Abstract Petroleum systems within rifted margin basins affected by volcanism continue to remain challenging for the exploration of hydrocarbons, most notably owing to the volume of intrusions that pose imaging, drilling and exploration problems. Typically, intrusions possess small thermal aureoles, but despite this, there is evidence that intrusions could none the less be responsible for the generation of commercial volumes of hydrocarbons. Here we shed new light on this petroleum systems challenge by integrating organic geochemical and Raman spectroscopic techniques to produce potential volumetric data for hydrocarbons generated as a result of igneous intrusion. The results indicate that, in areas with immature source rock intervals, it may be possible for intrusions to generate volumes of oil that would be capable of comfortably filling likely known oil reservoirs. This is a critical step forward in integrating several analytical techniques, indicating that under the right conditions there is the potential for hydrocarbon generation as a result of igneous intrusion.

Abstract Raman spectroscopy allows thermal maturation of carbonaceous sediments to be determined. The technique has been employed on metamorphic samples exceeding temperatures of 270°C, but recently has been shown to be effective at lower temperatures. Thermal maturation techniques commonly depend on sample size, have varying efficacies at different temperatures and in different conditions. The underlying processes are not well understood, thus data interpretation can be ambiguous. Here we show the efficacy of Raman as a low-temperature thermal marker in a thrust belt. The Bornes region, in a French Subalpine chain, provides an opportunity to test the technique against published vitrinite reflectance data and thermal modelling for the first time. In doing so we show that Raman is an effective thermal marker to temperatures as low as 75°C, has a small error and is consistent with previous work. The Raman data allow us to postulate the relative thickness of the sedimentary succession across the chain, the timing of thermal maturation and the timing and thickness variations of the over-thrust Prealpine nappe. The work establishes Raman as a low-temperature thermal marker for correlation with other techniques to ensure effective and robust interpretation, that can readily be applied to fold–thrust belts in hydrocarbon provinces.

Abstract The degree of structural order in the organic carbon preserved in grey–black shales of the Neoproterozoic Torridon Group was characterized using Raman spectroscopy. All the samples contained kerogen rather than graphite, which is consistent with a low level of metamorphism. Samples of shale from the Diabaig Formation from six widely separated localities exhibited a consistently greater structural order than shales from five localities in formations higher in the Torridon Group. This supports previous models invoking an unconformity between the Diabaig Formation and the rest of the Torridon Group. The data further suggested that the Diabaig Formation experienced an additional episode of heating in the late stages of Grampian deformation.