Organic matter content of sediments in lake or alluvial deposits is usually used as an indicator to understand the conditions prevailed in the ancient erosional and depositional environments, and then to unravel the paleo-climate. For such studies, loss on ignition (LOI) of sediments in ancient deposits can be used as a proxy for organic matter content. Is this approach adequately accurate?
I think as a first step you should plot LOI vs. TOT/C to see any positive covariance between them.
In my experience from soil LOI is a bad indicator for OM. In one of our practicals we compare LOI (550°) and C analysis in a CNS analyzer. The LOI is always an overestimation of OM and sometimes gives double concentrations compared to OM calculated from C content. As soon as you have substantial amounts of clay in your samples LOI does not give you accurate results. In sediments the error might be smaller because OM content is higher. However, C Analysis is generally more accurate.
I agree with all of the comments above. The reproducibility of LOI is relatively good for a particular sediment type, but if the lithology of the core changes with depth, the LOI concentrations may be variably consistent with actual carbon values in the sediment, and the relation may change with sediment type. You can develop a relation with C if the sediment mineralogy doesn't change with depth, but you are in essence needing to do some C analyses to check LOI values and to establish the correlation. However, if the mineralogy is consistent you can use LOI in a relative sense (to look at trends) down core. Given these difficulties I agree it would be better to actually measure C. However, if a C analyzer isn't available you can get some information out of LOI that is useful as long as you recognize the limitations of the analysis.
Whereas the colleagues before gave you a good overview about the analytical limitations of LOI. I would like to add only some remarks on its paleoenvironmental value.
First LOI values give you a good estimation of the composition of a sample (soil, sediment, or biomass). It is most often a reflection of organic matter content but also of for example clay content (that leaves water via heating). Therefore the relation with biomass is best in sandy material.
If it is "an indicator to understand the conditions prevailed in the ancient erosional and depositional environments, and then to unravel the paleo-climate" depends highly on additional data- first of all recognition of stratigraphy and dating (Luminescence, radiocarbon), and of additional data more indicative for erosion (e.g. discontinuities in stratigraphy, grain size) or climate (e.g. soil type, composition of lake sediments, isotopes).
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