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1 year ago in Diagenesis , Sedimentology By Govind

Fe nodules of derived origin found in Alluvium overlain by Laterite. What is the point of view of fellow researchers on genesis of such Fe nodules?

My field area shows a clear Holocene alluvial unit, overlain by a ferricrete, with abundant Fe nodules within the sands and gravels. They aren't in situ weathering products of the bedrock. I'm debating between a purely detrital origin (eroded from older laterites) and an authigenic model (precipitated in situ). What's the weight of opinion in the sedimentology community?

 

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By Kriya Answered 1 year ago

This is a classic and ongoing debate I've encountered in tropical sedimentology. The consensus I've observed leans towards a polygenetic origin. While some nodules are indeed detrital, reworked from older duricrusts, many show microscopic evidence of multiple growth zones, indicating complex diagenesis. I would recommend a micro-analytical approach: look at the internal fabric using thin section and SEM. Authigenic nodules often exhibit colloform textures and sharp boundaries with the host sediment, while detrital ones are more likely abraded and have a weathering rind. The key is that the lateritic cap provides a source of Fe-rich groundwater, driving precipitation within the permeable alluvium below.

 

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