Diagenetic modification of Sm-Nd model ages in Tertiary sandstones and shales, Texas Gulf Coast
- Univ. of Texas, Austin, (USA)
Sm-Nd model ages of sandstones and shales from the Oligocene Frio Formation of south Texas and the Paleocene-Eocene Wilcox Group of south-central Texas increase with increasing depth of burial. The sampling scheme employed minimizes, but does not eliminate, the possibility that these trends in depleted-mantle model ages (T{sub dm}) are due to detrital variability. Close correlation of these trends with diagenetic changes in the rock and evidence of rare earth element mobility preserved in the diagenetic products suggests that diagenesis has modified T{sub dm}. Diagenetic modification of T{sub dm} in Frio sandstone and Wilcox shale is due primarily to loss of radiogenic Nd, whereas increased {sup 147}Sm/{sup 144}Nd (Sm/Nd) produces elevated T{sub dm} in deeper Wilcox sandstones. The T{sub dm} of Frio shales does not change appreciably with depth, owing to the opposite effects on T{sub dm} of decreased Sm/Nd and decreased {epsilon}{sub Nd}(0). Loss of radiogenic Nd is due primarily to reactions involving unstable volcanic detritus, which is more abundant in Frio than in the Wilcox. Decreased Sm/Nd in authigenic illite, and consequent increased Sm/Nd in pore fluids, results in elevated T{sub dm} in Wilcox and Frio sandstones containing late-diagenetic cement, and in decreased Sm/Nd in deeper Frio shale. The similar T{sub dm} trends observed in both units, which have different detrital characteristics, suggest that modification of Sm-Nd model ages in siliciclastic rocks may be commonplace during burial diagensis.
- OSTI ID:
- 5611236
- Journal Information:
- Geology; (USA), Vol. 19:4; ISSN 0091-7613
- Country of Publication:
- United States
- Language:
- English
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Diagenetic resetting of Sm-Nd isotope systematics in Wilcox Group sandstones and shales, San Marcos Arch, south-central Texas
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Related Subjects
GEOLOGIC FORMATIONS
AGE ESTIMATION
GULF COAST
DEPTH
DIAGENESIS
EARTH MANTLE
GEOCHEMISTRY
ILLITE
MASS TRANSFER
MODIFICATIONS
NEODYMIUM 144
RARE EARTHS
RESERVOIR FLUIDS
SAMARIUM 147
SAMPLING
SANDSTONES
SEDIMENTARY BASINS
SHALES
TERTIARY PERIOD
TEXAS
VOLCANIC ROCKS
ALPHA DECAY RADIOISOTOPES
CENOZOIC ERA
CHEMISTRY
CLAYS
DEVELOPED COUNTRIES
DIMENSIONS
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION VI
FLUIDS
GEOLOGIC AGES
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOTOPES
METALS
NEODYMIUM ISOTOPES
NORTH AMERICA
NUCLEI
RADIOISOTOPES
RARE EARTH ISOTOPES
RARE EARTH NUCLEI
ROCKS
SAMARIUM ISOTOPES
SEDIMENTARY ROCKS
USA
YEARS LIVING RADIOISOTOPES
580000* - Geosciences