March/April Geological Society of America Bulletin media highlights

A unique global warming event occurred about 55 million years ago. Previous works suggest that the event started abruptly with a 5°C warming, which lasted for nearly 100,000 years. It took another 100,000 years to recover from this warming before the temperature conditions on Earth were back to "normal" again, or rather, what was normal 54–55 million years ago. This warming event, commonly referred to as the Paleocene-Eocene Thermal Maximum, or PETM for short, resulted in, for example, huge changes in ocean chemistry and a mass extinction of a group of sand-grain sized bottom-living organisms (benthic foraminifera). The geological hallmark of the PETM event is a strong and complex carbon isotope excursion, considered to have been caused by a massive (more than 4000 gigatons) and rapid addition of light carbon (carbon-12) into the oceans and atmosphere at this time. Because the PETM may represent an analog of the present accelerated emission of greenhouse gases caused by humans, it has attracted much interest both with respect to data collecting and modeling efforts. It has been pointed out by many specialists that a more comprehensive understanding of the carbon isotope excursion event requires the study of numerous high quality sedimentary records from a range of different latitudes and water depths. Giusberti et al.’s integrated study of a new section (Forada section), located near the city of Belluno north of Venice in northern Italy, provides one such much-needed record. This record provides important insight into the much-debated problem of the duration of the carbon isotope excursion. The Paleocene-Eocene boundary sediments preserved in the continuously deposited Forada section show an exceptionally expanded (3.3 m) interval containing the main carbon isotope excursion event (105,000 ± 10,000 years) and an unusually clearly defined "recovery" interval (126,000 ± 12,000 years). The data obtained from Forada suggest that the source of the light carbon ceased to be added to the ocean-atmosphere system exactly at the transition between the top of the main carbon isotope excursion event and the base of the recovery interval.

Diagenesis, sediment strength, and pore collapse in sediment approaching the Nankai Trough subduction zone
Glenn A. Spinelli, New Mexico Tech, Earth & Environmental Science Department, Socorro, NM 87801, U.S.A.; et al. Pages 377-390.