Anisotropy of magnetic susceptibility applied to diamictites of the Rio do Sul formation, Paraná basin: initial results

ANISOTROPY OF MAGNETIC SUSCEPTIBILITY APPLIED TO DIAMICTITES OF THE RIO DO SUL FORMATION, PARANÁ BASIN: INITIAL RESULTS

C

ARLOS J. ARCHANJO

¹, JOEL C. CASTRO

² and MARÍLIA R. CASTRO

¹

¹Instituto de Geociências, USP, São Paulo, SP.

²Instituto de Geociências e Ciências Exatas, UNESP, Rio Claro, SP.

Presented by ANTONIO C. ROCHA-CAMPOS

Massive diamictites interbedded with sandstones constitute the upper part of the Permo-Carboniferous Rio do Sul Formation (Itararé Group). These diamictites consist of dispersed centimeter to meter size clasts in a muddy to muddy-sandy matrix deposited in a subaqueous "rain-out'' glaciogenic environment. They frequently have transitional contacts with crudely stratified diamictites. These facies probably formed as a result of downslope resedimentation in areas of the basin receiving fine-grained sediments from suspension and sandy turbidites. The fabric patterns of diamictites from Rio do Sul Formation have been studied through anisotropy of magnetic susceptibility. A subhorizontal to weakly imbricate magnetic planar fabric, corresponding to bedding plane, appears in whole samples. The magnetic lineation occurs dispersed on the bedding or has a faint alignment generally to NW or SE directions. This fabric pattern is attributed to settling of sediments into a weak current on basin floor. Five stations have a well defined N- to NW-trending magnetic lineation, suggestive of a post-depositional alignement process. These rocks have weak susceptibility magnitudes (k < 0.2 x 10^-3 SI) and anisotropy degree. A strong paramagnetic contribution characterizes the hysteresis loop and no lattice transitions due to ferromagnetic fraction are observed in the susceptibility versus temperature variation diagrams. MEV investigations detected the presence of chlorite blades coating detrital grains or partially infilling the pore spaces. If these paramagnetic phyllosilicates controll the anisotropy of susceptibility, the magnetic fabric pattern of the diamictites has an important diagenetic contribution. (December 10, 1999)

Publication Dates

• Publication in this collection
  05 Jan 2001
• Date of issue
  Dec 2000