Ichnofacies of a Modern Size-Graded Shelf, Northwestern Gulf of Mexico

Biogenic sedimentary structures decrease in diversity and abundance with increasing water depth across the size-graded shelf of south-central Texas. Regional biorurbation patterns are related to macrobenthic infaunal assemblages and sediment facies. Dense and diverse assemblages of biogenic sedimentary structures are associated with shallow-water areas with relatively coarse substrates, low sedimentation rates, and dense and diverse infaunal assemblages. The outer shelf zone exhibits little biorurbation due to the presence of very few organisms, high sedimentation rates, and an underconsolidated substrate of muddy sediments of near-uniform grain size. Most traces have limited distribution ranges, high preservation potential, and vertical to subvertical orientation (or represent deep subhorizontal burrowing). In the rock record, estimating the degree of bioturbation in mud beds is the key to correctly interpreting regional bioturbation patterns for size-graded shelf deposits.