This is a big and complex topic with many strong opinions. If you are looking for a starting point, you could look at Tyson's 2005 paper in SEPM. Basically, he argued that final TOC in rock is related to 3 factors: organic-matter input, organic-matter preservation, and dilution by mineralic sediment components. So you could answer your question by assessing the relative contributions of OM input, presevation, and dilution. Knowing the context (mineralogy, lithology, depositional environment, diagenesis, etc.) will help you constrain the answer. If tectonics was a significant factor in the source of the sediments, may be it is having a dilution effect on the TOC content? Maybe you can check on the timing of tectonics in Malaysia for a clue of whether it is reasonable that tectonics contributed to greater sedimentation rates, etc.

Thanks, Dr Mathew,

Tectonics do have some involvement. I appreciate the quick response and will go through Tyson's 2005 paper.

I think tectonics surely has an effect. Since the S2 is the amount of HC generated during thermal cracking of nonvolatile organic content; the volcanic eruption could have constituted a natural heating of rocks causing the loss of the rich organic contents. Same goes for TOC which could have also been affected by exposure to aerobic environment.

How confident are you that the rocks are turbidite? See various papers by Shanmugam.

Low TOC is expected in volcanic rock. The organic conncentrations tends to be reduced with increased volcanic contents.