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.