Mastodawn

#ThinSectionThursday 🔥 Hot off the microscope this morning! 🤓 This may look dull, but the big clear (grey) grain with faint WSW-ENE parallel lines, on the right hand side of the image is a shocked quartz (produced by a meteorite impact).

The smaller greenish (orange) grain to the left is epidote. All the fragmental grains here been cemented together by turbid brown albite. From the enigmatic Stac Fada unit, (Proterozoic), in NW Scotland.

More info in Alt text.

#Geology #StacFada #Impact

@FaithfullJohn Nice!

@FaithfullJohn Cool. 😎
I didn’t know about this, what would you recommend reading?

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John Faithfull 🌍🇪🇺🏴󠁧󠁢󠁳󠁣󠁴󠁿🧡✊🏻✊🏿1d ago

@BashStKid There's lots of literature on this since the discovery in 2008. It's clear that the unit does include a lot of impact debris, but almost everything else remains the subject of disagreement/ambiguity. Most literature is behind paywalls. But some Open Access ones like this: https://onlinelibrary.wiley.com/doi/full/10.1111/maps.14035 (NB I'm not 100% convinced by the claims in this paper about coesite and diamond). Rob Butler did a nice YouTube video (although some would disagree with some of this): https://www.youtube.com/watch?v=HmOf6TODAL0

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BashStKid 1d ago

@FaithfullJohn Thanks. No problem with disagreement and argument, just shows it’s alive.

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John Faithfull 🌍🇪🇺🏴󠁧󠁢󠁳󠁣󠁴󠁿🧡✊🏻✊🏿1d ago

@BashStKid Exactly. But many of the issues about this unit are particularly unresolved - even basic things like transport directions during deposition! I was taken there on a field trip a long while ago, before it was reinterpreted as an impact deposit. I need to go back!😊

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BashStKid 1d ago

@FaithfullJohn Looking through previous interpretations usually reminds you how easy it is to fool yourself.

Put us back 70 years, we’d all be talking about eugeosynclines.

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John Faithfull 🌍🇪🇺🏴󠁧󠁢󠁳󠁣󠁴󠁿🧡✊🏻✊🏿1d ago

@BashStKid