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

Abstract

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:
Research Org.:
Univ. of California, Berkeley
OSTI Identifier:
5717494
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; (United States); Journal Volume: 14:12
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)

Citation Formats

Montanari, A. Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: the problem of outcrop contamination. United States: N. p., 1986. Web. doi:10.1130/0091-7613(1986)14<1024:SFTCBC>2.0.CO;2.
Montanari, A. Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: the problem of outcrop contamination. United States. doi:10.1130/0091-7613(1986)14<1024:SFTCBC>2.0.CO;2.
Montanari, A. Mon . "Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: the problem of outcrop contamination". United States. doi:10.1130/0091-7613(1986)14<1024:SFTCBC>2.0.CO;2.
@article{osti_5717494,
title = {Spherules from the Cretaceous/Tertiary boundary clay at Gubbio, Italy: the problem of outcrop contamination},
author = {Montanari, A.},
abstractNote = {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.},
doi = {10.1130/0091-7613(1986)14<1024:SFTCBC>2.0.CO;2},
journal = {Geology; (United States)},
number = ,
volume = 14:12,
place = {United States},
year = {Mon Dec 01 00:00:00 EST 1986},
month = {Mon Dec 01 00:00:00 EST 1986}
}
  • The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, butmore » this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where the average Ir concentration is 3,000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.« less
  • Microbial activity and redox-controlled precipitation have been of major importance in the process of metal accumulation in the strongly Ir-enriched Cretaceous-Tertiary (K-T) boundary clay, the Fish Clay, at Stevns Klint in Denmark. Two important findings support this view: (1) Kerogen, recovered by leaching the Fish Clay in HCl and HF, shows an Ir concentration of 1100 ppb; this represents about 50% of the Ir present in the bulk sample Fish clay. Strong organometallic complexes is the most probable carrier phase for this fraction of Ir. Kerogen separated from the K-T boundary clay at Caravaca, Spain, similarly exhibits enhanced Ir concentrations.more » (2) Sulfur isotope analyses of metal-rich pyrite spherules, which occur in extreme abundance (about 10% by weight) in the basal Fish Clay, give a delta/sup 34/S value of -32 per thousand. This very low value shows that sulfide formation by anaerobic bacteria was intensive in the Fish Clay during early diagenesis. Since the pyrite spherules are major carriers of elements such as Ni, Co, As, Sb and Zn, microbial activity may have played an important role for concentrating these elements. In the Fish Clay large amounts of rare earth elements have precipitated from sea water on fish scales. Analyses reveal that, compared with sea water, the Fish Clay is only about four times less enriched in sea-water derived lanthanides than in Ir. This shows that a sea-water origin is plausible for elements that are strongly enriched in the clay, but whose origin cannot be accounted for by a lithogenic precursor.« less
  • When fullerenes were first discovered to form spontaneously in condensing carbon vapors, it was suggested that they might be widely distributed in the Universe. Searchers for fullerenes in meteorites were unsuccessful, but C[sub 60] and C[sub 70] were reported to occur on Earth in samples of shungite, a meta-anthracite from a deposit near Shunga, Russia, and in [open quotes]fulgurite[close quotes], a substance formed when lightning strikes certain soils or rocks. The occurrence of fullerenes in shungite is particularly surprising since fullerene synthesis in the laboratory has always involved gas phase chemistry at temperatures over 1000[degrees]C. Such conditions may be attainedmore » during lightning strikes, but shungite is believed to have formed from carbonaceous material creeping into fissures of a Precambrian rock which metamorphosed under extreme pressures. If the original carbonaceous material did not already contain fullerenes perhaps from wildfires, they must have formed during the metamorphism by as yet unknown solid- or liquid-phase mechanisms.« less
  • No abstract prepared.
  • This study presents data for Ir and the chalcophile elements As, Sb, and Zn in seventeen samples from continental K/T boundary layers in the western interior of the USA. The results show that in contrast to previously studied marine boundary clays, the continental boundary layers show no correlation between Ir and any of the chalcophile elements. Compared with average shale, the continental boundary layers are significantly to strongly enriched in Ir, As, and Sb, but show ordinary Zn concentrations. The Ir enrichments can be attributed to fallout of extraterrestrial matter, whereas As and Sb enrichments can be readily explained bymore » the close spatial association of the boundary layers with coal and the abundance in the layers of jarosite, goethite, and other weathering products of pyrite. If compared to jarosite-rich coal-associated background samples, the boundary layers show much higher Ir concentrations but similar (or possibly slightly enhanced) concentrations of As, Sb, and Zn. The correlation between chalcophile elements and Ir in marine boundary clays, and the absence of such a correlation in continental boundary clays, concurs with the idea that a major fraction of the Ir in extremely Ir-rich (30-460 ppb Ir) marine boundary clays has precipitated from seawater that was enriched in Ir being derived from a vaporized asteroid.« less