Wooster’s Fossil of the Week: An encrusted and bored oyster from the Upper Jurassic of northern England
Mark Wilson August 28th, 2015
This week’s fossil is a celebration of classes beginning again at Wooster, and a memory of excellent summer fieldwork. It isn’t especially attractive, but it has paleontological significance. We are looking at a broken surface through a thick oyster from the Passage Beds Member of the Coralline Oolite Formation (Upper Jurassic, Oxfordian) exposed on the north side of Filey Brigg, North Yorkshire, England. It was collected by Meredith Mann (’16) as part of her Senior Independent Study research in June. One of her project goals is to assess the sclerobionts (encrusters and borers) that lived on and within hard substrates in this interval. This thick shell is a start.
In this closer view we can see three rounded objects penetrating the oyster shell. These are bivalve borings called Gastrochaenolites. They were open holes excavated by drilling bivalves that were later filled with sediment and cement.
The outer surface of the oyster shell is covered with encrusting oysters and serpulid worm tubes. These will be more visible later after Meredith prepares the specimens. The first thing she is likely to do is use some bleach to remove the modern marine algae. Our specimens were all collected near the high-water tide level on the rocky north coast of Filey Brigg (N54.21823°, W00.26904°).
Meredith is here standing against the Passage Beds Member on June 14, 2015. Her feet are on the top of the underlying Saintoft Member of the Lower Calcareous Grit Formation. About a meter and a half above her head is the base of the overlying Hambleton Oolite Member (Lower Leaf) of the Coralline Oolite Formation. As we took this photo the sea was pounding behind us on a rising tide.
Here is a cluster of oysters preserved in the lowest unit of the Passage Beds. It is a sandstone distinct from the overlying limestones. There is much evidence of high-energy transportation of shelly material.
Here are Meredith’s specimens from this site, all cleaned and in stratigraphic order. A critical part of her work will be a petrographic analysis of the Passage Beds Member. We hope to show you these thin-sections next month.
Meredith celebrating the end of her fieldwork as she confronts the rising sea on the tip of Filey Brigg (N54.21560°, W00.25842°).