Taghi:

The enlarged image corresponds to a Globotruncana sp. in thin section. Several specimens need to be examined for species identificatiion. Kindly see this link:

http://www.omicsonline.org/biostratigraphy-of-gurpi-formation-late-cretaceous-in-interior-fars-bavan-area-central-zagros-southwestern-iran-2157-7617.1000137.php?aid=13678

Best

Syed

Certainly a Globotruncanid. Some authors have published detailed works on these bugs in thin section: Bill Sliter, Isabella Premoli-Silva and Hanspeter Luterbacher are the experts that come to mind. 

Hi,

I agree with previous interpretations (Globotruncanid), moreover I can recomend book with many pictures of Cretaceous planktic forams, also in thin sections:

Premoli Silva I., Sliter W.V. 2002. Practical manual of Cretaceous planktonic Foraminifera. University of Perugia, Dipartimento di Scienze della Terra, Perugia.

Hi

Globotruncana cf. arca

Cheers

B

Hi,

I think that the species marked with green curved line corresponds to Contusotruncana fornicata. you can see the practical manual of cretaceous planktonic foraminifera (Primoli Silva & Sliter, 2002)

Best regards,

The widely spaced keels are reminiscent of G. arca, but the inflation in the chamber is also reminiscent of G. bulloides. I feel that it is probably closer to Globotruncana arca but the left hand side of the specimen is not clear enough to be positive. Both have a range of Campanian to Maastrichtian, with G. bulloides probably not extending quite to the K.Pg boundary

Taghi:

Strong affinity is suggested with Globotruncana arca (Cushman) of Late Campanian age. 

Best

Syed

Hi,

In addition to the large keeled form (Contusotruncana) your thin section contains some Hedbergella sp. and Heterohelix sp.

Best regard,

Hi,

Well, thin sections are not the best way for species indentification because you do not see all spiral, lateral, and umbilical sides. If you have any chance to get washed specimens then I strongly recommend you to do that. What I see is high trochospiral double keeled form. Umbilical keel is tilted to umbilicus in first chambers of the last whorl. Two keels widely seperated on the last chamber. In G. orientalis these two keels get closer and even absent in last three to final chambers. So if it is an orientalis form then you would see 1 peripheral keel on the last chambers. Thus, it cannot be an orientalis. It cannot be a bulloides either because bulloides form is low trochospiral and keels get closer on final chambers, and keels are slightly tilted towards to umbilical side what we see is strong tilt towards to umbilicus. It is definitely not an Globotruncanita elevata form because elevata has one keel and almost flat trochospire. It might be an Globotruncana arca but it has higher trochospire with respect to arca forms according to my experience. So we only get very high trochospire forms with two strong keels, which are Contusotruncana (Rosita in old name) species. It is most likely a Contusotruncana fornicata form (I'm repeating thin sections are not the best way for species identification). Apart from that, the biserial form below of the Contusotruncana seems like Heterohelix planata because each chambers overlap each other. I see a Globogerinelloides form upper right and maybe a Hedbergellid form and maybe a Pseudotextularia nuttalli in middle right. Hope this would help.

Best,

Uygar

Good comments from Mr. Uygar Karabeyoğlu.

I'm Ok with him for all his Suggestions .

Best regard,

Getting a processed residue is OK, even hard limestones can be broken down with the hot acetic acid method. However, thin sections are not all 'bad news' - and in many parts of the world this is what is available and it is a good skill to learn. Sadly few people stick with it and learn how to use thin-sections.

The important point is these species are described according to their 3-dimensional morphology. Thin section gives you 2d view and let’s say if you get an oblique section then your conclusion would not be as concrete as your identification from washed specimens. It might work and indeed it is practical especially for Globotruncanids. However, for example, how do you differentiate Gansserina gansseri from Globotruncanita angulata in thin section? Both have almost identical lateral view (flat dorsal side and semi circular ventral side) and quite similar in equatorial section. The main difference is in gansseri you don't have adumbilical ridges and you have rough and spiny surface on first chambers of final whorl on umbilical side. This is just one example. On the other hand, I am completely agree with you I am using thin sections as well and indeed it is good skill to learn.

Thank you all very much for your time and explanations.

I managed to gain access to the book Practical Manual Of Cretaceous Planktonic Foraminifera by Permoli Silva & Verga. A species very close to mine is named Globotruncana bulloides. I cropped the picture and attached it to this message. the keels and the inflation are simmilar to bulloides'.

DO YOU AGREE?

Yes, that is probably G. bulloides. Do retain an interest in using thin sections. It is a good skill, especially with larger benthic foraminifera, algae, calpionellids and, especially, look at macrofaunal fragments such as Echinoidea plates and spines, asteroid laterals, inoceramus prisms, etc. All thus information informs you about the environment.

Hi Taghi

It seems to be Globotruncana arca, as it has two keels and a relatively high trochspire.

ir looks like GLOBOTRUNCANA ARCA ARCA

OF LATE CAMPANIAN AGE