Schoenmakerskop Stromatolites

[PietAlberts]

Slide 20
In slide 8 I referred to the floor of the stromatolite column, on closer inspection it looks like solidified lava with interspersed stromatolitic formation. It seems that the stromatolite column was formed near or on top of a magmatic dyke. Could the stromatolitic patterns be due to the results of lava flow? I could not find examples on the internet of this kind of pattern due to lava flow yet.

Very puzzling and intriguing indeed! I still stick with my conclusion that the patterns in picture19 above are stromatolitic. Any other ideas will be appreciated!

Looking down the dyke one sees pretty convincing evidence of magma bursting through fissures in the quartzitic sandstone bedrock. How did this influence the formation of stromatolites or similar looking formations?

Picture 20


(The structure in picture 18 above is indicated by the yellow rectangle)

Edited June 11, 2015 by PietAlberts

[PietAlberts]

Slide 21

Stromatolitic structure encroached with mangled overturned sandstone plates and lava. The sandstone seems to have buckled under the heat and pressure.

Picture 21

(The section in the picture is about 300 mm across)

[PietAlberts]

Slide 22

Looking in the other direction towards the sea again, this depression seems to be the source of the magma, one can visualize the magma streaming to the left and right from the dyke. This position is currently intertidal.

Picture 22

Edited June 11, 2015 by PietAlberts

[PietAlberts]

Slide 23

Another picture of the lava crust closer to the low tide mark.

Picture 23

[PietAlberts]

Something fun to do - 3D sterogram:

Cross your eyes (not too close to the screen) until the two adjacent pictures are on top of each other and you may see a 3D perspective of the stromatolitic patterns described above

Edited June 11, 2015 by PietAlberts

[PietAlberts]

Slide 24

I photographed a few sample fragments with stromatolitic patterns characteristic of the structures in slide 18, 19 and 20

Picture 24

Edited June 11, 2015 by PietAlberts

[PietAlberts]

Slide 25

A sample with irregular shape and laminae

Picture 25 (sample 100mm across)

Picture 26 (picture width 25mm)

Edited June 11, 2015 by PietAlberts

[PietAlberts]

Slide 26

Eroded and rounded sample with stromatolitic laminar patterns

Picture27 (sample 80mm across)

Picture28 (picture width 40mm)

[PietAlberts]

Slide 27

This sample has some color variation as well

Picture 29 (sample length 180mm)

Picture 30 (picture width 30mm)

Picture31 (sample length 180mm)

[PietAlberts]

Slide 28

Investigating again around the area where the current living cyanobacteria pools are, I am yet again amazed at the relatively large structures with stromatolitic characteristics. I made some reference to the pools in slide 1 – 5. The current pools are relatively small but I can imagine that there were larger and deeper pools around here at some time. The pools were formed by lava upwelling originating from cracks in the bedrock aided by stromatolite growth which made up perfect habitats for cyanobacteria. Most of the ancient pools have since eroded away but one can still see the signs of their previous existence.

One of the compelling features of most of the structures around here is the near vertical arranged layers in the rock. There could be various conjunctures for that but for me the most natural possibility is that they are stromatolitic.

Here are some more examples of the layer structures:

Picture 32 (the sky is at the top of this picture, size of the structure in the middle is about 1.5m square)

[PietAlberts]

Slide 29

Vertical layers, the top of this structure could indicate the water level in the pool at the time it was formed

Picture 33 (Sky at the top of picture, this structure is about 500 mm across)

[PietAlberts]

Slide 30

Vertically layered stromatolitic structures eroded by the elements

Picture 34

[Jays Knots]

I have been studying these structures for more than a dozen years ( last weekend identified them inland) and would like to contact PietAlberts to compare notes.....