GEOSCAN, résultats de la recherche

Menu GEOSCAN


TitreZebra and boxwork fabrics in hydrothermal dolomites of northern Canada: Indicators for dilational fracturing, dissolution or in situ replacement?
AuteurMorrow, D W
SourceSedimentology vol. 61, issue 4, 2014 p. 915-951, https://doi.org/10.1111/sed.12094
Année2014
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130276
ÉditeurWiley Online Library
Lang.anglais
DOIhttps://doi.org/10.1111/sed.12094
Mediapapier; en ligne; numérique
Formatspdf
ProvinceTerritoires du Nord-Ouest; Yukon
SNRC75D; 75E; 85A; 85B; 85C; 85D; 85E; 85F; 85G; 85H; 95A; 95B; 95C; 95F; 95G; 95H
Lat/Long OENS-126.0000 -110.0000 62.0000 60.0000
Sujetsdolomites; système hydrothermal; dolomitisation; porosité
Illustrationslocation maps; correlation charts; geological sketch charts; tables; diagrams; photographs; photomicrographs; graphs; histograms
ProgrammeCorridor et delta du Mackenzie, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Zebra and boxwork fabrics in Manetoe and Presqu¿ile hydrothermal dolomites provide critical data for discrimination between hypotheses for their origin. In a unique occurrence, sets of weakly imbricated, decimeter-sized curvilinear lenticles of white dolospar are developed within sub-meter-sized tongues of greyish-white dolomitized crinoidal packstone and grainstone. This nascent zebra fabric has developed along wavy to nodular intra-bed sedimentary partings. Primary bedding can be traced through dolomitized masses containing these fabrics into the surrounding undolomitized limestone. All zebra and boxwork fabrics are confined within single beds, consistent with an early burial time of origin. No change of bed thickness occurs across zebra or boxwork fabrics within beds. This indicates a dissolutional, rather than a dilational origin, for the creation of pore space partly cemented with white dolospar. The dolomitized groundmass displays an abruptly gradational or sharp transition to centripetal saddle dolomite cement, which partially, to nearly completely occludes vugs. Circulation of geothermally heated hypersaline Devonian Elk Point basinal seawater brines led to dissolution and replacive dolomitization of limestone adjacent to vugs and near-contemporaneous precipitation of white dolospar within dissolutional vugs,consistent with geochemical simulations. The presence of downward extending galleries of white dolospar-cemented solution-collapse breccia provides further support for an interpretation of regional thermally-driven convection of hydrothermal vaporative seawater brines across a broad area of northern Canada. The absence of gases under pressure in vacuoles within fluid inclusions from Manetoe and Presqu¿ile dolospars is also more consistent with a dissolutional and contemporaneous dolomitization origin for these fabrics, rather than an origin involving dilational fracturing for space creation and dolospar precipitation. The ubiquitous presence of zebra and boxwork fabrics in hydrothermal dolomite reservoirs indicates that they are not confined fault zones and instead occur whereever precursor limestones had relatively greater porosity and permeability prior to dolomitization.
Résumé(Résumé en langage clair et simple, non publié)
Des bandes de dolosparite blanche inclinées à litées (fabrique rubanée) et des réseaux rectilignes de dolosparite blanche (fabrique cloisonnée) sont bien en évidence dans de grandes masses de dolomie hydrothermale (haute température) qui a remplacé les calcaires du Dévonien dans le nord du Canada. Ces affleurements indiquent que les fabriques rubanée et cloisonnée ont été formées ensemble par un processus de dissolution des calcaires, accompagné d¿une dolomitisation et d¿une précipitation de la dolosparite blanche dans les cavités de dissolution. Cela signifie que les masses de dolomie hydrothermale, prometteuses comme réservoirs de pétrole, ne sont pas limitées à des zones de failles, comme on le prétendait auparavant, mais pourraient se trouver partout où des calcaires précurseurs avaient une porosité relativement forte.
GEOSCAN ID293142