Facies, well-log patterns, geometries and sequence stratigraphy of a wave-dominated margin: insight from the Montney Formation (Alberta, British Columbia, Canada)
Résumé
This study illustrates a basin-scale sequence stratigraphic framework based on wireline well-logs, cores and outcrops from the Early Triassic Montney Formation in the Western Canada Sedimentary Basin. A very dense and well-constrained database (2200 wells, 18 cores and 4 outcrops) derived from petroleum exploration made it possible to implement and test common workflows and terminologies used for sequence stratigraphic analysis along an ancient wave-dominated margin. Following facies definition from cores and outcrops and recognition of associated well-log patterns, a two-step approach allows for the reconstruction of large-scale geometries: 1) the model-independent definition of surfaces and units; and 2) the interpretation of the sequence boundaries and systems tracts based on a depositional sequence model.
The typical facies association and log pattern of different sedimentary environments including tidal, as well as wave-dominated foreshore, shoreface and offshore settings are presented. The spatial distribution of characteristic sedimentary environments associated with stratigraphic surfaces and systems tracts is also detailed at the basin scale. Among other results, this study highlights the differences in the sedimentary facies geometries across two different types of sequence boundaries: the facies geometries of the first sequence boundary are quite similar to Haq et al. (1988) sequence model, whereas the geometries of the second are similar to the Hunt and Tucker (1992) sequence model. This work shows that during a rapid, high amplitude base level fall on a high gradient slope, turbidites are more likely to occur, whereas, during slow, low amplitude base level fall on a low gradient topography, forced regressive shoreface will be more likely to occur.