Today has been a geologic extravaganza, as I have tried to
decipher the stratigraphy and structure of the Grampians. To assist me I went
in about ten different (short) hikes in different portions of the park, and on
every one of them thought that it would be great fun to teach Field Geology
here.
The one interpretive geology board I saw was, in my not so
humble opinion, completely wrong, assigning the rocks to the late Cretaceous.
Ha! I saw a “winged” brachiopod in one of the outcrops, so I am pretty certain
that these are Silurian rocks. To remind you, in Silurian time neither plants
nor animals had colonized the land, so imagine a landscape of low-lying barren mountains
where physical weathering dominated to release enormous volumes of sand into
the streams, which braided their way down to the coast, where coastal lagoons
and shallow marine sands hosted a teeming ensemble of brachiopods and trilobites.
This is what the southern portion of Australia must have looked like 400
million years ago.
The Grampian sandstones were then deformed and intruded by
red porphyries (which I happen to remember from my Historical Geology are
Devonian in age). Silurian biologists would have spread fear among the first
plant “sticks” venturing out unto the land by telling them about the impending
dangers from global warming and the rise of sea level, but the sedimentary
sequence appears regressive to me, with shallow marine bioturbated fine
sandstones in the bottom, finely laminated coastal lagoon deposits in the middle,
and cross-bedded fluvial conglomeratic sandstones on top. As for the structural
deformation, all I can say is that it was pretty strong, so when you stand at
any of the
vista points you can look at long cuestas dipping
away from the crest of the mountains both to the west and to the east, which is
why the whole mountain massif has a north-south elongation.
After making up the story told above, I was looking
somewhere for a geology display in both the park or the visitors center. No
luck. Everybody here is fascinated with the wildlife (and yes, I keep meeting wallabies
and kangaroos, but so far have not seen any giant spiders), but there is no mention
about the geology.
The park is a place of great beauty, where the rays of the
sun and sudden intrusion of clouds make every valley a canvas of contrasts and
color. The forest itself looks like the rendition of another world, worthy of
the Martian forests imagined by Edgar Rice Burroughs. They are perfectly good
forests, mind you, but when you look at them in detail you notice that there is
bewildering variety of eucalyptus forms (big imposing trees, skinny ones with
dense foliage, or lollipop ones with a bare trunk and a dollop of leaves on the
very top), interspersed with innocent looking plants bristling with thorny leaves,
or tufts of grass growing out of meter-tall pedestals. I need to also add the
variety of brightly colored parrots, black-and-white magpies, and laughing
kookaburras, which make a walk through the woods a musical experience.
I am now back at the campground, and the warmed pool is
beckoning, so I think I will bring today’s reflection short. Cheers!
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