Late Eocene North American microtektites and clinopyroxene‐bearing spherules

Abstract

Approximately 35 m.y. ago two events, separated by only 10,000–20,000 years, each spread roughly 1 billion metric tons of silicate spherules over large areas of the Earth's surface. The older event produced mostly clinopyroxene‐bearing spherules (cpx spherules). The cpx spherules have been found in the Caribbean Sea, Gulf of Mexico, equatorial Pacific, and eastern equatorial Indian Ocean. The cpx spherule layer is associated with an iridium anomaly and appears to coincide with the extinction of several species of Radiolaria. The composition and widespread distribution of the cpx spherules indicate that they were formed by an impact event. The younger layer of spherules consists of microtektites belonging to the North American tektite strewn field based on age and elemental and isotopic composition. The North American microtektites have been found in the western equatorial Atlantic, on Barbados, in the Caribbean Sea, and in the Gulf of Mexico. The North American microtektite layer is not synchronous with an iridium anomaly, nor does it appear to be associated with any major changes in the microfossils. Neither the cpx spherule event nor the North American tektite event appears to be associated with a climatic change, but no detailed studies have been made across either layer. Excluding the cpx layer, which contains mostly crystal‐bearing spherules, the evidence at the present time indicates that there is only one late Eocene microtektite layer and it is part of the North American strewn field.