Glacial fluctuations in the Cryogenian Marinoan Snowball Earth

Abstract

The Marinoan glaciation represents the pinnacle of glacial severity in Earth’s geological history. Deep-water glacial deposits have revealed a complex interplay of at least two glacial advance-retreat cycles. However, the extent to which these glacial episodes are mirrored in shallow-water settings has received less attention. To shed light on this, we undertook an exhaustive lithofacies analysis of three shallow-water sections within the Nantuo Formation in South China. Our findings delineate six distinct lithofacies within the Nantuo Formation: massive diamictite, crudely stratified diamictite, pebbly sandstone, massive sandstone, dropstone-bearing laminated siltstone/mudstone, and laminated mudstone/siltstone. The vertical successions of these lithofacies have allowed us to identify two facies associations indicative of glacial dynamics; they are the ice-grounding line fan facies association and the ice-distal facies association. By juxtaposing our findings with the facies analysis of three deep-water sections, we have established a lateral correlation, confirming the presence of at least two glacial advance and retreat cycles in shallow-water environments. Each glacial advance is marked by the presence of inversely graded massive diamictite, indicative of ice-proximal, glaciomarine conditions. In contrast, each retreat phase is characterized by a fining-upward sequence from siltstone to mudstone, interspersed with dropstones, signifying ice-distal, glaciomarine settings. This study not only underscores the dynamic character of the Marinoan snowball Earth glaciation but also suggests that the glacial oscillations observed in deep-water environments have counterparts in shallow waters. It provides evidence that the scale of the Marinoan glacial fluctuations was not confined to the deep ocean but extended to encompass the entire basin, offering a more comprehensive understanding of the Earth’s climatic and glacial history during this critical period.