Spring 2021
| Speaker: |
Jochen Mezger |
| Title: | Bent out of Shape by the Mountain: How Deformed Fossils Enhance our Understanding of Tectonic Activity |
| Date: | February 26, 2021 |
| Time: | 11:45am |
| Location: | Contact instructor for details. jemezger@alaska.edu |
About:
Jochen Mezger is the Field Camp director at UAF’s Department of Geosciences. He is
a structural and metamorphic geologist by training and conviction, and has spent many
summers in the southwestern Yukon Territory, the Highlands of Sri Lanka and his favorite
mountain range, the Pyrenees. He loves ֱֻ and his Geology Field Camp, but secretly
wishes that the rocks he takes his students to map would be stronger deformed. He
was very excited to one day find deformed belemnite rostra during Field Camp in the
Talkeetna Mountains that reminded him of ductile deformation his beloved schists and
mylonites enjoy. He realized that microtectonics and paleontology are not necessarily
mutually exclusive.
Abstract:
Deformed fossils provide valuable information about deformation of rocks in the uppermost
crust. Since their original shape is known, the distortion of the shell allows
us to reconstruct the amount of strain the fossils have endured. These fossils include
ammonites, trilobites, brachiopods and belemnites, common in Paleozoic and Mesozoic
marine sediments. Lower Cretaceous sediments in the Talkeetna Mountains of eastern
Central ֱֻ contain abundant belemnite rostra, the rod-shaped internal skeleton
of a squid-like marine creature, that show 
signs of plastic deformation, e.g. they are bent or sheared, indicative of compression.
Thin sections reveal calcite veins serve as a “glue” to hold the deformed fossil together.
Microstructural, cathodoluminescence and fluorescence studies show that the deformation
occurred after the death and burial of the animal. The sedimentary layer in which
the deformed fossils were found is located along a reverse or thrust fault. The deformation
can be linked to the activity of the fault. The microstructures provide information
on the temperature and pressure that were prevalent when the fault was active. Thus,
bent out of shape, the deformed belemnites help to understand the tectonic activity
in the Talkeetna Mountains a little bit better.
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