Review
of the Argentine Precordillera Cambrian System
BORDONARO, O.
The Cambrian rocks of the Argentine
Precordillera are analyzed in space and time getting a new interpretation of
the precordilleran continental margin. The lithostratigraphy and
biostratigraphy are placed in a nonpalinspastic paleogeographic model
according with the structural distribution of the Precambrian rocks. In the
later Early Cambrian there started an open carbonate platform with located
preceding siliciclastic and evaporites of the intracontinental graben system
or sinrift. A rimmed platform with lagoons and marginal terrigenous or
coastal sabkha facies developed in the Middle Cambrian. While shoals or
sand-oolitic barriers were as built at the west margin of the shelf, evolving
seaward with an open subtidal platform. During the Late Cambrian a broad
peritidal platform prograded to the west in the basin, bounded by sand
barriers or tidal islands mainly in the southern areas, the northern areas
remaining more or less restricted. In the Cambrian-Ordovician boundary a new
rimmed platform was established but the platform margin retreated to the
east as a flooding event.
The structural colapse of the carbonate
platform began in the latest Cambrian, first in the southern areas and then
in the Early Ordovician in the western Precordillera producing a
tectonically active olistostromic slope.
The Precambrian outcrops in the western
Pampeanas Range, interpreted as the Cambrian basin basement, are responsible
for the distribution and facies changes in the paleogeographic evolution of
the basin.
The
biostratigraphic scheme based on trilobites is separated into a restricted
shelf biozones to the East, characterized by sparse, endemic and low diversity
polymeroid faunules. To the West an outer open shelf biozones is characterized
by abundant, high diversity, mixed endemic and cosmopolitan polymeroid and
agnostoid faunas. The lithostratigraphic and biostrastratigraphic analysis
allow