STROMATOLITE DIVERSITY IN THE MESOPROTEROZOIC MIMICS ENVIRONMENTAL HETEROGENEITY

One must only take a short excursion into the Belt Supergroup to explore a sampling of stromatolite diversity in the Mesoproterozoic. From the sinusoidal stromatolites of the Altyn Formation to the conical forms of the Helena Formation; to a broad range of domal, columnar, and branching columnar forms, the Belt Supergroup provides a snapshot of stromatolite diversity of the Mesoproterozoic. It is well understood that stromatolites represent laminated organo-sedimentary structures produced by the interaction of microbial communities, detrital sediment, and autochthonous carbonate precipitation, but the formation of stromatolite macrostructure is surprisingly less well-understood. The striking similarities of stromatolite form across multiple basins in the Precambrian, however, as well as a well-documented peak of morphological diversity in the Mesoproterozoic, suggest that stromatolite morphology is linked to broad patterns of environmental evolution.

Here, we explore how macroscopic stromatolite morphology can best be understood as a combination of lamina morphology as it is expressed over time. Because stromatolite laminae represent the active growth surface of the mat and therefore record the topography of the depositional surface, synoptic relief, which reflects the interactions between the emergent microbialite and its environment, is arguably the critical parameter in understanding stromatolite morphology. Inheritance then describes the degree to which successive laminae inherit pre-existing morphology, providing a parameter interpretable in terms of sedimentary process. Here we explore the range of stromatolite morphologies preserved in the Belt Supergroup (and the Mesoproterozoic more generally) and show that the diversity of stromatolite morphologies represents and interplay between spatially heterogeneous environments and rapid lithification of the sedimentary substrate.