Archive for December 16th, 2012

Geological fieldwork on the streets of Dublin

December 16th, 2012

DublinRainbow121612DUBLIN, IRELAND — What could be more Irish than a rainbow over Dublin? (I know better than to write of leprechauns and pots of gold.)  It certainly crowned the end of a delightful afternoon spent with my friend Tim Palmer looking at building stones.

I am in Dublin attending the annual meeting of the Palaeontological Association. After a long editorial meeting, Tim and I went to the center of the city to look for a particular kind of stone that may have been used in the Medieval portions of the two Dublin cathedrals: St. Patrick’s (National Cathedral of the Church of Ireland) and Christ Church (also for the Church of Ireland but claimed by Roman Catholics — it’s confusing, especially since they are only a short walk from each other). Tim was looking for a limestone called Dundry Stone, part of the Inferior Oolite (Middle Jurassic) in Great Britain. It is notable as a non-oolitic part of the Inferior Oolite, made mostly of tiny fragments of crinoids and calcite cement. Tim quickly found the stone in both cathedrals.

StPatricks121612This is St. Patrick’s Cathedral. Its exterior is mostly restored, but the interior still retains part of its Medieval core. It dates back to 1191.

StPatricksChapelDoorway121612We asked at the door to see the oldest part of St. Patrick’s, and were immediately directed to this small chapel. At the time the cathedral was filling with people for a choir concert, so we were surrounded with the sounds of bells and children practicing their pieces. This chapel was used as a storeroom as well as a tourist site, so there are some incongruities (such as the folding chairs!). Almost all the stone is either covered with cement or replacements except in a few places, like the frame of this small doorway. That white rock is Dundry stone.

ChristChurchCathedral121612This is Christ Church Cathedral, just down the road from St. Patrick’s. (A rivalry between the two dates back to the 12th Century. Two cathedrals in one city is very rare, apparently.) Christ Church is the older of the two cathedrals, dating back to about 1040 when a Viking king of Dublin started construction. It also has a mostly restored exterior, and it too has Dundry stone making up surviving doorways and lintels.

ChapterHouse121612This is an excavated “Chapter House” just outside Christ Cathedral on the grounds. Tim Palmer can be seen in the corner making notes. Apparently monks, priests and other church notables would meet in this building and sit on the stone benches just like Tim. The stones in this ruin include original materials (like the Dundry) and a variety of other lithologies.

I had a great time learning about stonework, Medieval building techniques, and the various structural properties of limestones, all thanks to Tim. Tomorrow I’ll be back in the more secular pews of the paleontological meeting. I’m happy to have had this spot of unexpected fieldwork!

Wooster’s Fossil of the Week: A bivalve boring from the Upper Ordovician of southern Ohio

December 16th, 2012

This week’s fossil is from close to home. In fact, it sit in my office. The above is a trace fossil named Petroxestes pera. It was produced on a carbonate hardground by a mytilacean bivalve known as Modiolopsis (shown below). Apparently the clam rocked back and forth on this substrate to make a small trench to hold it in place for its filter-feeding. This particular specimen of Petroxestes was found in the Liberty Formation (Upper Ordovician) of Caesar Creek State Park in southern Ohio. This is a place many Wooster paleontology students know well from field trips.
The original Petroxestes was at first known only from the Cincinnatian Group, but now it is known from many other places and time intervals, even including the Cretaceous and Miocene. It is a good lesson about trace fossils. They are defined by their morphology, not what organisms made them. It turns out that this slot-shaped trace can be made by other animals besides Modiolopsis, which went extinct in the Permian.

References:

Jagt, J.W.M., Neumann, C. and Donovan, S.K. 2009. Petroxestes altera, a new bioerosional trace fossil from the upper Maastrichtian (Cretaceous) of northeast Belgium. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 79: 137-145.

Pickerill, R.K., Donovan, S.K. and Portell, R.W. 2001. The bioerosional ichnofossil Petroxestes pera Wilson and Palmer from the Middle Miocene of Carriacou, Lesser Antilles. Caribbean Journal of Science 37: 130-131.

Pojeta Jr., J. and Palmer, T.J. 1976. The origin of rock boring in mytilacean pelecypods. Alcheringa 1: 167-179.

Tapanila, L. and Copper, P. 2002. Endolithic trace fossils in Ordovician-Silurian corals and stromatoporoids, Anticosti Island, eastern Canada. Acta Geologica Hispanica 37: 15–20.

Wilson, M.A. and Palmer, T.J. 1988. Nomenclature of a bivalve boring from the Upper Ordovician of the midwestern United States. Journal of Paleontology 62: 306-308.

Wilson, M.A. and Palmer, T.J. 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109–112.