Boron and lithium isotopic signatures of nanometer-sized smectite-rich mixed-layers of bentonite beds from Campos Basin (Brazil)

Norbert Clauer, Lynda B. Williams, I. Tonguç Uysal

Research output: Contribution to journalArticlepeer-review

Abstract

Boron and lithium were analyzed in three nanometer-sized (<20, 20-50 and 50-100 nm) separates of two Santonian (85.8-83.5 Ma) bentonite samples collected closely in the Campos Basin along the southeastern Atlantic coast (Brazil). The B and Li data give various trends that suggest varied crystallization conditions for separates that consist of overwhelming smectite with less than 9% illitic layers. The δ11B of the few illitic tetrahedral sites from one of the samples remains quite constant, while its contents are strictly correlated with those of K, which suggests that illitization proceeded by interaction with pore fluids of the host sediments that supplied the K. In the second sample, the δ11B of the illite layers from the two coarser fractions is indicative of an early volcanic origin, while the smaller size fraction also interacted with sedimentary fluids. Favored by octahedral substitutions of the smectite layers, the δ7Li is more strictly regulated by a volcanic link. In turn, the information of the B and Li isotopic compositions and contents from studied mixed-layers suggests a various origin for the few illite layers of the smectite-rich I-S that contain more B than the smectite layers that host more Li. The difference appears to be sample-site and crystal-size dependent, fueled by pore fluids of the hosting turbidites.

Original languageEnglish (US)
Pages (from-to)72-83
Number of pages12
JournalClays and Clay Minerals
Volume70
Issue number1
DOIs
StatePublished - Feb 2022
Externally publishedYes

Keywords

  • bentonite beds
  • Campos Basin (Rio de Janeiro State, Brazil)
  • nanometer-sized fractions
  • smectite and illite authigenesis
  • smectite-rich size separates
  • δB and δLi signatures

ASJC Scopus subject areas

  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)

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