Original paper

Morphology, internal structure and chemical composition of oxidized pyrite framboids from sediments of Lake Baikal, Siberia

Sapota, Tomasz

Abstract

Scanning electron microscopy together with energy dispersive spectroscopy and electron microprobe analyses were used to study texture and chemical composition of oxidized pyrite framboids found in silty-clay horizons within the hemipelagic facies (upper ≈280 m) of 600-m-long BDP-98 sediment section from Lake Baikal. Since the framboids are sometimes extensively oxidized and loose their framboidal texture, they are often called herein with a general term "microspheroids". The microspheroids are usually 10 – 30 μm in diameter, although some reach 60 μm, and occur in clusters up to 2 mm large. Some of the microspheroids display framboidal textures on the surface while others are strongly oxidized and coated with goethite crusts. Gypsum crystals are often associated with the goethite-coated type of the microspheroids. Size distribution of the preserved pyrite framboids suggests diagenetic formation in anoxic zone of the sediment under the well oxygenated water column. The exceptionally large framboids suggest a low sedimentation rate at the cored site during glacial periods. Oxidation of the pyrite framboids can be related to diagenesis, which was associated with microbial activity and presence of oxidizing agents.

Keywords

lake baikalframboidal pyritepyrite oxidationgoethitegypsumlake sediments