From sand rich to mixed sand-mud ramp deep-water system: a conceptual model for the apiuna succession (Cambrian, Itajaí valley, Brazil)

FROM SAND RICH TO MIXED SAND-MUD RAMP DEEP-WATER SYSTEM: A CONCEPTUAL MODEL FOR THE APIUNA SUCCESSION (CAMBRIAN, ITAJAÍ VALLEY, BRAZIL) ^*

GIORGIO BASÍLICI

Instituto de Geociências, UNICAMP, Campinas, SP.

Presented by ANTONIO C. ROCHA-CAMPOS

The Apiúna succession is one of the best-exposed deep-water deposits in Brazil. Deep-water deposits represent 88.6% of the oil reserves in Brazil and their study is, therefore, of great importance for the oil industry. This work proposes a new depositional and geometric interpretation of the Apiuna succession, based on a very detailed facies analysis (scale perception < 3 cm of thickness) and on currently circulating scientific ideas on deep-water sediments.

Alongside road BR-470 (in the central-eastern Sate of Santa Catarina), 209 m thick of deep-water deposits were examined. Four informal stratigraphic units, from A at bottom to D to the top, are recognized. Unit A records a slightly inclined slope made up of sand-starved silty argillites and twisted muddy strata. Unit B consists of sandstone strata, 4-100 cm thick, alternating with silty argillites, abruptly overlying unit A. Unit C comprises amalgamated sandstones, 25-180 cm thick. The sandstone strata in unit B and C have a sheet shape. In unit C the sandstones are massive and coarser, while those in unit B have frequent cross-laminated at the top. Sandstone sheets were mainly deposited by sandy debris flows; depositional flows were bipartite: debris flows deposits were reworked at the top by turbidity currents. Absence of vertical organization of the B and C unit sandstone suggests a multisource sandy input. Units C and B represent a distal and proximal part of a sandy-rich ramp setting respectively. Unit D is a coarsening and thinning upward sequence, going from erosively based conglomeratic sandstones to lenticular sandstones alternated with silty-argillites. It represents an erosive depression fill passing upward to levee sediments within a mixed sand-mud ramp.

In conclusion the depositional environment of the Apiúna succession changes from sand-starved muddy slope (unit A), to irregular sandy-sheet built ramp (unit B and C) and channel-levee of sand-mud ramp (unit D) caused complicated depositional architectures. Tectonically induced morphological variations may have controlled the environmental modifications. — ( December 8, 2000 )

Publication Dates

• Publication in this collection
  05 Oct 2001
• Date of issue
  Sept 2001