QUANTITATIVE ANALYSIS OF AN ICHNOASSEMBLAGE WITHIN A LEGACY-MUD CUTBANK, NESHAMINY CREEK (TYLER STATE PARK, PENNSYLVANIA)

Bioturbation of riverbanks is beneficial to many (semi-)aquatic species, providing food and shelter, however, this activity also affects the morphology of the riverbanks and suspended sediment load. To investigate this zoogeomorphic impact and ichnological significance of aquatic traces, thirteen openings in legacy mud were studied on the right (west) cutbank of Neshaminy Creek (Tyler State Park, Bucks County, Pennsylvania). The traces were mapped and measured at lowered water levels (five weeks following a record flood event; Ida, 2021) and varied in size and orientation. Using height/width/depth metrics, three clusters were identified: 1) shallow, vertically elongated burrows; 2) horizontally elongated burrows, and 3) deep, circular burrows. The traces ranged from 3-18 cm in height, 3-25 cm in width, and 8-43 cm in depth into the bank. Elongated traces had depths ranging from 8-19 cm, whereas narrow spherical burrows (tunnels and shafts) had depths >20 cm. The latter are attributed to crayfish, whereas shallower sub-vertical pits are likely produced by the feeding of abundant common carp (Cyprinus carpio), and sub-horizontal indentations may be related to several species of turtles. The volume of excavated sediment ranged from 200-4,600 cm³. Our study indicates that attention must be paid to a biogenic cause of the geomorphic processes along riverbanks. Our findings suggest that feeding and dwelling traces of semi-aquatic and fully aquatic animals should be considered when assessing riverbank erosion and permeability hotspots. Furthermore, some of the deeper burrows can be potentially incorporated into soil profiles as a result of channel diversion and rapid burial, with implications for interpreting ancient fluvial and riparian ichnocoenoses.