Cute lil dropstone!
My initial interpretation:
Once upon a time and long long ago, an existing rock fell into squishy mud. Time, pressure, & natural cementing hardened the mud into rock ...with rocks stuck in it.
My initial interpretation:
Once upon a time and long long ago, an existing rock fell into squishy mud. Time, pressure, & natural cementing hardened the mud into rock ...with rocks stuck in it.
https://twitter.com/Sydonahi/status/1312841299708444672
This isn’t the only possible story!
I’m basing my interpretation on location (beach), that the rock looks gritty (grains not crystals), and that the boundary between the colours looks raised lips (not weathering rind or contact metamorphism).
I’m basing my interpretation on location (beach), that the rock looks gritty (grains not crystals), and that the boundary between the colours looks raised lips (not weathering rind or contact metamorphism).
All those dimples look like places other pebbles were plucked from the host rock* as it was exposed & eroded.
(*former mud/silt/sand now mudstone/siltstone/sandstone depending on proportion of fines).
(*former mud/silt/sand now mudstone/siltstone/sandstone depending on proportion of fines).
What I DON’T see are ripples.
That means my story only makes sense if this particular patch wasn’t exposed coast, but something more sheltered like a bay or protected delta.
That’s not unusual. Coastlines shift back & forth with changing (local & global) sea levels.
That means my story only makes sense if this particular patch wasn’t exposed coast, but something more sheltered like a bay or protected delta.
That’s not unusual. Coastlines shift back & forth with changing (local & global) sea levels.
Rocks need to exist before anything can happen to them, so we know the smaller embedded rock is older.
It looks similar enough in texture that it might be a bit of even older muck. Then we have 3 beaches in 1 photo: modern sand, old mudstone, older embedded pebbles & cobbles!
It looks similar enough in texture that it might be a bit of even older muck. Then we have 3 beaches in 1 photo: modern sand, old mudstone, older embedded pebbles & cobbles!
I like this interpretation, too, and it works with the “everything looks very, very similar.”
A concretion is when a bit of initial precipitation nucleus results in sediment cementing together harder than surrounding sediment, like the geological equivalent of a pearl.
A concretion is when a bit of initial precipitation nucleus results in sediment cementing together harder than surrounding sediment, like the geological equivalent of a pearl.
https://twitter.com/cirquelar/status/1312862773047521281
That initial precipitation nucleus would be in the centre of the concretion.
It can be fun to discover what the nucleus is: leaf, tooth, fossil, shell fragment, although in England they’ve also found concrétions formed around WWII shrapnel!
It can be fun to discover what the nucleus is: leaf, tooth, fossil, shell fragment, although in England they’ve also found concrétions formed around WWII shrapnel!
A similar variation is instead of concretions, this could be nodules: no nucleus, but a mineral replacement sometime later because of Reasons.
I don’t like that interpretation as well for this particular circumstance as nodules tend to be more dramatic contrast (& that lip-rind)
I don’t like that interpretation as well for this particular circumstance as nodules tend to be more dramatic contrast (& that lip-rind)
Oooh, this rock is on a NZ beach, so our alternate story could start:
Once upon a time and long, long ago, a penguin died and was buried in muck.
Once upon a time and long, long ago, a penguin died and was buried in muck.
https://twitter.com/coastalpaleo/status/1312866841824550912
We could tell these stories apart with a bit of SMASHY-SMASHY to see if we can find something in the centres of the globs.
We could also look at the wider landscape to see if we can spy more context or additional examples with more hints.
We could also look at the wider landscape to see if we can spy more context or additional examples with more hints.
Another idea is this could be a trace fossil of old structures in the mud.
If so, the two globs could be part of the same burrow but we’re only seeing part of it exposed, the rest of the network still hidden within the host rock.
If so, the two globs could be part of the same burrow but we’re only seeing part of it exposed, the rest of the network still hidden within the host rock.
https://twitter.com/funkydeathworms/status/1312850310222708742
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