Hi,

Red colours shows oxdation as mentionned by Jorge, but the latter can be actual or herited. We need more detail, pictures, description ,etc...

Dear Atul,

I agree with Dr. Jorge Costa-de-Moura.The red colour of Quaternary sedimentary beds are basically due to presence of hematitic pigment forms by diagenetic processes including: oxidation of Fe following the alteration of ferromagnesian minerals and oxidation of Fe sulfides.

Thankyou all for your comments.

Jérôme Juilleret , @ Jorge

I get this point that reddening is the result of oxidation or may be inherited. I am attaching a field photograph to present my question in a better way. I want to understand why there is deep reddening of some layers whereas the layers lying above or below of these layers have not been oxidized.

I feel that the oxidation in this case is syn-deposition and not post deposition which generally is not the case in the sand dunes.

Please shed some light on it.

I think that you have a combination of sedimentological (black lines) and pedological phenomena (red lines).

In the bottom unit (hammer), you see oblic fine sand layers. Some of them are already reddish in colour, but the colouration is in line with the lamination. I think that the reddish colour is due to clay material. Indeed those clay are the result of previous weathering/pedogenesis. Take into account that this fluvial sediment was before saprolite/soil material which have been eroded.

I think that those tiny clay lamination constitute a clay stock. The latter is actually moving downwards after rain period, and constitute the bigger reddish layers above (red line)called argic horizon: illuvial accumulation of clay,. This are probably more clayey than the surroubnding sands, gravelly sediment., please check if it is more clayey.

Cheers

I agree with Jorge Costa-de-Moura 's comment.

I think oxidation of iron can be responsible for the red sedimentation.

Dr Jérôme Juilleret additions to the photo nicely highlight the depositional and post-depositional events of this sequence. Although the oxidation can be caused by several processes, in profiles such as this, it has been my experience in the western U.S., southern Italy, Jordan and Iran, that they occur under conditions of fluctuating water table, and their location in a profile is often linked to zones of lateral movement of ground water across a sedimentary profile due to the presence of zones of increased grain size. These more permeable units allow more rapid movement ground water. When these units occur at the top of the ground water table, oxidation also commonly occurs. The variable occurrence of these units in your profile more than likely record different levels of your water table

I agree with Peter Ernest Wigand's comment.

due to oxidation of iron

Red colori in sedimentare is a postdepositional characteristic,due to the oxidation of iron minerale in a subaerial environment under particolare clonate coditions.red colori May be considered a pedogenic characteristic.

The coloration is due to the oxidation of ferromagnesian minerals in the sediment or from soil as where iron-bearing chlorophyll is included. Oxidation can occur both in terrestrial and marine environments where oxygen is available just as reducing conditions can also occur in both such as, in the formation of free carbon (coal) or sulphide minerals (in the ocean). Sediments deposited in water get oxidized to such red, yellow, purple, brown or purple. Some iron minerals are green. Such layers of colours occurring inter-bedded with unaltered sediments might indicate depositional or post depositional chemical changes. If the layer is coarse-grained it might allow post depositional oxidation under moist conditions, giving black ironstone at times . Lateritization is the end product.

Obianuju P. Umeji

I am thinking a bit differently. I feel that that the oxidation of these beds happened shortly after the deposition due to change in depositional environment. The layers which are dark red in colour represent a time when river channel was dammed which led to shallow lake kind condition. I think so because this section lies near Himalayan Frontal Thrust (HFT). Once the river was able to breach the dam it deposited sediments in normal fashion leading to grey beds. This damming was repeated many times in the past each represented by dark red bed. Darker the bed greater the time of damming.

I don't think that these red bands are result of post depositional activity because such activities will result in reddening of whole surface instead of few horizons.

The whole section is about 10 m thick and this particular part is the lower unit, Is it possible to have oxygenated water at this depth? If we assume this to be a result of underground activity.

Please correct me if am wrong. I am attaching a field photograph. The box represent the earlier attached image.

Thanks

The photo of Atul above shows a cross-bedded deposit indicative of unidirectional current. The brown oxidized units follow the mod-drapes, which were deposited during slack water as the current carrying coarser particles slow. Other fine lines mark the planes between the deposition of individual cross-beds. Again oxidation could be syn- or post-depositional. Minerals are often the hydrated oxides of iron. With continued exposure to weathering, the entire surface would turn brown.

Obianuju P. Umeji

In the geological past, in England occured Old Red Sandstones of Devonian and New Red Sandstones of Triassic indicating arid periods. I mentioned different colours of oxides of iron. I seem not to have included red coloration.

Forgive me Ken for that omission and thanks for the reminder.

Obianuju P. Umeji

Atul Singh

The whole lacustrine sequence represents a single damming event. These landslide dammed lacustrine deposits are quite common in active orogens like Himalayas. The red coloration I suspect was mostly due to mineralogical changes in the sequence as these layers are typically coarse grained and has iron containing minerals. Red coloration happens once these lacustrine sediments are exposed to oxidation. I have worked on similar profiles in Spiti valley, NW Himalayas

Dear Atul

I think the sequence is a banded iron formation and the reason for the red color is the presence of secondary hematite

Best Regards

The chemical decomposition under acidic conditions must have lead to produce iron oxides causing red colorization of these units.

In addition, red coloration in a generally white background is mostly secondary, resulting from decomposition and less commonly original.

Obianuju P. Umeji

Hi Atul, the red color comes from iron contamination in sediment archive. The source rocks are often Fe-rich. For example, the quartzites of the Lesser Himalaya in the northwest, has Fe-inclusions. Therefore, once they are eroded, they irons are released. More so, there is Middle Siwalik red sandstones, they also contribute to the red color in recent sediments.