Lower Cretaceous lithostratigraphy across a regional subaerial unconformity in spitsbergen: The Rurikfjellet and Helvetiafjellet Formations

摘要

During development of the Lower Cretaceous succession in the Spitsbergen domain of the epicontinental Boreal Basin, a fall in relative sea-level caused a major subaerial unconformity to form. This unconformity forms the lithostratigraphic boundary between the Rurikfjellet Formation below, and the Helvetiafjellet Formation above. The previous Ullaberget Member in the upper part of the Rurikfjellet Formation was originally defined using the Ullaberget section in Nathorst Land as its stratotype. The Ullaberget section is not representative for the upper sandstone-rich member of the Rurikfjellet Formation, but is chosen here as the stratotype for the new Louiseberget Bed of the Festningen Member. The Louiseberget Bed consists of deltaic sandstone, located above the subaerial unconformity capping the Rurikfjellet Formation, and forms a facies body within the Festningen Member, the fluvially-dominated lower member of the Helvetiafjellet Formation. The Kikutodden Member is here defined as a new member substituting for the Ullaberget Member as the upper, sand-rich part of the Rurikfjellet Formation; the Kikutodden section in S?rkapp Land being the stratotype and the Strykejernet section being new hypostratotype for the member. The Festningen Member and the Glitrefjellet Member in the lower and upper parts of the Helvetiafjellet Formation, respectively, are re-established as formal members.