Microbially Induced Sedimentary Structures in a Mesoproterozoic Erg System: A Case Study from the Mangabeira Formation, Brazil

Microbially Induced Sedimentary Structures (MISS) are syndepositional primary structures that occur both in some of the earliest forms of life and in modern environments. Throughout geological time, microorganisms developed metabolic strategies that enabled their establishment and proliferation in a wide range of settings, including arid environments such as deserts. However, MISS are widely recognized in tidal flats and other shallow-marine environments, whereas examples preserved in continental deposits remain comparatively scarce. A comprehensive review of Precambrian MISS occurrences indicates a notable expansion of documented records during the Mesoproterozoic, coincident with the assembly of the Columbia supercontinent and a concurrent rise in atmospheric oxygenation. These global transitions may have promoted the ecological diversification of microbial communities and facilitated their dispersal into progressively drier continental interiors. Under favorable conditions, microorganisms proliferate and form microbial mats that interact with external factors such as sedimentation, currents, erosional processes, and other physical drivers. Their presence in arid terrestrial deposits is thus of considerable importance, as it underscores how microbial communities evolved and developed adaptive capabilities that enabled them to colonize and persist within intermittently wet landscapes subjected to elevated environmental stress. This study documents the occurrence of MISS within continental desert depositional systems of the Mangabeira Formation, São Francisco Craton, Brazil (1.6 Ga), preserved in wet sandsheet deposits. These occurrences broaden the sparse record of MISS in Proterozoic desert environments and offer new constraints on the capacity of early microbial communities to endure highly stressful and intermittently wet conditions. To investigate the conditions that enabled microbial establishment in this ancient desert, this study applies a multi-method approach integrating sedimentological, stratigraphic, petrographic, and microtextural datasets. The vertical succession reveals six distinct drying-upward cycles, each associated with fluctuations in groundwater level that periodically generated stable, moisture-rich surfaces suitable for microbial mat development. Within these intervals, MISS occur in millimetric heterolithic laminites displaying wavy–crinkly lamination, wrinkle marks, roll-up structures, deformational features, authigenic minerals with convolute morphologies, trapped grains, and organic carbon remnants. Complementary Raman analyses reveal characteristic carbonaceous peaks (at ~1370, 1590, and 1610 cm⁻¹), confirming the presence of organic carbon and kerogen. Collectively, the integrated dataset indicates that microbial colonization in the Mangabeira Formation was episodically favored by groundwater-controlled moisture stability, which enhanced substrate cohesion and enabled the formation of distinctive biosedimentary fabrics. These findings, contextualized within the broader Mesoproterozoic expansion of MISS, highlight the capacity of early microbial communities to establish themselves in hydrologically stressed desert landscapes and refine the sedimentological and geochemical criteria necessary for recognizing MISS in deep-time continental systems.