The role of environmental pressures on stromatolite morphology: Insights from the Ediacaran Salitre Formation, Irecê Basin, Brazil

Abstract

Stromatolites are laminated biosedimentary structures that record long-standing interaction between environmental conditions and coevolving microbial life. Although they are among the oldest and most persistent forms of life on Earth, the extent to which environmental parameters affect their morphology and distribution remains poorly understood. In this study, we investigated the well-exposed stromatolites of the Ediacaran Salitre Formation (Irecê Basin, Brazil) to assess how physical sedimentary processes and early lithification dynamics controlled stromatolite growth and form. Through integrated sedimentological and petrographic analyses, we documented a stratigraphic transition from stratiform to columnar morphologies, which closely correlates with variations in hydrodynamic energy, sediment influx, and local relief. Our results demonstrate that increased hydrodynamic energy and detrital input promoted the development of columnar, often inclined or branched forms, whereas low-energy conditions allowed for the development of stratiform structures, especially within protected scour depressions. The occurrence of inclined, yet unbroken stromatolite columns and their alignment with the paleoflow indicators suggest growth under dynamic, high-energy conditions with weak or incomplete synsedimentary lithification. Despite the high-energy setting, grains are concentrated only within the intercolumnar spaces and are almost absent from the stromatolite laminae, suggesting that lamination resulted primarily from microbial carbonate precipitation rather than sediment trapping. Additionally, the internal lamination patterns and detrital material distribution reflect episodic sedimentation and microbial mat disruption, further emphasizing the sensitivity of stromatolite morphology to environmental changes. Our findings highlight that the stromatolites in the Salitre Formation provide a valuable snapshot of the intricate interplay between physical parameters and biological activity during the terminal Neoproterozoic.