Last month we featured a fossil slab kindly donated by Dale Chadwick of Lancaster, Pennsylvania. Dale is an enthusiastic fossil collector with a very useful website for his favorite sites and specimens. I promised to show the other side of this rock, and here it is.
Again, this is a fine sandstone from the famous Calvert Formation (lower to middle Miocene) exposed at the Calvert Cliffs, Plum Point, Calvert County, Maryland, in the stratigraphic Shattuck Zone 10. Some horizons are especially fossiliferous with large numbers of gastropods and bivalves. This is what we refer to us a death assemblage, meaning these shells are not preserved in their life positions but how they accumulated just before final burial. These rocks and their fossils were the initial basis of Susan Kidwell’s important work on taphonomic feedback, or how shell accumulations affect the succeeding living communities.
So what are the prominent fossils in this slab? Dale has the answers on his website. I’ve annotated the image and made a list below:
A Astarte sp. (a veneroid bivalve)
B Glycymeris parlis (an arcoid bivalve)
C Siphonalia devexa (a buccinid gastropod)
D Turritella variablis (a turritellid gastropod)
Thank you again to Dale Chadwick for this gift! I will use it in my paleontology course this very month.
References:
Kelley, P.H., 1983, Evolutionary patterns of eight Chesapeake Group molluscs: Evidence for the model of punctuated equilibria: Journal of Paleontology 57: 581–598.
Kelley, P.H. 1988. Predation by Miocene gastropods of the Chesapeake Group: stereotyped and predictable. Palaios 3: 436-448.
Kidwell, S.M. 1986. Taphonomic feedback in Miocene assemblages: Testing the role of dead hardparts in benthic communities: Palaios 1: 239–255.
Kidwell, S.M., Powars, D.S., Edwards, L.E. and Vogt, P.R. 2015. Miocene stratigraphy and paleoenvironments of the Calvert Cliffs, Maryland, in Brezinski, D.K., Halka, J.P. and Ortt, R.A., Jr., eds., Tripping from the Fall Line: Field Excursions for the GSA Annual Meeting, Baltimore, 2015: Geological Society of America Field Guide 40, p. 231–279.
