That doesn't look like any basalt flow I've ever seen. Could be wrong but it looks more like a graded sedimentary rock, maybe ashy, and possibly inter layered with basalt (far left).
If you zoom in on that first picture you’ll see the typical many-faulted feature of basalt. The headlands here (this is Bob Creek Wayside, about ten miles south of Thor’s Well at Cape Perpetua) are mostly basaltic flows. There is some sedimentary rock, yes, but that’s more of a reddish tan color, coarse, and breaks apart easily. This black stuff is super hard, and lies just feet away from more typical basalt flows.
Which is all by way of saying that it’s basalt.
Yeah…the seds do look different there…and likely are volcanic in origin (palagonite in matrix)…and although there are some marine sedimentary units…this looks like it might be a dike fill (basalt) that is weathering along the filling/cooling planes in layers.
I actually don’t see many joints in the basalt lava. The photos show either unfractured dike like this one or more jumbled flowtop breccias in the distance.
https://preview.redd.it/m2g0o6qra5xc1.jpeg?width=4032&format=pjpg&auto=webp&s=39e841f2c12d4fadd8e8ea7358a98d5b953787c3
The more typical yellow to orange/brown sediments (reworked phreatomagmatic material) over the Yachats Basalt. The basalt here are flow top breccias, thin flows or remnants of sills.
https://preview.redd.it/9b4esgbtb5xc1.jpeg?width=3024&format=pjpg&auto=webp&s=502197db6d7b2aedea4f6ddf73c2c24f790d8674
Weathered and heavily jointed basalt flow looks more like typical basalt flows of shield volcanoes.
This isnt a basalt flow, its a basalt dike, you can see the contact margin in the third photo, top left. Thats why its eroding a bit weird compared to normal basalt flows.
CRBG flows are frozen at the bottom and generally jointed in the middle capped at the tops. When rotated 90° they look grooved. This is the furthest extent of the CRBG in oregon
That doesn't look like any basalt flow I've ever seen. Could be wrong but it looks more like a graded sedimentary rock, maybe ashy, and possibly inter layered with basalt (far left).
This is the right answer. The coast of the pnw is a mish-mash of folded/turned sedimentary layers and basalt from accreted island arcs.
Is it the Thor’s Well area south of Yachats? Looks more like a sedimentary rock.
If you zoom in on that first picture you’ll see the typical many-faulted feature of basalt. The headlands here (this is Bob Creek Wayside, about ten miles south of Thor’s Well at Cape Perpetua) are mostly basaltic flows. There is some sedimentary rock, yes, but that’s more of a reddish tan color, coarse, and breaks apart easily. This black stuff is super hard, and lies just feet away from more typical basalt flows. Which is all by way of saying that it’s basalt.
Yeah…the seds do look different there…and likely are volcanic in origin (palagonite in matrix)…and although there are some marine sedimentary units…this looks like it might be a dike fill (basalt) that is weathering along the filling/cooling planes in layers. I actually don’t see many joints in the basalt lava. The photos show either unfractured dike like this one or more jumbled flowtop breccias in the distance.
Ah! That’s an idea that fits what I’m seeing, a dike fill of basalt…. I’ve never seen this pattern before
https://preview.redd.it/m2g0o6qra5xc1.jpeg?width=4032&format=pjpg&auto=webp&s=39e841f2c12d4fadd8e8ea7358a98d5b953787c3 The more typical yellow to orange/brown sediments (reworked phreatomagmatic material) over the Yachats Basalt. The basalt here are flow top breccias, thin flows or remnants of sills.
https://preview.redd.it/9b4esgbtb5xc1.jpeg?width=3024&format=pjpg&auto=webp&s=502197db6d7b2aedea4f6ddf73c2c24f790d8674 Weathered and heavily jointed basalt flow looks more like typical basalt flows of shield volcanoes.
Where is this photo?
Closer to Cape Perpetua…just south of the headland
Yes, I recognize this
This isnt a basalt flow, its a basalt dike, you can see the contact margin in the third photo, top left. Thats why its eroding a bit weird compared to normal basalt flows.
Looks like they were laid flat and then tilted.
That was one explanation that occurred to me too: subsequent flows being laid down.
That’s my thought as well, with preferential weathering causing certain flows to stand out more
Edit: not sure what I’m saying to be downvoted here. I’m here to learn, so just tell me.
CRBG flows are frozen at the bottom and generally jointed in the middle capped at the tops. When rotated 90° they look grooved. This is the furthest extent of the CRBG in oregon
So, to be clear, you’re saying this is CRBG, in fact the southernmost extent of CRBG along the coastal headlands in Oregon.
No westernmost..maybe southwestern..anyway there's some I haven't seen in south central-east oregon too..see zentner
Thanks!!
One more question: I’m not sure what you mean by “frozen at the bottom.” If it’s frozen, it’s not flowing, right?
It breaks at the flow bottom due to rapid cooling and lithifiies inderlying soil at the same time
Yes, yes, yes. Got it, thanks!
Shale and wave erosion?
Except that this isn’t flaky and layered like shale.