Cyclicity in the Egret Member (Kimmeridgian) Oil Source Rock, Jeanne d'Arc Basin, Offshore Eastern Canada

Z. Huang, M. A. Williamson, K. D. MCAlpine, J. Bateman, M. G. Fowler

The origin of the observed variability in lithology, total organic carbon, and petrophysical properties of the Egret Member (source rock interval) in the Jeanne d'Arc Basin, offshore eastern Canada is examined. Detailed analyses of petrophysical logs indicate that the Egret Member is cyclic, with three different orders of cycles recognizable on well logs. The large and medium scale cycles are correlatable among wells.

The large-scale cyclicity is estimated to be about 413 ky, with the medium-scale cycles about 100 ky and the small-scale cycles about 20 ky. This suggests that the depositional cycles are the product of orbitally forced sea level and climatic changes and also implies that the Egret Member was deposited in at least about 1.65 million years. Using chronological information drawn from sedimentary cycles, we examine both spatial and vertical (temporal) variations in sedimentation rate for the member. The sedimentation rate for the Egret Member varies from 3.8 cm/ky to 14.7 cm/ky. The wells on the west side of the basin mostly have sedimentation rates around and lower than 5 cm/ky, whereas the wells along the eastern margin have sedimentation rates of about 7 cm/ky. A correlation exists be ween low sedimentation rates and high total organic content values in this basin. It is most probable that the organic-rich layers were deposited during times of high sea level stands and warmer periods.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995