Platinum group element enrichments and possible chondritic Ru:Ir across the Frasnian-Famennian boundary, western New York State.
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.
Over
D J
DJ
Department of Geological Sciences, SUNY College at Geneseo 14454, USA.
Conaway
C A
CA
Katz
D J
DJ
Goodfellow
W D
WD
Gregoire
D C
DC
D000818:Animals; D005075:Biological Evolution; D018534:Earth, Planet; D019419:Evolution, Planetary; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis*; D007448:Invertebrates; D007495:Iridium; D019110:Meteoroids; D009518:New York; D010163:Paleontology; D010165:Palladium; D010984:Platinum; D012413:Rubidium
D007495:Iridium; D010984:Platinum; D010165:Palladium; D012413:Rubidium