August 10, 2022
The Funzie conglomerate started off as a thick package of pebbles, cobbles, and boulders within a sandy matrix that were eroded off of an immense mountain range formed during the Caledonian orogeny, a relatively early phase of the larger collision between what are now the eastern and southern edges of North America and parts of Europe and South America. This broader event shaped the geology of much of North America, including the Appalachians and the Ancestral Rocky Mountains uplifts! As the Caledonian orogeny progressed, the sediments of the Funzie were buried and deformed. However, the total penetrative strain that these rocks accumulated varied in space due to heterogeneous deformation (see figure). These differences are recorded in the shape of clasts, that is the clasts act as strain markers.
Several properties of the Funzie conglomerate make it an ideal target for this work. First, both the clasts and matrix material are chiefly made up of the mineral quartz. Quartz is ubiquitous throughout Earth’s crust, meaning that findings from this project are applicable to many rocks far beyond the shores of Shetland. Second, clasts in the Funzie commonly stand proud in outcrops (see photo), allowing us to collect some of the most accurate measurements of clast dimension and orientation ever recorded! Finally, the Funzie is very well exposed along the wild and rugged cliffs of the Fetlar coastline (see example in photo), which means we were able to measure clasts with few gaps across a wide area to better characterize the variations in deformation. All in all, we were able to characterize over 800 clasts! Although the wind and cold made fieldwork challenging, the beautiful landscape and friendly people easily made up for it.
Going forward, we will apply newly developed statistical methods to our dataset and gain a better understanding of how crustal rocks deform. Our analysis will also integrate observations from the microscale, where we can observe how deformation is accommodated within individual quartz grains.
(Also see the prior post about this project.)
— Snir Attia, Field Geologist, NMBGMR