Terminal Ordovician extinction: geochemical analysis of the Ordovician/Silurian boundary, Anticosti Island, Quebec

Journal Article · Thu May 01 00:00:00 EDT 1986 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1986)14<433:TOEGAO>2.0.CO;2· OSTI ID:5587416

Orth, C J; Gilmore, J S; Quintana, L R; Sheehan, P M

Elemental abundances (including Ir), carbon and oxygen ratios in carbonates, mineral content, and thin sections have been measured in samples collected across the conodont-defined Ordovician/Silurian (O/S) boundary exposed on Anticosti Island, Quebec. The Ir concentrations ranged from 5 to a maximum at the boundary of 58 parts per trillion (ppt). However, there is no evidence, on the basis of these Ir results, for the association of a large-body-Earth impact with the O/S extinction, because the Ir concentrations, like those of most other trace elements, are simply proportional to the clay (Al) content in the carbonate sequence. The /sup 13/C//sup 12/C and /sup 18/O//sup 16/O ratios decrease abruptly at the boundary, then just as abruptly increase to a long period of higher than preboundary ratios. These patterns are probably related to the salinity in the seaway, which was shallowing up to boundary time and then deepened and developed patch-reefs. Fresh-water input from rivers would have been most influential during the shallow-water conditions. 32 references, 4 figures.

• Research Organization: Los Alamos National Lab., NM
• OSTI ID: 5587416
• Journal Information: Geology; (United States), Vol. 14:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CLAYS
GEOCHEMISTRY
ORDOVICIAN PERIOD
BOUNDARY CONDITIONS
SILURIAN PERIOD
ABUNDANCE
CARBON
CARBON 12
CARBON 13
CARBONATE ROCKS
IRIDIUM
ISOTOPE RATIO
OXYGEN
OXYGEN 16
OXYGEN 18
QUEBEC
SALINITY
SEAWATER
CANADA
CARBON ISOTOPES
CHEMISTRY
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
HYDROGEN COMPOUNDS
ISOTOPES
LIGHT NUCLEI
METALS
NONMETALS
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOZOIC ERA
PLATINUM METALS
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
TRANSITION ELEMENTS
WATER
580400* - Geochemistry- (-1989)
580100 - Geology &amp; Hydrology- (-1989)