Trace-element patterns at the Cretaceous-Tertiary boundary—Consequences of a large impact

A sequence of events across the Cretaceous-Tertiary boundary

“…Evidence for a dysaerobic environment arc the near absence of benthic foraminifera (El Kef, Caravaca, Stevns Klint, DSDP hole 465A), the widespread occurrence of pyrite in this layer [29,30], the anomalies of chalcophile elements (As, Se, Sb and Zn) in some of the sections and the sometimes very conspicuous slowing down of bioturbation. Also, during the following 5 15 kyr sediments (the boundary clay of unit 3) were carbonate free to carbonate poor [1]. Unit 2 invariably indicates the level of the main mass-mortality and mass-extinction.…”

“…Enhanced Ir levels in this unit and also in the next, are probably either due to bioturbation/reworking or to erosion and redeposition from other eroded fall-out deposits, e.g. on land [1,8].…”

“…That clay has usually a much greater thickness and is part of the next unit. Unit 2 shows the peak in lr concentration [1,13,27,28] and now appears to contain microtektite-like spherules [2] in almost every section where the iridium anomaly has been found ( Fig. 2), and corresponds thus to the direct fallout and ejecta level of the K/T impact(s).…”

“…This unit probably has had an initial thickness of less than 0.5 cm [1,27] when an (estimated) correction is made for mixing by drilling or bioturbation, tectonic interference or other sedimentological processes like turbidity currents, winnowing or slumping. Only a few sections (DSDP hole 465A, Caravaca) allow a direct estimate of its thickness, because of reduced bioturbation.…”

“…Smit and ten Kate [1] earlier hypothesized a sequence of K/T boundary events from the paleontology and lithology of the most complete / "¢) \. 3 \ sections.…”