Magnetostratigraphy of the Canadian Continental Drilling Program Cretaceous-Tertiary (K-T) Boundary Project core holes, western Canada

Abstract

The Canadian Continental Drilling Program (CCDP) Cretaceous-Tertiary Boundary Project cored three holes, to 160, 188, and 170 m in southern Alberta, Saskatchewan, and Manitoba, respectively, to intersect the Cretaceous-Tertiary boundary. One hundred and seventy to 200 samples from 50 to 60 levels were taken from each of these unoriented cores for magnetostratigraphy. Samples were subjected to both alternating field (AF) and thermal cleaning. AF demagnetization in steps of 5 mT up to 30 mT showed that samples from all three cores carried only a low-coercivity viscous overprint, which was largely removed at 10 mT. Thus, three samples from each depth were routinely demagnetized at 10 mT or 100°C. The magnetic inclination of the sample giving the smallest measuring error was chosen to indicate the polarity at that depth. With the aid of palynologic control, magnetochrons 29n to 30r inclusively, in the Ravenscrag, Frenchman, Battle, Whitemud, and Eastend formations, were identified in the Elkwater core hole, western Cypress Hills, Alberta (49°36'N, 110°18'W). The Cretaceous-Tertiary boundary is missing at the Frenchman-Ravenscrag contact. The Wood Mountain core hole (49°05'N, 106°16'W) spans the interval from magnetozone 28n to 30r in the Ravenscrag, Frenchman, Battle, Whitemud, Eastend, and Bearpaw formations. The Cretaceous-Tertiary boundary is present in 29r. The Turtle Mountain core (49°01'N, 100°33'W) has a number of significant disconformities; only magnetozones 28n, 28r, 29n, 30n, and 32n or 33n are present in the Turtle Mountain, Boissevain, and Pierre formations. At the Cretaceous-Tertiary contact near the base of the Turtle Mountain Formation, there is a hiatus of 0.6 × 106 to 0.8 × 106 years. At the Campanian-Maastrichtian contact, between the Odanah and Coulter members of the Pierre Formation, there is a time gap of at least 3 × 106 years but probably about 6 × 106 years.