The Rock Stream Formation near Ithaca, New York, is a proximal, submarine fan-like deposit of an epicratonic sea. Turbidites and interbedded shale were deposited in alternating channel and interchannel facies. This lithology is in sharp contact with overlying mudstones which were probably deposited on a progradational slope.

The complex environmental parameters which affect the distribution of trace-making organisms is shown by their ichnologic distribution. Three associations occur within the submarine fan. (1) The Paleodictyon association consists of five ichnogenera representing pascichnia. These are followed stratigraphically by (2) the Arenicolites association consisting of 12 ichnogenera representing domichnia and fodinichnia. Two repichnia compose (3) the Pteridichnites association. This last association is ubiquitous to the study section. Food resources significantly influenced behavior as the population shows a trophic shift within a lithologically consistent section, from grazing (like Nereites) to the endobenthic feeding and dwelling behavior of a shallow-water assemblage. Within the Arenicolit s association, substrate texture and cohesion differentially influence the distribution of suspension-feeders and deposit-feeders through a trophically consistent assemblage. Multiple ichnogenera among any one behavioral class rarely occur in the same bed. Ecologic competition affects the distribution of individual phylotaxa within a behavioral class. Ecologic competition may have depended mostly on spot concentration at the time of substrate availability. On muddy substrates which may vary widely in cohesiveness, trophic group ammensalism allows fodinichnia to inherit a similar lithology from domichnia. The complexity of ichnogeneric distribution is produced by ichnotaxa ambiguities as well as ecological controls.

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