TOC is a problematic value.  It will be the sum of all losses in weight resulting from decomposition of organic matter, hydromicas and carbonates in the sample.  You may use it as a "quick and dirty method" but unless you know the mineral composition of the\actual deposit, your results will not necessarily be a true measure of the hydrocarbon content of the deposit.  Remember too, that sediments usually vary in composition laterally and this must be taken into account when interpreting the results.  This means that unless you have a substantial amount of data from the same stratum in a relatively small area, your results need to be interpreted with caution..