Martin Baron

Thermal alteration of organic matter in an impact crater and the duration of postimpact heating

The 24-km-diameter Tertiary Haughton impact structure formed in rocks that contained preexisting liquid hydrocarbons. Biomarker ratios in the hydrocarbons show a consistent pattern of variation in degree of heating across the structure. The heating reached a maximum at the crater center and is attributed to hydrothermal activity following impact. Kinetic modeling suggests a time scale of ∼5 k.y. for the heating, at a maximum temperature of 210 °C. The short time scale suggests that in moderate-sized craters, which are abundant on Mars, heating is not so extensive that fossil or extant organic matter would be obliterated.

Dolomitic breccia veins as evidence for extension and fluid flow in the Dalradian of Argyll

Veins of red dolomite occur extensively in the Dalradian rocks of Argyll, Scotland and adjacent areas. The veins represent brittle extensional deformation, preferentially reactivating Caledonian quartz veins. The dolomite is associated with reddening of the adjacent Dalradian country rock, which it partially replaced. Dolomite was also precipitated in overlying Old Red Sandstone, and probably dates to late Carboniferous–early Permian. Fluid inclusion studies show that the veining involved moderate-temperature (75 to 115 °C) fluids. Stable isotope data suggest that these fluids were basinal brines. Traces of chalcopyrite, paragenetically late in the veins, may reflect the mineralization which occurs more widely in the Dalradian rocks of Argyll. The red colour of the dolomite is due to abundant haematite crystallites that grew in the dolomite crystal fabric. Palaeomagnetic analysis yields a consistent late Permian–early Triassic age for the haematite growth in the dolomite veins and the reddened Dalradian country rocks. This age represents the time of haematite precipitation from iron-rich dolomite that may have been related to deep oxidizing weathering. Gold anomalies associated with reddened basement rock must be of this age or younger.

Controls on kaolinite and dickite distribution, Highland Boundary Fault Zone, Scotland and Northern Ireland

Kaolinite and dickite occur widely in central Scotland and Northern Ireland. Stable hydrogen and oxygen isotope compositions of both minerals are similar, suggesting that the formation of kaolinite occurred first at temperatures of <50°C from meteoric water, probably as a result of alteration of Lower Carboniferous volcanic rocks, and that dickitization followed locally as a result of local heating that accompanied the intrusion of dykes during Late Carboniferous–Permian times. This mechanism of dickite formation explains why the higher‐temperature polytype dickite occurs in a region from the Firth of Clyde to Perthshire, in association with dyke swarms, whilst kaolinite occurs elsewhere. The original kaolinite precipitation was focused along the high permeability fault zone now marked by the Highland Boundary Fault Zone and its presumed trace in Northern Ireland.

Multiple fluid migration events along the Moine Thrust Zone, Scotland

A palaeomagnetic study of different lithologies exposed along the Moine Thrust Zone from Skye to Durness, Scotland, has identified three chemical remanent magnetizations (CRMs), a potential fourth CRM, and one possible primary component that all reside in hematite. Local and regional fold tests suggest that the CRMs are post-folding and post-thrusting. A contact test in the Torridon Group sandstone indicates that a Permian CRM is localized in and near the fault zone. The Permian CRM, which is also found in the Durness Group, and associated alteration are direct evidence for post-orogenic activity, in which the thrusts vented excess heat during regional crustal extension. On the Isle of Skye, sandstones (Sleat, Torridon and Eriboll Groups) in and around the fault zone contain a Tertiary CRM interpreted to be related to hydrothermal fluids associated with Tertiary intrusions. A possible Mesozoic CRM is also present but it could represent the vector addition of the Permian and Tertiary CRMs. A Devonian CRM is interpreted to be related to hydrothermal fluids associated with Devonian volcanic rocks or to fluids triggered by late stages of the Caledonian orogeny. Geochemical and petrographical studies provide supporting evidence for multiple fluid flow events along the Moine Thrust Zone. These results show that palaeomagnetism can be used to date multiple fluid migration events and that dormant fault zones can act as conduits for flow.

Oil migration and bitumen formation in a hydrothermal system, Cuba

Abstract Veins of bitumen occur in the Jurassic-Cretaceous of northern Cuba in the vicinity of oil fields dominated by extra-heavy crude. Some bitumen veins are associated with hydrothermal mineralization. Calcite vein rock at Soroa contains evidence for three phases of hydrocarbon migration: fresh oil fluid inclusions, followed by thermally altered oil (coeval aqueous fluid inclusions at up to 221 °C), then less altered oil. In addition to demonstrating a mechanism for producing altered oil other than by biodegradation, these observations support a model of multi-episodic hydrocarbon migration, which may be related to thrusting of the source beds.

The preservation of fluid inclusions in diverse surface precipitates: the potential for sampling palaeo-water from surface deposits on Mars

A wide range of surface deposits have been suggested as targets for the search for evidence of life on the surface of Mars. We show that duricrusts, biogenic lacustrine precipitates, hydrothermal and chemosynthetic precipitates, speleothems, travertines and evaporites all contain low-temperature fluid inclusions which represent surface/very-near-surface fluids. These fluid inclusions have good preservation potential. The recording of abundant inclusions in sulphate crusts is particularly important as they may be widespread on Mars. The inclusion fluids represent the surface waters from which the precipitates were deposited, so they may contain biomolecules from any ambient life in the surface environment. As problems of analytical sensitivity and contamination are overcome, such surface deposits have the potential to yield samples of Martian palaeo-water and any entrained biomolecules.

Preservation of pre-orogenic palaeofluids within the Caledonides of northwest Scotland

Abstract Fluid inclusion microthermometric data are reported from early diagenetic mineral phases from NW Scotland that have subsequently been involved in Caledonian deformation. The original information concerning the physicochemical conditions of the parent fluid that precipitated diagenetic minerals is often lost from fluid inclusions that have experienced excessive overheating. Although the diagenetic mineral phases in this study have experienced temperatures of approximately 275 °C in response to Caledonian deformation, they still retain some fluid inclusions that yield temperature and compositional information about the original pre-orogenic early diagenetic environment of formation.

The Potential for Survival of Organic Matter in Fluid Inclusions at Impact Sites

Fluid inclusions within rocks have potential for the preservation of organic molecules. Trace quantities of biomolecules could be entrapped inside micrometer-scale inclusions during the growth of surface precipitates, reflecting any ambient life in the surrounding waters. Developing technologies for the high-resolution detection of biomolecules offer encouragement for the future detection of these trace biomolecules. The terrestrial geological record shows that organic molecules can survive relatively high temperatures within inclusions, including the temperatures of hydrothermal systems in impact craters.

Record of fluid flow history through fractured conglomerates, Lower Old Red Sandstone of central Scotland

Synopsis Extensively fractured quartzite clasts in Lower Old Red Sandstone conglomerates adjacent to the Highland Boundary Fault Zone in central Scotland contain multiple populations of healed microfractures delimited by fluid inclusion planes. Microthermometric analysis indicates that the healing of microfractures oriented perpendicular to the trend of the Highland Boundary Fault Zone, which probably formed during Acadian overthrusting towards the SE along the fault zone in Middle Devonian times, involved moderate temperature (Th 102 to 238°C), low to moderate salinity (3 to 17 wt% NaCl eq.) aqueous fluids. The clasts also contain a second set of fluid inclusion planes oriented parallel to the Highland Boundary Fault Zone, which formed during extension associated with the intrusion of late Carboniferous quartz dolerite dykes. The healing of this set of microfractures involved low temperature (Th 58 to 155°C), low to moderate salinity (1 to 12 wt% NaCl eq.) aqueous fluids.