COMMON CHALLENGES WHEN USING ANCIENT BORINGS TO UNDERSTAND THE BIOEROSION PROCESS

Biologists and geologists studying bioerosion use various approaches for the common goal of describing, quantifying and modeling the behavior of bioerosion as a process in Earth systems. Carbonate bioerosion studies have a long history that points to the importance and limitations of field description and modern experiments in working toward a synthesis of bioerosion through geologic time.

Descriptive studies employing ichnotaxonomy have been foundational to the progress of carbonate bioerosion research. Precise description of borings provides the best indication of tracemaker affinity and behavior, and the ichnotaxonomic framework is the best modern system to organize the diversity of bioerosion behaviors. Current ichnotaxonomic practice, however, presents some obstacles to identifying trace fossil and tracemaker diversity by prohibiting the use of substrate or surrounding geochemistry as a diagnostic character. Biotaxa are limited by the substrates they can excavate, and through their activity may leave a distinctive chemical legacy that should be incorporated in the description of the boring.

Quantification of ancient bioerosion has generally lagged behind studies of modern systems, primarily owing to the challenge of recognizing time. Measuring the amount of substrate removed by borings is most commonly presented as a rank, percentage, or volume, and can be easily acquired with digital imaging and processing. But exposure time and bioerosion intensity are positively correlated, and the relationship often is nonlinear and sensitive to physical conditions as well as the biotaxa responsible for the erosion. A solution to this problem lies in correlating boring intensity with exposure time using modern experimental deployment studies, or by identifying the timing of geochemical alterations associated with boring excavation. This aspect of carbonate bioerosion research remains elusive, and has, so far, limited the extrapolation of fossil data in modeling the effects and changes of bioerosion on carbonate systems through time.