Dear Mr. Li,

You mentioned only smectite. Is there any other clay mineral, e.g., illite or muscovite? How precisely did you investigate smectite? There exists a wide range of smectite-mica mixed layers. The only recommendation I can give to you is:

1. Investigate meticulously the clay mineral association. Do not use a bulk composition but split it into different grain size fractions, because smectite is very grain-size-sensitive and mainly accumulated in the finest grain-size fraction

2. Try and find K-bearing micaceous clay minerals as individual grains or in mixed-layers with other clay minerals such as smectite and carry out K/Ar or Ar/Ar dating and compare the data with those of the host rock sediments and the provenance area

3. Determine the chemistry of clay minerals not only with regard to the major elements, e.g., K, Al, Fe but also with regard to minor elements such as Cr, V and Ni which are accommodated in some clay minerals and used as marker phyllosilicates for supergene and hypogene processes, processes which you might not expect in the coastal environment of deposition under study.

4. Do not only focus on clay minerals but also take a keen eye on heavy minerals and light minerals which may be detrital but also may form in-situ (“do not put all your eggs in one basket”)

With kind regards H.G.Dill

I think scanning electron microscopy (SEM) and petrographic study will be helpful in determining grain morphology, overgrowth textures and ghost textures which are related to authigenic origin.

palygorskite and sepiolite also mineralized authigenictically , i think the quick method is SEM and TEM , to check the grain shape are rounded or subrounded or euhedral . and the check the minerals relationship , to understand the two authentic types

diagenetic transformed

or

direct precipitate

thanks

We can determine clay minerals by Bromoform chemical solution

Dear Colleagues,

morphological studies using the common classification schemes from well rounded to angular to get an idea of the distance of transport or intensity of reworking for siliceous material fails, excluding glauconite. The latter may occur shaped as pellets in some glauconite sandstones. It is one of the only marker phyllosilicates which is indicative of authigenic marine origin. As it is mostly no true mica but a mixed-layer of smectite and illite it is a good marker for in-situ formation and also amenable to K/Ar and Ar/Ar dating (papers of mine on this matter are available on the RG server). The amount of smectite in these glauconite aggregates gets reduced along with depth/pressure and age. As we have to deal with shallow marine (?) sediments near the coast glauconite is likely to be still enriched in smectite. I am reluctant to go any further due to the lack of knowledge about the precise composition of the clay mineral assemblage in question and I try and avoid to embark on a wild speculation. Further information on the caly mineralogy and the environment of deposition should be presented.

H.G.Dill

It is a difficult question indeed. I worked on clay minerals from sediments in two papers (present on RG) and it was very difficult to distinguished authogenic from transported particles! and really I did not try to do it.

I think Dr Dill's answer is the best.

It depends on the aspect which you want to study.For Mineral you can go for spectroscopy techniques like fluorescence and for micro-structural and density variations you can go for micro-CT experiments.

Dear Fangliang Li

May be this imagination help You. For our Far East region ther is (as I imagine) an approximate scheme for authigenic minerals. In surface sediments under normal conditions (temperature 25 ° C, pH -7-8), smectite forms above the northern tropic and it is poorly ordered. Disordered mixed layered smectite-illite are also present. Carbonates, opal-C / T and zeolites (volcanogenic rocks) may form too. All other minerals (layered silicates, etc.) are usually clastic. They are recognized by x-ray analysis by sharp, narrow symmetrical peaks. While authigenic minerals have broad, blurry peaks broadening toward the bottom. From the present time until approximately the Oligocene time, crystallization of smectite and illite-smectite increases (peaks become sharper and higher) and the proportion of terrigenous components decreases. In the Paleogene (Paleocene-Eocene), highly ordered minerals appear (rectorites and corrensites), opal goes into quartz. Chlorite and mica appear in the Upper and Lower Cretaceous. May be I am misteken.

Sincerely Yours

I thinking its belong to microsphically studiesd to distinguish rounded (Allochthonous) and angularity (Autochthouns) of clay minerals and this belong to weathering and transportantion of clay particals. and we have roentnographic method for partical studies.

Dear Mr. Rasouli,

your suggestion with regard to grain morphology may be true for a wide range of heavy and light minerals but not for individual particles of phyllosilicates which used to occur as sheetlike grains due to their perfect cleavage and layer texture.

H.G.Dill

Dear Fangliang Li,

I had a similar problem. However when you think about the formation of clays at the river/sea boundary formation of smectite is not likely. For my expirience smectite undergo transformations in the marine water into illite and/or chlorite.

The suggestion of prof. Harald G. Dill to date the K-bearing clays seems to be the most reasnable. Perhaps isotopic analyzis would also work, because sygnature of adsorbed water should be diffrent for marine and fresh water.

MK

Dear Fangliang,

Actually it is very difficult to differantiate detrital and authigenic clay minerals. The key things are; to know age, depth and tempereture of clay bearing rock for determining the diagenetic stage, presence of mixed clay layer such as illite-smectite, change in illite/smectite or chlorite/smectite with burial depth; those will give you a sign for the source. Additionaly, by the use of SEM, morphology of clay minerals will be a proxy to estimate the origin.

to differentiate between the detrital clay and the non-detrital clay (authigenic clay) is to use thin section and then after interpreting thin section you can discriminate between the two types. if you are working on a sandy sediments, even macroscopic view can help you to define the two types. Mud clasts, Mud drapes & mud-lines burrows are considered as detrital clays. In case that you still interested on that, I can share with you some recent work about that in which I was involved.