Packstones and floatstones: Ambiguous textures and origins in need of critical appraisal

The depositional textural classification of allochthonous limestones by Dunham (1962) and its modifications by Embry III and Klovan (1971) are widely used by carbonate petrologists during petrographic, field studies and core examinations. The origin and textures of packstones and floatstones used in this classification scheme need re-appraisal towards their unified and unequivocal usage by carbonate petrologists in academia and the petroleum industry. Such usage will help avoiding inadequate interpretations of the depositional, sequence stratigraphic or reservoir-quality distribution models. Based on examination of Jurassic, Cretaceous and Holocene carbonate deposits from United Arab Emirates and Oman, it is suggested here that packstones should not be used to interpret energy of depositional environments because the majority are originally deposited as grainstones (i.e. free of mud matrix). Thus, sand and mud sized particles are expected to be hydraulically separated, i.e. not deposited simultaneously. Therefore, packstones might be originally grainstones that have incorporated variable amounts of mud matrix by various post-depositional processes, primarily bioturbation and/or compaction deformation of peloids (known as pseudomatrix; Dickinson, 1970). We further observed that the >2 mm allochems in floatstones float in grainstones and packstones and not in mud/wackestone matrix. •Petrographic examinations of Jurassic, Cretaceous and Holocene platform limestones suggest instead that mud matrix in packstones and floatstones is not depositional in origin.•Floatstones are limestones which the > 2 mm allochem are initially floating in co-deposited grainstone matrix and not in mud/wackestone matrix.•Grainstones are converted diagenetically into packstones by the incorporation of mud matrix by bioturbation and pseudoplastic deformation of peloids.•Inaccurate description of these limestone textures may result in misinterpretation of energy of depositional environments and inadequate evaluation of reservoir properties of the limestones.