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Oncolites are algae colonies that form spheres or oval shapes as differentiated from Stromatolites which are algae colonies forming cylindrical or tube shapes. I recently acquired three end cuts that contain large oncolite colonies. On average these oncolites measure between a half and three quarters of an inch on the longest axis (11mm to 19mm). Many of these colonies have been preserved in these end cuts with a bit of iron oxide. All three pieces are a polished end cut with cross sectioning of colonies on the cut and polished face and colonies weathering out on the all-natural back side. The oncolites are taxonomically identified as Girvanella sp. These pieces come from the Lower Cambrian Chambless Limestone Formation in San Bernardino County, California, most likely from lower (older) strata of the Chambliss Fm. All pictures were taken with the pieces dry; the end cut individual pictures by camera and the oncolite close-up pictures by digital microscope. End Cut 1 (1114g 120mm by 115mm by 45mm thick) End Cut 2 (486g 165mm by 85mm by 22mm thick) End Cut 3 (529g 120mm by 90mm by 32mm thick) Marco Sr.
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- 6
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- oncolites
- lower cambrian
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While out on a trilobite hunt several years ago in the Marble Mountains, San Bernardino Cty, CA, I found these two pieces on the surface in the region of a Latham shale exposure, so I think they would have belonged to the Chambless shale, which is in fact exposed as a bluff above the surface. Here's one: Here's the other: I'm not sure about these. They might not even be organic or in the same genus if organic. The source field might be a zone with Chambless and Zabriskie quartzite mixed. So there's a chance they're inorganic, I guess. However, on the same surface/field we found a lot of fossiliferous rock that included oncolites, which are definitely known to be in the Chambless. What do you think?
- 8 replies
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- cambrian
- california
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