The real reason to come to Australia

I learned the top reasons people go to Australia at an astronomy talk by Ranger Kevin Poe at Bryce.  If I remember his list correctly, the top reasons were to see the Sydney Opera House, koalas and kangaroos, and the southern stars - or that was the essence of it.  (Incidentally, the southern stars seriously disorient me.  It's easy to forget I'm in an unfamiliar hemisphere until I look up at the sky at night and don't recognize what's above me.  Someday I should do something about that... the recognition, I mean.  It would be difficult to change the southern sky.)

Anyway, that's not the point.  The point is that Ranger Kevin Poe missed what is, in my book, the best reason to go to Australia.  And that is, of course, the geology (I hope you guessed that).  I've only gotten to see a few good sites so far, but this stuff is seriously cool.

Wollongong is in the Sydney Basin, tucked alongside the low mountains of the Illawarra Escarpment.  The area is rich in coal seams, unusual minerals, and intriguing landform features.  I can walk twenty minutes to North Beach, wander around in a pebbly area, and pick up plenty of petrified wood that came out of the Illawarra Coal Measures.  And that's on a public beach.

Imbricated boulders

A couple weeks ago I was in the right place at the right time to sign up for the student geology club and grab the last seat on the bus to go see some interesting sedimentary deposits in Jervis Bay and nearby areas.  The only thing that I've heard about Jervis Bay is that it's beautiful, and nobody had lied to me when they'd said that.  It did not disappoint, complete with classic crescent beaches and a dolphin playing just offshore. 

Twinned glendonite crystals

There's controversy about whether some very striking deposits in the area were the result of major storms or of a tsunami.  Some of those deposits include imbricated boulders - 10-20 tons each.  A deposit is "imbricated" when the rocks line up in a preferred direction.  This is often seen in small rocks and pebbles in streambeds.  But it would take a heck of a lot of energy to do that to boulders.  In another area we saw glendonite crystals, which are pseudomorphs after ikaite - that is, they are minerals that replaced crystals that had previously formed in the area.  Ikaite only occurs at temperatures less than 4˚C, so it is an excellent paleotemperature indicator.  The crystals were sticking up out of the rock on the beach, and could sometimes reach six or eight inches long.  At another site we saw spectacular Permian fossils - bryozoans, brachiopods, gastropods, and others. 

Kiama SS (bottom) and Bumbo flow

My favorite geology, though, is at Kiama and  Bombo.  Bombo is just north of Kiama, a couple bays over.  I'm spending the semester doing research with Professor Paul Carr, and my field site is at Bombo.  It really doesn't feel like a field site - it's way too convenient.  There's easy access from the train station and highway, and it's right next to Kiama, which has all the amenities you could wish.

Wall remnant with dike

Paul took Adam Burnett and I out to see the area around the site during the first week of classes, and I'll highlight some of the cooler bits.  We started in the Bumbo Latite, a basalt flow overlying the Kiama Sandstone in a fantastic, clean contact (the units in the area are about 260Ma).  We wandered around an old basalt quarry, where they'd left walls sticking up to block the spray from the sea.  The leftover walls have spectacular columnar jointing.  Running through the area are at least five dikes dating to 200Ma that come up between the columnar joints, sometimes making right angle turns to go through cracks.  The large and beautiful xenocrysts have been identified as originating from the lower crust/upper mantle, about 70km down in the earth. 

Altered breccia (including black calcite)

Then we went over to see some aspects of the Blowhole Latite, not far away.  There are three separate flows within this basalt unit, with the middle one being the most interesting.  The lava was emplaced in a shallow marine environment, so in some places interaction with cold seawater caused the basalt to crack and break apart into a volcanic breccia, which has since been hydrothermally altered into a truly fantastic mess.  There are lots of colorful minerals, such as green chlorite and orange hematite, that have replaced material or filled in the cracks.  Vugs are full of beautifully-crystallized quartz, calcite, and the white bladed clay mineral laumontite. Some of the calcite is black, which is bizarre, so we've sampled that and are planning to do some analysis on it (some of it is bubbling away in hydrochloric acid as I write this).

In addition to the breccia, the middle flow has spectacular infilled lava tubes.  These formed when lava was flowing in channels, in which the outside cooled but the insides were warm enough to continue flowing through the tube.  In some places in the world these tubes then empty out and end up hollow, but here the lava inside cooled enough to keep them filled in.  And they're huge - apparently getting to 20m across in some spots.  I'm in the picture next to one of them for scale.

Little Blowhole

The last thing Paul showed us were two blowholes - the large one in Kiama, and the Little Blowhole just to the south.  The smaller one was going the best that day, and looked rather like a geyser.  I loved the sound of it, as well - as the water bounced around under the blowhole, it made such a low-frequency noise that you felt it more than you heard it.

Last weekend the Colgate group went out to see the geology at Bombo, and I got to help lead the trip.  It was definitely exciting to me!!  And I think most people were at least marginally interested.   At very least it's an absolutely gorgeous area, and they enjoyed seeing that.

Flow tube cross-section

My field site, however, is down on a platform at water level, and floods at high tide (you can see the platform down to the left in the picture above showing the contact between the Bumbo flow and Kiama sandstone).  I've been to Bombo five times now and we were only able to get down to the platform for the first time this week - and weren't able to stay long, at that.  For some unknown reason, when the Bumbo flow was emplaced over wet sediments, it seems that the fluids in the sediments escaped in discrete horizontal tubes.  This isn't normal, and there are a host of mysteries surrounding the tubes.  It's like a huge puzzle with, for the most part, very clear-cut pieces that just don't fit together.  If we figure it out it will be amazingly cool, but we may not find anything at all.  Who knows.  In the meantime lab = life, with most of my time spent crushing rock samples. 

A note on Australian geologists.  There is a truly inexorable force that operates on all Australian geologists at about 10:30 every morning.  Around that time, no matter where they are, what they're doing, how many samples are left to be collected, or how much the tide is threatening the field site, they break for morning tea.  It is phenomenally consistent.  When there's no nice coffee shop in the area, they sense this in advance and come prepared with thermoses of coffee and tea and enough mugs for everyone.  I've astounded many by the fact that I drink neither coffee nor tea, but I gladly accept hot chocolate, which redeems me a little.  But only a little.  Not to sound like I'm criticizing - I rather enjoy this practice.  It seems very civilized to me, and it comes at a nice time for a break.