Precambrian Glaciations and Their Associated Petroleum Systems

Abstract

For the last 1 billion years the Earth has experienced alternating periods of ‘greenhouse’ and ‘icehouse’ climate. The global climate record appears to be cyclical, with periods of ‘greenhouse’ climate lasting some 250 million years and intervening ‘icehouse’ periods lasting around 100 million years. Major Phanerozoic glaciations during the Permo-Carboniferous and Late Tertiary, correspond with periods of low carbon dioxide levels in the Earth’s atmosphere (low ’greenhouse’ gas concentration) and ’icehouse’ climate. The global eustatic sea level curve for the Phanerozoic exhibits the same broad long-term cyclicity as the global climate record with periods of high global sea level corresponding to periods of ‘greenhouse’ climate and, therefore, low ice volumes. There is a strong correlation between global climate, sea level and the distribution of the world’s major petroleum source rocks through Phanerozoic time. The richest source rocks were deposited either during periods of high global sea level (e.g. Late Jurassic, Cretaceous) or immediately following periods of global glaciation (e.g. Early Silurian). The obvious implication of this is that the deposition of many of the world’s major petroleum source rocks is intimately linked to periods of marine transgression and that many of these transgressions are glacially driven. The situation earlier in the geological time is less clear, but it would seem logical to test whether the global climate, sea level and source rock deposition relationships observed in the Phanerozoic record also occur during the Late Mesoproterozoic and Neoproterozoic.