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]
Fragmented bioclastic wackestoneA Wackestone in thin section (width of image is 10 mm)
The identification of wackestoneEdit
Schematic wackestone as seen in thin section under the petrographic microscope. Type of carbonaceous rock according to the depositional texture: Alloctonous carbonates – Original components not bound at the deposition time. Less than 10% of components larger than sand size (> 2 mm) Contains carbonate mud (micrite, silt/clay size <63 μm) Fabric supported by carbonate mud (micrite, <63 μm) 10% or more composed of 63 μm or greater grains Legend: Dotted background: micritic matrix. Curved blue particles: bioclasts (indeterminate fossils, e.g. bivalve fragments). Blue cones: bioclasts (e.g. fossils of gastropods) Black spheroids: bioclasts (pellets).
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).
ReferencesEdit
^ abDunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: W.E. Ham (Ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir. American Association of Petroleum Geologists, Tulsa, Oklahoma, pp. 108–121.
^ abLokier, Stephen W.; Al Junaibi, Mariam (2016-12-01). "The petrographic description of carbonate facies: are we all speaking the same language?". Sedimentology. 63 (7): 1843–1885. doi:10.1111/sed.12293. ISSN 1365-3091.
^Embry, A.F. and Klovan, J.E., 1971. A Late Devonian reef tract on Northeastern Banks Island, NWT. Bulletin of Canadian Petroleum Geology, 19(4)), 730–781.
^Wright, V.P., 1992. A revised classification of limestones. Sedimentary Geology, 76(3–4), 177–185.
wackestone, under, dunham, classification, dunham, 1962, system, limestones, wackestone, defined, supported, carbonate, rock, that, contains, greater, than, grains, most, recently, this, definition, been, clarified, carbonate, dominated, rock, which, carbonate. 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 lt 63 mm component supports a fabric comprising 10 or more very fine sand grade 63 mm or larger grains but where less than 10 of the rock is formed of grains larger than sand grade gt 2 mm 2 Fragmented bioclastic wackestoneA Wackestone in thin section width of image is 10 mm The identification of wackestone Edit nbsp Schematic wackestone as seen in thin section under the petrographic microscope Type of carbonaceous rock according to the depositional texture Alloctonous carbonates Original components not bound at the deposition time Less than 10 of components larger than sand size gt 2 mm Contains carbonate mud micrite silt clay size lt 63 mm Fabric supported by carbonate mud micrite lt 63 mm 10 or more composed of 63 mm or greater grains Legend Dotted background micritic matrix Curved blue particles bioclasts indeterminate fossils e g bivalve fragments Blue cones bioclasts e g fossils of gastropods Black spheroids bioclasts pellets 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 lt 20 mm in diameter This definition was redefined by Embry amp Klovan 1971 3 to a grain size of less than or equal to 30 mm 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 mm References Edit a b Dunham R J 1962 Classification of carbonate rocks according to depositional texture In W E Ham Ed Classification of Carbonate Rocks American Association of Petroleum Geologists Memoir American Association of Petroleum Geologists Tulsa Oklahoma pp 108 121 a b Lokier Stephen W Al Junaibi Mariam 2016 12 01 The petrographic description of carbonate facies are we all speaking the same language Sedimentology 63 7 1843 1885 doi 10 1111 sed 12293 ISSN 1365 3091 Embry A F and Klovan J E 1971 A Late Devonian reef tract on Northeastern Banks Island NWT Bulletin of Canadian Petroleum Geology 19 4 730 781 Wright V P 1992 A revised classification of limestones Sedimentary Geology 76 3 4 177 185 External links Edithttp strata geol sc edu thinsections Carbonate glossary html nbsp This article related to petrology is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Wackestone amp oldid 1159206961, wikipedia, wiki, book, books, library,
