Dear Dr. Md-Sultan-Ul: certainly sedimentary depositional environments produce typical colors in sediments, especially in pelitic and psammitic ones, these colors could even be changed by weathering processes in outcrops, and I assume these should be very intense in a tropical area such as the Bengal Basin. Clays deposited in oxydising environments are usually red or brown, those in reducing environments, rich in organic matter, tend to be gray to black. Something similar occurs in sandstones. Since you just say: "Different colors of sedimentary facies in the same formation of Tertiary rocks", it is impossible to give a proper answer. You must specify which colors and facies are present, and the stratigraphic order in which they appear, at least that! I'm not familiar with the Begal Basin, by I assume it is somewhat related -or similar- to the more known Siwaliks Basin located further west. Am I right? With regards, Sebastian. 

I agree with Sebastian, please provide more informations on the sediment.

However, colours as mentionned reflects the depositional environments at a first step,  however colours will change according to weathering and pedogenetic provesses involving processes like rebufaction, gleyification, bioturbation etc...

Good day Dears colleagues. I agree with the answers given above.

As Jérôme says colours will change depending on the weathering and the pedogenesis.  Grossly this will largely be determined by climate, but hydrothermal activities can also be a spectacular factor as can e.g. be seen in the example from Iceland (see link)

http://www.panoramio.com/photo/133173550

Dear Prof. Ul - Islam,

In addition to the earlier answers, the colours of sediments depend on the composition  of the  constituents of the rock.  Carbonaceous organic matter imparts black and dark shades which preservation depends on low content or absence of oxygen. White and such shades indicate their absence and oxygenated environments. Yes they are facies dependent. These I think obtain in every climatic regime.

Also the presence of mineral constituents and their oxidation states impart their own hues as well. Some black sands contain opaque heavy minerals like ilmenite, magnetite, etc. as well, irrespective of climate; while in the weathering environment, iron in the ferrous and ferric states, hydroxides show the black, brown, purple, yellow hues and so on depending on the degree of progression. These laterite colours occur under the topical climate irrespective of rock type including coal.

Obianuju P. Umeji

Thanks many to all of you dear. Yours reply will help me lots.

Dear Pr Sultan-Ul- Islam ,

providing some pictures of samples and outcrop of your sediment will enhance the discussion.

Cheers

Although stratigraphy and sedimentology are not my subject. Yet try to add a point like Rawalpindi group of Miocene age comprises Murree formation (red clay, red sandstone red shale/mudstone) as lower part while the upper one Kamlial formation having thick beds/massive sandstone bearing greenish grey color. 

Dear Ahmad,

do you have pictures?

Rawalpindi group show contienental (fluvial) formation, Murree formation is more reddish, consequently it is possible that you have paleosol due to emersion, I mean sediment where in contact with air and strong oxydation occured . The overlying Kamlial formation exhibit colours usually founded in sediment/soil where wwith water fluctuation. Indeed greenish grey are typical colour of gleyification processes.

At the moment, not able to provide pictures with so sorry. When I will have pictures, will be shared here. You said very right that Rawalpindi group show continental (fluvial) formation. In oil industry, well-site geologists during drilling mostly prefer colour of a formation to separate it from an other formation when updating a well-log. Colour of a formation so looks as an index property being used. A thirst quenching comment from an expert will be very helpful for me as a lay man.

If these are (or were) near-surface sediments, then keep in mind the traditional soil forming factors (climate, organisms, relief-drainage, parent material, and time).  All of these aspects can affect soil color, including through various geological and pedological processes mentioned in above comments.   Various combinations are likely but locally a single factor could dominate.

Dear Dr. Sultan-Ul-Islam,

Although our colleagues have given proper answers to your question, but still I can not understand what kind of sample are you dealing with? Is it core sample from existing lake or marine, or is it outcrop? Because th color of sediments then will have an other story. So it is better to give complete information about the type of sample and its different colors.

With regards,

Dear Dr. Sultan-Ul-Islam,

Your question seems to derive from the use of colour to identify sedimentary deposits; eg, where black shale from one formation overlies white sandstones of another formation, such may be possible but be warned that this is not the best for correlation. The same formation can change colour depending on the constituent mineralogy and facies. Lithological correlation must be backed by palaeontology. Also the colours must be primary for we know that weathering produce variable colours from same deposit and same colour from different deposits of different ages. To colour must be included other attributes to avert stratigraphic misinterpretation.

Obianuju P. Umeji

An interesting question. Agree largely with Sabastian on this. Care is required to establish that the colour that is recorded is the primary colour of the sediment and not of the weathered outcrop.

There are some sediments with colours that can be very diagnostic of the environment of deposition (eg: Red Sandstones and Black Shales). Greenish tinge in sandstones may often suggest glauconite as another example. 

As a thumb-rule, I would suggest that 'changes in (primary - not of a wethered outcrop) colour' of the successive layers in a sedimentary suite could be used to infer changes in environment or depositional system. This inference will however need to be validated by sedimentological and mineralogical studies of the sediment.

Once established, the characteristic colours may then be used to correlate strata across a basin in an intra-basinal mode ONLY. Trying to use that parameter in an inter-basinal correlation would be hazardous / speculative at best.

Thanks many to all of you dear friends for give me lots of suggestions regarding colour of sediments. Thanks again