Geochemical evidence for a catastrophic biotic event at the Frasnian/Famennian boundary in South China

A strong δ13C anomaly coincides with a weak Ir anomaly at the Frasnian/Famennian (F/F) boundary exposed at Xiangtian, Guangxi, south China. The maximum whole-rock Ir abundance is 0.23 ppb (0.35 ppb on a carbonate-free basis) compared with averages of 0.016 and 0.044 ppb above and below the boundary...

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Bibliographic Details
Published in:Geology (Boulder) 1991-08, Vol.19 (8), p.776-779
Main Authors: Wang, Kun, Orth, Charles J, Attrep, Jr, Chatterton, Brian D. E, Hou Hongfei, Hou Hongfei, Geldsetzer, Helmut H. J
Format: Article
Language:English
Subjects:
anomalies
Asia
biostratigraphy
breccia
C-13/C-12
carbon
carbonate rocks
catastrophes
Chemistry
China
clastic rocks
Conodonta
Devonian
Famennian
Far East
Frasnian
geochemical indicators
geochemistry
Geology
Guangxi China
impacts
Invertebrata
iridium
isotopes
lithofacies
mass extinctions
metals
microfossils
Minerals
North Pacific
Northwest Pacific
O-18/O-16
oxygen
Pacific Ocean
paleoecology
Paleozoic
platinum group
rock, sediment, soil
sedimentary rocks
South China Sea
southern China
stable isotopes
stratigraphic boundary
stratigraphy
trace elements
Upper Devonian
West Pacific
Xiangian
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Summary:A strong δ13C anomaly coincides with a weak Ir anomaly at the Frasnian/Famennian (F/F) boundary exposed at Xiangtian, Guangxi, south China. The maximum whole-rock Ir abundance is 0.23 ppb (0.35 ppb on a carbonate-free basis) compared with averages of 0.016 and 0.044 ppb above and below the boundary interval. The δ13C in carbonate abruptly shifts from a late Frasnian level of about +1ppm to -2.49ppmin the boundary interval and then abruptly returns to pre-boundary levels, suggesting a temporary reduction of surface-water biomass. A widely distributed (over at least several hundred kilometres) limestone breccia unit of possible wave-deposit origin is present directly below the boundary in south China. Enrichments of Al, V, Cr, As, and U, and a dip in the Mn abundance in the boundary interval indicate that reducing conditions might have been associated with the element enrichment. However, an alternative hypothesis is that oceanic impact(s) at the F/F boundary near south China provided the excess Ir and caused the biotic crisis and the formation of breccia deposits observed in the Late Devonian South China Sea.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1991)019<0776:GEFACB>2.3.CO;2