Hi Eoin
Check the attached tgd illustrating how you get the Distribution shader to er distribute the strata.
Some settings to note: Distribution Shader coverage 0.5, Fractal Breakup 1.
In the Fractal Breakup power fractal check my Scale and Colour settings. Note no warping applied, and Buoyancy of Variation set to 0 to keep the black/white (strata/no-strata) shading from being distorted.
Hope this helps.
John