Evidence of High-Frequency Storm Disturbance in the Middle Devonian Arkona Shale, Southwestern Ontario.
Cameron J. Tsujita, Carlton E. Brett, Michael Topor, John Topor.
Keywords: MUDROCK (SHALE), STORM DEPOSITION, EVENT STRATIGRAPHY, DEVONIAN,
SHELL BEDS, TAPHONOMY
The importance of storms as agents of deposition and erosion is obvious in many ancient offshore marine
successions. Indeed, storm-generated shell beds are among the most prominent small-scale features in
otherwise monotonous successions, particularly those dominated by mudstones. Shell beds are usually
interpreted as products of rare episodes of storm-generated disturbance punctuating long periods (tens, to
hundreds, to thousands of years) of quiescence, the shell beds representing storms of greatest severity.
The taphonomic attributes of shell beds in the Middle Devonian Arkona Shale (southwestern
Ontario) indicate that even “simple” shell beds can have complex histories. Shell-rich beds dominated by
well-preserved remains of small rugose corals, spiriferid brachiopods, and a variety of crinoids, are
commonly associated with pavements of shell debris reworked by earlier storms. Taphonomic dissection
of five examples, informally called the lower Arthroacantha bed, the in situ Mucrospirifer bed, the upper
Arthroacantha bed, the auloporid bed, and the Microcyclus bed, reveals a common theme; initial priming
of the seafloor by one or more storms, was followed by colonization of the primed substrate by shelly
benthic fauna which, in turn, was followed by final disturbance and burial of the faunal remains by a later
For storms to have produced multiple signatures in single shell beds of the Arkona Shale, the
frequencies of seafloor disturbance must have been very high, probably on the order of a few years.
Such frequencies are much higher than those implied by stratigraphic occurrences of conspicuous shell beds
(i.e., without considering internal features of the shell beds). This implies that individual shell beds do
not necessarily represent the most severe storms recorded in mudstone successions but can, in some
cases, merely represent the most obvious products of storm disturbance by virtue of their shell content.
Regardless of storm severity, the disturbance of a muddy seafloor lacking abundant shell material would
produce an indistinct mud-on-mud contact that would be much less likely to be noticed than a shell-rich
horizon. By the same token, both low-magnitude (but high-frequency) storms and high magnitude (but
low-frequency) storms can produce shell beds, provided that sufficient shell material is available for
reworking. Obviously, the key to the formation of shell-rich horizon is an abundance of shelly material
on the seafloor. For this, a cause other than storm deposition must be sought; in most cases, these beds
also record interludes of relative sediment starvation and increased seafloor oxygenation.
Interpretations of storm severity from storm-generated shell beds should therefore be approached with
caution and be considered in context of the faunal dynamics and depositional characteristics of a
sedimentary succession as a whole.
The Taphonomy of Owl-Deposited Fish Remains and the Origin of the Homestead Cave Ichthyofauna.
Jack M. Broughton, Virginia I. Cannon, Shannon Arnold, Raymond J. Bogiatto, Kevin Dalton.
Keywords: BARN OWL, FISH REMAINS, GREAT BASIN, HOMESTEAD CAVE, OWL PELLETS, RAPTOR DEPOSITS, TAPHONOMY, TUI CHUB
We report a case of fish prey dominating the diet of modern barn owls (Tyto alba) and conduct a
descriptive taphonomic analysis on the fish remains the owls deposited. From a sample of 14 barn owl
pellets collected on the floor of a Nevada barn, we identified 3294 tui chub (Gila bicolor) bones. These
remains, derived from very small-sized fish, comprised nearly 90% of the total pellet NISP and were
characterized by relatively complete skeletal part representation, and minimal bone fragmentation and
digestive surface damage. We use this data-set, along with tui chub samples deposited by other agents,
to evaluate the origin of fish remains derived from late Quaternary deposits of Homestead Cave, located
in the northern Bonneville Basin, Utah. Quantitative comparisons of skeletal part representation and
digestive damage show that the Homestead Cave fish assemblage is statistically indistinguishable from
the owl-derived collection but different from chub samples originating from coyote (Canis latrans) scat
and human faeces. Qualitative evaluations of other agents also suggest an owl-based origin of the fauna.
Our analysis calls attention to the important role that owls can play in depositing fish in caves and
rockshelters and provides useful information to researchers interested in deciphering the taphonomic
history of fish remains recovered from these settings around the world.
Success in Identification of Experimentally Fragmented Limb Bone Shafts: Implications for Estimates of Skeletal Element Abundance in Archaeofaunas.
Travis R. Pickering, Charles P. Egeland, Amy G. Schnell, Daniel L. Osborne, Jake Enk.
Keywords: FAUNAL ANALYSIS, ZOOARCHAEOLOGICAL ASSEMBLAGES, SKELETAL PART FREQUENCY, HINDLIMBS, DIAPHYSES, CROSS-SECTIONAL GEOMETRY
A strong pattern of high hindlimb representation (especially tibiae) was recognized in our survey of
zooarchaeological analyses that included limb bone shafts in estimates of element abundance in
assemblages from the Old and New Worlds, from widely spread time periods and with various hominid
species that acted as bone accumulators. Inter-element differences in bone mineral density and carcass
transport behavior by hominids do not explain the pattern satisfactorily. We hypothesized that shaft
fragments of hindlimb elements (especially tibiae) might be more “intrinsically identifiable” than are
fragments from other limb bones, and constructed an experiment to test this idea. Whole limb bones
were sectioned into shaft fragments of various sizes using a bandsaw. An experienced faunal analyst
(TRP), who was uninvolved in the bone selection and preparation, was required to identify the fragments
as accurately as possible to specific skeletal element. Identification bouts were divided into 14 individual
sorts, each consisting of 24 randomly assigned specimens. Sorts were constructed to replicate an
increasing degree of communition across three stages: two “Stage I” sorts contain large specimens, four
“Stage II” sorts contain smaller specimens and eight “Stage III” sorts contain the smallest specimens.
Refitting and guessing were not allowed and fragments identified to a non-element-specific category
(i.e.: upper limb segment, humerus or femur; intermediate limb segment, radius or tibia; lower limb
segment, metacarpal or metatarsal; limb bone shaft only) were not counted as a correct identification.
Of 336 total specimens, 195 (58.0 %) were correctly identified to element. Overall, the differences in
proportions of skeletally identified fragments for all six elements are not statistically significant. This
finding seemingly falsifies the hypothesis that shaft fragments from hindlimb elements (especially
tibiae) are more intrinsically identifiable than are fragments of other limb bones. However, our study
also highlights the need for additional testing of the hypothesis since most actual archaeofaunas preserve
many more specimens with complete or nearly complete diaphyseal circumference than does our
experimental sample, which is composed entirely of specimens with preserving <50 % of their original circumferences. Our results suggest that bone specimen cross-sectional information, mostly lacking in the experimental sample but not in real archaeofaunas, is one of the most important classes of data on which accurate identification of shaft fragments are made.