Biostratigraphic review of the Cretaceous/Tertiary boundary transition, mid‐Waipara River section, North Canterbury, New Zealand

Abstract

The mid‐Waipara River section is the most complete known record of the Cretaceous/Tertiary (K/T) boundary transition in a South Pacific neritic setting. For local studies it provides a crucial link between bathyal marine and terrestrial records. The section contains abundant and diverse palynomorphs, including dinoflagellate cysts and terrestrial spores and pollen, as well as significant occurrences of biostratigraphically important foraminiferal, calcareous nannofossil, and radiolarian species. Examination of new and existing micropaleontology samples reveals a potentially complete early Paleocene foraminiferal succession correlated to Foraminiferal Zones P0 to P1a‐c. Although Cretaceous and basal Paleocene radiolarian assemblages lack age‐diagnostic species, higher Paleocene radiolarian assemblages can be correlated to Radiolarian Zones RP2‐RP4. Analysis of the distribution of RP3 and RP4 zonal markers in archival samples indicates that the sample sequence of Jenkins, previously published in 1971, is not in stratigraphic order. Bioturbation through the boundary interval and postdepositional leaching are thought to have contributed to relatively low levels of enrichment of K/T boundary fingerprint elements: Ir, Ni, Cr, and Zn. The K/T boundary coincides with a marked decrease in carbonate content, while correlated trends in Si/Al andBa/Al indicate that biosiliceous productivity increased across the boundary. Extremely low carbonate content and common siliceous microfossils through 30 m of lower Paleocene strata suggest that cool oceanographic conditions prevailed in the northern Canterbury Basin for the first 1–2 m.y. of the Cenozoic.