Highly Allochthonous

The first picture below shows a bedding plane topped by a greenish, chlorite-rich layer which appears to have been partially eroded. What's interesting is the manner of erosion, in that discrete planar pieces appear to have been ripped out of the green layer and transported or flipped over without being dissociated. The best example is the hole to the right of my (increasingly valueless) rand scale marker, where two boot-shaped fragments have been torn out and flipped over, but are still attached to the lower rim. This seems to show strong currents damaging and ripping apart a coherent sheet on top of the sediments, consistent with damage inflicted on bacterial mats in modern marine environments.

The second picture shows a bedding surface with a polygonal topography - the most easily spotted one is right in the centre. If you're thinking that these look like a form of dessication cracking, produced when a wet surface dries and shrinks, then you'll be pleased to know that that's exactly how they're interpreted, but with a microbial twist. The key thing to spot is the altered cavities at the centre of many of the polygons. As bacterial mats dry out and crack, they also decay, producing gases like hydrogen sulphide and methane which collect in bubbles underneath the centre of each polygon. The cavities are though to represent these gas domes, which therefore represent the remains of a dessicated bacterial mat (in some cases there is also evidence of 'healing' - regrowth of mat bacterial over the dessication cracks after the water rose again).

It's always interesting to find the signs of ancient life, but the important point about finding them here is that, as I've mentioned several times before, the Pongola Supergroup is one of the oldest relatively unaltered cratonic cover sequences that we know about, and hence once of the earliest sequences where you can really look for these microbially influenced structures without having to worry about later deformation and alteration completely obscuring things. And if you look, there they are - evidence of a thriving bacterial ecosystem in the distant past, which are much more difficult to argue away as resulting from non-biological processes.

This makes it all the more disappointing that the section has already suffered the blight of professional geovandalism. Many of the outcrops that were described in Nora's paper have been aggressively sampled, by people who clearly knew what they were doing, and what they were looking for:

What makes this worse is that the perpetrators apparently didn't seem to feel that it was necessary to ask the owner of the farm that the section is found on - who was actually quite interested and excited by these discoveries - for his permission before hacking the outcrop to bits. I don't know about you, but regardless of whether there is any scientific justification for removing these structures wholesale from their original geological context, I find such an apparently cavalier attitude profoundly embarrassing. These people should know better.