Revised Ichnopedofabric Indices That Semiquantitatively Analyzes the Degree of Pedogenic Modification: Recognizing the Effects of Subaerial Exposure on Continental and Marine Deposits

The field classification of ichnofabric (Droser and Bottjer 1986) streamlined communication between geologists concerning the degree of bioturbation observed in outcrop or core. Six ichnofabric indices (ii) were developed for marine strata relative to the degree of pattern recognition and percentage of sedimentary fabric disruption by bioturbation. This classification is inaccurate when applied to pedogenically modified continental and marine deposits and does not accurately communicate the fabrics produced by abiotic and biotic pedogenic processes. Some workers have proposed that all pedogenic processes are mediated by bioturbation and, therefore, abiotic pedogenic processes can be ignored. Such assumptions are inappropriate because biotic activity is one of the five soil-forming factors resulting in pedogenesis of subaerially exposed deposits and there is no realistic method to tease out biotic- from abiotic-produced fabrics in soils or paleosols. A revised system is necessary to incorporate bioturbation and the other four soil-forming factors to interpret better the degree of pedogenic fabric and postdepositional history of strata. One way to modify the ii is to create ichnopedofabric indices (ipi) using a lettering system in conjunction with the numbering system to delineate the contribution of fabrics from burrows (b), rhizoliths (r), mottles (m), nodules (n), soil structure (s), and horizontaion (h). As pedoturbation outpaces sedimentation with longer duration of subaerial exposure, deposits will have additional pedogenic fabrics. Continental and marine strata with no bioturbation or pedogenic features have a score of 1. A term of 3br denotes 10–40% of bedding disruption (3b) and the presence of rhizoliths (r). A term of 6brm denotes complete homogenization (6b), the presence of rhizoliths (r) and mottles (m). A term of 6brmnh denotes complete homogenization (6b), the presence of rhizoliths (r), mottles (m), pedogenic nodules (n), and horizontaion (h).