Milliken’s (2014) classification scheme for fine-grained sediments and sedimentary rocks is an attempt to provide an improved classification that relies on interpreted grain origin to replace existing nomenclature schemes based on sedimentary structures, grain size, and composition. Milliken posits that existing terminology is confusing and therefore proposes new terms, viz. tarl, carl, and sarl, to define three main types of mudstone categories. We consider the proposed classification impracticable because there are: (a) ambiguities associated with interpreting grain origins (intrabasinal or extrabasinal), (b) difficulties in determining the original mineralogy of diagenetically altered particles, and (c) requirements for specialized equipment and techniques not widely available to many geologists. In our opinion, the proposed classification does not improve geological understanding over prior established classification approaches.

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