DIAGNOSING GROWTH PATTERNS IN COMPLEX STROMATOLITE BIOHERMS: AN EXAMPLE FROM THE MESOPROTEROZOIC CHANDI FORMATION, CHHATTISGARH BASIN, INDIA

Stromatolites develop in a wide variety of depositional environments and the influence of these environments (e.g. light availability, wave or current energy) have been shown to influence growth patterns observed in the rock record. Individual forms can range from planar to domal to columnal to branching columnal, to conical. Here we utilize lamina style to explore a complex stromatolitic bioherm from the ~1.0 Ga Chandi Formation, Chhattisgarh Basin, India. Specifically, we observed images of three faces of the exposed bioherm, traced the lamina of the stromatolite, and identified whether changes in lamination are associated with changes in branching and column orientation to explore changes in the pattern of growth through bioherm formation. The front face of the outcrop displays a primarily branching fan-like morphology of 2-5 cm-scale columns. Columns show irregular branching; synoptic relief of the individual columns is low (cm-scale) but combine to form an overall bioherm with greater and variable synoptic relief. We also identify at least 3 distinct stages within the growth succession defined by both the angle of columns and their branching pattern. One region continues the primary fan-shape of the front face of the bioherm. A smaller section shows a distinct difference in growth direction. A third section shows strong unidirectional growth of nearly horizontal columns that comprise the near-perpendicular side of the outcrop. These near-horizontal columns have decimeter-scale spacing show secondary columns and branching columns that protrude downward from the branches. These underside protrusions defy expectations of stromatolite growth due to the expected phototrophic component of microbial mats that form stromatolites. Our goal is to refine our understanding of growth morphologies to determine the relative timing of distinct growth and to better understand how bioherm growth may be reflecting the surrounding depositional environment.