Fossils - Silurian

Seastars (Salteraster sp) from the Silurian. Recovered from Clonbinane, Victoria. The seastars are approximately 5cm wide. Photographed at the Melbourne Museum on the 7/5/2015 by Ant. There doesn't seem to be a whole lot of biodiversity represented in this rock.

Places I've been: Eric the Red, Otway Basin, Victoria

 

The anchor of Eric the Red, a ship that sank in 1880. The local council periodically cements the anchor back down as the erosive action of the waves on the shore platform  frees it.

The anchor is located near the Eric the Crawfish dinosaur dig site. The dig is organised by Museum Victoria. It operates for one month in Summer and typically consists of 12-18 volunteers and Museum staff. This dig is the partner to the Dinosaur Dreaming dig on Flat Rocks, Inverloch. The sediments here are 120 million year old feldspathic sandstone with scour structures that are filled with mudstone ripup clasts and coal deposits. The depositional environment was a broad river that took advantage of the emerging East-West rift valley as Australia and Antartica started to break apart. Many notable dinosaur fossils have been found at these sites.

Jasperlite from Western Australia

 

 Jasperlite (aka BIF), 2.5 billion years old. Ord Ridley Ranges, Western Australia. Photographed at the Melbourne Museum on the 7/5/2015 by Ant.

Melbourne's limestone coast

 

Loving the limestones at Loch Ard Gorge.

The Melbourne Museum

A visit to the Melbourne Museum geological section isn't complete without the obligatory 'Help I got eaten by something bitey' picture. I highly recommend checking out the geological history of Victoria section as well as their beautiful rocks and minerals bit. They have some lovely meteorites and ore samples.

Australian fossils - Elvisaurus (Cryolophosaurus)

This is part of a travelling fossil-life of Australia exhibit which I managed to catch at the Geelong Wool Mill Museum (of all places). I joined one of Jim and Julies Field Trips and we went and saw these fossils before journeying across the bay to search for fossils in the Inverloch area.

The Crylophosaurus, the first carnivorous dinosaur to be discovered in Antarctica, 190 million years old (Early Jurassic). It has commonly been called the Elvisaurus due to the unique crest on the skull. Photo by Ant.

Places I've been: Blue Lake, Mount Gambier, South Australia

 

The most recent field camp took me to the Mt Gambier marr complex along the limestone coast. Mt Gambier's marr complex consists of four (or more) craters, two of which are now above the water table. The largest, Blue Lake, is approximately 70m deep and houses the towns water supply. The local aquifer is composed of limestone, and needless to say, the local population has a minor calcite scale issue inside their pipes. During Summer, the Blue Lake turns a vibrant blue as the warmer water contains more micro-crystals of calcite which reflect the blue wavelength. Mt Gambier is part of the Australia's Newer Volcanics which extends from Mt Gambier to the CBD of Melbourne. The Newer Volcanics is composed of 437 volcanoes (the awesome Dr Julie Boyce counted them!) and the most recently dated eruption is Mt Shank, about 10 minutes south of Mt Gambier.

 

As I as there after summer, the water had returned to it's typical slate blue/grey colour.

 

I've always wondered if this is a fault where you can see the offset between the limestone, basalt and ash layers. This may also be an optical illusion created by a cove. Someday I'll get to the other side of the lake and check it out.

Countertop geology: Tiger eye, Hamersley Range, Western Australia

Some seections of the Marra Mumba tigers eye from Hamersley Range (WGS84 21° 53′ 0″ S, 116° 46′ 0″ E). Photographed on the 7/5/2015 at the Melbourne Museum by Ant.

Geology around town - Basalts at Southern Cross Station, Melbourne, Aus

 

This is a picture of something residents of Melbourne take pretty much for granted - basalt pavers. They're everywhere, we've used them in to make gutters, pave the city and build old churches and public buildings. Why you ask? Do the people of Melbourne like having a grey city or do the architects have something about igneous rocks? Nope, we've used them because there are 437 volcanoes (at last count - thanks Dr Julie Boyce!) between the CBD of Melbourne and Mt Gambier in Souther Australia. These have provided a plentiful supply of basalt which is both easy to access and a reasonably good building material (compared to limestone).

As a result, we as Melbournians, see it everywhere. Recently, the Melbourne City council decided it wanted to replicate the 'laneway' feel of the city so many internal walking zones have been paved with this stuff too.

