I am getting a thick sequence of sand beds which contain fragments of rocks which are polished along the Tista River in the Lesser Himalayas. I think these deposits to be of glacio-fluvial origin but the glacial deposits have not been reported to extend this much south.
What methods I can use to verify the glacial origin of these sediments?
You can look in the field for typical sedimentary structures like Os, Kames, Glacial series and so on. Glacial sediments are often overconsolidated relative to their depostional depth because of the former load of the ice shield.
Dear Mr. Singh,
I have attached a rough scheme with two images taken by me in the field which will give you an overview of the grain size and morphology of each subenvironment. Fluvio-glacial has in parts all the hallmarks also known from fluvial deposits such as bedding, gradation, and water worn grain size and morphology. But all of these features do not reach the ultimate state found in fluvial deposits as the distance to the source glacier is small and the fluvial gradient moderate.
There are numerous chapters written on this topic and it would go far beyond my remarks given here to cover all aspects. Both remarks and the attached file should not prevent you from consulting a good textbook on sedimentology (e.g. Reading..).
Good luck for your field work in the Himalayas where I did sedimentology in Nepal.
H.G.Dill
Dear Atul,
the title of your question is more general that what you realy want to know according to your field observation.
First, glacial, fluvio-glacial and fluvial sediments are in mountainous landscape a kind of trilogy and form a sequence. As you deal with quaternary sediment, you are also link to the geomorphology to understand the sedimentogenese. Pure glacial sediment like till will be formed in front, laterally and above the ice, however you will have also running water during summer wich will reyworked the previous pure glacial sediment to form fluvial sediment. There is also a scale issue, looking at one outcrop you can find pure fluvial or glacial but at a map unit, you will group both into "fluvio-glacial" sediment.
Second, do you have pictures of your sand sequence? What is the shape, size of your polished rock fragments? Rounded, angular? What do you mean by polished?
Regards
Considering your requirement to differentiate fluvial, fluvio-glacial, and glacial sedimentary strata, in the FIELD, physical sedimentary structures, presence-absence of biogenic structures, color, grain-matrix ratio and relationships, external morphology of larger clasts, in the order of decreasing importance can help to differentiate between glacial and fluvial sedimentary records.
Dear Atul,
I am working in the Tista basin on the palaeoglacitions (N sikkim), I can give you some idea on this if you tell me exactly where you are working. As far as our observations, the Tista valley has witnessed multiple glaciations and the related features are well preserved in the tributary as well as the main Tista valley.
so i can suggest you some thing only after knowing the location that you are taking about.
regards
- Badges
- Science topic
- Similar topics
- Geoscience
- Asia
- India