Leigh C. Price, 2002. "Geological and geochemical consequences of basin exhumation, and commercial implications", Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration, A. G. Doré, J. A. Cartwright, M. S. Stoker, J. P. Turner, N. White
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In the past, petroleum basins were traditionally largely viewed as either static or uniformly evolving entities. It is now more widely recognized that petroleum basins are subject to various intense geological processes, and hence substantial changes, during their evolutionary histories. One such geological process is exhumation, which is usually accompanied by significant erosion, decrease in both burial temperatures and fluid pressures, and often decrease in geothermal gradients. These changes can have profound consequences regarding hydrocarbon (HC) deposits. Besides all the obvious consequences (halting source-rock generation, damaging or destroying seals, expansion of gas with trap flushing, etc.), less obvious, but none the less equally meaningful, consequences also result.
For example, in basins with high geothermal gradients (e.g. Central Sumatra, Los Angeles), migration-accumulation processes result in most of the basin's reservoired oil being emplaced within the first 1-2 km of the surface. Strong erosion can largely destroy almost the entire oil resource of the basin, leaving a gas-only province (e.g. San Juan Basin, USA). Pore waters at high temperatures and pressures carry large amounts of both dissolved HC gases and inorganic mineral species (ions). Significant falls in burial temperatures from exhumation thus cause two results in the deeper regions of petroleum basins: (1) basin-centred gas deposits; (2) widespread destruction of deep-basin porosity, but especially permeability, from wholesale precipitation of dissolved mineral species as diagenetic minerals. In the case of basin-centred gas deposits, in going updip from the basin depocentre, eventually a location is reached where insufficient HC gas was dissolved in the
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Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration
Northwest Europe has undergone repeated episodes of exhumation (the exposure of formerly buried rocks) due to such factors as post-orogenic unroofing, rift-shoulder uplift, hotspot activity, compressive tectonics, eustatic sea-level change, glaciation and isostatic readjustment. The main observational legacy of this exhumation around the North Atlantic is preserved in the comparatively young (Mesozoic and Cenozoic) geological record of this region. Despite a rapid increase in the understanding of the exhumation of this area, there are still many unknowns: the relative intensity of the various phases and their geographical variation; mechanisms of uplift; primary causes of exhumation. Tied to these problems is the larger-scale question of whether the circum-North Atlantic is unique or whether its behaviour is typical for passive margins.
There have been several attempts in recent years to bring together researchers to address these questions, but these have often focused on one particular geographical area or one particular exhumation phase. Before an integrated story can emerge, disciplines that have traditionally remained apart need to come together: geomorphology and offshore seismic interpretation; Palaeogene and Neogene studies; Scandinavian and British-Irish research schools. This volume represents a first step in this direction by providing an inter-disciplinary set of studies over a wide latitudinal range of the NW European margin.
The studies presented here are based on a variety of techniques that have been employed to address the main concerns of North Atlantic exhumation history, including timing, mechanisms and the sedimentary response of the continental margin. The 25 papers presented in this volume have been arranged in four sections to reflect the highly varied approach to this subject and the commercial implications. Part 1 is concerned with exhumation mechanisms, focusing primarily on the Iceland Plume. Parts 2 and 3 present ongoing research on the continental margin record offshore Scandinavia, Britain, Ireland and the Faroes. The papers in these two parts illustrate the communication that is now occurring between the two regional research schools and the acknowledgement of a multiphase Cenozoic denudation chronology for both areas. Part 4 contains five papers describing the significant changes to the hydrocarbon systems that occur in exhumed basins, detailing the implications for hydrocarbon-bearing basins.
Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration is the most up-to-date and complete volume integrating all aspects of the Mesozoic-Cenozoic exhumation of North Atlantic borderlands. Itwill be of interest to those within the oil industry, geomorphologists and other workers with an interest in NW European regional geology.