From Greenhouse to Icehouse: The Marine Eocene-Oligocene Transition

By Donald R. Prothero; Linda C. Ivany et al. | Go to book overview

CHAPTER 30
The Marine Eocene-Oligocene Transition:
A Synthesis

Linda C. Ivany, Elizabeth A. Nesbitt, and Donald R. Prothero


ABSTRACT

Progressive global cooling and increasing seasonality brought on by a combination of tectonic and oceanographic factors led to a series of worldwide pulsed turnovers through the middle Eocene and into the Oligocene. Real patterns of evolutionary turnover are often obscured in shelf settings by regional tectonism and facies changes, but, as seen in this volume, progress is being made at seeing the global pattern through the regional overprint. Most taxonomic groups show significant perturbations at or near the middle/late Eocene boundary and near or shortly after the Eocene/Oligocene boundary. Other events were noted in some groups in the late middle Eocene, within the late Eocene, and later into the Oligocene. Difficulties in establishing good age control and correlating widely separated sections limit our ability to determine the degree to which these events were isochronous, but the strong similarity of records from disparate regions, environments, and taxonomic groups suggests that these turnovers were global and hence triggered by changes occurring on a global basis, such as climate cooling. Extinction seems to have played a more important role in low-latitude turnovers, while origination was a significant component at high latitudes. Warm-water taxa were, without exception, hit harder than cool-water taxa, particularly at the middle/late Eocene boundary. While cosmopolitan taxa are more likely to survive turnovers, at high latitudes the reverse is true, and at the Eocene/Oligocene boundary itself taxa seem to have been affected indiscriminately.


INTRODUCTION

It has been well over a decade since the 1989 Penrose Conference on the Eocene-Oligocene transition was convened (Prothero and Berggren, 1992). Since that time, much new information has come to light, and work that was initiated as a result of that first conference has come to fruition. This volume, based on the 1999 Penrose Conference (Prothero et al., 2000), offers the most up-to-date views on the nature of the Eocene-Oligocene transition from climatic, oceanographic, and paleontologic perspectives. The majority of the papers presented here are chosen to represent the varied and ongoing work in Eocene-Oligocene marine shelf sections, from which much of our macrofossil record comes, and to draw comparisons between these data and those from open-ocean and terrestrial sources. Additional papers focus on deepsea and coastal-lowland-forest environments. As editors, we intend that this selection provide a comprehensive look at the patterns and processes that characterize the time period from the middle Eocene through the Oligocene, spanning geographic, taxonomic, and methodological boundaries to allow for a global, multidisciplinary perspective.

The transition from global “greenhouse” conditions of the early and middle Eocene to global “icehouse” conditions of the early Oligocene marks a turning point in Cenozoic Earth history. The early Eocene world is characterized by palm trees growing in Alaska (Scotese, 2002) and the northern Rocky Mountains (Greenwood and Wing, 1995), crocodiles living on Ellesmere Island well above the Arctic Circle

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