Under the Dunham classification (Dunham, 1962[1]) system of limestones, a wackestone is defined as a mud-supported carbonate rock that contains greater than 10% grains. Most recently, this definition has been clarified as a carbonate-dominated rock in which the carbonate mud (<63 μm) component supports a fabric comprising 10% or more very fine-sand grade (63 μm) or larger grains but where less than 10% of the rock is formed of grains larger than sand grade (>2 mm).[2]
The identification of wackestone
A study of the adoption and use of carbonate classification systems by Lokier and Al Junaibi (2016)[2] highlighted that the most common problem encountered when describing a wackestone is to incorrectly estimate the volume of 'grains' in the sample – in consequence, misidentifying wackestone as mudstone or vice versa. The original Dunham classification (1962)[1] defined the matrix as clay and fine-silt size sediment <20 μm in diameter. This definition was redefined by Embry & Klovan (1971)[3] to a grain size of less than or equal to 30 μm. Wright (1992)[4] proposed a further increase to the upper limit for the matrix size in order to bring it into line with the upper limit for silt (62 μm).