Oxygen, carbon and U-series isotopes of aragonites from Vestfold Hills, Antarctica: Clues to geochemical processes in subglacial environments

Journal Article · Thu Sep 01 00:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90134-2· OSTI ID:5254433

Aharon, P ^[1]

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1. Louisiana State Univ., Baton Rouge (USA)

Aragonites occurring in situ on the gneissic bedrock at Vestfold Hills, an ice-free coastal Antarctic oasis possess morphologic and petrographic characteristics typical of subglacial carbonate precipitates. The {sup 14}C chronology of the samples is invalidated by modern carbon contamination and a {sup 14}C/{sup 12}C reservoir correction of unknown magnitude. In contrast, U and Th isotope analyses suggest that the subglacial deposits can be treated as closed, datable, systems, if allowance is made for the excess {sup 230}Th derived from the small and variable detrital silicate fraction coexisting with the aragonites. The mean {sup 230}Th depositional age of 35,000 {plus minus} 2,000 yrs correlates with late isotope stage 3 of deep sea glacial chronology and represents the time when the Vestfold Hills were partially or completely buried under the advancing East Antarctic ice sheet. The survival of the aragonites following the ice sheet retreat during the Holocene is attributed to the extreme arid climate of the area. The aragonites are anomalously depleted in {sup 18}O and slightly depleted in {sup 13}C relative to SMOW and PDB standards, respectively ({delta}{sup 18}O = 15.7 {plus minus} 0.9{per thousand}; {delta}{sup 13}C = {minus}3.6 {plus minus} 0.4{per thousand}). The melt water with which the aragonites would have equilibrated at 0{degree}C is about 7 to 9{per thousand} more depleted in {sup 18}O relative to the extant basal ice source ({delta}{sup 18}O = {minus}41{per thousand}). Part of this enhanced {sup 18}O deficiency (i.e. 4 to 6{per thousand}) is ascribed to temporal shifts in {delta}{sup 18}O of the Antarctic ice, the rest to isotope effects of the subglacial hydrology. A model of subglacial aragonite precipitation is proposed on the basis of water flow between warm melting zones and cold freezing zones at the ice sheet sole.

• OSTI ID: 5254433
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:9; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARAGONITE
ISOTOPE DATING
ISOTOPE RATIO
PETROGRAPHY
PRECIPITATION
ANTARCTICA
CARBON 12
CARBON 13
CARBON 14
GEOCHEMISTRY
GEOLOGIC HISTORY
GLACIERS
GNEISSES
HYDROLOGY
OXYGEN 18
PETROGENESIS
THORIUM ISOTOPES
URANIUM ISOTOPES
ACTINIDE ISOTOPES
AGE ESTIMATION
ALKALINE EARTH METAL COMPOUNDS
ANTARCTIC REGIONS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBON ISOTOPES
CARBONATE MINERALS
CARBONATES
CHEMISTRY
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
METAMORPHIC ROCKS
MINERALS
NUCLEI
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
POLAR REGIONS
RADIOISOTOPES
ROCKS
SEPARATION PROCESSES
STABLE ISOTOPES
YEARS LIVING RADIOISOTOPES
580000* - Geosciences