Movie 2: The second movie was created by Roberta Hotinski and Andrew Hoover as part of a project for a Carbonate Sedimentology class.
"This movie shows our best effort to simulate mixed
carbonate-siliciclastic deposition as expressed in Middle to Late
Ordovician deposits of central Pennsylvania. This period is
characterized by a transition from peritidal carbonates to siliciclastic
domination, with intermediate interlayered clays and carbonates. The
sequence is believed to have been caused by the influence of the Taconic
orogeny on the Great American Carbonate Bank; tectonic and clastic
loading first deepened the basin in which the carbonates were forming,
then clastic material shed from the orogen swamped the platform. We
expected to reproduce a gently sloping carbonate platform which first
gradually deepened, then showed mixed carbonate-clay deposition, and
finally was overwhelmed by siliciclastic depositon.
Reasonable values were chosen for carbonate deposition rate and
subsidence and the basin was allowed to subside using the passive margin
profile. The foreland basin-type profile was created by supplying a
sufficient clastic load to depress the lithosphere in the east. Once
this basic model had been established, carbonate deposition rates,
diffusion rates, and subsidence were adjusted in attempt to simulate
Middle to Late Ordovician deposition. Carbonate productivity and
subsidence rate had to be balanced so that neither flooding nor
exclusively supratidal carbonate deposition occurred, so the flexibility
of these parameters was limited. What proved to be surprisingly
important was the diffusion rate, which controls the erosion of
deposited sediment. One rate controls both carbonate and clastic
sediments, which made it difficult to preserve the carbonate platform
while transporting clastic material far enough across the basin to
interfinger with carbonate deposits. The movie shows our best attempt
to flux material from east to west while preserving the western
carbonate platform. Carbonate/clastic interaction does occur in this
simulated foreland basin, but it is relegated to the toe of the
carbonate platform where diffused carbonate sediments are deposited with
deep-water siliciclastic sediments. Because carbonate and clastic
compositions are not distinguished by Strata2.1, this interaction is not
visible in the model output."
-Roberta Hotinski