IDENTIFICATION OF SILICIFIED TRACE FOSSILS IN THE PERMIAN OF NORTHWESTERN UTAH

Silicification of both body and trace fossils is common in the abundant chert-bearing Permian strata of the northwest desert of Utah. This process is common with fossil material and trace, because decaying organics can facilitate silicification by serving as nucleation points for chert accumulation. Identification of trace fossils is especially onerous in the mixed chert/carbonate medium present. Chert demonstrates the ability to grow outside the constraints of its original template. Due to this, the original trace may be obscured by the diagenetic growth of the nodule. Observation of silicified trace in northwestern Utah, as well as literature research, has led to the compilation of macroscopic criteria useful for identification of trace preserved in this medium. These include: uniformity of dimensions (i.e. diameter); complexity of pattern (i.e. presence, number, and angle of branching); textural differences preserved in chert versus the surrounding material; lack of correlation with other sedimentological or structural controls (i.e. presence of current alignment; strong relationship with fracturing). These common techniques of trace identification take on a new meaning when applied to observing silicified traces.