8 January 2015

Stromatolite at the Strasburg Museum

The other fossil I saw at the eclectic and haphazardly-curated Strasburg Museum was this stromatolite.

Top view:

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Side view:

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Probably this comes from the Cambrian-aged Conococheague Formation, although the Beekmantown Formation (early Ordovician) is another possibility.

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7 January 2015

A mafic sill in Antarctica

My friend and colleague Lauren Michel, the King Family Fellow at the Perot Museum of Nature and Science in Dallas, Texas, sent me this image from her recent trip to Antarctica:

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This is a beautiful example of a mafic igneous sill, probably of the rock known as “dolerite” (or diabase, to us Yanks). Lauren and I think it must be part of the Ferrar Large Igneous Province. (They are Jurassic in age, emplaced upon the breakup of Pangea.) The location is apparently in the Beacon Valley, near the Taylor Glacier. At first, the middle of the photo looks strongly like a fault. However, upon closer inspection, I’m not so sure.

Here, I have annotated it to show the apparent continuity of bedding:

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Let’s take a closer look:

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It seems like the thing that first looks like a fault is really a dike, and that the strata are more or less continuous across the field of view, with the exception of regions “A” and “B,” which don’t obviously match up, though the layers immediately below them do…

Well, is there anything else to see here? Sure there is!

There are various details of the igneous intrusion to be seen, like on the right side of the photo, where we can witness the fresh production of xenoliths along the roof of the magma chamber, where these “alien rocks” are being liberated through the process of stoping:

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(I’ve previously highlighted stoping in Torres del Paine, Patagonia.)

And off to the left, we can see a subsidiary sill that’s opened off due to an offshoot dike from the main sill.

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Great stuff – my students and I will see a similar sill/dike/sill relationship in the Purcell Sill, cropping out in the cirque above Grinnell Glacier in Glacier National Park, Montana, this coming summer.

Thanks for sharing, Lauren!

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5 January 2015

Pygidium from the Strasburg Museum

My family and I went to the Strasburg Museum in Strasburg, Virginia, last fall, because (1) we’ve lived out here for two and a half years now without stopping in, and we felt “overdue” for checking it out, and (2) a big train is prominently featured out front, and my son is really keen on trains right now due to the “Thomas the Tank Engine” series of books. I don’t have much to report about the museum, but they do have a couple of fossils, and so I figured it was my duty as a geoblogger to document them and share them with the world.

Fossil trilobite pygidium (“tail plate”):

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(About 1 inch or 2.5 cm across)

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2 January 2015

Friday folds: Cabbage Island, Maine

Devonian metamorphic rocks (garnet-bearing gneiss) exposed on the western side of Cabbage Island, Maine:

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And here it is in GigaPan form:

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1 January 2015

2014 Yard List

A list of birds seen in my yard this year.

Lists for 2013 (52 species) and 2012 (32 species) here.

  1. Downy woodpecker
  2. Mourning dove
  3. Dark-eyed junco
  4. Tufted titmouse
  5. White-breasted nuthatch
  6. Black-capped chickadee
  7. Goldfinch
  8. Pileated woodpecker
  9. Red-bellied woodpecker
  10. Turkey vulture
  11. Hairy woodpecker
  12. Eastern phoebe
  13. Red-tailed hawk
  14. American crow
  15. American robin
  16. Cardinal
  17. Bald eagle
  18. Brown creeper
  19. Barred owl
  20. Carolina wren
  21. Brown-headed cowbird
  22. Chipping sparrow
  23. Whippoorwill
  24. Turkey
  25. Broad-winged hawk
  26. Black vulture
  27. Blue-gray gnatcatcher
  28. Ruby-throated hummingbird
  29. Yellow-throated vireo
  30. Sharp-shinned hawk
  31. Rose-breasted grosbeak
  32. Blue jay
  33. Indigo bunting
  34. Raven
  35. Red-eyed vireo
  36. Barn swallow
  37. Baltimore oriole
  38. Yellow-rumped warbler
  39. Yellow warbler
  40. Ovenbird
  41. Hermit thrush
  42. Great crested flycatcher
  43. Scarlet tanager
  44. Common nighthawk
  45. Great blue heron
  46. Eastern wood-peewee
  47. Yellow-billed cuckoo
  48. Cedar waxwing
  49. Chimney swift
  50. Flicker
  51. Eastern bluebird
  52. Red-shouldered hawk
  53. Black and white warbler
  54. Yellow-bellied sapsucker
  55. Black-throated blue warbler
  56. Purple finch
  57. European starling
  58. Red-winged blackbird

Again, the total species count went up. This pleases me. It means I’m probably spending more time outside and learning to identify new birds.

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31 December 2014

Tril-o-bits-and-pieces in a boulder on the Athabasca Glacier moraine

I love moraines, rocky beaches, gravel bars – they are like a giant smorgasbord of delicious goodies. Here, for instance, are some close-ups of a trilobite-bearing boulder on the south lateral moraine of the Athasbasca Glacier, Jasper National Park, Alberta.

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And what are these things? Any ideas?

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30 December 2014

Skolithos in Gog quartzite, on the trail to Helen Lake

Some boulders seen on the trail to Helen Lake sported lovely sets of Skolithos trace fossils. Here are two boulders, with the perspective on the tubular paleo-vertical Skolithos burrows being “map view”:

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Another boulder, in the middle of the trail, showed them in a fine cross-sectional view:

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It also included some interesting “ribbed” vertical traces that I didn’t recognize as familiar:

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Diplocraterion, perhaps? Seems too “linear” and not curved enough for that, though. They are about 3 or 4 times as thick as a “typical” Skolithos, which I would say is 3-4 mm.

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29 December 2014

Intense bioturbation in limy mudrock on the trail to Helen Lake

Look at this! A whole boulder made of trace fossils. Three photos, each more progressively zoomed in than the last.

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Update: The @ichnologist identifies these as perhaps Thalassinoides.

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26 December 2014

Friday fold: another gem from the Chancellor Slate

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That pretty much speaks for itself, I reckon.

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25 December 2014

The stromatolites of Helen Lake 2: GigaPans

Posted this morning as my “Christmas gift” to blog readers in both photo and GigaPan form, here are the exquisite stromatolites of Helen Lake, Banff National Park, Alberta.

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Finally, three other non-stromatolitic GigaPans from the site:

One of Artomys Formation siltstone / shale interbeds…
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…and two of Cirque Peak itself, showing its gorgeous internal folding:
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Happy holidays to you!

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