SOME PHOTOS FROM MY CURRENT WORK PROJECT IN THE YARROL AREA, CENTRAL QUEENSLAND

The Yarrol Project centres on the Mount Morgan area, and extends from Ridgelands in the north to Monto in the south. The main focus was on the rocks deposited during the Permian to Silurian times (250 to 480 million years ago). For most of that time, the edge of the Australian continent was near Emerald, and the Rockhampton area was a chain of volcanic islands a long way off shore.

Here are a few photos of some scenery and rocks in the area.

This shot is of the Mount Morgan mine. It was one of the largest gold mines in the history of Queensland. It produced 250,000kg of Gold, and 360,000t of copper.

One of the great things about being a geologist is that you occasionally get to go to some interesting places. This photo is of an old steam boiler from the Rose mine. The Cania Dam and the cliff-forming Precipice Sandstone of the Cania Gorge area are visible in the background. It is quite a scenic spot that I was able to work around for several days.

Unfortunately, even though the scenery can be interesting, geologists have to look at the rocks

This is an outcrop of basaltic lava that flowed under water, probably deep marine, and is referred to as a "pillow" basalt. The water causes the skin of the lava to cool and behave like a plastic. This causes the lava to flow as many tube-like blobs, which eventually overlie each other. The ovals above are sections through the tubes, and you can see the dark, "chilled" margins of the lava.

This photo is of some thinly bedded, very fine-grained sedimentary rocks. Evidence indicates that they were deposited in a deep marine environment, in water depths between 750m and 1000m deep. The water was very still, allowing these very fine sediments to slowly accumulate on the sea floor. Examining these sediments under a microscope revealed that they contained abundant radiolarian fossils. Radiolarians are beautiful, microscopic, single-celled animals that built skeletons out of silica. See the picture below. The abundance of rads indicates that the sediments accumulated very slowly. The slower the deposition, the more rads are able to die and be deposited within a single layer.

The conditions on the sea floor were usually very calm, but occasionally you get sub-marine avalanches that rush into the area with a lot of power, ripping up part of the sea floor sediments as they go. The above photo is an example. You can see flat, platy fragments that were pieces of sea floor sediments before they were ripped up.

The deepwater rocks shown above are from the eastern part of the Yarrol Province. As you go west (towards the old continental margin), the environment of deposition gets shallower.

As the water becomes shallower, it is more common for sunlight to reach the ocean floor, particularly once the water depths are less than 100m, and certainly once it is less than 30m. Most marine organisms and ecosystems are reliant on sunlight, particularly corals which are dependant on photosynthetic, symbiotic algae within their tissues that help them build their skeletons. The photo above is of a limestone that contains abundant fragments of corals

In the western part of the Yarrol Province, the environment of deposition becomes very shallow. This outcrop is a pavement of large, fossilised ripple-marks. These are a peculiar type of ripple that is only created by wave action (as opposed to currant action), and indicate that these rocks were probably deposited in less than 10m of water. (Note: the person in the background isn't me)

Also in the western part of the Yarrol Province are rocks known as ignimbrites. These are formed when a volcano erupts explosively, which then causes a "white" hot cloud of ash, dust and rock fragments to surge away from the volcano at close to the speed of sound. They are so hot when they finish surging, that they often "weld" them selves into glassy rocks. The final eruption in the movie "Dante's Peak" was an ignimbritic eruption, but the ones in the Yarrol Province would have been much bigger explosions than the one in the movie. The above rock is a fairly typical ignimbrite. The recessive patches are flattened pieces of pumice, you can see hard, protruding, rock fragments, and the small white specks that are visible throughout the rock are feldspars.

These rocks also indicate very shallow water, or terrestrial environment. If they surged into deep water they cool too quickly, and would not "weld" themselves.

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