Not avilable.

Author(s)

Leandro Menezes Donatti

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Geociências (IG/BT)
• Defense date: 2002-08-14

Examining board members

Paulo César Fonseca Giannini; Claudio Riccomini

• Advisor: Paulo César Fonseca Giannini

Abstract

The sandstones of the succession Pirambóia - Botucatu - Serra Geral (Paleozoic-Mesozoic Paraná Basin, Southeastern Brazil), in the Paraná State, was subdivided into four facies associations. From the base for the top, these associations correspond to: A) Sand sheets on tidal plain, B) Coastal dunefields with flooded interdunes, C) Alluvial plain with braided rivers and small eolian dunes, and D) Dry dunefields. The first three associations record a wet eolian depositional system (that is, a system whose freatic level was close to the surface), the Pirambóia system. The high freatic level in this system can be attributed to the proximity of the paleocost. The fourth facies association, of dry dunefields, is put abruptly upon to the Pirambóia fluvio-eolian deposits. It corresponds to the Botucatu dry eolian depositional system. The contrast between the Pirambóia (wet) and Botucatu (dry) eolian systems is an important criterion to define the regional unconformity that separates the sandstones of these two systems. The dry system would have been interrupted by a surface of bacinal extensional, associated with the manifestation of the Serra Geral volcanism. The grain-size results confirm the coarse to conglomeratic sandstone facies (ACg) as the main feature of the superior half of the Pirambóia system. The petrographic, SEM/EDS and heavy minerals results characterize the tendence for greater chemical maturity and cementation degree of the Botucatu sandstones. The abundance of smectite cement in the sandstones of the two systems is an indication of eodiagenesis with scarcy circulating water. Iron oxides, present mainly in the Botucatu sandstones, can be related to cementation in the vadose zone, therefore in conditions of low freatic level. The poligorskite presence in subaqueous facies of the top of the Pirambóia sandstones indicates that evaporitic conditions were already present in the end of wet eolian system. The tectonic conditions would not have stayed constant, losing, in the installation of the system Botucatu, the activity degree demonstrated in the ending of the Pirambóia system. The geographical distribution of the facies and of the modal dip directions of eolian cross-beddings allow to interpret the existence of two eolian influxes in the Pirambóia system, a continental influx, from North, and a coastal one, from South. The convergence of these paleowind directions could be associated with the existence of a high area along the Guapiara alignment. The Botucatu system would have been dominated by influ7x towards SW and SE, with increasing dispersion to the top. (AU)