Geochemistry of Ni in the Cretaceous-Tertiary succession Fiskeler (Fish Clay) at Stevns Klint (Denmark): cheto-smectite of the black marl

Abstract

The Cretaceus-Tertiary (KT) boundary at Stevns Klint (the Hojerup succession), Fiskeler, consists of a thin red clay layer overlain by a thick one of black marl. These two layers are made up mainly from cheto-smectite and biogenic calcite. The black marl shows an enhanced concentration of Ni (655 ppm) within its smectite fraction. Additionally, its carbonate fraction also shows an enhanced concentration of Ni (245 ppm). It is reasoned that these enrichments represent a sudden and rapid input of high amounts of Ni into the late Cretaccus seawater at Stevns Klint. The ultimate source of Ni in both the carbonate and smectite fractions of the black marl was probably impact fallout, produced by the KT asteroidal impact, deposited on the nearby soil and 1 ached by the (acid) surface waters. The geochemistry of the Ni supports the hypothesis that the smectite of this marl most likely has a local (marine or terrestrial) provenance and was probably redeposited, after its formation, from the original site to its present location at the KT boundary.