Saturday, November 29, 2008

Geopetal structure

During my first real field day I came across some very nice sedimentary structures that looked just like in the textbook. Unfortunately I forgot to take ma camera to the field. However, I could take home this nice example of geopetal structure within limestone.

(Click image to enlarge)

It can be nicely observed how the complete shell was infilled at the bottom with mud during deposition and subsequently calcite crystals formed after deposition or diagenesis. It is a wonderful example of how to tell palaeo-up from down especially in tilted sediments. The complete preservation of the shell leads me to assume that it was deposited either in-situ or without much transport. Long transport or strong wave and current action would have seperated the two shell parts.

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