Hi Hesam: can you provide context please? Are these Recent or old; are they in terrestrial, lacustrine or marine sediments; geographic location?

Hi, Chris

Thanks for your intrest in answering this question.They are in deep marine setting, Age is probably Jurassic to Early Creteous. location is in Tethys realm in Central Iran Basin.

With best regards

Hesam

Hello Hesam,

Size and texture look similar to examples of calcispheres I have seen. Pages 60-62 in Scholle and Scholle 2003 provide an overview on this topic:

Color Guide to the Petrography of Carbonate Rocks: Grains, Textures, Porosity, Diagenesis: Scholle, Peter A., Ulmer-Scholle, Dana S.: 9780891813583: Books - Amazon.ca I would highly recommend this book to anyone doing carbonate petrography.

Typically, calcispheres are interpreted to be of algal origin (photic zone) - but they may be transported far from their site of formation, into the deeper basinal setting. Interpretation needs to keep the broader context in mind, using information from your regional mapping. Hope this helps,

Very best, Eva

Dear Ms. Drivet

Thanks alot for responding to my question and bringing up vital key points.

I have the book and I have several times refered to it. As you mentioned it is comprehensive and concise but images are very typical. Rarely we confront such good cross sections, so it is a good starting point but one needs to refere to related articles with plates in which more reallistic images can be found.

I will certainly take your advice and refere to pages mentioned . It is absolutely kind of you to remind me that, since this time I overlooked refering to it.

With many thanks and best regards

Hesam

Glad it helped. Best wishes with your project. Eva

Thanks alot Ms. Drivet

Yes, these microfossils look like calcispheres.

Hello,

they look like calcispheres. I am pretty sure they are.

Hello Hesam,

In order to be categorically attributed the both sections from the photos to the calcispheres (interpreted as calcareous cysts of dinoflagellates), they must have the definitive features of this group: 1) The most common calcareous dinoflagellate cysts are 20 to 180 micrometers in diameter (the section of the picture 2 is about 400 microns in size !) ; 2) single or double wall with layer/layers and good visible inner and outer margin; 3) good visible crystallographic orientation of calcite crystals forming the calcareous wall (or at least its outer part).

I would not define these two cross-sections shown in the pictures as calcispheres, despite the fact that they represent spherical to slightly oval form. Calcareous dinocysts constitute one of the most abundant planktonic calcareous microfossil group of many Late Jurassic – Early Cretaceous pelagic limestones. If your material (thin sections) comes from rocks with Late Jurassic- Early Cretaceous age there should be a lot of sections of calcareous dinocysts, but you should look for more representative sections.

Good luck!

Daria K. Ivanova

Dear Hesam,

I agree with Dr.Ivanova if your samples from Upper Jurassic-Lower Cretaceous you will find more good sections of calcispheres. The attached is one of my works on the same age from Kurdistan , hoping it will be useful.

all the best

Ibrahim

Hello Hesam,

Regarding what Ibrahim M. J. Mohialdeen wrote, if you wish to see photos of Upper Jurassic-Lower Cretaceous calcareous dinocysts, you can view my profile at the Research Gate, where articles on the subject can be found.

Good luck!

Daria K. Ivanova

Thanks all for sharing your views. Especially Dr. Ivanova for guidance on Calcareous dinocysts specifications and Dr. Mohialdeen for sharing his article.

I have one further question addressing Dr Ivanova. Whether you agree with group Calcitarch suggested by Versteegh et al., 2009, to separate calcispheres that are not affiliated with Calcareous dinocysts. And what would be the taxonomical and biostratigraphical implications of accepting such nomenclature.Besides can images above belong to calcitarchs?

With my best regards

Hesam

Hello Hesam,

Happy New year! With sincere wishes for health, prosperity, success and respect in 2021!

Now to answer your question! Whether or not I accept the inclusion of all calcareous microorganisms in a group called Calcitarcha, is irrelevant to biostratigraphy. Biostratigraphy is only possible because species evolve and become extinct at specific times, and the evolution of one species is not repeatable! Proper biostratigraphy requires very precise taxonomic determination at the species level. The article Ivanova & Keupp, 1999 clearly shows (using scanning microscopy), the belonging of the fossils described by Waner, 1940 as calcispheres to the group of calcareous dinoflagellate cysts. Despite the revision made in accordance with the taxonomy of calcareous dinoflagellate cysts, the higher species divisions were not used in my later publications as I work only with dinoflagellate cysts in sections, not in isolated form and only in the Late Jurassic-Early Cretaceous chronostratigraphic interval. So if you work with carbonates in this interval (Late Jurassic-Early Cretaceous) you can use my articles, for sediments younger than Valanginian you should use literature on isolated calcareous dinocysts.

By the way, the representatives of the group of Calcitarcha are also up to 250 microns in size!

Success in your work!

Greetings,

Prof. Daria K. Ivanova

If they are fossils, they are considered unclear, but they can be considered the light part of the neomorphism and the dark circular shape of the bioclast from outside the sedimentary basin