Characterisation of the Source of Sedimentary Organic Matter

Introduction

Compounds formed from the aromatisation and rearrangement of natural product precursors, and their presence in sedimentary matter, are currently being investigated. Biomarkers such as methylretenes and moorarene are a few of the many compounds derived from higher plants that have recently been identified. The presence and abundance of such biomarkers are successfully employed in oil/source rock correlation for mapping palaeoenvironmental change.

Sedimentary compounds derived from totarol and cembranoids

Totarol is a naturally occurring diterpenoid phenol which occurs abundantly in Podocarpus species. There are only a few reports of the occurrence of totarol and related compounds in sedimentary material. Thus, products formed from aromatisation and rearrangement of totarol are currently under investigation. Laboratory experiments suggest that processes such as alkylation, dealkylation, isomerisation, ring-opening, ring-closure and migration of gem-dimethyl groups, take place upon aromatisation, leading to the formation of many different compounds which are potentially useful in characterising samples containing higher plant-derived material.

This study is also concerned with compounds derived from cembranoids, which are macrocyclic diterpenoids. There is only one previous report of the occurrence of cembranoids in the geosphere where it was suggested that these compounds originate from resinous plants and that they are markers of semi-arid depositional environments. In this study, we have carried out off-line pyrolysis on a cembrene and a Coeleneterata (soft coral) extract reported to contain euniolide. Pyrolysis products included alkylnaphthalenes and alkylphenanthrenes. The alkylnaphthalenes have also been identified in high relative abundance in algal derived crude oils and sedimentary matter from Ancient reef systems.

Personnel

B. van Aarssen, T. Bastow, R. Alexander, R. Kagi

Funding

Australian Petroleum CRC, MERIWA