Carbon and oxygen isotopes in Pennsylvanian biogenic and abiogenic aragonite (Otero County, New Mexico): A laser microprobe study

Journal Article · Sun Sep 01 04:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90376-G· OSTI ID:7049749

Dickson, J A.D. ^[1]; Smalley, P C ^[2]; Kirkland, B L ^[3]

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1. Univ. of Cambridge (United Kingdom)
2. Inst. for Energy Technology, Kjeller (Norway)
3. Louisiana State Univ., Baton Rouge (United States)

Phylloid algal plates and encrusting botryoidal marine cements from the Holder Formation (Pennsylvanian), Dry Canyon in Otero County, New Mexico, USA, have been discovered that are largely preserved as aragonite. Laser microsampling enabled {delta}{sup 13}C and {delta}{sup 18}O multiple analyses within algal thalli and cement crusts, and allowed discrimination of the effects of later calcitization. The alga Eugonophyllum gives {delta}{sup 13}C = +1.2 PDB and {delta}{sup 18}O = {minus}3.2 PDB. Botryoidal aragonite cement crusts ({delta}{sup 13}C = +4.2{per thousand}; {delta}{sup 18}O = {minus}0.5{per thousand}) have been patchily converted to calcite ({delta}{sup 13}C = +4.5{per thousand}; {delta}{sup 18}O = {minus}6.0{per thousand}), yielding an approximate 5{per thousand} shift in {delta}{sup 18}O values. This calcitization occurred in a system closed with respect to carbon. A {delta}{sup 13}C and {delta}{sup 18}O depletion of algal aragonite compared to cement aragonite exists. The biogenic fractionation effect is {minus}3.0{per thousand} for carbon and {minus}2.7{per thousand} for oxygen. {delta}{sup 13}C values proposed previously for Pennsylvanian ocean water, based principally on data derived from brachiopod shells, usually diverge 2-3{per thousand} from modern seawater. The Dry Canyon aragonite cements have {delta}{sup 13}C values the same, and {delta}{sup 18}O values 1 to 1.7{per thousand} lighter, than modern equivalent material. This indicates that either previous estimates of Pennsylvanian ocean water were made from fractionated material, a temperature difference exists between Pennsylvanian and modern oceans, or the single Dry Canyon sample was precipitated in anomalous Pennsylvanian seawater. Only the fine scale of laser microsampling has allowed the special preservation of coexisting biogenic and abiogenic aragonite and its partial alteration to be unravelled.

• OSTI ID: 7049749
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:9; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALGAE
ARAGONITE
CARBON 13
CARBON CYCLE
CARBON ISOTOPES
CARBONATE MINERALS
CARBONIFEROUS PERIOD
CHEMICAL COMPOSITION
CHEMISTRY
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
EVALUATION
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION VI
FOSSILS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC HISTORY
HYDROGEN COMPOUNDS
ISOTOPE RATIO
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LIGHT NUCLEI
MICROANALYSIS
MINERALS
NEW MEXICO
NORTH AMERICA
NUCLEI
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOZOIC ERA
PLANTS
SEAWATER
STABLE ISOTOPES
USA
WATER