Tectonic evolution of the Colorado Basin, offshore Argentina, inferred from seismo-stratigraphy and depositional rates analysis

International audienceBased on a dense 2D seismic reflection dataset and information from 8 exploration wells, we reinterpreted the stratigraphic evolution of the Colorado Basin. The basin is located on the continental shelf and slope within 50 to 2250 m of bathymetry. The total sediment fill can be up to 16,000 m. Seismic-to-well log correlations provide a chrono-stratigraphic framework for the interpreted seismic sequences. We show that the Colorado Basin records the development of a Permian pre-rift period, a Triassic/Jurassic to Early Cretaceous rift phase and a Lower Cretaceous to Tertiary drift phase. This passive margin represents the evolution of lithospheric extension from active rifting to the thermal subsidence/drift stage. Several Cretaceous to Cenozoic slumping episodes were identified and related to progradation of the sequences and sediment build-up in the slope, as well as to the development of seaward dipping extensional faults

Colorado Basin 3D structure and evolution, Argentine passive margin

International audienceThis 3D structural model of the Colorado Basin provides new insights into the crustal geometry of the basin and its evolution in relation with the Argentine passive margin. Three NW-SE segments (oblique to the N30°E-trending margin) structure the basin. The oldest infill is generally thought to be coeval with the rifting of the South Atlantic margins in Late Jurassic-Early Cretaceous. This coeval development of the Colorado Basin and of the passive margin is still under debate and gives rise to several hypotheses that we investigate in the light of our observations. We propose that reactivation of inherited structures is predominant in the evolution of the Colorado Basin: (1) the Western segment follows the continental continuation of the Colorado transfer zone; (2) the Central segment consists in the continental continuation of the Tona deformation zone; (3) the Eastern segment is superimposed over the Palaeozoic Claromecó Basin. In addition to the 3 segments, the Central High, separating the Central segment to the Eastern segment, corresponds to the Palaeozoic Sierras Australes Fold Belt. The direction of extension responsible for the South Atlantic opening cannot explain the syn-rift infill and thinning of the basin. The structural analysis shows two phases of syn-rift deformation with different directions. Thus, we suggest that the Colorado Basin and the South Atlantic margin are not coeval but that a first extensional event, probably oblique, predates the extension responsible for the South Atlantic opening. This event is then followed by the formation of the N30°-trending distal margin and the reactivation of Palaeozoic N70°-trending faults occurs under the NW-SE opening of the South Atlantic. This two-phase evolution is consistent with the fault chronology and the two directions of thinned crust observed in the distal margin

The generation and migration of sulphur-rich petroleums in a low-maturity carbonate source rock sequence from Italy

Auf der Basis eines interdisziplinären Ansatzes wurden die Genese und Migration von Schwerölen am Beispiel eines niedrig reifen karbonatischen Muttergesteins der Trias Italiens untersucht. Dabei sind organisch-geochemische, sedimentpetrographische und petrophysikalische Methoden an Proben aus vier verschiedenen Bohrungen, in denen das Muttergestein in unterschiedlichen Tiefen angetroffen worden war, angewendet worden. In der untersuchten Muttergesteinsformation wurden vier Lithofazien unterschieden: Mudstones/Wackestones, Laminite, Tonsteine und Dolomite . Die Mudstones und Wackestones enthielten auch Stylolithe und Lösungssäume, die gesondert beprobt wurden. Die Mudstone/Wackestone Lithofazies war durch geringe Mengen an organischem Material (0 TOC=O.28%) und einem Kerogen vom Typ II charakterisiert. Laminite, Stylolithe und Lösungssäume enthielten in der Regel höhere Mengen an organischem Material (0 TOC=1 .2%) und waren durch ein Kerogen Typ II-S charakterisiert . Die Tonsteine enthielten die höchsten Mengen an organischem Material (0 TOC=8 .9 %) und enthielten, in der Regel, ein Kerogen Typ I-S . Die Dolomite waren durchweg mit Schweröl imprägniert und fungierten als intraformationelle Reservoire. Die Muttergesteinsformation wurde in einem „Tidal Flat" Milieu mit erhöhten Salinitäten abgelagert. Dabei wurde die Mudstone/Wackestone Lithofazies im subtidalen Bereich, die Laminite und Tonsteine im intertidalen, und die Dolomite im supratidalen Bereich abgelagert. Die hohen Gehalte an organischem Material waren durch das ungehinderte Wachstum von Algenmatten im intertidalem Bereich bedingt . Der hohe organische Schwefelgehalt der Kerogene ist durch das Fehlen von Eisen im karbonatisch/evaporitischem Ablagerungsraum zu erklären. Die Reduktion von Sulphat zu Schwefelwasserstoff durch anaerobe Microorganismen führt zu einem Überangebot an H2S im Porenwasser des Systems . Dieser Überschuß führt entweder zu der Reaktion von Schwefelwasserstoff mit Eisen(II) zu Pyrit, oder bei fehlendem Eisen zum Einbau von Schwefel in die organische Substanz . Die Inkorporation von Schwefel, gepaart mit einer intensiven bakteriellen Aufarbeitung der abgelagerten Algenmatten, führte in den Tonsteinen zur, Entstehung von einem schwefelreichen und wasserstoffreichen Kerogen Typ I-S

