COMPUTER SIMULATION OF SUPERIMPOSED TRACE FOSSILS: ANALOGS FOR CAMBRIAN-AGE SKOLITHOS DISTRIBUTIONS

DILLIARD, K. A., and SIMPSON, E. L., Department of Physical Sciences, Kutztown University, Kutztown, PA 19530, dill5029@kutztown.edu and simpson@kutztown.edu.

Bedding plane views of trace fossils can yield important paleoecological information by looking at the trace fossil spatial distributions with regards to feeding habit. For instance, bedding planes covered with Skolithos -tubes can potentially record sediment modifications made by a single population or successive generations. Successive generations may reflect continued occupancy of the same substrate thru time, colonization by different organisms producing identical traces, or penetrations of the bedding planes by traces from overlying strata. Would successive generations affect population statistics, potentially permitting incorrect interpretations of feeding habits?

Bedding plane views were simulated by computer models. Successive generations were represented by the addition of random points onto the original bedding plane. The modified bedding plane was then studied using Clark and Evan's (1954) nearest neighbor technique. The nearest neighbor techniques uses the distance from each point to the nearest neighbor point. Distributions are then compared using the R-value, which is the ratio of observed mean tube spacing for a random distribution. R-values of less than, equal to, or greater than one indicate a clustered, random, or uniform distribution, respectively.

Several programs were written to add random points (trace fossils) onto random, uniform, and clumped distributions. The deviation of R-values from the original distribution was then compiled. Results show that 100 randomly generated points added to uniform distributions will significantly decrease the R-values (from 2 to a mean of 1.22). Increments of random points were then added to a set of uniform distribution to observed the change in R-values. The R-values progressively move towards random. Clumped distributions, with 100 added random points, move towards random ( from .89 to a mean of .98). Increments of ten random points were also added to a clumped distribution. The R-values move towards random. Random distributions, on the other hand, remain random. Numerous studies have reported R-values of ~1.1 for Cambrian-age Skolithos . This study indicates that all of the above scenarios mimic the reported distributions of Cambrian-age Skolithos .

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D.J. Moore
Oct. 2002
Last modified Sept. 2004
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