Abstract

The potential of ichnofabrics to yield information on endobenthic communities, organism behaviors, and paleoenvironmental conditions is widely recognized among sedimentary geologists. However, the extreme range in both ichnologic fidelity and temporal resolution of ichnofabrics is commonly not fully appreciated. Ichnofabrics developed in slowly deposited pelagic sediments, such as the Cretaceous Demopolis Chalk (U.S. Gulf coastal plain), represent one extreme. Ichnofabrics in the Demopolis Chalk, preeminently expressed only at transitions between marls and chalks, are time-averaged composites that formed over periods exceeding 8 kyr. Ichnologic fidelity is low; distinct biogenic structures reflect only the work of elite deep-tier tracemakers. Moreover, modeling that employs densities of elite burrows and burrow systems, sedimentation rates, and conservative estimates of trace-maker life spans indicates that preserved ichnofossils likely represent less than 10% of the time recorded in associated host sediments. Limited temporal resolution and completeness of these and comparable ichnofabrics call for caution in paleoenvironmental and paleoecologic interpretations and have implications for understanding behaviors, spatial distributions (patchiness), and vertical segregation (tiering) of tracemakers in marine pelagic substrates.

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