CAMPANIAN-MAASTRICHTIAN CLAY-RICH SEQUENCES ALONG THE NORTH PACIFIC MARGIN: KEY SEQUENCES FOR EARLY COOLING HISTORY OF CRETACEOUS GREENHOUSE EARTH
This study examines the Campanian-Maastrichtian interval. Its chronostratigraphy, including detailed δ13C stratigraphy, has been summarized recently (Voigt et al., 2012) and it records the initial phase of global cooling of the Cretaceous greenhouse Earth (Moriya, 2011; Friedrich et al., 2012). As the northern paleo-Pacific Ocean had a large heat capacity, its paleoceanography should provide insights for understanding the subsequent environmental transition from greenhouse to ice house Earth.
The Yezo Group and its equivalent in Hokkaido (Japan) and Sakhalin (Russian Far East), as well as the Nanaimo Group of the Canadian Pacific coast (British Columbia), are examined in this study. From the Yezo Group, a clear negative δ13C excursion as large as 1.4–2 per mil has been identified. On Sakhalin, its Campanian-Maastrichtian boundary age is constrained by local bio- and magnetostratigraphy, and the excursion is thus identified as the Campanian Maastrichtian Boundary Event (CMBE), associated with some subevents.
δ13C stratigraphy of the Nanaimo Group is under analysis. On the basis of magneto- and biostratigraphy (Haggart et al., 2011; Ward et al., 2012), the CMBE interval is expected to be located in the mudstone-dominated intervals of the overlying Northumberland or Spray formations.
Friedrich, et al., 2012, Geology, 40, 107-110; Haggart et al., 2011, Can. Paleont. Conf., Field Trip Guidebook No. 16, 31-62; Hasegawa et al., 2003, Palaeo-3, 189, 97-115; Moriya, 2011, Paleont. Res, 15, 77-88; Moriya et al., 2003, Geology, 31,167–170; Voigt et al., 2012, Newsl. Str., 45, 25-53; Ward et al., 2012, GSA Bull., 124, 957-974.