AN ACTUALISTIC APPROACH TO THE SEMI-QUANTITATIVE SCALE FOR THE TAPHONOMY OF FISH DISARTICULATION BASED ON THE OBSERVATIONS FROM THE SALTON SEA SHORELINE, CALIFORNIA, USA

During a catastrophic breach in the Imperial Irrigation Canal (1905 – 07), the Salton sink was partially flooded with water from the Colorado River. Since the initial flooding event, the ecosystem has evolved under conditions of increasing salinity and eutrophication. High-wind events subject the lake to: 1) overturning of the chemically stratified water column, 2) generation of algal blooms reducing dissolved oxygen, and 3) high mortality events in the hybrid tilapia (Oreochromis mossambicus x O. uroepis) due to phosphates and sulfides stirred up from bottom sediments. We developed a semi-quantitative fish articulation scale to understand and report on the shoreline taphonomy of these fish kills in the Salton Sea and extend our findings to interpret shoreline fish kills preserved in the rock record of the Triassic Newark basin.

Our semi-quantitative scale ranges from whole (1) to total disarticulation (5) of fish. Category 1 reflects whole, pliable fish with little or no degradation. Category 2 is defined as a loss of pliability (as a result of initial desiccation) and no external loss of skeletal ornamentation. Category 3 records initial disarticulation with total scale loss and preservation of partial axial skeletons. Category 4 comprises, isolated, disarticulated skeletal components (e.g. vertebral strings and skulls). Category 5 is the total disarticulation of skeletal elements. Whole, bloated fish raft to the high water level strand line (1) where desiccation occurs (2 and 3). Above the high water line, categories 3, 4, and 5 are present. The overall trend is from shoreline articulation to backshore disarticulation. The role of high-wind events with respect to disarticulation is unknown, but deflation of sediment and formation of skeletal elemental lags suggest that wind plays a role in exposing, but not necessarily transporting, skeletal elements.

Application of our semi-quantitative scale to fish bone beds present in the Triassic Lockatong Formation of Collegeville, PA demonstrates the utility and use of the scale. Triassic samples consist of graded beds topped with category 5, completely disarticulated fish skeletal elements; in some instances, categories 3 and 4 are mixed in with category 5. These deposits are consistent with deposition and disarticulation taking place above the high water line in the rift lake.