Cesare Emiliani

The Brunhes Epoch: Isotopic Paleotemperatures and Geochronology

Oxygent isotopic analysis of a long piston core from the western equatorial Pacific has produced a record for the entire Brunhes epoch. This record can be correlated point by point with the isotopic records of previously analyzed Atlantic and Caribbean cores, leading to the construction of a generalized temperature curve for the entire Brunhes epoch.

Sudden death at the end of the Mesozoic

Abstract A paleoecological analysis of the fossil record before and after the Cretaceous/Tertiary boundary indicates that the widespread extinctions and biological stresses around the boundary are best explained in terms of a sudden, significant, but short temperature rise. L. Alvarez and co-authors, having found an enrichment in iridium at the same boundary, postulated that it was associated with the impact of an extraterrestrial body. If this body struck the ocean, the water injected into the atmosphere may have led to a transient increase in the global surface temperature. This temperature pulse may have been primarily responsible for the effects observed in the biosphere. The pattern of extinction of higher plant species suggests that splash down occurred in the northern Pacific-Bering Sea area.

Absolute Dating of Deep-Sea Cores by the

Oxygen isotopic analysis of Globigerina-ooze cores from the Atlantic and adjacent seas showed that surface ocean temperatures underwent numerous, apparently periodical, variations during the past few hundred thousand years. C14 dating showed that the last temperature minimum of the deep-sea cores was synchronous with the last major glaciation, the Main Würm. Previous attempts to date deep-sea cores were based on the decay of uranium-unsupported Th230 (ionium). This method requires, among other conditions, that the supply of uranium-supported Th230 in sea water and the rate of non-carbonate sedimentation remained essentially constant over the time interval to be dated. Attempts to correct for possible variations in the non-carbonate sedimentation rate have been made by using such ratios as Th230/Th232 or Th230/Fe2O3. The validity of these corrections is questionable because Th230 produced in sea water by the decay of U238 and U234 has a geochemical history different from that of Th232 and Fe2O3. The requirements mentioned above need not be met if the ratio

Method

Pa^{231}/Th^{230}

On glaciations and their causes

is used. Since Pa231 and Th230 are daughters of the same element, uranium, and since they decay at different rates, their ratio is a function of time alone. While information from deep-sea cores, bearing directly on Pleistocene history, has been obtained almost exclusively by isotopic and micropaleontological analysis of the foraminiferal component of Globigerina-ooze cores, dating by the decay of uranium-unsupported Th230 or by the ratio

Little Salt Spring, Florida: a Unique Underwater Site

Pa^{231}/Th^{230}