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

摘要

The Canadian Continental Drilling Program (CCDP)Cretaceous-tertiary boundary project cored three holes, to 160,188, and 170 m in southern Aoberta, saskatchewan, and manitoba,respectively, to intersect the cretaceous-tertiary boundary. Onehunderd and seventy to 200 samples from 50 to 60 levels weretaken from each of these unoriented cores for magnetostratigraphy.Samples were subjected to both alternating field (AF) and thermalcleaning. AF demagnetization in steps of 5 mT up to 30 mTshowed 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 demagnetizedat 10 mT or 100degC. The magnetic inclination of the samplegiving the smallest measuring error was chosen to indicate thepolarity at that depth. With the aid of palynologic control,magnetochrons 29n to 30r inclusively, in the Ravenscrag,Frenchman, Battle, Whitemud, and Eastend formations, wereidentified in the Elkwater core hole, western Cypress Hills, Alberta(49deg 36minN, 110deg18minW). The Cretaceous-Tertiaryboundary is missing at the Frenchman-Ravenscrag contact. ThWood Mountain core hole (49deg05minN, 106deg 16minW)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 TurtleMountain core (49deg 01minN, 100deg33minW) has a number ofsignificant disconformities; only magnetozones 28n, 28r, 29n, 30n,and 32n or 3n are present in the Turtle Mountain, Boissevain, andPierre formations. At the Cretaceous-Tertiary contact near the baseof the Turtle Mountain Formation, there is a hiatus of 0.6 X 10~6to 0.8 X 10~6 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 X 10~6 years but probably about 6X 10~6 years.