Archive for July 10th, 2011

A Day in Tallinn, Estonia

July 10th, 2011

TALLINN, ESTONIA–Like our Wooster Geology colleagues in Iceland, we also have a nearly-final day in a city. Tallinn is the capital of Estonia, the medieval town square of which is shown above. We started here briefly at the airport, and will leave from the same place early  tomorrow morning. The only difference is that we have one more big city to go: Stockholm, Sweden.

Tallinn, or at least a significant settlement in this place, goes back to the 11th Century, and before that there are Bronze Age artifacts. After the Danes conquered it in the 13th Century, it became known as Reval until the Estonian War of Independence in 1918-1920 when the Estonians could finally give it their own name: Tallinn (or Tallinna). It was a member of the Hanseatic League, being an important trade link between northern Europe and Russia. (And so the merchants in the town square are dressed in the Medieval garb of “Old Hansa”.) This year it is a European Capital of Culture. Tallinn does not sit on a major river but takes advantage of Ordovician limestone heights to raise it above the coastal swamps and bogs.

We enjoyed a day off in the city under (as you might have predicted) sunny skies. Tomorrow is another travel day, and then back to work one more time in Stockholm!

The newly renovated Freedom Square in Tallinn. The memorial is for the Estonian War of Independence (1918-1920).

Rachel and Nick can be barely made out here on the other side of Freedom Square.

Wooster’s Fossil of the Week: Ancient shrimp burrows (Middle Jurassic of Israel)

July 10th, 2011

This week we have a trace fossil, the burrow Thalassinoides. It is represented by one of my favorite images, reproduced above, showing a very large Thalassinoides suevicus in the Zohar Formation (Middle Jurassic, Callovian) of Makhtesh Qatan in the Negev of southern Israel. Holding the scale is Wooster geologist and Independent Study student Allison Mione (’05) during our 2004 Israel expedition. These burrows were originally described as giant desiccation cracks, but I.S. student Kevin Wolfe (’05), Israeli geologist Yoav Avni and I reinterpreted them as burrows in a rocky shore complex (see Wilson et al., 2005).

Thalassinoides is a complex trace fossil that is today made primarily by thalassinidean crustaceans (a type of shrimp; see below). We know a lot about how the burrows are made today by shrimp, and our knowledge is growing about how the ancient systems were excavated, at least in the Mesozoic and later. We have fossil shrimp preserved in Thalassinoides from the Jurassic (Sellwood, 1971) and the Cretaceous (Carvalho et al., 2007).

Pestarella tyrrhena, a modern thalassinidean shrimp. Image from Wikipedia.

Reconstruction of Mecochirus rapax in a Cretaceous Thalassinoides. A) In its burrowing life mode; B) Predominantly horizontal Thalassinoides suevicus burrow systems showing two successive event levels, with Mecochirus in life position. From Carvalho et al. (2007, fig. 3).

The burrow systems in the Zohar Formation of Israel were critical in working out the depositional environment of these carbonate sediments. We could see that first the water was comparatively deep (below wavebase) with worm burrows (Planolites). Then relative sea level dropped and the Thalassinoides burrows cut through the Planolites fabric, showing that the sediment was become stiffer. Finally bivalve borings (Gastrochaenolites) in the same rock indicated that the sediment had cemented into a shallow water hardground. This hardground showed tidal channels cut into its top surface (Wilson et al., 2005).

This work was done with virtually no “body fossils”, meaning evidence of the actual bodies of the organisms living in and on the sediment. Trace fossils, evidence of organism activity, were the only indications of this significant environmental change. This is why the study of trace fossils (ichnology) should be a part of the education of every paleontologist and sedimentologist.


Carvalho, C.N., Viegas, P.A. and Cachao, M. 2007. Thalassinoides and its producer: Populations of Mecochirus buried within their burrow systems, Boca Do Chapim Formation (Lower Cretaceous), Portugal. Palaios 22: 104-109.

Sellwood, B.W. 1971. A Thalassinoides burrow containing the crustacean Glyphaea undressieri (Meyer) from the Bathonian of Oxfordshire. Palaeontology 14: 589-591.

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171–178.