INVESTIGADORES
GOMEZ Fernando Javier
artículos
Título:
Paleoenvironmental and carbo-oxygen isotope record of Middle Cambrian carbonates (La Laja Formation) in the Argentine Precordillera
Autor/es:
GOMEZ, F.J., OGLE, N., ASTINI, R.A., Y KALIN, R.M
Revista:
JOURNAL OF SEDIMENTARY RESEARCH
Editorial:
Allen Press, Inc.
Referencias:
Lugar: Lawrence (Kansas, U.S.A.); Año: 2007 vol. 77
ISSN:
1073-130X
Resumen:
The La Laja Formation (Early to Middle Cambrian) is one of the oldest units exposed at the base of the lower
Paleozoic carbonate platform of the Argentina Precordillera. This is a key unit regarding the hypothesis of the Precordillera as
a Laurentia-derived allochthonous terrane currently located in the south-central Andes. According to the faunal affinity and
stratigraphic development of the thick Cambrian carbonate bank, the Argentine Precordillera would have been attached to
Laurentia. The La Laja Formation contrasts with the rest of the overlying units of the Cambro-Ordovician carbonate platform
by being partly mixed carbonates?siliciclastics. This dominantly shallow subtidal unit is internally arranged into several Grand
Cycles indicating a complex environmental mosaic, probably with local depocenters related to variable subsidence. This unit
records the stabilization of the rifted margin of the Precordillera terrane, prior to the broadening of the carbonate
sedimentation during the passive-margin drifting stage.
A high-resolution d13C and d18O isotope study, in concert with a detailed paleoenvironmental analysis, was carried out to
better understand both environmental and chronostratigraphic evolution of the La Laja Formation. Three d13C positive
excursions were recorded; the first one at the Glossopleura biozone within the Soldano Member, the second beginning at the
base of the Rivadavia Member, and the third during deposition of the Las Torres Member. Comparisons with other Middle
Cambrian curves, in the Precordillera and elsewhere (Rocky Mountains and Great Basin, U.S.A., the western Hunan Province
in south China, and the Amadeus, Georgina, and Daly basins in Australia) suggest a global control on these excursions.
Mechanisms to produce these positive excursions could be related to high bio-productivity and increased burial of Corg (organic
carbon) produced by high nutrient influx to the ocean associated with a relative sea-level fall. Local environmental controls
could have in part altered the original isotopic signal.