Mechanism of cementation in beachrocks based on petrographic and geochemical evidence

MECHANISM OF CEMENTATION IN BEACHROCKS BASED ON PETROGRAPHIC AND GEOCHEMICAL EVIDENCE

NUBIA S. CHAVES

NEG-LABISE, UFPE, C.P. 7852, 50732-970 Recife, PE, Brazil

Presented by ALCIDES N. SIAL

Sedimentologic study and geochemical analyses were carried out on carbonate beachrocks samples from the littoral of the state of Pernambuco. Framework detrital composition is siliciclastic and cemented by calcite and/or aragonite. Three stages of cementation have been identified. The first corresponds to micritic envelope; the second to a circular fringe; and the third to a cryptocrystalline cement filling pores. C values vary between +3.6 º/oo_(PDB) and -2.0 º/oo_(PDB) and O values between +1.3 º/oo_(PDB) and -2.1 º/oo_(PDB). C values and diagenesis features suggest what type of cementation occurred in meteoric-vadose and/or marine-phreatic by loss of CO₂ (evaporation) the interstitial water. The interaction of the carbonated fluid in subsuperficie led to a discontinuous beachrock formation. The elevation of the mean sea level caused the deposition of new sediments, that once cemented, completed the preexisting base of the beachrocks, or created a new one, explaining the variable lengths of these rocks on the littoral. — ( May 18, 2001 )

Publication Dates

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