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Identity HelpStromatolite?
1st Dec 2018 06:39 UTCCraig Howard
I am hoping for your opinion on this piece of chert I found years ago near Moora, Western Australia.
At the time I just thought it was just an interesting rock. However, having developed an interest in stromatolites since then, I've recognised stromatolitic characteristics in this rock, e.g. fine and gently convex laminations, distinct columns with relatively smooth margins, and - towards the top - a mixture of parallel and divergent branches with small projections.
These attributes are especially visible if you increase the image contrast - see third image below. What do you all think? Is this a stromatolite? And if so, any thoughts on possible species?
1st Dec 2018 15:56 UTCAlfredo Petrov Manager
1st Dec 2018 18:04 UTCUwe Kolitsch Manager
1st Dec 2018 20:20 UTCRalph S Bottrill 🌟 Manager
2nd Dec 2018 00:23 UTCCraig Howard
Thank you for your feedback, and Ralph in particular for your detailed response. Here are some close-ups of details that seemed stromatolitic to me; do these provide any more clues for determining this rock's nature?
2nd Dec 2018 02:38 UTCGregg Little 🌟
One further observation on the tiny white dots that define the algal layers. These may be the included gas cavities from the algal decay, see "birdseye limestone" in the literature.
Algal development was wide spread in the Mesoproterozoic to Neoproterozoic from simple mats (layer textures like yours) to more structured stromatolite development as well as binders of fragmented material in higher energy depositional environments. Distinct algal structures like pisolites and oolites also form in these higher energy environments, possibly in association with bacterial activity.
2nd Dec 2018 07:39 UTCCraig Howard
I think it is safe to conclude that this rock is a piece of laminated algal mat that has been dolomitised and then silicified.
Thank you all for your wisdom.
2nd Dec 2018 07:46 UTCRalph S Bottrill 🌟 Manager
Thats a bit clearer, but again it seems like fracture-related carbonate and/or silica alteration cutting algal-mat laminations in carbonate sediments as Gregg has said very well. The pictures could be upside down if you consider the fluid expulsion would have buckled the soft algal sediments. A great specimen in the story it tells!
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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: March 29, 2024 12:55:42