Platinum group element enrichments and possible chondritic Ru:Ir across the Frasnian-Famennian boundary, western New York State.
Palaeogeogr Palaeoclimatol Palaeoecol
; 132(1-4): 399-410, 1997 Aug.
Article
em En
| MEDLINE
| ID: mdl-11541728
ABSTRACT
The Frasnian-Famennian boundary is recognized as the culmination of a global mass extinction in the Late Devonian. In western New York State the boundary is a distinct horizon within a pyritic black shale bed of the upper Hanover Shale defined by the first occurrence of Palmatolepis triangularis in the absence of Frasnian conodonts. The boundary is characterized by a minor disconformity marked by a lag concentration of conodonts. Iridium at the boundary is 0.11-0.24 ng/g, two to five times background levels of <0.05 ng/g; other Ir enrichments of 0.38 ng/g and 0.49 ng/g occur within 50 cm of the conodont-constrained boundary. Numerous Ir enrichments in the boundary interval suggest extraterrestrial accretion and platinum group element (PGE) concentration at disconformities, or mobilization and concentration in organic-rich/pyritic-rich laminations from cosmic or terrestrial sources. PGE ratios of Pt/Pd and Ku/Ir at the boundary horizon approximate chondritic ratios and are suggestive of an unaltered extraterrestrial source. These values do not conclusively establish a single extraterrestrial impact as the ultimate cause of the Frasnian-Famennian mass extinction, especially given the presence of similar Ir enrichments elsewhere in the section and the absence at the boundary of microtektites and shocked mineral grains.
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Bases de dados:
MEDLINE
Assunto principal:
Paleontologia
/
Meteoroides
/
Sedimentos Geológicos
/
Evolução Planetária
/
Evolução Biológica
Limite:
Animals
País/Região como assunto:
America do norte
Idioma:
En
Revista:
Palaeogeogr Palaeoclimatol Palaeoecol
Ano de publicação:
1997
Tipo de documento:
Article
País de afiliação:
Estados Unidos