Dear Mr. Cevik,

there is simple recommendation I can give to you; determine everything in the field what you cannot determine in the laboratory, e.g., facial and structural architectural elements and save everything for the laboratory analyses such as the examination of thin section what you cannot determine with the hand lens or the unarmed eye. Then you become a very good geoscientists, because you are on the safe side and provide a good platform to create a model. If you have not done your work in the field properly the remaining downstream part does not deserve to be done at all. Your laboratory work cannot compensate for voids and deficiencies left after field work.

Kind regards H.G.Dill

Thanks a lot Mr. Dill, Thanks a lot Mr.Köster

To add to the above. Apart from a detailed as possible description of the hand specimen, field observation should also put your specimen in context. By that I mean. It should give you a location and a geological context on a regional and local scale. Field observations should help in determining the geological environment, the depositional environment, for example, from the adjacent rock types and macro sedimentary structures that they contain. Thin sections should confirm what you see in hand specimen and reveal the internal texture of the rock and mineralogical information. The two are interdependent and crucial still to the proper description of any rock specimen

Thanks a lot Mr. Craven

I fully subscribe to everything that colleagues Dill and Koster wrote. But. Following field observations and definitions, analytical studies of samples in a certified laboratory must follow, otherwise your field materials can always be challenged, like the personal impressions of a field geologist.

It is a matter of scale. Information gained in the field is on a macro scale (the big picture) while information gained from thin sections is on a micro-scale. Both pieces of information are telling you something, your job is to figure how they are compatible.

Dear Gökhan Çevik: this problem is not unique of limestone thin sections, but it happens in any kind of either highly inequigranular and/or coarse grained rock, including conglomerates, porphyritic granitoids, porphydoblastic gneiss and augengneiss, some skarns and most volcanic breccias. Thin sections should only be made out of medium to fine grained rocks, never in very inequigranular or coarse grained ones, since the small area of a thin section should represent the rock itself, not just a part of it, for example only groundmass or phenocrysts. When these irregularly grained rocks are studied, most details should be ascertained in the field, at outcrop level, or at least in large hand samples. I studied two thin sections made of the same sample of volcanic breccia from Colombia, in one of them appear two fragments or xenoliths of a sillimanite gneiss, in the other there no sign of any sillimanite gneiss! In coquine limestones I suppose then same could be true, one part could contain a type of fossil (shell fragments), and another part a different fossil assemblage (calcareous algae). The problem is in the fabric and grain size of the rocks.

Regards, Sebastián.

Thanks a lot Mrs. Sharon Cornelius , Thanks a lot Mr. V. M. Anokhin , Thanks a lot Mr. Sebastián Grande .

Dear Mr. Cevik,

I think that your question became clear from the above mentioned satisfied answers. Detailed study of any type sedimentary rocks necciates lithologic description of rock types in the field to know about rock facies and environmental setting. Petrography is critical to depict clear view about mineral composition, stages of cementation, micro-structures, porosity and relative burial depth of sediment to shed light on microfacies ananalysis.

Thanks a lot Mr. Walid Abdulqader Saqqa

Depending upon laboratory technique.

hand samples.

A Geoscientist is expected to observe and record as much as possible during the tenure of field and this applies to collection of samples as well, by way of physically observing the features concerned or the features a Geoscientist is interested for in field itself.

However, many a times, it becomes difficult to arrive at some conclusion particularly in case of identification of select minerals. To arrive at better identification and suppliment the field based information with relevant laboratory backup, preparation of think section samples and their laboratory based studies are expected and are definitely helpful.

Best,

AK

Thanks a lot Mr. Mahendra Dhande , Thanks a lot Mr. Atul Kohli

You might also need to determine the directions of the thin-sectioning, i.e. relative to the bedding plane, in the field so as to get maximum information.

Obianuju P. Umeji

Dear Obianuju: surely, this is especially true in metamorphic foliated rocks. A thin section of a schists made parallel to foliation will show mostly basal sections of micas, which have low interference color, and perhaps some lineation, but it will not be apparent that the rock is foliated. A section made orthogonal to foliation can be made in two different ways: orthogonal to foliation and orthogonal to lineation; or orthogonal to foliation and parallel to lineation. It all depends what the study is about. So, when thin sections are made by a technician it is the geologist's responsibility to mark in the sample the exact direction the cut should be made, else the section could be quite useless and misleading. Regards, Sebastian.