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.

On Earth, biology, hydrology, and geology are interlinked such that certain types of life are often associated with specific conditions, including rock type, pressure, temperature, and chemistry. Life on Earth has established itself in diverse and extreme niches, presenting the possibility that Mars, too, may hold records of fossilized and/or extant life in diverse environments. Geologic, paleohydrologic, and climatic conditions through the evolution of Mars are similar in many respects to conditions occurring during the evolution of Earth and, as such, may point to environments on Mars with potential to have supported living systems. Here, we discuss examples of those Martian settings. Such extraterrestrial environments should be targeted by international robotic and/or manned missions to explore potential fossilized or extant life on Mars.

Abstract Field and diagenetic studies of injected sandstones occurring within the Dinantian oil-shale group of Scotland show that they provided subvertical pathways for petroleum fluid flow from host oil shales. Despite rapid cementation by pre- compactional ankerite, the injected sandstones became reactivated as fluid conduits during subsequent deformation that caused pervasive fracturing. An early phase of Fe dolomite and Fe ankerite veins shows no evidence of petroleum migration; however, abundant primary petroleum inclusions in a second phase of calcite veins, probably formed during Upper Carboniferous to Lower Permian Variscan deformation, suggests that the oil shales had reached maturity. Igneous intrusions may have been a heat source that caused oil maturation. This study shows that injected sandstones may form important fluid conduits for prolonged periods. Even when cemented, they form competent, subvertical structures that are ideally suited for localized faulting, fracturing, and fluid flow during deformation.