Guild structure of paleocommunity types from the Yorktown Formation (Pliocene)

G.M. Daley
GSA Abstracts with Program 30(7): A-33

Any species with preservable hard parts which occurs in abundance under particular environmental conditions should be found wherever the fossils from that paleoenvironment are preserved. If the species of a particular guild tend to be very abundant under those paleonenvironmental conditions, then that guild should also be well represented in the paleocommunity type. The occurrence and recurrence of guilds over a wide geographic range and through a paleoenvironmental gradient were tested using the well-exposed and grossly fossiliferous strata of the Pliocene Yorktown Formation.

Replicate samples of the silty sands of the Rushmere Member and sandy silts of the Morgart's Beach Member were taken at 30 cm intervals at several localities in eastern Virginia. The 140 samples yielded 145 species of primarily bivalves and gastropods. Each species was assigned to one of 16 ecological guilds based on its life habit. The data set was subjected to ANOVA and factor analysis to test for the recurrence of individual species and the recurrence of each guild.

Previous work on the Yorktown Formation has shown that the same paleoenvironment sampled at different localities does tend to yield the same starring cast of a few (usually 1-2) very abundant species. Beyond these hyper-abundant species, there is no strong correlation between the abundances of the other species.

However, when the species are grouped by their ecologic guilds, a strong pattern of recurrence is seen. The same guilds are found in the same relative abundances whenever the same paleonenvironmental conditions occur. The dominant guilds also shift in a predictable way as the paleoenvironmental conditions change.