Logging Tasks:
Click on ‘Message this owner’, or send an email here with answers to the following logging tasks:
- Standing at the posted coordinates and considering Steno’s four principles of stratigraphy, describe what you see in the cliff face in front of you.
- Considering your answer to Q1, does it sit well to the principle of uniformitarianism and why?
- What is the 'catchphrase' for uniformitarianism?
Please include a photo with a personal/identifying item in your log.
The Theory
Scientists look at modern-day geologic events—whether as sudden as an earthquake or as slow as the erosion of a river valley—to get a window into past events. This is known as uniformitarianism: the idea that Earth has always changed in uniform ways and that, the present is the key to the past.
So I want to take a moment to talk about a very important concept and that's uniformitarianism. Now uniformitarianism is an idea thought up by James Hutton (1726-1797) and what he realised is that basic geologic principles that occur today have probably always occurred that way in the past so that's why the little catchphrase for uniformitarianism is the present is the key to the past. So this basically states, for example, that as we know, rivers deposit material on deltas, all rivers do. Now deltas might look a little different but they generically work the same. Water brings sediment down to the oceans and it gets deposited. So odds are it's always happened that way. So we can look at delta deposits today, see how they form, see what it looks like in the rock, and then be able to use that and look at what we see in the rocks of maybe 100 million years ago or a billion years ago and see those same kind of structures. So, we can use what we see in the present to help us understand what we see in the rocks of the past.
I would like to revisit Nicholas Steno, who is considered the father of modern stratigraphy, which is the study of layers of rock. He described four principles of stratigraphy that still hold true today:
Principle of superposition: States that in an uninterrupted sequence of sedimentary rocks, the rock layers below are older than the rock layers above (as long as they have not been deformed).
Principle of original horizontality: States that sediments forming sedimentary rocks are usually laid down in a horizontal position (due to gravity). Therefore, rock layers that appear vertical have been moved from their original, horizontal position by some natural force (such as an earthquake).
Principle of lateral continuity: States that when sediments are laid down, creating sedimentary rocks, they spread out until they reach some other object that confines them. This principle is illustrated when you fill your bathtub with water. The water spreads to fill all the space, confined only by the edges of the tub. Pour that same amount of water on the bathroom floor, and it spreads out until it hits the bathroom walls. Sedimentary rocks, like water, continue laterally until they are stopped by some other object.
Principle of cross-cutting relationships: States that where one type of rock cuts across or through another type of rock, the rock being cut is older and the rock cutting through is younger. After all, a rock must already exist, in order to be cut through by another rock.
The Earthcache
The rock feature here is a part of the Castlemaine Group, which is 485.4 - 458.4 Million years old. The Castlemaine Group comprises marine turbitic sandstone, mudstone, black shale and minor granule quartz conglomerate. Mostly thick bedded sandstone, course to fine grained, moderately to well sorted, sparsely fossiliferous with graptolites.
As indicated above, the rock at GZ is mostly thick bedded sandstone that is course to fine grained. Observation here clearly shows that the layers have undergone some changes when considering the principles of stratigraphy as theorised by Steno.
With the principles of uniformitarianism in mind, that the present gives us a window to the past, we see from our observations that there has been significant structural changes occuring at this location.
The Location
Vaughan Springs was formerly a large gold rush township called ‘The Junction’. It became a favoured alluvial gold and market gardening locality for Chinese miners. The immediate area is now a public access reserve, manged by Parks Victoria.