The bubble trails in the basalt give them texture and visual interest. By looking at the bubbles you can often tell which way they were traveling and thus which side is 'up'. The gas bubbles are created when volitiles in the magma are able to exsolve due to the decrease in pressure as the magma rises to the surface. The gas bubbles then move to the surface of the magma but quick cooling will often trap some of the bubbles leaving these delightful trails behind. If you look at the bubbles they will often have a hot-balloon shape. The thin part of the bubble points to the direction it came from where the top of the balloon heads towards the area of least pressure (i.e. the top of the lava). In the image above I spotted three balloon shaped bubbles but as they are in the minority, and point in three different directions I'm of the opinion that this bubble trail was actually rising towards the viewer.

Photos taken at Southern Cross Station, Melbourne on the 2nd of September 2015 with an Iphone 4.

Countertop geology - Sheared spashback

 

This lovely rock has been used as the splashback for my friends kitchen. It was sold to her as 'black granite' but you and I know there is no such thing.

 

A closer inspection shows that the white veins are composed of feldspars while the darker matrix contains a significant amount of greyish quartz. The rock has undergone a significant amount of stress as shown by the sigmoidal shape of the feldspar vein in the image above. I'd love to get my hands on a raw edge of this rock, or perhaps see it in strong sunlight so I can determine the composition better. It is however, a lovely rock.

Sedimentology!

 

Sedimentology - the quartz rich sands of a beach near San Remo

On a date with a geologist - Date 4, part 1.

 

Wall made of local stone at The Cloisters. 

Date four was amazing! We traveled to various locations in Eastern America and saw a lot of rocks. We spent a day checking out The Cloisters, a museum dedicated to Medieval art in New York to satisfy my other interests. The museum overlooks the Hudson River and is composed of three reconstructed cloisters acquired from various areas in Europe as well as a great many artifacts and artworks from the 12th - 15th century. The buildings are based in a beautiful park land and feature both imported and local stone. One of the beautiful rocks used for the carpark walls is a local garnet schist. It has undergone significant metamorphism and shows bands of garnets as well as aluminosilicates.

 

Garnet in the schists

We did take a moment or two to head out onto a balcony and take some happy snaps of the river, the bridge we crossed onto the island over and of course, each other. Out here we discovered some interesting things.

 

The river.

Part of The Coisters are clad in micro-granite blocks. I do not know if they are local but given the presence of the schist, it stands to reason there was once a local subduction zone so there should be some local granites forming. Some of these micro-granite blocks feature lovely aplites dykes as pictured below. Aplite is a fine grained intrustive rock composed of quartz and feldspare (thus the pink colour). It is often produced as the final spurt of melt which fills in / takes advantage of small cracks in the rapidly cooling batholith.

 

Aplite dyke in a micro-granite blocks.

The balcony has also been crafted of local stone and displays a rather lovely meta-psammo-pelite aka gneiss. Below is a photograph of a rather lovely specimen showing dark and light banding.

Geology around town: Flinders St Station, Victoria, Australia

 

Flinders Street Station, with an iconic Melbourne tram.

During a recent trip to the city of Melbourne I spent some time admiring the granites at Flinders Street Station. The granites most likely originate from the Harcourt Granite, located near Castlemaine, Victoria. They are a lovely creamy colour, course grained and feature a number of xenoliths and enclaves.

 

A xenolith, hornfels (with remnant bedding?)

 

An enclave featuring large K-feldspars located under the ticker sellers window.

 

Under the clocks to the right this xenolith is halfway up a pillar.

Countertop geology: sheared granite

Today's countertop geology was brought to you by friends in Queensland. They have the most lovely granite table on their verandah and the fed me delicious Canadian breakfast foods while I took these photos.

This granite has been sheared and the phenocrysts are surrounded by almost sigma-shaped matrix. The picture below shows a grain that is probably at right angles to shear direction and as such hasn't rotated like some of the others.

Places I've been: Organ pipes National Park, Victoria, Australia

 

Looking east at the leading edge of the organ pipes structure.

The second stop on our Igneous Geology field trip is the Organ Pipes National Park. As this was part of our first date, I've already posted about this location so won't go into much more detail. I will however show to pictures of new things I got to see this time:

 

Basaltic columns near the edge of Jacksons Creek just past the Tesselated Pavement. Hexagonal columns are created by the contraction of the cooling lava cracking at approximately 120 degrees. These cracks propagate downward as the body of lava cools creating columns.

 

The contact between the basalt and the underlying sediments. The white line is the metamorphised sedimentary rock, and is about 5mm thick.

 

Just below the contact, something I've never noticed before!

 

A conglomerate containing rounded quartz pebbles (1cm) and large angular sandstone cobbles (up to 10cm). This indicates the rock is not the Ordovician sediments but reworked into terrestrial sediments from the Eocene.

