Thin section photomicrograph of Orbitolinid foraminifera floatstone with a fragmented bioclast packstone matrix, plane polarised lightA Floatstone: few, but relatively large components in micritic matrix (width of picture is 20 mm)
The original Dunham classification (Dunham, 1962) of limestones did not consider the separate classification of coarse grained carbonate lithologies. In an attempt to rectify this, Embry & Klovan (1971) introduced the terms rudstone (grain supported) and floatstone (matrix supported) for coarse-grained allochthonous limestones. This definition of a floatstone was most recently clarified as "a carbonate-dominated rock where more than 10% of the volume is grains larger than 2 mm and the fabric is supported by the component that is 2 mm and smaller".
References
↑Dunham, R.J. (1962) Classification of carbonate rocks according to depositional texture. In: Classification of Carbonate Rocks (Ed. W.E. Ham), Am. Assoc. Pet. Geol. Mem., 1, 108–121.
↑Embry, A.F. and Klovan, J.E. (1971) A Late Devonian reef tract on Northeastern Banks Island, NWT. Bull. Can. Pet. Geol., 19, 730–781.