Tuesday, July 01, 2008

Rottnest rocks

We know Rottnest is the antipode of Bermuda. Or is it the other way around?

Anyway…the beautiful island and its far-away equivalent have more in common than appears at first geographical think. We got our rocks off with this information, ‘Stratigraphy and timing of eolianite deposition on Rottnest Island, Western Australia’, by a boffin at a Queensland uni.

Would you believe: “Over 100 whole-rock amino acid racemization (AAR) ratios from outcrops around Rottnest Island (32.0° S Latitude near Perth) indicate distinct pulses of eolian deposition during the late Quaternary.”

We kid you not. It’s late and we're still baffled at Demelza winning A'sNTM, but racemization is some sort of geological process, and eolian is to do with wind erosion.

There’s some discussion – including numbers (never Rotto Bloggo’s meanest point) – about modal classes of rock ratios, but the Rotto stuff under discussion seems to have been deposited around 70,000-80,000 years ago.

“Oceanographic evidence indicates the area was subjected to much colder conditions during MIS 2–4 (10,000 to 70,000 yr ago), greatly slowing the epimerization rate. Eolianite deposition resumed in the mid Holocene ( 6000 yr ago) up to the present.”

Damn that slow epimerization rate. The Rottnest Island Authority would’ve stopped that. Or they would’ve taxed it. But here’s the Bermuda angle:

“The A/I epimerization pathway constructed from Rottnest Island shows remarkable similarity to that of Bermuda in the North Atlantic (32° N Latitude). These findings suggest that, like Bermuda, the eolian activity on Rottnest occurred primarily during or shortly after interglacial highstands when the shoreline was near the present datum, rather than during glacial lowstands when the coastline was positioned 10–20 km to the west.”

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