Rock formations near Parliament house, Canberra, 8/2/2012
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher Lucy Wenger, TS Rock formations near Parliament house, Canberra, 8/2/2012 GPS Coordinates: S 35° 18' 26.0454", E 149° 7' 30.813" Localisation of the sites: Site 1 Site 2 Geological map of the region:
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher Stratigraphiccolumn of the Canberra urban area: Geological cut of the Canberra Urban Area State Circle State Circle Source: GeoscienceAustralia
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher Site 1: Parliament House, Canberra At the parliament, we found many different types of rocks: Rock Colour Type of rock Texture/structure Photo Mosaic (granites or related rocks) red, orange, yellow, grey, brown, black Plutonicrocks Coarsegrained(large cristals of quartz, mica, feldspath) Stone bench (granite) red/ orange Plutonicrock Coarsegrained(large cristals of quartz, mica, feldspath) Small columns at the entrance (marble) Beige and pink/orange Metamorphicrock Foliated Pale in colour, indicating that before metamorphism, it was a sedimentary rock.
Columns (white marble) White with grey veins Metamorphicrock Foliated Pale in colour, indicating that before metamorphism, it was a sedimentary rock. Columnsinsid eParliament house (actinolite marble.) Green and white Metamorphicrock Foliated This is an actinolite marble.
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher Wallsoutside Parliament House Beige Sedimentary rocks: agglomerationof several sedimentary rocks (limestones etc.), assembled by humans Fragments mainly fine-grained (limestone...) Photos : Sophie Kloetzli
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher Site 2 : Roches sédimentaires du Silurien à State Circle, Canberra Afterwards, we went to discover the rock cutting at State Circle, Canberra. Here’s a photo of the site: Photo : Lucy Wenger 1. Types of rock We found two different types of sedimentary rocks at State Circle, both from the Silurian period (416 to 443 million years ago), separated by an unconformity. The rock situated on top is some Camp Hill Sandstone, dated from around 428 million years ago. The other rock, situated underneath, is some shale (State Circle Shale), from around 434 to 435 million years ago (see the geological cut and the stratigraphic column p2).
Camp Hill Sandstone (428mya) State Circle Shale (434 to 435mya) Strata Photos: Sophie Kloetzli
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher 2. The structure of the rocks a) Angular unconformity The unconformity that separates the two layers of rock represents an interval of around 10 million years. This unconformity is angular, because the layers of sandstone were deposited on tilted and eroded layers of shale. The sandstone’s strata are horizontal, while those of the shale form a 45o angle to the horizontal. Direction of the strata Angular unconformity b) The faults State Circle is located at the point number 8 on the geological map (p.1).
There are several important fault lines in this area, which indicate that the area has known high levels of seismic activity. Indeed, at the rock cutting at State Circle, there are several easily observable faults (both normal and reverse) that fracture the rock. For example, the following fault is a normal fault, created through extension. Photo: Google maps
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher We also find reverse faults and thrust faults, both occurring through compression. Thrust faults are reverse faults, but where the movement occurs at a low angle. It is possible to determine the direction of the slide from thedirection of the folds created by the faults. Thrust fault Folds Thrust fault 3. Interpretations : From all this information, it is possible to recreate the history of these rocks from the Silurian period. - First of all, the shale was formed: fine sediments were deposited on the ocean floor and then were compressed.
The strata that are visible show that it is indeed a sedimentary rock. - Then, there was a tectonic movement that pushed the shale out of the water. During these tectonic activities, the strata were tilted, creating an angle of 45o to the horizontal. This movement also created several faults. Normal fault Photo: Google maps Photo: Google maps
Lucy Wenger, TS, LFAC Australie 2012 Fieldwork with Caroline Prevot, Science Teacher - Afterwards, there was a gap of 10 million years, during which the shale was eroded. After those 10 million years, the shale was resubmerged in water. This allowed the sandstone to form, as it is another sedimentary rock. - Today, the two rocks are yet again above sea level, following other seismic activity creating faults and folds, and are currently being eroded. Bibliography : Map and several photos:Google maps Other photos: taken by Sophie Kloetzliand Lucy Wenger Geological map of Canberra and Stratigraphic column: Geology of the Australian Capital Territory, Geoscience Australia (2008) Diagrams of faults: http://www.suu.edu/faculty/colberg/Hazards/Earthquakes/Earthquake_SG.html