CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
A Neoproterozoic paleokarstic surface in the upper Villa M´onica Formation, Tandilia System, Argentina: preliminary constraints on its origin and diagenesis
Autor/es:
LUCÍA E. GÓMEZ PERAL, DANIEL G. POIRÉ, ALCIDES N. SIAL, Y MARIA JULIA ARROUY
Lugar:
San Pablo
Reunión:
Congreso; 6th Latin American Congress of Sedimentology; 2013
Institución organizadora:
University of Sao Paulo, Brazil
Resumen:
The Neoproterozoic sedimentary successions of the Tandilia Basin are constituted by a
wide range of sedimentary rocks. We analyse the upper section of the Villa M´onica Formation
constituted almost entirely by dolostones. C-isotope pathways and mudstones with
dropstones, just below the dolostones, suggest this succession is a probable cap carbonate.
Therefore, the model of its diagenetic evolution is consistent with trends of primary marine
origin. The age of this unit is still under debate, but stromatolites, Sr isotope data and δ13C
curve suggest Cryogenian age. An uplift registered on top of the formation is related to period
of intense erosion and weathering with generation of a karstic surface over the dolostones as a
telodiagenetic surface. This important unconformity was situated, from palaeomagnetic studies,
in 595 Ma and is characterized by dedolomitization, intense dissolution and precipitation
if iron oxide minerals, chert and calcite. Siliceous cementation and replacement have probably
occurred when pH dropped during sub-aerial exposure associated to sea-level fall of uncertain
relation with glaciations. This surface constitutes the contact between Villa M´onica and
Colombo formations, representing an extensive period of erosion, and called Piedra Amarilla
surface. A few meters below, further evolution of the dissolution processes developed a paleokarstic
subsurface recognized by presence of up to 3 m caverns filled by weathered dolomite.
C-O isotope data in this level are typical of meteoric fluids interaction showing lower with
respect to unaltered dolostone, δ13C varying from -0.45 to -1.87and δ18O VPDB from -6.16
to -10.25