Berthierine-rich ooidal ironstone from the Late Palaeocene-Middle Eocene Subathu Formation, Dogadda area, NW Himalaya and its stratigraphic significance.

Berthierine-rich ooidal ironstone occurs within carbonaceous shale in the lower part of the Late Palaeocene-Middle Eocene Subathu Formation in Dogadda, Uttarakhand Himalaya. Berthierine/chamosite occurs both as ooids and as matrix. Ooids are spherical with 1-2 mm diameter and have concentric layer structure around a nucleus. Quartz is coarse-grained and occurs as embayed grains. Carbonate phase is absent in the ooids. Berthierine and chamosite assemblage indicates a temperature of ∼130-160°C of burial diagenesis for Dogadda ironstone. The lithological association, distinct mineralogy and texture suggest that the mineralogy of the Dogadda ooidal ironstone is in situ, formed in a shallow-marine environment under conditions of low net sediment accumulation. Dogadda ooidal ironstones, along with coeval ash beds in the foreland basin are useful in stratigraphic correlation. [ABSTRACT FROM AUTHOR]