{'fraction_non_alphanumeric': 0.0079155672823219, 'fraction_numerical': 0.005277044854881266, 'mean_word_length': 5.325, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Biological marker compounds as indicators of the depositional environments of petroleum source rocks

Summary Recent studies concerned with the use of biological marker compounds for assessing the source of organic matter in sediments and crude oils are reviewed and critically assessed. Compounds which are indicative of inputs from bacteria and phytoplankton are reviewed as well as some compounds for which origins have not been determined. The use of ratios of C27 and C29 steranes for assessing the depositional environment of petroleum source rocks is shown to be particularly open to misinterpretation. Some inferences based on pristane/phytane ratios also need to be reassessed. Areas of research where more studies would be valuable are highlighted.