Foraminiferal and carbon isotope stratigraphy through the Paleocene‐Eocene transition at Dee Stream, Marlborough, New Zealand

Abstract

Dee Stream in the Clarence River valley of New Zealand bisects a well‐exposed section of marine sedimentary rocks deposited in the early Paleogene at high southern latitudes. One hundred metres of strata lying within this section and comprising cm‐dm well‐bedded, siliceous limestone with marly partings was mapped, logged, and sampled to establish a detailed foraminiferal and carbon isotope stratigraphy and to examine environmental changes across the Paleocene‐Eocene thermal maximum (PETM). Although low abundance and poor preservation of planktic and benthic foraminifera characterises much of the Paleocene, foraminifera and carbon isotopes clearly show that the section spans the upper Paleocene to lower Eocene planktic foraminiferal zones from Zone P4 to Subzone P6b, and the Subbotina triloculinoides to Pseudohastigerina wilcoxensis Zones. The δ13 C record correlates closely to other δ13 C curves generated from other key early Paleogene carbonate sequences. The Dee Stream logged section contains a1m thick PETM interval at 26.5 m at the base of Zone P5, or the Morozovella velascoensis Subzone. Here, benthic foraminifera undergo significant extinction, Morozovella aequa makes its first appearance, and the δ13 C of carbonate decreases by 2‰. The benthic foraminifer Bulimina tuxpamensis dominates benthic assemblages immediately following the onset of the PETM interval, suggesting dysoxic bottom waters during this event. In conjunction with other recently examined sections from the Marlborough region, the thick and apparently continuous Paleogene record at Dee Stream provides an important site for understanding environmental change on high‐latitude continental margins during the Paleogene, including the PETM.