ABSTRACT

On the basis of the time-frequency scaling property of the wavelet transform, accumulation rates and stratigraphic completeness can be calculated for various observation time spans (ot) by using wavelet analysis. Wavelet analysis also allows automatic detection of high-frequency sedimentary cyclicity, and abrupt and gradual variations in sedimentation rate. The preservation of different frequency cycles is strongly dependent on variations of the intensity-to-noise ratio of the original cycles and accumulation rate through time, as demonstrated by computer models.

Wavelet analysis was used to detect and correlate periodic-cyclic successions of marine sediments in the Western Canada Sedimentary Basin in observation time spans ranging from 100 kyr to 3.8 Myr. Cycles in gamma-ray data are in accordance with sonic logging, lithology, and biotic change. Cyclic units embedded in the upper Albian Westgate and Joli Fou Formations are almost periodic with 11 and 10 repetitions, respectively. Accumulation rates at ot = 100 kyr vary from 5-7 cm/kyr in mudstone successions to 29 cm/kyr in sandstone successions of the Rocky Mountains Foothills. These 100 kyr cycles are preserved from 30% in the Manitoba Escarpment to 100% in SE Alberta in the Westgate Formation.

These cycles can be correlated throughout facies belts of siliciclastic sedimentation in the entire basin. In gamma-ray logging the cyclicity is most pronounced in the foredeep succession and almost without fluctuations in the basin center. Cyclic changes from wet to dry climate probably forced by Milankovitch cycles of 100 kyr eccentricity may have controlled the stable periodic sedimentary cyclicity.