sup 18 O/ sup 16 O and sup 13 C/ sup 12 C in lower Paleozoic articulate brachiopods: Implications for the isotopic composition of seawater

Journal Article · Tue Dec 31 23:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90143-7· OSTI ID:7049641

Wadleigh, M A ^[1]; Veizer, J ^[2]

---

1. Univ. of Ottawa, Ontario (Canada)
2. Univ. of Ottawa, Ontario (Canada) Ruhr Univ., Bochum (Germany)

Three hundred and eleven articulate brachiopods, with extensive geographic coverage, spanning the Cambrian to Silurian stratigraphic interval, were analyzed for oxygen and carbon isotopic composition. Cambrian samples have {delta}{sup 18}O {le} {minus}7{per thousand}, Ordovician samples {le} {minus}2.4{per thousand}, and Silurian samples {le} {minus}1.9{per thousand}, confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the Lower Paleozoic. Forty-nine best preserved' Ordovician and Silurian samples were identified based on scanning electron microscopy and trace element analysis. They were found to bracket the isotopic compositions of over 85% of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal. Some latest Ordovician and Lower Ludlovian samples associated with shale sequences are apparently enriched' in {sup 18}O. These are interpreted as an environmental phenomenon, perhaps related to water temperature and glaciation. A number of Silurian samples of varying genera and stratigraphic levels are highly enriched in {sup 13}C, up to +6{per thousand}. Some are shale related, but some are associated with carbonate-bearing basins. These are also thought to represent near-original' compositions, but a single environmental cause is unknown. The present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation. Whole-shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon.

• OSTI ID: 7049641
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:1; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540310 -- Environment
Aquatic-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000* -- Geosciences
ANIMALS
CAMBRIAN PERIOD
CARBON 12
CARBON 13
CARBON ISOTOPES
CHEMICAL COMPOSITION
CHEMISTRY
DATA
ELECTRON MICROSCOPY
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
FOSSILS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGY
HYDROGEN COMPOUNDS
INFORMATION
INVERTEBRATES
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
LITHOLOGY
LUMINESCENCE
MICROSCOPY
NUCLEI
NUMERICAL DATA
ORDOVICIAN PERIOD
OXYGEN 16
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOZOIC ERA
SAMPLING
SCANNING ELECTRON MICROSCOPY
SEAWATER
SILURIAN PERIOD
STABLE ISOTOPES
STRATIGRAPHY
TRACE AMOUNTS
VARIATIONS
WATER