Tl, Cl and SEM Yaxcopoil-1

Comparison of foram-like shapes (TL), (CL) (SEM) from core Yaxcopoil-1 794.11m -794.60 m depth in the Chicxulub crater. Keller (2004, 2004a) interpreted these shapes as cross sections of foraminifer. On this page is argued that these shapes are in fact dolomite grains overgrown with a rim of zonede dolomite, probably during hydrothermal alteration of this porous fine sandstone


Backscatter image of sample yax315. The scale from left to right is 5mm. Dark grey areas are dolomite (Mg, CaCO3), bright is calcite (CaCO3) and dark is empty porespace or silicate. The region in pink is enlarged on the right (top)		Enlargement of colored area of image on the left. The bright areas are pore-filling blocky calcite (the filling is one single crystal). The calcite encloses authigenic low-temperature quartz idomorphic crystals, as is show on the enlargement here below, where the different chemical elements are X-ray mapped on the electron microprobe. Below enlargement of coloured area

X-ray map of the Mg Ka peak, showing clearly that dolomite is the dominant composition. The large dark area does not show any Mg Ka peak, because the region is pure CaCO3, normal for low-temperature calcite top	Backscatter image of the X-ray mapped region. Clearly visible is that all dolomite crystals have the same complex zoned idiomorphic overgrowth, the porespace is dark because it is either empty, or filled with clayminerals	X-ray map of the Si Ka peak, showing the quartz crystals, and the clay mineral filling of the porespaces	X-ray map of the Ca Ka peak. Calcite CaCO3 shows stronger reflection than dolomite (Mg, CaCO3). Quartz and the porespaces do not show Ca reflections. This rock is not a micrite

henken
This thin section produced a look-alike of the shapes interpreted as Plummerita hantkeninoides by Keller (above and inset left), but here on the left you can see that it is a clear dolomite crystal. It has a dark rim, impostering for a foraminiferal shell, no doubt, that has fooled Keller.
Sample yax325 (793.86m)

If you move your cursor over and away from the picture, you can see what it is: a dolomite crystal, with a Mn-rich (and Cl reflective) rim around the core, and not Plummerita hantkeninoides

How a true foraminifer should look like in both Cl and Tl Images.

The wall pores are well visible. The light (mud micrite) infilling has more Cl reflectance than the relatively pure calcite shell

Thin-section from the Scaglia Rossa, Gubbio, Italy.

	Sample Yax315, in the interval qualified as "laminated micritic limestone" by(op.cit. Keller and Stinnesbeck). Overlay images of Cathode luminescence and transmitted light
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	Sample Yax315, in the interval qualified as "laminated micritic limestone" by(op.cit. Keller and Stinnesbeck). Overlay images of Catode luminescence and backscatter SEM image
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	Sample Yax315, in the interval qualified as "laminated micritic limestone" by(op.cit. Keller and Stinnesbeck). Overlay images of Transmitted light and backscatter SEM image
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Sample Yax310. When you move your mouse back and forth over the image you will see a quick comparison of cathode luminescence and Backscatter electron image.
Same area as the image above

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Sample Yax310, When you move your mouse back and forth over the image you will see a quick comparison of cathode luminescence and transmitted light images of exactly the same area at the same magnification.
At first you will have a hard time believing that the two images are from exactly the same area. But watch first the two dolomite crystals in the lower two third of the middle of the image, then you will recognize others, in some areas you will not see a similarity.
That is because with Cl you image only the very surface of the thin section, while the Tl image is a composite through the entire thickness of the thin section

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SEM bs image

CL image

TL image

Similar TL image published by Keller et al (2004, 2004a)

(A) from Keller et al (PNAS and MAPS (here)

(B) Tl image of dolomite crystals, in an arrangement that greatly resembles A, so-called" foraminiferal chambers"

(D) backscatter SEM image of same area as B and C. The dolomite core is porous and filled with (white) calcite.Also the porespace between the dolomite crystals is filled with sparitic calcite

All images of the same dolomite crystals in sample yax310. (B=Tl , C=CL and D= SEM) (see detailed comparison) top

Images published by Keller et al (2004, left 2004b, right)
So far, Keller has only published these TL images of these samples

1-12 are legitimate foraminifers (see here) because they have nice curved teswalls, with apertures and a good testwall structure on Cl and SEM images.
13-19 are probably fortuitous configurations of dolomite crystals
20-26 are images of foraminifers. have a nice curved testwall, some are double layered, and some show nice pores.

Click on the pink area to compare these shapes in other imaging methods

Keller, G., Adatte, T., Stinnesbeck, W., Rebolledo-Vieyra, M., Urrutia Fucugauchi, J., Kramar, U., and Stuben, D., 2004, Chicxulub impact predates the K-T boundary mass extinction: PNAS, v. 101, no. 11, p. 3753-3758.
Keller, G., T. Adatte, Stinnesbeck, W., Rebolledo-Vieyra, M., Fucugauchi, J. U., Kramar, U., and Stueben, D., 2004a, More evidence that the Chicxulub impact predates the K/T mass extinction: Meteoritics and Planetary Science, v. 39, no. 7, p. 1127–1144.

		Images published by (Keller 2004, 2004a)
		SEM, CL and TL images of two dolomite crystals	last updated: July 10, 2018
		Micritic limestone with foraminifers? Dolomitic sand
		Foraminifers from the Scaglia Rossa
		Foraminifers and dolomite crystals from ODP leg 1049
		Cl and Tl compared in sample 315	rollover images of Tl and Cl of sample yax309

Rollover images,click on number to reach those
1	2	3	4	5	6	7	8	9	10

Forum on the Geological Society debate, forams and dolomite crystals