The aeolian calcarenites of the Fernando de Noronha Island, Northeastern Brazil - a new approach

THE AEOLIAN CALCARENITES OF THE FERNANDO DE NORONHA ISLAND, NORTHEASTERN BRAZIL - A NEW APPROACH

ELDEMAR A. MENOR¹, LUCIA M. M. VALENÇA², VIRGINIO H. NEUMANN²AND ARMAND BOUJO³

¹Departamento de Engenharia de Minas, Universidade Federal de Pernambuco, 50732-970 Recife, PE

²Departamento de Geologia, Universidade Federal de Pernambuco, 50732-970 Recife, PE

³Instituto de Geociências, Universidade de São Paulo, São Paulo.

Presented by ALCIDES N. SIAL

A new approach of the quaternary ''aeolian sandstones'' from Fernando de Noronha Island (FN) is presented on the basis of field observations, mineralogical and geochemical investigations, and whole rock radiocarbon data.

Two different calcarenite facies were distinguished in the meridional FN's coast, representing at least two different stages of aeolian dune formation followed by diagenesis. The oldest one includes calcarenites preserved in the summit places of the FN cliff border mainly, at 15 to 50m over the present mean sea level (PMSL). Typical large-scale cross-bedded units with internal high angle stratification characterize the sedimentary rocks that include low contents of silicates plus heavy minerals ( < 3%). The radiocarbon dating range between 42,000 to 28,000 years BP as minimum ages.

The new one is represented by the ''Tamandaré'' calcarenites, whose outcrops lie 10 to 15m over the PMSL, and include small-scale cross-bedded units with internal low angle stratification. No negligible quantities of mafic silicates plus heavy minerals (5-15%) characterize its composition. The radiocarbon dating range between 10,500 to 9,500 years BP as minimum ages.

The sub-actual dunes areas, including that which overlies the Tamandaré calcarenites, represent a last stage. The sedimentary characteristics and geographical setting suggest 10,000 to 6,000 years BP for these deposits, in agreement to a worldwide period of dune landward migration.

The general results confirm that large aeolian dune field usually were developed in the last glacial stage of the Quaternary, when extensive sand beaches surfaces were exposed to the wind by a gradual and strong sea level dropping. The calcarenite records and the sub-actual dunes both exclusively observed at the meridional FN's coast are in agreement to the predominant quaternary wind directions. The studied outcrops are the diagenetic relicts of a large and continuous aeolian dune field formed over the actual meridional FN's platform at the Würm glacial stage. — ( May 18, 2001 )

Publication Dates

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