Marine connections in North America during the late Maastrichtian: palaeogeographic and palaeobiogeographic significance of Jeletzkytes nebrascensis Zone cephalopod fauna from the Elk Butte Member of the Pierre Shale, SE South Dakota and NE Nebraska

The Elk Butte Member of the Pierre Shale of southeast South Dakota and nort heast Nebraska yields a late Maastrichtian cephalopod fauna of nautiloids, belemnites and ammonites of the Jeletzkytes nebrascensis Zone, best known f rom the near-shore facies of the Fox Hills Formation. The nebrascensis Zone is the highest distinct. marine assemblage that can be recognised in the W estern Interior, although ammonites occur as rarities high in the Lance For mation in Wyoming. Elements of the fauna occur in the Gulf Coast and Atlant ic Seaboard, and extend into the highest,Maastrichtian nannofossil Subzone CC26b, of Micula prinsii, in Texas. These occurrences point to the existenc e of a southerly marine route for migration into and out of the northern In terior during the late late Maastrichtian. An analysis of Maastrichtian amm onite occurrences in West Greenland reveals no evidence for a marine link t o the Western Interior at this time, but rather indicates an open marine li nk to the North Atlantic region. The presence of upper upper Maastrichtian Pierre Shale in southeast South D akota and northeast Nebraska, deposited in water depths that are conservati vely estimated at 100-200 m, suggests that marine conditions (evidence for which has been removed by post-Cretaceous erosion) may have extended well t o the north of the shoreline position indicated in recent palaeogeographic reconstructions. (C) 1998 Academic Press Limited.