Glacioeustatic sea level fall marking the base of supercycle TA-1 at 66.5 Ma recorded by the kaolinization of the Whitemud Formation and the Colgate Member of the Fox Hills Formation

摘要

The Maastrichtian continental Whitemud Formation in the Cypress Hills of southwestern Saskatchewan, Canada, has been kaolinized by in situ leaching to a depth of at least 20 m, produced by a lowered water table. The first stage of leaching took place during accumulation of the coal zone in the middle of the 20 m-thick Whitemud. A second stage took place after deposition of the lower few meters of the overlying organic-rich Battle Formation. The U-Pb age on bentonite zircon in the lower Battle is 66.5 ± 0.2 Ma, indicating the last stage of sea fall. Using an average compacted sediment accumulation rate of 72 m/m.y., based upon the thicknesses of magnetozones 29r and 30r, the time spanning the two stages of lowered sea level is 200,000 years or less. The Colgate Member of the Fox Hills Formation in Montana is an exact correlative of the Whitemud, and kaolinization of the Colgate is due to the same sea level fall from the International Boundary to central North Dakota. The age correlates to the sea level cycle marking the base of supercycle TA-1, and the short duration indicates that this sea level cycle was glacioeustatic.