Orbitally controlled cyclicity around the Cretaceous/Tertiary boundary, northern South Island, New Zealand

Abstract

Outcrop gamma ray measurements are used as a proxy for terrigenous clastic component in Cretaceous‐Paleocene carbonate‐chert successions in northern South Island, New Zealand, and show Milankovitch‐scale periodicity above the Cretaceous/Tertiary (K/T) boundary. Higher baseline values of the gamma ray records from sections in the south compared to those in the north reflect increased terrigenous clay content associated with shallowing in paleobathymetry towards the south. In each northern section, the gamma ray baseline level increases across the K/T boundary, consistent with an increase in terrigenous clay in the early Paleocene; this might record increased erosion due to destruction or change of vegetation or a fall in relative sea level. Peak amplitudes in the gamma ray record are higher for the early Paleocene, perhaps recording more pronounced climatic variability after the K/ T boundary event, and consistent with a South Atlantic record. Cycle frequencies in the Late Cretaceous are not well constrained due to the sparseness of biostratigraphic events but could be consistent with eccentricity. Biostratigraphic age control in the Paleocene constrains cycle frequency to c. 120 000 yr and suggests the early Paleocene climate in the high latitude, southwest Pacific, was modulated by orbital eccentricity.

Keywords:

• Paleocene
• orbital cycles
• Milankovitch
• Marlborough
• Mead Stream
• Branch Stream
• Woodside Creek
• Waipara River
• gamma ray
• paleoclimate