skip to main content

Title: Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: the problem of outcrop contamination

Surficial outcrop contamination has occurred in some well-known stratigraphic sections of carbonate rocks in the northern Apennines. A critical case involves several contaminated clay partings, including the Cretaceous/Tertiary boundary clay in the classic Bottaccione section near Gubbio, Italy. These clay layers contain shiny spherules which, in several recent studies, have been said to consist of volcanic glass and have been used to support the hypothesis that the terminal Cretaceous mass extinction was caused by widespread volcanism. Laboratory tests, however, indicate that these shiny spherules are made of HF-insoluble and combustible material and are therefore of recent biological origin. These objects were introduced into the Cretaceous/Tertiary boundary clay and other clay layers from the surrounding soil along with abundant detrital contaminants derived from erosion of the middle Miocene flysch exposed at the head of the Bottaccione Gorge. They are completely different from the altered and flattened microtektitelike spheroids that are found only in the iridium-rich Cretaceous/Tertiary boundary clay and that provide strong evidence for a large impact.
Authors:
Publication Date:
OSTI Identifier:
5717494
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; (United States); Journal Volume: 14:12
Research Org:
Univ. of California, Berkeley
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CRETACEOUS PERIOD; BOUNDARY CONDITIONS; GEOLOGIC DEPOSITS; GEOCHEMISTRY; ITALY; TERTIARY PERIOD; CARBONATE ROCKS; CLAYS; CONTAMINATION; ENVIRONMENTAL TRANSPORT; GEOLOGIC HISTORY; LAYERS; CENOZOIC ERA; CHEMISTRY; EUROPE; GEOLOGIC AGES; MASS TRANSFER; MESOZOIC ERA; ROCKS; SEDIMENTARY ROCKS; WESTERN EUROPE 580400* -- Geochemistry-- (-1989); 580100 -- Geology & Hydrology-- (-1989)