INVESTIGADORES
BRESSAN Graciela Susana
artículos
Título:
Diagenesis of a bioclastic oyster deposit from the Lower Cretaceous (Chachao Formation). Neuquén Basin. Mendoza Province, Argentina
Autor/es:
PALMA, RICARDO M.; BRESSAN, GRACIELA S.; KIETZMANN, DIEGO A.
Revista:
CARBONATES AND EVAPORITES
Referencias:
Año: 2008 p. 39 - 49
ISSN:
0891-2556
Resumen:
ABSTRACT: The Lower Cretaceous Chachao Formation in the Malargüe
anticline area consists of wackestone, packstone, and minor grainstone and
mudstone rich in benthonic fauna that were deposited in a carbonate ramp. The
carbonate diagenesis in the Valanginian Chachao Formation contains many
processes with conspicuous effects, including micritization, dissolution, neomorphism, and cementation. The early
diagenetic process is characterized by micritization, dissolution and
mineralogic stabilization of components, and earlier cement phase represented
by micrite cement and isopachous calcite cement, which have petrographic
characteristics consistent with precipitation in a marine-phreatic diagenetic
environment. Later diagenetic phenomena
include granular calcite and syntaxial cement. Both of cement types are interpreted as typical of a meteoric-phreatic
environment. Concentriczoning pattern of alternating dull, and blotchy-
to bright luminescent zones is
interpreted as being caused by a decrease in redox potential (Eh), under
conditions of a progressive marine burial meteoric-phreatic diagenetic
environment. Geochemical data (Sr++,
Na+, Mg++, Fe++, Mn++) and SEM
features of the micrite suggest that original calcareous mud could have been
calcite dominated (CDP). The δ18O
composition of the granular calcite cement ranging from 2.84%0 to 4.27%0
PDB and the δ13C values of the cement between 2.46%0 and 3.50%0 PDB
are compatible with precipitation from a fluid that evolved meteoric-phreatic
composition. The high depleted δ18O values of the Gryphaea shells can be related to the
dilution of the marine water with a fresh water influx, whereas shells with the
heaviest δ13C isotopic
compositions are probably related to the original marine signal, which suggest
a closed diagenetic system for carbon.