Packstone






A Packstone: grain supported by small grains (width of picture is 7mm)


Under the Dunham classification (Dunham, 1962[1]) system of limestones, a packstone is defined as a grain-supported carbonate rock that contains 1% or more mud-grade fraction. This definition has been clarified by Lokier and Al Junaibi (2016)[2] as a carbonate-dominated lithology containing carbonate mud (<63 μm) in a fabric supported by a sand grade (63 μm to 2 mm) grain-size fraction and where less than 10% of the volume consists of grains >2 mm'.



The identification of packstone




Thin section photomicrograph of peloid packstone with fragmented bioclasts.


A study of the adoption and use of carbonate classification systems by Lokier and Al Junaibi (2016)[2] identified three common problems encountered when describing a packstone:



  • Failure to identify the fabric as supported by the sand grade grain-size fraction - resulting in misidentification as wackestone.

  • Packstones with very small volumes of carbonate mud may be misclassified as grainstone.

  • Incorrectly estimating the volume of the component grains >2 mm.



References




  1. ^ 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.


  2. ^ ab 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..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}








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