Algal stromatolites composed of quartz sandstone, which are heretofore undescribed from ancient rocks, are present in the New Richmond Sandstone (L. Ord.) in southeastern Minnesota. Although these stromatolites resemble their common carbonate counterparts in the field, the stromatolite structure is at best obscure in thin section. These quartz sandstone stromatolites correlate with similar carbonate structures nearby and probably represent an environment of deposition at or near the boundary between a shallow quartz sand environment and an intertidal carbonate environment.

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