia and anoxia alternated. Over the mid-ocean ridge conditions were oxic. A ‘barrier’ in the region of the present-day Bermuda Rise separated two areas of distinct clay mineral deposition. The transition to the Plantagenet phase (Event E2) corresponds to low sedimentation rates. It was immediately preceded by, or was coincident with, deposition of a black shale rich in marine organic matter. The Plantagenet phase (Turonian-Senonian) was a period of uniform sedimentation under oxic conditions. Possible causes of these changes in sedimentation are outlined.

Anoxia vs. Productivity: What Controls the Formation of Organic-Carbon-Rich Sediments and Sedimentary Rocks?: Discussion

Abstract: The prevailing explanation for the origin of organic-rich sediments and rocks invokes deposition under conditions of anoxia. However, recent research suggests that high primary production and not water-column anoxia provides the first-order control on the accumulation of organic-rich facies in the modern oceans. Oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments. Sediments accumulating in the modern Black Sea, the type euxinic basin, are not particularly enriched in organic matter despite the presence of an anoxic water column, although a sapropel containing extremely high carbon concentrations was deposited during the Holocene at a time when the basin was oxic. Results of a recently published co pled ocean-atmosphere model indicate that during the Cretaceous, thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions, despite the overall equable climate. Such conditions confound the idea that circulation in the Cretaceous Atlantic, for example, was punctuated by oceanic anoxic events brought about by more sluggish circulation. Sporadic temporal and spatial increases in primary production, reflecting changes in the behavior and/or state of the ocean-atmosphere system, constitute a more tenable explanation for the occurrence of modern and Quaternary carbon-rich sediments and Cretaceous black shales. Consequently, the fundamental control on the accumulation of carbon-rich facies in the oceans and marginal seas is not the presence or absence of anoxia.

Rock-Eval 6 Technology: Performances and Developments

Abstract: The Rock-Eval 6 apparatus is the latest version of the Rock-Eval product line, commercialized since 1996 by Vinci Technologies. The present work describes the methodology developed at IFP for reliable data acquisition and endorses the quality of geochemical parameters acquired with Rock-Eval 6. Data were obtained on 147 source rocks from various sedimentary basins, of different organic matter types and maturity stages. Intrinsic correlations for two different Rock-Eval 6 apparatus were performed and the obtained data set shows an excellent consistency and good reproducibility conditions for the whole set of Rock-Eval parameters. Complete recovery of total carbon (TC) by Rock-Eval 6 was confirmed by comparison with elemental analysis. In order to check the carbon partition (mineral vs. organic) determined by Rock-Eval 6, measurements of mineral carbon (MinC) and total organic carbon (TOC) were performed by alternative techniques. TOC measured by Rock-Eval 6 was compared to that obtained either by: the Leco apparatus for bulk rocks; elemental analysis for kerogens; and calculation from the mass balance determined after destruction of mineral matrix and the carbon concentration determined by elemental analysis on recovered kerogens for bulk rocks. The results display a good correlation for the whole concentration range (0-90 wt% TOC), when comparing elemental analyses and Rock-Eval 6 for source rocks and kerogens. However, comparison of Rock-Eval 6 with Leco data leads to larger deviations while correlation factors are still good. For a subset of kerogen samples, preparative pyrolysis was performed in order to confirm the value of 83 wt% for the organic carbon of the total S2 peak for any rock with any organic type and to check the absolute value of the S2 peak by gas chromatography analysis of pyrolysis by-product. MinC measured with Rock-Eval 6 was compared to that determined by: weight loss after HCl treatment; the acidimetry technique; and calculation after TC, mass balance from kerogen isolation and organic carbon measurement on kerogen by elemental analysis. The results display a good correlation for the whole concentration range (0-12 wt% MinC), when comparing elemental analyses and Rock-Eval 6. However, comparison of Rock-Eval 6 with acidimetry data leads to larger deviations while correlation factors are still good while comparison with weight loss is poor. As a whole an excellent reliability of TOC and MinC obtained by Rock-Eval 6 was demonstrated, and consequently, it is now possible to get at once the total organic and mineral carbon mass balance for a given rock. Recommendations are proposed regarding the standard samples and analytical methods selected for calibrating the Rock-Eval 6 over a large mineral and organic carbon range. Consistency between S2 and Tmax measured by Rock-Eval 2 and Rock-Eval 6 for Types I and II bulk rocks was also checked. A good correlation was obtained for S2, even though S2 values are slightlyhigher when measured with Rock-Eval 2. It was demonstrated that this is due to carrier gas (nitrogen vs. helium) by running measurements with a Rock-Eval 6 under helium, the difference ranging from 5 to 10 relative wt% for most studied samples. For Tmax correlation, data are much more scattered and as a general trend Tmax obtained by Rock-Eval 6 are higher than Tmax obtained by Rock-Eval 2 and the difference increases with Tmax: this is due to the fact that the probe measuring the temperature in the Rock-Eval 2 is located in the oven wall, consequently Tmax determination is highly dependent on the setup and calibration of the apparatus. A special attention was given for temperature measurement in the Rock-Eval 6, where the probe is in contact with the crucible containing the sample, leading to much more reliable data.