High-resolution transmission electron microscopy study of newly formed sediments in the Atlantis II Deep, Red Sea

Iron and silicon in various proportions are the major components of the new ly formed hydrothermal sediments in the Atlantis II Deep. Red Sea. Iron-ric h 2:1 phyllosilicates with morphologies varying from ribbons to plates repr esent clays in initial formation stage. Well-crystallized goethite particle s contain domains of hundreds of nanometers in length with the rare presenc e of dislocations, Molar compositions show ratios of Si/Fe = 0.12 and Al/Fe = 0.05. Euhedral feroxyhyte with curled edges forms clusters with the goet hite. The feroxyhyte has ratios of Si/Fe = 0.3 and are the major Si-associa ted iron oxides. Two nanometer-size phases showing short range periodity ar e common in the newly formed Atlantis II sediments: (I) hematite with trace s of Si and (2) ferrihydrite with Si/Fe molar ratios varying between 0.17-0 .89. The ferrihydrite forms large clusters. Hematite appears also as well-c rystallized large crystals. Feroxyhyte probably forms at the transition zon e between Red Sea Deep Water and the upper convective layer in the brine. w hereas goethite and ferrihydrite form in the upper convective layer. The tw o forms of hematite represent two stages of recrystallization, which occur within the brine.