This is a view looking down on a bedding surface in sandstone. The dark, elongate objects are concretions formed mainly of siderite (ferrous carbonate). They appear to have formed around roots in a palaeosol below a coal seam, and are termed rhizocretions. Some define originally horizontal roots parallel to the bedding surface; others represent shorter vertical roots.
What does the presence of siderite indicate about the chemical environment in the sediment at the time the concretions were formed?
|image credit: Roger Suthren. Coal Measures, Upper Carboniferous, Amroth, S Wales|
-- images of sediments and sedimentary rocks at virtual-geology.info
This page is maintained by Roger Suthren. Last updated 1 April, 2013 22:31