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Sedimentary Petrology and Stratigraphic Analysis of the Subsurface Reindeer Formation (Early Tertiary) Mackenzie Delta-Beaufort Sea Area, Canada
The hydrocarbon-bearing Reindeer Formation (Lower Tertiary), consisting mainly of sandstone, shale, and mudstone, can be traced in the subsurface of the Mackenzie Delta-Beaufort Sea area by lithological, paleontological, geophysical well-log and seismic characteristics. Cross-sections de rived from the correlations demonstrate the relationships between stratigraphy, structure, and petroleum occurrences in this complex deltaic succession of sediments. Trap-determining features are faults, including growth faults, structures related to shale-cored diapirs or anticlines, and uplifts of uncertain origin.
Composition and texture of the sandstones, which are all litharenites, show significant variations. Compositional variations can be related directly to grain size, and show only slight evidence of the local influences of depositional environments within the deltaic complex. Minimal reworking of the sediments in a high-constructional, fluvially-dominated delta is thus indicated.
The predominant provenance indicators suggest a sediment source to the west or southwest, although minor contributions from other sources are possible. The significant proportions of chert, volcanic and phylloid grains from the principal source area play an important role in the diagenesis of the sandstones of the Reindeer Formation.
The diagenetic history of the sandstones can be related to composition and grain size as well as burial depths. Mechanical compaction and cementation by kaolinite and quartz are the main early diagenetic factors related to reduction in primary porosity. Extensive carbonate cementation, with significant intragranular and grain-margin replacement com prises an intermediate stage of porosity reduction. Subsequent carbonate dissolution is the main cause of secondary porosity, which includes enhanced lamellar, moldic, and intragranular types. Reduction of secondary porosity by framework collapse and late quartz cementation is evident in deeply-buried sandstones. Diagenetic features demonstrate, in some places, that deeply-buried sandstones have been brought to shallower depths by subsequent tectonic or diapiric activity. In addition, the distribution of carbonate cementation-decementation zones within thick sand bodies is non-uniform, defining vertically-segregated zones of high and low secondary porosity. These phenomena are important in terms of their influence on the post-diagenetic movements of subsurface fluids, particularly hydrocarbons.
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