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:
State Circle
Geological cut of the Canberra Urban Area
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
Mosaic
(granites or
related rocks)
Colour
red, orange,
yellow,
grey,
brown,
black
Type of rock
Plutonicrocks
Texture/structure
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
Columns
(white
marble)
White with
grey veins
Metamorphicrock
Pale in colour,
indicating that
before
metamorphism, it
was a sedimentary
rock.
Foliated
Columnsinsid
eParliament
house
(actinolite
marble.)
Green and
white
Photo
Pale in colour,
indicating that
before
metamorphism, it
was a sedimentary
rock.
Metamorphicrock
Lucy Wenger, TS, LFAC Australie 2012
Foliated
This is an
actinolite marble.
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)
Photos: Sophie Kloetzli
Strata
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.
Photo: Google maps
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.
Lucy Wenger, TS, LFAC Australie 2012
Fieldwork with Caroline Prevot, Science Teacher
Photo: Google maps
WeNormal
also findfault
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
Photo: Google maps
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.
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
Lucy Wenger, TS, LFAC Australie 2012
Fieldwork with Caroline Prevot, Science Teacher