A revised textural classification of gravel-free muddy sediments on the basis of ternary diagrams

A revised textural classification of gravel-free muddy sediments based on t he adaptation, modification and expansion of previous schemes using ternary plots is presented. The new approach increases the range of application an d the environmental sensitivity of textural sediment classification. In the case of simple two-component sand/mud mixtures, six sediment types based o n mud (silt + clay) or sand content are distinguished: sand (<5% mud), slig htly muddy sand (5-25% mud), muddy sand (25-50% mud), sandy mud (50-75% mud ), slightly sandy mud (75-95% mud), and mud (>95% mud). The class names acc urately describe a sediment within defined textural limits, and the scheme can thus be used to divide a depositional environment into textural sub-env ironments or facies. By diagonally subdividing the two-component system, a more complex three-component classification scheme based on sand/silt/clay ratios has been generated. In this scheme, 25 sediment classes are distingu ished, each defined by a generic name and a letter-number code. It not only allows a more detailed textural subdivision of sedimentary environments th an the two-component system, but also incorporates a genetic element by dis tinguishing between different hydrodynamic regimes. Thus, sandier and more silty sediments, reflecting deposition under higher energy conditions, are progressively segregated from muddier and more clayey sediments which refle ct deposition under lower energy conditions. This is illustrated with examp les from a Variety of intertidal and open shelf environments. In addition, the letter-number codes can be used to label sediment facies maps, annotate stratigraphic sections and structure data banks. The two classification sc hemes are complementary, offering two levels of resolution and fulfilling t he basic requirements of practicality, ease of use and global applicability . (C) 2000 Elsevier Science Ltd. All rights reserved.