Dinosaurs, spherules, and the “magic” layer: A new K-T boundary clay site in Wyoming

By: , and 



A new Cretaceous-Tertiary (K-T) boundary clay site has been found along Dogie Creek in Wyoming in the drainage of Lance Creek—the type area of the Lance Formation of latest Cretaceous age. The boundary clay was discovered in the uppermost part of the Lance Formation, 4–7 cm beneath the lowest lignite in the Paleocene Fort Union Formation and approximately 1 m above a fragmented dinosaur bone.

The boundary clay consists of a basal kaolinitic claystone layer as much as 3 cm thick containing hollow goyazite spherules, overlain by a 2–3 mm smectitic layer (the “magic” layer) containing both shock-metamorphosed minerals and an iridium anomaly of 21 ppb. A palynological break coincides with the base of the claystone layer; numerous Late Cretaceous palynomorph species terminate at this boundary.

The paleontological significance of this new boundary site lies in its close association with the well-studied assemblage of dinosaurs and other vertebrates and flora within the type area of the Lance Formation. The spherules at the Dogie Creek site are extremely well preserved by virtue of their replacement by the mineral goyazite. This preservation should facilitate the resolution of the origin of the spherules and of their host layer.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Dinosaurs, spherules, and the “magic” layer: A new K-T boundary clay site in Wyoming
Series title Geology
DOI 10.1130/0091-7613(1987)15<896:DSATML>2.0.CO;2
Volume 15
Issue 10
Year Published 1987
Language English
Publisher Geological Society of America
Description 4 p.
First page 896
Last page 899
Country United States
State Wyoming
Google Analytic Metrics Metrics page
Additional publication details