Wyomingpaleo's Sedline News:

Triassic Coffee Beans!

Dave — Thu, 19 Mar 2009 02:22:37 +0000

The other day Steve, Mary, and I were out in the Early Triassic beds of central WY and ran across these silly buggers, they look for all the world like coffee beans. I believe it is a trace of some critter or another, but I haven’t figured out what yet. Who knows, maybe its a little bivalve ‘sitz’ mark or bug burrow. Until I find out, Triassichnus coffeebeanensis is born!

Slab containing Triassic Coffee Beans

Close up - a collection of

Even closer view!

Coffee bean!

Flame structures and more!

Dave — Mon, 16 Mar 2009 06:17:11 +0000

I was out visiting some outcrop earlier today (it’s been a while since I’ve moved to WI that I have gotten onto some good rocks… ergo the delay in posts! Sorry!) and ran across some pretty/cool flame structures throughout the lower 1/2 of the block. There wasn’t much of a grain size variation in this little package (all lower/upper very fine) and was a muddy silt below (less resistant). The muddy silt had minor ripples and an almost varve-like alternating darker/lighter banding along the order of 1-2 mm sets.

These structures are from Early Triassic rocks and are about 1 meter above the next set of images. Rhynchosaur tracks are commonly found just above this interval.

The image below is about a meter below (stratigraphicaly) the image above. It exhibits planar bedding, and parting lineations (seen in the next two images that follow). This is a fallen block that was easier to sample than the 3 meter cliff former. The base of this unit has nice cross bedding, and becomes laminar at the top and is capped by about 10 cm of ripples with some stoss side preservation.

The next two images are the same piece in slightly different light in order to express the parting lineations (or at least I think they are!?). The raised bumps are bits of hematite that typically stain these rocks their characteristic red colour.

References

Fielding, C. R., 2006, Upper flow regime sheets, lenses and scour fills: Extending the range of architectural elements for fluvial sediment bodies, Sedimentary Geology, v. 190, p. 227-240

Beware: Premature withdrawal leads to slumping

Dave — Wed, 01 Oct 2008 04:31:56 +0000

Jelle Wiersma and I were checking out an outcrop of Morrison between two sections we (Deb Jennings and I) measured the previous summer. On our way along the contact between the Sundance FM and the overlying Morrison, we ran across some sauropod tracks in the upper portion of the Sundance. This is a foreshore(?) deposit capped by beach dunes (no thin sections of this eolian sand yet, but the ones about 3 miles down strike are composed of oolites and sand).

The image below shows the cross section of the track in the foreshore sandstone. There is a block at Jelle’s feet, it contains the other half of the footprint. If I can get a permit and figure out how to slice of a section (big ass portable rock saw?) it would make a cool museum display and maybe a tight little paper (including a detailed measured section of Sundance!)?

Jelle Wiersma, Sundance FM, sauropod track in cross section.

Jelle Wiersma, Sundance FM, sauropod track in cross section (w/outline of deformation).

The image above has been traced out to better show where the shear is. The breccia is not very visible in the picture unfortunately, but it is quite apparent on outcrop. The micro detail is amazing, you can see a series of normal faults with 1-3 cm displacement on the back side (heel) and the breccia is in the middle and towards the front (toes) most likely from withdrawal of the foot. The surface feature produced (at the time of deposition) was covered and it is very difficult to see these prints on the surface (née impossible!).

I wonder if they’d show up in a GPR study? Tracks from the Upper Sundance aren’t unheard of, but this is unique in terms of preservation and environment. ‘Normally’ the tracks are in a limestone that typifies the Sundance/Morrison contact. Oh, and there are at least 7 tacks in cross section along the small section we walked that day, one of which was likely a juvenile or possibly another taxa.

Happy Sauropods! …er Seds! Oh wait… this is the best of both worlds!

Happy Sauropods! AND Seds!

45 degree burrows in sandstone (fluvial)

Dave — Sun, 21 Sep 2008 01:59:01 +0000

This is an image I took a while back, and it recently surfaced again. The 45 degree angle traces are evident in a few places laterally along this section of sandstone (nice structures too!). I am currently in a class (SedPaleo Seminar) that is discussing bioturbation and I hope after going through the literature over the next few months I will have a better story for this image.

If anyone has images of wasps burrows in cross section, or anything that demonstrates a burrow like this I would love to see/hear about it. I have looked through Hasiotis’s (2004?) Morrison trace paper, but I didn’t see anything that really looked like this. The search continues…

Happy Sauropods! Seds!