Thursday, 14 February 2013

Mystery rock!


This week’s wow of the week! is a mystery rock that I was sawing today. It is so interesting and unusual I thought it would be good to share. The rock is a cementstone, with a complicated structure, as you can see from the photo below. The bottom part consists of a conglomerate, with clasts of cementstone in a black matrix that is packed with plant, shell and fish fragments. The top part consists of bioturbated (burrowed) muddy sediment, with no large fossils. The mystery is that in the bottom part are large calcite spheres, with radial crystals growing into a void in the centre. These crystal structures may be replacing gypsum, thin section analysis is needed to find out, but all of them are spherical. I saw a similar structure in a sandstone that occurred near to this cementstone (see photo). It might indicate that gypsum grew in these rocks due to evaporation, but it also looks like the spheres may have been transported in the conglomerate itself. Very unusual! Please message me if you have seen this before and can give me any tips!


Top: the mystery rock, a cut section through two of the spheres. Bottom: calcite spheres in a nearby sandstone.

What else has been happening? Rock sawing/slicing/grinding/analysis continues…. And this week I have started systematically sieving and picking through the samples I collected in the field. I am very lucky to have a volunteer helping me, Tom Worthington, a graduate from the University of Leicester, who is getting some micropalaeontology work experience. With Tom’s help we can hopefully uncover the hidden microfossils in hundreds of samples, and generate a lot of useful data.

News from even smaller fossils is that the palynology work is well underway, with John Marshall at the University of Southampton. With palynology we aim to date the key tetrapod finds as well as build up a stratigraphic framework and further understand environmental and climatic changes. In my next post I will update you on the tetrapod finds discovered so far.

A quick advert now for our local geology group seminar on Saturday 2nd March: We are having a day of geological talks to celebrate the life work of Dr Trevor Ford OBE, one of the founders of the Department of Geology at Leicester. The talks range from Charnia fossils to the geology of the Grand Canyon, everyone is welcome. For more information visit the Charnia website or message me.

Until next time
Carys