Figure 1. The Muzzle Group at Mead Stream, New Zealand.

Abstract

In terms of global climate change, the late Cretaceous through early Paleogene represents one of the more dynamic periods in Earth history. Paleoclimate reconstructions based on investigation of deep sea sediments reveal a rather complex history of gradual and rapid warming and cooling for the Cretaceous and Paleogene. This includes a 5 myr long global warming trend that began in the late Paleocene and climaxed in the early Eocene in a 1-2 myr long climatic optimum (EECO), and a 12 myr long, step-like cooling trend that began in the early middle Eocene and culminated in the earliest Oligocene with the appearance of continental scale ice-sheets. A brief but extreme greenhouse period known as the Late Paleocene Thermal Maximum (LPTM) ca. 55.5 Ma occurs midway through the Paleocene/Eocene warming trend. Another notable transient is the earliest Oligocene Glacial Maximum (EOGM, a.k.a. Oi-1), a brief but extreme glacial interval ca. 33.4 Ma that coincides with the transition to permanent glacial conditions on Antarctica. This transient, like the LPTM, has been linked to major changes in ocean chemistry and ecology. Finally, at least one major impact event occurred at the K/T boundary.

Multiple hypotheses have been forwarded to explain the large scale, long-term changes in Paleogene climate though none have gained universal acceptance. In general, among the many factors, ocean gateways (continental geography) and greenhouse gas levels are recognized as the two key variables. Theoretical models have invoked either higher greenhouse gas levels or the absence of a circum-Antarctic current or some combination to account for EECO. Similarly, the Oligocene glaciation has been attributed to both a reduction in greenhouse levels and the initiation of the Antarctic circumpolar current. The more abrupt transient excursions are more likely to have been forced by rapid changes in greenhouse gas levels, because they transpire over short time scales (e.g., 103-104 yr), are single events, and, most importantly, are accompanied by geochemical and isotopic anomalies suggestive of major perturbations in the carbon and sulfur cycles.

Progress in characterizing Paleogene oceanography and climate history, particularly the abrupt transient events, has been hampered by the lack of high quality, high resolution sequences. Most existing sites suffer from poor exposure, and the few exceptions are mostly in drill sites recovered in the open ocean so that continent-ocean links cannot be assessed directly. The high resolution records produced from these sites have yielded a wealth of exciting, potentially important ideas about climate change that require additional data to more fully explore. Gaining a more complete description of these events in four dimensions along continental margins is critical, because such knowledge will provide crucial constraints for both formulating and testing hypotheses of climate change.

One of the more promising locations for recovering expanded late Cretaceous and Paleogene sections along ancient continental margins is the Clarence Valley in the south Island of New Zealand. Here, the Muzzle Group, a thick, neritic to bathyal sequence consisting of siliceous limestone, has been uplifted and tilted to form a 35 km stike ridge. Because a series of streams bisects the Muzzle Group in the Clarence Valley (Fig. 1), the region provides a special opportunity to study environmental change on a continental margin from shelf to slope during key events of the late Cretaceous and Paleogene. This project focuses on the stratigraphy and chemical and mineralogical evolution of the ancient New Zealand margin.