Hydrocarbon distribution along the Soapaga thrust (Eastern Cordillera, Colombia) based on new strategic geochemistry samples

The Colombian Eastern Cordillera constitutes a region with potential for finding hydrocarbon reserves that are still under-explored, despite the existence of oil and tar sand production. The intense tectonic deformation affects the petroleum systems and increases exploration challenges due to the different generation, maturation, and entrapment conditions that they produce. Diverse geochemical analysis conducted on strategic samples determines that these are likely generated by the same anoxic marine source rock type. Two source rock samples we investigated are characterized by very different biomarker signals as compared to the tar sands and oil samples. Both samples are dominated by hopanes as compared to tri- and tetracyclic terpanes, with very low (Tibasosa Formation) to no (Chipaque Formation) extended tricyclic terpanes. The Soapaga Thrust, along which the analyzed samples are located, has exercised first-rate regional structural control of the distribution of hydrocarbons in the studied area. The uplift of their Mesozoic hanging wall produces intense erosion with sediment transport towards the eastern footwall forming the present infill of the Arcabuco basin. The kitchen areas were connected with the shallower entrapment sectors where excellent reservoir levels such as the Picacho Formation before the Soapaga Thrust movement. The high degree of biodegradation observed in the Picacho Fm. tar sands support early charge before the Soapaga thrust movement, and severe biodegradation following the thrust movement when hydrocarbon supply from the kitchen was interrupted. This work aims to contribute to a better understanding of the geochemical characteristics of the petroleum systems due to the action of the Soapaga Thrust.Fil: Rossello, Eduardo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Di Primio, Rolando. No especifíca

Evidence of a large upper-Cretaceous depocentre across the Continent-Ocean boundary of the Congo-Angola basin. Implications for palaeo-drainage and potential ultra-deep source rocks

International audienceThe analysis of 2D deep-seismic-reflection profiles across the slope and abyssal plain of the Angola oceanic basin reveals the existence of a significant and formerly unknown depocentre beneath the giant Cenozoic Congo deep-sea fan, between 7000 m and 9000 m depth, deposited directly onto the Aptian oceanic crust. The unit, which is up to 2.5 km thick and extends for more than 200 km basinwards of the Continent-Ocean boundary, is probably aged Albian-Turonian. Its radial fan-shaped depocentre is centred on the present-day Congo River outlet and contains at least 0.2 Mio km(3) of sediments. These observations and the results from flexural modelling indicate that (1) the location of the Congo River's outlet has remained fairly stable since the Late Cretaceous, and (2) the basal unit was indeed sourced by a palaeo-Congo River probably located nearby the present-day one. Thus, the Atlantic sedimentary system related to the exoreism of the Congo River is much older than previously thought. Thermal modelling indicates that the maturation history of this upper-Cretaceous deposits is highly influenced by the interaction between the initial high heat flow of the young oceanic crust and further increase in sediment supply due to the progradation of the overlying Tertiary deep-sea fan during the Miocene. Hence, despite low present-day heat-flow values, should the unit have source rock potential, its basal section may be currently generating hydrocarbons.;All in all, the results from our models also suggest that the interplay between an initially high heat flow and the further high sediment supply in areas of major river input, may be a key factor for the thermal maturation of potential source rocks deposited onto a present-day "cold" oceanic crust