Places I've been: You Yangs granite, Victoria, Australia

It's that time of year again - yes the end of May. This comes with the inevitable two or three weekends of teaching the 1st year geology igneous field trip. Our first stop is the You Yangs granite. One of the biggest, and closest examples of a granite to CBD Melbourne (WGS84 37° 57′ 0″ S, 144° 25′ 48″ E), it towers over the basaltic plain to the west of the city. On a clear day the views are lovely, and you can even just see the Menzies building towering over Clayton in the far distance.

The You Yangs are a small granite body, more of a stock than a batholith. The granite is rich in quartz, oligoclase and orthoclase with minor mafic minerals such as biotite and hornblende. The You Yangs are porphyritic with large K-feldspar (orthoclase) crystals up to 7cm long and a course grained groundmass. The granite also contains numerous xenoliths and enclaves.

 

A granitic tor located behind the picnic ground bathrooms.

 

An enclave in the tor - note the concentration of dark minerals and the presence of large K-feldspar crystals suggesting a similar chemistry to the granite. This is a large example of an enclave and spans 25cm. Some of the enclaves I've seen in this granite are 60cm wide.

 

A close up of the side of the granite

 

Closer still - a xenolith is bisected by two aplite veins. Xenoliths are pieces of country rock that have been surrounded by the magma during intrusion. They are then metamorphised by the heat produced by the cooling granite. The xenoliths seen in the You Yangs are typically hornfels, formed from metamorphising the Ordovician siltstones and sandstones (marine). Aplite is a quartz rich vein with small amounts of feldspar. It is thought to be the residual melt that solidifies in the cracks formed in the cooling granite.

 

Pseudofossils - 12 Apostles, Victoria

I spotted some beautiful faux fossils in the sandy-limestone used to make the underpass at the 12 Apostles while I was there with the JMSS geology class a month ago. These dendritic patterns are formed by the deposition of minerals by hydrothermal fluids. They are often mistaken for plant fossils by the geologically-uneducated. Still, they're quite pretty.

 

Sandy-limestone? in the underpass at the 12 Apostles, Victoria.

How I feel about geology

 

Medium grained, feldspathic sandstone from the Otway Basin with a tiny bit of coal.

Fancy folds - Chile

 

A fold in Rio Leon Park, Chile. (-52.740004, -72.148885) Fold is approximately 2.8km wide.

 

Parasitic folds near the hinge - wavelength of ~250m

 

Second fold to the east (400m wide), faulted off the main complex?

Counter top geology: 4/2/2015 - Galaxy 'granite', Andhra Pradesh, India

Galaxy Granite is mined in various places in India such as Chimakurthi. Though it is marketed under the term 'granite' because it is hard and dark it is actually Gabbro. Light coloured and soft rocks are almost always marketed under the term Marble. The Galaxy Granite is unusual because it contains small crystals of bronzite which give it a bright sparkly effect and as such is occasionally marketed as Star Granite. Massive shout out to Wendy Kirt and David Cook who published Graveyard Geology.  It isn't amazing in a photograph but would like great as a counter or some other decorative stone.

 

Photo from Stone Network.

Date Idea - 28/1/2015 - Losar, Tibet

Image from the Harvard Art Museum, item 2.2002.107. Photograph taken by Samuel Bourne (1834-1912) of Contorted Strata at Losar in 1967.

It'd be awesome to find this uplifted strata and take a gigapan pic to compare with Sam's image. I'm not sure how 'contorted' the strata is, I suspect the appearence of much of the folding is actually due to erosion and faulting.

Places I've Been - Volcano, Aeolian Islands, Italy

In August 2014 I went on a wonderful second date to Europe. We visited Germany, Holland and Italy and saw many beautiful things and ate lots of tasty things. Most of our trip to Italy was spent in the Aeolian Islands. The Aeolian Islands are a volcanic arc with two active volcanos, Vulcano (where we stayed) and Stromboli (which we visited).

It was a lovely trip involving a hike to the peak of Vulcano, a swim in the effervescent sea and an evening cruise around Stromboli to watch it erupt.

The Peak/Crater of Vulcano.

Counter top geology: Verde Smeraldo

Countertop geology - as a quartzite, this would make a lovely countertop. The high silicon content would result in a strong surface that doesn't scratch easily and retains it's lustre.
Verde Smeraldo - Green Quartzite from Bahia, Brazil. Image from quarry owner here.

Date ideas: 7/1/2015 - Waimea Canyon, Hawaii

There are many, many things in Hawaii that I wish to see. Waimea Canyon just made the list.

Located in Kauai, part of this canyon structure was create by water, the rest by a sequence of faults after volcanic collaspe. What appear to be sedimentary layers are actually basalts which have weathered in the humid climes to a charateristic red colour.
A friend of mine who's completed this hike about a month ago tells me somewhere here there is a waterfall and a pool that he recomends swimming in. I might have to look into that.