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Micritization of crinoids by diagenetic dissolution
Author(s) -
NEUGEBAUER JOACHIM
Publication year - 1978
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1978.tb00312.x
Subject(s) - micrite , diagenesis , calcite , crinoid , geology , cementation (geology) , dissolution , bioerosion , sediment , mineralogy , arenite , geochemistry , sedimentary rock , paleontology , cement , clastic rock , chemistry , oceanography , materials science , composite material , coral , facies , structural basin
Bands within the Chalk of Kansas made up of masses of Uintacrinus socialis show an unusual preservation of crinoid ossicles: in contrast to their normal preservation in full relief as single large calcite crystals the ossicles are compressed and transformed to micrite. The micrite originated by a process different from the well‐known micritization by algal and fungal borings and subsequent cementation of the borings: it is the outcome of partial dissolution. Dissolution proceeded inside the sediment and preferentially attacked the echinoderms as the most soluble calcareous component of the chalk sediment. Later, the remains of the Uintacrinus crystals preferentially attracted syntaxial cement so that the layer changed to a hard band of limestone within the soft chalk. In addition to a second process of micritization the preservation of Uintacrinus demonstrates (1) that the magnesium content of magnesian calcites survives the earliest stages of diagenesis within chalk, and (2) that a diagenetic comminution of large crystals (in an optical sense) to smaller ones is possible. Provided the ossicles of echinoderms are true single crystals (the knowledge in this field is summarized), this is an example of the often discussed ‘crystal diminution’.