SLOW SEDIMENTATION AND IR ANOMALIES AT THE CRETACEOUS TERTIARY BOUNDARY/

Iridium enrichments, at or close to the K/T boundary, are often cited as evidence for impacts of cosmic bodies or volcanic events, or both, that resulted in mass extinctions. A third possible explanation for th e high Ir concentrations, that the enrichments were caused by the cosm ic micrometeorite flux during times of slow sediment accumulation, has generally been rejected. In this study we examine the Ir/Au ratios an d conclude that they may indicate enrichment of siderophile elements b y slow sedimentation. In addition, the concept of slow sedimentation a t the K/T boundary is consistent with many aspects of the K/T boundary research such as the gradual decline of the species before the major extinction level and recent reports of faunal transitions from Cretace ous to Tertiary without sudden extinctions, hiatuses or Ir anomalies.