Paleo-Environmental
Evolution of an Extensional Cretaceous Continental Sequence, Northern Precordillera, Central Argentine Andes
Reijenstein, Hernan
M.1 (1) University of Houston, Houston, TX
Sedimentation in extensional basins
characterized the early Mesozoic tectono-stratigraphic
framework along the central and western margin of South America. Triassic Rift deposits
of the Cuyo Basin have been widely
studied in contrast to the Cretaceous sequences, which were thought to be
missing in the Northern Precordillera. Recent biostratigraphic information helped to define the presence
of a new Cretaceous unit, the Cienaga del Rio Huaco Formation (Maastrichtian).
This study is based on information gathered from field data, rock sampling, lab
work, and sandstone petrographic descriptions. Dickinson's provenance
discrimination diagrams were used to investigate sandstone composition and
possible source areas. Most of the sampled sandstones showed a combined Magmatic Arc and Recycled Orogen
provenance, suggesting a possible source from the widely distributed Permo-Triassic vulcanites and
Paleozoic metamorphic rocks of the Central Argentine Andes region. A detailed
180 meters-thick sedimentary section of the Cretaceous Cienaga
del Rio Huaco Formation shows the evolving stages of a rift related sedimentation. The first stage is represented
by a 25 meters-thick, fining upwards coarse-grained conglomerates and
sandstones unit overlaying an unconformity. This succession is overlain by at
least a hundred meters of laterally continuous strata composed of sandstones,
shale, and gypsum, capped by 30 meters of fine laminated red shale. Different paleo-environments were interpreted along this sequence.
The basal unit was deposited in a high-energy braided fluvial system composed
of conglomerates and inter-layered coarse-grained sandstones, which gradually
evolved into a finer grained meandering system. This event derived into an
ephemeral lacustrine-fluvial depositional system with
variations in the position of the shoreline.