Early Cenozoic Climate and Carbon Cycling: The Sedimentary Record of Global Warming and Massive Carbon Input

Jerry Dickens
Rice University, Houston, Texas([email protected])

Abstract

The “Greenhouse Earth” of the late Paleocene and early Eocene was generally characterized by warm temperatures and elevated pCO₂. Climate and carbon cycling were, however, far from equable during this interval, as once believed. Surface temperatures slowly warmed by about 5 °C from 59 Ma to the Early Eocene Climatic Optimum centered about 50 Ma. This long-term warming generally coincided with greater inputs of carbon, presumably caused by volcanism. Superimposed on this background change were a series of “hyperthermals”, the most pronounced corresponding to the Paleocene/Eocene Boundary ca. 55 Ma. These were geologically brief (<200 kyr) events that began with rapid warming across the globe and massive input of ¹³C-depleted carbon. They were also times of extreme variations in ecosystems and the hydrological cycle.

Our current understanding of the late Paleocene and early Eocene allows us to link disparate and unusual observations in strata from across the globe with a holistic perspective.

In particular, the start of the PETM is clearly identified in scores of sedimentary records by a prominent negative carbon isotope excursion in carbonate, organic carbon, or both.
This excursion precisely coincides with profound mammal and plant migrations in the northern hemisphere, a mass extinction of benthic foraminifera, elevated terrigenous discharge to many continental margins, laminated sediment facies on continental slopes, and a carbonate dissolution horizon in the deep-ocean. Similar changes, though of lesser magnitude, appear to mark the other hyperthermals. Although cause and effect relationships during hyperthermals, as well as links between them, remain uncertain, the hyperthermals and their sedimentary expressions are, without doubt, somehow related to extreme global warming and tremendous additions of carbon to the ocean and atmosphere. Speculative links will be discussed.

AAPG Search and Discovery Article #90086 © 2008 AAPG Foundation Distinguished Lecturer Series 2008-2009