Abstract Mudrock is a major category of fine-grained sedimentary rocks,and there have been different understandings of its definition and classification in China,resulting in much confusion for academic research. This paper reviews the evolution of mudrock-related concepts and definitions in the development of sedimentology at home and abroad and attempts to provide a practical classification system for mudrock. Scholars in European and American tend to use the term “mudrock”, which refers to fine-grained terrestrial clastic rocks with a grain size less than 0.063 mm,including siltstone(two-thirds or more silt content),mudstone(neither silt nor clay content greater than two-thirds)and claystone(more than two-thirds clay content),in which the laminated rock is called shale. However, scholars in the former Soviet Union tend to use the term “глинистые породы” (argillaceous rock) to refer to sedimentary rocks containing more than 50% of clay minerals,in which the fissile rock is called shale. There are essentially two classification schemes for mudrock and other fine-grained sedimentary rocks,classified by texture(grain size),composition and sedimentary structure. One is a multi-element comprehensive rock classification,and the other is an end-members diagrammatic classification. We recommend the term “mudrock”as a general name for the fine-grained terrestrial sedimentary rocks consisting mainly of silt-sized(0.004-0.063 mm)and clay-sized(less than 0.004 mm)clasts. A triangular prism diagram classification method is adopted to classify fine-grained sedimentary rocks into fine-grained terrestrial sedimentary rock(i.e. mudrock)and fine-grained endogenous sedimentary rock,based on three end-elements of detrital minerals(mainly felsic detrital minerals),clay minerals and other endogenous minerals. Mudrock is further classified into three subgroups of siltstone,mudstone and claystone,or “-shale” if laminations or fissility are developed. Taking the TOC contents of 0.5% and 2% as the dividing points,fine-grained sedimentary rocks are classified into organic-poor,organic-bearing,and organic-rich ones. It is expected that this classification scheme will contribut to the mudrock classification.
Fund:Shanxi Province Science and Technology Plan Unveiled Bidding Project(No.20201101004),Surface Project of the National Natural Science Foundation of China(No.41572090),Yueqi Scholars Class A grant of China University of Mining and Technology(Beijing)
About author: SHAO Longyi,born in 1964,is a professor and doctoral supervisor at the College of Geoscience and Surveying Engineering of China University of Mining and Technology(Beijing)with a doctorate degree in engineering. He is mainly engaged in teaching and research on sedimentology and coal geology. E-mail: ShaoL@cumtb.edu.cn.
Cite this article:
SHAO Longyi,ZHANG Tianchang. Discussion on definition and classification of mudrock[J]. JOPC, 2023, 25(4): 742-751.
SHAO Longyi,ZHANG Tianchang. Discussion on definition and classification of mudrock[J]. JOPC, 2023, 25(4): 742-751.
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