Could any person make critical comments on the environments of deposition of the Bhuban and Boka Bil Formation of Bengal Basin?

Dear Dr. Ul-Islam:

According to my experience which I gathered mainly during my stay in the Chittagong Hill Tracks, the Bhuban Fm. is arenaceous to argillaceous. It is representative of a prograding deltaic depositional environment replacing near-shore marine deposits. Minor transgressive events are marked by foram tests. The younger Boka Bil Fm. shows stronger reworking. Being of the same siliciclastic type it is, however, finer-grained than the underlying strata. The marine foraminiferous microfossils are rare and brackish conditions may be invoked. Desiccation cracks are indicative of phases of emersion. In combination with the paleontological inventory these estuarine deposits encompass supratidal facies elements which more landward are replaced by fluvial deposits.

Best regards

H.G.Dill

Here is some examples of flood plain deposits. Alternation of flood plain(fine clay rich strata) over river canal( coarse with pebbles and cobles strata) deposits can be detected easily. The example is from South-West Bulgaria. Such alatrnation of flood palin sediments over river canal alluvium is a mark for negative to stable tectonic stress field during deposition time, now a tectonic uplift exposed the sediments. In your case I think you need facial feature of delta sediments which can be deffine by the presents of tilted ( in the direction of current) huge lenses of coarser sediments covered by horisontal strata of fine sediments. Tidal plain sediments I geuss should be rich of marine fosils. 

Best regards

M. Ivanov

Thank you Miroslav Ivanov. Actually I need to know what are the facies characteristics of tidal deposits by which I can differentiate it from floodplain depositd.

Reworked sediments from tidal plains while river flood plains are with sediments distribution according to power of water current that spreads these sediments.

Regards

Dear Professor Dr. Md.Sultan-Ul- Islam,

To  differentiate tidal plain sediments from river floodplain sediments,one might study the physical and biogenic sedimentary structures.  Considering the  cross -beds, the palaeocurrent rose  shows bipolar and bidirectional azimuth in the tidal plain deposits. Cross-beds may also show herringbone pattern while the river floodplain has unidirectional azimuths.Mud drapes in the tidal deposits could be quite thick also.

Fossils of brackish water flora and fauna will occur in the tidal zone, with low diversity with abundance of opportunistic species. A times nearshore fossils could be washed into the tidal flat by storm waves. Ichnofossils are also abundant in the  tidal plain. The river floodplains will on the other hand carry terrestrial microflora and fresh water algaeWood fragments may occur in both but coal deposits will be more likely in fluvial domain.

Regards..

Obianuju P. Umeji

Dear Professor Obianuju P. Umeji

Thank you very much for your valuable comments. It will be helpful for me.

Regards, 

Dr. Sultan-Ul-Islam

Dear Professor Harald G. Dill

Thanks many sir for your valuable comments on Boka Bil and Bhuban rocks in Bengal Basin. It will be very helpful to my work.

Prof. Dr. Sultan-Ul-Islam