The thermal and burial history of the Herzkamp syncline, located in the transition zone between the Variscan Rhenish Massif and the Ruhr foreland basin (western Germany), was reconstructed using PDI/PC-1D-basin modelling software (IES). The models were calibrated with new vitrinite reflectance data measured on Palaeozoic outcrop samples. High sample density and quality of the calibration data allowed a 3D reconstruction of the heat flow as well as of burial and erosion history. Vitrinite reflectance values range from 0.8 to 4.9%R r and generally increase with increasing stratigraphic age. The coalification pattern confirms pre-tectonic maturation, especially in the western part of the study area. A ªlow-coalification zoneº showing stagnating/decreasing coalification with increasing stratigraphic age exists, however, northeast of the Ennepe thrust, indicating synorogenic coalification. This anomaly is explained by early thrusting in the northern Rhenish Massif resulting in restricted burial/early uplift and thus lower thermal maturity. One result of numerical modelling is that palaeo-heat flows during maximum burial (Westphalian or post-Westphalian) decreased southwards from approximately 65 to less than 50 mW/m 2 . Maximum burial depths for the base and top of the Namurian also decrease southwards from 7000 to 3600 m and 4600 to 1800 m, respectively, resulting in southwards-decreasing coalification of the respective stratigraphic horizon. Eroded overburden increases southwards (3100±5700 m), with the exception of the low-coalification zone, which is characterised by lower amounts of eroded overburden (1300±2900 m) and an earlier onset of erosion, i.e. in the Westphalian B rather than Westphalian D or post-Westphalian.

The accumulation of high H S concentrations in oil and gas fields is usually associated with deeply buried high-temperature carbonate reservoirs and is attributed to the abiological oxidation of hydrocarbons by sulfatethermochemical sulfate reduction (TSR). This review aims at providing an overview of the literature and assessing existing uncertainties in the current understanding of TSR processes and their geological significance. Reaction pathways, various reaction products, the autocatalytic nature of TSR, and reaction kinetics are discussed. Furthermore, various criteria for recognizing TSR effects, such as petrographic/diagenetic alterations and stable isotope geochemistry of the inorganic as well as the organic reactants, are summarized and evaluated. There is overwhelming geological evidence of TSR taking place at a minimum temperature of 110-140°C, but the temperature discrepancy between experimental data and nature still exists. However, the exact nature and mechanisms of catalysts which influence TSR are not known. Local H S variations may reflect steady-state conditions dominated by H S buildups and flux out of the system. The latter is controlled by lithological and geological factors.

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Vitrinite re¯ectance data from a petroleum exploration well in the northern Upper Rhinegraben show an unusual vertical maturity trend. Above and below a 500 m thick marl layer the vitrinite re¯ectance levels are consistent with modern, conductive, geothermal gradients. Between about 1000 and 1500 m depth, however, vitrinite re¯ectance levels are signi®cantly elevated (about 0.6%Ro). This anomaly cannot be explained with one-dimensional conductive or conductive-convective heat transfer models, and thermal effects of sedimentation or igneous intrusion seem implausible for this geological setting. The thermal anomaly that formed this maturation anomaly must have been hydrothermal in origin, two-dimensional in nature, and persisted long enough to elevate the vitrinite re¯ectance values within this marl unit, yet it must have dissipated before the thermal perturbation would have altered the organic matter below and above the unit.In this study, we propose that the vitrinite re¯ectance anomalies were caused by a transient thermal inversion induced by episodic, lateral¯ow of hot (130±1608C) groundwater along conductive fractures and bedding planes. Heat¯ow constraints suggest that¯uids must have moved rapidly up a vertical feeder fault from a depth of at least 3.6 km before migrating laterally. To test this hypothesis, we present a suite of simple, idealized mathematical models of groundwater¯ow, heat transfer, thermal degradation of kerogen and vitrinite systematics to explore the episodic ow that could have produced the observed thermal anomaly. In these simulations, a single, horizontal aquifer is sandwiched between two less permeable units: the total dimensions of the vertical section model are 4 km thick by 10 km long. The top of the aquifer coincides with the position of the observed thermal maturity anomaly in the Rhinegraben. Boundary conditions along the left edge of this aquifer were varied through time to allow for the migration of hot¯uids out into the basin. In¯ow temperature, horizontal velocity, duration and frequency of¯ow and thickness of the aquifer were varied. We found that a thermal maturity anomaly could only be produced by a rather restrictive set of hydrothermal conditions. It was possible to produce the observed vitrinite re¯ectance anomaly by a single hydrothermal¯ow event of 1308C¯uid migrating laterally into the aquifer at a rate of 1 ma À1 for about 10 000 years. The anomaly is spatially con®ned to near the left edge of the basin, near the feeder fault. If the¯ow event lasted longer than 100 000 years, then the maturation anomaly disappeared as the lower con®ning unit approached steady-state thermal conditions. It is possible that such an event occurred about 5 million years ago in response to increases in fault permeability associated with far ®eld Alpine tectonism.