Computed tomography (CT) scans in conjunction with thin section petrographic analyses of North American conventional cores reveal the persistent presence of biogenic structures in mudstones previously thought to have been devoid of any evidence of life forms. Characteristic assemblages of these features include burrows and grazing trails and can be classified as ichnofacies that have been well documented from basins worldwide.
An integrated petrologic analysis, using CT scans and thin section petrology of continuous cores from 3 vertical wells representing a proximal to distal transect across the Anadarko Basin, Oklahoma revealed that the majority of the ichnofacies observed represent a reduced Chondrites Ichnofacies that is indicative of dysoxic conditions at the sediment-water interface. Changes within this ichnofacies assemblage reflect variations in relative stages of dysoxia, with the most dysoxic environment prevailing at the most distal setting. Lack of burrows is most commonly associated with disruptions by distal turbidites rather than the existence of conditions of anoxia.
Although mudrocks are generally thought to be laminated, intervals with sediment disruptions associated with burrowing are common and add to the complexity of the rock. An understanding of how burrow-associated heterogeneities control flow pathways within sedimentary units can help with optimizing production from these bioturbated reservoirs.
