Standardizing Texture and Facies Codes for A Process-Based Classification of Clastic Sediment and Rock

TLDR

Clastic sediment is defined as any eroded, transported, and deposited particle regardless of composition, and hydrofacies codes act as nondirectional permeability indicators for aquifer or reservoir potential. The authors propose a universally applicable, texturally based classification of clastic sediment that modifies Folk’s system with new assumptions and broader textural fields to be independent of composition, cementation, and geologic environment. The revised classification employs ternary diagrams with additional gravel, sand, and mud textural fields, ensures all end members are represented with volumetric estimates summing to 100%, and extends Folk’s fine‑grained diagram to maintain consistency across all size fractions. These modifications provide a basis for standardized vertical texture displays in graphic logs and lithofacies codes, ensuring that process sedimentology principles are consistently applied across compositionally variable rock sequences.

Abstract

Abstract Proposed here is a universally applicable, texturally based classification of clastic sediment that is independent from composition, cementation, and geologic environment, is closely allied to process sedimentology, and applies to all compartments in the source-to-sink system. The classification is contingent on defining the term “clastic” so that it is independent from composition or origin and includes any particles or grains that are subject to erosion, transportation, and deposition. Modifications to Folk’s (1980) texturally based classification that include applying new assumptions and defining a broader array of textural fields are proposed to accommodate this. The revised ternary diagrams include additional textural fields that better define poorly sorted and coarse-grained deposits, so that all end members (gravel, sand, and mud size fractions) are included in textural codes. Revised textural fields, or classes, are based on a strict adherence to volumetric estimates of percentages of gravel, sand, and mud size grain populations, which by definition must sum to 100%. The new classification ensures that descriptors are applied consistently to all end members in the ternary diagram (gravel, sand, and mud) according to several rules, and that none of the end members are ignored. These modifications provide bases for standardizing vertical displays of texture in graphic logs, lithofacies codes, and their derivatives—hydrofacies. Hydrofacies codes are nondirectional permeability indicators that predict aquifer or reservoir potential. Folk’s (1980) ternary diagram for fine-grained clastic sediments (sand, silt, and clay size fractions) is also revised to preserve consistency with the revised diagram for gravel, sand, and mud. Standardizing texture ensures that the principles of process sedimentology are consistently applied to compositionally variable rock sequences, such as mixed carbonate–siliciclastic ramp settings, and the extreme ends of depositional systems.